Method and device for condition-based handover using artificial intelligence and machine learning in wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting higher data transmission rates. A method of a terminal in a wireless communication system according to an embodiment of the present disclosure comprises the steps of: receiving, from a source base station, conditional handover configuration information including at least one candidate base station for conditional handover and a conditional handover execution condition including a measurement-based condition and a prediction-based condition for each candidate base station; determining, as a target base station, a candidate base station satisfying both the measurement-based condition and the prediction-based condition among the at least one candidate base station; and performing handover to the target base station.

Description

Method and device for condition-based handover using artificial intelligence and machine learning in a wireless communication system

[0001] The present disclosure relates to the operation of a terminal and a base station in a mobile communication system. Specifically, the present disclosure relates to a method for handover in a wireless communication system and a device capable of performing the same.

[0002] 5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and can be implemented not only in the sub-6GHz frequency band such as 3.5 gigahertz (3.5GHz), but also in the ultra-high frequency band called millimeter wave (mmWave) such as 28GHz and 39GHz ('Above 6GHz'). In addition, for 6G mobile communication technology, which is called the system after 5G communication (Beyond 5G), implementation in the terahertz band (for example, the 3 terahertz (3THz) band at 95GHz) is being considered to achieve a transmission speed that is 50 times faster than 5G mobile communication technology and an ultra-low latency time that is reduced to one-tenth.

[0003] In the early stages of 5G mobile communication technology, the goal is to support services and satisfy performance requirements for enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine-Type Communications (mMTC). These include beamforming and massive MIMO to mitigate path loss of radio waves in ultra-high frequency bands and increase the transmission distance of radio waves, support for various numerologies (such as operation of multiple subcarrier intervals) and dynamic operation of slot formats for efficient use of ultra-high frequency resources, initial access technology to support multi-beam transmission and wideband, definition and operation of BWP (Bidth Part), new channel coding methods such as LDPC (Low Density Parity Check) codes for large-capacity data transmission and Polar Code for reliable transmission of control information, and L2 pre-processing (L2). Standardization has been made for network slicing, which provides dedicated networks specialized for specific services, and pre-processing.

[0004] Currently, discussions are underway to improve and enhance the initial 5G mobile communication technology in consideration of the services that 5G mobile communication technology was intended to support, and physical layer standardization is in progress for technologies such as V2X (Vehicle-to-Everything) to help autonomous vehicles make driving decisions and increase user convenience based on their own location and status information transmitted by vehicles, NR-U (New Radio Unlicensed) for the purpose of system operation that complies with various regulatory requirements in unlicensed bands, NR terminal low power consumption technology (UE Power Saving), Non-Terrestrial Network (NTN), which is direct terminal-satellite communication to secure coverage in areas where communication with terrestrial networks is impossible, and Positioning.

[0005] In addition, standardization of wireless interface architecture / protocols for technologies such as intelligent factories (Industrial Internet of Things, IIoT) to support new services through linkage and convergence with other industries, Integrated Access and Backhaul (IAB) that provides nodes for expanding network service areas by integrating wireless backhaul links and access links, Mobility Enhancement technology including Conditional Handover and Dual Active Protocol Stack (DAPS) handover, and 2-step RACH for NR that simplifies random access procedures is also in progress, and standardization of system architecture / services for 5G baseline architecture (e.g., Service-based Architecture, Service-based Interface) for grafting Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) that provides services based on the location of the terminal is also in progress.

[0006] Once these 5G mobile communication systems are commercialized, an explosive increase in connected devices will be connected to the communication network, necessitating enhanced functionality and performance of 5G mobile communication systems and integrated operation of these connected devices. To this end, new research will be conducted on improving 5G performance and reducing complexity, supporting AI services, supporting metaverse services, and drone communications by utilizing eXtended Reality (XR), Artificial Intelligence (AI), and Machine Learning (ML) to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR).

[0007] In addition, the development of these 5G mobile communication systems includes new waveforms to ensure coverage in the terahertz band of 6G mobile communication technology, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), Array Antenna, and Large Scale Antenna, metamaterial-based lenses and antennas to improve the coverage of terahertz band signals, high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM), Reconfigurable Intelligent Surface (RIS) technology, as well as full duplex technology to improve the frequency efficiency and system network of 6G mobile communication technology, satellite, AI (Artificial Intelligence) from the design operation and internalize end-to-end AI support functions to realize system optimization, and ultra-high-performance communication and computing resources to provide services with complexity that exceeds the limits of terminal computing capabilities. It can serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing them.

[0008] The present disclosure seeks to provide a device and method capable of effectively providing a service in a mobile communication system.

[0009] The present disclosure aims to introduce an AI / ML algorithm-based handover mechanism to solve problems of existing reactive handovers that may occur in high-density micro-cell environments and environments with high mobility, and to improve the overall performance and stability of the network.

[0010] According to one embodiment of the present disclosure, a method of a terminal in a wireless communication system includes the steps of: receiving, from a source base station, conditional handover configuration information including at least one candidate base station for conditional handover and conditional handover execution conditions including a measurement-based condition and a prediction-based condition for each candidate base station; determining, as a target base station, a candidate base station satisfying both the measurement-based condition and the prediction-based condition among the at least one candidate base station; and performing a handover to the target base station.

[0011] According to various embodiments of the present disclosure, a device and method capable of effectively providing a service in a mobile communication system are provided.

[0012] According to various embodiments of the present disclosure, the efficiency of the handover process can be increased, proactive response can be enabled before problems occur, network operation and configuration decisions can be improved, and wireless resource management performance can be improved.

[0013] FIG. 1A is a diagram illustrating the structure of a mobile communication system according to one embodiment of the present disclosure.

[0014] FIG. 1b is a diagram for explaining a wireless connection state transition in a mobile communication system according to one embodiment of the present disclosure.

[0015] FIG. 1c is a flowchart illustrating a process in which a terminal performs cell measurement and reporting operations according to one embodiment of the present disclosure.

[0016] FIG. 1D is a diagram illustrating an operation of reporting cell measurement results when a specific condition is satisfied according to one embodiment of the present disclosure.

[0017] FIG. 1e is a flowchart illustrating a condition-based handover process according to one embodiment of the present disclosure.

[0018] FIG. 1f is a first flowchart illustrating a condition-based handover process based on AI / ML prediction of a terminal according to one embodiment of the present disclosure.

[0019] FIG. 1g is a second flowchart illustrating a condition-based handover process based on AI / ML prediction of a terminal according to one embodiment of the present disclosure.

[0020] FIG. 1h is a flowchart illustrating a condition-based handover process based on AI / ML prediction of a base station or network according to one embodiment of the present disclosure.

[0021] FIG. 1i is a diagram illustrating the structure of a terminal according to one embodiment of the present disclosure.

[0022] FIG. 1J is a diagram illustrating the structure of a base station according to one embodiment of the present disclosure.

[0023] According to one embodiment of the present disclosure, a method of a terminal in a wireless communication system includes the steps of: receiving, from a source base station, conditional handover configuration information including at least one candidate base station for conditional handover and conditional handover execution conditions including a measurement-based condition and a prediction-based condition for each candidate base station; determining, as a target base station, a candidate base station satisfying both the measurement-based condition and the prediction-based condition among the at least one candidate base station; and performing a handover to the target base station.

[0024] According to one embodiment of the present disclosure, a method of a source base station in a wireless communication system includes the steps of: receiving, from a terminal, a measurement result and a prediction result corresponding to the measurement result; determining a conditional handover for the terminal based on the measurement result and the prediction result; receiving configuration information for executing a conditional handover from at least one candidate base station; generating, based on the measurement result, the prediction result, the at least one candidate base station and the configuration information for executing a conditional handover for each of the candidate base stations, a conditional handover execution condition including a measurement-based condition and a prediction-based condition for each of the candidate base stations; and transmitting, to the terminal, conditional handover configuration information including a conditional handover execution condition for the at least one candidate base station and each of the candidate base stations.

[0025] According to one embodiment of the present disclosure, a terminal of a wireless communication system includes a transceiver and a control unit connected to the transceiver, wherein the control unit is configured to: receive, from a source base station, conditional handover configuration information including at least one candidate base station for conditional handover and a conditional handover execution condition including a measurement-based condition and a prediction-based condition for each candidate base station; determine a candidate base station that satisfies both the measurement-based condition and the prediction-based condition among the at least one candidate base station as a target base station; and perform handover to the target base station.

[0026] According to one embodiment of the present disclosure, a source base station of a wireless communication system includes a transceiver; and a control unit connected to the transceiver, wherein the control unit is configured to: receive, from a terminal, a measurement result and a prediction result corresponding to the measurement result; determine a conditional handover for the terminal based on the measurement result and the prediction result; receive configuration information for executing a conditional handover from at least one candidate base station; generate a conditional handover execution condition including a measurement-based condition and a prediction-based condition for each candidate base station based on the measurement result, the prediction result, the at least one candidate base station and the configuration information for executing a conditional handover for each of the candidate base stations; and transmit conditional handover configuration information including a conditional handover execution condition for the at least one candidate base station and each of the candidate base stations to the terminal.

[0027] In describing the embodiments of this disclosure, descriptions of technical details that are well known in the technical field to which this disclosure pertains and are not directly related to this disclosure will be omitted. This is to more clearly convey the gist of this disclosure without obscuring it by omitting unnecessary explanations.

[0028] For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted. Furthermore, the dimensions of each component do not entirely reflect its actual size. Identical or corresponding components in each drawing are assigned the same reference numbers.

[0029] The advantages and features of the present disclosure, and methods for achieving them, will become clearer with reference to the embodiments described below in detail with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided solely to ensure that the disclosure is complete and to fully inform those skilled in the art of the scope of the disclosure, and the present disclosure is defined only by the scope of the claims. Like reference numerals designate like elements throughout the disclosure.

[0030] At this time, it will be understood that each block of the processing flow diagrams and combinations of the flow diagrams can be performed by computer program instructions. These computer program instructions can be installed in a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, so that the instructions executed by the processor of the computer or other programmable data processing equipment create a means for performing the functions described in the flow diagram block(s). These computer program instructions can also be stored in a computer-available or computer-readable memory that can direct a computer or other programmable data processing equipment to implement the functions in a specific manner, so that the instructions stored in the computer-available or computer-readable memory can also produce a manufactured item that includes an instruction means for performing the functions described in the flow diagram block(s). Since the computer program instructions may be installed on a computer or other programmable data processing device, a series of operational steps may be performed on the computer or other programmable data processing device to create a computer-executable process, and the instructions that cause the computer or other programmable data processing device to perform the steps for performing the functions described in the flowchart block(s) may also provide steps for performing the functions described in the flowchart block(s).

[0031] Additionally, each block may represent a module, segment, or portion of code that contains one or more executable instructions for performing a specific logical function(s). It should also be noted that in some alternative implementation examples, the functions described in the blocks may occur out of order. For example, two blocks depicted in succession may actually be executed substantially concurrently, or the blocks may sometimes be executed in reverse order, depending on their respective functions.

[0032] Here, the term '~ unit' used in the present embodiment means a software or hardware component such as an FPGA or ASIC, and the '~ unit' performs certain roles. However, the '~ unit' is not limited to software or hardware. The '~ unit' may be configured to be on an addressable storage medium and may be configured to play one or more processors. Accordingly, as an example, the '~ unit' includes components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and '~ units' may be combined into a smaller number of components and '~ units' or further separated into additional components and '~ units'. Additionally, components and '~parts' may be implemented to regenerate one or more CPUs within a device or secure multimedia card.

[0033] FIG. 1A is a diagram illustrating the structure of a mobile communication system according to one embodiment of the present disclosure.

[0034] Referring to FIG. 1a, a wireless access network of a mobile communication system (New Radio, NR) according to an embodiment of the present disclosure may be composed of a base station (next generation Node B, hereinafter referred to as gNB) (1a-10) and an AMF (1a-05, access and mobility management function or New Radio Core Network). A user terminal (New Radio User Equipment, hereinafter referred to as (NR) UE or terminal) (1a-15) may access an external network through the gNB (1a-10) and the AMF (1a-05). The mobile communication system according to an embodiment of the present disclosure may be a next generation mobile communication system, and the base station may be a next generation base station.

[0035] In FIG. 1a, the gNB (1a-10) may correspond to the eNB (1a-30) (Evolved Node B) of the existing LTE system. The gNB is connected to the NR UE (1a-15) via a wireless channel (1a-20) and may provide a service superior to that of the existing Node B. In the next-generation mobile communication system according to an embodiment of the present disclosure, since all user traffic is serviced through a shared channel, a device that collects status information such as buffer status, available transmission power status, and channel status of UEs and performs scheduling is required, and the gNB (1a-10) may be responsible for this. One gNB can typically control multiple cells. In order to implement ultra-high-speed data transmission compared to the existing LTE, it may have a bandwidth higher than the existing maximum bandwidth, and an orthogonal frequency division multiplexing (OFDM) scheme may be used as a wireless access technology, and additional beamforming technology may be incorporated. Additionally, an adaptive modulation and coding (AMC) method that determines the modulation scheme and channel coding rate according to the channel status of the terminal can be applied.

[0036] AMF (1a-05) can perform functions such as mobility support, bearer setup, and QoS (quality of service) setup. AMF (1a-05) is a device that handles various control functions as well as mobility management functions for terminals and can be connected to multiple base stations.

[0037] In addition, the mobile communication system according to one embodiment of the present disclosure can be interoperable with an existing LTE system, and an AMF (1a-05) can be connected to an MME (1a-25, mobility management entity) through a network interface. The MME (1a-25) can be connected to an existing base station, an eNB (1a-30). An NR UE (1a-15) supporting LTE-NR Dual Connectivity can transmit and receive data while maintaining a connection (1a-35) with not only a gNB (1a-10) but also an eNB (1a-30).

[0038] FIG. 1b is a diagram for explaining a wireless connection state transition in a mobile communication system according to one embodiment of the present disclosure.

[0039] A mobile communication system according to an embodiment of the present disclosure may have three radio connection states (RRC (radio resource control) states) or RRC modes. The connected mode (RRC_CONNECTED, 1b-05) is a radio connection state in which a terminal can transmit and receive data. The idle mode (RRC_IDLE, 1b-30) is a radio connection state in which a terminal monitors whether paging is transmitted to itself. The two modes (connected mode and idle mode) are radio connection states that can also be applied to an LTE system, and the detailed technology is the same as that of the LTE system. The mobile communication system according to an embodiment of the present disclosure may be a next-generation mobile communication system.

[0040] In a mobile communication system according to one embodiment of the present disclosure, an inactive (RRC_INACTIVE) radio connection state (1b-15) may be defined. In the inactive radio connection state, the UE context is maintained between the base station and the terminal, and RAN (radio access network)-based paging may be supported. The characteristics of the inactive radio connection state are listed below.

[0041] - Cell re-selection mobility;

[0042] - CN - NR RAN connection (both C / U-planes (control plane / user plane)) has been established for UE;

[0043] - The UE AS (Access Stratum) context is stored in at least one gNB and the UE;

[0044] - Paging is initiated by NR RAN;

[0045] - RAN-based notification area is managed by NR RAN;

[0046] - NR RAN knows the RAN-based notification area which the UE belongs to;

[0047] According to one embodiment of the present disclosure, a terminal in an inactive wireless connection state can transition to a connected mode or a standby mode using a specific procedure. The transition (1b-10) between the connected mode and the inactive mode can be performed through Resume or Release with suspend. For example, the terminal can transition from INACTIVE mode to connected mode through the Resume procedure, and can transition from connected mode to INACTIVE mode by receiving a Release message including suspend configuration information (1b-10). The above procedure is performed by transmitting and receiving one or more RRC messages between the terminal and the base station, and can consist of one or more operations. In addition, the terminal can transition from INACTIVE mode to standby mode through the Release procedure after Resume (1b-20). The transition (1b-25) between the connected mode and the standby mode can follow the existing LTE technology. For example, the transition between the modes can be performed through the establishment or release procedure.

[0048] FIG. 1c is a flowchart illustrating a process in which a terminal performs cell measurement and reporting operations according to one embodiment of the present disclosure.

[0049] According to one embodiment of the present disclosure, in operation 1c-15, the terminal (1c-05) may report its capability information to the base station (1c-10). In operation 1c-20, the base station (1c-10) may transmit an RRCReconfiguration message including configuration information (measConfig IE) related to the cell measurement operation to the terminal (1c-05).

[0050] The configuration information (measConfig IE) may include information necessary for reporting the results measured by the terminal (1c-05) to the base station (1c-10) depending on the type of measurement report (e.g., periodical, event-triggered, event-triggered periodical). For example, in the case of “event-triggered” or “event-triggered periodical,” the terminal (1c-05) may report a given measurement result when a specific event configured based on the configuration information (measConfig IE) is satisfied. For example, the following events may be configured in the NR system.

[0051] - Event(s) related to intra- / inter-RAT measurements are as shown in Table 1 below.

[0052] - Event A1: Serving becomes better than absolute threshold;- Event A2: Serving becomes worse than absolute threshold;- Event A3: Neighbour becomes amount of offset better than PCell / PSCell;- Event A4: Neighbour becomes better than absolute threshold;- Event A5: PCell / PSCell becomes worse than absolute threshold1 AND Neighbour / SCell becomes better than another absolute threshold2;- Event A6: Neighbour becomes amount of offset better than SCell;- Event D1: Distance between UE and a reference location referenceLocation1 becomes larger than configured threshold distanceThreshFromReference1 and distance between UE and a reference location referenceLocation2 becomes shorter than configured threshold distanceThreshFromReference2;- Event B1: Neighbour becomes better than absolute threshold;- Event B2: PCell becomes worse than absolute threshold1 AND Neighbour becomes better than another absolute threshold2;

[0053] - Similar to condition-based measurement reporting, in condition-based handover, when a specific event is satisfied, the terminal (1c-05) can perform a handover according to condition-based handover configuration information. Event(s) related to condition-based handover are as shown in Table 2 below.

[0054] - CondEvent A3: Conditional reconfiguration candidate becomes amount of offset better than PCell / PSCell;- CondEvent A4: Conditional reconfiguration candidate becomes better than absolute threshold;- CondEvent A5: PCell / PSCell becomes worse than absolute threshold1 AND Conditional reconfiguration candidate becomes better than another absolute threshold2;- CondEvent D1: Distance between UE and a reference location referenceLocation1 becomes larger than configured threshold distanceThreshFromReference1 and distance between UE and a reference location referenceLocation2 of conditional reconfiguration candidate becomes shorter than configured threshold distanceThreshFromReference2;- CondEvent T1: Time measured at UE becomes more than configured threshold t1-Threshold but is less than t1-Threshold + duration;

[0055] - (Sidelink) Relay에서 특정 Event가 만족될 때, 단말(1c-05)은 소정의 동작을 수행할 수 있다. Relay와 관련된 Event(들)은 아래의 표 3과 같다.

[0056] - Event X1: Serving L2 U2N Relay UE becomes worse than absolute threshold1 AND NR Cell becomes better than another absolute threshold2;- Event

[0057] - In the case of NR-U (Unlicensed), when a specific event is satisfied, the terminal (1c-05) can perform a specific action. Event(s) related to NR-U are as shown in Table 4 below.

[0058] - Event I1: Interference becomes higher than absolute threshold.

[0059] In operation 1c-25, terminal (1c-05) can evaluate whether the configured Events are satisfied. If the Events described above continue to satisfy a predetermined condition for a predetermined time interval (time-to-trigger), terminal (1c-05) can consider the Event to be satisfied.

[0060] In operation 1c-30, the terminal (1c-05) may report a MeasurementReport message containing measurement results to the base station (1c-10) when a set condition is satisfied. Alternatively, the terminal (1c-05) may perform a predetermined operation corresponding to the above condition, for example, a condition-based handover.

[0061] The base station (1c-10) that receives the measurement result from the terminal (1c-05) can use the measurement result for a predetermined purpose. For example, in operation 1c-35, the base station (1c-10) can determine whether to trigger a handover of the terminal (1c-05). In operation 1c-40, if the base station (1c-10) triggers a handover, it can request a handover to the target cell(s). In operation 1c-45, the base station (1c-10) can transmit handover configuration information configured based on predetermined configuration information received from the target cell(s) to the terminal (1c-05). In operation 1c-50, the terminal (1c-05) that receives the handover configuration information can perform a handover.

[0062] FIG. 1D is a diagram illustrating an operation of reporting cell measurement results when a specific condition is satisfied according to one embodiment of the present disclosure.

[0063] Referring to FIG. 1d, the terminal (1d-10) can evaluate the signal strength or quality of the base station (1d-05) signal based on the SSB (synchronization signal block or SS / PBCH block) or CSI-RS (channel state information reference singal) transmitted from the base station (1d-05). Hereinafter, for convenience of explanation, the cell measurement result reporting operation of the terminal (1d-10) is described mainly with respect to SSB, but the same can be applied to CSI-RS.

[0064] In the case of SSB, the transmission cycle of SSB can be determined according to the settings of the base station (1d-05). Typically, the transmission cycle of SSB can be set to 20 ms, and the base station (1d-05) can transmit SSB with a cycle of up to 160 ms.

[0065] When the base station (1d-05) sets Event A2 to the terminal (1d-10), the terminal (1d-10) can continuously evaluate whether the RSRP value measured based on SSB is lower than the threshold during a predetermined time period (time-to-trigger, TTT) from the time point (1d-15) when the RSRP (reference signal received power) value measured based on SSB by the terminal (1d-10) becomes lower than the set absolute threshold value.

[0066] If the measured RSRP value based on SSB is continuously lower than the threshold from the initial time point (1d-15) when the RSRP value becomes lower than the set absolute threshold value to the time point (1d-20) when a predetermined time-to-trigger (TTT) has elapsed, the terminal (1d-10) may consider that the Event A2 is satisfied and may report a measurement report triggered by Event A2 to the base station (1d-05). As described above, by considering the TTT in determining whether the conditions for performing the measurement report are satisfied, the variability of the measurement signal can be compensated for. The TTT value may be set by the base station (1d-05) for each Event.

[0067] If the above-described Events continuously satisfy a predetermined condition for a predetermined time interval (TTT), the terminal (1d-10) can perform an action corresponding to the purpose of the Event according to the purpose of the configured Event. If the type of measurement report according to the measurement-related setting information received by the terminal (1d-10) is set to “periodical” or “event-triggered periodical,” the terminal (1d-10) can perform a measurement report periodically.

[0068] In the existing L3 (Layer 3) handover mechanism, handover can be triggered and executed by the network or base station based on historical cell measurement results and / or cell measurement event(s) reported in the past. That is, it can be understood as a kind of reactive manner.

[0069] Reactive handover schemes can be effective for existing services when UEs move between macro cells or when UEs have low mobility. However, reactive handover schemes can be problematic when UEs have high mobility, when UEs move between dense micro cells, or for future services such as XR. For example, reactive handover schemes can cause unintended consequences, such as handover failures, radio link failures, ping-pong behavior, throughput loss, or premature / late handovers. Accordingly, conditional handovers were introduced in Rel-16 to improve handover robustness, and lower-layer triggered mobility (LTM) handovers were introduced in Rel-18 to reduce service interruption due to frequent handovers between small cells. However, these two handover mechanisms (conditional handover and LTM) are still reactive and may not be sufficient.

[0070] On the other hand, handover mechanisms based on AI / ML (Artificial Intelligence and Machine Learning) algorithms can enable proactive approaches. For example, a UE can generate predicted cell measurement information for the future using an AI / ML model and report this predicted cell measurement information to the base station (or network). This allows the base station to prepare for handovers in advance, preventing delays. Furthermore, by proactively instructing the UE to perform a handover, the UE can be handed over to another base station or cell before a problem (e.g., Radio Link Failure (RLF)) occurs. Furthermore, by receiving predicted cell measurement information for the UE, the base station can achieve improved handover and / or Radio Resource Management (RRM) performance compared to reactive approaches. For example, the base station can make better network operation / configuration decisions or take proactive measures to avoid unintended events. Alternatively, the base station or network may generate predictive information by running an AI / ML model using report information received from the terminal, and the base station or network may instruct the terminal to perform a preemptive handover using the generated predictive information.

[0071] The AI / ML prediction results of a terminal or base station can be utilized not only for conventional handover, but also for CHO (Conditional handover) or CPAC (Conditional PSCell Addition or Change), CPA (Conditional PSCell Addition), and CPC (Conditional PSCell Change). For convenience of explanation, embodiments limited to CHO may be described in this disclosure, but the same can be applied / utilized to CPAC, CPA, and CPC by taking SCell or PSCell into consideration.

[0072] FIG. 1e is a flowchart illustrating a condition-based handover process according to one embodiment of the present disclosure.

[0073] In operation 1e-05, a connected mode terminal may transmit UE measurement and / or conditional handover (CHO)-related terminal capabilities to a base station via a UE capability information message. The UE capability information message may be a message transmitted by the terminal to the base station in response to a UE capability inquiry message previously received by the terminal from the base station.

[0074] In operation 1e-10, the terminal may receive terminal measurement-related settings from the base station (e.g., via an RRCReconfiguration message), and report the measurement results to the base station according to the measurement settings (e.g., the terminal measurement results may be reported to the base station via a MeasurementReport message).

[0075] At operation 1e-15, the base station may decide to use CHO (e.g., the decision to use CHO may be made based on measurement results received by the base station from the terminal).

[0076] In operation 1e-20, the base station (source base station) may request CHO for one or more candidate cells from candidate target base stations (e.g., the CHO request for one or more candidate cells of the base station may be performed via a HANDOVER REQUEST message). The source base station may transmit a CHO request message (e.g., a HANDOVER REQUEST message) for each cell.

[0077] In operation 1e-25, the candidate base station(s) may transmit a CHO response message (e.g., the CHO response message of the candidate base station(s) may be a HANDOVER RESPONSE ACKNOWLEDGE message) to the source base station. The CHO response message may include configuration information about the CHO candidate cell(s) and / or CHO execution condition(s).

[0078] In operation 1e-30, the source base station may generate / determine CHO configuration information to be transmitted to the terminal based on configuration information for the CHO candidate cell(s) and / or CHO execution condition(s) and / or measurement result report received from the terminal.

[0079] In operation 1e-35, the source base station may transmit the CHO configuration information generated / determined in operation 1e-30 to the terminal via an RRC Reconfiguration message. The CHO configuration information may include configuration information regarding the CHO candidate cell(s) and / or CHO execution condition(s). The terminal receiving the CHO configuration information may store the CHO configuration information.

[0080] At operation 1e-40, the terminal can evaluate whether the CHO execution conditions for the candidate cell(s) are satisfied.

[0081] In operation 1e-45, if the terminal determines that the CHO execution condition is satisfied (for a time period indicated by the TTT value) for at least one candidate cell, the terminal may release the connection with the source cell to perform a handover to a cell (target cell) that satisfies the CHO execution condition. In addition, the terminal may apply / use the stored configuration information for the corresponding cell. In addition, the terminal may perform synchronization with the target cell and then transmit an RRC Reconfiguration Complete message to the target cell or the target base station. After a successful handover, the terminal may release the stored CHO configuration information.

[0082] In operation 1e-50, the target base station may transmit a HANDOVER SUCCESS message to the source base station, and the HANDOVER SUCCESS message may mean that the terminal has successfully performed a handover to the target base station or target cell.

[0083] In operation 1e-55, the source base station may transmit a HANDOVER CANCEL message to other candidate target cells or base stations other than the target cell, and the HANDOVER CANCEL message may be for the other candidate target cells or base stations to cancel CHO for the terminal.

[0084] FIG. 1f is a first flowchart illustrating a condition-based handover process based on UE-sided AI / ML prediction according to one embodiment of the present disclosure.

[0085] In operation 1f-05, a connected mode terminal may transmit its capabilities related to UE measurement and / or conditional handover (CHO) to a base station via a UE capability information message. The UE capability information message may be a message transmitted by the terminal to the base station in response to a UE capability inquiry message previously received by the terminal from the base station. The terminal may indicate to the base station via the UE capability information message whether the terminal supports at least one of the following capabilities.

[0086] - Capability 1. Ability to support at least one of cell measurement value (RSRP / RSRQ / SINR) information prediction (based on (UE-sided) AI / ML), HOF (Handover failure) information prediction, RLF (Radio link failure) information prediction, or TOS (Time of stay) information prediction.

[0087] - Capability 2. Ability to support CHO using at least one of cell measurement value (RSRP / RSRQ / SINR) information prediction (based on (UE-sided) AI / ML), HOF (Handover failure) information prediction, RLF (Radio link failure) information prediction, or TOS (Time of stay) information prediction.

[0088] - Capability 3. Ability to support CHO execution conditions using at least one of cell measurement value (RSRP / RSRQ / SINR) information prediction (based on (UE-sided) AI / ML), HOF (Handover failure) information prediction, RLF (Radio link failure) information prediction, or TOS (Time of stay) information prediction.

[0089] The terminal may indicate to the base station that it supports (at least one of) the above capabilities by including a specific indicator in the UE capability information message or setting it to a specific value (e.g., true). The terminal may indicate to the base station that it does not support (at least one of) the above capabilities by omitting a specific indicator in the UE capability information message or setting it to a specific value (e.g., false).

[0090] In operation 1f-10, the terminal may receive terminal measurement-related configuration from the base station (e.g., the terminal may receive the terminal measurement-related configuration from the base station via an RRCReconfiguration message) and report a measurement result to the base station according to the measurement configuration (e.g., the terminal may transmit the measurement result to the base station via a MeasurementReport message). The terminal may report at least one of cell measurement values ​​(RSRP / RSRQ / SINR), HOF, , RLF, and TOS-related predicted values ​​(e.g., for each cell) (e.g., predicted RSRP / RSRQ / SINR values, HOF probability, RLF probability, and TOS time values) to the base station. To this end, the base station may set configuration information for at least one of HOF, RLF, or TOS-related prediction to the terminal in advance (e.g., when transmitting the measurement-related configuration).

[0091] According to one embodiment of the present disclosure, the setting information may include settings regarding conditions for triggering a measurement report.

[0092] The above measurement report trigger condition may be at least one of the conditions below.

[0093] - Condition 1. If the predicted measurement value for the serving cell or SpCell (or the value plus the offset for the serving cell or SpCell) (e.g. RSRP, RSRQ, SINR) is less than a certain threshold (even if a certain hysteresis value is added).

[0094] - Condition 2. If the predicted measurement value for the serving cell or SpCell (or the value plus the offset for the serving cell or SpCell) (e.g. RSRP, RSRQ, SINR) is greater than a certain threshold (even after deducting a certain hysteresis value).

[0095] - Condition 3. If the predicted measurement value for the neighbor cell (or candidate cell) (or the value plus an offset for the neighbor cell (or candidate cell)) (e.g., RSRP, RSRQ, SINR) is greater than the predicted measurement value for the serving cell or SpCell (or the value plus an offset for the serving cell or SpCell) (by a certain offset or more) (even after deducting a certain hysteresis value).

[0096] - Condition 4. If the predicted measurement value for a neighbor cell (or candidate cell) (or the value plus an offset for the neighbor cell (or candidate cell)) (e.g., RSRP, RSRQ, SINR) is smaller (by a certain offset or more) than the predicted measurement value for the serving cell or SpCell (or the value plus an offset for the serving cell or SpCell) (even if a certain hysteresis value is added).

[0097] - Condition 5. If the predicted measurement value (or offset for the neighboring cell (or candidate cell) plus the value) (e.g. RSRP, RSRQ, SINR) for the neighboring cell (or candidate cell) is greater than a certain threshold (even after deducting a certain hysteresis value).

[0098] - Condition 6. If the predicted measurement value (or offset for the neighboring cell (or candidate cell) plus the offset for the neighboring cell (or candidate cell)) (e.g. RSRP, RSRQ, SINR) is less than a certain threshold (even if a certain hysteresis value is added)

[0099] - Condition 7. If the predicted HOF occurrence probability for a neighboring cell (or candidate cell) (or the offset for the neighboring cell (or candidate cell) plus the value) is less than a certain threshold (even if a certain hysteresis value is added)

[0100] - Condition 8. If the predicted HOF occurrence probability for a neighboring cell (or candidate cell) (or the offset for the neighboring cell (or candidate cell) plus the value) is greater than a certain threshold (even after deducting a certain hysteresis value).

[0101] - Condition 9. If the predicted probability of RLF occurrence (or the offset for the candidate cell plus the probability of RLF occurrence) for a neighboring cell (or candidate cell) (when connecting to a neighboring cell (or candidate cell) in the future) is less than a certain threshold (even if a certain hysteresis value is added)

[0102] - Condition 10. If the predicted probability of RLF occurrence (or the offset for the candidate cell plus the probability of RLF occurrence) for a neighboring cell (or candidate cell) (when connecting to a neighboring cell (or candidate cell) in the future) is greater than a certain threshold (even after deducting a certain hysteresis value).

[0103] - Condition 11. If the predicted TOS expected / predicted time (or the offset for the neighboring cell (or candidate cell) plus the value) for the neighboring cell (or candidate cell) (when connecting to the candidate cell later) is greater than a certain threshold (even after deducting a certain hysteresis value)

[0104] - Condition 12. If the predicted TOS expected / predicted time (or the offset for the neighboring cell (or candidate cell) plus the value) for the neighboring cell (or candidate cell) (when connecting to the candidate cell later) is less than a certain threshold (even if a certain hysteresis value is added)

[0105] - Condition 13. If the predicted HOF occurrence probability for a neighboring cell (or candidate cell) (or the value obtained by adding an offset for the neighboring cell (or candidate cell)) is less than (by a certain offset or more) the predicted RLF occurrence probability for the serving cell or SpCell (or the value obtained by adding an offset for the serving cell or SpCell) (even if a certain hysteresis value is added)

[0106] - Condition 14. If the predicted HOF occurrence probability for a neighboring cell (or candidate cell) (or the value obtained by adding an offset for the neighboring cell (or candidate cell)) is greater than the predicted RLF occurrence probability for the serving cell or SpCell (or the value obtained by adding an offset for the serving cell or SpCell) (by a specific offset or more) (even after deducting a specific hysteresis value)

[0107] - Condition 15. If the predicted HOF occurrence probability for a serving cell or SpCell (or the value obtained by adding an offset for the serving cell or SpCell) is greater than a certain threshold (even after deducting a certain hysteresis value).

[0108] - Condition 16. If the predicted HOF occurrence probability for a serving cell or SpCell (or the value obtained by adding an offset for the serving cell or SpCell) is less than a certain threshold (even if a certain hysteresis value is added)

[0109] - Condition 17. If the predicted RLF occurrence probability (or the value obtained by adding an offset for the serving cell or SpCell) for the serving cell or SpCell (when connecting to the serving cell or SpCell later) is greater than a certain threshold (even after deducting a certain hysteresis value)

[0110] - Condition 18. If the predicted RLF occurrence probability (or the value obtained by adding an offset for the serving cell or SpCell) for the serving cell or SpCell (when connecting to the serving cell or SpCell later) is less than a certain threshold (even if a certain hysteresis value is added)

[0111] - Condition 19. If the predicted TOS expected / predicted time (or the value including the offset for the serving cell or SpCell) for the serving cell or SpCell (when connecting to the serving cell or SpCell later) is less than a certain threshold (even if a certain hysteresis value is added)

[0112] - Condition 20. If the predicted TOS expected / predicted time (or the offset for the serving cell or SpCell plus the value) for the serving cell or SpCell (when connecting to the serving cell or SpCell later) is greater than a certain threshold (even after deducting a certain hysteresis value).

[0113] - Condition 21. A combination of multiple conditions (at least two) from Conditions 1 to 20. The terminal may determine that Condition 21 is satisfied if all of the multiple conditions set are satisfied. The terminal may not satisfy Condition 21 if at least one of the multiple conditions set is not satisfied.

[0114] - Condition 22. A combination of at least one of the (prediction-based) conditions 1 to 21 and at least one of the (actual measurement-based) conditions (e.g., Event A3, CondEvent A3). The terminal may determine that Condition 22 is satisfied if both conditions (at least one prediction-based condition and at least one actual measurement-based condition) are satisfied. The terminal may determine that Condition 22 is not satisfied if at least one of the two conditions is not satisfied.

[0115] The threshold value, hysteresis value, and offset value described above can be different values, and can be fixed values ​​defined in the standard or values ​​variably set by the network.

[0116] The aforementioned conditions may be event entering conditions, and the corresponding leaving (opposite of entering) conditions may be defined in reverse. For example, the leaving condition of Condition 1 may be defined as if the predicted measurement value for the serving cell or SpCell (or the value plus an offset for the serving cell or SpCell) (e.g., RSRP, RSRQ, SINR) is greater than a certain threshold (even after deducting a certain hysteresis value). The leaving conditions may be defined in the same manner for other conditions.

[0117] In operation 1f-10, the configuration information for the conditions for triggering a measurement report, which is included in the measurement configuration transmitted by the base station to the terminal, may include the threshold value, the hysteresis value, an indicator of whether to report when the leaving condition is satisfied (e.g., reportOnLeave), a TTT (time to trigger) value, and / or an offset value.

[0118] In operation 1f-10, the terminal can evaluate whether the above measurement report trigger condition is satisfied.

[0119] In operation 1f-10, the terminal may transmit a measurement report to the base station if the above (entering) condition is satisfied (for a time period indicated by the TTT value) for at least one cell.

[0120] According to one embodiment of the present disclosure, when a terminal is configured with an indicator (e.g., reportOnLeave) indicating whether to report when a leaving condition is satisfied, and when the leaving condition is satisfied (for a time period indicated by a TTT value) for at least one cell, the terminal may report to the base station the fact that the leaving condition is satisfied in a specific cell and / or related information (e.g., actual cell measurement value, predicted cell measurement value, predicted HOF probability / RLF probability / TOS value).

[0121] In operation 1f-15, the base station may decide to use CHO (e.g., the base station may decide whether to use CHO based on measurement results and prediction results received from the terminal).

[0122] In operation 1f-20, the base station (source base station) may request CHO for one or more candidate cells from candidate target base stations (e.g., the CHO request for one or more candidate cells may be performed via a HANDOVER REQUEST message). The source base station may transmit a CHO request message (e.g., a HANDOVER REQUEST message) for each cell.

[0123] In operation 1f-25, the candidate base station(s) may transmit a CHO response message (e.g., the CHO response message may be a HANDOVER RESPONSE ACKNOWLEDGE message) to the source base station. The CHO response message may include configuration information about the CHO candidate cell(s) and / or CHO execution condition(s).

[0124] In operation 1f-30, the source base station may generate / determine CHO configuration information to be transmitted to the terminal based on at least one of the CHO candidate cell(s), configuration information for CHO execution condition(s), or measurement / prediction result report received from the terminal.

[0125] In operation 1f-35, the source base station may transmit the CHO configuration information generated / determined in operation 1f-30 to the terminal via an RRC Reconfiguration message. The CHO configuration information may include configuration information regarding CHO candidate cell(s) and / or CHO execution condition(s). The terminal receiving the CHO configuration information may store the CHO configuration information. The execution condition(s) may be at least one of the following conditions.

[0126] - Condition 1. If the predicted measurement value for the serving cell or SpCell (or the value plus the offset for the serving cell or SpCell) (e.g. RSRP, RSRQ, SINR) is less than a certain threshold (even if a certain hysteresis value is added)

[0127] - Condition 2. If the predicted measurement value for the candidate cell (or the value plus an offset for the candidate cell) (e.g., RSRP, RSRQ, SINR) is greater than the predicted measurement value for the serving cell or SpCell (or the value plus an offset for the serving cell or SpCell) (by a certain offset or more) (even after subtracting a certain hysteresis value).

[0128] - Condition 3. If the predicted measurement value for the candidate cell (or the value plus the offset for the candidate cell) (e.g. RSRP, RSRQ, SINR) is greater than a certain threshold (even after subtracting a certain hysteresis value).

[0129] - Condition 4. Combination of Conditions 1 and 3. The terminal can determine that Condition 4 is satisfied if both conditions are satisfied. The terminal can determine that Condition 4 is not satisfied if at least one of the two conditions is not satisfied.

[0130] - Condition 5. If the predicted HOF occurrence probability for a candidate cell (or the value obtained by adding an offset for the candidate cell) is less than a certain threshold (even if a certain hysteresis value is added)

[0131] - Condition 6. If the predicted probability of RLF occurrence (or the value obtained by adding an offset for the candidate cell) for the candidate cell (when connecting to the candidate cell later) is less than a certain threshold (even if a certain hysteresis value is added)

[0132] - Condition 7. If the predicted TOS expected / predicted time for the candidate cell (or the value plus the offset for the candidate cell) (when connecting to the candidate cell later) is greater than a certain threshold (even after deducting a certain hysteresis value).

[0133] - Condition 8. If the predicted HOF occurrence probability for the candidate cell (or the value obtained by adding an offset for the candidate cell) is less than the predicted RLF occurrence probability for the serving cell or SpCell (or the value obtained by adding an offset for the serving cell or SpCell) (even if a specific hysteresis value is added) by a specific offset or more.

[0134] - Condition 9. If the predicted HOF occurrence probability for a serving cell or SpCell (or the value obtained by adding an offset for the serving cell or SpCell) is greater than a certain threshold (even after deducting a certain hysteresis value).

[0135] - Condition 10. If the predicted RLF occurrence probability (or the value obtained by adding an offset for the serving cell or SpCell) for the serving cell or SpCell (when connecting to the serving cell or SpCell later) is greater than a certain threshold (even after deducting a certain hysteresis value)

[0136] - Condition 11. If the predicted TOS expected / predicted time (or the value including the offset for the serving cell or SpCell) for the serving cell or SpCell (when connecting to the serving cell or SpCell later) is less than a certain threshold (even if a certain hysteresis value is added)

[0137] - Condition 12. If it is predicted that HOF will not occur for the candidate cell.

[0138] - Condition 13. If it is predicted that RLF will not occur for the candidate cell (when connecting to the candidate cell in the future)

[0139] - Condition 14. When it is predicted that handover ping-pong phenomenon will not occur for the candidate cell (when connecting to the candidate cell later)

[0140] - Condition 15. If HOF occurrence is predicted for a serving cell or SpCell

[0141] - Condition 16. When RLF is expected to occur for the serving cell or SpCell (when connecting to the serving cell or SpCell in the future)

[0142] - Condition 17. When a handover ping-pong phenomenon is expected to occur for the serving cell or SpCell (when connecting to the serving cell or SpCell in the future).

[0143] - Condition 18. A combination of multiple conditions (at least two) from Conditions 1 to 17. The terminal may determine that Condition 18 is satisfied if all of the multiple conditions set are satisfied. The terminal may determine that Condition 18 is not satisfied if at least one of the multiple conditions set is not satisfied.

[0144] - Condition 19. A combination of at least one new condition (prediction-based) from Conditions 1 to 18 and at least one condition (actual measurement-based) (e.g., Event A3, CondEvent A3). If both conditions are satisfied, the terminal may determine that Condition 19 is satisfied. If at least one of the two conditions is not satisfied, the terminal may determine that Condition 19 is not satisfied.

[0145] The threshold value, hysteresis value, and offset value described above can be different values, and can be fixed values ​​defined in the standard or values ​​variably set by the network.

[0146] The aforementioned conditions may be event entering conditions, and the corresponding leaving (opposite of entering) conditions may be defined in reverse. For example, the leaving condition of Condition 1 may be defined as if the predicted measurement value for the serving cell or SpCell (or the value plus an offset for the serving cell or SpCell) (e.g., RSRP, RSRQ, SINR) is greater than a certain threshold (even after deducting a certain hysteresis value). The leaving conditions may be defined in the same manner for other conditions.

[0147] In operation 1f-35, the configuration information for the CHO execution condition included in the CHO configuration transmitted by the base station to the terminal may include at least one of the threshold value, the hysteresis value, the indicator of whether to report when the leaving condition is satisfied (e.g., reportOnLeave), the TTT (time to trigger) value, or the offset value.

[0148] In operation 1f-40, the terminal can evaluate whether the CHO execution conditions for the candidate cell(s) are satisfied.

[0149] In operation 1f-45, if a CHO entering condition is satisfied (for a time period indicated by the TTT value) for at least one candidate cell, the terminal may release the connection with the source cell to perform a handover to a cell (target cell) that satisfies the CHO entering condition. In addition, the terminal may apply / use the stored configuration information for the corresponding cell. In addition, the terminal may perform synchronization with the target cell and then transmit an RRC Reconfiguration Complete message to the target cell or the target base station. After a successful handover, the terminal may release the stored CHO configuration information.

[0150] According to one embodiment of the present disclosure, when a terminal is configured with an indicator (e.g., reportOnLeave) indicating whether to report when a leaving condition is satisfied, and when a CHO execution leaving condition is satisfied (for a time period indicated by a TTT value) for at least one candidate cell, the terminal may report to the base station the fact that the leaving condition is satisfied in a specific cell and / or related information (e.g., actual cell measurement value, predicted cell measurement value, predicted HOF probability / RLF probability / TOS value).

[0151] In operation 1f-50, the target base station may transmit a HANDOVER SUCCESS message to the source base station, and the HANDOVER SUCCESS message may mean that the terminal has successfully performed a handover to the target base station or target cell.

[0152] In operation 1f-55, the source base station may transmit a HANDOVER CANCEL message to other candidate target cells or base stations other than the target cell, and the HANDOVER CANCEL message may be for the other candidate target cells or base stations to cancel CHO for the terminal.

[0153] FIG. 1g is a second flowchart illustrating a condition-based handover process based on UE-sided AI / ML prediction according to one embodiment of the present disclosure.

[0154] Operation 1g-05 may be identical to at least one of operations 1e-05 or 1f-05, and for detailed operations of operation 1g-05, reference may be made to the description provided above for at least one of operations 1e-05 or 1f-05. According to one embodiment of the present disclosure, a terminal may indicate to a base station whether the terminal supports the following capabilities through a UE capability information message.

[0155] - Capability 1. Ability to support candidate target cell selection / decision in CHO using thresholds related to at least one of cell measurement values ​​(RSRP / RSRQ / SINR), Handover failure (HOF), Radio link failure (RLF), or Time of stay (TOS) (based on (UE-sided) AI / ML).

[0156] Action 1g-10 may be identical to at least one of actions 1e-10 or 1f-10, and for the detailed actions of action 1g-10, reference may be made to the description given above for at least one of 1e-10 or 1f-10.

[0157] Action 1g-15 may be identical to at least one of actions 1e-15 or 1f-15, and for the detailed actions of action 1g-15, reference may be made to the description given above for at least one of 1e-15 or 1f-15.

[0158] Action 1g-20 may be identical to at least one of actions 1e-20 or 1f-20, and for the detailed actions of action 1g-20, reference may be made to the description given above for at least one of 1e-20 or 1f-20.

[0159] Action 1g-25 may be identical to at least one of actions 1e-25 or 1f-25, and for the detailed actions of action 1g-25, reference may be made to the description given above for at least one of 1e-25 or 1f-25.

[0160] Action 1g-30 may be identical to at least one of actions 1e-30 or 1f-30, and for the detailed actions of action 1g-30, reference may be made to the description given above for at least one of 1e-30 or 1f-30.

[0161] Operation 1g-35 may be identical to at least one of operations 1e-35 or 1f-35, and for detailed operations of operation 1g-35, reference may be made to the description given above for at least one of 1e-35 or 1f-35. According to one embodiment of the present disclosure, in operation 1g-35, the base station may transmit a prediction-related threshold (threshold A) (e.g., at least one of a threshold for HOF probability, a threshold for RLF probability, or a threshold for TOS time) to the terminal in the CHO configuration transmitted.

[0162] Action 1g-40 may be identical to at least one of actions 1e-40 or 1f-40, and the description given above for at least one of 1e-40 or 1f-40 may be referred to for the detailed operation of action 1g-40. The terminal may acquire cell(s) satisfying at least one CHO execution condition (e.g., a CHO triggered cell).

[0163] In operation 1g-45, the terminal may calculate AI / ML predicted values ​​(e.g., HOF probability, RLF probability, and / or TOS time) for candidate cell(s) that satisfy the CHO execution condition. If the predicted values ​​(e.g., HOF probability, RLF probability, and / or TOS time) for the candidate cell are not better than the threshold value A set in 1g-35 (e.g., if the HOF predicted probability for the corresponding candidate cell is greater than the threshold value for HOF probability set as threshold A) (e.g., if the RLF predicted probability for the corresponding candidate cell is greater than the threshold value for RLF probability set as threshold A, or, e.g., if the TOS predicted time for the corresponding candidate cell is less than the threshold value for TOS time set as threshold A), the terminal may consider the corresponding candidate cell to no longer be a CHO triggered cell and may consider the corresponding candidate cell to be a cell prohibited from performing CHO (e.g., a CHO prohibited cell).

[0164] Operation 1g-50 may be identical to at least one of operations 1e-45 or 1f-45, and for detailed operations of operation 1g-50, reference may be made to the description given above for at least one of 1e-45 or 1f-45. According to one embodiment of the present disclosure, a terminal may perform a handover by selecting one cell from among CHO triggered cells and / or candidate cells that are not CHO prohibited cells.

[0165] Action 1g-55 may be identical to at least one of actions 1e-50 or 1f-50, and for the detailed actions of action 1g-55, reference may be made to the description given above for at least one of 1e-50 or 1f-50.

[0166] Action 1g-60 may be identical to at least one of actions 1e-55 or 1f-55, and for detailed actions of action 1g-60, reference may be made to the description given above for at least one of 1e-55 or 1f-55.

[0167] FIG. 1h is a flowchart illustrating a condition-based handover process based on (NW-sided) AI / ML prediction of a base station or network according to one embodiment of the present disclosure.

[0168] Operation 1h-05 may be identical to at least one of operations 1e-05 or 1f-05, and for detailed operations of operation 1h-05, reference may be made to the description provided above for at least one of 1e-05 or 1f-05. According to one embodiment of the present disclosure, a terminal may indicate to a base station whether the terminal supports the following capabilities through a UE capability information message.

[0169] - Capability 1. Ability to support at least one of cell measurement value (RSRP / RSRQ / SINR) information prediction (based on (NW-sided) AI / ML), HOF (Handover failure) information prediction, RLF (Radio link failure) information prediction, or TOS (Time of stay) information prediction.

[0170] - Capability 2. Ability to support CHO using at least one of cell measurement value (RSRP / RSRQ / SINR) information prediction (based on (NW-sided) AI / ML), HOF (Handover failure) information prediction, RLF (Radio link failure) information prediction, or TOS (Time of stay) information prediction.

[0171] - Capability 3. Ability to support CHO execution conditions using at least one of cell measurement value (RSRP / RSRQ / SINR) information prediction ((NW-sided) AI / ML-based), HOF (Handover failure) information prediction, RLF (Radio link failure) information prediction, or TOS (Time of stay) information prediction.

[0172] - Ability 4. Ability to support setting of CHO forbidden cells (lists) transmitted from the network (based on (NW-sided) AI / ML decisions).

[0173] Action 1h-10 may be identical to at least one of actions 1e-10 or 1f-10, and for the detailed actions of action 1h-10, reference may be made to the description given above for at least one of 1e-10 or 1f-10.

[0174] Action 1h-15 may be identical to at least one of actions 1e-15 or 1f-15, and for the detailed actions of action 1h-15, reference may be made to the description given above for at least one of 1e-15 or 1f-15.

[0175] Action 1h-20 may be identical to at least one of actions 1e-20 or 1f-20, and for the detailed actions of action 1h-20, reference may be made to the description given above for at least one of 1e-20 or 1f-20.

[0176] Action 1h-25 may be identical to at least one of actions 1e-25 or 1f-25, and for the detailed actions of action 1h-25, reference may be made to the description given above for at least one of 1e-25 or 1f-25.

[0177] Action 1h-30 may be identical to at least one of actions 1e-30 or 1f-30, and for the detailed actions of action 1h-30, reference may be made to the description given above for at least one of 1e-30 or 1f-30.

[0178] Action 1h-35 may be identical to at least one of actions 1e-35 or 1f-35, and for the detailed actions of action 1h-35, reference may be made to the description given above for at least one of 1e-35 or 1f-35.

[0179] Action 1h-40 may be identical to at least one of actions 1e-40 or 1f-40, and for the detailed actions of action 1h-40, reference may be made to the description given above for at least one of 1e-40 or 1f-40.

[0180] At action 1h-45, the terminal can perform cell measurement reporting (still as at action 1h-10).

[0181] At operation 1h-50, the base station can calculate the AI / ML predicted values ​​(e.g., HOF probability, RLF probability, and / or TOS time) of the UE (for each candidate cell). The base station can calculate this based on the cell measurement report (1h-10, 1h-40) of the UE. As a result, the base station can select cells on which CHO performance is (temporarily) prohibited (e.g., CHO prohibited cells). For example, if the base station determines that the HOF predicted probability for the candidate cell is high, or the RLF predicted probability is high, or the TOS predicted time for the candidate cell is short, or the predicted cell measurement values ​​(RSRP / RSRQ / SINR) for the candidate cell are poor, the base station can (temporarily) set the cell as a CHO prohibited cell.

[0182] At step 1h-55, the base station may transmit a CHO forbidden cell (list) to the terminal (e.g., via an RRC Reconfiguration message). According to one embodiment of the present disclosure, the base station may set a timer length for the forbidden time for each CHO forbidden cell to the terminal.

[0183] Operation 1h-60 may be identical to at least one of operations 1e-40 or 1f-40, and for detailed operations of operation 1h-60, reference may be made to the description provided above for at least one of 1e-40 or 1f-40. The terminal may evaluate whether the CHO execution conditions for the remaining candidate cells, excluding the CHO-forbidden cell (received from the base station), are satisfied. According to one embodiment of the present disclosure, when the terminal receives the timer length for the CHO-forbidden cell and the prohibition time in 1h-55, the terminal may start the timer. If the timer is running, the terminal may regard the cell as a CHO-forbidden cell. The timer may expire after a time set by the base station, and after the timer expires, the terminal may no longer regard the cell as a CHO-forbidden cell. When the timer is running, when new timer information for the cell is received from the base station, the existing running timer may be stopped and a new timer may be started.

[0184] Action 1h-65 may be identical to at least one of actions 1e-45 or 1f-45, and for action 1h-65, reference may be made to the description given above for at least one of 1e-45 or 1f-45.

[0185] Action 1h-70 may be identical to at least one of actions 1e-50 or 1f-50, and for action 1h-70, reference may be made to the description given above for at least one of 1e-50 or 1f-50.

[0186] Action 1h-75 may be identical to at least one of actions 1e-55 or 1f-55, and for action 1h-75, reference may be made to the description given above for at least one of 1e-55 or 1f-55.

[0187] According to one embodiment of the present disclosure, the process of the terminal receiving the prediction-based CHO execution condition and determining whether the condition is satisfied (e.g., 1f-40) may be an operation that takes a certain amount of time. For example, depending on the AI / ML model used by the terminal, the terminal may not be able to calculate the predicted cell measurement value, event, or probability within a short period of time. To prepare for a situation where the terminal is unable to calculate the predicted cell measurement value, event, or probability within a short period of time, the base station may set a timer (e.g., by setting a timer length) for the terminal. The terminal may start the timer when checking the (prediction-based) CHO execution condition, and may stop the timer when the CHO execution condition determination is completed (e.g., the determination is completed whether the CHO execution condition is satisfied or not). When the timer expires (i.e., if the CHO execution condition check fails within the set timer period), the terminal may fallback to the CHO execution condition based on the actual measurement value (e.g., set by the network) to determine whether the CHO execution condition based on the actual measurement value is satisfied.

[0188] According to one embodiment of the present disclosure, when the timer expires, the terminal may report to the base station that the timer has expired or that the CHO execution condition determination has failed within the limited timer period (e.g., via a MeasurementReport message, a UEInformationResponse message, or a UEAssistanceInformation message). According to one embodiment of the present disclosure, the timer length may be a fixed value defined in the standard.

[0189] According to one embodiment of the present disclosure, the operation of the terminal to derive a predicted value (e.g., HOF probability, RLF probability, and / or TOS time) for a candidate cell (e.g., 1g-45) may be an operation that takes a certain amount of time. For example, depending on the AI / ML model used by the terminal, the terminal may not be able to calculate the HOF probability within a short period of time. To prepare for a situation where the terminal is unable to calculate the predicted cell measurement value, event, or probability within a short period of time, the base station may set a timer (e.g., by setting a timer length) for the terminal. The terminal may start the timer when calculating (starting) the predicted value for the candidate cell, and may stop the timer once the predicted value is derived. When the timer expires (i.e., if the predicted value is not derived within the set time period), the terminal may consider the corresponding candidate cell as a CHO-forbidden cell and may not perform a handover to the cell considered as a CHO-forbidden cell. Not performing a handover to a cell considered as a CHO forbidden cell may be because the predicted value derivation failed, which may cause future problems (e.g., HOF, RLF, short TOS) when handing over to that cell.

[0190] According to one embodiment of the present disclosure, when the timer expires (i.e., when the predicted value is not derived within the set timer period), the terminal may not consider the candidate cell for which the predicted value is not derived within the timer period as a CHO-forbidden cell. The reason for not considering the candidate cell for which the predicted value is not derived within the timer period as a CHO-forbidden cell may be to provide the terminal with an opportunity to perform a handover to the cell when the actual value-based CHO condition is satisfied.

[0191] According to one embodiment of the present disclosure, when the timer expires, the terminal may report to the base station that the timer has expired or that the prediction value has failed to be derived within the limited timer period (e.g., via a MeasurementReport message, a UEInformationResponse message, or a UEAssistanceInformation message). According to one embodiment of the present disclosure, the timer length may be a fixed value defined in the standard.

[0192] According to embodiments of the present disclosure (e.g., FIGS. 1G and 1H), CHO-allowed cells may be defined / used for the same purpose as CHO-disallowed cells in the operation of a terminal or a base station. For example, instead of the terminal determining or configuring CHO-disallowed cells and not performing CHO on those cells, the terminal may determine or configuring CHO-allowed cells and perform CHO (only) on those cells.

[0193] FIG. 1i is a diagram illustrating the structure of a terminal according to one embodiment of the present disclosure.

[0194] Referring to FIG. 1i, the terminal includes an RF (Radio Frequency) processing unit (1i-10), a baseband processing unit (1i-20), a storage unit (1i-30), and a control unit (1i-40).

[0195] The RF processing unit (1i-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1i-10) up-converts the baseband signal provided from the baseband processing unit (1i-20) into an RF band signal and transmits it through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1i-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital to analog convertor (DAC), an analog to digital convertor (ADC), etc. In the drawing, only one antenna is illustrated, but the terminal may be equipped with multiple antennas. In addition, the RF processing unit (1i-10) may include multiple RF chains. Furthermore, the RF processing unit (1i-10) may perform beamforming. For the above beamforming, the RF processing unit (1i-10) can adjust the phase and size of each signal transmitted and received through multiple antennas or antenna elements. In addition, the RF processing unit can perform MIMO, and can receive multiple layers when performing the MIMO operation.

[0196] The baseband processing unit (1i-20) performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the system. For example, when transmitting data, the baseband processing unit (1i-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (1i-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (1i-10). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (1i-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. In addition, when receiving data, the baseband processing unit (1i-20) divides the baseband signal provided from the RF processing unit (1i-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT (fast Fourier transform) operation, and then restores the received bit string through demodulation and decoding.

[0197] The baseband processing unit (1i-20) and the RF processing unit (1i-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (1i-20) and the RF processing unit (1i-10) may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. Furthermore, at least one of the baseband processing unit (1i-20) and the RF processing unit (1i-10) may include a plurality of communication modules to support a plurality of different wireless access technologies. In addition, at least one of the baseband processing unit (1i-20) and the RF processing unit (1i-10) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. Additionally, the different frequency bands may include a super high frequency (SHF) (e.g., 2.NRHz, NRhz) band and a millimeter wave (mm wave) (e.g., 60GHz) band.

[0198] The above storage unit (1i-30) stores data such as basic programs, application programs, and setting information for the operation of the terminal. The above storage unit (1i-30) provides the stored data upon request from the control unit (1i-40).

[0199] The above control unit (1i-40) controls the overall operations of the terminal. For example, the control unit (1i-40) transmits and receives signals through the baseband processing unit (1i-20) and the RF processing unit (1i-10). In addition, the control unit (1i-40) records and reads data in the storage unit (1i-30). For this purpose, the control unit (1i-40) may include at least one processor. For example, the control unit (1i-40) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as application programs, and may include a multi-connection processing unit (1i-42) as illustrated in the drawing.

[0200] FIG. 1J is a diagram illustrating the structure of a base station according to one embodiment of the present disclosure.

[0201] Referring to FIG. 1j, a base station according to an example of the present disclosure is configured to include an RF processing unit (1j-10), a baseband processing unit (1j-20), a backhaul communication unit (1j-30), a storage unit (1j-40), and a control unit (1j-50).

[0202] The RF processing unit (1j-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1j-10) up-converts the baseband signal provided from the baseband processing unit (1j-20) into an RF band signal and transmits it through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1j-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. In the drawing, only one antenna is shown, but the base station may have multiple antennas. In addition, the RF processing unit (1j-10) may include multiple RF chains. Furthermore, the RF processing unit (1j-10) may perform beamforming. For the above beamforming, the RF processing unit (1j-10) can adjust the phase and magnitude of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit can perform a downlink MIMO operation by transmitting one or more layers.

[0203] The baseband processing unit (1j-20) performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the wireless access technology. For example, when transmitting data, the baseband processing unit (1j-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (1j-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (1j-10). For example, in the case of OFDM, when transmitting data, the baseband processing unit (1j-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols through IFFT operation and CP insertion. In addition, when receiving data, the baseband processing unit (1j-20) divides the baseband signal provided from the RF processing unit (1j-10) into OFDM symbol units, restores the signals mapped to subcarriers through FFT operation, and then restores the received bit string through demodulation and decoding. The baseband processing unit (1j-20) and the RF processing unit (1j-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (1j-20) and the RF processing unit (1j-10) may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0204] The above backhaul communication unit (1j-30) provides an interface for performing communication with other nodes within the network. That is, the backhaul communication unit (1j-30) converts a bit string transmitted from the main base station to another node, such as an auxiliary base station or core network, into a physical signal, and converts a physical signal received from the other node into a bit string.

[0205] The storage unit (1j-40) stores data such as basic programs, application programs, and setting information for the operation of the main base station. In particular, the storage unit (1j-40) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit (1j-40) can store information that serves as a judgment criterion for whether to provide or terminate multiple connections to a terminal. In addition, the storage unit (1j-40) provides the stored data at the request of the control unit (1j-50).

[0206] The above control unit (1j-50) controls the overall operations of the base station. For example, the control unit (1j-50) transmits and receives signals through the baseband processing unit (1j-20) and the RF processing unit (1j-10) or through the backhaul communication unit (1j-30). In addition, the control unit (1j-50) records and reads data in the storage unit (1j-40). For this purpose, the control unit (1j-50) may include at least one processor, and may include a multi-connection processing unit (1j-52) as illustrated in the drawing.

[0207] Meanwhile, the embodiments of the present disclosure disclosed in this disclosure and the drawings are merely specific examples presented to easily explain the technical content of the present disclosure and aid in understanding of the present disclosure, and are not intended to limit the scope of the present disclosure. In other words, it will be apparent to those skilled in the art to which the present disclosure pertains that other modified examples based on the technical concepts of the present disclosure are possible.

[0208] Furthermore, the above embodiments may be combined and operated as needed. For example, parts of one embodiment of the present disclosure and parts of another embodiment may be combined to operate a base station and a terminal. Furthermore, the embodiments of the present disclosure are applicable to other communication systems, and other modifications based on the technical concepts of the embodiments may also be implemented. For example, the embodiments may be applied to LTE systems, 5G, NR systems, or 6G systems. Therefore, the scope of the present disclosure should not be limited to the described embodiments, but should be determined not only by the scope of the following claims but also by equivalents thereof.

Claims

1. In a method of a terminal in a wireless communication system, A step of receiving, from a source base station, conditional handover setup information including at least one candidate base station for conditional handover and conditional handover execution conditions including measurement-based conditions and prediction-based conditions for each candidate base station; A step of determining a candidate base station that satisfies both the measurement-based condition and the prediction-based condition among at least one candidate base station as a target base station; and A method comprising the step of performing a handover to the target base station.

2. In paragraph 1, The step of determining a candidate base station that satisfies both the measurement-based condition and the prediction-based condition among at least one candidate base station as a target base station is as follows: A step of determining whether at least one of the candidate base stations satisfies the measurement-based condition; A step of determining whether triggered cells that satisfy the above measurement-based condition satisfy the above prediction-based condition; and A step of determining a candidate base station that satisfies the prediction-based condition among the triggered cells as a target base station, A method in which a candidate base station satisfying the prediction-based condition among the triggered cells is set as a prohibited cell.

3. In paragraph 1, A method further comprising the step of transmitting terminal capability information including prediction-related capabilities to the source base station.

4. In paragraph 1, The above prediction-based conditions are: A method comprising a condition related to at least one of a handover failure occurrence probability, a radio link failure (RLF) occurrence probability, and a time of stay (TOS) prediction time.

5. In a method of a source base station in a wireless communication system, A step of receiving a measurement result and a prediction result corresponding to the measurement result from a terminal; A step of determining a conditional handover for the terminal based on the measurement result and the prediction result; A step of receiving configuration information for executing conditional handover from at least one candidate base station; A step of generating a conditional handover execution condition including a measurement-based condition and a prediction-based condition for each candidate base station based on the measurement result, the prediction result, the at least one candidate base station, and the configuration information for executing a conditional handover for each candidate base station; and A method comprising the step of transmitting conditional handover setup information including conditional handover execution conditions for at least one candidate base station and each of the candidate base stations to the terminal.

6. In paragraph 5, A method further comprising the step of receiving terminal capability information including a capability related to prediction from the terminal.

7. In paragraph 5, The above prediction-based conditions are: A method comprising a condition related to at least one of a handover failure occurrence probability, a radio link failure (RLF) occurrence probability, and a time of stay (TOS) prediction time.

8. In the terminal of a wireless communication system, Transmitter and receiver; and A control unit connected to the above transmitter and receiver, wherein the control unit: Receive conditional handover configuration information from a source base station, including at least one candidate base station for conditional handover and conditional handover execution conditions including measurement-based conditions and prediction-based conditions for each candidate base station; Among the at least one candidate base station, a candidate base station that satisfies both the measurement-based condition and the prediction-based condition is determined as a target base station, A terminal configured to perform handover to the target base station.

9. In paragraph 8, The above control unit, Determine whether at least one of the above candidate base stations satisfies the above measurement-based condition, For triggered cells that satisfy the above measurement-based conditions, determine whether the above prediction-based conditions are satisfied, It is configured to determine a candidate base station that satisfies the prediction-based condition among the triggered cells as a target base station, A terminal in which a candidate base station satisfying the above prediction-based condition among the above triggered cells is set as a prohibited cell.

10. In paragraph 8, The above control unit, A terminal configured to transmit terminal capability information including prediction-related capabilities to the source base station.

11. In paragraph 8, The above prediction-based conditions are: A terminal including conditions related to at least one of a handover failure occurrence probability, a radio link failure (RLF) occurrence probability, and a time of stay (TOS) prediction time.

12. In the source base station of a wireless communication system, Transmitter and receiver; and A control unit connected to the above transmitter and receiver, wherein the control unit: Receive measurement results and prediction results corresponding to the measurement results from the terminal, Based on the above measurement results and the above prediction results, a conditional handover is determined for the terminal, Receive configuration information for executing conditional handover from at least one candidate base station, Based on the measurement result, the prediction result, the at least one candidate base station, and the configuration information for executing conditional handover for each candidate base station, a conditional handover execution condition including a measurement-based condition and a prediction-based condition is generated for each candidate base station, A source base station configured to transmit conditional handover setup information including conditional handover execution conditions for at least one candidate base station and each of the candidate base stations to the terminal.

13. In paragraph 12, The above control unit, A source base station configured to receive terminal capability information including prediction-related capabilities from the terminal.

14. In paragraph 12, The above prediction-based conditions are: A source base station including conditions related to at least one of a handover failure occurrence probability, a radio link failure (RLF) occurrence probability, and a time of stay (TOS) prediction time.

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