Method and device for visible region handover in communication system

Abstract

The present invention relates to a visible region handover technology in a communication system, and can provide a method of a base station, comprising the steps of: receiving first information required to determine whether to initiate a visible region handover from user equipment (UE); determining whether to initiate the visible region handover on the basis of the first information; and, if it is determined that the initiation of the visible region handover is required, attempting a first visible region handover on the basis of antenna elements adjacent to a visible region in use.

Description

Method and device for handover in a visible area in a communication system

[0001] The present disclosure relates to improved communication technology, and more particularly, to a line-of-sight handover technology in a communication system capable of providing a suitable line-of-sight area to a terminal.

[0002] Communication networks (e.g., 5G communication networks, 6G communication networks, etc.) are being developed to provide improved communication services compared to existing communication networks (e.g., long term evolution (LTE), advanced LTE-A (LTE-A), etc.). 5G communication networks (e.g., new radio (NR) communication networks) can support frequency bands above 6 GHz as well as frequency bands below 6 GHz. That is, 5G communication networks can support frequency range (FR) 1 band and / or FR2 band. 5G communication networks can support various communication services and scenarios compared to LTE communication networks. For example, usage scenarios of 5G communication networks can include enhanced Mobile Broadband (eMBB), Ultra Reliable Low Latency Communication (URLLC), massive Machine Type Communication (mMTC), etc.

[0003] Compared to 5G, 6G communication networks can support a wider range of communication services and scenarios. 6G communication networks can meet requirements for ultra-high performance, ultra-high bandwidth, ultra-high space, ultra-high precision, ultra-intelligence, and / or ultra-reliability. 6G communication networks can support diverse and wide frequency bands and be applied to various usage scenarios (e.g., terrestrial communications, non-terrestrial communications, sidelink communications, etc.).

[0004] Meanwhile, 5G communication networks can simultaneously service multiple terminals and use massive MIMO ((multiple-input multiple-output)) systems to achieve higher information transmission rates. Base stations can achieve higher information transmission rates by utilizing massive MIMO systems, and when transmitting information to terminals, they can transmit by concentrating the beam at a specific location, thereby achieving low inter-user interference and high energy efficiency. In the future, 6G communication networks can go beyond massive MIMO systems and use extra-large scale massive MIMO (XL-MIMO) systems. Here, the XL-MIMO system can be a system that places multiple antenna elements on the walls of large buildings such as airports, shopping malls, and stadiums to obtain additional spatial dimensions. Such XL-MIMO systems may have difficulty communicating due to unsuitable visibility region (VR) settings. In such cases, the XL-MIMO system can create a new visibility region suitable for the terminal rather than changing the base station. A visible area handover process may be required to provide this.

[0005] The purpose of the present disclosure to solve the above problems is to provide a method and device for handover in a communication system capable of providing a suitable visible area to a terminal.

[0006] In order to achieve the above object, a method for line-of-sight handover in a communication system according to a first embodiment of the present disclosure may include, as a method of a base station, the steps of: receiving first information necessary to determine whether to initiate a line-of-sight handover from a UE (user equipment); determining whether to initiate the line-of-sight handover based on the first information; and attempting a first line-of-sight handover based on antenna elements adjacent to the line-of-sight area in use when it is determined that initiation of the line-of-sight handover is necessary.

[0007] The first information is information about a received signal strength measured by the UE with respect to a signal transmitted from the base station to the UE through the visible area in use, and the step of determining whether to initiate the visible area handover based on the first information includes the step of determining whether the received signal strength is less than or equal to a first threshold; and if the received signal strength is less than or equal to the first threshold, the step of determining whether a duration of a state in which the received signal strength is less than or equal to the first threshold is greater than or equal to a second threshold, and if the duration of a state in which the received signal strength is less than or equal to the first threshold is greater than or equal to the second threshold, it may be determined that the visible area handover is necessary.

[0008] The first information is information about the speed of the UE, and the step of determining whether to initiate the visible area handover based on the first information includes the step of determining whether the speed is equal to or greater than a third threshold; and, if the speed is equal to or greater than the third threshold, the step of determining whether the duration of the state in which the speed is equal to or greater than the third threshold is equal to or greater than a fourth threshold, and if the duration of the state in which the speed is equal to or greater than the third threshold is equal to or greater than the fourth threshold, it may be determined that the visible area handover is necessary.

[0009] The first information includes information about the received signal strength measured by the UE with respect to a signal transmitted from the base station to the UE through the visible area in use and information about the speed of the UE, and the step of determining whether to initiate the visible area handover based on the first information includes the steps of: determining whether the received signal strength is less than or equal to a first threshold; if the received signal strength is less than or equal to the first threshold, determining whether a duration of a state in which the received signal strength is less than or equal to the first threshold is greater than or equal to a second threshold; if the duration of a state in which the received signal strength is less than or equal to the first threshold is greater than or equal to the second threshold, determining whether the speed is greater than or equal to a third threshold; and if the speed is greater than or equal to the third threshold, determining whether a duration of a state in which the speed is greater than or equal to the third threshold is greater than or equal to a fourth threshold. If the duration of a state in which the speed is greater than or equal to the third threshold is greater than or equal to the fourth threshold, it may be determined that the visible area handover is necessary.

[0010] The second threshold value and the fourth threshold value may be the same.

[0011] If it is determined that initiation of the above line-of-sight handover is necessary, the step of attempting the first line-of-sight handover based on antenna elements adjacent to the in-use line-of-sight area may include the steps of: if it is determined that initiation of the line-of-sight handover is necessary, setting candidate antenna groups using antenna elements adjacent to the in-use line-of-sight area; transmitting reference signals to the UE using the candidate antenna groups; receiving information about received signal strengths of the reference signals from the UE; selecting one of the candidate antenna groups based on the received signal strengths; and attempting the first line-of-sight handover by replacing the in-use line-of-sight area with a line-of-sight area formed by the selected one of the candidate antenna groups.

[0012] The number of antenna elements in each of the above candidate antenna groups may be equal to the number of antenna elements located in the visible region being used.

[0013] The number of first antenna elements in the first direction of each of the candidate antenna groups may be equal to the number of second antenna elements positioned in the first direction in the visible area being used, and the number of third antenna elements in the second direction of each of the candidate antenna groups may be equal to the number of fourth antenna elements positioned in the second direction in the visible area being used.

[0014] The step of transmitting reference signals to the UE using the candidate antenna groups may include: assigning a group index to each of the candidate antenna groups; assigning a beam index to each of the beams of the candidate antenna groups; generating the reference signals including the group index and the beam index of each of the candidate antenna groups; and transmitting the reference signals to the UE.

[0015] The step of selecting one candidate antenna group based on the received signal intensities may include the step of comparing the received signal intensities with a first threshold value; the step of selecting candidate antenna groups having a received signal intensity greater than or equal to the first threshold value based on a result of the comparison; and the step of selecting a candidate antenna group having the maximum received signal intensities among the selected candidate antenna groups as one of the candidate antenna groups.

[0016] If the above first line-of-sight handover attempt fails, the step of attempting a second line-of-sight handover based on all antenna elements of the antenna may be further included.

[0017] The step of attempting a second line-of-sight handover based on all antenna elements of the antenna when the first line-of-sight handover attempt fails may include the steps of: setting candidate antenna groups using the all antenna elements of the antenna when the first line-of-sight handover attempt fails; transmitting reference signals to the UE using the candidate antenna groups; receiving information about received signal strengths of the reference signals from the UE; selecting one of the candidate antenna groups based on the received signal strengths; and attempting the second line-of-sight handover by replacing the currently used line-of-sight area with a line-of-sight area formed by the selected one of the candidate antenna groups.

[0018] If the above second visible area handover attempt fails, the step of attempting a handover to another base station may be further included.

[0019] Meanwhile, in a communication system according to a second embodiment of the present disclosure for achieving the above purpose, a method for a line-of-sight handover may include a step of receiving threshold information necessary for determining whether to initiate a line-of-sight handover from a base station, a step of determining whether to initiate the line-of-sight handover based on the threshold information, and a step of requesting the base station to initiate the line-of-sight handover if it is determined that initiation of the line-of-sight handover is necessary.

[0020] The threshold information includes information on a first threshold value and a second threshold value, and the step of determining whether to initiate the visible area handover based on the threshold information includes the steps of: receiving a reference signal from the base station; measuring a received signal strength of the reference signals; determining whether the received signal strength is less than or equal to the first threshold value; and, if the received signal strength is less than or equal to the first threshold value, determining whether a duration of a state in which the received signal strength is less than or equal to the first threshold value is greater than or equal to the second threshold value. If the duration of a state in which the received signal strength is less than or equal to the first threshold value is greater than or equal to the second threshold value, it may be determined that the visible area handover is necessary.

[0021] The above threshold information includes information on a third threshold value and a fourth threshold value, and the step of determining whether to initiate the visible area handover based on the threshold information includes the steps of: measuring a speed of the UE; determining whether the speed is equal to or greater than the third threshold value; and, if the speed is equal to or greater than the third threshold value, determining whether a duration of a state in which the speed is equal to or greater than the third threshold value is equal to or greater than the fourth threshold value. If the duration of a state in which the speed is equal to or greater than the third threshold value is equal to or greater than the fourth threshold value, it may be determined that the visible area handover is necessary.

[0022] The method may further include: receiving reference signals including group indices of each of candidate antenna groups transmitted from the base station based on a request for the visible area handover and beam indices of each of beams formed from each of the candidate antenna groups; measuring received signal intensities for the reference signals; and transmitting information about the received signal intensities to the base station.

[0023] Meanwhile, in a communication system according to a third embodiment of the present disclosure for achieving the above purpose, a visible area handover device is a UE (user equipment) including at least one processor, wherein the at least one processor can cause the UE to receive threshold information necessary to determine whether to initiate a visible area handover from a base station; determine whether to initiate the visible area handover based on the threshold information; and request the base station to initiate the visible area handover if it is determined that initiation of the visible area handover is necessary.

[0024] The threshold information includes information about a first threshold value and a second threshold value, and in the step of determining whether to initiate the visible area handover based on the threshold information, the at least one processor causes the UE to receive a reference signal from the base station; measure a received signal strength of the reference signals; determine whether the received signal strength is less than or equal to the first threshold value; and if the received signal strength is less than or equal to the first threshold value, determine whether a duration of a state in which the received signal strength is less than or equal to the first threshold value is greater than or equal to the second threshold value, and if the duration of a state in which the received signal strength is less than or equal to the first threshold value is greater than or equal to the second threshold value, it may be determined that the visible area handover is necessary.

[0025] The above threshold information includes information on a third threshold value and a fourth threshold value, and in the step of determining whether to initiate the visible area handover based on the threshold information, the at least one processor causes the UE to measure a speed of the UE; determine whether the speed is equal to or greater than the third threshold value; and if the speed is equal to or greater than the third threshold value, determine whether a duration of a state in which the speed is equal to or greater than the third threshold value is equal to or greater than the fourth threshold value, and if the duration of a state in which the speed is equal to or greater than the third threshold value is equal to or greater than the fourth threshold value, it may be determined that the visible area handover is necessary.

[0026] According to the present disclosure, a base station can change a line-of-sight area to improve communication quality when communication quality deteriorates during communication with a terminal using an ultra-large MIMO system. Furthermore, according to the present disclosure, the base station can establish a new line-of-sight area among the lines of sight generated by antenna elements adjacent to the line-of-sight area currently being used. Furthermore, according to the present disclosure, the base station can establish a new line-of-sight area among the lines of sight generated by antenna elements throughout the antenna.

[0027] Figure 1 is a conceptual diagram illustrating embodiments of a communication system.

[0028] Figure 2 is a block diagram illustrating embodiments of communication nodes constituting a communication system.

[0029] Figure 3 is a block diagram illustrating embodiments of communication nodes that perform communication.

[0030] Figure 4a is a block diagram illustrating embodiments of a transmission path.

[0031] Figure 4b is a block diagram illustrating embodiments of a receiving path.

[0032] Figure 5 is a conceptual diagram illustrating embodiments of system frames in a communication system.

[0033] Figure 6 is a conceptual diagram illustrating embodiments of subframes in a communication system.

[0034] Figure 7 is a conceptual diagram illustrating embodiments of slots in a communication system.

[0035] Figure 8 is a conceptual diagram illustrating embodiments of time-frequency resources in a communication system.

[0036] FIG. 9 is a conceptual diagram illustrating a first embodiment of scatters existing in a communication link between a base station and a terminal and a visible area corresponding to each scatter.

[0037] Fig. 10 is a flowchart illustrating a first embodiment of a visible area handover method in a communication system.

[0038] FIG. 11 is a flowchart illustrating a first embodiment of a line-of-sight handover process through all antenna elements of FIG. 10.

[0039] Fig. 12 is a flowchart illustrating a second embodiment of a visible area handover method in a communication system.

[0040] This disclosure may be subject to various modifications and various embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the disclosure to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the disclosure.

[0041] While terms such as "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present disclosure, a first component could be referred to as a "second component," and similarly, a second component could also be referred to as a "first component." The term "and / or" may refer to a combination of multiple related items described herein or to any of multiple related items described herein.

[0042] In the present disclosure, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B.” Additionally, in the present disclosure, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B.”

[0043] In the present disclosure, (re)transmission may mean “transmission,” “retransmission,” or “transmission and retransmission,” (re)setting may mean “setting,” “resetting,” or “setting and resetting,” (re)connection may mean “connection,” “reconnection,” or “connection and reconnection,” and (re)connection may mean “connection,” “reconnection,” or “connection and reconnection.”

[0044] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0045] The terminology used in this disclosure is only used to describe specific embodiments and is not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0046] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this disclosure pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0047] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding in describing the present disclosure, the same reference numerals will be used for identical components in the drawings, and redundant descriptions of identical components will be omitted. In addition to the embodiments explicitly described in the present disclosure, operations may be performed according to combinations of embodiments, extensions of embodiments, and / or modifications of embodiments. The performance of some operations may be omitted, and the order of operation may be changed.

[0048] In an embodiment, even if a method (e.g., transmitting or receiving a signal) performed by a first communication node among communication nodes is described, a corresponding second communication node can perform a method (e.g., receiving or transmitting a signal) corresponding to the method performed by the first communication node. That is, if an operation of a UE (user equipment) is described, a corresponding base station can perform an operation corresponding to the operation of the UE. Conversely, if an operation of a base station is described, a corresponding UE can perform an operation corresponding to the operation of the base station.

[0049] A base station may be referred to as a NodeB, an evolved NodeB, a gNodeB (next generation node B), a gNB, a device, an apparatus, a node, a communication node, a BTS (base transceiver station), a RRH (radio remote head), a TRP (transmission reception point), a RU (radio unit), an RSU (road side unit), a radio transceiver, an access point, an access node, etc. A UE may be referred to as a terminal, a device, an apparatus, a node, a communication node, an end node, an access terminal, a mobile terminal, a station, a subscriber station, a mobile station, a portable subscriber station, an OBU (on-broad unit), etc.

[0050] In the present disclosure, signaling may be at least one of upper layer signaling, medium access control (MAC) signaling, or physical (PHY) signaling. A message used for upper layer signaling may be referred to as an "upper layer message" or an "upper layer signaling message." A message used for MAC signaling may be referred to as a "MAC message" or a "MAC signaling message." A message used for PHY signaling may be referred to as a "PHY message" or a "PHY signaling message." Upper layer signaling may refer to a transmission and reception operation of system information (e.g., a master information block (MIB), a system information block (SIB)) and / or a radio resource control (RRC) message. MAC signaling may refer to a transmission and reception operation of a MAC control element (CE). PHY signaling may refer to the transmission and reception of control information (e.g., downlink control information (DCI), uplink control information (UCI), sidelink control information (SCI)).

[0051] In the present disclosure, “an operation (e.g., a transmission operation) is set” may mean that “setting information for the operation (e.g., an information element, a parameter)” and / or “information instructing the performance of the operation” is signaled. “An information element (e.g., a parameter) is set” may mean that the information element is signaled. In the present disclosure, “a signal and / or a channel” may mean a signal, a channel, or “a signal and a channel,” and a signal may be used to mean “a signal and / or a channel.”

[0052] The communication network to which the embodiment is applied is not limited to what is described below, and the embodiment may be applied to various communication networks (e.g., 4G communication networks, 5G communication networks, and / or 6G communication networks). Here, the communication network may be used in the same sense as the communication system.

[0053] Figure 1 is a conceptual diagram illustrating embodiments of a communication system.

[0054] Referring to FIG. 1, the communication system (100) may include a plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). In addition, the communication system (100) may further include a core network (e.g., a serving-gateway (S-GW), a packet data network (PDN)-gateway (P-GW), a mobility management entity (MME)). If the communication system (100) is a 5G communication system (e.g., a new radio (NR) system), the core network may include an access and mobility management function (AMF), a user plane function (UPF), a session management function (SMF), etc.

[0055] A plurality of communication nodes (110 to 130) can support a communication protocol (e.g., LTE communication protocol, LTE-A communication protocol, NR communication protocol, etc.) specified in the 3GPP (3rd generation partnership project) standard. The plurality of communication nodes (110 to 130) may support CDMA (code division multiple access) technology, WCDMA (wideband CDMA) technology, TDMA (time division multiple access) technology, FDMA (frequency division multiple access) technology, OFDM (orthogonal frequency division multiplexing) technology, Filtered OFDM technology, CP (cyclic prefix)-OFDM technology, DFT-s-OFDM (discrete Fourier transform-spread-OFDM) technology, OFDMA (orthogonal frequency division multiple access) technology, SC (single carrier)-FDMA technology, NOMA (non-orthogonal multiple access) technology, GFDM (generalized frequency division multiplexing) technology, FBMC (filter bank multi-carrier) technology, UFMC (universal filtered multi-carrier) technology, SDMA (space division multiple access) technology, etc. Each of the plurality of communication nodes may have the following structure.

[0056] Figure 2 is a block diagram illustrating embodiments of communication nodes constituting a communication system.

[0057] Referring to FIG. 2, a communication node (200) may include at least one processor (210), a memory (220), and a transmission / reception device (230) that is connected to a network and performs communication. In addition, the communication node (200) may further include an input interface device (240), an output interface device (250), a storage device (260), etc. Each component included in the communication node (200) may be connected by a bus (270) and communicate with each other.

[0058] The processor (210) can execute program commands stored in at least one of the memory (220) and the storage device (260). The processor (210) may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which the methods according to embodiments of the present disclosure are performed. Each of the memory (220) and the storage device (260) may be configured with at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory (220) may be configured with at least one of a read-only memory (ROM) and a random access memory (RAM).

[0059] Referring again to FIG. 1, the communication system (100) may include a plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) and a plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) may form a macro cell. Each of the fourth base station (120-1) and the fifth base station (120-2) may form a small cell. The fourth base station (120-1), the third terminal (130-3), and the fourth terminal (130-4) may be within the cell coverage of the first base station (110-1). The second terminal (130-2), the fourth terminal (130-4), and the fifth terminal (130-5) may be within the cell coverage of the second base station (110-2). The fifth base station (120-2), the fourth terminal (130-4), the fifth terminal (130-5), and the sixth terminal (130-6) may be within the cell coverage of the third base station (110-3). The first terminal (130-1) may be within the cell coverage of the fourth base station (120-1). The sixth terminal (130-6) may be within the cell coverage of the fifth base station (120-2).

[0060] Here, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be referred to as a NodeB (NB), an evolved NodeB (eNB), a gNB, an advanced base station (ABS), a high reliability-base station (HR-BS), a base transceiver station (BTS), a radio base station, a radio transceiver, an access point, an access node, a radio access station (RAS), a mobile multihop relay-base station (MMR-BS), a relay station (RS), an advanced relay station (ARS), a high reliability-relay station (HR-RS), a home NodeB (HNB), a home eNodeB (HeNB), a road side unit (RSU), a radio remote head (RRH), a transmission point (TP), a transmission and reception point (TRP), etc.

[0061] Each of the plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) may be referred to as a user equipment (UE), terminal equipment (TE), advanced mobile station (AMS), high reliability-mobile station (HR-MS), terminal, access terminal, mobile terminal, station, subscriber station, mobile station, portable subscriber station, node, device, on board unit (OBU), etc.

[0062] Meanwhile, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may operate in a different frequency band or may operate in the same frequency band. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be connected to each other via an ideal backhaul link or a non-ideal backhaul link, and may exchange information with each other via the ideal backhaul link or the non-ideal backhaul link. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be connected to the core network via the ideal backhaul link or the non-ideal backhaul link. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can transmit a signal received from the core network to the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6), and can transmit a signal received from the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) to the core network.

[0063] Additionally, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may support MIMO transmission (e.g., single user (SU)-MIMO, multi user (MU)-MIMO, massive MIMO, etc.), coordinated multipoint (CoMP) transmission, carrier aggregation (CA) transmission, transmission in an unlicensed band, sidelink communication (e.g., device to device communication (D2D), proximity services (ProSe)), Internet of Things (IoT) communication, dual connectivity (DC), etc. Here, each of the plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) can perform an operation corresponding to the base station (110-1, 110-2, 110-3, 120-1, 120-2) and an operation supported by the base station (110-1, 110-2, 110-3, 120-1, 120-2). For example, the second base station (110-2) can transmit a signal to the fourth terminal (130-4) based on the SU-MIMO scheme, and the fourth terminal (130-4) can receive a signal from the second base station (110-2) by the SU-MIMO scheme. Alternatively, the second base station (110-2) can transmit signals to the fourth terminal (130-4) and the fifth terminal (130-5) based on the MU-MIMO method, and each of the fourth terminal (130-4) and the fifth terminal (130-5) can receive signals from the second base station (110-2) based on the MU-MIMO method.

[0064] Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) can transmit a signal to the fourth terminal (130-4) based on the CoMP scheme, and the fourth terminal (130-4) can receive a signal from the first base station (110-1), the second base station (110-2), and the third base station (110-3) based on the CoMP scheme. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can transmit and receive a signal with terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) within its cell coverage based on the CA scheme. Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) can control sidelink communication between the fourth terminal (130-4) and the fifth terminal (130-5), and each of the fourth terminal (130-4) and the fifth terminal (130-5) can perform sidelink communication under the control of the second base station (110-2) and the third base station (110-3), respectively.

[0065] Meanwhile, communication nodes performing communication in a communication network may be configured as follows. The communication node illustrated in Fig. 3 may be a specific embodiment of the communication node illustrated in Fig. 2.

[0066] Figure 3 is a block diagram illustrating embodiments of communication nodes that perform communication.

[0067] Referring to FIG. 3, each of the first communication node (300a) and the second communication node (300b) may be a base station or a UE. The first communication node (300a) may transmit a signal to the second communication node (300b). The transmission processor (311) included in the first communication node (300a) may receive data (e.g., a data unit) from a data source (310). The transmission processor (311) may receive control information from the controller (316). The control information may include at least one of system information, RRC configuration information (e.g., information configured by RRC signaling), MAC control information (e.g., MAC CE), or PHY control information (e.g., DCI, SCI).

[0068] The transmitting processor (311) may perform a processing operation on data (e.g., an encoding operation, a symbol mapping operation, etc.) to generate data symbol(s). The transmitting processor (311) may perform a processing operation on control information (e.g., an encoding operation, a symbol mapping operation, etc.) to generate control symbol(s). In addition, the transmitting processor (311) may generate synchronization / reference symbol(s) for a synchronization signal and / or a reference signal.

[0069] The Tx MIMO processor (312) may perform a spatial processing operation (e.g., a precoding operation) on data symbol(s), control symbol(s), and / or synchronization / reference symbol(s). The output (e.g., a symbol stream) of the Tx MIMO processor (312) may be provided to modulators (MODs) included in the transceivers (313a to 313t). The modulators (MODs) may perform a processing operation on the symbol stream to generate modulation symbols, and may perform an additional processing operation (e.g., an analog conversion operation, an amplification operation, a filtering operation, an upconversion operation) on the modulation symbols to generate signals. The signals generated by the modulators (MODs) of the transceivers (313a to 313t) may be transmitted via the antennas (314a to 314t).

[0070] Signals transmitted by the first communication node (300a) may be received by antennas (364a to 364r) of the second communication node (300b). Signals received by the antennas (364a to 364r) may be provided to demodulators (DEMODs) included in transceivers (363a to 363r). The demodulator (DEMOD) may perform a processing operation (e.g., a filtering operation, an amplification operation, a downconversion operation, a digital conversion operation) on the signal to obtain samples. The demodulator (DEMOD) may perform an additional processing operation on the samples to obtain symbols. The MIMO detector (362) may perform a MIMO detection operation on the symbols. The receiving processor (361) may perform a processing operation (e.g., a deinterleaving operation, a decoding operation) on the symbols. The output of the receiving processor (361) may be provided to a data sink (360) and a controller (366). For example, data may be provided to the data sink (360), and control information may be provided to the controller (366).

[0071] Meanwhile, the second communication node (300b) can transmit a signal to the first communication node (300a). The transmitting processor (368) included in the second communication node (300b) can receive data (e.g., data units) from a data source (367) and perform a processing operation on the data to generate data symbol(s). The transmitting processor (368) can receive control information from the controller (366) and perform a processing operation on the control information to generate control symbol(s). In addition, the transmitting processor (368) can perform a processing operation on a reference signal to generate reference symbol(s).

[0072] The Tx MIMO processor (369) may perform spatial processing operations (e.g., precoding operations) on data symbol(s), control symbol(s), and / or reference symbol(s). The output (e.g., symbol stream) of the Tx MIMO processor (369) may be provided to modulators (MODs) included in the transceivers (363a to 363t). The modulators (MODs) may perform processing operations on the symbol streams to generate modulation symbols, and may perform additional processing operations (e.g., analog conversion operations, amplification operations, filtering operations, upconversion operations) on the modulation symbols to generate signals. The signals generated by the modulators (MODs) of the transceivers (363a to 363t) may be transmitted via the antennas (364a to 364t).

[0073] Signals transmitted by the second communication node (300b) may be received by the antennas (314a to 314r) of the first communication node (300a). The signals received by the antennas (314a to 314r) may be provided to demodulators (DEMODs) included in the transceivers (313a to 313r). The demodulator (DEMOD) may perform a processing operation (e.g., a filtering operation, an amplification operation, a downconversion operation, a digital conversion operation) on the signal to obtain samples. The demodulator (DEMOD) may perform an additional processing operation on the samples to obtain symbols. The MIMO detector (320) may perform a MIMO detection operation on the symbols. The receiving processor (319) may perform a processing operation (e.g., a deinterleaving operation, a decoding operation) on the symbols. The output of the receiving processor (319) may be provided to a data sink (318) and a controller (316). For example, data may be provided to the data sink (318) and control information may be provided to the controller (316).

[0074] Memories (315 and 365) can store data, control information, and / or program code. Scheduler (317) can perform scheduling operations for communication. The processors (311, 312, 319, 361, 368, 369) and controllers (316, 366) illustrated in FIG. 3 may be the processor (210) illustrated in FIG. 2 and may be used to perform the methods described in the present disclosure.

[0075] FIG. 4a is a block diagram illustrating embodiments of a transmission path, and FIG. 4b is a block diagram illustrating embodiments of a reception path.

[0076] Referring to FIGS. 4A and 4B, a transmission path (410) may be implemented in a communication node that transmits a signal, and a reception path (420) may be implemented in a communication node that receives a signal. The transmission path (410) may include a channel coding and modulation block (411), an S-to-P (serial-to-parallel) block (512), an N IFFT (Inverse Fast Fourier Transform) block (413), a P-to-S (parallel-to-serial) block (414), a CP (cyclic prefix) addition block (415), and an UC (up-converter) (UC) (416). The receiving path (420) may include a DC (down-converter) (421), a CP removal block (422), an S-to-P block (423), an N FFT block (424), a P-to-S block (425), and a channel decoding and demodulation block (426). Here, N may be a natural number.

[0077] In the transmission path (410), information bits may be input to a channel coding and modulation block (411). The channel coding and modulation block (411) may perform a coding operation (e.g., a low-density parity check (LDPC) coding operation, a polar coding operation, etc.) and a modulation operation (e.g., a quadrature phase shift keying (QPSK), a quadrature amplitude modulation (QAM), etc.) on the information bits. The output of the channel coding and modulation block (411) may be a sequence of modulation symbols.

[0078] The S-to-P block (412) can convert modulation symbols in the frequency domain into parallel symbol streams to generate N parallel symbol streams. N can be an IFFT size or an FFT size. The N IFFT block (413) can perform an IFFT operation on the N parallel symbol streams to generate signals in the time domain. The P-to-S block (414) can convert the output (e.g., parallel signals) of the N IFFT block (413) into a serial signal to generate a serial signal.

[0079] The CP addition block (415) can insert a CP into a signal. The UC (416) can up-convert the frequency of the output of the CP addition block (415) to an RF (radio frequency) frequency. Additionally, the output of the CP addition block (415) can be filtered at the baseband before up-conversion.

[0080] A signal transmitted from a transmission path (410) may be input to a reception path (420). An operation in the reception path (420) may be the reverse operation of the operation in the transmission path (410). A DC (421) may down-convert the frequency of the received signal to a baseband frequency. A CP removal block (422) may remove a CP from a signal. The output of the CP removal block (422) may be a serial signal. An S-to-P block (423) may convert the serial signal into parallel signals. An N FFT block (424) may perform an FFT algorithm to generate N parallel signals. A P-to-S block (425) may convert the parallel signals into a sequence of modulation symbols. A channel decoding and demodulation block (426) may perform a demodulation operation on the modulation symbols and perform a decoding operation on the result of the demodulation operation to restore data.

[0081] In FIGS. 4A and 4B , Discrete Fourier Transform (DFT) and Inverse DFT (IDFT) may be used instead of FFT and IFFT. Each of the blocks (e.g., components) in FIGS. 4A and 4B may be implemented by at least one of hardware, software, or firmware. For example, some of the blocks in FIGS. 4A and 4B may be implemented by software, and the remaining blocks may be implemented by hardware or a “combination of hardware and software.” In FIGS. 4A and 4B , a block may be subdivided into multiple blocks, multiple blocks may be integrated into a single block, some blocks may be omitted, and blocks supporting other functions may be added.

[0082] Figure 5 is a conceptual diagram illustrating embodiments of a system frame in a communication system.

[0083] Referring to FIG. 5, time resources in a communication system can be divided into frame units. For example, system frames can be set consecutively in the time domain of the communication system. The length of a system frame can be 10 ms (milliseconds). The system frame number (SFN) can be set from #0 to #1023. In this case, 1024 system frames can be repeated in the time domain of the communication system. For example, the SFN of the system frame after system frame #1023 can be #0.

[0084] A system frame may include two half frames. A half frame may be 5 ms long. A half frame located at the beginning of the system frame may be referred to as "half frame #0," and a half frame located at the end of the system frame may be referred to as "half frame #1." A system frame may include 10 subframes. A subframe may be 1 ms long. The 10 subframes within a system frame may be referred to as "subframes #0-9."

[0085] Figure 6 is a conceptual diagram illustrating embodiments of subframes in a communication system.

[0086] Referring to FIG. 6, one subframe may include n slots, where n may be a natural number. Accordingly, one subframe may be composed of one or more slots.

[0087] Figure 7 is a conceptual diagram illustrating embodiments of slots in a communication system.

[0088] Referring to FIG. 7, a single slot may include one or more symbols. A single slot illustrated in FIG. 7 may include 14 symbols. The length of a slot may vary depending on the number and length of symbols contained in the slot. Alternatively, the length of a slot may vary depending on numerology.

[0089] In a communication system, the numerology applied to physical signals and channels may be variable. The numerology may be variable to meet various technical requirements of the communication system. In a communication system applying CP (cyclic prefix)-based OFDM waveform technology, the numerology may include subcarrier spacing and CP length (or CP type). Table 1 may be a first embodiment of a method for configuring a numerology for a CP-OFDM-based communication system. At least some of the numerologies in Table 1 may be supported depending on the frequency band in which the communication system operates. In addition, the communication system may additionally support numerologies not listed in Table 1.

[0090] Subcarrier spacing 15kHz 30kHz 60kHz 120kHz 240kHz 480kHz OFDM symbol length [μs] 66.733.316.78.34.22.1 CP length [μs] 4.762.381.190.600.300.151 Number of OFDM symbols in ms 142856112224448

[0091] When the subcarrier spacing is 15 kHz (e.g., μ=0), the slot length can be 1 ms. In this case, one system frame can contain 10 slots. When the subcarrier spacing is 30 kHz (e.g., μ=1), the slot length can be 0.5 ms. In this case, one system frame can contain 20 slots. When the subcarrier spacing is 60 kHz (e.g., μ=2), the slot length can be 0.25 ms. In this case, one system frame can contain 40 slots. When the subcarrier spacing is 120 kHz (e.g., μ=3), the slot length can be 0.125 ms. In this case, one system frame can contain 80 slots. When the subcarrier spacing is 240 kHz (e.g., μ=4), the slot length can be 0.0625 ms. In this case, one system frame can contain 160 slots.

[0092] A symbol may be configured as a downlink (DL) symbol, a flexible (FL) symbol, or an uplink (UL) symbol. A slot consisting solely of DL symbols may be referred to as a "DL slot," a slot consisting solely of FL symbols may be referred to as an "FL slot," and a slot consisting solely of UL symbols may be referred to as a "UL slot."

[0093] The slot format can be semi-statically configured by higher layer signaling (e.g., RRC signaling). Information indicating the semi-static slot format can be included in the system information, and the semi-static slot format can be configured cell-specifically. In addition, the semi-static slot format can be additionally configured for each terminal through terminal-specific higher layer signaling (e.g., RRC signaling). The flexible symbol of the cell-specifically configured slot format can be overridden to a downlink symbol or an uplink symbol by terminal-specific higher layer signaling. In addition, the slot format can be dynamically indicated by physical layer signaling (e.g., a slot format indicator (SFI) included in DCI). The semi-statically configured slot format can be overridden by a dynamically indicated slot format. For example, the semi-statically configured flexible symbol can be overridden to a downlink symbol or an uplink symbol by the SFI.

[0094] The reference signal may be a channel state information-reference signal (CSI-RS), a sounding reference signal (SRS), a demodulation-reference signal (DM-RS), a phase tracking-reference signal (PT-RS), etc. The channel may be a physical broadcast channel (PBCH), a physical downlink control channel (PDCCH), a physical downlink shared channel (PDSCH), a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH), a physical sidelink control channel (PSCCH), a physical sidelink shared channel (PSSCH), etc. In the present disclosure, a control channel may mean a PDCCH, a PUCCH, or a PSCCH, and a data channel may mean a PDSCH, a PUSCH, or a PSSCH.

[0095] Figure 8 is a conceptual diagram illustrating embodiments of time-frequency resources in a communication system.

[0096] Referring to FIG. 8, a resource consisting of one symbol (e.g., an OFDM symbol) in the time domain and one subcarrier in the frequency domain may be defined as a "RE (resource element)". Resources consisting of one OFDM symbol in the time domain and K subcarriers in the frequency domain may be defined as a "REG (resource element group)". A REG may include K REs. A REG may be used as a basic unit for resource allocation in the frequency domain. K may be a natural number. For example, K may be 12. N may be a natural number. In the slot illustrated in FIG. 7, N may be 14. N OFDM symbols may be used as a basic unit for resource allocation in the time domain.

[0097] In the present disclosure, RB may mean CRB (common RB). Alternatively, RB may mean PRB or VRB (virtual RB). In a communication system, CRB may mean RB that constitutes a set of consecutive RBs (e.g., a common RB grid) based on a reference frequency (e.g., point A). Carriers and / or bandwidth portions may be arranged on the common RB grid. That is, the carrier and / or bandwidth portions may be composed of CRB(s). RBs or CRBs that constitute the bandwidth portions may be referred to as PRBs, and within the bandwidth portions, the CRB index may be appropriately converted to the PRB index.

[0098] Downlink data can be transmitted via the PDSCH. The base station can transmit PDSCH configuration information (e.g., scheduling information) to the terminal via the PDCCH. The terminal can obtain the PDSCH configuration information by receiving the PDCCH (e.g., downlink control information (DCI)). For example, the PDSCH configuration information can include the MCS (modulation coding scheme) used for transmitting and receiving the PDSCH, time resource information of the PDSCH, frequency resource information of the PDSCH, feedback resource information for the PDSCH, etc. The PDSCH can refer to a radio resource through which downlink data is transmitted and received. Alternatively, the PDSCH can refer to the downlink data itself. The PDCCH can refer to a radio resource through which downlink control information (e.g., DCI) is transmitted and received. Alternatively, the PDCCH can refer to the downlink control information itself.

[0099] A terminal can perform a monitoring operation on the PDCCH to receive a PDSCH transmitted from a base station. The base station can inform the terminal of the configuration information for the PDCCH monitoring operation using a higher layer message (e.g., an RRC (radio resource control) message). The configuration information for the PDCCH monitoring operation can include CORESET (control resource set) information and search space information.

[0100] CORESET information may include PDCCH DMRS (demodulation reference signal) information, PDCCH precoding information, PDCCH occasion information, etc. The PDCCH DMRS may be a DMRS used to demodulate the PDCCH. The PDCCH occasion may be a region where the PDCCH can exist. That is, the PDCCH occasion may be a region where DCI can be transmitted. The PDCCH occasion may be referred to as a PDCCH candidate. The PDCCH occasion information may include time resource information and frequency resource information of the PDCCH occasion. In the time domain, the length of the PDCCH occasion may be indicated in symbol units. In the frequency domain, the size of the PDCCH occasion may be indicated in RB units (e.g., in PRB (physical resource block) units or CRB (common resource block) units).

[0101] The search space information may include a coreset identifier (ID) associated with the search space, a period of PDCCH monitoring, and / or an offset. Each of the PDCCH monitoring period and offset may be indicated on a slot-by-slot basis. In addition, the search space information may further include an index of the symbol at which the PDCCH monitoring operation begins.

[0102] A base station can configure a bandwidth part (BWP) for downlink communication. The BWP can be configured differently for each terminal. The base station can inform the terminal of the BWP configuration information using higher layer signaling. The higher layer signaling can mean "transmission operation of system information" and / or "transmission operation of RRC (radio resource control) message." The number of BWPs configured for one terminal can be one or more. The terminal can receive BWP configuration information from the base station and check the BWP(s) configured by the base station based on the BWP configuration information. When multiple BWPs are configured for downlink communication, the base station can activate one or more BWPs among the multiple BWPs. The base station can transmit the configuration information of the activated BWP(s) to the terminal using at least one of higher layer signaling, a medium access control (MAC) control element (CE), or DCI. The base station can perform downlink communication using the activated BWP(s). The terminal can identify the activated BWP(s) by receiving configuration information of the activated BWP(s) from the base station, and perform a downlink reception operation in the activated BWP(s).

[0103] Meanwhile, 5G communication networks can simultaneously service multiple terminals and use massive MIMO (multiple-input multiple-output) systems to achieve higher data transmission rates. Base stations can achieve higher data transmission rates by utilizing massive MIMO systems, and when transmitting information to terminals, they can focus beams on specific locations, thereby achieving low inter-user interference and high energy efficiency. In addition, technologies utilizing multiple antennas such as massive MIMO can compensate for the reduced communication range due to high path attenuation in millimeter-wave and terahertz communications. Conversely, current massive MIMO systems may have limitations in that it is difficult to obtain sufficient spatial dimensions because they generally use a very large number of antenna elements arranged in a narrow space.

[0104] Therefore, future 6G communication networks may go beyond massive MIMO systems and utilize extra-large scale massive MIMO (XL-MIMO) systems. XL-MIMO systems may deploy multiple antenna elements on the walls of large buildings, such as airports, shopping malls, and stadiums, to gain additional spatial dimensions.

[0105] In these XL-MIMO systems, a very large number of antenna elements can be widely distributed over a large area, such as a large building wall. Consequently, channels can vary across distinct antenna regions formed by antenna groups of antenna elements. These channels are referred to as non-stationary channels. The XL-MIMO system can exploit this channel variation to achieve spatial dimensionality. This non-stationarity allows signals transmitted from a specific antenna region of an antenna to be significantly observed by the terminal. This specific antenna region can be defined as a visibility region (VR). The VR can vary depending on the location of the terminal, the surrounding environment, etc., and can also vary depending on the number and location of scatterers present in the communication link between the XL-MIMO system and the terminal.

[0106] A base station can communicate with a terminal through an XL-MIMO system. Accordingly, the terminal can transmit a signal to the XL-MIMO system of the base station. At this time, the signal transmitted from the terminal can be concentrated on a VR of the XL-MIMO system of the base station. Conversely, the base station can transmit a signal to the terminal using the XL MIMO system. At this time, the XL-MIMO system of the base station can transmit a signal to the terminal through antenna elements belonging to the VR. At this time, the terminal can receive a signal from the base station. The RSRP (reference signal received power) of the signal received by the terminal can be greater than or equal to an RSRP threshold.

[0107] Thus, it can be crucial for an XL-MIMO system to communicate with a terminal through VR. In an XL-MIMO system, VR can change due to terminal movement or changes in the surrounding environment. When VR changes, the XL-MIMO system may need to reconfigure it to suit the terminal.

[0108] In existing 5G communication networks, base stations can determine the need for a handover due to performance degradation during the handover process. If a base station determines that a handover is necessary due to performance degradation, it can transmit the necessary information to the terminal so that it can communicate with another base station. Thus, existing 5G communication networks can consider handovers between base stations when performance degradation occurs.

[0109] Meanwhile, the XL-MIMO system of a base station may have difficulty communicating with a terminal due to an inappropriate VR setting. In such a case, the XL-MIMO system may require a VR handover process to find a new VR suitable for the terminal rather than changing the base station. Therefore, the present disclosure proposes a line-of-sight handover process that provides a new VR suitable for the terminal when communication is no longer possible through the VR currently used for communication in an XL-MIMO system, and allows communication by resetting a beam suitable for the terminal through the new VR.

[0110] XL-MIMO systems can refer to antenna structures that deploy a larger number of antenna elements than Massive MIMO, often on the walls of large buildings such as airports, shopping malls, and stadiums. XL-MIMO systems offer high data rates, low inter-device interference, and high energy efficiency. Furthermore, by distributing antenna elements widely, they can achieve spatial dimensions not possible with Massive MIMO systems.

[0111] In an XL-MIMO system, a terminal may have different physical channel characteristics depending on the antenna region formed by the antenna group of antenna elements. This phenomenon of different physical channel characteristics depending on the antenna region can be defined as channel non-stationarity. Due to channel non-stationarity, a signal transmitted by a terminal may be limited to a specific antenna region within the XL-MIMO system. Conversely, the XL-MIMO system may transmit a signal through a specific antenna region. At this time, the terminal may receive a signal from the XL-MIMO system. The RSRP of the signal received by the terminal may exceed the RSRP threshold. This specific antenna region can be defined as a visibility region (VR). In this way, the communication performance of a terminal may depend on the VR associated with the terminal. When communicating between an XL-MIMO system and a terminal, it may be important from the perspective of communication resource efficiency for the XL-MIMO system to estimate the VR associated with the terminal in advance and exchange signals with the terminal through the estimated VR.

[0112] In a 5G communication network, a terminal can perform a handover to a new base station when communication performance deteriorates between the terminal and the base station. The handover process in a 5G communication network can be very similar to the handover process in an LTE communication network. In an LTE communication network, the base station can determine that a handover is necessary. At this time, the base station can request RSRP measurements from the terminal via an RRC (radio resource control) connection reconfiguration message. Accordingly, the terminal can receive the connection reconfiguration message from the base station and confirm the request for RSRP measurements. Afterwards, the terminal can transmit an RRC connection reconfiguration complete message to the base station. Additionally, the terminal can transmit the RSRP measurements to the base station via a measurement report message.

[0113] In this example, the base station can determine whether to perform a handover based on RSRP measurements. Alternatively, the base station can utilize RSRQ (reference signal received quality) and CQI (channel quality indicator) instead of RSRP during the handover process. Here, RSRP and RSRQ can be types of received signal strength.

[0114] The base station can receive RSRP measurements from the terminal. Based on the received RSRP measurements, the base station can determine whether a handover is necessary. If the base station determines that a handover is necessary, it can transmit the information necessary to perform the handover to the terminal via an RRC connection reconfiguration message.

[0115] The terminal can receive the information necessary for performing a handover from the base station via an RRC connection reconfiguration message. The terminal can then transmit a physical random access channel (PRACH) to a new base station, rather than the one it was currently communicating with. The terminal can then receive a random access channel (RACH) response message from the new base station in response to the PRACH.

[0116] Next, the terminal can transmit information about the connection success to the new base station via an RRC connection re-establishment complete message. If the connection is successful, the terminal can exchange additional information necessary to communicate with the new base station, completing the handover process.

[0117] Four types of timers can be used during this handover process. Parameters related to the timers used during the handover process may include the time-to-trigger (TTT) parameter, the measurement gap (MG) parameter, the time-to-connect (TTC) parameter, and the time-to-release (TTR) parameter.

[0118] The TTT parameter used during the handover process can be used to determine whether a handover is necessary. A base station can perform a handover when communication performance below the baseline continues to be maintained for a period defined by the TTT. These TTT parameters are key parameters required to determine whether to perform a handover and can play a significant role in determining the base station's overall communication performance.

[0119] Next, the measurement gap parameter can be a parameter that indicates the period during which signal measurements from the currently communicating base station are suspended to reduce interference at the terminal. Because the length of the MG affects the accuracy of the measurements, it can influence the decision process during the handover process, based on the measurements, to move to a new base station. Next, the time to transmit (TTC) parameter can be a parameter required to establish a connection with the new base station after the handover. Finally, the time to transmit (TTR) parameter can be a parameter required to disconnect the terminal from the existing base station after the handover. This TTR parameter can affect the resource availability of the base station.

[0120] FIG. 9 is a conceptual diagram illustrating a first embodiment of scatters existing in a communication link between a base station and a terminal and a visible area corresponding to each scatter.

[0121] Referring to FIG. 9, a base station may communicate with a terminal (930) using an XL-MIMO system. The XL-MIMO system may include a first antenna. The first antenna may be an antenna that supports XL-MIMO communication. The first antenna may be composed of a plurality of antenna elements (910-1, 910-2, to 910-n). An antenna group may be composed of a plurality of antenna elements. Here, the antenna group may be referred to as an array antenna. The plurality of antenna elements constituting the array antenna may be arranged in a row. The plurality of antenna elements constituting the array antenna may be arranged in a lattice structure or a square array structure. The plurality of antenna elements constituting the first antenna may be arranged in, for example, an M×N lattice structure. Here, M and N may be natural numbers greater than 1. M and N may have the same value or different values. In this case, the first antenna may be composed of MN antenna elements forming an M×N lattice structure.

[0122] There may be three different scatters (911, 912, 913) in the XL-MIMO system and the terminal-to-terminal communication link. Each scatter may be in a visible area. For example, the first scatter (911) may correspond to the first visible area (921), the second scatter (912) may correspond to the second visible area (922), and the third scatter (913) may correspond to the third visible area (923).

[0123] The signal transmitted from the terminal to the XL-MIMO system of the base station can be concentrated in the line-of-sight area. Conversely, when the XL-MIMO system of the base station transmits a signal to the terminal, the signal can be transmitted to the terminal through an antenna group of antenna elements belonging to the line-of-sight area. At this time, the terminal can meaningfully receive the signal. In other words, the terminal can transmit a signal to the XL-MIMO system of the base station, and the XL-MIMO system can receive a signal from the terminal through the line-of-sight area. At this time, the XL-MIMO system can measure the RSRP of the received signal. The RSRP measured by the XL-MIMO system can be greater than or equal to the RSRP threshold.

[0124] Conversely, when an XL-MIMO system transmits a signal to a terminal, the signal can be transmitted to the terminal through an antenna group of antenna elements in the line-of-sight area. At this time, the terminal can receive the signal in the XL-MIMO system and measure the RSRP of the received signal. The RSRP of the signal measured by the terminal may be higher than the RSRP threshold. Conversely, when an XL-MIMO system transmits a signal to a terminal, the signal can be transmitted without using antenna elements in the line-of-sight area. At this time, the terminal can receive the signal in the XL-MIMO system and measure the RSRP of the received signal. The RSRP of the signal measured by the terminal may be lower than the RSRP threshold. In this way, when an XL-MIMO system transmits a signal through antenna elements in an antenna area other than the line-of-sight area, it may be difficult for the terminal to receive a signal with an RSRP higher than a certain RSRP threshold.

[0125] In this way, if the XL-MIMO system attempts to communicate with a terminal through antenna elements other than the line-of-sight area suitable for the current communication environment of the terminal, communication with the terminal may become difficult. This situation may occur, for example, due to changes in the surrounding environment between the base station and the terminal. Alternatively, this situation may occur due to a change in the channel between the base station and the terminal due to the terminal moving. In such a situation, the XL-MIMO system may have difficulty communicating through the line-of-sight area that it was currently using for communication. Accordingly, the XL-MIMO system may need to reconfigure the line-of-sight area to adapt to the changed channel.

[0126] 5G communication networks may consider handovers to adjacent base stations when a base station determines that communication between the base station and the terminal is no longer possible. These 5G communication networks may not handle operations related to line-of-sight and line-of-sight reestablishment at the base station.

[0127] Therefore, the present disclosure can propose a visible area handover that searches for other visible areas around the base station or the entire visible area to discover a new visible area suitable for the changed channel when it is determined that communication is no longer possible through the currently used visible area during communication between a base station and a terminal in a future XL-MIMO system.

[0128] The present disclosure can assume a situation in which downlink communication is performed between a base station and a terminal in an XL-MIMO system. The present disclosure can propose a line-of-sight handover method that changes the line-of-sight area when the terminal cannot properly receive signals due to movement of the terminal or changes in the surrounding environment in an environment in which information is transmitted from the base station to the terminal. Conversely, the present disclosure can be extended and applied to an uplink communication environment in which line-of-sight handover is performed in an environment in which information is transmitted from the terminal to the base station.

[0129] The present disclosure can propose a process for determining whether to initiate a line-of-sight handover and the parameters necessary for the process. Furthermore, the present disclosure can propose a process for performing a line-of-sight handover using antenna elements near the currently used line-of-sight area, and a process for performing a line-of-sight handover using all antenna elements.

[0130] Fig. 10 is a flowchart illustrating a first embodiment of a visible area handover method in a communication system.

[0131] Referring to FIG. 10, the base station can receive information necessary to determine whether to initiate a line-of-sight handover from the terminal (S1001). For example, the base station can generate signals (e.g., CSI-RSs) and then transmit the signals to the terminal via beams using antenna elements located in the line-of-sight. Then, the terminal can receive signals from the base station via the beams, measure RSRPs of the received signals, and report the measured RSRP values ​​to the base station. Accordingly, the base station can receive the measured RSRP values ​​from the terminal. The base station can determine whether to initiate a line-of-sight handover based on the RSRP values ​​received from the terminal (S1002). If the RSRP measurements received from the terminal remain below the line-of-sight handover RSRP threshold for a period longer than the duration set by the line-of-sight handover initiation timer, the base station can determine that the current communication link is unsuitable or likely to be unsuitable, and thus determine that a line-of-sight handover needs to be initiated. Accordingly, the base station may initiate a visible area handover. Here, a period longer than the duration may mean a period of time greater than the duration.

[0132] Alternatively, the terminal may report its speed to the base station. Then, the base station may receive information about the terminal's speed from the terminal. The base station may determine whether to initiate a line-of-sight handover based on the terminal's speed received from the terminal (S1002). If the terminal's speed received from the terminal is maintained above a line-of-sight handover mobility threshold (VR handover mobility threshold) for a period longer than a duration set by a line-of-sight handover initiation timer, the base station may determine that the current communication link is not suitable or is likely to be unsuitable, and may determine that a line-of-sight handover needs to be initiated. Accordingly, the base station may initiate a line-of-sight handover.

[0133] In the process of determining whether to initiate the above-described visible-area handover, the terminal can report either the RSRP measurement values ​​of the signals received from the base station or the speed of the terminal to the base station. Then, the base station can receive either the RSRP measurement values ​​or the speed of the terminal from the terminal. Then, the base station can compare the received RSRP measurement values ​​with the visible-area handover RSRP threshold to determine whether to initiate the visible-area handover. Alternatively, the base station can compare the received speed of the terminal with the visible-area handover mobility threshold to determine whether to initiate the visible-area handover.

[0134] In contrast, in the process of determining whether to initiate a visible-area handover, the terminal can report the RSRP measurements of the received signal and the terminal's speed to the base station. Then, the base station can receive the RSRP measurements and the terminal's speed from the terminal. Then, the base station can determine whether to initiate a visible-area handover by comparing either the received RSRP measurements or the terminal's speed with either the visible-area handover RSRP threshold or the visible-area handover mobility threshold.

[0135] Alternatively, in the process of determining whether to initiate a visible-area handover, the terminal may report the RSRP measurements of the received signal and the terminal's speed to the base station. Then, the base station may receive the RSRP measurements and the terminal's speed from the terminal. In addition, the base station may determine to initiate a visible-area handover if the received RSRP measurements are less than or equal to the visible-area handover RSRP threshold and the terminal's speed is greater than or equal to the visible-area handover mobility threshold.

[0136] In other words, the terminal can report all values ​​(e.g., RSRP measurements and terminal speed) necessary to determine whether to initiate a line-of-sight handover to the base station, and the base station can operate in a manner that performs a line-of-sight handover even if only one condition is satisfied. Alternatively, the terminal can report all values ​​(e.g., RSRP measurements and terminal speed) necessary to determine whether to initiate a line-of-sight handover to the base station, and the base station can operate in a manner that performs a line-of-sight handover when all conditions are satisfied.

[0137] Additionally, the visible area handover initiation timer may be a parameter used to determine whether the RSRP measurement value remains below the visible area handover RSRP threshold. Alternatively, the visible area handover initiation timer may be a parameter used to determine whether the terminal's speed remains above the visible area handover mobility threshold.

[0138] The base station may reset the line-of-sight handover initiation timer if the RSRP measurements are greater than or equal to the line-of-sight handover RSRP threshold for even a brief period of time. Alternatively, the base station may reset the line-of-sight handover initiation timer if the speed of the terminal drops below the line-of-sight handover mobility threshold for even a brief period of time.

[0139] Meanwhile, the base station may determine that a line-of-sight handover is not necessary based on its assessment of whether to initiate one. Then, the base station may repeatedly perform the process of receiving the information necessary to determine whether to initiate a line-of-sight handover. Alternatively, if the base station determines that a line-of-sight handover is necessary, it may perform a line-of-sight handover process using antenna elements adjacent to the currently active line-of-sight area.

[0140] (1) A process of performing a line-of-sight handover through antenna elements adjacent to the line-of-sight area currently in use.

[0141] In a downlink environment where information is transmitted to a terminal, a base station may determine that the currently used line-of-sight area is unsuitable due to the terminal's movement or changes in the surrounding environment. In such situations, the base station can perform a line-of-sight handover to a different line-of-sight area adjacent to the current line-of-sight area through a line-of-sight handover process using antenna elements adjacent to the current line-of-sight area in the XL-MIMO system.

[0142] Table 2 can show the parameters required to determine whether to initiate a line-of-sight handover at a base station in an XL-MIMO system.

[0143] Parameter Threshold Visible Area Handover RSRP Threshold (VR handover RSRP threshold) R VRHO VR handover mobility threshold (V) VRHO VR handover initiation timerT VRHO

[0144] Table 2 Visible area handover RSRP threshold R VRHOIt can be a parameter that serves as a reference for determining whether the RSRP measurement value of the received signal reported from the terminal to the base station has fallen below a certain level. The visible area handover RSRP threshold can be a parameter that is used to determine whether the communication performance measured based on the currently used visible area requires the initiation of a visible area handover, or in other words, whether the visible area needs to be changed due to low performance when communicating through the current visible area.

[0145] Visible area mobility threshold V in Table 2 VRHO can be a parameter that serves as a reference for determining whether the speed of the terminal has increased beyond a certain level. The visible area handover mobility threshold can be a parameter used to determine whether the degree of change in the environment around the terminal requires the initiation of a visible area handover based on the speed of the terminal. In other words, the visible area handover mobility threshold can be a parameter used to determine whether the initiation of a visible area handover is necessary because the currently used visible area may not be suitable due to the rapid movement of the terminal. In this visible area handover mobility threshold, mobility is an indicator of how fast the terminal moves, and can mean, for example, the speed of the terminal.

[0146] In Table 2, the visible area handover initiation timer may be a parameter that serves as a reference for determining whether the RSRP measurement value is lower than or equal to the visible area handover RSRP threshold or whether the speed of the terminal is higher than or equal to the visible area handover mobility threshold for a certain period of time. The visible area handover initiation timer may be a parameter that is used to determine whether the initiation of a visible area handover is necessary based on the RSRP measurement value and the speed of the terminal, whether the phenomenon is temporary or continuously observed and the initiation of a visible area handover is necessary. Here, R VRHO , V VRHOand T VRHO could be a mistake.

[0147] The base station determines that the RSRP measurements reported by the terminal are less than or equal to the visible area handover RSRP threshold, based on the visible area handover initiation timer, for a duration threshold T. VRHO A line-of-sight handover may be performed if the condition persists longer than the duration threshold based on the line-of-sight handover initiation timer, wherein the reported speed of the terminal is greater than or equal to the line-of-sight handover mobility threshold. Alternatively, the base station may perform a line-of-sight handover if the condition persists longer than the duration threshold based on the line-of-sight handover initiation timer. In the present disclosure, the term "continues" may mean that a limited condition (e.g., RSRP measurement value < line-of-sight handover RSRP threshold, etc.) is maintained for a specific time period from the start time.

[0148] Based on the parameters defined above, the base station can summarize the operation by comparing the RSRP measurement of the received signal measured and reported by the terminal with the line-of-sight handover RSRP threshold. If the period during which the RSRP measurement is less than the line-of-sight handover RSRP threshold is longer than the duration threshold based on the line-of-sight handover initiation timer, the base station determines that a line-of-sight handover is necessary and can perform a line-of-sight handover.

[0149] Additionally, the base station can compare the reported speed of the terminal with the visible-area mobility threshold. If the duration for which the terminal's speed is greater than the visible-area handover mobility threshold is longer than the duration threshold based on the visible-area handover initiation timer, the base station can determine that a visible-area handover is necessary and perform a visible-area handover.

[0150] In the above operation, the terminal can transmit the RSRP measurement value of the received signal and the current speed information of the terminal to the base station through the CSI (channel state information) reporting process. The above example can show an example in which the terminal can report only one of the RSRP measurement value of the received signal or the speed of the terminal to the base station to determine whether the initiation of a line-of-sight handover is necessary, and the base station can determine whether the initiation of a line-of-sight handover is necessary based on one of the parameters of the line-of-sight handover RSRP threshold or the line-of-sight handover mobility threshold. However, the terminal can report all values ​​necessary to determine whether a line-of-sight handover is necessary, that is, both the RSRP measurement value and the speed information, to the base station, and the base station can operate in a manner in which the line-of-sight handover is performed when only one condition is satisfied, or when all conditions are satisfied.

[0151] Additionally, the base station may use the same line-of-sight handover initiation timer when determining a line-of-sight handover based on RSRP measurements and when determining a line-of-sight handover based on the speed of the terminal. However, the base station may use the RSRP-based line-of-sight handover initiation timer when determining a line-of-sight handover based on RSRP measurements. And, the base station may use the mobility-based line-of-sight handover initiation timer when determining a line-of-sight handover based on the speed of the terminal. In this case, the base station may operate in a manner of determining whether to perform a line-of-sight handover by setting each timer parameter differently.

[0152] The above example may represent an example of a base station determining whether to initiate a visible area handover. However, the base station may transmit a visible area handover RSRP threshold, a visible area handover mobility threshold, and a duration threshold based on a visible area handover initiation timer to the terminal through MAC CE, RRC re-establishment, or other new RRC signaling. Then, the terminal may receive the visible area handover RSRP threshold, the visible area handover mobility threshold, and the duration threshold based on the visible area handover initiation timer from the base station.

[0153] The terminal can determine whether a line-of-sight handover needs to be initiated based on the received parameters, the RSRP measurement value measured by the terminal, and the speed information. Then, the terminal can define the information indicating the need for a line-of-sight handover as a new parameter and transmit it to the base station via UCI (uplink control information). Then, the base station can receive the information indicating the need for a line-of-sight handover from the terminal and initiate the line-of-sight handover based on the received information.

[0154] Finally, the base station can also utilize RSRP measurements to initiate a line-of-sight handover by performing a line-of-sight handover when the RSRP difference between the currently used line-of-sight and an adjacent line-of-sight is greater than a predefined offset.

[0155] In order to perform a line-of-sight handover process using adjacent antenna elements in the currently used line-of-sight area, the base station can group several nearby antenna elements and configure them as a single candidate antenna group. At this time, the size of each candidate antenna group configured, in other words, the number of antenna elements in the candidate antenna group can be set to be the same as the number of antenna elements in the currently used line-of-sight area. Alternatively, the number of antenna elements in the candidate antenna group can be set to be smaller or larger than the number of antenna elements in the currently used line-of-sight area, taking into account the amount of antenna elements that the base station can allocate based on the current traffic volume.

[0156] More specifically, the base station may set the number of antenna elements in the first direction (e.g., vertical direction) and the number of antenna elements in the second direction (e.g., horizontal direction) to be the same as the number of antenna elements in the currently used line-of-sight area. Alternatively, the base station may set the number of antenna elements in the first direction and the number of antenna elements in the second direction to be different from the number of antenna elements in the currently used line-of-sight area, depending on the status of allocable antennas.

[0157] In Table 3, the base station can designate an antenna group containing antenna elements adjacent to the currently used line-of-sight area as a candidate antenna group in order to first attempt a line-of-sight handover through adjacent antenna elements in the currently used line-of-sight area. The base station can assign group indices based on the number of candidate antenna groups. At this time, the base station can assign the group indices using bits.

[0158] When the base station sets the maximum group index value of the candidate antenna group to n, the process of transmitting the group index of the candidate antenna group is log2. nThe bits of can be allocated and transmitted to the terminal. Here, n can be a natural number. The terminal can receive the CSI-RS including the group index transmitted from the candidate antenna group and know from which candidate antenna group the received signal was transmitted.

[0159] Similarly, the base station can set beam indices for beams belonging to each candidate antenna group. When the number of beams that can be formed in one candidate antenna group is m, the base station transmits the beam indices of the beams included in the candidate antenna group by using log2 m The bits of can be allocated and transmitted to the terminal. Here, m can be a natural number. The terminal can receive the CSI-RS including the beam index transmitted from the candidate antenna group and know from which candidate antenna group the received signal was transmitted.

[0160] Table 3 illustrates an example in which a total of four candidate antenna groups can exist, and the number of beams that can be formed within each candidate antenna group is the same at three. Thereafter, the base station can transmit CSI-RS through each candidate antenna group and each beam, and can transmit information about the beam of the base station used when transmitting the CSI-RS (e.g., candidate antenna group index and beam index) through DCI, MAC CE, RRC reconfiguration, or other new RRC signaling. At this time, the base station can also utilize transmission configuration indicator (TCI) states and quasi co-location (QCL) information as information corresponding to the beam index. Here, the beam index can be shared between candidate antenna groups. Even if the beam index is the same, if the group index is different, it can indicate different beams. Therefore, in the present disclosure, different combinations of group indices and beam indices can be associated with different SSBs or CSI-RSs, and can be mapped to resources of separate RACH occasions. The terminal can determine through which candidate antenna group and beam it was able to receive the reference signal from the base station based on the group index and beam index.

[0161] In this way, in a line-of-sight handover through antenna elements adjacent to the line-of-sight area currently in use, the base station can define candidate antenna groups as shown in Table 3 centered on the antenna elements adjacent to the line-of-sight area currently in use (S1003). Here, the number of candidate antenna groups can be, for example, four, and can be denoted as AG#1, AG#2, AG#3, and AG#4. The base station can assign an antenna group index to each of the candidate antenna groups (S1004). For example, the antenna group index assigned to candidate antenna group AG#1 can be 0, the antenna group index assigned to candidate antenna group AG#2 can be 1, the antenna group index assigned to candidate antenna group AG#3 can be 2, and the antenna group index assigned to candidate antenna group AG#4 can be 3.

[0162] The base station can assign beam indices to beams formed in each of the candidate antenna groups (S1005). For example, the beam indices assigned to beams formed in candidate antenna group AG#1 may be 0, 1, and 2. The beam indices assigned to beams formed in candidate antenna group AG#2 may be 0, 1, and 2. The beam indices assigned to beams formed in candidate antenna group AG#3 may be 0, 1, and 2. The beam indices assigned to beams formed in candidate antenna group AG#4 may be 0, 1, and 2.

[0163] Candidate Antenna Group Candidate Antenna Group Index (2 bits) Beam Index (2 bits) AG#10(00)0(00)1(01)2(10) AG#21(01)0(00)1(01)2(10) AG#32(10)0(00)1(01)2(10) AG#43(11)0(00)1(01)2(10)

[0164] In this way, the base station can define candidate antenna groups for antenna elements located near the currently used visible area. The base station can generate CSI-RSs including candidate antenna group indices and beam indices (S1006). Then, the base station can generate beams using the candidate antenna groups and transmit the corresponding CSI-RSs to the terminal using the generated beams (S1007). Then, the terminal can receive the CSI-RSs through the beams transmitted by the candidate antenna groups. The terminal can measure the RSRPs of the received CSI-RSs as shown in Table 4. In addition, the terminal can check the candidate antenna group index and beam index in each of the received CSI-RSs.

[0165] Candidate Antenna Group Candidate Antenna Group Index (2 bits) Beam Index (2 bits) RSRP Value (in dB) AG#10(00)0(00)881(01)742(10)95 AG#21(01)0(00)661(01)942(10)90 AG#32(10)0(00)751(01)802(10)85 AG#43(11)0(00)691(01)782(10)75

[0166] The terminal can report the RSRP values ​​measured for the CSI-RSs to the base station, including the candidate antenna group index and beam index corresponding to each. Then, the base station can receive the RSRP values ​​together with the corresponding candidate antenna group index and beam index from the terminal (S1008). Referring to Table 4, the terminal can measure the RSRP of each of the 12 CSI-RSs transmitted by the base station in Table 3, and transmit the group index and beam index together with the RSRP measurement value to the base station. Then, the base station can receive the RSRP measurement value, group index, and beam index from the terminal. The terminal can transmit the RSRP measurement value of each CSI-RS to the base station through the CSI reporting process. Then, the terminal can transmit the group index and beam index to the base station through UCI. Thereafter, the base station can determine the performance of each beam formed in each candidate antenna group based on the RSRP measurement value, group index, and beam index transmitted by the terminal.

[0167] Based on the RSRP measurement value received from the terminal, the base station can determine whether there is a candidate antenna group and beam having an RSRP measurement value greater than or equal to an RSRP threshold for communicating with the terminal (S1009). If the base station determines that there is a candidate antenna group and beam having an RSRP measurement value greater than or equal to the RSRP threshold, the base station can set the line-of-sight area formed by the candidate antenna group as a new line-of-sight area. The base station can use the antenna elements in the set new line-of-sight area to communicate with the terminal (S1010). Alternatively, if there is no candidate antenna group and beam having an RSRP measurement value greater than or equal to the RSRP threshold as shown in Table 5, the base station can perform a line-of-sight area handover using all antenna elements (S1011). Here, the RSRP threshold may be, for example, 100 dB by mistake.

[0168] Candidate Antenna Group Candidate Antenna Group Index (2 bits) Beam Index (2 bits) RSRP Value (in dB) RSRP Threshold Satisfied AG#10(00)0(00)88X1(01)74X2(10)95XAG#21(01)0(00)66X1(01)94X2(10)90XAG#32(10)0(00)75X1(01)80X2(10)85XAG#43(11)0(00)69X1(01)78X2(10)75X

[0169] Referring to Table 5, the base station can compare each RSRP measurement value with the RSRP threshold, which is the minimum requirement for communicating with the terminal, based on the information received from the terminal. The base station can arbitrarily set the RSRP threshold. Alternatively, the base station can set the RSRP threshold based on UE capability information received from the terminal. For example, the terminal can transmit information about the subcarrier spacing, maximum bandwidth, modulation scheme, and MIMO layers that it can support to the base station through feature sets parameters. The base station can receive information about the subcarrier spacing, maximum bandwidth, modulation scheme, and MIMO layers that it can support from the terminal, and set an RSRP threshold suitable for the terminal based on the received information. Alternatively, the terminal can additionally set the UE performance requirement, which is a parameter required for setting the RSRP threshold. In addition, the terminal can transmit the UE performance requirement to the base station through UCI. Then, the base station can receive the UE performance requirement from the terminal and set the RSRP threshold based on the received UE performance requirement. Alternatively, the base station can transmit a UE performance request including information about the UE performance requirement information reporting instruction of the terminal to the terminal. The terminal can receive the UE performance request from the base station. The terminal can transmit a UE information response including the UE performance requirement to the base station. The base station can receive the UE information response from the terminal and confirm the UE performance requirement through the received UE information response.

[0170] In addition, the base station can transmit information regarding the UE performance requirement information reporting instruction of the terminal to the terminal through a system information block (SIB) or new RRC signaling. The terminal can receive the UE performance requirement information reporting instruction through the SIB or RRC signaling. In addition, the terminal can transmit a measurement report including the UE performance requirement and UE assistance information to the base station. Accordingly, the base station can receive the measurement report and UE assistance information from the terminal and confirm the UE performance requirement. Alternatively, the terminal can transmit RRC signaling including the UE performance requirement to the base station. Accordingly, the base station can receive the measurement report and UE assistance information from the terminal and confirm the UE performance requirement.

[0171] Referring to Table 5, the base station may determine that the performance of the 12 beams received from the terminal may be lower than the RSRP threshold. Accordingly, the base station may determine that the line-of-sight handover cannot be performed using the antenna elements adjacent to the line-of-sight area currently in use. The base station may select the candidate antenna group and beam received from the terminal based on the RSRP threshold set by the base station in advance if the RSRP threshold is satisfied for each candidate antenna group and each beam. Alternatively, the base station may perform the line-of-sight handover using all antenna elements if the RSRP threshold is not satisfied for each candidate antenna group and each beam received from the terminal.

[0172] In this way, the base station can set up a candidate antenna group centered on the antenna elements near the currently used line-of-sight area during the line-of-sight area handover process using the antenna elements adjacent to the currently used line-of-sight area. Then, the base station can measure the performance of each beam formed through the candidate antenna group to check whether it satisfies the RSRP threshold, and if it satisfies the RSRP threshold, it can select the candidate antenna group and beam combination. The base station can measure the performance of each beam formed through the candidate antenna group to check whether it satisfies the RSRP threshold, and if it does not satisfies the RSRP threshold, it can determine that the line-of-sight area handover attempt based on the adjacent antenna elements has failed and perform the line-of-sight area handover process using all antennas.

[0173] FIG. 11 is a flowchart illustrating a first embodiment of a line-of-sight handover process through all antenna elements of FIG. 10.

[0174] Referring to FIG. 11, the base station can set a candidate antenna group from all antenna elements during a line-of-sight handover process through all antenna elements (S1101).

[0175] (2) Process of performing line-of-sight handover through all antenna elements

[0176] The base station can configure candidate antenna groups from all antenna elements and determine whether there are candidate antenna groups and beam combinations that satisfy the RSRP threshold. If there are candidate antenna groups and beam combinations that satisfy the RSRP threshold, the base station can select that combination as a new visible area and then use the antenna elements in the new visible area to communicate with the terminal.

[0177] To perform a line-of-sight handover process using all antenna elements, the base station can group multiple antenna elements across the antennas and configure them as a single candidate antenna group. At this time, the size of each candidate antenna group, or in other words, the number of antenna elements in the candidate antenna group, can be set to be equal to the number of antenna elements in the currently used line-of-sight. Alternatively, the number of antenna elements in the candidate antenna group can be set to be smaller or larger than the number of antenna elements in the currently used line-of-sight, taking into account the amount of antenna elements that the base station can allocate based on the current traffic volume.

[0178] More specifically, the base station may set the number of antenna elements in the first direction (e.g., vertical direction) and the number of antenna elements in the second direction (e.g., horizontal direction) to be the same as the number of antenna elements in the currently used line-of-sight area. Alternatively, the base station may set the number of antenna elements in the first direction and the number of antenna elements in the second direction to be different from the number of antenna elements in the currently used line-of-sight area, depending on the status of allocable antennas.

[0179] In Table 6, the base station can designate antenna groups containing antenna elements located throughout the antenna as candidate antenna groups in order to attempt line-of-sight handovers using antenna elements located throughout the antenna. The base station can assign group indices based on the number of candidate antenna groups. At this time, the base station can assign group indices using bits. In Table 6, there can be a total of 16 candidate antenna groups, and group indices can be assigned using 4 bits.

[0180] When the base station sets the maximum group index value of the candidate antenna group to n, the process of transmitting the group index of the candidate antenna group is log2. nThe bits of can be allocated and transmitted to the terminal. Here, n can be a natural number. The terminal can receive the CSI-RS including the group index transmitted from the candidate antenna group and know from which candidate antenna group the received signal was transmitted.

[0181] Similarly, the base station can set beam indices for beams belonging to each candidate antenna group. When the number of beams that can be formed in one candidate antenna group is m, the base station transmits the beam indices of the beams included in the candidate antenna group by using log2 m The bits of can be allocated and transmitted to the terminal. Here, m can be a natural number. The terminal can receive the CSI-RS including the beam index transmitted from the candidate antenna group and know through which beam transmitted from which candidate antenna group the received signal can be received.

[0182] Table 6 illustrates an example in which a total of 16 candidate antenna groups can exist, and the number of beams that can be formed within each candidate antenna group is the same at 3. Thereafter, the base station can transmit CSI-RS through each candidate antenna group and each beam, and can transmit information about the beam of the base station used when transmitting the CSI-RS (e.g., candidate antenna group index and beam index) through DCI, MAC-CE, RRC reconfiguration, or other new RRC signaling. At this time, the base station may also utilize TCI states and QCL information as information corresponding to the beam index. Here, the beam index can be shared between candidate antenna groups. Even if the beam index is the same, if the group index is different, it can indicate different candidate beams. Therefore, in the present disclosure, different combinations of group indices and beam indices can be associated with different SSBs or CSI-RSs, and can be mapped to resources of separate RACH occasions. Based on the group index and beam index, the terminal can determine through which candidate antenna group and beam it was able to receive the corresponding reference signal from the base station.

[0183] In this way, the base station can define candidate antenna groups as shown in Table 6 using antenna elements in the entire antenna. Here, the candidate antenna groups can be, for example, 16, and can be denoted as AG#5, AG#6, AG#7 to AG#20. The base station can assign an antenna group index to each of the candidate antenna groups (S1102). For example, the antenna group index assigned to candidate antenna group AG#5 can be 0, and the antenna group index assigned to candidate antenna group AG#6 can be 1. In this way, the base station can assign antenna group indexes to the remaining candidate antenna groups (candidate antenna group AG#7 to candidate antenna group AG#20).

[0184] The base station can assign beam indices to the beams formed in each of the candidate antenna groups (S1103). For example, the beam indices assigned to the beams formed in candidate antenna group AG#5 can be 0, 1, and 2. The beam indices assigned to the beams formed in candidate antenna group AG#6 can be 0, 1, and 2. In this manner, the base station can assign beam indices to the beams formed in the remaining candidate antenna groups (candidate antenna group AG#7 to candidate antenna group AG#20).

[0185] Candidate Antenna Group Candidate Antenna Group Index (4 bits) Beam Index (2 bits) AG#50 (0000) 0 (00) 1 (01) 2 (10) AG#61 (0001) 0 (00) 1 (01) 2 (10) ........ AG#2015 (1111) 0 (00) 1 (01) 2 (10)

[0186] In this way, the base station can define candidate antenna groups for antenna elements in the entire antenna. The base station can generate CSI-RSs including candidate antenna group indices and beam indices (S1104). Then, the base station can generate beams using the candidate antenna groups and transmit the corresponding CSI-RSs to the terminal using the generated beams (S1105). Then, the terminal can receive the CSI-RSs through the beams transmitted by the candidate antenna groups. The terminal can measure the RSRPs of the received CSI-RSs as shown in Table 7. In addition, the terminal can check the candidate antenna group index and beam index in each of the received CSI-RSs.

[0187] Candidate Antenna Group Candidate Antenna Group Index (4 bits) Beam Index (2 bits) RSRP Value (in dB) AG#50(0000)0(00)941(01)832(10)108 AG#61(0001)0(00)721(01)1122(10)98............AG#2015(1111)0(00)881(01)942(10)96

[0188] The terminal can report the RSRP values ​​measured for the CSI-RSs to the base station, including the candidate antenna group index and beam index corresponding to each. Then, the base station can receive the RSRP values ​​together with the corresponding candidate antenna group index and beam index from the terminal (S1106). Referring to Table 7, the terminal can measure the RSRP of each CSI-RS transmitted by the base station in Table 6, and transmit the group index and beam index together with the RSRP measurement value to the base station. Then, the base station can receive the RSRP measurement value, the group index, and the beam index from the terminal. The terminal can transmit the RSRP measurement value of each CSI-RS to the base station through the CSI reporting process. And, the terminal can transmit the group index and the beam index to the base station through UCI. Thereafter, the base station can determine the performance of each beam formed in each candidate antenna group based on the RSRP measurement value, the group index, and the beam index transmitted by the terminal.

[0189] The base station can determine whether there is a candidate antenna group and beam having an RSRP measurement value greater than or equal to the RSRP threshold for communicating with the terminal based on the RSRP measurement value received from the terminal (S1107). If, as shown in Table 8, there exists a candidate antenna group and beam having an RSRP measurement value greater than or equal to the RSRP threshold as a result of the determination, the base station can set the visible area formed by the candidate antenna group as a new visible area. At this time, the RSRP measurement value of the second beam of antenna group 6 may be greater than the RSRP value of the third beam of antenna group 5. Accordingly, the base station can select antenna group 6 and the second beam of antenna group 6. Then, the base station can set the antenna area associated with antenna group 6 as a new visible area. The base station can communicate with the terminal using the antenna elements of the new visible area (S1108). Alternatively, if there is no candidate antenna group and beam having an RSRP measurement value greater than or equal to the RSRP threshold, the base station can perform a handover to another base station (S1109). Here, the RSRP threshold can be 100 dB, for example.

[0190] Candidate Antenna Group Candidate Antenna Group Index (4 bits) Beam Index (2 bits) RSRP Value (in dB) RSRP Threshold Satisfied AG#50(0000)0(00)94X1(01)83X2(10)108OAG#61(0001)0(00)72X1(01)112O2(10)98X...............AG#2015(1111)0(00)88X1(01)94X2(10)96X

[0191] Referring to Table 8, the base station can compare each RSRP measurement value with the RSRP threshold, which is the minimum requirement for communicating with the terminal, based on the information received from the terminal. The base station can arbitrarily set the RSRP threshold. Alternatively, the base station can set the RSRP threshold based on the UE capability information received from the terminal. For example, the terminal can transmit information about the subcarrier spacing, maximum bandwidth, modulation scheme, and MIMO layers that it can support to the base station through the feature set parameters. The base station can receive information about the subcarrier spacing, maximum bandwidth, modulation scheme, and MIMO layers that it can support from the terminal, and set an RSRP threshold suitable for the terminal based on the received information. Alternatively, the terminal can additionally set UE performance requirements as parameters necessary for setting the RSRP threshold. In addition, the terminal can transmit the UE performance requirements to the base station via UCI. Then, the base station can receive the UE performance requirements from the terminal and set the RSRP threshold based on the received UE performance requirements. Alternatively, the base station may transmit a UE performance request to the terminal, which includes information regarding the UE performance requirement information reporting instruction of the terminal. The terminal may receive the UE performance request from the base station. The terminal may transmit a UE information response containing the UE performance requirements to the base station. The base station may receive the UE information response from the terminal and confirm the UE performance requirements through the received UE information response.

[0192] In addition, the base station can transmit information regarding the UE performance requirement information reporting instruction of the terminal to the terminal through SIB or new RRC signaling. The terminal can receive the UE performance requirement information reporting instruction through SIB or RRC signaling. In addition, the terminal can transmit a measurement report including the UE performance requirement information and UE assistance information to the base station. Accordingly, the base station can receive the measurement report and UE assistance information from the terminal and confirm the UE performance requirement. Alternatively, the terminal can transmit RRC signaling including the UE performance requirement information to the base station. Accordingly, the base station can receive the measurement report and UE assistance information from the terminal and confirm the UE performance requirement information.

[0193] The above description may illustrate an operational example of transmitting beams through candidate antenna groups after a line-of-sight handover has been initiated and measuring the performance of each beam. However, to prevent handover delays, the base station may periodically perform performance measurement operations on candidate antenna groups regardless of whether a line-of-sight handover has been initiated.

[0194] Meanwhile, the base station may determine that the performance of beams received from the terminal is lower than the RSRP threshold. Accordingly, the base station may determine that it cannot perform a line-of-sight handover through antenna elements located throughout the antenna array. If the base station cannot find a suitable candidate antenna group and beam combination even through all antennas, the process of performing a suitable line-of-sight handover through the line-of-sight handover process may be inefficient. Furthermore, if the base station cannot find a suitable combination within the time set by the line-of-sight handover expiration timer, the process of performing a suitable line-of-sight handover through the line-of-sight handover process may be inefficient. In such a case, the base station may perform a handover process to another base station.

[0195] Meanwhile, Table 9 may indicate a visible area handover expiration timer (VR handover expire timer). Here, the visible area handover expiration timer may be a parameter that serves as a reference for determining whether to terminate a visible area handover during the process of performing a visible area handover.

[0196] Parameter Threshold Visible Area Handover Expiration Timer (VR handover expire timer) T VRHOE

[0197] Specifically, if the base station fails to find a suitable visible area within a certain period of time while performing a line-of-sight handover for all antennas, the base station may determine that it is inefficient for the current base station to find a suitable visible area. Accordingly, the base station may terminate the line-of-sight handover process. In this way, the line-of-sight handover expiration timer may be a parameter that serves as a reference for determining whether to terminate the line-of-sight handover process and whether it is efficient to continue searching for a new line-of-sight area that satisfies the criteria within the current XL-MIMO system. The base station may arbitrarily set the line-of-sight handover expiration timer. Alternatively, the base station may set the line-of-sight handover expiration timer based on a delay requirement received from the terminal. The terminal may transmit the delay requirement to the base station via UCI. Accordingly, the base station may receive the UCI and determine the delay requirement of the terminal. Alternatively, the base station may transmit a UE information request including information regarding the delay requirement information reporting instruction of the terminal to the terminal. The terminal may receive the UE information request from the base station. In addition, the terminal may transmit a UE information response including the delay requirement to the base station in response to the UE information request. Then, the base station can receive a UE information response including a delay requirement from the terminal.

[0198] Alternatively, the base station can transmit information regarding the UE's delay requirement information reporting instruction to the UE via SIB or new RRC signaling. The UE can report to the base station via measurement report, UE assistance information, and new RRC signaling in response to the reporting instruction. If the base station has not found a new visible region after the visible region handover expiration timer has elapsed since the start of the branch region handover process, the base station may determine that it is inefficient to continue searching for a visible region within the current XL-MIMO system. Then, the base station can perform a handover to another base station.

[0199] Fig. 12 is a flowchart illustrating a second embodiment of a visible area handover method in a communication system.

[0200] Referring to FIG. 12, the base station can transmit a visible area handover RSRP threshold, a visible area handover mobility threshold, and a visible area handover initiation timer to the terminal through MAC-CE, RRC reset, or other new RRC signaling. Then, the terminal can receive the visible area handover RSRP threshold, the visible area handover mobility threshold, and the visible area handover initiation timer from the base station (S1201).

[0201] After generating signals, the base station can transmit the signals to the terminal via beams using antenna elements located in the line-of-sight area. Then, the terminal can receive signals from the base station via the beams, measure RSRPs of the received signals, and determine whether a line-of-sight handover is necessary based on the measured RSRP values ​​(S1202). If the measured RSRP values ​​remain below the line-of-sight handover RSRP threshold for a period longer than the line-of-sight handover initiation timer, the terminal can determine that the current communication link is not suitable or is likely to be unsuitable, and thus determine that a line-of-sight handover needs to be initiated. Accordingly, the terminal can request the base station to initiate a line-of-sight handover (S1203). Accordingly, the base station can receive a line-of-sight handover initiation request from the terminal and initiate the line-of-sight handover.

[0202] Alternatively, the terminal may determine whether to initiate a line-of-sight handover based on the measured speed of the terminal. If the measured speed of the terminal is maintained above the line-of-sight handover mobility threshold for a period longer than the line-of-sight handover initiation timer, the terminal may determine that the current communication link is unsuitable or likely unsuitable, and thus determine that a line-of-sight handover needs to be initiated. Accordingly, the base station may receive a line-of-sight handover initiation request from the terminal and initiate the line-of-sight handover.

[0203] Accordingly, the base station can initiate a visible area handover. In the process of determining whether to initiate the visible area handover, the terminal can determine whether to initiate the visible area handover by comparing one of the parameters among the RSRP measurement values ​​or the terminal speed with one of the visible area handover RSRP thresholds or the visible area handover mobility thresholds.

[0204] Alternatively, in the process of determining whether to initiate a visible area handover, the terminal may determine whether to initiate a visible area handover by comparing one of the RSRP measurements and the speed of the terminal with either the visible area handover RSRP threshold or the visible area handover mobility threshold. Alternatively, in the process of determining whether to initiate a visible area handover, the terminal may determine whether to initiate a visible area handover if the RSRP measurements are greater than or equal to the visible area handover RSRP threshold and the speed of the terminal is greater than or equal to the visible area handover mobility threshold. The terminal may reset the visible area handover initiation timer if the RSRP measurements are greater than or equal to the visible area handover RSRP threshold for even a brief period of time. Alternatively, the terminal may reset the visible area handover initiation timer if the speed of the terminal drops below the visible area handover mobility threshold for even a brief period of time.

[0205] Meanwhile, the terminal may determine that a visible-area handover is not necessary based on its judgment of whether to initiate a visible-area handover. Then, the terminal may perform a process of receiving the information necessary to determine whether to initiate a visible-area handover from the base station. The visible-area handover initiated by the base station may be as described above.

[0206] The operations of the method according to the present disclosure can be implemented as a computer-readable program or code on a computer-readable recording medium. A computer-readable recording medium includes any type of recording device that stores information readable by a computer system. Furthermore, a computer-readable recording medium can be distributed across network-connected computer systems, allowing the computer-readable program or code to be stored and executed in a distributed manner.

[0207] Additionally, the computer-readable recording medium may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. The program instructions may include not only machine language codes produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc.

[0208] While some aspects of the present disclosure have been described in the context of a device, they may also represent a description of a corresponding method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may also be described as a corresponding block or item or a feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, at least one or more of the most significant method steps may be performed by such a device.

[0209] A programmable logic device (e.g., a field-programmable gate array) may be used to perform some or all of the functions of the methods described in the present disclosure. The field-programmable gate array may operate in conjunction with a microprocessor to perform one of the methods described in the present disclosure. In general, the methods are preferably performed by some hardware device.

[0210] Although the present disclosure has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

Claims

1. As a method of base station, A step of receiving first information necessary to determine whether to initiate a visible area handover from a UE (user equipment); A step of determining whether to initiate the visible area handover based on the first information; and If it is determined that the initiation of the above line-of-sight handover is necessary, a step of attempting a first line-of-sight handover based on antenna elements adjacent to the line-of-sight in use is included. Method of base station.

2. In claim 1, The above first information is information on the received signal strength measured by the UE for a signal transmitted from the base station to the UE through the visible area in use. The step of determining whether to initiate the visible area handover based on the first information is as follows: a step of determining whether the received signal strength is less than or equal to a first threshold value; and If the received signal strength is lower than or equal to the first threshold value, a step of determining whether the duration of the state in which the received signal strength is lower than or equal to the first threshold value is greater than or equal to a second threshold value is included, and if the duration of the state in which the received signal strength is lower than or equal to the first threshold value is greater than or equal to the second threshold value, it is determined that the visible area handover is necessary. Method of base station.

3. In claim 1, The above first information is information about the speed of the UE, The step of determining whether to initiate the visible area handover based on the first information is as follows: a step of determining whether the above speed is greater than or equal to a third threshold value; and If the speed is greater than or equal to the third threshold value, a step of determining whether the duration of the state in which the speed is greater than or equal to the third threshold value is greater than or equal to the fourth threshold value is included. If the duration of the state in which the speed is greater than or equal to the third threshold is greater than or equal to the fourth threshold, it is determined that the visible area handover is necessary. Method of base station.

4. In claim 1, The above first information includes information on the received signal strength measured by the UE for a signal transmitted from the base station to the UE through the visible area in use and information on the speed of the UE. The step of determining whether to initiate the visible area handover based on the first information is as follows: A step of determining whether the received signal strength is less than or equal to a first threshold value; A step of determining whether the duration of a state in which the received signal strength is lower than or equal to the first threshold value is higher than or equal to a second threshold value when the received signal strength is lower than or equal to the first threshold value; A step of determining whether the speed is greater than or equal to a third threshold value if the duration of the state in which the received signal strength is less than or equal to the first threshold value is greater than or equal to the second threshold value; and If the speed is greater than or equal to the third threshold value, a step of determining whether the duration of the state in which the speed is greater than or equal to the third threshold value is greater than or equal to the fourth threshold value is included. If the duration of the state in which the speed is greater than or equal to the third threshold is greater than or equal to the fourth threshold, it is determined that the visible area handover is necessary. Method of base station.

5. In claim 4, The second threshold value and the fourth threshold value are the same, Method of base station.

6. In claim 1, When it is determined that the initiation of the above line-of-sight handover is necessary, the step of attempting the first line-of-sight handover based on the antenna elements adjacent to the line-of-sight in use is as follows: A step of setting up candidate antenna groups using antenna elements adjacent to the active visible area when it is determined that the initiation of the above visible area handover is necessary; A step of transmitting reference signals to the UE using the above candidate antenna groups; A step of receiving information on received signal strengths of reference signals from the UE; A step of selecting one of the candidate antenna groups based on the received signal intensities; and Including a step of attempting the first visible area handover by replacing the visible area in use with a visible area formed by one of the selected candidate antenna groups. Method of base station.

7. In claim 6, The number of antenna elements of each of the above candidate antenna groups is equal to the number of antenna elements located in the visible region being used. Method of base station.

8. In claim 6, The number of first antenna elements in the first direction of each of the candidate antenna groups is equal to the number of second antenna elements located in the first direction in the visible area being used, and the number of third antenna elements in the second direction of each of the candidate antenna groups is equal to the number of fourth antenna elements located in the second direction in the visible area being used. Method of base station.

9. In claim 6, The step of transmitting reference signals to the UE using the above candidate antenna groups is: A step of assigning a group index to each of the above candidate antenna groups; A step of assigning a beam index to each of the beams of the above candidate antenna groups; generating the reference signals including the group index and the beam index of each of the candidate antenna groups; and Comprising the step of transmitting the above reference signals to the UE, Method of base station.

10. In claim 6, The step of selecting one candidate antenna group based on the above received signal strengths is: A step of comparing the above received signal intensities with a first threshold value; A step of selecting candidate antenna groups having a reception signal strength greater than or equal to the first threshold value based on the compared results; and A step of selecting a candidate antenna group having the maximum reception signal strength from among the above-mentioned selected candidate antenna groups as one of the candidate antenna groups, Method of base station.

11. In claim 1, If the first line-of-sight handover attempt fails, further comprising the step of attempting a second line-of-sight handover based on all antenna elements of the antenna. Method of base station.

12. In claim 11, If the above first line-of-sight handover attempt fails, the step of attempting a second line-of-sight handover based on all antenna elements of the antenna is as follows: If the above first line-of-sight handover attempt fails, a step of setting up candidate antenna groups using the above total antenna elements of the above antenna; A step of transmitting reference signals to the UE using the above candidate antenna groups; A step of receiving information on received signal strengths of reference signals from the UE; A step of selecting one of the candidate antenna groups based on the received signal intensities; and Including a step of attempting the second visible area handover by replacing the visible area in use with a visible area formed by one of the selected candidate antenna groups. Method of base station.

13. In claim 11, If the above second visible area handover attempt fails, further comprising the step of attempting a handover to another base station. Method of base station.

14. As a method of UE (user equipment), A step of receiving threshold information necessary to determine whether to initiate a visible area handover from a base station; A step of determining whether to initiate the visible area handover based on the above threshold information; and If it is determined that the initiation of the visible area handover is necessary, a step of requesting the initiation of the visible area handover to the base station is included. UE's method.

15. In claim 14, The above threshold information includes information about a first threshold value and a second threshold value, The step of determining whether to initiate the visible area handover based on the above threshold information is as follows: A step of receiving a reference signal from the above base station; A step of measuring the received signal strength of the above reference signals; a step of determining whether the received signal strength is less than or equal to the first threshold value; and If the received signal strength is lower than or equal to the first threshold value, the step of determining whether the duration of the state in which the received signal strength is lower than or equal to the first threshold value is higher than or equal to the second threshold value, If the duration of the state in which the received signal strength is lower than or equal to the first threshold is longer than or equal to the second threshold, it is determined that the visible area handover is necessary. UE's method.

16. In claim 14, The above threshold information includes information about the third threshold and the fourth threshold, The step of determining whether to initiate the visible area handover based on the above threshold information is as follows: A step of measuring the speed of the above UE; a step of determining whether the above speed is greater than or equal to the third threshold value; and If the speed is greater than or equal to the third threshold value, a step of determining whether the duration of the state in which the speed is greater than or equal to the third threshold value is greater than or equal to the fourth threshold value is included. If the duration of the state in which the speed is greater than or equal to the third threshold is greater than or equal to the fourth threshold, it is determined that the visible area handover is necessary. UE's method.

17. In claim 14, A step of receiving reference signals including group indices of each of candidate antenna groups transmitted from the base station based on a request for the above-mentioned visible region handover and beam indices of each of beams formed from each of the candidate antenna groups; A step of measuring the received signal intensities for the above reference signals; and Further comprising the step of transmitting information about the received signal strengths to the base station, UE's method.

18. As a UE (user equipment), Contains at least one processor, At least one processor of the UE, Receive threshold information required to determine whether to initiate a visible area handover from a base station; Determining whether to initiate the visible area handover based on the above threshold information; and If it is determined that the initiation of the above visible area handover is necessary, causing the base station to request the initiation of the above visible area handover, UE.

19. In claim 18, The above threshold information includes information about a first threshold value and a second threshold value, In the step of determining whether to initiate the visible area handover based on the above threshold information, the at least one processor determines whether the UE, Receive a reference signal from the above base station; Measure the received signal strength of the above reference signals; determining whether the received signal strength is less than or equal to the first threshold value; and If the received signal strength is lower than or equal to the first threshold value, it causes a determination to be made whether the duration of the state in which the received signal strength is lower than or equal to the first threshold value is higher than or equal to the second threshold value. If the duration of the state in which the received signal strength is lower than or equal to the first threshold is longer than or equal to the second threshold, it is determined that the visible area handover is necessary. UE.

20. In claim 18, The above threshold information includes information about the third threshold and the fourth threshold, In the step of determining whether to initiate the visible area handover based on the above threshold information, the at least one processor determines whether the UE, Measure the speed of the above UE; determine whether the above speed is greater than or equal to the third threshold value; and If the speed is greater than or equal to the third threshold, it causes a determination to be made as to whether the duration of the state in which the speed is greater than or equal to the third threshold is greater than or equal to the fourth threshold; If the duration of the state in which the speed is greater than or equal to the third threshold is greater than or equal to the fourth threshold, it is determined that the visible area handover is necessary. UE.

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