Method and apparatus for connecting to cell without random access in next-generation mobile communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The present disclosure discloses an apparatus and a method for a terminal connecting to a base station without a random access process. According to one embodiment of the present disclosure, the terminal acquires a suitable TA value in advance according to preset information, and updates and maintains the TA value and connects to a cell without a random access process, thereby enabling the provision of a delay-sensitive service.

Description

Method and device for connecting to a cell without random access in a next-generation mobile communication system

[0001] The present disclosure relates to a technology for a terminal to perform connection with a base station without a random access process.

[0002] 5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and can be implemented not only in the sub-6GHz frequency band such as 3.5 gigahertz (3.5GHz), but also in the ultra-high frequency band called millimeter wave (mmWave) such as 28GHz and 39GHz ('Above 6GHz'). In addition, for 6G mobile communication technology, which is called the system after 5G communication (Beyond 5G), implementation in the terahertz band (for example, the 3 terahertz (3THz) band at 95GHz) is being considered to achieve a transmission speed that is 50 times faster than 5G mobile communication technology and an ultra-low latency time that is reduced to one-tenth.

[0003] In the early stages of 5G mobile communication technology, the goal is to support services and satisfy performance requirements for enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine-Type Communications (mMTC). These include beamforming and massive MIMO to mitigate path loss of radio waves in ultra-high frequency bands and increase the transmission distance of radio waves, support for various numerologies (such as operation of multiple subcarrier intervals) and dynamic operation of slot formats for efficient use of ultra-high frequency resources, initial access technology to support multi-beam transmission and wideband, definition and operation of BWP (Bidth Part), new channel coding methods such as LDPC (Low Density Parity Check) codes for large-capacity data transmission and Polar Code for reliable transmission of control information, and L2 pre-processing (L2). Standardization has been made for network slicing, which provides dedicated networks specialized for specific services, and pre-processing.

[0004] Currently, discussions are underway to improve and enhance the initial 5G mobile communication technology in consideration of the services that 5G mobile communication technology was intended to support, and physical layer standardization is in progress for technologies such as V2X (Vehicle-to-Everything) to help autonomous vehicles make driving decisions and increase user convenience based on their own location and status information transmitted by vehicles, NR-U (New Radio Unlicensed) for the purpose of system operation that complies with various regulatory requirements in unlicensed bands, NR terminal low power consumption technology (UE Power Saving), Non-Terrestrial Network (NTN), which is direct terminal-satellite communication to secure coverage in areas where communication with terrestrial networks is impossible, and Positioning.

[0005] In addition, standardization of wireless interface architecture / protocols is in progress for technologies such as intelligent factories (Industrial Internet of Things, IIoT) to support new services through linkage and convergence with other industries, Integrated Access and Backhaul (IAB) that provides nodes for expanding network service areas by integrating wireless backhaul links and access links, Mobility Enhancement technology including Conditional Handover and Dual Active Protocol Stack (DAPS) handover, and 2-step random access (2-step RACH for NR) that simplifies random access procedures. Standardization is also in progress for system architecture / services such as 5G baseline architecture (e.g., Service-based Architecture, Service-based Interface) for grafting Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) that provides services based on the location of the terminal.

[0006] Once these 5G mobile communication systems are commercialized, an explosive increase in connected devices will be connected to the communication network, necessitating enhanced functionality and performance of 5G mobile communication systems and integrated operation of these connected devices. To this end, new research will be conducted on improving 5G performance and reducing complexity, supporting AI services, supporting metaverse services, and drone communications by utilizing eXtended Reality (XR), Artificial Intelligence (AI), and Machine Learning (ML) to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR).

[0007] In addition, the development of these 5G mobile communication systems includes new waveforms to ensure coverage in the terahertz band of 6G mobile communication technology, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), Array Antenna, and Large Scale Antenna, metamaterial-based lenses and antennas to improve the coverage of terahertz band signals, high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM), Reconfigurable Intelligent Surface (RIS) technology, as well as full duplex technology to improve the frequency efficiency and system network of 6G mobile communication technology, satellite, AI (Artificial Intelligence) from the design stage and AI-based communication technology that realizes system optimization by internalizing end-to-end AI support functions, and ultra-high-performance communication and computing resources to provide services with complexity that exceeds the limits of terminal computing capabilities. It could serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing this technology.

[0008] For a terminal to connect to a base station, a random access process is required to synchronize uplinks, etc. However, to solve problems such as the delay in connecting to the base station due to performing this random access process, technologies that enable connection to a cell without a random access process (RACH-less) have been introduced. For example, technologies such as RACH-less handover, which can omit the random access process even in handover situations and reduce service interruption time, have been discussed.

[0009] However, when accessing a cell without a random access process like this, there is a problem in that the valid TA (timing advance) values ​​that the terminal can apply are limited to already known values, such as the TA values ​​applied in PTAG or STAG.

[0010] One object of the present disclosure is to provide a method for updating and maintaining a valid TA value for RACH-less access.

[0011] In order to solve the above problem, in accordance with an example of the present disclosure, a method of a terminal in a wireless communication system comprises the steps of: receiving, from a base station, an RRC release message instructing a transition from a radio resource control (RRC) connected state to an RRC inactive state, the RRC release message including first information used to determine timing advance (TA) validity and second information regarding a preamble used for TA update; in the RRC inactive state, if a current TA value is determined to be invalid based on the first information, transmitting a random access preamble to the base station based on the second information; if a random access response including a TA command is received from the base station, updating the current TA value based on the TA command; storing the updated TA value and initiating a validity determination operation for the stored TA value using the first information; And when the preset service is triggered, based on the stored TA value being determined to be valid, a step of transmitting a PUSCH (physical uplink shared channel) to the base station using the stored TA value may be a TA value last stored in the terminal by the validity determination operation before the preset service is triggered.

[0012] In addition, in a method of a base station in a wireless communication system according to an example of the present disclosure, the method includes: receiving, from a terminal, an RRC release message instructing a transition from a radio resource control (RRC) connected state to an RRC inactive state, wherein the RRC release message includes first information used to determine timing advance (TA) validity and second information regarding a preamble used for TA update; receiving, from the terminal in the RRC inactive state, at least one random access preamble based on the second information; transmitting, to the terminal, at least one random access response in response to the at least one random access preamble; and receiving, from the terminal, a physical uplink shared channel (PUSCH) related to a preset service, wherein the PUSCH is received based on a TA command, and the TA command may be included in a last random access response among the at least one random access response transmitted to the terminal before receiving the PUSCH.

[0013] In addition, in a wireless communication system according to an example of the present disclosure, a terminal includes a transceiver; And controlling the transceiver to receive an RRC release message from a base station, which instructs a transition from a radio resource control (RRC) connected state to an RRC inactive state, wherein the RRC release message includes first information used to determine the validity of timing advance (TA) and second information about a preamble used for TA update, in the RRC inactive state, if a current TA value is determined to be invalid based on the first information, controlling the transceiver to transmit a random access preamble to the base station based on the second information, if a random access response including a TA command is received from the base station, updating the current TA value based on the TA command, storing the updated TA value, and initiating a validity determination operation for the stored TA value using the first information, and if a preset service is triggered, transmitting a PUSCH (physical uplink shared channel) to the base station using the stored TA value based on the determination that the stored TA value is valid. A control unit for controlling a transceiver is included, and the stored TA value may be a TA value last stored in the terminal by the validity determination operation before the preset service is triggered.

[0014] In addition, in a wireless communication system according to an example of the present disclosure, in a base station, a transceiver; And a control unit for controlling the transceiver to receive an RRC release message instructing a transition from a radio resource control (RRC) connected state to an RRC inactive state, wherein the RRC release message includes first information used to determine timing advance (TA) validity and second information about a preamble used for TA update, and for controlling the transceiver to receive at least one random access preamble from the terminal in the RRC inactive state based on the second information, and for controlling the transceiver to transmit at least one random access response to the terminal in response to the at least one random access preamble, and for controlling the transceiver to receive a physical uplink shared channel (PUSCH) related to a preset service from the terminal, wherein the PUSCH is received based on a TA command, and the TA command may be included in a last random access response among the at least one random access response transmitted to the terminal before receiving the PUSCH.

[0015] According to one embodiment of the present disclosure, a terminal can effectively receive delay-sensitive services by obtaining an appropriate TA value in advance according to preset information, updating and maintaining the same, and connecting to a cell without a random access process.

[0016] FIG. 1 is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0017] FIG. 2 is a flowchart of a CG-SDT process in a mobile communication system according to an embodiment of the present disclosure.

[0018] FIG. 3 is a flowchart of a RACH-less handover process in a mobile communication system according to an embodiment of the present disclosure.

[0019] FIG. 4 is a flowchart of a process in which a terminal accesses a terminal through pre-TA acquisition according to an embodiment of the present disclosure.

[0020] FIG. 5 is a flowchart of a process in which a terminal accesses a pre-TA acquisition using LR (LP-WUR) according to an embodiment of the present disclosure.

[0021] FIG. 6 is a flowchart of terminal operations for accessing through pre-TA acquisition according to an embodiment of the present disclosure.

[0022] FIG. 7 is a flowchart of a base station operation for accessing through pre-TA acquisition according to an embodiment of the present disclosure.

[0023] FIG. 8 is a flowchart of a process in which a terminal performs a handover operation through pre-TA acquisition according to an embodiment of the present disclosure.

[0024] FIG. 9 is a flowchart of a process in which a terminal performs a condition-based handover operation through pre-TA acquisition according to an embodiment of the present disclosure.

[0025] FIG. 10 is a flowchart of terminal operations for performing a handover operation through pre-TA acquisition according to an embodiment of the present disclosure.

[0026] FIG. 11 is a flowchart of a base station operation for performing a handover operation through pre-TA acquisition according to an embodiment of the present disclosure.

[0027] FIG. 12 is a block diagram illustrating the internal structure of a terminal according to an embodiment of the present invention.

[0028] Figure 13 is a block diagram showing the configuration of a base station according to one embodiment of the present invention.

[0029] In the following description of the present invention, detailed descriptions of known functions or configurations will be omitted if they are deemed to unnecessarily obscure the gist of the present invention. Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

[0030] Figure 1 is a diagram illustrating the structure of a next-generation mobile communication system.

[0031] Referring to FIG. 1, as illustrated, a wireless access network of a next-generation mobile communication system (New Radio, NR) is composed of a next-generation base station (New Radio Node B, hereinafter referred to as gNB) (1a-10) and an access and mobility management function (AMF) (1a-05, New Radio Core Network). A user terminal (New Radio User Equipment, hereinafter referred to as NR UE or terminal) (1a-15) accesses an external network through the gNB (1a-10) and the AMF (1a-05).

[0032] In Fig. 1, the gNB corresponds to the eNB (Evolved Node B) of the existing LTE (long term evolution) system. The gNB (1a-10) is connected to the NR UE via a wireless channel and can provide a service that is superior to the existing Node B (1a-20). In the next-generation mobile communication system, since all user traffic is serviced through a shared channel, a device that collects status information such as the buffer status of the UEs, the status of available transmission power, and the channel status and performs scheduling is required, and the gNB (1a-10) is in charge of this. One gNB typically controls multiple cells. In NR, in order to implement ultra-high-speed data transmission compared to the existing LTE, it can have a bandwidth higher than the existing maximum, and beamforming technology can be additionally grafted using the orthogonal frequency division multiplexing (OFDM) method as a wireless access technology. In addition, an adaptive modulation and coding (AMC) method is applied, which determines the modulation scheme and channel coding rate according to the channel status of the terminal.

[0033] AMF (1a-05) performs functions such as mobility support, bearer setup, and QoS (quality of service) setup. AMF (1a-05) is a device that is responsible for various control functions as well as mobility management functions for terminals and is connected to multiple base stations. In addition, the next-generation mobile communication system can also be linked with the existing LTE system, and AMF (1a-05) is connected to MME (mobility management entity) (1a-25) through a network interface. MME (1a-25) is connected to eNB (1a-30), which is an existing base station. Terminals that support LTE (E-UTRA)-NR Dual Connectivity (EN-DC) can transmit and receive data while maintaining connection to not only gNB but also eNB (1a-35).

[0034] FIG. 2 is a flowchart of a CG-SDT process in a mobile communication system according to an embodiment of the present disclosure.

[0035] SDT (Small Data Transmission) is a technology that allows terminals and networks to transmit and receive small amounts of data without switching to a connected mode. SDT is achieved through a Random Access (Random Access) or Configured Grant (CG) process. The CG process can be implemented by periodically allocating radio resources to terminals in advance (1b-35) and using these resources to quickly transmit and receive data when necessary. SDT utilizing the CG process is referred to as CG-SDT.

[0036] The terminal (1b-05) receives an RRCRelease message from the base station (1b-10) (1b-15). The RRCRelease message includes configuration information and SDT-Config IE required to perform the SDT, and the terminal (1b-05) receiving the message switches from a connected mode (RRC_CONNECTED) to an inactive mode (RRC_INACTIVE). The configuration information includes the cg-SDT-TimeAlignmentTimer and cg-SDT-RSRP-ChangeThreshold parameters. The cg-SDT-TimeAlignmentTimer indicates one timer value, and when the terminal (1b-05) receives the RRCRelease message including the cg-SDT-TimeAlignmentTimer, it starts a corresponding timer based on the value of the cg-SDT-TimeAlignmentTimer (1b-20). And, if the effective RSRP (reference signal received power) value measured from the reference signal of the cell does not change by a greater amount than the configured cg-SDT-RSRP-ChangeThreshold value compared to the effective downlink pathloss reference RSRP value stored at a predetermined point in time before the timer expires (1b-25), the terminal (1b-05) considers the TA (Timing Advance) currently applied to the cell to be valid. If the TA is valid, the terminal (1b-05) can transmit data to the base station (1b-10) using the configured CG radio resources without a random access process (1b-30). However, if the terminal (1b-05) performs reselection from the cell that provided the RRCRelease message to another cell, it cannot perform the operation of transmitting data without the random access process.

[0037] The ability to transmit data to the base station without a random access process (RACH-less) means that the time required from the access process to data transmission is reduced. However, the RACH-less CG-SDT introduced in the existing mobile communication system is limited to SDT operation and cannot be applied when the cg-SDT-TimeAlignmentTimer timer expires or the measured downlink pathloss reference RSRP value changes beyond a certain threshold.

[0038] FIG. 3 is a flowchart of a RACH-less handover process in a mobile communication system according to an embodiment of the present disclosure.

[0039] Handovers performed without a random access (RA) process are called RACH-less handovers. RACH-less handovers were first introduced in the LTE system to reduce service interruption time during handovers.

[0040] The terminal (1c-05) reports its capability information to the source base station (1c-10) (1c-20). The capability information includes an indicator indicating that the terminal can support RACH-less handover.

[0041] The source base station (1c-10) determines handover of the terminal (1c-05) based on the cell measurement result information reported from the terminal (1c-05). At this time, the source base station (1c-10) exchanges information for the handover with the target base station (1c-15) (1c-25).

[0042] The source base station (1c-10) transmits to the target base station (1c-15) an indicator indicating that RACH-less handover will be performed for the terminal (1c-05). The target base station (1c-15) provides the source base station (1c-10) with a TA (Timing Advance) value to be applied by the terminal (1c-05), and optionally, the terminal (1c-05) may transmit together with radio resource information (i.e., ul-Grant, ul-StartSubframe, ul-SchedInterval) for monitoring the PDCCH (physical downlink control channel) of the target base station (1c-15). If the radio resource information is not provided, the terminal (1c-05) performs PDCCH monitoring for all radio resources of the target cell provided by the target base station (1c-15). In addition, the TA value here may indicate one of the following: a value of 0, a TA value applied to a PTAG (primary timing advance group) in an existing MCG (master cell group), a TA value applied to a PTAG in an existing SCG (secondary cell group), a TA value applied to a STAG (secondary timing advance group) in an existing MCG, or a TA value applied to a STAG in an existing SCG. That is, since one of the TA values ​​that the terminal (1c-05) was previously applying is applied except for the value of 0, if a TA value that cannot be indicated by the above values ​​is required, it may be difficult to trigger and successfully complete the RACH-less handover.

[0043] The source base station (1c-10) that has received the above configuration information transmits the RACH-less configuration information together with the handover configuration information to the terminal (1c-05) (1c-30). The RACH-less configuration information (1c-35) includes the TA information and radio resource information on which the terminal (1c-05) must perform PDCCH monitoring in the target cell (1c-15).

[0044] The terminal (1c-05) that has received the above information checks whether there is a scheduling for the terminal (1c-05) in the radio resource (1c-45) indicated by the radio resource information, and transmits a PUSCH (physical uplink shared channel) including a predetermined RRC (radio resource control) message (RRCConnectionReconfigurationComplete) to the target base station (1c-15) according to the scheduling information (1c-40).

[0045] According to the aforementioned process, it can be seen that the RACH-less handover introduced in the existing mobile communication system has a limitation in that it can only use known TA values.

[0046] FIG. 4 is a flowchart of a process in which a terminal accesses a terminal through pre-TA acquisition according to an embodiment of the present disclosure.

[0047] In this embodiment, a method is proposed to not perform random access when a terminal in an inactive mode (RRC_INACTIVE) state switches to a connected mode (RRC_CONNECTED) while updating or maintaining a valid TA value according to preset information. Since the method proposed in this embodiment requires additional procedures compared to existing methods, it is expected to be useful for terminals that must support delay-sensitive services such as extended reality (XR) services and emergency services.

[0048] Referring to FIG. 4, a terminal (1d-05) in a connected mode reports capability information of the terminal (1d-05) to a base station (1d-10) (1d-15). The capability information includes an indicator indicating that the terminal (1d-05) supports RACH-less access. Alternatively, the capability information may include an indicator indicating that the terminal (1d-05) supports a function of pre-acquiring a TA value of a base station that is camping on in an inactive mode (early TA acquisition).

[0049] When the terminal (1d-05) determines that a delay-sensitive service is required, it determines that RACH-less access (or early TA acquisition for this) is required for this (1d-20). Then, the terminal (1d-05) reports to the base station (1d-10) using a predetermined RRC message (UEAssistanceInformation) that RACH-less access (or early TA acquisition for this) is required due to the above preference, that is, the delay-sensitive service (1d-25).

[0050] The base station (1d-10) transmits an RRCRelease message containing predetermined configuration information to the terminal (1d-05) (1d-30). The configuration information includes configuration information (suspendConfig IE) required to switch the terminal (1d-05) from a connected mode to an inactive mode, configuration information required to update and maintain a valid TA value (e.g., a value of a first timer and a first RSRP threshold for verifying the validity of a TA value, preamble information that can be used for TA update), indicator information indicating RACH-less access, and configuration information related to a CG (configured grant) for the same.

[0051] The terminal (1d-05) receiving the RRC message starts a first timer (e.g., a validity timer related to TA as illustrated in the drawing) (1d-35) and switches to an inactive mode (RRC_INACTIVE) (1d-40). When the first timer expires, the terminal (1d-05) considers that the currently applied TA value is no longer valid. When the TA value is updated through a random access process, the first timer is restarted (1d-60). The configuration information required to update and maintain the above-mentioned valid TA value (e.g., the value of the first timer, preamble information that can be used for TA update, the first RSRP threshold for verifying the validity of the TA value), indicator information indicating RACH-less access, and CG-related configuration information therefor may also be provided through system information. In this case, the base station (1d-10) may provide the terminal with an instruction to apply the configuration information included in the system information in the RRCRelease message. If the configuration information is provided in both the RRCRelease message and the system information (1d-45), the terminal (1d-05) preferentially applies the configuration information provided in the RRCRelease message. The configuration information provided in the RRCRelease message may be valid only within the cell that provided the RRCRelease message, or only within a predetermined time, and if the configuration information provided in the RRCRelease message is no longer valid, the terminal (1d-05) applies the configuration information provided in the system information. In addition, when the terminal (1d-05) reselects a neighboring cell, the preset information may be applied as is, or the configuration information provided by the neighboring cell through the system information may be newly applied.

[0052] If the first timer is about to expire, or if the effective RSRP value measured from the reference signal of the cell changes by a larger amount than the first RSRP threshold value set at a predetermined point in time (e.g., the point in time when the RRCRelease message is received or the point in time when the cell switches to an inactive mode), the terminal (1d-05) transmits a preamble set in advance to the base station (1d-10) for TA update (1d-50).

[0053] The base station (1d-10) that receives the above preamble transmits a TA command to the terminal (1d-05) via a RAR (Random Access Response) message (1d-55). If the transmitted preamble is a UE-specific preamble set only for the terminal (1d-05), no competition with other terminals occurs, and thus a simplified RAR containing only a RAP (random access preamble) ID (identity) and a TA command can be transmitted to the terminal (1d-05). Conversely, if the preamble for the TA purpose can also be used by other terminals, the terminal (1d-05) may need to perform a conventional random access procedure (contention-based RA procedure) that supports contention resolution.

[0054] The terminal (1d-05) that receives the RAR updates the TA value using the TA command information included in the RAR, and restarts the first timer at this time (1d-40). In addition, the terminal (1d-05) stores the measured downlink pathloss reference RSRP value when updating the TA value, and determines whether the effective RSRP value measured in the future changes by a greater amount than the first RSRP threshold value set above. If the random access process is not successfully completed, the terminal (1d-05) considers that it no longer has a valid TA value. When the random access process fails, the random access process may be repeated a predetermined number of times, and the number of repetitions may be set by the base station (1d-10).

[0055] The terminal (1d-05), which updates and maintains a valid TA value according to the above procedure, decides to switch to connected mode (RRC_CONNECTED) when a delay-sensitive service is triggered (1d-65). If the terminal (1d-05) has a valid TA value, it performs RACH-less access. Then, the terminal (1d-05) transmits a PUSCH using the CG radio resources (1d-75) provided by the base station (1d-10) (1d-70).

[0056] FIG. 5 is a flowchart of a process in which a terminal accesses a pre-TA acquisition using LR (LP-WUR) according to an embodiment of the present disclosure.

[0057] In this embodiment, a method is proposed in which a terminal in an inactive mode (RRC_INACTIVE) state does not perform random access when switching to a connected mode (RRC_CONNECTED) while updating and maintaining a valid TA value according to preset information. The TA value update can be performed through a random access process in LR.

[0058] LR (Low Power-Wake Up Receiver) refers to a transmit / receive module with superior power efficiency compared to the Main Radio (MR) for the purpose of reducing power consumption of terminals and base stations. Terminals and base stations have transmit / receive modules corresponding to the LR. Typically, LR (1e-15) is expected to use a narrower frequency band than MR (1e-20), and while all functions provided by a typical cell are provided through MR, LR is expected to provide only limited functions due to its limited capabilities. Since the method proposed in this embodiment requires additional procedures compared to the existing one, it is expected to be useful for terminals that must support delay-sensitive services such as XR services and emergency services.

[0059] Referring to FIG. 5, a terminal (1e-05) in a connected mode reports capability information of the terminal (1e-05) to a base station (1e-10) (1e-25). The capability information includes an indicator indicating that the terminal (1e-05) supports RACH-less access. Alternatively, the capability information may include an indicator indicating that the terminal (1e-05) supports a function of pre-securing a TA value of a base station that is camping on in an inactive mode (early TA acquisition). In addition, the capability information may include an indicator indicating that the terminal (1e-05) can perform random access through LR for purposes such as TA acquisition.

[0060] When the terminal (1e-05) determines that the terminal (1e-05) requires a delay-sensitive service, it determines that RACH-less access (or early TA acquisition for this) is required for this (1e-30). Then, the terminal (1e-05) reports to the base station (1e-10) the preference, that is, that RACH-less access (or early TA acquisition for this) is required, using a predetermined RRC message (UEAssistanceInformation) (1e-35).

[0061] The base station (1e-10) transmits an RRCRelease message (1e-40) containing predetermined configuration information to the terminal (1e-05). The configuration information includes configuration information (suspendConfig IE) required to switch the terminal (1e-05) from a connected mode to an inactive mode, configuration information required to update and maintain a valid TA value (e.g., a value of a first timer and a first RSRP threshold for verifying the validity of a TA value, preamble information that can be used in MR or LR for TA update), indicator information indicating RACH-less access, and CG-related configuration information for the same.

[0062] The terminal (1e-05) receiving the above message starts the first timer (1e-45) and switches to the inactive mode (1e-50). When the first timer expires, the terminal (1e-05) considers that the currently applied TA value is no longer valid. When the TA value is updated through a random access process using LR, the first timer is restarted (1e-75). The configuration information required to update and maintain the valid TA value (e.g., the value of the first timer, preamble information that can be used in the MR or LR for TA update, and the first RSRP threshold for verifying the validity of the TA value), indicator information indicating RACH-less access, and CG-related configuration information therefor may also be provided through system information, and the system information may be broadcasted by the MR or LR (1e-55, 1e-60). If the above configuration information is provided in both the RRCRelease message and the system information, the terminal (1e-05) preferentially applies the configuration information provided in the RRCRelease message. The configuration information provided in the RRCRelease message may be valid only within the cell that provided the RRCRelease message or only within a certain period of time, and if the configuration information provided in the RRCRelease message is no longer valid, the terminal (1e-05) applies the configuration information provided in the system information. When the terminal (1e-05) reselects a neighboring cell, the preset information may be applied as is, or the configuration information provided by the neighboring cell through the system information may be newly applied.

[0063] If the first timer is about to expire, or if the effective RSRP value measured from the reference signal of the cell changes by a larger amount than the configured first RSRP threshold value compared to the effective downlink pathloss reference RSRP value stored at a predetermined time (e.g., the time of receiving the RRCRelease message or the time of switching to an inactive mode, etc.), the terminal (1e-05) transmits a preamble configured in advance for TA update to the MR (1e-20) or LR (1e-15) of the base station (1e-10) (1e-65). Whether the random access is performed in the MR (1e-20) or the LR (1e-15) may be configured by the base station (1e-10) through the dedicated RRC message or system information, or may be determined according to a predetermined condition. For example, if terminal (1e-05) is provided with random access setting information from both MR (1e-20) and LR (1e-15), terminal (1e-05) can preferentially perform a random access process for the purpose of acquiring TA through LR (1e-15). If random access from LR (1e-15) fails, terminal (1e-05) can retry random access from MR (1e-20).

[0064] The base station (1e-10), which receives the above preamble through LR (1e-15), transmits a RAR (Random Access Response) message containing a TA command to the terminal (1e-05) through the LR (1e-15) (1e-70). If the transmitted preamble is a UE-specific preamble set only for the terminal (1e-05), no competition with other terminals occurs, and thus a simplified RAR containing only the RAP ID and the TA command can be transmitted to the terminal (1e-05). On the other hand, if the preamble for the TA purpose can also be used by other terminals, the terminal (1e-05) must perform a conventional random access process that supports contention resolution.

[0065] The terminal (1e-05) that receives the RAR updates the TA value using the TA command information included in the RAR, and restarts the first timer at this time (1e-75). If the random access process is not successfully completed, the terminal (1e-05) considers that it no longer has a valid TA value. If the random access fails, the random access process may be repeated a predetermined number of times, and the number of repetitions may be set by the base station (1e-10).

[0066] A terminal (1e-05) that updates and maintains a valid TA value according to the above procedure triggers a delay-sensitive service (1e-80). If the terminal (1e-05) has a valid TA value, it performs RACH-less access. Then, the terminal (1e-05) transmits a PUSCH using the CG radio resources (1e-90) provided by the base station (1e-10) (1e-85).

[0067] FIG. 6 is a flowchart of terminal operations for accessing through pre-TA acquisition according to an embodiment of the present disclosure.

[0068] In step 1f-05, the terminal reports its capability information to the base station. The capability information may include an indicator indicating that the terminal can update and maintain a valid TA value for a base station camping on in an inactive mode.

[0069] In step 1f-10, the terminal transmits to the base station a predetermined RRC message including an indicator indicating that RACH-less access is required to receive delay-sensitive service.

[0070] In step 1f-15, the terminal receives an RRCRelease message from the base station. The RRCRelease message includes configuration information (suspendConfig IE) required to switch the terminal from a connected mode to an inactive mode, configuration information required to update and maintain a valid TA value (e.g., a value of a first timer and a first RSRP threshold for verifying the validity of a TA value, preamble information that can be used in MR or LR for TA update), indicator information indicating RACH-less access, and CG-related configuration information for the same.

[0071] At step 1f-20, the terminal switches to inactive mode.

[0072] In step 1f-25, the terminal triggers a random access process for the purpose of acquiring TA according to predetermined conditions and transmits a preamble preset to MR or LR.

[0073] In step 1f-30, the terminal receives an RAR message corresponding to the preamble from the base station. The terminal applies the TA command included in the message.

[0074] At step 1f-35, the terminal triggers a delay-sensitive service and decides to switch to connected mode for this purpose.

[0075] In step 1f-40, the terminal transmits a PUSCH to the base station without a random access process and determines the uplink transmission timing by applying the valid TA value maintained. A predetermined RRC message, for example, an RRCResumeRequest message, is transmitted via the PUSCH.

[0076] In step 1f-45, the terminal receives an RRCResume message from the base station and switches to connected mode.

[0077] FIG. 7 is a flowchart of a base station operation for accessing through pre-TA acquisition according to an embodiment of the present disclosure.

[0078] In step 1g-05, the base station receives capability information from the terminal. The capability information may include an indicator indicating that the terminal can update and maintain a valid TA value for the base station that is camping on in an inactive mode.

[0079] In step 1g-10, the base station receives from the terminal a predetermined RRC message including an indicator indicating that RACH-less access is required to provide a delay-sensitive service.

[0080] In step 1g-15, the base station transmits an RRCRelease message to the terminal. The RRCRelease message includes configuration information (suspendConfig IE) required to transition the terminal from a connected mode to an inactive mode, configuration information required to update and maintain a valid TA value (e.g., a value of a first timer and a first RSRP threshold for verifying the validity of a TA value, preamble information that can be used in MR or LR for TA update), indicator information indicating RACH-less access, and CG-related configuration information for the same.

[0081] In step 1g-20, the base station receives a preset preamble for the purpose of TA acquisition from the terminal.

[0082] In step 1g-25, the base station transmits a RAR message corresponding to the preamble to the terminal. The base station includes a TA command indicating a TA value derived from the received preamble in the RAR message.

[0083] In step 1g-35, the base station receives an RRCResumeRequest message from the terminal via PUSCH.

[0084] FIG. 8 is a flowchart of a process in which a terminal performs a handover operation through pre-TA acquisition according to an embodiment of the present disclosure.

[0085] In this embodiment, a terminal performs a handover to a target cell without a random access process by applying a TA value acquired in advance from the target cell. Hereinafter, the procedure for acquiring the TA value in advance is referred to as early TA acquisition. Since the method proposed in this embodiment requires additional procedures compared to existing methods, it is expected to be useful for terminals that must support delay-sensitive services such as XR services and emergency services.

[0086] Referring to FIG. 8, the terminal (1h-05) reports capability information of the terminal (1h-05) to the source base station (1h-10) (1h-20). The capability information includes indicators indicating that the terminal (1h-05) supports early TA acquisition and RACH-less handover.

[0087] The terminal (1h-05) determines that a delay-sensitive service is required and, for this purpose, determines that a RACH-less handover (or early TA acquisition for this) is required (1h-25). Then, the terminal (1h-05) reports to the source base station (1h-10) using a predetermined RRC message (UEAssistanceInformation) that a RACH-less handover (or early TA acquisition for this) is required due to the above preference, i.e., the delay-sensitive service (1h-30).

[0088] The terminal (1h-05) transmits a MeasurementReport message to the source base station (1h-10) according to a preset cell measurement operation (1h-35), and the source base station (1h-10) decides to perform RACH-less handover using early TA acquisition based on the preferences of the terminal (1h-05) received from the terminal (1h-05) and the measurement-related information included in the measurement report message. To this end, the source base station (1h-10) first exchanges a control signal for early TA acquisition with the target base station (1h-15) (1h-40). The source base station (1h-10) requests the target base station (1h-15) for configuration information for the early TA acquisition operation, and for this request, transmits a new indicator to the target base station (1h-15). The target base station (1h-15) that received the above indicator from the source base station (1h-10) transmits to the source base station (1h-10) target base station ID information (PCI (physical cell identity), CGI (cell global identity), frequency information, etc.) and predetermined random access setting information for the early TA acquisition, for example, preamble information and RACH (random access channel) radio resource information used for the purpose of TA acquisition for the target base station.

[0089] The source base station (1h-10) that has received the above configuration information transmits the above configuration information to the terminal (1h-05) using an RRC message (1h-45). The above configuration information may also be provided to the terminal (1h-05) through certain system information broadcast by the target base station (1h-15) (1h-50).

[0090] After receiving the RRC message, or when receiving a PDCCH (physical downlink control channel) order (1h-47) from a source base station (1h-10), the terminal (1h-05) applies the received configuration information to perform a random access process toward the target base station (1h-15). The PDCCH order may include information indicating a target cell to which the terminal (1h-05) should transmit the preset preamble.

[0091] The terminal (1h-05) transmits a preamble for the purpose of acquiring a preset TA to the target base station (1h-15) (1h-55). The target base station (1h-15) that receives the preamble derives an uplink TA value using the preamble, and transmits the derived TA information to the terminal (1h-05) via an RAR message (hereinafter, the first method) or during a subsequent handover process (hereinafter, the second method).

[0092] For example, according to the first method, when the derived TA information is transmitted to the terminal (1h-05) via a RAR message (1h-60), the RAR message transmitted by the target base station (1h-15) may include at least a RAP ID and a TA command. At this time, if the transmitted preamble is a UE-specific preamble set only for the terminal (1h-05), competition with other terminals does not occur, so a simplified RAR including only the RAP ID and the TA command may be transmitted to the terminal (1h-05). Conversely, if the preamble for the TA purpose can also be used by other terminals, the terminal (1h-05) may need to perform a conventional random access process that supports contention resolution. The terminal (1h-05) that receives the RAR in this way starts a predetermined validity timer (1h-65) and determines that the TA value is valid until the validity timer expires.

[0093] As another example, according to the second method, the TA value derived by the target base station (1h-15) may be transmitted to the terminal (1h-05) via an HO command. Details related to this will be described later.

[0094] The target base station (1h-15) that receives the above preamble stores the TA value derived from the preamble together with the terminal ID information or C-RNTI (cell-radio network temporary identity) information. In addition, the target base station (1h-15) can evaluate whether the TA value is valid using a predetermined implementation timer. For example, the timer is started when the preamble is received or when the TA value is derived, and when the timer expires, the derived TA value can be considered no longer valid. Thereafter, when a handover request for the terminal (1h-05) is received from the source base station (1h-10), the target cell (1h-15) transmits a valid TA value together with handover configuration information to the source base station (1h-10).

[0095] The terminal (1h-05) transmits a MeasurementReport message to the source base station (1h-10) according to the preset cell measurement operation (1h-70). Then, the source base station (1h-10) decides to handover the terminal (1h-05) to the target base station (1h-15) based on the cell measurement result reported from the terminal (1h-05) (1h-75). Since the terminal (1h-05) has a TA value derived through the early TA acquisition operation, it can utilize it during the handover process.

[0096] When the source base station (1h-10) requests a RACH-less handover using a predetermined new indicator, the target base station (1h-15) configures handover configuration information and transmits it to the source base station (1h-10) (1h-80). At this time, RACH-less related configuration information is also transmitted to the source base station (1h-10) together with the handover configuration information. The RACH-less related configuration information provided from the target base station (1h-15) to the terminal (1h-05) through the source base station (1h-10) includes radio resource information for which the terminal (1h-05) should monitor a PDCCH for the target base station (1h-15) (1h-85). At this time, in the case of following the second method described above, the previously derived TA value may be included in the RACH-less related configuration information. If the TA value has already been provided to the terminal (1h-05) through a RAR message according to the first method, instead of the TA value, a predetermined indicator indicating the use of the value may be provided to the terminal (1h-05) through the RACH-less related configuration information.

[0097] Meanwhile, if the reception time of the preamble received to derive the above TA value is old and the derived TA value is determined to be no longer valid, the target base station (1h-15) may trigger a normal handover instead of the RACH-less handover requested by the source base station (1h-10). If the RACH-less related configuration information is not provided by the target base station (1h-15), this means that a normal handover should be performed, and in this case, the terminal (1h-05) should perform a normal handover operation involving a random access process for the target base station (1h-15). In addition, if the RACH-less related configuration information includes TA related information (including the above-mentioned instruction to use the derived TA value or the existing TA value transmitted via RAR) but does not include the above-mentioned radio resource information or includes a predetermined instruction (for example, an instruction to monitor the PDCCH from the target base station in all radio resources), the terminal (1h-05) must perform a PDDCH monitoring operation in all radio resources to check whether there is scheduling for the terminal (1h-05) provided by the target base station (1h-15).

[0098] A terminal (1h-05) that has received a predetermined RRC message including the handover configuration information and RACH-less configuration information from a source base station (1h-10) performs a PDDCH monitoring operation to determine whether there is scheduling information for the terminal (1h-05) in the configured radio resource (1h-95). When scheduling information is received, the terminal (1h-05) transmits a PUSCH to a target base station (1h-15) in consideration of the uplink transmission timing derived from the TA value in the radio resource indicated by the scheduling information. Here, the PUSCH may include an RRCReconfigurationComplete message.

[0099] FIG. 9 is a flowchart of a process in which a terminal performs a condition-based handover operation through pre-TA acquisition according to an embodiment of the present disclosure.

[0100] In this embodiment, a terminal performs a conditional handover (CHO) to a target cell without a random access process by applying a TA value acquired in advance from the target cell. Here, the procedure for acquiring a TA value in advance is called early TA acquisition. Since the method proposed in this embodiment requires an additional procedure compared to the existing method, it is expected to be useful for terminals that must support delay-sensitive services such as XR services and emergency services.

[0101] Referring to FIG. 9, the terminal (1i-05) reports capability information of the terminal (1i-05) to the source base station (1i-10) (1i-20). The capability information includes indicators indicating that the terminal (1i-05) supports early TA acquisition and RACH-less condition-based handover.

[0102] The terminal (1i-05) determines that a delay-sensitive service is required and, for this purpose, determines that a RACH-less condition-based handover (or early TA acquisition for this) is required (1i-25). Then, the terminal (1i-05) reports to the source base station (1i-10) the preference, that is, the need for a RACH-less condition-based handover (or early TA acquisition for this) using a predetermined RRC message (UEAssistanceInformation) (1i-30).

[0103] The terminal (1i-05) transmits a MeasurementReport message to the source base station (1i-10) according to a preset cell measurement operation (1i-35), and the source base station (1i-10) decides to perform RACH-less conditional handover using early TA acquisition based on the preferences of the terminal (1i-05) and the measurement information received from the terminal (1i-05) (1i-40). To this end, the source base station (1i-010) exchanges control signals for performing early TA acquisition and conditional handover with the candidate target base station(s) (1i-15) (1i-45). The source base station (1i-10) may request the target base station (1i-15) setting information for the early TA acquisition operation together with a request for conditional handover using a predetermined new indicator. The target base station (1i-15), which has received the above-mentioned indicator from the source base station (1i-10), transmits, to the source base station (1i-10), predetermined random access configuration information, i.e., preamble information and RACH radio resource information used for the purpose of TA acquisition at the target base station (1i-15), for the early TA acquisition, together with condition-based handover-related configuration information.

[0104] The source base station (1i-10) that has received the above-described configuration information transmits the above-described configuration information to the terminal (1i-05) using an RRC message (1i-50). After receiving the RRC message, or when receiving a PDDCH order (1i-55) from the source base station (1i-05), the terminal (1i-05) applies the received configuration information to perform a random access process to the target base station (1i-15). The terminal (1i-05) transmits a preamble for the purpose of acquiring a preset TA to the target base station (1i-15) (1i-60).

[0105] The target base station (1i-15) that receives the above preamble derives an uplink TA value using the preamble, and the derived TA information is transmitted to the terminal (1i-05) via an RAR message (1i-70). At this time, the RAR message transmitted from the target base station (1i-15) to the terminal (1i-05) can contain at least RAPID and a TA command. Alternatively, the target base station (1i-15) may transmit the derived TA information to the source base station (1i-10), and the source base station (1i-10) may transmit the TA information to the terminal (1i-05) using a predetermined RRC message, a MAC (medium access control) CE (control element), or L1 signaling (DCI (downlink control information)). The terminal (1i-05) that receives the TA information starts a predetermined validity timer (1i-65) and determines that the TA value is valid until the timer expires. In condition-based handover, there may be multiple target candidate cells. Therefore, the early TA acquisition can be permitted for each target candidate cell and related configuration information can be provided, and the terminal (1i-05) that has received the configuration information performs a random access operation for TA acquisition for each target candidate cell.

[0106] The terminal (1i-05) determines whether the above-described predetermined CHO condition is satisfied (1i-75), and if there is a target candidate cell that satisfies the condition and has a valid TA value for the target candidate cell, it performs a RACH-less condition-based handover to the target candidate cell. If it is determined that the timer that was run has expired and the TA value is no longer valid, the terminal (1i-05) performs a normal condition-based handover involving a random access process, or if there is no candidate target cell that satisfies the condition yet, it can re-perform the random access process for the purpose of acquiring the TA to update a valid TA value.

[0107] The terminal (1i-05) performs a PDDCH monitoring operation to determine whether its own scheduling information exists in the wireless resources set above. Then, when the scheduling information of the terminal (1i-05) is received, the terminal (1i-05) transmits a PUSCH to the target base station (1i-15) in the wireless resources indicated by the scheduling information, taking into account the uplink transmission timing derived from the TA value. The PUSCH may include an RRCReconfigurationComplete message.

[0108] Afterwards, if the condition-based handover is successfully completed, the terminal (1i-05) can delete the TA values ​​of the candidate target cells that it has stored.

[0109] FIG. 10 is a flowchart of terminal operations for performing a handover operation through pre-TA acquisition according to an embodiment of the present disclosure.

[0110] In step 1j-05, the terminal reports capability information of the terminal to the source base station. The capability information includes indicators indicating that the terminal supports early TA acquisition and RACH-less (conditional-based) handover.

[0111] In step 1j-10 of FIG. 1, the terminal reports to the source base station, using a predetermined RRC message (UEAssistanceInformation), that the preference, i.e., RACH-less (condition-based) handover (or early TA acquisition for this) is required.

[0112] In step 1j-15 of FIG. 1, the terminal receives configuration information for an early TA acquisition operation from the source base station. The early TA acquisition configuration information includes target base station ID information and predetermined random access configuration information.

[0113] In step 1j-20, the terminal transmits a preamble (MSG1) to the target base station.

[0114] In step 1j-25 of FIG. 1, the terminal receives a RAR message including a TA command from the target base station.

[0115] In step 1j-30, the terminal reports the cell measurement results to the source base station.

[0116] In step 1j-35, the terminal receives a HO command from the source base station.

[0117] In step 1j-40, the terminal performs RACH-less (condition-based) handover and transmits PUSCH to the target base station without a random access process.

[0118] FIG. 11 is a flowchart of a base station operation for performing a handover operation through pre-TA acquisition according to an embodiment of the present disclosure.

[0119] In step 1k-05, the base station receives capability information from the terminal. The capability information includes indicators indicating that the terminal supports early TA acquisition and RACH-less (conditional-based) handover.

[0120] In step 1k-10, the base station receives from the terminal a predetermined RRC message (UEAssistanceInformation) containing information indicating the need for the preference, i.e., RACH-less (condition-based) handover (or early TA acquisition therefor).

[0121] In step 1k-15, the base station exchanges configuration information for early TA acquisition operation and RACH-less handover with the target base station.

[0122] In step 1k-20, the base station transmits to the terminal a predetermined early TA acquisition operation and RACH-less handover-related configuration information received from the target base station.

[0123] In step 1k-25, the base station receives cell measurement information from the terminal.

[0124] In step 1k-30, the base station transmits a HO command to the terminal.

[0125] Figure 12 is a block diagram showing the internal structure of a terminal to which the present invention is applied.

[0126] Referring to FIG. 12, the terminal according to the present embodiment includes an RF (Radio Frequency) processing unit (11-10), a baseband processing unit (11-20), a storage unit (11-30), and a control unit (11-40).

[0127] The RF processing unit (11-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (11-10) up-converts the baseband signal provided from the baseband processing unit (11-20) into an RF (radio frequency) band signal and transmits it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (11-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC (digital to analog convertor), an ADC (analog to digital convertor), etc. In the drawing, only one antenna is illustrated, but the terminal may be equipped with multiple antennas. In addition, the RF processing unit (11-10) may include multiple RF chains. Furthermore, the RF processing unit (11-10) may perform beamforming. For the above beamforming, the RF processing unit (11-10) can adjust the phase and size of each signal transmitted and received through multiple antennas or antenna elements. In addition, the RF processing unit can perform MIMO (multiple input multiple output) and can receive multiple layers when performing MIMO operation.

[0128] The baseband processing unit (11-20) performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the system. For example, when transmitting data, the baseband processing unit (11-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (11-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (11-10). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (11-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols by performing an inverse fast Fourier transform (IFFT) operation and inserting a cyclic prefix (CP). In addition, when receiving data, the baseband processing unit (11-20) divides the baseband signal provided from the RF processing unit (11-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT (fast Fourier transform) operation, and then restores the received bit string through demodulation and decoding.

[0129] The baseband processing unit (11-20) and the RF processing unit (11-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (11-20) and the RF processing unit (11-10) may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. Furthermore, at least one of the baseband processing unit (11-20) and the RF processing unit (11-10) may include a plurality of communication modules to support a plurality of different wireless access technologies. In addition, at least one of the baseband processing unit (11-20) and the RF processing unit (11-10) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. Additionally, the different frequency bands may include a super high frequency (SHF) (e.g., 2.NRHz, NRhz) band and a millimeter wave (mm wave) (e.g., 60GHz) band.

[0130] The storage unit (1l-30) stores data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the storage unit (1l-30) can store information related to a second access node that performs wireless communication using a second wireless access technology. In addition, the storage unit (1l-30) provides the stored data at the request of the control unit (1l-40).

[0131] The control unit (11-40) controls the overall operations of the terminal. For example, the control unit (11-40) transmits and receives signals through the baseband processing unit (11-20) and the RF processing unit (11-10). In addition, the control unit (11-40) records and reads data in the storage unit (11-30). For this purpose, the control unit (11-40) may include at least one processor. For example, the control unit (11-40) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as application programs.

[0132] Figure 13 is a block diagram showing the configuration of a base station according to the present invention.

[0133] Referring to FIG. 13, the base station according to the present embodiment is configured to include an RF processing unit (1m-10), a baseband processing unit (1m-20), a backhaul communication unit (1m-30), a storage unit (1m-40), and a control unit (1m-50).

[0134] The RF processing unit (1m-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1m-10) upconverts the baseband signal provided from the baseband processing unit (1m-20) into an RF band signal and transmits it through an antenna, and downconverts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1m-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. In the drawing, only one antenna is shown, but the first access node may have multiple antennas. In addition, the RF processing unit (1m-10) may include multiple RF chains. Furthermore, the RF processing unit (1m-10) may perform beamforming. For the above beamforming, the RF processing unit (1m-10) can adjust the phase and magnitude of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit can perform a downlink MIMO operation by transmitting one or more layers.

[0135] The baseband processing unit (1m-20) performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the first wireless access technology. For example, when transmitting data, the baseband processing unit (1m-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (1m-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (1m-10). For example, in the case of OFDM, when transmitting data, the baseband processing unit (1m-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols through IFFT operation and CP insertion. In addition, when receiving data, the baseband processing unit (1m-20) divides the baseband signal provided from the RF processing unit (1m-10) into OFDM symbol units, restores the signals mapped to subcarriers through FFT operation, and then restores the received bit string through demodulation and decoding. The baseband processing unit (1m-20) and the RF processing unit (1m-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (1m-20) and the RF processing unit (1m-10) may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0136] The above backhaul communication unit (1m-30) provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit (1m-30) converts a bit string transmitted from the main base station to another node, such as an auxiliary base station or core network, into a physical signal, and converts a physical signal received from the other node into a bit string.

[0137] The storage unit (1m-40) stores data such as basic programs, application programs, and configuration information for the operation of the main base station. In particular, the storage unit (1m-40) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit (1m-40) can store information that serves as a judgment criterion for whether to provide or terminate multiple connections to a terminal. In addition, the storage unit (1m-40) provides the stored data at the request of the control unit (1m-50).

[0138] The control unit (1m-50) controls the overall operations of the base station. For example, the control unit (1m-50) transmits and receives signals through the baseband processing unit (1m-20) and the RF processing unit (1m-10) or through the backhaul communication unit (1m-30). In addition, the control unit (1m-50) records and reads data in the storage unit (1m-40). For this purpose, the control unit (1m-50) may include at least one processor.

[0139] Meanwhile, the embodiments of the present disclosure disclosed in this specification and drawings are merely specific examples to easily explain the technical contents of the present disclosure and to help understand the present disclosure, and are not intended to limit the scope of the present disclosure. In other words, it will be apparent to those skilled in the art that other modified examples based on the technical idea of ​​the present disclosure are possible. In addition, the above-described embodiments can be combined and operated as needed. For example, parts of one embodiment of the present disclosure and another embodiment can be combined to operate a base station and a terminal. In addition, the embodiments of the present disclosure are applicable to other communication systems, and other modified examples based on the technical idea of ​​the embodiments may also be implemented. For example, the embodiments may be applied to LTE systems, 5G, NR systems, or 6G systems. Therefore, the scope of the present disclosure should not be limited to the described embodiments, but should be defined not only by the scope of the following claims but also by equivalents thereof.

Claims

1. In a method of a terminal in a wireless communication system, A step of receiving, from a base station, an RRC release message indicating a transition from a radio resource control (RRC) connected state to an RRC inactive state, wherein the RRC release message includes first information used to determine timing advance (TA) validity and second information regarding a preamble used for TA update; In the RRC inactive state, if it is determined that the current TA value is invalid based on the first information, a step of transmitting a random access preamble to the base station based on the second information; A step of updating the current TA value based on the TA command when a random access response including a TA command is received from the base station; A step of storing the updated TA value and initiating a validity determination operation for the stored TA value using the first information; and When a preset service is triggered, a step of transmitting a PUSCH (physical uplink shared channel) to the base station using the stored TA value is included based on the determination that the stored TA value is valid. A method of a terminal, characterized in that the above-mentioned stored TA value is the TA value last stored in the terminal by the validity determination operation before the above-mentioned preset service is triggered.

2. In paragraph 1, The first information includes at least one of information about the value of the timer or information about the threshold value of the signal strength, If the first information includes information about the value of the timer, the validity determination operation is initiated based on driving the TA validity timer with the value of the timer from the time at which the updated TA value is stored, A method of a terminal, characterized in that if the first information includes information on a threshold value of the signal strength, the validity determination operation is initiated based on monitoring whether the magnitude of the signal strength measured at the time when the updated TA value is stored changes by more than the threshold value.

3. In paragraph 1, Further comprising a step of transmitting capability information of the terminal to the base station, the capability information indicating that the terminal supports an operation for maintaining TA validity in the RRC inactive state, The RRC release message further includes an indicator for instructing an operation to maintain the validity of the TA based on the capability information of the terminal and information about a set grant for transmission of the PUSCH. The above-described preset service includes a delay-sensitive service, A method of a terminal, characterized in that when an RRC resume message is received from the base station in response to transmission of the PUSCH, the terminal switches to the RRC connected state.

4. In paragraph 3, A step of receiving a first RRC reset message including setup information for acquiring TA for a target base station from the base station in the RRC connection state; A step of transmitting a preamble to the target base station based on the setting information; After transmitting a measurement report to the base station, a step of receiving a second RRC reset message including handover setup information and radio resource information for PDCCH (physical downlink control channel) monitoring from the base station; and If the wireless resource scheduled by the target base station is confirmed based on the wireless resource information, the step of transmitting data to the target base station using a target TA value for the target base station is further included. A method of a terminal, characterized in that the target TA value is obtained based on a TA command included in a random access response message received from the target base station in response to the preamble, or is obtained from the second RRC reset message.

5. In a method of a base station in a wireless communication system, A step of receiving, by a terminal, an RRC release message indicating a transition from a radio resource control (RRC) connected state to an RRC inactive state, wherein the RRC release message includes first information used to determine timing advance (TA) validity and second information regarding a preamble used for TA update; A step of receiving at least one random access preamble based on the second information from the terminal in the RRC inactive state; a step of transmitting at least one random access response to the at least one random access preamble to the terminal; and A step of receiving a PUSCH (physical uplink shared channel) related to a preset service from the terminal is included, The above PUSCH is received based on the TA command, A method of a base station, characterized in that the TA command is included in the last random access response among the at least one random access response transmitted to the terminal before receiving the PUSCH.

6. In paragraph 5, A method of a base station, characterized in that the first information includes at least one of information on a timer value or information on a threshold value of signal strength.

7. In paragraph 5, A step of receiving capability information of the terminal from the terminal, which indicates that the terminal supports an operation for maintaining TA validity in the RRC inactive state; and Further comprising a step of transmitting an RRC resume message to the terminal based on reception of the PUSCH to transition the terminal to the RRC connected state, The RRC release message further includes an indicator for instructing an operation to maintain the validity of the TA based on the capability information of the terminal and information about a set grant for transmission of the PUSCH. A method of a base station, characterized in that the above-described preset service includes a delay-sensitive service.

8. In paragraph 7, A step of receiving, from a target base station, setting information for acquiring TA of the terminal for the target base station; A step of transmitting a first RRC reset message including the setting information to the terminal in the RRC connection state; Upon receiving a measurement report from the terminal, a step of transmitting an indicator requesting RACH (random access channel)-less handover to the target base station; A step of receiving, from the target base station, handover setup information, a target TA value of the terminal for the target base station, and radio resource information for PDCCH (physical downlink control channel) monitoring based on the indicator; and A method of a base station, characterized in that it further comprises a step of transmitting a second RRC reset message including the handover setting information, the target TA value, and the radio resource information to the terminal.

9. In a wireless communication system, at the terminal, Transmitter and receiver; and Controlling the transceiver to receive, from a base station, an RRC release message instructing a transition from a radio resource control (RRC) connected state to an RRC inactive state, wherein the RRC release message includes first information used to determine timing advance (TA) validity and second information about a preamble used for TA update, and controlling the transceiver to transmit, to the base station, a random access preamble based on the second information when a current TA value is determined to be invalid based on the first information, and updating the current TA value based on the TA command when a random access response including a TA command is received from the base station. A control unit that stores the updated TA value, initiates a validity determination operation for the stored TA value using the first information, and controls the transceiver to transmit a PUSCH (physical uplink shared channel) to the base station using the stored TA value when a preset service is triggered based on the stored TA value being determined to be valid. A terminal characterized in that the above-mentioned stored TA value is the TA value last stored in the terminal by the validity determination operation before the above-mentioned preset service is triggered.

10. In paragraph 9, The first information includes at least one of information about the value of the timer or information about the threshold value of the signal strength, The terminal characterized in that the control unit, if the first information includes information about the value of the timer, initiates the validity determination operation based on driving the TA validity timer with the value of the timer from the time at which the updated TA value is stored, and if the first information includes information about the threshold value of the signal strength, initiates the validity determination operation based on monitoring whether the magnitude of the signal strength measured at the time at which the updated TA value is stored changes by more than the threshold value.

11. In paragraph 9, The control unit controls the transceiver to transmit capability information of the terminal to the base station, which instructs the terminal to support an operation for maintaining TA validity in the RRC inactive state. The RRC release message further includes an indicator for instructing an operation to maintain the validity of the TA based on the capability information of the terminal and information about a set grant for transmission of the PUSCH. The above-described preset service includes a delay-sensitive service, A terminal characterized in that, when an RRC resume message is received from the base station in response to transmission of the PUSCH, the terminal switches to the RRC connected state.

12. In paragraph 11, The above control unit, Controlling the transceiver to receive, from the base station in the RRC connection state, a first RRC reconfiguration message including configuration information for acquiring TA for a target base station; Controlling the transceiver to transmit a preamble to the target base station based on the configuration information; Controlling the transceiver to receive, from the base station, a second RRC reconfiguration message including handover configuration information and radio resource information for PDCCH (physical downlink control channel) monitoring after transmitting a measurement report to the base station; and controlling the transceiver to transmit data to the target base station using the target TA value when a radio resource scheduled by the target base station is confirmed based on the radio resource information. A terminal characterized in that the target TA value is obtained based on a TA command included in a random access response message received from the target base station in response to the preamble, or is obtained from the second RRC reset message.

13. In a wireless communication system, at a base station, Transmitter and receiver; and A control unit for controlling the transceiver to receive an RRC release message instructing a transition from a radio resource control (RRC) connected state to an RRC inactive state, wherein the RRC release message includes first information used to determine timing advance (TA) validity and second information about a preamble used for TA update, and for controlling the transceiver to receive at least one random access preamble from the terminal in the RRC inactive state based on the second information, and for controlling the transceiver to transmit at least one random access response to the terminal in response to the at least one random access preamble, and for controlling the transceiver to receive a physical uplink shared channel (PUSCH) related to a preset service from the terminal, The above PUSCH is received based on the TA command, A base station, characterized in that the TA command is included in the last random access response among the at least one random access response transmitted to the terminal before receiving the PUSCH.

14. In paragraph 13, The first information includes at least one of information about the value of the timer or information about the threshold value of the signal strength, The control unit controls the transceiver to receive capability information of the terminal indicating that the terminal supports an operation for maintaining TA validity in the RRC inactive state from the terminal, and controls the transceiver to transmit an RRC resume message to the terminal for switching the terminal to the RRC connected state based on reception of the PUSCH. The RRC release message further includes an indicator for instructing an operation to maintain the validity of the TA based on the capability information of the terminal and information about a set grant for transmission of the PUSCH. A base station characterized in that the above-described preset service includes a delay-sensitive service.

15. In paragraph 14, the control unit, Control the transceiver to receive, from the target base station, setting information for acquiring TA of the terminal for the target base station; Controlling the transceiver to transmit a first RRC reset message including the setting information to the terminal in the RRC connection state; When receiving a measurement report from the terminal, the transceiver is controlled to transmit an indicator requesting RACH (random access channel)-less handover to the target base station; Controlling the transceiver to receive, from the target base station, handover setup information, a target TA value of the terminal for the target base station, and radio resource information for PDCCH (physical downlink control channel) monitoring based on the indicator; and A base station characterized in that it controls the transceiver to transmit a second RRC reset message including the handover setting information, the target TA value, and the radio resource information to the terminal.

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