Method and apparatus for performing handover

Abstract

The present disclosure discloses a method and apparatus for performing an efficient handover. A method of a terminal comprises the steps of: receiving a message from a first transmitting and receiving point connected to the terminal instructing to obtain a terminal-based timing advance; receiving an SSB from one or more transmitting and receiving points belonging to a surrounding cell in accordance with the instruction of the first transmitting and receiving point; determining a timing advance based on the SSB; transmitting the timing advance to the first transmitting and receiving point; receiving a cell switch command from the first transmitting and receiving point; and establishing a connection with a second transmitting and receiving point selected in accordance with the cell switch command among the one or more transmitting and receiving points belonging to the surrounding cell.

Description

Technology Field

[0001] The present disclosure relates to wireless communication, and more specifically, to technology for efficient mobility management of terminals. Background Technology

[0002] In mobile communication systems, a technology called handover can be utilized to enable users to receive continuous communication services even while on the move. Handover is a procedure performed to maintain the continuity of the connection with a base station when a terminal moves from one base station to another.

[0003] However, for a terminal to perform a handover, it may need to transmit information related to the terminal to the network through upper layers. Consequently, it may take a significant amount of time for the terminal to transmit this information to the network. Therefore, terminals transmitting and receiving large amounts of data may experience a degradation in transmission rates due to a decrease in the Signal-to-Noise Ratio (SNR) at the boundaries of cells formed by different base stations. If the terminal moves at a very high speed, the transmission delay caused by the handover can negatively impact delay-sensitive services.

[0004] To address the aforementioned problems, a technique known as soft handover can be proposed. Soft handover is a method in which a terminal switches links with a base station while simultaneously connected to both the current cell and a new cell. However, in the case of soft handover, since the terminal transmits and receives signals through a higher layer to establish a connection with the base station, it can take a significant amount of time, and this prolonged duration may result in excessive signaling overhead. The problem to be solved

[0005] The purpose of the present disclosure to solve the above-mentioned problems is to provide a method and apparatus for performing efficient handover through rapid switching of wireless links. means of solving the problem

[0006] A method of a terminal according to embodiments of the present disclosure for achieving the above objective comprises: receiving a message from a first transmitting and receiving point connected to the terminal instructing to obtain a terminal-based timing advance; receiving an SSB from one or more transmitting and receiving points belonging to a surrounding cell in accordance with the instruction of the first transmitting and receiving point; determining a timing advance based on the SSB; transmitting the timing advance to the first transmitting and receiving point; receiving a cell switch command from the first transmitting and receiving point; and establishing a connection with a second transmitting and receiving point selected in accordance with the cell switch command among the one or more transmitting and receiving points belonging to the surrounding cell.

[0007] The above message instructing the acquisition of terminal-based timing advance may be MAC-CE.

[0008] The method of the above terminal may include the step of transmitting capability information of the terminal to the first transmitting and receiving point before receiving a message instructing the acquisition of the terminal-based timing advance.

[0009] The capability information of the terminal may include at least one of information indicating whether to perform a cross-correlation operation for an SSB received by the terminal from one or more transmitting and receiving points belonging to the surrounding cell, or a message indicating whether to perform a timing difference update operation based on the timing advance.

[0010] The method of the above terminal may include the step of disabling the RACH-based timing advance acquisition method using RAR-less mode after receiving the message instructing terminal-based timing advance acquisition.

[0011] The above timing advance can be determined by the terminal performing a cross-correlation operation with respect to the SSB.

[0012] The cell switch command above may include at least one of a MAC-CE index field, a cell ID field, a beam index field, a TA field, or a terminal-based TA measurement instruction field.

[0013] A method of a first transmitting and receiving point according to embodiments of the present disclosure for achieving the above objective comprises: receiving capability information of the terminal from a terminal connected to the transmitting and receiving point; transmitting a message instructing the terminal to acquire a terminal-based timing advance; receiving a timing advance for one or more transmitting and receiving points belonging to a surrounding cell of the terminal from the terminal; and transmitting a cell switch command to the terminal instructing the terminal to establish a connection with a second transmitting and receiving point belonging to the surrounding cell.

[0014] The above message instructing the acquisition of terminal-based timing advance may be MAC-CE.

[0015] The step of transmitting a message instructing the terminal to acquire a terminal-based timing advance may be performed after the transmitting and receiving points receive capability information of the terminal, when the terminal is moving at a speed greater than a threshold or when there is a request from the terminal.

[0016] The method of the first transmission and reception point above may include the step of determining the first timing advance by receiving the timing advance and reflecting the downlink transmission timing difference in the timing advance.

[0017] A terminal according to embodiments of the present disclosure for achieving the above objective comprises at least one processor, wherein the at least one processor causes the terminal to receive a message instructing the acquisition of a terminal-based timing advance from a first transmission / reception point connected to the terminal, receive an SSB from one or more transmission / reception points belonging to a surrounding cell in accordance with the instruction of the first transmission / reception point, determine a timing advance based on the SSB, transmit the timing advance to the first transmission / reception point, receive a cell switch command from the first transmission / reception point, and establish a connection with a second transmission / reception point selected in accordance with the cell switch command among the one or more transmission / reception points belonging to the surrounding cell.

[0018] The above message instructing the acquisition of terminal-based timing advance may be MAC-CE.

[0019] The at least one processor may further cause the terminal to transmit capability information of the terminal to the first transmitting and receiving point before receiving a message instructing the terminal-based timing advance acquisition.

[0020] The capability information of the terminal may include at least one of information indicating whether to perform a cross-correlation operation for an SSB received by the terminal from one or more transmitting and receiving points belonging to the surrounding cell, or a message indicating whether to perform a timing difference update operation based on the timing advance.

[0021] The above at least one processor may further cause the terminal to disable the RACH-based timing advance acquisition method using RAR-less mode after receiving a message instructing the terminal-based timing advance acquisition.

[0022] The above timing advance can be determined by the terminal performing cross-correlation on the SSB.

[0023] The cell switch command above may include at least one of a MAC-CE index field, a cell ID field, a beam index field, a TA field, or a terminal-based TA measurement instruction field. Effects of the invention

[0024] According to the present disclosure, a Transmission and Reception Point (TRP) connected to a terminal can transmit a Physical Downlink Control Channel (PDCCH) order to the terminal. The transmitted PDCCH order may include a field indicating a Random Access Response (RAR)-less mode. Due to the aforementioned field, the terminal may not receive a RAR message. In conventional methods, it may take a long time for the terminal to receive a RAR message from a TRP connected to the terminal. However, when the above-described method is applied to the terminal, the problem of taking a long time can be resolved.

[0025] According to the present disclosure, when a terminal is moving at a very high speed, the terminal may receive a Radiation Resource Control (RRC) message containing information instructing to 'obtain a terminal-based timing advance' from a TRP currently connected to the terminal. When the terminal receives the aforementioned RRC message, the terminal may determine a timing advance based on a Synchronization Signal Block (SSB) received from a TRP in the vicinity of the terminal. When the terminal is moving at a very high speed, there may be issues with transmission rate and stability for the terminal to maintain two links. However, as described above, if the terminal determines the timing advance independently, the issues of transmission rate and stability can be resolved even when the terminal is moving at a very high speed. Brief explanation of the drawing

[0026] FIG. 1 is a conceptual diagram illustrating embodiments of a communication system. FIG. 2 is a block diagram illustrating embodiments of the device. FIG. 3 is a conceptual diagram illustrating embodiments of transmitting and receiving points that communicate with a moving terminal. FIG. 4 is a conceptual diagram illustrating embodiments of transmitting and receiving points that communicate with a moving terminal. FIG. 5 is a flowchart illustrating embodiments of a method for a terminal to perform a handover. FIG. 6 is a flowchart illustrating embodiments of a method for a terminal to perform a handover. FIG. 7 is a flowchart illustrating embodiments of a method for a terminal to perform a handover. FIG. 8 is a flowchart illustrating embodiments of a method for a terminal to perform a handover. FIG. 9 is a flowchart illustrating embodiments of a method for a terminal to perform a handover. FIG. 10 is a flowchart illustrating embodiments of a method for a terminal to perform a handover. FIG. 11 is a flowchart illustrating embodiments of a method for switching the determination method of a timing advance. FIG. 12 is a flowchart illustrating embodiments of a method for switching the determination method of a timing advance. Specific details for implementing the invention

[0027] The present disclosure is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present disclosure to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present disclosure.

[0028] Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. Such terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present disclosure, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of a plurality of related described items or any of a plurality of related described items.

[0029] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0030] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as “comprising” or “having” are intended to specify the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0031] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which this disclosure pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0032] Throughout the specification, the network may include, for example, wireless internet such as WIFI, mobile internet such as WiBro (wireless broadband internet) or WiMax (world interoperability for microwave access), 3G mobile communication networks such as GSM (global system for mobile communication) or CDMA (code division multiple access) or CDMA2000, 3.5G (3.5th generation) mobile communication networks such as HSDPA (high speed downlink packet access) or HSUPA (high speed uplink packet access), 4G (4th generation) mobile communication networks such as LTE (long term evolution) network or LTE-Advanced, and 5G (5th generation) mobile communication networks.

[0033] Throughout the specification, the term "terminal" may refer to a mobile station, mobile terminal, subscriber station, portable subscriber station, user equipment, access terminal, etc., and may include all or part of the functions of a terminal, mobile station, mobile terminal, subscriber station, portable subscriber station, user equipment, access terminal, etc.

[0034] The aforementioned terminal may refer to various devices that can be used by users of mobile communication services, such as a communication-capable desktop computer, laptop computer, tablet PC, wireless phone, mobile phone, smartphone, smart watch, smart glass, VR glasses, e-book reader, PMP (portable multimedia player), portable game console, navigation device, digital camera, DMB (digital multimedia broadcasting) player, digital audio recorder, digital audio player, digital picture recorder, digital picture player, digital video player.

[0035] Throughout the specification, a base station may refer to an access point, a radio access station, a node B, an evolved node B, a base transceiver station, a Mobile Multi-hop Relay - Base Station, etc., and may include all or part of the functions of a base station, access point, radio access station, node B, eNodeB, base transceiver station, MMR-BS, etc.

[0036] Throughout the specification, a non-ground node may refer to a communication node mounted on a satellite. Throughout the specification, a ground node may refer to a communication node located on the ground. Throughout the specification, the term communication node may be used to encompass both non-ground nodes and ground nodes. Throughout the specification, a cell may refer to a service area where mobile communication services are provided through a base station. Throughout the specification, cell (re)selection may refer to cell selection, where a terminal selects a serving cell to receive mobile communication services upon initial connection to a mobile communication network, and / or cell re-selection, where the terminal selects a serving cell to camp on.

[0037] 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 of the present disclosure, the same reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0038] FIG. 1 is a conceptual diagram illustrating embodiments of a communication system.

[0039] 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). Additionally, the communication system (100) may further include a core network (e.g., an S-GW (serving-gateway), a P-GW (PDN (packet data network)-gateway), and an MME (mobility management entity)). If the communication system (100) is a 5G communication system (e.g., a new radio (NR) system), the core network may include an AMF (access and mobility management function), a UPF (user plane function), an SMF (session management function), etc.

[0040] Multiple communication nodes (110 to 130) can support communication protocols defined in 3GPP (3rd generation partnership project) standards (e.g., LTE communication protocol, LTE-A communication protocol, NR communication protocol, etc.). Multiple 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 multiple communication nodes may mean an apparatus or a device. The embodiments may be performed by a device or device. The structure of the device (e.g., device) may be as follows.

[0041] FIG. 2 is a block diagram illustrating embodiments of the device.

[0042] Referring to FIG. 2, the device (200) may include at least one processor (210), a memory (220), and a transceiver (230) that is connected to a network to perform communication. Additionally, the device (200) may further include an input interface device (240), an output interface device (250), a storage device (260), etc. Each component included in the device (200) may be connected by a bus (270) to perform communication with each other. However, each component included in the communication node (200) may be connected via an individual interface or an individual bus centered on the processor (210), rather than via a common bus (270). For example, the processor (210) may be connected to at least one of the memory (220), the transceiver (230), the input interface device (240), the output interface device (250), and the storage device (260) through a dedicated interface.

[0043] The processor (210) can execute a program command stored in at least one of the memory (220) and the storage device (260). The processor (210) may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which the methods according to embodiments of the present disclosure are performed. Each of the memory (220) and the storage device (260) may be composed of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory (220) may be composed of at least one of read-only memory (ROM) and random access memory (RAM).

[0044] 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 located 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 located 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 located within the cell coverage of the third base station (110-3). The first terminal (130-1) may be located within the cell coverage of the fourth base station (120-1). The sixth terminal (130-6) may be located within the cell coverage of the fifth base station (120-2).

[0045] Here, each of the multiple base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be referred to as NB (NodeB), eNB (evolved NodeB), gNB, ABS (advanced base station), HR-BS (high reliability-base station), BTS (base transceiver station), radio base station, radio transceiver, access point, access node, RAS (radio access station), MMR-BS (mobile multihop relay-base station), RS (relay station), ARS (advanced relay station), HR-RS (high reliability-relay station), HNB (home NodeB), HeNB (home eNodeB), RSU (road side unit), RRH (radio remote head), TP (transmission point), TRP (transmission and reception point), etc.

[0046] Each of the multiple terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) may be referred to as a UE (user equipment), terminal, access terminal, mobile terminal, station, subscriber station, mobile station, portable subscriber station, node, device, IoT (Internet of Thing) device, mounted module / device / terminal or on board device / terminal, etc.

[0047] Meanwhile, each of the multiple base stations (110-1, 110-2, 110-3, 120-1, 120-2) may operate in different frequency bands or in the same frequency band. Each of the multiple 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 an ideal backhaul link or a non-ideal backhaul link. Each of the multiple base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be connected to a core network via an ideal backhaul link or a non-ideal backhaul link. Each of the multiple 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.

[0048] In addition, each of the multiple base stations (110-1, 110-2, 110-3, 120-1, 120-2) can support MIMO transmission (e.g., SU (single user)-MIMO, MU (multi user)-MIMO, massive MIMO, etc.), CoMP (coordinated multipoint) transmission, carrier aggregation (CA) transmission, transmission in an unlicensed band, device-to-device communication (D2D) (or ProSe (proximity services)), IoT (Internet of Things) 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 method, and the fourth terminal (130-4) can receive a signal from the second base station (110-2) based on the SU-MIMO method. Alternatively, the second base station (110-2) can transmit a signal 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 a signal from the second base station (110-2) by the MU-MIMO method.

[0049] 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 method, 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) by the CoMP method. Each of the multiple base stations (110-1, 110-2, 110-3, 120-1, 120-2) can transmit and receive signals based on the CA method with terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) within its cell coverage area. Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) can control D2D 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 D2D by controlling each of the second base station (110-2) and the third base station (110-3).

[0050] Even if a method performed at a first communication node among the communication nodes (e.g., transmission or reception of a signal) is described, the corresponding second communication node may perform a method corresponding to the method performed at the first communication node (e.g., reception or transmission of a signal). That is, if the operation of a terminal is described, the corresponding base station may perform an operation corresponding to the operation of the terminal. Conversely, if the operation of a base station is described, the corresponding terminal may perform an operation corresponding to the operation of the base station.

[0051] FIG. 3 is a conceptual diagram illustrating embodiments of transmitting and receiving points that communicate with a moving terminal.

[0052] Referring to Figure 3, as mobile communication technology develops, the utilization of the ultra-high frequency band can increase. As the utilization of the ultra-high frequency band increases, a Multi-Transmission Reception Point (Multi-TRP) can be considered to improve transmission efficiency and stability in the band to which radio waves with small coverage and strong directivity belong. In a Multi-TRP environment, a terminal can exchange data with multiple transmission and reception points via uplinks or downlinks simultaneously or sequentially. In a Multi-TRP environment, the number of links requiring switching may increase when the terminal moves at high speed. A terminal communicating with multiple transmission and reception points in a small coverage area may experience a greater number of link switchings. Frequent link switching can impair the transmission efficiency and stability of the entire mobile communication system. However, frequent link switching may be an unsolvable problem in environments where communication with multiple transmission and reception points is essential. Therefore, performing link switching faster than before can be a solution to this problem.

[0053] After establishing a connection with the first transmission / reception point (310) during the initial connection phase, the terminal (330) can additionally establish a connection with the second transmission / reception point (320) located near the first transmission / reception point (310). The terminal (330) can receive services from two transmission / reception points. At this time, the terminal (330) can move to the right. As the terminal (330) moves to the right, the terminal (330) can move away from the first transmission / reception point (310). As the terminal (330) moves away from the first transmission / reception point (310), the connection between the terminal (330) and the first transmission / reception point (310) can be severed.

[0054] In order for the terminal (330) to receive stable service from two transmission and reception points, the terminal (330) may need to establish a connection with other transmission and reception points, excluding the first and second transmission and reception points (310, 320), before the connection with the first transmission and reception point (310) is severed.

[0055] FIG. 4 is a conceptual diagram illustrating embodiments of transmitting and receiving points that communicate with a moving terminal.

[0056] Referring to FIG. 4, the terminal (440) may be connected to the first and second transmission / reception points (410, 420). The terminal (440) may move in a direction that approaches the third transmission / reception point (430). As the terminal (440) moves in a direction that approaches the third transmission / reception point (430), the terminal (440) may move away from the first transmission / reception point (410). As the terminal (440) moves away from the first transmission / reception point (410), the connection between the terminal (440) and the first transmission / reception point (410) may be severed. Therefore, the terminal (440) may need to establish a connection with the third transmission / reception point (430) before the connection with the first transmission / reception point (410) is severed.

[0057] The third transmission / reception point (430) may be a transmission / reception point belonging to a cell different from the cell to which the first and second transmission / reception points (410, 420) belong. Therefore, the information broadcast by the third transmission / reception point (430) may be information elements different from the information elements broadcast by the first and second transmission / reception points (410, 420) to the terminal. The broadcasted information may include a Physical Cell Identity (PCI). Therefore, the Physical Cell Identity included in the information broadcast by the third transmission / reception point (430) may be different from the Physical Cell Identity included in the information broadcast by the first and second transmission / reception points (410, 420).

[0058] All embodiments described below may be presented under the assumption that the terminal and the transmitting and receiving points are placed in the situation presented in FIG. 4. In each of the embodiments below, if the number assigned to each communication node is the same as the number assigned to the communication node shown in FIG. 4, each communication node may be the same communication node as the communication node shown in FIG. 4.

[0059] FIG. 5 is a flowchart illustrating embodiments of a method for a terminal to perform a handover.

[0060] Referring to FIG. 5, the first transmission / reception point (410) may periodically receive surrounding cell search information from the terminal (440). Alternatively, the first transmission / reception point (410) may receive surrounding cell search information from the terminal (440) at the request of the first transmission / reception point (410). Based on the surrounding cell search information of the terminal (440), the first transmission / reception point (410) may identify a candidate cell (e.g., a candidate transmission / reception point) to which the terminal (440) must establish a connection when the terminal (440) loses connection with the first transmission / reception point (410).

[0061] The first transmission / reception point (410) may determine that a connection switch is necessary because the connection between the terminal (440) and the first transmission / reception point (410) is unstable. If the first transmission / reception point (410) determines that a connection switch is necessary, it may transmit a Physical Downlink Control Channel (PDCCH) order to the terminal (440) (S510). The PDCCH order may be included in a Medium Access Control Element (MAC CE) and transmitted to the terminal (440). The MAC CE may include at least one of a physical cell identifier, a preamble index, or information regarding a Preamble Occasion (RO) for the third transmission / reception point (430). The preamble must be transmitted through a pre-arranged location in the time and frequency domain so that the base station or transmission / reception point can receive it. Here, the 'pre-arranged location in the time and frequency domain' may refer to the RO.

[0062] The terminal (440) can receive a PDCCH order from the first transmission / reception point (410) and can transmit a PRACH preamble (Physical Random Access Channel preamble) to the third transmission / reception point (430) based on the information included in the PDCCH order (S520). The third transmission / reception point (430) can receive the PRACH preamble from the terminal (440) and can measure a Timing Advance (TA) based on the PRACH preamble. The measured TA value can be transmitted to a third network (e.g., a base station) connected to the third transmission / reception point (430).

[0063] The third network can receive the measured TA value from the third transmission / reception point (430). The third network, having received the measured TA value from the third transmission / reception point (430), can transmit the measured TA value to the first network connected to the first transmission / reception point (410). The first network connected to the first transmission / reception point (410) can transmit the TA value to the first transmission / reception point (410). The first transmission / reception point (410) can receive the TA value from the first network. The first transmission / reception point (410) can generate a Random Access Response Message (RAR) containing the received TA value. The first transmission / reception point (410) can transmit the generated RAR message to the terminal (440) (S530). The terminal (440) can receive the RAR message from the first transmission / reception point.

[0064] The reason why the terminal (440) receives the TA value from the first transmission / reception point (410) rather than directly receiving the TA value from the third transmission / reception point (430) will be presented below. If the terminal (440) receives the TA value from the third transmission / reception point (430), consistency with the existing random access procedure may not be maintained. The method of the terminal (440) receiving the TA value from the first transmission / reception point (410) may be inefficient. However, the method of the terminal (440) receiving the TA value from the first transmission / reception point (410) may have the advantage of minimizing modifications to existing 3GPP standards.

[0065] When the terminal (440) receives a TA value, the terminal (440) can obtain a TA value for the third transmission / reception point (430) (S540). Unlike a handover through an upper layer, a handover through a lower layer can be performed quickly. The first transmission / reception point (410) can transmit a MAC CE containing a cell switch command to the terminal (440) (S550). The terminal (440) can receive the MAC CE containing a cell switch command from the first transmission / reception point (410). The first transmission / reception point (410) can maintain the existing link with the terminal (440) without transmitting a cell switch command to the terminal (440). However, if the first transmission / reception point (410) determines that the connection between the terminal (440) and the first transmission / reception point (410) may be severed, the link between the first transmission / reception point (410) and the terminal (440) can be switched by transmitting a cell switch command to the terminal (440).

[0066] By transmitting a cell switch command to the terminal (440) by the first transmission / reception point (410), the first transmission / reception point (410) can cause the terminal (440) to establish a new connection with the third transmission / reception point (430). The terminal (440) can establish a connection with the third transmission / reception point (430) based on the TA value for the third transmission / reception point (430) (S540).

[0067] FIG. 6 is a flowchart illustrating embodiments of a method for a terminal to perform a handover.

[0068] Referring to FIG. 6, unlike in FIG. 5, the second transmission / reception point (420) can transmit a PDCCH order to the terminal (440) (S610). The transmitted PDCCH order may include at least one of a physical cell identifier, a beam index, a preamble index, and RO setting information for the third transmission / reception point (430). The terminal (440) can receive the PDCCH order from the second transmission / reception point (420).

[0069] A terminal (440) that has received a PDCCH order can transmit a PRACH preamble to the third transmission / reception point (430) to obtain a TA value for the third transmission / reception point (430) (S620). The third transmission / reception point (430) can receive the PRACH preamble from the terminal (440).

[0070] The third transmission / reception point (430) can receive the received PRACH preamble from the terminal (440) and then measure the TA value for the link between the terminal (440) and the third transmission / reception point (430) based on the PRACH preamble. The third transmission / reception point (430) can transmit the measured TA value to a third network connected to the third transmission / reception point (430). The third network can receive the measured TA value from the third transmission / reception point (430).

[0071] The first transmission / reception point (410) can support DCI transmission in the Type 1 Common Search Space (Type 1 CSS). The third network connected to the third transmission / reception point (430) can transmit a TA value to the first transmission / reception point (410) that supports DCI transmission in the Type 1 search space through the network connected to the first transmission / reception point (410).

[0072] The first transmission / reception point (410) can receive a TA value from the first network connected to the first transmission / reception point (410). Upon receiving the TA value, the first transmission / reception point (410) can generate a RAR message. The generated RAR message may include the TA value. The first transmission / reception point (410) can transmit the generated RAR message to the terminal (440) (S630). The terminal (440) can receive the generated RAR message from the first transmission / reception point (410). The reason why the first transmission / reception point (410), rather than the second transmission / reception point (420), transmits the RAR message to the terminal (440) is as follows.

[0073] PDCCH can be transmitted in the Common Search Space and / or the UE-Specific Search Space. The Common Search Space may be used to transmit RAR messages. This may be because RAR messages are responses to the PRACH preamble and must be received by all terminals. Therefore, only senders and receivers that support DCI transmission in the Common Search Space (e.g., PDDCH transmission) may need to transmit RAR messages.

[0074] The terminal (440) can receive a RAR message from the first transmission / reception point (410). The received RAR message may include a TA value for the third transmission / reception point (430). Therefore, after receiving the RAR message, the terminal (440) can obtain a TA value for the third transmission / reception point (430) (S640).

[0075] When the terminal (440) obtains a TA value for the third transmission / reception point (430), it may report the terminal (440)'s acquisition of the TA value to the first transmission / reception point (410). The second transmission / reception point (420) may determine that the terminal (440) has obtained the TA value based on the terminal's report. In this case, the second transmission / reception point (420) may transmit a cell switch command to the terminal (440) (S650). The terminal (440) may receive the cell switch command from the second transmission / reception point (420). The cell switch command may include information instructing to disconnect the connection between the terminal (440) and the first transmission / reception point (410). When the terminal (440) receives a cell switch command from the second transmission / reception point (420), the terminal (440) can disconnect from the first transmission / reception point (410) and establish a new connection with the third transmission / reception point (430) (S660). Disconnection from the first transmission / reception point (410) can be performed through an upper layer.

[0076] When the terminal (440) performs the switching of the link in the manner described above, it can receive data and control signals from the second and third transmission and reception points (420, 430). However, control signals transmitted in the first type common search space may still need to be received from the first transmission and reception point (410). This may be because the first transmission and reception point (410) supports the first type common search space. The fact that the terminal (440) still receives control signals from the first transmission and reception point (410) even after disconnecting from the first transmission and reception point (410) can cause complex terminal operation. Complex terminal operation can lead to high power consumption of the terminal.

[0077] The terminal (440) can receive control signals that are not transmitted in the first type common search space from the transmitting and receiving point that sends the PDCCH order. However, at the same time, the terminal (440) can receive information transmitted in the first type common search space from a different transmitting and receiving point than the transmitting and receiving point that sends the PDCCH order. Therefore, the number of links that the terminal (440) must manage may increase. The terminal (440) can continuously perform management to maintain connections with multiple links. If a transmitting and receiving point that supports DCI transmission in the first type common search space is far from the terminal, the terminal (440) may need to search for a transmitting and receiving point that supports DCI transmission in another first type common search space. The operations of the terminal described above may be very inefficient.

[0078] Existing RAR messages may contain various information in addition to information for obtaining a TA. Therefore, existing RAR messages may be inefficient if the purpose is solely to obtain a TA for the terminal (440). It may take a long time for the terminal (440) to receive a RAR message after transmitting a PRACH preamble. To solve the aforementioned problems, a RAR-less solution may be proposed. A specific description of the RAR-less solution will be provided in the description of FIG. 7.

[0079] FIG. 7 is a flowchart illustrating embodiments of a method for a terminal to perform a handover.

[0080] Referring to FIG. 7, a RAR-less solution may be proposed. The RAR-less solution may be a method in which the terminal (440) does not receive existing RAR messages when performing TA acquisition for link switching. A method to prevent the terminal (440) from receiving RAR messages may be presented as follows.

[0081] The second transmission / reception point (420) can transmit a PDCCH order to the terminal (440) so that the terminal (440) does not receive a RAR message (S710). The terminal (440) can receive the PDCCH order from the second transmission / reception point (420). The PDCCH order transmitted by the second transmission / reception point (420) to the terminal (440) may include a field indicating a RAR-less mode. The main fields included in the PDCCH order transmitted by the second transmission / reception point are as shown in [Table 1] below.

[0082] Downlink Control Index (DCI) Index Field RAR Mode Field (Original RAR / Modified RAR / RAR-less) Cell ID field Beam index field PRACH preamble index field RO(RACH occasion) field Retransmission instruction field TA Field

[0083] The terminal (440) can receive a PDCCH order and can confirm that the RAR-less mode is enabled based on the information included in the PDCCH order. In other words, the terminal (440) can determine that the transmission and reception operation of the RAR message, which is a response to the PRACH preamble, is not performed. The terminal (440) that receives the PDCCH order may not receive the RAR message. By including a field indicating the RAR-less mode in the PDCCH order, the second transmission / reception point may not transmit a separate RRC message to the terminal (440) to set the RAR-less mode. By not transmitting the RRC message to the terminal (440) by the second transmission / reception point (420), signaling overhead may not occur. The second transmission / reception point (420) may also set the RAR-less mode to the terminal (440) in advance through the RRC layer.

[0084] The terminal (440) can receive a PDCCH order from the second transmission / reception point (420) (S710). When the terminal (720) receives the PDCCH order, the terminal (440) can transmit a PRACH preamble to the third transmission / reception point (430) (S720). However, the third transmission / reception point (430) may not receive the PRACH preamble. However, even if the terminal (440) transmits the PRACH preamble, it may not set a Response Window for receiving RAR messages. Therefore, even if the terminal (440) does not receive the RAR message, it may not retransmit the PRACH preamble to the third transmission / reception point (430). In the existing RAR mode, the terminal (440) can set a Response Window when it transmits the PRACH preamble. If the terminal (440) does not receive a RAR message within the response window, it can send the PRACH preamble again to the transmitting and receiving point.

[0085] If the terminal (440) does not set a response window, a problem may occur in which the third transmission / reception point (430) does not properly receive the PRACH preamble. The second transmission / reception point (420) transmitting the PDCCH order may not receive the TA value from the third transmission / reception point (430) even after a certain amount of time has passed. If the second transmission / reception point (420) does not receive the TA value from the third transmission / reception point (430) even after a certain amount of time has passed, the second transmission / reception point (420) may determine that the transmission of the PRACH preamble to the third transmission / reception point (430) was not performed smoothly. The second transmission / reception point (420) may transmit the PDCCH order to the terminal (440) again (S730). The transmitted PDCCH order may include a field indicating that the PDCCH order is being retransmitted.

[0086] The terminal (440) that receives the PDCCH order again can check a field indicating that the PDCCH order is being retransmitted. The terminal (440) that performs the check operation can transmit the PRACH preamble again to the third transmission / reception point (430) (S740). When the terminal (440) transmits the PRACH preamble, the terminal (440) may need to increase the transmission power.

[0087] The third transmission / reception point (430) can receive the PRACH preamble retransmitted by the terminal (440). The third transmission / reception point (430) that receives the PRACH preamble can measure the TA value. The measured TA value can be transmitted to a third network connected to the third transmission / reception point (430). The third network connected to the third transmission / reception point (430) can transmit the measured TA value to the second transmission / reception point (420) through a second network connected to the second transmission / reception point (420).

[0088] The second transmission / reception point (420) can receive a TA value from a second network connected to the second transmission / reception point (420). The second transmission / reception point (420) can transmit a cell switch command containing the received TA value to the terminal (440) (S750). The second transmission / reception point (420) can transmit an Absolute Timing Advance Command containing the TA value to the terminal (440). The terminal (440) can receive a cell switch command containing the TA value and / or an Absolute Timing Advance Command from the second transmission / reception point (420).

[0089] The cell switch command and absolute timing advance command described above may both include a field and / or cell ID indicating which transmission / reception point's TA value is included in the command. This is because the terminal (440) cannot know whether the received cell switch command and / or absolute timing advance command is a response to the PRACH preamble previously transmitted by the terminal (440) to the third transmission / reception point (430) or a TA update for the second transmission / reception point (420). One bit may be assigned to the field indicating which transmission / reception point's TA value is included. The fields included in the cell switch command and / or absolute timing advance command may be represented as shown in [Table 2] below.

[0090] MAC-CE index field Cell ID or instruction field TA Field

[0091] The terminal (440) can receive a cell switch command or an absolute timing advance command. The terminal (440) that has performed the receiving operation can obtain a TA value for the third transmission / reception point (430) by checking the TA value included in the cell switch command or the absolute timing advance command (S760). The terminal (440) that has obtained the TA value for the third transmission / reception point (430) can disconnect the connection between the terminal and the transmission / reception point (not shown) that was previously connected. The terminal (440) that has disconnected the connection between the terminal (440) and the transmission / reception point (not shown) that was previously connected can establish a new connection with the third transmission / reception point (430) (S770).

[0092] The second transmission / reception point (420) can set the third transmission / reception point (430) as a transmission / reception point for transmitting and receiving data and control signals with the terminal (440) through RRC signaling (Radio Resource Control signaling). The second transmission / reception point (420) can cause the transmission / reception point previously connected to the terminal (440) to disconnect from the terminal (440) through RRC signaling.

[0093] There may also be problems with the RAR-less solution described above. According to the RAR-less solution, a PDCCH order is transmitted from the transmitting and receiving point to the terminal (440), and the terminal (440) that receives the PDCCH order can transmit a PRACH preamble to another transmitting and receiving point. After that, the terminal (440) can obtain the TA value after receiving a message containing the TA value from the transmitting and receiving point. The above-described series of procedures may have a negative impact on the transmission rate and stability of the terminal (440) while it is moving at very high speed. This may be because the terminal (440) must maintain two links while moving at high speed. Therefore, a method to quickly obtain the TA value when the terminal (440) is moving at high speed may be requested. As a method to quickly obtain the TA value when the terminal (440) is moving at high speed, a 'terminal-based TA acquisition' method will be proposed in the description of FIG. 8.

[0094] FIG. 8 is a flowchart illustrating embodiments of a method for a terminal to perform a handover.

[0095] Referring to FIG. 8, a terminal-based TA acquisition procedure, which is one of the methods for a terminal (820) to perform a handover, may be initiated. Generally, the terminal (820) may periodically report to the transmitting and receiving point information regarding the channel to which the link currently connected to the terminal (820) belongs (hereinafter referred to as the 'current channel') at the transmitting and receiving point, either at the time or at the request of the transmitting and receiving point. The information regarding the current channel may include the Reference Signal Received Power (RSRP), Channel Quality Indicator (CQI), etc. The terminal (820) may periodically report to the transmitting and receiving point information regarding the links (e.g., surrounding channels) provided by cells existing around the cell to which the terminal (820) currently belongs (hereinafter referred to as 'surrounding cells'). The information regarding the surrounding channels may include the Reference Signal Received Power (RSRP). The terminal (820) transmitting information about surrounding channels as well as information about the current channel to the transmitting and receiving point may be so that the terminal (820) can quickly switch to another link in the event that an error occurs in the link currently connected to the terminal (820).

[0096] A terminal-based TA measurement method may be a method in which the terminal (820) measures the timing difference with the reference cell in addition to the signal strength during the process of the terminal (820) searching for surrounding cells. The timing difference measured by the terminal (820) may represent the TA value measured by the terminal (820). In order for the terminal (820) to measure the timing difference, the terminal (820) may perform cross-correlation on the SSB (Synchronization Signal Block) transmitted from the surrounding cells to the terminal (820). By performing cross-correlation, the terminal (820) may need to find the point in time when the maximum peak occurs. Therefore, the terminal (820) performing cross-correlation may cause more power consumption compared to the terminal (820) measuring the signal strength.

[0097] The terminal-based TA measurement method may be subject to many limitations due to the operations of the terminals (820) described above. This is because the number of times the terminal (820) can perform cross-correlation on SSBs received from surrounding cells, and the ability to manage cross-correlation and update timing differences, may vary depending on the capability of the terminal (820). Therefore, the transmitting and receiving point may need to know in advance the 'terminal-based TA measurement' capability possessed by each terminal (820). Based on the 'terminal-based TA measurement' capability of the terminals (820) known in advance, the transmitting and receiving point may cause the terminal (820) to perform 'terminal-based TA measurement'.

[0098] The terminal (820) may transmit an RRC message containing information indicating the capability (UE Capability) of the terminal (820) to the first transmission / reception point (810) during the initial connection phase with the first transmission / reception point (810) or while connected with the first transmission / reception point (810) (S810). Upon receiving the RRC message containing information indicating the capability of the terminal, the first transmission / reception point (810) may initiate a 'terminal-based TA acquisition' procedure if it determines that the terminal (820) is moving at high speed or if there is a request from the terminal (820).

[0099] The first transmission / reception point (810) may transmit an RRC message containing information instructing the terminal (820) to 'acquire terminal-based TA' (S820). In the following, all messages instructing the terminal (820) on the method of acquiring timing advance may also be transmitted via MAC-CE. The terminal (820) may receive an RRC message containing information instructing 'acquire terminal-based TA' from the first transmission / reception point (810). The terminal (820) may receive instructions regarding 'acquire terminal-based TA' from the first transmission / reception point (810). The terminal (820) may receive SSBs from transmission / reception points existing in surrounding cells, such as the second, third, and fourth transmission / reception points, at specified intervals (S830). The terminal (820) may measure the timing difference for each transmission / reception point by performing cross-correlation on the received SSBs (S840). The terminal (820) can update the timing difference with the measured timing difference. The number of timing differences the terminal (820) measures can be determined by the instructions of the first transmission / reception point (810).

[0100] When the first transmission / reception point (810) requests the terminal (820) to report the measured TA value, the terminal (820) can transmit the measured TA value to the first transmission / reception point (810) (S850). Upon receiving the TA value from the terminal (820), the first transmission / reception point (810) may determine that a link switching is necessary. When the first transmission / reception point (810) determines that a link switching is necessary, it may select one of the surrounding cells (hereinafter referred to as the 'target cell') reported by the terminal (820).

[0101] The first transmission / reception point (810) that has selected the target cell can transmit a cell switch command to the terminal (820) (S860). The terminal (820) can receive the cell switch command from the first transmission / reception point (810). By receiving the cell switch command, the terminal (820) can receive instructions regarding switching to the link provided by the target cell of the first transmission / reception point (810). Upon receiving instructions regarding switching to the link provided by the target cell, the terminal can establish a new connection with the transmission / reception point belonging to the target cell (or the transmission / reception point forming the target cell) (S870). The cell switch command described above may include at least one of a cell ID, a beam index, and a TA value. The cell ID and beam index may be the cell ID and beam index of the target cell. The TA value may be the TA value for the transmission / reception point belonging to the target cell. The cell switch command used in the terminal-based TA measurement procedure may include fields as shown in [Table 3] below.

[0102] MAC-CE index field Cell ID field Beam index field TA Field Terminal-based TA measurement instruction field

[0103] The TA value transmitted by the first transmitting / receiving point (810) to the terminal (820) may be the same as or different from the TA value measured by the terminal (820) itself. The reason the TA value transmitted by the first transmitting / receiving point (810) to the terminal (820) and the TA value measured by the terminal (820) itself are different may be due to the existence of a Downlink TX Timing Difference between surrounding cells. Assuming a non-ideal backhaul, a Downlink TX Timing Difference may occur because the time synchronization between the cell previously connected to the terminal (820) and the target cell is not aligned.

[0104] If the first transmission / reception point (810) transmits information to the terminal (820) indicating the downlink transmission timing difference, the TA value measured by the terminal (820) itself can be trusted. Therefore, if the terminal (820) receives information indicating the downlink transmission timing difference from the first transmission / reception point (810), the procedure for the terminal (820) to report the TA value to the first transmission / reception point (810) may not be necessary. However, if the terminal (820) does not receive information indicating the downlink transmission timing difference from the first transmission / reception point (810), the TA value measured by the terminal (820) cannot be trusted, so the procedure for the terminal (820) to report the TA value measured by the terminal (820) to the first transmission / reception point (810) may be necessary. The first transmission / reception point (810) can generate the actual TA value to be used by the terminal (820) by reflecting the downlink transmission timing difference in the TA value received from the terminal (820). The generated TA value can be transmitted to the terminal (820). The terminal (820) that receives the TA value can perform uplink communication with the target cell using the TA value generated by the first transmission / reception point (810).

[0105] If the cell switch command transmitted by the first transmitting / receiving point (810) to the terminal (820) does not include a TA field, it may imply that the terminal (820) should use a TA value measured by itself.

[0106] FIG. 9 is a flowchart illustrating embodiments of a method for a terminal to perform a handover.

[0107] Referring to FIG. 9, the terminal (920) can transmit an RRC message containing the capabilities of the terminal (920) to the first transmission / reception point (910) (S910). Upon receiving the RRC message containing the capabilities of the terminal (920), the first transmission / reception point (910) can transmit an RRC message containing information instructing 'terminal-based TA acquisition' to the terminal (920) (S920). A message instructing the terminal (920) on the timing advance acquisition method can also be transmitted via MAC-CE or an RRC message. The first transmission / reception point (910) can transmit information elements instructing the downlink transmission timing difference for surrounding cells to the terminal (920) (S930).

[0108] A terminal (920) that has received an RRC message containing information instructing a 'terminal-based TA measurement' from a first transmission / reception point (910) can receive SSBs from transmission / reception points including surrounding cells, such as second, third, and fourth transmission / reception points (S940). The terminal (920) can measure TA values ​​itself by performing cross-correlation on the received SSBs (S950). Since the terminal (920) has received information elements instructing a downlink transmission timing difference for surrounding cells from the first transmission / reception point (910), the terminal (920) may not perform the procedure of reporting the TA values ​​measured by the terminal to the first transmission / reception point (910).

[0109] The first transmission / reception point (910) can transmit a cell switch command to the terminal (920) (S960). The cell switch command transmitted by the first transmission / reception point (910) may not include information indicating a TA value. The terminal (920) can receive the cell switch command from the first transmission / reception point (910). Upon receiving the cell switch command, the terminal (920) can establish a connection for data transmission / reception with the transmission / reception point belonging to the target cell (S970).

[0110] FIG. 10 is a flowchart illustrating embodiments of a method for a terminal to perform a handover.

[0111] Referring to FIG. 10, the terminal (1020) can transmit an RRC message containing the capabilities of the terminal (1020) to the first transmission / reception point (1010) (S1010). The first transmission / reception point (1010), having received the RRC message containing the capabilities of the terminal (1020) from the terminal (1020), can transmit information elements indicating a downlink transmission timing difference for a surrounding cell to the terminal (1020) (S1020).

[0112] A terminal (1020) that has received information elements indicating a downlink transmission timing difference for surrounding cells may receive an SSB from transmission and reception points (e.g., a second transmission and reception point, a third transmission and reception point, a fourth transmission and reception point) included in the surrounding cells (S1030). The terminal (1020) that has received the SSB may not immediately perform a procedure to obtain a TA value by performing cross-correlation on the SSB. This may be because a large amount of power may be consumed in the procedure for the terminal (1020) to obtain a TA value for the surrounding cells.

[0113] The first transmitting / receiving point (1010) can transmit a cell switch command to the terminal (1020) (S1040). The transmitted cell switch command may include information elements indicating a cell ID, a beam index, and a terminal-based TA measurement. Upon receiving the cell switch command from the first transmitting / receiving point (1010), the terminal (1020) can perform a procedure to measure the TA values ​​for surrounding cells (S1050). The terminal (1020) can use the measured TA values ​​to establish a new connection with the transmitting / receiving point belonging to the target cell (S1060).

[0114] As previously discussed, the present disclosure may present a 'UE-based TA measurement' method and a 'RACH-based TA acquisition' method. The RACH-based TA acquisition method can be distinguished into a RAR method and a RAR-less method. Using only one of the three methods described above may not be efficient. The RACH-based TA acquisition method may be useful when the terminal (1020) is moving at a medium speed. The terminal-based TA measurement method may be useful when the terminal (1020) is moving at a very high speed. When the terminal (1020) performs a handover, it may be necessary to apply all three methods depending on the movement speed of the terminal (1020). Therefore, a method of flexibly selecting and using one of the three methods may be required as needed. A method of flexibly selecting and using one of the three methods will be explained in the description of FIGS. 11 and 12.

[0115] FIG. 11 is a flowchart illustrating embodiments of a method for switching the determination method of Timing Advance.

[0116] Referring to FIG. 11, the transmitting and receiving point (1110) may select various TA measurement methods considering the movement speed of the terminal (1120). The selected TA measurement method may be presented to the terminal (1120) by the transmitting and receiving point (1110). When the terminal (1120) is moving at a medium speed, a RACH-based TA acquisition method may be useful. When the terminal (1120) is moving at a very high speed, a terminal-based TA measurement method may be useful.

[0117] The transmitting and receiving point (1110) can transmit a MAC CE (Medium Access Control Control Element) instructing the terminal (1120) to activate TA measurement (S1110). The transmitted MAC CE may include a field instructing a RACH-based TA acquisition method using RAR-less mode. The terminal (1120) that receives the MAC CE can set the TA acquisition method to a 'RACH-based TA acquisition method using RAR-less mode' (S1120).

[0118] The transmitting and receiving point (1110) may transmit a MAC CE instructing the terminal (1120) to disable TA measurement (S1130). The transmitted MAC CE may include a field instructing a RACH-based TA acquisition method using RAR-less mode. Upon receiving the MAC CE, the terminal (1120) may disable the 'RACH-based TA acquisition method using RAR-less mode' (S1140).

[0119] The MAC CE transmitted by the transmitting and receiving point (1110) to the terminal (1120) may include fields such as those in [Table 4] below.

[0120] MAC-CE index field Enable / Disable Terminal-based TA measurement / RACH-based TA acquisition using RAR-less / RACH-based TA acquisition using RAR

[0121] FIG. 12 is a flowchart illustrating embodiments of a method for switching the determination method of Timing Advance.

[0122] Referring to FIG. 12, the transmitting and receiving point (1210) may transmit a MAC CE instructing the terminal (1220) to enable TA measurement (S1210). The transmitted MAC CE may include a field instructing a RACH-based TA acquisition method using RAR-less mode. Upon receiving the MAC CE, the terminal (1220) may set the TA acquisition method to a 'RACH-based TA acquisition method using RAR-less mode' (S1220).

[0123] The transmitting and receiving point (1210) may transmit a MAC CE instructing the terminal (1220) to activate TA measurement (S1230). The transmitted MAC CE may include a field instructing a terminal-based TA measurement method. Upon receiving the MAC CE, the terminal (1220) may disable the 'RACH-based TA acquisition method using RAR-less mode' and then activate the terminal-based TA measurement method (S1240).

[0124] In this way, the transmitting and receiving point (1210) can enable the terminal (1220) to automatically disable the TA measurement method it previously used by transmitting a MAC CE that instructs the terminal to activate the TA measurement method, without transmitting a MAC CE that instructs the terminal to disable the TA measurement method to the terminal (1220).

[0125] Some aspects of the present disclosure have been described in the context of a device, but may also be described according to 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 according to 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 of the most important method steps may be performed by such a device.

[0126] In the embodiments, 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 herein. In the embodiments, a field-programmable gate array may operate with a microprocessor to perform one of the methods described herein. Generally, it is preferable that the methods be performed by some hardware device.

[0127] Although the present disclosure has been described with reference to preferred embodiments, those skilled in the art will understand that various modifications and changes can be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the following claims.

Claims

Claim 1 A method of a terminal comprising: receiving a message instructing to obtain a terminal-based Timing Advance (TA) from a first Transmission and Reception Point (TRP) connected to the terminal; receiving a Synchronization Signal Block (SSB) from one or more transmission and reception points belonging to a surrounding cell according to the instruction of the first transmission and reception point; determining a Timing Advance based on the SSB; transmitting the Timing Advance to the first transmission and reception point; receiving a Cell Switch Command from the first transmission and reception point; and establishing a connection with a second transmission and reception point selected according to the Cell Switch Command among the one or more transmission and reception points belonging to the surrounding cell. Claim 2 A method of a terminal according to claim 1, wherein the message indicating the acquisition of a terminal-based timing advance is a MAC-CE (Medium Access Control Element). Claim 3 A method of a terminal according to claim 1, comprising the step of transmitting capability information of the terminal to the first transmitting and receiving point before receiving a message instructing the acquisition of the terminal-based timing advance. Claim 4 A method of a terminal according to claim 3, wherein the capability information of the terminal comprises at least one of information on the number of times the terminal can perform cross-correlation on a received SSB or information on the update capability for a timing advance determined based on the cross-correlation. Claim 5 A method of a terminal according to claim 1, comprising the step of receiving the message instructing to acquire a terminal-based timing advance, and then disabling a RACH (Random Access Channel) based timing advance acquisition method using a RAR-less (Random Access Response less) mode. Claim 6 A method of a terminal according to claim 1, wherein the timing advance is determined by the terminal performing a cross-correlation operation with respect to the SSB. Claim 7 A method of a terminal according to claim 1, wherein the cell switch command comprises at least one of a MAC-CE index field, a cell ID field, a beam index field, a TA field, or a terminal-based TA measurement instruction field. Claim 8 A method of a first transmission and reception point (TRP), comprising: receiving capability information of a terminal from a terminal connected to the first transmission and reception point; transmitting a message to the terminal instructing it to acquire a terminal-based timing advance; receiving timing advances for one or more transmission and reception points belonging to a surrounding cell of the terminal from the terminal; and transmitting a cell switch command to the terminal instructing the terminal to establish a connection with a second transmission and reception point belonging to the surrounding cell. Claim 9 A method of a first transmitting and receiving point, wherein the message indicating the acquisition of a terminal-based timing advance is a MAC-CE (Medium Access Control Element). Claim 10 A method of a first transmitting and receiving point according to claim 8, wherein the step of transmitting a message instructing the terminal to acquire a terminal-based timing advance is performed when the first transmitting and receiving point receives capability information of the terminal, and the terminal is moving at a speed greater than or equal to a threshold or there is a request from the terminal. Claim 11 A method of a first transmission and reception point according to claim 8, comprising the step of determining a first timing advance by reflecting a downlink transmission timing difference (Downlink TX timing difference) in the timing advance after receiving the timing advance. Claim 12 A method of a first transmitting and receiving point according to claim 8, wherein the cell switch command comprises at least one of a MAC-CE (Medium Access Control-Control Element) index field, a cell ID field, a beam index field, a TA field, or a terminal-based TA measurement instruction field. Claim 13 A method of a first transmission and reception point according to claim 12, wherein the TA field includes information indicating a first timing advance in which a downlink transmission timing difference (Downlink TX timing difference) is reflected in the timing advance. Claim 14 A terminal comprising at least one processor, wherein the at least one processor causes the terminal to receive a message instructing it to obtain a terminal-based Timing Advance (TA) from a first Transmission and Reception Point (TRP) connected to the terminal, receive a Synchronization Signal Block (SSB) from one or more transmission and reception points belonging to a surrounding cell in accordance with the instruction of the first transmission and reception point, determine a Timing Advance based on the SSB, transmit the Timing Advance to the first transmission and reception point, receive a Cell Switch Command from the first transmission and reception point, and cause it to establish a connection with a second transmission and reception point selected in accordance with the Cell Switch Command among the one or more transmission and reception points belonging to the surrounding cell. Claim 15 In claim 14, the terminal, wherein the message indicating the acquisition of a terminal-based timing advance is a MAC-CE (Medium Access Control Control Element). Claim 16 In claim 14, the at least one processor further causes the terminal to transmit capability information of the terminal to the first transmitting and receiving point before receiving a message instructing the terminal-based timing advance acquisition. Claim 17 The terminal according to claim 16, wherein the capability information of the terminal comprises at least one of information on the number of times the terminal can perform cross-correlation on a received SSB or information on the update capability for a timing advance determined based on the cross-correlation. Claim 18 In claim 14, the at least one processor further causes the terminal to disable a RACH (Random Access Channel) based timing advance acquisition method using a RAR-less (Random Access Response less) mode after receiving a message instructing the terminal to acquire a terminal-based timing advance. Claim 19 In claim 14, the timing advance is determined by the terminal performing cross-correlation on the SSB. Claim 20 The terminal according to claim 14, wherein the cell switch command comprises at least one of a MAC-CE (Medium Access Control-Control Element) index field, a cell ID field, a beam index field, a TA field, or a terminal-based TA measurement instruction field.

Images