Method and apparatus for deactivating and activating a secondary base station in a wireless communication system

Abstract

This disclosure relates to a communication technology for integrating IoT technology with a 5G communication system for supporting data transmission rates higher than those of 4G systems, and a system therefor. This disclosure also relates to a method performed by a terminal in a wireless communication system, and may include the steps of: receiving a deactivation command regarding a secondary cell group (SCG) from a first base station associated with a primary cell group (MCG); performing a measurement on at least one beam associated with the SCG while the SCG is deactivated; and performing random access to a second base station associated with the SCG based on a random access preamble associated with a downlink beam when a beam failure is detected based on the measurement.

Description

Technical Field

[0001] This disclosure relates to a method for using dual connectivity (DC) in a wireless communication system. More specifically, this disclosure relates to a method for deactivating and reactivating an SCG when a primary base station (primary gNB or primary cell group (MCG)) and a secondary base station (secondary gNB or secondary cell group (SCG)) are used simultaneously in a DC. Background Technology

[0002] Since the commercialization of 4G communication systems, significant efforts have been made to develop and improve 5G or near-5G communication systems to meet the ever-growing demand for wireless data services. Therefore, 5G or near-5G communication systems are also referred to as "super-4G networks" or "post-LTE systems." To achieve higher data rates, 5G communication systems implemented in extremely high frequency (mmWave) bands (e.g., the 60GHz band) are being considered. To reduce path loss and increase transmission distance in the mmWave band, various technologies are being considered for 5G communication systems, including beamforming, massive MIMO, full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive MIMO. Furthermore, to improve the system network in 5G communication systems, technologies such as evolved small cells, advanced small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, coordinated multipoint (CoMP), and interference cancellation are under development. In addition, advanced coding and modulation (ACM) schemes such as hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), as well as advanced access technologies such as filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) are also under development for 5G communication systems.

[0003] Simultaneously, the internet is evolving from a human-centric network where humans create and consume information into the Internet of Things (IoT), where distributed elements or things process and exchange information. The Internet of Everything (IoE) technology, combining IoT with big data processing through connections to cloud servers, has also emerged. To realize IoT services, foundational technologies related to sensing, wired / wireless communication and network infrastructure, service interfaces, and security are required, while technologies interconnecting things such as sensor networks, machine-to-machine (M2M), or machine-type communication (MTC) are under development. In the IoT environment, it is possible to provide intelligent internet technology services that collect and analyze data created by interconnected things to add new value to human life. Through the integration and combination of existing information technologies with technologies from various fields, IoT technology can be applied to a wide range of areas, such as smart homes, smart buildings, smart cities, smart or connected cars, smart grids, healthcare, smart consumer electronics, and advanced medical services.

[0004] Therefore, various attempts have been made to apply 5G communication systems to IoT networks. For example, sensor networks and machine-to-machine or machine-type communication are being achieved using 5G communication technologies including beamforming, MIMO, and array antennas. The application of cloud RAN as a means of processing the aforementioned big data technologies can be seen as an example of the convergence of 5G and IoT technologies.

[0005] With the recent development of wireless communication technology, research is actively underway on dual connectivity (DC) in wireless communication systems. In particular, issues regarding the deactivation and reactivation of secondary cell groups (SCGs) exist within this dual connectivity technology. Therefore, a method and apparatus are needed for the smooth operation of mobile communication systems. Summary of the Invention

[0006] [Technical Issues]

[0007] Based on the above discussion, this disclosure proposes a method for uplink timing of a secondary cell group (SCG) that is disabled in a wireless communication system for terminal management, a method for detecting and recovering beam faults, and a method for reactivating the SCG.

[0008] [Solution to the problem]

[0009] To address the above issues, the method disclosed herein, performed by a terminal, may include: receiving a deactivation command for a secondary cell group (SCG) from a first base station associated with a primary cell group (MCG); performing measurements on at least one beam associated with the SCG while the SCG is deactivated; and performing random access to a second base station associated with the SCG based on a random access preamble associated with the downlink beam if a beam failure is detected based on the measurements.

[0010] Additionally, the terminal disclosed herein may include at least one transceiver; and at least one processor, wherein the at least one processor may be configured to: receive a deactivation command for a secondary cell group (SCG) from a first base station associated with a primary cell group (MCG); perform measurements on at least one beam associated with the SCG while the SCG is deactivated; and perform random access to a second base station associated with the SCG based on a random access preamble associated with a downlink beam if a beam failure is detected based on the measurements.

[0011] [Advantages of the Invention]

[0012] When the primary cell group (MCG) is reactivated by the terminal for a deactivated secondary cell group (SCG), the apparatus and method according to embodiments of the present disclosure enable the terminal to manage the effective uplink timing and effective beam of the corresponding SCG, thereby reducing latency.

[0013] Furthermore, even when the SCG is in a deactivated state, the apparatus and method according to embodiments of this disclosure can enable the terminal to run and monitor the time alignment timer (TAT) associated with the SCG, thereby reducing uplink transmission latency when the SCG is reactivated.

[0014] Furthermore, the apparatus and methods according to embodiments of this disclosure enable the terminal to perform beam fault detection (BFD) and beam fault recovery (BFR) when the SCG is in a deactivated state, thereby reducing downlink transmission latency when the SCG is reactivated. Attached Figure Description

[0015] Figure 1a This is a diagram illustrating the architecture of the new radio (NR) system mentioned in this disclosure.

[0016] Figure 1b This is a diagram illustrating the structure of radio protocols in the Long Term Evolution (LTE) and NR systems mentioned in this disclosure.

[0017] Figure 1c This is a diagram used to illustrate carrier aggregation in a UE.

[0018] Figure 1dThis is a diagram used to illustrate the concept of multiple connectivity in LTE and NR.

[0019] Figure 1e This diagram illustrates the contention-based four-step random access process for a UE to perform base station operations.

[0020] Figure 1f This diagram illustrates the two-step random access process used by a UE to perform base station access.

[0021] Figure 1g This is a schematic diagram of the frame structure of the downlink and uplink channels when performing beam-based communication in an NR system.

[0022] Figure 1h This diagram illustrates the necessity and role of the uplink timing synchronization process in a system using Orthogonal Frequency Division Multiplexing (OFDM).

[0023] Figure 1i This is a schematic diagram of the sequence of UE operations when the PSCell's Time Alignment Timer (TAT) expires in a state where the SCG configured in the UE is disabled.

[0024] Figure 1j This is a schematic diagram of the sequence of UE operations when the UE performs beam fault detection and recovery of the PSCell while the UE is in a state where the configured SCG is disabled.

[0025] Figure 1k This is the first schematic diagram of the sequence of UE operations when the UE reactivates the SCG in a state where the configured SCG is deactivated.

[0026] Figure 11 This is the second schematic diagram of the sequence of UE operations when the UE reactivates the SCG in a state where the configured SCG is deactivated.

[0027] Figure 1m The illustration shows a configuration of a UE according to an embodiment of the present disclosure. Detailed Implementation

[0028] In the description of embodiments in this specification, descriptions of technical details well-known in the art and not directly related to this disclosure may be omitted. This is to convey the spirit of this disclosure more clearly without ambiguity by omitting unnecessary descriptions.

[0029] Similarly, in the accompanying drawings, some elements are exaggerated, omitted, or only briefly outlined. Furthermore, the size of each element does not necessarily reflect its actual size. The same reference numerals are used throughout the drawings to refer to the same or corresponding parts.

[0030] The advantages and features of this disclosure, as well as the methods for achieving these advantages and features, will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings. However, this disclosure is not limited to the embodiments disclosed below, but can be implemented in various different ways. The embodiments are provided merely to complete this disclosure and to fully inform those skilled in the art of its scope, and this disclosure is defined only by the scope of the claims. The same reference numerals are used throughout the specification to refer to the same parts.

[0031] Furthermore, it should be understood that the frames of a flowchart and the combination of the flowchart itself can be executed by computer program instructions. These computer program instructions can be loaded onto the processor of a general-purpose computer, a special-purpose computer, or a programmable data processing device, and the instructions, executed by the processor of the computer or programmable data processing device, create components for performing the functions described in the frames of the flowchart. To achieve this functionality in a certain way, the computer program instructions can also be stored in a computer-usable or readable storage device applicable to the special-purpose computer or programmable data processing device, and the computer program instructions stored in the computer-usable or readable storage device can potentially produce an article of art containing components for performing the functions described in the frames of the flowchart. Since computer program instructions can be loaded onto a computer or programmable data processing device, when the computer program instructions are executed on the computer or programmable data processing device as a process having a series of operations, they can provide steps for performing the functions described in the frames of the flowchart.

[0032] Additionally, each box in the flowchart may correspond to a module, segment, or code containing one or more executable instructions for performing one or more logical functions, or a portion thereof. It should also be noted that in some alternative cases, the functions described by the boxes may be executed in a different order than listed. For example, two boxes listed in sequence may be executed substantially simultaneously, or in reverse order depending on their corresponding functionality.

[0033] Here, the terms "unit," "module," etc., used in the embodiments can refer to software or hardware components capable of performing functions or operations, such as FPGAs or ASICs. However, "unit," etc., is not limited to hardware or software. Units, etc., can be configured to reside in addressable storage media or drive one or more processors. For example, units, etc., can refer to components such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, or variables. The functionality provided by components and units can be a combination of smaller components and units, and this functionality can be combined with other components and units to form larger components and units. In addition, components and units can be implemented as one or more processors in a driving device or secure multimedia card.

[0034] The operating principles of this disclosure will be described in detail below with reference to the accompanying drawings. In the following description of this disclosure, descriptions of well-known functions and structures incorporated herein may be omitted so as not to obscure the subject matter of this disclosure. Furthermore, the terms described below are defined in regard to their function in this disclosure, and these terms may vary according to the intent of the user, operator, or custom. Therefore, their meaning should be determined based on the entire contents of this specification.

[0035] For ease of description, those terms used in the following description to identify access nodes, indicate network entities, indicate messages, indicate interfaces between network entities, and indicate various identifying information are considered descriptive. Therefore, this disclosure is not limited to the terms described later, and other terms referring to objects with equivalent technical meanings may be used.

[0036] For ease of description, this disclosure uses the terms and names defined in the LTE and NR standards, which are the most recent standards defined by the 3rd Generation Partnership Project (3GPP) organization among existing communication standards. However, this disclosure is not limited to the terms and names above and can be applied equivalently to systems conforming to other standards. Specifically, this disclosure can be applied to 3GPP NR (or 5th generation (5G) mobile communication standards).

[0037] Figure 1a This is a diagram illustrating the architecture of the NR system mentioned in this disclosure. (Reference) Figure 1a The wireless communication system consists of multiple base stations 1a-05, 1a-10, 1a-15, and 1a-20, an Access and Mobility Management Function (AMF) 1a-20, and a User Plane Function (UPF) 1a-30. User Equipment (UE or terminal) 1a-35 connects to the external network via base stations 1a-05, 1a-10, 1a-15, or 1a-20 and UPF 1a-30.

[0038] Base stations 1a-05, 1a-10, 1a-15, and 1a-20 are access nodes of the cellular network and provide radio access to UEs connected to the network. That is, base stations 1a-05, 1a-10, 1a-15, and 1a-20 support the connection between the UE and the core network (CN, specifically, the CN in NR is called 5GC (5th generation core)) to serve user services, where they perform scheduling by collecting UE state information (such as buffer state, available transmission power state, and channel state). Simultaneously, in communication, the user plane (UP) related to actual user data transmission and the control plane (CP) related to connection management can be partitioned and configured separately; in this diagram, gNB 1a-05 and 1a-20 use the UP and CP technologies defined in NR technology, and ng-eNB 1a-10 and 1a-15 use the UP and CP technologies defined in LTE technology, but are connected to the 5GC.

[0039] The AMF / SMF 1a-25 is an entity responsible for various control functions and UE mobility management functions and is connected to multiple base stations, while the UPF 1a-30 is a gateway device that provides data transmission.

[0040] Figure 1b This is a diagram illustrating the structure of the radio protocols in the LTE and NR systems mentioned in this disclosure.

[0041] refer to Figure 1bIn the UE or eNB / gNB, the radio protocol of the LTE or NR system consists of Packet Data Convergence Protocol (PDCP) 1b-05 or 1b-40, Radio Link Control (RLC) 1b-10 or 1b-35, and Media Access Control (MAC) 1b-15 or 1b-30. PDCP 1b-05 or 1b-40 performs IP header compression and decompression, and RLC 1b-10 or 1b-35 reconfigures PDCP PDUs (Packet Data Units) to appropriate sizes. MAC 1b-15 or 1b-30 connects to multiple RLC entities in the UE, multiplexing RLC PDUs into MAC PDUs and demultiplexing MACP PDUs into RLC PDUs. The Physical Layer (PHY) 1b-20 or 1b-25 uses channel coding and modulation to convert higher-layer data into OFDM symbols and transmit these symbols via a radio channel, or it demodulates OFDM symbols received via the radio channel, performs channel decoding, and forwards the result to the higher layer. Additionally, in the Physical Layer, HARQ (Hybrid ARQ) is used for additional error correction, and the receiver transmits a bit indicating that it has received a packet from the transmitter. This is called HARQ ACK / NACK information. In LTE, downlink HARQ ACK / NACK information for uplink data transmission is transmitted via the Physical Hybrid ARQ Indicator Channel (PHICH); in NR, the need for retransmission or new transmission can be determined based on the scheduling information of the corresponding UE on the Physical Dedicated Control Channel (PDCCH), which is used to transmit downlink / uplink resource allocation, etc. This is because asynchronous HARQ is applied in NR. Uplink HARQ ACK / NACK information for downlink data transmission can be sent via physical channels (Physical Uplink Control Channel (PUCCH) or Physical Uplink Shared Channel (PUSCH)). Typically, the PUCCH is sent in the uplink of the PCell, which will be described later; however, when the UE supports it, the PUCCH can be additionally provided to the UE by the base station via the SCell (referred to as PUCCHSCell), which will be described later.

[0042] Although not shown in the diagram, the Radio Resource Control (RRC) layer exists on top of the PDCP layer in both the UE and the base station, and the RRC layer can send and receive configuration control messages related to connection and measurement for radio resource control.

[0043] Meanwhile, the PHY layer can consist of one or more frequencies / carriers, and the technique for simultaneously configuring and using multiple frequencies in a single base station is called carrier aggregation (CA). A single carrier can be used for communication between the UE and the base station (eNB in ​​LTE or gNB in ​​NR), but when CA is used, the primary carrier and one or more secondary carriers can be used for communication, thus significantly increasing the data transmission rate by the amount corresponding to the number of additional secondary carriers. In LTE, the cell in a base station that utilizes the primary carrier is called the primary cell (PCell), while the cell that utilizes the secondary carrier is called the secondary cell (SCell). The technique for extending CA functionality to two base stations is called dual connectivity (DC). In DC, the UE is simultaneously connected to both the primary base station (primary E-UTRAN NodeB, referred to as MeNB) and the secondary base station (secondary E-UTRAN NodeB, referred to as SeNB); cells belonging to the MeNB are called the primary cell group (MCG), and cells belonging to the SeNB are called the secondary cell group (SCG). Each cell group has a representative cell; the representative cell of the MCG is called the primary cell (PCell), while the representative cell of the SCG is called the primary-secondary cell (PSCell). When using NR, the UE can simultaneously utilize LTE and NR by using an LTE-based MCG and an NR-based SCG. In NR, a maximum of 16 serving cells can be provided for each cell group (i.e., MCG or SCG) (PCell and SCell for MCG; PSCell and SCell for SCG).

[0044] Although not shown in the diagram, the Radio Resource Control (RRC) layer exists on top of the PDCP layer in both the UE and the base station, and the RRC layer can send and receive connection and measurement-related configuration control messages for radio resource control. For example, it is possible to instruct the UE to perform measurements using RRC layer messages, and the UE can report measurement results to the base station using RRC layer messages.

[0045] Figure 1c This is a diagram used to illustrate carrier aggregation in a UE.

[0046] refer to Figure 1c A base station can transmit and receive multiple carriers across multiple frequency bands. For example, when base station 1c-05 transmits carrier 1c-15 with a center frequency f1 and carrier 1c-10 with a center frequency f3, a conventional UE can use either of these carriers to transmit and receive data. However, a UE with carrier aggregation capability can transmit data to and receive data from multiple carriers simultaneously. Base station 1c-05 can assign more carriers to UE 1c-30 with carrier aggregation capability as needed, thereby increasing the data rate of UE 1c-30.

[0047] In the traditional sense, when a cell consists of a downlink carrier and an uplink carrier provided by a single base station, carrier aggregation can be understood as a situation where a UE simultaneously transmits and receives data through several cells. Therefore, the maximum data rate can increase proportionally to the number of aggregated carriers.

[0048] In the following description of this disclosure, for a UE, data reception via a downlink carrier and data transmission via an uplink carrier can be conceptually equivalent to data transmission and reception via a control and data channel provided by a cell corresponding to the center frequency and frequency band characterizing the above carrier. Furthermore, for ease of explanation, embodiments of this disclosure will be described based on an LTE system; however, this disclosure can be applied to various wireless communication systems that support carrier aggregation.

[0049] Even with or without carrier aggregation, the uplink transmission output must be maintained at an appropriate level because uplink transmission (i.e., from the UE to the base station) causes interference in the uplink direction of another cell. To this end, in order to perform uplink transmission, the UE calculates the uplink transmission output using a specific function and performs uplink transmission using the calculated uplink transmission output. For example, the UE calculates the required uplink transmission output value by inputting the specific function with scheduling information at the modulation and coding scheme (MCS) level to be applied, as well as input values ​​for estimating channel conditions (such as path loss values), and performs uplink transmission by applying the calculated required uplink transmission output value. The uplink transmission output value that can be applied by the UE is limited by the UE's maximum transmission value; and if the calculated required transmission output value exceeds the UE's maximum transmission value, then the UE performs uplink transmission by applying the maximum transmission value. In this case, the quality of uplink transmission may be degraded because insufficient uplink transmission output is applied. The base station preferably performs scheduling such that the required transmission output does not exceed the maximum transmission output. However, since the base station cannot identify some parameters such as path loss, the UE transmits a Power Headroom Report (PHR) when necessary to inform the base station of its available transmission output (power headroom, PH) status.

[0050] Factors affecting available transmission output include 1) the amount of allocated transmission resources, 2) the MCS to be applied to uplink transmission, 3) the path loss of the associated downlink carrier, and 4) the cumulative output adjustment command value. The path loss (PL) or cumulative output adjustment command value can be different for individual uplink carriers; if multiple uplink carriers are clustered in a single UE, then configuring PHR transmission for each uplink carrier is appropriate. However, for efficient PHR transmission, the UE can report all PHs of multiple uplink carriers on a single uplink carrier. Depending on the operational strategy, it may be necessary to transmit PHs of carriers that have not yet occurred during actual PUSCH transmission. Therefore, in this case, the scheme of reporting all PHs of multiple uplink carriers on a single uplink carrier may be more efficient. For this purpose, the existing PHR must be extended. Multiple PHs to be included in a single PHR will be configured according to a preset order.

[0051] A PHR (Progressive Backhaul) is typically triggered when the path loss of the connected downlink carrier changes beyond a specific reference value, when the PHR disable timer expires, or when a specific period has elapsed since the PHR was generated. Even if a PHR is triggered, the UE does not transmit it immediately but waits until a possible uplink transmission point (e.g., the point at which uplink transmission resources are allocated). This is because the PHR is not information that needs to be processed immediately.

[0052] Figure 1d This is a diagram used to illustrate the concept of biconnectivity.

[0053] Dual connectivity (DC) allows a UE to connect to and use two base stations simultaneously. This diagram illustrates UE 1d-05 transmitting and receiving data by simultaneously connecting to a macro base station 1d-00 using LTE technology and a small cell base station 1d-10 using NR technology. This is called EN-DC (E-UTRAN-NR Dual Connectivity). The macro base station is called MeNB (Primary E-UTRAN NodeB), and the small cell base station is called SgNB (Secondary 5G NodeB). Several small cells can exist within the service area of ​​the MeNB, and the MeNB is connected to the SgNB via a wired backhaul network 1d-15. The set of serving cells provided by the MeNB is called the Primary Cell Group (MCG) 1d-20, and one serving cell of the MCG must be the primary cell (PCell) 1d-25, which has all the functions that traditional cells perform, such as connection establishment, connection reconstruction, and handover. Additionally, the PCell has a PUCCH as the uplink control channel. Serving cells other than the PCell are called secondary cells (SCell) 1d-30. Figure 1dThe illustration depicts a scenario where the MeNB provides one SCell and the SeNB provides three SCells. The set of serving cells provided by the SeNB is referred to as the Secondary Cell Group (SCG) 1d-40. When the UE sends and receives data from two base stations, the MeNB issues commands to the SeNB to add, change, or remove serving cells provided by the SeNB. To issue such commands, the MeNB can configure the UE as a measurement service and neighboring cell. The UE must report measurement results to the MeNB according to the configuration information. In order for the SeNB to efficiently send and receive data from the UE, a serving cell is needed that plays a similar role to the PCell of the MCG, and this is referred to in this disclosure as the Primary SCell (PSCell). The PSCell is identified as one of the serving cells of the SCG and is characterized by having a PUCCH as an uplink control channel. The UE uses the PUCCH to send HARQ ACK / NACK information, Channel State Information (CSI), Scheduling Requests (SR), etc., to the base station.

[0054] Meanwhile, in the DC scenario, MCG and SCG each have separate MAC entities. That is, there are two MAC entities in the DC. Therefore, various MAC functions (such as PHR reporting) are executed independently for each base station.

[0055] Figure 1e This diagram illustrates a contention-based four-step random access process performed by the UE in various scenarios requiring random access to a base station (such as initial access, reconnection, and handover).

[0056] In order to access base station 1e-03, UE 1e-01 can, according to the... Figure 1e The description is used to select the PRACH and transmit the random access preamble (1e-11) via the corresponding PRACH. One or more UEs may transmit random access preambles simultaneously via PRACH resources. A PRACH resource may span a subframe or may use only some symbols within a single subframe. Information about the PRACH resources is included in system information broadcast by the base station (e.g., SIB 1 (System Information Block 1)), and therefore it is possible to identify which time-frequency resource should be used to transmit the preamble. Furthermore, the random access preamble is a specially designed sequence that can be received even if transmitted before full synchronization with the base station, and according to the standard, multiple preamble identifiers (indices) may exist; if multiple preamble identifiers exist, the preamble transmitted by the UE may be a preamble randomly selected by the terminal or a specific preamble specified by the base station.

[0057] Upon receiving the preamble, the base station can send a Random Access Response (RAR) message (also known as Msg2) (1e-21) to the UE. The RAR message may include identifier information for the preamble used in step 1e-11, and may include uplink transmission timing adjustment information, uplink resource allocation information to be used in subsequent steps (i.e., step 1e-31), temporary UE identifier information, etc. For example, when multiple UEs attempt random access in step 1e-11 by sending different preambles, the RAR message may include responses for individual preambles. In this case, preamble identifier information may be sent to indicate which preamble the corresponding response is for. The uplink resource allocation information included in each response for each preamble is detailed information about the resources to be used by the UE in step 1e-31, and may include the physical location and size of the resources, the modulation and coding scheme (MCS) used for transmission, power adjustment information during transmission, etc. The temporary UE identifier information may be a value sent to be used when a UE that has already sent a preamble but does not have an identifier assigned by the base station for communicating with the base station performs initial access.

[0058] In addition to responses to individual preambles(s), the RAR message may optionally include a backoff indicator (BI). The backoff indicator can be a sent value that randomly delays transmission based on its value, rather than immediately retransmitting the preamble if retransmission is required due to unsuccessful random access. More specifically, the UE may have to retransmit the random access preamble if it does not receive the RAR correctly or if contention resolution (described later) is not correctly implemented. Here, the value indicated by the backoff indicator can be an index value, and the UE randomly selects a value from 0 to the value indicated by the index and retransmits the random access preamble after the time corresponding to the selected value. For example, if the base station indicates 5 (i.e., 60ms) as the BI value, when the UE randomly selects a value of 23ms from the range of 0ms to 60ms, the UE can store the selected value in a variable called PREAMBLE_BACKOFF and perform the process of retransmitting the preamble after 23ms. If there is no transmission backoff indicator, the UE will immediately send the random access preamble when it needs to be retransmitted due to unsuccessful random access.

[0059] [Table 1]

[0060]

[0061]

[0062] RAR messages should be sent within a preset time period starting from a specific time after the preamble is sent, and this time period is called the 'RAR window'. The RAR window begins at a point in time when a specific time has elapsed since the preamble was sent. The specific time may be the time when the PDCCH for scheduling RAR messages is first monitored. Furthermore, the length of the RAR window may be a specific value set by the base station in a system information message broadcast by the base station for each PRACH resource or for each set of one or more PRACH resources. On the other hand, when sending a RAR message, the base station schedules the RAR message via the PDCCH, and the corresponding scheduling information can be scrambled using a Random Access Radio Network Temporary Identifier (RA-RNTI). The RA-RNTI is mapped to the PRACH resource used to send message 1e-11; a UE that has already sent a preamble via a specific PRACH resource can determine whether a corresponding RAR message exists by attempting to receive the PDCCH based on the corresponding RA-RNTI. That is, if the RAR message is a response to the preamble sent by the UE in step 1e-11, as shown in the diagram, then the RA-RNTI used for scheduling the RAR message may include information about the corresponding transmission 1e-11. Therefore, RA-RNTI can be calculated using the following equation.

[0063] RA-RNTI=1+s_id+14×t_id+14×80×f_id+14×80×8×ul_carrier_id (Equation 1)

[0064] Here, s_id is the index corresponding to the first OFDM symbol in the preamble transmission in step 1e-11, and has a value of 0 ≤ s_id < 14 (i.e., the maximum number of OFDM symbols in a time slot). Furthermore, t_id is the index corresponding to the first time slot in the preamble transmission in step 1e-11, and has a value of 0 ≤ t_id < 80 (i.e., the maximum number of time slots in a system frame (10 ms)). Additionally, f_id indicates the ordinality of the PRACH resource on the frequency of the preamble transmission in step 1e-11, and has a value of 0 ≤ f_id < 8 (i.e., the maximum number of PRACHs on the same frequency within the same time period). Furthermore, when two carriers are used in the uplink of a cell, ul_carrier_id is a factor used to distinguish whether the preamble is transmitted via the normal uplink (NUL) (0 in this case) or via the supplementary uplink (SUL) (1 in this case).

[0065] Upon receiving the RAR message, the UE sends different messages using the resources allocated via the RAR message, according to the various purposes described above (1e-31). This message is the third message sent in this illustrative diagram and is also referred to as Msg3 (that is, the preamble in step 1e-11 is referred to as Msg1, and the RAR in step 1e-21 is referred to as Msg2). As examples of Msg3 sent by the UE, the RRCSetupRequest message, as an RRC layer message, is sent for initial access, the RRCReestablishmentRequest message is sent for reconnection, and the RRCReconfigurationComplete message is sent for handover. Alternatively, a Buffer Status Report (BSR) message can be transmitted to request resources.

[0066] Subsequently, in the case of initial transmission (i.e., when Msg3 does not include base station identifier information previously assigned to the UE, etc.), the UE receives a contention resolution message (1e-41) from the base station; the contention resolution message includes the content actually sent by the UE in Msg3, so that even if there are multiple UEs that have selected the same preamble in step 1e-11 or 1e-13, it is possible to notify which UE the response is for.

[0067] Figure 1f This diagram illustrates the two-step random access process for a UE to perform base station access.

[0068] As above Figure 1c As described, in a typical contention-based random access procedure, at least four steps are performed, and if an error occurs in one step, the process may be further delayed. Therefore, scenarios where the random access procedure can be shortened to a two-step process can be considered.

[0069] To this end, the UE sends MsgA (1f-15) to the base station, which continuously transmits the preamble (Msg1) (1f-11) (corresponding to 1c-11) and Msg3 (1f-13) (corresponding to 1c-31) for the four-step random access procedure. Then, the base station sends MsgB (1f-19) to the UE, which includes information from Msg2 (RAR) (corresponding to 1c-21) and Msg4 (corresponding to 1c-41) for the four-step random access procedure, thus shortening the random access procedure. Figure 1f The procedure for this situation is described in part 1f-00.

[0070] Here, when shown in chronological order, MsgA may consist of PRACH resource 1f-21 for transmitting Msg1, PUSCH resource 1f-23 for transmitting Msg3, and gap resource 1f-22 for resolving interference issues that may arise due to PUSCH resource transmission. Furthermore, Msg3 includes information about Msg1, so that it is known that Msg3 was transmitted by a UE that has already transmitted a specific preamble (Msg1).

[0071] As above Figure 1c As described, a UE performs random access for various purposes. For example, a UE may perform random access to send connection messages when not yet connected to a base station or to send messages to restore a connection when an established connection is lost due to an error. In this case, these messages belong to the Common Control Channel (CCCH). Control messages belonging to the CCCH include RRCSetupRequest (transition from idle mode (RRC_IDLE) to connected mode), RRCResumeRequest (transition from inactive mode (RRC_INACTIVE) to connected mode), RRCReestablishmentRequest (restore connection), and RRCSystemInfoRequest (request system information broadcast by the base station). Therefore, when a UE performs two-step random access, the UE may send MsgA including the above messages. If the UE performs random access in the connected state after connecting to a base station, the UE sends a C-RNTIMAC CE including the UE identifier information via MsgA, thereby notifying the UE that the subject performing the random access is the corresponding UE.

[0072] Upon receiving both Msg1 and Msg3 included in MsgA, the base station sends MsgB (1f-19) to the UE. Here, MsgB may include the aforementioned BI. Additionally, when MsgA includes the aforementioned CCCH message, it includes uplink transmission timing information (Timing Advance Command (TAC)) sent via Msg2, a temporary UE identifier (temporary C-RNTI) to be used by the UE for the base station, and contention resolution related information (UE contention resolution identifier) ​​sent via Msg4. Furthermore, if the UE is already connected to the base station and sends a C-RNTI MAC CE including UE identifier information via MsgA, then the base station's message for allocating resources to the corresponding UE via PDCCH using the corresponding UE identifier (C-RNTI) becomes MsgB.

[0073] On the other hand, if multiple MsgA are sent in step 1f-15, causing a collision, the base station may only receive Msg1 (1f-61) included in MsgA, but not Msg3 (1f-63). In this case, the base station can send Msg2 (1f-65) to the terminal instead of MsgB (1f-19), thereby enabling a handover. Figure 1c The four-step random access procedure described herein is used to execute the remaining random access procedures. Figure 1f This is described in part 1f-50, and the mode of switching from two-step random access to four-step random access is called fallback mode. That is, when the base station receives messages (1f-21) from the UE only via PRACH resources (1f-61), the base station responds to the corresponding UE using fallbackRAR (1f-65) similar to Msg2 used in the four-step random access process, thereby allowing the UE to send and receive Msg3 (1f-71) and Msg4 (1f-73) of the four-step random access process.

[0074] Figure 1g This is a schematic diagram of the frame structure of the downlink and uplink channels when performing beam-based communication in an NR system.

[0075] exist Figure 1g In this diagram, base station 1g-01 transmits signals in the form of beams to enable wider coverage or stronger signals (1g-11)(1g-13)(1g-15)(1g-17). Therefore, UE 1g-03 within the cell must transmit and receive data using a specific beam transmitted by the base station (beam #1 (1g-13) in this illustrative diagram).

[0076] Furthermore, depending on whether the UE is connected to the base station, the UE's state can be divided into idle mode (RRC_IDLE) and connected mode (RRC_CONNECTED). Therefore, the base station does not know the location of a UE in idle mode.

[0077] If a UE in idle mode wants to switch to connected mode, it receives synchronization signal blocks (SSBs) 1g-21, 1g-23, 1g-25, and 1g-27 sent by the base station. These SSBs are signals sent periodically according to a periodicity set by the base station, and each SSB may include a primary synchronization signal (PSS) 1g-41, a secondary synchronization signal (SSS) 1g-43, and a physical broadcast channel (PBCH).

[0078] This illustrative diagram assumes a scenario where SSBs are transmitted for each beam. For example, assume that SSB#0 (1g-21) is transmitted using beam #0 (1g-11), SSB#1 (1g-23) is transmitted using beam #1 (1g-13), SSB#2 (1g-25) is transmitted using beam #2 (1g-15), and SSB#3 (1g-27) is transmitted using beam #3 (1g-17). In this illustrative diagram, it is assumed that the UE in idle mode is located at beam #1, but when the UE in connected mode performs random access, the UE selects the SSB received during the random access process.

[0079] Therefore, in this diagram, the UE receives SSB#1 transmitted via beam #1. After receiving SSB#1, the UE can obtain the physical cell identifier (PCI) of the base station through the PSS and SSS and receive the PBCH, enabling it to identify the identifier of the currently received SSB (i.e., #1), the position of the currently received SSB within a 10ms frame, and the SFN of the currently received SSB within a system frame number (SFN) with a periodicity of 10.24 seconds. Furthermore, the PBCH includes a Master Information Block (MIB), and this MIB can indicate the position of System Information Block Type 1 (SIB1) that can receive broadcasts of more detailed cell configuration information. Upon receiving SIB1, the UE can identify the total number of SSBs transmitted by the base station and the location of the Physical Random Access Channel (PRACH) timing (in this illustrative diagram, it is assumed that a PRACH timing is allocated every 1 ms: from 1g-30 to 1g-39). At this location, random access can be performed to transition to connected mode (more precisely, a preamble, a physical signal specifically designed for uplink synchronization, can be transmitted). Furthermore, based on the above information, the UE can identify which PRACH timing is mapped to which SSB index. For example, in this illustrative diagram, it is assumed that a PRACH timing is allocated every 1 ms, and that each PRACH timing is allocated 1 / 2 SSB (i.e., 2 PRACH timings per SSB). Therefore, the diagram illustrates a scenario where two PRACH timings are allocated to each SSB, starting from the PRACH timings based on the SFN value. In other words, PRACH opportunities 1g-30 and 1g-31 are assigned to SSB#0, PRACH opportunities 1g-32 and 1g-33 are assigned to SSB#1, and so on. After all SSBs have been assigned, PRACH opportunities 1g-38 and 1g-39 can be reassigned to the first SSB.

[0080] Therefore, the UE identifies the positions of PRACH times 1g-32 and 1g-33 for SSB#1, and then transmits a random access preamble at the earliest PRACH time (e.g., 1g-32) from the current time point among the PRACH times 1g-32 and 1g-33 corresponding to SSB#1. The base station that has already received the preamble at PRACH time 1g-32 knows that the corresponding UE has selected SSB#1 and transmitted the preamble, and therefore, when performing subsequent random access, it transmits and receives data through the corresponding beam.

[0081] Simultaneously, when a UE in a connected state moves from its current (source) base station to a target base station due to handover or other reasons, the UE performs random access to the target base station, whereby the UE selects an SSB and performs the random access transmission operation as described above. Additionally, during handover, the source base station sends a handover command to the UE to move to the target base station. In this case, the above message can assign a dedicated random access preamble identifier to the corresponding UE for each SSB of the target base station for use when performing random access to the target base station. Here, the base station may not assign dedicated random access preamble identifiers to all beams (depending on the UE's current location or other locations), and correspondingly, may not assign dedicated random access preambles to some SSBs (e.g., dedicated random access preambles only assigned to beams #2 and #3). If no dedicated random access preamble is assigned to the SSB selected by the UE for preamble transmission, then the UE randomly selects a contention-based random access preamble to perform random access. For example, in this diagram, it is possible for the UE to send a dedicated preamble at beam #3 when retransmitting the random access preamble after initially attempting random access at beam #1 but failing. In random access, that is, within a random access procedure, when the current preamble retransmission occurs, contention-based and contention-free random access procedures can be mixed, depending on whether a dedicated random access preamble is assigned to the SSB selected for each preamble transmission.

[0082] Additionally, if a UE suddenly moves within a base station, it can leave the beam currently used for data transmission and reception, even without the aforementioned handover. If the base station does not recognize this and does not change the beam, a beam fault can be detected. This is called beam fault detection (BFD).

[0083] For example, if the base station has configured a connected UE to detect beam faults in the SSBs corresponding to beams #1 (1g-13) and #2 (1g-15) using RRC layer messages, when the UE moves to beam #3 (1g-17), since the UE fails to detect both beams #1 and #2, the UE's physical layer sends a beam fault instance indication to the UE's MAC layer. Upon receiving the beam fault instance indication, the MAC layer activates beamFailureDetectionTimer (or reactivates beamFailureDetectionTimer if it is already running) and increments the counter (BFI_COUNTER) by 1. When the counter value reaches the threshold (beamFailureInstanceMaxCount) set by the RRC layer message (i.e., equal to or greater than), the UE determines that a beam fault has occurred and performs a process to recover from the beam fault (beam fault recovery).

[0084] This type of beam failure can occur in either a SpCell or a SCell. For example, a beam failure can occur in a SCell when a SpCell uses low frequencies that hardly use the beam, and a SCell uses high frequencies that utilize narrow beams.

[0085] If a beam failure occurs in a SCell, the UE can notify the specific SCell of this fact by sending a MAC Control Element (MAC CE) as a MAC layer control message. More specifically, additional information about which SCell has the beam failure and which beam from the corresponding SCell should be used can also be included in the MAC CE. To send the MAC CE, the UE should request uplink resources from the base station. A MAC CE used for this purpose is called a Beam Failure Recovery (BFR) MAC CE or a SCell BFR MAC CE.

[0086] In existing LTE and NR, uplink resource requests are made via Transmission Buffer Status Report (BSR) MAC CE; in the case of a regular BSR among the conditions that trigger BSR transmission, the base station can be allowed to perform uplink allocation for transmitting BSR by triggering a scheduling request (SR) and sending 1 bit of information to the base station via the PUCCH resources previously allocated for the SR assigned by the RRC layer message.

[0087] However, in order to request the transmission of a BFR MAC CE, the base station can perform uplink allocation for transmitting the BFR MAC CE by sending 1 bit of information to the base station via the PUCCH resources previously allocated for the SR assigned for this purpose by the RRC layer message. After sending the SR, the UE with the uplink allocation sends the BFR MAC CE, which will be described later, to notify the base station that a BFR is required for the corresponding SCell.

[0088] If a beam failure occurs in the SpCell, the UE can recover from the beam failure using a random access procedure. For example, the base station can assign a dedicated random access preamble to each beam to prepare for a beam failure on the UE; for instance, if a dedicated preamble identifier is set for beam #3 in this diagram, when the UE selects beam #3 by performing random access after beam failure detection, it immediately notifies the base station that it has selected beam #3 due to beam failure detection by sending the corresponding dedicated preamble identifier, allowing the base station to adjust the beam for the corresponding UE. Alternatively, even when no dedicated random access preamble is assigned, the UE can perform contention-based random access to notify the base station that the corresponding UE is currently operating on the beam selected during the current random access period. Furthermore, the UE can send this message, including a separate additional message, to notify the base station that the UE has performed random access due to BFR.

[0089] Figure 1h This diagram illustrates the necessity and role of uplink timing synchronization in a system using an OFDM scheme.

[0090] UE1 (Terminal 1) represents the UE located near the base station (gNB), while UE2 (Terminal 2) represents the UE located far from the gNB. The first propagation delay time (T_pro1) represents the propagation delay time in radio transmission to UE1, and the second propagation delay time (T_pro2) represents the propagation delay time in radio transmission to UE2. For example... Figure 1h As shown in Figure 4, UE1 is located closer to the gNB than UE2, thus indicating that UE1 has a relatively smaller propagation delay time. (In Figure 4, T_pro1 is 0.333us, and T_pro2 is 3.33us)

[0091] When UE1 and UE2 are Figure 1h When a gNB in ​​a cell is powered on or when UE1 and UE2 are in idle mode, the following problem occurs: the uplink timing synchronization of UE1, the uplink timing synchronization of UE2, and the uplink timing synchronization of UE2 detected by the gNB within the cell do not match each other.

[0092] Mark (1h-01) indicates the timing synchronization of the uplink transmission of OFDM symbols for UE1, and (1h-03) indicates the timing synchronization of the uplink transmission of OFDM symbols for UE2. Considering the propagation delay time of the uplink transmissions for UE1 and UE2, the timing for the NB to receive the uplink OFDM symbols is indicated by (1h-05), (1h-07), and (1h-09), respectively. That is, the uplink symbol for UE1 indicated by (1h-01) is received by the gNB at the timing indicated by (1h-07) after its propagation delay time, and the uplink symbol for UE2 indicated by (1h-03) is received by the gNB at the timing indicated by (1h-09) after its propagation delay time. Figure 1h As shown, (1h-07) and (1h-09) are still before the uplink timing synchronization is established for UE1 and UE2. Therefore, it can be seen that the start timing (1h-05) of the NB that has received uplink OFDM symbols for decoding, the timing (1h-07) of receiving OFDM symbols from UE1, and the timing (1h-09) of receiving OFDM symbols from UE2 are different.

[0093] Therefore, the uplink symbols sent from UE1 and UE2 are not orthogonal and interfere with each other, resulting in the following problem: due to the above interference and the asynchrony between the uplink symbol reception timing (1h-07) and (1h-09) and (1h-05), the gNB is unable to successfully decode the uplink symbols (1h-01) and (1h-03) sent from UE1 and UE2.

[0094] The uplink timing synchronization process is a process of ensuring that the uplink symbol reception timing is equal for UE1, UE2, and NB. When the uplink timing synchronization process is complete, as indicated in (1h-11), (1h-13), and (1h-15), the timing for starting decoding of received uplink OFDM symbols in the NB, the timing for receiving uplink OFDM symbols from UE1, and the timing for receiving uplink OFDM symbols from UE2 are matched. More specifically, timing is matched by aligning the uplink symbol reception timing with the error within the cyclic prefix (CP) length, thereby enabling the base station to perform decoding.

[0095] During uplink timing synchronization, the base station sends timing advance (TA) information to the UE to provide information on how much timing should be adjusted. More specifically, based on a specific downlink (1h-21), the base station provides the UE with information on how early transmissions should be performed relative to the corresponding downlink.

[0096] Here, the TA information can be sent by the base station via the Timing Advance Command MAC Control Element (TAC MAC CE) or via a response message (Random Access Response, RAR) to the random access preamble sent by the UE performing random access, as will be described later. This applies to both LTE and NR.

[0097] To illustrate this more thoroughly using LTE as an example, in the case of RAR, the TA information is 12 bits, and correspondingly, it is transmitted through N... TA =TA*16 is used to perform the calculation. Additionally, in the case of TAC MAC CE, this TA information has a 6-bit TA value, and the calculation is based on the existing N... TA Value (N) TA,old The relative value of the change. That is, it follows the equation: N TA,new =N TA,old +(TA-31)*16. Therefore, the uplink transmission is earlier than the downlink reference (1h-23) by (N). TA *N TA_offset )*T s Transmission. For FDD systems, N TA_offset The value is 0, while for TDD systems, N TA_offset The value is 624. Furthermore, T s It has a value of 1 / (3048 * subcarrier spacing). Therefore, the UE can adjust the uplink transmission timing based on the TA information.

[0098] Upon receiving a TA (Time Alignment) message, the UE activates the time alignment timer (TAT). The TAT is a timer that indicates whether the TA is valid. That is, it determines that the TA is valid during the period when the TAT is running, but it cannot guarantee that the TA will be valid after the TAT expires.

[0099] When another TA information is received later, the UE reactivates the TAT; when the TAT expires after a specific period of time, the UE determines that the TA information received from the base station is no longer valid and stops uplink communication with the corresponding gNB.

[0100] When the timing is matched as described above, the uplink symbols sent from UE1 and UE2 can maintain orthogonality, and the gNB can successfully decode the uplink symbols (1h-01) and (1h-03) sent from UE1 and UE2.

[0101] Meanwhile, during the aforementioned random access procedure, it is unnecessary to apply the TA value when transmitting the preamble. This is because the preamble signal is designed to be decodeable even when arrival times are generally asynchronous, as described above. However, in the case of performing two-step random access, both data (PUSCH) and the preamble are transmitted. Here, the UE needs to define which N value should be applied. TA The value is used to send PUSCH.

[0102] Simultaneously, TATs are managed using TA groups (TAGs) as units. A TA group is a group unit of the serving cell (SpCell or SCell). The TAG to which an SpCell (i.e., PCell or PSCell) belongs is called the primary TAG (PTAG), and other TAGs are called secondary TAGs (STAGs). The base station assigns a tag-Id to the serving cell, thus allowing the UE to know which TAG the corresponding serving cell belongs to. The base station can configure the TAT length of each TAG for the UE using messages such as RRCReconfiguration, and when adding an SCell or PSCell to the UE, it can specify which tag-Id the corresponding serving cell belongs to using messages such as RRCReconfiguration.

[0103] Figure 1i This is a schematic diagram of the sequence of UE operations when the time alignment timer (TAT) of the PSCell (primary and secondary cell) expires while the SCG (secondary cell group) configured in the UE is disabled.

[0104] exist Figure 1i In this example, assume the UE is connected to a base station (Main Cell Group (MCG)) and is in connected mode with data communication enabled (RRC_CONNECTED) (1i-01). Subsequently, the UE receives configuration information from the MCG for adding an SCG including the aforementioned PSCell and sends an acknowledgment message to the MCG for this purpose (1i-03). The configuration information sent by the MCG can be received via an RRCReconfiguration message included in the RRC layer, and the acknowledgment message sent by the UE can be sent via an RRCReconfigurationComplete message included in the RRC layer. The configuration information may include at least one of the following: TA-related configuration information for the PSCell, parameters related to Beam Failure Detection (BFD), or parameters related to Beam Failure Recovery (BFR). The UE, having received the configuration information, can perform random access to the configured PSCell to utilize it.

[0105] Therefore, both MCG and SCG are activated, and the UE is in a state where it can send and receive data through both base stations. Furthermore, since the UE has already performed random access to the PSCell, when the TAT (Time Alignment Timer) of the TAG to which the PSCell belongs is running, the UE can send uplink data through the serving cell belonging to the corresponding TAG (Timing Advance Group). Additionally, before or after the TAT of the primary Timing Advance Group (PTAG) of the SCG expires, the base station can send a Physical Downlink Control Channel (PDCCH) order to the UE. The PDCCH order can be a PDCCH instructing the UE to begin random access. A UE that has received the PDCCH order can receive a new TA value (included in the Random Access Response (RAR)) and (re)activate the TAT during the random access process.

[0106] Simultaneously, the UE can receive a command from the MCG to disable the currently active SCG (1i-05). This can be determined by the MCG or SCG base station based on the amount of data transmitted through the SCG, etc. This disable command can be received as an RRC message at the Radio Resource Control (RRC) layer, or via a MAC Control Element (CE) as a control message at the Media Access Control (MAC) layer, or via the PDCCH. Upon receiving the disable command, the UE can send a message to the MCG confirming receipt of the corresponding command. This confirmation message can be sent as an RRC message at the RRC layer, or via a MAC Control Element (CE) as a control message at the MAC layer, or via HARQ feedback. Therefore, the UE can disable the corresponding SCG and stop data transmission and reception within the corresponding SCG (1i-07), thereby reducing power consumption due to communication with the corresponding SCG.

[0107] On the other hand, even after receiving a deactivation command, the UE may not stop the TAT of the PTAG to which the existing PSCell belongs. Therefore, even if the SCG is deactivated, the TAT of the PTAG to which the SCG's PCell belongs may still be running. Later, when the base station reactivates the SCG, if the TAT is running, the UE can immediately send uplink data to the SCG, thus reducing activation delay.

[0108] Therefore, if the TAT to which the PSCell belongs expires when the SCG is deactivated, the UE can reactivate the TAT by performing one of the following operations (1i-11).

[0109] The first option is for the UE to perform random access to the PSCell to obtain the TA for the PSCell. Here, when performing random access, the UE sends a C-RNTI MAC CE via Msg3 or MsgA, which includes the C-RNTI used in the SCG that was in the previous active state. Therefore, when the UE successfully completes random access, the UE reactivates the TAT, and the corresponding SCG remains in an inactive state.

[0110] The second option is for the UE to receive a PDCCH command from the MCG base station indicating that random access to the PSCell should be performed, and then perform random access to the PSCell. That is, in order to receive the updated TA value of the PSCell from the MCG base station before the PSCell's TAT ​​expires, the UE performs random access to the PSCell. For this purpose, a separate indicator indicating that random access to the PSCell should be performed is included in the PDCCH command.

[0111] The third option is a method where the UE receives the SCG activation instruction from the MCG base station. That is, before the PSCell's TAT ​​expires, the UE receives the SCG activation instruction from the MCG base station and activates the corresponding PSCell (i.e., SCG).

[0112] By using one of the above options, the UE continues to use the TA value in the inactive state, which can reduce uplink transmission latency when activated.

[0113] Figure 1j This is a schematic diagram of the sequence of UE operations when the UE performs beam fault detection and recovery of the PSCell (primary and secondary cell) while the configured SCG (secondary cell group) is disabled.

[0114] exist Figure 1j In this example, assume the UE is connected to a base station (Main Cell Group (MCG)) and is in connected mode with data communication enabled (RRC_CONNECTED) (1j-01). Subsequently, the UE receives configuration information from the MCG for adding an SCG including the aforementioned PSCell and sends an acknowledgment message to the MCG for this purpose (1j-03). The configuration information sent by the MCG can be received via an RRCReconfiguration message included in the RRC layer, and the acknowledgment message sent by the UE can be sent via an RRCReconfigurationComplete message included in the RRC layer. The configuration information may include at least one of the following: TA-related configuration information for the PSCell, parameters related to Beam Failure Detection (BFD), or parameters related to Beam Failure Recovery (BFR). The UE that has received the configuration information can perform random access to the configured PSCell to utilize it.

[0115] Therefore, both MCG and SCG are activated, and the UE is in a state where it can send and receive data through both base stations. Furthermore, since the UE has already performed random access to the PSCell, when the TAT (Time Alignment Timer) of the TAG to which the PSCell belongs is running, the UE can send uplink data through the serving cell belonging to the corresponding TAG (Timing Advance Group). Additionally, before or after the TAT of the primary Timing Advance Group (PTAG) of the SCG expires, the base station can send a Physical Downlink Control Channel (PDCCH) command to the UE. The PDCCH command can be a PDCCH indicating the start of random access. The UE that has received the PDCCH command can receive a new TA value and (re)activate the TAT during the random access process.

[0116] Simultaneously, the UE can receive a command from the MCG to disable the currently active SCG (1j-05). This can be determined by the MCG or SCG base station based on the amount of data transmitted through the SCG, etc. This disable command can be received as an RRC message at the Radio Resource Control (RRC) layer, or via a MAC Control Element (CE) as a control message at the Media Access Control (MAC) layer, or via the PDCCH. Upon receiving the disable command, the UE can send a message to the MCG confirming receipt of the corresponding command. This confirmation message can be sent as an RRC message at the RRC layer, or via a MAC Control Element (CE) as a control message at the MAC layer, or via HARQ feedback. Therefore, the UE can disable the corresponding SCG and stop data transmission and reception within that SCG (1j-07), thereby reducing power consumption due to communication with the corresponding SCG.

[0117] On the other hand, even after receiving a deactivation command, the UE can continuously measure the signal of the PSCell. This is to immediately restore data communication when the SCG is reactivated later. Therefore, in the state of deactivating the SCG, that is, in the state of deactivating the PSCell, the UE can detect the aforementioned BFD, in which the signal of the beam transmitted by the PSCell is lost (1j-09). If the UE detects the BFD of the PSCell, then it can perform one of the following operations (1j-11).

[0118] The first option is for the UE to perform random access to the corresponding PSCell via BFR. Here, during BFD in the SCGPSCell, the UE can perform contention-free random access (CFRA) by using random access resources previously configured by the MCG or SCG and specifically allocated for BFR. Alternatively, if such dedicated resources do not exist, or if dedicated resources are allocated but unavailable (e.g., when the signal strength of the selected beam is less than a preset threshold), then the UE can perform contention-based random access (CBRA). When performing contention-based random access, the UE transmits a C-RNTI MAC CE via Msg3 or MsgA, including the C-RNTI used in the previously active SCG. Therefore, when the UE successfully completes random access, the SCG also knows the corresponding UE's beam position (Synchronization Signal Block (SSB)), and the UE still keeps the corresponding SCG in an inactive state.

[0119] The second option is for the UE to notify the MCG that a BFR (Brightness Frame) has occurred for the corresponding PSCell. To do this, the UE can notify the MCG that a BFR has occurred for the SCG by using a new BFR MAC CE. Alternatively, the UE can include information about candidate beams available for the PSCell in the BFR MAC CE and send this information to the MCG, and can also deliver the information sent via the BFR MAC CE to the SCG.

[0120] By using one of the above options, the UE continues to use the beam information used in the inactive state, which can reduce downlink transmission latency when activated.

[0121] On the other hand, while the above options offer the advantage of immediate recovery from beam failures, they impose the burden of requiring the UE to continuously measure the signal strength of the disabled PSCell. Therefore, as another option, it is possible to consider not performing BFD when the SCG is disabled, but instead, upon receiving the SCG activation command, having the UE report detailed beam information when the PSCell is activated. For example, when multiple SCG beams exist, the SSB information selected individually by the UE during random access may be insufficient for communication with the corresponding UE. To address this, when the MCG sends the SCG activation command, the SCG can transmit a separate reference signal (Channel State Information-Reference Signal (CSI-RS)) for temporary channel measurements in a dense and temporary manner (temporary RS). In this case, the UE can additionally measure the CSI-RS and SSB during or before random access, and thus can include one or more CSI-RS measurements in Msg3 or MsgA and transmit this measurement information to the SCG during random access. Based on this information, data communication with the SCG (PSCell) can be quickly restored.

[0122] Figure 1k This is the first schematic diagram of the sequence of UE operations when the UE reactivates the SCG after it has been configured and is disabled.

[0123] exist Figure 1k In this example, assume the UE is connected to the base station (MCG) and is in a connected mode with data communication enabled (RRC_CONNECTED) (1k-01). Subsequently, the UE receives configuration information from the MCG for adding an SCG including the aforementioned PSCell and sends an acknowledgment message to the MCG for this purpose (1k-03). The configuration information sent by the MCG can be received via an RRCReconfiguration message included in the RRC layer, and the acknowledgment message sent by the UE can be sent via an RRCReconfigurationComplete message included in the RRC layer. The configuration information may include at least one of the following: TA-related configuration information for the PSCell, parameters related to beam fault detection (BFD), or parameters related to beam fault recovery (BFR). The UE, having received the configuration information, can perform random access to the configured PSCell to utilize it.

[0124] Therefore, both MCG and SCG are activated, and the UE is in a state where it can send and receive data through both base stations. Furthermore, since the UE has already performed random access to the PSCell, when the TAT of the TAG to which the PSCell belongs is running, the UE can send uplink data through the serving cell belonging to the corresponding TAG. Additionally, before or after the TAT of the PTAG of the SCG expires, the base station can send a PDCCH command to the UE. The PDCCH command can be a PDCCH instructing the UE to begin random access. A UE that has received a PDCCH command can receive a new TA value and (re)activate the TAT during the random access process.

[0125] Simultaneously, the UE can receive a command to disable the currently active SCG from the MCG (1k-05). This can be determined by the MCG or SCG base station based on the amount of data transmitted through the SCG, etc. This disable command can be received via an RRC message included in the RRC layer, a MAC control element (CE) as a control message in the MAC layer, or a PDCCH. Upon receiving the disable command, the UE can send a confirmation message to the MCG acknowledging receipt of the command. This confirmation message can be sent via an RRC message included in the RRC layer, a MAC control element (CE) as a control message in the MAC layer, or a HARQ feedback. Therefore, the UE can disable the corresponding SCG and stop data transmission and reception within that SCG (1k-07), thereby reducing power consumption due to communication with the corresponding SCG.

[0126] Subsequently, due to the increased amount of data to be transmitted via SCG, the UE can receive a command from the MCG to activate a currently deactivated SCG (1k-09). This activation command can be received as an RRC message at the RRC layer, or via a MAC control element (CE) as a control message at the MAC layer, or via the PDCCH. Upon receiving this activation command, the UE can send an acknowledgment message to the MCG notifying it that the corresponding command has been received (1k-11). This acknowledgment message can be sent as an RRC message at the RRC layer, or via a MAC control element (CE) as a control message at the MAC layer, or via HARQ feedback.

[0127] Meanwhile, regarding the TA and beam selection of PSCell, there are cases where the UE needs to perform random access to the PSCell (1k-15) and cases where it is not necessary to perform random access to the PSCell (1k-17).

[0128] In other words, the UE will perform random access to the PSCell if one of the following conditions is met.

[0129] The first condition is when the TAT of the PSCell has expired. In this case, since uplink transmission of the SCell including the PSCell using the same TAT as the PSCell cannot be performed, random access is required.

[0130] The second condition is when the PSCell uses multiple beams. That is, this is when the UE is configured with multiple SSBs or when a Configuration Indication (TCI) state is sent. This is because when the PSCell is deactivated, the UE can move, and there is a possibility that the UE may no longer use the previously used beams for communication. As mentioned above, when performing random access, since the UE selects a specific SSB and sends a preamble through the corresponding resource, the base station can know which SSB the UE is located on.

[0131] As a third condition, when the signal strength of the beam used during the deactivation of the SCG changes beyond a threshold previously set by the MCG or SCG (i.e., weakening), the UE performs random access. Under this condition, as with the second condition, the strength of the last used beam has weakened after the UE's PSCell is deactivated, indicating the possibility that the UE and PSCell can no longer use the previously used beam for communication.

[0132] As a fourth condition, when the SCG activated upon receiving an SCG change (i.e., PSCell change) configuration from the MCG after the SCG has been deactivated is different from the previously deactivated SCG, the UE performs random access. In this case, the UE should perform random access to the PSCell for the newly configured TA and beam selection.

[0133] If any of the above conditions apply (1k-13), the UE performs a random access procedure for the PSCell of the activated SCG to resume data communication with the SCG (1k-15); if no applicable condition applies, the UE resumes data communication with the SCG without performing a random access procedure for the PSCell (1k-17). Through the above process, the UE can resume communication by obtaining the TA and beam information of the activated PSCell.

[0134] Figure 11 This is the second schematic diagram of the sequence of UE operations when the UE reactivates the SCG after it has been configured and is in a deactivated state.

[0135] exist Figure 11In this example, assume the UE is connected to the base station (MCG) and is in a connected mode with data communication enabled (RRC_CONNECTED) (1l-01). Subsequently, the UE receives configuration information from the MCG for adding an SCG including the aforementioned PSCell and sends an acknowledgment message to the MCG for this purpose (1l-03). The configuration information sent by the MCG can be received via an RRCReconfiguration message using the RRC layer, and the acknowledgment message sent by the UE can be sent via an RRCReconfigurationComplete message using the RRC layer. The configuration information may include at least one of the following: TA-related configuration information for the PSCell, parameters related to beam fault detection (BFD), or parameters related to beam fault recovery (BFR). The UE, having received the configuration information, can perform random access to the configured PSCell to utilize it.

[0136] Therefore, both MCG and SCG are activated, and the UE is in a state where it can send and receive data through both base stations. Furthermore, since the UE has already performed random access to the PSCell, when the TAT of the TAG to which the PSCell belongs is running, the UE can send uplink data through the serving cell belonging to the corresponding TAG. Additionally, before or after the TAT of the PTAG of the SCG expires, the base station can send a PDCCH command to the UE. The PDCCH command can be a PDCCH instructing the UE to begin random access. A UE that has received a PDCCH command can receive a new TA value and (re)activate the TAT during the random access process.

[0137] Simultaneously, the UE can receive a command from the MCG to disable the currently active SCG (1l-05). This can be determined by the MCG or SCG base station based on the amount of data transmitted through the SCG, etc. This disable command can be received as an RRC message at the RRC layer, or via a MAC control element (CE) as a control message at the MAC layer, or via the PDCCH. Upon receiving the disable command, the UE can send a confirmation message to the MCG acknowledging receipt of the corresponding command. This confirmation message can be sent as an RRC message at the RRC layer, or via a MAC control element (CE) as a control message at the MAC layer, or via HARQ feedback. Therefore, the UE can disable the corresponding SCG and stop data transmission and reception within the corresponding SCG (1l-07), thereby reducing power consumption caused by communication with the corresponding SCG.

[0138] Subsequently, due to the increased amount of data to be transmitted via SCG, the UE can receive a command from the MCG to activate the currently deactivated SCG (1l-09). This activation command can be received via an RRC message included in the RRC layer, via a MAC control element (CE) that is a control message in the MAC layer, or via a PDCCH. Upon receiving the activation command, the UE can send an acknowledgment message to the MCG notifying it that the activation command has been received (1l-11). This acknowledgment message can be sent via an RRC message included in the RRC layer, via a MAC control element (CE) that is a control message in the MAC layer, or via a HARQ feedback.

[0139] In addition, the UE generates a separate activation confirmation message to send to the SCG to notify it that it is ready to communicate with the SCG (11-13). This activation confirmation message can be generated as an RRC message at the RRC layer or as a MAC control element (CE) as a control message at the MAC layer. Alternatively, for the purpose of the activation confirmation message, the previously used C-RNTI MAC CE can be used; alternatively, although the format is the same as C-RNTI MAC CE, this format can be sent using a separate Logical Channel Identifier (LCID) to separately notify the corresponding UE that it is ready to activate the SCG.

[0140] Then, in order to send the generated message, the UE determines whether the TAT of the TAG to which the PSCell to which the activation command has been received is running (1l-15). If the TAT of the TAG to which the PSCell to which the activation command has been received is running, the UE sends a scheduling request (SR) to the base station via the PSCell's PUCCH in response to the activation confirmation message. Therefore, when the base station allocates uplink resources to the UE, the UE sends the generated activation confirmation message via the corresponding resources (1l-17). The SR resources used in the above process are pre-configured from the MCG or SCG before the corresponding SCG is deactivated. If the corresponding SR resources are not configured from the base station or if the TAT of the TAG to which the PSCell to which the activation command has been received is not running, the UE sends Msg3 or MsgA, including the generated activation confirmation message, to the SCG by performing a random access procedure (1l-19). Through the above process, the UE can directly notify the SCG that data communication is ready in the activated PSCell and can be resumed.

[0141] Figure 1m The illustration shows a block configuration of a UE according to an embodiment of the present disclosure.

[0142] refer to Figure 1mThe UE may include a radio frequency (RF) processor 1m-10, a baseband processor 1m-20, a storage device 1m-30, and a controller 1m-40.

[0143] The RF processor 1m-10 performs functions for transmitting and receiving signals over a radio channel, such as signal band conversion and amplification. That is, the RF processor 1m-10 up-converts the baseband signal provided by the baseband processor 1m-20 into an RF band signal and transmits that signal through an antenna, and down-converts the RF band signal received through the antenna back into a baseband signal. For example, the RF processor 1m-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC). Although in Figure 1m Only one antenna is shown in the diagram, but the UE can be configured with multiple antennas. Furthermore, the RF processor 1m-10 can include multiple RF chains. Additionally, the RF processor 1m-10 can perform beamforming. For beamforming, the RF processor 1m-10 can adjust the phase and amplitude of signals transmitted and received through multiple antennas or antenna elements.

[0144] The baseband processor 1m-20 performs the conversion between baseband signals and bitstreams according to the system's physical layer specifications. For example, during data transmission, the baseband processor 1m-20 generates complex symbols by encoding and modulating the transmitted bitstream. Conversely, during data reception, the baseband processor 1m-20 recovers the received bitstream by demodulating and decoding the baseband signal provided from the RF processor 1m-10. For example, in the case of using Orthogonal Frequency Division Multiplexing (OFDM), for data transmission, the baseband processor 1m-20 generates complex symbols by encoding and modulating the transmitted bitstream, maps the complex symbols to subcarriers, and assembles OFDM symbols using Inverse Fast Fourier Transform (IFFT) operations and cyclic prefix (CP) insertion. Conversely, for data reception, the baseband processor 1m-20 divides the baseband signal provided from the RF processor 1m-10 into units of OFDM symbols, recovers the signals mapped to subcarriers using Fast Fourier Transform (FFT) operations, and recovers the received bitstream through demodulation and decoding.

[0145] The baseband processor 1m-20 and RF processor 1m-10 generally transmit and receive signals as described above. Therefore, the baseband processor 1m-20 and RF processor 1m-10 can be referred to as a transmitter, receiver, transceiver, or communication unit. Furthermore, to handle signals from different frequency bands, at least one of the baseband processor 1m-20 or RF processor 1m-10 may include different communication modules. These different frequency bands may include ultra-high frequency (SHF) bands (e.g., 2.5 GHz, 5 GHz) and millimeter wave (mmWave) bands (e.g., 60 GHz).

[0146] The storage device 1m-30 stores data such as basic programs, application programs, and configuration information for UE operation.

[0147] Controller 1m-40 controls the overall operation of the UE. For example, controller 1m-40 transmits and receives signals via baseband processor 1m-20 and RF processor 1m-10. Additionally, controller 1m-40 writes data to or reads data from storage device 1m-40. For this purpose, controller 1m-40 may include at least one processor. For example, controller 1m-40 may include a communication processor (CP) for controlling communications and a higher-level application processor (AP) for controlling applications. According to embodiments of this disclosure, controller 1m-40 includes a multi-connectivity processor 1m-42 that performs operational processing in a multi-connectivity mode. For example, controller 1m-40 may control the UE to perform... Figure 1m The process illustrated in the UE operation shown.

[0148] According to embodiments of this disclosure, when the SCG is disabled, the UE can manage the TA or detect and recover from beam faults, enabling it to reduce latency when the SCG is later activated by having effective uplink timing and managing effective beams. Furthermore, when the SCG is activated, the UE directly notifies it that it is ready to communicate with the SCG, allowing the SCG to explicitly determine the timing of data transmission and reception.

[0149] The methods described in the claims or specification of this disclosure can be implemented in hardware, software, or a combination thereof.

[0150] When implemented using software, a computer-readable storage medium may be provided to store one or more programs (software modules). The one or more programs stored in the computer-readable storage medium may be configured to be executable by one or more processors of an electronic device. The one or more programs may include instructions to cause the electronic device to perform methods according to the embodiments described in the claims or specification of this disclosure.

[0151] Such programs (software modules, software) can be stored in random access memory, non-volatile memory such as flash memory, read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), disk storage devices, optical disc ROM (CD-ROM), digital versatile optical disc (DVD), other types of optical storage devices, or cassette tapes. Alternatively, such programs can be stored in a memory consisting of some or all of these. Furthermore, multiple component memories may be included.

[0152] Furthermore, such a program can be stored in an attachable storage device that can be accessed via a communication network such as the Internet, intranet, local area network (LAN), wide area network (WLAN), or storage area network (SAN), or a communication network consisting of a combination thereof. This storage device can access the device carrying out embodiments of this disclosure via an external port. Additionally, a separate storage device on the communication network can access the device carrying out embodiments of this disclosure.

[0153] In specific embodiments of this disclosure, elements included in this disclosure are represented in either a singular or plural form according to the presented embodiments. However, for ease of description, singular or plural representations are suitably chosen based on the presented circumstances, and this disclosure is not limited to a single element or multiple elements. Elements described in plural form may also be configured as a single element, while elements described in singular form may be configured as multiple elements.

[0154] On the other hand, although specific embodiments have been described in the detailed description of this disclosure, various modifications are possible without departing from the scope of this disclosure. Therefore, the scope of this disclosure should not be limited to the described embodiments, but should be determined by both the claims described below and their equivalents.

[0155] The embodiments of the disclosure disclosed in this specification and drawings are provided as specific examples to readily illustrate the technical content of this disclosure and to aid in understanding it, and are not intended to limit the scope of this disclosure. It will be apparent to those skilled in the art that other modifications can be made based on the technical spirit of this disclosure, in addition to the embodiments disclosed herein.

Claims

1. A method performed by a user equipment (UE) in a wireless communication system, the method comprising: A first radio resource control (RRC) reconfiguration message is received from a first base station associated with a primary cell group (MCG), the first RRC reconfiguration message including configuration information for configuring a secondary cell group (SCG) associated with a second base station; Receive a second RRC message from the first base station for disabling the SCG; When the SCG is deactivated, a beam fault is detected on the primary and secondary cells PSCell of the SCG. as well as A beam fault recovery (BFR) media access control (MAC) control element (CE) is sent to the first base station to notify of the detected beam fault on the PSCell of the SCG, wherein the BFR MAC CE includes information about candidate beams on the PSCell, and When the SCG is deactivated, the UE maintains the time alignment timer TAT of the primary timing advance group PTAG to which the PSCell belongs.

2. The method according to claim 1, further comprising: Based on receiving the second RRC message used to disable the SCG, an acknowledgment message confirming that the second RRC message has been received is sent to the first base station.

3. The method according to claim 1, in, The configuration information also includes counter information for detecting beam faults, and Specifically, a beam fault is detected when the counter used to indicate a beam fault instance is equal to or greater than the counter information.

4. The method according to claim 1, in, The configuration information also includes at least one first piece of information associated with timing advance TA or a second piece of information regarding beam fault recovery.

5. A method performed by a first base station associated with a primary cell group (MCG) in a wireless communication system, the method comprising: Send a first Radio Resource Control (RRC) reconfiguration message to the User Equipment (UE), the first RRC reconfiguration message including configuration information for configuring the secondary cell group (SCG) associated with the second base station; Send a second RRC message to the UE to disable the SCG; as well as In the event that a beam fault is detected on the primary and secondary cell PSCell of the SCG in a deactivated state, the UE receives a Beam Fault Recovery BFR Media Access Control (MAC) control element (CE) to notify the UE of the detected beam fault on the PSCell of the SCG. The BFR MAC CE includes information about candidate beams for the PSCell. When the SCG is deactivated, the time alignment timer TAT of the main timing advance group PTAG to which the PSCell belongs is running.

6. The method according to claim 5, further comprising: The UE receives an acknowledgment message confirming that the second RRC message has been received, as a response to the second RRC message used to disable the SCG.

7. The method according to claim 5, in, The configuration information also includes counter information for detecting the beam fault; and Specifically, a beam fault is detected when the counter used to indicate a beam fault instance is equal to or greater than the counter information.

8. The method according to claim 5, in, The configuration information also includes at least one first piece of information associated with timing advance TA or a second piece of information regarding beam fault recovery.

9. A user equipment (UE) in a wireless communication system, the UE comprising: transceiver; as well as A controller, coupled to the transceiver and configured to: A first radio resource control (RRC) reconfiguration message is received from a first base station associated with a primary cell group (MCG), the first RRC reconfiguration message including configuration information for configuring a secondary cell group (SCG) associated with a second base station; Receive a second RRC message from the first base station for disabling the SCG; When the SCG is deactivated, a beam fault is detected on the primary and secondary cells PSCell of the SCG. as well as A beam fault recovery (BFR) media access control (MAC) control element (CE) is sent to the first base station to notify of the detected beam fault on the PSCell of the SCG, wherein the BFR MAC CE includes information about candidate beams on the PSCell, and When the SCG is deactivated, the UE maintains the time alignment timer TAT of the primary timing advance group PTAG to which the PSCell belongs.

10. The UE according to claim 9, wherein the controller is further configured to: Based on receiving the second RRC message used to disable the SCG, an acknowledgment message confirming that the second RRC message has been received is sent to the first base station.

11. The UE according to claim 9, in, The configuration information also includes counter information for detecting beam faults, and Specifically, a beam fault is detected when the counter used to indicate a beam fault instance is equal to or greater than the counter information.

12. The UE according to claim 9, in, The configuration information also includes at least one first piece of information associated with timing advance TA or a second piece of information regarding beam fault recovery.

13. A first base station associated with a primary cell group (MCG) in a wireless communication system, the first base station comprising: transceiver; as well as A controller, coupled to the transceiver and configured to: Send a first Radio Resource Control (RRC) reconfiguration message to the User Equipment (UE), the first RRC reconfiguration message including configuration information for configuring the secondary cell group (SCG) associated with the second base station; Send a second RRC message to the UE to disable the SCG; as well as In the event that a beam fault is detected on the primary and secondary cell PSCell of the SCG in a deactivated state, the UE receives a Beam Fault Recovery BFR Media Access Control (MAC) control element (CE) to notify the UE of the detected beam fault on the PSCell of the SCG. The BFR MAC CE includes information about candidate beams for the PSCell. When the SCG is deactivated, the time alignment timer TAT of the main timing advance group PTAG to which the PSCell belongs is running.

14. The first base station according to claim 13, wherein the controller is further configured to: The UE receives an acknowledgment message confirming that the second RRC message has been received, as a response to the second RRC message used to disable the SCG.

15. The first base station according to claim 13, in, The configuration information also includes counter information for detecting the beam fault; and Specifically, a beam fault is detected when the counter used to indicate a beam fault instance is equal to or greater than the counter information.

16. The first base station according to claim 13, in, The configuration information also includes at least one first piece of information associated with timing advance TA or a second piece of information regarding beam fault recovery.

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