Handoff method and apparatus for next-generation mobile communication systems

Abstract

The present disclosure relates to a communication method and system for supporting the convergence of a fifth-generation (5G) communication system, which supports higher data rates than a fourth-generation (4G) system, with Internet of Things (IoT) technology. The present disclosure can be applied to intelligent services based on 5G communication technology and IoT-related technologies, such as smart home, smart building, smart city, smart car, connected car, healthcare, digital education, smart retail, security, and safety services. Additionally, the present disclosure relates to a method performed by a source node in a wireless communication system, the method including: sending a handover request message to a target node, the handover request message including a target cell identifier related to conditional handover; receiving a handover request response message including a handover command message from the target node, the handover command message having configuration information about a target cell for conditional handover; and sending a radio resource control (RRC) reconfiguration message including the handover command message and conditional information for conditional handover to a terminal.

Description

Technical Field

[0001] The present disclosure relates to operations of a terminal and a base station in a mobile communication system. The present disclosure relates to a method and apparatus for handover in a next-generation mobile communication system. The present disclosure relates to a handover command signal method and apparatus for conditional handover in a next-generation mobile communication system. The present disclosure relates to a method and apparatus for performing beam-based handover in a wireless communication system. Background Art

[0002] In order to meet the increasing wireless data traffic demand since the deployment of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also referred to as "beyond 4G networks" or "post-LTE systems". The 5G communication system is considered to be implemented in a higher frequency (millimeter wave) band (e.g., 60 GHz band) to achieve higher data rates. In order to reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple-input multiple-output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and large antenna technologies are discussed in the 5G communication system. In addition, in the 5G communication system, system network improvements based on advanced small cells, cloud radio access network (RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, mobile network, cooperative communication, coordinated multi-point (CoMP), receiver-side interference cancellation, etc. are being developed. In the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superimposed coding (SWSC) as advanced coding modulation (ACM), and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as advanced access technologies have been developed.

[0003] The Internet is a human-centric connectivity network where humans generate and consume information, and is now evolving into the Internet of Things (IoT), in which distributed entities such as things exchange and process information without human intervention. The Internet of Everything (IoE) is a product of combining IoT technology and big data processing technology through connection to a cloud server. In order to implement the IoT, technical elements such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology", and "security technology" are required, and recently, sensor networks, machine-to-machine (M2M) communication, machine-type communication (MTC), etc. have been studied. Such an IoT environment can provide intelligent Internet technology services, creating new value for human life by collecting and analyzing data generated between connected things. Through the fusion and combination of existing information technology (IT) and various industrial applications, the IoT can be applied to various fields, including smart home, smart building, smart city, smart car or connected car, smart grid, healthcare, smart appliances, and advanced medical services.

[0004] Accordingly, various attempts have been made to apply the 5G communication system to the IoT network. For example, technologies such as sensor networks, MTC, and M2M communications can be implemented through beamforming, MIMO, and array antennas. The application of cloud RAN as the above-mentioned big data processing technology can also be considered an example of the convergence between 5G technology and IoT technology.

[0005] With the development of wireless communication systems, there is a need for a method for controlling the activation of multiple RLC layer devices in a system that supports high-reliability low-latency services. Summary of the Invention

[0006] [Technical Problem]

[0007] Embodiments of the present disclosure are directed to providing a method and apparatus for handover in a next-generation mobile communication system.

[0008] Embodiments of the present disclosure are directed to proposing a method for generating a conditional handover command transmitted by a network to perform conditional handover, and signaling between a terminal and a network and between a source base station and a target base station, thereby proposing an inter-node signaling system that can prevent node dependency that may occur when a source node directly transmits handover conditions to a terminal, and signal the success and failure of each cell during multi-target cell handover.

[0009] Embodiments of the present disclosure are directed to providing a method and apparatus for performing beam-based terminal autonomous handover in a wireless communication system.

[0010] Embodiments of the present disclosure are directed to solving the following problem: If the beam configuration information of contention-free random access resources that can be configured when a terminal performs conditional handover is very likely to change from the moment a conditional handover command is received to the time point of performing conditional handover, then contention-based random access is performed instead of contention-free random access.

[0011] [Technical Solution]

[0012] Embodiments of the present disclosure may provide a method performed by a source node in a wireless communication system, the method including: sending a handover request message to a target node, the handover request message including a target cell identifier related to conditional handover; receiving a handover request response message including a handover command message from the target node, the handover command message including configuration information of a target cell for conditional handover; and sending a radio resource control (RRC) reconfiguration message to a terminal, the RRC reconfiguration message including the handover command message and conditional information for conditional handover.

[0013] Embodiments of the present disclosure may provide a source node in a wireless communication system. The source node includes a transceiver. The source node is configured to: send a handover request message to a target node via the transceiver, the handover request message including a target cell identifier related to conditional handover; receive a handover request response message including a handover command message from the target node via the transceiver, the handover command message including configuration information of a target cell for conditional handover; and perform control to send a radio resource control (RRC) reconfiguration message to a terminal via the transceiver, the RRC reconfiguration message including the handover command message and conditional information for conditional handover.

[0014] Embodiments of the present disclosure may provide a method performed by a target node in a wireless communication system. The method includes: receiving a handover request message from a source node, the handover request message including a target cell identifier related to conditional handover; and sending a handover request response message including a handover command message to the source node, the handover command message including configuration information of a target cell for conditional handover, wherein a radio resource control (RRC) reconfiguration message including the handover command message and conditional information for conditional handover is sent from the source node to a terminal.

[0015] Embodiments of the present disclosure may provide a target node in a wireless communication system. The target node includes a transceiver and a controller. The controller is configured to: receive a handover request message from a source node via the transceiver, the handover request message including a target cell identifier related to conditional handover; and perform control to send a handover request response message including a handover command message to the source node via the transceiver, the handover command message including configuration information of a target cell for conditional handover, wherein a radio resource control (RRC) reconfiguration message including the handover command message and conditional information for conditional handover is sent from the source node to a terminal.

[0016] Embodiments of the present disclosure propose a method of adding conditional handover conditions to a handover command to improve performance or maintain node dependency. Embodiments of the present disclosure propose an inter-node message for signaling a handover configuration result value and a handover preparation request of a selected target cell in a target node to multiple target cells, thereby eliminating time and resource inefficiencies caused by repeated signaling due to an existing signaling system for a single target cell.

[0017] In embodiments of the present disclosure, a condition is generated based on beam intensity information not considered in existing handovers among conditions for conditional handover, and this condition is used together with existing cell-based handovers to perform conditional handover on a target cell capable of performing contention-free random access.

[0018] [Advantages of the Invention]

[0019] Embodiments of the present disclosure may provide a method and apparatus for handover in a next-generation mobile communication system. Embodiments of the present disclosure may provide a handover command signal method and apparatus for conditional handover in a next-generation mobile communication system.

[0020] Through the present disclosure, when transmitting conditional handover to a terminal, a source base station may transmit a handover command message received from a target base station without decoding, thereby achieving time efficiency or reducing inter-node signaling without breaking node dependencies. When performing conditional handover for multiple target cells, the time and resource efficiency can be improved by displaying the cells capable of performing handover between the target node and the source node to prepare for exchanging handover inter-node message signaling to a single target cell.

[0021] According to an embodiment of the present disclosure, beam-based handover can be efficiently performed in a wireless communication system.

[0022] According to an embodiment of the present disclosure, when performing conditional handover in a next-generation mobile communication system, handover can be performed on a target cell capable of using contention-free random access by adding or separately operating a condition based on beam intensity in addition to a condition based on cell intensity. The contention-free random access can be configured by the target base station when performing conditional handover. When performing conditional handover, the handover success probability can be increased by performing contention-free random access, and additional processes caused by contention-based random access can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a diagram showing the structure of an LTE system according to an embodiment of the present disclosure;

[0024] Figure 2 is a diagram showing the radio protocol structure of an LTE system according to an embodiment of the present disclosure;

[0025] Figure 3 is a diagram showing the structure of a next-generation mobile communication system according to an embodiment of the present disclosure;

[0026] Figure 4 is a diagram showing the radio protocol structure of a next-generation mobile communication system according to an embodiment of the present disclosure;

[0027] Figure 5 is a diagram showing the configuration of a terminal according to an embodiment of the present disclosure;

[0028] Figure 6 is a diagram showing the configuration of a base station according to an embodiment of the present disclosure;

[0029] Figure 7It is a diagram showing the process in which a source node determines a conditional handover and then transmits the conditions to a corresponding target node, and the target node generates a handover command according to an embodiment of the present disclosure;

[0030] Figure 8 It is a diagram showing the process in which a source node directly transmits the conditions of a conditional handover to a terminal according to an embodiment of the present disclosure;

[0031] Figure 9 It is a diagram showing the operation in which a source node attaches control information of the source node to a conditional handover command generated from a target node according to an embodiment of the present disclosure;

[0032] Figure 10 It is a diagram showing the operation of adding multiple cells to one conditional handover command when a source node is preparing for a multi-cell conditional handover according to an embodiment of the present disclosure;

[0033] Figure 11 It is a diagram showing the operation of adding one cell to one conditional handover command when a source node is preparing for a multi-cell conditional handover according to an embodiment of the present disclosure;

[0034] Figure 12 It is a diagram showing the operation related to determining a field for adding multi-target cell information in RCC reconfiguration information according to an embodiment of the present disclosure;

[0035] Figure 13 It is a diagram showing the signal flow of the process of performing a conditional handover when only beam-level conditions and no cell-level conditions are given to a terminal, corresponding to the 2-1st embodiment and the 2-2nd embodiment;

[0036] Figure 14 It is a diagram showing the signal flow of the process of performing a conditional handover when both cell-level conditions and beam-level conditions are given to a terminal, corresponding to the 2-3rd embodiment and the 2-4th embodiment;

[0037] Figure 15 It is a diagram showing the signal flow of the process of performing a conditional handover when a CFRA configuration is used as a beam-level condition configuration; and

[0038] Figure 16 It is a diagram showing the operation of performing a handover in a terminal considering beam-level and cell-level conditions according to an embodiment of the present disclosure. Detailed implementation manners

[0039] In the following, the operating principle of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description of the present disclosure, detailed descriptions of known functions or configurations incorporated herein will be omitted to avoid unnecessarily obscuring the subject matter of the present disclosure. The terms described below are defined in consideration of the functions in the present disclosure and may vary according to the user, their intention, or custom. Therefore, the definition of the terms should be determined based on the content of the entire specification.

[0040] For the same reason, in the accompanying drawings, some elements may be exaggerated, omitted, or schematically shown. Additionally, the size of each element does not exactly reflect the actual size. In the drawings, the same or corresponding elements have the same reference numerals.

[0041] Advantages and features of the present disclosure, as well as its implementation, will become more apparent by referring to the embodiments described in detail below with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments described below, but can be implemented in various different forms. The following embodiments are provided only to completely disclose the present disclosure and to inform those skilled in the art of the scope of the present disclosure, and the present disclosure is defined only by the scope of the appended claims. Throughout the specification, the same or similar reference numerals denote the same or similar elements.

[0042] In this context, it should be understood that each block shown in the flowchart, and combinations of blocks shown in the flowchart, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device to produce an article of manufacture such that the instructions executed by the processor of the computer or other programmable data processing device create a means for implementing the functions specified in one or more of the flowchart blocks. These computer program instructions can also be stored in a computer-usable or computer-readable memory, which can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-usable or computer-readable memory produce an article of manufacture including an instruction means that implements the functions specified in one or more of the flowchart blocks. The computer program instructions can also be loaded onto a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device, thereby producing a computer-implemented process such that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more of the flowchart blocks.

[0043] Additionally, each block illustrated in the flowchart may represent a module, a code segment, or a portion of code that includes one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative embodiments, the functions described in the blocks may not occur in the order shown. For example, depending on the functions involved, two consecutive blocks shown may actually be executed almost simultaneously or sometimes in the reverse order.

[0044] As used herein, a "unit" refers to a software element or a hardware element that performs a predetermined function, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) that performs a predetermined function. However, the meaning of "unit" is not always limited to software or hardware. A "unit" can be configured to be stored in an addressable storage medium or executed by one or more processors. Thus, a "unit" includes, for example, software elements, object-oriented software elements, class elements or task elements, processes, functions, attributes, programs, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and parameters. The elements and functions provided by a "unit" can be combined into a smaller number of elements or "units", or divided into a larger number of elements or "units". Additionally, the elements and "units" can be implemented as one or more CPUs within a reproduction device or a secure multimedia card. Additionally, a "unit" in an embodiment can include one or more processors.

[0045] In the following description, for ease of explanation, terms identifying access nodes, terms indicating network entities, terms indicating messages, terms indicating interfaces between network entities, and terms indicating various identification information, etc. are used. Therefore, the present disclosure is not limited to the terms used below, and other terms of a subject having an equivalent technical meaning can be used.

[0046] In the following description, for ease of description, the present disclosure uses the terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard. However, the present disclosure is not limited to these terms and names, and can be equally applicable to communication systems conforming to other standards.

[0047] Figure 1 is a diagram showing the structure of an LTE system according to an embodiment of the present disclosure.

[0048] Reference Figure 1 , as shown in the figure, the radio access network in the LET system can include next generation base stations (evolved Node B, hereinafter referred to as eNB, Node B, or base station) 1-05, 1-10, 1-15, and 1-20, a mobility management entity (MME) 1-25, and a serving gateway (S-GW) 1-30. A user terminal (user equipment, hereinafter referred to as UE or terminal) 1-35 can access an external network via eNBs 1-05 to 1-20 and S-GW 1-30.

[0049] In Figure 1Among them, ENBs 1-05 to 1-20 may correspond to existing Node Bs in the UMTS system. The ENBs are connected to UEs 1-35 via radio channels and may act as more complex roles compared to existing Node Bs. In the LTE system, all user services, including real-time services such as Voice over Internet Protocol (VoIP) over Internet Protocol, can be served through shared channels. Therefore, a device for collecting status information (such as buffer status, available transmission power status, and channel status of the UE) is required to perform scheduling, and ENBs 1-05 to 1-20 may be responsible for this operation. A single ENB usually can control multiple cells. For example, the LTE system may use a radio access technology such as Orthogonal Frequency Division Multiplexing (OFDM) with a 20 MHz bandwidth to achieve a data rate of 100 Mbps. Additionally, Adaptive Modulation and Coding (AMC) that determines the modulation scheme and channel decoding rate according to the channel status of the UE can be applied. The S-GW 1-30 is a device that provides data bearers and can establish or release data bearers under the control of the MME 1-25. The MME is a device responsible for various control functions and mobility management functions for terminals and can be connected to multiple base stations.

[0050] Figure 2 FIG. is a diagram showing the radio protocol structure of an LTE system according to an embodiment of the present disclosure.

[0051] Referring to Figure 2 , the radio protocol of the LTE system may include Packet Data Convergence Protocol (PDCP) 2-05 and 2-40, Radio Link Control (RLC) 2-10 and 2-35, and Medium Access Control (MAC) 2-15 and 2-30 in the terminal and the ENB, respectively. The PDCP may be responsible for operations such as IP header compression / recovery. The main functions of the PDCP can be summarized as follows.

[0052] - Header compression and decompression function: (Header compression and decompression: only ROHC)

[0053] - User data transmission function (transmission of user data)

[0054] - In-sequence delivery function (in-sequence delivery of upper layer PDUs during PDCP re-establishment process for RLC AM)

[0055] - Reordering function (for split bearers in DC (only RLC AM supported): routing of PDCP PDUs for transmission and reordering of PDCP PDUs for reception)

[0056] - Duplicate detection function (duplicate detection of lower layer SDUs during PDCP re-establishment process for RLC AM)

[0057] - Retransmission function (retransmit PDCP SDUs during handover for split bearers in DC; and retransmit PDCP PDUs during PDCP data recovery for RLC AM)

[0058] - Encryption and decryption function (encryption and decryption)

[0059] - Timer-based SDU discard function (timer-based SDU discard in the uplink)

[0060] Radio Link Control (RLC) 2-10 and 2-35 can reconfigure PDCP packet data units (PDUs) to appropriate sizes to perform ARQ operations, etc. The main functions of RLC are summarized as follows.

[0061] - Data transfer function (transfer of upper layer PDUs)

[0062] - ARQ function (error correction via ARQ (only for AM data transfer))

[0063] - Concatenation, segmentation, and reassembly function (concatenation, segmentation, and reassembly of RLC SDUs (only for UM and AM data transfer))

[0064] - Resegmentation function (resegmentation of RLC data PDUs (only for AM data transfer))

[0065] - Reordering function (reordering of RLC data PDUs (only for UM and AM data transfer))

[0066] - Duplicate detection function (duplicate detection (only for UM and AM data transfer))

[0067] - Error detection function (protocol error detection (only for AM data transfer))

[0068] - RLC SDU discard function (RLC SDU discard (only for UM and AM data transfer))

[0069] - RLC reconstruction function (RLC reconstruction)

[0070] MAC 2-15 and 2-30 can be connected to multiple RLC layer devices configured in a terminal, can multiplex RLC PDUs into MAC PDUs, and can demultiplex RLC PDUs from MAC PDUs. The main functions of MAC are summarized as follows.

[0071] - Mapping function (mapping between logical channels and transport channels)

[0072] - Multiplexing and demultiplexing functions (multiplexing MAC SDUs belonging to one or different logical channels into transport blocks (TBs) transmitted to the physical layer via a transport channel, or demultiplexing MAC SDUs from TBs transmitted from the physical layer via a transport channel)

[0073] - Scheduling information reporting function (scheduling information reporting)

[0074] - HARQ function (error correction via HARQ)

[0075] - Priority handling function between logical channels (priority handling between logical channels of a UE)

[0076] - Priority handling function between terminals (priority handling between UEs by means of dynamic scheduling)

[0077] - MBMS service identification function (MBMS service identification)

[0078] - Transmission format selection function (transmission format selection)

[0079] - Padding function (padding)

[0080] The NR PHY layer 2-20 and 2-25 can perform channel coding and modulation of upper layer data, form OFDM symbols from the channel-coded and modulated upper layer data, and transmit the OFDM symbols via a radio channel, or can demodulate and channel-decode the OFDM symbols received via the radio channel and transmit them to the upper layer.

[0081] Figure 3 is a diagram showing the structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0082] Reference Figure 3 , the radio access network of a next-generation mobile communication system (hereinafter referred to as NR or 5G) may include a next-generation base station (new radio node B, hereinafter referred to as NR gNB or NR base station) 3-10 and a next-generation radio core network (new radio core network, NR CN) 3-05. A next-generation radio user terminal (new radio user equipment, NR UE or terminal) 3-15 can access an external network via the NR gNB 3-10 and the NR CN 3-05.

[0083] In Figure 3Among them, NR gNB 3-10 can correspond to the evolved Node B (eNB) in the existing LTE system. The NR gNB can be connected to the NR UE 3-15 via a radio channel and can provide services superior to those of the existing Node B. In the next-generation mobile communication system, all user services can be provided via a shared channel. Therefore, a device for collecting status information (such as buffer status, available transmission power status, and channel status of the UE) for performing scheduling is required, and the NR NB 3-10 can be responsible for this operation. A single NR gNB can control multiple cells. In the next-generation mobile communication system, to achieve ultra-fast data transmission compared with the current LTE, a bandwidth greater than or equal to the current maximum bandwidth can be applied. Orthogonal frequency division multiplexing (OFDM) can be used as the radio access technology, and beamforming technology can also be combined. In addition, an adaptive modulation and coding (hereinafter referred to as AMC) scheme for determining the modulation scheme and channel coding rate according to the channel status of the terminal can be applied. The NR CN 3-05 can perform functions such as mobility support, bearer configuration, and QoS configuration. The NR CN 3c-05 is a device responsible for various control functions and the mobility management function of the terminal and can be connected to multiple base stations. The next-generation mobile communication system can be linked to the existing LTE system, and the NR CN 3c-05 can be connected to the MME 3-25 via a network interface. The MME 3-25 can be connected to the eNB3-30, which is an existing base station.

[0084] Figure 4 FIG. is a diagram showing the radio protocol structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0085] Referring to Figure 4 , the radio protocol of the next-generation mobile communication system can include an NR service data adaptation protocol (SDAP) 4-01 and 4-45, an NR PDCP 4-05 and 4-40, an NR RLC 4-10 and 4-35, and an NR MAC4-15 and 4-30 in the terminal and the NR base station, respectively.

[0086] The main functions of the NR SDAP 4-01 and 4-45 can include some of the following functions.

[0087] - User data transmission function (transmission of user plane data)

[0088] - Mapping function of QoS flows and data bearers in the uplink and downlink (mapping between QoS flows and DRBs in DL and UL)

[0089] - Function of marking QoS flow IDs in the uplink and downlink (marking QoS flow IDs in DL packets and UL packets)

[0090] - Mapping function of the reflected QoS flow of the uplink SDAP PDU to the data bearer (for the UL SDAP PDU, mapping of the reflected QoS flow to the DRB)

[0091] For the SDAP layer device, the terminal can be configured via radio resource control (RRC) messages to use the header of the SDAP layer device or the function of the SDAP layer device for each PDCP layer device, for each bearer, or for each logical channel. When the SDAP header is configured, the terminal can use the access stratum (AS) QoS reflection configuration 1-bit indicator (AS reflected QoS) and the non-access stratum (NAS) quality of service (QoS) reflection configuration 1-bit indicator (NAS reflected QoS) of the SDAP header to perform the indication, so that the terminal updates or reconfigures the mapping information of the QoS flow and the data bearer for the uplink and downlink. The SDAP header can include QoS flow ID information indicating QoS. The QoS information can be used as data processing priority, scheduling information, etc. to support smooth services.

[0092] The main functions of NR PDCP 4-05 and 4-40 can include some of the following functions.

[0093] - Header compression and decompression function: (Header compression and decompression: only ROHC)

[0094] - User data transfer function (Transfer of user data)

[0095] - In-sequence delivery function (In-sequence delivery of upper-layer PDUs)

[0096] - Out-of-sequence delivery function (Out-of-sequence delivery of upper-layer PDUs)

[0097] - Reordering function (PDCP PDU reordering for reception)

[0098] - Duplicate detection function (Duplicate detection of lower-layer SDUs)

[0099] - Retransmission function (Retransmission of PDCP SDUs)

[0100] - Encryption and decryption function (Encryption and decryption)

[0101] - Timer-based SDU discard function (Timer-based SDU discard in the uplink)

[0102] In the above description, the reordering function of the NR PDCP device may refer to the function of reordering the PDCP PDUs received from the lower layer in sequence based on the PDCP sequence number (SN). The reordering function of the NR PDCP device may include the function of transmitting data to the upper layer in the reordering order, or the function of directly transmitting data regardless of the order, and may include the function of performing reordering and recording the lost PDCP PDUs, including the function of reporting the status of the lost PDCP PDUs to the sending end, and including the function of requesting retransmission of the lost PDCP PDUs.

[0103] The main functions of NR RLC 4-10 and 4-35 may include some of the following functions.

[0104] - Data transfer function (transmission of upper layer PDUs)

[0105] - In-sequence delivery function (in-sequence delivery of upper layer PDUs)

[0106] - Out-of-sequence delivery function (out-of-sequence delivery of upper layer PDUs)

[0107] - ARQ function (error correction by ARQ)

[0108] - Concatenation, segmentation, and reassembly function (concatenation, segmentation, and reassembly of RLC SDUs)

[0109] - Resegmentation function (resegmentation of RLC data PDUs)

[0110] - Reordering function (reordering of RLC data PDUs)

[0111] - Duplicate detection function (duplicate detection)

[0112] - Error detection function (protocol error detection)

[0113] - RLC SDU discard function (RLC SDU discard)

[0114] - RLC reconstruction function (RLC reconstruction)

[0115] In the above description, the in-sequence delivery function of the NR RLC device may refer to the function of delivering the RLC SDUs received from the lower layer to the upper layer in sequence. When an original RLC SDU is divided into multiple RLC SDUs and received, the in-sequence delivery function of the NR RLC device may include the function of reassembling these RLC SDUs and transmitting them.

[0116] The in-sequence delivery function of the NR RLC device may include the function of reordering the received RLC PDUs according to the RLC sequence number (SN) or the PDCP sequence number (SN), may include the function of reordering and recording the lost RLC PDUs, may include the function of reporting the status of the lost RLC PDUs to the sending end, and may include the function of requesting retransmission of the lost RLC PDUs.

[0117] The in-sequence delivery function of the NR RLC device may include: the function of in-sequentially delivering only the RLC SDUs before the lost RLC SDU to the upper layer when there is a lost RLC SDU.

[0118] The in-sequence delivery function of the NR RLC device may include: the function of in-sequentially delivering all the RLC SDUs received before the start of the timer to the upper layer even if there is a lost RLC SDU if a predetermined timer expires.

[0119] The in-sequence delivery function of the NR RLC device may include: the function of in-sequentially delivering all the currently received RLC SDUs to the upper layer even if there is a lost RLC SDU if a predetermined timer expires.

[0120] The NR RLC device may process the RLC PDUs in the order of receipt of the RLC PDUs regardless of the order of the sequence numbers (out-of-sequence delivery), and may deliver the processed RLC PDUs to the NR PDCP device.

[0121] When the NR RLC device receives fragments, the NR RLC device may receive the fragments stored in the buffer or to be received later, may reconfigure these fragments into a complete RLC PDU, and then may send it to the NR PDCP device.

[0122] The NR RLC layer may not include the concatenation function, and this function may be performed in the NR MAC layer or may replace the multiplexing function of the NR MAC layer.

[0123] In the above description, the out-of-sequence delivery function of the NR RLC device may refer to the function of directly delivering the RLC SDUs received from the lower layer to the upper layer regardless of the order. The out-of-sequence delivery function of the NR RLC device may include the function of reorganizing the RLC SDUs and then delivering them when an original RLC SDU is divided into multiple RLC SDUs and then received. The out-of-sequence delivery function of the NR RLC device may include storing the RLC SN or PDCP SN of the received RLC PDUs, performing reordering, and recording the lost RLC PDUs.

[0124] NR MAC 4-15 and 4-30 can be connected to multiple NR RLC layer devices included in a terminal, and the main functions of NR MAC may include some of the following functions.

[0125] - Mapping function (mapping between logical channels and transport channels)

[0126] - Multiplexing / demultiplexing function (multiplexing / demultiplexing of MAC SDUs)

[0127] - Scheduling information reporting function (scheduling information reporting)

[0128] - HARQ function (error correction via HARQ)

[0129] - Priority handling function between logical channels (priority handling between logical channels of a UE)

[0130] - Priority handling function between terminals (priority handling between UEs by means of dynamic scheduling)

[0131] - MBMS service identification function (MBMS service identification)

[0132] - Transmission format selection function (transmission format selection)

[0133] - Padding function (padding)

[0134] NR PHY layers 4-20 and 4-25 can perform channel coding and modulation on the upper layer data, form the channel-coded and modulated upper layer data into OFDM symbols, and transmit the OFDM symbols via a radio channel, or can demodulate and channel-decode the OFDM symbols received via the radio channel and transmit them to the upper layer.

[0135] Figure 5 It is a diagram showing the configuration of a terminal according to an embodiment of the present disclosure.

[0136] Reference Figure 5 , the terminal may include a radio frequency (RF) processor 5-10, a baseband processor 5-20, a storage unit 5-30, and a controller 5-40. The controller 5-40 may further include a multi-connection processor 5-42.

[0137] The RF processor 5-10 can perform functions of transmitting or receiving signals via a radio channel, such as channel band conversion and signal amplification. That is, the RF processor 5-10 can up-convert the baseband signal provided from the baseband processor 5-20 into an RF band signal, transmit the up-converted RF band signal via an antenna, and then down-convert the RF band signal received via the antenna into a baseband signal. For example, the RF processor 5-10 can include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only one antenna is shown in the figure, the terminal can have multiple antennas. The RF processor 5-10 can include multiple RF chains. Additionally, the RF processor 5-10 can perform beamforming. For beamforming, the RF processor 5-10 can adjust the phase and amplitude of each signal transmitted or received via multiple antennas or antenna elements. The RF processor can perform MIMO operations and can receive multiple layers when performing MIMO operations.

[0138] The baseband processor 5-20 performs the conversion between the baseband signal and the bit stream according to the physical layer specification of the system. For example, during data transmission, the baseband processor 5-20 generates complex symbols by encoding and modulating the transmit bit stream. When data is received, the baseband processor 5-20 reconstructs the received bit stream by demodulating and decoding the baseband signal provided by the RF processor 5-10. For example, in the case of conforming to the orthogonal frequency division multiplexing (OFDM) scheme, during data transmission, the baseband processor 5-20 generates complex symbols by encoding and modulating the transmit bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols via an inverse fast Fourier transform (IFFT) operation and cyclic prefix (CP) insertion. Additionally, during data reception, the baseband processor 5-20 separates the baseband signal provided by the RF processor 5-10 in units of OFDM symbols, reconstructs the signal mapped to subcarriers via a fast Fourier transform (FFT), and then reconstructs the received bit stream via demodulation and decoding.

[0139] The baseband processor 5-20 and the RF processor 5-10 transmit and receive signals in the above-described manner. Accordingly, the baseband processor 5-20 and the RF processor 5-10 may be referred to as a transmitter, a receiver, a transceiver, a transceiver device, or a communication unit. Additionally, at least one of the baseband processor 5-20 and the RF processor 5-10 may include a plurality of communication modules to support a variety of different radio access technologies. At least one of the baseband processor 5-20 and the RF processor 5-10 may include different communication modules to process signals of different frequency bands. For example, different radio access technologies may include wireless LAN (e.g., IEEE 802.11), cellular networks (e.g., LTE), etc. Different frequency bands may include super high frequency (SHF) (e.g., 2NRHz, NRHz) bands and millimeter wave (e.g., 60 GHz) bands.

[0140] The storage unit 5-30 stores data for operating the terminal, such as default programs, application programs, and configuration information. In particular, the storage unit 5-30 may store information related to a second access node that performs radio communication by using a second radio access technology. The storage unit 5-30 provides the stored data in response to a request from the controller 5-40.

[0141] The controller 5-40 controls the overall operation of the terminal. For example, the controller 5-40 transmits or receives signals via the baseband processor 5-20 and the RF processor 5-10. The controller 5-40 records and reads data in the storage unit 5-30. To this end, the controller 5-40 may include at least one processor. For example, the controller 5-40 may include a communication processor (CP) configured to perform communication control and an application processor (AP) configured to control upper layers (such as application programs).

[0142] According to an embodiment of the present disclosure, the controller 5-40 may transmit a handover request message including a target cell identifier related to conditional handover to a target node via a transceiver, may receive a handover request response message including a handover command message from the target node via the transceiver, the handover command message including configuration information of a target cell for conditional handover, and may control to transmit a radio resource control (RRC) reconfiguration message including the handover command message and conditional information for conditional handover to the terminal via the transceiver.

[0143] The conditional information can be determined by the source node. The handover command message can be transmitted via the RRC container, and the source node may not modify the configuration information of the target cell included in the handover command message. The handover request response may include the cell identification information of the target cell for conditional handover, and the handover command message may include the delta configuration based on the source configuration information. The RRC reconfiguration message may include the information of one or more target cells for conditional handover, and the conditional information may be configured based on the measurement identifier (measurement ID) including the measurement object and the reporting configuration.

[0144] Figure 6 FIG. is a diagram showing the configuration of a base station according to an embodiment of the present disclosure.

[0145] Reference Figure 6 , the base station may include an RF processor 6-10, a baseband processor 6-20, a backhaul communication unit 6-30, a storage unit 6-40, and a controller 6-50. The controller 6-50 may further include a multi-connection processor 6-52. The base station may be an NR base station.

[0146] The RF processor 6-10 may perform functions of transmitting or receiving signals via a radio channel, such as channel band conversion and signal amplification. That is, the RF processor 6-10 may up-convert the baseband signal provided from the baseband processor 6-20 to an RF band signal, transmit the up-converted RF band signal via an antenna, and then down-convert the RF band signal received via the antenna to a baseband signal. For example, the RF processor 6-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is shown in the figure, the first access node may include multiple antennas. The RF processor 6-10 may include multiple RF chains. In addition, the RF processor 6-10 may perform beamforming. For beamforming, the RF processor 6-10 may adjust the phase and amplitude of each signal transmitted or received via multiple antennas or antenna elements. The RF processor may perform downlink MIMO operations by transmitting one or more layers.

[0147] The baseband processor 6-20 performs the conversion function between the baseband signal and the bit stream according to the physical layer specification of the first radio access technology. For example, during data transmission, the baseband processor 6-20 generates complex symbols by encoding and modulating the transmitted bit stream. When receiving data, the baseband processor 6-20 reconstructs the received bit stream by demodulating and decoding the baseband signal provided by the RF processor 6-10. For example, in the case of conforming to the OFDM scheme, during data transmission, the baseband processor 6-20 generates complex symbols by encoding and modulating the transmitted bit stream, maps the complex symbols to subcarriers, and then configures the OFDM symbols via IFFT operation and CP insertion. Additionally, during data reception, the baseband processor 6-20 separates the baseband signal provided by the RF processor 6-10 in units of OFDM symbols, reconstructs the signal mapped to the subcarriers via FFT operation, and then reconstructs the received bit stream via demodulation and decoding. The baseband processor 6-20 and the RF processor 6-10 send and receive signals in the above manner. Therefore, the baseband processor 6-20 and the RF processor 6-10 can be referred to as a transmitter, a receiver, a transceiver, a transceiver device, a communication unit, or a radio communication unit.

[0148] The backhaul communication unit 6-30 provides an interface for performing communication with other nodes within the network. That is, the backhaul communication unit 6-30 converts the bit stream sent from the master base station to another node (e.g., the secondary base station and the core network) into a physical signal, and converts the physical signal received from another node into a bit stream.

[0149] The storage unit 6-40 stores data for operating the master base station, such as default programs, application programs, and configuration information. In particular, the storage unit 6-40 can store information related to the bearers assigned to the connected terminals, measurement results reported from the connected terminals, etc. The storage unit 6-40 can store information used as a criterion for determining whether to provide multi-connection to the terminal or to suspend multi-connection. The storage unit 6-40 provides the stored data in response to a request from the controller 6-50.

[0150] The controller 6-50 controls the overall operation of the master base station. For example, the controller 6-50 sends or receives signals via the baseband processor 6-20 and the RF processor 6-10 or via the backhaul communication unit 6-30. The controller 6-50 records and reads data in the storage unit 6-40. To this end, the controller 6-50 can include at least one processor.

[0151] According to an embodiment of the present disclosure, the controller 6-50 may be controlled to receive a handover request message from a source node via a transceiver, the handover request message including a target cell identifier related to conditional handover; and transmit a handover request response message including a handover command message to the source node via the transceiver, the handover command message including configuration information of a target cell for conditional handover.

[0152] A radio resource control (RRC) reconfiguration message including a handover command message and conditional information for conditional handover may be sent from the source node to the terminal. The conditional information may be determined by the source node. The handover command message may be transmitted via an RRC container, and the configuration information of the target cell included in the handover command message may not be modified in the source node. The handover request response may include cell identification information of the target cell for conditional handover, and the handover command message may include an incremental configuration based on source configuration information. The RRC reconfiguration message may include information on one or more target cells for conditional handover, and the conditional information may be configured based on a measurement identifier (measurement ID) including a measurement object and a reporting configuration.

[0153] <First Embodiment>

[0154] Figure 7 is a diagram showing a process in which a source node determines a conditional handover according to an embodiment of the present disclosure, then transmits conditions to a corresponding target node, and the target node generates a handover command. In this case, the resource configuration validity period may also be transmitted to the corresponding target cell together with the conditions, and may be added to the conditional handover command to be sent to the terminal.

[0155] Reference Figure 7 , the communication system may include a terminal (UE), a source node (SN), and a target node (TN). In 710, the source node may determine a conditional handover (CHO). After the source node determines the conditional handover, in 720, the source node determines the corresponding target cell and transmits a HO preparation inter-node message to the target node operating the target cell. The source node may transmit the conditional information to be applied to each target cell included in the message. The HO preparation inter-node message may be a handover request message.

[0156] In 730, the target node finally determines a candidate target cell considering the handover applicability of the target cell given by the source node, and generates a handover command message having configuration values to be applied during the handover in the corresponding cell. For each candidate target cell, the handover execution conditional information already transmitted to the source base station may be added. Optionally, information for modifying the condition may be added if necessary.

[0157] In 740, the handover command message can be transmitted via a handover request confirmation message as an Xn message. The handover command message is an RRC message and can be included in the Xn message in the form of an octet string for transmission to the source node. The configuration information of the target cell that can be included in the handover command message can include CFRA resources (e.g., for all wide beams / cell-specific beams, and a given delay between CHO configuration and execution), PCell (dedicated and common) configuration, T304 (to ensure the actual CHO execution phase, i.e., starting after the conditions are met), radioBearerConfig, RLCbearerConfig, MAC config, measConfig, etc., and these can include a container for each target cell within a conditional handover, or a conditional handover command can be generated for each target cell and the corresponding information can be included therein. This information applies to Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 and Figure 11 all cases of.

[0158] (Conditional) The handover command message is an incremental signal based on the source configuration information of the terminal when the command message is transmitted to the terminal. Therefore, at the time point when the terminal receives the handover command, the newly added information can be used in the target cell, where the newly added information is obtained by overwriting, erasing, or changing the content included in the conditional handover command message compared to the current configuration information of the terminal itself. In another embodiment, for each target cell, the handover command message can be an incremental signal based on the conditional handover configuration information of the target cell that has been previously transmitted to the terminal. In this case, for a specific target cell, the terminal always updates the configuration information of the target cell by overwriting the newly received configuration information on the basis of the previously received configuration information, or by erasing or replacing the previous configuration information. This operation also applies to Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 and Figure 11 all cases of.

[0159] If octet strings are generated for each of multiple cells, for each cell, a specific factor in the respective octet string can have the same value, and in this case, for the convenience of signaling, the specific factor can have an indication that the specific factor is the same as another factor in the octet string list entry. The specific factor of a specific target cell with this indication can refer to the value of the corresponding factor of another cell in the octet string list.

[0160] In 750, since there is no separate decoding, the source node may transmit a handover command message of the octet string received from the target node to the terminal as an RRC reconfiguration message. The RRC reconfiguration message may include dedicated resource configuration information for each candidate target cell and condition information as a basis for determining the execution of conditional handover. The terminal that receives this message starts measurement according to the added conditions and determines whether the conditions are satisfied. If the conditions are satisfied, the terminal performs conditional handover to the target cell that satisfies the conditions.

[0161] Figure 8 FIG. is a diagram showing a process in which a source node directly transmits conditions for conditional handover to a terminal according to an embodiment of the present disclosure. In this case, the resource configuration valid time may also be transmitted to the corresponding target cell together with the conditions and directly transmitted to the terminal.

[0162] Reference Figure 8 , the communication system may include a terminal (UE), a source node (SN), and a target node (TN). In 810, the source node may determine conditional handover (CHO). After the source node determines conditional handover, in 820, the source node determines the corresponding target cell and transmits an HO preparation inter-node message to the target node operating the target cell. The source node does not transmit the condition information to be applied to each target cell included in this message.

[0163] In 830, the target node finally determines candidate target cells in consideration of the handover applicability of the target cell given by the source node and generates a handover command message having configuration values to be applied during handover in the corresponding cell. In 840, this handover command message may be transmitted via a handover request confirmation message as an Xn message. The handover command message is an RRC message and may be included in the Xn message in the form of an octet string to be transmitted to the source node.

[0164] In 850, the source node may decode the handover command message of the octet string received from the target node to check each target cell, and may add the conditions for conditional handover to the corresponding target cell for each cell. In 860, the source node adds the conditions for conditional handover for each cell, and then transmits the conditions in the RRC reconfiguration message back to the terminal via performing encoding. The RRC reconfiguration message may include dedicated resource configuration information for each candidate target cell and condition information as a basis for determining the execution of conditional handover.

[0165] The terminal that receives this RRC reconfiguration message starts measurement according to the added conditions and determines whether the conditions are satisfied. If the conditions are satisfied, the terminal may perform conditional handover to the target cell that satisfies the conditions.

[0166] In various embodiments of the present disclosure, it has been described that a source node sends an RRC reconfiguration message to a terminal, but this corresponds to an example of an RRC message, and other RRC messages may be used. When the radio access technology (RAT) of the source node of the present disclosure is LTE, the RRC message may be an RRC connection reconfiguration message.

[0167] Figure 9 FIG. is a diagram showing an operation in which a source node attaches control information of the source node to a conditional handover command generated by a target node according to an embodiment of the present disclosure. In this case, the resource configuration valid time may also be transmitted to the corresponding target cell together with the condition, and may be added to the conditional handover command or may be added by the source node to a separate field to be sent to the terminal.

[0168] Reference Figure 9 , a communication system may include a terminal (UE), a source node (SN), and a target node (TN). In 910, the source node may determine a conditional handover (CHO). After the source node determines the conditional handover, in 920, the source node determines the corresponding target cell and transmits an HO preparation inter-node message to the target node operating the target cell. The HO preparation inter-node message may be a handover request message. The source node does not transmit the condition information to be applied to each target cell included in this message.

[0169] In 930, the target node finally determines a candidate target cell in consideration of the handover applicability of the target cell given by the source node and generates a handover command message having configuration values to be applied during the handover in the corresponding cell. In 940, the handover command message is transmitted via a handover request confirmation message that is an Xn message. The handover command message is an RRC message and may be included in the Xn message in the form of an octet string to be transmitted to the source node. Here, in the case of multiple target cells, the handover command message may be included in the Xn message in the form of a list of octet strings.

[0170] In 950, the source node may add information controlled by the source node to a separate field separate from the handover command message of the octet string received from the target node. In this process, the octet string received from the target cell is not decoded, and the conditions for performing conditional handover and other information for controlling the terminal by the source node are added to this separate field. Since the octet string is not decoded, the source node does not modify the handover command message received from the target node or the information included in the handover command message. The information that can be added to the separate field can be information that needs to be reconfigured in the current source cell or common condition information for all or some groups of target cells rather than the configuration of conditional handover. Optionally, the source node may transmit the conditions of conditional handover to the target node, and the target node may generate a conditional handover command including the conditions and make it into an octet string to transmit the octet string back to the source node. In this case, the separate field of the aforementioned information controlled by the source node may not include the conditions of conditional handover, but may include the configuration information of the terminal configuration in the current source node.

[0171] After the encoding process, in 960, the source node may transmit this field as an information element separate from the octet string to the terminal through an integrated single RRC reconfiguration message. This RRC reconfiguration message may include dedicated resource configuration information of candidate target cells in each group or a specific group, condition information as the basis for determining the execution of conditional handover, and terminal configuration information unrelated to conditional handover required by the current source cell. The terminal receiving this message applies the terminal configuration required by the source cell, and updates and stores the configuration information in the target cell for conditional handover. Measurements may be started according to the added conditions of conditional handover, and it may be determined whether the conditions are met. If the conditions are met, the terminal may perform a conditional handover to the target cell that meets the conditions.

[0172] Table 1 below shows an example of the ASN.1 code of the RRCReconfiguration message generated in this way.

[0173] [Table 1]

[0174]

[0175] SN_control is the terminal control information separately added by the source node and may include the condition information of handover. tn_HO_CMD is the handover command octet string received from the target node for conditional handover. In Figure 7 、 Figure 8 and Figure 9In all embodiments, a plurality of target cells for conditional handover are requested from a target node, and the CGI of the plurality of target cells should be added to the target cell global ID field of the HANDOVER REQUEST message transmitted to the Xn interface. Table 2 below shows the content of the target cell global ID field in the HANDOVER REQUEST message. Multiple global CGI information segments of each target cell using the current target node ID and the ID of the target cell operating in the target node can be added to the target cell global ID field. The handover request message may include conditional handover information or conditional handover indication information.

[0176] [Table 2]

[0177]

[0178] The target node that receives the message may perform admission control and dedicated resource allocation for each target cell. Figure 10 is a diagram showing the operation of adding multiple cells to a conditional handover command when preparing for multi-cell conditional handover according to an embodiment of the present disclosure.

[0179] Reference Figure 10 , the communication system may include a terminal (UE), a source node (SN), and a target node (TN). In 1010, the source node may determine a conditional handover (CHO). In 1020, the source node may request the target node to prepare for handover to a plurality of target cells. The source node may send a handover preparation message (handover preparation INM message) including conditions for each cell or each cell group to the target node.

[0180] In 1030, when the target node generates a handover command for a target cell, the target node may generate a handover command for the corresponding target cell instead of generating one handover command. Each handover command is an octet string, and in 1040, it may be included as a separate octet string in the handover request confirmation message sent from the target node to the source node. Therefore, the following transparent container field from the target NG-GAN node to the source NG-RAN node may have separate octet strings based on the target cell global ID or index of the candidate target cells determined in each target node. For this purpose, a list of target cell CGIs or a list of indexes of the determined target cells may be added to the HANDOVER REQUEST ACKNOWLEDGE message, and the following transparent container field may include multiple octet strings in the order of the corresponding list.

[0181] [Table 3]

[0182]

[0183] In this case, the conditions for each target cell can be included in each handover command. At 1050, the source node may generate an RRC reconfiguration message including each handover command received from the target node to send the generated RRC reconfiguration message to the terminal. The source node does not need to decode the handover commands received from the target node.

[0184] Figure 11 is a diagram illustrating an operation of adding one cell to one conditional handover command when a source node is preparing for multi-cell conditional handover according to an embodiment of the present disclosure.

[0185] Refer to Figure 11 , a communication system may include a terminal (UE), a source node (SN), and a target node (TN). At 1110, the source node may determine a conditional handover (CHO). At 1120, the source node requests the target node to prepare for handover of multiple target cells. The source node may send a handover preparation message (handover preparation INM message) including conditions for each cell or each cell group to the target node.

[0186] At 1130, when generating a handover command for a target cell, the target node may generate a handover command by adding dedicated configuration information and handover condition configuration information for multiple candidate target cells to one handover command. In this case, information about multiple target cells is included in the handover command message but represented as one octet string, such that the target cells selected as candidate target cells are not likely to be unknown in the Xn message of HANDOVER REQUEST ACKNOWLEDGE.

[0187] At 1140, the target node may send an Xn message carrying the handover command message represented as a single octet string to the source node. At 1150, the source node sends an RRC reconfiguration message including this handover command message to the terminal without decoding.

[0188] Figure 12 is a diagram illustrating an operation related to determining a field for adding multi-target cell information in RCC reconfiguration information according to an embodiment of the present disclosure.

[0189] Refer to Figure 12, when a handover command message is included in the RRC reconfiguration message given to the terminal, if the message includes information about multiple candidate target cells, an option for configuring the detailed location of the condition may be provided. The first option is that the handover command message is included in the SpcellConfig IE but outside reconfigWithSync. The second option is that the handover command message is included in the reconfigWithSync IE but outside spcellConfigCommon. The third option is that the handover command message is within the spcellConfigCommon IE. The last option is the method where the handover command message is within cellGroupConfig and outside SpcellConfig. In particular, in this case, the handover command message may be within the measConfig IE, where each condition is displayed together with the candidate target cell ID (i.e., physical cell ID or CGI).

[0190] As another configuration method, by including the target cell id information in SpcellConfig, the dedicated resource configuration information of each candidate target cell can be listed multiple times at the SpcellConfig level. Optionally, by including the target cell id information at the reconfigWithSync level, it can be listed multiple times at the reconfigWithSync level. In the latter case, the dedicated configuration information of each target cell can be added to reconfigWithSync, and the common configuration information of the cell can be outside reconfigWithSync of SpcellConfig without the target cell id. Optionally, the dedicated configuration information of each target cell can be transmitted to SpcellConfigCommon by using the target cell id. Optionally, by adding the target cell id to SpcellConfigDedicated located within SpcellConfig and outside reconfigWithSync, the dedicated resource configuration information of the corresponding target cell can be transmitted to the terminal.

[0191] In another embodiment, there may be various methods to signal the conditions included in the RRCReconfiguration message. Each method is necessary for the method of reducing signaling overhead. For the current source cell and each target cell or a specific target cell group, the following options are possible.

[0192] - Option 1. Signal the measObject and reportConfig that constitute each condition.

[0193] - Option 2. Mention the measObject id used in the current source spcell cell and signal a separate reportConfig.

[0194] - Option 3. As a measObject, signal the target cell id (CGI or physical cell id) to which the corresponding conditions are to be applied and a separate reportConfig.

[0195] - Option 4. As a measObject, signal the target cell id (CGI or physical cell id) to which the corresponding conditions are to be applied and the reportConfig id used in the current source cell. Optionally, when signaling the reportConfig id used in the current source cell, only the configuration information to be changed can be added.

[0196] - Option 5. Signal the measurement id used in the current spcell and reconfigure the sub - fields present in the corresponding measObject and reportConfig so that the fields changed from the currently used configuration can be signaled.

[0197] - Option 6. In the absence of a signal of the measurement id used in the current spcell, the measurement objects and report configurations used when performing a report to add target cells to which each condition is applied are used as a basis, and only the sub - fields of the measurement objects and report configurations are reconfigured to signal. The terminal recognizes this changed configuration as an incremental configuration and applies it to the measurement and condition evaluation of CHO performance conditions.

[0198] The changeable parts in the options can be, for example, the event type or the offset value used in each event type, the thresholds of the serving cell and target cells, the offset value for each frequency, the offset value for each cell, the serving cell and target cell frequencies to be measured, the sub - carrier spacing information, the SMTC information, the reference signal type, the maximum number of RS or beams required for beam combining, the threshold for determining the beam - specific reception intensity for each measurement beam, etc.

[0199] In Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 and Figure 11In the case where a terminal receives an RRCReconfiguration message, if source cell conditions are included, an RRCReconfigurationComplete message is always transmitted to the source node. If only configurations related to conditional handover are included, when the terminal receives the reconfiguration message, the completion message may not be transmitted. Instead, when the conditions are invoked and conditional handover starts, if successful access to the corresponding target cell is achieved, a completion message may be sent to the target cell.

[0200] Figure 13 is a diagram of a signal flow of a process of performing conditional handover when only beam-level conditions and no cell-level conditions are given to a terminal according to an embodiment of the present disclosure, corresponding to Embodiment 2-1 and Embodiment 2-2. Refer to Figure 13 In 1305, the source node (serving base station) may determine to perform conditional handover (CHO). Then, in 1310, the source node may send a message for requesting conditional handover preparation to the target node. The message for requesting conditional handover preparation may include an indication of a handover message for conditional handover. The message for requesting conditional handover preparation may include beam-based condition configurations for conditional handover and cell IDs of candidate cells.

[0201] In 1315, the target node that receives the message for requesting conditional handover preparation may determine whether the target cell indicated by the serving node can perform conditional handover, and may generate a conditional handover command message by adding dedicated resource configuration information to be used in the target cell. The conditional handover command message may include beam-level condition configuration information of candidate target cells capable of performing conditional handover. In 1320, the target node may transmit the generated conditional handover command message to the source node.

[0202] In 1325, the source node may transmit the conditional handover command received from the target node to the terminal via an RRCReconfiguration message. If the source node did not transmit beam-level configuration condition information to the target node during the previous handover preparation, the handover command message may not include beam-level configuration conditions, and in this case, the source node may directly add beam-level configuration conditions applied to each candidate target node in the RRCReconfiguration message to transmit the beam-level configuration conditions to the terminal.

[0203] In 1330, 1335, and 1340, the terminal that receives the RRCReconfiguration message may start measuring the intensities of the beams configured in the source cell and each target cell, which are beams configured for beam-level condition configuration, and may evaluate whether the measured beam intensities satisfy the beam-level conditions.

[0204] In 1345, if there is a target cell that meets the transmitted beam level condition during the measurement of the beam intensity, the terminal can perform a conditional handover to the target cell that meets the beam level condition. In 1350, the terminal can perform a random access to the target cell selected to perform the conditional handover.

[0205] According to the 2-1 embodiment, the serving base station (source node) can send a configuration for conditional handover to the terminal. The serving base station can configure an event condition based on beam intensity for each handover candidate target cell or each group of candidate target cells. The terminal can be given a specific beam of the serving cell (i.e., N beam indices of the synchronization signal block (SSB) or the channel state information reference signal (CSI-RS)) and / or M specific beams of the corresponding target cell (i.e., indices of the SSB or CSI-RS) as configuration information for the beam intensity-based condition. An evaluation condition for comparing the beam of the serving cell with the beam of the target cell can be given to the terminal. The reference signal received power (RSRP), the reference signal received quality (RSRQ), the received signal strength indicator (RSSI), or the reference signal interference noise ratio (Rs-SINR) can be considered as the intensity unit of each beam. If the foregoing beam information is given to the terminal, the terminal can start beam measurement and can determine whether the measured beam meets the evaluation condition. If the beam of the target cell meets the given condition, the terminal can perform a handover to the target cell that meets the condition.

[0206] There can be a type A1 as the beam intensity evaluation condition. As a parameter related to type A1, a threshold for comparison with the beam intensity value can be configured for the terminal. When the N beam indices of the serving cell, the event type information, and the threshold are given, the terminal can measure the received intensity of the N beams of the configured serving cell; and if the average value of the N beam intensities, the minimum value among the N beam intensities, or the maximum value among the N beam intensities of the serving cell is greater than the given threshold, the terminal considers that event A1 is satisfied.

[0207] There can be a type A2 as another beam intensity evaluation condition. As a parameter related to type A2, a threshold for comparison with the beam intensity value can be configured for the terminal. When the N beam indices of the serving cell, the event type information, and the threshold are given, the terminal can measure the received intensity of the N beams of the configured serving cell; and if the average value of the N beam intensities, the minimum value among the N beam intensities, or the maximum value among the N beam intensities of the serving cell is less than the given threshold, the terminal considers that event A2 is satisfied.

[0208] There may be a type A3 as another beam intensity evaluation condition. As a parameter related to type A3, an offset value for comparing the beam intensity of the serving cell with the beam intensity of the target cell may be configured for the terminal. When the beam index of the serving cell, the beam index of the target cell, the event type information, and the offset value are given, the terminal may measure the received intensities of N beams of the configured serving cell and the received intensities of M beams of the configured target cell; and if the average value of the N beam intensities of the serving cell is smaller than the average value of the M beam intensities of the target cell by the offset amount, the terminal may consider that event A3 is satisfied. Optionally, if the minimum value of the N beam intensities of the serving cell is smaller than the minimum value of the M beam intensities of the target cell by the offset amount, or if the maximum value of the N beam intensities of the serving cell is smaller than the maximum value of the M beam intensities of the target cell by the offset amount, the terminal may consider that event A3 is satisfied. Optionally, if the maximum value of the N beam intensities of the serving cell is smaller than the minimum value of the M beam intensities of the target cell by the offset amount, the terminal may consider that event A3 is satisfied.

[0209] There may be a type A4 as another beam intensity evaluation condition. As a parameter related to type A4, a threshold for comparing with the beam intensity value may be configured for the terminal. When the M beam indices of the target cell, the event type information, and the threshold are given, the terminal may measure the received intensities of the M beams of the configured target cell; and if the average value of the M beam intensities, the minimum value among the M beam intensities, or the maximum value among the M beam intensities of the target cell is greater than the given threshold, the terminal considers that event A4 is satisfied.

[0210] There may be a type A5 as another beam intensity evaluation condition. As a parameter related to type A5, a threshold for comparing with the beam intensity value and a threshold for comparing with the beam intensity value of the target cell may be configured for the terminal. When the N beam indices of the serving cell, the threshold of the serving cell, the M beam indices of the target cell, the threshold of the target cell, and the event information type are given, the terminal may measure the received intensities of the N beams of the configured serving cell and may measure the received intensities of the M beams of the configured target cell; wherein if the average value of the N beam intensities, the maximum value among the N beam intensities, or the minimum value among the N beam intensities of the serving cell is smaller than the threshold of the serving cell, and if the average value of the M beam intensities, the minimum value among the M beam intensities, or the maximum value among the M beam intensities of the target cell is greater than the given threshold, the terminal may consider that event A5 is satisfied.

[0211] Among the parameters related to the aforementioned types A1 to A5, the parameters related to type A3 may include a serving cell specific offset and a measurement object specific offset of the serving cell, and the values of these parameters may be added to the serving cell part of the offset of type A3 above. The parameters related to type A3 may also include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the target cell part of the offset of type A3 above. The parameters related to type A4 may include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the value part of the target beam to be compared with the threshold of type A4 above. The parameters related to type A5 may include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the value part of the target beam to be compared with the threshold of the target cell of type A5 above.

[0212] According to the 2-2 embodiment, the serving base station may send a configuration for conditional handover to the terminal. The serving base station may configure beam intensity-based event conditions for the terminal for each switched candidate target cell or each candidate target cell group. The number of beams N to be considered for event determination conditions in the serving cell and / or the number of beams M to be considered for event determination conditions in the target cell may be given to the terminal as configuration information of the beam intensity-based conditions. Configuration information regarding the reference signal (RS) type of each beam to be considered in the serving cell and / or the target cell may also be transmitted to the terminal. The configuration information regarding the RS type may be information indicating that the RS type of each beam is SSB or CSI-RS. An evaluation condition for comparison between the beams of the serving cell and the beams of the target cell may be given to the terminal. RSRP, RSRQ, RSSI, or Rs-SINR may be considered as the intensity unit of each beam. If the above information regarding the number of beams is given to the terminal, the terminal may start measuring all the beams corresponding to the corresponding RS type and may determine whether the measured beams satisfy the evaluation condition. If the beams of the target cell satisfy the given condition, the terminal may perform a handover to the target cell that satisfies the condition.

[0213] There may be a type A1 as the beam intensity evaluation condition. As a parameter related to type A1, a threshold for comparison with the beam intensity value may be configured for the terminal. When the N value of the serving cell, the event type information, and the threshold are given, the terminal may measure the reception intensity of all the beams of the serving cell; and if the average value of the intensities of the N beams with the maximum reception intensity among the measured beams of the serving cell, the minimum value among the intensities of the N beams with the maximum reception intensity, or the maximum value among the intensities of the N beams with the maximum reception intensity is less than the given threshold, the terminal may consider that event A1 is satisfied.

[0214] There may be a type A2 as another beam intensity evaluation condition. As a parameter related to type A2, a threshold for comparison with the beam intensity value can be configured for the terminal. When the N value of the serving cell, the event type information, and the threshold are given, the terminal can measure the received intensities of all beams of the serving cell; and if the average value of the N beam intensities with the maximum received intensities among the measured beams of the serving cell, the minimum value among the N beam intensities with the maximum received intensities, or the maximum value among the N beam intensities with the maximum received intensities is less than the given threshold, the terminal can consider that event A2 is satisfied.

[0215] There may be a type A3 as another beam intensity evaluation condition. As a parameter related to type A3, an offset value for comparison between the beam intensity of the serving cell and the beam intensity of the target cell can be configured for the terminal. When the number of beams N of the serving cell, the number of beams M of the target cell, the event type information, and the offset value are given, the terminal can measure the received intensities of all beams of the serving cell and the received intensities of all beams of the target cell; and if the average value of the N beam intensities with the maximum received intensities among the measured beams of the serving cell is smaller than the average value of the M beam intensities with the maximum received intensities among the measured beams of the target cell by a certain offset amount, the terminal can consider that event A3 is satisfied. Optionally, if the minimum value among the N beam intensities with the maximum received intensities of the serving cell is smaller than the minimum value among the M beam intensities with the maximum received intensities of the target cell by a certain offset amount, or if the maximum value among the N beam intensities with the maximum received intensities of the serving cell is smaller than the maximum value among the M beam intensities with the maximum received intensities of the target cell by a certain offset amount, the terminal can consider that event A3 is satisfied. Optionally, if the maximum value among the N beam intensities with the maximum received intensities of the serving cell is smaller than the minimum value among the M beam intensities with the maximum received intensities of the target cell by a certain offset amount, the terminal can consider that event A3 is satisfied.

[0216] There may be a type A4 as another beam intensity evaluation condition. As a parameter related to type A4, a threshold for comparison with the beam intensity value can be configured for the terminal. When the M value of the target cell, the event type information, and the threshold are given, the terminal can measure the received intensities of all beams of the target cell, and if the average value of the M beam intensities with the maximum received intensities among the measured beams of the target cell, the minimum value among the M beam intensities with the maximum received intensities, or the maximum value among the M beam intensities with the maximum received intensities is less than the given threshold, the terminal can consider that event A4 is satisfied.

[0217] There may be a type A5 as another beam intensity evaluation condition. As parameters related to type A5, a threshold for comparison with the beam intensity value and a threshold for comparison with the beam intensity value of the target cell may be configured for the terminal. When the N value of the serving cell, the threshold of the serving cell, the M value of the target cell, the threshold of the target cell, and the type of event information are given, the terminal may measure the received intensity of all beams of the serving cell and may measure the received intensity of all beams of the target cell; wherein if the average value of the N beam intensities with the maximum received intensity among the measured beams of the serving cell, the maximum value among the N beam intensities with the maximum received intensity, or the minimum value among the N beam intensities with the maximum received intensity is less than the threshold of the serving cell, and if the average value of the M beam intensities with the maximum received intensity among the measured beams of the target cell, the minimum value among the M beam intensities with the maximum received intensity, or the maximum value among the M beam intensities with the maximum received intensity is greater than the given threshold, the terminal may consider that event A5 is satisfied.

[0218] Among the parameters related to the foregoing types A1 to A5, the parameters related to type A3 may include a serving cell specific offset and a measurement object specific offset of the serving cell, and the values of these parameters may be added to the serving cell part of the offset of the above type A3. The parameters related to type A3 may also include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the target cell part of the offset of the above type A3. The parameters related to type A4 may include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the value part of the target beam for comparison with the threshold of the above type A4. The parameters related to type A5 may include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the value part of the target beam for comparison with the threshold of the target cell of the above type A5.

[0219] Figure 14 is a signal flow diagram in the case where both cell-level conditions and beam-level conditions are given to the terminal according to an embodiment of the present disclosure, corresponding to the 2-3rd embodiment and the 2-4th embodiment. Refer to Figure 14 , in 1405, the source node may determine to perform conditional handover (CHO). Then, in 1410, the source node may send a message for requesting conditional handover preparation to the target node. The message for requesting conditional handover preparation may include an indication of the handover message for conditional handover. The message for requesting conditional handover preparation may include the cell id of the candidate cell for conditional handover and the cell and beam-based condition configuration.

[0220] In 1415, a target node that receives a message for requesting conditional handover preparation may determine whether a target cell indicated by a serving node is capable of performing a conditional handover, and may generate a conditional handover command message by adding dedicated resource configuration information to be used in the target cell. The conditional handover command message may include cell-level and beam-level condition configuration information of candidate target cells capable of performing a conditional handover. In 1420, the target node may transmit the generated conditional handover command message to the source node.

[0221] In 1425, the source node may transmit the conditional handover command received from the target node to the terminal via an RRCReconfiguration message. If the source node did not transmit cell-level and beam-level configuration condition information to the target node during a previous handover preparation, the handover command message may not include cell-level and beam-level configuration conditions, and in this case, the source node may directly add cell-level and beam-level configuration conditions applied to each candidate target node in the RRCReconfiguration message to transmit the cell-level and beam-level configuration conditions to the terminal.

[0222] In 1430, 1435, and 1440, a terminal that receives an RRCReconfiguration message may start measuring the intensity of beams configured for cell-level and beam-level conditions for each candidate target cell and the source cell, and may evaluate whether the measured beam intensity satisfies the cell-level and beam-level conditions. In 1445, if, during the measurement of the beam intensity, there is a target cell that satisfies the transmitted cell-level condition, the terminal may further determine whether the target cell that satisfies the cell-level condition satisfies the beam-level condition configured for the target cell, and if there is even a target cell that satisfies the transmitted beam-level condition, the terminal may perform a conditional handover to the target cell. In 1450, the terminal may perform random access to the target cell selected to perform a conditional handover.

[0223] According to the second to third embodiments, the serving base station may send configurations for conditional handover to the terminal. The serving base station may simultaneously configure cell strength-based conditions and beam strength-based conditions for each switched candidate target cell or each candidate target cell group. The cell strength-based conditions may include reporting configuration information and measurement object information for determining A1, A2, A3, A4, A5, and A6 events and corresponding events in LTE and NR standards, as well as beam combination-related configurations (RS type, threshold for determining the received strength of each beam, maximum number of beams to consider cell strength among beams with values exceeding the threshold, etc.). Different from the above, the serving base station may configure beam strength-based event conditions to the terminal. The terminal may be given a specific beam of the serving cell (i.e., N beam indices of the synchronization signal block (SSB) or the channel state information reference signal (CSI-RS)) and / or M specific beams of the corresponding target cell (i.e., indices of the SSB or CSI-RS) as configuration information for the beam strength-based conditions. The terminal may be given an evaluation condition for comparing the beams of the serving cell with those of the target cell. RSRP, RSRQ, RSSI, or Rs-SINR may be considered as the strength unit for each beam. If the foregoing beam information is given to the terminal, the terminal may start beam measurement and determine whether the measured beams meet the evaluation condition.

[0224] If the target cell meets the cell strength-based conditions given in the conditional handover configuration information and the target cell also meets the beam strength conditions given to the target cell with respect to the cell strength-based conditions and the beam strength-based conditions, the terminal may switch to the target cell that meets both conditions. When the corresponding cell and beam strength-based condition configuration information is given, cell and beam strength measurements may be performed. If there are multiple target cells that meet the cell strength-based conditions simultaneously, the terminal may preferentially switch to the target cell that meets the given beam strength-based conditions among the target cells that meet the cell strength-based conditions.

[0225] There may be a type A1 as the beam strength evaluation condition. As a parameter related to type A1, a threshold for comparison with the beam strength value may be configured for the terminal. When the N beam indices of the serving cell, event type information, and the threshold are given, the terminal may measure the received strength of the N beams of the configured serving cell, and if the average value of the N beam strengths, the minimum value among the N beam strengths, or the maximum value among the N beam strengths of the serving cell is greater than the given threshold, the terminal may consider that event A1 is satisfied.

[0226] There may be a type A2 as another beam intensity evaluation condition. As a parameter related to type A2, a threshold used to compare with the beam intensity value can be configured for the terminal. When the N beam indices of the serving cell, the event type information, and the threshold are given, the terminal can measure the received intensities of the N beams of the configured serving cell, and if the average value of the N beam intensities, the minimum value among the N beam intensities, or the maximum value among the N beam intensities of the serving cell is less than the given threshold, the terminal can consider that event A2 is satisfied.

[0227] There may be a type A3 as another beam intensity evaluation condition. As a parameter related to type A3, an offset value for comparison between the beam intensity of the serving cell and the beam intensity of the target cell can be configured for the terminal. When the beam index of the serving cell, the beam index of the target cell, the event type information, and the offset value are given, the terminal can measure the received intensities of the N beams of the configured serving cell and the received intensities of the M beams of the configured target cell, and if the average value of the N beam intensities of the serving cell is smaller than the average value of the M beam intensities of the target cell by the offset amount, the terminal can consider that event A3 is satisfied. Optionally, if the minimum value among the N beam intensities of the serving cell is smaller than the minimum value among the M beam intensities of the target cell by the offset amount, or if the maximum value among the N beam intensities of the serving cell is smaller than the maximum value among the M beam intensities of the target cell by the offset amount, the terminal can consider that event A3 is satisfied. Optionally, if the maximum value among the N beam intensities of the serving cell is smaller than the minimum value among the M beam intensities of the target cell by the offset amount, the terminal can consider that event A3 is satisfied.

[0228] There may be a type A4 as another beam intensity evaluation condition. As a parameter related to type A4, a threshold used to compare with the beam intensity value can be configured for the terminal. When the M beam indices of the target cell, the event type information, and the threshold are given, the terminal can measure the received intensities of the M beams of the configured target cell, and if the average value of the M beam intensities, the minimum value among the M beam intensities, or the maximum value among the M beam intensities of the target cell is greater than the given threshold, the terminal considers that event A4 is satisfied.

[0229] There may be a type A5 as another beam intensity evaluation condition. As parameters related to type A5, a threshold for comparison with a beam intensity value and a threshold for comparison with a beam intensity value of a target cell may be configured for a terminal. When the N beam indices of a serving cell, the threshold of the serving cell, the M beam indices of a target cell, the threshold of the target cell, and the type of event information are given, the terminal may measure the received intensities of the N beams of the configured serving cell and may measure the received intensities of the M beams of the configured target cell, where if the average value of the N beam intensities, the maximum value among the N beam intensities, or the minimum value among the N beam intensities of the serving cell is less than the threshold of the serving cell, and if the average value of the M beam intensities, the minimum value among the M beam intensities, or the maximum value among the M beam intensities of the target cell is greater than the given threshold, the terminal may consider that event A5 is satisfied.

[0230] Among the parameters related to the foregoing types A1 to A5, the parameters related to type A3 may include a serving cell specific offset and a measurement object specific offset of the serving cell, and the values of these parameters may be added to the serving cell part of the offset of the above type A3. The parameters related to type A3 may also include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the target cell part of the offset of the above type A3. The parameters related to type A4 may include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the value part of the target beam (e.g., the beam configured to be measured in the target cell) for comparison with the threshold of the above type A4. The parameters related to type A5 may include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the value part of the target beam for comparison with the threshold of the target cell of the above type A5.

[0231] As an example of the above-described second to third embodiments, in the handover preparation in each target cell, contention-free random access may be performed using dedicated random access configuration information for a specific beam of the corresponding target cell. The configuration information for contention-free random access may include an index of a beam capable of transmitting a contention-free RACH preamble, contention-free preamble information to be used in the beam, time / frequency information used for preamble transmission in the beam, threshold information to be considered when performing contention-free random access if there is a beam whose intensity exceeds a specific threshold in the corresponding beam, and the like. A target cell that has requested conditional handover preparation may configure contention-free random access resources for a specific beam, and may add cell-based conditions and beam intensity-based conditions for the target cell to the corresponding conditional handover command to send the conditional handover command to the terminal. Alternatively, the source cell may receive information of the target cell and send cell-based and beam intensity-based conditions to the terminal. Information on beam-based conditions may be as follows. For each target cell, an evaluation condition of type A4 and beam index information may be notified to the terminal as beam intensity-based conditions to be used for the evaluation of type A4, the beam index information being configured as index information of M beams of the target cell enabling contention-free random access preamble transmission; and a threshold for beam evaluation when performing contention-free random access may be notified to the terminal as a threshold of type A4. To perform conditional handover, the terminal may evaluate cell-based conditions, may preferentially select, from cells that satisfy the cell-based conditions, a target cell that satisfies the beam intensity-based conditions of type A4 among cells in which contention-free random access has been configured, and may perform conditional handover to one of the selected cells.

[0232] According to the second to fourth embodiments, the serving base station may send configurations for conditional handover to the terminal. The serving base station may simultaneously configure conditions based on cell strength and conditions based on beam strength for each switched candidate target cell or candidate target cell group. The conditions based on cell strength may include report configuration information and measurement object information for determining A1, A2, A3, A4, A5, and A6 events and corresponding events in LTE and NR standards, as well as configurations related to beam combination (RS type, threshold for determining the reception strength of each beam, maximum number of beams for which cell strength is to be considered among the beams having values exceeding the threshold, etc.). Different from the above, the serving base station may configure event conditions based on beam strength to the terminal. The number of beams N to be considered for event determination conditions in the serving cell and / or the number of beams M to be considered for event determination conditions in the target cell may be given to the terminal as configuration information for the conditions based on beam strength. Configuration information regarding the reference signal (RS) type for each beam to be considered in the serving cell and / or the target cell may also be transmitted to the terminal. The configuration information regarding the RS type may be information indicating that the RS type of each beam is SSB or CSI-RS. An evaluation condition for comparing the beams in the serving cell with the beams in the target cell may be given to the terminal. RSRP, RSRQ, RSSI, or Rs-SINR may be considered as the intensity unit for each beam. If the above information regarding the number of beams is given to the terminal, the terminal may start measuring all the beams corresponding to the corresponding RS type and may determine whether the measured beams satisfy the evaluation condition.

[0233] If, with respect to the conditions based on cell strength and the conditions based on beam strength, the target cell satisfies the conditions based on cell strength given in the conditional handover configuration information and the target cell also satisfies the beam strength conditions given for the target cell, the terminal may hand over to the target cell that satisfies both conditions. When the corresponding configuration information based on cell and beam strength is given, cell and beam strength measurements may be performed. If there are multiple target cells that satisfy the conditions based on cell strength simultaneously, the terminal may preferentially hand over to the target cell that satisfies the conditions based on cell strength and also satisfies the given conditions based on beam strength among the target cells that satisfy the conditions based on cell strength.

[0234] There may be a type A1 as the beam strength evaluation condition. As a parameter related to type A1, a threshold for comparison with the beam strength value may be configured for the terminal. When the N value of the serving cell, event type information, and the threshold are given, the terminal may measure the reception strength of all the beams in the serving cell, and if the average value of the strengths of the N beams with the maximum reception strength among the measured beams in the serving cell, the minimum value among the strengths of the N beams with the maximum reception strength, or the maximum value among the strengths of the N beams with the maximum reception strength is less than the given threshold, the terminal may consider that event A1 is satisfied.

[0235] There may be a type A2 as another beam intensity evaluation condition. As a parameter related to type A2, a threshold for comparison with the beam intensity value can be configured for the terminal. When the N value of the serving cell, the event type information, and the threshold are given, the terminal can measure the received intensity of all beams of the serving cell, and if the average value of the N beam intensities with the maximum received intensity among the measured beams of the serving cell, the minimum value among the N beam intensities with the maximum received intensity, or the maximum value among the N beam intensities with the maximum received intensity is less than the given threshold, the terminal can consider that event A2 is satisfied.

[0236] There may be a type A3 as another beam intensity evaluation condition. As a parameter related to type A3, an offset value for comparison between the beam intensity of the serving cell and the beam intensity of the target cell can be configured for the terminal. When the number of beams N of the serving cell, the number of beams M of the target cell, the event type information, and the offset value are given, the terminal can measure the received intensity of all beams of the serving cell and the received intensity of all beams of the target cell, and if the average value of the N beam intensities with the maximum received intensity among the measured beams of the serving cell is smaller than the average value of the M beam intensities with the maximum received intensity among the measured beams of the target cell by a certain offset amount, the terminal can consider that event A3 is satisfied. Optionally, if the minimum value among the N beam intensities with the maximum received intensity of the serving cell is smaller than the minimum value among the M beam intensities with the maximum received intensity of the target cell by a certain offset amount, or if the maximum value among the N beam intensities with the maximum received intensity of the serving cell is smaller than the maximum value among the M beam intensities with the maximum received intensity of the target cell by a certain offset amount, the terminal can consider that event A3 is satisfied. Optionally, if the maximum value among the N beam intensities with the maximum received intensity of the serving cell is smaller than the minimum value among the M beam intensities with the maximum received intensity of the target cell by a certain offset amount, the terminal can consider that event A3 is satisfied.

[0237] There may be a type A4 as another beam intensity evaluation condition. As a parameter related to type A4, a threshold for comparison with the beam intensity value can be configured for the terminal. When the M value of the target cell, the event type information, and the threshold are given, the terminal can measure the received intensity of all beams of the target cell, and if the average value of the M beam intensities with the maximum received intensity among the measured beams of the target cell, the minimum value among the M beam intensities with the maximum received intensity, or the maximum value among the M beam intensities with the maximum received intensity is less than the given threshold, the terminal can consider that event A4 is satisfied.

[0238] There may be a type A5 as another beam intensity evaluation condition. As parameters related to type A5, a threshold for comparison with the beam intensity value and a threshold for comparison with the beam intensity value of the target cell may be configured for the terminal. When the N value of the serving cell, the threshold of the serving cell, the M value of the target cell, the threshold of the target cell, and the event information type are given, the terminal may measure the received intensity of all beams of the serving cell and may measure the received intensity of all beams of the target cell, where if the average value of the N beam intensities with the maximum received intensity among the measured beams of the serving cell, the maximum value among the N beam intensities with the maximum received intensity, or the minimum value among the N beam intensities with the maximum received intensity is less than the threshold of the serving cell, and if the average value of the M beam intensities with the maximum received intensity among the measured beams of the target cell, the minimum value among the M beam intensities with the maximum received intensity, or the maximum value among the M beam intensities with the maximum received intensity is greater than the given threshold, the terminal may consider that event A5 is satisfied.

[0239] Among the parameters related to the foregoing types A1 to A5, the parameters related to type A3 may include a serving cell specific offset and a measurement object specific offset of the serving cell, and the values of these parameters may be added to the serving cell part of the offset of the foregoing type A3. The parameters related to type A3 may further include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the target cell part of the offset of the foregoing type A3. The parameters related to type A4 may include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the value part of the target beam for comparison with the threshold of the foregoing type A4. The parameters related to type A5 may further include a target cell specific offset and a measurement object specific offset of the target cell, and the values of these parameters may be added to the value part of the target beam for comparison with the threshold of the target cell of the foregoing type A5.

[0240] In the case where both a cell intensity based condition and a beam intensity based condition are given in a conditional handover command or configuration information, if there are multiple cells that satisfy the cell intensity based condition: 1) if there is no beam level condition for each cell or even if there is a beam level condition, the beam level condition is not satisfied, the terminal may perform conditional handover according to the implementation of the terminal or in the order of the cell with the maximum beam reception intensity in the target cell; 2) if there is a cell that satisfies the beam level condition for each cell, the terminal may perform conditional handover to that cell; or 3) if there are multiple cells that satisfy the beam level condition for each cell, the terminal may perform conditional handover according to the implementation of the terminal or in the order of the cell with the maximum beam reception intensity in the target cell.

[0241] As another embodiment, an indication for treating a contention-free RACH (CFRA) configuration as a beam-level condition may be transmitted to a terminal via an RRCReconfiguration message carrying a conditional handover command. That is, if the terminal receives an indication for treating a CFRA configuration as a beam-level condition for a specific target cell or a target cell group, then after the terminal performs cell and beam measurements, if there are multiple cells that satisfy the cell-level conditions, the CFRA configuration (i.e., the SSB / CSI-Rs id of the beam for which the intensity is to be considered, the RSRP threshold, etc.) may be treated as a beam-based condition for the target cell for the target cell. That is, even if there is one beam among the beams determining the CFRA operation condition of a given target cell that exceeds a given RARP threshold, the target cell may be considered to satisfy the beam-level condition. If there are multiple cells that satisfy the beam-level condition, the terminal may perform a handover to the cell with the maximum cell-level reception intensity among the cells that satisfy the beam-level condition, or may select a cell for which a conditional handover is to be performed according to the terminal implementation method.

[0242] Figure 15 is a signal flow diagram of a process for performing conditional handover when a CFRA configuration is used as a beam-level condition configuration according to an embodiment of the present disclosure. Refer to Figure 15 , in 1505, the source node may determine to perform a conditional handover. Then, in 1510, the source node may send a message for requesting conditional handover preparation to the target node. The message for requesting conditional handover preparation may include an indication of a handover message for conditional handover. The message for requesting conditional handover preparation may include the cell id of a candidate cell for conditional handover and cell-based and beam-based condition configurations.

[0243] In 1515, the target node that receives the message for requesting conditional handover preparation may determine whether the target cell indicated by the serving node can perform conditional handover, and may generate a conditional handover command message by adding dedicated resource configuration information to be used in the target cell. The conditional handover command message may include cell-level and beam-level condition configuration information of candidate target cells capable of performing conditional handover. If CFRA configuration information is configured for a specific target cell, the conditional handover command message may include an indication for using the CFRA configuration information instead of the beam-level condition configuration information for the target cell, rather than including the beam-level condition configuration information. In 1520, the target node transmits the generated conditional handover command message to the source node.

[0244] In 1525, the source node may transmit a conditional handover command received from the target node to the terminal via an RRCReconfiguration message. If the source node did not transmit cell-level and beam-level configuration condition information to the target node during the previous handover preparation, the handover command message may not include cell-level and beam-level configuration conditions, and in this case, the source node may directly add cell-level and beam-level configuration conditions applied to each candidate target node in the RRCReconfiguration message to transmit the cell-level and beam-level configuration conditions to the terminal.

[0245] In 1530, 1535, and 1540, the terminal that receives the RRCReconfiguration message may start measuring the intensity of the beams configured for cell-level and beam-level conditions for each candidate target cell and the source cell, and may evaluate whether the measured beam intensity meets the cell-level and beam-level conditions. If the conditional handover command message transmitted via the RRCReconfiguration message indicates that the beam-level condition configuration information is replaced by the CFRA configuration information, the terminal may evaluate whether an event of type A4 (i.e., the case where the maximum value in the beam intensity configured for the target cell exceeds the rsrpThresh threshold) that has applied the rsrpThresh threshold is met for the beam configured as the monitoring beam for the CFRA configuration.

[0246] If, during the measurement of the beam intensity, there is a target cell that meets the transmitted cell-level conditions, the terminal may re-determine whether the target cell that meets the cell-level conditions meets the beam-level conditions configured for the target cell (in the case of using CFRA as an indication of the beam-level conditions, an event of type A4), and if there is a target cell that even meets the beam-level conditions, the terminal may perform a conditional handover to the target cell in 1545. In 1550, the terminal may perform a random access to the target cell selected to perform the conditional handover.

[0247] Figure 16FIG. is a diagram showing an operation of performing handover in a terminal in consideration of beam-level and cell-level conditions according to an embodiment of the present disclosure. When the terminal receives a conditional handover (CHO) command at 1605, the terminal may determine at 1610 whether the received command includes only cell-level conditions or also beam-level conditions. If the conditional handover command includes only cell-level commands, the terminal may perform signal strength measurement on the reference signal configured for cell-level reception strength measurement for each candidate target cell and serving cell pair at 1615. If, at 1620, a cell that satisfies the cell-level conditions is found during the signal strength measurement, the terminal may perform conditional handover to that cell at 1625. If the conditional handover command includes beam-level conditions and cell-level conditions at 1630, the terminal may measure the strength of the reference signal (RS) configured for beam-level strength measurement and the RS configured for cell-level strength measurement for the candidate target cell and the source cell at 1635. If the cell-level conditions are satisfied at 1640, the terminal may determine whether the given beam-level conditions of each cell are satisfied only for the cells that satisfy the cell-level conditions at 1645. If there is a cell that also satisfies the beam-level conditions, the terminal may select one of the cells at 1650 to perform conditional handover. If the cell-level conditions are satisfied but no cell satisfies the beam-level conditions, the terminal may select one cell from the target cells that satisfy the cell-level conditions at 1655 to perform conditional handover. If the conditional handover command does not include cell-level conditions or beam-level conditions, the terminal may perform reconfiguration on it only by using other reconfiguration information at 1660.

[0248] The methods disclosed in the claims and / or the methods according to the embodiments described in the specification of the present disclosure may be implemented in hardware, software, or a combination of hardware and software.

[0249] When the method is implemented by software, a computer-readable storage medium for storing one or more programs (software modules) may be provided. One or more programs stored in the computer-readable storage medium may be configured to be executed by one or more processors within the electronic device. At least one program may include instructions that cause the electronic device to execute the methods according to various embodiments of the present disclosure defined by the appended claims and / or disclosed herein.

[0250] The program (software module or software) may be stored in a non-volatile memory, including random access memory and flash memory, read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), magnetic disk storage devices, compact disc-ROM (CD-ROM), digital versatile disc (DVD), or other types of optical storage devices, or magnetic tape cartridges. Optionally, any combination of some or all of them may form a memory for storing the program. Additionally, multiple such memories may be included in the electronic device.

[0251] In addition, the program can be stored in an attachable storage device, and the storage device can be accessed by an electronic device through a communication network such as the Internet, intranet, local area network (LAN), wide area LAN (WLAN), and storage area network (SAN), or a combination thereof. Such a storage device can be accessed by the electronic device via an external port. Additionally, a separate storage device on the communication network can be accessed by a portable electronic device.

[0252] In the above detailed embodiments of the present disclosure, according to the presented detailed embodiments, the elements included in the present disclosure are expressed in singular or plural. However, for ease of description, the singular or plural form is appropriately selected for the presented situation, and the present disclosure is not limited to the elements expressed in singular or plural. Therefore, an element expressed in plural may also include a single element, or an element expressed in singular may also include multiple elements.

[0253] The embodiments of the present disclosure described and illustrated in the specification and drawings are only specific embodiments presented for the purpose of easily explaining the technical content of the present disclosure and helping to understand the present disclosure, and are not intended to limit the scope of the present disclosure. Therefore, in addition to the embodiments disclosed herein, the scope of the present disclosure should be construed as also including all changes and modifications obtained on the basis of the technical concept of the present disclosure.

Claims

1. A method performed by a source node in a wireless communication system, the method comprising: Sending a message for handover preparation to a target node, the message for handover preparation including an identifier of a target cell for conditional handover; Receiving a handover request response message from the target node, the handover request response message including a handover command message in the form of an octet string and the identifier of the target cell for conditional handover, wherein the handover command message includes configuration information related to the target cell for conditional handover; Generating a radio resource control (RRC) reconfiguration message, the RRC reconfiguration message including the handover command message in the form of an octet string generated by the target node and condition information for conditional handover, wherein the condition information is configured based on a measurement identity associated with a measurement object and a reporting configuration; and Sending the RRC reconfiguration message to a terminal, the RRC reconfiguration message including the handover command message and the condition information for the conditional handover.

2. The method according to claim 1, Among them, wherein the condition information is determined by the source node.

3. The method according to claim 1, Among them, wherein the handover command message is transmitted via a transparent container, and wherein the condition information is added to a separate field separated from the octet string in the RRC reconfiguration message.

4. The method according to claim 1, Among them, wherein the handover command message includes an incremental configuration based on source configuration information, and wherein the RRC reconfiguration message includes information on one or more cells for the conditional handover.

5. A source node in a wireless communication system, the source node comprising: a transceiver, and a controller coupled to the transceiver and configured to: send a message for handover preparation to a target node, the message for handover preparation including an identifier of a target cell for conditional handover; receive a handover request response message from the target node, the handover request response message including a handover command message in the form of an octet string and the identifier of the target cell for conditional handover, wherein the handover command message includes configuration information related to the target cell for conditional handover; generate a radio resource control (RRC) reconfiguration message, the RRC reconfiguration message including the handover command message in the form of an octet string generated by the target node and condition information for conditional handover, wherein the condition information is configured based on a measurement identity associated with a measurement object and a reporting configuration; and send the RRC reconfiguration message to a terminal, the RRC reconfiguration message including the handover command message and the condition information for the conditional handover.

6. The source node according to claim 5, Among them, wherein the condition information is determined by the source node.

7. The source node according to claim 5, Among them, wherein the handover command message is transmitted via a transparent container, and wherein the condition information is added to a separate field separated from the octet string in the RRC reconfiguration message.

8. The source node according to claim 5, Among them, wherein the handover command message includes incremental configuration based on source configuration information, and wherein the RRC reconfiguration message includes information on one or more cells for the conditional handover.

9. A method performed by a target node in a wireless communication system, the method comprising: receiving, from a source node, a message for handover preparation, the message for handover preparation including an identifier of a target cell for conditional handover; and sending, to the source node, a handover request response message, the handover request response message including a handover command message in the form of an octet string and an identifier of a target cell for conditional handover, wherein the handover command message includes configuration information related to the target cell for conditional handover, wherein a radio resource control (RRC) reconfiguration message is sent from the source node to a terminal, the RRC reconfiguration message including the handover command message in the form of an octet string generated by the target node and conditional information for the conditional handover, wherein the conditional information included in the RRC reconfiguration message is configured based on a measurement identity associated with a measurement object and a reporting configuration.

10. The method according to claim 9, Among them, wherein the conditional information is determined by the source node.

11. The method according to claim 9, Among them, wherein the handover command message is transmitted via a transparent container, and wherein the conditional information is added to a separate field separated from the octet string in the RRC reconfiguration message.

12. The method according to claim 9, Among them, wherein the handover command message includes incremental configuration based on source configuration information, and wherein the RRC reconfiguration message includes information on one or more cells for the conditional handover.

13. A target node in a wireless communication system, the target node comprising: a transceiver; and a controller, coupled to the transceiver and configured to: receive, from a source node, a message for handover preparation, the message for handover preparation including an identifier of a target cell for conditional handover; and send, to the source node, a handover request response message, the handover request response message including a handover command message in the form of an octet string and an identifier of a target cell for conditional handover, wherein the handover command message includes configuration information related to the target cell for conditional handover, wherein a radio resource control (RRC) reconfiguration message is sent from the source node to a terminal, the RRC reconfiguration message including the handover command message in the form of an octet string generated by the target node and conditional information for the conditional handover, wherein the conditional information included in the RRC reconfiguration message is configured based on a measurement identity associated with a measurement object and a reporting configuration.

14. The target node according to claim 13, Among them, wherein the conditional information is determined by the source node, wherein the handover command message is transmitted via a transparent container, and Wherein, the conditional information is added to a separate field separated from the octet string in the RRC reconfiguration message.

15. The target node according to claim 13, Among them, The handover command message includes delta configuration based on source configuration information, and wherein, the RRC reconfiguration message includes information of one or more cells for the conditional handover.

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