KR20240090117A - Handover method and apparatus for multiple transmission and reception points - Google Patents

Abstract

The terminal's method for handover includes: detecting a beam change within a dual access TRP (transmission and reception point) through a beam search procedure; reporting a beam search result indicating a change in the beam to a serving DU (distributed unit) through the dual connectivity TRP; Receiving a command message instructing DU switching for switching the serving TRP to the target TRP from a central unit (CU) connected to the terminal through the dual connectivity TRP; And it may include performing a connection procedure to the target DU.

Description

Handover method and device for multiple transmission/reception points {HANDOVER METHOD AND APPARATUS FOR MULTIPLE TRANSMISSION AND RECEPTION POINTS}

The present invention relates to handover technology, and more specifically, to a method/device for implementing a borderless cell by overcoming the decrease in wireless signal performance at the boundary of a cell/TRP in an environment where multiple transmission/reception points are used, and a wireless interface for the same. It relates to an operation method/device of the DU interface.

In a mobile communication system, a base station connected to a network can provide wireless connection to terminals moving in a certain area. The terminal can be bidirectionally connected to the network through the process of bidirectionally exchanging data with the connected base station. A moving terminal can maintain connection to the network by changing the connected base station using a handover method. The base station can proactively manage resources within the wireless area that provides connectivity to the terminal. A terminal managed by a base station can exchange data with the base station through the process of transmitting and receiving wireless signals in two allocated resources.

Base stations can be configured in various ways depending on the size of the area providing connectivity. Base stations providing various areas can be deployed overlappingly to provide wireless access to terminals. In general, the size of the area provided by a base station is dependent on frequency and decreases as the frequency increases. A plurality of transmission and reception points (TRPs) are devices that transmit and receive wireless signals to and from a terminal, form part of a base station, and can form the base station at the same location or in dispersed locations. The base station may be configured in a manner where the wireless access functions are centralized or in a manner where the functions are distributed. A base station with distributed wireless access functions may be composed of a central unit (CU) that provides upper functions and a distributed unit (DU) that provides lower functions.

The purpose of the present invention to solve the above problems is to provide a method and device for handover of a terminal in an environment where multiple transmission/reception points are used.

Another purpose of the present invention to solve the above problems is to provide a method and device for handover of a terminal for a dual access TRP.

The present invention for achieving the above object is a method of a terminal for handover, comprising: performing a procedure for searching for adjacent TRPs including a target TRP (transmission and reception point); Transmitting a neighbor TRP information report message including information about the discovered neighbor TRPs to the current serving TRP; Receiving, from a distributed unit (DU) to which the terminal is connected, a command message instructing TRP switching to switch the serving TRP of the terminal from the current serving TRP to the target TRP through the serving TRP; and performing a connection procedure for the target TRP according to the command message instructing the TRP switching, wherein the TRP switching may be determined based on the neighbor TRP information reporting message.

The current serving TRP and the target TRP may be TRPs commonly connected to the DU.

The neighbor TRP information report message may include the beam identifier of the target TRP.

The method includes: transmitting a TRP switching complete message to the DU; And it may further include receiving a TRP switching acknowledgment message from the DU.

The present invention for achieving the above other object is a method of a terminal for handover, comprising: detecting a beam change within a dual access transmission and reception point (TRP) through a beam search procedure; reporting a beam search result indicating a change in the beam to a current serving distributed unit (DU) through the dual connectivity TRP; Receiving a command message instructing DU switching to switch the serving DU of the terminal from the current serving DU to the target DU from a central unit (CU) to which the terminal is connected through the dual connectivity TRP; And it may include performing a connection procedure to the target DU.

The DU switching may be determined in the current serving DU and notified to the CU, or may be determined by the CU based on the beam search result from the terminal.

The current serving DU is a master DU connected to the dual connectivity TRP and the target DU is a secondary DU connected to the dual connectivity TRP, or the current serving DU is a secondary DU connected to the dual connectivity TRP and the target The DU may be a master DU connected to the dual connectivity TRP.

Radio resources managed by the current serving DU may be mutually exclusive with radio resources managed by the target DU.

The command message instructing DU switching may be a radio resource control (RRC) reconfiguration message.

The command message instructing the DU switching may be transmitted through radio resources managed by the current serving DU.

The access procedure to the target DU may be performed through radio resources managed by the target DU.

The method includes: transmitting a DU change complete message to the CU; And it may further include receiving an acknowledgment message for the DU change completion message transmitted by the terminal from the CU.

The DU change complete message and the confirmation message are transmitted and received through radio resources managed by the current serving DU, the DU change complete message is an RRC reconfiguration complete message, and the confirmation message is a radio link control (RLC) message. ) It may be an ACK (acknowledgement) message.

The method further includes receiving a synchronization signal/physical broadcast channel (SS/PBCH) of the CU, a system information block (SIB) associated with the current serving DU, and a SIB associated with the target DU from the dual connectivity TRP. It can be included.

The present invention for achieving the above other object is a method of a terminal, which receives a master information block (MIB) from a master distributed unit (DU) connected to the first TRP through a first transmission and reception point (TRP). receiving; And receiving, through the first TRP, a first system information block (SIB) of the master DU and a second SIB of a first secondary DU connected to the first TRP, and the master DU and At least one secondary DU including the first secondary DU belongs to the same central unit (CU) or different CUs, and different radio resources may be allocated to the master CU and the first secondary DU.

The MIB includes information on resources for reception of the first SIB and can be received through radio resources allocated to the master DU.

The first SIB may include information related to reception of the second SIB.

The first SIB may include information about resources for receiving the second SIB.

At least a portion of the second SIB may be received while being included in the first SIB.

Common information of the first SIB and the second SIB is received through resources allocated to the master DU, and difference information between the first SIB and the second SIB is received through resources allocated to the first secondary DU. It can be.

Embodiments of the present invention can provide a method for transmitting SS/PBCH and SIB of a dual connectivity TRP and an initial access procedure for the dual connectivity TRP. Additionally, embodiments of the present invention can provide a TRP switching method and a DU switching method for a terminal in a communication system in which multiple TRPs exist and in a communication system in which a dual access TRP exists. Therefore, according to the embodiments of the present invention as described above, the mobility of the terminal can be efficiently supported in a communication system in which multiple TRPs exist and a communication system in which a dual access TRP exists.

1 is a conceptual diagram illustrating an embodiment of a wireless communication network.
Figure 2 is a block diagram showing an example of a communication node constituting a wireless communication network.
FIG. 3 is a diagram illustrating the connection between a base station and a core network in a wireless communication network using a distributed base station to which the present disclosure can be applied.
Figure 4 is a configuration diagram for explaining the connection of base stations with a plurality of TRPs according to an embodiment of the present disclosure.
Figure 5 is a diagram illustrating a hierarchical configuration of base stations including a dual access TRP according to the present disclosure.
Figure 6a is a conceptual diagram of a base station network to explain the connection between DU and TRP according to an embodiment of the present disclosure.
FIG. 6B is an example diagram illustrating handover of a single access TRP according to an embodiment of the present disclosure.
FIG. 6C is an example diagram illustrating handover of a single access TRP according to another embodiment of the present disclosure.
FIG. 6D is an example diagram illustrating handover of a single access TRP according to another embodiment of the present disclosure.
FIG. 6E is an example diagram illustrating handover of a dual connectivity TRP according to an embodiment of the present disclosure.
FIG. 6F is an example diagram illustrating handover of a dual access TRP and coordinated multi-point (CoMP) transmission and reception of multiple transmission and reception points according to an embodiment of the present disclosure.
Figure 7a is an example diagram to explain direct connection methods between DU and RU constituting a base station.
Figure 7b is an example diagram to explain relay connection methods between DU and RU constituting the base station.
Figure 7c is an example diagram to explain connection methods between base stations in which DUs and RUs constituting the base station are different.
Figure 8 is an example diagram to explain transmission processing time based on connection methods between DU and RU constituting the base station.
Figure 9 is an example diagram configuring a network with dual access TRP according to an embodiment of the present disclosure.
Figure 10 is an example diagram for explaining SS/PBCH transmission areas and SIB transmission areas according to an embodiment of the present disclosure.

Since the present disclosure can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present disclosure to specific embodiments, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present disclosure.

Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, a first component may be referred to as a second component, and similarly, the second component may be referred to as a first component without departing from the scope of the present disclosure. The term “and/or” includes any of a plurality of related stated items or a combination of a plurality of related stated items.

In embodiments of the present disclosure, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B.” Additionally, in embodiments of the present disclosure, “one or more of A and B” may mean “one or more of A or B” or “one or more of combinations of one or more of A and B.”

When a component is said to be "connected" or "connected" to another component, it is understood that it may be directly connected to or connected to the other component, but that other components may exist in between. It should be. On the other hand, when it is mentioned that a component is “directly connected” or “directly connected” to another component, it should be understood that there are no other components in between.

The terms used in this disclosure are only used to describe specific embodiments and are not intended to limit the disclosure. Singular expressions include plural expressions unless the context clearly dictates otherwise. In the present disclosure, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the technical field to which this disclosure pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted in an idealized or overly formal sense unless explicitly defined in the present disclosure. No.

Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In order to facilitate overall understanding in explaining the present disclosure, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

A communication network to which embodiments according to the present disclosure are applied will be described. The communication network may be a 4G communication network (e.g., long-term evolution (LTE) communication network, LTE-A communication network), a 5G communication network (e.g., new radio (NR) communication network), a 6G communication network, etc. there is. The 4G communication network can support communication in frequency bands below 6GHz, and the 5G communication network can support communication in frequency bands above 6GHz as well as frequency bands below 6GHz. Communication networks may include terrestrial networks and non-terrestrial networks. The communication networks to which the embodiments according to the present disclosure are applied are not limited to those described below, and the embodiments according to the present disclosure can be applied to various communication networks. Here, communication network may be used in the same sense as communication system, “LTE” may indicate “4G communication network”, “LTE communication network” or “LTE-A communication network”, and “NR” may indicate “5G communication network”. It may refer to “communication network” or “NR communication network”.

In an embodiment, “an operation (e.g., a transmission operation) being set in a communication node” means “setting information (e.g., an information element, parameter) for the operation” and/or “the corresponding operation.” This may mean that “information instructing the performance of” is signaled to the communication node. In other words, “an operation (e.g., a transmission operation) being set in a communication node” means that the communication node provides “setting information (e.g., information element, parameter) for the operation” and/or “the corresponding operation.” It may mean receiving “information instructing the performance of.” “An information element (e.g. a parameter) is set at a communication node” means “the information element is signaled to the communication node (e.g. the communication node receives the information element)” It can mean.

Signaling includes system information (SI) signaling (e.g., transmission of system information block (SIB) and/or master information block (MIB)), RRC signaling (e.g., transmission of RRC parameters and/or upper layer parameters) , MAC control element (CE) signaling, or PHY signaling (e.g., transmission of downlink control information (DCI), uplink control information (UCI), and/or sidelink control information (SCI)). The signaling message may be an SI signaling message (e.g. SI message), an RRC signaling message (e.g. RRC message), a MAC CE signaling message (e.g. MAC CE message, MAC message), or a PHY signaling message (e.g. For example, it may be at least one of a PHY message).

In a mobile communication system, a base station connected to a network can provide wireless connectivity to mobile terminals within a certain area (coverage). A mobile terminal can be bidirectionally connected to the network through a process of bidirectionally exchanging data with a base station to which the mobile terminal is connected. The mobile terminal can maintain connection to the network while changing the connected base station according to the handover method. The base station can proactively manage resources within the area that provides connectivity to the terminal. A terminal managed by a base station can exchange data with the base station through the process of transmitting and receiving wireless signals in permitted resources.

Base stations can be configured in various ways depending on the size of the area providing connectivity. Base stations providing various areas can be arranged in an overlapping manner to provide wireless access to terminals. In general, the size of the area provided by a base station is dependent on frequency and decreases as the frequency increases. A plurality of transmission and reception points (TRPs) are devices that transmit and receive wireless signals to and from a terminal and form part of a base station, and may form a base station at the same location or at dispersed locations. The base station may be configured in a manner where the wireless access function is centralized or in a manner where the wireless access function is distributed. A base station configured with distributed wireless access functions may be composed of a central unit (CU) that provides upper-level functions and a distributed unit (DU) that provides lower-level functions.

The terminal transmits and receives wireless signals with cells provided by the base station in the wireless section, and can transmit and receive data using a hierarchical wireless access protocol that performs a wireless access function. Service packets generated at the service layer can be delivered to the other party through a wireless access protocol. The base station can distribute the wireless access protocol to distributed devices in functional units, and can be composed of a set of these distributed devices. The wireless access function provided by the wireless access protocol generally uses a single frequency band and can be performed in the bandwidth part (BWP) within the band. Methods of using multiple frequency bands can be classified into carrier aggregation (CA) and dual connectivity (DC) depending on the configuration of the wireless access protocol.

A method of using frequencies in the terahertz band is multi-transmission point (Multi-TRP) technology. One TRP can configure a short service radius for wireless communication with the terminal. For a moving terminal, the signal suddenly decreases at the boundary of the TRP, causing a decrease in the quality of the wireless signal. Therefore, a method that allows a terminal to receive wireless signals with high quality at the TRP boundary is required.

1. Wireless communication network

1.1. wireless communication network

A wireless communication network to which embodiments according to the present invention are applied will be described. The wireless communication networks to which the embodiments according to the present invention are applied are not limited to those described below, and the embodiments according to the present invention can be applied to various wireless communication networks. Here, a wireless communication network may be used in the same sense as a wireless communication system.

1 is a conceptual diagram illustrating an embodiment of a mobile communication network to which embodiments of the present invention are applied.

Referring to FIG. 1, the mobile communication network 100 may include a plurality of communication nodes 110, 111, 120, 121, 140, 150, 180, 190, 191, 192, 193, 194, and 195. . Each of the plurality of communication nodes may support at least one communication protocol. For example, each of the plurality of communication nodes may use a communication protocol based on code division multiple access (CDMA), a communication protocol based on wideband CDMA (WCDMA), a communication protocol based on time division multiple access (TDMA), and a frequency division multiple access (FDMA)-based communication protocol. access)-based communication protocol, OFDM (orthogonal frequency division multiplexing)-based communication protocol, OFDMA (orthogonal frequency division multiple access)-based communication protocol, SC (single carrier)-FDMA-based communication protocol, NOMA (Non-orthogonal Multiple) Access) and SDMA (Space Division Multiple Access)-based communication protocols can be supported.

The mobile communication network 100 includes a plurality of base stations (BS: base stations, 110, 111, 120, 121, 140, 150) and a plurality of terminals (UE: user equipments, 190, 191, 192, 193, 194, 195, 180). Each of the plurality of base stations 110, 111, and 140 may form a macro cell. or. Each of the plurality of base stations 120, 121, and 150 may form a small cell. A plurality of terminals 190 and 191 may belong to the cell coverage of the base station 110. A plurality of base stations 120 and 121 and a plurality of terminals 191, 192, 193, 194 and 195 may belong to the cell area of the base station 111. The base station 150 and a plurality of terminals 191, 192, and 180 may belong to the cell area of the base station 140.

A plurality of communication nodes (110, 111, 120, 121, 140, 150, 180, 190, 191, 192, 193, 194, 195) each perform cellular communication (e.g., 3rd generation partnership project (3GPP) ) It can support the wireless access protocol specifications of wireless access technology based on (LTE (long term evolution), LTE-A (advanced), NR (new radio), etc.) specified in the standard. Each of the plurality of base stations 110, 111, 120, 121, 140, and 150 may operate in a different frequency band or may operate in the same frequency band. Each of the plurality of base stations 110, 111, 120, 121, 140, and 150 may be connected to each other through an ideal backhaul or a non-ideal backhaul, and may be connected to each other through an ideal backhaul or a non-ideal backhaul. We can exchange information with each other. Each of the plurality of base stations 110, 111, 120, 121, 140, and 150 may be connected to a core network (not shown) through a backhaul. Each of the plurality of base stations (110, 111, 120, 121, 140, 150) can transmit data received from the core network to the corresponding terminal (190, 191, 192, 193, 194, 195, 180), and the corresponding terminal Data received from (190, 191, 192, 193, 194, 195, 180) can be transmitted to the core network.

Each of the plurality of communication nodes (110, 111, 120, 121, 140, 150, 180, 190, 191, 192, 193, 194, 195) constituting the wireless communication network 100 has a beam forming function using multiple antennas. Through the beam formed, signals can be exchanged with the other communication node without interference.

Each of the plurality of base stations 110, 111, 120, 121, 140, and 150 transmits multiple input multiple output (MIMO) using multiple antennas (e.g., single user (SU)-MIMO, multi-user ( multi user (MU)-MIMO, massive MIMO, etc.), coordinated multipoint (CoMP) transmission, frequency aggregation (CA) transmission, unlicensed band transmission, direct terminal-to-device transmission It can support device to device communication (D2D), proximity services (ProSe), dual connectivity transmission, etc.

Each of the plurality of base stations 110, 111, 120, 121, 140, and 150 includes NodeB, evolved NodeB, gNB, ng-eNB, radio base station, access point, and access node. It may be referred to as an access node, node, radio side unit (RSU), etc. Each of the plurality of terminals 190, 191, 192, 193, 194, 195, and 180 is a user equipment (UE), a terminal, an access terminal, a mobile terminal, and a station. , subscriber station, mobile station, portable subscriber station, node, device, internet of thing (IoT) device, mounted module /device/terminal or on board device/terminal, etc.). The content of the present invention is not limited to the terms mentioned above and can be replaced with other terms that perform the corresponding function depending on the wireless access protocol according to radio access technology (RAT) and the functional configuration supporting the same.

1.2. communication node

Figure 2 is a block diagram showing an example of a communication node constituting a mobile communication network.

Referring to FIG. 2, the communication node 200 may include at least one processor 210, a memory 220, and a transmitting and receiving device 230 that is connected to a network and performs communication. Additionally, the communication node 200 may further include an input interface device 240, an output interface device 250, a storage device 260, etc. Each component included in the communication node 200 is connected by a bus 270 and can communicate with each other.

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260. The processor 210 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may be comprised of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 220 may be comprised of at least one of read only memory (ROM) and random access memory (RAM).

Each of the plurality of communication nodes (110, 111, 120, 121, 140, 150, 180, 190, 191, 192, 193, 194, 195) constituting the mobile communication network 100 is in the form of a communication node 200. It can be implemented as:

1.3. Distributed base station

FIG. 3 is a diagram illustrating the connection between a base station and a core network in a wireless communication network using a distributed base station to which the present disclosure can be applied.

Referring to FIG. 3, in a wireless communication network 300 including a core network 380, base stations 310, 311, and 312 are connected to the end node 381 of the core network 380 by backhaul. You can.

In addition, the base stations 310, 311, and 312 transmit data exchanged between the plurality of terminals 390, 391, and 392 and the core network 380 in a bidirectional manner, that is, from the plurality of terminals 390, 391, and 392 to the core network. It can be transmitted in the direction to (380) and from the core network (380) to a plurality of terminals (390, 391, and 392).

The core network 380 illustrated in FIG. 3 may correspond to a 4G core network supporting 4G communication, a 5G core network supporting 5G communication, etc. Here, the core network 380 supporting 4G communication includes a mobility management entity (MME), a serving-gateway (S-GW), a packet data network (PDN) gateway, P-GW), etc. The core network 380 that supports 5G communication may include an Access and Mobility Management Function (AMF) entity, a User Plane Function (UPF) entity, and a P-GW.

Here, the end node 381 of the core network 380 has a user plane function to exchange packets consisting of service data with a plurality of terminals 390, 391, and 392 and a control plane function to manage the connection and mobility of the terminals. provides.

The user plane function of the end node 381 may be a serving gateway (SGW) in the case of a 4G system, a user plane function (UPF) in the case of a 5G system, and other systems. In this case, the system may be a network entity that transmits specific service data, that is, user data to a plurality of terminals 390, 391, and 392.

In the case of a 4G system, the control plane function of the end node 381 may be a mobility management entity (MME), and in the case of a 5G system, it may be an access and mobility management function (AMF). In the case of other systems, it may be a network entity for mobility management and/or session management of a plurality of terminals 390, 391, and 392 in the system.

In this disclosure, to aid understanding, the terms 'SGW', 'UPF', 'MME', and 'AMF' used in 4G networks and/or 5G networks are explained as examples. However, the present disclosure is not limited to these 4G networks and/or 5G networks, and performs the corresponding function according to the wireless access protocol according to radio access technology (RAT) and the configuration function supporting the same or the configuration function of the core network. It can be replaced with another term.

The base station 311 is composed of a set of distributed devices configured by dividing the functions of the wireless access protocol, a central unit (CU) 320 with concentrated functions, and a plurality of distributed units (DU) with distributed functions. It may be composed of (330, 331, 332, 333, 334) and a plurality of transmission and reception points (TRPs) (340, 341, 342) for transmitting and receiving signals. In FIG. 3, only the base station 311 is shown as a base station with a distributed structure, but the remaining base stations 310 and 312 may also be configured identically or similarly to the base station 311 with a distributed structure.

The central device 320, which includes the upper functions of the wireless access protocol, is connected to a plurality of distributed devices 330, 331, 332, 333, and 334 in the direction of the wireless section and the end node 381 in the direction of the core network 380. can be connected with Additionally, the central device 320 may be connected to a plurality of adjacent base stations 310 and 312.

Each of a plurality of distributed devices (330, 331, 332, 333, 334) including sub-functions of the wireless access protocol may be connected to a plurality of transmission/reception points (351, 352, 353) located in the same geographical location, Each of the plurality of distribution devices 330 and 334 may be connected to a plurality of transmission and reception points 341, 342, 343, and 344 located in separate locations.

Each of the plurality of base stations 310, 311, and 312 may include a plurality of transmitting and receiving points for transmitting and receiving wireless signals. Each of the transmission/reception points can transmit a signal to at least one terminal (390, 391, 392) and receive a signal from at least one terminal (390, 391, 392). Each of the transmitting and receiving points can provide a signal from at least one terminal 390, 391, and 392 to the central device through a distribution device connected to it.

Each of the plurality of transmission/reception points (341, 342, 343, 344, 361, 362, 363) may be operated independently or in cooperation with adjacent transmission/reception points. The operation of the plurality of transmitting and receiving points 341, 342, 343, 344, 361, 362, and 363 will be further explained in other drawings.

Additionally, each of the plurality of transmitting/receiving points (341, 342, 343, 344, 361, 362, 363) can use a beam forming function using multiple antennas. FIG. 3 illustrates a case where beamforming is performed using multiple antennas at the transmission/reception points 341 and 361. FIG. 3 illustrates a case in which beam forming is performed at two transmitting/receiving points 341 and 361 due to limitations in the drawing, but other transmitting/receiving points may also use the beam forming function. Each of the plurality of transmitting and receiving points (341, 342, 343, 344, 361, 362, 363) can exchange signals with the other communication node without interference through the plurality of beams (350, 352) formed. Each of the plurality of transmitting and receiving points 341, 342, 343, 344, 361, 362, and 363 includes a remote radio transceiver, a remote radio head (RRH), a wireless antenna, and a transmission point ( It may be referred to as a transmission point (TP), transmission and reception point (TRP), etc.

Each of the plurality of distributed devices 330, 331, 332, 333, and 334 may be connected to a communication node in the direction of the core network 380 by wire or wirelessly. The communication node towards the core network 380 may be another distributed device or a central device 320.

Each of a plurality of distributed devices 330, 331, and 332 connected by wire to a communication node in the direction of the core network 380 configures some functions of the base station wireless access protocol in the wireless section to provide wireless access to at least one terminal. It can be connected to the central device 320 in the wired section.

Each of the plurality of distributed devices 333 and 334, which are wirelessly connected to the communication node in the direction of the core network 380, configures some functions of the base station wireless access protocol in the wireless section to provide wireless access to at least one terminal. In the wireless section, some functions of the terminal wireless access protocol can be configured to wirelessly connect to a relay device in the direction of the central device 320 to be bidirectionally connected to the central device 320. Therefore, the distributed devices 333 and 334 wirelessly connected to the communication node in the direction of the core network 380 must have both some functions of the base station wireless access protocol and some functions of the terminal wireless access protocol.

For example, the distributed device 333 may be wirelessly connected to the distributed device 332 in the direction of the central device 32. Therefore, the distribution device 332 may be a relay device that relays the connection between the distribution device 333 and the central device 332. The distributed device 334 may be wirelessly connected to the distributed device 333 in the direction of the central device 320. Therefore, the distribution device 333 may be a relay device that relays the connection between the distribution device 334 and the central device 332. A plurality of transmission/reception points 343, 344 connected to the distribution device 334 may form a beam or be configured in an area where interference is reduced by physical methods. The transmission/reception point 343 may configure some functions of the base station wireless access protocol, and the transmission/reception point 344 may configure some functions of the terminal wireless access protocol.

When a plurality of communication nodes exchange signals using a plurality of beams (160, 161, 162, 350, 351, 352) formed by each communication node, they exchange signals through a beam paired (set) with the other node. can do. To this end, a plurality of beams of the other communication node can be searched, the reception strength of each beam can be measured, and at least one beam for exchanging signals can be set by selecting a communication node participating in communication. Additionally, at least one beam for exchanging signals, that is, a beam set by a specific communication node participating in communication, can be changed. Wireless channel quality can be maintained by changing the beam of the communication node to respond to a change in the wireless channel due to a change in wireless channel status or movement of the communication node.

Next, the structure and layer-specific functions of the wireless access protocol that provides wireless access between the base station and the terminal in a wireless communication network will be explained. In this disclosure, the structure and layered functions of the wireless access protocol are described only for the purpose of explaining specific embodiments and are not intended to limit the content of this disclosure, and include changes or substitutes included in the concept and scope of the proposed technology. can do.

1.4. wireless access protocol

The wireless access protocol provides a function for multiple communication nodes to exchange data and control information using wireless resources in a wireless section, and can be configured hierarchically. In cellular communications (e.g., 3GPP (3rd generation partnership project) standards LTE (long term evolution), LTE-A (advanced), NR (new radio), etc.), the wireless access protocol is the layer below. ) may include.

1) Radio layer 1 (RL1), which constitutes the physical signal,

2) Radio layer 2 (RL2), which controls wireless transmission on wireless resources shared by a plurality of communication nodes and transmits and matches data to the other node, and

3) Radio layer 3 (RL3), which controls radio resources such as network information sharing, wireless connection management, mobility management, and QoS (quality of service) management for multiple communication nodes participating in the wireless network.

Wireless layer 1 is the physical layer and can provide functions for data transmission. Wireless layer 2 includes medium access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), and service data adaptation protocol (SDAP). ), etc. may be composed of sub-layers. Wireless layer 3 is a radio resource control (RRC) layer and can provide AS layer control functions.

In relation to the operation of the timer defined or explained in the present invention, operations such as start, stop, reset, restart, or expiration of the timer do not need to be separately explained. It means or includes the operation of the timer or the counter for the timer.

Next, operating methods of a communication node in a wireless communication network will be described. Even when a method (e.g., transmission or reception of a signal) performed in a first communication node among communication nodes is described, the corresponding second communication node is described as a method (e.g., transmitting or receiving a signal) corresponding to the method performed in the first communication node. For example, reception or transmission of a signal) can be performed. That is, when the operation of the terminal is described, the corresponding base station can perform the operation corresponding to the operation of the terminal. Conversely, when the operation of the base station is described, the corresponding terminal can perform the operation corresponding to the operation of the base station.

FIG. 4 is a configuration diagram illustrating the connection of base stations with a plurality of TRPs according to an embodiment of the present disclosure.

Referring to FIG. 4, the internal configuration of the base stations 401 and 402 are respectively illustrated. The base station 401 exemplifies a form including a CU 410, DUs 411, 412, and RUs/TRPs (431, 432, 433, 434, 435, 436). Additionally, the base station 402 illustrates a form including a CU 420, DUs 421, 422, and RUs/TRPs 436, 437, 438, 439, 440, 441, 442. In the example of FIG. 4, the base stations 401 and 402 will be described assuming that they are gNBs according to the 5G communication system.

The DU 411 included in the base station 401 is connected to three different TRPs 431, 432, and 433, and the DU 412 included in the base station 401 is connected to four different TRPs 433 and 433. 434, 435, 436). The DU 421 included in the base station 402 is connected to four different TRPs (436, 437, 4438, 439), and the DU 422 included in the base station 402 is also connected to four different TRPs ( 439, 440, 441, 442).

In the present disclosure illustrated in FIG. 4, RUs/TRPs assume a form in which one RU corresponds to one TRP. According to one embodiment of the present disclosure, one RU may correspond to one TRP. According to another embodiment of the present disclosure, multiple TRPs may correspond to one RU. According to another embodiment of the present disclosure, one TRP may correspond to multiple RUs. Corresponding here means that each component can be connected by wire or based on a wireless communication method. Therefore, in the present disclosure, except in cases where RU and TRP are specifically described, TRP may be understood as RU.

TRPs according to the present disclosure can be divided into single access TRP (Single Access TRP) and dual access TRP (Dual Access TRP) depending on the connection state. Referring to Figure 4, single connection TRPs (431, 432, 435, 437, 438, 440, 441, 442) and dual connection TRPs (433, 436, 439) are illustrated.

2. Dual Access TRP

Dual access TRP can be connected to one or multiple gNBs and can transmit signals from the gNB to the terminal and receive signals from the terminal. More specifically, the TRP may include a function of generating a wireless signal from data received from the gNB and transmitting it to the terminal, or generating data to be transmitted to the gNB from a wireless signal received from the terminal. In other words, the TRP corresponds to a device that performs the function of transmitting and receiving wireless signals and is a part of a base station, for example, gNB, as illustrated in FIG. 4. The TRP described above may be understood as RU.

The TRP 433 included in the base station 401 is connected to different DUs 411 and 412 within the same base station 401. Additionally, the TRP 439 included in the base station 402 is connected to different DUs 421 and 422 within the same base station 420. However, the TRP 436 is simultaneously connected to the DU 412 of the base station 401 and the DU 421 of the base station 402. In this way, dual access TRPs may belong to different base stations or to one base station.

Meanwhile, as illustrated in FIG. 4, an interface 451 between CUs 410 and 420 and an interface 452 between DUs 412 and 421 included in different base stations are illustrated. The interface between CUs 410 and 420 can use the X2 interface, which is used as an interface standard between base stations in the 5G system. Additionally, the interface between the DUs 412 and 421 may be used by newly defining a direct interface between the DUs, or may be connected through CUs 410 and 420 connected to the corresponding base station. Another way is to connect through the TRP shared with DUs.

Let's take a closer look at the operation of each component according to the present disclosure using the configuration described above and illustrated in FIG. 4.

2.1. Architecture

TRP is a transmission point that transmits and receives wireless signals. gNB, the base station of the 5G communication system, can functionally be composed of a central unit (CU), a distributed unit (DU), and a remote unit (RU), and the RU includes a TRP. From the functional division perspective of Cloud-RAN, RU can be configured according to the selection of functional split. The RU divides the high physical layer and the low physical layer (High-PHY <> Low-PHY) based on Option 7, or the physical layer and wireless layer based on Option 8. It may include division into (PHY <> RF) sections.

DU operation: Each of the DUs (411, 412, 4211, and 422) generates data to be transmitted to the terminal using radio signals for limited radio resources, and each of the corresponding RUs (431, 432, 433, 434,435, 436, It can be sent to 437, 438, 439, 440, 441, 442). Each of the DUs 411, 412, 4211, and 422 may receive data corresponding to limited radio resources from data received from the corresponding RU.

Dual access RU operation (Dual Access RU operation): Dual access RUs (433, 436, 439) receive data to be transmitted to the terminal from multiple DUs, and wireless signals to transmit data to the corresponding terminal(s) can be generated and data can be transmitted to the terminal through a wireless signal. Dual connectivity RUs 433, 436, and 439 may transmit radio signals received from the terminal to multiple DUs.

Single Access RU operation: Single access RUs (431, 432, 434, 435, 437, 438, 449, 441, 442) are connected to one DU within the same base station and operate in the wireless section. It is possible to transmit and receive wireless signals with at least one terminal and exchange (transmit/receive) data with the corresponding DU.

Synchronization condition: Each of the RUs 431-442 can compensate for errors in synchronization signals used by multiple DUs.

RU/TRP: RU device is a device that includes TRP, which means signal transmission point in the standard, and is connected to DU to perform some functions of the physical (PHY) layer. From a wireless interface perspective, RU can be interpreted as an element that constitutes a network after TRP. As mentioned above, in this disclosure, TRP is used to represent a RU device, and cases where TRP is described separately from RU are described separately.

2.1.1. Dual Access TRP

Dual Access TRP (Dual Access TRP): Dual access RU/TRPs (433, 436, 439) are devices that are each connected to two or more DUs and perform some functions of the PHY layer. Dual access RU/TRPs (433, 436, 439) can perform some functions of the PHY layer, including receiving and multiplexing data provided by two or more DUs for transmitting signals or data to the terminal. there is. The dual access RU/TRPs 433, 436, and 439 generate signals for transmission in the wireless interface, and the TRP transmits the generated signal. For reception operations from the terminal, the dual access RU/TRPs 433, 436, and 439 may perform some functions of the PHY layer on the wireless signal received from the wireless interface. Dual connectivity TU/TRPs 433, 436, and 439 may provide received data to the corresponding DU.

Functional split example (Function Split example): Dual Access TRPs (433, 436, 439) are connected to multiple DUs and implement DU and PHY functions by distributing each. Let's look at this with reference to FIG. 5.

Figure 5 is a diagram illustrating a hierarchical configuration of base stations including a dual access TRP according to the present disclosure.

Referring to FIG. 5, CUs 510 and 520 have Radio Resource Control (RRC) and Service Data Adaptation Protocol (SDAP) layers and Packet Data Convergence Protocol (PDCP). can perform the function. The SDAP layer is a layer defined for Quality of Service flow processing in the 5G wireless interface.

DUs 511 and 521 are a Radio Link Control (RLC) layer, a Medium Access Control (MAC) layer, and a Physical (PHY) High (PHY-High) sub-layer. -layer) function. However, the configuration of the protocol between the CU (510, 520) and the DU (511, 521) in FIG. 5 corresponds to one example and can be configured in various ways depending on the implementation method.

In addition, the physical layer (PHY layer) divided between the DU (511, 521) and the dual access TRP (433, 436, 439, 531) is divided into a physical upper (PHY-High) sublayer and a physical lower layer (PHY-Low) separation. -S) It can be composed of a sub-layer and a physical lower common (PHY-Low-Comm) sublayer. The PHY-High sublayer refers to functions located in DUs (411, 412, 421, 422, 511, 521), respectively, and corresponds to the upper function of the PHY layer. The PHY-High sublayer may vary depending on how the Cloud-RAN system is built, as seen above.

Meanwhile, in this disclosure, since the PHY layer is divided into three small parts, it will be described as divided into sub-layers. However, it should be noted that this sub-layer is only for explaining the divided form and is not intended to limit the present disclosure.

The dual connection TRPs 433, 436, 439, and 531 have a physical lower separation (PHY-Low-S) sub-layer and a physical lower common (PHY-Low-Comm) sublayer, as illustrated in FIG. 5. May include hierarchies. Since the PHY-Low-S sublayer is a function located in the TRP 531 and performed in response to each DU, there is a PHY-Low-S sublayer corresponding to the connected DU. The PHY-Low-S sublayer of the dual connectivity TRPs (433, 436, 439, and 531) may be provided one for each connected DU. That is, each of the plurality of PHY-Low-S sublayers included in the dual connectivity TRPs 433, 436, 439, and 531 may be connected to one corresponding DU.

The PHY-Low-Comm sublayer, which interfaces with each of the PHY-Low-Ss corresponding to each DU, refers to the PHY-Low function associated with the wireless signal transmitted and received on the wireless interface of the TRP 531, and a plurality of PHY-Low -It has the characteristic of being connected to the S subclass. The PHY-Low-Comm sublayer can provide a wireless interface for transmitting data received from each PHY-Low-S sublayer to the terminal. Additionally, the PHY-Low-Comm sublayer can provide data received from the terminal through a wireless interface to the PHY-Low-S sublayer.

DUs (411, 412, 421, 422, 511, 521) can be configured by dividing the corresponding CUs (410, 420, 510, 520) and wireless interface protocols.

Terminal position: A terminal connected to a gNB having the type of base station illustrated in FIG. 4 and the protocol structure illustrated in FIG. 5 can configure a wireless protocol on a wireless interface to transmit and receive wireless signals for transmitting data with the gNB, which is the base station. . The terminal can configure and use a wireless protocol by transmitting and receiving wireless signals at the TRP 531. The terminal can be operated by determining the corresponding DU. More specifically, a DU corresponding to a random time is determined, and the wireless protocol corresponding to this DU can be determined including the PHY-High sublayer, PHY-Low-S sublayer, and PHY-Low-Comm sublayer.

For example, when a specific terminal communicates with the DU (511) at a random time, the PHY-Low-Comm sublayer in the TRP (531), the PHY-Low-S sublayer connected to the DU (511), and the PHY of the DU (511) -High sub-layer wireless protocols can be used. Likewise, considering the case where the terminal communicates with the DU (521) at a random time, the PHY-Low-Comm sublayer in the TRP (531), the PHY-Low-S sublayer connected to the DU (521), and the DU The wireless protocol of the PHY-High sublayer of (521) can be used.

These protocols operate as protocols corresponding to the wireless protocol of the terminal and exchange data with the terminal in wireless signals transmitted and received with the terminal. Depending on the DU that is subsequently changed, the PHY-High sublayer and PHY-Low-S sublayer may be changed and operated. As a DU change procedure, change point detection and change procedures must be performed. If the TRP does not change during the DU change process, the PHY-Low-Comm sublayer that ultimately generates the wireless signal has the characteristic of being maintained.

Implementation Features: Dual connectivity RU/TRPs (433, 436, 439, 531) respectively receive data from the corresponding DU (412, 421, 512, 521) and generate wireless signals transmitted to the wireless interface. Since the wireless signal received by the terminal is generated in the PHY-Low-Comm sublayer, if the TRP is maintained even if the DU is changed, the terminal can maintain wireless signal characteristics such as band/frequency/synchronization signal. In particular, in the process of receiving and generating data signals from different DUs for two terminals connected to one dual access TRP, the important band/frequency/synchronization of the wireless signal can be operated by the PHY-Low-Comm sublayer. . This has the advantage that the DU does not affect errors in the wireless signal because the wireless signal is generated by one RU (or TRP) even if the wireless signal is generated by data generated in each DU.

2.1.2. Inter-DU Coordination

Scheduling for each DU: Scheduling, which allocates radio resources in multiple dimensions such as time/frequency/space, is important as a main function in DUs (411, 412, 421, 422, 511, 521). The function of allocating radio resources to users such as base stations/terminals by operating unit (including slots, TTI, etc.) in the wireless interface can be performed in the DU (411, 412, 421, 422, 511, 521). A DU that performs the function of allocating radio resources operated on the radio interface of the Dual Access TRP (433, 436, 439, 531) is required. In general, the scheduler, which functions to allocate wireless resources to users, is a function performed by DUs 411, 412, 421, 422, 511, and 521. That is, a scheduler (not shown in the figure) located in the DUs 411, 412, 421, 422, 511, and 521 can allocate wireless resources to users. This means that if a corresponding scheduler is determined for each radio resource at a specific time for a specific dual access TRP, the corresponding DU is determined. Therefore, from the perspective of each DU (412, 421, 511, 521) connected to the dual connectivity TRPs (431, 436, 439, 531), the radio resource managed by the scheduler can be fixed. Each of the DUs (412, 421, 511, 521) connected to the dual access TRPs (431, 436, 439, 531) determines a user to allocate wireless resources for each wireless resource and shares resource allocation information on the wireless interface. And, transmission and reception operations of the base station and terminal can be performed for each radio resource.

Inter-DU Coordination: As described above, DUs (412, 421, 511, 521) connected to dual access TRPs (431, 436, 439, 531) to determine the radio resources managed by each DU. A consultation process is required. In order to determine the radio resources managed by each DU (412, 421, 511, 521) connected to the dual access TRPs (431, 436, 439, 531) at each unit time, the dual access TRPs (431, 436, 439, It may be included in a negotiation procedure for radio resources between DUs (412, 421, 511, 521) connected to 531).

In the present disclosure, the DUs (412, 421, 511, 521) connected to the dual access TRPs (431, 436, 439, 531) use radio resources available in the TRP connected to the DUs (412, 421) as needed. , 511, 521) will be explained assuming a case where it can be used through agreement. However, when the DUs (412, 421, 511, 521) connected to the dual access TRPs (431, 436, 439, 531) perform scheduling using only predetermined radio resources, the negotiation procedure for radio resources is It is not necessary. The present disclosure does not exclude the case where the DUs (412, 421, 511, 521) connected to the dual connectivity TRPs (431, 436, 439, 531) perform scheduling using only predetermined radio resources.

Depending on the increase or decrease in wireless traffic processed by each DU, a proportional increase or decrease in wireless resources operated by the DU is required. A negotiation procedure between DUs can be carried out as a procedure to divide and operate fixed radio resources between DUs in the wireless interface. In a method of variably operating radio resources in such a way that radio resources are increased or decreased according to the increase or decrease of radio traffic for each DU, radio resource negotiation between DUs is required. Therefore, in a method of variably operating radio resources in a way that radio resources increase or decrease according to the increase or decrease of wireless traffic for each DU, a negotiation procedure between DUs can be performed on a unit time basis. For this collaboration, a direct interface can be configured to form a connection path between DUs.

X2 structure: The interface between gNB devices, which are base stations in the 5G communication system, is configured as an X2 interface, so information negotiated between DUs can be exchanged on the X2 interface. In the current standard, the X2 interface defines signaling procedures between gNBs. Therefore, the negotiation process related to scheduling between DUs on a per-time basis can be carried out over the connection provided by the X2 interface. When using the X2 interface between DUs, the actual negotiation information may consist of the connection of the F1 interface between the DU and CU and the X2 interface between the CU. As a result, in the example of FIG. 5, the transfer of negotiation information between DU 511 and DU 521 is provided to CU 510 through the F1 interface between DU 511 and CU 510, and CU 510 provides Negotiation information can be transmitted to the CU 520 using the X2 interface. The CU 520 may provide negotiation information received from the DU 511 through the CU 510 to the DU 521 through the F1 interface. Even when the DU 521 provides negotiation information to the DU 511, it can be transmitted through the reverse direction of the described interfaces.

TRP structure: As described in Figures 4 and 5, TRP (431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 531) is DU (411, 412, 421, 422) , 411, 521), the connection between DUs may be made via the corresponding dual connection TRP. The DUs (412, 421, 511, 521) connected to the dual access TRPs (433, 436, 439, 531) have a two-way communication path between the corresponding TRPs (433, 436, 439, 531), so that The connection can be configured in the structure of DU <> TRP <> DU. In this case, the capacity allocated for the connection between DUs is additionally required for the connection between DU<>TRPs.

Figure 6a is a conceptual diagram of a base station network to explain the connection between DU and TRP according to an embodiment of the present disclosure.

Referring to FIG. 6A, DUs 611, 612, 613, and 614 are connected to at least one TRP (621, 622, 623, 624, and 625). Specifically, DU (611) is connected to TRP (621, 622), DU (612) is connected to TRP (622, 623), DU (613) is connected to TRP (624), and DU (614) is connected to TRP (625). Also, in the example of FIG. 6, DUs 611 and 612 constitute one gNB 610, and DUs 613 and DU 614 may be included in different base stations. More specifically, the TRP 624 and DU 613 may be included in one gNB, and the TRP 625 and DU 614 may be included in a gNB other than the gNB containing the TRP 624 and DU 613. there is.

As another example, DUs 613 and DUs 614 may be included in one base station. That is, TRPs 624 and 625 and DUs 613 and 614 may be included in one gNB. Additionally, in FIG. 6, reference numeral 610 may refer to a base station or an area covered by the base station.

The inter-DU cooperation (Inter-DU Cooperation) described above can be performed between the DUs 611 and DUs 612 included in one gNB 610. Collaboration between DUs can be done through a CU (not shown in FIG. 6) to which the DUs 611 and DUs 612 are connected. As another example, DU 611 and DU 612 share the TRP 622, so they can collaborate using the DU <> TRP <> DU method. As another example, if a separate interface is defined between the DU 611 and DU 612 included in the gNB 610, collaboration may be performed using that interface. The connection 601 between the DU 611 and DU 612 illustrated in FIG. 6 graphically illustrates collaboration in one of the methods described above.

In addition, collaboration between the DU 611 included in one gNB 610 and the DU 613 included in another gNB is also possible using the methods described between the DU 611 and DU 612 included in one gNB 610. You can collaborate through one of the following methods: The connection 602 between the DU 611 included in one gNB 610 and the DU 613 included in another gNB graphically illustrates collaboration between DUs included in different base stations.

In Figure 6a, the terminal 631 is also illustrated. When the terminal 631 moves from the communication area of the TRP 625 connected to the DU 614, as indicated by reference numeral 641, it can move to the area of the TRP 624 connected to the DU 613. Additionally, when the terminal 631 moves from the communication area of the TRP 624 connected to the DU 613, as indicated by reference numeral 641, it can move to the area of the TRP 623 connected to the DU 612.

2.2. terminal experience

Single access, typical handover (Single access, Typical HO): The terminal 631 can receive a signal transmitted by the TRP. As the terminal 631 moves away from the TRP with which it is communicating, the strength of the received signal decreases. When the terminal 631 is located at the boundary of a specific TRP (hereinafter referred to as 'serving TRP') through which a service is provided, it can receive a signal from another TRP. Let's look at handover between TRPs when the serving TRP for the terminal 631 and an adjacent TRP operate separately.

Referring to FIG. 6A, when two different TRPs operate separately, the configuration may be between the TRP 625 and the TRP 624 or between the TRP 624 and the TRP 623. This is because the single connection TRP 624 is connected to the DU 613, and the single connection TRP 625 is connected to the DU 614. Similarly, referring to FIG. 6A, the single connection TRP 624 is connected to the DU 613, and the single connection TRP 623 is connected to the DU 612. However, since collaboration 602 can be performed between the DU 612 and DU 613, additional operations can be performed. Therefore, a single connection, a general HO, will be explained with reference to FIG. 6B using the configuration between the TRP 625 and the TRP 624.

FIG. 6B is an example diagram illustrating handover of a single access TRP according to an embodiment of the present disclosure.

FIG. 6B is a diagram separately extracted and illustrated to explain the handover between the TRP 625 and the TRP 624 in FIG. 6A described above. Therefore, the same configuration as in FIG. 6A will be described using the same reference numerals.

DU 614 may be connected to one TRP 625, and another DU 613 may be connected to another TRP 624. It is assumed that the terminal 631 communicates in the area of the TRP 624 initially connected to the DU 614. Therefore, the serving TRP of the first terminal 631 may be TRP 625. A case where the terminal 631 moves to the target TRP, TPR 624, as illustrated by reference numeral 641 in FIG. 6A may be considered.

When the terminal 640 communicating at the location of the TRP 625 moves in the direction of the TRP 624 and enters the handover area, the signal strength 625a received from the TRP 625 decreases. . In Figure 6b, reference numerals 624a and 624b graphically illustrate signal intensity values in log scale proportional to the distance between the TRP 624 and the terminal 631, and reference numeral 625a represents the signal strength value between the TRP 625 and the terminal 631. This is a graph illustrating the signal intensity value in log scale proportional to the distance.

Looking a little closer at the graph illustrated in FIG. 6B, the strength of the signal received from the TRP 625 in the terminal 631 generally increases or decreases in proportion to the square of the distance. Therefore, since the signal intensity in FIG. 6B illustrates the signal intensity based on a logarithmic scale, the logarithmic scale signal intensity 625a corresponding to the distance from the TRP 625 in the direction of the TRP 624 is from the TRP 625. It decreases linearly in proportion to the distance. Since the signal strength is proportional to the square of the distance, the signal strength is taken on a logarithmic scale, so it can have linear characteristics. Additionally, the example of FIG. 6B may be an ideal case assuming that there are no other obstacles or interference between the TRP 625 and the terminal 631.

When interference is considered, the signal received by the terminal 631 from the serving TRP 625 has an SINR value as indicated by reference numeral 651. That is, because signals received from other nearby base station(s) act as interference, it has a lower SINR than reference numeral 625a.

The virtual point where handover occurs is illustrated by reference numeral 661. When the terminal 631 moves as shown by reference numeral 641 illustrated in FIG. 6A, the terminal 631, which has received signals transmitted by two separately operating TRPs 624 and 625, moves to the boundary between the TRPs 624 and 625. It experiences -3dB SINR and has the characteristic of a sharp decrease in the received signal. Therefore, a traditional handover occurs at a virtual handover point as illustrated by reference numeral 661, and the terminal 631 experiences disconnection time due to the handover. It should be noted that the example of the virtual handover point 661 here is called a virtual point because it is difficult to specify the point where the actual handover is performed.

In a single access handover (Typical HO) environment, signals transmitted from adjacent TRPs affect terminals located at the border by interference. If the serving TRP increases the power of the transmitted signal to reduce interference in the terminal, the signal received by the terminal 631 may increase, but since this requires high-power transmission in neighboring TRPs, the resulting interference signal also increases. A phenomenon that increases together occurs. Therefore, the quality of the terminal reception signal does not increase as the TRP density increases.

FIG. 6C is an example diagram illustrating handover of a single access TRP according to another embodiment of the present disclosure.

FIG. 6C is also a diagram separately extracted and illustrated to explain the handover between the TRP 625 and the TRP 624 in FIG. 6A described above. Therefore, the same configuration as in FIG. 6A will be described using the same reference numerals.

DU 612 may be connected to one TRP 623, and another DU 613 may be connected to another TRP 624. It is assumed that the terminal 631 communicates in the area of the TRP 624 initially connected to the DU 613. Therefore, the serving TRP of the first terminal 631 may be TRP 624. A case where the terminal 631 moves to the target TRP, TPR 623, as illustrated by reference numeral 641 in FIG. 6A may be considered.

Single access, typical handover, resource nulling (Single access, Typical HO, Resource Nulling): FIG. 6C explains the operation corresponding to the single access typical handover procedure as described in FIG. 6B. However, as indicated by reference numeral 602, the case of collaboration between DUs 612 and 613 is considered.

Cooperation between the control plane and data plane may proceed at the X2 interface between gNBs. In the HO procedure through the X2 interface, the terminal 631 can change the serving gNB. This handover may involve collaboration functions that do not appear in the standard and may include negotiation functions for wireless resources. The Resource Nulling function, in which the radio resources used by the serving gNB are not used by the neighboring gNB, can eliminate the phenomenon in which the signal of the neighboring TRP experienced by the UE acts as interference. Let's look at this with reference to FIG. 6C.

When the terminal 631 moves from the area of the TRP 624 in the direction where the TRP 623 is located, as indicated by reference numeral 641 illustrated in FIG. 6A, the TPR 624 is connected to a single DU 613. Access). Additionally, the TRP 623 to which the UE 631 moves corresponds to a TRP located in another gNB. Therefore, when the terminal 631 moves from the center of the TRP 624 in the direction of the TRP 623 and is located at a random point 662 on the border of the TRP 624, the terminal 640 opens the serving TRP 624. A handover that changes may occur. That is, handover from the old serving TPR 624 to the new TRP 623 may occur. In this case, according to the present disclosure, interference during handover can be reduced through inter-gNB cooperation between the DU 612 of the new TRP 623 and the old TRP 624.

According to the present disclosure, the TRP ( 623) can perform resource nulling to prevent signals from being transmitted through the same resource. In addition, according to the present disclosure, for a predetermined time after handover, the previous serving TRP 624 is prevented from transmitting a signal to the terminal 631 using the same resources as the resources allocated by the target TRP 623 through which the handover was performed. Emptying can be performed. As a result, the terminal 631 experiences less interference at the border and has the advantage of receiving a high quality signal. In this case, a handover that changes the serving gNB occurs at the border using the X2 interface, and the terminal 631 experiences disconnection time due to the handover. However, the signal received by the terminal 631 from the serving TRP (624 or 623) may be a signal without an interference signal. That is, the received signal of the terminal 631 has SNR quality without interference. As described above, since the terminal 631 receives an interference signal from an adjacent TRP, interference is considered in the received signal, such as a signal to interference noise ratio (SINR). However, when interference from an adjacent TPR is removed through resource freeing, only the signal to noise ratio (SNR) is considered, so transmission efficiency can be improved in terms of the terminal's reception environment.

In addition, SNR quality is a characteristic affected by the wireless channel of the serving TRP and is mainly affected by the distance between the serving TRP and the terminal, obstacles, etc. As a method of providing high quality received signals to the terminal 631, the TRP density can be increased by shortening the distance between the serving TRP and the terminal.

FIG. 6D is an exemplary diagram illustrating TRP switching of a single connection TRP according to another embodiment of the present disclosure.

The example of FIG. 6D is also a diagram separately extracted and illustrated to explain TRP switching between the TRP 623 and the TRP 622 in FIG. 6A described above. Therefore, the same configuration as in FIG. 6A will be described using the same reference numerals.

DU 612 may be connected to the TRP 623 and TRP 622, and another DU 613 may be connected to another TRP 622. It is assumed that the terminal 631 communicates in the area of the single access TRP 623 connected to the DU 612. Therefore, the serving TRP of the terminal 631 may be the TRP 623. A case where the terminal 631 moves to the target TRP, TPR 622, as illustrated by reference numeral 641 in FIG. 6A may be considered.

The terminal 631 can move to the area of the TRP 622 while communicating with the TRP 623 as the serving TRP. At this time, it can be seen that the log scale graph 623a of the signal intensity from the TRP 623 decreases in proportion to the distance. Conversely, the log scale graph 622b of the signal strength from the TRP 622 to the terminal 631 also shows that the signal strength decreases in proportion to the distance between the terminal 631 and the TRP 622.

In the case of FIG. 6D, even if the UE 631 performs handover between TRPs, the DU 612 that performs scheduling does not change, and only the TRPs 622 and 623 connected to one DU 612 change. In this disclosure, the case where the DU 612 that performs scheduling is not changed and handover of the UE 631 occurs only in TRPs is referred to as “TRP Switching.”

Therefore, the DU 612 does not require collaboration between DUs during handover of the UE 631, which was previously described with reference to FIG. 6C. That is, when a handover occurs in the UE 631, the DU 612 can perform resource nulling in each of the TRPs 622 and 623. However, as illustrated in FIG. 6D, the TRP 622 corresponds to a dual connection TRP also connected to another DU 611. Therefore, when resource clearing is performed to provide handover of the terminal 631, the resources of the target TRP (622) are freed while the terminal 631 is connected to the serving TRP (623) through collaboration with the DU (611). Collaboration may be necessary to do this.

Dual Access, Resource Nulling:

Let's take a look at dual access and resource emptying with reference to FIG. 6d described above.

Figure 6d shows a structure in which multiple TRPs 622 and 623 are connected to one DU 612. Signals transmitted and received in each TRP (622, 623) are concentrated in the DU (612) and processed in the DU (612). When the terminal 631 moves and changes the TRP for the purpose of providing continuous service, for example, when the terminal 631 moves as shown in reference numeral 641 illustrated in FIG. 6A, the TRP is changed in the same DU 612. In this way, when the TRPs 622 and 623 connected to one DU 612 are changed, the TRP change procedure is performed in the concentrated DU 612 and the procedure with adjacent nodes can be omitted. In this way, changing the TRPs connected to one DU can be a TRP switching operation, as described above. The TRP switching operation, in which handover is performed in TRPs connected to one DU, can minimize signal disconnection time from the perspective of the terminal 631. This has an advantage in that the target TRPs are connected to the same DU. To emphasize the meaning of a function performed by being connected to the same DU, this disclosure may also refer to it as an “Inter-TRP Switching procedure.” TRP switching or change between transmission points can apply a resource nulling function that prevents adjacent TRPs from using radio resources used by the serving TRP. The terminal receiving the radio resource used by the serving TRP does not receive an interference signal because the adjacent TRP does not transmit the signal on the same resource, so the received signal has SNR quality. Since the nature of SNR quality has been explained previously, redundant explanation will be omitted. As a result, as shown in Figure 6d, handover between TRPs connected to one DU has the advantage of experiencing SNR quality received signal performance and almost 0 level TRP switching disconnection time.

Figure 6e is an example diagram for explaining handover in dual access TRP according to an embodiment of the present disclosure.

In the example of FIG. 6E, the same configuration as that of FIG. 6A described above will be described using the same reference numerals. Also, Figure 6e may be a case where the TRP 622 is maintained, but the DUs 611 and 612 are changed.

TRP 622 may be connected to DU 612 and simultaneously connected to DU 611. At this time, let us assume that the terminal 631 moves from the area of the DU 612 to the area of the DU 611. When the UE 631 moves from the area of the DU 612 to the area of the DU 611, the DU performing scheduling must be changed even if it is located within the same TRP 622. Therefore, in the present disclosure, the DU can be changed based on the movement of the terminal 631. This will be referred to as “DU Switching” in this disclosure.

The conditions under which DU switching occurs may be the same as the conditions for TRP switching, or may be different.

In the case of TRP switching, it can be basically done based on the strength of the received signal between the terminal and the TRP, the distance between the TRP and the terminal, and the presence or absence of an adjacent TRP. Specifically, in TRP switching, when the terminal moves from the serving TRP to an adjacent target TRP, the TRP switching conditions may be conditions such as signal strength and distance between the terminal and the serving TRP.

Cases where the conditions for DU switching and TRP switching are the same may be cases where DU and TRP are individually connected. Specifically, as illustrated in FIG. 6B, each of the DUs 613 and 614 may be connected to the corresponding TRPs 624 and 625. In this way, when each of the DUs 613 and 614 is connected to the corresponding TRPs 624 and 625, DU switching may have the same conditions as the TRP switching conditions.

A case in which the conditions for DU switching and TRP switching are different may be the case as illustrated in FIG. 6E. DU 611 and DU 612 may be connected to the same TRP 622. In this way, when each of the DUs 611 and DUs 612 is connected to one TRP 622, that is, when connected to the dual connectivity TRP according to the present disclosure, the DU switching conditions may be different from the TRP switching conditions.

DU switching conditions can be made based on the area of the DU. Referring again to FIG. 6E, the DUs 611 and 612 may know the DU areas in advance. This DU area will be explained in Figure 10 below. Therefore, the DU can recognize that the dual connectivity TRP corresponds to the edge of the DU's area. Even at the edge of the DU area, the strength of the signal received from the dual connectivity TRP may not decrease from the perspective of a terminal connected to the dual connectivity TRP. Therefore, the DU may determine that the DU switching condition is satisfied when the terminal connected to the dual connectivity TRP moves to its edge area.

Based on this, referring to FIG. 6e, the DU 612 can identify that the terminal 631 is moving to the edge area of the DU 612. This identification is based on signal strength information reported by the terminal to the DU 612 through the dual connectivity TRP 622, history information about the movement of the terminal 631, sector information from the dual connectivity TRP, and MIMO information from the dual connectivity TRP 622. When the method is adopted, identification can be made using at least one of the beam direction information of beam forming.

When the DU 612 moves to the edge of its area, it may decide to switch DU to the adjacent DU 611. In general, if DUs 611 and 612 are included in one base station, the DUs 611 and 612 know about adjacent DUs. Additionally, even if the DUs are included in different base stations, each DU may have information about DUs adjacent to it for purposes such as scheduling and handover. Since the disclosure of FIG. 6E is a diagram extracted from FIG. 6A, the DUs may be DUs included in one base station. However, DUs included in different base stations may have information on adjacent DUs. In this disclosure, it is assumed that DUs have information on adjacent DUs regardless of whether the base station is the same or not.

Therefore, when the DU 612 decides to switch DUs, the DUs can cooperate with the adjacent DUs 611 so that communication with the terminal 631 can be maintained through the dual connectivity TRP 622. Collaboration between DUs, that is, collaboration for DU switching, provides information on the services provided by the DU 612 through the dual access TRP 622, as well as information on resources used by the dual access TRP 622, and It can be a procedure that provides information about when switching should occur. Information about the service may include the type of service and required transmission rate. The required data rate may include a guaranteed minimum data rate. In particular, in the case of the XR service described as an example in this disclosure, the guaranteed minimum data rate can be one of the very important factors.

The DU 612 may provide DU switching collaboration information (or DU switching collaboration request message) to the DU 611 and receive a response therefrom. Upon receiving a positive response from the DU (611), that is, a message accepting the use of the resource at the time DU (612) requested, the UD (612) sends a DU switching message based on the switching collaboration information to the dual access TRP (622). Can be transmitted. The DU switching message disconnects from the dual connectivity TRP (622) at that point when DU switching is performed so that the dual connectivity TRP (622) maintains communication with the terminal (631) connected to the DU (612), and the target DU, This may be a message instructing to connect between the DU 611 and the terminal.

At this time, the dual connectivity TRP 622 of the DU 611 may be scheduled to use the same resources from the DU 611 for the same terminal 631. Therefore, the terminal 631 can only switch at the upper level while maintaining radio resources in the dual access TRP 622. Additionally, if new information needs to be provided to the terminal due to a change in DU, the information can be provided to the terminal. As described in FIG. 5, a change in DU can be notified to the terminal 631 using RLC layer information or MAC layer information.

Additionally, if the DU 611 cannot accept at least one content included in the DU switching collaboration request message of the DU 612, a negative response or modification request message may be provided to the DU 612. A negative response may include information about the reason why it cannot be accepted. When a negative response is received, the DU 612 may update at least one piece of information in the DU, switching collaboration message and transmit it to the DU 611. Additionally, the modification request message provided by the DU 611 may include modification information on at least one of the elements included in the DU switching collaboration request message. For example, when it is desired to change the viewpoint information, the DU 612 may transmit a modification message including the changed viewpoint information to the DU 611. Therefore, when a correction message is received, the DU 611 can provide a response to the DU 611.

Collaboration between DUs may proceed using at least some of the methods described above. Also, in the above, it was assumed that DUs are included in one base station. However, the above operation is possible even when DUs are included in different base stations.

If the base station changes, the RRC layer can use the RRC message to notify the terminal of the base station change information.

Meanwhile, when switching DUs, information between DUs may be provided through a dual access TRP, or information between DUs may be provided using a higher-level CU, and if a separate interface between DUs is defined, that interface may be used. there is.

Meanwhile, during DU switching, the source DU 612 may provide a DU switching message to the dual connectivity TRP 622. This may include information instructing the terminal 631 to maintain communication based on control from another DU, that is, an adjacent DU 611, from a specific point in time. Therefore, when the dual connectivity TRP 622 receives a DU switching message from the source DU, it can disconnect from the source DU from the corresponding point in time.

As described in FIG. 5, the dual connectivity TRP 622 disconnects the source DU by disconnecting the physical lower-level separation (PHY-Low-S) sublayer between the source DU and the terminal and physical lower-level separation of the target DU. (PHY-Low-S) This can be a procedure for connecting to the sublayer. At this time, as described in FIG. 5, the physical lower common (PHY-Low-Comm) sublayer of the dual connectivity TRP 622 may have the characteristic of not being changed. Therefore, the dual connectivity TRP 622 can transmit scheduled information from the target DU, DU 611, through the physical lower common (PHY-Low-Comm) sublayer at the time DU switching is performed for the terminal 631.

In the above, the case where the DU 612, which is the source DU, transmits a DU switching message to the dual connectivity TRP 622 has been described. However, the target DU, DU 611, may transmit a DU switching message to the dual connectivity TRP 622. In this case, when the DU 611 transmits an affirmative response message corresponding to the DU switching collaboration information (or DU switching collaboration request message) to the DU 612, the DU switching message may be provided to the dual connectivity TRP 622. Therefore, when the dual connectivity TRP 622 receives a DU switching message from the DU 612, which is the source DU, or the DU 611, which is the target DU, it can perform the same operation as described above.

DU switching may be performed at a specific location 664 where the signal strength is high in the TRP 622, as illustrated in FIG. 6E. Therefore, unlike general handover, DU switching can occur when the strength of the signal received from the TRP 622 is high. Additionally, during DU switching, the TRP 622 may share the PHY-Low-Comm sublayer as previously described in FIG. 5. And the TRP 622 may include PHY-Low-S sublayers corresponding to each DU (611, 612).

FIG. 6F is an example diagram illustrating dual access handover and Coordinated Multi-Point (CoMP) transmission and reception of multiple transmission and reception points according to an embodiment of the present disclosure.

In the example of FIG. 6F, the same configuration as that of FIG. 6A described above will be described using the same reference numerals. Also, Figure 6f shows a case where two different TRPs 621 and 622 are connected to the DU 611. Therefore, the morphological structure may be similar to that of Figure 6d. In FIG. 6F, a method that further considers CoMP transmission and reception in two different TRPs 621 and 622 connected to one DU 611 will be explained in addition to the method described above.

DU (611) may have a configuration connected to TRP (621) and TRP (622). It is assumed that the terminal 631 communicates in the area of the TRP 622 connected to the DU 611. Therefore, the serving TRP of the terminal 631 may be the TRP 622. A case where the terminal 631 moves to the target TRP, TPR 622, as illustrated by reference numeral 641 in FIG. 6A may be considered.

The terminal 631 can move to the area of the TRP 621 while communicating with the TRP 622 and the serving TRP. At this time, it can be seen that the log scale graph 622a of the signal intensity from the TRP 622 decreases in proportion to the distance. Conversely, the log scale graph 621b of the signal strength from the TRP 621 to the terminal 631 also shows that the signal strength decreases in proportion to the distance between the terminal 631 and the TRP 622.

In the case of FIG. 6F, even if the UE 631 performs handover between TRPs, the DU 611 that performs scheduling does not change, and only the TRPs 621 and 622 connected to one DU 611 change. In other words, the TRP switching described above may occur.

In the embodiment of FIG. 6F, one DU 611 can utilize the CoMP transmission/reception technique. The CoMP transmission/reception technique may generally include the resource clearing operation described above when the TRP 522 is a serving TRP. In addition, when using a beamforming method using multiple antennas with resource emptying, this may include preventing the transmission beam of the TRP 621 from being directed to the terminal 631 currently receiving service from the TRP 622. In addition, in another form of the CoMP method, the terminal 631 can transmit the same data using the same resources during the handover period from the TRP 622 to the TRP 621. This may make it easier for handover to occur in the TRPs 621 and 622 included in the DU 611.

Now, let's take a look at the operations of Figures 6e and 6f discussed above.

Dual Access (CoMP):

Referring to FIG. 6F, a plurality of TRPs 621 and 622 are connected to one DU 611, and services can be continuously provided to a moving terminal 631 by changing the TRP. The DU 611 may generate a signal corresponding to data to be transmitted to a specific terminal and transmit it to the TRPs 621 and 622. At this time, the DU 611 can control transmission of data to the terminal 631 using the same resources and data through the TRPs 621 and 622. Therefore, the terminal 631 can receive signals transmitted by the TRPs 621 and 622. The terminal 631 can increase the quality of the received signal by combining and processing signals received from different TRPs 621 and 622 through a signal processing process.

Since the terminal 631 receives signals from two TRPs 621 and 622, as shown in reference numeral 651 in FIG. 6f, the performance of the wireless channel increases by 3 dB as shown in reference numeral 671, resulting in a high SNR + 3 dB. You can experience wireless signal performance. That is, since the DU 611 does not transmit signals to other terminals through the same radio resources provided to the terminal 631, there is no need to consider interference. Additionally, since the same signal is received using the same resources from two different TRPs 621 and 622, signal reception efficiency can be further improved. That is, the terminal 631 can continuously receive high quality signals without signal decrease at the boundary between two TRPs.

Meanwhile, as seen in FIG. 6e, the DU switching procedure for changing the DU in the same TRP 622 was examined. Looking more closely at DU switching, since the procedure for changing the DU is performed at the point when good quality signals are exchanged between the terminal 631 and the TRP 622, the signal quality of the wireless signal can be maintained high during the DU change procedure. there is. The procedure for changing a DU can be done by applying the wired and wireless procedures for changing a node in a general HO. In particular, continuous data exchange is possible because wired and wireless procedures can be used to reduce interruptions in data transmission and reception.

On the other hand, the terminal 631 described in this disclosure has the characteristic of providing continuous service by transmitting and receiving high quality wireless signals using signals transmitted and received in the CoMP method at the TRP boundary. Additionally, at a location where the terminal 631 transmits and receives high-quality wireless signals near a TRP, performance improvement due to signals received from an adjacent TRP is small. Therefore, the terminal 631 has sufficient reception performance only with the signal received from the serving TRP.

The process of changing the TRP in the terminal according to the present disclosure will be described in more detail. A terminal located close to the serving TRP can transmit and receive signals at the serving TRP. When the terminal moves to the boundary of the serving TRP, a new adjacent TRP can be added. Afterwards, the terminal can move the TRP, which was previously an adjacent TRP, to the area of the new serving TRP at the TRP boundary. When moving to a new serving TRP, the previous serving TRP becomes an adjacent TRP, and you can proceed with the procedure to delete the previous serving TRP. The above procedure is TRP Switching described previously. The operation of adding or deleting a TRP is a procedure performed while the serving TRP is connected, so there is no time interruption in data transmission. The TRP switching procedure can proceed through preparation and execution procedures. In the TRP switching procedure, the basis for judgment can be determined based on the size of the signal received from each TRP. In order to prevent the ping-pong phenomenon (continuous movement between different TRPs), a hysteresis range can be set for the signal size on the basis of judgment or conditional execution can be additionally considered.

2.3. Extreme Reality (XR) and transfer processing time

XR services require features of high-capacity transmission and low-latency transmission. Efforts to improve user transmission rates at cell boundaries or TRP boundaries are ongoing in 5G with the goal of providing services uniformly. The Dual Access method provided according to the present disclosure can receive high quality wireless signals by configuring a wireless environment in which multiple TRPs participate. Therefore, when configuring a wireless communication network environment according to the present disclosure, large capacity transmission is possible.

Low-latency transmission depends on the transmission processing time, which is the processing time between the data transmitted through the DU decision and transmission as a signal from the RU. If the transmission processing time is shortened in the downlink, the time to transmit data to the terminal is shortened, making it possible to achieve low-delay transmission.

FIGS. 7A to 7C are exemplary diagrams for explaining connection methods between DUs and RUs constituting a base station.

Before referring to FIGS. 7A to 7C, the present disclosure describes a method of using Cloud-RAN, and explains that in Cloud-RAN, one base station can be composed of a CU, one or more DUs, and one or more RU/TRP. did. In addition, this disclosure also describes an interface method between DUs included in different base stations (gNB). In Figure 7, we will look at the ways in which DU and RU/TRP are connected based on these methods.

DU and RU can be divided into direct type, relay type, and gNB cooperation type (Inter-gNB type) depending on the connection method.

Figure 7a illustrates a direct type connection structure between DU and RU. Referring to FIG. 7A, the connection between the DU 701 and the TRP 711 is a direct connection, and in the present disclosure, it is referred to as a direct type connection. Therefore, the direct method consists of one hop because the DU (701) and the RU (711) are directly connected, and the DU (701) and the RU (711) can be connected by fronthaul.

Figure 7b illustrates the relay type connection structure between DU and RU. The same configuration as in FIG. 7A will be denoted by the same reference numeral in FIG. 7B. Referring to FIG. 7B, it is different from FIG. 7A in that another DU (702) is included between the DU (701) and the TRP (711). That is, the DU 701 can be connected to the RU 711 through another DU 702, and since the DU 701 is connected to the RU 711 through the DU 702, it is a two-hop case. In the example of FIG. 7B, only one DU 702 exists between the DU 701 and the RU 711, but a plurality of DUs may be included between the DU 701 and the RU 711. Additionally, all DUs illustrated in FIG. 7b may be DUs included in one and the same base station. Therefore, a relay-type connection may be configured as a multi-hop in which the fronthaul passes through adjacent DUs within one base station.

Figure 7c illustrates the connection structure of the gNB cooperation method (Inter-gNB type) between DU and RU. In FIG. 7C, the same reference numerals are used for the same components as those in FIGS. 7A and 7B.

Referring to Figure 7c, the inter-gNB cooperation method is a configuration in which gNBs are interconnected and cooperate. In the configuration illustrated in FIG. 7C, the DU 703 and DU 701 may be included in different base stations. When the components DU (701) and RU (711) illustrated in FIG. 7A are included in the first base station, the DU (703) is a component that is different from the first base station, for example, a second base station adjacent to the first base station. It can be. The DU 703 included in the second base station may be connected to the RU 711 included in the first base station through Inter-gNB Cooperation between the DU 703 and DU 701. Since there is no protocol for direct communication between the DU 703 and DU 701 in collaboration between base stations, transmission can be accomplished through CUs (not shown in FIG. 7C) included in each base station. However, if an interface for direct communication between DUs is provided in the future, that interface may be used. This disclosure does not place any restrictions on interfaces that may be developed in the future.

Additionally, as illustrated in FIG. 7C, the DU (701) and the RU (711) may be connected through fronthaul. Based on this connection, the data requested to be transmitted by the DU 703 included in the second base station, which is a neighboring gNB, can be received by the DU 701 of the second base station directly from the first base station or through the CU of the second base station. there is. The DU 701 included in the second base station can transmit a wireless signal in the downlink through the RU 711 connected through the fronthaul.

Figure 8 is an example diagram to explain transmission processing time based on connection methods between DU and RU constituting the base station.

Referring to FIG. 8, the time according to the inter-gNB delay (801), the processing delay (DU processing delay) in one DU (802) time, the fronthaul delay (fronthaul delay) (803) time, and The RU processing delay (RU processing delay) 804 time is illustrated. Since fronthaul is generally performed using optical transmission, the fronthaul delay 803 can be a very short time.

As shown in Figure 7a, the transmission processing time in the direct connection between the DU (701) and the RU (711) is the DU processing delay (802) time in the downlink and the front haul delay connecting between the DU (701) and the RU (711) ( 803) can be determined as the sum of time and RU processing delay 804.

When at least one DU 702 is included between the DU 701 and the RU 711 as shown in Figure 7b, the transmission processing time may vary depending on the number of hops. Basically, as illustrated in FIG. 8, if at least one DU exists between the DU 701 and the RU 711, the number of hops between the DU and the RU increases. For example, if the DU (701) and the RU (711) are directly connected as shown in Figure 7a, it is 1 hop, and if one DU (702) is passed between the DU (701) and the RU (711) as shown in Figure 7b, It becomes 2 hops. Therefore, when the number of relaying DUs increases by one, the number of hops also increases by one. Accordingly, the processing delay (802) time of the DU also increases. In other words, it can be seen that the DU processing delay 802 increases in proportion to the number of hops.

In the case of multi-hop, in which downlink data is transmitted to the RU via a plurality of DUs including FIG. 7B, the DU processing delay 802 may increase by the number of hops.

In fact, as the number of hops increases, the fronthaul delay 803 may also increase. However, since the fronthaul itself is performed using an optical transmission method as described above, the increase in fronthaul delay can be negligible. If the fronthaul delay is also accurately considered, the fronthaul delay can also be considered based on the number of hops.

Next, in the case of collaboration between base stations, as illustrated in FIG. 7C, DUs 701 and 703 included in different base stations can transmit data between the DUs 701 and 703 based on collaboration between base stations. The collaboration delay 801 time between base stations may vary depending on the interface method between DUs. That is, as described above, the delay time may vary depending on whether a direct interface exists between DUs and when it must pass through the CU. The delay time in the case illustrated in FIG. 7C can be calculated as the sum of the collaboration delay between base stations (801), DU processing delay (808), front haul delay (803), and RU processing delay (804).

Therefore, the delay times in Figures 7a to 7c are the shortest for the direct connection in Figure 7a, and in the relay connection in Figure 7b, delay time may be added depending on the number of hops, and with collaboration delay between base stations The case of Figure 7c may have the longest transmission processing time.

The transmission processing time or transmission processing delay time based on FIGS. 7A to 7C discussed above may vary depending on the connection between the DU and RU, that is, the configuration of the DU and RU. However, since the Dual Access method proposed in this disclosure uses a direct connection configuration, transmission processing time can be minimized. This shortening of the transmission processing time will be evaluated as a method suitable for low-latency transmission such as XR described above.

3. Handover within dual access TRP

3.1. Master DU and Secondary DU

Figure 9 is an example diagram configuring a network with dual access TRP according to an embodiment of the present disclosure.

Referring to FIG. 9, it includes DU A (901) and DU B (902), and DU A (901) and DU B (902) may be included in one base station or may be included in different base stations. Below DU A (901), three TRPs (911, 912, 913) are connected. Below DU B (902), three TRPs (913, 914, 915) are connected.

Each of the TRPs 911, 912, 913, 914, and 915 may have a TRP coverage based on the distance that the wireless signal can reach. In Figure 9, the area of TRP #1 (911) and the area of TRP #2 (912) are not illustrated, and the area (912a) of TRP A (912) and the area (913a) of TRP B (913) TRP C ( Only the area 914a of 914) is illustrated.

As illustrated in FIG. 9, TRP areas (912a, 913a, 914a) are formed up to the location where the wireless signal transmitted from the TRP arrives, and when a terminal is located between two TRPs, the same wireless resources are provided in each TRP. When transmitting the same data using , the signal has the effect of being added. In this way, when different TRPs transmit the same data through the same radio resource, the quality of the signal increases for the terminal, and when different TRPs transmit different data through the same radio resource, it acts as a mutual interference signal from the terminal's point of view. The quality of the signal is reduced.

Here, TRP B (913) is a dual connection TRP and can be connected to one master DU (901) and one or more secondary DUs (902). At this time, TRP B (913), which is a dual connectivity TRP, can configure a master DU association (association) with the master DU (901) and a secondary DU association (association) with the secondary DU (902).

In this case, each of the master DU 901 and the secondary DU 902 can exclusively use physical resource block (PRB)(s), which are radio resources. At a specific point in time, the DU to which PRB(s), which are frequency axis radio resources, are allocated may be determined. The dual connectivity TRP (913) can integrate resources managed by the master DU (901) and resources managed by the secondary DU (902), and can transmit and receive wireless signals in PRBs in the frequency domain.

PRB resources used between DUs may change depending on the time of day based on shared information. Management authority for PRB resources can be operated fixedly for a specific time. Management authority for PRB resources in a certain time unit is determined by agreement between DUs, and a specific DU manages PRB resources during this time unit. This time unit can be configured as the minimum time unit of the wireless resource. For example, this time unit may be a symbol unit, a slot unit, or a frame unit.

The dual access TRP (913) can generate and transmit a wireless signal based on data received from the master DU (901) and the secondary DU (902) in the downlink direction, and can generate and transmit a wireless signal obtained from the wireless signal received in the uplink direction. Data can be provided to all or part of the master DU (901) and secondary DU (902).

The dual access TRP (913) generates a wireless signal based on data received from the master DU (901) and the secondary DU (902) and manages the PRB(s) managed by the master DU (901) and the secondary DU (902). PRB(s) can transmit in the downlink direction through integrated resources. Dual access TRP can transmit the generated wireless signal to the terminal.

The dual access TRP (913) receives a wireless signal transmitted by the terminal through a resource that integrates the PRB (s) managed by the master DU (901) and the PRB (s) managed by the secondary DU (902) in the uplink direction. And, data can be obtained from the received wireless signal and transmitted to the master DU (901) and the secondary DU (902). Each DU can separate data corresponding to the PRB(s) it manages from the data received from the dual connectivity TRP 913. Alternatively, the dual connectivity TRP 913 may obtain data by receiving a wireless signal transmitted by the terminal in the uplink direction and separate the data corresponding to the PRB(s) managed by each DU. That is, the dual connectivity TRP 913 can deliver data separated for each DU to the corresponding DU.

Figure 10 is an example diagram for explaining SS/PBCH transmission areas and SIB transmission areas according to an embodiment of the present disclosure.

3.2. SS/PBCH (synchronization signal/physical broadcast channel)

Since SS/PBCH includes base station unit (or CU) information, TRPs connected to the same DU can transmit the same SS/PBCH. Each TRP can repeatedly transmit the same SS/PBCH at a predetermined time period. The terminal can repeatedly receive SS/PBCH and obtain SS/PBCH information using the received SS/PBCHs.

In general, SS/PBCH may include a cell identifier and a master information block (MIB) of a broadcast channel (BCH). The MIB may contain information about the resource through which the SIB (system information block) is transmitted. SS/PBCH may be associated with a base station including the master DU (901). SIB transmitted from resources obtained from MIB may be associated with the master DU (901).

In FIG. 10, the dual access TRP 913 can transmit SS/PBCH A in the TRP B area. SS/PBCH A may include information about the resource through which SIB A is transmitted.

3.3. SIB

In general, SIB can be transmitted for each TRP. In general, the TRP can transmit a SIB through resources indicated in SS/PBCH (i.e., MIB of SS/PBCH), and the SIB can include information about the base station associated with the master DU. Dual access TRP can transmit both the SIB associated with the master DU and the SIB associated with the secondary DU. In this case, the dual access TRP can transmit the SIB in one of the following ways.

Master DU-led SIB transmission: The dual connectivity TRP 913 can receive both the SIB associated with the master DU 901 and the SIB associated with the secondary DU 902 from the master DU. The master DU (901) can obtain the SIB generated by the secondary DU (902) through a signal exchange procedure with the secondary DU (902) and deliver it to the dual connectivity TRP (913). All SIBs (SIBs associated with the master DU and SIBs associated with the secondary DUs) may be transmitted on radio resources managed by the master DU (901).

Secondary DU transmits SIB: The dual connectivity TRP can receive the SIB associated with the master DU from the master DU and the SIB associated with the secondary DU from the secondary DU. Each SIB may be transmitted on radio resources managed by the DU with which each SIB is associated.

SIB A allocates radio resources of SIB B: Allocation information of radio resources that can receive a SIB (e.g., SIB B) associated with the secondary DU (902) from a SIB (e.g., SIB A) associated with the master DU (901) can be obtained. The terminal receives the SS/PBCH transmitted by the dual connectivity TRP (913) in the area of the dual connectivity TRP (913), and the SIB (i.e. SIB A) associated with the master DU (901) included in the SS/PBCH is transmitted. You can check the allocation information of wireless resources. The terminal can check the allocation information of radio resources through which the SIB (i.e., SIB B) associated with the secondary DU 902 is transmitted from SIB A. Afterwards, the UE can receive the SIB (i.e., SIB B) associated with the secondary DU. The radio resource on which SIB B transmitted by the dual access TRP 913 is transmitted may be different from the radio resource on which SIB B transmitted by the adjacent TRP (eg, TRP 914) is transmitted.

Continuous SIB B radio resource utilization: A dual connectivity TRP 913 transmitting a SIB (e.g., SIB B) associated with the secondary DU 902 and an adjacent TRP (e.g., TRP 914) may transmit SIB B on the same radio resource. . The terminal that received SIB B from an adjacent TRP (e.g., 914) can receive SIB B using the radio resource information on which SIB B was received. In addition, SIB B can be transmitted in the dual access TRP 913 by using the same radio resources used to transmit SIB B in the adjacent TRP (eg, 914).

SIB A includes information on SIB B: In a method of transmitting SIB led by the master DU (901), the master DU (901) receives the SIB (e.g., SIB B) from the secondary DU (902) and transmits the received secondary DU The contents of the SIB (eg, SIB B) of 902 may be included in the SIB (eg, SIB A) associated with the master DU. The dual access TRP (913) is a SIB that includes both the contents of the SIB (i.e., SIB A) associated with the master DU (901) and the contents of the SIB (i.e., SIB B) associated with the secondary DU (902) in the wireless resources of the master DU. (i.e., SIB A + SIB B) can be transmitted. Additionally, the dual connectivity TRP 913 may transmit the SIB (i.e., SIB B) associated with the secondary DU through the radio resources of the secondary DU 902.

Transfer of difference information between SIBs: The dual connectivity TRP 913 is responsible for the difference between the contents of the SIB associated with the master DU 901 (i.e., SIB A) and the contents of the SIB associated with the secondary DU 902 (i.e., SIB B). Information regarding this can be transmitted through the wireless resources of the master DU (901). Common information between the contents of the SIB (i.e., SIB A) associated with the master DU and the contents of the SIB (i.e., SIB B) associated with the secondary DU is included only in the SIB (i.e., SIB A) associated with the master DU 901 and is included in the master DU. Can be transmitted through resources. Difference information between the contents of the SIB associated with the master DU and the contents of the SIB associated with the secondary DU may be included in the SIB associated with the secondary DU and transmitted through the resources of the secondary DU.

Below, a specific example of utilizing SIB is described with reference to FIG. 10.

TRP B (913), which is a dual access TRP, can configure a master DU association with DU A (901) and a secondary DU connection with DU B (902). Since the dual connectivity TRP (913) configures a master DU connection with DU A (901), it can configure and transmit SS/PBCH A related to DU A (901).

The dual connectivity TRP (913) is included in the coverage of DU A (901) and the coverage of DU B (902), and must be able to transmit both SIB A and SIB B. SS/PBCH A may include radio resource information allocating radio resources of SIB A. The terminal can receive SS/PBCH A to acquire radio resources of SIB A and receive SIB A from the radio resources.

SIB method configured in a distributed manner (distributed SIB method): Radio resource information allocating the radio resources of SIB B may be included in SIB A. SIB A, which includes radio resource information allocating the radio resources of SIB B, can be expressed as SIB A'. The terminal can receive SIB A', obtain radio resource information allocating the radio resources of SIB B from SIB A', and receive SIB B through the radio resources of SIB B.

SIB method configured in an integrated manner (integrated SIB method): SIB A and SIB B can be transmitted together in radio resources managed by DU A, the master DU. The terminal can receive both SIB A and SIB B after receiving SS/PBCH A.

The integrated SIB method and the distributed SIB method can be operated together. In Figure 10, an example is provided by configuring the SIB in an integrated manner, where SIB A and SIB B are transmitted on radio resources managed by DU A, the master DU, and SIB B is transmitted on radio resources managed by DU B, the secondary DU. do. The terminal can receive SIB B after receiving SS/PBCH A from the dual connectivity TRP (913).

Meanwhile, the terminal that receives SIB B from TRP C (914) and moves to TRP B (913) can receive SIB B from TRP B (913). When SIB is configured in a distributed manner, the terminal receives SS/PBCH A from the TRP B (913) area, receives SIB A from the resource indicated by SS/PBCH A, and receives SIB B from the resource indicated by SIB A. You can receive it. Alternatively, the terminal can receive SIB B using the same radio resource allocation information of SIB B that was received from TRP C (914).

When the SIB is configured in an integrated manner, the terminal that moves from TRP C (914) to TRP B (913) receives SS/PBCH A from TRP B (913) and receives SIB B from the resource indicated by SS/PBCH A. You can receive it. A terminal located in TRP B can receive both SIB A and SIB B.

3.3.1. DU selection information (terminal selection support)

A terminal located in the area of a dual connectivity TRP can select a PRB(s) from among the PRB(s) of the master DU and the PRB(s) of the secondary DU. For this purpose, information regarding the conditions for selecting the PRB(s) of the master DU and the conditions for selecting the PRB(s) of the secondary DU (i.e., DU selection information) may be included in the SIB and transmitted. If information about the above conditions is not included in the SIB or the UE does not satisfy any of the above conditions, the UE may use the PRB(s) of the master DU.

The UE can receive the SIB associated with the master DU based on SS/PBCH. The terminal can obtain DU selection information from the received SIB and select a DU according to the condition(s) indicated by the DU selection information. The UE can use PRB(s) managed by the selected DU.

3.3.2. Configuring intra-base station SIB

The base station may be composed of DU and RU/TRP. Since a single access TRP is associated with one DU, a SIB can be configured to reflect one DU.

3.3.3. Inter-base station SIB configuration

The base station may be composed of DU and RU/TRP. Since the dual connectivity TRP is associated with two DUs (master DU and secondary DU), the SIB can be configured to reflect the two DUs.

3.3.4. Network information SIB configuration

A wireless environment can be created by connecting a base station to another network. The SIB can be configured to include configuration information of adjacent networks.

3.4. Initial access procedure

The terminal can perform a process of searching for a TRP with a good wireless channel and use the TRP information obtained through this process to proceed with the initial access procedure.

3.4.1. Beam navigation

Beam search: A DU that manages radio resources can configure the service area (coverage) of the base station using multiple TRPs. A beam search procedure can be used as a method to distinguish multiple TRPs within a DU. The base station can operate TRPs by allocating one or more beams to each TRP. The base station can transmit a wireless signal by allocating time/space resources to each beam. The wireless signal may be a wireless signal including SS/PBCH. The terminal can check the TRP of the area where the terminal is located by checking the received beam through a beam search procedure. The terminal can identify the TRP based on the radio resource from which the radio signal was received. The terminal can transmit information about the preferred beam identified through the beam search procedure to the base station.

TRP confirmation using beam search history: The number of beams operated by multiple TRPs may be less than the number of beams that the base station can use. The base station can utilize beam search by activating multiple spatially differentiated beams from a radio resource that identifies a specific beam. The terminal can check the TRP by simultaneously using information about the good channel beam and information about neighboring beams. Alternatively, the terminal can transmit information about beams to the base station, and the base station can check the TRP where the terminal is located. For example, when information about 4 beams is used, even if beam 1 is indicated as the preferred beam, if the next priority beams are different, the TRP where the terminal is located may be identified differently depending on the next priority beams. .

Adjacent beam search information: Information on preferred beams and information on lower priority beams can be obtained in the beam search procedure. In the beam search procedure, the terminal can store information obtained at each search opportunity and give priority to beams according to the received signal strength of the beams. The terminal can identify information (eg, identifier) of the corresponding beam from information on the radio resource from which the beam was received. The terminal may transmit information on lower priority beams along with information on the best (eg, highest priority) beam to the base station. The terminal can transmit the information on the beams obtained through the beam search procedure in the range and method requested by the base station.

Meanwhile, the terminal performs the initial access procedure (3.4.2) to the master DU using the preferred beam selected through the beam search procedure, or selects the master DU or secondary DU in the beam search procedure and performs the initial access procedure (3.4.3). can be performed.

3.4.2. Perform initial connection procedure with master DU

Random access to master DU: The terminal may attempt an initial access procedure including a random access procedure using the most preferred beam space. The base station that receives the random access message (random access preamble) can transmit a random access response through all beams using the same beam space. If the TRP has not yet been identified, it is not possible to specify a specific beam included in the TRP.

Beam search result reporting: The terminal reports information on the beam(s) received as a result of the beam search procedure to the base station. In the case of single-connection TRP, the TRP is connected to one DU, so the process of selecting a DU is not necessary. In the case of dual connectivity TRP, the terminal can transmit information on the received beam(s) to the connected master DU.

Delivering the first message to the master DU: The UE can transmit the beam search history by transmitting the first message after random access to the base station containing the master DU. The base station that has received the beam search history can use the received beam search history to identify the TRP where the terminal is located. The base station may transmit a response message to the initial message through the beam of the identified TRP.

Base station selection of DU: The base station can select the master DU or secondary DU using the location of the terminal specified by the beam in the TRP. The base station can transmit information about the selected DU to the terminal by including it in a response message. The terminal that has received information about the selected DU can proceed with the connection procedure using resources managed by the selected DU. If the master DU is selected according to information about the selected DU, the terminal does not need to change the DU. If a secondary DU is selected according to information about the selected DU, the terminal can proceed with the initial access procedure using the PRB(s) managed by the secondary DU.

3.4.3. The terminal selects DU and performs the initial access procedure.

Providing DU selection conditions through SIB: The base station can transmit information about the conditions for the UE to select a DU in the beam search procedure by including it in the SIB. For example, DU selection condition(s) may be provided to select a DU using radio information including the most preferred beam and beam history.

DU selection by the terminal: The terminal can select a DU that is the target of the initial access procedure using the beam search results and the provided DU selection condition(s). The UE can select a DU that satisfies the DU selection conditions. If there is no DU that satisfies the DU selection conditions, the UE can select a master DU, select a random DU, or select a fixed DU.

Use of PRB(s) of the selected DU: The UE may proceed with the initial access procedure using the PRB(s) managed by the selected DU. The terminal can proceed with the initial access procedure, including the random access procedure, with the selected DU.

TRP confirmation using beam search history: The number of beams operated in multiple TRPs may be less than the number of beams that the base station can use. The base station can utilize beam search by activating multiple spatially differentiated beams from a radio resource that identifies a specific beam. The terminal can check the TRP by simultaneously using information about the good channel beam and information about neighboring beams.

Providing TRP information in random access: The terminal can provide information on the TRP of the area in which it is located using the code used in the random access procedure. The base station can configure random access codes as many as the number of TRPs operated by the base station, and provide information about the configured random access codes to the terminal through SIB. The terminal transmits a random access code corresponding to the TRP identified in the random access process to the base station, and the base station can check the TRP through the random access code. The base station may transmit a random access response message to the terminal through the identified TRP and the beam of the identified TRP.

Providing TRP information in a message: If the random access procedure does not include a procedure for identifying the TRP (a procedure in which the terminal provides TRP information), the terminal may provide the base station with information on the TRP in the area where it is located through a message. You can. In the procedures before information on the TRP of the area where the terminal is located is provided, the wireless resources through which the terminal's wireless signal is transmitted and the wireless resource through which the base station's wireless signal is transmitted may be equally allocated to all TRPs sharing the beam. there is. The base station that has received the TRP information may transmit a random access response message to the terminal through the identified TRP and the beam of the identified TRP.

3.4.4. Message access procedure

After the selected TRP information is shared between the terminal and the base station, message exchange for the initial access procedure may be performed.

3.5. Handover Procedure

In the process of moving the UE, the TRP area change procedure (3.5.2) within the same DU may be performed in the process of moving the boundary of the TRP area (coverage). Additionally, the terminal may proceed with the DU area change procedure (3.5.3) within the dual access TRP.

3.5.1. Explore adjacent TRPs

The terminal may periodically perform a beam search procedure while moving. The base station may provide beam areas for the terminal to search for beams and allocate resources for each beam to each beam area. The base station transmits a beam for each beam area resource, and the terminal can search for the beam by obtaining beam area resource information at the location where the beam is received. In the beam search procedure, the UE can search for a beam through reception of SS/PBCH provided by the current TRP.

In the beam search procedure, the UE can proceed with the process of receiving adjacent SS/PBCH from the radio signal received for each beam area resource and simultaneously search for the beam of the adjacent TRP. The terminal may identify information (eg, identifier) of the beam based on the beam area resources in which the beam was received, and determine the TRP based on the beam information.

3.5.2. Change of TRP area within the same DU

In the process of moving between TRP areas, the UE can proceed with a procedure to search for neighboring TRPs, and in the procedure for searching for neighboring TRPs, the UE can determine a candidate TRP (target TRP) that is the target of handover.

Neighboring TRP information report, target TRP switching request: A TRP area change is detected, but it can be confirmed that the serving TRP and the target TRP are included in the same DU (e.g., confirmed based on the SIB received from the serving TRP and the target TRP) . The terminal may obtain a beam identifier from the radio resource information of the changed beam and report this identifier to the serving TRP (i.e., transmit a neighboring TRP information report message). This means requesting TRP switching to the target TRP. The adjacent TRP information report message includes the beam identifier of the target TRP or the radio resource identifier of the searched area, and may additionally include information such as the signal strength of the received beam. The serving TRP may forward the received neighboring TRP information report message to the DU.

TRP switching command: DU may decide TRP switching based on the neighbor TRP information report message received from the serving TRP. To start the procedure of switching the serving TRP for the UE to the target TRP, the DU may transmit a TRP switching command to the UE via the serving TRP. The UE may receive a TRP switching command from the DU, change the serving TRP to the target TRP, and change the serving beam to the beam associated with the target TRP.

Random access to the target TRP: The terminal can start the access procedure to the target TRP through a random access procedure on the radio resources allocated to the target TRP. If the radius of the target TRP area is narrow, the terminal can skip the random access procedure to the target TRP and start the TRP switching completion procedure.

TRP switching completion: The terminal may transmit a TRP switching completion message on the radio resource allocated to the target TRP. The terminal can access the target TRP and use the target TRP as a serving TRP according to the transmission of the TRP switching completion message.

TRP switching confirmation: To confirm that the UE's TRP switching procedure has been completed, the DU may transmit a TRP switching acknowledgment message to the UE. The DU may confirm that the UE's TRP switching procedure has been completed by transmitting data to the UE without transmitting a TRP switching confirmation message. The terminal that receives the TRP switching confirmation message or data from the DU can recognize that the TRP area change procedure within the DU has been completed.

3.5.3. Change of DU area within dual access TRP

The UE may perform a beam search procedure while moving within the dual access TRP and perform a procedure for DU change according to beam change. A change in DU may require a change in the protocol including the MAC that performs scheduling. Protocol changes require an RRC reconfiguration procedure between the base station and the terminal.

Reporting beam search results to DU: The UE that detects a beam change within the dual access TRP can report the beam search results (including information about the target DU) to the current serving DU. The operation of determining DU change based on the beam search result reported by the UE may be performed in the DU or CU. If the serving DU decides to change the DU, the serving DU can transmit information indicating that it has decided to switch (change) the DU to the CU. Meanwhile, the serving DU may be a master DU connected to the dual connectivity TRP, and the target DU may be a secondary DU connected to the dual connectivity TRP. Alternatively, the serving DU may be a secondary DU connected to the dual connectivity TRP and the target DU may be a master DU connected to the dual connectivity TRP.

The CU decides to change the DU and commands the DU to change: The CU that receives the beam search result from the terminal or the DU change decision from the serving DU can determine the change of the DU. Afterwards, the CU may transmit a DU change command message (command message instructing DU switching) to the UE. The DU change command message transmitted from the CU to the UE may be an RRC reconfiguration message. The DU change command message transmitted from the CU to the UE may be transmitted on radio resources managed by the serving DU. The CU may instruct the serving DU and target DU to perform procedures for changing DUs.

Terminal's DU change complete: The terminal that has received the DU change command message from the CU can perform a connection procedure to the target DU on the radio resource managed by the target DU. The UE may transmit a DU change completion message to the CU on radio resources managed by the target DU. The DU change complete message transmitted from the UE to the CU may be an RRC reconfiguration complete message.

The UE confirms the DU change: The CU may transmit a confirmation message (e.g., radio link control (RLC) ACK) to the UE for the DU change completion message transmitted by the UE. The terminal that receives the confirmation message (eg, RLC ACK) can confirm that the DU change has been completed.

The operation of the method according to an embodiment of the present invention can be implemented as a computer-readable program or code on a computer-readable recording medium.　Computer-readable recording media include all types of recording devices that store information that can be read by a computer system.　Additionally, computer-readable recording media can be distributed across networked computer systems so that computer-readable programs or codes can be stored and executed in a distributed manner.

Additionally, computer-readable recording media may include hardware devices specially configured to store and execute program instructions, such as ROM, RAM, or flash memory.　Program instructions may include not only machine language code such as that created by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like.

Although some aspects of the invention have been described in the context of an apparatus, it may also refer to a corresponding method description, where a block or device corresponds to a method step or feature of a method step.　Similarly, aspects described in the context of a method may also be represented by corresponding blocks or items or features of a corresponding device.　Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer, or an electronic circuit.　In some embodiments, at least one or more of the most important method steps may be performed by such a device.

In embodiments, a programmable logic device (e.g., a field programmable gate array) may be used to perform some or all of the functionality of the methods described herein.　In embodiments, a field-programmable gate array may operate in conjunction with a microprocessor to perform one of the methods described herein.　In general, it is desirable for the methods to be performed by some hardware device.

Although the present invention has been described above with reference to preferred embodiments, those skilled in the art may make various modifications and changes to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand that it is possible.

Claims (20)

As a terminal method for handover,
Performing a procedure to search for adjacent TRPs including a target TRP (transmission and reception point);
Transmitting a neighbor TRP information report message including information about the discovered neighbor TRPs to the current serving TRP;
Receiving, from a distributed unit (DU) to which the terminal is connected, a command message instructing TRP switching to switch the serving TRP of the terminal from the current serving TRP to the target TRP through the serving TRP; and
Comprising a step of performing a connection procedure for the target TRP according to the command message instructing the TRP switching,
The TRP switching is determined based on the neighbor TRP information report message,
method. In claim 1,
The current serving TRP and the target TRP are TRPs commonly connected to the DU,
method. In claim 1,
The neighbor TRP information report message includes a beam identifier of the target TRP,
method. In claim 1,
Transmitting a TRP switching complete message to the DU; and
Comprising receiving a TRP switching acknowledgment message from the DU,
method. As a terminal method for handover,
Detecting a beam change within a dual access transmission and reception point (TRP) through a beam search procedure;
reporting a beam search result indicating a change in the beam to a current serving distributed unit (DU) through the dual connectivity TRP;
Receiving a command message instructing DU switching to switch the serving DU of the terminal from the current serving DU to the target DU from a central unit (CU) to which the terminal is connected through the dual connectivity TRP; and
Including performing a connection procedure to the target DU,
method. In claim 5,
The DU switching is determined in the current serving DU and notified to the CU, or determined by the CU based on the beam search result from the terminal.
method. In claim 5,
The current serving DU is a master DU connected to the dual connectivity TRP and the target DU is a secondary DU connected to the dual connectivity TRP, or the current serving DU is a secondary DU connected to the dual connectivity TRP and the target DU is a master DU connected to the dual access TRP,
method, In claim 7,
The radio resources managed by the current serving DU are mutually exclusive from the radio resources managed by the target DU.
method. In claim 8,
The command message instructing DU switching is an RRC (radio resource control) reconfiguration message,
method. In claim 9,
The command message instructing the DU switching is transmitted through radio resources managed by the current serving DU.
method. In claim 8,
The connection procedure to the target DU is performed through radio resources managed by the target DU,
method. In claim 8,
Transmitting a DU change completion message to the CU; and
Comprising the step of receiving an acknowledgment message for the DU change completion message transmitted by the terminal from the CU,
method. In claim 12,
The DU change complete message and the confirmation message are transmitted and received through radio resources managed by the current serving DU, the DU change complete message is an RRC reconfiguration complete message, and the confirmation message is a radio link control (RLC) message. ) ACK (acknowledgement) message,
method. In claim 5,
Further comprising receiving a synchronization signal/physical broadcast channel (SS/PBCH) of the CU, a system information block (SIB) associated with the current serving DU, and a SIB associated with the target DU from the dual connectivity TRP,
method. By terminal method,
Receiving a master information block (MIB) from a master distributed unit (DU) connected to the first TRP through a first transmission and reception point (TRP); and
Comprising the step of receiving, through the first TRP, a first system information block (SIB) of the master DU and a second SIB of a first secondary DU connected to the first TRP,
At least one secondary DU including the master DU and the first secondary DU belongs to the same central unit (CU) or different CUs, and different radio resources are allocated to the master CU and the first secondary DU. ,
method. In claim 15,
The MIB contains information about resources for reception of the first SIB and is received through radio resources allocated to the master DU.
method. In claim 15,
The first SIB includes information related to reception of the second SIB,
method. In claim 17,
The first SIB includes information about resources for reception of the second SIB,
method. In claim 17,
At least a portion of the second SIB is received and included in the first SIB,
method. In claim 15,
Common information of the first SIB and the second SIB is received through resources allocated to the master DU, and difference information between the first SIB and the second SIB is received through resources allocated to the first secondary DU. felled,
method.

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