Method and apparatus for controlling UE context in a wireless communication system

Abstract

The present disclosure relates to a communication method and system for integrating a fifth generation (5G) communication system supporting a higher data rate than a fourth generation (4G) system with an Internet of Things (IoT) technology. The present disclosure can be applied to intelligent services based on 5G communication technology and IoT-related technologies, such as smart homes, smart buildings, smart cities, smart cars, Internet of Vehicles, healthcare, digital education, smart retail, security and safety services. A method and apparatus for controlling a user equipment (UE) context between multiple nodes are provided. The method includes sending a first message requesting a user equipment (UE) context update to a second node, receiving a second message indicating completion of the UE context update or a third message indicating failure of the UE context update from the second node in response to the sending of the first message, and determining whether to resend the first message to the second node based on the reception of the second message or the third message. The process of UE context update can be initiated by sending a message from the second node to the third node requesting an operation of UE context update performed between the UE and the third node.

Description

Technical Field

[0001] The present disclosure relates to methods and apparatus for controlling User Equipment (UE) context among multiple nodes. Background Art

[0002] In order to meet the increasing demand for wireless data traffic after the commercialization of the fourth generation (4G) communication system, an enhanced fifth generation (5G) communication system or a pre-5G communication system is being developed. For this reason, the 5G communication system or the pre-5G communication system is called a super 4G network communication system or a post-long term evolution (LTE) system. In order to achieve a high data transfer rate, the 5G communication system is considered to be implemented in the millimeter wave frequency band (e.g., the 60 GHz band). In order to reduce the loss of radio waves and increase the transfer distance of radio waves in the millimeter wave frequency band, beamforming, massive MIMO, full-dimensional MIMO (FD-MIMO), array antenna, analog beam-forming, and large-scale antenna technologies are being discussed in the 5G communication system. In addition, in order to improve the network of the system, technologies such as improved small cell, advanced small cell, cloud RAN, ultra-dense network, device-to-device communication (D2D), wireless backhaul, moving network, cooperative communication, coordinated multipoint (CoMP), and reception interference cancellation are being developed in the 5G communication system. In addition, hybrid frequency shift key and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC) belonging to the advanced coding modulation (ACM) scheme, improved filter bank multi-carrier (improved FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) are being developed in the 5G system.

[0003] The Internet has evolved from a human-centered connected network on which humans generate and consume information to the Internet of Things (IoT) where information is exchanged and processed between distributed elements such as things. Internet of Everything (IoE) technology, which is a big data processing technology combined with IoT technology through connection with a cloud server, is emerging. In order to implement IoT, technical elements such as sensing technology, wired / wireless communication and network infrastructure, service interface technology, and security technology are required. Therefore, technologies for connection between things, such as sensor networks, machine-to-machine (M2M), and machine type communication (MTC), are being studied recently.

[0004] In addition, in the IoT environment, intelligent Internet technology (IT) services can be provided to create new value for human life by collecting and analyzing data generated by connected objects. IoT can be applied to fields such as smart homes, smart buildings, smart cities, smart cars or vehicle networks, smart grids, healthcare, smart appliances, and advanced medical services through the integration and combination of existing information technology (IT) and various industries.

[0005] In 5G technology, a non-standalone (NSA) new radio (NR) standard in which LTE technology and new radio (NR) technology operate together has been introduced, and an evolved universal terrestrial radio access (EUTRA) NR dual connection (EN-DC) structure between an LTE base station and an NR base station is supported. In such a multi-radio access technology (RAT) dual connection type connection structure, a device such as a terminal uses an LTE base station as a master node and uses an NR base station as a secondary node to perform radio access.

[0006] In addition, as the amount of data requested for processing during wireless communication has exploded, the technology of separating the existing protocol layers within the base station and implementing them as a central unit (CU) and a distributed unit (DU) has been introduced into 5G. The layers included in a single base station for configuring the protocol stack are separated into a CU base station and a DU base station, and a fronthaul interface is configured between the CU base station and the DU base station, so that signaling can be sent and received.

[0007] The above information is presented merely as background information to assist in understanding the present disclosure, and no determination is made as to whether any of the above may be applicable as prior art with respect to the present disclosure. Summary of the invention

[0008] Technical issues

[0009] If the UE needs a change or update of the UE context in a state where the UE has accessed an LTE base station and an NR base station in an EN-DC connection structure, it is necessary to efficiently perform signaling operations between several nodes such as a CU base station and a DU base station separated from the NR base station and the LTE base station.

[0010] Technical Solution

[0011] According to one aspect of the present disclosure, a method of a first node in a wireless communication system is provided. The method includes sending a first message requesting a user equipment (UE) context update to a second node, receiving a second message indicating completion of the UE context update or a third message indicating failure of the UE context update from the second node in response to the sending of the first message, and determining whether to retransmit the first message to the second node based on the reception of the second message or the third message. The process of UE context update can be initiated by sending a message from the second node to the third node requesting an operation of UE context update performed between the UE and the third node.

[0012] According to another aspect of the present disclosure, a method of a second node in a wireless communication system is provided. The method includes receiving a first message requesting a user equipment (UE) context update from a first node, sending a message requesting an operation of UE context update performed between the third node and the UE to a third node in response to receiving the first message, confirming a result of the UE context update initiated based on the message sent to the third node, and sending a second message indicating completion of the UE context update or a third message indicating failure of the UE context update to the first node based on the confirmed result.

[0013] According to another aspect of the present disclosure, a first node in a wireless communication system is provided. The first node includes a transceiver and at least one processor, the processor being configured to control the transceiver to send a first message requesting a user equipment (UE) context update to a second node, and in response to the sending of the first message, receive a second message indicating completion of the UE context update or a third message indicating failure of the UE context update from the second node, and determine whether to resend the first message to the second node based on the reception of the second message or the third message. The process of UE context update can be initiated by sending a message from the second node to the third node requesting an operation of UE context update performed between the UE and the third node.

[0014] According to another aspect of the present disclosure, a second node in a wireless communication system is provided. The second node includes a transceiver and at least one processor, the processor being configured to control the transceiver to receive a first message requesting a user equipment (UE) context update from a first node, and in response to receiving the first message, to send a message requesting an operation of UE context update performed between the third node and the UE to a third node, confirm a result of the UE context update initiated based on the message sent to the third node, and send a second message indicating completion of the UE context update or a third message indicating failure of the UE context update to the first node based on the confirmed result.

[0015] Other aspects, advantages, and salient features of the present disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the accompanying drawings, discloses various embodiments of the present disclosure.

[0016] Advantageous Effects of the Invention

[0017] Aspects of the present disclosure will at least solve the above problems and / or disadvantages and provide at least the following advantages. Therefore, one aspect of the present disclosure is to provide a method for efficiently performing a user equipment (UE) context update process between several nodes in a non-standalone (NSA) architecture.

[0018] Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the presented embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following description in conjunction with the accompanying drawings, in which:

[0020] Figure 1 is a conceptual diagram illustrating a multi-radio access technology (RAT) dual connectivity structure according to an embodiment of the present disclosure;

[0021] Figure 2 is a conceptual diagram illustrating a connection between a node and a user equipment (UE) according to an embodiment of the present disclosure;

[0022] Figure 3 is a conceptual diagram illustrating a protocol stack configured in a node and a UE according to an embodiment of the present disclosure;

[0023] Figure 4 is a flow chart illustrating signaling for controlling the context of a UE between nodes according to an embodiment of the present disclosure;

[0024] Figure 5 is a diagram illustrating a situation where a UE context update process fails in each node according to an embodiment of the present disclosure;

[0025] Figure 6a is a flow chart for describing signaling when a distributed unit (DU) continuously triggers an update of a UE context according to an embodiment of the present disclosure;

[0026] Figure 6b is a flow chart for describing signaling when a DU continuously triggers an update of a UE context according to an embodiment of the present disclosure;

[0027] Figure 7 is a flow chart illustrating the operation of a DU for controlling a UE context according to an embodiment of the present disclosure;

[0028] Figure 8 is a flow chart illustrating the operation of a central unit (CU) for controlling UE context according to an embodiment of the present disclosure;

[0029] Fig. 9 is a flowchart for describing an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU in various situations in which an update process of a UE context fails according to an embodiment of the present disclosure;

[0030] Fig.10 is a flowchart for describing an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU in various situations in which an update process of a UE context fails according to an embodiment of the present disclosure;

[0031] Fig.11 is a flowchart for describing an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU in various situations in which an update process of a UE context fails according to an embodiment of the present disclosure;

[0032] Fig.12 is a flowchart for describing an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU in various situations in which an update process of a UE context fails according to an embodiment of the present disclosure;

[0033] Fig.13 is a flowchart for describing an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU in various situations in which an update process of a UE context fails according to an embodiment of the present disclosure;

[0034] Fig.14 is a diagram illustrating an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU under a given condition according to an embodiment of the present disclosure;

[0035] Fig.15is a diagram illustrating an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU in a handover situation according to an embodiment of the present disclosure;

[0036] Fig.16 is a diagram illustrating an example in which a base station in which a CU and a DU have been separated performs an update of a UE context according to an embodiment of the present disclosure;

[0037] Fig.17 is a diagram illustrating a configuration of a base station according to an embodiment of the present disclosure;

[0038] Fig.18 is a diagram illustrating a configuration of a UE according to an embodiment of the present disclosure;

[0039] Fig.19 is a diagram for describing an embodiment of not using a UE context modification reject message according to an embodiment of the present disclosure;

[0040] Fig. 20 is a flowchart for describing a method for notifying a UE of a failure of a context procedure using an F1 UE context modification confirmation message according to an embodiment of the present disclosure;

[0041] Fig.21 is a diagram for describing a method for notifying a UE of a failure in a context update process and indicating that an RRC container IE is not included in an F1UE context confirmation modification message according to an embodiment of the present disclosure;

[0042] Fig. 22 is a diagram for describing an embodiment for changing after requesting confirmation of UE context modification according to an embodiment of the present disclosure; and

[0043] Fig.23 is a diagram for describing an embodiment for changes after requesting confirmation for UE context modification according to an embodiment of the present disclosure.

[0044] Throughout the drawings, like reference numerals will be understood to refer to like parts, components, and structures. DETAILED DESCRIPTION

[0045] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of the various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in understanding, but these are to be regarded as exemplary only. Therefore, it will be appreciated by those of ordinary skill in the art that various changes and modifications may be made to the various embodiments described herein without departing from the scope and spirit of the present disclosure. In addition, descriptions of known functions and structures may be omitted for clarity and brevity.

[0046] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Therefore, it is apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustrative purposes only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

[0047] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0048] When describing the present disclosure, if it is considered that a detailed description of a related known function or configuration makes the subject of the present disclosure unnecessarily ambiguous, it will be omitted. In addition, the terms to be described below have been defined in consideration of the functions in the present disclosure and may be different depending on the intention or practice of the user or operator. Therefore, each term should be defined based on the content of the entire specification.

[0049] In addition, while the embodiments of the present disclosure are described in detail, the main subject matter of the present invention may be slightly modified and applied to other communication systems with similar technical backgrounds and channel forms without significantly departing from the scope of the present disclosure, which can be determined by a person having skilled technical knowledge in the corresponding technical field of the present disclosure.

[0050] According to the embodiments described in detail in conjunction with the drawings, the advantages and characteristics of the present disclosure and the methods for achieving these advantages and characteristics will become more apparent. However, the present disclosure is not limited to the disclosed embodiments, but can be implemented in various different ways. The embodiments are provided only to complete the present disclosure and allow those skilled in the art to fully understand the scope of the present disclosure. The present disclosure is limited by the scope of the claims. The same reference numerals will be used to refer to the same or similar elements throughout the drawings.

[0051] In the present disclosure, it is understood that each block in the flowchart and the combination of blocks in the flowchart can be performed by computer program instructions. These computer program instructions can be installed on a processor of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the instructions executed by the processor of the computer or other programmable data processing device create a method for performing the functions specified in the flowchart block.

[0052] These computer program instructions may also be stored in a computer-usable or computer-readable memory that is capable of directing a computer or other programmable data processing device to implement functions in a specific manner, so that the instructions stored in the computer-usable or computer-readable memory generate an article of manufacture including instruction means for implementing the functions specified in the flowchart block.

[0053] The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus so that a series of operations are executed on the computer or other programmable apparatus to generate a computer-implemented process, so that the instructions executed by the computer or other programmable apparatus provide operations for performing the functions described in the flowchart blocks.

[0054] In addition, each block of the flow chart may represent a module, segment or part of the code, which includes one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks may appear out of order. For example, depending on the functions involved, two blocks shown in succession may actually be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order.

[0055] The term "unit" used in this embodiment refers to a software or hardware component, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), and the "unit" performs a specific task. The "unit" can be advantageously configured to reside on an addressable storage medium and configured to operate on one or more processors.

[0056] Thus, a "unit" may include, for example, components, such as software components, object-oriented software components, class components and task components, processes, functions, properties, procedures, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays and variables. The functions provided in components and "units" may be combined into fewer components and "units", or may be further separated into additional components and "units". In addition, components and "units" may be implemented to operate on one or more central processing units (CPUs) within a device or a security multimedia card.

[0057] Hereinafter, a method for efficiently performing signaling between nodes for control of a user equipment (UE) context in a DC structure between multiple radio access technologies (RATs) according to an embodiment of the present disclosure will be described in more detail with reference to the accompanying drawings.

[0058] Figure 1is a conceptual diagram illustrating a multi-RAT dual connectivity structure according to an embodiment of the present disclosure.

[0059] Reference Figure 1 , the structure for EN-DC used to describe the embodiment of the present disclosure may be configured as follows Figure 1 shown.

[0060] More specifically, the connection structure for EN-DC according to an embodiment of the present disclosure may be a structure in which a long term evolution (LTE) base station 11 (i.e., a main eNB) anchors the control plane (C-plane) signaling of the NR, the NR base station 12 is configured as a secondary eNB, and each base station uses an evolved packet core (EPC) 1 as a core network.

[0061] According to an embodiment of the present disclosure, the UE 100 can use the LTE base station 11 as a master eNB and the NR base station 12 as a secondary eNB to access each base station through dual connectivity.

[0062] Figure 2 is a conceptual diagram illustrating a connection between a node and a UE according to an embodiment of the present disclosure.

[0063] Figure 3 is a conceptual diagram illustrating a protocol stack configured in a node and a UE according to an embodiment of the present disclosure.

[0064] Reference Figure 2 , the NR base station according to an embodiment of the present disclosure can be configured by separating the protocol stack included in one base station for each function and separating the protocol stack into a central unit (CU) and a distributed unit (DU). In this case, the CU and DU can be implemented as separate base stations, and the respective operations of the base station can be performed. In the following embodiments, the CU and DU may be described as base stations, units, or nodes.

[0065] Figure 2 The diagram illustrates a state in which a UE 200 according to an embodiment of the present disclosure has accessed an LTE base station (RAT#1) 21 and an NR base station 22 separated into a CU base station (RAT#2-CU) 22b and a DU base station (RAT#2-DU) 22a.

[0066] Reference Figure 2 , the CU 22b of the LTE base station 21 and the NR base station 22 can be connected through the X2 interface (RAT#1-RAT#2-I / F). The CU 22b of the NR base station 22 and the DU 22a of the NR base station 22 can be connected through the fronthaul interface (RAT#2-CU-DU-I / F). In the following, for the convenience of description, the CU base station is described as CU and the DU base station is described as DU.

[0067] A more detailed protocol stack is available in Figure 3 is shown in .

[0068] Reference Figure 3 In the LTE base station 31, all functions of the radio resource control (RRC) layer, the packet data convergence protocol (PDCP) layer, the radio link control (RLC) layer, the medium access control (MAC) layer, the physical (PHY) layer and the radio frequency (RF) layer can be implemented and can operate.

[0069] In contrast, in the NR base station 32, the protocol layers may be separated based on their respective functions. The RRC layer and the PDCP layer may be configured as a CU 32b, and the RLC layer, the MAC layer, the PHY layer, and the RF function may be configured as a DU 32a. That is, the CU 32b may perform functions corresponding to the RRC layer and the PDCP layer, and the DU 32a may perform functions of the RLC layer, the MAC layer, the PHY layer, and the RF.

[0070] According to an embodiment of the present disclosure, all protocol stacks of UE300 configured for dual connectivity with LTE base station 31 and NR base station 32 may be included and implemented like LTE base station 31.

[0071] The functions of each layer are briefly described as follows. The PDCP layer is responsible for operations such as IP header compression / reconstruction. The RLC layer reconfigures the PDCP packet data unit (PDU) with an appropriate size. The MAC layer is connected to several RLC layers and performs operations of multiplexing RLC PDUs into MAC PDUs and demultiplexing MAC PDUs into RLC PDUs. The PHY layer performs operations of performing channel coding and modulation on higher layer data, generating data into OFDM symbols, transmitting OFDM symbols to a radio channel or demodulating OFDM symbols received through a radio channel, channel decoding the symbols, and transmitting them to a higher layer. In addition, the PHY layer uses hybrid automatic repeat query (HARQ) together with the MAC layer for error correction. The receiving stage sends 1 bit indicating whether the data packet sent by the transmitting stage has been received. This is called HARQ ACK / NACK information. The RRC layer is defined only in the control plane. The RRC layer is responsible for controlling other channels related to configuration, reconfiguration and release of radio bearers.

[0072] If the protocol layer is separated for each function in the NR base station 32 and implemented as DU 32a and CU 32b as described above, the number of nodes that perform signaling according to wireless communication with the UE 300 in connection with the UE 300 through EN-DC may be 3 or more. This may mean that a given operation related to the UE is triggered or three or more nodes may be involved in controlling a given operation for the UE.

[0073] For example, measurement values, scheduling information, antenna information, or beam characteristic information for each cell are parameters related to the RF or MAC layer or the PHY layer, and may need to be controlled for each UE. If a change in these parameters is necessary, the RF or MAC layer or the PHY layer may perform a report related to the parameter change to the RRC layer so as to generate an RRC message including the parameter in the RRC layer. In this case, in the case where the NR base station is divided into CU and DU as proposed in the present disclosure, the DU needs to send a message to the CU requesting a parameter change.

[0074] If the signaling for parameter change is transmitted from the DU to the CU as described above, the CU may transmit a message requesting the parameter change to the LTE base station. The LTE base station may perform an operation for parameter change through wireless communication with the UE.

[0075] If the update of the UE context related to the parameters as described above is necessary, it is necessary to send and receive corresponding signaling between the LTE base station and the three nodes of the CU and DU. That is, the communication process for controlling the UE context is performed between several nodes. Therefore, there may be a problem of resource waste or inefficient management of the communication process.

[0076] In the following, for the convenience of description, the DU and the first node of the NR base station, the CU and the second node of the NR base station, and the LTE base station and the third node can be used interchangeably.

[0077] refer to Figure 4 , Figure 5 , Figure 6a and Figure 6b , more detailed examples are described.

[0078] Figure 4 is a flow chart illustrating signaling for controlling the context of a UE between nodes according to an embodiment of the present disclosure.

[0079] Figure 5 is a diagram illustrating a situation where a UE context update process fails in each node according to an embodiment of the present disclosure.

[0080] Figure 6a and Figure 6b is a flow chart for describing signaling when a DU continuously triggers an update of a UE context according to various embodiments of the present disclosure.

[0081] Reference Figure 4 If it is determined that an update of the UE context is necessary, the first node (gNB-DU) 42a may send a message (S401) requesting modification of the UE context (UE context modification required) to the second node (gNB-CU) 42b.

[0082] In this case, the UE context modification required message requesting modification of the UE context may include, for example, the following information.

[0083] [Form 1]

[0084]

[0085] The second node 42b having received the message requesting modification of the UE context from the first node 42a may send a corresponding confirmation message (F1 UE context modification confirmation) to the first node 42a (S402). In addition, in response to the request for modification of the UE context received from the first node 42a, the second node 42b may send a message requesting an update of the UE context to the third node (MeNB) 41 through the X2 interface (X2 SGNB modification required) (S403).

[0086] The third node 41 may perform a context update procedure for the UE 400 based on the UE context request message (X2SGNB modification required) received from the second node 42b. Figure 4 As shown, the third node 41 may send an RRC message (RRC ConnReconfiguration) for updating the UE context to the UE 400 (S404).

[0087] UE 400 may perform an operation of updating the context of UE 400 based on information included in a radio resource control (RRC) message received from third node 41. When the context update is completed, UE 400 may transmit an RRC message (RRC ConnReconfiguration) containing corresponding information to third node 41 (S405).

[0088] The third node 41 having received the RRC connection reconfiguration complete (RRC ConnReconfiguration Complete) message from the UE 400 may transmit information included in the RRC connection reconfiguration complete (RRCConnReconfiguration Complete) message received from the UE to the second node 42b through the X2 interface (S406).

[0089] The second node 42b, which has received the message including the information on the update of the UE context (X2 SGNB Modify Confirm) from the third node 41, may perform a process of changing the context of the UE based on the information (S407).

[0090] In performing such a process, although the update of the UE context has been triggered by the first node 42a, the result indicating whether the process of the UE context has been correctly executed is not sent to the first node 42a. In other words, when the UE context modification required message received from the first node 42a is received, regardless of whether the context update process of the UE 400 has been completed or has been correctly executed, the second node 42b performs an operation of sending a UE context modification confirmation message to the first node 42a to notify the UE that the context modification required message has been successfully received.

[0091] For example, the UE context modification confirmation message may be sent from the second node 42b to the first node 42a in the sense of informing that it has been received (ACK), which is to inform that the message received from the first node 42a has only been successfully received before the start of the context update process for the UE 400 while the context update process of the UE 400 is being performed or after the context update process of the UE 400 is completed. That is, the UE context modification confirmation message may be sent by Figure 4 Any one of the arrows indicated by the dotted line (S402-①, ② and ③) is sent.

[0092] As described above, because the UE context modification confirmation message is sent from the second node 42b to the first node 42a regardless of whether the substantial update of the UE context has been completed, the first node 42a cannot confirm whether the UE context has been successfully updated. In particular, the update process of the UE context is performed by signaling between multiple nodes as described above. Therefore, if an abnormal condition such as a failure in any node or for the transmission and reception of any signaling occurs, a problem will occur.

[0093] Reference Figure 5, the first node 52a may send a message for updating the UE context (UE context needs to be modified) to the second node 52b (S501). In response to this, the second node 52b may send a confirmation message for updating the UE context (UE context modification confirmation) to the first node 52a (S502).

[0094] Reference Figure 5 In the operation of starting the update process of the UE context based on the message received from the first node 52a, an error may occur in the second node 52b (S510). Therefore, an abnormal situation may occur that the update process of the UE context is not started.

[0095] On the contrary, the second node 52b may initiate the update process of the UE context based on the message received from the first node 52a, and may send a message (X2 SGNB needs to be modified) requesting the update of the UE context to the third node 51 (S503). In this case, an abnormal situation may occur, in which the RRC message requesting the context update is not sent to the UE 500 due to a given error occurring in the third node 51 (S520) and the update process of the UE context ends with failure in the update process.

[0096] For another example, the third node 51 may send an RRC message for performing a context update procedure to the UE 500 based on the update request message (X2 SGNB modification required) for the UE context received from the second node 52b (S504). In this case, the reception and processing of the RRC message in the UE 500 may fail or an abnormal condition may occur, wherein the execution of the UE context update procedure ends in failure due to an error caused by wireless communication (S530).

[0097] For another example, the UE 500 may normally perform a context update operation based on the RRC message received from the third node 51, and may send a corresponding completion message (RRC ConnReconfiguration Complete) to the third node 51 (S505). In this case, an error of failure to receive the RRC connection reconfiguration complete message may occur in the third node 51 (S540). Therefore, an abnormal situation in which the execution of the UE context update process ends in failure may occur.

[0098] For another example, after the third node 51 receives a message (RRC ConnReconfiguration Complete) from the UE 500 notifying that the update process of the UE context has been completed, it sends a message (X2 SGNB Modification Confirm) notifying the completion of the update of the UE context to the second node 52b through the X2 interface (S506). However, an abnormal situation may occur in the second node 52b that the update process of the UE context ends in failure due to a given error (S550).

[0099] If, as described above, the NR base station is separated into a CU node and a DU node when the UE has accessed the LTE base station and the NR base station through an EN-DC connection, problems may arise in the execution of a given operation once three or more nodes involved in performing a given operation related to the UE result in a resource allocation failure, a sending or receiving error, or an error in receiving information processing.

[0100] As described above, if the processing in any node fails or the sending or receiving of any signaling between the two nodes fails, the update process of the UE context may not be performed. If the request for updating the UE context triggered by the first node is not correctly executed, the first node must trigger the request again. However, in this case, the first node will not receive any information from the second node indicating that the update of the UE context has failed. Therefore, there is a problem that the first node cannot perform any operation related to the first node having to send the corresponding re-request message again because the modification of the requested UE context has failed, or how many re-request messages the first node must repeat.

[0101] In the first node, the request for updating of the UE context may be triggered multiple times. For example, the first node may trigger the sending of a first context request message because a change in a parameter related to the beam characteristic information received from the UE is necessary, and may then trigger the sending of a second context request message because a change in a measurement parameter for handover of the UE is necessary. If update requests for different parameter information are continuously triggered as described above, problems may occur because the corresponding signaling is sent between several nodes.

[0102] Reference Figure 6a When the first node 62a determines that the update of the UE context is necessary, it may send a message (UE context modification required-first need) requesting the update of the UE context to the second node 62b (S601). The second node 62b may send a confirmation message (UE context modification confirmation) to the first node 62a in response to the UE context modification required message received from the first node 62a (S602), and may then start the context update process for the UE 600.

[0103] After the first node 62a sends a UE context update request message to the second node 62b (S601), when it is determined that a parameter change different from the context for which update has been requested is necessary, the first node 62a may send a message (UE context modification required-second required) to the second node 62b requesting to change another parameter (S603). After the second node 62b sends a confirmation message (UE context modification confirmation) in response to the second context update request (S604), it may start a context update procedure for UE600.

[0104] When the context update procedure for UE 600 is initiated, the second node 62b may send a message (X2 SGNB modification required) requesting the update of the UE context to the third node 61 (S605). In response thereto, the third node 61 may send an RRC message (RRC reconfiguration) for context update to UE 600 (S606). If the operation for context update is performed in UE 600 and the update is completed, UE 600 sends an RRC message (RRC reconfiguration complete) including corresponding information to the third node 61 (S607). The third node 61 having received the RRC message may send a message (X2 SGNB modification confirmation) to the second node 62b in order to notify the completion of the update of the UE context (S608).

[0105] The second node 62b having received information indicating that the update of the UE context has been completed from the third node 61 may send a message (UE context modification request) including an indicator (completion indicator) indicating that the update has been completed to the first node 62a based on the information to request the update of the UE context (S609).

[0106] In this case, the completion indicator is an indicator notifying that parameter information related to the context of the UE has been updated, and does not include information about which parameter the updated context of the UE is related to. In addition, the content related to the update of the context of the UE is included in the RRC container and is sent from the second node to the first node through the UE context modification request message, but the second node cannot confirm whether the update of the UE context has been completed because it only performs a function of sending the information included in the RRC container to the UE without analyzing the information.

[0107] Therefore, the problem occurs when the first node receives such a completion indicator after making two context update requests, and the first node does not know which parameter information in the two context requests the update completion indicated by the completion indicator is for. That is, the first node that has received the completion indicator does not know whether the update of the context requested in one of the first context update request and the second context update request has been completed. Therefore, there is a problem that the first node cannot determine whether to send a message requesting the first context update again or to send a message requesting the second context update again.

[0108] Reference Figure 6b , when it is determined that the update of the UE context is necessary, the first node 62a may send a message requesting the update of the context (UE context modification required-first need) to the second node 62b (S611). In response to this, the second node 62b may send a confirmation message (UE context modification confirmation) to the first node 62a (S612). In addition, when it is determined that the update of parameter information different from the parameter information according to the request (S611) is necessary, the first node 62a may additionally send a UE context update request message (UE context modification required-second need) to the second node 62b (S613). In response to this, the second node 62b may send a confirmation message (UE context modification confirmation) to the first node 62a (S614).

[0109] The second node 62b, which has received the request for updating the UE context from the first node 62a, may send a message requesting updating of the UE context to the third node 61. In this case, Figure 6b As shown, the update request message (X2 SGNB modification required) for UE context sent from the second node 62b to the third node 61 may be sent to the third node 61 for each request triggered by the first node 62a (S615, S616).

[0110] The third node 61 may send an RRC message (RRC reconfiguration) to the UE 600 according to the request for updating the UE context received from the second node 62b. Similarly, each RRC message may be sent in response to each UE context update request message (X2 SGNB modification required) received from the second node 62b (S617, S618). The UE 600 may perform an update operation of the UE context based on the RRC message received from the third node 61, and may send a corresponding completion message (RRC reconfiguration complete) to the third node 61 (S619, S620).

[0111] The third node 61 may send a message (X2 SGNB Update Confirm) notifying completion of context update to the second node 62b (S621, S622) in response to each RRC reconfiguration complete message received from the UE 600. In response to reception of the message, the second node 62b may send a message (UE Context Modification Request) including an indicator (Completion Indicator) of completion of the update of the UE context to the first node 62a (S623, S625).

[0112] Although the UE context update request first triggered by the first node 62a and the UE context update request second triggered by the first node 62a are executed sequentially, the update process according to the first triggering UE context update request may be later than the update process according to the second triggering UE context update request.

[0113] If the Figure 6b In this situation, although the first node 62a receives the first message (S623) from the second node 62b notifying that the update of the UE context has been completed, since the completion indicator included in the message does not notify which parameter information the update is for, the first node cannot know whether the corresponding message is related to the first request or the second request.

[0114] Therefore, if Figure 6b As shown in , the first node 62a cannot know which UE context has been updated even after it has sent a response message (UE context modification response) to the message (UE context modification request) received from the second node 62b to the second node 62b (S624). Figure 6b As shown, although a message (UE context modification request) notifying completion of the update of the UE context is received from the second node (S625), the first node cannot know whether such a message is related to the first request or the second request.

[0115] That is, after the first node 62a sends messages requesting an update of the UE context several times, although information indicating that the context update has been completed is received from the second node 62b in response to the message, the problem is that the first node cannot know which of the several request messages corresponds to the context that has been updated.

[0116] In particular, as mentioned above Figure 5 As described, if the update process of the UE context related to any one of the multiple nodes fails, it is unknown which of the multiple requests has failed and which context of the request has been updated. Therefore, there is a problem that the subsequent operation of the first node (for example, the operation of whether to send a message requesting the failed update of the context again) cannot be clarified.

[0117] Therefore, the present disclosure proposes an embodiment for effectively performing signaling for controlling the UE context in a state where an NR base station and an LTE base station configured with a CU and a DU have been connected to the UE through an EN-DC structure.

[0118] More specifically, an embodiment of the present disclosure proposes a method of sending corresponding information to a DU when the update process of the UE context is not performed normally.

[0119] Furthermore, an embodiment of the present disclosure proposes a method for the DU to confirm information on which context update has been completed, in a case where the update of the UE context has been completed based on a request for the update of the UE context.

[0120] In the first embodiment of the present invention, a UE context modification reject message transmitted through an interface between a DU and a CU is defined so that the DU is notified of information on failure of updating of the UE context.

[0121] In this case, the UE context modification rejection message is a message sent through the interface between the CU and the DU, and the purpose is to notify the DU that an abnormal condition may occur when the update process of the UE context is started after the CU receives the request message for the UE context from the DU. That is, the UE context modification rejection message according to the embodiment of the present disclosure is sent after determining that the update process of the UE context is due to the abnormal condition of the UE context. Figure 5 In the case where a given reason of the various examples described in has failed, it may be a message notifying that the execution of the DU context update procedure has failed.

[0122] Such a UE context modification reject message may already include various types of information. For example, the UE context modification reject message may include information about the UE that has failed in the context update (e.g., the ID of the UE, i.e., the ID of the UE for the CU and the ID of the UE for the DU) and information about the RRC container to be sent to the UE. In addition, the UE context modification reject message may also include information about the time (waiting time) during which the DU that has received the UE context modification reject message can request again the update of the UE context that has failed to update, and count information such as how many requests for the same context may be (retry count). In addition, the UE context modification reject message may include information about the cause of failure of the update of the UE context (information about the reason for rejecting the need for UE context modification).

[0123] More specifically, the information that may be included in the UE context modification reject message according to an embodiment of the present disclosure may be summarized as in the following table.

[0124] [Form 2]

[0125]

[0126]

[0127] Figure 7 is a flowchart illustrating the operation of a DU for controlling a UE context according to an embodiment of the present disclosure.

[0128] Figure 8 is a flowchart illustrating the operation of a CU for controlling a UE context according to an embodiment of the present disclosure.

[0129] Reference Figure 7 , the first node (DU) according to an embodiment of the present disclosure may detect the need for updating certain parameters according to the communication while performing wireless communication with the UE. For example, the first node according to an embodiment of the present disclosure may determine that a parameter change related to a measurement value of a cell configured in the UE is necessary, or may determine that a parameter change related to beam characteristic information for each cell is necessary, based on the result of wireless communication with the UE.

[0130] As described above, the first node may report to the second node (CU) including the RRC layer at least one parameter that has been determined to be changed as necessary. That is, the first node may send a first message to request an update of the UE context related to the parameter that has been determined to be changed as necessary (S710).

[0131] In this case, the first message may be a UE context modification required message sent via a fronthaul interface connected between the first node and the second node. The corresponding message may include several pieces of information in Table 1.

[0132] After sending the first message as described above, the first node according to an embodiment of the present disclosure may confirm which message is received from the second node in response to the sending of the first message (S720).

[0133] For example, the first node may receive a second message indicating completion of updating of the UE context from the second node in response to sending the first message. In this case, the second message indicating completion of updating of the UE context may be, for example, a UE context modification request message sent via a fronthaul interface.

[0134] The second message according to an embodiment of the present disclosure may include an indication as described above regarding Figure 6a and Figure 6b The information described for completion of the update of the requested UE context (e.g., completion indicator). That is, the second message according to an embodiment of the present disclosure may include information about the UE or information such as which UE context has been updated when multiple UE context update requests for multiple UEs have been made.

[0135] When the second message as described above is received, the first node according to an embodiment of the present disclosure may perform wireless communication with the UE based on the UE context for which the update has been completed ( S730 ).

[0136] In addition, for example, the first node may receive a third message indicating that the update of the UE context failed from the second node in response to sending the first message. In this case, the third message indicating the failure of the update of the UE context may be, for example, a UE context modification rejection message sent via a fronthaul interface.

[0137] The third message according to an embodiment of the present disclosure may include information about the reasons for and at which node the corresponding process fails during the process of updating the UE context performed between the UE, the second node, and the third node. For example, the third message may include information such as that the third node has failed in the corresponding process after the UE context update request message for initiating the UE context update process is sent from the second node to the third node, or information such as that the UE that has received an indication of the UE context update process from the third node has failed in the corresponding process when performing the update of the corresponding context.

[0138] In addition, the third message according to an embodiment of the present disclosure may include several pieces of information in Table 2 as described above. That is, the third message may include the ID of the UE for the first node and the second node, or information such as when and how many times the first message for requesting an update of the corresponding UE context may be sent.

[0139] When the third message is received, the first node according to an embodiment of the present disclosure may again send the first message for requesting update of the UE context to the second node based on information included in the third message ( S740 ).

[0140] Reference Figure 8 According to an embodiment of the present disclosure, the second node (CU) may receive a first message requesting an update of a UE context from the first node (DU) (S810).

[0141] When the first message is received, the second node according to an embodiment of the present disclosure may initiate an update process of the UE context. For example, the second node according to an embodiment of the present disclosure may send a message to the third node requesting execution of an update operation of the UE context between the third node and the UE (S820).

[0142] When a message is sent from the second node to the third node as described above, the third node may perform an update operation of the UE context between the third node and the UE. For example, the third node may use an RRC message to indicate an update operation of the UE context for the UE. The UE may perform an update operation of the UE context based on the indication. In addition, in response, the UE may send an RRC message including corresponding result information to the third node.

[0143] The third node may send result information of the update operation of the UE context between the third node and the UE to the second node. For example, if the update operation of the UE context fails in the third node or the UE due to a given reason, the third node may send a message (rejection message) including corresponding information to the second node through the X2 interface. In addition, when the update operation of the UE context is successfully completed, the third node may send a message (confirmation message) including corresponding information to the second node through the X2 interface.

[0144] After initiating the update procedure of the UE context, the second node according to an embodiment of the present disclosure may confirm a result of the update procedure of the UE context based on a message received from the third node (S830).

[0145] For example, when the completion of the update of the UE context is confirmed based on the confirmation message received from the third node, the second node may send a second message (S840) requesting the update of the corresponding UE context to the first node. In this case, the second message may be a UE context modification request message sent through the fronthaul interface between the first node and the second node.

[0146] For another example, when the failure of the update of the UE context is confirmed based on the rejection message received from the third node, the second node may send a third message (S850) notifying the failure of the update of the corresponding UE context to the first node. In this case, the third message may be a UE context modification rejection message sent through the fronthaul interface, including information received by the third node or corresponding information when the update of the corresponding UE context fails in the second node due to a given reason.

[0147] As described above, after the update of the UE context is requested, the DU according to an embodiment of the present disclosure can quickly determine whether to request to start the update process of the corresponding UE context again based on the information included in the message received from the CU, or can quickly determine whether the DU must perform wireless communication with the UE based on the updated context. In particular, if the update of the UE context has been successfully completed, the CU according to an embodiment of the present disclosure sends information such as which UE context update has been completed, and if the update of the UE context has failed, the cause of the failure and information related to the operation for recovering the failure are provided to the DU. Therefore, there is an effect that the update process of the UE context can be performed more efficiently without delay.

[0148] Figures 9 to 13 4 is a flowchart for describing an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU in various situations in which an update process of a UE context fails according to an embodiment of the present disclosure.

[0149] Reference Fig. 9 , when the update of the UE context is determined to be necessary, the first node 92a may send a message (UE context modification required) requesting the update of the UE context to the second node 92b (S901). When the message is received from the first node 92a, the second node 92b may initiate the update process of the UE context based on the received message. For reference, Fig. 9 A third node 91 and a UE 900 are also illustrated.

[0150] Reference Fig. 9 , an abnormal situation may occur in the operation for the second node 92b to initiate the UE context update process. For example, the UE context update process may not be initiated due to a problem such as the second node 92b failing to receive a UE context modification required message from the first node 92a.

[0151] If the update process of the UE context is not started as described above, the second node 92b according to an embodiment of the present disclosure may send a UE context modification rejection message to the first node 92a to notify the first node 92a that the update process of the UE context has not been started (S902). For example, the UE context modification rejection message may include information about the failure of the UE context process due to the reception failure in the second node 92b.

[0152] The first node 92a having received the rejection message as described above can quickly confirm that the process requested from the second node 92b has failed. Therefore, the first node can then send an update request for the same context to the second node 92b again.

[0153] Reference Fig.10, when the update of the UE context is determined to be necessary, the first node 102a may send a message (UE context modification required) requesting the update of the UE context to the second node 102b (S1001). When receiving the message from the first node 102a, the second node 102b may start the update process of the UE context based on the received message. That is, the second node 102b may send a message (X2UE context modification required) requesting the update of the UE context to the third node 101 based on the request message received from the first node 102a (S1002).

[0154] like Fig.10 As shown, in response to the UE context update request received from the second node 102b, the third node 101 needs to send an RRC message for execution of context update to the UE 1000, but an abnormal situation may occur before the execution of the corresponding operation. For example, a problem such as the third node 101 failing to receive the X2 SGNB modification required message or failing to send the corresponding RRC message to the UE 1000 may occur.

[0155] In this case, the third node 101 may send a message (X2 SGNB modification reject) to the second node 102b via the X2 interface to notify that the update process of the UE context has failed (S1003).

[0156] In response to this, the second node 102b, which has received a message including information about the failure of updating the UE context from the third node 101, may send a rejection message according to an embodiment of the present disclosure to the first node 102a (S1004). The first node 102a may determine whether to send a message requesting an update of the corresponding context again based on the rejection message received from the second node 102b. For example, after a given time (waiting time) expires, the first node 102a may send a message requesting an update of the context to the second node 102b based on the rejection message.

[0157] Reference Fig.11 When the update of the UE context is determined to be necessary, the first node 112a may send a message (UE context modification required) requesting the update of the UE context to the second node 112b (S1101). When receiving the message from the first node 112a, the second node 112b may send a message (X2 SGNB modification required) requesting the update of the UE context to the third node 111 based on the received message (S1102).

[0158] The third node 111 may send an RRC message for performing context update to the UE 1100 in response to the UE context update request received from the second node 112b (S1103). The UE 1100 may initiate an operation for updating the context based on the RRC message received from the third node 111. In this case, the reception of the RRC message may fail or the context update process may fail due to reasons such as wireless communication conditions.

[0159] In this case, the UE 1100 sends an RRC message (RRC Connection Reconfiguration Request) for connection reconfiguration of the third node 111 to the third node 111 (S1104). In response to this, the UE 1100 reconfigures the RRC connection with the third node 111 based on the message (RRC ConnReestablishment) received from the third node 111 (S1105). When the RRC connection is reconfigured, the UE 1100 may send a message (RRCConnReestablishment) notifying completion of the RRC connection reconfiguration to the third node 111 (S1106).

[0160] In this case, the UE 1100 has reconfigured the RRC connection with the third node 111 as described above, but has not yet performed the update operation of the UE context triggered by the first node 112a. Therefore, after the third node 111 receives the reconfiguration complete message for the RRC connection, it can send a message (X2 SGNB modification reject) to the second node 112b notifying that the update of the UE context has failed (S1107).

[0161] In response to this, the second node 112b may send a message notifying the failure of the update of the UE context (UE context modification rejection) to the first node 112a (S1108). When receiving the rejection message from the second node 112b, the first node 112a according to an embodiment of the present disclosure determines whether to request the context update again based on the rejection message. For example, the first node 112a may determine whether to send the message requesting the update of the corresponding context again based on the comparison between the update failure count and the retry count information for the corresponding context included in the rejection message.

[0162] Reference Fig.12, when the update of the UE context is determined to be necessary, the first node 122a may send a message (UE context modification required) requesting the update of the UE context to the second node 122b (S1201). When receiving the message from the first node 122a, the second node 122b may send a message (X2 SGNB modification required) requesting the update of the UE context to the third node 121 (S1202). The third node 121 may send an RRC message for execution of context update to the UE 1200 in response to the UE context update request received from the second node 122b (S1203). The UE 1200 may initiate an operation for updating the context based on the RRC message received from the third node 121. In addition, when the context update operation is completed, the UE 1200 may send an RRC message (RRC ConnReconfiguration Complete) including corresponding information to the third node 121 (S1204).

[0163] An abnormal situation may occur when the third node 121 performs an operation for notifying the second node 122b of the completion of the update of the UE context based on the RRC message received from the UE 1200. In this case, the third node 121 may send a rejection message (X2SGNB MODIFY REJECT) including information indicating that the update of the UE context has failed to the second node 122b (S1205).

[0164] The second node 122b having received the X2 SGNB Modify Reject from the third node 121 as described above may send a message (UE Context Modify Reject) notifying that the update of the UE context has failed to the first node 122a (S1206). The first node 122a may determine whether to resend the message requesting the update of the UE context based on the received message.

[0165] Reference Fig.13 When the update of the UE context is determined to be necessary, the first node 132a may send a message (UE context modification required) requesting the update of the UE context to the second node 132b (S1301). When receiving the message from the first node 132a, the second node 132b may send a message (X2 SGNB modification required) requesting the update of the UE context to the third node 131 based on the received message (S1302).

[0166] The third node 131 may send an RRC message for execution of context update to the UE 1300 in response to the UE context update request received from the second node 132b (S1303). The UE 1300 may start an operation for updating the context based on the RRC message received from the third node 131. In addition, when the context update operation is completed, the UE 1300 may send an RRC message (RRC ConnReconfiguration Complete) including corresponding information to the third node 131 (S1304).

[0167] The third node 131 may transmit a message (X2 SGNB Modify Confirm) (S1305) for notifying the completion of the update of the UE context to the second node 132b based on the RRC message received from the UE 1300. In this case, a situation such as failure in the execution of the update procedure of the UE context or impossibility of the update procedure due to a given reason may occur although the second node 132b has received the message.

[0168] In this case, the second node 132b may send a message (UE context modification rejection) notifying the failure of the update process of the UE context to the first node 132a (S1306). In addition, the second node 132b may send a message (X2 SGNB modification required) including a rollback indicator indicating the cancellation of the corresponding context update process due to the failure of the corresponding context update to the third node 131 (S1307).

[0169] The third node 131 may send an RRC message including information for rolling back the updated corresponding context to the UE 1300 based on the X2 SGNB modification required message (S1308). After performing the operation for rolling back the UE context, the UE 1300 may send a message (RRC ConnReconfiguration) notifying the corresponding completion to the third node (S1309).

[0170] When receiving the RRC ConnReconfiguration Complete message from the UE, the third node 131 may send a message (X2 SGNB Modification Confirm) including corresponding information to the second node 132b (S1310).

[0171] exist Figures 9 to 13 In addition to the embodiments related to sending of a reject message caused by a failure of a UE context procedure for any one node, the reject message may also be used for various reasons.

[0172] For example, if a UE context modification required message about a given UE is received from the DU while a handover process for the same UE is being performed, the CU may reject the corresponding request using a UE context modification reject message. For another example, although the CU has sent a UE context modification request message about a given UE to the DU, if the DU sends a UE context modification required message again, the CU may reject the corresponding request using a UE context modification reject message based on a session previously in progress for the UE context modification request.

[0173] Although the update of the UE context has not failed, the second node according to an embodiment of the present disclosure may use a UE context modification reject message to notify the UE that the update of the UE context cannot be performed now under given conditions.

[0174] Fig.14 and 15 is a diagram illustrating an example in which a CU sends a rejection message according to an embodiment of the present disclosure to a DU under a given situation according to an embodiment of the present disclosure.

[0175] Reference Fig.14 , when the update of the UE context is determined to be necessary, the first node 142a according to an embodiment of the present disclosure may send a message (UE context modification required-first need) requesting the update of the UE context to the second node 142b (S1401). The second node 142b may send a message (UE context modification confirmation) for confirming the reception of the message to the first node 142a (S1402). In addition, the second node 142b according to an embodiment of the present disclosure may send a message (SGNB context modification required-first need) for updating the UE context to the third node 141 in response to the request (S1403).

[0176] After the first request, the first node 142a according to an embodiment of the present disclosure may further send a request for another UE context (UE context modification required-second required) to the second node 142b (S1404). In response to this, the second node 142b according to an embodiment of the present disclosure may send a rejection message (UE context modification rejection) to the first node 142a (S1405).

[0177] That is, unlike the related art in which only the confirmation of reception is simply performed through the confirmation message, the second node 142b according to the embodiment of the present disclosure uses a rejection message in a given situation where the update process of the UE context cannot be started. Therefore, there is an effect of being able to solve the ambiguous situation that the first node does not know whether the update process of the UE context is in progress.

[0178] In response to the first request for UE context, several pieces of signaling for context update are sent and received between the third node 141 and UE1400 (S1406, S1407). The third node 141 may send a message (SGNB modification confirmation) including result information to the second node 142b according to the signaling (S1408). The second node 142b may send a message (UE context modification request) including information indicating that the update of the UE context has been completed (completion indicator) to the first node 142a based on the message (S1409).

[0179] Reference Fig.15 According to the second node of the embodiment of the present disclosure, it can be determined that switching is necessary. Hereinafter, the existing second node is referred to as the second source node, and the second node as the target of switching is referred to as the second target node.

[0180] According to an embodiment of the present disclosure, the second source node 152b may send a signaling (SGNB change required) for a handover procedure trigger to the third node 151 (S1501). The third node 151 having received the signaling may trigger a new call setup procedure by sending an SGNB add request message to the second target node 152b' (S1502). When all call setups are completed, according to an embodiment of the present disclosure, the second target node 152b' may send an SGNB add request Ack message to the third node 151 (S1503).

[0181] When the SGNB add request Ack message is received, the third node 151 may send signaling for RRC reconfiguration to the UE 1500 (S1504). In response to this, the UE 1500 may send an RRC completion message to the third node 151 (S1505), so that the RRC reconfiguration process may be performed. According to an embodiment of the present disclosure, the third node 151 sends an SGNB change confirmation message to the second source node 152b in response to the completion of the RRC reconfiguration process (S1506), and sends an SGNB reconfiguration completion message to the second target node 152b' (S1507). In this case, after receiving the SGNB change confirmation message, because the SgNB to which the UE managed by the first source node belongs is changed, the second source node 152b may request necessary operations by sending a UE context modification request message including a completion indicator to the first node 152a (S1510). The corresponding necessary operations include data forwarding to the target node and corresponding source side UE context release. Therefore, the SgNB change procedure for the corresponding UE can be completed.

[0182] The first node 152a according to an embodiment of the present disclosure may send a message (UE context modification required) requesting an update of the UE context (S1508) in a state where the first node is unaware of the handover status between the second source node 152b and the second target node 152b'. In this case, the second source node 152b may determine that the update of the UE context is impossible in a state where the handover is in progress, and may send an F1 UE context modification rejection message (S1509) according to an embodiment of the present disclosure to the first node 152a. Therefore, the first node 152a may confirm that the update of the UE context cannot be performed.

[0183] In the drawings, an embodiment has been described in which the CU sends a rejection message notifying the failure of the context update process of the UE to the DU. However, according to an embodiment of the present disclosure, the CU may send a message notifying the UE that the progress of the context process has been suspended.

[0184] For example, if the context update process of the UE cannot be performed, the CU according to an embodiment of the present disclosure may send a UE context modification suspension message for sending corresponding information to the DU. In this case, the DU is able to know that the update of the corresponding context has been suspended until the UE context modification resumption message notifying the progress (or resumption) of the context update process of the UE is received from the CU. Therefore, although the message notifying that the update of the corresponding context has been successfully completed is not received within a given time, the DU according to an embodiment of the present disclosure may not perform a separate re-request.

[0185] Fig.16 is a diagram illustrating an example in which a base station in which a CU and a DU have been separated performs context update of a UE according to an embodiment of the present disclosure.

[0186] Reference Fig.16 According to an embodiment of the present disclosure, the NR base station (gNB) 162 may start a service beam based on a physical random access channel (PRACH) transmitted by a UE 1600 that has performed initial access to the NR base station 162, and may transmit an RRC reconfiguration message (S1601) including configuration information related to an RRC connection with the UE 1600 to the UE 1600. In addition, the NR base station (gNB) 162 may receive CSI report information (S1602) from the UE 1600 based on the RRC reconfiguration message. In this case, the CSI report information may include a synchronization signal block rank indicator (SSBRI), a reference signal received power (RSRP), and the like.

[0187] The NR base station 162 may determine that modification of the beam-related UE context is necessary based on the CSI report information received from the UE 1600. For example, the NR base station 162 according to an embodiment of the present disclosure may determine modification of the UE context information related to the parameters included in Table 3 and related to the beam control of the MAC layer.

[0188] [Form 3]

[0189]

[0190]

[0191]

[0192]

[0193]

[0194]

[0195] According to an embodiment of the present disclosure, the DU of the NR base station 162 can send a UE context modification request message to the CU of the NR base station 162, and the UE context modification request message includes UE context information for a given parameter among the parameters belonging to the RRC IEs included in Table 3, and UE context information that needs to be updated through communication with UE 1600.

[0196] For example, when an update of the UE context related to the csi_ResourceConfig in the beam control-related parameters is determined to be necessary, the DU of the NR base station 162 may send a corresponding request message to the CU of the NR base station 162. In addition, after the request message is sent, if an update of the UE context related to the CSI_ReportConfig for the BM is determined to be necessary, the DU of the NR base station 162 may send a message requesting an update of the corresponding UE context to the CU of the NR base station 162 independently of the request message.

[0197] According to an embodiment of the present disclosure, the CU of the NR base station 162 that receives the UE context update request from the DU of the NR base station 162 as described above may perform the UE context update process. In addition, the CU of the NR base station 162 may send result information indicating whether the service beam for the UE 1600 has been changed to the DU of the NR base station 162 (S1603).

[0198] Reference Fig.16If the UE context update related to the service beam for UE 1600 is confirmed, the NR base station 162 according to an embodiment of the present disclosure can perform wireless communication with the UE based on the service beam updated based on the SSBRI feedback of UE 1600.

[0199] For example, the NR base station 162 according to an embodiment of the present disclosure may send an RRC reconfiguration message (S1604) or a MAC control element (CE) (S1605) to the UE 1600 based on the updated service beam.

[0200] Fig.17 is a diagram illustrating a configuration of a base station according to an embodiment of the present disclosure.

[0201] Fig.18 is a diagram illustrating a configuration of a UE according to an embodiment of the present disclosure.

[0202] Reference Fig.17 , the base station according to an embodiment of the present disclosure may include a DU of a NR base station, a CU of a NR base station and an LTE base station.

[0203] The base station according to an embodiment of the present disclosure may include a transceiver 1710, a controller 1720 (eg, at least one processor), and a memory 1730. In the present disclosure, the controller 1720 of the base station may be defined as a circuit or an application specific integrated circuit or at least one processor.

[0204] First, the transceiver 1710 of the base station according to an embodiment of the present disclosure can send a signal to another network entity and receive a signal from another network entity. For example, the transceiver 1710 can perform wireless communication with an external device such as a UE through a wireless interface, or can perform communication with another base station or network function entity using a given interface unit 1711.

[0205] For example, the interface unit 1711 of the transceiver 1710 of the CU of the NR base station may include a fronthaul interface unit for communicating with the DU of the NR base station, and may include an X2 interface unit for communicating with the LTE base station. In addition, for example, the interface unit 1711 of the transceiver 1710 of the DU of the NR base station may include a fronthaul interface unit for communicating with the CU of the NR base station. In addition, for example, the interface unit 1711 of the transceiver 1710 of the LTE base station may include an X2 interface unit for communicating with the CU of the NR base station.

[0206] The controller 1720 of the base station according to an embodiment of the present disclosure may control the overall operation of the base station according to an embodiment proposed in the present disclosure. For example, the controller 1720 may control the transceiver 1710 and the memory 1730 to perform operations according to the embodiments described in the drawings.

[0207] More specifically, the controller 1720 of the DU of the NR base station can detect whether an update of the UE context is necessary by communicating with the UE, and can control the transceiver 1710 to send a message requesting a corresponding context update to the CU of the NR base station. For another example, the controller 1720 of the CU of the NR base station can start the UE context update process in response to a request message received from the DU of the NR base station, and can control the transceiver 1710 to send a message including corresponding information to the DU of the NR base station. For another example, the controller 1720 of the LTE base station can perform a context update process with the UE based on the UE context update request received from the NR base station, and can control the transceiver 1710 to send the corresponding result to the NR base station.

[0208] The memory 1730 of the base station according to an embodiment of the present disclosure may store at least one of information sent and received by the transceiver 1710 and information generated by the controller 1720. For example, the memory 1730 of the NR base station may store a function separation method of a fronthaul interface configured between the CU and the DU and parameters for each layer.

[0209] Reference Fig.18 , the UE according to an embodiment of the present disclosure may include a transceiver 1810, a controller 1820 (eg, at least one processor), and a memory 1830. In the present disclosure, the controller 1820 of the UE may be defined as a circuit or an application specific integrated circuit or at least one processor.

[0210] First, the transceiver 1810 of the UE according to an embodiment of the present disclosure can send and receive signals to and from another network entity. For example, the transceiver 1810 can send and receive radio signals to and from an external device or a base station through a radio interface.

[0211] In addition, the controller 1820 of the UE according to an embodiment of the present disclosure may control the overall operation of the UE according to an embodiment proposed in the present disclosure. For example, the controller 1820 may control the execution of the UE context update operation based on the RRC message received from the base station.

[0212] In addition, the memory 1830 of the UE according to an embodiment of the present disclosure may store information transmitted and received by the transceiver 1810 and information generated by the controller 1820 .

[0213] Different from Fig.14 and Fig.15In the case where the reject message described in is sent, according to another embodiment of the present disclosure, a method of notifying the F1 UE of the failure of the context modification requirement / confirmation process by sending an F1 UE context confirm message instead of using an F1 UE context modify reject message may be used.

[0214] Fig.19 is a diagram for describing an embodiment in which a UE context modification reject message is not used according to an embodiment of the present disclosure.

[0215] Reference Fig.19 After sending the UE context modification required to the CU, the DU according to an embodiment of the present disclosure drives a timer for sending a message. After receiving the corresponding message, the CU sends an X2 SGNB modification required to the eNB and then drives the timer. If the RRC reconfiguration process fails due to a given reason (e.g., UE side process failure), the eNB sends an X2 SGNB modification reject to the CU after the timer expires.

[0216] The CU that has received the X2 SGNB Modification Reject may not send any message instead of using the F1UE Context Modification to notify the UE that the context modification procedure has failed. If no response is received, since the timer is being driven, the DU may determine that the F1 UE Context Modification Required procedure has failed after the timer expires (however, the corresponding scheme requires a prerequisite, that is, the CU can send the F1 UE Context Modification Confirm message to the DU only when the CU must periodically receive the X2 SGNB Modification Confirm from the eNB).

[0217] For another example, a method without an F1 UE context modification reject message but informing the F1 UE that the context modification is required / confirmation procedure failed by including a reject indication IE while sending an F1 UE context modification confirm message may be used.

[0218] Fig. 20 is a flowchart for describing a method for notifying a UE of a failure of a context procedure using an F1 UE context modification confirm message according to an embodiment of the present disclosure.

[0219] Reference Fig. 20 , after sending UE context modification required to the CU, the DU drives the timer for sending the message. After receiving the corresponding message, the CU sends X2 SGNB modification required to the eNB and then drives the timer. If the RRC reconfiguration process fails due to a given reason (e.g., UE side process failure), the eNB sends X2 SGNB modification rejection to the CU after the timer expires.

[0220] The CU that has received the X2 SGNB reject modification can notify the UE that the context modification procedure has failed by sending an F1 UE context modification confirm message including a reject indication IE without using the F1 UE context modification reject. The following table illustrates the F1 UE context modification confirm message format to which the corresponding reject indication IE has been added.

[0221] [Form 4]

[0222]

[0223]

[0224] As another example, a method of not including the RRC container IE in the F1 UE context modification confirmation may be taken into consideration.

[0225] Fig.21 1 is a diagram for describing a method of notifying a UE of a failure in a context update procedure and indicating that an RRC container IE is not included in an F1UE context confirmation modification message according to an embodiment of the present disclosure.

[0226] Reference Fig.21 , a method of not using the F1 UE context modification reject message but notifying the F1 UE of the failure of the context modification requirement / confirmation procedure by not intentionally including the mandatory RRC container IE while sending the F1 UE context modification confirm message may be used.

[0227] The following table illustrates the F1 UE Context Modification Confirm message format where the RRC Container IE has been omitted.

[0228] [Form 5]

[0229]

[0230] Fig. 22 and 23 It is a diagram for describing a method for changing after confirmation of a UE context modification request from a first node to a second node according to various embodiments of the present disclosure. As described above, the first node according to an embodiment of the present invention can be understood as a DU (gNB-DU) of a NR base station, the second node can be understood as a CU (gNB-CU) of a NR base station, and the third node can be understood as an LTE base station.

[0231] Reference Fig. 22 and 23, if it is determined that UE context update is necessary, the first node 222a, 232a according to an embodiment of the present disclosure may send a message requesting UE context update (UE context modification required) to the second node 222b, 232b (S2201, S2301). The second node 222b, 232b may send a message for confirming the reception of the message (UE context modification confirmation) to the first node 222a, 232a (S2202, S2302). In addition, in response to the request, the second node 222b, 232b according to an embodiment of the present disclosure may send a message for UE context update (SGNB context modification required) to the third node 221, 231 (S2203, S2303).

[0232] If Fig. 22 As shown, no X2 SGNB modification confirmation is received from the third node 221, 231 before the timer expires or as shown in FIG. Fig.23 As shown, an X2 SGNB reject modification message (S2204) has been received from the third node 221, 231 as a response to the X2 SGNB modification requirement sent from the second node 222b, 232b to the third node 221, 231, then according to an embodiment of the present disclosure, the second node 222b, 232b can send a UE context modification request message, and when it sends the UE context modification request message to the first node 222a, 232a, the UE context modification request message includes a completion indicator having a value of "false" (S2204, S2304).

[0233] Thereafter, when a completion indicator having a value of "false" is received, the first node 222a, 232a according to an embodiment of the present disclosure may resend the UE context modification required message to the second node 222b, 232b.

[0234] As described above, a confirmation message including a completion indicator may be understood as a "meaningful confirmation" as shown.

[0235] According to an embodiment of the present disclosure, in a situation where a plurality of nodes are involved in the UE context update, the result information of the UE context update process is notified to the node that first requests the UE context update. Therefore, the effect is that the node can perform operations suitable for each situation of success or failure of the corresponding process without unnecessary resource consumption.

[0236] While the present disclosure has been shown and described by reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.

Claims

1. A method performed by a distributed unit DU of a next generation Node B gNB in ​​a wireless communication system, wherein the gNB is connected to a user equipment UE with an evolved Node B eNB according to a dual connectivity DC, the method comprising: A UE context modification required message is sent to a central unit CU of the gNB to request UE context modification of the UE, wherein the UE context modification required message includes: gNB-CU UE identifier ID, used to identify the UE within the CU, and gNB-DU UE ID, used to identify the UE within the DU; A UE context modification rejection message indicating that the UE context modification is unsuccessful is received from the CU, where the UE context modification rejection message includes: gNB-CU UE ID, gNB-DU UE ID, and Information about the cause of the unsuccessful UE context modification, and A UE context modification request message is received from the CU, wherein the UE context modification request message includes a completion indicator of a procedure for DC operation between the eNB and the gNB.

2. The method according to claim 1, in, The gNB DU and gNB CU are connected via the F1 interface. Among them, the CU of gNB is connected to the eNB through the X2 interface. The CU is configured to perform the functions of the radio resource control RRC layer and the packet data convergence protocol PDCP layer, and Among them, the DU is configured to perform the functions of the radio link control RLC layer, the medium access control MAC layer and the physical PHY layer.

3. The method according to claim 2, in, The UE context modification required message includes identification information about one or more data radio bearers DRB to be modified and downlink DL user plane UP tunnel TNL information.

4. The method according to claim 1, in, The UE context modification requires a message including a resource coordination transport container. The resource coordination transport container includes a secondary gNB SgNB resource coordination information element IE for the eNB, and Among them, the SgNB resource coordination IE includes information about the new radio NR cell global identifier CGI and coordination information.

5. A method performed by a central unit CU of a next generation node base station gNB in ​​a wireless communication system, wherein the gNB is connected to a user equipment UE with an evolved NodeB eNB according to a dual connectivity DC, the method comprising: A UE CONTEXT MODIFICATION REQUIRED message is received from a distributed unit DU of a gNB to request UE context modification of the UE, wherein the UE CONTEXT MODIFICATION REQUIRED message includes: gNB-CU UE identifier ID, used to identify the UE within the CU, and gNB-DU UE ID, used to identify the UE within the DU; If the UE context modification is unsuccessful, a UE context modification reject message is sent to the DU, where the UE context modification reject message includes: gNB-CU UE ID, gNB-DU UE ID, and Information about the cause of the unsuccessful UE context modification, and A UE context modification request message is sent to the DU, wherein the UE context modification request message includes a completion indicator of the process for DC operation between the eNB and the gNB.

6. The method according to claim 5, in, The gNB DU and gNB CU are connected via the F1 interface. Among them, the CU of gNB is connected to the eNB through the X2 interface. The CU is configured to perform the functions of the radio resource control RRC layer and the packet data convergence protocol PDCP layer, and Among them, the DU is configured to perform the functions of the radio link control RLC layer, the medium access control MAC layer and the physical PHY layer.

7. The method according to claim 6, in, The UE context modification required message includes identification information about one or more data radio bearers DRB to be modified and downlink DL user plane UP tunnel TNL information.

8. The method according to claim 5, in, The UE context modification requires a message including a resource coordination transport container. The resource coordination transport container includes a secondary gNB SgNB resource coordination information element IE for the eNB, and Among them, the SgNB resource coordination IE includes information about the new radio NR cell global identifier CGI and coordination information.

9. A distributed unit DU of a next generation Node B gNB in ​​a wireless communication system, wherein the gNB is connected to a user equipment UE with an evolved Node B eNB according to a dual connectivity DC, and the DU comprises: a memory for storing instructions; Transceiver; and at least one processor, Wherein, when the instructions are executed by the at least one processor, the DU: Control the transceiver to send a UE context modification required message to a central unit CU of the gNB to request UE context modification of the UE, wherein the UE context modification required message includes: gNB-CU UE identifier ID, used to identify the UE within the CU, and gNB-DU UE ID, used to identify the UE within the DU; and Control the transceiver to receive a UE context modification rejection message from the CU indicating that the UE context modification is unsuccessful, wherein the UE context modification rejection message includes: gNB-CU UE ID, gNB-DU UE ID, and Information about the cause of the unsuccessful UE context modification, and Control the transceiver to receive a UE context modification request message from the CU, wherein the UE context modification request message includes a completion indicator of a process for DC operation between the eNB and the gNB.

10. The DU of the gNB according to claim 9, in, The gNB DU and gNB CU are connected via the F1 interface. Among them, the CU of gNB is connected to the eNB through the X2 interface. The CU is configured to perform the functions of the radio resource control RRC layer and the packet data convergence protocol PDCP layer, and Among them, the DU is configured to perform the functions of the radio link control RLC layer, the medium access control MAC layer and the physical PHY layer.

11. The DU of the gNB according to claim 10, in, The UE context modification required message includes identification information about one or more data radio bearers DRB to be modified and downlink DL user plane UP tunnel TNL information.

12. The DU of the gNB according to claim 9, in, The UE context modification requires a message including a resource coordination transport container. The resource coordination transport container includes a secondary gNB SgNB resource coordination information element IE for the eNB, and Among them, the SgNB resource coordination IE includes information about the new radio NR cell global identifier CGI and coordination information.

13. A central unit CU of a next generation node base station gNodeB gNB in ​​a wireless communication system, wherein the gNB is connected to a user equipment UE with an evolved NodeB eNB according to a dual connection DC, and the CU comprises: a memory for storing instructions; Transceiver; and at least one processor, Wherein, when the instruction is executed by the at least one processor, the CU: Control the transceiver to receive a UE context modification required message from a distributed unit DU of the gNB to request UE context modification of the UE, wherein the UE context modification required message includes: gNB-CU UE identifier ID, used to identify the UE within the CU, and gNB-DU UE ID, used to identify the UE within the DU, Control the transceiver to send a UE context modification rejection message to the DU indicating that the UE context modification is unsuccessful, wherein the UE context modification rejection message includes: gNB-CU UE ID, gNB-DU UE ID, and Information about the cause of the unsuccessful UE context modification, and Control the transceiver to send a UE context modification request message to the DU, wherein the UE context modification request message includes a completion indicator of a process for DC operation between the eNB and the gNB.

14. The CU of the gNB according to claim 13, in, The DU of the gNB and the CU of the gNB are connected via the F1 interface, and the CU of the gNB is connected to the eNB via the X2 interface, and The UE context modification required message includes identification information about one or more data radio bearers (DRBs) to be modified and downlink (DL) user plane (UP) tunnel (TNL) information.

15. The CU of the gNB according to claim 13, in, The CU is configured to perform the functions of the radio resource control RRC layer and the packet data convergence protocol PDCP layer, and Among them, the DU is configured to perform the functions of the radio link control RLC layer, the medium access control MAC layer and the physical PHY layer.

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