Method and apparatus for performing cell change procedure in a wireless communication system

Abstract

The present invention relates to a method performed by a UE (User Equipment) in a wireless communication system. In particular, the method includes receiving information regarding candidate cells from a first cell, receiving a cell change command for a connection switch from the first cell to a second cell among the candidate cells from the first cell, and omitting a RA (Random Access) procedure related to the second cell and performing cell switching based on the cell change command including a valid TA (timing advance) value.

Description

Technical Field

[0001] The present invention relates to a wireless communication system, and more particularly, to a method for performing a cell change procedure in a wireless communication system and an apparatus therefor.

Background Art

[0002] With the introduction of new wireless communication technologies, not only the number of UEs that a base station serves in a predetermined resource area but also the amount of data and control information transmitted and received between the base station and the UEs it serves is increasing. Since the amount of wireless resources available for the base station to communicate with UEs is finite, new solutions are required for the base station to efficiently transmit and receive uplink / downlink data and / or uplink / downlink control information from / to UEs using the limited wireless resources. In particular, the number of applications whose performance is greatly affected by delay / latency is increasing. Therefore, solutions for suppressing delay / latency compared to existing systems are required.

Summary of the Invention

Problems to be Solved by the Invention

[0003] An object of the present invention is to provide a method for performing a cell change procedure in a wireless communication system and an apparatus therefor.

Means for Solving the Problems

[0004] The object of the present invention can be achieved by a method performed by a UE (User Equipment) in a wireless communication system, the method comprising receiving, from a first cell, information regarding a candidate cell; receiving, from the first cell, a cell change command for a connection switch from the first cell to a second cell among the candidate cells; and omitting a RA (Random Access) procedure related to the second cell and performing cell switching based on the cell change command including a valid TA (timing advance) value.

[0005] Also proposed is a UE (User Equipment) in a wireless communication system, the UE including at least one transceiver, at least one processor, and at least one computer memory operably connectable to the at least one processor and storing instructions which, when executed, cause the at least one processor to perform operations for a RLC (Radio Link Control) entity of the UE, the operations comprising receiving, from a first cell, information regarding a candidate cell; receiving, from the first cell, a cell change command for a connection switch from the first cell to a second cell among the candidate cells; and omitting a RA (Random Access) procedure related to the second cell and performing cell switching based on the cell change command including a valid TA (timing advance) value.

[0006] Preferably, the method further comprises performing the cell switching based on a RA procedure related to the second cell based on the cell change command not including the valid TA value.

[0007] Preferably, the valid TA value includes an Absolute TA value.

[0008] Preferably, the cell change command includes an identifier of the second cell.

[0009] Preferably, the first cell and the second cell belong to the same RRC (radio resource control) entity.

[0010] The effects achievable by the present invention are not limited to the content mentioned above, and other advantages of the present invention will be clearly understandable to those skilled in the art from the following detailed description.

Effects of the Invention

[0011] According to the present invention, when the cell is changed to another cell belonging to the same CU, the UE performs UL transmission without performing the RA procedure. Therefore, the time for performing the RA procedure can be omitted, and the delay due to cell change can be reduced.

[0012] The effects obtained by the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understandable to those having ordinary knowledge in the technical field to which the present invention pertains from the following description.

Brief Description of the Drawings

[0013] The drawings attached below are for helping the understanding of the present invention, and explain the principle of the present invention together with the detailed description.

[0014]

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MODE FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description to be described together with the accompanying drawings is for explaining the exemplary embodiments of the present invention, and is not the only embodiment form that can be implemented by the present invention. In the following detailed description, specific details are included to provide a complete understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without such specific details.

[0016] The following technologies can be used in various radio access systems such as CDMA (Code Division Multiple Access), FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), OFDMA (Orthogonal Frequency Division Multiple Access), SC-FDMA (Single Carrier Frequency Division Multiple Access), etc. CDMA can be implemented by radio technologies such as UTRA (Universal Terrestrial Radio Access) and CDMA2000. TDMA can be implemented by radio technologies such as GSM (Global System for Mobile communications) / GPRS (General Packet Radio Service) / EDGE (Enhanced Data Rates for GSM Evolution). OFDMA can be implemented by radio technologies such as IEEE802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE802-20, E-UTRA (Evolved UTRA), etc. IEEE 802.16m is an evolution of IEEE 802.16e and provides backward compatibility with systems based on IEEE 802.16e. UTRA is part of UMTS (Universal Mobile Telecommunications System). 3GPP (3rd Generation Partnership Project) LTE (long term evolution) is part of E-UMTS (Evolved UMTS) that uses E-UTRA, adopts OFDMA in the downlink, and adopts SC-FDMA in the uplink. LTE-A (Advanced) is an evolution of 3GPP LTE.

[0017] For the sake of convenience in explanation, the present specification will be described below in relation to a 3GPP-based communication system. However, the technical features of the present specification are not limited thereto. For example, even if the following detailed description is given based on a mobile communication system corresponding to a 3GPP-based system, matters other than those specific to the 3GPP-based system are applicable to any other mobile communication system. Regarding the terms and technologies described in the present specification, for terms and technologies not specifically mentioned, reference can be made to wireless communication standard documents before the publication of the present specification. For example, the following documents can be referred to.

[0018] 3GPP LTE

[0019] - 3GPP TS36.211:Physical channels and modulation

[0020] - 3GPP TS36.212:Multiplexing and channel coding

[0021] - 3GPP TS36.213:Physical layer procedures

[0022] - 3GPP TS36.214:Physical layer; Measurements

[0023] - 3GPP TS36.300:Overall description

[0024] - 3GPP TS36.304:User Equipment(UE) procedures in idle mode

[0025] - 3GPP TS36.314:Layer 2-Measurements

[0026] - 3GPP TS36.321:Medium Access Control(MAC) protocol

[0027] - 3GPP TS36.322: Radio Link Control (RLC) protocol

[0028] - 3GPP TS36.323: Packet Data Convergence Protocol (PDCP)

[0029] - 3GPP TS36.331: Radio Resource Control (RRC) protocol

[0030] 3GPP NR (e.g. 5G)

[0031] - 3GPP TS38.211: Physical channels and modulation

[0032] - 3GPP TS38.212: Multiplexing and channel coding

[0033] - 3GPP TS38.213: Physical layer procedures for control

[0034] - 3GPP TS38.214: Physical layer procedures for data

[0035] - 3GPP TS38.215: Physical layer measurements

[0036] - 3GPP TS38.300: Overall description

[0037] - 3GPP TS38.304: User Equipment (UE) procedures in idle mode and in RRC inactive state

[0038] - 3GPP TS38.321: Medium Access Control (MAC) protocol

[0039] - 3GPP TS38.322: Radio Link Control (RLC) protocol

[0040] - 3GPP TS38.323: Packet Data Convergence Protocol (PDCP)

[0041] - 3GPP TS38.331: Radio Resource Control (RRC) protocol

[0042] - 3GPP TS37.324: Service Data Adaptation Protocol (SDAP)

[0043] - 3GPP TS37.340: Multi-connectivity; Overall description

[0044] In this specification, a UE may be fixed or mobile, and includes various devices that communicate with a base station (BS) to transmit and receive user data and / or various control information. A UE can be referred to as a terminal equipment, MS (Mobile Station), MT (Mobile Terminal), UT (User Terminal), SS (Subscribe Station), wireless device, PDA (Personal Digital Assistant), wireless modem, handheld device, etc. Also, in this specification, a BS generally refers to a fixed station that communicates with a UE and / or another BS, and exchanges various data and control information with the UE and the other BS. A BS can also be referred to by other terms such as ABS (Advanced Base Station), NB (Node-B), eNB (evolved-NodeB), BTS (Base Transceiver System), access point, PS (Processing Server), etc. In particular, the BS of UMTS is called an NB, the BS of EPC / LTE is called an eNB, and the BS of an NR (new radio) system is called a gNB.

[0045] As used in this specification, a "node" refers to a fixed point that can communicate with a UE to transmit / receive radio signals. Various forms of eNBs can be used as nodes regardless of their names. For example, BS, NB, eNB, pico cell eNB (PeNB), home eNB (HeNB), relay, repeater, etc. can be regarded as nodes. Also, the node does not have to be an eNB. For example, it can be a radio remote head (RRH) or a radio remote unit (RRU). RRH, RRU, etc. generally have a lower power level than the power level of an eNB. Since an RRH or an RRU (hereinafter referred to as RRH / RRU) is generally connected to an eNB by a dedicated line such as an optical cable, the coordinated communication between the RRH / RRU and the eNB can generally be carried out more smoothly than the coordinated communication by an eNB connected by a wireless link. At least one antenna is installed in one node. The above antenna can mean a physical antenna, an antenna port, a virtual antenna, or an antenna group.

[0046] As used in this specification, "cell" refers to a certain geographical area where one or more nodes provide communication services, or to radio resources. The "cell" of a geographical area can be understood as the coverage within which a node can provide services using a carrier wave, and the "cell" as radio resources (e.g., time-frequency resources) is related to the bandwidth (BW) which is the frequency range configured by the carrier wave. The "cell" associated with radio resources is defined by a combination of downlink resources and uplink resources, for example, a combination of a downlink (DL) component carrier (CC) and an uplink (UL) CC. A cell can be configured with downlink resources alone, or a combination of downlink and uplink resources. Since the downlink coverage, which is the range within which a node can transmit an effective signal, and the uplink coverage, which is the range within which a UE can receive an effective signal, depend on the carrier wave carrying the signal, the coverage of a node may also be related to the coverage of the "cell" of the radio resources used by the said node. Therefore, the term "cell" can be used to mean, at times, the coverage of services by a node, at times, radio resources, and at times, the range within which a signal using the said radio resources can reach with an effective intensity.

[0047] In the present invention, a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) respectively refer to a set of time-frequency resources or resource elements (REs) that carry downlink control information (DCI), and a set of time-frequency resources or REs that carry downlink data. Also, a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH), and a physical random access channel (PRACH) respectively refer to a set of time-frequency resources or REs that carry uplink control information (UCI), a set of time-frequency resources or REs that carry uplink data, and a set of time-frequency resources or REs that carry random access signals.

[0048] In carrier aggregation (CA), two or more component carriers (CCs) are aggregated. A UE can receive or transmit one or multiple CCs simultaneously depending on its capabilities. CA is supported for both contiguous and non-contiguous CCs. When CA is configured, only the UE forms a single radio resource control (RRC) connection with the network. In RRC connection establishment / re-establishment / handover, one serving cell provides non-access stratum (NAS) mobility information, and in RRC connection re-establishment / handover, one serving cell provides security inputs. This cell is referred to as the primary cell (PCell). The PCell is a cell operating on the primary frequency, at which frequency the UE performs the initial connection establishment procedure or starts the connection re-establishment procedure. Depending on the UE capabilities, secondary cells (SCells) are configured to form a set of serving cells together with the PCell. An SCell is a cell that provides additional radio resources in addition to the special cell. Thus, the set of serving cells configured for a UE always consists of one PCell and one or more SCells. For the operation of dual connectivity, the term special cell (SpCell) refers to the PCell of the master cell group (MCG) or the PSCell of the secondary cell group (SCG). The SpCell supports PUCCH transmission and contention-based random access and is always active. The MCG is a serving cell group associated with the master node, including the SpCell (PCell) and optionally one or more SCells. The SCG is a subset of the serving cells associated with the secondary node, consisting of the PSCell and zero or more SCells for a UE configured for dual connectivity (DC). For an RRC_CONNECTED UE not configured for CA / DC, only one serving cell consisting of the PCell exists.For a UE in RRC_CONNECTED state configured with CA / DC, the term "serving cell" is used to indicate the set of cells consisting of the SpCell and all SCell.

[0049] MCG is a group of serving cells associated with the master BS that terminates at least S1-MME, and SCG is a group of serving cells associated with a secondary BS that provides additional radio resources for the UE but is not the master BS. SCG consists of a primary SCell (PSCell) and optionally one or more SCell. In DC, two MAC entities, namely, the MAC entity for MCG and the MAC entity for SCG, are configured in the UE. Each MAC entity is configured by RRC in a serving cell that supports PUCCH transmission and contention-based random access. In the present invention, the term "SPCell" refers to such a cell, while the term "SCell" refers to other serving cells. The term "SPCell" indicates the PCell of MCG or the PSCell of SCG depending on whether the MAC entity is associated with MCG or SCG respectively.

[0050] In the present invention, channel monitoring means attempting to decode a channel. For example, PDCCH monitoring means attempting to decode a PDCCH (or a candidate of PDCCH).

[0051] In this specification, "C-RNTI" indicates a cell RNTI, "SI-RNTI" indicates a system information RNTI, "P-RNTI" indicates a paging RNTI, "RA-RNTI" indicates a random access RNTI, "SC-RNTI" indicates a single cell RNTI, "SL-RNTI" indicates a sidelink RNTI, "SPS C-RNTI" indicates a semi-persistent scheduling C-RNTI, and "CS-RNTI" indicates a configured scale RNTI.

[0052] FIG. 1 illustrates a communication system to which the present invention is applied.

[0053] The three main requirement areas of 5G include (1) the enhanced mobile broadband (eMBB) area, (2) the massive machine type communication (mMTC) area, and (3) the ultra-reliable and low latency communications (URLLC) area.

[0054] In some use cases, multiple areas may be required for optimization, and in other use cases, only one key performance indicator (KPI) may be focused on. 5G supports such various use cases in a flexible and reliable manner.

[0055] eMBB goes far beyond basic mobile Internet access, covering rich two-way operations and media and entertainment applications in cloud or augmented reality. Data is one of the core driving forces of 5G, and dedicated voice services may not be seen for the first time in the 5G era. In 5G, voice can be expected to be processed as an application using the data connection provided by the communication system alone. The main causes of the increased traffic volume are the increase in content size and the increase in the number of applications demanding high data transmission rates. Streaming services (audio and video), conversational video, and mobile Internet access will be more widely used as more devices connect to the Internet. Many such applications require always-on connectivity to push real-time information and notifications to users. Cloud storage and applications are increasing rapidly in the mobile communication platform, which is applicable to both business and entertainment. Also, cloud storage is a special use case that drives the growth of uplink data transmission rates. 5G is also used for cloud remote operations and requires much lower end-to-end latency to maintain an excellent user experience when tactile interfaces are used. Entertainment, such as cloud gaming and video streaming, is another core element that increases the requirements for mobile broadband capabilities. Entertainment is essential on smartphones and tablets everywhere, including highly mobile environments such as trains, cars, and airplanes. Another use case is augmented reality and information search for entertainment. Here, augmented reality requires very low latency and instantaneous data volume.

[0056] Also, one of the most anticipated use cases of 5G is the function that can smoothly connect embedded sensors in all fields, that is, related to mMTC. It is predicted that the number of potential IoT devices will reach 20.4 billion by 2020. Industrial IoT is one of the areas where 5G plays a major role in enabling smart cities, asset tracking, smart utilities, agriculture, and security infrastructure.

[0057] URLLC includes new services that change industries through links with extremely high reliability / low latency such as remote control of critical infrastructure and self-driving vehicles. The levels of reliability and latency are essential for smart grid control, industrial automation, robotics, drone control, and regulation.

[0058] 5G is a means of providing streams evaluated from hundreds of megabits per second to gigabits per second, and can complement fiber-to-the-home (FTTH) and cable-based broadband (or DOCSIS). Such high speeds are required not only for virtual reality and augmented reality but also for transmitting TV at resolutions above 4K (6K, 8K, and higher). VR (Virtual Reality) and AR (Augmented Reality) applications include mostly immersive sports competitions. Certain applications may require special network settings. For example, in the case of VR games, game companies must integrate the core server with the edge network server of the network operator to minimize latency.

[0059] Automobiles are expected to be an important new driver in 5G, along with many use cases for mobile communications for vehicles. For example, entertainment for passengers requires high simultaneous capacity and high-mobility mobile broadband. The reason is that future users expect to continue to have high-quality connections regardless of their location and speed. Another use case in the automotive field is the augmented reality dashboard. This superimposes and displays information on what the driver sees through the front window, identifying objects in the darkness and telling the driver about the distance and movement of the objects. In the future, wireless modules will enable information exchange between vehicles, between vehicles and the supporting infrastructure, and between automobiles and other connected devices (e.g., devices carried by pedestrians). Safety systems can guide alternative courses of action to allow the driver to drive more safely and reduce the risk of accidents. The next step is for vehicles to be remotely controlled or self-driven. This requires very reliable and very fast communication between different self-driven vehicles and between automobiles and the infrastructure. In the future, self-driven vehicles will perform all driving activities, allowing the driver to focus only on traffic anomalies that the vehicle itself cannot identify. The technical requirements for self-driven vehicles require ultra-low latency and ultra-high-speed reliability such that traffic safety increases to a level that humans cannot achieve.

[0060] Smart cities and smart homes, referred to as the smart society, are embedded in high-density wireless sensor networks. A distributed network of intelligent sensors identifies the conditions for the cost and energy-efficient maintenance of the city or home. Similar setups can be done for each home. Temperature sensors, window and heating controllers, burglar alarms, and household appliances are all wirelessly connected. Many of these sensors typically have low data transmission speeds, low power, and low cost. However, for example, real-time HD video may be required by certain types of devices for monitoring.

[0061] The consumption and distribution of energy, including heat or gas, is highly decentralized and requires automated control of distributed sensor networks. Smart grids use digital information and communication technologies to collect information and act accordingly, interconnecting such sensors. Since this information can include the actions of suppliers and consumers, smart grids can improve the distribution of fuels such as electricity in an efficient, reliable, economical, sustainable, and automated manner. Smart grids can also be viewed as other sensor networks with low latency.

[0062] Mission critical applications (such as e-health) are one of the 5G usage scenarios. The health sector has many applications that can benefit from mobile communication. Communication systems can support telemedicine, which provides clinical care from a distance. This helps reduce the barrier of distance and improve access to healthcare services that are not continuously available in remote rural areas. It is also used to save lives in critical medical and emergency situations. Wireless sensor networks based on mobile communication can provide remote monitoring and sensors for parameters such as heart rate and blood pressure.

[0063] Wireless and mobile communication are becoming increasingly important in industrial application areas. Wiring is expensive to install and maintain. Therefore, the replaceability with wireless links that can reconfigure cables is an attractive opportunity in many industrial sectors. However, to achieve this, it is required that wireless connections operate with latency, reliability, and capacity similar to cables and that their management is simplified. Low latency and a very low error probability are new requirements that need to be connected to 5G.

[0064] Logistics and freight tracking are important use cases for mobile communication that utilize location-based information systems to enable inventory and package tracking anywhere. Use cases for logistics and freight tracking typically require low data speeds but demand wide coverage and reliable location information.

[0065] Referring to FIG. 1, communication system 1 includes wireless devices, a base station (BS), and a network. For example, FIG. 1 shows a 5G network as an example of the network of communication system 1. However, the implementation of the present invention is not limited to 5G systems and can be applied to next-generation communication systems beyond 5G systems.

[0066] The BS and the network are implemented by wireless devices, and a specific wireless device 200a can operate as a BS / network node with respect to other wireless devices.

[0067] A wireless device refers to a device that communicates using a radio access technology (RAT) (e.g., 5G NR, LTE), and can be called a communication / wireless / 5G device. Not limited to this, wireless devices include robot 100a, vehicles 100b-1, 100b-2, XR (Extended Reality) device 100c, hand-held device 100d, home appliance 100e, IoT (Internet of Thing) device 100f, and AI device / server 400. For example, vehicles include vehicles equipped with a wireless communication function, autonomous driving vehicles, and vehicles capable of vehicle-to-vehicle communication. Here, vehicles include UAVs (Unmanned Aerial Vehicles) (e.g., drones). The XR device includes AR (Augmented Reality) / VR (Virtual Reality) / MR (Mixed Reality) devices, and is embodied in the form of an HMD (Head-Mounted Device), HUD (Head-Up Display) equipped on a vehicle, TV, smartphone, computer, wearable device, home appliance, digital signboard, vehicle, robot, etc. Hand-held devices include smartphones, smart pads, wearable devices (e.g., smartwatches, smart glasses), computers (e.g., notebook computers, etc.). Home appliances include TVs, refrigerators, washing machines, etc. IoT devices include sensors, smart meters, etc.

[0068] In the present invention, the wireless devices 100a to 100f are also called UEs. The UEs include, for example, mobile phones, smartphones, notebook computers, digital broadcast terminals, PDAs (personal digital assistants), PMPs (portable multimedia players), car navigation systems, Slate PCs, tablet PCs, ultrabooks, vehicles, vehicles with autonomous driving functions, connected cars, UAVs, AI (artificial intelligence) modules, robots, AR (augmented reality) devices, VR (virtual reality) devices, MR (mixed reality) devices, hologram devices, devices for public safety, MTC devices, IoT devices, medical devices, fintech devices (or financial devices), security devices, weather / environment devices, devices related to 5G services, or devices related to the fourth industrial revolution field, etc. The UAV is, for example, an aircraft that does not carry people and flies by a wireless control signal. The VR device includes, for example, a device for embodying an object or background in a virtual world. The AR device includes, for example, a device that is embodied so as to connect an object or background in a virtual world to an object or background in the real world. The MR device includes, for example, a device that is embodied so as to merge an object or background in a virtual world with an object or background in the real world. The hologram device includes, for example, a device for embodying a 360° stereoscopic video by recording and reproducing three-dimensional information using an interference phenomenon of light generated when two lasers called holography are combined. The devices for public safety include, for example, wearable video relay devices or video devices that can be worn on a user's body. The MTC devices and IoT devices include devices that do not require direct human interference or operation. For example, the MTC devices and IoT devices include smart meters, vending machines, thermometers, smart light bulbs, door locks, or various sensors. The medical devices are, for example, devices used for diagnosis, medical treatment, palliative care, treatment, and disease prevention. The medical devices are, for example, devices for diagnosing, treating, palliating, or correcting injuries or disabilities. For example, the medical devices are devices used for examining, replacing, or correcting rescue or functions.For example, the medical device is a device for pregnancy regulation. For example, the medical device includes a device for medical treatment, a device for surgery, a device for (in vitro) diagnosis, a hearing aid, and a device for treatment. The security device is, for example, a device provided to prevent possible dangers and protect safety. For example, security devices include cameras, CCTVs, recording devices (Recorders), or black boxes. The fintech device is, for example, a device that provides financial services such as mobile payment. For example, the fintech device includes a payment device or a POS (point of sales) system. The weather / environment device includes, for example, a device for monitoring the weather / environment.

[0069] The wireless devices 100a to 100f are connected to the network 300 via the BS200. AI (Artificial Intelligence) technology is applied to the wireless devices 100a to 100f, and the wireless devices 100a to 100f are connected to the AI server 400 via the network 300. The network 300 is configured using a 3G network, a 4G (e.g., LTE) network, or a 5G (e.g., NR) network, and a beyond 5G network, etc. The wireless devices 100a to 100f can communicate with each other via the BS200 / network 300, but can also communicate directly without going through the BS / network (e.g., sidelink communication). For example, the vehicles 100b-1 and 100b-2 can communicate directly (e.g., V2V (Vehicle to Vehicle) / V2X (Vehicle to everything) communication). Also, IoT devices (e.g., sensors) can communicate directly with other IoT devices (e.g., sensors) or other wireless devices 100a to 100f.

[0070] Wireless communication / connection 150a and 150b are performed between the wireless devices 100a to 100f / BS200 - BS200. Here, the wireless communication / connection is performed by various RATs (for example, 5G NR) such as uplink / downlink communication 150a and sidelink communication 150b (or, D2D communication). The wireless devices and the BS / wireless devices can transmit and receive wireless signals to / from each other through the wireless communication / connection 150a and 150b. For example, the wireless communication / connection 150a and 150b can transmit and receive signals through various physical channels. For this purpose, based on various proposals of the present invention, any one of the setting process of various configuration information for the transmission / reception of wireless signals, various signal processing processes (for example, channel encoding / decoding, modulation / demodulation, resource mapping / demapping, etc.), and the resource allocation process is performed.

[0071] FIG. 2 is a block diagram showing an example of a communication device that executes the method according to the present invention.

[0072] Referring to FIG. 2, the first wireless device 100 and the second wireless device 200 can transmit and receive wireless signals to / from an external device through various RATs (for example, LTE, NR). In FIG. 2, {the first wireless device 100 and the second wireless device 200} corresponds to {the wireless devices 100a to 100f and BS200} of FIG. 1 and / or {the wireless devices 100a to 100f and the wireless devices 100a to 100f}.

[0073] The first wireless device 100 includes one or more processors 102 and one or more memories 104, and further includes one or more transceivers 106 and / or one or more antennas 108. The processor 102 controls the memory 104 and / or the transceiver 106, and is configured to implement the functions, procedures, and / or methods disclosed in this specification. For example, after the processor 102 processes the information in the memory 104 to generate a first piece of information / signal, the transceiver 106 transmits a wireless signal including the first piece of information / signal. Also, after the processor 102 receives a wireless signal including a second piece of information / signal by the transceiver 106, the information obtained from the signal processing of the second piece of information / signal is stored in the memory 104. The memory 104 is connected to the processor 102 and stores various information related to the operation of the processor 102. For example, the memory 104 stores software code including instructions to perform some or all of the processes controlled by the processor 102, or to perform the procedures and / or methods disclosed in this specification. Here, the processor 102 and the memory 104 are part of a communication modem / circuit / chip designed to implement a RAT (e.g., LTE, NR). The transceiver 106 is connected to the processor 102 and transmits and / or receives wireless signals via one or more antennas 108. The transceiver 106 includes a transmitter and / or a receiver. The transceiver 106 can also be used interchangeably with an RF (radio Frequency) unit. In this disclosure, the wireless device can also mean a communication modem / circuit / chip.

[0074] The second wireless device 200 includes one or more processors 202 and one or more memories 204, and further includes one or more transceivers 206 and / or one or more antennas 208. The processor 202 controls the memory 204 and / or the transceiver 206, and is configured to implement the functions, procedures, and / or methods disclosed in this specification. For example, after the processor 202 processes the information in the memory 204 to generate a third piece of information / signal, the transceiver 206 transmits a wireless signal including the third piece of information / signal. Also, after the processor 202 receives a wireless signal including a fourth piece of information / signal by the transceiver 206, the information obtained from the signal processing of the fourth piece of information / signal is stored in the memory 204. The memory 204 is connected to the processor 202 and stores various information related to the operation of the processor 202. For example, the memory 204 stores software code including instructions for performing part or all of the processes controlled by the processor 202, or for performing the procedures and / or methods disclosed in this specification. Here, the processor 202 and the memory 204 are part of a communication modem / circuit / chip designed to implement a RAT (e.g., LTE, NR). The transceiver 206 is connected to the processor 202 and transmits and / or receives wireless signals via one or more antennas 208. The transceiver 206 includes a transmitter and / or a receiver. The transceiver 206 can also be used interchangeably with an RF unit. In this disclosure, the wireless device can also mean a communication modem / circuit / chip.

[0075] Hereinafter, the hardware elements of the wireless devices 100 and 200 will be described in more detail. Although not limited thereto, one or more protocol layers are implemented by one or more processors 102 and 202. For example, one or more processors 102 and 202 implement one or more layers (e.g., physical (PHY) layer, medium access control (MAC) layer, radio link control (RLC) layer, packet data convergence protocol (PDCP) layer, radio resource control (RRC) layer, service data adaption protocol (SDAP) like functional layers). One or more processors 102 and 202 generate one or more protocol data units (PDUs) and / or one or more service data units (SDUs) according to the descriptions, functions, procedures, proposals, and / or methods disclosed in this specification. One or more processors 102 and 202 generate messages, control information, data, or information according to the functions, procedures, proposals, and / or methods disclosed in this specification. One or more processors 102 and 202 generate signals (e.g., baseband signals) including PDUs, SDUs, messages, control information, data, or information according to the functions, procedures, proposals, and / or methods disclosed in this specification and provide them to one or more transceivers 106 and 206. One or more processors 102 and 202 receive signals (e.g., baseband signals) from one or more transceivers 106 and 206 and can obtain PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, proposals, and / or methods disclosed in this specification.

[0076] The one or more processors 102, 202 may also be referred to as a controller, a microcontroller, a microprocessor, or a microcomputer. The one or more processors 102, 202 are implemented by hardware, firmware, software, or a combination thereof. As an example, the one or more processors 102, 202 may include one or more ASICs (Application Specific Integrated Circuits), one or more DSPs (Digital Signal Processors), one or more DSPDs (Digital Signal Processing Devices), one or more PLDs (Programmable Logic Devices), or one or more FPGAs (Field Programmable Gate Arrays). The functions, procedures, proposals, and / or methods disclosed in this specification are implemented using firmware or software, and the firmware or software is implemented to include modules, procedures, functions, and the like. The firmware or software configured to perform the functions, procedures, proposals, and / or methods disclosed in this specification is included in the one or more processors 102, 202, or stored in the one or more memories 104, 204 and driven by the one or more processors 102, 202. The functions, procedures, proposals, and / or methods disclosed in this specification are implemented using firmware or software in the form of code, instructions, and / or sets of instructions.

[0077] One or more memories 104, 204 are connected to one or more processors 102, 202 and store various forms of data, signals, messages, information, programs, codes, instructions and / or commands. The one or more memories 104, 204 are composed of ROM, RAM, EPROM, flash memory, hard drive, register, cache memory, computer-readable storage medium and / or combinations thereof. The one or more memories 104, 204 are located inside and / or outside the one or more processors 102, 202. Also, the one or more memories 104, 204 are connected to the one or more processors 102, 202 by various techniques such as wired or wireless connection.

[0078] One or more transceivers 106, 206 can transmit user data, control information, radio signals / channels, etc. mentioned in this specification, such as methods and / or flowcharts, to one or more other devices. One or more transceivers 106, 206 can receive user data, control information, radio signals / channels, etc. mentioned in the descriptions, functions, procedures, proposals, methods, and / or flowcharts disclosed in this specification from one or more other devices. For example, one or more transceivers 106, 206 are connected to one or more processors 102, 202 and transmit and receive radio signals. For example, one or more processors 102, 202 can control one or more transceivers 106, 206 to transmit user data, control information, or radio signals to one or more other devices. Also, one or more processors 102, 202 can control one or more transceivers 106, 206 to receive user data, control information, or radio signals from one or more other devices. One or more transceivers 106, 206 are connected to one or more antennas 108, 208, and one or more transceivers 106, 206 are configured to transmit and receive user data, control information, radio signals / channels, etc. mentioned in the descriptions, functions, procedures, proposals, methods, and / or flowcharts disclosed in this specification by one or more antennas 108, 208. In this specification, one or more antennas are multiple physical antennas or multiple logical antennas (e.g., antenna ports). One or more transceivers 106, 206 convert the received radio signals / channels, etc. from RF band signals to baseband signals in order to process the received user data, control information, radio signals / channels, etc. using one or more processors 102, 202 (Convert). One or more transceivers 106, 206 convert the user data, control information, radio signals / channels, etc. processed using one or more processors 102, 202 from baseband signals to RF band signals. For this purpose, one or more transceivers 106, 206 include (analog) oscillators and / or filters.For example, transceivers 106 and 206 convert an OFDM baseband signal to a carrier frequency by an (analog) oscillator and / or filter of the transceiver under the control of processors 102 and 202, and transmit the OFDM signal converted to the carrier frequency. Transceivers 106 and 206 can receive an OFDM signal at the carrier frequency and convert the OFDM signal to an OFDM baseband signal by an (analog) oscillator and / or filter of the transceiver under the control of processors 102 and 202.

[0079] In an embodiment of the present invention, the UE operates as a transmitter in the uplink and as a receiver in the downlink. In an embodiment of the present invention, the BS operates as a receiver in the uplink and as a transmitter in the downlink. Hereinafter, for convenience of explanation, unless otherwise mentioned or explained, it is assumed that the first wireless device 100 operates as a UE and the second wireless device 200 operates as a BS. For example, a processor 102 connected to, mounted on, or launched in the first wireless device 100 is configured to perform UE operations according to an embodiment of the present invention or to control the transceiver 106 to perform UE operations according to an embodiment of the present invention. A processor 202 connected to, mounted on, or launched in the second wireless device 200 is configured to perform BS operations according to an embodiment of the present invention or to control the transceiver 206 to perform BS operations according to an embodiment of the present invention.

[0080] In the present invention, at least one memory (e.g., 104 or 204) stores instructions or programs that, when executed, cause at least one processor operably coupled thereto to perform operations according to some embodiments or implementations of the present invention.

[0081] In the present invention, a computer-readable storage medium stores at least one instruction or computer program that, when executed by at least one processor, causes the at least one processor to perform operations according to some embodiments or implementations of the present invention.

[0082] In the present invention, a processing device or apparatus includes at least one processor and at least one computer memory that can be connected to the at least one processor and that stores instructions which, when executed, cause the at least one processor to perform operations according to some embodiments or implementations of the present invention.

[0083] FIG. 3 is a diagram illustrating a frame structure in a 3GPP-based wireless communication system.

[0084] The frame structure of FIG. 3 is merely an example, and in a frame, the number of sub-frames, slots, and / or symbols can be changed variously. In a 3GPP-based wireless communication system, for one UE, different OFDM numerologies (e.g., subcarrier spacing (SCS), transmission time interval (TTI) interval) are set among a plurality of cells integrated for the UE. For example, if the UE is set with different SCSs for cells integrated for the cell, the (absolute time) intervals of time resources (e.g., sub-frames, slots, or TTIs) composed of the same number of symbols can be different among the integrated cells. Here, a symbol includes an OFDM symbol (or a CP-OFDM symbol), an SC-FDMA symbol (or a DFT-s-OFDM (discrete Fourier transform-spread-OFDM) symbol).

[0085] Referring to FIG. 3, uplink and downlink transmissions are composed of frames. Each frame has a period of T f = 10 ms and is divided into two half-frames, each having a period of 5 ms. Each half-frame is composed of five sub-frames, and the period (T sf) is 1 ms. Each subframe is divided into slots, and the number of slots in a subframe varies depending on the subcarrier spacing. Each slot is composed of 14 or 12 OFDM symbols based on the CP (cyclic prefix). In the case of normal CP, each slot is composed of 14 OFDM symbols, and in the case of extended CP, each slot is composed of 12 OFDM symbols. The numerology is based on a subcarrier spacing (Δf = 2 u * 15 kHz). The following table shows the number of OFDM symbols per slot, the number of slots per frame, and the number of slots for normal CP depending on the subcarrier spacing (Δf = 2 u * 15 kHz).

[0086]

Table 1

[0087] The following table shows the number of OFDM symbols per slot, the number of slots per frame, and the number of slots per subframe for extended CP depending on the subcarrier spacing (Δf = 2 u * 15 kHz).

[0088]

Table 2

[0089] A slot contains a plurality (e.g., 14 or 12) of symbols in the time domain. For each numerology (e.g., subcarrier spacing) and carrier, a common resource block (CRB) (N start,u grid ) indicated by upper layer signaling (e.g., radio resource control (RRC) signaling) starts from, N size,u grid,x * N RB sc subcarriers and Nsubframe,u symb A resource grid for a number of OFDM symbols is defined. Here, N size,u grid,x is the number of resource blocks (RB) in the resource grid, and the subscript x is DL for the downlink and UL for the uplink. N RB sc is the number of subcarriers per RB. In a 3GPP-based wireless communication system, N RB sc is generally 12. For a given antenna port (p), subcarrier spacing configuration (u), and transmission direction (DL or UL), there is one resource grid. The carrier bandwidth (N size,u grid ) for the subcarrier spacing configuration (u) is given by a higher layer parameter (e.g., an RRC parameter). Each element in the resource grid for the antenna port (p) and subcarrier spacing configuration (u) is called a resource element (RE), and one complex symbol is mapped to each resource element. Each resource element in the resource grid is uniquely identified by an index (k) in the frequency domain and an index (l) indicating the symbol position relative to the reference point in the time domain. In a 3GPP-based wireless communication system, an RB is defined by 12 consecutive subcarriers in the frequency domain.

[0090] In the 3GPP NR system, RBs are classified into common resource blocks (CRB) and physical resource blocks (PRB). CRBs are numbered in the increasing direction from 0 in the frequency domain for the subcarrier spacing configuration (u). The center of subcarrier 0 of CRB 0 for the subcarrier spacing configuration (u) coincides with 'point A', which is the common reference point for the resource block grid. In the 3GPP NR system, PRBs are defined within a bandwidth part (BWP) and are numbered from 0 to N size BWP,iIt is numbered up to -1. Here, i is the number of the above bandwidth part. The physical resource block (n PRB ) and the common resource block (n CRB ) have the following relationship: JPEG2025525071000004.jpg582 Here, N size BWP,i is the common resource block where the bandwidth part starts with respect to CRB 0. A BWP includes a plurality of consecutive RBs in the frequency domain. A carrier includes a maximum of N (for example, 5) BWPs. A UE is configured as one or more BWPs on a given configured carrier. Only one of the BWPs configured for a UE is activated at a time. The activated BWP defines the operating bandwidth of the UE within the operating bandwidth of the cell.

[0091] The NR frequency band is defined by two types of frequency ranges, FR1 and FR2. FR2 is also called millimeter wave (mmW). The frequency ranges in which NR can operate are distinguished as shown in Table 3.

[0092]

Table 3

[0093] Figure 4 is a diagram illustrating a protocol stack in a 3GPP-based wireless communication system.

[0094] In particular, FIG. 4(a) illustrates the radio interface user plane protocol stack between a UE and a base station (BS), and FIG. 4(b) illustrates the radio interface control plane protocol stack between the UE and the BS. The control plane means a path through which control messages used by the UE and the network to manage a call are transmitted. The user plane means a path through which data generated at the application layer, e.g., voice data or Internet packet data, is transmitted. Referring to FIG. 4(a), the user plane protocol stack is divided into a first layer (Layer 1) (i.e., the physical (PHY) layer) and a second layer (Layer 2). Referring to FIG. 4(b), the control plane protocol stack is divided into Layer 1 (i.e., the PHY layer), Layer 2, and Layer 3 (e.g., the radio resource control (RRC) layer and the non-access stratum (NAS) layer). Layers 1, 2, and 3 are referred to as the access stratum (AS).

[0095] The NAS control protocol is terminated at the access management function (AMF) on the network side and performs authentication, mobility management, security control, etc.

[0096] In the 3GPP LTE system, Layer 2 is divided into the following sub-layers: Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP). In the 3GPP NR (New Radio) system, Layer 2 is divided into the following sub-layers: MAC, RLC, PDCP, and Service Data Adaptation Protocol (SDAP). The PHY layer provides transport channels to the MAC sub-layer, the MAC sub-layer provides logical channels to the RLC sub-layer, the RLC sub-layer provides RLC channels to the PDCP sub-layer, and the PDCP sub-layer provides radio bearers to the SDAP sub-layer. The SDAP sub-layer provides QoS flows to the 5G core network.

[0097] In the 3GPP NR system, the main services and functions of SDAP include the following: mapping between QoS flows and data radio bearers; marking of QoS Flow ID (QFI) in both DL and UL packets. A single protocol entity of SDAP is configured for each PDU session.

[0098] In the 3GPP NR system, the main services and functions of the RRC sublayer include the following: broadcasting of system information related to AS and NAS; paging disclosed by the 5GC or NG-RAN; establishment, maintenance, and release of the RRC connection between the UE and the NG-RAN; security functions including key management; establishment, configuration, maintenance, and release of signaling radio bearers (SRBs) and data radio bearers (DRBs); (handover and context transfer; UE cell selection, reselection, and control of cell selection and reselection; mobility functions including mobility between RATs); QoS management functions, UE measurement reporting, and control of reporting; detection of radio link failure and recovery from radio link failure; transmission of NAS messages from the UE to the NAS and from the NAS to the UE.

[0099] In the 3GPP NR system, the main services and functions of the PDCP sublayer for the user plane include the following: sequence numbering; header compression and decompression (only in the case of robust header compression (ROHC)); user data transfer; reordering and duplicate detection; sequential transmission; PDCP PDU routing (in the case of split bearer); retransmission of PDCP SDUs; ciphering, deciphering, and integrity protection; PDCP SDU discard; PDCP re-establishment and data recovery for RLC AM; PDCH status reporting for RLC AM; duplication of PDCP PDUs and indication of duplicate discard to the lower layer. The main services and functions of the PDCP sublayer for the control plane include the following: sequence numbering; ciphering, deciphering, and integrity protection; transmission of control plane data; reordering and duplicate detection; sequential transmission; duplication of PDCP PDUs, and indication of duplicate discard to the lower layer.

[0100] In the 3GPP NR system, the RLC sublayer supports three transmission modes, namely, transparent mode (TM), unacknowledged mode (UM), and acknowledged mode (AM). The RLC configuration is independent of the new numerology and / or transmission interval and is applied for each logical channel. In the 3GPP NR system, the main services and functions of the RLC sublayer depend on the transmission mode, including transmission of upper layer PDUs; sequence numbering independent of the numbering in PDCP (in the case of UM and AM); error correction by ARQ (automatic repeat request) (only in the case of AM); segmentation of RLC SDUs (in the case of UM and AM) and re-segmentation (only in the case of AM); reassembly of SDUs (in the case of UM and AM); discard of RLC SDUs (in the case of UM and AM); RLC re-establishment; and protocol error detection (only in the case of AM).

[0101] In the 3GPP NR system, the main services and functions of the MAC sublayer include the following: mapping between logical channels and transport channels; multiplexing / demultiplexing of MAC SDUs belonging to one or different logical channels to / from transport blocks (TBs) transmitted to / from the PHY layer via transport channels; scale information reporting; error correction by HARQ (hybrid automatic repeat request) (one HARQ entity per cell in the case of CA); priority handling among UEs using dynamic scheduling; priority handling among the logical channels of one UE using logical channel priorities; padding. A single MAC entity supports multiple numerologies, transmission timings, and cells. In logical channel priorities, the mapping constraints control which numerology, cell, and transmission timing a logical channel uses. Different types of data transmission services are provided by the MAC. To accommodate different types of data transmission services, a number of logical channel types, i.e., logical channel types each supporting a specific type of information transmission, are defined. Each logical channel type is defined by what type of information is transmitted. Logical channels are classified into two groups, i.e., control channels and traffic channels. Control channels are used to transmit only control plane information, and traffic control channels are used to transmit only user plane information.The broadcast control channel (BCCH) is a downlink logical channel for broadcasting system control information. The paging control channel (PCCH) is a downlink logical channel for transmitting paging information, system information change notifications, and instructions for ongoing PWS broadcasts. The common control channel (CCCH) is a logical channel for transmitting control information between the UE and the network, and is used for UEs that do not have an RRC connection with the network. The dedicated control channel (DCCH) is a point-to-point two-way logical channel for transmitting dedicated control information between the UE and the network, and is used by UEs that have an RRC connection. The dedicated traffic channel (DTCH) is a point-to-point logical channel dedicated to a single UE for transmitting user information. The DTCH exists on both the uplink and the downlink. In the downlink, the mapping between the logical channel and the transport channel is as follows: BCCH is mapped to BCH; BCCH is mapped to the downlink shared channel (DL-SCH); PCCH is mapped to PCH; CCCH is mapped to DL-SCH; DCCH is mapped to DL-SCH; DTCH is mapped to DL-SCH. In the uplink, the mapping between the logical channel and the transport channel is as follows: CCCH is mapped to the uplink shared channel (UL-SCH); DCCH is mapped to UL-SCH; DTCH is mapped to UL-SCH.

[0102] Figure 5 shows an example of the data flow in a 3GPP NR system.

[0103] In FIG. 5, "RB" is a radio bearer and "H" is a header. The radio bearer is classified into two groups: a data radio bearer (DRB) for user plane data and a signaling radio bearer (SRB) for control plane data. The MAC PDU is transmitted and received with an external device via the PHY layer using radio resources. The MAC PDU reaches the PHY layer in the form of a transport block.

[0104] In the PHY layer, the UL-SCH and RACH, which are uplink transport channels, are mapped to the PUSCH and PRACH respectively, and the DL-SCH, BCH, and PCH, which are downlink transport channels, are mapped to the PDSCH, physical broadcast channel (PBCH), and PDSCH respectively. In the PHY layer, the uplink control information (UCI) is mapped to the PUCCH, and the downlink control information (DCI) is mapped to the PDCCH. The MAC PDU related to the UL-SCH is transmitted by the UE via the PUSCH based on an uplink grant, and the MAC PDU related to the DL-SCH is transmitted by the BS via the PDSCH based on a downlink allocation.

[0105] To transmit the data unit of the present invention via UL-SCH, the UE must have uplink resources available to the UE. To receive the data unit of the present invention via DL-SCH, the UE must have downlink resources available to the UE. Resource allocation includes time-domain resource allocation and frequency-domain resource allocation. In the present invention, uplink resource allocation is also referred to as an uplink grant, and downlink resource allocation is also referred to as a downlink allocation. The uplink grant is dynamically received by the UE via PDCCH within a random access response, or is semi-persistently configured for the UE by RRC. The downlink allocation is dynamically received by the UE via PDCCH, or is semi-persistently configured for the UE by RRC signaling from the BS.

[0106] In the uplink, the BS can dynamically allocate resources to the UE on the PDCCH using the cell radio network temporary identifier (C-RNTI). The UE always monitors the PDCCH to find available grants for uplink transmission when the UE's downlink reception is enabled (at setup time, during an activity controlled by discontinuous reception (DRX)). Also, using the configured grant, the BS can allocate uplink resources to the UE for initial HARQ transmission. Two types of configured uplink grants are defined: namely, type 1 and type 2. In the case of type 1, the RRC directly provides the configured uplink grant (including the period). In the case of type 2, the RRC either signals and activates the configured uplink grant when the PDCCH addressed to the configured scheduling RNTI (CS-RNTI) is set, or defines the period of the configured uplink grant while it can be deactivated. That is, the PDCCH addressed to the CS-RNTI indicates that the uplink grant can be implicitly reused according to the period defined by the RRC until the uplink grant is deactivated.

[0107] In the downlink, the BS can dynamically allocate resources to the UE on the PDCCH using the C-RNTI. The UE always monitors the PDCCH to search for possible grants when the UE's downlink reception is enabled (at setup, active controlled by DRX). Also, using semi-persistent scheduling (SPS), the BS can allocate downlink resources to the UE for initial HARQ transmissions. The RRC signals and activates or deactivates a downlink allocation with a PDCCH addressed to the CS-RNTI, or defines the period of the configured downlink allocation while it can be signaled and activated or deactivated. That is, the PDCCH addressed to the CS-RNTI indicates that the downlink allocation can be implicitly reused according to the period defined by the RRC until the downlink allocation is deactivated.

[0108] <Resource Allocation by PDCCH (i.e., Resource Allocation by DCI)>

[0109] The PDCCH is used to schedule downlink transmissions on the PDSCH and uplink transmissions on the PUSCH, where the DCI on the PDCCH includes: a downlink allocation related to the DL-SCH, at least including modulation and coding format (e.g., modulation and coding scheme (MCS) index (IMCS)), resource allocation and hybrid ARQ information; or an uplink scheduling grant related to the UL-SCH, including modulation and coding format, resource allocation and hybrid ARQ information. The size and use of the DCI carried by one PDCCH vary according to the DCI format. For example, in the 3GPP NR system, DCI format 0_0 or DCI format 0_1 is used for scheduling the PUSCH in one cell, and DCI format 1_0 or DCI format 1_1 is used for scheduling the PDSCH in one cell.

[0110] FIG. 6 is a diagram showing an example of PDSCH time domain resource allocation by PDCCH and an example of PUSCH time resource allocation by PDCCH.

[0111] To schedule PDSCH or PUSCH, the DCI carried by PDCCH includes a value m for row index m+1 with respect to an allocation table for PDSCH or PUSCH. A predetermined default PDSCH time domain allocation A, B, or C is applied to the allocation table for PDSCH, or an RRC-configured PDSCH-TimeDomainAllocationList is applied to the allocation table for PDSCH. A predetermined default PUSCH time domain allocation A is applied to the allocation table for PUSCH, or an RRC-configured PUSCH-TimeDomainAllocationList is applied to the allocation table for PUSCH. Which PDSCH time domain resource allocation setting to apply and which PUSCH time domain resource allocation table to apply are determined by fixed / predetermined rules (e.g., Table 5.1.2.1.1-1 of 3GPP TS 38.214 v15.3.0, Table 6.1.2.1.1-1 of 3GPP TS 38.214 v15.3.0).

[0112] In the configuration of PDSCH time-domain allocation, each indexed row directly defines the slot offset K0, the start and length indicator SLIV or the start symbol S and the allocation length L, and the PDSCH mapping type assumed for PDSCH reception. In the configuration of PUSCH time-domain allocation, each indexed row directly defines the slot offset K2, the start and length indicator SLIV or the start symbol S and the allocation length L, and the PUSCH mapping type assumed for PUSCH reception. K0 for PDSCH or K2 for PUSCH is the time difference between the slot where the PDCCH is located and the slot where the PDSCH or PUSCH corresponding to the PDCCH is located. SLIV is a joint indicator of the start symbol S regarding the start of the slot where the PDSCH or PUSCH is located and the number L of consecutive symbols counted from symbol S. In the case of the PDSCH / PUSCH mapping type, there are two mapping types: one is mapping type A where the demodulation reference signal (DMRS) is located in the third or fourth symbol of the slot by mapping RRC signaling, and the other is mapping type B where the DMRS is located in the first allocated symbol.

[0113] The scheduling DCI includes a frequency-domain resource allocation field that provides allocation information regarding the resource blocks used for PDSCH or PUSCH. For example, the frequency-domain resource allocation field provides the UE with information regarding the cell for PDSCH or PUSCH transmission, information regarding the bandwidth part for PDSCH or PUSCH transmission, and information regarding the resource blocks for PDSCH or PUSCH transmission.

[0114] <Resource Allocation by RRC>

[0115] As described above, in the uplink, there are two types of transmissions without dynamic grants, namely, configured grant type 1 and configured grant type 2. In the case of configured grant type 1, the uplink grant is stored as a grant provided by RRC and configured. In the case of configured grant type 2, the uplink grant is provided by PDCCH and stored or cleared as an uplink grant configured based on L1 signaling that indicates activation or deactivation of the configured uplink grant. Type 1 and type 2 are configured by RRC signaling for each serving cell and for each BWP. Multiple configurations can be activated simultaneously only on serving cells with different configurations. In the case of type 2, activation and deactivation are independent among serving cells. For the same serving cell, the MAC entity is configured as type 1 or type 2.

[0116] When configured grant type 1 is configured, at least the following parameters are provided to the UE by the BS via RRC signaling:

[0117] - s-RNTI, which is the CS-RNTI for retransmission;

[0118] - periodicity, which provides the period of configured grant type 1;

[0119] - timeDomainOffset, which indicates the offset of the resource for system frame number (SFN) = 0 in the time domain;

[0120] - timeDomainAllocation value m, which provides the row index m+1 of the allocation table indicating the combination of start symbol S, length L, and PUSCH mapping type;

[0121] - frequencyDomainAllocation, which provides the frequency domain resource allocation; and

[0122] - mcsAndTBS that provides an IMCS indicating the modulation order, target code rate, and size of the transport block. When a configured grant type 1 for the serving cell is set by RRC, the UE stores the uplink grant provided by RRC as the configured uplink grant for the indicated serving cell, and initializes or re-initializes the configured uplink grant such that the uplink grant configured with timeDomainOffset and symbols set by S (derived from SLIV) starts and recurs periodically. After the uplink grant is configured for the configured grant type 1, the UE considers the uplink grant to recur in association with each symbol that satisfies the following: [(SFN * numberOfSlotsPerFrame * (numberOfSymbolsPerSlot) + (Slot number in the frame × numberOfSymbolsPerSlot) + symbol number in the slot] = (timeDomainOffset * numberOfSymbolsPerSlot + S + N * periodicity) modulo (1024 * numberOfSlotsPerFrame * numberOfSymbolsPerSlot), for all N >= 0.

[0123] When the configured grant type 2 is set, at least the following parameters are provided to the UE by the BS via RRC signaling:

[0124] - cs-RNTI, which is a CS-RNTI for activation, deactivation, and retransmission; and

[0125] - periodicity that provides the configured grant type 2 period. The actual uplink grant is provided to the UE by the PDCCH (addressed to the CS-RNTI). After the uplink grant is configured for the configured grant type 2, the UE is considered to reoccur associated with each symbol for which the uplink grant satisfies: [(SFN * numberOfSlotsPerFrame * numberOfSymbolsPerSlot)+(Slot number in the frame * numberOfSymbolsPerSlot)+symbol number in the slot]=[(SFNstart time * numberOfSlotsPerFrame * numberOfSymbolsPerSlot + slotstart time * numberOfSymbolsPerSlot + symbol start time )+N * periodicity] modulo (1024×numberOfSlotsPerFrame * numberOfSymbolsPerSlot), for all N>=0, where SFN start time , slot start time and symbol start time respectively indicate the SFN, slot, and symbol of the first transmission opportunity of the PUSCH for which the configured grant was (re)initialized. numberOfSlotsPerFrame and numberOfSymbolsPerSlot respectively indicate the number of consecutive slots per frame and the number of consecutive OFDM symbols per slot.

[0126] For the configured uplink grant, the HARQ process ID associated with the first symbol of the uplink transmission is derived from the following formula.

[0127] HARQ Process ID = [floor(CURRENT_symbol / periodicity)] modulo nrofHARQ - Processes

[0128] Here, CURRENT_symbol = (SFN × numberOfSlotsPerFrame × numberOfSymbolsPerSlot + slot number in the frame × numberOfSymbolsPerSlot + symbol number in the slot), and numberOfSlotsPerFrame and numberOfSymbolsPerSlot indicate the number of consecutive slots per frame and the number of consecutive symbols per slot, respectively, as specified in TS 38.211. CURRENT_symbol indicates the symbol index of the first transmission opportunity of the occurring repetition. The HARQ process is configured for the configured uplink grant if the configured uplink grant is activated, and the associated HARQ process ID is smaller than nrofHARQ - Processes.

[0129] For the downlink, the UE is configured with SPS for each serving cell and each BWP by RRC signaling from the BS. Multiple configurations are activated simultaneously on different serving cells. The activation or deactivation of downlink SPS is independent between serving cells. For downlink SPS, the downlink allocation is provided to the UE by the PDCCH and stored or removed based on the L1 signaling indicating SPS activation or deactivation. When SPS is configured, the following parameters are provided to the UE by the BS via RRC signaling:

[0130] - cs - RNTI, which is the CS - RNTI for activation, deactivation, and retransmission;

[0131] - nrofHARQ - Processe, which provides the number of configured HARQ processes for SPS;

[0132] - periodicity, which provides the configured downlink allocation period for SPS.

[0133] When the SPS is released by a higher layer, all applicable settings must be released.

[0134] After the downlink allocation for SPS is configured, the UE shall assume that the Nth downlink allocation occurs in sequence in the slots that satisfy the following: (numberOfSlotsPerFrame * SFN + slot number in the frame) = [(numberOfSlotsPerFrame * SFN start time + slot start time ) + N * periodicity * numberOfSlotsPerFrame / 10] modulo (1024 * numberOfSlotsPerFrame), where SFN start time and slot start time indicate the SFN, slot, and symbol of the first transmission of the PDSCH at which the configured downlink allocation was (re)initialized, respectively.

[0135] For a configured downlink allocation, the HARQ process ID associated with the slot at which the downlink transmission starts is derived from the following formula:

[0136] HARQ Process ID = [floor (CURRENT_slot × 10 / (numberOfSlotsPerFrame × periodicity))] modulo nrofHARQ - Processes

[0137] where CURRENT_slot = [(SFN × numberOfSlotsPerFrame) + slot number in the frame], and numberOfSlotsPerFrame indicates the number of consecutive slots per frame as specified in TS38.211.

[0138] The cyclic redundancy check (CRC) of the corresponding DCI format is scrambled with the CS-RNTI provided by the RRC parameter cs-RNTI. When the new data indicator field for the valid transport block is set to 0, the UE confirms that the downlink SPS allocation PDCCH or the configured uplink grant type 2 PDCCH is valid for scheduling activation or deactivation. When all fields for the DCI format are set according to Table 4 or Table 5, the validation of the DCI format is achieved. Table 4 illustrates specific fields for the validation of the scheduling activation PDCCH for downlink SPS and uplink grant type 2, and Table 5 illustrates specific fields for the validation of the scheduling deactivation PDCCH for downlink SPS and uplink grant type 2.

[0139]

Table 4

[0140]

Table 5

[0141] The actual downlink allocation and the actual uplink grant, and the corresponding modulation and coding scheme are provided by the resource allocation fields (e.g., the time domain resource allocation field that provides the time domain allocation value m, the frequency domain resource allocation field that provides the frequency resource block allocation, the modulation and coding scheme field) within the DCI format carried by the downlink SPS or the scheduling activation PDCCH of the uplink grant type 2. When the validation is achieved, the UE regards the information within the DCI format as a valid activation or a valid deactivation of the downlink SPS or the configured uplink grant type 2.

[0142] In the case of the uplink, the processor 102 of the present invention transmits the data unit of the present invention (or controls the transceiver 106 to transmit) based on the uplink grant available to the UE. The processor 202 of the present invention receives the data unit of the present invention (or controls the transceiver 206 to receive) based on the uplink grant available to the UE.

[0143] In the case of the downlink, the processor 102 of the present invention receives the downlink data of the present invention (or controls the transceiver 106 to receive) based on the downlink allocation available to the UE. The processor 202 of the present invention transmits the downlink data of the present invention (or controls the transceiver 206 to transmit) based on the downlink allocation available to the UE.

[0144] Before the data unit of the present invention is transmitted via the radio interface, physical layer processing is performed on the transmission side, and physical layer processing is performed on the radio signal carrying the data unit of the present invention on the reception side. For example, the MAC PDU including the PDCP PDU according to the present invention is physically layer processed as follows.

[0145] FIG. 7 is a diagram showing an example of physical layer processing on the transmission side.

[0146] The following table shows the mapping of the transport channel (TrCH) and control information to the corresponding physical channel. In particular, Table 6 shows the mapping of the uplink transport channel to the corresponding physical channel, Table 7 shows the mapping of the uplink control channel information to the corresponding physical channel, Table 8 shows the mapping of the downlink transport channel to the corresponding physical channel, and Table 9 shows the mapping of the downlink control channel information to the corresponding physical channel.

[0147]

Table 6

[0148]

Table 7

[0149]

Table 8

[0150]

Table 9

[0151] <Encoding>

[0152] Data and control streams from / to the MAC layer are encoded to provide transport and control services over a wireless transmission link at the PHY layer. For example, a transport block from the MAC layer is encoded into codewords at the transmitting side. Channel coding schemes are error sensing, error correction, rate matching, interleaving and a combination of transport channels mapped to or demultiplexed from a physical channel, or control information.

[0153] In the 3GPP NR system, the following channel coding schemes are used for different types of TrCHs and different types of control information.

[0154]

Table 10

[0155]

Table 11

[0156] For the transmission of a downlink transport block (i.e., DL MAC PDU) or an uplink transport block (i.e., UL MAC PDU), a transport block CRC sequence is attached to provide error detection for the receiving side. In the 3GPP NR system, communication devices use low density parity check (LDPC) codes when encoding / decoding UL-SCH and DL-SCH. The 3GPP NR system supports two LDPC base graphs (i.e., two LDPC base matrices): namely, LDPC base graph 1 optimized for small transport blocks and LDPC base graph 2 optimized for larger transport blocks. LDPC base graph 1 or 2 is selected based on the size of the transport block and the coding rate R. The coding rate R is indicated by the MCS index (IMCS). The MCS index is provided to the UE by the PDCCH that activates or (re)initializes the uplink-configured grant 2 or downlink SPS, or is dynamically applied to the UE by the PDCCH that schedules the PUSCH or PDSCH and is provided to the UE by RRC signaling related to the uplink-configured grant type 1. If the transport block with attached CRC is larger than the maximum code block size for the selected LDPC base graph, the transport block with attached CRC is divided into code blocks, and an additional CRC sequence is attached to each code block. The maximum code block sizes of LDPC base graph 1 and LDPC base graph 2 are 8448 bits and 3480 bits respectively. If the transport block with attached CRC is not larger than the maximum code block size for the selected LDPC base graph, the transport block with attached CRC is encoded using the selected LDPC base graph. Each code block of the transport block is encoded using the selected LDPC base graph. Subsequently, the LDPC-coded blocks are individually rate-matched. Code block concatenation is performed to generate codewords for transmission on the PDSCH or PUSCH. In the case of the PDSCH, a maximum of two codewords (i.e., a maximum of two transmission blocks) are transmitted simultaneously on the PDSCH.The PUSCH can be used to transmit UL-SCH data and layer 1 / 2 control information. Although not shown in FIG. 8, the layer 1 / 2 control information can be multiplexed with the codewords for the UL-SCH data.

[0157] <Scrambling and Modulation>

[0158] The bits of the codewords are scrambled and modulated to generate a block of complex-valued modulation symbols.

[0159] <Layer Mapping>

[0160] The complex-valued modulation symbols of the codewords are mapped to one or more multiple input multiple output (MIMO) layers. The codewords are mapped to a maximum of 4 layers. Since the PDSCH can transmit 2 codewords, the PDSCH can support up to 8-layer transmission. Since the PUSCH supports a single codeword, the PUSCH can support up to 4-layer transmission.

[0161] <Transform Precoding>

[0162] The downlink transmission waveform is a conventional OFDM that uses a cyclic prefix (CP). In the case of the downlink, transform precoding (i.e., discrete Fourier transform (DFT)) is not applied.

[0163] The uplink transmission waveform is a conventional OFDM that uses a CP with a transform precoding function that can perform DFT spreading that can be made invalid or valid. In the 3GPP NR system, in the case of the uplink, transform precoding is selectively applied when it is enabled. Transform precoding is to spread uplink data in a special manner to reduce the peak-to-average power ratio (PAPR) of the waveform. Transform precoding is a form of DFT. That is, the 3GPP NR system supports two options for the uplink waveform: one is CP-OFDM (the same as the downlink waveform), and the other is DFT-s-OFDM. Whether the UE uses CP-OFDM or DFT-s-OFDM is set by the BS according to the RRC parameter.

[0164] <Subcarrier mapping>

[0165] Layers are mapped to antenna ports. In the downlink, a mapping in a transparent manner (non-codebook based) for layer-antenna port mapping is supported, and how beamforming or MIMO precoding is performed is transparent to the UE. In the uplink, both non-codebook based mapping and codebook based mapping for layer-antenna port mapping are supported.

[0166] For each antenna port (i.e., layer) used for the transmission of a physical channel (e.g., PDSCH, PUSCH), the complex-valued modulation symbols are mapped to subcarriers in the resource blocks allocated to the physical channel.

[0167] <OFDM modulation>

[0168] The communication device on the transmitting side adds a CP and performs an inverse fast Fourier transform (IFFT) to generate a time - continuous OFDM baseband signal in the setting u of the antenna port p and the sub - carrier spacing for the OFDM symbol l in the TTI for the physical channel. For example, for each OFDM symbol, the communication device on the transmitting side can perform IFFT on the complex - valued modulated symbols mapped to the resource block in the corresponding OFDM symbol, and add a CP to the IFFT - processed signal to generate an OFDM baseband signal.

[0169] <Up - conversion>

[0170] The communication device on the transmitting side up - converts the OFDM baseband signal for the antenna port p, the sub - carrier spacing setting u, and the OFDM symbol l to the carrier frequency f0 of the cell to which the physical channel is assigned.

[0171] In FIG. 2, the processors 102 and 202 are configured to perform encoding, scrambling, modulation, layer mapping, (for uplink) transform precoding, sub - carrier mapping, and OFDM modulation. The processors 102 and 202 control the transceivers 106 and 206 connected to the processors 102 and 202 to up - convert the OFDM baseband signal to the carrier frequency to generate a radio frequency (RF) signal. The radio frequency signal is transmitted to an external device via the antennas 108 and 208.

[0172] FIG. 8 is a diagram showing an example of physical layer processing on the receiving side.

[0173] The physical layer processing on the receiving side is basically the reverse process of the physical layer processing on the transmitting side.

[0174] <Down - conversion>

[0175] The communication device on the receiving side receives an RF signal at the carrier frequency via an antenna. The transceivers 106 and 206 that receive the RF signal at the carrier frequency down-convert the carrier frequency of the RF signal to the baseband to obtain an OFDM baseband signal.

[0176] <OFDM Demodulation>

[0177] The communication device on the receiving side obtains complex-valued modulated symbols by CP separation (detachment) and FFT. For example, for each OFDM symbol, on the receiving side, the communication device removes the CP from the OFDM baseband signal and performs an FFT on the OFDM baseband signal from which the CP has been removed to obtain complex-valued modulated symbols for the antenna port p, subcarrier spacing u, and OFDM symbol l.

[0178] <Subcarrier Demapping>

[0179] Subcarrier demapping is performed on the complex-valued modulated symbols to obtain the complex-valued modulated symbols of the corresponding physical channel. For example, the processor 102 can obtain the complex-valued modulated symbols mapped to the subcarriers belonging to the PDSCH from the complex-valued modulated symbols received in the BWP. As another example, the processor 202 can obtain the complex-valued modulated symbols mapped to the subcarriers belonging to the PUSCH from the complex-valued modulated symbols received in the BWP.

[0180] <Inverse Transform Decoding>

[0181] Inverse transform decoding (e.g., IDFT) is performed on the complex-valued modulated symbols of the uplink physical channel when transform precoding is enabled for the uplink physical channel. Inverse transform decoding is not performed for the downlink physical channel and the uplink physical channel for which transform precoding is disabled.

[0182] <Layer Demapping>

[0183] Complex-valued modulation symbols are demapped to one or two codewords.

[0184] <Demodulation and descrambling>

[0185] The complex-valued modulation symbols of the codewords are demodulated to the bits of the codewords and descrambled.

[0186] <Decoding>

[0187] The codewords are decoded to transport blocks. For UL-SCH and DL-SCH, LDPC base graph 1 or 2 is selected based on the size and coding rate of the transport block. The codewords include one or more coded blocks. Each coded block is decoded to a code block with CRC attached or a transport block with CRC attached using the selected LDPC base graph. When splitting the code block for a transport block with CRC attached at the transmitter side, the CRC sequence is removed from each of the code blocks with CRC attached to obtain the code blocks. The code blocks are concatenated to the transport block with CRC attached. The transport block CRC sequence is removed from the transport block with CRC attached to obtain the transport block. The transport block is transmitted to the MAC layer.

[0188] In the above-described physical layer processing at the transmitter and receiver sides, the time and frequency domain resources (e.g., OFDM symbols, subcarriers, carrier frequencies) related to subcarrier mapping, OFDM modulation, and frequency up / down conversion are determined based on resource allocation (e.g., uplink grant, downlink allocation).

[0189] For uplink data transmission, the processor 102 of the present invention applies the above-described physical layer processing on the transmission side to the data unit of the present invention (or controls the transceiver 106 to apply it) to wirelessly transmit the data unit. For downlink data reception, the processor 102 of the present invention applies the above-described physical layer processing on the reception side to the received wireless signal (or controls the transceiver 106 to apply it) to obtain the data unit of the present invention.

[0190] For downlink data transmission, the processor 202 of the present invention applies the above-described physical layer processing on the transmission side to the data unit of the present invention (or controls the transceiver 206 to apply it) to wirelessly transmit the data unit. For uplink data reception, the processor 202 of the present invention applies the above-described physical layer processing on the reception side to the received wireless signal (or controls the transceiver 206 to apply it) to obtain the data unit of the present invention.

[0191] On the other hand, the MAC entity manages one PTAG (Primary Timing Advance Group) and zero or more STAGs (Secondary Timing Advance Group). The PTAG (Primary Timing Advance Group) refers to a TAG (Timing Advance Group) including the SpCell of the MAC entity, and the STAG (Secondary Timing Advance Group) refers to other TAGs not including the SpCell.

[0192] The SpCell is a special cell that supports PUCCH transmission and contention-based random access and is always activated. In DC (Dual Connectivity) operation, when the MAC entity is related to MCG or SCG, the special cell refers to the PCell of MCG or the PSCell (Primary Secondary Cell) of SCG. Otherwise, the special cell refers to the PCell.

[0193] For DC operation, the UE configures two MAC entities, one of which is the MAC entity for the MCG (Master Cell Group) and the other is the MAC entity for the SCG (Secondary Cell Group). Each MAC entity controls one PTAG and zero or more STAGs.

[0194] TA (Timing Advance) is maintained in TAG (Timing Advance Group) units, and all serving cells belonging to one TAG apply the same TA. Each TAG maintains its TA using the TAT (Time Alignment Timer). While the TAT is running, the UE can perform uplink transmissions assuming that the uplink timing of all serving cells belonging to the TAG is aligned with the network.

[0195] When the TAT of the STAG expires, the UE flushes all HARQ buffers for all serving cells belonging to the STAG and clears the uplink resources. On the other hand, when the TAT of the PTAG expires, it flushes all HARQ buffers for all serving cells belonging to the MAC entity and clears the uplink resources.

[0196] When the TAT related to the TAG to which the serving cell belongs is not running, the MAC entity needs not perform uplink transmissions for the serving cell, except for RAP (Random Access Preamble) and MSGA transmissions.

[0197] When performing a RA (Random Access) procedure for a serving cell belonging to a TAG, the UE acquires the Absolute TA of the TAG. The Absolute TA is provided by the 12-bit TAC field included in the RAR (Random Access Response) in the case of 4-step RA, and is provided by the Absolute TAC MAC CE in the case of 2-step RA. When the Absolute TA is acquired, the UE applies the Absolute TA to the TAT of the TAG and starts the TAT.

[0198] During the execution of the TAT, the TA value can vary. To adjust the TA variation, the network sends a TAC (Timing Advance Command) MAC CE to the UE. The TAC MAC CE includes a 6-bit TAC field indicating the index value TA (0, 1, 2... 63) used to control the amount of timing adjustment applied by the MAC entity. The TAC MAC CE also includes a 2-bit TAG ID field indicating the TAG ID of the specified TAG. When the UE receives the TAC MAC CE, the UE adjusts the TAT of the specified TAG and starts the TAT again.

[0199] In 3GPP NR standard release 18, a new mobility scenario called L1 / L2 inter-cell mobility is considered.

[0200] Figure 9 shows an example of L1 / L2 inter-cell mobility considered in 3GPP NR standard release 18. In particular, Figure 9 shows an intra-DU mobility scenario.

[0201] Also, Figure 10 shows another example of L1 / L2 inter-cell mobility considered in 3GPP NR standard release 18. In particular, Figure 10 shows an intra-CU inter-DU mobility scenario.

[0202] In FIGS. 9 and 10, CU means gNB Central Unit, and DU means gNB Distributed Unit. Also, CU-CP means gNB-CU-Control Plane, and CU-UP means gNB-CU-User Plane.

[0203] More specifically, gNB-CU means a logical node that hosts the RRC, SDAP, and PDCP protocols of gNB or the RRC and PDCP protocols of en-gNB, and controls the operation of one or more gNB-DUs. gNB-CU terminates the F1 interface connected to gNB-DU.

[0204] Also, gNB-DU indicates a logical node that hosts the RLC, MAC, and PHY layers of gNB or en-gNB, and its operation is partially controlled by gNB-CU. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU. gNB-DU terminates the F1 interface connected to gNB-CU.

[0205] Also, gNB-CU-CP refers to a logical node that hosts the RRC and the control plane part of the PDCP protocol of gNB-CU for en-gNB or gNB. gNB-CU-CP terminates the E1 interface connected to gNB-CU-UP and the F1-C interface connected to gNB-DU.

[0206] Also, gNB-CU-UP refers to a logical node that hosts the user plane part of the PDCP protocol of gNB-CU for en-gNB and the user plane parts of the PDCP protocol and SDAP protocol of gNB-CU for gNB. gNB-CU-UP terminates the E1 interface connected to gNB-CU-CP and the F1-U interface connected to gNB-DU.

[0207] In the mobility between L1 / L2 cells, the RRC is not changed, and only the serving cell is changed. Since RRC, SDAP, and PDCP are not changed, the excessive mobility procedures defined in the prior art are not required, and a simple cell change is sufficient.

[0208] The problem of the prior art is that in order to obtain the absolute TA of the TAG, the UE needs to perform a RA procedure for the serving cell to which the TAG belongs. Since the RA procedure requires several steps of mutual execution procedures between the UE and the network, it takes time to obtain the absolute TA.

[0209] In the mobility between L1 / L2 cells, since the RRC is not changed, the network can know the absolute TA of other cells belonging to the same CU.

[0210] Therefore, according to the present invention, when the UE connects to the central unit (CU) of the network by the first cell, it is proposed that the network provides the UE with the information of the candidate cells belonging to the CU and the absolute TA of the candidate cells. When the UE moves to the second cell, if the UE has the absolute TA of the second cell, the UE performs UL transmission without performing a RA procedure in the second cell.

[0211] However, if the UE does not have the absolute TA of the second cell, the UE performs a RA procedure for the second cell. After the RA procedure is completed and the absolute TA for the second cell is obtained, the UE performs UL transmission for the second cell.

[0212] The UE performs a RA procedure in the first cell and connects to the CU of the network by the first cell. During the RA procedure, the UE obtains the absolute TA of the first cell.

[0213] After the UE connects to the CU, it receives information about the candidate cells belonging to the CU. The candidate cell information includes the candidate cell index belonging to the CU, the PCI (Physical Cell Identity), the TAG ID of the candidate cell, the frequency, the UL resources, etc. The candidate cell index is assigned to the candidate cell in a short form.

[0214] Also, the UE receives information about the absolute TA of each candidate cell from the network. The absolute TA information can be received together with the candidate cell information. In this case, the absolute TA information is provided for each candidate cell.

[0215] The absolute TA information can also include the valid time for the UE to determine that the absolute TA for the candidate cell is valid. After the valid time, the UE considers that there is no absolute TA for the candidate cell.

[0216] The absolute TA information can be received separately after receiving the candidate cell information. The network provides the candidate cell information first, and when the network tries to move the UE to the candidate cell, it provides the absolute TA information later.

[0217] To provide the absolute TA information separately, a new absolute TAC MAC CE can also be used. The new absolute TAC MAC CE includes the candidate cell identifier and the absolute TA of the candidate cell. The candidate cell identifier is provided by the physical cell ID, the abbreviation of the candidate cell index, the candidate TAG ID to which the candidate cell belongs, etc. The new absolute TAC MAC CE also includes the UL resources available in the candidate cell.

[0218] When the network attempts to move the UE to a second cell, the network provides a cell change command to the UE via L1 / L2 signals. The L1 / L2 signals include PDCCH, other physical signals, MAC CE, etc. The network can transmit an absolute TAC MAC CE together with the cell change command.

[0219] After the UE moves to the second cell, the UE checks whether it has the absolute TA of the second cell. If the UE has the absolute TA of the second cell, the UE does not perform an RA procedure and directly transmits UL data from the second cell using the absolute TA of the second cell. However, if the UE does not have the absolute TA of the second cell, the UE performs an RA procedure for the second cell to obtain the absolute TA of the second cell. After obtaining the absolute TA of the second cell, the UE transmits UL data in the second cell.

[0220] Even if the second cell is one of the candidate cells and the absolute TA has already been provided, if the validity period of the absolute TA has expired, the UE considers that it does not have the absolute TA of the second cell.

[0221] FIG. 11 shows an example of serving cell change according to the present invention. In FIG. 11, it is assumed that the absolute TA information is provided by the candidate cell information.

[0222] Referring to FIG. 11, in S1101, the UE camps on the first cell and performs an RA procedure for the first cell. After the RA procedure is successfully completed, the UE connects to the CU (Central Unit) of the network. The UE obtains the absolute TA of the first cell during the RA procedure.

[0223] In S1102, the UE receives candidate cell information regarding candidate cells belonging to the CU. The candidate cell information includes a candidate cell identifier, UL resources of the candidate cell, etc.

[0224] The UE also receives the absolute TA information of each candidate cell based on the candidate cell information. The absolute TA information also includes the valid time of the absolute TA.

[0225] In S1103, the UE exchanges data with the network of the first cell by using the absolute TA of the first cell.

[0226] In S1104, the UE receives a cell change command for the second cell from the network. The cell change command includes the identifier of the second cell.

[0227] In S1105, the UE moves to the indicated second cell.

[0228] In S1106, the UE checks whether a valid absolute TA for the second cell is available.

[0229] If a valid absolute TA for the second cell is available, in S1107, the UE performs UL transmission in the second cell by using the absolute TA of the second cell without performing an RA procedure.

[0230] On the other hand, if the absolute TA value for the second cell cannot be used, the UE performs an RA procedure for the second cell and obtains the absolute TA of the second cell in S1108. After obtaining the absolute TA of the second cell, the UE performs UL transmission in the second cell by using the absolute TA of the second cell.

[0231] FIG. 12 shows another example of the serving cell change according to the present invention. In FIG. 12, it is assumed that the absolute TA information is provided by the absolute TAC MAC CE.

[0232] Referring to FIG. 12, in S1201, the UE camps on the first cell and performs a random access (RA) procedure for the first cell. After the RA procedure is successfully completed, the UE connects to the Central Unit (CU) of the network. The UE obtains the Absolute TA of the first cell during the RA procedure.

[0233] In S1202, the UE receives candidate cell information regarding candidate cells belonging to the CU. The candidate cell information includes a candidate cell identifier, UL resources of the candidate cell, etc.

[0234] In S1203, the UE exchanges data with the network of the first cell using the Absolute TA of the first cell.

[0235] In S1204, the UE receives the Absolute TA information of the candidate cell from the network by means of the Absolute TAC MAC CE. The Absolute TAC MAC CE includes the identifier of the candidate cell and the Absolute TA of the candidate cell.

[0236] In S1205, the UE moves to the specified candidate cell.

[0237] In S1206, the UE performs UL transmission in the candidate cell without performing the RA procedure, using the Absolute TA of the candidate cell.

[0238] FIG. 13 shows another example of serving cell change according to the present invention. In FIG. 13, it is assumed that the Absolute TA information is provided by a cell change command.

[0239] Referring to FIG. 11, in S1101, the UE camps on the first cell and performs a random access (RA) procedure for the first cell. After the RA procedure is successfully completed, the UE connects to the Central Unit (CU) of the network. The UE obtains the Absolute TA of the first cell during the RA procedure.

[0240] In S1302, the UE receives candidate cell information regarding candidate cells belonging to the CU. The candidate cell information includes a candidate cell identifier, UL resources of the candidate cell, and the like.

[0241] In S1303, the UE exchanges data with the network of the first cell using the absolute TA of the first cell.

[0242] In S1304, the UE receives a cell change command from the network to the second cell. The cell change command includes an identifier of the second cell.

[0243] Also, the UE receives the absolute TA information of the second cell by the cell change command. Alternatively, the UE receives the absolute TA information of the candidate cell. The absolute TA information also includes the valid time of the absolute TA.

[0244] In S1305, the UE moves to the indicated second cell.

[0245] In S1306, the UE checks whether a valid absolute TA for the second cell is available.

[0246] If a valid absolute TA for the second cell is available, the UE does not perform an RA procedure in S1307 and performs UL transmission in the second cell using the absolute TA of the second cell.

[0247] On the other hand, if the absolute TA value for the second cell cannot be used, the UE performs an RA procedure for the second cell and obtains the absolute TA of the second cell in S1308. After obtaining the absolute TA of the second cell, the UE performs UL transmission in the second cell using the absolute TA of the second cell.

[0248] According to the present disclosure, when a cell is changed to another cell belonging to the same CU, UL transmission is performed without performing an RA procedure. Therefore, the time for performing the RA procedure can be omitted, and the delay due to cell change can be reduced.

Claims

1. A method performed by a UE (User Equipment) in a wireless communication system, receiving information about a candidate cell from a first cell; receiving, from the first cell, a cell change command for a connection switch from the first cell to a second cell among the candidate cells; and and performing cell switching by skipping a Random Access (RA) procedure related to the second cell based on the cell change command including a valid timing advance (TA) value. method.

2. and performing the cell switching based on an RA procedure associated with the second cell based on the cell change command not including the valid TA value. The method of claim 1.

3. The valid TA values include absolute TA values. The method of claim 1.

4. the cell change command includes an identifier of the second cell. The method of claim 1.

5. The first cell and the second cell belong to the same radio resource control (RRC) entity. The method of claim 1.

6. In a wireless communication system, a UE (User Equipment) at least one transceiver; at least one processor; and and at least one computer memory operably connected to the at least one processor and storing instructions that, when executed, cause the at least one processor to perform operations for the UE, the operations including: receiving information about a candidate cell from a first cell; receiving, from the first cell, a cell change command for a connection switch from the first cell to a second cell among the candidate cells; and and performing cell switching by skipping a Random Access (RA) procedure related to the second cell based on the cell change command including a valid timing advance (TA) value. UE.

7. The operation is and performing the cell switching based on an RA procedure associated with the second cell based on the cell change command not including the valid TA value. The UE of claim 5.

8. The valid TA values include absolute TA values. The UE of claim 5.

9. the cell change command includes an identifier of the second cell. The UE of claim 5.

10. The first cell and the second cell belong to the same radio resource control (RRC) entity. The UE of claim 5.

11. An apparatus for a UE (User Equipment), comprising: at least one processor; and and at least one computer memory operably connected to the at least one processor and storing instructions that, when executed, cause the at least one processor to perform operations for the UE, the operations including: receiving information about a candidate cell from a first cell; receiving, from the first cell, a cell change command for a connection switch from the first cell to a second cell among the candidate cells; and and performing cell switching by skipping a Random Access (RA) procedure related to the second cell based on the cell change command including a valid timing advance (TA) value. Device.

12. 1. A computer-readable storage medium, comprising: The storage medium stores at least one program code including instructions that, when executed, cause at least one processor to perform an operation for a Radio Link Control (RLC) entity of a User Equipment (UE), the operation comprising: receiving information about a candidate cell from a first cell; receiving, from the first cell, a cell change command for a connection switch from the first cell to a second cell among the candidate cells; and and performing cell switching by skipping a Random Access (RA) procedure related to the second cell based on the cell change command including a valid timing advance (TA) value. A computer-readable storage medium.

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