Method and device for managing mobility in wireless communication system

Abstract

The present disclosure relates to a method for reducing a handover interruption time on the basis of an LTM procedure. When a time difference value between a point in time at which whether to transmit a message requesting a handover command is determined and a first L1 connection quality measurement result report resource after the point in time is smaller than a threshold value, a cell change request message is transmitted as a handover request message before a point in time at which the resource is configured.

Description

Method and device for mobility management in a wireless communication system

[0001] The present disclosure relates generally to wireless communication systems, and more specifically to methods and devices for managing mobility.

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

[0003] The 6G communication system, which is expected to be realized around 2030, has a maximum transmission speed of Tera (1000 gigabit) bps (bit per second) and a wireless delay time of 100 microseconds (μsec), making it 50 times faster than the 5G communication system and reducing the wireless delay time to one-tenth.

[0004] To achieve these high data rates and ultra-low latency, 6G communication systems are being considered for implementation in terahertz bands (e.g., 95 gigahertz (GHz) to 3 terahertz (THz)). Compared to the millimeter wave (mmWave) band introduced for 5G, the terahertz band suffers from more severe path loss and atmospheric absorption, making it increasingly important to ensure signal reach, or coverage, in this band. Key technologies to ensure coverage include RF (Radio Frequency) components, antennas, new waveforms that offer better coverage than OFDM (Orthogonal Frequency Division Multiplexing), beamforming, and multiple antenna transmission technologies such as massive MIMO, full-dimensional MIMO (FD-MIMO), array antennas, and large-scale antennas. In addition, new technologies such as metamaterial-based lenses and antennas, high-dimensional spatial multiplexing using Orbital Angular Momentum (OAM), and Reconfigurable Intelligent Surfaces (RIS) are being discussed to improve the coverage of terahertz band signals.

[0005] In addition, in order to improve frequency efficiency and system network, 6G communication systems are developing full duplex technology that allows uplink (terminal transmission) and downlink (base station transmission) to utilize the same frequency resources at the same time; network technology that integrates satellites and HAPS (High-altitude Platform Stations), network structure innovation technology that supports mobile base stations and enables optimization and automation of network operation, dynamic spectrum sharing technology through collision avoidance based on spectrum usage prediction, AI-based communication technology that utilizes AI from the technology design stage and internalizes end-to-end AI support functions to realize system optimization, and next-generation distributed computing technology that realizes services with complexity that exceeds the limits of terminal computing capabilities by utilizing ultra-high-performance communication and computing resources (MEC, cloud, etc.). In addition, efforts are being made to further strengthen connectivity between devices, further optimize networks, promote softwareization of network entities, and increase the openness of mobile communications through the design of new protocols to be used in 6G communication systems, the implementation of hardware-based security environments, the development of mechanisms for the safe use of data, and the development of technologies for maintaining privacy.

[0006] Research and development of these 6G communication systems are expected to enable a new level of hyper-connected experience (The Next Hyper-Connected Experience) through the hyper-connectivity of 6G communication systems, which encompass not only connections between things but also connections between people and things. Specifically, 6G communication systems are expected to enable services such as truly immersive extended reality (XR), high-fidelity mobile holograms, and digital replicas. Furthermore, services such as remote surgery, industrial automation, and emergency response, which are provided through 6G communication systems through enhanced security and reliability, will find application in diverse fields such as industry, medicine, automobiles, and home appliances.

[0007] In particular, due to the short packet arrival time of uplink (UL) XR (extended reality) traffic, when the UL transmission cycle and the UL traffic arrival cycle are similar, the conventional technique of allocating a UL grant only to a single hybrid automatic repeat and request (HARQ) process may cause additional delay time. To solve the above-mentioned problems and ensure smooth communication between the base station and the terminal, various technologies related to uplink transmission and retransmission are being considered.

[0008] Based on the discussion described above, the present disclosure seeks to provide a device and method capable of performing effective signal transmission and reception in a wireless communication system.

[0009] More specifically, the present disclosure provides a device and method for performing a handover based on an LTM procedure according to a terminal request.

[0010] According to various embodiments of the present disclosure, in a wireless communication system, a method performed by a terminal comprises the steps of: receiving, from a base station, a radio resource control (RRC) reconfiguration message related to a Layer 1 (L1) / Layer 2 (L2) triggered mobility (L1 / L2) procedure, the RRC reconfiguration message including information on a condition for determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold for determining a method of transmitting the message requesting the handover command; performing L1 link quality measurement based on the LTM procedure for the base station and at least one candidate base station; determining whether to transmit the message requesting the handover command based on the condition for determining whether to transmit the message requesting the handover command; and determining, if it is determined to transmit the message requesting the handover command, a method of transmitting the message requesting the handover command based on the threshold. And, based on the determined method, including a step of transmitting a message requesting the handover command to the base station, wherein, if a time difference between a time point at which it is determined whether to transmit the message requesting the handover command and the first L1 connection quality measurement result report resource after the time point is less than the threshold value, a cell change request message may be transmitted as a message requesting the handover command before the time point at which the first L1 connection quality measurement result report resource is set.

[0011] In addition, according to various embodiments of the present disclosure, a method performed by a base station in a wireless communication system, the method comprising: transmitting, to a user equipment, a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility (LTM)) procedure triggered by Layer 1 (L1) / Layer 2 (L2), the RRC reconfiguration message including information on a condition related to determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold related to determining a method of transmitting the message requesting the handover command; A method for requesting a handover command is determined based on a condition related to determining whether to transmit a message requesting a handover command and a threshold value, and a step of receiving a message requesting the handover command from the terminal, wherein, if a time difference between a time point at which it is determined whether to transmit a message requesting the handover command and a first L1 connection quality measurement result reporting resource after the time point is less than the threshold value, a cell change request message may be received as a message requesting the handover command before a time point at which the first L1 connection quality measurement result reporting resource is set.

[0012] Additionally, according to various embodiments of the present disclosure, in a wireless communication system, a terminal (user equipment) includes: a transceiver; And a controller connected to the transceiver, wherein the controller receives, from a base station, a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2), and the RRC reconfiguration message includes information on a condition for determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold for determining a method of transmitting the message requesting the handover command, and performs L1 link quality measurement based on the LTM procedure for the base station and at least one candidate base station, and determines whether to transmit the message requesting the handover command based on the condition for determining whether to transmit the message requesting the handover command, and when it is determined to transmit the message requesting the handover command, determines a method of transmitting the message requesting the handover command based on the threshold, and transmits the message requesting the handover command to the base station based on the determined method. However, if the time difference between the time at which it is determined whether to transmit a message requesting the handover command and the first L1 connection quality measurement result reporting resource after the time at which the transmission is determined is less than the threshold value, a cell change request message may be transmitted as a message requesting the handover command before the time at which the first L1 connection quality measurement result reporting resource is set.

[0013] Additionally, according to various embodiments of the present disclosure, in a wireless communication system, a base station comprises: a transceiver; And a controller connected to the transceiver, wherein the controller transmits, to a user equipment, a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2), and the RRC reconfiguration message includes information on a condition related to determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold related to determining a method of transmitting the message requesting the handover command, and is configured to receive, from the user equipment, a message requesting the handover command based on a method determined based on the condition related to determining whether to transmit the message requesting the handover command and the threshold, wherein when a time difference value between a time point at which it is determined whether to transmit the message requesting the handover command and a first L1 connection quality measurement result reporting resource after the time point is less than the threshold value, a cell change request message is transmitted before a time point at which the first L1 connection quality measurement result reporting resource is set. It can be received as a message requesting the above handover command.

[0014] The present disclosure has the effect of providing a device and method capable of effectively providing a service in a wireless communication system.

[0015] The present disclosure has the effect of reducing downtime in handover based on an LTM procedure in a wireless communication system.

[0016] The effects that can be obtained from the present disclosure are not limited to the effects mentioned in the various embodiments, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure belongs from the description below.

[0017] FIG. 1 illustrates a wireless environment network in a wireless communication system according to various embodiments of the present disclosure.

[0018] FIG. 2 illustrates a functional configuration of a base station in a wireless communication system according to various embodiments of the present disclosure.

[0019] FIG. 3 illustrates a functional configuration of a terminal in a wireless communication system according to various embodiments of the present disclosure.

[0020] FIG. 4 illustrates an example of a wireless resource region in a wireless communication system according to embodiments of the present disclosure.

[0021] FIG. 5 is a flowchart illustrating an example of L3 handover according to various embodiments of the present disclosure.

[0022] FIG. 6 is a diagram illustrating an example of a downtime occurring in an L3 handover procedure according to various embodiments of the present disclosure.

[0023] FIG. 7 is a diagram illustrating an example of an LTM procedure according to various embodiments of the present disclosure.

[0024] FIG. 8 is a diagram illustrating an example of additional downtime resulting from periodic L1 measurement reporting in an LTM procedure, according to various embodiments of the present disclosure.

[0025] FIG. 9 is a diagram illustrating an example of an LTM procedure according to various embodiments of the present disclosure.

[0026] FIG. 10 is a diagram illustrating an example of a method for configuring information through PUCCH format 0 according to various embodiments of the present disclosure.

[0027] FIG. 11 illustrates an example of a method for indicating LTM candidate cells through PUCCH format 0 according to various embodiments of the present disclosure.

[0028] FIG. 12 and FIG. 13 are diagrams showing an example of a method for indicating an LTM candidate cell through PUCCH format 0 according to various embodiments of the present disclosure.

[0029] FIG. 14 is a diagram illustrating an example of an LTM procedure according to various embodiments of the present disclosure.

[0030] FIG. 15 is a flowchart showing an example of a method of operating a terminal according to various embodiments of the present disclosure.

[0031] FIG. 16 is a flowchart illustrating an example of a method of operating a base station according to various embodiments of the present disclosure.

[0032] The terms used in this disclosure are used only to describe specific embodiments and may not be intended to limit the scope of other embodiments. The singular expression may include the plural expression unless the context clearly indicates otherwise. Terms used, including technical or scientific terms, may have the same meaning as commonly understood by those of ordinary skill in the art described in this disclosure. Terms used in this disclosure that are defined in general dictionaries may be interpreted as having the same or similar meaning as the meaning they have in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined in this disclosure. In some cases, even if a term is defined in this disclosure, it cannot be interpreted to exclude embodiments of the present disclosure.

[0033] The various embodiments of the present disclosure described below illustrate hardware-based approaches. However, since the various embodiments of the present disclosure include technologies utilizing both hardware and software, the various embodiments of the present disclosure do not exclude software-based approaches. Furthermore, terms referring to network entities, terms referring to device components, and the like are provided for convenience of explanation. Therefore, the present disclosure is not limited to the terms described below, and other terms with equivalent technical meanings may be used.

[0034] Additionally, although this disclosure describes various embodiments using terms defined by certain communication standards (e.g., 3rd generation partnership project (3GPP) and European Telecommunication Standards Institute (ETSI)), these are merely illustrative examples. The various embodiments of this disclosure can be easily modified and applied to other communication systems.

[0035] Additionally, in the present disclosure, expressions such as "more than" or "less than" may be used to determine whether a specific condition is satisfied or fulfilled. However, this is merely a description for expressing an example and does not exclude descriptions of more than or less than. Conditions described as "more than" may be replaced with "more than," conditions described as "less than" may be replaced with "less than," and conditions described as "more than and less than" may be replaced with "more than and less than."

[0036] The terms used in the following description, including terms referring to signals, channels, control information, network entities, and device components, are provided for convenience of explanation. Therefore, the present disclosure is not limited to the terms described below, and other terms with equivalent technical meanings may be used.

[0037] 5G systems must support services that simultaneously satisfy diverse requirements, allowing them to freely reflect the diverse needs of users and service providers. Services being considered for 5G systems include enhanced mobile broadband (eMBB), massive machine type communication (mMTC), and ultra-reliable and low-latency communication (URLLC).

[0038] eMBB aims to provide data transmission rates that are significantly higher than those supported by existing LTE, LTE-A, or LTE-Pro. For example, in a 5G system, eMBB must be able to support a peak data rate of 20 Gbps in the downlink and a peak data rate of 10 Gbps in the uplink from the perspective of a single base station. Furthermore, 5G systems must provide both peak data rates and increased user-perceived data rates. To meet these requirements, improvements in various transmission and reception technologies, including improved multi-input, multi-output (MIMO) transmission technologies, may be required. Furthermore, while LTE systems transmit signals using a maximum 20 MHz transmission bandwidth in the 2 GHz band, 5G systems can use a wider bandwidth than 20 MHz in the 3 to 6 GHz or higher frequency bands, thereby meeting the data transmission rates required by 5G communication systems.

[0039] At the same time, mMTC is being considered to support application services such as the Internet of Things (IoT) in 5G systems. To efficiently provide the IoT, mMTC requires supporting large-scale terminal connections within a cell, improved terminal coverage, improved battery life, and reduced terminal costs. The IoT requires the ability to support a large number of terminals (e.g., 1,000,000 terminals / km2) within a cell, as it connects to various sensors and devices to provide communication functions. Furthermore, terminals supporting mMTC are likely to be located in shadow areas, such as basements, beyond cell coverage due to the nature of the service, requiring wider coverage than other services provided by 5G communication systems. Terminals supporting mMTC must be comprised of low-cost terminals, and since frequent battery replacement is difficult, they require extremely long battery lifespans, such as 10 to 16 years.

[0040] Finally, URLLC refers to cellular-based wireless communication services used for mission-critical purposes. Examples include remote control of robots or machinery, industrial automation, unmanaged aerial vehicles, remote health care, or emergency alerts. Therefore, URLLC communications must provide extremely low latency and high reliability. For example, services supporting URLLC must meet air interface latency requirements of less than 0.5 milliseconds and a packet error rate of less than 10-5. Therefore, for services supporting URLLC, 5G systems must provide shorter transmit time intervals (TTIs) than other services, while simultaneously allocating ample resources in the frequency band to ensure the reliability of the communication link.

[0041] Furthermore, data traffic from the three aforementioned services—eMBB, URLLC, and mMTC—can be multiplexed and transmitted within the 5G and / or 6G systems. To meet the varying requirements of each service, different transmission and reception techniques and parameters may be used across the services.

[0042] FIG. 1 illustrates a wireless environment network in a wireless communication system according to various embodiments of the present disclosure. FIG. 1 illustrates a base station (110), a first terminal (120), and a second terminal (130) as some of the nodes utilizing a wireless channel in the wireless communication system. While FIG. 1 illustrates only one base station, other base stations identical to or similar to the base station (110) may be included.

[0043] The base station (110) is a network infrastructure that provides wireless access to terminals (120, 130). The base station (110) has coverage defined as a certain geographical area based on the distance at which a signal can be transmitted. In addition to the base station, the base station (110) includes an 'access point (AP)', an 'eNodeB (eNB)', and a '5G node (5 th It may be referred to as 'next generation node (gNB)', 'wireless point', 'transmission / reception point (TRP)' or other terms having equivalent technical meaning.

[0044] Each of the first terminal (120) and the second terminal (130) is a device used by a user and communicates with the base station (110) via a wireless channel. In some cases, at least one of the first terminal (120) and the second terminal (130) may be operated without the involvement of the user. That is, at least one of the first terminal (120) and the second terminal (130) is a device that performs machine type communication (MTC) and may not be carried by the user. Each of the first terminal (120) and the second terminal (130) may be referred to as a 'user equipment (UE)', a 'mobile station', a 'subscriber station', a 'remote terminal', a 'wireless terminal', a 'user device', or other terms having an equivalent technical meaning thereto.

[0045] The base station (110), the first terminal (120), and the second terminal (130) can transmit and receive wireless signals in the millimeter wave (mmWave) band (e.g., 28 GHz, 30 GHz, 38 GHz, 60 GHz). At this time, in order to improve channel gain, the base station (110), the first terminal (120), and the second terminal (130) can perform beamforming. Here, the beamforming can include transmission beamforming and reception beamforming. That is, the base station (110), the first terminal (120), and the second terminal (130) can provide directionality to a transmission signal or a reception signal. To this end, the base station (110) and the terminals (120, 130) can select serving beams through a beam search or beam management procedure. After serving beams are selected, subsequent communications can be performed through resources that are in a quasi-co-located (QCL) relationship with the resource that transmitted the serving beams.

[0046] If large-scale characteristics of a channel carrying a symbol on a first antenna port can be inferred from a channel carrying a symbol on a second antenna port, the first antenna port and the second antenna port can be evaluated to have a QCL relationship. For example, the large-scale characteristics may include at least one of delay spread, Doppler spread, Doppler shift, average gain, average delay, and a spatial receiver parameter.

[0047] FIG. 2 illustrates the functional configuration of a base station in a wireless communication system according to various embodiments of the present disclosure. The configuration illustrated in FIG. 2 may be understood as the configuration of a base station (110). Terms such as "... unit" and "... unit" used hereinafter refer to a unit that processes at least one function or operation, which may be implemented using hardware, software, or a combination of hardware and software.

[0048] Referring to FIG. 2, the base station includes a wireless communication unit (210), a backhaul communication unit (220), a storage unit (230), and a control unit (240).

[0049] The wireless communication unit (210) performs functions for transmitting and receiving signals via a wireless channel. For example, the wireless communication unit (210) performs a conversion function between baseband signals and bit streams according to the physical layer specifications of the system. For example, when transmitting data, the wireless communication unit (210) encodes and modulates the transmitted bit stream to generate complex symbols. Additionally, when receiving data, the wireless communication unit (210) restores the received bit stream by demodulating and decoding the baseband signal.

[0050] In addition, the wireless communication unit (210) upconverts a baseband signal into an RF (radio frequency) band signal and transmits it through an antenna, and downconverts an RF band signal received through the antenna into a baseband signal. To this end, the wireless communication unit (210) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital to analog convertor (DAC), an analog to digital convertor (ADC), etc. In addition, the wireless communication unit (210) may include a plurality of transmission and reception paths. Furthermore, the wireless communication unit (210) may include at least one antenna array composed of a plurality of antenna elements.

[0051] In terms of hardware, the wireless communication unit (210) may be composed of a digital unit and an analog unit, and the analog unit may be composed of a plurality of sub-units depending on operating power, operating frequency, etc. The digital unit may be implemented with at least one processor (e.g., a digital signal processor (DSP)).

[0052] The wireless communication unit (210) transmits and receives signals as described above. Accordingly, all or part of the wireless communication unit (210) may be referred to as a "transmitter," a "receiver," or a "transceiver." Furthermore, in the following description, transmission and reception performed via a wireless channel are used to mean that the wireless communication unit (210) performs the processing described above.

[0053] The backhaul communication unit (220) provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit (220) converts a bit string transmitted from a base station to another node, such as another access node, another base station, an upper node, a core network, etc., into a physical signal, and converts a physical signal received from another node into a bit string.

[0054] The storage unit (230) stores data such as basic programs, application programs, and setting information for the operation of the base station. The storage unit (230) may be composed of volatile memory, non-volatile memory, or a combination of volatile and non-volatile memory. In addition, the storage unit (230) provides stored data upon request from the control unit (240).

[0055] The control unit (240) (or controller) controls the overall operations of the base station. For example, the control unit (240) transmits and receives signals through the wireless communication unit (210) or the backhaul communication unit (220). In addition, the control unit (240) records and reads data in the storage unit (230). In addition, the control unit (240) can perform the functions of the protocol stack required by the communication standard. According to another implementation example, the protocol stack can be included in the wireless communication unit (210). To this end, the control unit (240) can include at least one processor.

[0056] According to various embodiments, the control unit (240) can control the base station to perform operations according to various embodiments described below.

[0057] FIG. 3 illustrates the functional configuration of a terminal in a wireless communication system according to various embodiments of the present disclosure. The configuration illustrated in FIG. 3 may be understood as the configuration of terminals (120, 130). Terms such as "...unit" and "...unit" used hereinafter refer to a unit that processes at least one function or operation, which may be implemented using hardware, software, or a combination of hardware and software.

[0058] Referring to FIG. 3, the terminal includes a communication unit (310), a storage unit (320), and a control unit (330).

[0059] The communication unit (310) performs functions for transmitting and receiving signals via a wireless channel. For example, the communication unit (310) performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the system. For example, when transmitting data, the communication unit (310) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the communication unit (310) restores a reception bit stream by demodulating and decoding the baseband signal. In addition, the communication unit (310) upconverts a baseband signal to an RF band signal and transmits it through an antenna, and downconverts an RF band signal received through the antenna to a baseband signal. For example, the communication unit (310) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc.

[0060] In addition, the communication unit (310) may include a plurality of transmission and reception paths. Furthermore, the communication unit (310) may include at least one antenna array composed of a plurality of antenna elements. In terms of hardware, the communication unit (310) may be composed of digital circuits and analog circuits (e.g., radio frequency integrated circuits (RFIC)). Here, the digital circuits and analog circuits may be implemented in a single package. In addition, the communication unit (310) may include a plurality of RF chains. Furthermore, the communication unit (310) may perform beamforming.

[0061] The communication unit (310) transmits and receives signals as described above. Accordingly, all or part of the communication unit (310) may be referred to as a "transmitter," a "receiver," or a "transmitting and receiving unit." Furthermore, in the following description, transmission and reception performed via a wireless channel are used to mean processing performed by the communication unit (310) as described above.

[0062] The storage unit (320) stores data such as basic programs, application programs, and setting information for the operation of the terminal. The storage unit (320) may be composed of volatile memory, non-volatile memory, or a combination of volatile and non-volatile memory. In addition, the storage unit (320) provides stored data upon request from the control unit (330).

[0063] The control unit (330) (or controller) controls the overall operations of the terminal. For example, the control unit (330) transmits and receives signals through the communication unit (310). In addition, the control unit (330) records and reads data in the storage unit (320). In addition, the control unit (330) can perform the functions of the protocol stack required by the communication standard. To this end, the control unit (330) may include at least one processor or microprocessor, or may be a part of a processor. In addition, a part of the communication unit (310) and the control unit (330) may be referred to as a CP (communication processor).

[0064] According to various embodiments, the control unit (330) can control the terminal to perform operations according to various embodiments described below.

[0065] FIG. 4 illustrates an example of a wireless resource region in a wireless communication system according to embodiments of the present disclosure. In various embodiments of the present disclosure, the wireless resource region may include a structure in the time-frequency domain. In one embodiment, the wireless communication system may include an NR communication system.

[0066] Referring to Fig. 4, in the wireless resource domain, the horizontal axis represents the time domain, and the vertical axis represents the frequency domain. The length of a radio frame (404) is 10 ms. The radio frame (404) may be a time domain section composed of 10 subframes. The length of a subframe (403) is 1 ms. The unit of configuration in the time domain may be an OFDM (orthogonal frequency division multiplexing) and / or a DFT-s-OFDM (DFT (discrete Fourier transform)-spread-OFDM) symbol, and N symb OFDM and / or DFT-s-OFDM symbols (401) may be grouped to form one slot (402). According to various embodiments of the present disclosure, an OFDM symbol may include a symbol for transmitting and receiving a signal using an OFDM multiplexing scheme, and a DFT-s-OFDM symbol may include a symbol for transmitting and receiving a signal using a DFT-s-OFDM or SC-FDMA (single carrier frequency division multiple access) multiplexing scheme. The minimum transmission unit in the frequency domain is a subcarrier, and the carrier bandwidth constituting the resource grid is a total of N scBW It may be composed of subcarriers (405). In addition, in the present disclosure, an embodiment regarding downlink signal transmission and reception is described for convenience of explanation, but this can also be applied to an embodiment regarding uplink signal transmission and reception.

[0067] According to one embodiment, the number of slots (402) constituting one subframe (403) and the length of the slots (402) may vary depending on the subcarrier spacing. This subcarrier spacing may be referred to as a numerology (μ). For example, the subcarrier spacing, the number of slots included in a subframe, the length of the slots, and the length of the subframe may be configured variably. For example, in an NR communication system, when the subcarrier spacing (SCS) is 15 kHz, one slot (402) constitutes one subframe (403), and the lengths of the slot (402) and the subframe (403) may each be 1 ms. In addition, for example, when the subcarrier spacing is 30 kHz, two slots may constitute one subframe (403). In this case, the length of the slot is 0.5 ms and the length of the subframe is 1 ms.

[0068] In one embodiment, the subcarrier spacing, the number of slots included in a subframe, the length of the slot, and the length of the subframe may be variably applied depending on the communication system. For example, in the case of an LTE system, the subcarrier spacing may be 15 kHz, two slots may constitute one subframe, and in this case, the length of the slot may be 0.5 ms and the length of the subframe may be 1 ms. As another example, in the case of an NR system, the subcarrier spacing (μ) may be one of 15 kHz, 30 kHz, 60 kHz, 120 kHz, 240 kHz, 480 kHz, and 960 kHz, and the number of slots included in one subframe depending on the subcarrier spacing (μ) may be 1, 2, 4, 8, 16, 32, and 64.

[0069] The basic unit of resources in the time-frequency domain may be a resource element (RE) (406), and the resource element (406) may be expressed by an OFDM symbol index and a subcarrier index. A resource block may include a plurality of resource elements. In an NR system, a resource block (RB) (or physical resource block (PRB)) (407) may be N in the frequency domain. SC RB can be defined as a series of consecutive subcarriers. The number of subcarriers N SC RB =12 can be. The frequency domain can include common resource blocks (CRBs). Physical resource blocks (PRBs) can be defined in the bandwidth part (BWP) of the frequency domain. The CRB and PRB numbers can be determined differently depending on the subcarrier spacing. In the LTE system, RBs are N in the time domain. symb It can be defined as a sequence of consecutive OFDM symbols and NSCRB consecutive subcarriers in the frequency domain.

[0070] In NR and / or LTE systems, scheduling information for downlink data or uplink data may be transmitted from a base station (110) to a terminal (120) via downlink control information (DCI). According to various embodiments of the present disclosure, DCI may be defined according to various formats, and each format may indicate whether the DCI includes scheduling information for uplink data (e.g., UL grant), scheduling information for downlink data (DL resource allocation), whether it is compact DCI with small control information size, whether it is fall-back DCI, whether spatial multiplexing using multiple antennas is applied, and / or whether it is DCI for power control. For example, NR DCI format 1_0 or NR DCI format 1_1 may include scheduling for downlink data. Also, for example, NR DCI format 0_0 or NR DCI format 0_1 ​​may include scheduling for uplink data.

[0071] As described above, FIG. 4 illustrates an example of a downlink and uplink slot structure in a wireless communication system. In particular, FIG. 4 illustrates the structure of a resource grid of a 3GPP NR system. Referring to FIG. 4, a slot may include a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. A signal may be composed of part or all of the resource grid. In addition, the number of OFDM symbols included in a slot may generally vary depending on the length of a cyclic prefix (CP). In FIG. 4, for convenience of explanation, a case in which a slot is composed of 14 OFDM symbols is illustrated, but the signal referred to in the present disclosure does not specify the symbol configuration. In addition, the modulation method of the generated signal is not limited to a specific value of QAM (Quadrature Amplitude Modulation), and can follow the modulation methods of various communication standards, such as BPSK (Binary phase-shift keying) and QPSK (Quadrature Phase Shift Keying).

[0072] According to various embodiments of the present disclosure, operations for controlling uplink retransmission for efficient signal transmission are described based on an LTE communication system or an NR communication system. However, the contents of the present disclosure are not limited thereto and can be applied to various wireless communication systems for transmitting downlink or uplink control information. Furthermore, it goes without saying that the contents of the present disclosure can be applied to unlicensed bands as well as licensed bands, as needed.

[0073] Hereinafter, in the present disclosure, higher layer signaling or higher signal may be a signal transmission method in which a base station (110) transmits a downlink data channel of a physical layer to a terminal (120), or a terminal (120) transmits a signal to a base station (110) using an uplink data channel of a physical layer. According to one embodiment, the higher layer signaling may include at least one of radio resource control (RRC) signaling, signaling according to an F1 interface between a centralized unit (CU) and a distributed unit (DU), or a signal transmission method transmitted through a medium access control (MAC) control element (MAC CE). In addition, according to one embodiment, the higher layer signaling or higher signal may include system information commonly transmitted to a plurality of terminals (120), for example, a system information block (SIB).

[0074] In a 5G wireless communication system, a synchronization signal block (SSB) (also referred to as an SS block, SS / PBCH block, etc.) may be transmitted for initial access, and the synchronization signal block may be composed of a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a physical broadcast channel (PBCH). In addition, the SSB may include information about a beam that the base station uses to transmit a signal, and the SSB index or SSB described below may mean at least one beam. In the initial access phase when a terminal first accesses the system, the terminal may obtain downlink time and frequency domain synchronization and obtain a cell ID from a synchronization signal through a cell search procedure. The synchronization signal may include a PSS and an SSS. The terminal may receive a PBCH including a master information block (MIB) from the base station to obtain system information and basic parameter values ​​related to transmission and reception, such as system bandwidth or related control information. Based on the received PBCH, the terminal can decode the physical downlink control channel (PDCCH) and physical downlink shared channel (PDSCH) to obtain a system information block (SIB). Afterwards, the terminal can exchange identities with the base station through a random access phase and undergo registration, authentication, and other steps to initially access the network.

[0075] As described above, one slot may include 14 symbols, and according to various embodiments of the present disclosure, the uplink-downlink configuration of symbols and / or slots in a 5G communication system may be set in three stages.

[0076] In the first method, the uplink-downlink of a symbol and / or slot can be configured semi-statically through cell-specific configuration information via system information at the symbol level. More specifically, the cell-specific uplink-downlink configuration information via system information may include uplink-downlink pattern information and reference subcarrier information. The uplink-downlink pattern information may indicate a pattern periodicity, the number of consecutive downlink slots from the start of each pattern, the number of symbols in the next slot, the number of consecutive uplink slots from the end of the pattern, and the number of symbols in the next slot. Slots and symbols that are not indicated as uplink or downlink may be considered flexible slots / symbols.

[0077] In a second way, through user-specific configuration information via dedicated upper layer signaling, a flexible slot or a slot containing flexible symbols can be indicated by the number of consecutive downlink symbols from the start symbol of the slot and the number of consecutive uplink symbols from the end of the slot, or by the entire downlink or the entire uplink of the slot, respectively.

[0078] In a third method, in order to dynamically change the downlink signal transmission and uplink signal transmission sections, symbols indicated as flexible symbols in each slot (e.g., symbols not indicated as downlink or uplink) can be indicated as downlink symbols, uplink symbols, or flexible symbols, through a slot format indicator (SFI) included in a downlink control channel. The slot format indicator can select one index from a table in which an uplink-downlink configuration of 14 symbols in one slot is preset.

[0079] 5G NR supports various mobility management methods for managing the mobility of terminals, and one example of various mobility management methods for managing the mobility of terminals in 5G NR is the L3 handover method.

[0080] FIG. 5 is a flowchart illustrating an example of L3 handover according to various embodiments of the present disclosure. In 5G NR, a base station (gNB) may be composed of two physical entities: a Centralized Unit (CU) and a Distributed Unit (DU). The CU may provide support for upper layers of the protocol stack, such as Service Data Adaptation Protocol (SDAP), Packet Data Convergence Protocol (PDCP), and radio resource control (RRC), while the DU may provide support for lower layers of the protocol stack, such as Radio Link Control (RLC), Medium Access Control (MAC), and the physical layer. A single CU constituting the gNB may control multiple DUs, and each DU of the gNB may support one or more cells. The CU and DU may be connected via an F1 interface.

[0081] In FIG. 5, a source DU (distributed unit) (503), a target DU (505), and a CU (centralized unit) (507) may constitute one base station (gNB), and the CU (507) may be controlled by the source DU (503) and the target DU (507) may be controlled by the CU (507). Since each of the source DU (503) and the target DU (507) may support one or more cells, a handover from the source DU (503) to the target DU (505) may mean a handover from one or more cells supported by the source DU (503) to one or more cells supported by the target DU (505).

[0082] Referring to FIG. 5, a source DU (503) can receive an L3 measurement report measured by the terminal for at least one DU from the terminal (510). The source DU (503) can forward the L3 measurement report received from the terminal to the CU (507) (515). The CU (507) can compare the L3 measurement reports measured for at least one DU to determine whether to perform a handover and which target DU will be the target of the handover (520).

[0083] When the CU (507) determines that a handover is to be performed, the CU (507) may transmit an L3 HO (handover) request (525) to notify the target DU (505) that the handover has been determined to be performed. At this time, the target DU (507) may determine whether to permit the handover by considering the traffic load of the cell supported by the target DU (507), etc.

[0084] If the target DU (505) decides to permit the handover, the target DU (505) may transmit an L3 HO acknowledgement, which is a response to the L3 HO request, to the CU (507) (530). At this time, the L3 HO acknowledgement may indicate that the handover from the source DU (505) to the target DU (507) is permitted. In addition, the L3 HO acknowledgement may include information about the radio resources and other settings used by the terminal (501) to connect to the target DU (507).

[0085] Thereafter, the CU (507) can transmit a UE context modification request including information about wireless resources and other settings used by the terminal (501) to access the target DU (507) to the source DU (503) (535), and the source DU (503) can transmit a UE context modification acknowledge as a response to the UE context modification request to the CU (507) (540).

[0086] Next, the source DU (503) may transmit to the terminal (501) an RRC reconfiguration message containing information about radio resources and other settings that the terminal (501) should use to access the target DU (507), which the source DU (503) received from the CU (507) (545). Thereafter, the source DU (503) may receive an RRC reconfiguration complete message from the terminal (501) (550).

[0087] The terminal (501) that has received information about radio resources and other settings used to connect to the target DU (505) attempts to connect to the target DU (505) through a RACH (random access channel) procedure, and if the connection is successful, the terminal can modify all existing settings configured for communication with the source DU (503) to settings required for communication with the target DU (5050) through RRC reconfiguration. The terminal (501) can disconnect from the source DU (503) and configure a connection so that a cell supported by the target DU (505) can be set as a new cell.

[0088] Referring to FIG. 5, the L3 handover procedure can be divided into four steps, including (1) a step in which the CU determines whether to perform a handover based on an L3 measurement report, (2) a step in which the target DU approves the start of the L3 handover procedure and transmits RRC basic settings for communication with the target DU to the UE, (3) a step in which the UE attempts to connect to the target DU through a RACH procedure, and (4) a step in which the UE resets the radio link settings to match the cell supported by the target DU, terminates the connection with the cell supported by the existing source DU, and selects the cell supported by the target DU as a new serving cell. In this case, in the case of the L3 handover procedure, since steps (1) to (3) may be performed sequentially and then step (4) may be performed, latency, interruption time, signaling overhead, etc. may occur.

[0089] FIG. 6 is a diagram illustrating an example of a downtime occurring in an L3 handover procedure according to various embodiments of the present disclosure.

[0090] Referring to FIG. 6, the interruption time (640) that occurs during handover of a terminal can be defined as the time from the time when the terminal receives a cell change command including information about a target cell from a source cell in a terminal reconfiguration procedure (610), to the time when the terminal transmits the first uplink data after a downlink synchronization procedure (620) and a RACH procedure (UL synchronization (RACH procedure)) (630) for uplink synchronization are performed.

[0091] Conditional handover can be used to reduce the downtime required for the UE reconfiguration procedure, but since the procedures that account for a large portion of the downtime are the downlink synchronization procedure and the uplink synchronization procedure, not the UE reconfiguration procedure, it may be difficult to significantly reduce the downtime through methods such as conditional handover that focus on reducing the time required for the UE reconfiguration procedure.

[0092] Meanwhile, the LTM (L1(layer 1) / L2(layer 2) Triggered Mobility) procedure can be considered as a mobility management method that can significantly reduce the time required for the downlink synchronization procedure and uplink synchronization procedure, which account for a large proportion of the downtime. In the case of the L3 handover procedure, the downlink and uplink synchronization procedures with the target cell are performed after the terminal receives the handover command message, whereas in the case of the LTM procedure, the terminal can synchronize with the target cell in advance through the early synchronization procedure. The downtime that occurs in the procedure for handover from the source cell to the target cell can be significantly reduced through the early synchronization procedure performed in the LTM procedure.

[0093] In addition, in the case of the L3 handover procedure, a handover command message instructing a handover from a source cell to a target cell is generated in the RRC layer based on an L3 measurement report, so a terminal receiving the handover command message must perform L3 layer processing. On the other hand, in the LTM procedure, a handover command message instructing a handover from a source cell to a target cell is generated in the MAC layer based on an L1 measurement report, so a terminal receiving the handover command message does not need to perform L3 layer processing, which has an advantage over the L3 handover procedure in that the downtime can be further reduced.

[0094] Hereinafter, in order to distinguish from the L3 handover procedure in the present disclosure, the mobility management method that can significantly reduce the time required for the downlink synchronization procedure and the uplink synchronization procedure may be referred to as the LTM procedure, the L1 handover procedure, or various expressions that can be interpreted identically or similarly thereto. In addition, in order to distinguish from the L3 handover that changes the serving cell through the L3 handover procedure, the operation of changing the serving cell through the LTM procedure may be referred to as a handover based on the LTM procedure, or various expressions that can be interpreted identically or similarly thereto.

[0095] Below, the LTM procedure is described in detail with reference to Fig. 7.

[0096] FIG. 7 is a diagram illustrating an example of an LTM procedure according to various embodiments of the present disclosure.

[0097] Referring to FIG. 7, an LTM preparation procedure may be performed (710). More specifically, the LTM preparation procedure (710) may include: a UE in an RRC connection state may transmit a measurement result report message to the gNB. At this time, the gNB may establish an LTM procedure and determine the start of LTM preparation. Next, the gNB may transmit an RRC reconfiguration message to the UE, including configurations for LTM candidate cells. Here, the LTM candidate cells may refer to cells other than the source cell that the UE may select as a new serving cell. The configurations for the LTM candidate cells that the gNB transmits to the UE may be those received by the gNB from the LTM candidate cells, but are not limited to the above example. The gNB (source cell) may select different candidate cells for each UE. The UE may store the configurations for the LTM candidate cells and transmit an RRC reconfiguration complete message to the gNB.

[0098] Next, an early synchronization procedure may be performed (720). More specifically, the early synchronization procedure (720) may be a procedure for performing downlink / uplink synchronization with candidate cells prior to receiving a cell change command. The cell change command may refer to a command that instructs the terminal to select a specific LTM candidate cell as a new serving cell based on the LTM procedure and perform a handover operation to connect to the new serving cell.

[0099] The terminal can perform downlink synchronization with the LTM candidate cell(s) before the terminal receives a cell switch command from the gNB.

[0100] Next, the UE can perform uplink synchronization with the LTM candidate cell(s). If UE-based TA (timing advance) measurement is configured, the UE can acquire the TA value of the LTM candidate cell(s) through the measurement. Before the UE receives a cell switch command from the gNB, the UE can perform early TA acquisition with the LTM candidate cell(s) at the request of the network. Early TA acquisition can be performed through a contention-free random access (CFRA) triggered by a physical downlink control channel (PDCCH) order from the source cell, and then the UE can transmit a random access preamble for the indicated candidate cell(s). To minimize data interruption of the source cell due to the CFRA for the candidate cell(s), the UE does not receive a random access response (RAR) for the purpose of TA value acquisition, and the TA value of the LTM candidate cell can be indicated by the cell switch command. Additionally, the UE does not maintain a TA timer for candidate cells, and TA validity guarantees may depend on network implementation.

[0101] Afterwards, an LTM execution procedure may be performed (730). More specifically, the LTM execution procedure (730) may include: the UE performing L1 measurements on the configured candidate cell(s) and transmitting L1 measurement report(s) to the gNB. The L1 measurements may be performed while the RRC reconfiguration received by the UE in the LTM preparation procedure (710) is applicable. Afterwards, the base station may decide to perform a cell switch / handover from the source cell to the target cell, and may transmit a medium access control (MAC) control element (CE) including a candidate configuration index of the target cell to trigger the cell switch to the UE. The UE may perform a switch from the source cell to the target cell and apply the configuration indicated by the candidate configuration index. At this time, if the UE does not have a valid TA of the target cell, the UE may perform a random access procedure for the target cell.

[0102] Next, an LTM completion procedure may be performed (740). More specifically, the LTM completion procedure (740) may be described as follows: the terminal may complete the LTM cell change procedure by transmitting an RRC reconfiguration completion message to the target cell. At this time, if the terminal performs a random access procedure for the target cell in the LTM execution procedure (730), when the random access procedure is successfully completed, the terminal may determine that the LTM cell change execution has been successfully completed. Alternatively, in the case of an LTM procedure in which a random access procedure is not performed (RACH-less LTM), when the terminal determines that the network has successfully received the first UL data to the terminal's target cell, the terminal may determine that the LTM cell change execution has been successfully completed.

[0103] In the case of the LTM procedure, the cell change procedure (handover based on the LTM procedure) is initiated by the L1 measurement report of the UE. By default, the L1 measurement report is set to periodic transmission, and the base station determines the LTM based on the L1 measurement report transmitted by the UE. Therefore, in the LTM procedure, even if the UE determines that the channel has deteriorated at a certain point in time between the L1 measurement report cycle and the next L1 measurement report cycle, the UE cannot transmit the L1 measurement report outside the L1 measurement report cycle, and therefore must wait until the next L1 measurement report cycle arrives to transmit the L1 measurement report to the base station. The periodic L1 measurement report in the LTM procedure may cause additional delay until the UE receives the cell change command MAC CE from the base station, which may result in additional downtime.

[0104] FIG. 8 is a diagram illustrating an example of additional downtime resulting from periodic L1 measurement reporting in an LTM procedure, according to various embodiments of the present disclosure.

[0105] Referring to FIG. 8, the terminal transmits an L3 measurement report (MR) to the base station, and based on this, receives an RRC reconfiguration message for handover based on the LTM procedure, and can perform L1 measurement (810). Thereafter, the terminal can transmit the L1 measurement report to the base station during the L1 measurement report cycle, and periodically receive a reference signal for L1 measurement, but cannot report the L1 measurement result to the base station at a time other than the L1 measurement report cycle (820). Therefore, even if the terminal identifies that the channel condition has deteriorated through the reference signal periodically received for L1 measurement, the terminal cannot transmit the L1 measurement report before the measurement report time according to the L1 measurement report cycle, and the base station also cannot receive the L1 measurement report, and therefore cannot transmit a cell change command MAC CE to the terminal. Therefore, this causes additional downtime.

[0106] The present disclosure describes a method for addressing the problem of additional downtime caused by periodic L1 measurement reporting in LTM procedures.

[0107] As one way to solve the problem of additional downtime caused by periodic L1 measurement reports in the LTM procedure, the transmission cycle of the L1 measurement report can be set to be shorter. That is, as the transmission cycle of the L1 measurement report is shortened, the probability of additional downtime occurring decreases, and even if additional downtime occurs, the additional downtime that occurs when the transmission cycle of the L1 measurement report is set to be short can be shortened compared to when the transmission cycle of the L1 measurement report is set to be long. However, according to the method of setting the transmission cycle of the L1 measurement report to be short, more radio resources must be allocated to the terminal as the transmission cycle of the L1 measurement report is shortened, and as the number of terminals within the base station coverage increases, there may be a problem that the amount of resource allocation for the L1 measurement report increases.

[0108] Another way to solve the problem of additional downtime caused by periodic L1 measurement reports in the LTM procedure is for the UE to aperiodically transmit L1 measurement reports to the base station via the PUSCH (physical uplink shared channel). According to the method of the UE aperiodically transmitting L1 measurement reports to the base station via the PUSCH (physical uplink shared channel), the UE can transmit L1 measurement reports to the base station at times other than the periodically configured L1 measurement report transmission times, and the base station, upon receiving the L1 measurement reports aperiodically transmitted via the PUSCH, can transmit a cell change command MAC CE based on the LTM procedure to the UE. However, the method of multiplexing L1 measurement reports onto the PUSCH and transmitting them may generate additional signaling. That is, in order to transmit an L1 measurement report transmitted aperiodically via PUSCH, 1) the terminal transmits a scheduling request (SR) to the base station, and 2) the base station receiving the SR can allocate a UL grant for transmitting a buffer status report MAC CE to the terminal. Thereafter, 3) the terminal can indicate the size of the L1 measurement report that the terminal wants to transmit in the buffer status report MAC CE and transmit it to the base station through the allocated UL grant. 4) The base station receiving the buffer status report MAC CE from the terminal can allocate a UL grant for transmitting the L1 measurement report to the terminal. 5) The terminal can transmit the L1 measurement report to the base station through the allocated UL grant. In this way, since a total of five signaling steps (1) to 5) are required for a terminal to transmit an L1 measurement report via PUSCH, the method of transmitting an aperiodic L1 measurement report via PUSCH cannot be considered effective in reducing additional interruption time.In addition, since the minimum resource allocation unit of PUSCH is larger than that of PUCCH (physical uplink control channel) (PUSCH can allocate at least 6 symbols in the time domain, while PUCCH can allocate 2 symbols), it may be difficult to view the method of transmitting L1 measurement reports through PUSCH as more efficient than PUCCH in terms of resource usage efficiency.

[0109] As another way to solve the problem of additional downtime caused by periodic L1 measurement reports in the LTM procedure, the terminal can perform a handover based on L3 measurement reports instead of a handover based on L1 measurement reports in the LTM execution procedure (730) of FIG. 7. That is, since L3 measurement reports can be performed aperiodically when an event condition for L3 measurement reports configured through measurement configuration is satisfied, the base station can instruct the terminal to perform a handover at a time other than the periodically configured L1 measurement report time. However, according to the method of performing a handover based on L3 measurement reports instead of a handover based on L1 measurement reports in the LTM execution procedure (730) of FIG. 7, an L3 handover instead of an LTM is caused, which may make it impossible to significantly reduce the downtime through LTM. In addition, additional signaling is required to allocate resources for transmitting L3 measurement reports, which may increase signaling overhead.

[0110] The methods described above may solve the problem of additional downtime caused by periodic L1 measurement reports to some extent, but may cause other problems, such as increased signaling overhead.

[0111] Below, we describe a method that addresses the issue of additional downtime caused by L1 measurement reports without causing other problems, such as increased signaling overhead. More specifically, we describe a method that allows a terminal to aperiodically transmit an LTM cell switch request to a base station at its own discretion, in order to address the issue of additional downtime caused by L1 measurement reports without causing other problems, such as increased signaling overhead.

[0112] LTM procedure

[0113] First, referring to FIG. 9, the overall LTM procedure to which the method described in the present disclosure is applied will be described.

[0114] FIG. 9 is a diagram illustrating an example of an LTM procedure according to various embodiments of the present disclosure.

[0115] In FIG. 9, a source distributed unit (DU) (903), a target DU (905), and a centralized unit (CU) (907) may constitute one base station (gNB), and the CU (907) may be controlled by the source DU (903) and the target DU (907) may be controlled by the CU (907). Since each of the source DU (903) and the target DU (907) may support one or more cells, an LTM procedure-based handover from the source DU (903) to the target DU (905) may mean an LTM procedure-based handover from one or more cells supported by the source DU (903) to one or more cells supported by the target DU (905).

[0116] Referring to FIG. 9, a source DU (903) may receive an L3 measurement report from a terminal (910) in which the terminal has measured at least one DU. The source DU (903) may forward the L3 measurement report received from the terminal to the CU (907) (915). Based on the L3 measurement report received from the terminal (901), the CU (907) may perform LTM candidate preparation (920). More specifically, the CU may receive configurations for LTM candidate cells from LTM candidate cells and perform LTM candidate preparation based on the received configurations for the LTM candidate cells. Here, the LTM candidate cells may refer to cells other than the source cell that the terminal may select as a new serving cell.

[0117] Hereinafter, when a terminal transmits an LTM cell switch request or an L1 measurement report, both the LTM cell switch request and the L1 measurement report receive a handover command MAC CE from the source cell (or, the source base station, or the source DU) in response thereto, so the LTM cell switch request or the L1 measurement report may be understood as a message requesting a handover command to the base station. That is, in the present disclosure, the terminal may send a message requesting a handover command to the base station to request a handover command MAC CE, and this may mean that the message requesting the handover command may be transmitted based on either a method of transmitting an LTM cell switch request or a method of transmitting an L1 measurement report. Hereinafter, various embodiments according to the present disclosure may be described based on the above description, unless otherwise stated.

[0118] Next, the terminal (901) may receive a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2) from the source DU (903). At this time, the RRC reconfiguration message may include information (or settings) about a condition (e.g., LTMCondition) for determining whether transmission of a message requesting a handover command based on the LTM procedure is necessary, and information (or settings) about a threshold (e.g., LTMRequestMinimumGap) for determining whether to transmit a cell switch request message as the message requesting the handover command or whether to transmit an L1 measurement report as the message requesting the handover command when transmission of the message requesting the handover command based on the LTM procedure is determined to be necessary. That is, the threshold may be used to determine how to transmit the message requesting the handover command. According to various embodiments of the present disclosure, a terminal may perform a handover based on an LTM procedure based on a method of transmitting a cell switch request message to a source cell as a message requesting a handover command, or the terminal may perform a handover based on an LTM procedure based on a method of transmitting an L1 measurement report to a source cell as a message requesting a handover command, as described above in FIG. 7.

[0119] Afterwards, the terminal (901) stores settings (settings for LTM candidate cells, information (or settings) on conditions for determining whether transmission of a message requesting a handover command based on the LTM procedure is necessary, information (or settings) on thresholds (e.g., LTMRequestMinimumGap) for determining whether to transmit a cell switch request message as a message requesting a handover command or whether to transmit an L1 measurement report as a message requesting a handover command) through an RRC reconfiguration message related to the LTM procedure, and transmits an RRC reconfiguration complete message to the gNB (930).

[0120] Next, an early sync procedure for downlink and uplink may be performed (935). More specifically, before the terminal (901) receives an LTM cell change command (MAC CE) from the source DU (903) or before the terminal (901) transmits an LTM cell change request message (cell switch request) to the source DU (903), the terminal (901) may perform downlink and uplink synchronization with LTM candidate cell(s) (LTM candidate cell(s) supported by candidate DUs). The cell change command MAC CE may mean a command that instructs the terminal to select a specific LTM candidate cell (an LTM candidate cell supported by the candidate DU) as a new serving cell based on the LTM procedure and to perform a handover operation to connect to the new serving cell.

[0121] Thereafter, the terminal (901) may perform L1 measurement and determine whether transmission of a message requesting a handover command based on the LTM procedure is necessary based on a condition (e.g., LTMCondition) for determining whether transmission of a message requesting a handover command based on the LTM procedure is necessary based on the L1 measurement result (940). Here, the L1 measurement may be performed only for neighboring DUs other than the source DU (at least one cell managed by each of the neighboring DUs), or may be performed for both the source DU (at least one cell supported by the source DU) and neighboring DUs other than the source DU (at least one cell managed by each of the neighboring DUs).

[0122] More specifically, if L1 measurement is performed only for neighboring DUs other than the source DU (at least one cell managed by each neighboring DU), and if there is at least one neighboring DU among the neighboring DUs (at least one cell managed by each neighboring DU) whose L1 measurement result satisfies a condition (e.g., LTMCondition) for determining whether transmission of a message requesting a handover command based on an LTM procedure is necessary, the terminal (901) can determine that transmission of a message requesting a handover command based on an LTM procedure is necessary.

[0123] In addition, when L1 measurement is performed for both the source DU (at least one cell supported by the source DU) and neighboring DUs other than the source DU (at least one cell managed by each of the neighboring DUs), if (1) the L1 measurement result for the source DU (at least one cell managed by the source DU) does not satisfy the condition (e.g., LTMCondition) for determining whether transmission of a message requesting a handover command based on the LTM procedure is necessary, and (2) there is at least one neighboring DU among the neighboring DUs (at least one cell managed by each of the neighboring DUs) whose L1 measurement result satisfies the condition (e.g., LTMCondition) for determining whether transmission of a message requesting a handover command based on the LTM procedure is necessary, the terminal (901) can determine that transmission of a message requesting a handover command based on the LTM procedure is necessary. Alternatively, (1) if the L1 measurement result for the source DU (at least one cell managed by the source DU) satisfies a condition (e.g., LTMCondition) for determining whether transmission of a message requesting a handover command based on the LTM procedure is necessary, the terminal (901) may determine that transmission of a message requesting a handover command based on the LTM procedure is not necessary regardless of the L1 measurement result for the neighboring DU. Additionally, the determination (940) of the terminal (901) that transmission of the request message is necessary may be a determination that handover to the target DU (or LTM cell change) based on the LTM procedure is necessary.

[0124] Next, when the terminal (901) determines that transmission of a message requesting a handover command based on an LTM procedure (or handover to a target DU based on an LTM procedure (or LTM cell change)) is necessary, the terminal (901) may calculate a time difference value between a time point at which transmission of a message requesting a handover command based on an LTM procedure is determined necessary and a preset L1 measurement report resource at a time point after the time point. The terminal (901) may compare the calculated time difference value with a threshold value (e.g., LTMRequestMinimumGap) for determining whether to transmit an LTM cell change request message (cell switch request) as a message requesting a handover command or whether to transmit an L1 measurement report as a message requesting a handover command when it is determined that transmission of a message requesting a handover command based on an LTM procedure is necessary. As a result of the comparison, if it is determined that the calculated time difference value is greater than the threshold, the terminal (901) may transmit an LTM cell change request message (cell switch request) to the source DU (903) (945). Conversely, if it is determined that the calculated time difference value is greater than the threshold, the terminal (901) may not transmit an LTM cell change request message (cell switch request) to the source DU (903). If the LTM cell change request message (cell switch request) is not transmitted, the terminal (901) may transmit an L1 measurement report to the source DU (903) on a preset L1 measurement report resource at a time point after the time point at which it is determined that transmission of a message requesting a handover command based on the LTM procedure is necessary. Of course, information about the target cell included in the LTM cell change request message (cell switch request) may also be transmitted together with the L1 measurement report on the L1 measurement report resource.

[0125] Thereafter, an LTM cell change decision procedure (950) may be performed. At this time, the CU (907) may transmit information about the target DU (905) necessary for the source DU (903) to generate an LTM cell change command MAC CE to the source DU (903) based on an LTM cell change request message (cell switch request) or an L1 measurement report that the CU (907) may receive from the source DU (903) (955). The source DU (903) may transmit the LTM cell change command MAC CE to the terminal (901) (955). The LTM cell change command MAC CE may include information instructing the terminal (901) to perform a handover from the source DU (903) to the target DU (905) based on the LTM procedure.

[0126] Next, the target DU (905) allocates an uplink grant for PUSCH transmission to the terminal (960), and the terminal can transmit a PUSCH to the target DU (905) based on the allocated uplink grant (965).

[0127] In Fig. 9, the case where the subjects performing the LTM procedure are a terminal (901), a source DU (903), a target DU (905), and a CU (907) is described, but the LTM procedure described in Fig. 9 can be equally / similarly applied to the LTM procedure from the perspective of a terminal, a source base station (gNB), and a target base station (gNB), or the LTM procedure from the perspective of a terminal, a source cell, and a target cell.

[0128] How to send an LTM cell switch request

[0129] Below, a method for transmitting an LTM cell change request (or LTM cell change request message) according to various embodiments of the present disclosure is described.

[0130] In order to transmit an LTM cell change request, PUCCH formats (0 to 4) can be used from the viewpoint of resource utilization efficiency. PUCCH format 0 and PUCCH format 1 can include up to 2 bits of information. In addition, PUCCH format 2, PUCCH format 3, and PUCCH format 4 can include 3 or more bits of information. In the case of PUCCH format 1, since 2 bits of information are expressed through QPSK (Quadrature Phase Shift Keying) modulation, there is no spare space in which additional information can be included other than the information defined in PUCCH format 1. Therefore, in the present disclosure, PUCCH formats 0, 2, 3, and 4 can be considered for transmitting an LTM cell change request.

[0131] According to the current 3GPP standard (Release 18), the maximum number of LTM candidate cells that can be considered in the LTM procedure can be 8. Therefore, 3 bits can be used to configure information to indicate a specific LTM candidate cell among the maximum 8 LTM candidate cells. Of course, the number of LTM candidate cells and the number of bits of information to indicate the LTM candidate cell are not limited to the above example.

[0132] First, an embodiment of configuring information for indicating a specific LTM candidate cell among up to eight LTM candidate cells based on PUCCH formats 2, 3, and 4 will be described. Since PUCCH formats 2, 3, and 4 are configured to include information of three or more bits, in addition to CRI (CSI-RS Resource Indicator), SSBRI (SSB Resource Indicator), RSRP (reference signal received power), and Differential RSRP information that can be included in PUCCH formats 2, 3, and 4, PUCCH formats 2, 3, and 4 can be configured to further include information for indicating a specific LTM candidate cell among the LTM candidate cells (e.g., which may be referred to as LTMCI (LTM cell indicator)). If information for indicating a specific LTM candidate cell among LTM candidate cells is further included in PUCCH formats 2, 3, and 4 and there is space left within PUCCH formats 2, 3, and 4, the remaining space may be filled using bit value 0 (zero padding).

[0133] An example of information configuration for indicating a specific LTM candidate cell among LTM candidate cells according to the present embodiment may be as shown in the table below.

[0134]

[0135] According to the present embodiment, an LTM cell change request may be transmitted to a source cell based on one of PUCCH formats 2, 3, and 4 on a preset PUCCH resource through a higher layer, and the request message may include information for indicating a specific LTM candidate cell among the LTM candidate cells.

[0136] Next, an embodiment of configuring information for indicating a specific LTM candidate cell among LTM candidate cells based on PUCCH format 0 is described. In the case of PUCCH format 0, up to 3 bits of information for HARQ ACK / NACK and SR purposes can be provided by applying a cyclic shift value to a sequence for PUCCH generation.

[0137] FIG. 10 is a diagram illustrating an example of a method for configuring information through PUCCH format 0 according to various embodiments of the present disclosure.

[0138] Referring to FIG. 10, when PUCCH format 0 is used to indicate only SR, only cyclic shift 0 may be used (1010). Furthermore, when PUCCH format 0 is used for ACK or NACK, cyclic shift 0 or 6 may be used (1020). Furthermore, when PUCCH format 0 is used to indicate ACK, NACK, ACK / SR, or NACK / SR, cyclic shift 0 (NACK), 3 (NACK, SR), 6 (ACK), or 9 (ACK, SR) may be used (1030). Finally, when PUCCH format 0 is used to indicate NACK / NACK, NACK / NACK / SR, NACK / ACK, NACK / ACK / SR, ACK / ACK, ACK / ACK / SR, ACK / NACK, or ACK / NACK / SR, a cyclic shift of 0 (NACK / NACK), 1 (NACK / NACK / SR), 3 (NACK / ACK), 4 (NACK / ACK / SR), 6 (ACK / ACK), 7 (ACK / ACK / SR), 9 (ACK / NACK), or 10 (ACK / NACK / SR) may be used (1040).

[0139] As illustrated in FIG. 10, since the cyclic shift values ​​2, 5, 8, and 11 are not used in the current standard, in the present disclosure, the cyclic shift values ​​2, 5, 8, and 11 can be used to express LTM candidate cells using PUCCH format 0 without affecting the existing standard operation. Each of the cyclic shift values ​​2, 5, 8, and 11 can indirectly indicate a specific LTM candidate cell, and since the number of cyclic shift values ​​(2, 5, 8, and 11) not used in PUCCH format 0 is 4, one cell can be indicated for up to 4 LTM candidate cells.

[0140] FIG. 11 illustrates an example of a method for indicating LTM candidate cells through PUCCH format 0 according to various embodiments of the present disclosure.

[0141] Referring to Fig. 11, when there are two LTM candidate cells, the lower values ​​of cyclic shift values ​​2, 5, 8, and 11, 2 and 5, can be used, and the LTM candidate cells can be sequentially associated with the lower cyclic shift values ​​in ascending order (1110). For example, when the values ​​of the identifiers (indexes) of the LTM candidate cells are 1 and 3, respectively, the LTM candidate cell whose identifier value is 1 can be associated with the cyclic shift value 2, and the LTM candidate cell whose identifier value is 3 can be associated with the cyclic shift value 5. According to this relationship, in the case of example 1110 of FIG. 11, if the terminal transmits an LTM cell change request based on PUCCH format 0 and a cyclic shift value of 5 is applied to the sequence for generating the corresponding PUCCH format 0, the base station that receives the PUCCH format 0 can obtain the cyclic shift value of 5 applied to PUCCH format 0, and then it can be seen that the terminal requested an LTM procedure-based handover to an LTM candidate cell whose identifier value is 3.

[0142] In addition, when there are three LTM candidate cells, the lower values ​​of cyclic shift values ​​2, 5, 8, and 11, which are 2, 5, and 8, can be used, and the LTM candidate cells can be sequentially associated with the lower cyclic shift values ​​in ascending order (1120). For example, when the identifier (index) values ​​of the LTM candidate cells are 1, 3, and 4, respectively, the LTM candidate cell whose identifier value is 1 can be associated with the cyclic shift value 2, the LTM candidate cell whose identifier value is 3 can be associated with the cyclic shift value 5, and the LTM candidate cell whose identifier value is 4 can be associated with the cyclic shift value 8. According to this relationship, in the case of example 1120 of FIG. 11, if the terminal transmits an LTM cell change request based on PUCCH format 0 and a cyclic shift value of 8 is applied to the sequence for generating the corresponding PUCCH format 0, the base station that receives the PUCCH format 0 can obtain the cyclic shift value of 8 applied to the PUCCH format 0, and then it can be seen that the terminal requested an LTM procedure-based handover to an LTM candidate cell whose identifier value is 4.

[0143] Finally, when there are four LTM candidate cells, the cyclic shift values ​​2, 5, 8, and 11 can all be used, and the LTM candidate cells can be sequentially associated with lower cyclic shift values ​​in ascending order (1130). For example, when the identifier (index) values ​​of the LTM candidate cells are 1, 3, 4, and 5, respectively, an LTM candidate cell whose identifier value is 1 can be associated with cyclic shift value 2, an LTM candidate cell whose identifier value is 3 can be associated with cyclic shift value 5, an LTM candidate cell whose identifier value is 4 can be associated with cyclic shift value 8, and an LTM candidate cell whose identifier value is 5 can be associated with cyclic shift value 11. According to this relationship, in the case of example 1130 of FIG. 11, if the terminal transmits an LTM cell change request based on PUCCH format 0 and a cyclic shift value 11 is applied to the sequence for generating the corresponding PUCCH format 0, the base station that receives the PUCCH format 0 can obtain the cyclic shift value 11 applied to the PUCCH format 0, and then it can be seen that the terminal requested an LTM procedure-based handover to an LTM candidate cell whose identifier value is 5.

[0144] PUCCH format 0 can represent one of four LTM candidate cells using four cyclic shift values ​​(2, 5, 8, 11), but PUCCH format 0 can also be used when the number of LTM candidate cells is five or more. That is, even when the number of LTM candidate cells is actually five or more, four LTM candidate cells can be selected from all LTM candidate cells according to a predetermined method for an operation to transmit a message requesting a handover command based on an LTM procedure, and an association with four cyclic shift values ​​(2, 5, 8, 11) related to PUCCH format 0 can be configured for the selected four LTM candidate cells. An operation for transmitting an LTM cell change request based on PUCCH format 0 when the number of actual LTM candidate cells is five or more will be described with reference to FIGS. 12 and 13.

[0145] FIG. 12 and FIG. 13 are diagrams showing an example of a method for indicating an LTM candidate cell through PUCCH format 0 according to various embodiments of the present disclosure.

[0146] First, referring to FIG. 12, based on the L1 measurement report (1210) that the terminal most recently transmitted to the source cell based on the L1 measurements measured for the five LTM candidate cells, four LTM candidate cells can be selected from the five LTM candidate cells to configure the correlation between the LTM candidate cells and the four cyclic shift values. The RS-RSRP unit in 1210 of FIG. 12 represents dBm. In FIG. 12, it is assumed that the condition (LTMCondition) for determining whether or not a message requesting a handover command based on the LTM procedure is necessary is set to -85 dBm.

[0147] According to Fig. 12, an LTM candidate cell with a cell identifier of 4, which does not satisfy the condition (LTMCondition) in the measurement result (RS-RSRP) value, is excluded, and an association relationship between four LTM candidate cells with cell identifiers of 1, 2, 3, and 5 and four cyclic shift values ​​(2, 5, 8, and 11) can be configured. The association relationship can be configured in such a way that the four LTM candidate cells are sequentially associated with lower cyclic shift values ​​in ascending order of the cell identifiers (1220). As a result, an LTM candidate cell with a cell identifier value of 1 can be associated with a cyclic shift value of 2, an LTM candidate cell with a cell identifier value of 2 can be associated with a cyclic shift value of 5, an LTM candidate cell with a cell identifier value of 3 can be associated with a cyclic shift value of 8, and an LTM candidate cell with a cell identifier value of 5 can be associated with a cyclic shift value of 11.

[0148] Next, referring to FIG. 13, an operation for transmitting an LTM cell change request based on the correlation between the configured LTM candidate cell and the cyclic shift value is described. In FIG. 13, it is assumed that the condition (LTMCondition) for determining whether or not to transmit a message requesting a handover command based on the LTM procedure is set to -85 dBm.

[0149] The terminal can perform a new L1 measurement (1310) immediately after the most recently transmitted L1 measurement report (1210) in FIG. 12. As a result, the terminal can transmit an LTM cell change request to the source cell, which requests a handover command based on an LTM procedure to the LTM candidate cell with cell identifier 3, which is the LTM candidate cell with the largest L1 measurement result value among the remaining cells, excluding the LTM candidate cell with cell identifier 1 that does not satisfy the condition (LTMCondition) and the LTM candidate cell with cell identifier 4 that is not included in the association configuration in FIG. 12. According to the association configured in FIG. 12, the LTM candidate cell with cell identifier 3 is associated with a cyclic shift value of 8, and therefore, the terminal can apply the cyclic shift value 8 to a sequence for generating a PUCCH format 0 associated with the LTM cell change request, and transmit the LTM cell change request to the source cell based on the PUCCH format 0 according to the sequence to which the cyclic shift value 8 is applied. The source cell can instruct the terminal to perform an LTM procedure-based handover to the LTM candidate cell identified by the request via the MAC CE.

[0150] Configuring radio resource control (RRC) parameters

[0151] For the LTM procedure according to various embodiments of the present disclosure, parameters to be included in the RRC reset message may be as shown in Tables 2 to 5 below.

[0152] First, when it is determined that it is necessary to transmit a message requesting a handover command based on an LTM procedure within the parameters related to the settings for CSI measurement (CSI-MeasConfig), a parameter (e.g., LTMRequestMinimumGap) for a threshold for determining whether to transmit an LTM cell change request as a message requesting a handover command may be added as shown in Table 2 below.

[0153]

[0154] The value of the corresponding parameter (TMRequestMinimumGap) can have a value from 0 to 20, for example, and the unit can be ms. The reason why the upper limit of the corresponding parameter is 20 is because the period value of SSB is 20 ms.

[0155] Next, a parameter (e.g., LTMCondition) for a condition for determining whether transmission of a message requesting a handover command based on an LTM procedure is required may be added to the parameters related to the settings for CSI measurement (CSI-MeasConfig), as shown in Table 3 below.

[0156]

[0157] The value of the corresponding parameter (e.g. LTMCondition) is expressed in 7 bits, the range can be expressed from -140 dBm to -44 dBm, and the resolution can be 1 dBm.

[0158] Next, a parameter (e.g., LTM-Index-RSRP) that instructs the terminal to write measurement results for LTM candidate cells when performing L1 measurement reporting may be included in the parameter (reportQuantity) related to the setting of the reporting object during CSI measurement, as shown in Table 4 below.

[0159]

[0160] Finally, a parameter (e.g., LTMCI) may be added to configure the UCI transmitted via PUCCH to include information indicating an LTM candidate cell within the parameter (reportQuantity) related to the setting of the reporting object during CSI measurement, as shown in Table 5 below.

[0161]

[0162] FIG. 14 is a diagram illustrating an example of an LTM procedure according to various embodiments of the present disclosure.

[0163] Below, the description in FIG. 14 may be the same as that in FIG. 9 described above, except for differences in information included in the RRC reconfiguration message.

[0164] In FIG. 14, a source distributed unit (DU) (1403), a target DU (1405), and a centralized unit (CU) (1407) may constitute one base station (gNB), and the CU (1407) may be controlled by the source DU (1403) and the target DU (1407) may be controlled by the CU (1407). Since each of the source DU (1403) and the target DU (1407) may support one or more cells, an LTM procedure-based handover from the source DU (1403) to the target DU (1405) may mean an LTM procedure-based handover from one or more cells supported by the source DU (1403) to one or more cells supported by the target DU (1405).

[0165] Referring to FIG. 14, a source DU (1403) may receive an L3 measurement report from a terminal in which the terminal has measured at least one DU (1410). The source DU (1403) may forward the L3 measurement report received from the terminal to a CU (1407) (1415). Based on the L3 measurement report received from the terminal (1401), the CU (1407) may perform LTM candidate preparation (1420). More specifically, the CU may receive configurations for LTM candidate cells from LTM candidate cells and perform LTM candidate preparation based on the received configurations for the LTM candidate cells. Here, the LTM candidate cells may refer to cells other than the source cell that the terminal may select as a new serving cell.

[0166] Next, the terminal (1401) may receive a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2) from the source DU (1403). At this time, the RRC reconfiguration message may include at least one of information (or setting) on ​​a condition (e.g., LTMCondition) for determining whether transmission of a message requesting a handover command based on an LTM procedure is necessary, and information (or setting) on ​​a threshold (e.g., LTMRequestMinimumGap) for determining whether to transmit a cell switch request message as a message requesting a handover command or whether to transmit an L1 measurement report as a message requesting a handover command when transmission of a message requesting a handover command based on an LTM procedure is determined to be necessary, information (e.g., LTM-Index-RSRP) for instructing the UE to write measurement results for LTM candidate cells when performing an L1 measurement report, or information (e.g., LTMCI) for configuring that information indicating an LTM candidate cell is included in a UCI transmitted through a PUCCH. That is, the threshold may be used for determining a method of transmitting a message requesting a handover command. According to various embodiments of the present disclosure, a terminal may perform a handover based on an LTM procedure based on a method of transmitting a cell switch request message to a source cell as a message requesting a handover command, or the terminal may perform a handover based on an LTM procedure based on a method of transmitting an L1 measurement report to a source cell as a message requesting a handover command, as described above in FIG. 7.

[0167] Afterwards, the terminal (1401) stores settings (settings for LTM candidate cells, information (or settings) on conditions for determining whether transmission of a message requesting a handover command based on the LTM procedure is necessary, information (or settings) on thresholds (e.g., LTMRequestMinimumGap) for determining whether to transmit a cell switch request message as a message requesting a handover command or whether to transmit an L1 measurement report as a message requesting a handover command) through an RRC reconfiguration message related to the LTM procedure, and transmits an RRC reconfiguration complete message to the gNB (1430).

[0168] Next, an early sync procedure for downlink and uplink may be performed (1435). More specifically, before the terminal (1401) receives an LTM cell change command (cell switch command MAC CE) from the source DU (1403) or before the terminal (1401) transmits an LTM cell change request message (cell switch request) to the source DU (1403), the terminal (1401) may perform downlink and uplink synchronization with LTM candidate cell(s) (LTM candidate cell(s) supported by candidate DUs). The cell change command MAC CE may mean a command that instructs the terminal to select a specific LTM candidate cell (an LTM candidate cell supported by the candidate DU) as a new serving cell based on the LTM procedure and to perform a handover operation to connect to the new serving cell.

[0169] Thereafter, the terminal (1401) performs L1 measurement and determines whether transmission of a message requesting a handover command based on the LTM procedure is necessary based on the L1 measurement result and a condition (e.g., LTMCondition) for determining whether transmission of a message requesting a handover command based on the LTM procedure is necessary (1440).

[0170] Next, when the terminal (1401) determines that transmission of a message requesting a handover command based on an LTM procedure (or handover to a target DU based on an LTM procedure (or LTM cell change)) is necessary, the terminal (1401) may calculate a time difference value between a time point at which transmission of a message requesting a handover command based on an LTM procedure is determined necessary and a preset L1 measurement report resource at a time point after the time point. The terminal (1401) may compare the calculated time difference value with a threshold value (e.g., LTMRequestMinimumGap) for determining whether to transmit an LTM cell change request message (cell switch request) as a message requesting a handover command or whether to transmit an L1 measurement report as a message requesting a handover command when transmission of a message requesting a handover command based on an LTM procedure is determined necessary. As a result of the comparison, if it is determined that the calculated time difference value is greater than the threshold, the terminal (1401) may transmit an LTM cell change request message (cell switch request) to the source DU (1403) (1445). Conversely, if it is determined that the calculated time difference value is greater than the threshold, the terminal (1401) may not transmit an LTM cell change request message (cell switch request) to the source DU (1403). If the LTM cell change request message (cell switch request) is not transmitted, the terminal (1401) may transmit an L1 measurement report to the source DU (1403) on a preset L1 measurement report resource at a time point after the time point at which it is determined that transmission of a message requesting a handover command based on the LTM procedure is necessary. Of course, information about the target cell included in the LTM cell change request message (cell switch request) may also be transmitted together with the L1 measurement report on the L1 measurement report resource.

[0171] Thereafter, an LTM cell change decision procedure (1450) may be performed. At this time, the CU (1407) may transmit information about a target DU (1405) necessary for the source DU (1403) to generate an LTM cell change command MAC CE to the source DU (1403) based on an LTM cell change request message (cell switch request) or an L1 measurement report that the CU (1407) may receive from the source DU (1403) (1455). The source DU (1403) may transmit the LTM cell change command MAC CE to the terminal (1401) (1455). The LTM cell change command MAC CE may include information instructing the terminal (1401) to perform a handover from the source DU (1403) to the target DU (1405) based on the LTM procedure.

[0172] Next, the target DU (1405) allocates an uplink grant for PUSCH transmission to the terminal (1460), and the terminal can transmit a PUSCH to the target DU (1405) based on the allocated uplink grant (1465).

[0173] In Fig. 14, the case where the subjects performing the LTM procedure are a terminal (1401), a source DU (1403), a target DU (1405), and a CU (1407) is described, but the LTM procedure described in Fig. 14 can be applied equally / similarly to the LTM procedure from the perspective of a terminal, a source base station (gNB), and a target base station (gNB), or the LTM procedure from the perspective of a terminal, a source cell, and a target cell.

[0174] According to various embodiments of the present disclosure, a terminal can determine the necessity of an LTM cell change ( / transmit a request message to request an LTM procedure-based handover / transmit a request message to request an LTM procedure-based handover) and aperiodically transmit an LTM cell change request to a base station, thereby reducing additional downtime that may occur due to the transmission of the LTM cell change request. Since the LTM cell change request can be transmitted using PUCCH formats, the efficiency of radio resource use can be increased.

[0175] FIG. 15 is a flowchart showing an example of a method of operating a terminal according to various embodiments of the present disclosure.

[0176] A terminal may receive a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2) from a base station (1510). At this time, the RRC reconfiguration message may include information on a condition for determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold for determining a method for transmitting the message requesting the handover command.

[0177] Next, the terminal can perform L1 link quality measurement based on the LTM procedure for the base station and at least one candidate base station (1520).

[0178] Thereafter, the terminal can determine whether to transmit the message requesting the handover command based on a condition for determining whether to transmit the message requesting the handover command (1530).

[0179] Thereafter, if the terminal decides to transmit a message requesting the handover command, the terminal may determine a method of transmitting the message requesting the handover command based on the threshold value (1540).

[0180] Finally, the terminal may transmit a message requesting the handover command to the base station based on the determined method (1550). Here, if the time difference between the time at which it is determined whether to transmit the message requesting the handover command and the first L1 connection quality measurement result report resource after the time at which the transmission is determined is less than the threshold, a cell change request message may be transmitted as the message requesting the handover command before the time at which the first L1 connection quality measurement result report resource is set.

[0181] FIG. 16 is a flowchart illustrating an example of a method of operating a base station according to various embodiments of the present disclosure.

[0182] First, a base station may transmit a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2) to a user equipment (1610). Here, the RRC reconfiguration message may include information about a condition related to determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold related to determining a method of transmitting the message requesting the handover command.

[0183] Next, the base station may receive a message requesting the handover command from the terminal based on a method determined based on conditions related to determining whether to transmit a message requesting the handover command and the threshold value (1620). At this time, if the time difference between the time at which it is determined whether to transmit the message requesting the handover command and the first L1 connection quality measurement result report resource after the time is less than the threshold value, a cell change request message may be received as a message requesting the handover command before the time at which the first L1 connection quality measurement result report resource is set.

[0184] The methods according to the embodiments described in the claims or specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

[0185] When implemented in software, a computer-readable storage medium storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. The one or more programs include instructions that cause the electronic device to execute methods according to embodiments described in the claims or specification of the present disclosure.

[0186] These programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, read only memory (ROM), electrically erasable programmable read only memory (EEPROM), magnetic disc storage devices, compact disc-ROMs (CD-ROMs), digital versatile discs (DVDs) or other forms of optical storage devices, magnetic cassettes, or may be stored in memories formed by a combination of some or all of these. In addition, each configuration memory may include multiple copies.

[0187] Additionally, the program may be stored on an attachable storage device that is accessible via a communication network, such as the Internet, an intranet, a local area network (LAN), a wide area network (WAN), a storage area network (SAN), or a combination thereof. Such a storage device may be connected to a device implementing an embodiment of the present disclosure via an external port. Additionally, a separate storage device on the communication network may be connected to a device implementing an embodiment of the present disclosure.

[0188] In the specific embodiments of the present disclosure described above, components included in the disclosure are expressed singularly or plurally, depending on the specific embodiment presented. However, the singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present disclosure is not limited to singular or plural components. Components expressed in plural may be composed of singular elements, or components expressed in singular may be composed of plural elements.

[0189] While the detailed description of this disclosure has described specific embodiments, it should be understood that various modifications are possible without departing from the scope of this disclosure. Therefore, the scope of this disclosure should not be limited to the described embodiments, but should be defined not only by the scope of the claims described below, but also by equivalents thereof.

Claims

1. In a method performed by a terminal (user equipment) in a wireless communication system, A step of receiving, from a base station, a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2), the RRC reconfiguration message including information on a condition for determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold for determining a method of transmitting the message requesting the handover command; A step of performing L1 link quality measurement based on the LTM procedure for the base station and at least one candidate base station; A step of determining whether to transmit a message requesting the handover command based on a condition for determining whether to transmit a message requesting the handover command; When it is decided to transmit a message requesting the handover command, a step of determining a method of transmitting the message requesting the handover command based on the threshold value; and A step of transmitting a message requesting the handover command to the base station based on the determined method, A method in which a cell change request message is transmitted as a message requesting the handover command before the time at which the first L1 connection quality measurement result reporting resource is set, when the time difference between the time at which it is determined whether to transmit a message requesting the handover command and the first L1 connection quality measurement result reporting resource after the time at which the decision is made is less than the threshold value.

2. In paragraph 1, A method in which, when the time difference between the time at which it is determined whether to transmit a message requesting the handover command and the first L1 connection quality measurement result reporting resource after the time is equal to or greater than the threshold, the result report of the L1 connection quality measurement is transmitted as a message requesting the handover command on the first L1 connection quality measurement result reporting resource.

3. In the second paragraph, the method, A method further comprising the step of receiving, from the base station, a medium access control (MAC) CE (control element) including information indicating the handover command to the one candidate base station.

4. In paragraph 1, A method for transmitting a handover request message based on the above LTM procedure, based on physical uplink control channel (PUCCH) format 0, PUCCH format 2, PUCCH format 3, or PUCCH format 4.

5. In paragraph 4, A method in which, when the transmission of a handover request message based on the LTM procedure is based on the PUCCH format 0, the one candidate base station is identified based on the PUCCH format 0 to which a cyclic shift of a specific value is applied based on the result of the L1 connection quality measurement transmitted last before the L1 connection quality measurement based on the LTM procedure is performed with the one candidate base station.

6. In paragraph 5, A method in which, when transmission of a handover request message based on the LTM procedure is based on the PUCCH format 2, the PUCCH format 3, or the PUCCH format 4, the one candidate base station is identified based on an LTM cell indicator (LTMCI) for indicating the one candidate base station included in the request message for performing the LTM procedure.

7. In a method performed by a base station in a wireless communication system, A step of transmitting a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2) to a user equipment, wherein the RRC reconfiguration message includes information about a condition related to determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold related to determining a method of transmitting the message requesting the handover command; Including a step of receiving a message requesting the handover command from the terminal based on a method determined based on a condition related to determining whether to transmit the message requesting the handover command and the threshold value, A method in which a cell change request message is received as a message requesting the handover command before the time at which the first L1 connection quality measurement result report resource is set, when the time difference between the time at which it is determined whether to transmit a message requesting the handover command and the first L1 connection quality measurement result report resource after the time at which the transmission of the message requesting the handover command is determined is less than the threshold value.

8. In paragraph 7, A method in which, when the time difference between the time at which it is determined whether to transmit a message requesting the handover command and the first L1 connection quality measurement result reporting resource after the time at which the determination is made is equal to or greater than the threshold value, the result report of the L1 connection quality measurement is received as a message requesting the handover command on the first L1 connection quality measurement result reporting resource.

9. In the 8th paragraph, the method, A method further comprising the step of transmitting, to the terminal, a MAC (medium access control) CE (control element) including information indicating the handover command to the one candidate base station.

10. In paragraph 7, Transmission of a handover request message based on the above LTM procedure is based on physical uplink control channel (PUCCH) format 0, PUCCH format 2, PUCCH format 3, or PUCCH format 4, A method in which, when the transmission of a handover request message based on the LTM procedure is based on the PUCCH format 0, the one candidate base station is identified based on the PUCCH format 0 to which a cyclic shift of a specific value is applied based on the result of the L1 connection quality measurement transmitted last before the L1 connection quality measurement based on the LTM procedure is performed with the one candidate base station.

11. In a wireless communication system, in a terminal (user equipment), the terminal, Transmitter and receiver; and Including a controller connected to the above transmitter and receiver, The above controller, Receive, from a base station, a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2), wherein the RRC reconfiguration message includes information on a condition for determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold for determining a method of transmitting the message requesting the handover command. Performing L1 link quality measurement based on the LTM procedure for the above base station and at least one candidate base station, Based on the condition for determining whether to transmit the message requesting the handover command, it is determined whether to transmit the message requesting the handover command, If it is decided to transmit a message requesting the handover command, a method for transmitting the message requesting the handover command is determined based on the threshold value, configured to transmit a message requesting the handover command to the base station based on the determined method, A terminal in which a cell change request message is transmitted as a message requesting the handover command before the time at which the first L1 connection quality measurement result report resource is set, when the time difference between the time at which it is determined whether to transmit a message requesting the handover command and the first L1 connection quality measurement result report resource after the time at which the transmission of the message requesting the handover command is determined is less than the threshold value.

12. In paragraph 11, A terminal in which, when the time difference between the time at which it is determined whether to transmit a message requesting the handover command and the first L1 connection quality measurement result reporting resource after the time at which the determination is made is equal to or greater than the threshold value, the result report of the L1 connection quality measurement is transmitted as a message requesting the handover command on the first L1 connection quality measurement result reporting resource.

13. In the 12th paragraph, the controller, A terminal further configured to receive, from the base station, a medium access control (MAC) CE (control element) including information indicating a handover command to the one candidate base station.

14. In paragraph 11, Transmission of a handover request message based on the above LTM procedure is performed by a terminal based on physical uplink control channel (PUCCH) format 0, PUCCH format 2, PUCCH format 3, or PUCCH format 4.

15. In a wireless communication system, there is a base station, Transmitter and receiver; and Including a controller connected to the above transmitter and receiver, The above controller, A terminal (user equipment) transmits a radio resource control (RRC) reconfiguration message related to a mobility (L1 / L2 triggered mobility: LTM) procedure triggered by Layer 1 (L1) / Layer 2 (L2), wherein the RRC reconfiguration message includes information about a condition related to determining whether to transmit a message requesting a handover command based on the LTM procedure and a threshold related to determining a method of transmitting the message requesting the handover command. A method is configured to receive a message requesting the handover command based on a condition related to determining whether to transmit a message requesting the handover command from the terminal and based on the threshold value, A base station, wherein a cell change request message is received as a message requesting the handover command before the time at which the first L1 connection quality measurement result report resource is set, when the time difference between the time at which it is determined whether to transmit a message requesting the handover command and the first L1 connection quality measurement result report resource after the time at which the transmission of the message requesting the handover command is determined is less than the threshold value.

Images