Method and device for inter-rat handover control

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. A terminal according to an embodiment may: receive, by a first RAT processing unit of the terminal connected to a cell of a first RAT, information about at least one cell of a second RAT from a network unit of the first RAT; convert, by the first RAT processing unit of the terminal, a format of the information about the at least one cell of the second RAT from an RRC format of the first RAT to an RRC format of the second RAT; transmit the converted information about the at least one cell of the second RAT; search for the at least one cell of the second RAT on the basis of configuration information about the at least one cell of the second RAT converted by a second RAT processing unit of the terminal; and transmit a report about a search result to the network unit of the first RAT.

Description

Method and device for controlling inter-RAT handover

[0001] The present disclosure relates to a technology for supporting fast handover between multiple RATs (radio access technologies) of a terminal capable of communicating with multiple RATs.

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

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

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

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

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

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

[0008] The present disclosure proposes a method for supporting inter-RAT handovers, which operate independently, by adding interworking technology and control functions to a new network or new network unit with some units of an existing network. Furthermore, the present disclosure proposes network and terminal operations that support superior performance compared to existing inter-RAT handovers.

[0009] A method for a terminal to perform inter-RAT (radio access technology) handover according to one embodiment of the present disclosure may include: a step in which a first RAT processing unit of a terminal connected to a cell of a first RAT receives information about at least one cell of a second RAT from a network unit of the first RAT; a step in which the first RAT processing unit of the terminal converts a format of information about at least one cell of the second RAT from an RRC (radio resource control) format of the first RAT to an RRC format of the second RAT; a step in which the converted information about at least one cell of the second RAT is transmitted to the second RAT processing unit of the terminal; a step in which the second RAT processing unit of the terminal performs a search for at least one cell of the second RAT based on configuration information about at least one cell of the second RAT that has been converted; and a step in which the first RAT processing unit of the terminal transmits a report about a search result to a network unit of the first RAT.

[0010] Structural improvements according to one embodiment of the present disclosure enable the network to support fast inter-RAT handover. Furthermore, a terminal according to one embodiment of the present disclosure can perform fast inter-RAT handover without changing the existing communication modem.

[0011] FIG. 1 is a diagram for explaining a linkage technique between RATs according to one embodiment of the present disclosure.

[0012] FIG. 2a is a diagram for explaining inter-RAT cooperation by 6G CU according to one embodiment of the present disclosure at the protocol layer level.

[0013] FIG. 2b is a diagram for explaining inter-RAT cooperation by 6G CUs according to another embodiment of the present disclosure at the protocol layer level.

[0014] FIG. 3 is a diagram for explaining a method for controlling 5G RAT through 6G RAT according to one embodiment of the present disclosure.

[0015] FIG. 4 is a diagram for explaining a procedure for a terminal to perform handover from 6G to 5G according to one embodiment of the present disclosure.

[0016] FIG. 5 is a diagram for explaining an operation when a terminal performs handover from a 5G cell to a 6G cell according to one embodiment of the present disclosure.

[0017] FIG. 6 is a diagram for explaining the operation when a terminal performs handover from a 5G cell to a 6G cell according to another embodiment of the present disclosure.

[0018] FIG. 7 is a block diagram illustrating the structure of a terminal according to some embodiments.

[0019] FIG. 8 is a block diagram illustrating the structure of a network unit according to some embodiments.

[0020] According to one embodiment of the present disclosure, a method for a terminal to perform a handover between radio access technologies (RATs) comprises the steps of: receiving, by a first RAT processing unit of a terminal connected to a cell of a first RAT, information about a cell (hereinafter, a neighboring cell) that can be a target of cell link information measurement and reporting for handover for at least one cell of a second RAT from a network unit of the first RAT; converting, by the first RAT processing unit of the terminal, a format of information about at least one neighboring cell of the second RAT from an RRC (radio resource control) format of the first RAT to an RRC format of the second RAT; transmitting, by the second RAT processing unit of the terminal, information about at least one neighboring cell of the second RAT that has been converted; and performing, by the second RAT processing unit of the terminal, a search for at least one neighboring cell of the second RAT based on configuration information about the at least one neighboring cell of the second RAT that has been converted. And it may include a step of transmitting a report on the search result from the first RAT processing unit of the terminal to the network unit of the first RAT.

[0021] A method for a terminal to perform inter-RAT (radio access technology) handover according to one embodiment of the present disclosure may further include a step of setting at least one cell as an additional measurement and control cell (hereinafter, a candidate cell) based on a report on the search result from a network unit of a first RAT, and receiving configuration information regarding the set at least one candidate cell.

[0022] A method for a terminal to perform inter-RAT (radio access technology) handover according to one embodiment of the present disclosure may further include the steps of: receiving a PRACH transmission instruction for a candidate cell of the second RAT from a network unit of the first RAT; and transmitting a PRACH to a network unit of the second RAT based on the PRACH transmission instruction.

[0023] A method for a terminal to perform inter-RAT (radio access technology) handover according to one embodiment of the present disclosure may further include the steps of: receiving RSs from each of a candidate cell of the first RAT and a candidate cell of the second RAT based on configuration information regarding the at least one candidate cell; and determining link quality of the first RAT and link quality of the second RAT based on each of the received RSs.

[0024] A method for a terminal to perform inter-RAT (radio access technology) handover according to one embodiment of the present disclosure may further include the steps of: performing a report on link quality of the first RAT and link quality of the second RAT to a network unit of the first RAT; and receiving a handover command to the second RAT from the network unit of the first RAT based on the report.

[0025] In a method for a terminal to perform inter-RAT (radio access technology) handover according to one embodiment of the present disclosure, the first RAT is 6G (6 th generation technology), and the second RAT is 5G (5 th generation technology).

[0026] A method for supporting inter-RAT handover by a network unit of a first RAT according to one embodiment of the present disclosure comprises the steps of: transmitting information about at least one neighboring cell of a second RAT to a terminal connected to a cell of the first RAT; and receiving a report about a search result of at least one neighboring cell of the second RAT from the terminal, wherein a format of the information about the at least one neighboring cell of the second RAT is converted from an RRC (radio resource control) format of the first RAT to an RRC format of the second RAT in a first RAT processing unit of the terminal, the converted information about the at least one neighboring cell of the second RAT is transmitted to the second RAT processing unit of the terminal, and the search for the at least one neighboring cell of the second RAT can be performed in the second RAT processing unit of the terminal based on configuration information about the at least one neighboring cell of the second RAT that has been converted.

[0027] A method for supporting inter-RAT handover by a network unit of a first RAT according to one embodiment of the present disclosure may further include a step of transmitting configuration information about at least one candidate cell established based on a report on the search result to the terminal.

[0028] A method for supporting inter-RAT handover by a network unit of a first RAT according to one embodiment of the present disclosure further includes a step of transmitting a PRACH transmission instruction to a candidate cell of the second RAT, and based on the PRACH transmission instruction, a PRACH can be transmitted from a second RAT processing unit of the terminal to the network unit of the second RAT.

[0029] A method for supporting inter-RAT handover by a network unit of a first RAT according to one embodiment of the present disclosure may further include the steps of: receiving a report on link quality of the first RAT and link quality of the second RAT from the terminal; and transmitting a handover command from the network unit of the first RAT to the second RAT based on the report.

[0030] A terminal performing inter-RAT (radio access technology) handover according to one embodiment of the present disclosure comprises: a transceiver; And at least one processor connected to the transceiver, wherein the at least one processor includes a first RAT processing unit and a second RAT processing unit, and the first RAT processing unit of a terminal connected to a cell of the first RAT receives information about at least one cell of the second RAT from a network unit of the first RAT, and the first RAT processing unit converts a format of information about at least one cell of the second RAT from an RRC (radio resource control) format of the first RAT to an RRC format of the second RAT, and transmits the converted information about at least one cell of the second RAT to the second RAT processing unit, and the second RAT processing unit performs a search for at least one cell of the second RAT based on the configuration information about the at least one cell of the second RAT that has been converted, and transmits a report about the search result from the first RAT processing unit to the network unit of the first RAT.

[0031] According to one embodiment of the present disclosure, a network unit of a first radio access technology (RAT) supporting inter-RAT handover comprises: a transceiver; and at least one processor connected to the transceiver, wherein the at least one processor: transmits information about at least one cell of a second RAT to a terminal connected to a cell of the first RAT, and receives a report about a search result of at least one cell of the second RAT from the terminal, wherein a format of information about at least one cell of the second RAT is converted from an RRC (radio resource control) format of the first RAT to an RRC format of the second RAT in a first RAT processing unit of the terminal, and the converted information about at least one cell of the second RAT is transmitted to the second RAT processing unit of the terminal, and a search for at least one cell of the second RAT can be performed in the second RAT processing unit of the terminal based on configuration information about at least one neighboring cell of the second RAT.

[0032] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings.

[0033] In describing the embodiments, descriptions of technical details that are well known in the technical field to which the present disclosure pertains and are not directly related to the present disclosure will be omitted. This is to ensure that the gist of the present disclosure is conveyed more clearly without obscuring it by omitting unnecessary explanations.

[0034] For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted. Furthermore, the dimensions of each component do not entirely reflect its actual size. Identical or corresponding components in each drawing are assigned the same reference numbers.

[0035] The advantages and features of the present disclosure, and methods for achieving them, will become clearer with reference to the embodiments described below in detail together with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present disclosure is complete and to fully inform those skilled in the art of the scope of the disclosure, and the present disclosure is defined only by the scope of the claims. Like reference numerals designate like elements throughout the specification. In addition, when describing the present disclosure, if a specific description of a related function or configuration is determined to unnecessarily obscure the gist of the present disclosure, the detailed description thereof will be omitted. In addition, the terms described below are terms defined in consideration of the functions of the present disclosure, and these may vary depending on the intention or custom of the user or operator. Therefore, their definitions should be made based on the contents throughout the specification.

[0036] Additionally, terms such as "~bu", "~gi", "~block", "~unit", and "~module" may refer to a unit that processes at least one function or operation. For example, the terms may refer to at least one piece of hardware, at least one piece of software stored in memory, or at least one process processed by a processor.

[0037] Hereinafter, a base station is an entity that performs resource allocation of a terminal, and may be at least one of a gNode B, an eNode B, a Node B, a BS (Base Station), a wireless access unit, a base station controller, a network unit, or a node on a network. The terminal may include a UE (User Equipment), an MS (Mobile Station), a cellular phone, a smartphone, a computer, or a multimedia system capable of performing a communication function.

[0038] In this disclosure, A / B means at least one of A or B.

[0039] In the present disclosure, downlink (DL) refers to a wireless transmission path of a signal transmitted from a base station to a terminal, and uplink (UL) refers to a wireless transmission path of a signal transmitted from a terminal to a base station.

[0040] In the present disclosure, a unit may be used with the same meaning as a corresponding unit device, and a layer may be used with the same meaning as a layer device. In addition, a core may be used with the same meaning as a core device or a core network device.

[0041] Inter-cell handover or support for terminal mobility is a core technology in mobile communications. The greater the number of nodes involved in a handover or the higher the control layer, the longer the processing time and delay required for the handover. Furthermore, the more careful handover management is required, making it difficult to initiate the handover process in a timely manner. Therefore, inter-RAT handover is the scenario where adequate performance support or assurance is the most challenging among all mobility control situations. While 5G has demonstrated overall mobility improvements compared to 4G, such as reduced interruption times and shorter handover decision delays in some scenarios, effective solutions for inter-RAT environments have not been found. This disclosure proposes an improved solution for efficiently controlling mobility between 5G and 6G.

[0042] A terminal receiving a service of a first RAT according to an embodiment of the present disclosure may, in addition to the function of connecting to a network of the first RAT and performing communication through the network of the first RAT, perform communication by connecting to a network of a second RAT as an alternative when connection to the first RAT network is not easy. In one embodiment, a terminal receiving a 6G service may, in addition to the function of connecting to a 6G network and performing communication through the 6G network, perform communication by connecting to a 5G network or a 5G transceiver node as an alternative when connection to a 6G network or a 6G transceiver node is not easy.

[0043] This process of a 6G terminal selectively connecting to a more suitable 6G or 5G node depending on the communication environment is called inter-5G-6G mobility. In a more general way, the series of processes in which a terminal selectively connects to a node corresponding to a different RAT system is called inter-RAT mobility or inter-RAT handover (hereinafter referred to as RAT-HO). When a commercial service is launched in a situation where a specific RAT cannot provide national coverage, RAT-HO must be supported to support a stable user experience, and as RAT evolves, better mobility management techniques must be introduced. For example, since 5G supports shorter interruption time and shorter handover decision latency compared to 4G, 5G-6G RAT-HO also needs to support such performance improvements compared to the existing 4G-5G RAT-HO.

[0044] RAT-HO inevitably requires interoperability between systems responsible for different RATs. Depending on the degree of interoperability supported, the delay and signaling overhead required for sharing measurement and control information between RATs will vary, as will the difficulty and cost of implementing the hardware / shardware required for system implementation. When a new RAT system is implemented to share a core with an existing RAT system, such as the 5G NSA system, the initial implementation cost of the new RAT system is reduced. However, supporting two different RAT systems through a single core can result in high control complexity. In addition, when inter-RAT linkage occurs in a network unit close to a terminal, the system in charge of each RAT performs lower layer control through inter-RAT cooperation, so control information, measurement information, or user data must be shared between RATs more frequently and with lower interface latency, which increases the burden of system implementation.

[0045] The present disclosure aims to provide a method for reducing the implementation burden as described above while simultaneously supporting an appropriate level of inter-RAT cooperation during the RAT-HO process. In an embodiment of the present disclosure, a technique for controlling mobility between a first RAT and a second RAT is proposed by granting control authority over a distributed unit (DU) of a second RAT to a central unit (CU) of the first RAT. For example, a 6G central unit (CU) according to one embodiment of the present disclosure may be granted control authority over a 5G distributed unit (DU), thereby controlling mobility between 5G and 6G.

[0046] FIG. 1 is a diagram for explaining a linkage technique between RATs according to one embodiment of the present disclosure.

[0047] In the embodiment of Fig. 1, for convenience of explanation, it is assumed that the first RAT is 6G and the second RAT is 5G.

[0048] Referring to FIG. 1, a 5G network may include four units: a 5G core (112), a 5G CU (114), a 5G DU (116), and a 5G RU (radio unit, 118). In addition, a 6G network may include a 6G core (122), a 6G CU (124), a 6G DU (126), and a 6G RU (128). However, this is merely an example, and in some cases, some of the above-described units may be included in other units. For example, the function performed by the 5G CU (114) may be included in the 6G CU (124), and the 6G network may be composed of a 6G core (112), a 6G CU (124) that performs the function performed by the 5G CU, a 6G DU (126), and a 6G RU (128).

[0049] FIG. 2a is a diagram illustrating inter-RAT cooperation by a 6G CU according to one embodiment of the present disclosure, at a protocol layer level. Furthermore, FIG. 2b is a diagram illustrating inter-RAT cooperation by a 6G CU according to another embodiment of the present disclosure, at a protocol layer level.

[0050] Referring to FIGS. 2A and 2B, a 5G network may include four units: a 5G core (212), a 5G CU (214), a 5G DU (216), and a 5G RU (218). The 5G core (212) may perform a quality of service (QoS) management function (230). In addition, the wireless protocol of the 5G network may be composed of a 5G radio resource control (RRC) layer (241), a 5G service data protocol (SDAP) layer (242), a 5G packet data convergence protocol (PDCP) layer (243), a 5G radio link control (RLC) layer (244), a 5G medium access control (MAC) layer (245), and a 5G physical (PHY) layer (246). The 5G PHY layer (246) may be divided into a 5G High-PHY layer including some of the functions performed and a 5G Low-PHY layer including the remaining functions. According to one embodiment, the 5G CU (214) may include a 5G RRC layer (241), a 5G SDAP layer (242), and a 5G PDCP layer (243). In addition, the 5G DU (216) may include a 5G RLC layer (244), a 5G MAC layer (245), and a 5G High-PHY layer, and the 5G RU (218) may include a 5G Low-PHY layer.

[0051] In addition, the 6G network may include four units: a 6G core (222), a 6G CU (224), a 6G DU (226), and a 6G RU (228). The 6G core (222) may perform a QoS management function (250). In addition, the wireless protocol of the 6G network may be composed of a 6G RRC layer (261), a 6G SDAP layer (262), a 6G PDCP layer (263), a 6G RLC layer (264), a 6G MAC layer (265), and a 6G PHY layer (266). The 6G PHY layer (266) may be divided into a 6G High-PHY layer including some of the functions to be performed and a 6G Low-PHY layer including the remaining functions. Referring to FIG. 2a, a 6G CU (224) according to one embodiment may include a 6G RRC layer (261), a 6G SDAP layer (262), and a 6G PDCP layer (263). Referring to FIG. 2b, in addition to the 6G RRC layer (261), the 6G SDAP layer (262), and the 6G PDCP layer (263), the 6G CU (224) may further include a 5G PDCP layer (247).

[0052] Additionally, the 6G DU (226) may include an RLC layer (264), a MAC layer (265), and a High-PHY layer, and the 6G RU (228) may include a Low-PHY layer.

[0053] According to one embodiment, a 6G core (222) can determine whether to control traffic in a 6G format or a 5G format, depending on the network connection status of the terminal, when transmitting downlink 6G traffic generated through communication of a 6G service or a 6G terminal to the terminal through definition and use of a new protocol. In addition, the 6G core (222) can transmit traffic controlled in the determined format to the 6G CU (224).

[0054] According to one embodiment, a 6G CU (224) may control packet transmission through a 6G DU (226) for traffic generated in a 6G format. Referring to FIG. 2a, traffic generated in a 5G format in a 6G SDAP layer (262) of the 6G CU (224) may be transmitted to a PDCP layer (243) of the 5G CU (214). In addition, referring to FIG. 2b, the 6G CU (224) may control packet transmission through a 5G DU (216) for traffic generated in a 5G format. For example, 5G traffic may be transmitted to an RLC layer (244) of the 5G DU (216) through a 5G PDCP layer (247) of the 6G CU (224).

[0055] According to one embodiment, a 6G core (222) controls all traffic targeting a 6G modem (290) of a terminal according to a 6G format, and then a 6G CU (224) can perform a task of maintaining data packets in a 6G format or changing them to a 5G format depending on the network transmission / reception unit to which the terminal is connected.

[0056] The method according to the aforementioned embodiments can also be applied to uplink traffic. For example, data packets received in 5G format at a 6G CU (224) can be converted to 6G format uplink traffic, or the 6G core (222) can be provided with the capability to support both 5G and 6G formats.

[0057] A terminal (270) capable of accessing both 5G and 6G RAT must configure modems (modems, 280, 290) corresponding to the 5G RAT and 6G RAT, and can support faster inter-RAT handover than before through coordination / cooperation between the 5G modem (280) and the 6G modem (290). Cooperation between the modems (280, 290) of the terminal can be implemented in various ways, and while the lower the layer in which cooperation is supported, the more precise the cooperation becomes, the more difficult the terminal implementation becomes. In an embodiment according to the present disclosure, a terminal structure is proposed that performs RRC configuration control of a 5G RAT through a 6G modem (290) for a 5G modem (280) that operates independently.

[0058] The terminal structure presented in this disclosure has the advantage of minimizing the impact on the implementation of existing 5G modems and enabling control of 5G RAT through 6G RAT.

[0059] FIG. 3 is a diagram for explaining a method for controlling 5G RAT through 6G RAT according to one embodiment of the present disclosure.

[0060] Referring to FIG. 3, the network can control (310) the 5G RAT operation of the terminal through the 6G transmit / receive unit (e.g., 6G CU / DU / RU) at the RRC unit, and can also directly report measurements for the terminal 5G RAT at the layer 3 level. In addition, the terminal can receive L1 level control for the 5G RAT through the 5G transmit / receive unit (e.g., 5G CU / DU / RU), and can report L1 level measurements for the 5G RAT to the 6G CU through the 5G transmit / receive unit (e.g., 5G CU / DU / RU).

[0061] In the above network and terminal architecture, the 6G transmit / receive unit and the 6G modem / chip perform direct upper layer-level control of the 5G link, and can share measurement results for the 5G link through the upper layer. On the other hand, the inter-RAT operation between the 5G transmit / receive unit and the 5G modem / chip of the terminal is restricted as described above. Due to this dual network-terminal operation between RATs, it is necessary to design two different handover processes optimized for each case: when the terminal hands over from 6G RAT to 5G RAT, and when the terminal hands over from 5G RAT to 6G RAT.

[0062] Hereinafter, a method for performing an inter-RAT handover according to an embodiment of the present disclosure will be described with reference to FIGS. 4 to 6. FIG. 4 illustrates an example of performing a handover from a first RAT to a second RAT, and a method for performing a handover from 6G to 5G. However, this is merely an example, and the first RAT is not limited to 6G, and the second RAT is not limited to 5G. In addition, FIGS. 5 and 6 illustrate an example of performing a handover from a second RAT to a first RAT, and a method for performing a handover from 5G to 6G.

[0063] In the present disclosure, the network of the first RAT may refer to at least one network unit among the RU, DU, or CU of the first RAT. For example, the 6G network may refer to at least one network unit among the 6G RU, DU, or CU. Furthermore, the network of the second RAT may refer to at least one network unit among the RU, DU, or CU of the second RAT. For example, the 5G network may refer to at least one network unit among the 5G RU, DU, or CU.

[0064] FIG. 4 is a diagram for explaining a procedure for a terminal to perform handover from 6G to 5G according to one embodiment of the present disclosure.

[0065] In the embodiment of FIG. 4, it is assumed that the terminal includes a 5G processing unit that performs 5G wireless protocol functions and a 6G processing unit that performs 6G wireless protocol functions. Meanwhile, the 6G processing unit corresponds to an example of the first RAT processing unit, and the 5G processing unit corresponds to an example of the second RAT processing unit.

[0066] The 5G processing unit and the 6G processing unit may be implemented on a single processor, or, in another example, on two or more processors. Furthermore, the one or more processors may be implemented on a single chip or on separate chips. For example, the 5G processor may be implemented on a 5G chip, and the 6G processor may be implemented on a 6G chip. The chips may include, for example, a modem chip.

[0067] Additionally, in the operations described with reference to FIG. 4, the operations described as being performed by the terminal are meant to be performed by at least one of the 5G processing unit of the terminal or the 6G processing unit of the terminal. In the following description, 6G is replaced with the first RAT, and 5G is replaced with the second RAT, and the embodiments of the present disclosure can be applied thereto.

[0068] As a first step operation (410), a 6G CU that directly controls a 5G cell or a 5G RU and a 5G DU has 5G cell deployment information and can use the information to provide 5G neighboring cell information to a 6G processing unit of a terminal that wishes to handover to a 5G cell. The 6G processing unit in the terminal can receive the provided 5G neighboring cell information. The 5G neighboring cell information can be transmitted in the form of at least one of a 5G neighboring cell list, an inter-RAT neighboring cell list, or an inter-RAT cell measurement configuration, for example. Information about each neighboring cell in the 5G neighboring cell information can include at least one of a cell ID of each cell or information about a reference signal (RS) for cell detection of each cell. Information about the RS may include at least one of information about the transmission method of the RS, information about the radio resources used for transmitting the RS, or information about terminal operations required for receiving the RS. For example, information about the RS includes information about the SSB transmission period of the corresponding cell, the transmission position on the frequency axis, and the transmission position on the time axis.

[0069] As another example, 5G neighbor cell information may include information on whether cell common information, such as a system information block (SIB), is broadcast or whether transmission is determined based on specific conditions.

[0070] Additionally, 5G neighbor cell information may include whether the cell is performing a specific transmission / reception mode. For example, information regarding whether the cell is performing a specific transmission / reception mode may include information regarding whether the cell is performing an energy saving mode. Information regarding whether the energy saving mode is performed may include, for example, an index indicating that SIB transmission is not being performed or detailed information indicating this. In another example, information regarding the deactivated function may be included if a portion of the cell's transmission / reception function is deactivated. Furthermore, information regarding a method for switching deactivation to activation may be included. For example, information regarding a method for switching deactivation to activation may include information regarding at least one of a transmission method of an uplink signal that activates the cell, a sequence of the uplink signal, a transmission location, or a transmission power control method (a power control parameter required to determine transmission power, RS information for pathloss measurement).

[0071] In addition, 5G neighboring cell information may include priority information for each cell. The priority information may include information about the cell that the terminal should give priority to when performing RAT-HO. A cell set to high priority as described above may be configured so that the terminal must report the link quality for the cell when reporting information about the 5G neighboring cell thereafter. In addition, a cell set to high priority may have separate settings applied when setting an event or condition that triggers neighboring cell reporting. For example, a cell set to high priority may be configured to perform neighboring cell reporting or include the cell in neighboring cell reporting even when it exhibits lower link quality than other cells, or may be configured to perform neighboring cell reporting or include the cell in neighboring cell reporting even when it satisfies the required link quality in a relatively shorter period of time.

[0072] In addition, when implementing information about neighboring cells, such as a 5G neighboring cell list, and transmitting it to the terminal in the form of an inter-RAT neighboring cell list, the information about each cell can be set to have different contents. For example, information about some cells can be set to include only information about cell ID, and information about other cells can be set to include information about the cell ID and the transmission method and location of the RS for cell search.

[0073] All of the above 5G neighboring cell information can be transmitted to the 6G processing unit of the terminal through the 6G serving cell. The 5G neighboring cell information is transmitted to the 6G processing unit of the terminal through a signaling method such as RRC or MAC CE (control element), and L1 layer level control signaling such as DCI (downlink control information) can be used to transmit the 5G neighboring cell information to the 6G processing unit of the terminal. In addition, the 5G neighboring cell information can be transmitted through a combination of at least some of the above-described signaling. For example, the 6G serving cell can transmit primary configuration information for the 5G neighboring cell to the 6G processing unit of the terminal through RRC signaling. Thereafter, the MAC CE can be used to instruct modification, down-selection, activation, or addition of the primary configuration information, thereby generating secondary configuration information. Downselection refers to the act of selectively setting at least some of the primary configuration information. Subsequently, tertiary configuration information can be generated in the form of downselection of secondary configuration information, using layer 1-level control information such as DCI. For example, at least some of the 5G neighbor cell information set via RRC signaling can be selected via MAC CE, and at least one of the selected pieces of information can be selected via DCI.

[0074] The 6G processing unit of the terminal receives 5G neighboring cell information and converts it into a 5G RRC configuration format, and the converted information can be applied to 5G neighboring cell search. In one embodiment, the 6G processing unit of the terminal can transmit the 5G neighboring cell information converted into a 5G RRC configuration format to the 5G processing unit of the terminal.

[0075] As a second step operation (420), the 5G processing unit of the terminal may perform 5G neighboring cell detection and reporting. The above 5G neighboring cell specification may be performed based on the 5G neighboring cell information set in the first step. The 5G processing unit of the terminal may preferentially perform a search for a cell with a high priority according to the cell-specific priority set in the first step operation (410). Alternatively, it may be defined or set to perform a search for a cell with a low priority only if no suitable cell is detected after performing a search for a cell with a high priority. Depending on the terminal capability or the 5G or 6G network settings, the 5G processing unit of the terminal may perform measurements on cells other than those set as 5G neighboring cells in the first step operation (410). In this case, the priority definition between the 5G neighboring cells set in the first step operation (410) and other cells may be set or defined such that the cells not set as 5G neighboring cells in the first step operation (410) have the lowest priority. Alternatively, if the 5G or 6G network desires to detect additional neighboring cells for purposes such as cell map updates, it may be set to give priority to searching for cells not defined as neighboring cells in the first step operation (410).

[0076] Neighbor cell discovery can be performed based on detecting cell detection RSs and channels, such as synchronization signal blocks (SSBs) of each cell. However, depending on network configuration, 5G neighbor cell discovery based on RSs designed for purposes other than cell discovery, such as channel state information-reference signals (CSI-RSs) and tracking reference signals (TRSs), can also be directed or performed. Alternatively, cell discovery based on one or more RSs transmitted and received via independent radio resources can be configured or performed. When cell discovery is performed via one or more RSs, the cell discovery can be performed by measuring at least one of an average, a weighted average, a least value, or a maximum value of link quality measured at each RS.

[0077] The above search result can be transmitted from the 5G processing unit of the terminal to the 6G processing unit of the terminal. The 6G processing unit can change the search result to a 6G reporting format. For the above change, the cell search result performed by the 5G processing unit of the terminal can be processed into a 6G format at the RRC level. However, this is only an example, and the cell search result can be further processed in the form of a layer 1 or layer 2 signal depending on the setting. Layer 1 refers to the PHY level, and layer 2 can include, for example, the MAC level. The 5G cell search result measured to be transmitted from the 5G processing unit of the terminal to the 6G processing unit can include at least one of a cell ID, link quality based on L1 measurement for each cell, or link quality based on L3 measurement for each cell. In the case of L1 measurement, considering that information sharing between chips is limited, it can be transmitted in the form of a burst of L1 measurement that simultaneously transmits multiple L1 measurements measured for different RSs for each cell, or measured at different times, in different frequency domains, or through different radio resources. Multiple L3 measurements can also be transmitted for each cell. Alternatively, the 5G cell search result can include a beam ID, link quality based on L1 measurement for each beam, and link quality based on L3 measurement for each beam, and as described above, burst L1 measurement, multiple L3 measurements for each beam, etc. can be defined and measured, and the measurement results can be transmitted to the 6G processing unit of the terminal.

[0078] The 6G processing unit of the terminal can perform reporting on neighboring cells to the 6G network. The reporting on the neighboring cells can be performed periodically. In addition, the reporting on the neighboring cells can be defined or configured so that the 6G processing unit of the terminal performs the reporting at a fixed or set time or within a set time after accepting the request upon a network request. Alternatively, the reporting on the neighboring cells can be performed based on whether a predefined or set event is met. In the case of periodic reporting, the 6G processing unit of the terminal can be configured to periodically report only the search results for high priority cells. Alternatively, the 6G processing unit of the terminal can be configured to perform reporting on the search results for each cell by priority. In addition, when multiple neighboring cells are reported simultaneously, the number of cells reporting simultaneously can be configured. In addition, information to be included in the report can be configured. For example, it can be set to report only cell ID and L3 link quality, it can be set to report cell ID and the most recently measured 'n' L1 measurements for each cell, it can be set to report cell ID and beam ID for each cell and L3 measurements for each beam, and it can be set to report a combination of various other information. When periodic reporting is set, information for one or more reports can be set, and each piece of information set for a report can include at least one of a reporting period, a time offset in the report, a radio resource used for the report, a radio resource used for the measurement or search, a cell that is the target of the report or search, or content included in the report. In addition, when multiple reports are set, the above information can be set differently for each setting for each report.

[0079] When 5G neighboring cell reporting is set to be performed based on event setup and determination of whether the event is satisfied, the event may be set to include a condition for one or more parameters of 6G serving cell link quality, 6G neighboring cell link quality, 6G candidate cell link quality, and 5G neighboring cell link quality. Each of the cell link qualities may include a cell specific link quality measurement, a beam specific link quality measurement, a measurement duration for decision, etc. The measurement duration includes information about a time period during which a measurement result, for example, a cell specific link quality measurement value, must satisfy a link quality condition, for example, a condition of -80 dBm or higher. An event may be configured to include a number of target objects indicating how many other measurement results or how many RSs the measurement results target must satisfy the condition, and may be configured to include parameters such as a target bandwidth indicating how wide a band the condition must be satisfied across.When setting the above event, the content of the report generated by the event and the wireless resources used for the report can be set. It is also possible to set multiple events, and the event settings described above can be set independently for each event, and some or all of the settings described above can be set and applied identically across multiple set events.

[0080] As a third step operation (430), the 6G network may set a candidate cell based on the report in the second step operation (420) and transmit it to the terminal. Alternatively, the 6G network may modify a 5G neighboring cell list based on neighboring cell measurement information reported in the second step operation (420) and transmit the updated 5G neighboring cell list to the terminal. The 6G network may instruct the terminal to stop the 5G neighboring cell search operation. The 6G processing unit of the terminal may transmit the updated neighboring cell list to the 5G processing unit of the terminal. The 6G processing unit of the terminal may transmit the updated neighboring cell list converted into a 5G RRC configuration format, for example, to the 5G processing unit of the terminal. However, this is only an example, and the updated neighboring cell list may be further processed in the form of a layer 1 or layer 2 signal depending on the setting. The 5G processing unit of the terminal may, based on the updated neighboring cell list, suspend the neighboring cell search operation or reduce the frequency of the search or the number of cells to be searched in order to perform more detailed measurements on candidate cells. Alternatively, the 5G processing unit of the terminal may reduce the number of RSs used for the search for each cell, or reduce the number or types of measurements used for the search. The above terminal operation may be defined by a standard or set by the 5G or 6G network, or the terminal may notify the 5G or 6G network of the above change after it is determined by the terminal. For example, after the 5G processing unit of the terminal determines, the determined information is converted into a 6G format and transmitted to the 6G processing unit, and the 6G processing unit may notify the 6G network of this.Alternatively, the 5G or 6G network may recognize that the terminal operation is performed by defining a capability that represents the terminal's ability to search for neighboring cells and measure candidate cells. For example, a terminal capability may be defined that represents the sum of the number of neighboring cell search targets that the terminal can support and the number of candidate cell measurement targets. For example, if the capability is defined as the number of supported non-serving cell search RSs in the terminal being 20 and the base station has configured three candidate cells and five measurement RSs for each candidate cell, the 6G network may recognize that the terminal will perform measurements on up to five RSs for neighboring cell search.

[0081] The above candidate cell configuration is a process in which a terminal recognizes a corresponding cell and transmits to the terminal a series of information necessary for measuring and reporting link quality for the corresponding cell. For this purpose, at least one of the candidate cell ID, information on the RS to be measured, information necessary for performing the RS measurement, information on the radio resources used to report the measurement results, or information on the time difference allowed between measurement and reporting when performing the measurement and reporting may be transmitted to the terminal. The above information may be set through separate configuration parameters for each candidate cell, or some of the above information may be set as part of a serving cell configuration. For example, information on each candidate cell may be set in the form of a candidate cell configuration, and information on the measured RS of each candidate cell may be set as part of a serving cell configuration. Information or part of the information regarding the above candidate cell configuration may be transmitted to a 5G network unit responsible for the 5G candidate cell, or information may be exchanged between a 6G network unit and a 5G network unit when configuring the above information.Through the above series of network internal operations, the 5G candidate cell recognizes that it has been selected as a candidate cell for RAT-HO, and can then be provided with the information necessary to receive uplink transmissions from the target UE. For example, the target UE may be provided with physical random access channel (PRACH) radio resources to be used for RACH (random access channel) and the information necessary for receiving the PRACH. Alternatively, the candidate cell may directly select the necessary information and then notify the 6G network unit of the same.

[0082] As a fourth step operation (440), the 6G network can trigger an inter-RAT RACH. The 6G network can instruct the terminal to transmit PRACH for a 5G candidate cell or 5G candidate cells. Since the instruction of the 6G network is performed through interworking between the 5G processing unit and the 6G processing unit in the terminal, a separate time offset or operation time can be defined between the PRACH transmission instruction and the PRACH transmission execution. The PRACH transmission is performed through the PRACH radio resource of the candidate cell set in the third step operation (430), and through this, the 5G RU / DU managing the 5G cell can recognize that the PRACH reception is for the purpose of RAT-HO. Accordingly, the 5G cell can transmit information acquired through PRACH reception, for example, information about uplink TA (timing advance), to a 6G network, for example, a 6G CU. If information about PRACH reception is not shared within a predefined or set time, the 6G network can interpret that the PRACH transmission has failed and instruct retransmission of the PRACH. Alternatively, when instructing the PRACH transmission, the 6G network can instruct two or more repeated transmissions. When repeated transmissions are instructed as described above, the 6G network notifies the 5G RU / DU managing the 5G cell of this, and the 5G RU / DU managing the 5G cell can transmit the result of the repeated transmission of the PRACH to the 6G network.For example, if three repeated transmissions are set and instructed but only one reception is successful, or only the PRACH corresponding to the second transmission among three repeated transmissions is received, the above information of the 5G network can be reported to the 6G network. When performing the repeated transmission, the 6G network can set the repeated PRACH transmissions to be performed with the same transmission power, set the independent uplink power control to be applied to each PRACH transmission, or set the power ramp-up to be performed to increase the power according to a certain standard during the repeated transmission.

[0083] Meanwhile, the above-described example is only an example, and the order of candidate cell setting of the third step operation (430) and PRACH transmission of the fourth step operation (440) may be performed interchangeably. For example, it is possible for the 6G network to instruct the 5G processing unit of the terminal to transmit PRACH to some of the 5G neighboring cells. After the 5G processing unit of the terminal transmits the PRACH, the reception result for the transmitted PRACH can be transmitted from the 5G network to the 6G network. Based on this, the 6G network can instruct the 6G processing unit of the terminal to set the 5G candidate cell.

[0084] As a fifth step operation (450), the terminal may perform link quality measurement for a 5G candidate cell and a 6G serving cell, and report the measurement result to a 6G network, for example, a serving cell. The 5G processing unit of the terminal may transmit the result of the link quality measurement based on the RS received from the 5G network to the 6G processing unit. The above measurement and reporting are based on the contents set in the third step operation (430), and the L1 measurement result for at least one of the multiple beams or multiple cells measured at different times may be reported simultaneously. Alternatively, measurement results belonging to different layer information, such as L3 measurement and L1 measurement, may be reported simultaneously. The above measurement result report, similar to the 5G neighboring cell report in the second step operation (420), may be configured to perform periodic reporting, may be instructed to report upon a network request, or may be determined by the terminal to report upon the fulfillment of a preset event. Similar to the report in the second step operation (420), the event may be defined through various measurement elements, and similar to the report in the second step operation (420), the report may be configured in various ways. The configuration of the report may be performed by changing the neighboring cell to a candidate cell in the report configuration presented in the second step operation (420).

[0085] In the sixth step operation (460), the 6G network can instruct the terminal to perform RAT-HO via a RAT-HO command. Simultaneously with the instruction, the 6G network can notify the 5G RU / DU managing the target 5G cell that the RAT-HO of the terminal has been instructed. The terminal can perform a handover to the 5G cell according to the RAT-HO command. For example, the 6G processing unit of the terminal can transmit the RAT-HO command received from the 6G network to the 5G processing unit of the terminal, and the 5G processing unit of the terminal can perform a handover to the 5G cell according to the received RAT-HO command. After the handover is completed, the 5G processing unit of the terminal reports (ACK) that the handover has been performed to the target 5G cell. The report may be performed by at least one of transmitting a PRACH / SR using a specific radio resource, transmitting a PUCCH through a preset resource, or transmitting a PUSCH through a preset resource. The 5G RU / DU managing the 5G cell that has received the report may report it to the 6G network. If the report is not performed within a predefined or preset time, the 6G network may interpret that the RAT-HO has failed and retransmit the RAT-HO command.

[0086] FIG. 5 is a diagram for explaining an operation when a terminal performs handover from a 5G cell to a 6G cell according to one embodiment of the present disclosure.

[0087] In the embodiment of FIG. 5, it is assumed that the terminal includes a 5G processing unit that performs 5G wireless protocol functions and a 6G processing unit that performs 6G wireless protocol functions. The 5G processing unit and the 6G processing unit may be implemented on a single processor, or, in another example, may be implemented on two or more processors. Furthermore, the one or more processors may be implemented on a single chip or on separate chips. For example, the 5G processor may be implemented on a 5G chip, and the 6G processor may be implemented on a 6G chip. The chips may include, for example, a modem chip.

[0088] In the present disclosure, a 6G network may mean at least one network unit among a 6G RU, DU, or CU. Additionally, a 5G network may mean at least one network unit among a 5G RU, DU, or CU.

[0089] Additionally, in the operation described with reference to FIG. 5, the operation described as being performed by the terminal means that it is performed in at least one of the 5G processing unit of the terminal or the 6G processing unit of the terminal.

[0090] In the description below, embodiments of the present disclosure can be applied by replacing 6G with the first RAT and 5G with the second RAT.

[0091] As a first step operation (510), the 6G processing unit of the terminal may perform a first search for a 6G cell, and may transmit a RAT-HO preparation request to a 6G cell that is determined to be capable of RACH after the search. The transmission may be a PRACH format transmission, and may include information that allows a 6G RU / DU / CU managing a 6G cell that receives the transmission to recognize that the transmission is a transmission requesting RAT-HO preparation. For example, the transmission may be a sequence that is distinguished from other PRACH transmissions, a transmission through radio resources, or a transmission that includes a specific index or indicator. The method of performing a transmission including the specific information may vary for each 6G cell, and the information may be broadcast or multicast in the form of cell specific information, for example, SIB. The 6G RU / DU / CU managing the 6G cell that received the above uplink transmission can notify the terminal that it has successfully received the information.

[0092] As a second step operation (520), the 6G RU / DU / CU managing the 6G cell may transmit information about radio resources to be used to share with the terminal the configuration and control information necessary to prepare for RAT-HO thereafter, to the terminal via the 6G RU / DU / CU. The transmission of the information may be in the form of a response to the first step PRACH transmission, for example, a random access response (RAR). Alternatively, the information may be transmitted by cell specific information, for example, a physical downlink shared channel (PDSCH) scheduled through a common physical downlink control channel (PDCCH), or may be notified to the terminal by indicating a specific resource among a plurality of resources notified to the terminal via an RAR in a format such as broadcasting / multicasting. While performing the above series of processes, the 6G network notifies the 5G network connected to the terminal that the above operations are being performed, thereby notifying that the RAT-HO preparation phase of the terminal has begun.

[0093] As a third step operation (530), the 6G network transmits a 6G neighboring cell list or a search target cell list to the terminal via the configured radio resources. The information about the neighboring cells is identical to the information setting method set for 6G-to-5G RAT-HO described above. In addition, the 6G network transmits to the terminal information about a 6G neighboring cell measurement and reporting method. This can be supported in the same manner as the setting for searching and reporting on 5G neighboring cells described above.

[0094] As a fourth step operation (540), the above-mentioned setting information can be transmitted from the 6G processing unit of the terminal to the 5G processing unit that controls the communication of the terminal. Since the reporting of the terminal to the 6G neighboring cell according to the above-mentioned setting is performed through the 5G processing unit, the setting for the reporting includes content for 5G radio resources rather than 6G radio resources, whereas the information for the measurement includes content for 6G radio resources, and also, information for the association between the measurement setting for the 6G radio resources and the radio resources for reporting through the 5G can be transmitted to the terminal.

[0095] According to the settings and instructions of the third step operation (530), the 6G processing unit of the terminal performs measurements on 6G neighboring cells. Reporting of the measurements is performed from the 5G processing unit of the terminal through the 5G network, and can be performed according to the settings and instructions defined in the third step operation. The measurement results of the 6G processing unit can be converted into a 5G format and transmitted to the 5G processing unit.

[0096] As a fifth step operation (550), the 6G network can transmit a 6G candidate cell configuration to the terminal through the 6G transceiver and the radio resources set in the second step operation (520). The 6G candidate cell configuration can be performed in the same manner as the candidate cell information setting for the 6G-to-5G handover described above.

[0097] As a sixth step operation (560), the 6G network transmits information about a condition for determining RAT-HO in the corresponding terminal through the radio resources set in the second step operation (520). The condition may be set to include a condition for one or more parameters among 5G serving cell link quality, 5G neighboring cell link quality, 6G candidate cell link quality, and 6G neighboring cell link quality, and each of the cell link qualities may include a cell-specific link quality measurement, a beam-specific link quality measurement, a measurement duration for decision, etc. The measurement duration includes information about a time period during which a measurement result, for example, a cell-specific link quality measurement value of -80 dBm or more, must be satisfied. It may include a number of target objects indicating how many other measurement results or measurement results targeting how many RSs must satisfy the condition, and parameters such as target bandwidth indicating how wide a band the condition must be satisfied across.

[0098] As a seventh step operation (570), the terminal can perform measurements on 6G candidate cells and 5G cells. The measurement results from the 5G processing unit of the terminal can be transmitted to the 6G processing unit of the terminal. The 6G processing unit of the terminal can convert the transmitted measurement results into a 6G format. The 6G processing unit of the terminal compares the measurement results with the RAT-HO condition defined in the sixth step operation (560), and if the condition is met, transmits a RAT-HO request to the 6G network.

[0099] As an 8th step operation (580), the 6G network can transmit a RAT-HO command to the 6G processing unit of the corresponding terminal and the corresponding 5G network. The 5G network can transmit the command to the 5G processing unit of the corresponding terminal.

[0100] Another method for supporting 5G-to-6G RAT-HO in this disclosure is to transmit necessary information to the terminal via the 5G transceiver without allocating separate radio resources for RAT-HO preparation between the 6G network and the terminal. The embodiment of FIG. 6 is an example of this. Furthermore, a method for selectively using the 6G transceiver and the 5G transceiver at each stage in which the network transmits configuration information to the terminal is also possible.

[0101] FIG. 6 is a diagram for explaining the operation when a terminal performs handover from a 5G cell to a 6G cell according to another embodiment of the present disclosure.

[0102] In the embodiment of FIG. 6, it is assumed that the terminal includes a 5G processing unit that performs 5G wireless protocol functions and a 6G processing unit that performs 6G wireless protocol functions. The 5G processing unit and the 6G processing unit may be implemented on a single processor, or, in another example, may be implemented on two or more processors. Furthermore, the one or more processors may be implemented on a single chip or on separate chips. For example, the 5G processor may be implemented on a 5G chip, and the 6G processor may be implemented on a 6G chip. The chips may include, for example, a modem chip.

[0103] In the present disclosure, a 6G network may mean at least one network unit among a 6G RU, DU, or CU. Additionally, a 5G network may mean at least one network unit among a 5G RU, DU, or CU.

[0104] Additionally, in the operation described with reference to FIG. 6, the operation described as being performed by the terminal means that it is performed in at least one of the 5G processing unit of the terminal or the 6G processing unit of the terminal.

[0105] In the description below, embodiments of the present disclosure can be applied by replacing 6G with the first RAT and 5G with the second RAT.

[0106] The first step operation (610) may correspond to the first step operation (510) of FIG. 5.

[0107] As a second step operation (620), the 6G RU / DU / CU managing the 6G cell may transmit information about radio resources to be used to share with the terminal the configuration and control information necessary to prepare for subsequent RAT-HO to the terminal via the 5G RU / DU. The transmission of the information may be in the form of a response to the first step PRACH transmission, for example, a random access response (RAR). Alternatively, the information may be transmitted by cell specific information, for example, a physical downlink shared channel (PDSCH) scheduled via a common physical downlink control channel (PDCCH), or may be notified to the terminal by indicating a specific resource among a plurality of resources notified to the terminal via the RAR in a format such as broadcasting / multicasting. The 5G processing unit of the terminal may transmit the received information to the 6G processing unit of the terminal.

[0108] As a third step operation (530), the 6G network transmits a 6G neighboring cell list, or a search target cell list, to the terminal via the 5G RU / DU. The information about the neighboring cells is identical to the information setting method set for 6G-to-5G RAT-HO described above. In addition, the 6G network transmits information about a 6G neighboring cell measurement and reporting method to the terminal via the 5G RU / DU. This can be supported in the same manner as the setting for searching and reporting on 5G neighboring cells described above. The 5G processing unit of the terminal can transmit the received information to the 6G processing unit of the terminal.

[0109] The fourth step operation (640) may correspond to the fourth step operation (540) of FIG. 5.

[0110] As a fifth step operation (650), the 6G network can transmit a 6G candidate cell configuration to the corresponding terminal via a 5G RU / DU. The 6G candidate cell configuration can be performed in the same manner as the candidate cell information setting for 6G-to-5G handover described above. The 5G processing unit of the terminal can transmit the received 6G candidate cell configuration to the 6G processing unit of the terminal.

[0111] As a sixth step operation (660), the 6G network transmits information about a condition for determining RAT-HO in the corresponding terminal through the 5G RU / DU. The condition may be set to include a condition for one or more parameters among 5G serving cell link quality, 5G neighboring cell link quality, 6G candidate cell link quality, and 6G neighboring cell link quality, and each of the cell link qualities may include a cell specific link quality measurement, a beam specific link quality measurement, a measurement duration for decision, etc. The above measurement duration includes information about the time period during which a measurement result, for example, a cell specific link quality measurement value, must satisfy a link quality condition, for example, a condition of -80 dBm or greater. In addition, the number of target objects may be included, indicating how many measurement results or measurement results targeting how many RSs must satisfy the condition, and parameters such as target bandwidth, indicating how wide a band the condition must be satisfied across, may be included.

[0112] The 7th step operation (670) and the 8th step operation (680) may correspond to the 7th step operation (570) and the 8th step operation (580) of FIG. 5.

[0113] FIG. 7 is a block diagram illustrating the structure of a terminal according to some embodiments.

[0114] Referring to FIG. 7, the terminal (700) may include a processor (710) and a transceiver (720). However, the components of the terminal (700) are not limited to the examples described above. For example, the terminal (700) may include more or fewer components than the components described above. The terminal (700) according to one embodiment may include one or more processors and may further include memory. In addition, the processor (710) and the transceiver (720) may be implemented in the form of a single chip.

[0115] The transceiver (720) can transmit and receive signals with a network (e.g., a base station or CU / RU / DU). Here, the signals can include control information and data. To this end, the transceiver (720) can be configured with an RF transmitter that up-converts and amplifies the frequency of a transmitted signal, and an RF receiver that low-noise amplifies and frequency-converts a received signal. However, this is only one embodiment of the transceiver (720), and the components of the transceiver (720) are not limited to the RF transmitter and RF receiver.

[0116] Additionally, the transceiver (720) can receive a signal through a wireless channel and output it to the processor (710), and transmit a signal output from the processor (710) through the wireless channel.

[0117] The processor (710) may implement the 5G processing unit and the 6G processing unit described above. However, this is only an example, and a processor performing the function of the 5G processing unit and a processor performing the function of the 6G processing unit may each be present.

[0118] The processor (710) can store programs and data required for the operation of the terminal (700). In addition, the processor (710) can store control information or data included in a signal acquired from the terminal (700). The processor (710) may include a memory configured as a storage medium or a combination of storage media, such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD. However, this is merely an example, and the memory may exist separately from the processor (710).

[0119] Additionally, the processor (710) can control a series of processes so that the terminal (700) can operate according to the operation of the 5G processing unit or the 6G processing unit in the above-described embodiment.

[0120] FIG. 8 is a block diagram illustrating the structure of a network unit according to some embodiments.

[0121] The network unit (800) may be at least one of a 5G RU / DU / CU, or at least one of a 6G RU / DU / CU. For example, the network unit (800) may be a 5G CU, or may be a 6G CU including some of the functions of a 5G CU. In another example, the network unit (800) may be a combination of a 5G DU and a CU. In the present disclosure, the network unit (800) may also be described as a base station.

[0122] Referring to FIG. 8, the network unit (800) may include a transceiver (820) and a processor (810). Depending on the communication method of the network unit (800) described above, the transceiver (820) and the processor (810) of the base station may operate. However, the components of the network unit (800) are not limited to the examples described above. The network unit (800) may include more or fewer components than the components described above. For example, the network unit (800) may include one or more processors or may further include memory. In addition, the transceiver (820) and the processor (810) may be implemented in the form of a single chip.

[0123] The transceiver (820) can transmit and receive signals with the terminal. Here, the signals may include control information and data. To this end, the transceiver (820) may be configured with an RF transmitter that up-converts and amplifies the frequency of a transmitted signal, and an RF receiver that low-noise amplifies and down-converts the frequency of a received signal. However, this is only one embodiment of the transceiver (820), and the components of the transceiver (820) are not limited to the RF transmitter and RF receiver.

[0124] Additionally, the transceiver (820) can receive a signal through a wireless channel and output it to the processor (810), and transmit the signal output from the processor (810) through the wireless channel.

[0125] The processor (810) can store programs and data required for the operation of the network unit (800). In addition, the processor (810) can store control information or data included in a signal obtained from the network unit (800). The processor (810) can include a memory configured as a storage medium or a combination of storage media, such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD.

[0126] The processor (810) can control a series of processes so that the network unit (800) can operate according to the embodiment of the present disclosure described above.

[0127] The above descriptions focus on how a terminal connected to a 5G or 6G network receives information about a neighboring cell or candidate cell for a heterogeneous network and performs measurement and reporting based on the information. However, the terminal may be configured to measure and report on neighboring / candidate cells for a heterogeneous network and neighboring / candidate cells for the same network, and may perform the above operations simultaneously. For example, the terminal may be instructed to perform reporting on candidate cells for a heterogeneous network and candidate cells for the same network simultaneously through reporting configuration. In this case, the terminal may be configured to report on 'n' candidate cells with the best link quality among all candidate cells, and the terminal may be configured to configure the report content by simultaneously considering measurement results for cells of other RATs.

[0128] In the present disclosure, the processor may include at least one of a conventional general-purpose processor (e.g., a central processing unit (CPU) or an application processor) or a graphics-only processor (e.g., a graphics processing unit (GPU)). The methods according to the embodiments described in the claims or specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software. In the case of software implementation, a computer-readable storage medium storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors in a terminal or base station. The one or more programs include instructions that cause an electronic device to execute the methods according to the embodiments described in the claims or specification of the present disclosure.

[0129] In the specific embodiments of the present disclosure described above, components included in the invention are expressed singularly or plurally, depending on the specific embodiment presented. However, the singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present disclosure is not limited to singular or plural components. Components expressed in plural may be composed of singular elements, or components expressed in singular may be composed of plural elements.

[0130] Meanwhile, the embodiments of the present disclosure disclosed in this specification and drawings are merely specific examples to easily explain the technical content of the present disclosure and facilitate understanding of the present disclosure, and are not intended to limit the scope of the present disclosure. In other words, it will be apparent to those skilled in the art to which the present disclosure pertains that other modifications based on the technical concept of the present disclosure are possible. Furthermore, the above-described embodiments may be combined and operated as needed.

Claims

1. In a method for a terminal to perform handover between RATs (radio access technology), A step in which a first RAT processing unit of a terminal connected to a cell of a first RAT receives information about at least one cell of a second RAT from a network unit of the first RAT; A step of converting, in a first RAT processing unit of the terminal, a format of information about at least one cell of the second RAT from an RRC (radio resource control) format of the first RAT to an RRC format of the second RAT; A step of transmitting information about at least one cell of the converted second RAT to the second RAT processing unit of the terminal; A step of performing a search for at least one cell of the second RAT based on configuration information for at least one cell of the converted second RAT in the second RAT processing unit of the terminal; and A method comprising the step of transmitting a report on the search result from the first RAT processing unit of the terminal to the network unit of the first RAT.

2. In paragraph 1, A method further comprising the step of receiving configuration information about at least one cell set based on a report on the search result from a network unit of the first RAT.

3. In paragraph 1, A step of receiving a PRACH transmission instruction for a cell of the second RAT from a network unit of the first RAT; and A method further comprising the step of transmitting a PRACH to a network unit of the second RAT based on the PRACH transmission instruction.

4. In paragraph 2, A step of receiving RS (reference signal) from each of the cell of the first RAT and the cell of the second RAT based on configuration information about at least one cell; and A method further comprising the step of determining the link quality of the first RAT and the link quality of the second RAT based on each of the received RSs.

5. In paragraph 4, A step of performing a report on the link quality of the first RAT and the link quality of the second RAT to the network unit of the first RAT; and A method further comprising the step of receiving a handover command from a network unit of the first RAT to the second RAT based on the above report.

6. In paragraph 1, The above first RAT is 6G (6 th generation technology), and the second RAT is 5G (5 th generation technology) method.

7. In a method for supporting handover between RATs (radio access technology) by a network unit of the first RAT, A step of transmitting information about at least one cell of a second RAT to a terminal connected to a cell of a first RAT; and A step of receiving a report on the search result of at least one cell of the second RAT from the terminal, In the first RAT processing unit of the terminal, the format of information about at least one cell of the second RAT is converted from the RRC (radio resource control) format of the first RAT to the RRC format of the second RAT, Information about at least one cell of the converted second RAT is transmitted to the second RAT processing unit of the terminal, A method in which a search for at least one cell of the second RAT is performed based on configuration information for at least one cell of the converted second RAT in the second RAT processing unit of the terminal.

8. In paragraph 7, A method further comprising the step of transmitting configuration information about at least one cell set based on a report on the search results to the terminal.

9. In paragraph 7, Further comprising a step of transmitting a PRACH transmission instruction for a cell of the second RAT, A method in which a PRACH is transmitted from a second RAT processing unit of the terminal to a network unit of the second RAT based on the PRACH transmission instruction.

10. In paragraph 7, A step of receiving a report on the link quality of the first RAT and the link quality of the second RAT from the terminal; and A method further comprising the step of transmitting a handover command from a network unit of the first RAT to the second RAT based on the above report.

11. In a terminal performing handover between RATs (radio access technology), Transmitter and receiver; and At least one processor connected to the transceiver, wherein the at least one processor includes a first RAT processing unit and a second RAT processing unit, The first RAT processing unit of a terminal connected to a cell of the first RAT receives information about at least one cell of the second RAT from a network unit of the first RAT, In the first RAT processing unit, the format of information for at least one cell of the second RAT is converted from the RRC (radio resource control) format of the first RAT to the RRC format of the second RAT, Transmitting information about at least one cell of the converted second RAT to the second RAT processing unit, In the second RAT processing unit, a search is performed for at least one cell of the second RAT based on the configuration information for at least one cell of the converted second RAT, A terminal that transmits a report on the search results from the first RAT processing unit to the network unit of the first RAT.

12. In the 11th paragraph, the first RAT processing unit, A terminal that receives configuration information about at least one cell based on a report on the search result from the network unit of the first RAT.

13. In paragraph 11, The first RAT processing unit receives a PRACH transmission instruction for a cell of the second RAT from a network unit of the first RAT, A terminal, wherein, based on the PRACH transmission instruction, the second RAT processing unit transmits a PRACH to a network unit of the second RAT.

14. In the 12th paragraph, the at least one processor, Receive each RS (reference signal) from a cell of the first RAT and a cell of the second RAT based on configuration information about at least one cell, A terminal that determines the link quality of the first RAT and the link quality of the second RAT based on each of the received RSs.

15. In the network unit of the first RAT supporting handover between RATs (radio access technology), Transmitter and receiver; and At least one processor connected to the transceiver, wherein the at least one processor: Transmitting information about at least one cell of a second RAT to a terminal connected to a cell of a first RAT, Receive a report on the search results of at least one cell of the second RAT from the terminal, In the first RAT processing unit of the terminal, the format of information about at least one cell of the second RAT is converted from the RRC (radio resource control) format of the first RAT to the RRC format of the second RAT, Information about at least one cell of the converted second RAT is transmitted to the second RAT processing unit of the terminal, A network unit of a first RAT, in which a search for at least one cell of the second RAT is performed based on configuration information for at least one neighboring cell of the converted second RAT in the second RAT processing unit of the terminal.

Images