Method and apparatus for selecting data cell for reducing network power in wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. A method performed by a terminal of a wireless communication system according to an embodiment of the present disclosure comprises the steps of: in a state of being camped on a first-type cell, identifying that a radio resource control (RRC) connection procedure has been triggered; receiving a first reference signal from a second-type cell that is in an active state; identifying whether a measurement value of the first reference signal exceeds a threshold value; if the measurement value of the first reference signal does not exceed the threshold value, transmitting an uplink signal for switching a second-type cell that is in an inactive state to an active state; receiving a second reference signal from the second-type cell that has been switched to the active state according to the uplink signal; on the basis of a measurement value of the second reference signal, determining a second-type cell for establishing an RRC connection; and establishing the RRC connection with the determined second-type cell.

Description

Method and device for selecting data cells for reducing network power in a wireless communication system

[0001] The present disclosure relates to the operation of a terminal and base station in a wireless communication system. More specifically, the present disclosure relates to a method and device for selecting a data cell for reducing network power in a wireless communication system.

[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 can serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing them.

[0008] With the advancement of wireless communication systems, the utilization of a power-saving network composed of sync cells and data cells is being discussed. In certain scenarios, some data cells in the power-saving network may be active, while others may be in a power-saving (inactive) state. In this case, a method for a terminal to determine which data cell (active or inactive) to perform an RRC connection procedure on has not been defined. The present disclosure proposes a method for a terminal to select a data cell for performing an RRC connection procedure in a power-saving network composed of sync cells and data cells in a wireless communication system.

[0009] According to one embodiment of the present disclosure, a method performed by a terminal of a wireless communication system is provided. The method comprises the steps of: identifying that a radio resource control (RRC) connection procedure has been triggered in a camp-on state for a first type of cell; receiving a first reference signal from a second type of cell that is active; identifying whether a measurement value of the first reference signal exceeds a threshold value; transmitting an uplink signal for switching a second type of cell that is in an inactive state to an active state when the measurement value of the first reference signal does not exceed the threshold value; receiving a second reference signal from a second type of cell that has been switched to an active state according to the uplink signal; determining a second type of cell for establishing an RRC connection based on a measurement value of the second reference signal; and establishing the RRC connection with the determined second type of cell.

[0010] According to one embodiment of the present disclosure, a terminal of a wireless communication system is provided. The terminal includes a transceiver and a control unit. The control unit is configured to identify that an RRC connection procedure has been triggered in a camp-on state for a first type of cell, receive a first reference signal from a second type of cell in an activated state through the transceiver, identify whether a measurement value of the first reference signal exceeds a threshold value, and, if the measurement value of the first reference signal does not exceed the threshold value, transmit an uplink signal for switching a second type of cell in an inactive state to an activated state through the transceiver, receive a second reference signal from a second type of cell switched to an activated state according to the uplink signal through the transceiver, determine a second type of cell for establishing an RRC connection based on the measurement value of the second reference signal, and establish the RRC connection with the determined second type of cell.

[0011] According to one embodiment of the present disclosure, in a power-saving network composed of a sync cell and a data cell of a wireless communication system, a terminal can efficiently select a data cell for performing an RRC connection procedure.

[0012] FIG. 1 is a diagram showing the structure of a mobile communication network including a base station according to one embodiment of the present disclosure.

[0013] FIG. 2 is a diagram illustrating a cell connection procedure according to one embodiment of the present disclosure.

[0014] FIG. 3 is a diagram illustrating a data cell connection procedure according to one embodiment of the present disclosure.

[0015] FIG. 4 is a diagram illustrating a data cell connection procedure according to one embodiment of the present disclosure.

[0016] FIG. 5 is a diagram illustrating a data cell connection procedure according to one embodiment of the present disclosure.

[0017] FIG. 6 is a diagram illustrating a data cell connection procedure according to one embodiment of the present disclosure.

[0018] FIG. 7 is a diagram illustrating an operation of setting a data cell connection method according to one embodiment of the present disclosure.

[0019] FIG. 8 is a diagram illustrating an operation of setting a data cell connection method according to one embodiment of the present disclosure.

[0020] FIG. 9 is a diagram illustrating an operation of setting a data cell connection method according to one embodiment of the present disclosure.

[0021] FIG. 10 is a diagram illustrating the structure of a base station according to one embodiment of the present disclosure.

[0022] FIG. 11 is a diagram illustrating the structure of a terminal according to one embodiment of the present disclosure.

[0023] In describing the embodiments herein, descriptions of technical details that are well-known in the technical field to which the present invention pertains and are not directly related to the present invention will be omitted. This is to avoid obscuring the gist of the present invention by omitting unnecessary explanations and to convey the gist more clearly.

[0024] For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted. Furthermore, the dimensions of each component do not entirely reflect its actual size. Identical or corresponding components in each drawing are assigned the same reference numbers.

[0025] The advantages and features of the present invention, and the methods for achieving them, will become clearer with reference to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals designate like elements throughout the specification.

[0026] At this time, it will be understood that each block of the processing flow diagrams and combinations of the flow diagrams can be performed by computer program instructions. These computer program instructions can be installed in a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, so that the instructions executed by the processor of the computer or other programmable data processing equipment create a means for performing the functions described in the flow diagram block(s). These computer program instructions can also be stored in a computer-available or computer-readable memory that can direct a computer or other programmable data processing equipment to implement the functions in a specific manner, so that the instructions stored in the computer-available or computer-readable memory can also produce a manufactured item that includes an instruction means for performing the functions described in the flow diagram block(s). Since the computer program instructions may be installed on a computer or other programmable data processing device, a series of operational steps may be performed on the computer or other programmable data processing device to create a computer-executable process, and the instructions that cause the computer or other programmable data processing device to perform the steps for performing the functions described in the flowchart block(s) may also provide steps for performing the functions described in the flowchart block(s).

[0027] Additionally, each block may represent a module, segment, or portion of code that contains one or more executable instructions for performing a specific logical function(s). It should also be noted that in some alternative implementation examples, the functions described in the blocks may occur out of order. For example, two blocks depicted in succession may actually be executed substantially concurrently, or the blocks may sometimes be executed in reverse order, depending on their respective functions.

[0028] Here, the term '~ unit' used in the present embodiment means a software or hardware component such as an FPGA or ASIC, and the '~ unit' performs certain roles. However, the '~ unit' is not limited to software or hardware. The '~ unit' may be configured to be on an addressable storage medium and may be configured to play one or more processors. Accordingly, as an example, the '~ unit' includes components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and '~ units' may be combined into a smaller number of components and '~ units' or further separated into additional components and '~ units'. Additionally, components and '~parts' may be implemented to regenerate one or more CPUs within a device or secure multimedia card.

[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] FIG. 1 is a diagram showing the structure of a mobile communication network including a base station according to one embodiment of the present disclosure.

[0031] Mobile operators (MOs) operating mobile communication networks may have multiple frequencies to provide services using these networks. Each frequency can have different coverage due to its propagation characteristics, and the bandwidth of the frequencies held by the operator can also vary depending on the carrier's frequency holdings. Meanwhile, high-frequency bands, which offer a relatively large bandwidth, are essential for high-speed data transmission. However, the propagation characteristics of high-frequency bands are highly linear and have short ranges, resulting in limited coverage. Conversely, low-frequency bands exhibit less signal strength degradation during transmission and diffraction, allowing for relatively greater coverage. For these reasons, mobile communication networks utilizing high-frequency bands require a large number of base stations, which can increase the power consumption and associated operating costs of the mobile communication network. Typically, a mobile communication network operated by a single operator is so wide that it covers a country or multiple regions within a country, so there may be a need for a method to reduce the power consumption and resulting operating costs of wireless communication networks that use high-frequency bands for high-speed data transmission.

[0032] Referring to Figure 1, a method in which a base station of a mobile communication network is operated by dividing it into a sync cell and a data cell is illustrated.

[0033] A sync cell (100) can be a cell where a terminal in RRC (Radio Resource Control) idle mode (RRC_IDLE) or RRC inactive mode (RRC_INACTIVE) can camp on without an RRC connection, thereby ensuring mobility. The sync cell can transmit a synchronization signal (e.g., a synchronization signal block, SSB) so that the terminal can receive information from a base station. The sync cell can transmit to the terminal at least one of essential system information that the base station must transmit to the terminal, random access resource information of a data cell for the terminal to access the data cell, an activation / deactivation status of the data cell, radio resources for a WUS (Wake Up Signal) of the data cell, and frequency information of the data cell. In addition, the sync cell can transmit a paging message that the base station instructs the terminal to transition to an RRC connected mode when the terminal is in an RRC idle mode or an RRC inactive mode.

[0034] Data cells (110, 111, 112, 113, 114, 115, 116) are cells in which a terminal transmits and receives data with a base station in an RRC connection mode, and can be cells in which mobility is guaranteed for a terminal in an RRC connection mode. The data cell can transmit a reference signal (RS) and / or a synchronization signal of the data cell so that the terminal can receive information from the base station. In some embodiments, the reference signal and the synchronization signal may be transmitted in the same SSB. The base station can transmit system information to be transmitted by the base station, random access information of the data cell, etc. to the terminal through the data cell. If there is no terminal having an RRC connection with the data cell, the data cell can perform an operation to increase power saving in an inactive state. In the power saving mode of the data cell, the data cell may not transmit at least one of the reference signal, the synchronization signal, and the system information. The terminal can transmit a signal to switch the data cell in an inactive state to an active state. In the present disclosure, the signal may be referred to as a WUS (Wake Up Signal). In some embodiments, a data cell in an inactive state may receive a WUS transmitted by a terminal to a base station using a separate radio resource (e.g., Wake Up Radio, WUR) that operates at low power for the WUS. In other embodiments, a data cell may receive a WUS using a WUR regardless of whether it is in an inactive state. In order for a terminal to transmit a WUS to a data cell, the terminal must know the WUS configuration information of the data cell, and the WUS configuration information may be received from a sync cell. The WUS configuration information of each data cell may be set differently, but in some embodiments, the WUS configuration information of multiple data cells may be set identically.

[0035] If the sync cell uses a relatively low frequency band and the data cell uses a relatively high frequency band, the coverage of the sync cell (105) may be wider than the coverage of each data cell (120, 121, 122, 123, 124, 125, 126) due to the propagation characteristics of the frequencies. However, depending on the embodiment, the sizes of the coverage of the sync cell and the coverage of the data cell may be different.

[0036] FIG. 2 is a diagram illustrating a cell connection procedure according to one embodiment of the present disclosure.

[0037] When a terminal generates transmission data in RRC idle mode or RRC inactive mode or receives a paging message from a base station, it may need to transition to RRC connected mode. At this time, if the terminal enters RRC connected mode and a cell (210) with which an RRC connection must be established is active, the terminal can receive a reference signal (211) from the active cell, and can measure the reference signal (RS) of the active cell without a separate WUS transmission to search for the active cell and perform initial access procedures such as random access.

[0038] On the other hand, if the terminal enters the RRC connected mode and the cell (220) that needs to establish the RRC connection uses WUR and is in an inactive state, it is necessary to transmit a WUS to the cell to switch the base station to an active state. At this time, it is necessary to configure whether the terminal will perform an operation to search for an active cell by measuring the reference signal of the active cell, or whether to transmit a WUS to switch the inactive cell to an active state. In some embodiments, it is necessary to configure conditions for the terminal to measure the reference signal of the active cell to search for an active cell, and then perform a random access to one of the searched active cells to transition to the RRC connected mode. In some embodiments, the terminal may measure the reference signal of the active cell to search for a cell, and then perform a random access to one of the searched active cells whose signal strength is equal to or greater than a threshold value to transition to the RRC connected mode. Otherwise, if the terminal measures the reference signal of the active cell to search for a cell, and the signal strength of the searched active cell is less than (or below) the threshold value, the terminal may perform a procedure to change the cell in an inactive state to an active state by transmitting a WUS.

[0039] Meanwhile, the activation cells and inactivation cells in the embodiment of Fig. 2 can be applied to any cell. Alternatively, the activation cells and inactivation cells described in Fig. 2 can be limited to the data cells described in Fig. 1.

[0040] FIG. 3 is a diagram illustrating a data cell connection procedure according to one embodiment of the present disclosure.

[0041] When a terminal generates transmission data in RRC idle mode or RRC inactive mode or receives a paging message from a base station, it may need to transition to RRC connected mode. At this time, if the terminal enters RRC connected mode and the cell for which an RRC connection must be established is active, the terminal can receive a reference signal from the active cell, and can measure the reference signal (RS) of the active cell without a separate WUS transmission to search for the active cell and perform initial access procedures such as random access.

[0042] On the other hand, if the terminal enters RRC connection mode and the cell to which the RRC connection must be established uses WUR and is in an inactive state, it is necessary to transmit WUS to the cell to switch the base station to an active state.

[0043] When a terminal measures a reference signal from an activated cell and performs initial access procedures such as random access to the activated cell to enter RRC connection mode, if the activated cell can provide sufficient Quality of Service (QoS) to the terminal, there is an advantage in that the terminal can perform a quick initial access. However, if the signal strength received by the terminal from the activated cell is low, the activated cell may not be able to provide sufficient QoS to the terminal, and thus an operation to activate another inactive cell may be necessary.

[0044] Since a terminal cannot accurately predict the base station distribution status of a mobile communication network, including inactive cells, the terminal needs to be configured by the mobile communication network to establish an RRC connection by entering RRC connection mode through an active cell, or to transmit a WUS to switch an inactive cell to an active state. Furthermore, if there is an active cell where the terminal can receive sufficient service quality, there may be no need to transmit a WUS to another inactive cell.

[0045] Below, a method is described for determining whether a terminal will establish an RRC connection by entering RRC connection mode through an activated cell based on the signal strength of the activated cell, or whether to switch an inactive cell to an activated state by transmitting a WUS.

[0046] In the embodiment of FIG. 3, it will be described below assuming that the cell for which the terminal must enter RRC connection mode and establish an RRC connection is the data cell described in FIG. 1, but the content regarding the operation of connecting to the cell for which an RRC connection must be established can be applied to any cell.

[0047] In step 310, an RRC connection procedure may be triggered in the terminal for a predetermined reason. In addition, the terminal may be configured / instructed in advance by the base station to perform signal strength-based cell selection of an activated data cell. Here, the predetermined reason for triggering the RRC connection procedure may include at least one of the following: transmission data occurs in the terminal in RRC idle mode or RRC inactive mode, or a paging message is received from the base station. The base station may configure whether the terminal performs signal strength-based cell selection. The message for configuring the signal strength-based cell selection may be configured by a System Information Block (SIB) or an RRC Release message. If the SIB message is configured by the SIB message, the SIB may be transmitted by the sync cell. This has the effect of preventing increased power consumption because the base station of the data cell does not need to switch to an active state to transmit the SIB configuring signal strength-based cell selection. To configure the SIB based cell selection, a first threshold value for the signal strength may be configured. The first threshold value may be applied to all cells selected by the terminal to perform the RRC connection procedure with the same value. However, in other embodiments, different cells may have different first threshold values, which may be set per cell (or per group of cells including multiple cells) in the system information block or RRC release message, which is a message that sets signal strength-based cell selection.

[0048] In step 320, the terminal can measure the reference signal of the activated data cell to determine whether there is a cell whose signal strength received by the terminal from the base station is equal to or greater than a first threshold value. At this time, the signal strength used by the terminal may be one of Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), or Received Signal Strength Indicator (RSSI). In addition, the reference signal may be at least one of SSB, a portion of SSB, Cell-specific RS (CRS), and Channel State Information - Reference Signal (CSI-RS). If there is a cell among the activated data cells whose reference signal strength is equal to or greater than the first threshold value, this may mean that there is a cell with sufficient signal strength for the terminal to perform an RRC connection procedure.

[0049] If, according to the operation of step 320, there is a data cell among the data cells activated in which the signal intensity of the reference signal is equal to or greater than the first threshold, the terminal may select one of the data cells in which the signal intensity of the reference signal is equal to or greater than the first threshold in step 330. In some embodiments, the terminal may select a data cell in which the signal intensity of the reference signal is the greatest among the data cells in which the signal intensity of the reference signal is equal to or greater than the first threshold.

[0050] Meanwhile, if there is no cell among the activated data cells whose reference signal strength is equal to or greater than the first threshold value, this may mean that there is no cell with sufficient signal strength for the terminal to perform the RRC connection procedure. If there is no data cell among the activated data cells whose reference signal strength is equal to or greater than the first threshold value according to the operation of step 320, the terminal may transmit a WUS to an inactive data cell in step 340. Through this procedure, the inactive data cell may be switched to an active state and may transmit a reference signal. The terminal may transmit a WUS to an inactive data cell using the WUS configuration information received in advance. Through this procedure, the inactive data cell that received the WUS may be switched to an active state and may transmit a reference signal. However, if the signal strength of the received WUS is not sufficiently strong, the data cell may not be switched to an active state.

[0051] After the inactive data cell is switched to the active state, the terminal can receive a reference signal from the data cell that has switched to the active state. Based on this, the terminal can select a data cell in step 350. In some embodiments, the terminal can select the data cell with the highest signal strength of the reference signal received. In other embodiments, among the data cells that have switched to the active state after the WUS transmission, the terminal can select the data cell with the highest signal strength of the reference signal received.

[0052] The terminal may perform an RRC connection procedure for the data cell selected in step 360. This RRC connection procedure may include a procedure in which the terminal transmits an RRC connection request (Connection / Setup Request) or RRC resume request (Resume Request) message to the base station, or performs random access.

[0053] FIG. 4 is a diagram illustrating a data cell connection procedure according to one embodiment of the present disclosure.

[0054] When a terminal generates transmission data in RRC idle mode or RRC inactive mode or receives a paging message from a base station, it may need to transition to RRC connected mode. At this time, if the terminal enters RRC connected mode and the cell for which an RRC connection must be established is active, the terminal can receive a reference signal from the active cell, and can measure the reference signal (RS) of the active cell without a separate WUS transmission to search for the active cell and perform initial access procedures such as random access.

[0055] On the other hand, if the terminal enters RRC connection mode and the cell to which the RRC connection must be established uses WUR and is in an inactive state, it is necessary to transmit WUS to the cell to switch the base station to an active state.

[0056] When a terminal measures a reference signal from an activated cell and performs initial access procedures such as random access to the activated cell to enter RRC connection mode, if the activated cell can provide sufficient Quality of Service (QoS) to the terminal, there is an advantage in that the terminal can perform a quick initial access. However, if the signal strength received by the terminal from the activated cell is low, the activated cell may not be able to provide sufficient QoS to the terminal, and thus an operation to activate another inactive cell may be necessary.

[0057] Since a terminal cannot accurately predict the base station distribution status of a mobile communication network, including inactive cells, the terminal needs to be configured by the mobile communication network to establish an RRC connection by entering RRC connection mode through an active cell, or to transmit a WUS to switch an inactive cell to an active state. Furthermore, if there is an active cell where the terminal can receive sufficient service quality, there may be no need to transmit a WUS to another inactive cell.

[0058] Below, a method is described in which a terminal determines whether to establish an RRC connection by entering RRC connection mode through an activated cell based on the signal strength of the activated cell, or to establish an RRC connection after switching an inactive cell to an activated state by transmitting a WUS.

[0059] In the embodiment of FIG. 4, it will be described below assuming that the cell for which the terminal must enter RRC connection mode and establish an RRC connection is the data cell described in FIG. 1, but the content regarding the operation of connecting to the cell for which an RRC connection must be established can also be applied to any cell.

[0060] In step 410, an RRC connection procedure may be triggered in the terminal for a predetermined reason. Furthermore, the terminal may be configured / instructed in advance by the base station to perform signal strength-based cell selection of an activated data cell. The predetermined reason for triggering the RRC connection procedure may include at least one of: transmission data occurring in the terminal in RRC idle mode or RRC inactive mode, or reception of a paging message from the base station. The base station may configure whether the terminal will perform signal strength-based cell selection. The message configuring the signal strength-based cell selection may be configured by a System Information Block (SIB) or an RRC Release message. If the SIB message configures the SIB, the SIB may be transmitted by the sync cell. This has the effect of preventing increased power consumption, since the base station of the data cell does not need to switch to an active state to transmit the SIB configuring the SIB configuring the SIB based on signal strength selection. To configure the SIB based cell selection, a first threshold value for signal strength may be configured. The first threshold value may be applied to all cells selected by the terminal to perform the RRC connection procedure with the same value. However, in other embodiments, different cells may have different first threshold values, which may be set per cell (or per group of cells including multiple cells) in the system information block or RRC release message, which is a message that sets signal strength-based cell selection.

[0061] In step 420, the terminal can measure the reference signal of the activated data cell to determine whether there is a cell whose signal strength received by the terminal from the base station is equal to or greater than a first threshold value. At this time, the signal strength used by the terminal may be one of Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), or Received Signal Strength Indicator (RSSI). In addition, the reference signal may be at least one of SSB, a portion of SSB, Cell-specific RS (CRS), and Channel State Information - Reference Signal (CSI-RS). If there is a cell among the activated data cells whose reference signal strength is equal to or greater than the first threshold value, this may mean that there is a cell with sufficient signal strength for the terminal to perform an RRC connection procedure.

[0062] If, according to the operation of step 420, there is a data cell among the data cells activated in which the signal intensity of the reference signal is equal to or greater than the first threshold, the terminal may select one of the data cells in which the signal intensity of the reference signal is equal to or greater than the first threshold in step 430. In some embodiments, the terminal may select a data cell in which the signal intensity of the reference signal is the greatest among the data cells in which the signal intensity of the reference signal is equal to or greater than the first threshold.

[0063] Meanwhile, if there is no cell among the activated data cells whose reference signal strength is equal to or greater than the first threshold value, this may mean that there is no cell with sufficient signal strength for the terminal to perform the RRC connection procedure. If there is no data cell among the activated data cells whose reference signal strength is equal to or greater than the first threshold value according to the operation of step 420, the terminal may transmit a WUS to the data cell in step 440. At this time, the terminal may transmit the WUS to the data cells around the terminal without distinguishing between inactive cells and active cells. The terminal may transmit the WUS to the data cell using the WUS configuration information received in advance. Through this procedure, the inactive data cell that received the WUS may switch to the active state and transmit the reference signal. However, if the signal strength of the received WUS is not sufficiently strong, the data cell may not switch to the active state.

[0064] After the inactive data cell transitions to the active state, the terminal can receive a reference signal from the data cell transitioned to the active state. Furthermore, the terminal can continue to receive reference signals from the existing active cell. Based on this, the terminal can select a data cell in step 450. In some embodiments, the terminal can select the data cell with the highest signal strength of the reference signal received.

[0065] The terminal may perform an RRC connection procedure on the data cell selected in step 460. This RRC connection procedure may include a procedure in which the terminal transmits an RRC connection request (Connection / Setup Request) or an RRC resume request (Resume Request) message to the base station, or performs random access.

[0066] FIG. 5 is a diagram illustrating a data cell connection procedure according to one embodiment of the present disclosure.

[0067] When a terminal generates transmission data in RRC idle mode or RRC inactive mode or receives a paging message from a base station, it may need to transition to RRC connected mode. At this time, if the terminal enters RRC connected mode and the cell for which an RRC connection must be established is active, the terminal can receive a reference signal from the active cell, and can measure the reference signal (RS) of the active cell without a separate WUS transmission to search for the active cell and perform initial access procedures such as random access.

[0068] On the other hand, if the terminal enters RRC connection mode and the cell to which the RRC connection must be established uses WUR and is in an inactive state, it is necessary to transmit WUS to the cell to switch the base station to an active state.

[0069] When a terminal measures a reference signal from an activated cell and performs initial access procedures such as random access to the activated cell to enter RRC connection mode, if the activated cell can provide sufficient Quality of Service (QoS) to the terminal, there is an advantage in that the terminal can perform a quick initial access. However, if the signal strength received by the terminal from the activated cell is low, the activated cell may not be able to provide sufficient QoS to the terminal, and thus an operation to activate another inactive cell may be necessary.

[0070] Since the terminal cannot accurately predict the base station distribution status of the mobile communication network, including inactive cells, it may perform an operation to switch an inactive cell to an active state by transmitting a WUS before performing an operation to measure a reference signal from an active cell. Furthermore, if there is an active cell where the terminal can receive sufficient service quality, there may be no need to transmit a WUS to another inactive cell. To this end, whether the terminal performs the operation to switch an inactive cell to an active state by transmitting a WUS can be determined based on the base station's settings.

[0071] Below, we describe a method for establishing an RRC connection after a terminal switches an inactive cell to an active state by transmitting a WUS.

[0072] In the embodiment of FIG. 5, it will be described below assuming that the cell for which the terminal must enter RRC connection mode and establish an RRC connection is the data cell described in FIG. 1, but the content regarding the operation of connecting to the cell for which an RRC connection must be established can also be applied to any cell.

[0073] In step 510, an RRC connection procedure may be triggered in the terminal for a predetermined reason. Furthermore, the terminal may be configured / instructed in advance by the base station to perform WUS priority cell selection. The predetermined reasons for triggering the RRC connection procedure may include at least one of: transmission data occurring in the terminal in RRC idle mode or RRC inactive mode, or reception of a paging message from the base station. The base station may configure whether the terminal performs WUS priority cell selection. The message configuring the WUS priority cell selection method may be configured by a System Information Block (SIB) or an RRC Release message. If the WUS priority cell selection method is configured by a SIB message, the SIB may be transmitted by the sync cell. This has the effect of preventing increased power consumption, since the base station of the data cell does not need to switch to an active state to transmit the SIB configuring the WUS priority cell selection method.

[0074] In step 540, a terminal whose RRC connection procedure has been triggered can transmit a WUS to a data cell. At this time, the terminal can transmit the WUS to data cells around the terminal, regardless of whether the cell is active or inactive. The terminal can transmit the WUS to the data cell using previously received WUS configuration information. Through this procedure, the inactive data cell that received the WUS transitions to the active state and can transmit a reference signal. However, if the signal strength of the received WUS is not sufficiently strong, the data cell may not transition to the active state.

[0075] After the inactive data cell transitions to the active state, the terminal can receive a reference signal from the data cell transitioned to the active state. Furthermore, the terminal can continue to receive reference signals from the existing active cell. Based on this, the terminal can select a data cell in step 550. In some embodiments, the terminal can select the data cell with the highest signal strength of the reference signal received.

[0076] The terminal may perform an RRC connection procedure on the data cell selected in step 560. This RRC connection procedure may include a procedure in which the terminal transmits an RRC connection request (Connection / Setup Request) or RRC resume request (Resume Request) message to the base station, or performs random access.

[0077] FIG. 6 is a diagram illustrating a data cell connection procedure according to one embodiment of the present disclosure.

[0078] When a terminal generates transmission data in RRC idle mode or RRC inactive mode or receives a paging message from a base station, it may need to transition to RRC connected mode. At this time, if the terminal enters RRC connected mode and the cell for which an RRC connection must be established is active, the terminal can receive a reference signal from the active cell, and can measure the reference signal (RS) of the active cell without a separate WUS transmission to search for the active cell and perform initial access procedures such as random access.

[0079] On the other hand, if the terminal enters RRC connected mode and the cell to establish the RRC connection uses WUR and is in an inactive state, it is necessary to transmit a WUS to the cell to switch the corresponding base station to an active state. When the terminal measures a reference signal from an activated cell and performs an initial access procedure such as random access to the activated cell to enter RRC connected mode, if the activated cell can provide sufficient quality of service (QoS) to the terminal, there is an advantage in that the terminal can perform a quick initial access. However, if the signal strength received by the terminal from the activated cell is low, the activated cell may not be able to provide sufficient quality of service to the terminal, so an operation to activate another inactive cell may be necessary.

[0080] Since the terminal cannot accurately predict the base station distribution status of the mobile communication network, including inactive cells, it may perform an operation to switch an inactive cell to an active state by transmitting a WUS before performing an operation to measure a reference signal from an active cell. Furthermore, if there is an active cell where the terminal can receive sufficient service quality, there may be no need to transmit a WUS to another inactive cell. To this end, whether the terminal performs the operation to switch an inactive cell to an active state by transmitting a WUS can be determined based on the base station's settings.

[0081] Below, a method is described in which a terminal selects a data cell and performs an RRC connection procedure by selecting a different method depending on which procedure was triggered when the RRC connection procedure was triggered.

[0082] In the embodiment of FIG. 6, it will be described below assuming that the cell for which the terminal must enter RRC connection mode and establish an RRC connection is the data cell described in FIG. 1, but the content regarding the operation of connecting to the cell for which an RRC connection must be established can be applied to any cell.

[0083] At step 610, an RRC connection procedure may be triggered at the terminal for a predetermined reason. The predetermined reason for triggering the RRC connection procedure may include at least one of the following: the terminal generating transmission data in RRC idle mode or RRC inactive mode, or receiving a paging message from the base station.

[0084] At step 620, the terminal can identify the reason for triggering the RRC connection procedure. The terminal can then use different data cell selection methods depending on the reason for triggering the RRC connection procedure.

[0085] If the RRC connection procedure is triggered when the terminal receives a paging message from the base station, the terminal may select a data cell using a first data cell selection method at step 630. The first data cell selection method may be one of the data cell selection methods described in FIG. 3 or FIG. 4. In some embodiments, the paging message received by the terminal may include information indicating a data cell selection method to be performed by the terminal. In this case, the terminal may select a data cell using the data cell selection method according to the information included in the paging message. In other embodiments, the base station may configure the terminal to use the first data cell selection method when the terminal receives a paging message in a system information block or an RRC release message. In other embodiments, if the RRC connection procedure is triggered when the terminal receives a paging message from the base station, the terminal may select a data cell using a second data cell selection method at step 630. The second data cell selection method may be the data cell selection method described in FIG. 5.

[0086] If the RRC connection procedure is triggered when transmission data is generated in the terminal in RRC idle mode or RRC inactive mode, the terminal may select a data cell using a second data cell selection scheme at step 650. The second data cell selection scheme may be the data cell selection scheme described in FIG. 5. In some embodiments, the base station may configure the terminal in the system information block or RRC release message which second data cell selection scheme to use when transmission data is generated in the terminal. In another embodiment, if the RRC connection procedure is triggered when transmission data is generated in the terminal in RRC idle mode or RRC inactive mode, the terminal may select a data cell using a first data cell selection scheme at step 650. The first data cell selection scheme may be one of the data cell selection schemes described in FIG. 3 or FIG. 4.

[0087] The terminal may perform an RRC connection procedure on the data cell selected in step 660. This RRC connection procedure may include a procedure in which the terminal transmits an RRC connection request (Connection / Setup Request) or an RRC resume request (Resume Request) message to the base station, or performs random access.

[0088] FIG. 7 is a diagram illustrating an operation of setting a data cell connection method according to one embodiment of the present disclosure.

[0089] When a terminal generates transmission data in RRC idle mode or RRC inactive mode or receives a paging message from a base station, it may need to transition to RRC connected mode. At this time, if the terminal enters RRC connected mode and the cell for which an RRC connection must be established is active, the terminal can receive a reference signal from the active cell, and can measure the reference signal (RS) of the active cell without a separate WUS transmission to search for the active cell and perform initial access procedures such as random access.

[0090] On the other hand, if the terminal enters RRC connection mode and the cell to which the RRC connection must be established uses WUR and is in an inactive state, it is necessary to transmit WUS to the cell to switch the base station to an active state.

[0091] The method by which the terminal selects a cell to transition to the RRC connected mode can be set by the base station (710) to the terminal (720). In the embodiment of FIG. 7, the base station (710) can transmit an RRC release message (730) to the terminal (720) to instruct to release the RRC connection and transition to the RRC idle mode or the RRC inactive mode. At this time, the RRC release message (730) can include information indicating a method by which the terminal selects a cell to establish an RRC connection when entering the RRC connected mode later.

[0092] If the cell that establishes the RRC connection when the terminal enters the RRC connection mode is a data cell, the cell selection method set in the RRC release message (730) may be a method for selecting a data cell. The method for selecting the data cell may be one of the data cell selection methods described in FIG. 3, FIG. 4, or FIG. 5. For example, the terminal may perform an operation of measuring a reference signal transmitted by a cell, checking whether there is a data cell with a signal intensity of the reference signal greater than or equal to a first threshold, and then selecting a cell with a signal intensity of the reference signal greater than or equal to the first threshold. Thereafter, if there is no cell with a signal intensity of the reference signal greater than or equal to the first threshold, the base station may transmit a WUS to a cell in an inactive state or to an arbitrary cell. In another embodiment, the base station may configure the terminal to transmit a WUS without performing an operation of measuring the signal intensity of the reference signal. In some embodiments, when the base station sets the first threshold value to the terminal, the terminal can perform the signal strength-based cell selection method described in FIG. 3 or FIG. 4, and when the first threshold value is not set, the terminal can transmit a WUS to the base station without measuring a reference signal.

[0093] The base station (710) transmitting the RRC release message (730) may also transmit a list of currently active cells (or active data cells) or inactive cells (or inactive data cells) in the RRC release message (730). At this time, the base station may also transmit a first threshold value for each cell. In some embodiments, the base station may also transmit WUS configuration information for each cell at this time.

[0094] FIG. 8 is a diagram illustrating an operation of setting a data cell connection method according to one embodiment of the present disclosure.

[0095] When a terminal generates transmission data in RRC idle mode or RRC inactive mode or receives a paging message from a base station, it may need to transition to RRC connected mode. At this time, if the terminal enters RRC connected mode and the cell for which an RRC connection must be established is active, the terminal can receive a reference signal from the active cell, and can measure the reference signal (RS) of the active cell without a separate WUS transmission to search for the active cell and perform initial access procedures such as random access.

[0096] On the other hand, if the terminal enters RRC connection mode and the cell to which the RRC connection must be established uses WUR and is in an inactive state, it is necessary to transmit WUS to the cell to switch the base station to an active state.

[0097] The method by which the terminal selects a cell to transition to the RRC connection mode can be set by the base station (810) to the terminal (820). In the embodiment of FIG. 8, the data cell base station (810) can transmit a system information / system information block message (830) transmitted by the data cell to the terminal (820), and at this time, the system information / system information block message (830) can include information indicating a method by which the terminal selects a data cell to establish an RRC connection when entering the RRC connection mode later.

[0098] The method for selecting the above data cell may be one of the data cell selection methods described in FIG. 3, FIG. 4, or FIG. 5. For example, the terminal may measure a reference signal transmitted by a cell, determine whether there is a data cell with a signal strength of the reference signal that is greater than or equal to a first threshold, and then perform an operation of selecting a cell with a signal strength of the reference signal that is greater than or equal to the first threshold. Thereafter, if there is no cell with a signal strength of the reference signal that is greater than or equal to the first threshold, the WUS may be transmitted to an inactive cell or an arbitrary cell. In another embodiment, the base station may configure the terminal to transmit the WUS without measuring the signal strength of the reference signal. In some embodiments, when the base station sets the first threshold to the terminal, the terminal may perform the signal strength-based cell selection method described in FIG. 3 or 4, and if the first threshold is not set, the terminal may transmit the WUS to the base station without measuring the reference signal.

[0099] The data cell (810) operated by the base station transmitting the system information / system information block message (830) may also transmit a list of currently active cells (or data cells) or inactive cells (or data cells) in the system information / system information block message (830). At this time, the data cell (810) may also transmit a first threshold value for each cell. In some embodiments, the data cell (810) may also transmit WUS configuration information for each cell.

[0100] FIG. 9 is a diagram illustrating an operation of setting a data cell connection method according to one embodiment of the present disclosure.

[0101] When a terminal generates transmission data in RRC idle mode or RRC inactive mode or receives a paging message from a base station, it may need to transition to RRC connected mode. At this time, if the terminal enters RRC connected mode and the cell for which an RRC connection must be established is active, the terminal can receive a reference signal from the active cell, and can measure the reference signal (RS) of the active cell without a separate WUS transmission to search for the active cell and perform initial access procedures such as random access.

[0102] On the other hand, if the terminal enters RRC connection mode and the cell to which the RRC connection must be established uses WUR and is in an inactive state, it is necessary to transmit WUS to the cell to switch the base station to an active state.

[0103] The method by which the terminal selects a cell to transition to the RRC connection mode can be set by the base station (910) to the terminal (920). In the embodiment of FIG. 9, the sync cell base station (910) can transmit the system information / system information block message (933) transmitted by the sync cell to the terminal (920), and at this time, the system information / system information block message (930) can set the method by which the terminal selects a data cell to establish an RRC connection when entering the RRC connection mode later.

[0104] The method for selecting the above data cell may be one of the data cell selection methods described in FIG. 3, FIG. 4, or FIG. 5. For example, the terminal may measure a reference signal transmitted by a cell, determine whether there is a data cell with a signal strength of the reference signal that is greater than or equal to a first threshold, and then perform an operation of selecting a cell with a signal strength of the reference signal that is greater than or equal to the first threshold. Thereafter, if there is no cell with a signal strength of the reference signal that is greater than or equal to the first threshold, the WUS may be transmitted to an inactive cell or an arbitrary cell. In another embodiment, the base station may configure the terminal to transmit the WUS without measuring the signal strength of the reference signal. In some embodiments, when the base station sets the first threshold to the terminal, the terminal may perform the signal strength-based cell selection method described in FIG. 3 or 4, and if the first threshold is not set, the terminal may transmit the WUS to the base station without measuring the reference signal.

[0105] A terminal (920) in RRC idle mode or RRC inactive mode can receive a system information / system information block message (930) from a sync cell (910), and based on this information, can apply settings for a data cell selection method to be used when accessing a data cell in the future. A sync cell (910) operated by a base station sending a system information / system information block message (930) may transmit a list of currently active cells (or data cells) or inactive cells (or data cells) in the system information / system information block message (930). At this time, the sync cell (910) may also transmit a first threshold value for each cell. In some embodiments, the sync cell (910) may also transmit WUS configuration information for each cell.

[0106] FIG. 10 is a diagram illustrating the structure of a base station according to one embodiment of the present disclosure.

[0107] Referring to FIG. 10, the base station may include a transceiver (1010), a control unit (1020), and a storage unit (1030). In the present disclosure, the control unit (1020) may be defined as a circuit or an application-specific integrated circuit or at least one processor. The transceiver (1010) may transmit and receive signals with other network entities. The transceiver (1010) may, for example, transmit system information to a terminal and transmit a synchronization signal or a reference signal. The control unit (1020) may control the overall operation of the base station according to the embodiments of FIGS. 3 to 9 described above in the present disclosure. For example, the control unit (1020) may control signal flow between each block to perform operations according to the flowchart described above. The storage unit (1030) may store at least one of information transmitted and received through the transceiver (1010) and information generated through the control unit (1020).

[0108] FIG. 11 is a diagram illustrating the structure of a terminal according to one embodiment of the present disclosure.

[0109] Referring to FIG. 11, the terminal may include a transceiver (1110), a control unit (1120), and a storage unit (1130). In the present disclosure, the control unit may be defined as a circuit or an application-specific integrated circuit or at least one processor. The transceiver (1110) may transmit and receive signals with other network entities. The transceiver (1110) may, for example, receive system information from a base station and may receive a synchronization signal or a reference signal. The control unit (1120) may control the overall operation of the terminal according to the embodiments of FIGS. 3 to 9 described above in the present disclosure. For example, the control unit (1120) may control signal flow between each block to perform operations according to the flowchart described above. The storage unit (1130) may store at least one of information transmitted and received through the transceiver (1110) and information generated through the control unit (1120).

[0110] Meanwhile, the embodiments of the present invention disclosed in this specification and drawings are merely specific examples to easily explain the technical content of the present invention and facilitate understanding of the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical concept of the present invention are possible in addition to the embodiments disclosed herein. Furthermore, the above-described embodiments can be combined and operated as needed.

Claims

1. A method performed by a terminal of a wireless communication system, A step for identifying that a radio resource control (RRC) connection procedure has been triggered in a camp-on state for a cell of type 1; A step of receiving a first reference signal from a second type of cell that is in an activated state; A step of identifying whether the measured value of the first reference signal exceeds a threshold value; A step of transmitting an uplink signal for switching a second type of cell in an inactive state to an active state when the measured value of the first reference signal does not exceed the threshold value; A step of receiving a second reference signal from a second type of cell that has been switched to an activated state according to the above uplink signal; A step of determining a second type of cell for establishing an RRC connection based on the measured value of the second reference signal; and A method comprising the step of establishing the RRC connection with the second type of cell determined above.

2. In paragraph 1, The above first type of cell is a cell configured to transmit a synchronization signal, A method characterized in that the second type of cell is a cell configured to perform data communication in an active state and to switch to a deactivated state when there is no terminal connected to the second cell.

3. In paragraph 1, A method characterized in that the above uplink signal is transmitted to cells of a second type that are in an inactive state.

4. In paragraph 1, A method characterized in that the above uplink signal is transmitted to any second type of cells regardless of whether they are activated or deactivated.

5. In paragraph 1, A method characterized in that the measurement value of the first reference signal is one of RSRP (reference signal received power), RSRQ (reference signal received quality), or RSSI (received signal strength indicator).

6. In paragraph 1, A method characterized in that the above threshold value is applied commonly to all cells of the second type or is applied individually to each cell of the second type.

7. In paragraph 1, A method further comprising the step of receiving, from the first type of cell, a message including at least one of information about a list of activated second type cells or deactivated second type cells, information indicating the threshold value, and configuration information for transmitting the uplink signal.

8. In the terminal of a wireless communication system, Transmitter and receiver; and comprising a control unit, said control unit comprising: In a camp-on state for a type 1 cell, identify that a radio resource control (RRC) connection procedure has been triggered, From a second type of cell that is activated, a first reference signal is received through the transceiver, Identify whether the measured value of the first reference signal exceeds the threshold value, If the measured value of the first reference signal does not exceed the threshold value, an uplink signal for switching the second type of cell in the inactive state to the active state is transmitted through the transceiver, From the second type of cell that has been switched to an activated state according to the above uplink signal, a second reference signal is received through the transceiver, Based on the measured value of the second reference signal, a second type of cell for establishing an RRC connection is determined, A terminal characterized by being configured to establish the RRC connection with the second type of cell determined above.

9. In paragraph 8, The above first type of cell is configured to transmit a synchronization signal, A terminal characterized in that the second type of cell is configured to perform data communication in an activated state and to switch to a deactivated state when there is no terminal connected to the second cell.

10. In paragraph 8, A terminal characterized in that the above uplink signal is transmitted to cells of a second type that are in an inactive state.

11. In paragraph 8, A terminal characterized in that the above uplink signal is transmitted to any second type of cells regardless of whether they are activated or deactivated.

12. In paragraph 8, A terminal characterized in that the measurement value of the first reference signal is any one of RSRP (reference signal received power), RSRQ (reference signal received quality), or RSSI (received signal strength indicator).

13. In paragraph 8, A terminal characterized in that the above threshold value is applied commonly to all cells of the second type or is applied individually to each cell of the second type.

14. In paragraph 8, The above control unit, A terminal configured to receive, through the transceiver, a message including at least one of information about a list of activated cells of the second type or deactivated cells of the second type, information indicating the threshold value, and setup information for transmitting the uplink signal from the first type of cell.

Images