Terminal device, base station, and communication method

Abstract

A terminal device, a base station, and a communication method capable of achieving high communication performance are proposed. The terminal device is capable of executing an L1 / L2 triggered mobility (LTM) and includes a communication control unit for executing a first LTM as a conditional handover. The first LTM is a conditional LTM without a random access procedure.

Description

Terminal device, base station, and communication method

[0001] The present disclosure relates to a terminal device, a base station, and a communication method.

[0002] Technologies related to wireless communication such as cellular communication have been actively developed. In such wireless communication, a change in the connection destination of a terminal device (handover) occurs as the terminal device moves. To achieve higher quality wireless communication, various handover methods have been developed. For example, LTM (L1 / L2 Triggered Mobility), which performs handover at a lower layer, has been developed in recent years.

[0003] RWS-230213, Samsung, “Mobility Enhancements in Rel-19,” 2023

[0004] However, simply applying LTM to a radio access network does not necessarily result in wireless communication with high communication performance (e.g., high resource utilization efficiency, large capacity, high speed, low latency, high reliability, large number of high density, low power consumption, or low processing load).

[0005] Therefore, the present disclosure proposes a terminal device, a base station, and a communication method that can achieve high communication performance.

[0006] It should be noted that the above problem or object is merely one of multiple problems or objects that can be solved or achieved by multiple embodiments disclosed in this specification.

[0007] In order to solve the above problem, a terminal device of one embodiment according to the present disclosure is a terminal device capable of executing LTM (L1 / L2 Triggered Mobility), and is equipped with a communication control unit that executes a first LTM as a conditional handover, and the first LTM is a conditional LTM without a random access procedure.

[0008] 1 is a diagram illustrating an example of the configuration of a communication system according to an embodiment. FIG. 1 is a diagram illustrating the configuration of a management device according to an embodiment. FIG. 2 is a diagram illustrating the configuration of a base station according to an embodiment. FIG. 3 is a diagram illustrating the configuration of a relay station according to an embodiment. FIG. 4 is a diagram illustrating the configuration of a terminal device according to an embodiment. FIG. 5 is a sequence diagram illustrating an example of a procedure for cell level mobility. FIG. 6 is a sequence diagram illustrating an example of a procedure for conditional handover. FIG. 7 is a sequence diagram illustrating an example of a procedure for LTM. FIG. 8 is a diagram illustrating a state in which multiple communication points are formed in one communication area. FIG. 9 is a diagram illustrating a state in which multiple communication points are formed in multiple communication areas. FIG. 10 is a diagram for explaining a technique for concentrating power on a specific point. FIG. 11 is a diagram illustrating an example of point forming with a single antenna having many antenna elements. FIG. 12 is a diagram for explaining near field and far field. FIG. 13 is a diagram illustrating the Fraunhofer distance, which is the boundary between the near field and the far field. FIG. 14 is a diagram illustrating an example of point forming in a distributed antenna environment. FIG. 15 is a sequence diagram illustrating an example of a procedure for RACH-less CLTM without early sync. FIG. 16 is a sequence diagram illustrating an example of a procedure for CLTM with early sync. FIG. 17 is a sequence diagram illustrating another example of a procedure for CLTM with early sync. FIG. 18 is a sequence diagram illustrating an example of a procedure for UL synchronization according to a fourth embodiment. 13 is a sequence diagram showing another example of the procedure of UL synchronization according to the fourth embodiment.FIG. 14 is a sequence diagram showing another example of the procedure of CLTM with early sync.FIG.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following embodiments, the same components are designated by the same reference numerals, and redundant description will be omitted.

[0010] Additionally, in this description / specification, the phrase "at least one of" following a list of elements is understood to mean that the listed elements are optional. For example, "at least one of A, B, and C" means "(A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C)." "At least one of A, B, or C" and "at least one of A, B, and / or C" are similar to "at least one of A, B, and C." Here, A, B, and C are all arbitrary expressions (e.g., words, phrases, clauses, terms, or items).

[0011] In addition, in this specification and drawings, multiple components having substantially the same functional configuration may be distinguished by adding different numbers to the same reference numeral. For example, multiple components having substantially the same functional configuration may be distinguished by adding different numbers to the same reference numerals to the terminal device 40 as needed. １ , 40 ２ , and 40 ３ However, when there is no need to particularly distinguish between multiple components having substantially the same functional configuration, only the same reference numerals are used. For example, the terminal device 40 １ , 40 ２ , and 40 ３ When there is no need to particularly distinguish between them, they will be simply referred to as terminal devices 40.

[0012] One or more embodiments (including examples and variations) described below can be implemented independently. However, at least a portion of the embodiments described below may be implemented in appropriate combination with at least a portion of another embodiment. These embodiments may include novel features that are different from one another. Therefore, these embodiments may contribute to solving different purposes or problems and may produce different effects.

[0013] The present disclosure will be described in the following order: 1. Overview 2. Configuration of a Communication System 2-1. Example of Configuration of a Management Device 2-2. Example of Configuration of a Base Station 2-3. Example of Configuration of a Relay Station 2-4. Example of Configuration of a Terminal Device 3. Handover 3-1. Basic Procedure 3-2. Conditional Handover 3-3. LTM 3-4. Conditional LTM 4. Communication Points 4-1. Definition of Communication Points 4-2. Types of Communication Points 4-3. Reinterpretation of Communication Points 4-4. Specific Examples 4-5. Point Forming 5. Operation of a Communication System 5-1. First Example 5-2. Second Example 5-3. Third Example 5-4. Fourth Example 5-5. Fifth Example 6. Modifications 7. Conclusion

[0014] <<1. Overview>> In recent years, discussions on next-generation wireless communications have been progressing. Wireless communication technologies have been actively developed to meet requirements such as even higher speeds than 5G NR, low-latency, highly reliable communications, large numbers of high-density communications, and simultaneous support of multiple of these. For example, Release 18 of 3GPP (registered trademark) newly introduced LTM (L1 / L2 Triggered Mobility) to achieve even lower-latency wireless communications. LTM is L1 / L2-based mobility (handover). LTM is also known as Lower Layer Triggered Mobility. It is expected that the introduction of LTM will shorten the interruption time due to handover.

[0015] However, simply applying LTM to a radio access network does not necessarily result in wireless communication with high communication performance (e.g., high resource utilization efficiency, large capacity, high speed, low latency, high reliability, large number of high density, low power consumption, or low processing load).

[0016] For example, in an environment where multiple base stations operate (or an environment where multiple cells exist), in the above-mentioned method (LTM), the terminal device must perform processing (random access procedure) related to initial connections with all base stations / cells. This increases the processing load on the terminal device (or the processing time required for handover). When one base station forms multiple cells, the processing load on the base station may also increase. As a result, wireless communication with high communication performance may not be achieved.

[0017] Therefore, in this embodiment, the above problem is solved as follows.

[0018] The communication system of the present embodiment is, for example, a mobile communication system. For example, the communication system of the present embodiment is a cellular communication system such as 5G. The communication system of the present embodiment includes a plurality of communication devices. For example, the communication system of the present embodiment includes a base station and a terminal device.

[0019] The terminal device of this embodiment is configured to be able to execute LTM (L1 / L2 Triggered Mobility). The terminal device is also configured to be able to execute conditional handover (CHO). CHO is a handover executed by the terminal device when one or more handover execution conditions are satisfied. Simply put, CHO is an autonomous switching operation of a connection destination (e.g., a cell) by the terminal device.

[0020] The terminal device may be capable of performing conditional LTM (CLTM) as a conditional handover (CHO). CLTM is an LTM performed by the terminal device when one or more handover execution conditions are satisfied. In short, CLTM is an autonomous connection destination (e.g., cell) switching operation (LTM) performed by the terminal device.

[0021] In this embodiment, the terminal device executes CLTM without a random access procedure (hereinafter referred to as first LTM) as a connection destination switching operation. In the following description, the absence of a random access procedure may be referred to as RACH-less. That is, in the following description, CLTM without a random access procedure may be referred to as RACH-less CLTM (RACH-less Conditional LTM).

[0022] Note that switching the connection destination requires timing advance information that can be used after the switch. Therefore, the first LTM may be a RACH-less CLTM with early sync. In this case, the terminal device may acquire timing advance information that can be used after the switch during early sync.

[0023] The first LTM may be a RACH-less CLTM without early sync. In this case, the terminal device may execute the RACH-less CLTM without early sync if it holds timing advance information that can be used after switching.

[0024] Here, the case where timing advance information that can be used after switching is held may be the case where at least one of the following conditions (A1) to (A4) is satisfied.

[0025] (A1) The timing advance information before the switching is valid even after the switching. (A2) The timing advance information that can be used after the switching is notified from the base station. (A3) The timing advance information that can be used after the switching is notified from another terminal device. (A4) The terminal device is able to measure the timing advance information that it will use after the switching.

[0026] This eliminates the need for a random access procedure when switching the connection destination, thereby reducing the processing load on the terminal device and / or the base station (or the processing time required for handover).As a result, the communication system can achieve wireless communication with high communication performance.

[0027] The outline of this embodiment has been described above, and the communication system 1 of this embodiment will now be described in detail.

[0028] <<2. Configuration of the Communication System>> First, the configuration of the communication system 1 will be described. Fig. 1 is a diagram showing an example configuration of the communication system 1 according to this embodiment. The communication system 1 includes a management device 10, a base station 20, a relay station 30, and a terminal device 40. The communication system 1 provides users with a wireless network (mobile network) that enables mobile communication by having the wireless communication devices that make up the communication system 1 operate in cooperation with each other.

[0029] The wireless network of this embodiment may be, for example, a cellular network configured of a radio access network RAN ​​and a core network CN. The mobile network may include a terminal device 40. In this embodiment, a wireless communication device is a device having a wireless communication function, and in the example of Fig. 1, this corresponds to the base station 20, the relay station 30, and the terminal device 40.

[0030] The communication system 1 may include a plurality of management devices 10, base stations 20, relay stations 30, and terminal devices 40. In the example of FIG. 1, the communication system 1 includes a management device 10 １ and 10 ２ and the base station 20 is provided with １ , 20 ２ , and 20 ３ The communication system 1 also includes a relay station 30. １ and 30 ２ The terminal device 40 is provided with the terminal device 40 １ , 40 ２ , and 40 ３ It is equipped with:

[0031] The terminal device 40 may be configured to connect to a network using radio access technologies (RATs) such as LTE (Long Term Evolution), NR (New Radio), B5G (Beyond 5G), 6G, Wi-Fi, Bluetooth (registered trademark), etc. In this case, the terminal device 40 may be configured to be able to use different radio access technologies (wireless communication methods). For example, the terminal device 40 may be configured to be able to use NR and Wi-Fi. Furthermore, the terminal device 40 may be configured to be able to use different cellular communication technologies (e.g., LTE, NR, B5G, or 6G). In the following description, the terminal device 40 may be referred to as UE (User Equipment) 40.

[0032] LTE and NR are types of cellular communication technologies that enable mobile communication for terminal devices by arranging multiple areas covered by devices with electromagnetic wave transmission and reception functions (for example, base stations or TRPs (Transmission Reception Points)) in the form of cells. 6G, as a type of cellular communication technology, has the potential to become a technology that enables mobile communication for terminal devices by arranging multiple areas covered by base stations in the form of cells.

[0033] In the following description, "LTE" includes LTE-A (LTE-Advanced), LTE-A Pro (LTE-Advanced Pro), and EUTRA (Evolved Universal Terrestrial Radio Access). NR includes NRAT (New Radio Access Technology) and FEUTRA (Further EUTRA). A single base station or one TRP may manage multiple cells. In the following description, a cell corresponding to LTE is referred to as an LTE cell, and a cell corresponding to NR is referred to as an NR cell.

[0034] NR is the next generation (5th generation) radio access technology after LTE (4th generation communications including LTE-Advanced and LTE-Advanced Pro). NR is a radio access technology that can support various use cases, including eMBB (Enhanced Mobile Broadband), mMTC (Massive Machine Type Communications), and URLLC (Ultra-Reliable and Low Latency Communications). NR was standardized in 3GPP (registered trademark) Rel-15 as a technical framework that supports the usage scenarios, requirements, and deployment scenarios of these use cases. 3GPP is also studying next-generation technologies, including enhancements to the NR standard. For example, in Rel-19, standardization activities are underway for 6G (B5G (Beyond 5G)), the next-generation communications standard.

[0035] 6G is the next generation of cellular communication technology, following NR and 5GS (5G system), which are fifth-generation mobile communications. 6G is required to simultaneously achieve multiple axes: high speed, large capacity, low latency, high reliability, and multiple simultaneous connections. 6G includes radio access technology and network technology between base stations, core networks, and data networks. 6G also includes technologies for the enhancement of eMBB, mMTC, and URLLC (extreme connectivity), which were major use cases or requirements of NR. 6G also includes new technologies in new areas. For example, 6G may include technologies related to AI (cognitive network, AI native air interface), sensing (including radar / RF sensing and network as a sensor), and terahertz communication.

[0036] The wireless network described above or below may correspond to at least one of radio access technologies (RATs) such as LTE, NR, B5G, and 6G. LTE, NR, and 6G are types of cellular communication technologies that enable mobile communication for terminal devices by arranging multiple areas covered by base stations in the form of cells. The wireless access method used by the communication system 1 is not limited to LTE, NR, B5G, and 6G, and may be other wireless access methods such as W-CDMA (Wideband Code Division Multiple Access) and cdma2000 (Code Division Multiple Access 2000).

[0037] Furthermore, the base station 20 and the relay station 30 may be terrestrial stations or non-terrestrial stations. The non-terrestrial stations may be satellite stations or aircraft stations. If the non-terrestrial stations are satellite stations, the wireless network may be a bent-pipe (transparent) type mobile satellite communication system.

[0038] In this embodiment, terrestrial stations and terrestrial base stations refer to base stations and relay stations installed on the ground. Here, "terrestrial" refers to terrestrial in a broad sense, including not only land but also underground, on water, and underwater. In the following description, the term "terrestrial station" may be replaced with "gateway."

[0039] Note that an LTE base station may be referred to as an eNodeB (Evolved Node B) or eNB. An NR base station may be referred to as a gNodeB or gNB. A 6G base station may be referred to as a 6G NodeB (6GNB). In LTE, NR, and 6G, a terminal device (also referred to as a mobile station or terminal) may be referred to as a UE (User Equipment). Note that a terminal device is a type of communication device and is also referred to as a mobile station or terminal.

[0040] The terminal device 40 may be able to connect to a network using a wireless access technology (wireless communication method) other than LTE, NR, B5G, 6G, Wi-Fi, or Bluetooth. For example, the terminal device 40 may be able to connect to a network using low power wide area (LPWA) communication. The terminal device 40 may also be able to connect to a network using proprietary wireless communication.

[0041] Here, LPWA communication refers to wireless communication that enables low-power, wide-area communication. For example, LPWA wireless refers to IoT (Internet of Things) wireless communication using a specific low-power radio (e.g., the 920 MHz band) or the ISM (Industry-Science-Medical) band. LPWA wireless may include LTE-M, which operates in the cellular frequency band, and / or C-IoT (Cellular IoT), represented by NB-IoT. The LPWA communication used by the terminal device 40 may conform to the LPWA standard. The LPWA standard may be, for example, at least one of ELTRES, ZETA, SIGFOX, LoRaWAN, LTE-M, and NB-IoT. Of course, the LPWA standard is not limited to these and may be another LPWA standard.

[0042] 1 may be considered as devices in a logical sense, i.e., a part of each wireless communication device may be realized by a virtual machine (VM), a container such as Docker, or the like, and these may be physically implemented on the same hardware.

[0043] In this embodiment, the concept of a wireless communication device includes not only portable mobile devices (terminal devices) such as mobile terminals, but also devices installed in structures or mobile bodies. The structures or mobile bodies themselves may be considered wireless communication devices. Furthermore, the concept of a wireless communication device includes not only terminal devices 40 but also base stations 20 and relay stations 30. A wireless communication device is a type of processing device or information processing device. A wireless communication device can also be referred to as a transmitting device or a receiving device.

[0044] The following describes in detail the configuration of each wireless communication device that makes up the communication system 1. Note that the configuration of each wireless communication device shown below is merely an example. The configuration of each wireless communication device may be different from the configuration shown below.

[0045] <2-1. Example of Configuration of Management Device> Next, an example of the configuration of the management device 10 will be described.

[0046] The management device 10 is an information processing device (computer) that manages a wireless network. For example, the management device 10 is an information processing device that manages communication of the base station 20.

[0047] The management device 10 may be a device constituting a core network CN. For example, the management device 10 may be a device having a function as an MME (Mobility Management Entity). The management device 10 may also be a device having a function as an AMF (Access and Mobility Management Function) and / or an SMF (Session Management Function). The MME, AMF, and SMF are control plane network function nodes in the core network CN. The management device 10 may be a device having a function as a control plane network function (6G CPNF) in 6G. The 6G CPNF may be composed of one or more logical nodes.

[0048] Of course, the functions of the management device 10 are not limited to MME, AMF, SMF, and 6G CPNF. The management device 10 may be a device having functions as a Network Slice Selection Function (NSSF), an Authentication Server Function (AUSF), a Policy Control Function (PCF), and a Unified Data Management (UDM). Furthermore, the management device 10 may be a device having functions as a Home Subscriber Server (HSS).

[0049] The management device 10 may have a gateway function. For example, the management device 10 may have a function as an S-GW (Serving Gateway) or a P-GW (Packet Data Network Gateway). The management device 10 may also have a function as a UPF (User Plane Function). In this case, the management device 10 may have multiple UPFs. The management device 10 may also be a device that has a function as a 6G User Plane Network Function (6G UPNF).

[0050] The core network CN is composed of multiple network functions, and each network function may be consolidated into one physical device or distributed across multiple physical devices. That is, the management device 10 may be distributed across multiple devices. Furthermore, this distributed distribution may be controlled to be executed dynamically. The base station 20, relay station 30, and management device 10 constitute a single network, providing wireless communication services to terminal devices 40. The management device 10 is connected to the Internet, and the terminal devices 40 can use various services provided via the Internet via the base station 20 and / or relay station 30.

[0051] The management device 10 does not necessarily have to be a device that constitutes the core network CN. For example, assume that the core network CN is a core network of W-CDMA (Wideband Code Division Multiple Access) or cdma2000 (Code Division Multiple Access 2000). In this case, the management device 10 may be a device that functions as an RNC (Radio Network Controller).

[0052] FIG. 2 is a diagram showing the configuration of the management device 10 according to this embodiment. The management device 10 includes a communication unit 11, a storage unit 12, and a control unit 13. The configuration shown in FIG. 2 is a functional configuration, and the hardware configuration may be different from this. Furthermore, the functions of the management device 10 may be statically or dynamically distributed and implemented in multiple physically separated configurations. The management device 10 may also be configured by multiple server devices.

[0053] The communication unit 11 is a communication interface for communicating with a wireless communication device (e.g., base station 20). The communication unit 11 may be a network interface or a device connection interface. The communication unit 11 may be a LAN (Local Area Network) interface such as a NIC (Network Interface Card), or a Universal Serial Bus (USB) interface configured by a USB host controller or a USB port. The communication unit 11 may be a wired interface or a wireless interface. The communication unit 11 is controlled by the control unit 13.

[0054] The storage unit 12 is a readable / writable storage device such as a DRAM, an SRAM, a flash memory, or a hard disk. The storage unit 12 stores, for example, the connection state of the terminal device 40. The storage unit 12 stores the state of the RRC (Radio Resource Control) of the terminal device 40 and the state of the ECM (EPS Connection Management) or the 5G System CM (Connection Management). The storage unit 12 may function as a home memory that stores location information of the terminal device 40.

[0055] The control unit 13 is a controller that controls each unit of the management device 10. The control unit 13 may be realized by a processor such as a CPU or MPU. In particular, the control unit 13 may be realized by a processor executing various programs stored in a storage device inside the management device 10 using RAM or the like as a work area. The control unit 13 may be realized by an integrated circuit such as an ASIC or FPGA. The control unit 13 may also be realized by a GPU. A CPU, MPU, ASIC, FPGA, and GPU can all be considered controllers. The control unit 13 may be composed of multiple physically separated objects. For example, the control unit 13 may be composed of multiple semiconductor chips.

[0056] The operation of the control unit 13 may be the same as the operation of the control unit (control unit 23 , control unit 33 , or control unit 43 ) of the base station 20 , relay station 30 , or terminal device 40 .

[0057] <2-2. Configuration Example of Base Station> Next, a configuration example of the base station 20 will be described.

[0058] The base station 20 is a wireless communication device that performs wireless communication with other wireless communication devices (e.g., a relay station 30, a terminal device 40, or another base station 20). The base station 20 may wirelessly communicate with the terminal device 40 via the relay station 30, or may wirelessly communicate with the terminal device 40 directly.

[0059] The base station 20 is a device equivalent to a wireless base station (for example, a base station, a Node B, an eNB, a gNB, or a 6GNB) or a wireless access point. In the following description, the base station 20 may be referred to as a BS (Base Station), a Node B, an eNB, a gNB, a 6GNB, or a BS20.

[0060] The base station 20 may be a wireless relay station (e.g., a relay station 30 described later). The base station 20 may be an optical device called a remote radio head (RRH). The base station 20 may be a receiving station such as a field pickup unit (FPU). The base station 20 may be an integrated access and backhaul (IAB) donor node or an IAB relay node that provides wireless access lines and wireless backhaul lines using time division multiplexing, frequency division multiplexing, or space division multiplexing.

[0061] The wireless access technology used by the base station 20 may be cellular communication technology. The wireless access technology used by the base station 20 may be wireless LAN technology. The wireless access technology used by the base station 20 may be low-power wide-area (LPWA) communication technology. However, the wireless access technology used by the base station 20 is not limited to these and may be other wireless access technologies. The wireless communication used by the base station 20 may be wireless communication using millimeter waves or wireless communication using terahertz waves. The wireless communication used by the base station 20 may be wireless communication using radio waves or wireless communication using infrared or visible light (optical wireless). Furthermore, the base station 20 may be capable of NOMA (Non-Orthogonal Multiple Access) communication with the terminal device 40. Here, NOMA communication refers to communication (transmission, reception, or both) using non-orthogonal resources. Note that the base station 20 may be capable of NOMA communication with other base stations 20.

[0062] The base station 20 may be able to communicate with the core network via a base station-core network interface (e.g., NG Interface, S1 Interface, etc.). This interface may be either wired or wireless. The base station may also be able to communicate with other base stations via an inter-base station interface (e.g., Xn Interface, X2 Interface, F1 Interface, etc.). This interface may be either wired or wireless.

[0063] The concept of a base station (also referred to as a "base station device") includes not only a donor base station but also a relay base station (also referred to as a "relay station"). A relay base station may be any one of an RF Repeater, a Smart Repeater, and an Intelligent Surface. The concept of a base station may also include a road-side unit (RSU). The concept of a base station may also include not only a structure having the functions of a base station but also a device installed in the structure.

[0064] Examples of structures include high-rise buildings, houses, steel towers, station facilities, airport facilities, port facilities, office buildings, school buildings, hospitals, factories, commercial facilities, stadiums, and other buildings. The concept of a structure includes not only buildings, but also non-building structures such as tunnels, bridges, dams, fences, and steel pillars, as well as equipment such as cranes, gates, and wind turbines. The concept of a structure includes not only land (ground in the narrow sense) or underground structures, but also water-based structures such as piers or megafloats, and underwater structures such as ocean observation facilities. A base station can also be referred to as an information processing device.

[0065] The base station 20 may be a donor station or a relay station (relay station). The base station 20 may also be a fixed station or a mobile station. A mobile station is a wireless communication device (e.g., a base station) configured to be mobile. In this case, the base station 20 may be a device installed in a mobile body, or may be the mobile body itself. For example, a relay station with mobility can be considered as the base station 20 as a mobile station. Furthermore, devices that are inherently mobile and have base station functionality (at least part of the base station functionality), such as vehicles, UAVs (Unmanned Aerial Vehicles) represented by drones, and smartphones, also fall under the category of the base station 20 as a mobile station.

[0066] Here, the moving body may be a mobile terminal such as a smartphone or a mobile phone. The moving body may also be a moving body that moves on land (ground in the narrow sense) (e.g., a vehicle such as an automobile, bicycle, bus, truck, motorcycle, train, or linear motor car), or a moving body that moves underground (e.g., in a tunnel) (e.g., a subway). The moving body may also be a moving body that moves on water (e.g., a ship such as a passenger ship, cargo ship, or hovercraft), or a moving body that moves underwater (e.g., a submersible vessel such as a submersible boat, submarine, or unmanned submersible). The moving body may also be a moving body that moves within the atmosphere (e.g., an aircraft such as an airplane, airship, or drone).

[0067] The base station 20 may be a terrestrial base station (ground station) installed on the ground. The base station 20 may be a base station located on a structure on the ground, or a base station installed on a mobile object moving on the ground. The base station 20 may be an antenna installed on a structure such as a building and a signal processing device connected to that antenna. The base station 20 may be the structure or the mobile object itself. "Ground" refers not only to land (ground in the narrow sense) but also to ground, on water, and underwater in a broad sense. The base station 20 is not limited to a terrestrial base station. If the communication system 1 is a satellite communication system, the base station 20 may be an aircraft station. From the perspective of a satellite station, an aircraft station located on Earth is a ground station.

[0068] The base station 20 is not limited to a ground station. The base station 20 may be a non-terrestrial base station (non-ground station) that can float in the air or space. The base station 20 may be an aircraft station or a satellite station.

[0069] A satellite station is a wireless communication device capable of floating outside the atmosphere. The satellite station may be a device mounted on a space vehicle such as an artificial satellite, or may be the space vehicle itself. A space vehicle is a vehicle that moves outside the atmosphere. The space vehicle may be at least one of an artificial satellite, a spacecraft, a space station, and a probe. Of course, the space vehicle may also be an artificial celestial body other than these. Note that a satellite that serves as a satellite station may be any of a low Earth orbiting (LEO) satellite, a medium Earth orbiting (MEO) satellite, a geostationary Earth orbiting (GEO) satellite, or a highly elliptical orbiting (HEO) satellite. The satellite station may be a device mounted on a low Earth orbiting (LEO), a medium Earth orbiting (MEO), a geostationary Earth orbiting (GEO), or a highly elliptical orbiting (HEO) satellite.

[0070] An aircraft station is a wireless communication device capable of floating in the atmosphere of an aircraft or the like. The aircraft station may be a device mounted on the aircraft or the like, or may be the aircraft itself. The concept of aircraft includes not only heavier-than-air vehicles such as airplanes and gliders, but also lighter-than-air vehicles such as balloons and airships. The concept of aircraft includes not only heavier-than-air vehicles or lighter-than-air vehicles, but also rotorcraft such as helicopters and autogyros. The aircraft station, or an aircraft equipped with an aircraft station, may be an unmanned aerial vehicle such as a drone.

[0071] The concept of unmanned aerial vehicles also includes unmanned aerial systems (UAS) and tethered unmanned aerial systems (TAS). The concept of unmanned aerial vehicles also includes lighter than air UAS (LTA) and heavier than air UAS (HTA). The concept of unmanned aerial vehicles also includes high altitude unmanned aerial system platforms (HAPs).

[0072] The coverage size of the base station 20 may be relatively large, such as a macrocell, or relatively small, such as a picocell. The coverage size of the base station 20 may be extremely small, such as a femtocell. The base station 20 may have a beamforming function. The base station 20 may form a cell or service area for each beam. Additionally or alternatively, in addition to beamforming, which imparts directionality to a beam, the base station 20 may have a function for pinpointing a desired wave to a specific point by further considering distance information from the antenna of the base station 20. This function may be called beam focusing or point forming. The base station 20 may also be configured to acquire sensing data by performing sensing using beams.

[0073] Fig. 3 is a diagram showing the configuration of a base station 20 according to this embodiment. The base station 20 includes a wireless communication unit 21, a storage unit 22, and a control unit 23. However, the configuration shown in Fig. 3 is a functional configuration, and the hardware configuration may be different. Furthermore, the functions of the base station 20 may be distributed and implemented in multiple physically separated units.

[0074] The base station 20 does not necessarily have to include all of the components described above or below, and may also include components other than the components described above or below.

[0075] The wireless communication unit 21 is a signal processing unit for wireless communication with other wireless communication devices (e.g., at least one of the terminal device 40 and another base station 20). The wireless communication unit 21 may be referred to as a wireless transceiver or simply as a transceiver. In this case, the wireless communication unit 21 may be a transceiver (hereinafter referred to as a 3GPP transceiver) conforming to the specifications defined in the Technical Specification (TS) of the 3rd Generation Partnership Project (3GPP). The 3GPP transceiver may be a 3G transceiver, a 4G (LTE) transceiver, a 5G (NR) transceiver, or a transceiver of a generation after 5G (e.g., 6G). The wireless communication unit 21 is controlled by the control unit 23. The wireless communication unit 21 supports one or more wireless access methods. The wireless communication unit 21 may support at least one of NR, LTE, B5G (Beyond 5G), and 6G. The wireless communication unit 21 may support W-CDMA, cdma2000, etc. in addition to NR, LTE, B5G, and 6G. The wireless communication unit 21 may support automatic retransmission techniques such as HARQ (Hybrid Automatic Repeat reQuest). Some or all of the processing performed by the wireless communication unit 21 may be performed by the control unit 23.

[0076] The wireless communication unit 21 includes a transmission processing unit 211, a reception processing unit 212, and an antenna 213. Alternatively, at least one of the transmission processing unit 211, the reception processing unit 212, and the antenna 213 may be considered as the wireless communication unit 21. The wireless communication unit 21 may include a plurality of transmission processing units 211, a plurality of reception processing units 212, and a plurality of antennas 213. When the wireless communication unit 21 supports a plurality of wireless access methods, each unit of the wireless communication unit 21 may be configured individually for each wireless access method. The transmission processing unit 211 and the reception processing unit 212 may be configured individually for LTE, NR, B5G, and 6G. The antenna 213 may be configured with a plurality of antenna elements, for example, a plurality of patch antennas. The wireless communication unit 21 may have a beamforming function. For example, the wireless communication unit 21 may have a polarization beamforming function that uses vertically polarized waves (V polarization) and horizontally polarized waves (H polarization) (or a polarization beamforming function that uses dual polarization in polarization directions of 45 degrees and −45 degrees from the vertical direction). Note that the wireless communication unit 21 may transmit the sensing signal described above or below.

[0077] The transmission processing unit 211 performs transmission processing of the downlink control information and downlink data. For example, the transmission processing unit 211 encodes the downlink control information and downlink data input from the control unit 23 using a coding method such as block coding, convolutional coding, or turbo coding. Here, the encoding may be performed using polar codes or low density parity check codes (LDPC codes). The transmission processing unit 211 then modulates the coded bits using a predetermined modulation method (e.g., BPSK, QPSK, 16QAM, 64QAM, 256QAM, or a higher-order multi-level modulation method). In this case, the signal points on the constellation do not necessarily need to be equidistant. The constellation may also be a non-uniform constellation (NUC). The transmission processing unit 211 then multiplexes the modulation symbols of each channel and the downlink reference signal and allocates them to predetermined resource elements. The transmission processing unit 211 then performs various signal processing on the multiplexed signal. For example, the transmission processing unit 211 performs processes such as conversion to the frequency domain by fast Fourier transform, addition of a guard interval (cyclic prefix), generation of a baseband digital signal, conversion to an analog signal, quadrature modulation, up-conversion, removal of unnecessary frequency components, power amplification, etc. The signal generated by the transmission processing unit 211 is transmitted from an antenna 213.

[0078] The reception processing unit 212 processes the uplink signal received via the antenna 213. For example, the reception processing unit 212 performs downconversion, removal of unnecessary frequency components, control of amplification level, quadrature demodulation, conversion to a digital signal, removal of guard intervals (cyclic prefixes), extraction of frequency domain signals by fast Fourier transform, and the like on the uplink signal. The reception processing unit 212 then separates uplink channels such as a PUSCH (Physical Uplink Shared Channel) and a PUCCH (Physical Uplink Control Channel) and an uplink reference signal from the signal that has undergone these processes. Furthermore, the reception processing unit 212 demodulates the received signal using a modulation method such as BPSK (Binary Phase Shift Keying) or QPSK (Quadrature Phase Shift Keying) for the modulation symbols of the uplink channel. The modulation method used for demodulation may be 16QAM (Quadrature Amplitude Modulation), 64QAM, or 256QAM. In this case, the signal points on the constellation do not necessarily have to be equidistant. The constellation may be a non-uniform constellation (NUC). The reception processing unit 212 then performs decoding processing on the coded bits of the demodulated uplink channel. The decoded uplink data and uplink control information are output to the control unit 23.

[0079] The antenna 213 is an antenna device that converts electric current and radio waves into each other. The antenna 213 may be composed of a single antenna element, for example, a single patch antenna. The antenna 213 may be composed of multiple antenna elements, for example, multiple patch antennas. When the antenna 213 is composed of multiple antenna elements, the wireless communication unit 21 may have a beamforming function. The wireless communication unit 21 may be configured to generate a directional beam by controlling the directivity of a wireless signal using the multiple antenna elements. The antenna 213 may be a dual-polarized antenna. When the antenna 213 is a dual-polarized antenna, the wireless communication unit 21 may use vertical polarization (V polarization) and horizontal polarization (H polarization) (or dual polarization with polarization directions at 45 degrees and -45 degrees from the vertical direction) when transmitting a wireless signal. The wireless communication unit 21 may control the directivity of a wireless signal transmitted using vertical polarization and horizontal polarization (or dual polarization with polarization directions at 45 degrees and -45 degrees from the vertical direction). Furthermore, the wireless communication unit 21 may transmit and receive spatially multiplexed signals via multiple layers each consisting of multiple antenna elements.

[0080] The storage unit 22 is a readable and writable storage device such as a DRAM, an SRAM, a flash memory, or a hard disk.

[0081] The control unit 23 is a controller that controls each unit of the base station 20. The control unit 23 controls the wireless communication unit 21 to perform wireless communication with other wireless communication devices (e.g., relay station 30, terminal device 40, or other base station 20). The control unit 23 may be implemented by a processor such as a CPU or MPU. Specifically, the control unit 23 may be implemented by a processor executing various programs stored in a storage device inside the base station 20 using RAM or the like as a work area. The control unit 23 may be implemented by an integrated circuit such as an ASIC or FPGA. The control unit 23 may also be implemented by a GPU. A CPU, MPU, ASIC, FPGA, and GPU can all be considered controllers. The control unit 23 may be composed of multiple physically separated objects. For example, the control unit 23 may be composed of multiple semiconductor chips.

[0082] The control unit 23 includes at least one block: a determination unit 231 and a communication control unit 232. The control unit 23 may include a plurality of each of these blocks, or may include only one of each.

[0083] Each block (discrimination unit 231 to communication control unit 232) constituting the control unit 23 is a functional block that indicates the function of the control unit 23. These functional blocks may be software blocks or hardware blocks. For example, each of the above-described functional blocks may be a software module implemented by software (including a microprogram), or may be a circuit block on a semiconductor chip (die). Of course, each functional block may be a processor or an integrated circuit. The control unit 23 may be configured with functional units different from the above-described functional blocks. The method of configuring the functional blocks is arbitrary. Note that the operation of the control unit 23 may be the same as the operation of the control unit (control unit 13, control unit 33, or control unit 43) of the management device 10, relay station 30, or terminal device 40.

[0084] In some embodiments, the base station 20 may be configured as a collection of multiple physical or logical devices. As an example, the base station 20 of this embodiment may be divided into multiple devices such as a baseband unit (BBU) and a radio unit (RU). The base station 20 may be interpreted as a collection of these multiple devices. Furthermore, the base station may be either a BBU or an RU, or may be both. The BBU and the RU may be connected by a predetermined interface such as an enhanced Common Public Radio Interface (eCPRI).

[0085] The RU may be referred to as an RRU (Remote Radio Unit) or an RD (Radio DoT). The RU may correspond to a gNB-DU (gNB Distributed Unit) described later. The BBU may correspond to a gNB-CU (gNB Central Unit) described later. The RU may be a device integrally formed with an antenna. The antenna of the base station 20, for example, an antenna integrally formed with the RU, may employ an Advanced Antenna System and support MIMO such as FD-MIMO or beamforming. The antenna of the base station 20 may include, for example, 64 transmitting antenna ports and 64 receiving antenna ports.

[0086] The antenna mounted on the RU may be an antenna panel consisting of one or more antenna elements, and the RU may be equipped with one or more antenna panels. The RU may be equipped with two types of antenna panels, a horizontally polarized antenna panel and a vertically polarized antenna panel. The RU may be equipped with two types of antenna panels, a right-handed circularly polarized antenna panel and a left-handed circularly polarized antenna panel, or an antenna panel with a polarization direction at 45 degrees from the vertical direction and an antenna panel with a polarization direction at -45 degrees from the vertical direction. Multiple antennas with these multiple polarization directions may be mounted on a single antenna panel. The RU may form and control an independent beam for each antenna panel.

[0087] A plurality of base stations 20 may be connected to each other. One or more base stations 20 may be included in a radio access network (RAN). In this case, the base station 20 may be simply referred to as a RAN, a RAN node, an AN (Access Network), an AN node, or the like. The RAN in LTE may be called an Enhanced Universal Terrestrial RAN (EUTRAN). The RAN in NR may be called an NGRAN. Furthermore, the RAN in 6G may be called a 6GRAN. The RAN in W-CDMA (UMTS) may be called a UTRAN.

[0088] An LTE base station 20 may be referred to as an eNodeB (Evolved Node B) or eNB. In this case, the EUTRAN includes one or more eNodeBs (eNBs). An NR base station 20 may be referred to as a gNodeB or gNB. In this case, the NGRAN includes one or more gNBs. A 6G base station may be referred to as a 6GNodeB, 6gNodeB, 6GNB, or 6gNB. In this case, the 6GRAN includes one or more 6GNBs. The EUTRAN may include a gNB (en-gNB) connected to a core network (EPC) in an LTE communication system (EPS). The NGRAN may include an ng-eNB connected to a core network 5GC in a 5G communication system (5GS).

[0089] When the base station 20 is an eNB, gNB, 6GNB, or the like, the base station 20 may be referred to as a 3GPP access. When the base station 20 is a wireless access point, the base station 20 may be referred to as a non-3GPP access. The base station 20 may be a radio device called an RRH (Remote Radio Head). When the base station 20 is a gNB, the base station 20 may be a combination of the gNB-CU and gNB-DU described above, or may be either a gNB-CU or a gNB-DU.

[0090] Here, the gNB-CU hosts multiple upper layers (e.g., RRC (Radio Resource Control), SDAP (Service Data Adaptation Protocol), PDCP (Packet Data Convergence Protocol)) of the access stratum for communication with the UE. On the other hand, the gNB-DU hosts multiple lower layers (e.g., RLC (Radio Link Control), MAC (Medium Access Control), PHY (Physical layer)) of the access stratum. That is, of the messages / information described below, RRC signaling (semi-static notification) may be generated by the gNB-CU, while MAC CE and DCI (dynamic notification) may be generated by the gNB-DU. Alternatively, of the RRC configuration (semi-static notification), some configurations such as IE:cellGroupConfig may be generated by the gNB-DU, and the remaining configurations may be generated by the gNB-CU. These configurations may be sent or received over the F1 interface.

[0091] The base station 20 may be configured to be able to communicate with other base stations. When multiple base stations 20 are eNBs or a combination of eNBs and en-gNBs, these base stations 20 may be connected to each other via an X2 interface. When multiple base stations 20 are gNBs or a combination of gn-eNBs and gNBs, these base stations 20 may be connected to each other via an Xn interface. When multiple base stations 20 are a combination of gNB-CUs and gNB-DUs, these base stations 20 may be connected to each other via an F1 interface. Messages / information (e.g., RRC signaling, MAC Control Element (CE), or Downlink Control Information (DCI)) may be transmitted between multiple base stations 20 via an inter-base station interface (e.g., an X2 interface, an Xn interface, or an F1 interface).

[0092] A cell provided by the base station 20 may be referred to as a serving cell. The concept of a serving cell includes a PCell (Primary Cell) and an SCell (Secondary Cell). When dual connectivity is provided to the terminal device 40, the PCell and zero or more SCells provided by a Master Node (MN) may be referred to as a Master Cell Group. The dual connectivity may be at least one of EUTRA-EUTRA Dual Connectivity, EUTRA-NR Dual Connectivity (ENDC), EUTRA-NR Dual Connectivity with 5GC, NR-EUTRA Dual Connectivity (NEDC), NR-NR Dual Connectivity, NR-6G Dual Connectivity, and 6G-NR Dual Connectivity. Of course, dual connectivity is not limited to these.

[0093] The serving cell may include a PSCell (Primary Secondary Cell or Primary SCG Cell). When dual connectivity is provided to the terminal device 40, the PSCell provided by a Secondary Node (SN) and zero or more SCells may be referred to as a Secondary Cell Group (SCG). Unless special configuration (e.g., PUCCH on SCell) is performed, the Physical Uplink Control Channel (PUCCH) is transmitted by the PCell and PSCell but not by the SCell. Radio link failure is detected by the PCell and PSCell but not (does not need to be detected by) the SCell. As such, the PCell and PSCell play special roles among serving cells and are therefore also referred to as Special Cells (SpCells).

[0094] One cell may be associated with one downlink component carrier and one uplink component carrier. The system bandwidth corresponding to one cell may be divided into multiple BWPs (Bandwidth Parts). In this case, one or multiple BWPs may be configured in the terminal device 40, and one BWP may be used by the terminal device 40 as an active BWP. Radio resources available to the terminal device 40, such as a frequency band, numerology (subcarrier spacing), or slot format (Slot configuration), may differ for each cell, each component carrier, or each BWP.

[0095] 2-3. Example of the Relay Station Configuration Next, an example of the configuration of the relay station 30 will be described.

[0096] The relay station 30 is a wireless communication device that serves as a repeater for the base station 20. The relay station 30 is a type of base station (for example, the above-mentioned base station 20). The relay station 30 is also a type of information processing device. The relay station 30 can also be called a relay base station. Note that the relay station 30 may also be a device called a repeater (for example, an RF Repeater, a Smart Repeater, or an Intelligent Surface). The relay station 30 is a wireless communication device that performs wireless communication with other wireless communication devices (for example, a base station 20, a terminal device 40, or another relay station 30).

[0097] The relay station 30 may be capable of NOMA communication with the terminal device 40. The relay station 30 relays communication between the base station 20 and the terminal device 40. The relay station 30 may be capable of wireless communication with other relay stations 30 and the base station 20. The relay station 30 may be a terrestrial station device or a non-terrestrial station device. The relay station 30, together with the base station 20, constitutes a radio access network RAN.

[0098] The relay station 30 may be a fixed device, a mobile device, or a floating device. The size of the coverage of the relay station 30 is not limited to a specific size. The cell covered by the relay station 30 may be a macrocell or a small cell.

[0099] The relay station 30 is not limited to a device that is installed as long as it fulfills the relay function. The relay station 30 may be installed in a terminal device such as a smartphone, a car, a train, a rickshaw, a hot air balloon, an airplane, a drone, or a home appliance such as a television, a game console, an air conditioner, a refrigerator, or a lighting fixture.

[0100] The configuration of the relay station 30 may be the same as the configuration of the base station 20 described above. Like the base station 20 described above, the relay station 30 may be a device installed in a mobile body, or may be the mobile body itself. As described above, the mobile body may be a mobile terminal such as a smartphone or a mobile phone. The mobile body may be a mobile body that moves on land (terrestrial in the narrow sense) or may be a mobile body that moves underground. The mobile body may be a mobile body that moves on water or may be a mobile body that moves underwater. The mobile body may be a mobile body that moves within the atmosphere or may be a mobile body that moves outside the atmosphere. The relay station 30 may be a terrestrial station device or a non-terrestrial station device. The relay station 30 may be an aircraft station, a satellite station, or the like.

[0101] The size of the coverage of the relay station 30 may be as large as a macrocell or as small as a picocell, similar to the base station 20. The size of the coverage of the relay station 30 may be extremely small, such as a femtocell. The relay station 30 may have a beamforming function. In this case, the relay station 30 may form a cell or service area for each beam. The relay station 30 may also have a pointforming function. In this case, the relay station 30 may form a cell or service area for each point.

[0102] Fig. 4 is a diagram showing the configuration of the relay station 30 according to this embodiment. The relay station 30 includes a wireless communication unit 31, a storage unit 32, and a control unit 33. However, the configuration shown in Fig. 4 is a functional configuration, and the hardware configuration may be different. Furthermore, the functions of the relay station 30 may be distributed and implemented in multiple physically separated units.

[0103] It should be noted that the relay station 30 does not necessarily have to include all of the components described above or below, and may also include components other than those described above or below.

[0104] The wireless communication unit 31 is a signal processing unit for wireless communication with other wireless communication devices (e.g., at least one of the terminal device 40 and another relay station 30). The wireless communication unit 31 may be referred to as a wireless transceiver or simply as a transceiver. In this case, the wireless communication unit 31 may be a transceiver of specifications defined in the 3GPP technical specifications (hereinafter referred to as a 3GPP transceiver). The 3GPP transceiver may be a 3G transceiver, a 4G (LTE) transceiver, a 5G (NR) transceiver, or a transceiver of a generation after 5G (e.g., 6G). The wireless communication unit 31 is controlled by the control unit 33. The wireless communication unit 31 supports one or more wireless access methods. The wireless communication unit 31 may support at least one of NR, LTE, B5G, and 6G. The wireless communication unit 31 may support W-CDMA, cdma3000, etc. in addition to NR, LTE, B5G, and 6G. The wireless communication unit 31 may support automatic repeat transmission techniques such as HARQ. Some or all of the processing performed by the wireless communication unit 31 may be performed by the control unit 33.

[0105] The wireless communication unit 31 includes a transmission processing unit 311, a reception processing unit 312, and an antenna 313. Alternatively, at least one of the transmission processing unit 311, the reception processing unit 312, and the antenna 313 may be considered as the wireless communication unit 31. The wireless communication unit 31 may include a plurality of transmission processing units 311, a plurality of reception processing units 312, and a plurality of antennas 313. When the wireless communication unit 31 supports a plurality of wireless access methods, each unit of the wireless communication unit 31 may be configured individually for each wireless access method. The transmission processing unit 311 and the reception processing unit 312 may be configured individually for LTE, NR, B5G, and 6G. The antenna 313 may be configured with a plurality of antenna elements, for example, a plurality of patch antennas. The wireless communication unit 31 may have a beamforming function. For example, the wireless communication unit 31 may have a polarization beamforming function that uses vertically polarized waves (V polarization) and horizontally polarized waves (H polarization) (or a polarization beamforming function that uses dual polarization in polarization directions of 45 degrees and −45 degrees from the vertical direction). Note that the wireless communication unit 31 may transmit the sensing signal described above or below.

[0106] The transmission processing unit 311 performs transmission processing of the downlink control information and downlink data. For example, the transmission processing unit 311 encodes the downlink control information and downlink data input from the control unit 33 using a coding method such as block coding, convolutional coding, or turbo coding. Here, the encoding may be performed using a polar code or an LDPC code. The transmission processing unit 311 then modulates the coded bits using a predetermined modulation method (e.g., BPSK, QPSK, 16QAM, 64QAM, 256QAM, or a higher-order multi-level modulation method). In this case, the signal points on the constellation do not necessarily need to be equidistant. The constellation may also be a non-uniform constellation. The transmission processing unit 311 then multiplexes the modulation symbols of each channel and the downlink reference signal and allocates them to predetermined resource elements. The transmission processing unit 311 then performs various signal processing on the multiplexed signal. For example, the transmission processing unit 311 performs processes such as conversion to the frequency domain by fast Fourier transform, addition of a guard interval (cyclic prefix), generation of a baseband digital signal, conversion to an analog signal, quadrature modulation, up-conversion, removal of unnecessary frequency components, power amplification, etc. The signal generated by the transmission processing unit 311 is transmitted from an antenna 313.

[0107] The reception processing unit 312 processes the uplink signal received via the antenna 313. For example, the reception processing unit 312 performs downconversion, removal of unnecessary frequency components, control of amplification level, quadrature demodulation, conversion to a digital signal, removal of guard intervals (cyclic prefixes), extraction of frequency domain signals using fast Fourier transform, and the like on the uplink signal. The reception processing unit 312 then separates uplink channels such as PUSCH and PUCCH and uplink reference signals from the processed signal. The reception processing unit 312 also demodulates the received signal using a modulation scheme such as BPSK or QPSK for the modulation symbols of the uplink channel. The modulation scheme used for demodulation may be 16QAM, 64QAM, or 256QAM. In this case, the signal points on the constellation do not necessarily have to be equidistant. The constellation may be a non-uniform constellation (NUC). The reception processing unit 312 then performs a decoding process on the coded bits of the demodulated uplink channel. The decoded uplink data and uplink control information are output to the control unit 33.

[0108] The antenna 313 is an antenna device that converts electric current and radio waves into each other. The antenna 313 may be composed of a single antenna element, for example, a single patch antenna. The antenna 313 may be composed of multiple antenna elements, for example, multiple patch antennas. When the antenna 313 is composed of multiple antenna elements, the wireless communication unit 31 may have a beamforming function. The wireless communication unit 31 may be configured to generate a directional beam by controlling the directivity of a wireless signal using the multiple antenna elements. The antenna 313 may be a dual-polarized antenna. When the antenna 313 is a dual-polarized antenna, the wireless communication unit 31 may use vertical polarization (V polarization) and horizontal polarization (H polarization) (or dual polarization with polarization directions at 45 degrees and -45 degrees from the vertical direction) when transmitting a wireless signal. The wireless communication unit 31 may control the directivity of a wireless signal transmitted using vertical polarization and horizontal polarization (or dual polarization with polarization directions at 45 degrees and -45 degrees from the vertical direction). Furthermore, the wireless communication unit 31 may transmit and receive spatially multiplexed signals via multiple layers each consisting of multiple antenna elements.

[0109] The storage unit 32 is a readable and writable storage device such as a DRAM, an SRAM, a flash memory, or a hard disk.

[0110] The control unit 33 is a controller that controls each unit of the relay station 30. The control unit 33 controls the wireless communication unit 31 to perform wireless communication with other wireless communication devices (e.g., base stations 20, terminal devices 40, or other relay stations 30). The control unit 33 may be implemented by a processor such as a CPU or an MPU. Specifically, the control unit 33 may be implemented by a processor executing various programs stored in a storage device inside the relay station 30 using RAM or the like as a work area. The control unit 33 may be implemented by an integrated circuit such as an ASIC or an FPGA. The control unit 33 may also be implemented by a GPU. A CPU, an MPU, an ASIC, an FPGA, and a GPU can all be considered controllers. The control unit 33 may be configured by multiple physically separated objects. For example, the control unit 33 may be configured by multiple semiconductor chips.

[0111] The control unit 33 includes at least one block: a determination unit 331 and a communication control unit 332. The control unit 33 may include a plurality of each of these blocks, or may include only one of each.

[0112] Each block constituting the control unit 33 (the discrimination unit 331 to the communication control unit 332) is a functional block that indicates the function of the control unit 33. These functional blocks may be software blocks or hardware blocks. For example, each of the above-described functional blocks may be a software module implemented by software (including a microprogram), or may be a circuit block on a semiconductor chip (die). Of course, each functional block may be a processor or an integrated circuit. The control unit 33 may be configured with functional units different from the above-described functional blocks. The method of configuring the functional blocks is arbitrary. The operation of the control unit 33 may be the same as the operation of the control unit (control unit 13, control unit 23, or control unit 43) of the management device 10, the relay station 30, or the terminal device 40.

[0113] The relay station 30 may be an IAB relay node. The relay station 30 operates as an IAB-MT (Mobile Termination) for an IAB donor node that provides backhaul, and operates as an IAB-DU (Distributed Unit) for a terminal device 40 that provides access. The IAB donor node may be, for example, a base station 20. In this case, the IAB donor node may operate as an IAB-CU (Central Unit).

[0114] 2-4. Example of the Configuration of the Terminal Device Next, an example of the configuration of the terminal device 40 will be described.

[0115] The terminal device 40 is a wireless communication device that performs wireless communication with other wireless communication devices (for example, a base station 20, a relay station 30, or another terminal device 40). In the following description, the terminal device 40 may be referred to as UE (User Equipment) or UE 40.

[0116] The terminal device 40 may be any type of information processing device (computer). For example, the terminal device 40 may be a mobile terminal such as a mobile phone, a smart device (smartphone or tablet), a PDA (Personal Digital Assistant), or a notebook PC. The terminal device 40 may also be a communication module that is connected to an information processing device (e.g., an imaging device without wireless communication capabilities) and provides the information processing device with wireless communication capabilities. The terminal device 40 may also be an imaging device with wireless communication capabilities (e.g., a camcorder).

[0117] The terminal device 40 may be a motorcycle or a mobile broadcasting vehicle equipped with a communication device such as a Field Pickup Unit (FPU). The terminal device 40 may be a Machine to Machine (M2M) device or an Internet of Things (IoT) device. The terminal device 40 may be a wearable device such as a smartwatch.

[0118] Furthermore, the terminal device 40 may be an XR (Extended Reality) device such as an AR (Augmented Reality) device, a VR (Virtual Reality) device, or an MR (Mixed Reality) device. In this case, the XR device may be a glasses-type device such as AR glasses or MR glasses, or a head-mounted device such as a VR head-mounted display. When the terminal device 40 is an XR device, the terminal device 40 may be a standalone device consisting only of a part worn by a user (e.g., a glasses part). Furthermore, the terminal device 40 may be a terminal-linked device consisting of a part worn by a user (e.g., a glasses part) and a terminal part (e.g., a smart device) linked to the part worn by a user.

[0119] The terminal device 40 may be capable of NOMA communication with other wireless communication devices (e.g., a base station 20, a relay station 30, or another terminal device 40). The terminal device 40 may use an automatic repeat request (ARQ) technique when communicating with other wireless communication devices. The terminal device 40 may be capable of sidelink communication with other terminal devices 40. The terminal device 40 may use an automatic repeat request (ARQ) technique when performing sidelink communication. The terminal device 40 may be capable of NOMA communication when performing sidelink communication with other terminal devices 40. The terminal device 40 may be capable of LPWA communication with other wireless communication devices. The wireless communication used by the terminal device 40 may be wireless communication using millimeter waves. The wireless communication used by the terminal device 40, including sidelink communication, may be wireless communication using radio waves, or wireless communication using infrared or visible light, i.e., optical wireless.

[0120] The terminal device 40 may be a mobile wireless communication device, i.e., a mobile device. The terminal device 40 may be a wireless communication device installed in a mobile device, or may be the mobile device itself. The terminal device 40 may be a vehicle that moves on a road, such as an automobile, bus, truck, or motorcycle, or a train that runs on a track, or may be a wireless communication device mounted on the vehicle. The mobile device may be a mobile terminal, or a mobile device that moves on land (in the narrow sense of the word), underground, on water, or underwater. The mobile device may also be a mobile device that moves within the atmosphere, such as an airplane, airship, balloon, or helicopter, or a mobile device that moves outside the atmosphere, such as an artificial satellite. The mobile device may also be a UAV (Unmanned Aerial Vehicle) such as a drone. The terminal device 40 may also be a wireless communication device mounted on the mobile device.

[0121] The terminal device 40 may be capable of simultaneously connecting to and communicating with a plurality of base stations 20 or a plurality of cells. When one base station 20 supports a communication area via a plurality of cells (e.g., pCell or sCell), the plurality of cells can be bundled together to enable communication between the base station 20 and the terminal device 40 by using carrier aggregation (CA) technology, dual connectivity (DC) technology, multi-connectivity (MC) technology, or the like. Alternatively, communication between the terminal device 40 and the plurality of base stations 20 can also be performed via cells of different base stations 20 by coordinated multi-point transmission and reception (CoMP) technology.

[0122] The terminal device 40 may be capable of connecting to and communicating with a plurality of base stations 20 or a plurality of cells. Furthermore, the terminal device 40 may transmit and / or receive a sensing signal to and from each of the plurality of base stations 20. The terminal device 40 may be configured to receive information about the sensing signal (e.g., information about resources) from at least one of the plurality of base stations 20, or may be configured to receive information about the sensing signal (e.g., information about resources) from each of the plurality of base stations 20. Furthermore, the terminal device 40 may transmit and / or receive a sensing signal in each of the plurality of cells. The terminal device 40 may be configured to receive information about the sensing signal (e.g., information about resources) from at least one of the plurality of cells, or may be configured to receive information about the sensing signal (e.g., information about resources) in each of the plurality of cells.

[0123] The terminal device 40 may be a relay terminal that relays communications to a remote terminal.

[0124] Multistatic sensing may be performed in the base station 20, the remote terminal, and the relay terminal. Specifically, a sensing signal may be transmitted from each of the base station 20 and the relay terminal. The remote terminal may receive the sensing signal transmitted from each of the base station 20 and the relay terminal.

[0125] The base station 20 and / or the relay terminal may transmit information regarding the sensing signals transmitted and / or received at the relay terminal and / or the remote terminal to the relay terminal and / or the remote terminal. In other words, the relay terminal and / or the remote terminal may receive information regarding the sensing signals transmitted and / or received at the relay terminal and / or the remote terminal from the base station 20 and / or the relay terminal.

[0126] Fig. 5 is a diagram showing the configuration of a terminal device 40 according to this embodiment. The terminal device 40 includes a wireless communication unit 41, a storage unit 42, and a control unit 43. The configuration shown in Fig. 5 is a functional configuration, and the hardware configuration may be different from this. Furthermore, the functions of the terminal device 40 may be distributed and implemented in multiple physically separated units.

[0127] It should be noted that the terminal device 40 does not necessarily have to have all of the configurations described above or below. Furthermore, the terminal device 40 may have a configuration other than the configurations described above or below. The terminal device 40 may have a beamforming function. Furthermore, the terminal device 40 may be configured to acquire sensing data by performing sensing using beams.

[0128] The wireless communication unit 41 is a signal processing unit for wireless communication with other wireless communication devices (e.g., the base station 20, the relay station 30, or another terminal device 40). The wireless communication unit 41 may be referred to as a wireless transceiver or simply as a transceiver. In this case, the wireless communication unit 41 may be a transceiver of a standard defined in the 3GPP technical specifications (hereinafter referred to as a 3GPP transceiver). The 3GPP transceiver may be a 3G transceiver, a 4G (LTE) transceiver, a 5G (NR) transceiver, or a transceiver of a generation after 5G. The wireless communication unit 41 is controlled by, for example, the control unit 43. The wireless communication unit 41 supports one or more wireless access methods. The wireless communication unit 41 may support at least one of NR, LTE, B5G, and 6G. The wireless communication unit 41 may support W-CDMA, cdma2000, etc. in addition to NR, LTE, B5G, and 6G. The wireless communication unit 41 may support automatic repeat transmission techniques such as HARQ. Some or all of the processing performed by the wireless communication unit 41 may be performed by the control unit 43.

[0129] The wireless communication unit 41 includes a transmission processing unit 411, a reception processing unit 412, and an antenna 413. At least one of the transmission processing unit 411, the reception processing unit 412, and the antenna 413 may be considered as the wireless communication unit 41. The wireless communication unit 41 may include a plurality of transmission processing units 411, a plurality of reception processing units 412, and a plurality of antennas 413. When the wireless communication unit 41 supports a plurality of wireless access methods, each unit of the wireless communication unit 41 may be configured individually for each wireless access method. The transmission processing unit 411 and the reception processing unit 412 may be configured individually for LTE, NR, B5G, and 6G. The antenna 413 may be configured with a plurality of antenna elements, for example, a plurality of patch antennas. The wireless communication unit 41 may have a beamforming function. For example, the wireless communication unit 41 may have a polarization beamforming function that uses vertically polarized waves (V polarization) and horizontally polarized waves (H polarization) (or a polarization beamforming function that uses dual polarization in polarization directions of 45 degrees and −45 degrees from the vertical direction). Note that the wireless communication unit 41 may transmit the sensing signal described above or below.

[0130] The storage unit 42 is a readable and writable storage device such as a DRAM, an SRAM, a flash memory, or a hard disk.

[0131] The control unit 43 is a controller that controls each unit of the terminal device 40. The control unit 43 controls the wireless communication unit 41 to perform wireless communication with other wireless communication devices (e.g., the base station 20, the relay station 30, or another terminal device 40). The control unit 43 may be implemented by a processor such as a CPU or an MPU. In particular, the control unit 43 may be implemented by a processor executing various programs stored in an internal storage device of the terminal device 40 using RAM or the like as a work area. The control unit 43 may be implemented by an integrated circuit such as an ASIC or FPGA. The CPU, MPU, ASIC, and FPGA can all be considered controllers. The control unit 43 may also be implemented by a GPU. The CPU, MPU, ASIC, FPGA, and GPU can all be considered controllers. The control unit 43 may be composed of multiple physically separated entities. For example, the control unit 43 may be composed of multiple semiconductor chips.

[0132] The control unit 43 includes at least one block: a determination unit 431 and a communication control unit 432. The control unit 43 may include a plurality of each of these blocks, or may include only one of each.

[0133] Each block constituting the control unit 43 (the discrimination unit 431 to the communication control unit 432) is a functional block that indicates the function of the control unit 43. These functional blocks may be software blocks or hardware blocks. For example, each of the above-described functional blocks may be a software module implemented by software (including a microprogram), or may be a circuit block on a semiconductor chip (die). Of course, each functional block may be a processor or an integrated circuit. The control unit 43 may be configured with functional units different from the above-described functional blocks. The method of configuring the functional blocks is arbitrary. The operation of the control unit 43 may be the same as the operation of the control unit (control unit 13, control unit 23, or control unit 33) of the management device 10, the base station 20, or the relay station 30.

[0134] <<3. Handover>> The configuration of the communication system 1 has been described above. Before describing the operation of the communication system 1 of this embodiment in detail, a basic handover procedure that can be executed by the communication system 1 will be described.

[0135] <3-1. Basic Procedure> First, the basic procedure of handover will be described.

[0136] Handover (mobility) is an operation of switching the connection destination of a terminal device 40 (UE). Handover (mobility) is broadly classified into two types: beam level mobility and cell level mobility. In beam level mobility, there is no need to explicitly trigger RRC (Radio Resource Control) signaling when switching the connection destination. On the other hand, in cell level mobility, there is a need to explicitly trigger RRC (Radio Resource Control) signaling when switching the connection destination.

[0137] Hereinafter, cell level mobility will be described as a basic handover procedure. Fig. 6 is a sequence diagram showing an example of the cell level mobility procedure. Fig. 6 shows a procedure of inter-base station (BS) handover (e.g., Inter-gNB handover) as an example of the cell level mobility procedure. As described above, cell level mobility is initiated by RRC signaling as a trigger.

[0138] In the following description, the base station 20 before the connection is switched (the connected base station 20) may be referred to as a source BS or simply as a source. Also, in the following description, the base station 20 after the connection is switched (the base station 20 that is the switching target) may be referred to as a target BS or simply as a target.

[0139] First, the source BS transmits a handover request to the target BS via the Xn interface (step S11).

[0140] The target BS that has received the handover request performs admission control (step S12), and then transmits the RRC configuration associated with the target BS to the source BS as part of a response to the handover request (HANDOVER REQUEST ACKNOWLEDGE) (step S13).

[0141] The source BS forwards the received RRC Reconfiguration message to the terminal device 40 (step S14). The RRC Reconfiguration message includes a cell ID. The RRC Reconfiguration message also includes all information necessary to access the target cell so that the terminal device 40 can access the target cell without reading system information. The RRC Reconfiguration message may also include information necessary for contention-based random access and / or contention-free random access. The access information to the target cell may include beam-specific information.

[0142] The terminal device 40 establishes an RRC connection with the target BS (step S15), and then notifies the target BS of RRC Reconfiguration Complete (step S16).

[0143] <3-2. Conditional Handover> Next, conditional handover (CHO) will be described.

[0144] CHO is a handover executed by the terminal device 40 (UE) when one or more handover execution conditions (hereinafter also referred to as first conditions) are satisfied. In short, CHO is an autonomous connection destination switching operation by the terminal device 40. When the terminal device 40 receives the CHO Configuration, it starts evaluating the execution conditions, and when the handover is executed, it stops evaluating the execution conditions.

[0145] CHO allows the terminal device 40 to execute handover processing according to its own measurements without receiving a notification from the base station 20 (BS). This eliminates the need to receive an RRC message from the base station 20 for each handover, making it possible to perform handover with low latency.

[0146] The following principles (B1) to (B4) may be applied to CHO.

[0147] (B1) CHO Configuration includes the CHO candidate cell configuration generated by the candidate BS and the execution conditions generated by the source BS.

[0148] (B2) The execution condition is composed of one or more trigger conditions (e.g., CHO events A3 / A5). Only a single RS (Reference Signal) type is supported. The terminal device 40 can simultaneously set up to two different trigger quantities (e.g., (RSRP and RSRQ), or (RSRP and SINR), etc.) to evaluate the CHO execution condition of a single candidate cell.

[0149] (B3) Upon receiving a handover command (without CHO configuration) or an LTM cell switch command MAC CE before any CHO execution condition is met, the terminal device 40 executes the handover procedure or the LTM cell switch procedure regardless of the previously received CHO configuration.

[0150] (B4) While CHO is being executed, the terminal device 40 does not monitor the source cell. That is, the terminal device 40 does not monitor the source cell from the time when synchronization with the target cell is started.

[0151] Fig. 7 is a sequence diagram showing an example of a conditional handover (CHO) procedure. Fig. 7 shows an example of a CHO procedure, which is an inter-base station (BS) CHO (e.g., Inter-gNB (Intra AMF / UPF) CHO).

[0152] First, the AMF of the core network CN provides mobility control information to each BS (step S20). Here, the information held by the source BS includes, as information related to the terminal device 40, information on roaming and access restrictions provided at the time of connection establishment or the last timing advance update.

[0153] The source BS configures a UE measurement procedure in the terminal device 40. The terminal device 40 performs reporting in accordance with the Measurement Configuration (step S21).

[0154] The source BS determines whether to implement CHO (step S22). In the example of Fig. 7, it is assumed that the source BS decides to implement CHO.

[0155] The source BS requests CHO for one or more candidate cells belonging to one or more candidate BSs (step S23). The source BS sends a CHO request message to each of the candidate cells.

[0156] The candidate BS performs admission control (step S24). The admission control may be performed by the target BS. If slice information is sent to the target BS, admission control is performed taking the slice information into consideration. In this case, if a PDU session is associated with a slice that does not support the PDU session, the target BS rejects the corresponding PDU session.

[0157] The candidate BS sends a CHO response (HANDOVER REQUEST ACKNOWLEDGE) including the configuration of the CHO candidate cell to the source BS (step S25). The candidate BS sends a CHO response message for each candidate cell.

[0158] The source BS transmits an RRC Reconfiguration message including the configuration of one or more CHO candidate cells and one or more CHO execution conditions to the terminal device 40 (step S26).

[0159] The terminal device 40 sends an RRC Reconfiguration Complete message to the source BS (step S27). If early data transfer is applied, the source BS sends an EARLY STATUS TRANSFER message to the candidate BS (step S27a).

[0160] After receiving the CHO Configuration, the terminal device 40 starts evaluating the CHO execution conditions for one or more candidate cells while maintaining the connection with the source cell. The terminal device 40 selects a candidate cell that satisfies the CHO execution conditions as a target cell. Then, the terminal device 40 releases the connection with the source cell and synchronizes with the target cell. The terminal device 40 completes the handover procedure by transmitting an RRC Reconfiguration Complete message to the target BS (step S28). After the handover procedure is successfully completed, the terminal device 40 releases the stored CHO Configuration.

[0161] The target BS sends a HANDOVER SUCCESS message to the source BS to inform it that the terminal device 40 has successfully accessed the target cell (step S28a). The source BS sends an SN STATUS TRANSFER message to the target BS (step S28b). The source BS sends a HANDOVER CANCEL message toward another signaling connection or one or more other candidate target BSs (if any) to cancel the CHO of the terminal device 40 (step S28c).

[0162] <3-3. LTM> Next, LTM (L1 / L2 Triggered Mobility) will be explained.

[0163] LTM is L1 / L2 based mobility (handover). LTM is also called Lower Layer Triggered Mobility. LTM reduces mobility delay.

[0164] LTM is executed, for example, in the following procedure. First, an L1 measurement report is transmitted from the terminal device 40 (UE) to the base station 20 (BS). Based on the L1 measurement report, the base station 20 transmits a cell switch command (hereinafter also referred to as an LTM cell switch command) to the terminal device 40. The cell switch command is transmitted via MAC CE. Upon receiving the cell switch command, the UE changes the serving cell. The cell switch command is linked to an LTM candidate configuration. The LTM candidate configuration is provided in advance from the base station 20 to the terminal device 40 via RRC signaling. The terminal device 40 switches its connection destination to the specified LTM candidate cell in accordance with the received cell switch command.

[0165] When the network performs LTM configuration, it can activate the TCI state of one or more cells different from the current serving cell. TCI stands for Transmission Configuration Indicator. For example, the TCI state of an LTM candidate cell is activated in advance before any of the LTM candidate cells becomes the serving cell. This allows the terminal device 40 to achieve DL (Downlink) synchronization with the LTM candidate cell. As a result, the terminal device 40 can quickly switch to one of the LTM candidate cells when a cell switch is triggered.

[0166] When the network performs LTM configuration, it initiates a procedure for acquiring the uplink (UL) timing advance of one or more cells other than the current serving cell. Hereinafter, the timing advance information acquired here (early acquired timing advance value) may be referred to as early TA. If the timing advance value (N_TA) of an LTM candidate cell is the same as that of the current serving cell, or if the timing advance value (N_TA) is 0, the early TA acquisition procedure is not performed. The network may request the terminal device 40 to acquire the early TA of the candidate cell before a cell switch. The early TA acquisition procedure is triggered by a Physical Downlink Control Channel (PDCCH) order defined in the random access procedure (hereinafter referred to as the RACH procedure, or simply RACH). Alternatively, early TA acquisition may be achieved by UE-based timing advance measurement, with configuration performed by RRC signaling. It should be noted that the timing advance value does not necessarily have to be acquired early, and the network may transmit the timing advance value to the terminal device 40 in the LTM cell switch command (MAC CE).

[0167] When the early TA acquisition procedure is triggered by a PDCCH order, the BS or DU (e.g., gNB-DU) to which the LTM candidate cell belongs calculates a timing advance value. Then, the BS or DU sends the calculated timing advance value to the BS or DU to which the serving cell belongs via the CU (e.g., gNB-CU). This indicates that LTM supports only inter-CU mobility (inner-CU mobility). Thereafter, when triggering an LTM cell switch, the serving cell transmits the timing advance value to the terminal device 40 in an LTM cell switch command (MAC CE).

[0168] In the case of UE-based timing advance measurement, the terminal device 40 performs timing advance measurement on an LTM candidate cell after configuration is performed by RRC signaling. Note that the exact time at which the terminal device 40 performs timing advance measurement may be left to the UE implementation. Upon receiving a cell switch command, the terminal device 40 performs LTM without performing a random access procedure. That is, the terminal device 40 performs RACH-less LTM. At this time, the terminal device 40 applies the timing advance value measured by itself to the timing advance value after switching.

[0169] Depending on whether the configured timing advance value is available, the terminal device 40 performs either a RACH-less LTM cell switch or a RACH-based LTM cell switch. If a valid timing advance value is provided in the cell switch command, the terminal device 40 applies the timing advance value as instructed by the network. If UE-based timing advance measurement is configured but a valid timing advance value is not specified in the cell switch command, the terminal device 40 sets a valid timing advance value based on its own measurement. If a valid timing advance value is available, the terminal device 40 performs a RACH-less LTM cell switch upon receiving the cell switch command. If a valid timing advance value is not available, the terminal device 40 performs a RACH-based LTM cell switch.

[0170] The terminal device 40 may follow the instruction of the PDCCH order including a request to perform a random access procedure to an LTM candidate cell, regardless of whether configuration by RRC signaling for UE-based timing advance measurement has been performed. This also applies to an LTM candidate cell from which the terminal device 40 can derive a timing advance value. Furthermore, regardless of whether a random access procedure for an LTM candidate cell has already been performed, if configuration by RRC signaling has been performed, the terminal device 40 may perform UE-based timing advance measurement in accordance with the configuration.

[0171] In the case of RACH-less LTM, the terminal device 40 accesses the target cell using either a Configured Grant or a Dynamic Grant. The Configured Grant is provided in the LTM candidate configuration. In this case, the terminal device 40 selects the Configured Grant Occasion associated with the beam indicated in the cell switch command. At the start of an LTM cell switch to the target cell, the terminal device 40 starts monitoring the PDCCH on the target cell for dynamic scheduling. If the triggered scheduling request (SR) does not have valid PUCCH resources, the terminal device 40 must not trigger a random access procedure before the RACH-less LTM procedure is completed.

[0172] The following principles can be applied to LTM: The security key defined in the PDCP layer does not change before and after the LTM cell switch. The LTM candidate configuration notified to the terminal device 40 is not discarded even after LTM is executed.

[0173] LTM supports both intra-DU mobility (e.g., intra-gNB-DU mobility) and inter-DU mobility within a CU (e.g., intra-gNB-CU inter-gNB-DU mobility). LTM supports both mobility between cells serving the same frequency and mobility between cells serving different frequencies.

[0174] In LTM, the following scenarios may be supported: PCell change in non-Carrier Aggregation (CA) and non-Dual Connectivity (DC) scenarios, PCell and SCell change in Carrier Aggregation (CA) scenarios, and DC (Dual Connectivity) scenarios.

[0175] In addition, in the DC scenario, changes to the PCell and MCG (Master Cell Group) SCell, and changes to the PSCell and SCG (Secondary Cell Group) SCell in a SN (Secondary Node) that does not involve the MN (Master Node) are supported. LTM for simultaneously changing the PCell and PSCell may not be supported.

[0176] While the terminal device 40 stores the LTM candidate configuration, the terminal device 40 can perform any L3 handover except for a DAPS (Dual Active Protocol Stack) handover.

[0177] FIG. 8 is a sequence diagram showing an example of the LTM procedure.

[0178] First, the terminal device 40 transmits a measurement report to the base station 20 (step S31). The base station 20, having received the measurement report, determines an LTM configuration and starts preparing for LTM. Then, the base station 20 transmits an RRC reconfiguration message including an LTM candidate configuration to the terminal device 40 (step S32). The terminal device 40 transmits an RRC reconfiguration complete message storing the LTM candidate configuration to the base station 20 (step S33).

[0179] Before receiving the cell switch command, the terminal device 40 may perform synchronization (early sync) with one or more LTM candidate cells (steps S34a and S34b).

[0180] For example, the terminal device 40 may perform downlink synchronization (early DL sync) with one or more LTM candidate cells before receiving the cell switch command (step S34a). The terminal device 40 may activate and deactivate the TCI state of one or more LTM candidate cells.

[0181] The terminal device 40 may also perform uplink synchronization (early UL sync) with one or more LTM candidate cells before receiving the cell switch command (step S34b). UL synchronization can be achieved by the terminal device 40 performing UE-based timing advance measurement and / or by the terminal device 40 transmitting a preamble toward the candidate cell. If UE-based timing advance measurement is configured, the terminal device 40 acquires timing advance values ​​of one or more candidate cells through measurement. Before receiving the cell switch command, the terminal device 40 performs early TA acquisition with candidate cell(s) requested by the network. This is triggered by a PDCCH order from the source cell and is performed via Contention Free Random Access (CFRA). The terminal device 40 then transmits a preamble toward the indicated candidate cell. To minimize data interruption of the source cell due to CFRA, the terminal device 40 does not need to receive a random access response from the network. In this case, the timing advance value of the candidate cell may be indicated in the cell switch command, and the terminal device 40 may leave the process of ensuring the validity of the timing advance value to the network implementation.

[0182] The terminal device 40 performs L1 measurement for one or more configured LTM candidate cells. Then, the terminal device 40 transmits an L1 measurement report to the base station 20 (step S35). The L1 measurement is performed as long as the RRC reconfiguration of step S32 is applicable.

[0183] The base station 20 decides to perform a cell switch for the target cell. Then, the base station 20 transmits an LTM cell switch command (MAC CE) to the terminal device 40 (step S36). The LTM cell switch command includes a target configuration ID indicating an index of a candidate configuration for the target cell, and information on the beam indicated by the TCI state or the beam indicated by DL and UL. The LTM cell switch command may also include a timing advance command for the target cell. The terminal device 40 switches its connection destination to the target cell. At this time, the terminal device 40 applies the candidate configuration indicated by the target configuration ID.

[0184] If the terminal device 40 does not have a valid timing advance value for the target cell, the terminal device 40 may execute a random access procedure toward the target cell (step S37).

[0185] The terminal device 40 completes the LTM cell switch procedure by transmitting an RRC Reconfiguration Complete message to the target cell (step S38). Note that, if a random access procedure is executed in step S37, the terminal device 40 may consider the execution of the LTM cell switch to be completed successfully when the random access procedure is completed successfully. In the case of RACH-less LTM, the terminal device 40 may consider the execution of the LTM cell switch to be completed successfully when it determines that the first UL data has been received by the network without any problems.

[0186] <3-4. Conditional LTM> The LTM that can be executed by the communication system 1 may be conditional LTM (CLTM). CLTM is LTM that is executed by the terminal device 40 (UE) when one or more handover execution conditions (hereinafter also referred to as first conditions) are satisfied. In short, CLTM is an autonomous connection destination switching operation (LTM) by the terminal device 40.

[0187] In the example of Fig. 8, in the LTM Cell Switch execution (steps S35 to S37), the base station 20 evaluates the switching of the connection destination (LTM decision shown in Fig. 8). However, in CLTM, the terminal device 40 performs the evaluation of the switching of the connection destination.

[0188] <<4. Communication Point>> In the above-mentioned <3. Handover>, the handover is mainly assumed to be a handover between base stations. However, the handover in this embodiment is not limited to a handover between base stations. The handover in this embodiment may be a handover between communication points. The above-mentioned and below-mentioned descriptions of base stations, relay stations, and cells can be replaced with communication points as appropriate. The following describes communication points.

[0189] <4-1. Definition of Communication Point> In this embodiment, a communication point refers to, for example, one radio resource when a communication service is provided. A communication point is typically a cell (a conventional planar cell formed by the base station 20 / relay station 30; hereinafter referred to as a classic cell), but is not limited to a cell and may be, for example, a beam in beamforming (hereinafter also referred to as a beam cell) or a point in pointforming (hereinafter also referred to as a point cell). Point forming will be described later.

[0190] Alternatively, a communication point may be a radio resource divided spatially, temporally, or frequency-wise. A communication point may be a plurality of radio resources multiplexed spatially, temporally, or frequency-wise. A radio communication device (e.g., at least one of the base station 20, the relay station 30, and the terminal device 40) can identify each communication point by some means. In the following description, a communication point may be simply referred to as a point.

[0191] <4-2. Types of Communication Points> In this embodiment, there are, for example, the following types of communication points.

[0192] Serving Communication Point: A serving communication point is a communication point that provides communication services to a certain terminal device 40. For example, if the communication point is a cell, the serving communication point refers to the serving cell. In the following description, the serving communication point may also be referred to as the serving point.

[0193] Candidate communication points are communication points from which a terminal device 40 can next receive service. For example, if the communication point is a cell, the candidate communication point refers to a candidate cell. There may be multiple candidate communication points, or there may be only one.

[0194] <4-3. Reinterpretation of communication points> The communication points of this embodiment may be any of the following (C1) to (C11). The description of "communication point" that appears in this embodiment can be replaced with a description indicating any of the following (C1) to (C11).

[0195] (C1) Base station (e.g., gNB) (C2) Relay station (C3) Cell (classic cell) (C4) Beam in beamforming (beam cell) (C5) Point in pointforming (point cell) (C6) CU (Central Unit) (C7) DU (Distributed Unit) (C8) RU (Radio Unit) (C9) Antenna (C10) Antenna element (C11) TRP (Transmission Reception Point)

[0196] Furthermore, the communication point of this embodiment may be a cluster formed by combining multiple elements selected from (C1) to (C11) above. The term "communication point" used in this embodiment may be replaced with a term indicating this cluster.

[0197] 4-4. Specific Example At least one communication point is formed in the communication area provided by the base station (for example, CU) of this embodiment.

[0198] Fig. 9 is a diagram showing a state in which a plurality of communication points are formed in one communication area. In the example of Fig. 9, communication points P1 to P4 are formed in one communication area formed by base station 20. In the example of Fig. 9, communication point P1 is the serving communication point, and communication points P2 to P4 are candidate communication points. In the example of Fig. 9, a plurality of candidate communication points are formed in one communication area.

[0199] 10 is a diagram showing a state in which a plurality of communication points are formed in a plurality of communication areas. In the example of FIG. 10, the base station 20 １ and base station 20 ２ In the example of Fig. 10, communication point P1 is the serving communication point, and communication points P2 to P6 are candidate communication points. In the example of Fig. 10, multiple candidate communication points are formed across multiple communication areas.

[0200] 9 and 10, one base station 20 forms multiple communication points, but one base station 20 may form one communication point. Also, multiple base stations 20 may cooperate to form one communication point. Also, a relay station 30 may form a communication point. As described above, the relay station 30 can be considered as a type of base station 20.

[0201] <4-5. Point forming> As described above, the communication point may be a point in point forming. Point forming is a technology that concentrates power at a specific point by utilizing a phase difference in the near field. The technology for concentrating power at a specific point (point forming) will be described below.

[0202] FIG. 11 is a diagram illustrating a technique for concentrating power at a specific point (point forming). In conventional cellular mobile communications, a base station 20 (e.g., an eNB (eNodeB), a gNB (gNodeB), or a RAN node (including EUTRAN and NGRAN)) concentrates power in a planar or beam-like manner to form a communication coverage area (including femtocells, small cells, and large cells). In the example of FIG. 11, the diagram on the left (classic cell) illustrates how the base station 20 forms a planar cell. The diagram in the center (beamforming) illustrates how the base station 20 forms a beam-shaped cell. In this way, the base station 20 provides communications to a terminal device 40 (e.g., a UE (User Equipment)). Next-generation cellular communications require maximizing the utilization efficiency of radio resources (e.g., at least one of frequency, space, and time) to meet even more advanced requirements (e.g., a greater number of terminal connections, low-latency, highly reliable communications, etc.).

[0203] In beamforming, a communication device increases the power value in a specific direction by cooperatively controlling multiple antennas. Currently, a technology that forms cells at a point (power concentration technology at a specific point) is attracting attention as the next technology after beamforming. This technology concentrates power at a single point in three dimensions by cooperatively controlling multiple transmitting devices (transmitting antennas or devices with one or more transmitting antennas), exceeding the spatial separation achieved by conventional beamforming. In the example of Figure 11, the diagram on the right (point forming) shows how a base station forms a point-like cell (hereinafter also referred to as a point cell). Hereinafter, this technology will be referred to as pointforming, but the terminology is not limited thereto. For example, pointforming may also be referred to as beamfocusing or beamfocal.

[0204] Conventional beamforming did not allow multiplexing of beam directions, but pointforming allows three-dimensional multiplexing. This allows for simultaneous communication with even more terminals. Pointforming also makes it possible to suppress interference with multiple terminals. As a result, we can expect to see improved communication quality across the entire system, a reduction in communication dropout rates, and even greater multi-connection communication.

[0205] Point forming is a technology that maximizes the received power at a specific location by taking into account the phase difference between radio waves transmitted from multiple transmitting antennas and coordinating the operation of multiple transmitting antennas so that the radio waves are combined in phase at the specific location. Outside the specific location, the radio waves transmitted from the multiple transmitting antennas are received with random phases, and the received power is suppressed by averaging. This achieves point forming, which forms a cell at the specific location. Here, in controlling the phase difference between the radio waves transmitted from the multiple transmitting antennas, the control device may, for example, control the initial phase of each transmitting antenna or the amplitude of each transmitting antenna.

[0206] The multiple antennas (multiple transmission points) used in point forming may be one or multiple transmission panels with multiple transmitting antennas (antenna elements). Figure 12 shows an example of point forming using a single antenna with multiple antenna elements. When radio waves are transmitted from a single transmission panel with multiple transmitting antenna elements, near-field characteristics may be taken into account.

[0207] FIG. 13 is a diagram for explaining near and far fields. Conventionally, it has been assumed that a base station communicates with a distant terminal device such as a smartphone. Therefore, conventional studies have been conducted based on the assumption of a far field as shown on the right side of FIG. 13. However, in the future, communications using even larger transmitting panels are expected. Therefore, it may become possible to communicate taking into account the phase difference, which is a characteristic of the near field region. Point forming may be used in this near field region. FIG. 14 is a diagram showing the Fraunhofer distance (also known as the Rayleigh distance), which is the boundary between the near field and the far field.

[0208] While the above example shows the application of point forming in the near field, point forming can be realized in any environment where phase differences can be taken into account. Therefore, in an environment where multiple distributed antennas are located around a receiving point, point forming can be implemented regardless of the Fraunhofer distance. Of course, if the phase difference at the power concentration point can be taken into account, a communication device can also implement point forming using a single antenna with multiple antenna elements.

[0209] FIG. 15 is a diagram illustrating an example of point forming in a distributed antenna environment. In the example of FIG. 15, a base station 20 includes a control unit (CU (Central Unit) in the example of FIG. 15) that controls multiple antennas, and controls the transmitting antenna. In the example of FIG. 15, one CU controls the transmitting antenna, but control by only one CU is not required. Multiple elements (e.g., DU (Distributed Unit), RAT (Radio Access Technology), and TRP (Transmission Reception Point)) may operate cooperatively. Also, in the example of FIG. 15, the CU and the transmitting antenna are optically connected, but this does not necessarily have to be an optical connection. Note that each of multiple transmission points (transmitting antennas) may be a single base station 20. Also, multiple transmission points (transmitting antennas) may be controlled by one or multiple base stations 20.

[0210] In general, the degree of power concentration in point forming varies depending on the number of transmit points used during power concentration. The number of transmit points used to form one or more receive points and the fine power control are positively correlated. In other words, the more transmit points there are, the more fine power control is possible.

[0211] Note that wireless communication related to point forming is not limited to wireless communication using a technology that concentrates power at a specific point by utilizing a phase difference in the near field (power concentration technology). Wireless communication related to point forming may also be near-field communication. Here, the near-field communication may be communication over a distance shorter than the Fraunhofer distance, which is determined by the frequency band and the aperture length of the transmitting panel.

[0212] In the above example, one base station 20 executes the processing related to point forming. However, multiple base stations 20 may execute the processing related to point forming in cooperation with each other. For example, multiple base stations 20 may form a point cell by controlling their respective transmitting antennas in cooperation with other base stations 20. The base station 20 may also perform cooperative control with the relay station 30.

[0213] <<5. Operation of the Communication System>> Based on the above, a detailed description will be given of the operation of the communication system 1. Five embodiments (first to fifth embodiments) will be described below, but these embodiments can be combined as appropriate.

[0214] <5-1. First Example> First, the operation of the communication system 1 according to the first example will be described. In the first example, RACH-less conditional LTM will be described. In the following description, conditional LTM may be referred to as CLTM.

[0215] The introduction of LTM is expected to shorten the interruption time due to handover. However, if a random access procedure occurs during handover, the processing load on the terminal device 40 (or the processing time required for handover) increases.

[0216] Therefore, in the first embodiment, the terminal device 40 executes RACH-less CLTM as a connection destination (communication point) switching operation. RACH-less CLTM is CLTM without a random access procedure. RACH-less CLTM is initiated, for example, by transmitting an uplink signal / channel (e.g., PUSCH) other than the PRACH preamble (Msg1). In RACH-less CLTM, the timing advance value does not need to be updated during the procedure.

[0217] In this embodiment, CLTM with a random access procedure is sometimes referred to as RACH-based CLTM. RACH-based CLTM starts with the transmission of a PRACH preamble (Msg1), for example.

[0218] The RACH-less CLTM may be executed when a predetermined condition (hereinafter also referred to as a second condition) is satisfied. For example, the terminal device 40 may execute the RACH-less CLTM when the predetermined condition is satisfied, and may execute the RACH-based CLTM when the predetermined condition is not satisfied. The predetermined condition (second condition) may be regarded as a condition different from the above-described first condition (condition for executing an autonomous handover). For example, when the first condition is not satisfied, the terminal device 40 may execute a non-conditional handover (i.e., a handover other than CHO and CLTM) regardless of whether the second condition is satisfied. Of course, the second condition may be regarded as the first condition itself or a condition included in the first condition.

[0219] Here, the second condition may be that timing advance information usable after switching is held. That is, the terminal device 40 may execute RACH-less CLTM when it holds timing advance (TA) information (timing advance value) usable after switching.

[0220] More specifically, the second condition may be at least one of the following conditions (D1) to (D3): That is, the terminal device 40 may execute RACH-less CLTM when at least one of the following conditions (D1) to (D3) is satisfied.

[0221] (D1) Timing advance information before switching is valid after switching For example, the terminal device 40 may execute RACH-less CLTM if the currently held timing advance value is valid for the target communication point at the timing when a CLTM (conditional LTM) event is triggered. In other words, the terminal device 40 may execute RACH-less CLTM if there is no problem in using the same timing advance value for the source communication point and the target communication point.

[0222] Here, the case where there is no problem in using the same timing advance value at the source communication point and the target communication point may be, for example, the case where at least one of the following (D1-1) to (D1-5) is satisfied.

[0223] (D1-1) When the difference between the distance (first distance) from the terminal device 40 to the source cell and the distance (second distance) from the terminal device 40 to the target cell is less than or equal to a predetermined threshold (for example, when the first distance and the second distance are the same); (D1-2) When the difference between the propagation delay (first propagation delay) from the terminal device 40 to the source cell and the propagation delay (second propagation delay) from the terminal device 40 to the target cell is less than or equal to a predetermined threshold (for example, when the first propagation delay and the second propagation delay are the same); (D1-3) When the source communication point (for example, the source cell) and the target communication point (for example, the target cell) belong to the same timing advance group; (D1-4) When the timing advance value is within the allowable error range (for example, when the base station 20 can guarantee the reception timing deviation even if the timing advance value is slightly off); (D1-5) When NOMA (Non-Orthogonal Multiple Access) is applied and operation is possible even when asynchronous.

[0224] (D2) Timing advance information available after switching is notified from the base station 20. For example, the terminal device 40 may execute the RACH-less CLTM if a valid timing advance value for the target cell is notified from the base station 20 before a CLTM event is triggered. For example, the terminal device 40 may not execute a random access procedure in CLTM if early UL sync is performed.

[0225] (D3) It is possible to obtain timing advance information that can be used after switching even without a random access procedure. For example, the terminal device 40 may perform RACH-less CLTM if it is possible to update the timing advance value for the target cell even without a random access procedure.

[0226] For example, the terminal device 40 may execute the RACH-less CLTM when a timing advance value that can be used after switching has been notified by another terminal device 40. For example, the terminal device 40 may execute the RACH-less CLTM when a timing advance value that can be used after switching has been notified by a terminal device 40 located at an adjacent communication point (for example, a target communication point).

[0227] Furthermore, for example, the terminal device 40 may execute the RACH-less CLTM when it is possible to measure a timing advance value to be used after switching. For example, the terminal device 40 may execute the RACH-less CLTM when UE-based timing advance measurement (UE-based TA measurement) is being executed.

[0228] <5-2. Second Example> Next, the operation of the communication system 1 according to a second example will be described. In the second example, a RACH-less conditional LTM without early sync will be described. In this example, the conditional LTM may also be referred to as CLTM.

[0229] The terminal device 40 may execute CLTM without early sync (CLTM without early sync) when a predetermined condition is satisfied. For example, the terminal device 40 may execute CLTM without early sync (CLTM without early sync) when valid timing advance information (timing advance value) can be acquired without executing early sync (early sync). Here, the CLTM without early sync may be RACH-less CLTM without early sync (RACH-less CLTM without early sync) or RACH-based CLTM without early sync (RACH-based CLTM without early sync). As described above, in the second embodiment, RACH-less CLTM without early sync (referred to as a first handover in this embodiment) will be described.

[0230] <5-2-1. Conditions for Executing CLTM Without Early Sync> As described above, the terminal device 40 may execute CLTM without early sync if it is possible to acquire valid timing advance information (timing advance value) without executing early sync. Here, if valid timing advance information can be acquired without executing early sync, it may be the case where the second condition described above is satisfied. For example, if valid timing advance information can be acquired without executing early sync, it may be the case where at least one of the conditions (D1) to (D3) described above is satisfied.

[0231] For example, the terminal device 40 may execute the RACH-less CLTM without early sync when the timing advance information before the switching remains valid after the switching. Furthermore, for example, the terminal device 40 may execute the RACH-less CLTM without early sync when timing advance information usable after the switching is notified from the base station 20. Furthermore, for example, the terminal device 40 may execute the RACH-less CLTM without early sync when it is possible to acquire timing advance information usable after the switching without a random access procedure. For example, the terminal device 40 may execute the RACH-less CLTM without early sync when it is notified from another terminal device 40 of timing advance information usable after the switching and / or when it is possible to measure timing advance information usable after the switching.

[0232] <5-2-2. Method for Determining Whether Timing Advance Information is Valid> The terminal device 40 may determine whether timing advance information (timing advance value) is valid based on the measurement result. For example, the terminal device 40 may determine whether timing advance information is valid based on the elapsed time since the time when timing advance information was last acquired. For example, if the terminal device 40 is unable to acquire new timing advance information even after a predetermined time has passed since the time when timing advance information was last acquired, the terminal device 40 may determine that the timing advance information is not valid (not valid). Note that the terminal device 40 may measure the timing advance value using a method other than the random access procedure.

[0233] Furthermore, the terminal device 40 may determine whether the timing advance information (timing advance value) is valid based on the notification. For example, the terminal device 40 may acquire from the base station 20 a determination result as to whether the timing advance information currently held by the terminal device 40 is valid. Then, the terminal device 40 may determine whether the timing advance information is valid based on the acquired determination result.

[0234] <5-2-3. Processing When the Second Condition Is Not Satisfied> When the second condition is not satisfied (for example, when the terminal device 40 determines that its own timing advance information is invalid), the terminal device 40 may perform a second handover, different from the first handover (RACH-less CLTM without early sync), as the connection destination switching operation. Here, the second handover may be a handover that can acquire timing advance information. For example, the second handover may be a RACH-based CLTM, or a RACH-based CHO other than a RACH-based CLTM. Furthermore, for example, the second handover may be a CLTM with early sync (for example, a RACH-less CLTM with early sync). Of course, the second handover may be a handover other than these.

[0235] If the second condition is not satisfied, the terminal device 40 may notify the base station 20 that its own timing advance information is invalid. Upon receiving the notification, the base station 20 may start early sync (e.g., early UL sync). For example, the base station 20 may transmit a PDCCH order to the terminal device 40 and start early UL sync. Note that if the base station 20 has already acquired valid timing advance information upon receiving the notification, the base station 20 may switch the handover from CLTM to unconditional handover (e.g., LTM). For example, the base station 20 may notify the terminal device 40 of an LTM cell switch command including valid timing advance information.

[0236] The base station 20, which has determined that the timing advance information held by the terminal device 40 is invalid, may notify the terminal device 40 of a second handover different from the first handover (RACH-less CLTM without early sync). The second handover may be RACH-based CLTM, RACH-based CHO other than RACH-based CLTM, or RACH-less CLTM with early sync. Of course, the second handover may be a conventional L3 handover. The base station 20 may notify the second handover via PDCCH, MAC CE, or RRC signaling. The terminal device 40 may execute the handover under the control of the base station 20. For example, the terminal device 40 may perform a second handover (for example, at least one of RACH-based CLTM and RACH-less CLTM with early sync) in accordance with the notification regarding the second handover.

[0237] <5-2-4. Setting by Base Station> The terminal device 40 may determine the type of handover to use in accordance with the setting by the base station 20 (an instruction from the base station 20). For example, the terminal device 40 may be configured to use a first handover (RACH-less CLTM without early sync) or a second handover (for example, RACH-based CHO (RACH-based CLTM, or RACH-based CHO other than RACH-based CLTM), or RACH-less CLTM with early sync) for the connection destination switching operation. This setting (instruction) may be notified to the terminal device 40 by PDCCH, MAC CE, or RRC signaling before the handover (CLTM / CHO) is executed. In other words, this setting (instruction) is information indicating whether timing advance information is valid for the target communication point. The terminal device 40 may execute either the first handover or the second handover in accordance with the setting by the base station 20 (an instruction from the base station 20).

[0238] Note that, if the terminal device 40 does not receive the above setting (instruction) from the base station 20 before executing the handover (CLTM / CHO), it may execute a default operation. The default operation may be determined statically / semi-statically. For example, the default operation may be determined by RRC signaling. The default operation may also be a second handover (for example, a RACH-based CHO (RACH-based CLTM, or a RACH-based CHO other than RACH-based CLTM), or a RACH-less CLTM with early sync). Furthermore, if the terminal device 40 does not receive the above setting (instruction) from the base station 20 before executing the handover (CLTM / CHO), it may not execute the conditional handover (CLTM / CHO) even if the execution conditions for the conditional handover (CLTM / CHO) are satisfied.

[0239] <5-2-5. Example of Information Notified Before Execution of RACH-less CLTM Without Early Sync> Before execution of RACH-less CLTM without early sync, information may be notified to the terminal device 40 from another communication device (e.g., base station 20). This information may be defined as one RRC message or one IE (Information Element). For example, this information may be defined as part of one IE.

[0240] The information (hereinafter referred to as pre-execution information) notified before the execution of RACH-less CLTM without early sync (before the communication point is switched) may be at least one of the following (E1) to (E4).

[0241] (E1) Pre-execution information regarding synchronization with a candidate communication point may be information regarding synchronization with a candidate communication point (target communication point). Here, the information regarding synchronization with a candidate communication point may be frequency band information (e.g., center frequency information) of the candidate communication point (target communication point). This information may be notified using an ARFCN (Absolute radio-frequency channel number). Note that if the frequency band information is notified in advance using an SSB (SS / PBCH block) or the like, it is not necessarily necessary to notify the frequency band information. Alternatively, the information regarding synchronization with a candidate communication point may be timing advance information or subcarrier spacing information.

[0242] (E2) Information specific to the target candidate communication point The pre-execution information may be information specific to the candidate communication point (target communication point). Here, the information specific to the candidate communication point may be at least one of the following identifiers: TCI state ID, CORESET ID, Physical Cell ID, SSB index, CSI-RS resource set ID.

[0243] (E3) Information Regarding Measurement of Communication Quality of Candidate Communication Point The pre-execution information may be information regarding measurement of communication quality of the candidate communication point (target communication point).

[0244] The information related to the measurement of the communication quality of the candidate communication point may be measurement resource location information, where the measurement resource location information may be at least one of the following: a location of an SSB designated for measurement, a location of a CSI-RS designated for measurement, a location of a DMRS of a PDCCH or PDSCH having a TCI state of a TCI state ID designated by the identifier, and a DMRS of a PDCCH transmitted in a CORESET of a CORESET ID (Control Resource Set ID) designated by the identifier.

[0245] The information regarding the measurement of the communication quality of the candidate communication point may be a measurement RS (Reference Signal) type. Here, the measurement RS type may be at least one of the following: -SS / PBCH block (SS / PBCH block) -CSI-RS (Channel State Information Reference Signal) -DMRS (Demodulation Reference Signal) of PDCCH (Physical Downlink Control Channel) -DMRS (Demodulation Reference Signal) of PDSCH (Physical Data Shared Channel)

[0246] The information on the measurement of the communication quality of the candidate communication point may be a communication quality index, where the communication quality index may be at least one of the following indices or a combination of multiple indices from the following indices: RSRP (Reference Signal Received Power), RSSI (Received Signal Strength Indicator), Path Loss, and RSRQ (Reference Signal Received Quality).

[0247] (E4) Information on Conditions The pre-execution information may be information on conditions. Here, the conditions indicated by the information on conditions may be conditions related to determining whether to switch the serving communication point to a candidate communication point. For example, the conditions indicated by the information on conditions may be at least one of the following conditions:

[0248] When the communication quality (e.g., RSRP) of the measured candidate communication point is equal to or greater than a threshold value When the communication quality (e.g., RSRP) of the measured serving communication point is equal to or less than a threshold value When the communication quality (e.g., RSRP) of the measured serving communication point is equal to or less than an offset from the communication quality (e.g., RSRP) of the measured candidate communication point When the communication quality (e.g., RSRP) of the measured candidate communication point is equal to or greater than an offset from the communication quality (e.g., RSRP) of the measured serving communication point When the communication quality (e.g., RSRP) of the measured serving communication point is equal to or greater than an offset from the communication quality (e.g., RSRP) of the measured serving communication point When the communication quality (e.g., RSRP) of the candidate communication point that was measured becomes worse than the communication quality (e.g., RSRP) of the candidate communication point that was measured When the communication quality (e.g., RSRP) of the candidate communication point that was measured becomes better than the communication quality (e.g., RSRP) of the serving communication point that was measured When a timer for detaching from the serving communication point is executed When the time to detach from the serving communication point is reached When a timer related to the implementation of switching to a certain candidate communication point is executed When the start time for implementation of switching to a certain candidate communication point is reached

[0249] The terminal device 40 may execute a communication point switching operation when at least one of the above conditions is satisfied. The above conditions can be regarded as a first condition and / or a second condition.

[0250] <5-2-6. Sequence Example> An example sequence of RACH-less CLTM (RACH-less CLTM without early sync) according to the second embodiment will be described below. Fig. 16 is a sequence diagram showing an example of the procedure of RACH-less CLTM without early sync. In the figure, operations indicated by solid lines indicate mandatory operations, and operations indicated by dotted lines indicate optional operations. The following processing is executed by the control unit 43 of the terminal device 40 and the control unit 23 of the base station 20 (or the control unit 33 of the relay station 30).

[0251] 16, only one base station 20 appears in the sequence, but multiple base stations 20 may appear in the sequence. For example, the base station 20 forming the serving communication point and the base station 20 forming the candidate communication point / target communication point may be different. Of course, the base station 20 forming the serving communication point and the base station 20 forming the candidate communication point / target communication point may be the same. Note that, when there are multiple candidate communication points, these multiple candidate communication points may be formed by multiple base stations 20, for example, as shown in FIG. 10. Of course, multiple candidate communication points may be formed by a single base station 20, for example, as shown in FIG. 9.

[0252] First, the terminal device 40 transmits a measurement report to the base station 20 (step S101). Here, the terminal device 40 may transmit information necessary for RACH-less CLTM without early sync (hereinafter simply referred to as necessary information) to the base station 20 along with the measurement report. Alternatively, the terminal device 40 may transmit the necessary information by including it in the measurement report. Here, the information (necessary information) transmitted by the terminal device 40 to the base station 20 may be at least one of the following (F1) to (F5).

[0253] (F1) Information Regarding Whether CLTM Can Be Implemented The necessary information may be information regarding whether the terminal device 40 can implement CLTM.

[0254] (F2) Information Regarding Synchronization with Candidate Communication Points The necessary information may be information regarding synchronization with candidate communication points (target communication points). Here, the information regarding synchronization with candidate communication points may be frequency band information (e.g., center frequency information) of the candidate communication points (target communication points). This information may be notified using ARFCN (Absolute radio-frequency channel number). Note that if the frequency band information has been notified in advance using SSB (SS / PBCH block) or the like, it is not necessarily necessary to notify the frequency band information. Alternatively, the information regarding synchronization with candidate communication points may be timing advance information or subcarrier spacing information.

[0255] (F3) Information specific to the target candidate communication point The required information may be information specific to the candidate communication point (target communication point). Here, the information specific to the candidate communication point may be at least one of the following identifiers: TCI state ID, CORESET ID, Physical Cell ID, SSB index, CSI-RS resource set ID.

[0256] (F4) Information Regarding Measurement of Communication Quality of Candidate Communication Point The pre-execution information may be information regarding measurement of communication quality of candidate communication point (target communication point).

[0257] The information related to the measurement of the communication quality of the candidate communication point may be measurement resource location information, where the measurement resource location information may be at least one of the following: a location of an SSB designated for measurement, a location of a CSI-RS designated for measurement, a location of a DMRS of a PDCCH or PDSCH having a TCI state of a TCI state ID designated by the identifier, and a DMRS of a PDCCH transmitted in a CORESET of a CORESET ID (Control Resource Set ID) designated by the identifier.

[0258] The information regarding the measurement of the communication quality of the candidate communication point may be a measurement RS (Reference Signal) type. Here, the measurement RS type may be at least one of the following: -SS / PBCH block (SS / PBCH block) -CSI-RS (Channel State Information Reference Signal) -DMRS (Demodulation Reference Signal) of PDCCH (Physical Downlink Control Channel) -DMRS (Demodulation Reference Signal) of PDSCH (Physical Data Shared Channel)

[0259] The information on the measurement of the communication quality of the candidate communication point may be a communication quality index, where the communication quality index may be at least one of the following indices or a combination of multiple indices from the following indices: RSRP (Reference Signal Received Power), RSSI (Received Signal Strength Indicator), Path Loss, and RSRQ (Reference Signal Received Quality).

[0260] The information regarding the measurement of the communication quality of the candidate communication point may be information regarding the capability of the terminal device 40. Here, the information regarding the capability of the terminal device 40 may be information regarding whether the terminal device 40 supports RACH-less CLTM.

[0261] The base station 20 that has received the measurement report may make a decision regarding RACH-less CLTM (for example, a configuration decision) (step S102). Then, the base station 20 starts preparation for RACH-less CLTM (step S103). Then, the base station 20 transmits a message including an LTM candidate configuration to the terminal device 40 (step S104). This message may include the above-mentioned pre-execution information (for example, at least one of the above-mentioned (E1) to (E4)). The terminal device 40 may transmit a completion message storing the LTM candidate configuration to the base station 20 (step S105).

[0262] The terminal device 40 starts evaluating the execution conditions for RACH-less CLTM (for example, the above-mentioned second condition) for one or more candidate communication points while maintaining the connection with the source communication point (step S106). The terminal device 40 selects a candidate communication point that satisfies the conditions as a target communication point. Then, the terminal device 40 switches the connection destination from the source communication point to the target communication point (step S107). For example, the terminal device 40 releases the connection with the source communication point and synchronizes with the target communication point.

[0263] Once synchronized with the target communication point, the terminal device 40 transmits a message (PUSCH transmission) to the base station 20 (step S108). The terminal device 40 may explicitly notify the base station 20 of information regarding the target communication point using this message (PUSCH). For example, the terminal device 40 may include information regarding the target communication point ID (e.g., target cell ID) in the message. Alternatively, the terminal device 40 may implicitly notify the base station 20 of information regarding the target communication point using the message (PUSCH). For example, a configured grant resource used for transmitting the message (PUSCH) may be linked to the target cell. Note that the message (PUSCH) may include identification information of the terminal device 40. Then, the base station 20 may perform contention resolution based on the received identification information and transmit a message to the terminal device 40 (step S109).

[0264] After performing various processes associated with the completion of the switch, the base station 20 and the terminal device 40 complete the RACH-less CLTM procedure. Here, the terminal device 40 may transmit a switch completion message to the base station 20.

[0265] <5-3. Third Example> Next, the operation of the communication system 1 according to a third example will be described. In the third example, a RACH-less conditional LTM with early sync will be described. In this example, the conditional LTM may also be referred to as CLTM.

[0266] In a third embodiment, when one or more handover execution conditions are satisfied, the terminal device 40 executes CLTM with early sync. In CLTM with early sync, for example, notification of a switch command (e.g., step S36 in FIG. 8 ) and a report for executing the switch command (e.g., step S35 in FIG. 8 ) are not executed.

[0267] In CLTM with early sync, timing advance information (timing advance value) is acquired by early sync. Therefore, in CLTM with early sync, a random access procedure does not necessarily have to be performed. The CLTM with early sync described in the third embodiment is a RACH-less CLTM.

[0268] An example sequence of RACH-less CLTM (CLTM with early sync) according to the third embodiment will be described below. Fig. 17 is a sequence diagram showing an example of the procedure of CLTM with early sync. In the figure, operations indicated by solid lines are mandatory operations, and operations indicated by dotted lines are optional operations. The following processing is executed by the control unit 43 of the terminal device 40 and the control unit 23 of the base station 20 (or the control unit 33 of the relay station 30).

[0269] 17, only one base station 20 appears in the sequence, but multiple base stations 20 may appear in the sequence. For example, the base station 20 forming the serving communication point and the base station 20 forming the candidate communication point / target communication point may be different. Of course, the base station 20 forming the serving communication point and the base station 20 forming the candidate communication point / target communication point may be the same. Note that, when there are multiple candidate communication points, these multiple candidate communication points may be formed by multiple base stations 20, for example, as shown in FIG. 10. Of course, multiple candidate communication points may be formed by a single base station 20, for example, as shown in FIG. 9.

[0270] First, the terminal device 40 transmits a measurement report to the base station 20 (step S201). The base station 20, having received the measurement report, makes a decision regarding RACH-less CLTM (for example, determines a configuration) (step S202). Then, the base station 20 starts preparation for RACH-less CLTM (step S203). Then, the base station 20 transmits a message including an LTM candidate configuration to the terminal device 40 (step S204). The terminal device 40 may transmit a completion message storing the LTM candidate configuration to the base station 20 (step S205).

[0271] Next, the terminal device 40 performs DL synchronization with one or more candidate communication points while maintaining the connection with the source communication point (step S206).Furthermore, the terminal device 40 performs UL synchronization with one or more candidate communication points while maintaining the connection with the source communication point (step S207).

[0272] The terminal device 40 starts evaluating the execution conditions for RACH-less CLTM for one or more candidate communication points while maintaining the connection with the source communication point (step S208). Here, the execution conditions for RACH-less CLTM may be the same as the second condition described above. The terminal device 40 selects a candidate communication point that satisfies the conditions as a target communication point. Then, the terminal device 40 switches the connection destination from the source communication point to the target communication point (step S209).

[0273] After switching the connection destination, the terminal device 40 transmits a message (PUSCH transmission) to the base station 20 (step S210). The terminal device 40 may explicitly notify the base station 20 of information related to the target communication point by using this message (PUSCH). For example, the terminal device 40 may include information on the target communication point ID (for example, a target cell ID) in the message. Furthermore, the terminal device 40 may implicitly notify the base station 20 of information related to the target communication point by using this message (PUSCH). For example, a configured grant resource used for transmitting the message (PUSCH) may be linked to the target cell.

[0274] The PUSCH resource used for CLTM may be set by the configured grant configuration. For example, when early UL sync is completed for the target communication point, the PUSCH resource used for CLTM may be activated by an instruction from the base station 20 (for example, a Random Access Response (RAR) in the early UL sync procedure). In other words, the configured grant resource may be deactivated until early sync is completed.

[0275] The message (PUSCH) may include identification information of the terminal device 40. Then, the base station 20 may perform contention resolution based on the received identification information and transmit a message to the terminal device 40 (step S211).

[0276] After performing various processes associated with the completion of the switch (for example, after transmitting a switch completion message), the terminal device 40 completes the RACH-less CLTM procedure.

[0277] <5-4. Fourth Example> Next, the operation of the communication system 1 according to the fourth example will be described. In the fourth example, RACH-less conditional LTM with early sync will also be described. In this example, the conditional LTM may also be referred to as CLTM.

[0278] In a fourth embodiment, timing advance information (timing advance value) is acquired by a PDCCH order (PDCCH-order) during early sync. The terminal device 40 determines candidate communication points to which PDCCH order transmission is to be performed based on a condition notified in advance. Then, the terminal device 40 notifies the base station 20 of the determined candidate communication points. In the following description, this notification may be referred to as a PDCCH order request.

[0279] <5-4-1. PDCCH Order Request> The PDCCH order request may include information indicating candidate communication points that are permitted to transmit PDCCH orders (hereinafter referred to as permission information). The permission information may include identification information (e.g., a bit sequence) of the candidate communication points. The permission information may also include information about resources associated with the candidate communication points. Here, the information about resources may include at least one of the following: Location of resources Number of resources Information about TCI state Information about QCL (Quasi-Co-Location)

[0280] <5-4-2. Processing when PDCCH order cannot be received> When a certain time has elapsed since the execution of a PDCCH order request, the terminal device 40 may determine that the PDCCH order has not been received from the base station 20. Furthermore, the terminal device 40 may determine that the PDCCH order has not been received from the base station 20 when the range of a window determined by information notified in advance has been exceeded.

[0281] If the PDCCH order is not received, the terminal device 40 may execute a PDCCH order request again. Alternatively, if the PDCCH order is not received, the terminal device 40 may execute a RACH-based CLTM. Alternatively, if the PDCCH order is not received, the terminal device 40 may execute another RACH-less CLTM.

[0282] <5-4-3. Processing when timing advance information cannot be acquired> Assume that a CLTM event is triggered in a state in which the terminal device 40 has not acquired timing advance information by a PDCCH order. In this case, the terminal device 40 may execute RACH-less conditional LTM without early sync, as shown in the second embodiment.

[0283] <5-4-4. Processing when CLTM execution conditions are met> The format of the notification that is executed when the CLTM execution conditions are met may be at least one of the following: UCI (Uplink Control Information) PUCCH (Physical Uplink Shared Channel) PUSCH (Physical Uplink Control Channel) MAC CE (MAC Control Element)

[0284] The execution condition of CLTM may be notified from the base station 20 to the terminal device 40 before executing CLTM. The execution condition of CLTM may be a condition related to the decision of whether to switch the serving communication point to a candidate communication point. For example, the condition indicated in the information on the condition may be the condition indicated in (E4) above and / or a condition related to whether to form a UL synchronization state with a specific candidate communication point. Here, the condition related to whether to form a UL synchronization state with a specific candidate communication point may be at least one of the conditions indicated below.

[0285] - When the communication quality (e.g., RSRP) of the measured candidate communication point is expected to be equal to or higher than a threshold. - When the communication quality (e.g., RSRP) of the measured serving communication point is expected to be equal to or lower than a threshold. - When the communication quality (e.g., RSRP) of the measured serving communication point is expected to be equal to or lower than an offset from the communication quality (e.g., RSRP) of the measured candidate communication point. - When the communication quality (e.g., RSRP) of the measured serving communication point is expected to be equal to or higher than an offset from the communication quality (e.g., RSRP) of the measured serving communication point. - When the communication quality (e.g., RSRP) of the measured candidate communication point is expected to be worse than the communication quality (e.g., RSRP) of the measured candidate communication point. - When the communication quality (e.g., RSRP) of the measured candidate communication point is expected to be better than the communication quality (e.g., RSRP) of the measured serving communication point. - When the time has come when an offset time has been subtracted / added from the start time of switching to a certain candidate communication point.

[0286] The terminal device 40 may execute a communication point switching operation when at least one of the above conditions is satisfied.

[0287] <5-4-5. Sequence Example> An example sequence of RACH-less CLTM (CLTM with early sync) according to the fourth embodiment will be described below. Fig. 18 is a sequence diagram showing another example of the procedure of CLTM with early sync. In the figure, operations indicated by solid lines indicate mandatory operations, and operations indicated by dotted lines indicate optional operations. The following processing is executed by the control unit 43 of the terminal device 40 and the control unit 23 of the base station 20 (or the control unit 33 of the relay station 30).

[0288] In the example of Figure 18, only one base station 20 appears in the sequence, but multiple base stations 20 may appear in the sequence. For example, the base station 20 forming the serving communication point and the base station 20 forming the candidate communication point / target communication point may be different. Of course, the base station 20 forming the serving communication point and the base station 20 forming the candidate communication point / target communication point may be the same. In addition, when there are multiple candidate communication points, these multiple candidate communication points may be formed by multiple base stations 20, for example, as shown in Figure 10. Of course, multiple candidate communication points may be formed by a single base station 20, for example, as shown in Figure 9.

[0289] First, the terminal device 40 transmits a measurement report to the base station 20 (step S301). The base station 20, having received the measurement report, makes a decision regarding RACH-less CLTM (for example, determines a configuration) (step S302). Then, the base station 20 starts preparation for RACH-less CLTM (step S303). Then, the base station 20 transmits a message including an LTM candidate configuration to the terminal device 40 (step S304). The terminal device 40 may transmit a completion message storing the LTM candidate configuration to the base station 20 (step S305).

[0290] Next, the terminal device 40 performs DL synchronization with one or more candidate communication points while maintaining connection with the source communication point (step S306). Then, the terminal device 40 starts evaluating the execution condition of the PDCCH order request (step S307). Here, the execution condition of the PDCCH order request may be the same as the second condition described above (for example, the condition shown in (E4) above and / or the condition shown in <5-4-4> above). If the condition is met, the terminal device 40 performs UL synchronization with one or more candidate communication points (step S308).

[0291] 19 is a sequence diagram showing an example of a procedure for UL synchronization according to the fourth embodiment. First, the terminal device 40 transmits a PDCCH order request to the base station 20 (step S401). As described above, the PDCCH order request may include information (permission information) indicating candidate communication points that are permitted to transmit the PDCCH order. The base station 20 that has received the PDCCH order request transmits a PDCCH order (step S402). The terminal device 40 that has received the PDCCH order transmits a preamble to the base station 20 (step S403). Then, the terminal device 40 transmits a measurement report to the base station 20 (step S404).

[0292] 20 is a sequence diagram showing another example of the UL synchronization procedure according to the fourth embodiment. First, the terminal device 40 transmits a PDCCH order request to the base station 20 (step S501). At this time, the terminal device 40 transmits a measurement report simultaneously with the PDCCH order request. The base station 20 that has received the PDCCH order request transmits a PDCCH order (step S502). The terminal device 40 that has received the PDCCH order transmits a preamble to the base station 20 (step S503).

[0293] 18 , the base station 20 may make a decision regarding the LTM (step S309). For example, if the terminal device 40 has successfully synchronized with multiple candidate communication points, the base station 20 may determine a candidate communication point to be a target communication point. Then, the base station 20 may transmit a switch command including identification information of the target communication point to the terminal device 40 (step S310).

[0294] The terminal device 40 switches the connection destination from the source communication point to the target communication point (step S311). After switching the connection destination, the terminal device 40 transmits a message (PUSCH transmission) to the base station 20 (step S312). The terminal device 40 may explicitly or implicitly notify the base station 20 of information regarding the target communication point by using this message (PUSCH). The PUSCH resource used for CLTM may be set by the configured grant configuration.

[0295] The message (PUSCH) may include identification information of the terminal device 40. Then, the base station 20 may perform contention resolution based on the received identification information and transmit a message to the terminal device 40 (step S313).

[0296] After performing various processes associated with the completion of the switch, the base station 20 and the terminal device 40 complete the RACH-less CLTM procedure. Here, the terminal device 40 may transmit a switch completion message to the base station 20.

[0297] <5-5. Fifth Example> Next, the operation of the communication system 1 according to the fifth example will be described. In the fifth example, the conditional LTM with early sync (RACH-less conditional LTM with early sync) will also be described. In this example, the conditional LTM may also be referred to as CLTM.

[0298] <5-5-1. Execution Conditions> In the fifth embodiment, as in the fourth embodiment, early sync is performed when the execution conditions are met. In the fifth embodiment, trigger events (execution conditions) are set for early sync and RACH-less CLTM, respectively. In the following description, the early sync in the fifth embodiment may be referred to as conditional early sync.

[0299] The trigger event (execution condition) set for the conditional Early Sync is different from the trigger event (execution condition) set for the RACH-less CLTM. For example, different types of events may be set for the Early Sync and the RACH-less CLTM. Of course, the same type of event may be set for the Early Sync and the RACH-less CLTM. In this case, the trigger thresholds may be different between the Early Sync and the RACH-less CLTM.

[0300] It is preferable that the trigger event set for the conditional early sync be set so as to be triggered earlier than the trigger event set for the RACH-less CLTM. As a result, the early sync is performed earlier than the RACH-less CLTM, and the terminal device 40 can acquire valid timing advance information (timing advance value).

[0301] <5-5-2. When Events are Triggered Simultaneously> When the conditional early sync and the RACH-less CLTM are triggered simultaneously, the terminal device 40 may execute latch-based CLTM (RACH-based CLTM). In this case, the terminal device 40 transmits a preamble to the base station 20.

[0302] Alternatively, if the conditional early sync and the RACH-less CLTM are triggered simultaneously, the terminal device 40 may execute only the conditional early sync without executing the RACH-less CLTM. In this case, the terminal device 40 may execute the CLTM when the RACH-less CLTM event is triggered again after the conditional early sync is completed.

[0303] The terminal device 40 may notify the base station 20 that the conditional early sync and CLTM have been triggered simultaneously. In this case, the terminal device 40 may perform subsequent operations in accordance with instructions from the base station 20. For example, upon receiving the notification, the base station 20 may instruct the terminal device 40 to start a random access procedure. Then, the terminal device 40 may execute the random access procedure in accordance with the instructions from the base station 20.

[0304] <5-5-3. Sequence Example> An example sequence of RACH-less CLTM (CLTM with early sync) according to the fifth embodiment will be described below. Fig. 21 is a sequence diagram showing another example of the procedure of CLTM with early sync. In the figure, operations indicated by solid lines indicate mandatory operations, and operations indicated by dotted lines indicate optional operations. The following processing is executed by the control unit 43 of the terminal device 40 and the control unit 23 of the base station 20 (or the control unit 33 of the relay station 30).

[0305] 21, only one base station 20 appears in the sequence, but multiple base stations 20 may appear in the sequence. For example, the base station 20 forming the serving communication point and the base station 20 forming the candidate communication point / target communication point may be different. Of course, the base station 20 forming the serving communication point and the base station 20 forming the candidate communication point / target communication point may be the same. Note that, when multiple candidate communication points exist, these multiple candidate communication points may be formed by multiple base stations 20, for example, as shown in FIG. 10. Of course, multiple candidate communication points may be formed by a single base station 20, for example, as shown in FIG. 9.

[0306] First, the terminal device 40 transmits a measurement report to the base station 20 (step S601). The base station 20, having received the measurement report, makes a decision regarding RACH-less CLTM (for example, determines a configuration) (step S602). Then, the base station 20 starts preparation for RACH-less CLTM (step S603). Then, the base station 20 transmits a message including an LTM candidate configuration to the terminal device 40 (step S604). The terminal device 40 may transmit a completion message storing the LTM candidate configuration to the base station 20 (step S605).

[0307] Next, the terminal device 40 performs DL synchronization with one or more candidate communication points while maintaining connection with the source communication point (step S606). Then, the terminal device 40 starts evaluating the execution conditions for conditional early sync (step S607). Here, the execution conditions for conditional early sync may be the same as the second condition described above (for example, the condition shown in (E4) above and / or the condition shown in <5-4-4> above).

[0308] If the conditions are met, the terminal device 40 performs UL synchronization with one or more candidate communication points. For example, the terminal device 40 transmits a PDCCH order request to the base station 20 (step S608). At this time, the terminal device 40 may transmit a measurement report simultaneously with the PDCCH order request. The base station 20 that has received the PDCCH order request transmits a PDCCH order to the terminal device 40 (step S609). The terminal device 40 that has received the PDCCH order transmits a preamble to the base station 20 (step S610). Note that the UL synchronization procedure may be the same as the procedure shown in FIG. 19 or 20.

[0309] Next, the terminal device 40 starts evaluating the execution conditions for RACH-less CLTM for one or more candidate communication points while maintaining the connection with the source communication point (step S611). Here, the execution conditions for RACH-less CLTM may be the same as the second condition described above. As described above, the execution conditions for RACH-less CLTM are different from the execution conditions for conditional early sync. The terminal device 40 selects a candidate communication point that satisfies the conditions as a target communication point.

[0310] Subsequently, the terminal device 40 switches the connection destination from the source communication point to the target communication point (step S612). After switching the connection destination, the terminal device 40 transmits a message (PUSCH transmission) to the base station 20 (step S613). The terminal device 40 may explicitly or implicitly notify the base station 20 of information regarding the target communication point by using this message (PUSCH). The PUSCH resource used for CLTM may be set by the configured grant configuration.

[0311] The message (PUSCH) may include identification information of the terminal device 40. Then, the base station 20 may perform contention resolution based on the received identification information and transmit a message to the terminal device 40 (step S614).

[0312] After performing various processes associated with the completion of the switch, the base station 20 and the terminal device 40 complete the RACH-less CLTM procedure. Here, the terminal device 40 may transmit a switch completion message to the base station 20.

[0313] <<6. Modifications>> The above-described embodiment is merely an example, and various modifications and applications are possible.

[0314] For example, in the above-described embodiment, the base station 20 performs processing related to a conditional handover (e.g., CLTM) in response to execution of a conditional handover (e.g., CLTM) by the terminal device 40. However, the relay station 30 may perform processing related to a conditional handover (e.g., CLTM) in response to execution of a conditional handover (e.g., CLTM) by the terminal device 40. In this case, the above-described description of the base station 20 can be replaced with the relay station 30. As described above, the relay station 30 can be considered as a type of base station 20.

[0315] The functions of the base station 20 in this embodiment may be separated into a plurality of functions such as a CU (Central Unit), a DU (Distributed Unit), and an RU (Radio Unit). In this case, the above description of the base station 20 can be replaced with the CU, DU, or RU.

[0316] The management device 10, the base station 20, the relay station 30, or the control device that controls the terminal device 40 in this embodiment may be realized by a dedicated computer system or a general-purpose computer system.

[0317] For example, a program for executing the above-described operations is stored and distributed on a computer-readable recording medium such as an optical disk, semiconductor memory, magnetic tape, or flexible disk. Then, for example, the program is installed on a computer and the above-described processing is executed to configure a control device. In this case, the control device may be a device (e.g., a personal computer) external to the management device 10, base station 20, relay station 30, or terminal device 40. Alternatively, the control device may be a device (e.g., control unit 13, control unit 23, control unit 33, or control unit 43) internal to the management device 10, base station 20, relay station 30, or terminal device 40.

[0318] The communication program may also be stored in a disk device provided in a server device on a network such as the Internet, and may be downloaded to a computer. The above-described functions may also be realized by a combination of an operating system (OS) and application software. In this case, the components other than the OS may be stored on a medium and distributed, or may be stored in a server device and downloaded to a computer.

[0319] Furthermore, among the processes described in the above embodiments, all or part of the processes described as being performed automatically can be performed manually, or all or part of the processes described as being performed manually can be performed automatically using a known method. In addition, the information including the processing procedures, specific names, various data, and parameters shown in the above documents and drawings can be changed as desired unless otherwise specified. For example, the various information shown in each drawing is not limited to the information shown in the drawings.

[0320] Furthermore, the components of each device shown in the figure are conceptual functional components and do not necessarily have to be physically configured as shown in the figure. In other words, the specific form of distribution and integration of each device is not limited to that shown in the figure, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

[0321] The above-described embodiments can be combined as appropriate within the scope of the present invention without causing any inconsistency in the processing content. The order of the steps shown in the sequence diagrams or flowcharts of the present embodiment can be changed as appropriate.

[0322] Furthermore, for example, the present embodiment can also be implemented as any configuration that constitutes an apparatus or system, such as a processor as a system LSI (Large Scale Integration), a module using multiple processors, a unit using multiple modules, a set in which other functions are added to a unit, or the like (i.e., a configuration of a part of an apparatus).

[0323] The functions performed by the components described herein may be implemented in a circuit or processing circuitry programmed to perform the described functions. Here, the circuit or processing circuitry may be a general-purpose processor, an application-specific processor, an integrated circuit, an ASIC (Application Specific Integrated Circuit), a CPU (a Central Processing Unit), a conventional circuit, and / or a combination thereof. A processor includes transistors and other circuits. A processor may be considered a circuit or a processing circuitry. A processor may be a programmed processor that executes a program stored in a memory.

[0324] In this specification, a circuit, a unit, or a means may be hardware that is programmed to realize a described function or that performs a described function. The hardware may be any hardware disclosed in this specification or any hardware that is programmed to realize or known to perform the described function. If the hardware is a processor that is considered to be a type of circuit, the circuit, a means, or a unit may be a combination of hardware and software used to configure the hardware and / or processor.

[0325] Furthermore, for example, the present embodiment can be implemented as any configuration constituting an apparatus or system. For example, the present embodiment can be implemented as a processor as a system LSI (Large Scale Integration), a module using multiple processors, a unit using multiple modules, or a set in which a unit further has additional functions. In other words, the present embodiment can also be implemented as a part of the configuration of an apparatus.

[0326] The system LSI may also be referred to as an SOC (System on Chip). In other words, each of the above-described or later-described devices (e.g., the management device 10, the base station 20, the relay station 30, and the terminal device 40) may be interpreted as a processor (e.g., a CPU) serving as a system LSI (e.g., SoC), or as a module using or constituting the processor. Additionally or alternatively, the present embodiment may be implemented by any configuration constituting a device or system (e.g., a modem chip (baseband chip) or an RF (Radio Frequency) unit, or a combination thereof). The RF unit may include at least one of an RF circuit and an RF front-end. In other words, each of the above-described or later-described devices may be interpreted as a modem chip (baseband chip) or an RF unit, or a combination thereof. Additionally or alternatively, each of the above-described or later-described devices may be interpreted as a module using or constituting a modem chip or an RF unit.

[0327] The modem chip performs signal processing for communications within a device (including the devices described above or below). The modem chip may have at least a modulator or demodulator function. The RF unit may have at least one of an RF transceiver (e.g., an RF upconverter and / or an RF downconverter), a power amplifier, and a low-noise amplifier function. The RF transceiver converts between baseband signals and RF frequencies. The power amplifier amplifies signals for transmission from an antenna. The low-noise amplifier amplifies weak signals received from the antenna. Additionally or alternatively, the RF unit (particularly, the RF front end) may include at least one of the above-mentioned power amplifier, low-noise amplifier, envelope tracker, filter, duplexer, multiplexer, antenna switch, and antenna tuner.

[0328] The combination of the modem chip and the RF unit may be referred to as a modem-RF system. At least a portion of the modem chip or the RF unit, or a combination thereof, may be included in a system LSI (e.g., SoC). For example, the processing performed by at least a portion of the modem chip or the RF unit, or a combination thereof (e.g., at least a portion of the MAC layer processing / PHY layer processing) may be realized by the system LSI. Here, the MAC layer processing or the PHY layer processing may be at least a portion of the processing performed by the devices (e.g., the management device 10, the base station 20, the relay station 30, and the terminal device 40) in the above-mentioned or later-described embodiments.

[0329] In this embodiment, a system refers to a collection of multiple components (devices, modules (components), etc.), regardless of whether all of the components are in the same housing. For example, multiple devices housed in separate housings and connected via a network, etc., and a single device in which multiple modules are housed in a single housing are both systems.

[0330] Furthermore, for example, this embodiment can have a cloud computing configuration in which one function is shared and processed jointly by a plurality of devices via a network.

[0331] <<7. Conclusion>> According to the present embodiment, the terminal device 40 included in the communication system 1 executes a first LTM as a conditional handover. The first LTM is a RACH-less conditional LTM. For example, the terminal device 40 executes a RACH-less CLTM without early sync as the first LTM. Alternatively, the terminal device 40 executes a conditional LTM without early sync as the first LTM. The base station 20 executes processing related to the conditional handover in response to the execution of the conditional handover by the terminal device 40.

[0332] As a result, a random access procedure is not required when switching the connection destination, which reduces the processing load (or the processing time required for handover) on the terminal device 40 and / or the base station 20. As a result, wireless communication with high communication performance is realized.

[0333] In addition, when a predetermined condition is satisfied, the terminal device 40 may execute a RACH-less CLTM without early sync as the first LTM. For example, when timing advance information usable after switching the connection destination is held, the terminal device 40 may execute a RACH-less CLTM without early sync. In this case, when the predetermined condition is not satisfied, the terminal device 40 may execute a second LTM different from the first LTM as a conditional handover. For example, when the terminal device 40 does not hold timing advance information usable after switching the connection destination, the terminal device 40 may execute an LTM capable of acquiring timing advance information (for example, a CLTM with a random access procedure or a RACH-less CLTM with early sync) as the second LTM.

[0334] As a result, the terminal device 40 can perform handover even when it is not suitable for performing RACH-less CLTM without early sync (when valid timing advance information is not held after switching). That is, the terminal device 40 can acquire timing advance information by a random access procedure or early sync and switch the connection destination. As a result, wireless communication with high communication performance is realized.

[0335] Although the embodiments of the present disclosure have been described above, the technical scope of the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present disclosure. Furthermore, components of different embodiments and modifications may be combined as appropriate.

[0336] Furthermore, the effects of each embodiment described in this specification are merely examples and are not intended to be limiting, and other effects may also be obtained.

[0337] The present technology may also be configured as follows. (1) A terminal device capable of executing LTM (L1 / L2 Triggered Mobility), the terminal device including a communication control unit that executes a first LTM as a conditional handover, the first LTM being a conditional LTM without a random access procedure. (2) The terminal device according to (1), the first LTM being a conditional LTM without an early sync. (3) The terminal device according to (2), the communication control unit executes the first LTM as the conditional handover when a predetermined condition is satisfied, the predetermined condition including holding timing advance information that can be used after switching of a connection destination. (4) The terminal device according to (3), the communication control unit executes the first LTM as the conditional handover when timing advance information before switching of a connection destination remains valid after switching. (5) The terminal device according to (3) or (4), wherein the communication control unit executes the first LTM as the conditional handover when a base station notifies the communication control unit of timing advance information usable after switching of the connection destination. (6) The terminal device according to any one of (3) to (5), wherein the communication control unit executes the first LTM as the conditional handover when another terminal device notifies the communication control unit of timing advance information usable after switching of the connection destination. (7) The terminal device according to any one of (3) to (6), wherein the communication control unit executes the first LTM as the conditional handover when it is possible to measure timing advance information to be used after switching of the connection destination. (8) The terminal device according to any one of (3) to (7), wherein the communication control unit executes a second LTM different from the first LTM as the conditional handover when the predetermined condition is not satisfied. (9) The terminal device according to (8), wherein the second LTM is a conditional LTM with a random access procedure.(10) The terminal device according to (8), wherein the second LTM is a conditional LTM with early sync. (11) The terminal device according to (8), wherein the communication control unit executes, as the conditional handover, either an LTM with a random access procedure or an LTM with early sync without a random access procedure, in accordance with control of a base station when the predetermined condition is not satisfied. (12) The terminal device according to (2), wherein the communication control unit executes, as the conditional handover, either the first LTM or a second LTM different from the first LTM, in accordance with setting by a base station. (13) The terminal device according to (12), wherein the second LTM is an LTM with a random access procedure. (14) The terminal device according to (12), wherein the second LTM is an LTM with early sync without a random access procedure. (15) The terminal device according to (1), wherein the first LTM is LTM with early sync. (16) The terminal device according to any one of (1) to (15), wherein the communication control unit performs a communication point switching operation as the conditional handover. (17) The terminal device according to (16), wherein the communication point is a beam cell or a point cell. (18) A base station that wirelessly communicates with a terminal device capable of executing LTM (L1 / L2 Triggered Mobility), comprising: a communication control unit that executes processing related to the conditional handover in response to execution of a conditional handover by the terminal device, wherein the conditional handover is LTM without a random access procedure. (19) A communication method executed by a terminal device capable of executing LTM (L1 / L2 Triggered Mobility), wherein a first LTM is executed as the conditional handover, and the first LTM is LTM without a random access procedure.(20) A communication method executed by a base station that wirelessly communicates with a terminal device capable of executing LTM (L1 / L2 Triggered Mobility), the communication method comprising: executing a process related to the conditional handover in response to execution of the conditional handover by the terminal device; and the conditional handover is LTM without a random access procedure.

[0338] REFERENCE SIGNS LIST 1 Communication system 10 Management device 20 Base station 30 Relay station 40 Terminal device 11 Communication unit 21, 31, 41 Wireless communication unit 12, 22, 32, 42 Storage unit 13, 23, 33, 43 Control unit 211, 311, 411 Transmission processing unit 212, 312, 412 Reception processing unit 213, 313, 413 Antenna 231, 331, 431 Determination unit 232, 332, 432 Communication control unit P1 to P5 Communication point

Claims

1. A terminal device capable of executing LTM (L1 / L2 Triggered Mobility), comprising: a communication control unit that executes a first LTM as a conditional handover, wherein the first LTM is a conditional LTM without a random access procedure.

2. The terminal device according to claim 1, wherein the first LTM is a conditional LTM without early sync.

3. The terminal device according to claim 2, wherein the communication control unit executes the first LTM as the conditional handover when predetermined conditions are met, and the predetermined conditions include holding timing advance information that can be used after switching the connection destination.

4. The terminal device according to claim 3, wherein the communication control unit executes the first LTM as the conditional handover when timing advance information before the switching of the connection destination remains valid after the switching.

5. The terminal device according to claim 3, wherein the communication control unit executes the first LTM as the conditional handover when timing advance information that can be used after switching the connection destination is notified from the base station.

6. The terminal device according to claim 3, wherein the communication control unit executes the first LTM as the conditional handover when timing advance information that can be used after switching the connection destination is notified from another terminal device.

7. The terminal device according to claim 3, wherein the communication control unit executes the first LTM as the conditional handover when timing advance information to be used after switching of the connection destination can be measured.

8. The terminal device according to claim 3, wherein the communication control unit executes a second LTM different from the first LTM as the conditional handover when the predetermined condition is not satisfied.

9. The terminal device according to claim 8, wherein the second LTM is a conditional LTM with a random access procedure.

10. The terminal device according to claim 8, wherein the second LTM is a conditional LTM with early sync.

11. The terminal device according to claim 8, wherein, when the predetermined condition is not satisfied, the communication control unit executes, in accordance with the control of the base station, either LTM with a random access procedure or LTM with early sync without a random access procedure as the conditional handover.

12. The terminal device according to claim 2, wherein the communication control unit executes either the first LTM or a second LTM different from the first LTM as the conditional handover in accordance with settings by the base station.

13. The terminal device according to claim 12, wherein the second LTM is an LTM with a random access procedure.

14. The terminal device according to claim 12, wherein the second LTM is an LTM with early sync and no random access procedure.

15. The terminal device according to claim 1, wherein the first LTM is an LTM with early sync.

16. The terminal device according to claim 1, wherein the communication control unit performs a communication point switching operation as the conditional handover.

17. The terminal device according to claim 16, wherein the communication point is a beam cell or a point cell.

18. A base station that wirelessly communicates with a terminal device capable of executing LTM (L1 / L2 Triggered Mobility), comprising: a communication control unit that executes processing related to a conditional handover in response to execution of the conditional handover by the terminal device, wherein the conditional handover is LTM without a random access procedure.

19. A communication method executed by a terminal device capable of executing LTM (L1 / L2 Triggered Mobility), the communication method comprising: executing a first LTM as a conditional handover; and the first LTM is an LTM without a random access procedure.

20. A communication method executed by a base station that wirelessly communicates with a terminal device capable of executing LTM (L1 / L2 Triggered Mobility), the communication method comprising: executing processing related to the conditional handover in response to execution of a conditional handover by the terminal device; and the conditional handover is LTM without a random access procedure.

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