Method and device for managing mobility considering cell range change in non-terrestrial network

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate beyond a 4G communication system such as LTE. According to an embodiment of the present invention, a method performed by a terminal in a wireless communication system may comprise the steps of: calculating an elevation angle between the terminal and a satellite associated with a neighbor cell; comparing the elevation angle with an elevation angle reference value; if the elevation angle is greater than the elevation angle reference value, performing measurement reporting for the neighbor cell; if the elevation angle is lower than the elevation angle reference value, comparing an RSRP for a serving cell of the terminal with a signal strength reference value; if the RSRP for the serving cell is lower than the signal strength reference value, performing measurement reporting for the neighbor cell; and if the RSRP for the serving cell is higher than the signal strength reference value, starting a timer for measurement reporting and deactivating measurement reporting of the terminal until the timer expires.

Description

Method and apparatus for managing mobility considering cell range changes in a non-terrestrial network

[0001] The present invention relates to the field of Non-Terrestrial Network (NTN) technology, which enables services to be provided to areas where communication services are impossible (e.g., ocean, polar regions, remote areas, air) by utilizing satellites in a mobile communication system. The mobile communication technology in the present invention may include NTN using the LTE standard used in existing terrestrial networks, NR including functions for improving NTN performance, as well as 6G, which is expected to be commercialized in 2030, and may include a mobile communication system, a satellite system, and a system combining a mobile communication system and a satellite system to support NTN.

[0002] Looking back at the evolution of wireless communication through successive generations, technologies have been developed primarily for human-oriented services, such as voice, multimedia, and data. Following the commercialization of 5G (5th-generation) communication systems, connected devices, which have been increasing explosively, are expected to be connected to communication networks. Examples of networked objects include vehicles, robots, drones, home appliances, displays, smart sensors installed in various infrastructures, construction machinery, and factory equipment. Mobile devices are expected to evolve into various form factors, such as augmented reality glasses, virtual reality headsets, and holographic devices. In the 6G (6th-generation) era, efforts are underway to develop improved 6G communication systems to connect hundreds of billions of devices and objects to provide diverse services. For this reason, 6G communication systems are referred to as "Beyond 5G" systems.

[0003] In the 6G communication system predicted to be realized around 2030, the maximum transmission speed is tera (i.e., 1,000 gigabit) bps, and the wireless latency is 100 microseconds (μsec). In other words, compared to the 5G communication system, the transmission speed in the 6G communication system is 50 times faster, and the wireless latency is reduced to one-tenth.

[0004] To achieve such high data transmission speeds and ultra-low latency, 6G communication systems are being considered for implementation in the terahertz band (e.g., the 95 GHz to 3 terahertz (3 THz) band). In the terahertz band, due to more severe path loss and atmospheric absorption compared to the millimeter wave (mmWave) band introduced in 5G, the importance of technology capable of guaranteeing signal reach, or coverage, is expected to increase. As key technologies to ensure coverage, radio frequency (RF) devices, antennas, new waveforms that offer better coverage than orthogonal frequency division multiplexing (OFDM), beamforming, and multi-antenna transmission technologies such as massive multiple-input and multiple-output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, and large-scale antennas must be developed. In addition, new technologies such as metamaterial-based lenses and antennas, high-dimensional spatial multiplexing technology using orbital angular momentum (OAM), and reconfigurable intelligent surface (RIS) are being discussed to improve coverage of terahertz band signals.

[0005] In addition, to improve frequency efficiency and system network, development is underway in 6G communication systems for full duplex technology, in which uplink and downlink simultaneously utilize the same frequency resources at the same time; network technology that integrates satellites and HAPS (high-altitude platform stations); network structure innovation technology that supports mobile base stations and enables network operation optimization and automation; dynamic spectrum sharing technology through collision avoidance based on spectrum usage prediction; AI-based communication technology that utilizes AI (artificial intelligence) from the design stage and internalizes end-to-end AI support functions to realize system optimization; and next-generation distributed computing technology that realizes services of complexity exceeding the limits of terminal computing capabilities by utilizing ultra-high performance communication and computing resources (mobile edge computing (MEC), cloud, etc.). In addition, attempts are continuing to further strengthen connectivity between devices, further optimize networks, promote the softwareization of network entities, and increase the openness of wireless communication through the design of new protocols to be used in 6G communication systems, the implementation of hardware-based security environments, the development of mechanisms for the safe utilization of data, and the development of technologies regarding privacy maintenance methods.

[0006] Due to the research and development of such 6G communication systems, it is expected that a new dimension of hyper-connected experience will become possible through the hyper-connectivity of 6G communication systems, which encompasses not only connections between objects but also connections between people and objects. Specifically, it is projected that 6G communication systems will enable the provision of services such as truly immersive extended reality (XR), high-fidelity mobile holograms, and digital replicas. Furthermore, services such as remote surgery, industrial automation, and emergency response, which are provided through 6G communication systems with enhanced security and reliability, will be applied in various fields including industry, healthcare, automotive, and home appliances.

[0007] NTN is a technology that utilizes satellites as repeaters to establish communication coverage in areas where the installation of mobile communication base stations is physically or economically impossible. Satellites usable in NTN include Geostationary Earth Orbit (GEO), Medium Earth Orbit (MEO), and Low Earth Orbit (LEO) satellites, depending on their altitude. Due to the correlation between satellite altitude and latency, using LEO satellites in NTN can guarantee relatively low latency.

[0008] NTN utilizing LEO satellites has the advantage of low latency due to short radio wave round-trip times, as they exist at lower altitudes (200 km to 2000 km) compared to other satellites (GEO, MEO). However, because they are much faster than other satellites (approximately 7.56 km / s at an altitude of 600 km), they have the characteristic of continuously changing frequency / time synchronization in immobile terminals or satellite antennas. Technologies for calculating and correcting changes in time and frequency synchronization caused by such satellite mobility, as well as mobility management technologies, are core technologies in NTN.

[0009] Accordingly, standards originally designed for terrestrial communication networks rather than NTN-based networks (e.g., terminal handover criteria, cell reselection criteria, etc.) need to be configured and applied differently in the case of NTN networks.

[0010] The purpose of the present invention is to manage the mobility of a terminal caused by changes in satellite cell coverage size according to the satellite's elevation angle, thereby resolving unnecessary cell changes (handover, cell selection) and the ping-pong phenomenon caused by repetitive changes in cell coverage. The above objective includes reducing power consumption caused by unnecessary mobility management in the terminal and preventing service interruption and degradation of Quality-of-Service (QoS) caused by unnecessary mobility management.

[0011] According to one embodiment of the present invention, a method performed by a terminal in a wireless communication system may be configured to include: a step of calculating an elevation angle between the terminal and a satellite associated with a neighbor cell; a step of comparing the elevation angle with an elevation angle reference value; a step of performing a measurement report for the neighbor cell if the elevation angle is greater than the elevation angle reference value; a step of comparing the RSRP for the terminal's serving cell with a signal strength reference value if the elevation angle is lower than the elevation angle reference value; a step of performing a measurement report for the neighbor cell if the RSRP for the serving cell is lower than the signal strength reference value; and a step of starting a timer for the measurement report and deactivating the measurement report of the terminal until the timer expires if the RSRP for the serving cell is higher than the signal strength reference value.

[0012] The method of the terminal may further include the step of determining whether a counter value is smaller than a threshold value when the RSRP for the serving cell is higher than the signal strength reference value; the step of increasing the counter value when the counter value is smaller than the threshold value; and the step of performing a measurement report for the neighboring cell when the counter value is greater than or equal to the threshold value.

[0013] The signal strength of the neighboring cell can be measured to be higher than the signal strength of the serving cell.

[0014] The signal strength of the neighboring cell may be measured higher than the first reference value, and the signal strength of the serving cell may be measured lower than the second reference value.

[0015] The elevation angle between the terminal and the satellite can be calculated based on the time difference of a signal transmitted from the satellite at regular time intervals.

[0016] The method of the above terminal may further include the step of determining whether to perform a measurement report for the neighboring cell based on the elevation angle reference value and a value related to the elevation angle change trend when the elevation angle is lower than the elevation angle reference value and the elevation angle is in a changing trend.

[0017] The method of the above terminal may further include the step of disabling cell selection or cell re-selection operations when the terminal is in an RRC IDLE state and the elevation angle is lower than the elevation angle reference value.

[0018] The above elevation angle reference value may be a value pre-set for the terminal.

[0019] According to another embodiment of the present invention, a terminal operating in a wireless communication system may be disclosed. The terminal may include a transceiver and a control unit, wherein the control unit calculates an elevation angle between the terminal and a satellite associated with a neighbor cell, compares the elevation angle with an elevation angle reference value, performs a measurement report for the neighbor cell if the elevation angle is greater than the elevation angle reference value, compares the RSRP for the terminal's serving cell with a signal strength reference value if the elevation angle is lower than the elevation angle reference value, performs a measurement report for the neighbor cell if the RSRP for the serving cell is lower than the signal strength reference value, and if the RSRP for the serving cell is higher than the signal strength reference value, starts a timer for the measurement report and may be configured to disable the measurement report of the terminal until the timer expires.

[0020] According to various embodiments of the present invention, handover or cell selection considering cell coverage that changes according to the elevation angle between the terminal and the satellite can be performed, thereby improving the communication quality of the terminal and preventing unnecessary operation of the terminal.

[0021] Figure 1 illustrates the operation method of a Quasi-earth fixed cell among the operation methods of an NTN cell, and Figure 2 illustrates the operation method of an Earth moving cell among the operation methods of an NTN cell.

[0022] Figure 3 is a diagram showing the change in beam area on the ground according to the elevation angle of the satellite.

[0023] Figure 4 is a diagram showing the change in cell size according to the satellite elevation angle.

[0024] FIG. 5 is a diagram illustrating a method for differentially setting handover parameters according to the satellite elevation angle in one embodiment of the present invention.

[0025] Figure 6 is a diagram showing the relationship between a cell and a satellite according to ntn-NeighCellClustered, which is information indicating whether neighbor cells are formed on the same satellite as the serving cell.

[0026] FIG. 7 is a flowchart of a method for differentially applying a measurement configuration according to a satellite elevation angle at a terminal according to an embodiment of the present invention.

[0027] FIG. 8 is a flowchart of a method for differentially applying a measurement configuration according to a satellite elevation angle at a terminal according to an embodiment of the present invention.

[0028] FIG. 9 is a flowchart of a method for a terminal according to an embodiment of the present invention to apply cell selection criteria differently depending on the satellite elevation angle.

[0029] FIG. 10 illustrates a method in which a terminal according to an embodiment of the present invention performs a Random Access (RACH) operation according to a satellite elevation angle.

[0030] FIG. 11 is a flowchart of a method for a terminal to differentially perform MR for handover according to an embodiment of the present invention.

[0031] FIG. 12 is a flowchart of a method for a terminal to differentially perform MR for handover according to an embodiment of the present invention.

[0032] FIG. 13 is a diagram illustrating a method for a terminal according to an embodiment of the present invention to differentially perform a Measurement Report (MR) according to an elevation angle and a direction of elevation angle change.

[0033] FIG. 14 is a diagram of a method for determining frequency priority based on the altitude of a satellite during the process of performing cell priority adjustment according to an embodiment of the present invention.

[0034] FIG. 15 is a diagram illustrating the structure of a terminal according to one embodiment of the present invention.

[0035] FIG. 16 is a drawing illustrating the structure of a base station according to one embodiment of the present invention.

[0036] In describing the embodiments in this specification, technical details that are well known in the technical field to which the present invention belongs and are not directly related to the present invention are omitted. This is intended to convey the essence of the present invention more clearly without obscuring it by omitting unnecessary explanations.

[0037] For the same reason, some components in the attached drawings have been exaggerated, omitted, or schematically depicted. Additionally, the size of each component does not entirely reflect its actual dimensions. Identical or corresponding components in each drawing have been assigned the same reference numbers.

[0038] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various different forms. These embodiments are provided merely 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. Throughout the specification, the same reference numerals refer to the same components.

[0039] At this time, it will be understood that each block of the process flow diagrams and combinations of the flow diagrams can be executed by computer program instructions. Since these computer program instructions can be loaded into the processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, the instructions executed through the processor of the computer or other programmable data processing equipment create means to perform the functions described in the flow diagram block(s). Since these computer program instructions can also be stored in computer-available or computer-readable memory that can be directed toward the computer or other programmable data processing equipment to implement the function in a specific way, the instructions stored in computer-available or computer-readable memory can also produce a manufactured item containing the means of instruction to perform the function described in the flow diagram block(s). Since computer program instructions can be loaded onto a computer or other programmable data processing equipment, instructions that perform a series of operation steps on the computer or other programmable data processing equipment to create a process executed by the computer can also provide steps for executing the functions described in the flowchart block(s).

[0040] Additionally, each block may represent a module, segment, or part of code containing one or more executable instructions for executing a specified logical function(s). It should also be noted that in some alternative execution examples, the functions mentioned in the blocks may occur out of order. For instance, two blocks described in succession may actually be executed substantially simultaneously, or the blocks may be executed in reverse order according to their corresponding functions.

[0041] In this embodiment, the term "part" refers to a software or hardware component, such as an FPGA or ASIC, and the "part" performs certain roles. However, the meaning of "part" is not limited to software or hardware. The "part" may be configured to reside in an addressable storage medium or configured to operate one or more processors. Accordingly, as an example, the "part" includes components such as software components, object-oriented software components, class components, and task components, as well as processes, functions, attributes, 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 "parts" may be combined into a smaller number of components and "parts" or further separated into additional components and "parts." Furthermore, the components and "parts" may be implemented to operate one or more CPUs within a device or secure multimedia card.

[0042] The operating principle of the present invention will be described in detail below with reference to the attached drawings. In describing the present invention below, specific descriptions of related known functions or configurations will be omitted if it is determined that such detailed descriptions would unnecessarily obscure the essence of the invention. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, their definitions should be based on the content throughout this specification.

[0043] Terms used in the following description to identify connection nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, etc., are examples provided for the convenience of explanation. Accordingly, the present invention is not limited to the terms described below, and other terms referring to objects having equivalent technical meanings may be used.

[0044] For the convenience of the following explanation, the present invention uses terms and names defined in the 5GS, NR, and 6G specifications among the standards defined by the 3GPP (The 3rd Generation Partnership Project) organization among existing communication standards. However, the present invention is not limited by the above terms and names and can be applied in the same way to wireless communication networks according to other standards. In particular, the present invention can be applied to 3GPP 6G (6th generation mobile communication standard).

[0045] Under 3GPP NR NTN, standardization was conducted to enable terminals to connect to a base station via satellite only after partially self-correcting frequency and time synchronization. For the terminal to correct frequency and time synchronization, the terminal's location, information regarding the terminal's mobility, and the satellite's location and mobility information are essential. Accordingly, the NR NTN standard requires the terminal to utilize the Global Navigation Satellite System (GNSS) to measure its mobility and location information, and to use the measurement results for frequency and time synchronization correction and terminal mobility management. Additionally, the terminal receives the satellite's location and mobility information through broadcasting messages transmitted by the base station connected to the satellite.

[0046] The above broadcasting message may include information including the position, velocity, and orbit information of the satellite, as well as various information related to the satellite cell formed by the satellite. 3GPP NR NTN defined System Information Block 19 (SIB19) as a broadcasting message containing such information, and NB-IoT defined System Information Block 31 (SIB31). Such messages may include an Information Element (IE) containing orbit information, position information, and velocity information of the satellite connected to the base station transmitting the broadcasting message, and may also include information related to satellite cell operation (e.g., satellite cell center position and diameter, surrounding satellite cell information).

[0047] Tables 1 and 2 illustrate various information that may be included in SIB19.

[0048] [Table 1]

[0049]

[0050] [Table 2]

[0051]

[0052] Figure 1 illustrates the operation method of a Quasi-earth fixed cell among the operation methods of an NTN cell, and Figure 2 illustrates the operation method of an Earth moving cell among the operation methods of an NTN cell.

[0053] The NR NTN for low-orbit satellites classifies cell operation methods into 1) quasi-earth fixed cell and 2) Earth moving cell. Quasi-earth fixed cell and Earth moving cell are classifications of two methods for forming satellite cells in satellites where the satellite's orbital period and the Earth's rotation period are not the same, such as MEO / LEO. Referring to Figure 1, a quasi-earth fixed cell is a method of forming a satellite cell in a specific area of ​​the Earth's surface. Since LEO and MEO satellites move relative to the Earth's surface, they cannot continuously form a cell in a specific area. In this case, the antenna of the beam forming the satellite cell is rotated so that a cell is formed in a specific area even if the satellite moves relative to the ground. If a satellite cell exists at a position greater than the maximum antenna rotation angle due to the satellite's movement and the satellite is unable to form a cell, another nearby satellite takes over and forms the cell at that location. In Fig. 1, the NTN terminal moves according to the change in time (from t1 to t2) and can cover a quasi-earth fixed cell by rotating a steerable spot beam to cover the cell.

[0054] Referring to Fig. 2, the Earth moving cell is an operational method in which the satellite cell moves along with the movement of the satellite when the antenna forming the cell of the MEO / LEO satellite cannot rotate. Although the NTN terminal moves according to the change in time (from t1 to t2), the cell covered by the NTN terminal (Earth moving cell) also moves together because the spot beam is not adjustable.

[0055] Figure 3 is a diagram showing the change in beam area on the ground according to the elevation angle of the satellite.

[0056] Referring to Fig. 3, the satellite transmits and receives radio waves by steering its antenna toward the ground from a position much higher than that of a ground network base station. This enables the satellite to communicate with a very wide area of ​​the ground. For the efficiency of network configuration and the convenience of network management, each satellite may propose a communication range. The criteria for proposing a communication range from a satellite use the satellite's elevation angle (the angular height of the satellite measured from the horizon) and can be determined based on the minimum elevation angle at which communication is possible. The spot beam formed by the satellite is steered toward a ground position greater than the minimum elevation angle, and the satellite can form cells in non-ground networks through the spot beam. The satellite exhibits various elevation angles depending on the position of the satellite and the position of the cell, and the beam area is formed differently depending on the elevation angle between the satellite and the cell; when the beam forms a single cell, the size of the cell area may be formed differently. For example, when forming cells on the ground with the same beam width at a high elevation angle, the cell size is relatively small, and when forming cells on the ground with the same beam width at a low elevation angle, the cell size is relatively large.

[0057] Figure 3 illustrates the cell size and time difference within the cell according to the elevation angle when a satellite at an altitude of 1200 km forms a cell with a single spot beam having a beam width of 4.41 degrees. Figure 3 illustrates the case where the maximum elevation angle is 10 degrees. Compared to when the satellite forms a cell at an elevation angle of 90 degrees, when a cell is formed at an elevation angle of 10 degrees, a difference in diameter size of approximately three times occurs.

[0058] Terminals on terrestrial networks can perform a handover operation to switch the connection to the cell with the best performance at the terminal's location while moving. Very similar handover operations exist in both 3GPP LTE and NR, and a brief description of these operations is as follows.

[0059] The terminal periodically measures the signal of the connected serving cell to determine whether the signal strength of the currently connected cell is sufficient for communication. Additionally, the terminal periodically measures the signal strength of neighboring cells to predict or calculate the performance when connecting to neighboring cells. The terminal performs a handover to a neighboring cell when the performance of the currently connected cell drops below a certain level, or when it is determined that switching the connection to a neighboring cell would be better in terms of performance because the signal of a neighboring cell is stronger than the signal of the currently connected cell.

[0060] Base station signals can be affected by large-scale fading, which is determined based on the distance between the base station and the terminal, and small-scale fading caused by reflection / absorption from surrounding objects and various other factors; consequently, signal strength fluctuations may occur. This frequently leads to situations where the cell signal strength ranking is temporarily reversed, and if the terminal selects a high-performance cell based on a single moment's signal strength to perform a handover, it may select the wrong cell, which could actually reduce communication performance. Therefore, in NR and LTE, various parameters that must be satisfied to perform a handover are set.

[0061] Representative handover-related parameters include Time To Trigger (TTT) and offset parameters. Both TTT and offset parameters play a crucial role in controlling handovers in LTE and NR. TTT is a parameter that sets the time for comparing signal strengths between base stations; it is the value that determines the time duration for maintaining the connection once the handover conditions are met. A small value leads to rapid handovers, increasing the likelihood of unnecessary handovers, while a large value allows for maintaining a stable connection but may result in handover delays in environments requiring rapid handovers. The offset parameter sets the reference value for comparing signal strengths related to handovers, such as RSRP, RSRQ, or SINR. For example, a handover condition may be satisfied if the signal strength of a target cell is higher than that of the current serving cell by the value of the offset parameter. For instance, when a vehicle is moving at high speed, a small offset value can be used to induce a rapid handover because the base station must be changed within a short time. Conversely, when receiving service from a fixed location, a large offset value can be set to maintain a stable connection. Therefore, by appropriately setting these parameters, efficient network resource management and service quality can be ensured.

[0062] Figure 4 is a diagram showing the change in cell size according to the satellite elevation angle.

[0063] Referring to FIG. 4, in order to form a fixed cell position on the ground regardless of satellite movement in a non-ground network, the satellite can set a destination point for spot beam steering on the ground and form a beam centered on that point. However, even if the beam is centered on the same location, the size of the beam coverage (cell coverage) centered on the point is formed differently depending on the satellite's elevation angle. FIG. 4 illustrates a situation where two satellite cells are assumed to be formed from the same satellite. In the above figure, the cell coverage indicated by the dotted line is a diagram of the cell coverage formed when steering the cell around two points from a satellite with a high elevation angle, and the cell coverage indicated by the solid line is a diagram of the cell coverage formed when steering the cell around two points from a satellite with a low elevation angle. In FIG. 4, assuming a situation where the terminal has no mobility, when the satellite's elevation angle is high, the terminal can only measure the signal of the cell indicated on the right side of the figure. However, as the satellite's elevation angle decreases, the size of the satellite cell increases, and in a situation where it descends below a certain angle, the terminal may be able to measure both cell signals. This is a phenomenon that does not occur when a non-mobile terminal is connected to a terrestrial network, but occurs when the terminal has mobility. Unlike the case of a terrestrial network, the mobility of the satellite affects the terminal in a non-terrestrial network, so the phenomenon described above through Fig. 4 may occur.

[0064] In cells provided by terrestrial networks, there is a significant difference in signal strength between terminals at the edge of the cell and those at the center. Consequently, terminal mobility management based on signal strength differences operates efficiently. However, in non-terrestrial networks, because satellites are located at very high altitudes, the difference in distance from the base station between terminals at the edge of the cell and those at the center is relatively small; consequently, the difference in signal strength is also likely to be smaller compared to terrestrial networks. Furthermore, in non-terrestrial networks, mobility management based on signal strength differences is less efficient at locations where cell coverage overlaps. Consequently, performance degradation due to mobility management failures (Radio Link Failure (RLF) and handover failure) may occur more frequently than in terrestrial networks due to factors such as the satellite's rapid movement speed and handover delays. Ultimately, since terminals experience a temporary and significant mobility management failure when connected to a cell formed by a satellite with a low elevation angle, this implies inherent performance instability where terminal performance varies depending on the satellite's altitude. Even with a fixed terminal, handovers occur frequently as the satellite cell coverage boundary continuously changes due to the satellite's moving orbit, and a ping-pong effect may occur in which the cell connected to the terminal continuously changes between the current cell and surrounding cells.

[0065] To resolve the aforementioned mobility management failure or ping-pong phenomenon, the most efficient method is to apply mobility management standards differently depending on changes in satellite cell size. However, current NR NTN standards do not include a function to account for such situations, nor do they include a method for transmitting standards to recognize such situations and apply mobility management standards differentially. Accordingly, the present invention proposes embodiments for setting mobility management standards differentially based on the satellite elevation angle, which is the cause of changes in satellite cell size.

[0066] [First Embodiment: Method for Differential Setting of Handover Parameters According to Satellite Elevation Angle]

[0067] FIG. 5 is a diagram illustrating a method for differentially setting handover parameters according to the satellite elevation angle in one embodiment of the present invention.

[0068] In this embodiment, it is assumed that the terminal manages mobility while in an RRC connected state. FIG. 5 illustrates a method of distinguishing between a low elevation angle and a high elevation angle based on the elevation angle of a neighbor cell according to the elevation angle criterion (elevationAngleThresh) and applying a measurement configuration differentially according to the distinguished elevation angles. According to one embodiment, the terminal applies a measurement configuration corresponding to Event A3E1 when the neighbor cell is provided through a satellite with a low elevation angle, and applies a measurement configuration corresponding to Event A3E2 when the neighbor cell is provided through a satellite with a high elevation angle. The measurement configuration of the A3E1 event may include parameters that enable efficient mobility management in the coverage area of ​​a neighbor cell that has increased in size, and the measurement configuration of the A3E2 event may include parameters that enable efficient mobility management in the coverage area of ​​a neighbor cell that has decreased in size.

[0069] In order to transmit the above parameters, an additional method is required in addition to the parameter transmission method used in the past. The additional method can be implemented in various forms, and the present invention proposes 1) a technical method for directly transmitting angle-specific application parameters classified according to a reference value, and 2) a method for describing and transmitting a change amount to be applied to existing parameters when the satellite is located in a low-altitude angle or high-altitude angle region according to the reference value.

[0070] [Table 3]

[0071]

[0072] Table 3 - Differential transmission method for measurement configuration settings based on angle

[0073] Table 3 shows the results of adding a measurement configuration that can be applied differentially according to the angle to the measurement configuration-related message, which signifies the conditions for transmitting a measurement report to perform a handover. In Table 3, the A3E1 event is the measurement configuration applied by the terminal when the satellite forming the neighbor cell is located at a low elevation angle, and the A3E2 event is the measurement configuration applied by the terminal when the satellite forming the neighbor cell is located at a high elevation angle. The parameters related to the A3E1 event can be set to result in fewer handovers compared to existing parameters to prevent unnecessary handovers that may occur when the neighbor cell's coverage increases and the neighbor cell's signal is observed to be temporarily strong. The parameters related to the A3E2 event are set assuming that the neighbor cell's coverage is small and the neighbor cell's signal is observed only at the edge of the cell; therefore, they can be set to values ​​that facilitate handovers more effectively than the parameters for the A3E1 event. For example, if the RSRP offset of A3E1 (a3e1-Offset) is set to 5dBm and the RSRP offset of A3E2 (a3e2-Offset) is set to 1dBm, the terminal will perform a handover only when the RSRP difference between the serving cell and the neighbor cell is very large when the neighbor cell is at a low elevation angle.In another example, when A3E1 timeToTrigger is set to 2,560ms and A3E2 timeToTrigger is set to 320ms, fewer handovers occur because the signal strength relationship between the serving cell and the neighbor cell needs to be reversed for a relatively long time when the neighbor cell is at a low elevation angle.

[0074] [Table 4]

[0075]

[0076] Table 4 - Method for transmitting applied values ​​for measurement configuration changes according to angle

[0077] Table 4 shows an example of a measurement configuration for an existing handover that includes the necessary change amount compared to existing parameters, applicable when the neighbor cell is at a low elevation angle. In Table 4, the change values ​​of a3-Offset and timeToTrigger (hereinafter delta values) were added to the measurement configuration of the A3 event for an existing handover, but this is not limited to this and the delta values ​​of hysteresis or other parameters may also be included.

[0078] In order to distinguish the aforementioned low and high elevation angle regions, a method is required for the terminal to recognize the distinction criteria. The present invention proposes a method of including the corresponding criterion value in a broadcasting message for an existing non-terrestrial network. The present invention also proposes a method of including information in the broadcasting message, in addition to the elevation angle criterion value, that enables the terminal to recognize whether the satellite elevation angle of the serving cell and the satellite elevation angle of the neighbor cell are identical (whether the serving cell and the neighbor cell are formed on the same satellite).

[0079] [Table 5]

[0080]

[0081] Table 5 - Elevation Angle Reference and Same-Satellite Forming Cell Information Included in Broadcasting Messages (SIB for NTN)

[0082] In Table 5, elevationAngleThresh is a criterion for the terminal to distinguish whether it is located at a low elevation angle or a high elevation angle depending on the satellite's elevation angle; in the above diagram, transmission is performed with an angle of 1 degree as the resolution, but more detailed transmission is also possible. ntn-NeighCellClustered is information regarding whether the neighbor cells of the cell transmitting the broadcast are formed on the same satellite as the serving cell, and it can be set to true if all neighbor cells form a spot beam formed on the same satellite as the serving cell. The relationship between the satellite and the cell according to ntn-NeighCellClustered can be confirmed through Figure 6.

[0083] Figure 6 is a diagram showing the relationship between a cell and a satellite according to ntn-NeighCellClustered, which is information indicating whether neighbor cells are formed on the same satellite as the serving cell.

[0084] Referring to Fig. 6, if neighbor cells are formed on the same satellite as the serving cells, ntn-NeighCellClustered is set to True and transmitted to the terminal, and if neighbor cells are formed on different satellites as the serving cells, ntn-NeighCellClustered is set to False and transmitted to the terminal.

[0085] [Table 6]

[0086]

[0087] Table 6 - Elevation Angle Reference and Same-Satellite Forming Cell Information Included in Broadcasting Messages (SIB for NTN)

[0088] Table 6 is an example of a case that includes information on whether all neighbor cells are formed on the same satellite as the serving cell, as well as information on whether each neighbor cell is formed on the same satellite as the serving cell. The NeighCellConfig in the figure above is a field containing information about the neighbor cells of the current cell, and a field called isSrvCellClustered has been added to this field. This field has a value of true if the neighbor cell is formed on the same satellite as the current cell, and since isSrvCellClustered is a field that exists for each neighbor cell, there will be as many values ​​as there are neighbor cells.

[0089] [Example 2-1] Method for performing differential handover according to satellite elevation angle

[0090] FIG. 7 is a flowchart of a method for differentially applying a measurement configuration according to a satellite elevation angle at a terminal according to an embodiment of the present invention.

[0091] According to one embodiment of the present invention, the terminal can determine the measurement configuration based on the satellite elevation angle reference and the actual elevation angle.

[0092] Referring to FIG. 7, the terminal can receive a reference value (elevationAngleThresh) for distinguishing low / high elevation angles, a value indicating whether neighbor cells and the current cell forming satellite are from the same satellite (ntn-NeighCellClustered), and satellite orbit information through a broadcasting message containing NTN information (S701). The terminal can check whether neighbor cells and the current serving cell are formed from the same satellite through the ntn-NeighCellClustered parameter (S703).

[0093] In step S703, if it is determined that neighboring cells and serving cells are formed from the same satellite, the terminal calculates the elevation angle of the satellite forming the serving cell (S705) and can compare the calculated elevation angle with an elevation angle reference value (elevationAngleTresh) (S707). If the calculated elevation angle is smaller than the elevation angle reference value, the measurement configuration for the A3E1 event can be applied and used as a setting for the measurement report (MR) (S709). Conversely, if the calculated elevation angle is larger than the elevation angle reference value, the measurement configuration for the A3E2 event can be applied and used as a setting for the measurement report (MR) (S711).

[0094] If it is determined in step S703 that the neighbor cell and the serving cell are not formed by the same satellite, the terminal calculates the elevation angle of the satellite forming the neighbor cell (S713) and can compare the calculated elevation angle with an elevation angle reference value (S715). If the calculated elevation angle is smaller than the elevation angle reference value, the measurement configuration for the A3E1 event can be applied and used as a setting for the measurement report (MR) (S717). If, on the other hand, the calculated elevation angle is larger than the elevation angle reference value, the measurement configuration for the A3E2 event can be applied and used as a setting for the measurement report (MR) (S719).

[0095] Figure 7 is a flowchart for applying parameters defined as events (A3E1 and A3E2 events) named differently depending on the low / high elevation angle. When related parameters (e.g., TTT parameters and offset parameters) are transmitted to the terminal with delta values, the terminal can use parameters obtained by adding delta values ​​to the measurement configuration of the A3 event when the reference elevation angle is below, and use the measurement configuration of the A3 event when the reference elevation angle is above.

[0096] [Example 2-2] Method for Differential Application of Handover Events According to Satellite Elevation Angle

[0097] FIG. 8 is a flowchart of a method for differentially applying a measurement configuration according to a satellite elevation angle at a terminal according to an embodiment of the present invention.

[0098] FIG. 8 is a diagram of an embodiment in which RSRP-based A3 / A5 events and distance-based D1 / D2 events between the terminal and the cell center, newly defined in NR Rel-17, are applied differentially according to the elevation angle. The terminal distinguishes whether it is a low or high elevation angle by utilizing NeighCellClustered and elevationAngleThresh. In the case of a low elevation angle, D1 / D2 events for distance-based handover are applied because inefficient handovers frequently occur in terms of performance during RSRP handover, and in the case of a high elevation angle, RSRP-based A3 / A5 events, which result in relatively efficient handovers frequently, can be applied.

[0099] Referring to FIG. 8, the terminal can receive a reference value (elevationAngleThresh) for distinguishing low / high elevation angles, a value indicating whether neighbor cells and the current cell forming satellite are from the same satellite (ntn-NeighCellClustered), and satellite orbit information through a broadcasting message containing NTN information (S801). The terminal can check whether neighbor cells and the current serving cell are formed from the same satellite through the ntn-NeighCellClustered parameter (S803).

[0100] In step S803, if it is determined that neighboring cells and serving cells are formed from the same satellite, the terminal calculates the elevation angle of the satellite forming the serving cell (S805) and can compare the calculated elevation angle with an elevation angle reference value (elevationAngleTresh) (S807). If the calculated elevation angle is greater than the elevation angle reference value, the terminal can perform a measurement report using a measurement configuration for A3 / A5 events based on RSRP (S809); otherwise, if the calculated elevation angle is smaller than the elevation angle reference value, the terminal can perform a measurement report using a measurement configuration for D1 / D2 events based on distance (S811).

[0101] In step S803, if it is determined that the neighbor cell and the serving cell are formed from the same satellite, the terminal calculates the elevation angle of the satellite forming the neighbor cell (S813) and can compare the calculated elevation angle with the elevation angle reference value (elevationAngleTresh) (S815). If the calculated elevation angle is greater than the elevation angle reference value, the terminal can perform a measurement report using a measurement configuration for the A3 / A5 event based on RSRP (S817); otherwise, if the calculated elevation angle is smaller than the elevation angle reference value, the terminal can perform a measurement report using a measurement configuration for the D1 / D2 event based on distance (S819).

[0102] [Example 3-1] Method for Differential Setting of Cell (Re)selection Parameters According to Satellite Elevation Angle

[0103] The present embodiment discloses a method for cell selection or cell re-selection when a terminal is in an RRC Idle state. A terminal in an RRC Idle state (re)selects a cell based on signal strength and frequency priority. Conventionally, in this process, the terminal has acquired only parameters from a base station or satellite that can be applied regardless of the satellite's elevation angle in relation to the criteria for cell (re)selection. The present invention proposes a method for receiving parameters from a base station that must be applied differentially according to the elevation angle when a terminal in an RRC Idle state (re)selects a cell and frequency.

[0104] [Table 7]

[0105]

[0106] Table 7 is the result of creating an example of parameters required for differential application of cell selection criteria based on satellite elevation angle. The information included in Table 7 may be included in a broadcasting message for NTN or in a broadcasting message where existing cell reselection parameters are located. In this embodiment, it is assumed that such information is included in a broadcasting message for NTN. In Table 7, NTN-CellReselctionServingFreqInfo is a parameter used when selecting a cell with a frequency different from the currently serving cell, i.e., in inter-frequency cell selection.

[0107] threshServingLowPLowA is a parameter that serves as a criterion for performing an action to move to a lower priority frequency if the RSRP of the serving cell is maintained below the RSRP signal strength indicated by the above parameter when the neighbor cell is at a low elevation angle. threshServingHighPLowA is a parameter that serves as a criterion for performing an action to move to a high priority frequency if the RSRP of the serving cell is maintained below the RSRP signal strength indicated by the above parameter when the neighbor cell is at a low elevation angle. threshServingLowPHighA is a parameter that serves as a criterion for performing an action to move to a lower priority frequency if the RSRP of the serving cell is maintained below the RSRP signal strength indicated by the above parameter when the neighbor cell is at a high elevation angle. threshServingHighPHighA is a parameter that serves as a criterion for performing an action to move to a high priority frequency if the RSRP of the serving cell is maintained below the RSRP signal strength indicated by the above parameter when the neighbor cell is at a high elevation angle. threshServingLowQLowA, threshServingHighQLowA, threshServingLowQHighA, and threshServingHighQHighA operate identically to the four parameters mentioned above, but represent reference values ​​for RSRQ rather than RSRP.

[0108] NTN-IntraFreqCellReselctionInfo is a parameter used when selecting a cell within the intra-frequency range. Q-RxLevMinLowA is a parameter that serves as a criterion for selecting a neighbor cell in the same frequency band if the serving cell's RSRP remains below Q-RxLevMinLowA for a certain period of time when the neighbor cell is at a low elevation angle. Q-RxLevMinHighA is a parameter that serves as a criterion for selecting a neighbor cell in the same frequency band if the serving cell's RSRP remains below Q-RxLevMinHighA for a certain period of time when the neighbor cell is at a high elevation angle. Q-QualMinLowA is a parameter that serves as a criterion for selecting a neighbor cell in the same frequency band if the serving cell's RSRQ remains below Q-QualMinLowA for a certain period of time when the neighbor cell is at a low elevation angle. Q-QualMinHighA selects a neighboring cell of the same frequency if the neighbor cell is at a high elevation angle and the serving cell's RSRQ remains below Q-QualMinHighA for a certain period of time.

[0109] [Example 3-2: Method for Differential Cell Selection at a Terminal According to Satellite Elevation Angle]

[0110] FIG. 9 is a flowchart of a method for a terminal according to an embodiment of the present invention to apply cell selection criteria differently depending on the satellite elevation angle.

[0111] Similar to the handover in the RRC Connected terminal described above, the terminal applies cell selection parameters differentially based on the elevation angle of the neighbor cell and whether the satellite forming the neighbor cell and the satellite forming the serving cell are identical.

[0112] The above diagram is a flowchart for differentially applying cell reselection parameters based on the target for calculating the satellite elevation angle at the terminal and the elevation angle criteria. The terminal can receive a reference value (elevationAngleThresh) capable of distinguishing low / high elevation angles, a value indicating whether neighboring cells and the current cell forming satellite are from the same satellite (ntn-NeighCellClustered), and satellite orbit information through a broadcasting message containing NTN information (S901). The terminal can confirm that neighboring cells and the current cell are formed from the same satellite through the ntn-NeighCellClustered parameter (S903).

[0113] In step S903, if it is determined that neighboring cells and serving cells are formed from the same satellite, the terminal can calculate the elevation angle of the satellite forming the serving cell (9705) and compare the calculated elevation angle with the elevation angle reference value (elevationAngleTresh) (S907). If the calculated elevation angle is lower than the elevation angle reference value, the terminal can perform cell (re)selection using intra / inter-frequency cell reselection parameters (threshServingLowPLowA, threshServingLowQLowA, q-RxLevMinLowA, q-QualMinLowA) corresponding to the low elevation angle (S909). If, on the other hand, the calculated elevation angle is greater than the elevation angle reference value, the terminal can perform cell (re)selection using cell reselection parameters (threshServingHighPLowA, threshServingHighPHighA, q-RxLevMinHighA, q-QualMinHighA) corresponding to the high elevation angle (S911).

[0114] If it is determined in step S903 that the neighbor cell and the serving cell are not formed by the same satellite, the terminal can calculate the elevation angle of the satellite forming the neighbor cell (S913) and compare the calculated elevation angle with the elevation angle reference value (elevationAngleTresh) (S915). If the calculated elevation angle is lower than the elevation angle reference value, the terminal can perform cell (re)selection using intra / inter-frequency cell reselection parameters (threshServingLowPLowA, threshServingLowQLowA, q-RxLevMinLowA, q-QualMinLowA) corresponding to the low elevation angle (S917). If the calculated elevation angle is higher than the elevation angle reference value, the terminal can perform cell (re)selection using cell reselection parameters (threshServingHighPLowA, threshServingHighPHighA, q-RxLevMinHighA, q-QualMinHighA) corresponding to the high elevation angle (S919).

[0115] [Example 4-1: Method for differentially performing Measurement Report (MR) according to elevation angle at a terminal]

[0116] FIG. 10 illustrates a method in which a terminal according to an embodiment of the present invention performs a Random Access (RACH) operation according to a satellite elevation angle.

[0117] FIG. 10 is a diagram of a method for selectively performing a Random Access (RACH) operation that occurs during Handover or cell selection based on the elevation angle of a Neighbor cell at a terminal.

[0118] According to one embodiment of the present invention, the elevation angle reference value may be a value that is pre-set for the terminal.

[0119] Referring to FIG. 10, the terminal can detect a signal from a neighbor cell that is distinct from the serving cell and calculate the elevation angle of the satellite forming the detected neighbor cell. According to one embodiment, when calculating the elevation angle with respect to the satellite, the terminal can perform the calculation based on the time difference of a signal transmitted from the satellite at regular time intervals. Subsequently, the terminal compares the calculated elevation angle with an elevation angle reference value; if the calculated elevation angle is lower than the elevation angle reference value, the Random Access operation may not be performed on the neighbor cell, and if the calculated elevation angle rises above the elevation angle reference value, the Random Access operation may be performed. According to one embodiment, if the terminal is in an RRC IDLE state and the elevation angle calculated by the terminal is lower than the elevation angle reference value, cell selection or cell re-selection operations may be disabled.

[0120] [Example 4-2: Method for Differentially Performing Measurement Report (MR) According to Elevation Angle at a Terminal]

[0121] FIG. 11 is a flowchart of a method for a terminal to differentially perform MR for handover according to an embodiment of the present invention.

[0122] When operating the terminal using the method disclosed in Example 4-1 above, additional unintended problems (e.g., failure of necessary handover) may occur. Therefore, the terminal needs to operate precisely by considering various situations, rather than simply performing the operation of not performing RACH at low elevation angles. Figure 11 shows that even if the elevation angle of a neighbor cell is determined to be a low elevation angle, if the signal of the current serving cell is lower than a certain reference value (nLoSThres), it is determined that the communication performance of the serving cell is very low (e.g., blockage, link change to Non-Line of Sight (Non-LoS), etc.), and in this case, a Measurement report can be transmitted to perform a handover event to the neighbor cell. Additionally, if the RSRP of the serving cell is higher than a certain reference value (nLoSThres), the terminal determines that the communication performance of both the serving cell and the neighbor cell is preserved and can delay the MR by a timer.

[0123] Referring to FIG. 11, the terminal checks whether the measurement configuration related to the A3 / A5 event is satisfied (S1101) and can operate according to the result (S1103). If the measurement configuration for the A3 / A5 event is satisfied, the terminal can calculate the elevation angle with the satellite of the neighboring cell (S1105). The A3 event may mean a case where the signal strength of the neighboring cell is measured to be higher than the signal strength of the serving cell, and the A5 event may mean a case where the signal strength of the neighboring cell is measured to be higher than a first reference value and the signal strength of the serving cell is measured to be lower than a second reference value.

[0124] The terminal can compare the elevation angle calculated in step S1105 with a reference elevation angle (S1107), and if the calculated elevation angle is greater than the reference elevation angle, i.e., in a high elevation angle situation, it can perform a measurement report for an A3 / A5 event (S1109). Conversely, if the calculated elevation angle is smaller than the reference elevation angle, i.e., in a low elevation angle situation, the terminal can determine whether the RSRP of the serving cell is higher than a certain reference value (nLoSThres) (S1111).

[0125] In step S1111, if the RSRP of the serving cell is lower than the reference value, the terminal determines that the communication performance of the serving cell is very low and can perform a measurement report through step S1109 for a handover to a neighboring cell even though it is a low elevation angle.

[0126] In step S1111, if the RSRP of the serving cell is higher than the reference value, the terminal uses a timer (T) for MR operation control in a low-altitude angle situation. lowNeighEA ) can be started (S1113), and the MR operation for the A3 / A5 event can be disabled until the timer expires (S1115).

[0127] [Example 4-3: Method for Differentially Performing Measurement Report (MR) According to Elevation Angle at a Terminal]

[0128] FIG. 12 is a flowchart of a method for a terminal to differentially perform MR for handover according to an embodiment of the present invention.

[0129] Referring to FIG. 12, the terminal checks whether the measurement configuration related to the A3 / A5 event is satisfied (S1201) and can operate according to the result (S1203). If the measurement configuration for the A3 / A5 event is satisfied, the terminal can calculate the elevation angle with the satellite of the neighboring cell (S1205).

[0130] The terminal can compare the elevation angle calculated in step S1205 with a reference elevation angle (S1207), and if the calculated elevation angle is greater than the reference elevation angle, i.e., in a high elevation angle situation, it can perform a measurement report for an A3 / A5 event (S1209). Conversely, if the calculated elevation angle is smaller than the reference elevation angle, i.e., in a low elevation angle situation, the terminal can determine whether the RSRP of the serving cell is higher than a certain reference value (nLoSThres) (S1211).

[0131] In step S1211, if the RSRP of the serving cell is lower than the reference value, the terminal determines that the communication performance of the serving cell is very low and can perform a measurement report through step S1209 for a handover to a neighboring cell even at a low elevation angle.

[0132] In step S1211, if the RSRP of the serving cell is higher than the reference value, the terminal checks whether the managed timer value is greater than the limit value c (S1213), and if the timer value is less than the limit value c, the timer for MR operation control (T lowNeighEA Start ) (S1215), and disable the MR operation for the A3 / A5 event until the timer expires (S1217).

[0133] In the above embodiment, the limit value c can serve to limit the maximum number of operations that delay the MR operation. In such an embodiment, the maximum number of MR operation delays is set, so the measurement report can be performed even if the terminal is located at a low elevation angle in relation to the satellite.

[0134] [Example 4-4: Method for differentially performing MR according to elevation angle and elevation angle change code at a terminal

[0135] FIG. 13 is a diagram illustrating a method for a terminal according to an embodiment of the present invention to differentially perform a Measurement Report (MR) according to an elevation angle and a direction of elevation angle change.

[0136] During the operation of the terminal, even if the elevation angle of the neighbor cell is low, if the period during which the elevation angle is low is relatively long, there are cases where it is advantageous in terms of performance to hand over to a cell with a better signal. Therefore, during the handover or cell selection process, it may be necessary to consider not only the elevation angle but also whether the elevation angle is rising or falling. For example, when a neighbor cell enters a low elevation angle, there are cases where the satellite moves from the low elevation angle to the lowest elevation angle, and then the changed satellite rises from the low elevation angle to the reference elevation angle value. In this case, since the neighbor cell remains accessible to the terminal for several seconds or more, it may be advantageous in terms of the terminal's QoS for the terminal to connect to the cell with the best signal strength among the serving cell and the neighbor cell. Referring to FIG. 13, this is a diagram showing differential MR applied in consideration of such a situation in one embodiment of the present invention.

[0137] FIG. 13(a) illustrates an example in which changes in the satellite's elevation angle are not considered, and the terminal does not transmit a measurement report for handover when detecting a neighbor cell that is below the elevation angle threshold value (elevationAngleThresh). FIG. 13(b) illustrates an example in which the direction of changes in the satellite's elevation angle is considered, and even if a neighbor cell that is below the elevation angle threshold value (elevationAngleThresh) is detected, the terminal allows a measurement report for neighbor cells in a state where the elevation angle is decreasing, but does not perform a measurement report for neighbor cells in a state where the elevation angle is increasing.

[0138] [Example 5: Method for adjusting cell priority according to satellite altitude]

[0139] FIG. 14 is a diagram of a method for determining frequency priority based on the altitude of a satellite during the process of performing cell priority adjustment according to an embodiment of the present invention.

[0140] In non-terrestrial networks, to minimize performance differences between cells caused by radio interference, a method is utilized in which a frequency different from that of neighboring cells is assigned to a cell. To set frequencies differently for each cell in this way, the frequency domain must be divided; this method of differential frequency allocation per cell is called Frequency Reuse, and the number used to divide the frequency is referred to as the Frequency Reuse Factor (FRF). For example, if the FRF is set to 3, the frequency is divided into three, and the base station can allocate frequencies to each cell so that they do not overlap with those of neighboring cells. This embodiment is applicable when frequency reuse is applied and the serving cell to which the terminal is connected is set to a frequency different from all neighboring cells. For example, this embodiment can be utilized when the FRF is set to 3 or higher, or 4 or higher.

[0141] Referring to FIG. 14(b), the terminal can measure the elevation angle of a satellite forming a serving cell and measure the period during which the frequency of the cells provided by the satellite is detected while the elevation angle is higher than a reference value (S1401).

[0142] Subsequently, the terminal may select frequencies among those measured in step S1401 for which the frequency detection period is longer than or equal to the reference period (S1403), set the priority of the selected frequencies to have a high priority, and set the priority of the unselected frequencies to have a low priority. In this process, the priority among the selected frequencies may be set identically or differently. If the priority among the selected frequencies is set differently, the criteria for determining the priority may be determined by various factors such as the frequency detection period, elevation angle, and signal strength. Similarly, the priority among the unselected frequencies may be set identically or differently. If the priority among the unselected frequencies is set differently, the criteria for determining the priority may be determined by various factors such as the frequency detection period, elevation angle, and signal strength.

[0143] According to one embodiment of the present invention, when a terminal in an RRC idle state performs camping on to one of the cells provided through a low-altitude angle satellite, it can camp on to a cell provided through a frequency set with high priority, and accordingly, the occurrence of ping-ping phenomena can be reduced.

[0144] FIG. 15 is a diagram illustrating the structure of a terminal according to one embodiment of the present invention.

[0145] Referring to FIG. 15, the terminal may include a transceiver (1510), a control unit (1520), and a storage unit (1530). In the present invention, the control unit may be defined as a circuit or an application-specific integrated circuit or at least one processor.

[0146] The transceiver (1510) can transmit and receive signals with other network entities. The transceiver (1510) can, for example, receive system information from a base station and receive a synchronization signal or a reference signal.

[0147] The control unit (1520) can control the overall operation of the terminal according to the embodiment proposed in the present invention. For example, the control unit (1520) can control the signal flow between each block to perform operations according to the flowchart described above. Specifically, the control unit (1520) can calculate the elevation angle of the satellite according to the embodiment of the present invention and control the terminal to operate based on the result of comparing the calculated elevation angle with a reference value.

[0148] The storage unit (1530) can store at least one of the information transmitted and received through the transmission and reception unit (1510) and the information generated through the control unit (1520). For example, the storage unit (1530) can store a reference elevation angle value, parameters to be applied in situations greater than the reference elevation angle, and parameters to be applied in situations less than the reference elevation angle.

[0149] FIG. 16 is a drawing illustrating the structure of a base station according to one embodiment of the present invention.

[0150] Referring to FIG. 16, the base station may include a transceiver (1610), a control unit (1620), and a storage unit (1630). In the present invention, the control unit may be defined as a circuit or an application-specific integrated circuit or at least one processor.

[0151] The transmitting and receiving unit (1610) can transmit and receive signals with other network entities. The transmitting and receiving unit (1610) can, for example, transmit system information to a terminal and transmit a synchronization signal or a reference signal.

[0152] The control unit (1620) can control the overall operation of the base station according to the embodiment proposed in the present invention. For example, the control unit (1620) can control the signal flow between each block to perform operations according to the flowchart described above. Specifically, the control unit (1620) can control the operation of the terminal and the satellite according to the embodiment of the present invention.

[0153] The storage unit (1630) can store at least one of the information transmitted and received through the transmission and reception unit (1610) and the information generated through the control unit (1620). For example, the storage unit (1630) can store a reference elevation angle value, parameters to be applied in situations greater than the reference elevation angle, and parameters to be applied in situations less than the reference elevation angle.

[0154] Although the various embodiments described in this specification are described independently of one another, this does not mean that each embodiment must be implemented individually, and two or more embodiments may be combined and implemented together. Accordingly, those skilled in the art will understand that some features or components of the various embodiments may be combined and applied within the scope of the invention.

[0155] The embodiments of the invention disclosed in this specification and drawings are provided merely as specific examples to facilitate the explanation of the technical content of the invention and to aid in understanding the invention, and are not intended to limit the scope of the invention. It is obvious to those skilled in the art that other variations based on the technical concept of the invention are possible in addition to the embodiments disclosed herein.

Claims

1. A method performed by a terminal in a wireless communication system, A step of calculating the elevation angle between the above terminal and the satellite associated with the neighboring cell; A step of comparing the above elevation angle and the elevation angle reference value; If the elevation angle is greater than the elevation angle reference value, a step of performing a measurement report for the neighboring cell; If the elevation angle is lower than the elevation angle reference value, a step of comparing the RSRP and signal strength reference value for the serving cell of the terminal; A step including performing a measurement report for the neighboring cell when the RSRP for the serving cell is lower than the signal strength reference value; and A method comprising the step of, when the RSRP for the serving cell is higher than the signal strength reference value, starting a timer for measurement reporting and disabling measurement reporting of the terminal until the timer expires.

2. In Paragraph 1, A step of determining whether the counter value is smaller than the threshold value when the RSRP for the serving cell is higher than the signal strength reference value; A step of increasing the counter value when the above counter value is smaller than the limit value; and A method comprising the step of performing a measurement report for the neighboring cell when the above counter value is greater than or equal to a limit value.

3. In Paragraph 1, A method in which the signal strength of the neighboring cell is measured to be higher than the signal strength of the serving cell.

4. In Paragraph 1, A method in which the signal strength of the neighboring cell is measured to be higher than a first reference value, and the signal strength of the serving cell is measured to be lower than a second reference value.

5. In Paragraph 1, A method characterized in that the elevation angle between the terminal and the satellite is calculated based on the time difference of a signal transmitted from the satellite at regular time intervals.

6. In Paragraph 1, A method further comprising the step of determining whether to perform a measurement report for the neighboring cell based on the elevation angle reference value and a value related to the elevation angle change trend when the elevation angle is lower than the elevation angle reference value and the elevation angle is in a changing trend.

7. In Paragraph 1, A method further comprising the step of disabling cell selection or cell re-selection operations when the terminal is in an RRC IDLE state and the elevation angle is lower than the elevation angle reference value.

8. In Paragraph 1, A method in which the above elevation angle reference value is a value pre-set for the above terminal.

9. In a terminal operating in a wireless communication system, Transmitter / receiver; and It includes a control unit, The above control unit is, Calculate the elevation angle between the above terminal and the satellite associated with the neighboring cell, and Comparing the above elevation angle and the elevation angle reference value, If the above elevation angle is greater than the above elevation angle reference value, a measurement report for the neighboring cell is performed, and If the above elevation angle is lower than the above elevation angle reference value, the RSRP for the serving cell of the terminal and the signal strength reference value are compared, If the RSRP for the above serving cell is lower than the above signal strength reference value, a measurement report is performed for the neighboring cell, and A terminal configured to start a timer for measurement reporting when the RSRP for the serving cell is higher than the signal strength reference value, and to disable measurement reporting of the terminal until the timer expires.

10. In Paragraph 9, The above control unit is, If the RSRP for the above serving cell is higher than the signal strength reference value, determine whether the counter value is smaller than the limit value, and If the above counter value is smaller than the limit value, the above counter value is increased, and A terminal further configured to perform a measurement report for the neighboring cell when the above counter value is greater than or equal to the threshold value.

11. In Paragraph 9, A terminal in which the signal strength of the neighboring cell is measured to be higher than the signal strength of the serving cell.

12. In Paragraph 9, A terminal in which the signal strength of the neighboring cell is measured to be higher than a first reference value, and the signal strength of the serving cell is measured to be lower than a second reference value.

13. In Paragraph 9, A terminal characterized in that the elevation angle between the terminal and the satellite is calculated based on the time difference of a signal transmitted from the satellite at regular time intervals.

14. In Paragraph 9, The above control unit is, A terminal further configured to determine whether to perform a measurement report for the neighboring cell based on the elevation angle reference value and a value related to the elevation angle change trend when the elevation angle is lower than the elevation angle reference value and the elevation angle is in a changing trend.

15. In Paragraph 9, The above control unit is, A terminal that is further configured to disable cell selection or cell re-selection operations when the above terminal is in an RRC IDLE state and the above elevation angle is lower than the above elevation angle reference value.

Images