Method and device for channel recovery using artificial intelligence in wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate than a 4G communication system such as LTE. A method performed by a first base station in a wireless communication system comprises the steps of: receiving, from a terminal, a measurement report including a radio link failure (RLF) prediction result; and transmitting, to a second base station, a first message including a terminal context, wherein the RLF prediction result includes first information indicating a serving cell at a time point when RLF is predicted, and second information indicating a cell in which a channel state is predicted to be good at the time point when the RLF is predicted.

Description

Method and device for channel recovery using artificial intelligence in a wireless communication system

[0001] The present disclosure relates to a device (terminal, base station, and / or mobile communication network equipment) that supports AI (artificial intelligence) / ML (machine learning) in a wireless communication system and a method performed by the device.

[0002] Looking back at the evolution of wireless communication over successive generations, technologies have primarily been developed for human-facing services such as voice, multimedia, and data. With the commercialization of the 5G (5th Generation) communication system, an explosive increase in connected devices is expected to be connected to communication networks. Examples of networked objects include vehicles, robots, drones, home appliances, displays, smart sensors installed in various infrastructures, construction equipment, and factory equipment. Mobile devices are also expected to evolve into diverse form factors, such as augmented reality glasses, virtual reality headsets, and holographic devices. In the 6G (6th Generation) era, efforts are being made to develop improved 6G communication systems to connect hundreds of billions of devices and objects and provide diverse services. For this reason, 6G communication systems are often referred to as "beyond 5G."

[0003] The 6G communication system, expected to be realized around 2030, will have a maximum transmission speed of terabytes (i.e., 1,000 gigabits) per second (bps) and a wireless latency of 100 microseconds (μsec). In other words, compared to 5G, the transmission speed in a 6G communication system will be 50 times faster and the wireless latency will be reduced to one-tenth.

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

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

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

[0007] The present disclosure introduces a connection disconnection prediction method based on an AI / ML algorithm in a high-density micro-cell environment and an environment with high mobility, and aims to improve the overall performance and stability of the network through rapid channel recovery when a connection disconnection occurs.

[0008] The present disclosure may have as its primary purpose the provision of a device (terminal, base station, and / or mobile communication network equipment) that supports AI (artificial intelligence) / ML (machine learning) in a wireless communication system and a method performed on the device.

[0009] A method according to embodiments of the present disclosure may include: receiving, from a base station, configuration information for predicting a channel state of a beam or cell based on artificial intelligence and machine learning (AL / ML), or for measuring a current beam or cell and predicting a radio link failure (RLF); performing, based on the configuration information, prediction of a channel state of a beam or cell based on AL / ML, or for measuring a channel state of a current beam or cell and predicting a disconnection; transmitting, based on the configuration information, a report of the prediction and measurement results to the base station; transmitting, by the base station having received the information, terminal context information necessary for reconnection to a base station predicted to be where a terminal will attempt to reconnect after a disconnection; and receiving, by the base station, a message for releasing a terminal context from the base station to which the terminal has reconnected when reconnection and connection recovery of the terminal are completed.

[0010] According to various embodiments of the present disclosure, channel state information between a user terminal and a base station can be proactively predicted, the user terminal can transmit the predicted information, and the network can transmit the terminal's registration information in advance based on the predicted information to a base station from which the terminal is likely to attempt connection recovery, thereby quickly restoring the connection between the terminal and the base station when a connection break occurs, thereby increasing the overall performance and stability of the network.

[0011] FIG. 1 is a diagram illustrating the structure of a mobile communication system according to embodiments of the present disclosure.

[0012] FIG. 2 is a diagram for explaining a wireless connection state transition in a mobile communication system according to embodiments of the present disclosure.

[0013] FIG. 3 is a flowchart for explaining a channel status measurement and reporting process of a terminal according to embodiments of the present disclosure.

[0014] Figures 4a, 4b and 4c are flowcharts illustrating an operating method according to embodiments of the present disclosure.

[0015] FIG. 5 is a flowchart illustrating an operating method according to embodiments of the present disclosure.

[0016] FIG. 6 is a flowchart illustrating an operating method according to embodiments of the present disclosure.

[0017] FIG. 7 is a flowchart illustrating an operating method according to embodiments of the present disclosure.

[0018] FIG. 8 is a flowchart illustrating an operating method according to embodiments of the present disclosure.

[0019] FIG. 9 is a diagram illustrating the structure of a terminal according to embodiments of the present disclosure.

[0020] FIG. 10 is a diagram illustrating the structure of a base station according to embodiments of the present disclosure.

[0021] In describing the embodiments in this specification, descriptions of technical details that are well known in the technical field to which the present disclosure pertains and are not directly related to the present disclosure will be omitted. This is to avoid obscuring the gist of the present disclosure by omitting unnecessary explanations and to convey the gist more clearly.

[0022] 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.

[0023] 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 together 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 only to ensure that the disclosure of the present 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 refer to like elements throughout the specification.

[0024] 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).

[0025] 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.

[0026] 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.

[0027] FIG. 1 is a diagram illustrating the structure of a mobile communication system according to embodiments of the present disclosure.

[0028] Referring to FIG. 1, a wireless access network of a mobile communication system (New Radio, NR) according to embodiments of the present disclosure may be composed of a base station (source next generation Node B, hereinafter referred to as source gNB) (110) and an AMF (access and mobility management function or New Radio Core Network, 105). A user equipment (New Radio User Equipment, hereinafter referred to as (NR) UE or terminal) (115) may access an external network through the source gNB (110) and the AMF (105). The terminal (115) may measure a signal of an adjacent gNB (130), which is an adjacent base station. Here, the adjacent base station including the adjacent gNB may be a base station of a 3GPP series mobile communication system including an eNodeB of an LTE system or an AP of another mobile communication series. The mobile communication system according to embodiments of the present disclosure may be a next generation mobile communication system, and the base station may be a next generation base station.

[0029] AMF (105) can perform functions such as mobility support, bearer setup, and QoS (quality of service) setup. AMF (105) is a device that is responsible for various control functions as well as mobility management functions for terminals and can be connected to multiple base stations.

[0030] Additionally, the mobile communication system according to the embodiments of the present disclosure can also be linked with an existing LTE system through connection with AMF (105).

[0031] FIG. 2 is a diagram for explaining a wireless connection state transition in a mobile communication system according to embodiments of the present disclosure.

[0032] A mobile communication system according to embodiments of the present disclosure may have three radio connection states (RRC (radio resource control) states) or RRC modes. The connected mode (RRC_CONNECTED, 205) is a radio connection state in which a terminal can transmit and receive data. The idle mode (RRC_IDLE, 230) is a radio connection state in which a terminal monitors whether paging is transmitted to itself. Both modes are radio connection states that are also applied to existing LTE systems, and the detailed technology is the same as that of the existing LTE system. The mobile communication system according to embodiments of the present disclosure may be a next-generation mobile communication system.

[0033] In the mobile communication system according to embodiments of the present disclosure, a new inactive (RRC_INACTIVE) radio connection state (215) is 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 can be supported. The characteristics of the inactive radio connection state are listed below.

[0034] - Cell re-selection mobility;

[0035] - CN - NR RAN connection (both C / U-planes (control plane / user plane)) has been established for UE;

[0036] - The UE AS (Access Stratum) context is stored in at least one gNB and the UE;

[0037] - Paging is initiated by NR RAN;

[0038] - RAN-based notification area is managed by NR RAN;

[0039] - NR RAN knows the RAN-based notification area which the UE belongs to;

[0040] According to embodiments 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 (210) 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 (210). The 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 steps. In addition, the terminal can transition from INACTIVE mode to standby mode through the Release procedure after Resume (220). The transition (225) between the connected mode and the standby mode can follow the existing LTE technology. For example, the transition between modes can be performed through the establishment or release procedure.

[0041] FIG. 3 is a flowchart illustrating a process in which a terminal performs cell measurement and reporting operations according to embodiments of the present disclosure.

[0042] According to embodiments of the present disclosure, in step 315, the terminal (305) may report its capability information to the base station (310). In step 320, the base station (310) may transmit an RRCReconfiguration message including configuration information (measConfig IE) related to cell measurement operation to the terminal (305).

[0043] The configuration information (measConfig IE) may include information necessary for reporting the results measured by the terminal (305) to the base station (310) 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 (305) may report a predetermined measurement result when a specific event set based on the configuration information is satisfied. For example, the following events may be set in the NR system.

[0044] - Event(s) related to typical intra- / inter-RAT measurements are as shown in Table 1 below.

[0045] 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;

[0046] - Similar to condition-based measurement reporting, in condition-based handover, when a specific event is satisfied, the terminal (305) 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.

[0047] 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;

[0048] - (Sidelink) When a specific event is satisfied in the Relay, the terminal (305) can perform a specific action. Event(s) related to the Relay are as shown in Table 3 below.

[0049] Event X1: Serving L2 U2N Relay UE becomes worse than absolute threshold1 AND NR Cell becomes better than another absolute threshold2;Event

[0050] - In the case of NR-U (Unlicensed), when a specific event is satisfied, the terminal (305) can perform a specific action. Event(s) related to NR-U are as shown in Table 4 below.

[0051] Event I1: Interference becomes higher than absolute threshold.

[0052] In step 325, the terminal (305) can evaluate whether the set events are satisfied. If the events described above are continuously satisfied with a predetermined condition for a predetermined time interval (time-to-trigger), the terminal (305) can consider the event to be satisfied.

[0053] In step 330, when a set condition is satisfied, the terminal (305) may report a MeasurementReport message containing the measurement result to the base station (310). Alternatively, the terminal (305) may perform a predetermined action corresponding to the condition, for example, a condition-based handover. The base station (310) that receives the measurement result may utilize the measurement result for a predetermined purpose (e.g., handover).

[0054] FIGS. 4A, 4B, 4C and 5 are diagrams for explaining connection recovery operations according to embodiments of the present disclosure.

[0055] Figures 4a, 4b, and 4c illustrate a case where a UE belonging to the Source gNB experiences an RLF and attempts connection recovery to another gNB, such as the Target gNB, which can be viewed as a type of Too-late handover failure. Referring to Figures 4a, 4b, and 4c, the process of performing connection recovery (RRC Re-establishment) may vary depending on the point in time when the UE experiences a connection failure (RLF, Radio Link Failure). In Figure 4a, the UE can exchange capability information with the Source gNB when establishing an RRC connection (405), and the Source gNB can transmit configuration information for channel state measurement to the UE based on the capability information. (410) Afterwards, the UE can measure the channel state and transmit an event as specified in [Table 1]-[Table 4] through a Measurement report (415). At this time, the Source gNB can make a Handover decision based on the information in the Measurement report, and the Source gNB can perform a Handover request to the Target gNB. The handover request transmitted at this time is transmitted as a message such as HANDOVER REQUEST (420). This message can use the Xn interface or Sn interface in 5G NR, and this handover request can be a CHO or legacy handover. If the target gNB can accept the handover, it can send a handover request acknowledgment to the source gNB (425). This process is called “handover preparation.”When the UE experiences RLF at a certain point after the handover preparation is completed (regardless of whether the source gNB has issued a handover command to the UE to instruct the handover), the UE can perform cell reselection to restore the RRC connection, and if the target gNB satisfies the reselection criteria, it requests an RRC re-establishment request to the target gNB. (435) At this time, the target gNB can obtain information about the UE by combining IEs such as c-RNTI and shortMAC-I in the handover request (420) and the RRC re-establishment request, and accepts the re-establishment request of the UE by using the UE Context in the handover request and transmits an RRC re-establishment message. (440) After the terminal notifies the completion of the connection recovery procedure through the RRC Re-establishment complete message (445), the target gNB sends a UE Context release message (450) to inform the source gNB that the connection of the terminal has moved and to release the context held by the source gNB.

[0056] In another embodiment, when a UE experiences an RLF and transmits an RRC Re-establishment request to the target gNB (470) when the Handover Request is not transmitted as illustrated in FIG. 4b, i.e., the Handover preparation is not completed, the target gNB may request the source gNB, where the RLF occurred, for context information to restore the RRC connection with the UE using a RETRIEVE UE CONTEXT REQUEST message (475) using physCellID, etc. in the message. When the source gNB transmits the context information of the UE using the RETRIEVE UE CONTEXT RESPONSE message, the connection restoration may be completed using the same procedure as the RRC re-establishment of FIG. 4a (480). As another example, when a RETRIEVE UE CONTEXT FAILURE (4110) message is received as illustrated in FIG. 4c, the target gNB may attempt a new RRC connection by sending an RRC Setup (4115) message to the UE.

[0057] FIG. 5 illustrates a case where a terminal belonging to a source gNB experiences an RLF in the gNB1 after moving an RRC connection to a new target gNB1 through legacy handover, LTM (Low-layer Triggered Mobility), CHO (Conditional Handover), etc., and then attempts to restore the connection to another target gNB2. This can be viewed as a type of WrongCell handover failure. Referring to FIG. 5, the Source gNB may attempt a handover to the Target gNB1 based on the measurement result of the Terminal (520). If the Target gNB1 accepts the handover request (525), the Source gNB transmits a handover indication message including the configuration value of the Target gNB1 to the Terminal (530). At this time, the handover indication may be a legacy HO or CHO. After the UE completes the handover to Target gNB1 and moves the RRC connection (535), the UE may experience an RLF while the handover is not yet complete (540). The UE may perform cell reselection to restore the RRC connection, and if Target gNB2 satisfies the reselection criteria, it requests an RRC Re-establishment request to Target gNB2. (545) At this time, Target gNB2 can combine IEs such as c-RNTI, shortMAC-I, and PhyCellID in the RRC re-establishment request to know where the RLF occurred for the UE, and if it recognizes the information of Target gNB1, it can request a RETRIEVE UE CONTEXT REQUEST (550) to Target gNB1.At this time, if the UE CONTEXT is received from Target gNB1, the RRC Re-establishment procedure can be completed, and after completion, a Context release message is transmitted to Target gNB1 (570). The Target gNB1 also transmits this message to Source gNB (575).

[0058] In addition to the embodiment described in FIG. 5, if Target gNB2 fails to obtain UE context, i.e., if the base station from which the terminal has requested an RRC Re-establishment request has not completed handover preparation in advance, such as through CHO, or if the UE context cannot be obtained through RETRIEVE UE CONTEXT during the Re-establishment process, Target gNB2 switches the procedure to RRC Setup.

[0059] In the embodiments shown in FIGS. 4a, 4b, 4c, and 5, when a terminal performs a connection recovery attempt and the base station that is the target of the recovery attempt does not have the UE CONTEXT for recovering the terminal's connection, the base station can perform an operation to obtain the UE CONTEXT after receiving an RRC Re-establishment request from the terminal. In the case of the LTE system, when there is no UE CONTEXT, the re-establishment is rejected, the connection is completely disconnected, and an initial attach procedure is performed to establish a connection from the beginning. In 5G-NR, in order to reduce the interruption time due to the procedure, the RETRIEVE UE CONTEXT message is used to find a base station that has an existing UE CONTEXT and request CONTEXT information. If the information is present, the re-establishment procedure is performed, and if not, the setup procedure is performed, thereby significantly reducing the interruption time.

[0060] Meanwhile, embodiments of the present disclosure can further reduce the time required to find UE CONTEXT during a connection recovery procedure of a terminal. To achieve this, the UE CONTEXT must be received in advance from a possible base station before the actual terminal attempts connection recovery, and the message may also be newly defined. Furthermore, in order to receive the UE CONTEXT in advance, it must be predicted which base station the terminal will attempt connection recovery with when it experiences an actual connection loss, and for this purpose, an AI / ML prediction result may be required. The AI / ML prediction result may include information such as the time at which the terminal experiences a connection loss, the channel condition at that time, the base station when the connection loss occurred, and the base station estimated to have the highest probability of reselection at that time. In addition, a configuration and reporting procedure may be defined that enable reporting the prediction result to the existing base station.

[0061] Although the embodiments of the present disclosure have been described with handover to aid understanding, the embodiments can be applied to other situations where RLF prediction using AI / ML is possible depending on the settings of the base station and the capabilities of the terminal in a situation where the terminal belongs to a network, and where UE CONTEXT for connection recovery is required.

[0062] FIG. 6 is a prediction result report according to embodiments of the present disclosure and a connection recovery process in a Too late handover failure case.

[0063] In step 605, the connected mode terminal may transmit a UE capability information message to the base station, indicating that the terminal is capable of AI / ML or measurement prediction. The UE capability information message may be a message transmitted by the terminal in response to a UE capability inquiry message previously received from the base station.

[0064] In step 610, the base station can transmit a configuration for reporting RLF prediction results to the terminal. This process is an example of a measurement configuration for indicating RLF prediction, and can indicate whether to include RLF prediction in the MeasID or reportConfigID. Additionally, a new MeasID can be set or the configuration can be configured for the entire RRC message. Table 5 below shows the configuration format for indicating the inclusion of RLF prediction results in the MeasID.

[0065]

[0066] The setting value for the result of RLF prediction can be directly entered as non-BOOLEAN setting information in the rlfPrediction IE within the corresponding MeasID and reportConfigID. Alternatively, if set to BOOLEAN as above, configurable IEs can be added or newly defined within the MeasConfig IE as shown in Table 6 below. In addition, the name of the IE was defined arbitrarily to aid understanding in this embodiment, but this name can be defined as a different name.

[0067]

[0068] The items that should be included in rlfPredictionConfig are as shown in Table 7.

[0069] Threshold: RLF report entering condition - Report when the RLF probability predicted by the terminal is higher than the threshold; Period: Window of time when the terminal predicts the RLF probability; Interval: Frequency at which the terminal measures RSRP(Q) / SINR and RLF probability within the set period; expectedServedCellInfo: Information about the served cell predicted by the terminal at the time when the RLF probability is higher than the threshold (PhyCellID, RSRP(Q) series); expectedBestCellInfo: Information about the cell with the strongest RSRP(Q) / SINR at the time of RLF occurrence

[0070] When transmitting expectedBestCellInfo information, if the servedCell and BestCell are the same, the terminal can include information about the Cell predicted to have the next best channel condition. If there are no other Cells, the IE may not be transmitted. In addition, the number of Cells to be included in expectedBestCellInfo can be variably selected depending on the network settings. In this embodiment, the name of the IE is arbitrarily defined to aid understanding, but this name can be defined with a different name.

[0071] In step 615, the terminal can transmit a Measurement report according to the RLF prediction-related settings received from the base station. At this time, the IE included in the Measurement report is the IE defined in rlfPredictionConfig set in step 610, and the reported value also follows the value set in rlfPredictionConfig. In this step, an example of event A3 linked to the target gNB is described to help understanding, but the measID can also be linked to the actually measured event A3, the AI / ML predicted event A3, or other events specified in [Table 1]-[Table 3].

[0072] In step 620, the source gNB that has received the RLF prediction result of the UE may transmit a PRERETRIEVE UE CONTEXT DELIVERY message to the target gNB. The source gNB may select whether to send a handover request for legacy handover, a handover request for conditional handover, a PRERETRIEVE UE CONTEXT DELIVERY, or both a handover request and PRERETRIVE UE CONTEXT DELIVERY depending on an event associated with the RLF prediction result. At this time, the PRERETRIEVE UE CONTEXT DELIVERY message may include the UE CONTEXT ID (including the PhyCellID, CellID, and C-RNTI of the source gNB), security information including integrity protection, and the PhyCellID and CellID of the target gNB. The source gNB that sent the message can trigger its own timer and retransmit the message if it does not receive a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE before the timer expires.

[0073] At step 625, the Target gNB may send a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE to the message from the Source gNB. After sending the message, the Target gNB may trigger its own timer and delete the UE CONTEXT when the timer expires.

[0074] Steps 620 and 625 specify the case where the PRERETRIEVE UE CONTEXT DELIVERY message is transmitted separately. At this time, the target gNB may process PRERETRIEVE UE CONTEXT DELIVERY as FAILURE if a handover request is transmitted for the same UE from the same source gNB and use the UE CONTEXT in the handover request. In addition, PRERETRIEVE UE CONTEXT DELIVERY may be defined as an IE in the handover request, or if an IE such as a more simplified RLF prediction result is included in the handover request, the UE CONTEXT in the corresponding message may be used. In addition, if the event transmitted in 615 is also a prediction value, the handover request may be set to CHO instead of legacy and the handover may be performed immediately.

[0075] If the UE actually experiences an RLF at step 630, the UE transmits a re-establishment request to the target gNB at step 635. If the target gNB receives the re-establishment request within the PRERETRIEVE UE CONTEXT RESPONSE timer, it completes RRC re-establishment with the UE using the corresponding UE CONTEXT. After the re-establishment procedure is completed, the target gNB instructs the source gNB to release the UE CONTEXT of the UE at step 650. The UE can transmit the RRC re-establishment request based on the cell indicated by expectedBestCellInfo included in the RLF prediction result. During the cell reselection process for performing the RRC re-establishment, the UE can select a cell by considering the criteria for selecting a cell and the cell indicated by expectedBestCellInfo. In addition, the UE can select a cell for transmitting the RRC re-establishment request to the cell indicated by expectedBestCellInfo. In Fig. 6, the Target gNB may be a base station operating a cell indicated by expectedBestCellInfo.

[0076] FIG. 7 is a prediction result report according to embodiments of the present disclosure and a connection recovery process in a WrongCell handover failure case.

[0077] Steps 705 and 710 are identical to steps 605 and 610 of FIG. 6. In step 715, unlike step 615, the expectedBestCellInfo indicated in the RLF prediction result reported by the UE is different from the target gNB1 of the predicted or measured event. That is, in this situation, the Source gNB can recognize that there is a possibility that an RLF will occur in the Target gNB1 to which the current handover request is sent, and that the UE can then attempt RRC connection reestablishment to the Target gNB2. In this embodiment, the procedure is described for one Target gNB2 to help understanding, but there may be more than one gNB to which the UE will attempt RRC connection reestablishment, and the target may be linked to the number of BestCells included in the Measurement report in the corresponding step.

[0078] In step 720, the Source gNB transmits a handover request to the Target gNB1. At this time, the Handover request includes the RLF prediction result reported by the UE and may include a notification bit indicating that there is a BestCell different from the Target gNB1 to which the current handover request is transmitted.

[0079] At step 730, Target gNB1, which has received the handover request, may transmit PRERETRIEVE UE CONTEXT DELIVERY to Target gNB2, which is indicated as the BestCell in the RLF prediction result in the handover request. To facilitate procedural understanding, step 730 is indicated as starting after step 725, but it is also possible to transmit PRERETRIEVE UE CONTEXT DELIVERY before transmitting a response to the handover request.

[0080] At step 735, Target gNB2 sends a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE and triggers its own timer. If Target gNB2 has already received a CHO request from the source gNB, it may send a FAILURE instead of a RESPONSE and specify the cause. However, if it performs this action, Target gNB2 may use the UE CONTEXT in the CHO handover request when performing connection recovery for the UE.

[0081] Steps 740 and 745 can be performed in the same manner as the existing method. After the terminal actually experiences an RLF and requests re-establishment with Target gNB2 as a result of cell reselection, if the request is received before the timer expires, connection recovery with Target gNB2 is completed.

[0082] Steps 750 to 760 may correspond to steps 635 to 645 of FIG. 6. The counterpart of the RRC Re-establishment procedure of the terminal may be Target gNB2.

[0083] In one embodiment, the terminal may transmit an RRC Re-establishment request based on the cell indicated by expectedBestCellInfo included in the RLF prediction result. During the cell reselection process for performing RRC Re-establishment, the terminal may select a cell by considering the criteria for cell selection and the cell indicated by expectedBestCellInfo. In addition, the terminal may select a cell for transmitting the RRC Re-establishment request to the cell indicated by expectedBestCellInfo. In FIG. 7, Target gNB2 may be a base station operating the cell indicated by expectedBestCellInfo.

[0084] At step 765, Target gNB2 forwards the UE CONTEXT to the Source gNB to be released.

[0085] At step 770, the Source gNB recognizes that the UE has experienced RLF immediately after the handover and has been handed over to Target gNB2, releases the UE CONTEXT of the UE it has, and instructs Target gNB1 to also release the UE CONTEXT.

[0086] Figure 8 is a flowchart illustrating a case where a terminal performs a normal handover and an RLF does not occur when both a handover request and a PRERETRIEVE UE CONTEXT DELIVERY are received. In this embodiment, for the sake of understanding, the procedure is described as transmitting PRERETRIEVE UE CONTEXT DELIVERY after receiving a handover response. However, PRERETRIEVE UE CONTEXT DELIVERY can be transmitted from the Source gNB to the Target gNB regardless of whether a handover response is received.

[0087] In operation 805, information about UE capabilities can be exchanged between the UE and the Source gNB.

[0088] In operation 810, the Source gNB may send an RRC reconfiguration message to the UE.

[0089] In operation 815, the UE can send a Measurement report to the Source gNB.

[0090] In operation 820, the Source gNB may send a Handover Request message including the RLF prediction result to the Target gNB.

[0091] In operation 825, the Target gNB may send a Handover request acknowledge (or Handover response) message to the Source gNB.

[0092] In operation 830, the Source gNB may send a PRERETRIEVE UE CONTEXT DELIVERY message to the Target gNB.

[0093] In operation 835, the Target gNB may send a PRERETRIEVE UE CONTEXT DELIVERY response message to the Source gNB.

[0094] In operation 840, the Source gNB may send an RRC reconfiguration message to the UE.

[0095] In operation 850, the UE may send an RRC reconfiguration complete message to the Target gNB.

[0096] In operation 855, the Target gNB may send a UE CONTEXT RELEASE message to the Source gNB.

[0097] For a description of each action, refer to the actions described in other drawings.

[0098] FIG. 9 is a diagram illustrating the structure of a terminal according to embodiments of the present disclosure.

[0099] Referring to FIG. 9, the terminal includes an RF (Radio Frequency) processing unit (910), a baseband processing unit (920), a storage unit (930), and a control unit (940).

[0100] The RF processing unit (910) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (910) up-converts the baseband signal provided from the baseband processing unit (920) 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 (910) 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 (910) may include multiple RF chains. Furthermore, the RF processing unit (910) may perform beamforming. For beamforming, the RF processing unit (910) can adjust the phase and amplitude of each signal transmitted and received through multiple antennas or antenna elements. In addition, the RF processing unit can perform MIMO and receive multiple layers when performing MIMO operations.

[0101] The baseband processing unit (920) 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 (920) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (920) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (910). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (920) 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 (920) divides the baseband signal provided from the RF processing unit (910) 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.

[0102] The baseband processing unit (920) and the RF processing unit (910) transmit and receive signals as described above. Accordingly, the baseband processing unit (920) and the RF processing unit (910) may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. Furthermore, at least one of the baseband processing unit (920) and the RF processing unit (910) 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 (920) and the RF processing unit (910) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. Additionally, different frequency bands may include super high frequency (SHF) (e.g., 2.NRHz, NRhz) bands, millimeter wave (mm wave) (e.g., 60GHz) bands.

[0103] The storage unit (930) stores data such as basic programs, application programs, and setting information for the operation of the terminal. The storage unit (930) provides the stored data upon request from the control unit (940).

[0104] The control unit (940) controls the overall operations of the terminal. For example, the control unit (940) transmits and receives signals through the baseband processing unit (920) and the RF processing unit (910). In addition, the control unit (940) records and reads data in the storage unit (930). For this purpose, the control unit (940) may include at least one processor. For example, the control unit (940) 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 (942) as illustrated in the drawing.

[0105] FIG. 10 is a diagram illustrating the structure of a base station according to embodiments of the present disclosure.

[0106] Referring to FIG. 10, a base station according to an example of the present disclosure is configured to include an RF processing unit (1010), a baseband processing unit (1020), a backhaul communication unit (1030), a storage unit (1040), and a control unit (1050).

[0107] The RF processing unit (1010) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1010) up-converts the baseband signal provided from the baseband processing unit (1020) 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 (1010) 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 illustrated, but the base station may have multiple antennas. In addition, the RF processing unit (1010) may include multiple RF chains. Furthermore, the RF processing unit (1010) may perform beamforming. For beamforming, the RF processing unit (1010) may adjust the phase and magnitude of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit can perform downlink MIMO operations by transmitting one or more layers.

[0108] The baseband processing unit (1020) 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 (1020) generates complex symbols by encoding and modulating the transmission bit stream. In addition, when receiving data, the baseband processing unit (1020) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (1010). For example, in the case of OFDM, when transmitting data, the baseband processing unit (1020) generates complex symbols by encoding and modulating the 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 (1020) divides the baseband signal provided from the RF processing unit (1010) 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 (1020) and the RF processing unit (1010) transmit and receive signals as described above. Accordingly, the baseband processing unit (1020) and the RF processing unit (1010) may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0109] The backhaul communication unit (1030) provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit (1030) converts a bit string transmitted from a primary base station to other nodes, such as auxiliary base stations or core networks, into a physical signal, and converts a physical signal received from other nodes into a bit string.

[0110] The storage unit (1040) stores data such as basic programs, application programs, and configuration information for the operation of the main base station. In particular, the storage unit (1040) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. Furthermore, the storage unit (1040) can store information that serves as a basis for determining whether to provide or terminate multiple connections to a terminal. Furthermore, the storage unit (1040) provides the stored data upon request from the control unit (1050).

[0111] The control unit (1050) controls the overall operations of the base station. For example, the control unit (1050) transmits and receives signals through the baseband processing unit (1020) and the RF processing unit (1010) or through the backhaul communication unit (1030). In addition, the control unit (1050) records and reads data in the storage unit (1040). For this purpose, the control unit (1050) may include at least one processor and, as illustrated in the drawing, may include a multi-connection processing unit (1052).

[0112] Meanwhile, the embodiments of the present disclosure disclosed in this specification and 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.

[0113] Furthermore, each embodiment can be combined and operated as needed. For example, parts of one embodiment of the present disclosure and parts of another embodiment can 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 can also be implemented. For example, the embodiments can 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 defined not only by the scope of the following claims but also by equivalents thereof.

Claims

1. A method performed by a first base station in a wireless communication system, A step of receiving a measurement report including a RLF (Radio Link Failure) prediction result from a terminal; and comprising the step of transmitting a first message including a terminal context to a second base station, A method wherein the RLF prediction result includes first information indicating a serving cell at the time when the RLF is predicted and second information indicating a cell whose channel condition is predicted to be good at the time when the RLF is predicted.

2. In paragraph 1, If the first message is a HANDOVER REQUEST message, further comprising a step of receiving a HANDOVER REQUEST ACKNOWLEDGE message from the second base station in response to the first message, The first information indicates a cell associated with the second base station, A method wherein the second information indicates a cell associated with a third base station.

3. In paragraph 2, If the first message is a PRERETRIEVE UE CONTEXT DELIVERY message, further comprising a step of receiving a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE message in response to the first message from the second base station, The first information indicates a cell associated with the first base station, A method wherein the second information indicates a cell associated with the second base station.

4. In paragraph 3, A method further comprising the step of receiving a message for releasing a terminal context from the second base station.

5. In a method performed by a second base station in a wireless communication system, A step of receiving a first message including a terminal context from a first base station; and A method comprising the step of transmitting a HANDOVER REQUEST ACKNOWLEDGE message to the first base station in response to the first message, when the first message is a HANDOVER REQUEST message.

6. In paragraph 5, A step of transmitting a PRERETRIEVE UE CONTEXT DELIVERY message including the terminal context to a third base station; and Further comprising the step of receiving a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE message from the third base station, The above first message includes the RLF (Radio Link Failure) prediction result, The above RLF prediction result includes first information indicating a serving cell at the time when RLF is predicted and second information indicating a cell whose channel condition is predicted to be good at the time when RLF is predicted. A method wherein the first information indicates a cell associated with the second base station, and the second information indicates a cell associated with the third base station.

7. In paragraph 5, A method comprising the step of transmitting a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE message to the first base station in response to the first message, when the first message is a PRERETRIEVE UE CONTEXT DELIVERY message.

8. In paragraph 7, A method further comprising the step of receiving an RRC (Radio Resource Control) re-establishment request message from a terminal.

9. In the first base station of the wireless communication system, Transmitter and receiver; and Includes a control unit connected to the above transmitter and receiver, The above control unit: Receive a measurement report including a RLF (Radio Link Failure) prediction result from the terminal, and is configured to transmit a first message including a terminal context to a second base station, A first base station, wherein the RLF prediction result includes first information indicating a serving cell at a time point when the RLF is predicted and second information indicating a cell whose channel condition is predicted to be good at the time point when the RLF is predicted.

10. In paragraph 9, the control unit: If the first message is a HANDOVER REQUEST message, it is set to receive a HANDOVER REQUEST ACKNOWLEDGE message from the second base station in response to the first message, The first information indicates a cell associated with the second base station, The second information indicates a cell associated with a third base station, the first base station.

11. In paragraph 10, the control unit: If the first message is a PRERETRIEVE UE CONTEXT DELIVERY message, the second base station is configured to receive a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE message in response to the first message, The first information indicates a cell associated with the first base station, The second information indicates a cell associated with the second base station, the first base station.

12. In paragraph 11, the control unit: A first base station configured to receive a message for releasing a terminal context from the second base station.

13. In the second base station of the wireless communication system, Transmitter and receiver; and Includes a control unit connected to the above transmitter and receiver, The above control unit: Receive a first message including a terminal context from a first base station, and A second base station, comprising a step of transmitting a HANDOVER REQUEST ACKNOWLEDGE message to the first base station in response to the first message, when the first message is a HANDOVER REQUEST message.

14. In paragraph 13, the control unit: Transmitting a PRERETRIEVE UE CONTEXT DELIVERY message including the terminal context to the third base station, and It is configured to receive a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE message from the third base station, The above first message includes the RLF (Radio Link Failure) prediction result, The above RLF prediction result includes first information indicating a serving cell at the time when RLF is predicted and second information indicating a cell whose channel condition is predicted to be good at the time when RLF is predicted. The first information indicates a cell associated with the second base station, The second base station, wherein the second information indicates a cell associated with the third base station.

15. In paragraph 13, the control unit: If the first message is a PRERETRIEVE UE CONTEXT DELIVERY message, transmit a PRERETRIEVE UE CONTEXT DELIVERY RESPONSE message to the first base station in response to the first message, and A second base station configured to receive an RRC (Radio Resource Control) re-establishment request message from a terminal.

Images