User equipment, base station, method for user equipment, and method for base station

Abstract

A user device (UE), a base station, and corresponding methods for the user device and base station are provided. The UE includes a transceiver that, when operating, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell, and a cell switching command indicating one of the at least one LTM candidate cells as the target cell to switch to. The UE further includes a circuit that, when operating, performs an LTM operation to switch from a source cell servicing the UE to the target cell in accordance with the cell switching command, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If the circuit determines that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects the source cell as a recovery cell, or selects one of at least one candidate recovery cells, including one or more of the at least one LTM candidate cells indicated by the LTM candidate setting, as a recovery cell, and performs an LTM operation to switch to the selected recovery cell.

Description

Technical Field

[0001] The present disclosure relates to the transmission and reception of signals in a communication system. In particular, the present disclosure relates to methods and apparatuses for such transmission and reception.

Background Art

[0002] The 3rd Generation Partnership Project (3GPP) (registered trademark) is working on the technical specifications of next-generation cellular technologies (also referred to as the 5th generation (5G)), including New Radio (NR) radio access technology (RAT) that operates in the frequency range up to 100 GHz. NR is a successor technology to the technologies represented by Long Term Evolution (LTE) and LTE Advanced (LTE-A).

[0003] In systems such as LTE and NR, further improvements and options may facilitate the efficient operation of the communication system and specific devices related to the communication system.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Summary of the Invention

[0005] One non-limiting and exemplary embodiment contributes to rapid recovery to the target in the event of a cell switching error.

[0006] In one embodiment, user equipment (UE) includes a transceiver that, during operation, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell, and a cell switching command indicating one of the at least one LTM candidate cells as the target cell to switch to. During operation, the UE further includes a circuit that performs an LTM operation to switch from a source cell servicing the UE to the target cell in accordance with the cell switching command, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects the source cell as a recovery cell, or selects one of at least one candidate recovery cells, including one or more of the at least one LTM candidate cells indicated by the LTM candidate setting, as a recovery cell, and performs an LTM operation to switch to the selected recovery cell.

[0007] It should be noted that general or specific embodiments can be implemented as systems, methods, integrated circuits, computer programs, storage media, or any selective combination thereof.

[0008] Further advantages and effects of one embodiment of this disclosure will be made apparent from the specification and drawings. Such advantages and / or effects are provided by several embodiments and features described in the specification and drawings, but not all of them are necessarily provided in order to obtain one or more identical features.

[0009] The following exemplary embodiments will be described in more detail with reference to the attached drawings. [Brief explanation of the drawing]

[0010] [Figure 1] Diagram showing a schematic architecture of the 3GPP NR system. [Figure 2] Schematic diagram showing the functional division between NG-RAN and 5GC. [Figure 3] Sequence diagram of RRC connection setup / reconfiguration procedure [Figure 4] This schematic diagram illustrates usage scenarios for high-speed, high-capacity communication (eMBB: enhanced Mobile Broadband), massive simultaneous connection communication (mMTC: massive Machine Type Communications), and ultra-reliable and low-latency communication (URLLC: Ultra Reliable and Low Latency Communications). [Figure 5] Block diagram illustrating an exemplary 5G system architecture for a non-roaming scenario. [Figure 6] This diagram illustrates the situation when a cell switching command is sent from the base station to the user's equipment. [Figure 7] This is a block diagram of a communication system including user equipment and base stations, showing the structure of each component. [Figure 8a] Block diagram showing the functional configuration of the processing circuit on the user device side. [Figure 8b] Block diagram showing the functional configuration of the base station's processing circuit. [Figure 9a] A flowchart illustrating exemplary steps performed by user equipment and a base station, according to a first embodiment, showing when authorized recovery to the source cell is successful. [Figure 9b] A flowchart illustrating exemplary steps performed by user equipment and a base station in a first embodiment, showing what happens if an authorized recovery to the source cell fails. [Figure 9c]Flowchart showing exemplary steps performed by a user equipment and a base station according to a first embodiment, indicating a case where recovery to a source cell is not permitted [Figure 10] Flowchart showing exemplary steps performed by a user equipment and a base station according to a variant of the first embodiment, indicating a case where permitted recovery to a source cell is successful and the base station provides a second cell switching command [Figure 11] Flowchart showing exemplary steps performed by a user equipment and a base station according to a second embodiment, indicating a case where the user equipment has at least one candidate recovery cell set [Figure 12a] Flowchart showing exemplary steps performed by a user equipment and a base station according to the second embodiment, indicating a case where recovery to a recovery cell is successful [Figure 12b] Flowchart showing exemplary steps performed by a user equipment and a base station according to the second embodiment, indicating a case where recovery to a recovery cell is not successful [Figure 13] Diagram showing an example of a MAC CE functioning as a cell switching command including notification of a recovery cell according to the second embodiment [Figure 14] Diagram showing an exemplary MAC CE functioning as a cell switching command including notification of the priority of a plurality of recovery cells

Embodiments for Carrying out the Invention

[0011] <5G NR System Architecture and Protocol Stack> 3GPP is working on the next release of fifth-generation cellular technology (simply referred to as "5G"), which includes the development of a new radio access technology (NR) operating at frequencies up to 100 GHz. The first version of the 5G standard was completed at the end of 2017, which enabled the testing and commercial deployment of smartphones compliant with the 5G NR standard.

[0012] In particular, the overall system architecture envisions an NG-RAN (Next Generation Radio Access Network) with gNBs, which terminate NR radio access user plane (SDAP / PDCP / RLC / MAC / PHY) protocols and control plane (Radio Resource Control (RRC)) protocols toward the UE. The gNBs are interconnected with each other via Xn interfaces. Furthermore, the gNBs are connected to the NGC (Next Generation Core) via Next Generation (NG) interfaces, more specifically to the AMF (Access and Mobility Management Function) (e.g., a specific core entity that performs the AMF) via the NG-C interface, and to the UPF (User Plane Function) (e.g., a specific core entity that performs the UPF) via the NG-U interface. The NG-RAN architecture is shown in Figure 1 (see, for example, Section 4 of Non-Patent Document 1).

[0013] The user plane protocol stack in NR (see, for example, Section 4.4.1 of Non-Patent Document 1) includes the PDCP (Paper Data Convergence Protocol, see Section 6.4 of Non-Patent Document 1) sublayer, the RLC (Radio Link Control, see Section 6.3 of Non-Patent Document 1) sublayer, and the MAC (Medium Access Control, see Section 6.2 of Non-Patent Document 1) sublayer, all of which terminate at the gNB on the network side. In addition, a new access layer (AS) sublayer (SDAP, Service Data Adaptation Protocol) is introduced on top of PDCP (see, for example, Section 6.5 of Non-Patent Document 1). A control plane protocol stack is also defined in NR (see, for example, Section 4.4.2 of Non-Patent Document 1). An overview of the Layer 2 functions is described in Section 6 of Non-Patent Document 1. The functions of the PDCP, RLC, and MAC sublayers are described in sections 6.4, 6.3, and 6.2 of Non-Patent Document 1, respectively. The function of the RRC layer is described in section 7 of Non-Patent Document 1.

[0014] For example, the Medium-Access-Control (MAC) layer handles scheduling and scheduling-related functions, including logical channel multiplexing and processing of various numerologies.

[0015] The Physical Layer (PHY) is responsible for, for example, encoding, PHY HARQ processing, modulation, multi-antenna processing, and mapping signals to appropriate physical time-frequency resources. The Physical Layer also handles the mapping of transport channels to physical channels. The Physical Layer provides services to the MAC layer in the form of transport channels. A physical channel corresponds to a set of time-frequency resources used for transmitting a particular transport channel, and each transport channel is mapped to a corresponding physical channel. For example, physical channels include PRACH (Physical Random Access Channel), PUSCH (Physical Uplink Shared Channel), and PUCCH (Physical Uplink Control Channel) for uplinks, and PDSCH (Physical Downlink Shared Channel), PDCCH (Physical Downlink Control Channel), and PBCH (Physical Broadcast Channel) for downlinks.

[0016] Use cases / deployment scenarios for NR include high-speed, high-capacity communication (eMBB), ultra-high-reliability, low-latency communication (URLLC), and massive simultaneous connection communication (mMTC), and these services have diverse requirements regarding data rate, latency, and coverage. For example, eMBB is expected to support peak data rates (20 Gbps for downlink and 10 Gbps for uplink) and user-perceived data rates on the order of three times that provided by IMT-Advanced. URLLC, on the other hand, imposes more stringent requirements, such as extremely low latency (0.5 ms for user plane latency in both UL and DL) and high reliability (1 to 10⁻⁵ within 1 ms). Furthermore, mMTC may preferably require high connection density (1,000,000 devices per 1 km² in urban environments), wide coverage in harsh environments, and extremely long-life batteries (15 years) to reduce device costs.

[0017] Therefore, OFDM numerology suitable for one use case (e.g., subcarrier spacing, OFDM symbol length, cyclic prefix (CP) length, number of symbols per scheduling interval) may not work well for another use case. For example, low-latency services may prefer shorter symbol lengths (and thus larger subcarrier spacings) and / or fewer symbols per scheduling interval (also known as TTI) than mMTC services. Furthermore, in configuration scenarios with large channel delay spreads, longer CP lengths may be preferred than in scenarios with smaller delay spreads. To maintain a similar level of CP overhead, the subcarrier spacing should be optimized according to the delay spread. NR may support two or more values ​​for subcarrier spacing. Currently, subcarrier spacings of 15kHz, 30kHz, 60kHz, ... are being considered. The symbol length Tu and subcarrier spacing Δf are directly related by the equation (Δf = 1 / Tu). As with LTE systems, the term "resource element" can be used to represent the smallest resource unit consisting of one subcarrier for the length of one OFDM / SC-FDMA symbol.

[0018] In the new wireless system 5G-NR, for each numerology and carrier, a resource grid of subcarriers and OFDM symbols is defined for both the uplink and the downlink respectively. Each element in the resource grid is called a resource element and is identified based on the frequency index in the frequency domain and the symbol position in the time domain (see, for example, Section 4 of Non-Patent Document 2). For example, the transmissions in the downlink and uplink are organized into frames at 10 ms intervals, and each frame consists of 10 subframes at 1 ms intervals respectively. In the implementation of 5G NR, the number of consecutive OFDM symbols per subframe depends on the setting of the subcarrier spacing. For example, in the case of a 15 kHz subcarrier spacing, one subframe has 14 OFDM symbols (similar to an LTE-compliant implementation assuming a normal cyclic prefix). On the other hand, in the case of a 30 kHz subcarrier spacing, one subframe has two slots, and each slot contains 14 OFDM symbols.

[0019] <Split of 5G NR functions between NG-RAN and 5GC> Figure 2 shows the split of functions between NG-RAN and 5GC. The logical nodes of NG-RAN are gNB or ng-eNB. The logical nodes of 5GC are AMF, UPF, and SMF.

[0020] In particular, gNB and ng-eNB handle the following main functions; - Functions of radio resource management such as radio bearer control, radio admission control, connection mobility control, and dynamic resource allocation (scheduling) to the UE in both the uplink and downlink directions - IP header compression, encryption, and integrity protection of data - Selection of AMF at UE attachment when the routing to AMF from the information provided by the UE cannot be determined — Routing user plane data to UPF — Routing of control plane information to AMF — Establishing and releasing connections — Scheduling and sending paging messages — Scheduling and transmission of system broadcast information (sent from AMF or OAM) — Setting up measurements and measurement reporting for mobility and scheduling — Transport-level packet marking on the uplink ― Session management — Support for network slicing — QoS flow management and mapping to data radio bearers — Support for UEs in the RRC_INACTIVE state — NAS message delivery function — Wireless access network sharing — Dual connectivity — Close interworking between NR and E-UTRA

[0021] The Access and Mobility Management Function (AMF) handles the following key functions: — Termination of Non-Access Stratum (NAS) signaling — NAS signaling security — Access Layer (AS) Security Control — Core Network (CN) node-to-node signaling for mobility between 3GPP access networks — Reachability of idle mode UE (including control and execution of paging retransmissions) — Registration Area Management — Support for intra-system and inter-system mobility ― Access Authentication — Access authorization including roaming rights checks — Mobility management and control (subscriptions and policies) — Support for network slicing — Selection of Session Management Function (SMF)

[0022] Furthermore, User Plane Functions (UPFs) handle the following key functions: — Anchor points for mobility within / between RATs (when applicable) — External PDU session points for interconnection with data networks — Packet routing and forwarding — User plane portion of packet inspection and policy rule enforcement — Traffic usage report — Uplink classifier to support routing of traffic flow to data networks — Branching points to support multi-homed PDU sessions — User plane QoS processing (e.g., packet filtering, gating, UL / DL rate enforcement) — Verification of upstream link traffic (mapping from SDF to QoS flow) — Buffering of downlink packets and triggering of downlink data notifications

[0023] Finally, the Session Management Function (SMF) handles the following main functions: ― Session management — Assignment and management of UE IP addresses — Selection and control of UP function - Configuration of traffic steering in the User Plane Function (UPF) for routing traffic to the correct destination - Policy enforcement and QoS control part - Downlink data notification

[0024] <Procedures for establishment and reconfiguration of RRC connection> Figure 3 shows the interaction among the UE, gNB, and AMF (5GC entity) in the NAS part when the UE transitions from RRC_IDLE to RRC_CONNECTED (see Non-Patent Document 1).

[0025] RRC is the upper layer signaling (protocol) used for the configuration of the UE and gNB. In particular, in this transition, the AMF creates UE context data (including, for example, PDU session context, security keys, UE radio capabilities, UE security capabilities, etc.) and sends it to the gNB by means of an INITIAL CONTEXT SETUP REQUEST (Initial Context Setup Request). Next, the gNB activates the AS security with the UE, which is executed by the gNB sending a SecurityModeCommand message to the UE and the UE responding to the gNB with a SecurityModeComplete message. After that, the gNB executes reconfiguration to establish signaling radio bearer 2 (SRB2) and data radio bearer (DRB: Data Radio Bearer), which is achieved by the gNB sending an RRCReconfiguration message to the UE and receiving RRCReconfigurationComplete from the UE in response. In the case of a signaling-only connection, since SRB2 and DRB are not established, these steps related to RRCReconfiguration are skipped. Finally, the gNB notifies the AMF by means of an INITIAL CONTEXT SETUP RESPONSE (Initial Context Setup Response) that the establishment procedure has completed.

[0026] Accordingly, this disclosure provides a fifth-generation core (5GC) entity (e.g., AMF or SMF) having a control circuit that, in operation, establishes a next-generation (NG) connection with a gNodeB so that a signaling radio bearer is established between the gNodeB and the user equipment (UE), and a transmitter that, in operation, sends an initial context setup message to the gNodeB via the NG connection. In particular, the gNodeB transmits radio resource control (RRC) signaling, including resource allocation setting information elements, to the UE via the signaling radio bearer. The UE then performs an uplink transmit or downlink receive based on this resource allocation setting.

[0027] <IMT Usage Scenarios from 2020 Onward> Figure 4 illustrates some use cases for 5G NR. The 3rd Generation Partnership Project NR (3GPP NR) considers three use cases envisioned to support a wide variety of services and applications through IMT-2020. Phase 1 specifications for high-speed, high-capacity communication (eMBB) have been finalized. Current and future work includes further expansion of eMBB support, as well as standardization for ultra-high reliability, low-latency communication (URLLC) and massive simultaneous connection communication (mMTC). Figure 4 shows some examples of IMT use scenarios envisioned for 2020 and beyond (see, for example, Figure 2 in Non-Patent Document 3).

[0028] URLLC use cases have stringent requirements regarding capabilities such as throughput, latency, and availability, and are envisioned as one means of realizing future vertical applications such as wireless control of industrial manufacturing or production processes, telemedicine surgery, power distribution automation in smart grids, and transportation safety. The ultra-high reliability of URLLC is supported by identifying the technology to meet the requirements set out by Non-Patent Document 4. For NR URLLC in Release 15, key requirements include a target user plane latency of 0.5 ms for UL (uplink) and 0.5 ms for DL ​​(downlink). Typical URLLC requirements for a single packet transmission are a BLER (block error rate) of 1E-5 for a packet size of 32 bytes with a user plane latency of 1 ms.

[0029] From a physical layer perspective, several ways to improve reliability are possible. Current approaches to reliability improvements include defining separate CQI tables for URLLC, a more compact DCI format, and PDCCH iterations. However, as NR becomes more stable and development progresses (regarding key requirements for NR URLLC), the scope for achieving ultra-high reliability may expand. Specific use cases for NR URLLC in Release 15 include augmented reality / virtual reality (AR / VR), e-health, e-safety, and mission-critical applications.

[0030] Furthermore, the technical enhancements targeted by NR URLLC aim to improve latency and reliability. Technical enhancements for improving latency include configurable numerology, non-slot-based scheduling using flexible mapping, grant-free (configured grant) uplink, slot-level iteration on data channels, and downlink preemption. Preemption means that a transmission for which resources have already been allocated is aborted, and those resources are used for another transmission requested later with lower latency / higher priority requirements. Thus, a transmission that has already been permitted is preempted by a later transmission. Preemption applies regardless of the specific service type. For example, a transmission of service type A (URLLC) can be preempted by a transmission of service type B (e.g., eMBB). Technical enhancements for improving reliability include a dedicated CQI / MCS table for the 1E-5 target BLER.

[0031] The use case for mMTC (Massively Multiple Connections Communication) is characterized by a very large number of connected devices transmitting relatively small amounts of data, which are generally less affected by latency. These devices need to be low-cost and have extremely long battery life. From a noise reduction (NR) perspective, utilizing a very narrow bandwidth is one possible solution to achieve power savings from a UE perspective and enable long battery life.

[0032] As described above, the range of reliability in NR is expected to broaden. One important requirement in all cases, especially for URLLC and mMTC, is high or very high reliability. Several mechanisms can be considered to improve reliability from both a radio and network perspective. In general, there are several important areas that can help improve reliability. These areas include compact control channel information, data channel / control channel repetition, and diversity related to the frequency domain, time domain, and / or spatial domain. These areas are generally applicable to reliability regardless of the specific communication scenario.

[0033] Regarding NR URLLC, further use cases with more stringent requirements are envisioned, such as factory automation, the transportation industry, and power supply. These stringent requirements include, depending on the use case, higher reliability (up to 10⁻⁶ levels), higher availability, packet sizes up to 256 bytes, time synchronization on the order of a few microseconds (values ​​ranging from 1 to several microseconds depending on the frequency range), and low latency on the order of 0.5 to 1 ms (with a target latency of 0.5 ms specifically for the user plane).

[0034] Furthermore, for NR URLLC, there can be several technical enhancements from the perspective of the physical layer. In particular, enhancements related to PDCCH (Physical Downlink Control Channel) include compact DCI, repetition of PDCCH, and increased PDCCH monitoring. Also, enhancements related to UCI (Uplink Control Information) include enhancement of HARQ (Hybrid Automatic Repeat Request) and enhancement of CSI feedback. In addition, enhancements of PUSCH related to mini-slot level hopping and retransmission / repetition have also been recognized. The term "mini-slot" means a transmission time interval (TTI: Transmission Time Interval) that contains fewer symbols than a slot (including 14 symbols).

[0035] <QoS Control> The 5G QoS (Quality of Service) model is based on QoS flows and supports both QoS flows that require a guaranteed flow bit rate (GBR QoS flows) and QoS flows that do not require a guaranteed flow bit rate (non-GBR QoS flows). Therefore, at the NAS level, the QoS flow is the finest granularity for QoS differentiation in a PDU session. The QoS flow is identified within a PDU session by a QoS flow ID (QFI) that is transmitted in the encapsulation header through the NG-U interface.

[0036] The 5GC establishes one or more PDU sessions for each UE. The NG-RAN establishes at least one Data Radio Bearer (DRB) with each PDU session for each UE, and can then configure additional DRBs for the QoS flow of that PDU session, as described above, for example with reference to Figure 3 (the NG-RAN decides when to configure them). The NG-RAN maps packets belonging to different PDU sessions to different DRBs. NAS-level packet filtering in the UE and 5GC associates UL and DL packets with QoS flows, and AS-level mapping rules in the UE and NG-RAN associate UL and DL QoS flows with DRBs.

[0037] Figure 5 shows the non-roaming standard architecture for 5G NR (see Section 4.23 of Non-Patent Document 5). Application Functions (AFs) (e.g., external application servers handling 5G services as illustrated in Figure 4) interact with the 3GPP Core Network for the purpose of providing services. For example, they support application influence on traffic routing, access Network Exposure Functions (NEFs), or interact with policy frameworks for policy control (e.g., QoS control) (see Policy Control Functions (PCFs)). Based on the operator's deployment, application functions (AFs) that are considered trusted by the operator may be allowed to interact directly with the relevant Network Functions. Application functions (AFs) that are not permitted by the operator to directly access Network Functions interact with the relevant Network Functions using external exposure frameworks via NEFs.

[0038] Figure 5 shows further functional units of the 5G architecture, namely the Network Slice Selection Function (NSSF), Network Repository Function (NRF), Unified Data Management (UDM), Authentication Server Function (AUSF), Access and Mobility Management Function (AMF), Session Management Function (SMF), and Data Network (DN) (e.g., operator services, internet access, or third-party services). All or some of the core network functions and application services may be deployed and run in a cloud computing environment.

[0039] Accordingly, the Disclosure provides an application server (e.g., AF in a 5G architecture) having: a transmitter that, when in operation, sends a request including QoS requirements for at least one of the URLLC service, eMMB service, and mMTC service to at least one of the 5GC functions (e.g., NEF, AMF, SMF, PCF, UPF, etc.) and establishes a PDU session including a radio bearer between the gNodeB and the UE in accordance with the QoS requirements; and a control circuit that, when in operation, executes the service using the established PDU session.

[0040] <Signal-to-noise ratio> SINR (Signal-to-Interference-plus-Noise Ratio) is an important metric used to evaluate the quality of wireless communication links. SINR calculates the ratio of the power of the desired signal to the combined power of interference and noise. Simply put, SINR measures the strength of a useful signal relative to unwanted signals and background noise present in the communication channel.

[0041] From the perspective of 5G NR, SINR is a major parameter that affects the overall data throughput and reliability of a wireless connection. A high SINR generally indicates better signal quality and reduced interference, meaning improved communication performance. SINR is used by both the user equipment (UE) and the network in making decisions regarding modulation and coding schemes, resource allocation, and other adaptive transmission strategies to ensure optimal data rates and reliable communication.

[0042] <L1 measurement> In 5G NR, the communication protocol is divided into different layers, and Layer 1 (L1) refers to the physical layer. L1 measurements involve evaluating the characteristics of physical signals, including aspects such as signal strength, quality, interference, and noise level. These measurements provide important information for determining the overall health and performance of the wireless link.

[0043] L1 measurements are essential for various purposes such as handover decisions, radio resource management, and service quality optimization. This enables the network to make informed decisions on when and how to initiate handovers between different cells, adjust transmission parameters, and manage resource allocation.

[0044] For example, when the UE is in the connected mode and moving between different cells or sectors, the network uses L1 measurements including SINR to evaluate the quality of the current connection and determine whether a handover is necessary to maintain a seamless and high-quality communication experience. These measurements contribute to ensuring that the UE is connected to the highest quality cell among the available cells with the least interference and strongest signal.

[0045] <Terminal> In LTE and NR, a terminal, user terminal, user device, mobile station, or mobile node is called User Equipment (UE). User equipment may be a mobile device or communication device, such as a radiotelephone, smartphone, tablet computer, or Universal Serial Bus (USB) stick with the functionality of a user device. However, the term mobile device is not limited to these, and generally, a repeater may also have the functionality of such a mobile device, and a mobile device may function as a repeater. For example, a terminal is a physical entity (physical node) in a communication network. Furthermore, a communication device may be any machine type of communication device, such as an IoT device. A single node may have several functional entities. A functional entity refers to a software or hardware module that implements and / or provides a predetermined set of functions to the same node, other nodes, or other functional entities in the network. A node may have one or more interfaces that allow the node to attach to a communication facility or medium that enables it to communicate. Similarly, a network entity may have logical interfaces that allow a functional entity to attach to a communication facility or medium that enables it to communicate with other functional entities or corresponding nodes.

[0046] <Base station> In this disclosure, a base station may be, for example, a Transmission Reception Point (TRP), a cluster head, an access point, a Remote Radio Head (RRH), an eNodeB (eNB), a gNodeB (gNB), a Base Station (BS), a Base Transceiver Station (BTS), a base unit, or a gateway. In side-link communication, a terminal may be used instead of a base station. A base station may be a relay device that relays communication between a higher-level node and a terminal. A base station may be a roadside unit. A base station may be, for example, a scheduling node or network node that forms part of a network for providing services to a terminal. In particular, a base station can provide radio access to a terminal. Communication between a terminal and a base station is generally standardized and may be defined by various layers such as PHY, MAC, and RRC. In LTE and NR, the radio interface protocol stack includes the physical layer, the medium access layer (MAC), and higher layers. The control plane is provided with a radio resource control protocol, which is a higher-layer protocol. Through RRC, the base station can control the configuration of a terminal, and the terminal can communicate with the base station to perform control tasks such as establishing and changing connections and bearers, measurements, and other functions. The term used in LTE is eNB (or eNodeB), and the term currently used in 5G NR is gNB. The term base station or radio base station here refers to a physical entity in a communication network. Like mobile stations, a base station may have several functional entities. A functional entity refers to a software or hardware module that implements and / or provides a given set of functions to the same node or other nodes or other functional entities in the network. A physical entity performs several control tasks related to a communication device, including one or more of scheduling and configuration. Note that base station functions and communication device functions can also be integrated within a single device.For example, a mobile terminal may also implement the functionality of a base station for other terminals. The term used in LTE is eNB (or eNodeB), while the term currently used in 5G NR is gNB.

[0047] <Frequency Band> This disclosure may apply to either the licensed band or the unlicensed band.

[0048] <Uplink / Downlink / Sidelink> This disclosure may apply to uplinks, downlinks, and sidelinks.

[0049] For example, this disclosure may be applied to uplink channels such as PUSCH, PUCCH, and PRACH, downlink channels such as PDSCH, PDCCH, and PBCH, and sidelink channels such as Physical Sidelink Shared Channel (PSSCH), Physical Sidelink Control Channel (PSCCH), and Physical Sidelink Broadcast Channel (PSBCH).

[0050] PDCCH, PDSCH, PUSCH, and PUCCH are examples of downlink control channels, downlink data channels, uplink data channels, and uplink control channels, respectively. PSCCH and PSSCH are examples of sidelink control channels and sidelink data channels, respectively. PBCH and PSBCH are examples of broadcast channels, and PRACH is an example of a random access channel.

[0051] <Data Channel / Control Channel> This disclosure may apply to either data channels or control channels. The channels in this disclosure may be replaced with data channels such as PDSCH, PUSCH, PSSCH, and / or control channels such as PDCCH, PUCCH, PBCH, PSCCH, PSBCH.

[0052] <harq-ack> HARQ-ACK (Hybrid Automatic Repeat Request - Acknowledgement) is a signaling mechanism used in wireless communication networks to enable error correction and retransmission of data. HARQ-ACK allows a receiving device to notify a transmitting device whether a transmitted packet was successfully received, enabling the sender to either send the next packet or retransmit the same packet. HARQ-ACK feedback can enable efficient use of wireless channels and contribute to improved reliability of data transmission.

[0053] <Reference signal> In this disclosure, a reference signal is a signal known to both the base station and the mobile station UE, and each reference signal is referred to as a reference signal (RS) or pilot signal. A reference signal may be one of the following: DMRS, Channel State Information-Reference Signal (CSI-RS), Tracking Reference Signal (TRS), Phase Tracking Reference Signal (PTRS), Cell-Specific Reference Signal (CRS), or Sounding Reference Signal (SRS).

[0054] <Channel State Information - Reference Signal (CSI-RS)> Channel State Information-Reference Signal (CSI-RS) is a signal used in LTE and 5G NR to estimate the quality of the radio channel between a UE and a base station. CSI-RS may be transmitted periodically by the base station in specific resource elements (resources) in the frequency domain, and the UE uses the received CSI-RS to estimate the channel quality that can be used for beamforming and other techniques. The UE can also use CSI-RS for feedback to the base station indicating the modulation and coding schemes that can be supported on the current channel. CSI-RS is a component for providing high data rates and reliable communications.

[0055] <CSI-RS Resource Set Group> A CSI-RS Resource Set Group is a concept that refers to a group of CSI-RS resource sets having similar transmission characteristics. The CSI-RS Resource Set Group may be used to optimize transmission efficiency and reduce the overhead associated with individualized control signaling. The CSI-RS Resource Set Group enables the base station to transmit a single CSI-RS resource set for multiple antennas or transmission points, thereby reducing the number of control signals required for beamforming and other transmission optimization techniques.

[0056] A CSI-RS Resource Set Group is characterized by a unique identifier known as the CSI-RS Configuration Index (CRI). The CRI is used by the UE to identify the CSI-RS Resource Set Group and associated communication characteristics. The CSI-RS Resource Set Group can be used for various transmission parameters including beamforming, channel quality measurement, and handover.

[0057] <CSI Report> For example, CSI reporting in LTE or 5G NR is a mechanism that allows an UE to provide feedback to a base station about the quality of the radio channel. For this purpose, the UE estimates the channel quality based on a reference signal transmitted by the base station and reports this information to the base station.

[0058] CSI reporting in 5G NR is more advanced than CSI reporting in LTE, and includes various types of feedback and reporting settings. The UE estimates channel quality based on reference signals transmitted by the base station, including CSI-RS and Demodulation Reference Signal (DMRS). The UE then reports this information to the base station using one or more types of feedback, such as the following: — Periodic CSI feedback: The UE transmits CSI feedback at regular intervals specified by the base station. — Aperiodic CSI feedback: The UE sends CSI feedback when the channel state changes significantly. — Semi-persistent CSI feedback: The UE periodically transmits CSI feedback using a specific offset. This allows the base station to anticipate when the feedback will be received.

[0059] The type of feedback can be configured using different reporting settings, including the number of bits used to encode the feedback, the frequency of the feedback report, and the aggregation of multiple subcarriers or antennas.

[0060] Base stations may use CSI feedback to adapt transmission parameters, such as modulation coding schemes, to current channel conditions. CSI reporting is a mechanism for achieving high data rates and efficient use of the radio spectrum in 5G NR.

[0061] <Power loss estimation> Power loss estimation in 5G NR refers to the mechanism by which the UE estimates the power loss in the radio channel between the UE and the base station. This estimation is crucial for determining the appropriate transmit power level to achieve the desired quality of service and minimize interference.

[0062] The UE estimates power loss based on a reference signal transmitted by the base station, such as CSI-RS. Power loss estimation is typically performed using a Channel Quality Indicator (CQI), which provides information about channel quality, or Reference Signal Received Power (RSRP), which provides information about received signal strength.

[0063] Power loss estimation may be used by the UE to adjust the transmit power level and improve the quality of the received signal. Depending on the estimated power loss, the UE may use different power levels for different subcarriers or antenna ports.

[0064] Base stations can also use power loss estimation to adjust transmission parameters such as beamforming vectors in order to improve the quality of transmitted signals and reduce interference.

[0065] Power loss estimation is a crucial aspect of wireless communication systems such as LTE and 5G NR, as it enables the efficient use of the radio spectrum and improves the quality of service for users.

[0066] <Upstream power control> Uplink power control refers to the process of adjusting the transmit power of a UE in the uplink direction to ensure that the signal received by the base station is neither too weak nor too strong. Uplink power control is performed to ensure the efficient use of radio resources and to maintain the target quality of service (QoS) for the UE. Power control can be either open-loop or closed-loop.

[0067] In open-loop power control, the UE adjusts its transmit power based on a power control offset without any feedback from the base station. In closed-loop power control, the base station provides feedback to the UE to better adjust transmit power based on channel conditions. The closed-loop power control mechanism may also be based on channel quality indicator (CQI) feedback from the base station. The UE adjusts its transmit power using the CQI to maintain the target signal-to-noise ratio (SNR) at the base station. CQI feedback is typically transmitted periodically from the base station to the UE, and the UE adjusts its transmit power based on the latest CQI value.

[0068] <Synchronization and Synchronization Signal Block (SSB)> In NR downlink synchronization, the UE detects the radio boundary (i.e., the timing at which the radio frame begins) and the OFDM symbol boundary (i.e., the timing at which the OFDM symbol begins). This is done by detecting and analyzing the Synchronization Signal Block (SSB). The components of the SSB include synchronization signals, namely the Primary Synchronization Signal (PSS) and the Secondary Synchronization Signal (SSS). The NR SSB may be transmitted in various different patterns depending on the numerology and several other parameters. The patterns are signaled within the system information.

[0069] In NR, the TRS may be provided as a dedicated RS to the UE, or as a common RS for multiple UEs in connection mode. Based on the TRS, the UE may be able to fine-tune synchronization without having to constantly receive a synchronization signal.

[0070] In some systems, such as NR (e.g., Release 15 / 16), the TRS / CSI resource is configured for the UE to be used by the UE in RRC_CONNECTED mode for measurements, for example, channel state estimation, time tracking, frequency tracking, and / or beam tracking. For UEs in other modes (RRC_IDLE and RRC_INACTIVE), such measurements may rely on the SSB. For NR in Release 17, the TRS / CSI-RS may also be used by some INACTIVE / IDLE UEs for time and frequency tracking, supporting this feature of additional TRS / CSI-RS opportunities notified to these UEs. Thus, in general, TRS / CSI and SSB are signals that can be used by the UE in any RRC state for channel state estimation, time tracking (e.g., time synchronization), frequency tracking, and / or beam tracking.

[0071] In general, SSB may be transmitted in a specific (spatial) direction, in which case the SSB may be called an "SSB beam." In particular, each SSB / SSB beam may also have and / or indicate a beam index (also known as an SSB index) that can be used to distinguish the SSB beam from other SSB beams transmitted in directions other than the SSB beam. The UE may then determine the SSB index of the received SSB beam based on the received signal of the SSB beam and determine the direction in which the received SSB beam was transmitted by the base station.

[0072] In general, the current SSB structure and signaling in SIB1 may be used by the base station to indicate to the UE which SSB beams the base station is using. The base station may then use ON / OFF instructions to notify the UE which beams should be switched ON or OFF for which period.

[0073] <Medium Access Control Element (MAC CE)> In LTE (Long-Term Evolution) and 5G NR (New Radio), "MAC CE" stands for "Medium Access Control - Control Element." MAC CE is a type of control information used in the MAC (Medium Access Control) layer of the communication protocol. MAC CE carries essential instructions and parameters for managing various aspects of the radio interface, including resource allocation, scheduling, power control, and other related functions.

[0074] In LTE, MAC CEs are control elements used to transmit specific commands and information regarding resource scheduling and other aspects of radio resource management. MAC CEs are part of MAC PDUs (Protocol Data Units). Different types of MAC CEs serve different purposes, such as indicating the modulation and encoding scheme used for data transmission, notifying user equipment (UEs) about downlink allocation, and issuing power control commands.

[0075] Similarly, in 5G NR, MAC CE is a control element that provides instructions and information to manage various aspects of wireless communication. In 5G NR, MAC CE is used to transmit control information that affects resource allocation, scheduling, power control, handover, and other critical functions.

[0076] In 5G NR, MAC CE is included in the MAC PDU and is used to signal various operations and settings to the UE. These control elements contribute to the dynamic nature of the 5G network, enabling efficient resource utilization and adaptation of communication parameters based on real-time conditions.

[0077] In both LTE and 5G NR, MAC CE enhances the flexibility, efficiency, and adaptability of communication systems. This allows networks to efficiently manage available resources, optimize data transmission, and provide users with reliable, high-quality connectivity.

[0078] <Lower-level triggered mobility (LTM)> In mobile networks, handover (also known as handoff) is the process of transferring an ongoing call or data session from one cell or base station to another without interrupting communication. This is essential to ensure continuous connectivity as users move within the cellular network's coverage area. Handovers are triggered for a variety of reasons, including signal degradation, congestion, load balancing, and UE mobility.

[0079] New Radio (NR) supports various types of handover. Basic handover in NR is based on the LTE handover mechanism, where the network controls the UE's mobility based on the UE's measurement report. In a basic handover, the source gNB triggers the handover by sending a handover request to the target gNB, and after receiving an ACK (acknowledgement) from the target gNB, initiates the handover by sending a handover command that includes the target cell configuration. The UE then accesses the target cell after the target cell configuration has been applied.

[0080] In the context of 5G New Radio (NR), lower-level triggered mobility refers to a mechanism that accelerates the handover process while maintaining reliable and seamless connectivity when user equipment (UE) hands over from one base station (gNB) to another. This mechanism is specifically designed to manage handovers triggered by specific events or conditions occurring at the lower levels within the radio network.

[0081] Lower-level (e.g., L1 / L2) triggered mobility (LTM) is introduced in 5G NR to reduce latency in the UE's mobility procedure and / or to enable rapid cell switching from the source cell to the target cell. For this purpose, a list of candidate cells is prepared by the base station and transmitted to the user equipment (UE) that supports LTM. This allows the UE to configure the LTM procedure. This configuration may be performed using the RRC LTMconfig Information Element (IE).

[0082] Next, the UE performs L1 measurements on the configured LTM candidate cells and sends the lower-layer L1 measurement report to the base station. The UE also performs channel quality measurements between the UE and the source cell and sends the CSI report to the base station. The measurement reports of the above measurement results can be scheduled by the base station to the UE as periodic, aperiodic, or semi-persistent reporting settings.

[0083] The base station then decides whether the UE should switch to a target cell among the LTM candidate cells. If it does, the base station sends a cell switch command to the UE indicating the target cell to switch to. For this purpose, the MAC CE may function as or contain a cell switch command.

[0084] When the UE receives a cell switch command (MAC CE), the UE starts an LTM monitoring timer. Subsequently, the UE initiates an LTM operation to switch to the specified target cell and transmits UL data through the target cell. If the UL data is successfully delivered before the LTM monitoring timer expires, the UE concludes that the LTM operation from the source cell to the target cell was successful.

[0085] In short, the LTM cell switching operation can be summarized in the following steps: The UE sends a measurement report message to the base station. The base station then decides to use LTM and begins preparing the LTM candidate. For this purpose, the base station sends an RRC reconfiguration message to the UE, which includes the configuration of one or more LTM target candidate cells. The UE then remembers the configuration of the LTM target candidate cells and sends an RRC reconfiguration complete message to the base station. The UE may perform downlink (DL) synchronization and timing advance (TA) acquisition with the target candidate cell before receiving the LTM cell switching command. The UE performs L1 measurements on the configured LTM target candidate cell and sends a lower layer measurement report to the base station. The base station then decides to perform an LTM cell switching to the target cell and sends a MAC control element (MAC-CE) that triggers the LTM cell switching. The UE applies the configuration of the LTM target candidate cell. If TA is unavailable, the UE performs a random access procedure on the target cell. The UE notifies that the LTM cell switching to the target cell has been successfully completed. In LTM, the UE may perform a partial or complete MAC reset, re-establish Radio Link Control (RLC), or perform data recovery using PDCP (Packet Data Convergence Protocol) during cell switching.

[0086] A cell switching (or handover) procedure may be performed, for example, when the channel condition of the source cell is poor (and / or unstable), and the quality of the wireless link deteriorates towards the cell edge of the source cell, resulting in degraded service to the UE.

[0087] Figure 6 shows the situation in which a cell switching command is sent from the base station to the user equipment. As can be seen from this figure, the UE, which is serviced by the source cell, is located at the edge of the source cell's coverage area. Based on the measurement results sent from the UE, the base station may decide that the UE should perform an LTM operation to switch from the source cell to a target cell among one or more LTM candidate cells. The base station then sends a cell switching command to the UE, for example by sending a MAC CE indicating the target cell, in order to have the UE perform the LTM cell switching operation to switch from the source cell to the target cell. Upon receiving the cell switching command, the UE performs the LTM cell switching operation to switch from the source cell to the target cell. As described above, the UE may determine whether the LTM cell switching operation was successful or not. If the LTM cell switching operation was unsuccessful (i.e., a cell switching error occurred), the UE can restore cell connectivity by applying a cell (re)selection process with neighboring cells to re-establish RRC connectivity.

[0088] However, such cell re-selection and re-establishment can cause delays and lead to prolonged data loss. This defeats the purpose of the LTM cell switching procedure. Therefore, in the event of a cell switching error, a rapid recovery, i.e., quickly selecting and connecting to another target cell, is desirable. This can be achieved by performing further LTM operations to switch to a recovery cell.

[0089] This disclosure has been made in view of the above-mentioned issues and provides user equipment, a base station, and a corresponding method that facilitate rapid recovery in the event of an LTM cell switching error.

[0090] <Embodiment> The following describes new radio access technologies envisioned for 5G mobile communication systems, including UEs, base stations, and procedures, which may also be used in LTE mobile communication systems. Various implementations and variations are also described. The following disclosures are facilitated by and, for example, based on the above discussions and findings, at least in part therein.

[0091] Generally, many assumptions are made in this specification to enable a clear and understandable explanation of the principles underlying this disclosure. However, these assumptions are merely illustrative examples and do not limit the scope of this disclosure.

[0092] Furthermore, while certain terminology used in the context of new radio access technologies for the next 3GPP 5G communication systems is not yet fully determined or may ultimately change, some of the terms used below, such as procedures, entities, and layers, are closely related to the terminology used in LTE / LTE-A systems or in current 3GPP 5G standardization. Therefore, while terminology may change in the future, this will not affect the functionality of the embodiments. Accordingly, it will be recognized by those skilled in the art that embodiments and their scope of protection are not limited to certain terms used exemplarily herein because no newer or finally agreed-upon terminology exists, but should be understood more broadly in terms of the functions and concepts that form the basis of the functionality and principles of this disclosure.

[0093] For example, a mobile station, mobile node, user terminal, or user equipment (UE) is a physical entity (physical node) in a communication network. A single node may have several functional entities. A functional entity refers to a software or hardware module that implements and / or provides a predetermined set of functions to the same node, other nodes, or other functional entities in the network. A node may have one or more interfaces that allow it to attach to a communication facility or medium that enables it to communicate. Similarly, a network entity may have logical interfaces that allow a functional entity to attach to a communication facility or medium that enables it to communicate with other functional entities or corresponding nodes.

[0094] In this specification, the terms “base station” or “radio base station” refer to a physical entity within a communication network. Similar to a mobile station, a base station may have several functional entities. A functional entity refers to a software or hardware module that implements and / or provides a predetermined set of functions to the same node, other nodes, or other functional entities in the network. A physical entity performs several control tasks relating to a communication device, including one or more of scheduling and configuration. It should be noted that base station functions and communication device functions can also be integrated within a single device. For example, a mobile terminal may also implement base station functions for other terminals. The term used in LTE is eNB (or eNodeB), while the term currently used in 5G NR is gNB.

[0095] Communication between the UE and the base station is typically standardized and can be defined by different layers such as PHY, MAC, and RRC (see the background technology explanation above).

[0096] This disclosure relates to user equipment, base stations, and methods for user equipment and base stations that address challenges related to LTM cell switching errors and rapid recovery.

[0097] Figure 7 shows a general and simplified exemplary block diagram of a user device 100 (also called a communication device) and a scheduling device such as an eNB or gNB (network node) as described herein, and a base station 200 as exemplary. However, generally, the scheduling device may be a terminal in the case of a side-link connection between two terminals. Furthermore, particularly with respect to the use cases of URLLC, eMBB, and mMTC, the communication device 100 may be a controller for a sensor device, a wearable device, a connected vehicle, or an automated machine in an industrial plant. The communication device 100 may also function as a relay between the base station and other communication devices (for example, this disclosure is not limited to communication “terminals” or user “terminals”).

[0098] The UE100 and the base station 200 (eNB / gNB) communicate with each other via a (wireless) physical channel 300 using their respective transceivers 110 (UE100 side) and transceiver 210 (base station 200 side). The base station 200 and the UE100 together form a communication system 10. The communication system 10 may further include other entities as shown in Figure 1.

[0099] UE100 may comprise a transceiver 110 and a (processing) circuit 120, and scheduling device 200 may comprise a transceiver 210 and a (processing) circuit 220. Transceiver units 110, 210 may comprise a receiver and / or a transmitter, and / or function as a receiver and / or a transmitter. In other words, in this disclosure, the term “transceiver” is used for hardware and software components that enable UE100 or base station 200 to transmit and / or receive radio signals, respectively, over radio channel 300. Thus, a transceiver corresponds to a receiver, a transmitter, or a combination of a receiver and a transmitter. Typically, it is assumed that base stations and UEs can both transmit and receive radio signals. However, particularly with respect to some applications of eMBB, mMTC, and URLLC (smart home, smart city, industrial automation, etc.), there may be cases where only a device such as a sensor receives a signal. Furthermore, the term “circuit” includes processing circuits formed by one or more processors or processing units, etc.

[0100] As shown in Figure 7, in some embodiments, the user equipment (UE) 100 includes a transceiver 110 that, when operating, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell. The transceiver further receives a cell switching command indicating one of the at least one LTM candidate cell as the target cell to switch to. When operating, the UE 100 further includes a circuit that, in accordance with the cell switching command, performs an LTM operation to switch from a source cell servicing the UE to a target cell, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects the source cell as the recovery cell, or selects one of at least one candidate recovery cells, which includes one or more of the at least one LTM candidate cells indicated by the LTM candidate setting, as the recovery cell, and performs an LTM operation to switch to the selected recovery cell.

[0101] In some embodiments, the user equipment (UE) 100 includes a transceiver 110 that, during operation, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell. The transceiver further receives a cell switching command indicating one of the at least one LTM candidate cell as the target cell to switch to. The UE 100 further includes a circuit that, during operation, performs an LTM operation to switch from a source cell servicing the UE to a target cell in accordance with the cell switching command, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects the source cell as the recovery cell and performs an LTM operation to switch to the selected recovery cell.

[0102] In some embodiments, the user equipment (UE) 100 includes a transceiver 110 that, during operation, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell. The transceiver further receives a cell switching command indicating one of the at least one LTM candidate cell as the target cell to switch to. During operation, the UE 100 further includes a circuit that, in accordance with the cell switching command, performs an LTM operation to switch from a source cell servicing the UE to a target cell, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects one of at least one candidate recovery cells, which includes one or more of the at least one LTM candidate cells indicated by the LTM candidate setting, as a recovery cell, and performs an LTM operation to switch to the selected recovery cell.

[0103] Figure 8a shows the functional structure of circuit 120. In particular, circuit 120 includes a transceiver control circuit 121. When in operation, the transceiver control circuit 121 controls the transceiver 110 to perform the operations described above. Furthermore, when in operation, circuit 120 includes a cell switching circuit 122 that executes the operations of circuit 120 as described above.

[0104] Furthermore, as shown in Figure 7, in some embodiments, the base station includes a transceiver 220 that, when operating, transmits an LTM candidate setting to the user equipment (UE) 100 indicating at least one lower-layer triggered mobility (LTM) candidate cell. The base station 200 further includes a circuit 220 that, when operating, determines whether the user equipment (UE) 100, which is serviced by the source cell, should switch from the source cell to the target cell. If it is decided that the UE 100 should switch to the target cell, the transceiver 210 transmits a cell switching command that designates at least one LTM candidate cell as the target cell to switch to.

[0105] Figure 8b shows the functional structure of circuit 220. In particular, circuit 220 includes a transceiver control circuit 221. When in operation, the transceiver control circuit 221 controls the transceiver 210 to perform the operations described above. Furthermore, when in operation, circuit 220 includes a cell switching control circuit 222 that executes the operations of circuit 220 as described above.

[0106] <Circuit> Circuits 120, 220 (or processing circuits) may be one or more pieces of hardware, such as one or more processors or any LSIs. There are input / output points (or nodes) 130, 230 between the transceiver units 110, 210 and the processing circuits 120, 220, and beyond the input / output points (or nodes) 130, 230, the processing circuits 120, 220 can control the transceiver units 110, 210 when in operation, i.e., control the receiver and / or transmitter, and exchange received / transmitted data. The transceiver units 110, 210 may include an RF front, such as one or more antennas, amplifiers, radio frequency (RF) modulators / demodulators, etc., as the transmitter and receiver. The processing circuits 120 and 220 may perform control tasks such as transmitting user data and control data provided by the processing circuits 120 and 220, and / or receiving user data and control data that has been further processed by the processing circuits 120 and 220, by controlling the transmitting and receiving units 110 and 210. The processing circuits 120 and 220 may also be responsible for performing other processes such as judgment, determination, calculation, and measurement. The transmitting unit may be responsible for performing the transmission process and other related processes. The receiving unit may be responsible for performing the reception process and other related processes.

[0107] It should be noted that circuits 120 and 220 may be general processing circuits including one or more processors, which may execute code instructions stored in memory (which may be part of circuits 120 and 220), and may include some code instructions corresponding to the functions described above for each circuit. Functions may be provided by hardware adaptation and / or software. This disclosure is not limited to any particular circuit, and embodiments of this disclosure may include dedicated or programmable hardware, general-purpose hardware, or any combination thereof.

[0108] It should be further noted that any of the steps / operations described below may be performed or controlled by circuit 120 (on the UE100 side) and / or circuit 220 (on the base station 200 side). In particular, in further descriptions, unless otherwise explicitly stated or specified in the context, details and embodiments apply to UE100, base station 200, and the method, respectively.

[0109] <First Embodiment> In the first embodiment, UE100 performs an LTM operation to the source cell if the LTM operation to the target cell is unsuccessful. In other words, UE100 recovers to the source cell after an LTM cell switching error occurs.

[0110] For this purpose, the UE100 includes a transceiver 110 that, when operating, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell. The transceiver further receives a cell switching command indicating one of the LTM candidate cells as the target cell to switch to. The UE100 further includes a circuit that, when operating, performs an LTM operation to switch from a source cell servicing the UE to a target cell in accordance with the cell switching command, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects the source cell as the recovery cell and performs an LTM operation to switch to the selected recovery cell.

[0111] In particular, when a base station transmits a cell switching command, for example, using MAC CE, the radio link between the source cell and UE100 may be sufficient for communication. The radio link may be considered sufficient if the source cell's SINR or signal quality is better than the target cell's SINR or signal quality. For example, when base station 200 decides to switch UE100 to the target cell, the source cell's SINR / signal quality may be 1 or 2 dB better.

[0112] Therefore, if the LTM operation to the target cell is unsuccessful, the UE100 recovers to the source cell as a recovery cell. When communicating with the source cell after recovery, the DL and UL synchronization characteristics and / or bearer settings of the source cell may be reused from those used by the UE100 before the (failed) attempt to switch to the target cell. This approach may reduce the additional signaling required to achieve DL / UL synchronization and / or bearer settings during recovery.

[0113] In other words, if a source cell is selected as a recovery cell, circuit 120, during operation, reuses the downlink (DL) and uplink (UL) synchronization characteristics and / or bearer settings that were applied to the transmission and reception with the source cell before receiving the cell switching command, after switching to the source cell selected as the recovery cell.

[0114] Whether or not an LTM recovery operation to the source cell is permitted may be instructed by the base station 200. That is, the cell switching command may indicate whether or not the selection of the source cell is permitted. If the cell switching command indicates that the selection of the source cell as the recovery cell is permitted, the circuit 120 may select the source cell as the recovery cell and perform an LTM operation to the source cell. Otherwise, that is, if the cell switching command indicates that the selection of the source cell as the recovery cell is not permitted, the circuit 120 may perform a cell selection and RRC (Radio Resource Control) connection re-establishment procedure.

[0115] Notification of whether the source cell can be selected as a recovery cell after a cell switching error may be included in the cell switching command. In other words, the cell switching command may be a cell switching command that instructs a cell switching with immediate recovery to the source cell, or a cell switching command that instructs a cell switching without immediate recovery to the source cell.

[0116] For example, if the cell switching command is one that involves a rapid recovery to the source cell, then the system may switch to the source cell after the LTM operation to switch to the target cell fails.

[0117] A cell switching command indicating whether or not to allow a rapid recovery to the source cell may be implemented by the MAC CE.

[0118] For example, MAC CEs with different identifiers can be used as cell switching commands with or without rapid recovery to the source cell. For instance, a MAC CE with a specific Logical Channel ID (LCID) may be considered a cell switching command with rapid recovery to the source cell. A MAC CE with an LCID different from the above specific LCID may be considered a cell switching command without rapid recovery to the source cell. In other words, the above specific LCID may be used to indicate to the UE 100 that recovery to the source cell is permitted by the base station 200.

[0119] Furthermore, as a potential implementation, a MAC CE field that functions as a cell switching command may include a parameter (e.g., a "recovery / revert to source" parameter) indicating whether recovery to the source cell is permitted after an LTM cell switching error. The value of this field may be set to "true" to indicate that recovery to the source cell is permitted, and to "false" to indicate that recovery to the source cell is not permitted. However, this disclosure is not limited to this particular implementation, and other values ​​may indicate whether recovery to the source cell is permitted.

[0120] Furthermore, as a potential implementation, recovery to the source cell may be set by default. That is, the MAC CE, which functions as a cell switching command, does not necessarily have to include an instruction on whether or not recovery to the source cell is permitted. In this case, when the UE100 performs the LTM operation to switch to the target cell, it may always return to the source cell as a recovery cell after a cell switching error occurs.

[0121] The UE100 starts the LTM monitoring timer when it receives a cell switch command, and may determine that a cell switch error occurred during the switch to the target cell if a synchronization error occurs, if the LTM monitoring timer expires before receiving a UL grant or PUSCH (Physical Uplink Shared Channel) resource, and / or if the number of errors in sending UL data or RACH (Random Access Channel) messages to the target cell exceeds a threshold.

[0122] In other words, if a wireless link error with the target cell occurs, for example, in the form of a downlink (DL) synchronization error, or if the number of transmission errors for UL data (in the case of switching without RACH) or RACH messages (in the case of switching based on RACH) exceeds a certain maximum threshold, the UE100 may conclude that a cell switching error has occurred. Alternatively, if the LTM monitoring timer expires, it may be determined that a cell switching error has occurred. This applies when the UE100 is waiting for a PUSCH resource or UL grant to send UL data.

[0123] If recovery to the source cell is permitted and UE100 switches to the source cell, the transceiver 110 may transmit first UL data via the source cell indicating that an error occurred while performing the LTM operation to switch to the target cell. Since UE100 transmits the first UL data via the source cell and not the target cell, the network may interpret any transmission of first UL data via the source cell as indicating a cell switching error.

[0124] In a potential implementation, the primary UL data may be the UL CSI report of the source cell. The network can use this information for channel evaluation between the source cell and UE100. In another implementation, a sounding reference signal (SRS) may be transmitted by UE100 on the uplink, allowing the network to evaluate the latest location of UE100 when it recovers to the source cell.

[0125] Another implementation allows for indicating a cell switching error by transmitting a MAC CE with a specific LCID value. In this regard, UE100 may require a scheduling request (SR) resource reserved by the source cell to transmit the MAC CE. If the base station provides UE100 with a scheduling grant or resource for UL transmission, UE100 is triggered to perform an L1 measurement, the results of which are reported along with the UL data. In this way, the latest channel status of the LTM candidate cell can be provided to base station 200, which can use this information to determine whether UE100 should perform an LTM operation to switch to a different (or previous) target cell.

[0126] UE100 may send a MAC CE on the uplink that has the same LCID used to instruct the LTM cell switch to the network instruct a cell switch error. In other words, a MAC CE with the same LCID that UE100 used to instruct the target cell to perform an LTM cell switch may be used on the uplink to indicate that the cell switch was not performed successfully. As described above, sending a MAC CE may require a scheduling request (SR) resource reserved by the source cell.

[0127] Alternatively, the UE may send an RRC reconfiguration failure message via the source cell to indicate a cell switch / handover error. The cell switch operation (i.e., the LTM execution procedure) is part of the RRC reconfiguration procedure, and the detection of a cell switch error is a network-side RRC (or CU) specific operation, and the sending of an RRC message to the network can be treated as a response from the original RRC message to the UE100.

[0128] Upon the first transmission of UL data to the source cell after a cell switching error to the target cell, UE100 may have reserved resources set, such as a PUCCH resource for CSI reporting, an SRS transmission resource, and / or a scheduling request (SR) resource. These resources may be notified to UE100 by base station 200 before the cell switching command is sent from base station 200 to UE100. In this case, UE100 may perform the first transmission of UL data through the source cell without performing the RACH procedure.

[0129] On the other hand, if the UL resource described above is not reserved for UE100 in the source cell, UE100 may perform a RACH-based first transmission. In this case, if a RACH message is sent to the source cell in msg3 to receive a UL grant from the source cell, the UL grant can be used for a first transmission of UL data, which may indicate that the cell switch to the target cell was unsuccessful (as described above).

[0130] If UE100 receives an acknowledgment of the first transmission to the source cell after performing the first transmission to the source cell, it can conclude that the recovery to the source cell was successful, and the recovery operation is complete.

[0131] As a potential implementation, a maximum time may be set for performing the LTM operation of switching to the source cell as a recovery cell. For this purpose, a timer with a predetermined or set operating time ("Timer A") may be used. If synchronization with the source cell as a recovery cell fails, or if an acknowledgment for the UL's first transmission is not received before Timer A expires, UE100 may determine that the recovery to the source cell was unsuccessful and perform the cell selection and RRC (Radio Resource Control) connection re-establishment procedure.

[0132] In other words, the UE100 may determine whether the LTM operation for switching to the source cell was successful or not, and if it determines that the LTM operation for switching to the source cell was unsuccessful, it may perform the cell selection and RRC (Radio Resource Control) connection re-establishment procedure.

[0133] Timer A may be started after it is determined that the LTM operation to switch to the target cell indicated by the cell switching command was unsuccessful. For example, Timer A may be started after the LTM monitoring timer has expired. In this approach, the determination of whether the LTM operation to switch to the target cell was successful and the determination of whether the recovery to the source cell was successful are performed independently and sequentially.

[0134] On the other hand, as a potential implementation, Timer A may be started after the UE receives a cell switching command and stopped when the recovery to the source cell is successfully completed. In this case, the LTM monitoring timer and Timer A may be started at the same time. These timers may have the same or different operating times.

[0135] As a variation of this implementation, the LTM monitoring timer may be used as Timer A. That is, if the LTM monitoring timer functions as Timer A, it is not necessary to define a new timer. In this case, the LTM monitoring timer may be restarted after it is determined that the LTM operation of switching from the source cell to the target cell was unsuccessful. However, the LTM monitoring timer does not need to be restarted when a cell switching error is detected.

[0136] In other words, cell switching (LTM operation to switch to a target cell) and cell recovery (LTM operation to switch to a recovery cell after detecting a cell switching error) are different operations, but they can be monitored sequentially using a single timer (e.g., an LTM monitoring timer). This can be achieved by restarting the timer after a cell switching error is detected. Alternatively, the timer is not restarted when a cell switching error is detected while it is running. In this case, cell switching and cell recovery are assumed to occur within the same operating time of the timer.

[0137] On the other hand, different / independent timers may be used as the LTM monitoring timer and Timer A. In this case, Timer A may be called the LTM recovery timer. Defining independent and separate timers increases flexibility in implementing rapid recovery in the event of a cell switchover error.

[0138] Figure 9a is a flowchart illustrating exemplary steps performed by user equipment and a base station according to a first embodiment, showing the case where authorized recovery to the source cell is successful.

[0139] Figure 9b is a flowchart illustrating exemplary steps taken by user equipment and a base station in a first embodiment, showing the case where authorized recovery to the source cell is unsuccessful.

[0140] In Figures 9a and 9b, corresponding steps are denoted by the same reference numerals.

[0141] In step S200, base station 200 decides that UE100 will perform an LTM operation to switch to the target cell (target cell 1). This decision may be based on the CSI report and L1 measurement results provided by UE100, as described above. Base station 200 also decides that the UE can perform a rapid recovery to the source cell. Accordingly, base station 200 sends a cell switching command, for example using MAC CE as detailed, notifying that recovery to the source cell is permitted if the LTM operation to switch to the target cell fails to execute successfully. In response, in step S100, UE100 starts the LTM monitoring timer and performs an LTM operation to switch to the target cell. As illustrated in Figures 9a and 9b, packet loss occurs in the transmission between UE100 and the target cell. As a result, in step S110, UE determines that the LTM operation to switch to the target cell failed to execute successfully. Since the cell switching command indicates that recovery to the source cell is permitted, UE100 performs an LTM operation to return to the source cell in step S120. For example, Timer A is started. Unlike the situation shown in Figure 9b, in the situation shown in Figure 9a, recovery to the source cell is successful. That is, in step S210, base station 200 receives the first UL transmission to the source cell and determines that a cell switching error occurred in the LTM operation to switch to the target cell. Service then continues between the source cell and UE100. On the other hand, as shown in Figure 9b, recovery to the source cell is unsuccessful. As illustrated exemplarily, packets transmitted by UE100 are lost. Therefore, in step S130, UE100 determines that recovery to the source cell was unsuccessful, for example, if Timer A expires without an acknowledgment for the first UL transmission being received. Therefore, in step S140, UE100 performs the cell selection and RRC (Radio Resource Control) connection re-establishment procedure.

[0142] Figure 9c is a flowchart illustrating exemplary steps performed by user equipment and a base station according to a first embodiment, showing a case where recovery to the source cell is not permitted. Step S200a differs from step S200 in Figures 9a and 9b in that the base station determines that recovery to the source cell is not permitted if an LTM operation to switch from the source cell to the target cell is performed. Thus, after performing an LTM operation in step S100 and detecting that the LTM operation to switch to the target cell failed in step S110, the UE100 performs a cell selection and RRC (Radio Resource Control) connection re-establishment procedure in step S140.

[0143] <Variation> As a variation of the first embodiment, after UE100 has successfully recovered to the source cell, for example after step 210 in Figure 9a, base station 200 decides that UE100 will perform an LTM operation to switch from the source cell to a different target cell (second target cell) than the previous target cell (first target cell). For this purpose, base station 200 may use information that the LTM operation to switch to the first target cell was not successfully performed. Alternatively, as detailed, base station 200 may use the latest L1 measurement results provided by UE100 after recovery to the source cell to determine the second target cell. When notifying the second target cell, base station 200 sends a second cell switching command (also called an auxiliary cell switching command).

[0144] This procedure allows the network to select a new target cell (second target cell) using information regarding the failure to switch to the first target cell. The MAC CE used as the second cell switching command may be of a different type than the MAC CE that functions as the cell switching command for switching to the first target cell. Similarly, the auxiliary cell switching command may indicate whether UE100 may (again) recover to the source cell if the cell switching to the target cell fails to complete successfully. UE100 may then recover to the source cell after the cell switching error, or perform cell selection and RRC (Radio Resource Control) connection re-establishment procedures.

[0145] UE100 may start a timer called Timer B to monitor whether the LTM operation to switch to the second target cell was successful. Similar to Timer A, Timer B may be started when UE100 receives an auxiliary cell switching command and stopped when the switch to the second target cell is successful. However, Timer B may be an LTM monitoring timer. That is, the LTM monitoring timer may be restarted when an auxiliary cell switching command is received from base station 200 via the source cell. On the other hand, a separate timer may be defined as Timer B for monitoring the cell switching operation by the auxiliary cell switching command. Such a timer may be called an LTM auxiliary monitoring timer.

[0146] Figure 10 is a flowchart illustrating exemplary steps performed by user equipment and a base station in a modified version of the first embodiment, showing the case where authorized recovery to the source cell is successful and the base station provides an auxiliary cell switching command. In the figure, steps corresponding to those shown in Figures 9a to 9c are denoted by the same reference numerals.

[0147] In steps S200 and S100-S120, operations are performed according to the steps described in Figure 9a. Specifically, in step S110, UE100 receives a cell switching command indicating that recovery to the source cell is permitted, detects that the LTM operation to switch to the target cell (i.e., target cell 1) was unsuccessful, and recovers to the source cell in step S120. For example, in the first UL transmission, UE100 provides the base station 200 with the latest L1 measurement results. In step S210a, the base station 200 determines the second target cell to which UE100 will switch, for example, using the L1 measurement results. Accordingly, the base station 200 sends an auxiliary cell switching command notifying target cell 2 as the cell to switch to, which is received by UE100. The auxiliary cell switching command also indicates that recovery to the source cell is not permitted. In step S150, UE100 performs an LTM operation to switch from the source cell to target cell 2, for example, by starting timer B. After the switch to target cell 2 is successful, service will continue between UE100 and target cell 2.

[0148] The auxiliary cell switching command may also indicate that recovery to the source cell is permitted. In this case, UE100 will recover to the source cell if the LTM operation to switch to target cell 2 does not complete successfully. On the other hand, if recovery to the source cell is not permitted and the LTM operation to switch to target cell 2 is unsuccessful, UE may perform cell selection and RRC (Radio Resource Control) connection re-establishment procedures.

[0149] <Second Embodiment> In a second embodiment, the UE 100 includes a transceiver 110 that, during operation, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell, and a cell switching command indicating one of the at least one LTM candidate cell as the target cell to switch to. The UE 100 further includes a circuit 120 that, during operation, performs an LTM operation to switch from a source cell servicing the UE to a target cell in accordance with the cell switching command, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit 120 selects one of at least one candidate recovery cells, which includes one or more of the at least one LTM candidate cells indicated by the LTM candidate setting, as a recovery cell, and performs an LTM operation to switch to the selected recovery cell.

[0150] In other words, within the framework of an LTM operation to switch to a target cell, if UE100 detects a cell switching error, UE100 will use one of the LTM candidates configured by the network in accordance with the LTM execution for a rapid recovery to restore cell connectivity.

[0151] This approach can be particularly useful when the SINR / signal quality of another LTM candidate cell is better than that of the target cell. A SINR / signal quality difference of 1 or 2 dB is considered better. For example, if UE100 moves to the boundary region between two candidate cells, the cell switching procedure to the target cell indicated by the cell switching command may fail, while switching to another LTM candidate cell may succeed.

[0152] To enable UE100 to select a recovery cell, UE100 may be configured with at least one candidate recovery cell from at least one LTM candidate cell. In other words, the transceiver 110 of UE100 may receive a recovery setting indicating at least one candidate recovery cell from at least one LTM candidate cell. The recovery setting may point to only one of the LTM candidate cells, a subset of the LTM candidate cells, or all of the LTM candidate cells as candidate recovery cells, and the recovery cell is selected from there by the circuit 120 of UE100.

[0153] According to the recovery mechanism of this embodiment, it may be possible to reduce the delay of the cell recovery operation compared to a cell (re)selection procedure to the same candidate cell or adjacent cell.

[0154] The recovery setting (hereinafter also referred to as ConfigA) may be semi-statically set / sent to the UE100 via an RRC reconfiguration message. In this case, the value of ConfigA may be set to a sequence of IDs of LTM candidate cells indicated to the UE100 by the LTM candidate setting. Alternatively, the recovery setting may be dynamically set to the UE using a MAC CE sent within the framework of a cell switching command. That is, the cell switching command may directly indicate a candidate recovery cell or include an instruction for one, from which the UE100 selects a recovery cell for cell recovery after detecting a switching error to the target cell. ConfigA is also called the LTM recovery setting.

[0155] ConfigA may be sent to UE100 along with the LTM settings at the start of the LTM cell switching operation. However, this disclosure is not limited thereto, and ConfigA may be sent separately to UE100 before or after the cell switching command is sent.

[0156] If the recovery configuration indicates multiple (i.e., two or more) candidate recovery cells, the priority of the candidate recovery cells may be indicated (this configuration may hereafter be referred to as ConfigB). ConfigB may be semi-statically configured and transmitted via RRC reconfiguration messages, or it may be dynamically configured using MAC CEs transmitted within the framework of the LTM cell switching procedure. For example, ConfigB may be indicated by or included in a cell switching command transmitted to UE100. In the case of a semi-static configuration of ConfigB, each value may be set to a sequence of LTM candidate cells ordered by priority (sent as ConfigA). ConfigB is also called the LTM priority.

[0157] ConfigB may be sent to UE100 together with ConfigA, i.e., the recovery settings indicating the LTM candidate cells that will function as candidate recovery cells, or separately from ConfigA. For example, if ConfigB is sent separately from ConfigA, it may be sent before the cell switching command is sent, or it may be sent together with the cell switching command. Also, ConfigA and ConfigB may consist of a candidate recovery cell and a single setting value indicating the priority of the candidate recovery cells. In particular, if ConfigA and ConfigB are sent simultaneously, the candidate recovery cells may be set in an order corresponding to the priority of candidate recovery cells applied by UE100. Such a setting may be called the LTM recovery order.

[0158] As a potential implementation, ConfigA and ConfigB, i.e., the list of recovery cells and their respective priorities, may be combined with an LTM candidate configuration indicating LTM candidate cells, which may be sent in the RRC reconfiguration message. In this case, the LTM candidate configuration may include parameters indicating whether each LTM candidate cell configured in UE100 is available for recovery. The LTM candidate configuration may also indicate the priority of the LTM candidate cells designated as recovery cells.

[0159] If all LTM candidate cells are intended to function as candidate recovery cells, then, as described above, all LTM candidate cells may be indicated as candidate recovery cells. This increases flexibility in configuring candidate recovery cells. However, the fact that all LTM candidate cells can function as candidate recovery cells may be indicated by the base station 200 using a dedicated indicator (called ConfigC). The value of ConfigC may be set to "All," but this disclosure is not limited to that. ConfigC may be transmitted with or separately from the LTM candidate configuration. In another potential implementation, all LTM candidate cells indicated in the LTM candidate configuration may be configured as candidate recovery cells by default. That is, UE100 may perceive all LTM candidate cells as candidate recovery cells without receiving a candidate recovery cell instruction, and a recovery cell may be selected from among them.

[0160] Cell switching errors may be detected by UE100 in a manner similar to or in the manner described in the first embodiment. That is, the circuit 120 of UE100 may start an LTM monitoring timer when it receives a cell switching command, and it may be determined that the LTM operation to switch from the source cell to the target cell was unsuccessful if a synchronization error occurs, if the LTM monitoring timer expires before receiving a UL grant or PUSCH (Physical Uplink Shared Channel) resource, and / or if the number of errors in sending UL data or RACH (Random Access Channel) messages to the target cell exceeds a threshold.

[0161] If UE100 determines that the LTM operation to switch to the target cell according to the cell switching command was unsuccessful, it selects a recovery cell from at least one candidate recovery cell indicated in ConfigA. If multiple candidate recovery cells are indicated in ConfigA, the selection of the recovery cell may be based on ConfigB, i.e., the priority of the candidate recovery cells.

[0162] In other words, if only one candidate recovery cell is configured in UE100, that candidate recovery cell is selected as the recovery cell, and after a switch error to the target cell is detected, the LTM operation to that recovery cell is executed. If multiple or all LTM candidate cells are configured as candidate recovery cells, UE100 selects the candidate recovery cell with the highest priority as the recovery cell and executes an LTM operation to switch to that recovery cell. If the cell switch operation to the recovery cell is unsuccessful, UE100 may select the candidate recovery cell with the second highest priority as the next recovery cell and execute an LTM operation to switch to that next recovery cell. If this LTM operation is unsuccessful again, UE100 may select the next recovery cell and execute an LTM operation to switch to the selected recovery cell.

[0163] In other words, the UE100 receives a priority indicator showing the priority of multiple candidate recovery cells and selects a recovery cell from among the multiple candidate recovery cells according to the priority. If none of the LTM operations to switch to a candidate recovery cell according to priority are successful, the UE100 may perform a cell selection and RRC (Radio Resource Control) connection re-establishment procedure.

[0164] However, instead of selecting a recovery cell according to priority, UE100 may perform an L1 measurement on all configured candidate recovery cells and select a recovery cell from among the multiple candidate recovery cells according to the channel state measurement results. Similarly, if recovery to a recovery cell is unsuccessful, UE100 may select the next recovery cell from the candidate recovery cells according to the L1 measurement results and perform an LTM operation. If none of the LTM operations to switch to candidate recovery cells according to priority are successful, the cell selection and RRC (Radio Resource Control) connection re-establishment procedure may be performed. In particular, if multiple candidate recovery cells are configured for UE100 but no order or priority is set for the candidate recovery cells, the recovery cell selection process according to the L1 measurement results may be performed.

[0165] If the UL transmission to the selected recovery cell is successful, that is, if UE100 determines that the LTM operation to switch to the selected recovery cell was successful, the cell recovery process is completed normally.

[0166] Similar to the first embodiment, a timer (Timer C) may be used to monitor the success of recovery to a recovery cell. Timer C may also be called the LTM recovery timer and may be a separate timer with dedicated uptime, as described in the first embodiment, or it may be an LTM monitoring timer. The LTM recovery timer may be started when rapid cell recovery of a candidate recovery cell is triggered and stopped when one of the candidate recovery cells is recovered. In an alternative implementation, a T311 timer may be used as Timer C. Details of the T311 timer (called the RRC connection re-establishment timer) are described, for example, in Non-Patent Document 6 of June 2023 (T "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Radio Resource Control (RRC) protocol specification (Release 17)"). This definition combines rapid LTM recovery with an RRC connection re-establishment procedure for cell (re)selection.

[0167] Similar to the description of the first embodiment, UE100 may perform a non-RACH or RACH-based transmission of the first UL data to the recovery cell. For example, if the UL channel is synchronized in the recovery cell, i.e., if UE100 knows the Timing Advance (TA) value of the recovery cell, UE100 may perform a non-RACH procedure. On the other hand, if UE100 does not know the TA value of the recovery cell, a RACH-based transmission may be performed, in which case UE100 may send a RACH message to the recovery cell to obtain the TA value and then perform a UL transmission of the first UL data to the recovery cell.

[0168] As the first UL data, an RRC reconstruction complete message may be sent to the recovery cell. That is, since an LTM recovery candidate cell can be set in UE100 using the DL's RRC reconstruction message, UE100 may send an RRC reconstruction complete message to the recovery cell as a UL response to the original RRC message during cell recovery, as described in the first embodiment.

[0169] Figure 11 is a flowchart illustrating exemplary steps performed by the user equipment and base station in a second embodiment, where the user equipment is configured to have at least one candidate recovery cell.

[0170] In Figure 11, UE100 receives service from base station 200 via a source cell. In step S500, the base station determines the priority of the LTM candidate cell, ConfigA (at least one candidate recovery cell), and ConfigB (at least one candidate recovery cell). The base station may determine only one candidate recovery cell. In this case, the determination or priority order is not necessarily required. Similarly, even if multiple candidate recovery cells are determined, base station 200 does not need to determine a priority order. In this case, UE100 may decide how to select a recovery cell from the configured candidate recovery cells (for example, based on the results of L1 measurements, as described above). The LTM candidate configuration, ConfigA, and ConfigB are transmitted from base station 200 to UE100. In step S510, the base station may determine new configurations for ConfigA and ConfigB and transmit these new ConfigA and ConfigB to UE100. This transmission to UE100 may be done in an RRC reconfiguration message. In step S520, the base station 200 decides that the UE100 will perform an LTM operation to switch to a specific target cell, and sends a corresponding cell switching command to the UE100, for example, using MAC CE. Upon receiving the cell switching command, the UE100 performs an LTM operation to switch to the notified target cell and determines whether the LTM operation was successful. If a cell switching error is detected in step S410, the UE100, in step S420, uses ConfigA and ConfigB (if configured) to select a recovery cell from the configured candidate recovery cells and performs an LTM operation to switch to the selected recovery cell.

[0171] Figure 12a is a flowchart illustrating exemplary steps performed by user equipment and a base station in a second embodiment, showing the case where recovery to a recovery cell is successful.

[0172] Figure 12b is a flowchart illustrating exemplary steps taken by user equipment and a base station in a second embodiment, showing the case where recovery to a recovery cell is unsuccessful.

[0173] Figures 12a and 12b show the case where UE100 has one candidate recovery cell configured. However, the disclosure is not limited thereto, and UE100 may have multiple candidate recovery cells configured as described above. In Figures 11, 12a, and 12b, the same or corresponding steps are denoted by the same reference numerals.

[0174] In step S520, the base station 200 decides that the UE100 will perform an LTM operation to switch to the target cell. A candidate recovery cell is also determined. A cell switching command indicating the target cell (target cell 1) and the recovery cell (candidate cell 2) is sent to the UE100. This transmission may be performed using MAC CE. In step S400, the UE100 performs an LTM operation to switch from the source cell to the target cell indicated in the cell switching command, or indicated by the cell switching command, and starts the LTM monitoring timer. Due to packet loss, in step S410, the UE100 determines that the LTM operation to switch to the target cell was unsuccessful. As a result, in steps S420 / S430, the UE selects the recovery cell indicated in the cell switching command and performs an LTM operation to switch to the recovery cell. If cell recovery is successful in step S600 in Figure 12a, service continues between the UE100 and the recovery cell, i.e., candidate cell 2. On the other hand, if it is determined in step S440 of Figure 12b that the LTM operation to switch to the recovery cell was unsuccessful, the UE100 performs the cell selection and RRC (Radio Resource Control) connection re-establishment procedure in step S450.

[0175] As described above, a cell switching command using a single MAC CE may include ConfigA and ConfigB. In other words, a single cell switching command (MAC CE) may be sent to UE100 indicating the target cell, at least one candidate recovery cell, and optionally, the priority of at least one candidate recovery cell (for example, if multiple candidate recovery cells are indicated). When UE100 receives the MAC CE, an LTM operation is performed to switch to the notified target cell. If a cell switching error is detected, an LTM operation may be performed in which a recovery cell is selected from the at least one candidate recovery cell indicated by the MAC CE, and the UE100 switches to the selected recovery cell.

[0176] <Variation> Figure 13 shows an example of a MAC CE that functions as a cell switching command including a recovery cell notification, according to a second embodiment.

[0177] MAC CE indicates the target cell by the target cell ID, DL BWP ID (Downlink Bandwidth part ID / optional), UL BWP ID (Uplink Bandwidth part ID / optional), TCI status indicator, and TA value. MAC CE also indicates candidate recovery cells by the candidate cell ID, DL BWP ID (Downlink Bandwidth part ID / optional), UL BWP ID (Uplink Bandwidth part ID / optional), TCI status indicator, and TA value. As described above, UE100 may select a candidate recovery cell as the recovery cell for executing the LTM operation to switch to a recovery cell after a cell switching error (when switching to a target cell) is detected. Although not shown in Figure 13, MAC CE may include information on further candidate recovery cells. In this case, the order in which the candidate recovery cells are indicated may determine the priority of candidate recovery cells used by UE100 when selecting a recovery cell from among multiple candidate recovery cells.

[0178] Figure 14 shows an example MAC CE that functions as a cell switching command, including instructions for prioritizing multiple recovery cells.

[0179] In the illustration in Figure 14, a MAC PDU (MAC Protocol Data Unit) contains multiple MAC CEs in order from the most significant bit (MSB) to the least significant bit (LSB). Each MAC CE may represent a cell. Specifically, the first MAC CE may represent the target cell to which UE100 switches within the framework of LTM operation. The following MAC CEs each represent a candidate recovery cell to be used by UE100 to select a recovery cell if the switch to the target cell fails. In particular, the order of the MAC CEs from MSB to LSB may indicate the priority of the candidate recovery cells.

[0180] In other words, repeated cell-switching MAC CEs are used within the same MAC PDU, and candidate recovery cells are set as ConfigA and ConfigB. No changes to the MAC CE definitions are necessary compared to the implementation shown in Figure 14. If only one candidate recovery cell is indicated in the MAC PDU, priority is clearly unnecessary. However, if multiple candidate recovery cells are indicated by each MAC CE in the MAC PDU, the order from MSB to LSB may indicate priority. However, priority may be indicated independently of the order of each MAC CE in the MAC PDU.

[0181] In implementations other than those illustrated in Figures 13 and 14, different types of MAC CEs may be used to distinguish whether each MAC CE is related to target cell designation or candidate recovery cell designation. In other words, two types of cell switching MAC CEs may be used to distinguish between a normal cell switching MAC CE with a target cell and a cell switching recovery MAC CE for performing recovery on a designated candidate cell.

[0182] When UE100 receives a cell switching MAC CE indicating a target cell and a cell recovery MAC CE indicating a candidate recovery cell (i.e., configA), it may perform an LTM operation to switch to the target cell. If a cell switching error is detected, it may perform an LTM operation to select a recovery cell from the candidate recovery cells indicated in the MAC CE and switch to the selected recovery cell. If multiple candidate recovery cells are indicated by each MAC CE, a priority order may be indicated to UE100. That is, a MAC CE indicating the priority order (i.e., configB) may be sent. UE100 may then use the priority order when selecting a recovery cell, as described above.

[0183] <Third Embodiment> In a third embodiment, the UE100 includes a transceiver 110 that, when operating, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell, and a cell switching command indicating one of the at least one LTM candidate cell as the target cell to switch to. The UE100 further includes a circuit that, when operating, performs an LTM operation to switch from a source cell servicing the UE100 to a target cell according to the cell switching command, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects the source cell as the recovery cell, or selects one of at least one candidate recovery cells, which includes one or more of the at least one LTM candidate cells indicated by the LTM candidate setting, as the recovery cell, and performs an LTM operation to switch to the selected recovery cell.

[0184] In other words, UE100 selects a recovery cell from the source cell and at least one candidate recovery cell. That is, the third embodiment can be considered a combination of the first and second embodiments. Therefore, all aspects described above for the first and second embodiments may also apply to the third embodiment.

[0185] For example, UE100 may be configured with at least one candidate recovery cell, as in the second embodiment, and furthermore, as in the first embodiment, the cell switching command may indicate that recovery to the source cell is permitted.

[0186] In this scenario, after determining that the LTM operation to switch to the target cell was unsuccessful, if the cell switching command indicates that the source cell can be selected as the recovery cell, UE100 may select the source cell as the recovery cell and execute an LTM operation to switch to the source cell. UE100 also determines whether the LTM operation to switch to the selected source cell as the recovery cell was successful. If the LTM operation to switch to the source cell as the recovery cell was unsuccessful, UE100 selects at least one of the candidate recovery cells as the next recovery cell and executes an LTM operation to switch to the selected next recovery cell.

[0187] In other words, UE100 may first select a source cell as the recovery cell, and if the switch to the source cell is unsuccessful, it may select one of at least one candidate recovery cell as the next recovery cell and perform the next LTM operation to switch to the selected next recovery cell. If multiple candidate recovery cells are set in the UE, UE100 may select the next recovery cell by applying the operation described in the second embodiment. That is, the next recovery cell (potentially the recovery cell after that if the switch to the recovery cell is unsuccessful) may be selected by applying the priority of the candidate recovery cells or by using the L1 measurement results.

[0188] In another implementation, UE100 performs channel state measurements on the source cell and at least one configured candidate recovery cell, and selects a recovery cell from the source cell and at least one candidate recovery cell according to the results of the channel state measurements. That is, instead of selecting the source cell as the first recovery cell by default, UE100 may select a recovery cell using the results of the channel state measurement of the source cell and the results of the L1 measurement of all candidate recovery cells.

[0189] In another implementation, if UE100 is configured with a source cell and at least one candidate recovery cell, UE100 may select a recovery cell according to predetermined conditions. For example, the above conditions may be based on the SINR / signal quality of the source cell and / or candidate recovery cell. As an example, a SINR threshold may be defined for the source cell and / or each candidate recovery cell. If the SINR of the source cell exceeds that threshold, UE100 selects the source cell as the recovery cell. If the SINR of the source cell does not exceed that threshold, UE100 may select a candidate recovery cell whose SINR exceeds the threshold and perform an LTM operation to switch to the selected recovery cell.

[0190] In other words, UE100 receives a recovery setting indicating at least one candidate recovery cell from at least one LTM candidate cell, and the cell switching command indicates that the source cell is permitted to be selected as the recovery cell. In this situation, UE may select a recovery cell from the source cell and at least one candidate recovery cell according to predetermined conditions. Subsequently, UE100 performs an LTM operation to switch to the selected recovery cell.

[0191] As in the first and second embodiments, the UE100 may start an LTM monitoring timer when it receives a cell switching command, and may determine that the LTM operation to switch from the source cell to the target cell was unsuccessful if a synchronization error occurs, if the LTM monitoring timer expires before receiving a UL grant or PUSCH (Physical Uplink Shared Channel) resource, and / or if the number of errors in sending UL data or RACH (Random Access Channel) messages to the target cell exceeds a threshold.

[0192] <Implementation of this disclosure through hardware and software> This disclosure can be implemented by software, by hardware, or by software working in conjunction with hardware. Each functional block used in the description of each embodiment above can be implemented in whole or in part by an LSI such as an integrated circuit, and each process described in each embodiment can be controlled in whole or in part by the same LSI or combination of LSIs. An LSI can be formed individually as a chip, or it can be formed as a single chip containing some or all of the functional blocks. An LSI can include data input / output units coupled to itself. Depending on the degree of integration, an LSI is also called an IC (integrated circuit), system LSI, super LSI, or ultra LSI. However, the technology for implementing an integrated circuit is not limited to LSIs and can be implemented using dedicated circuits, general-purpose processors, or dedicated processors. Furthermore, a Field Programmable Gate Array (FPGA) that can be programmed after the manufacture of the LSI, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells located inside the LSI can also be used. This disclosure can be implemented as a digital process or an analog process. If LSIs are replaced by future integrated circuit technologies as a result of advancements in semiconductor technology or other derivative technologies, functional blocks can be integrated using those future integrated circuit technologies. Biotechnology can also be applied.

[0193] This disclosure can be implemented by any type of device or system having communication capabilities (referred to as a communication device).

[0194] The communication device may include the above-described transmitting / receiving unit and processing / control circuit. The transmitting / receiving unit includes a receiving unit and a transmitting unit, and / or can function as a receiving unit and a transmitting unit. The transmitting / receiving unit as a transmitting and receiving unit may include an RF module including an amplifier, an RF (radio frequency) modulator / demodulator, etc., and one or more antennas.

[0195] Some non-exclusive examples of such communication devices include telephones (e.g., mobile phones, smartphones), tablets, personal computers (PCs) (e.g., laptops, desktops, notebooks), cameras (e.g., digital still / video cameras), digital players (digital audio / video players), wearable devices (e.g., wearable cameras, smartwatches, tracking devices), game consoles, e-readers, telemedicine / telemedicine devices, vehicles providing communication capabilities (e.g., automobiles, airplanes, ships), and various combinations thereof.

[0196] Communication devices are not limited to portable or mobile devices, but may include any type of non-portable or fixed device, device, or system, such as smart home devices (e.g., appliances, lighting, smart meters, control panels), vending machines, and any other "things" in the "Internet of Things (IoT)" network.

[0197] Communication may include steps such as exchanging data through cellular systems, wireless LAN systems, satellite systems, and others, and various combinations thereof.

[0198] A communication device may include devices such as controllers and sensors coupled to a communication device that performs the communication functions described in this disclosure. For example, a communication device may include a controller or sensor that generates control signals or data signals used by the communication device that performs the communication functions of the communication device.

[0199] Communication equipment may further include base stations, access points, and any other devices, devices, or systems that communicate with or control infrastructure equipment, such as the devices in the non-limiting examples above.

[0200] Furthermore, various embodiments may be implemented by software modules, which are executed by a processor or directly in hardware. Combinations of software modules and hardware implementations are also possible. The software modules can be stored in any type of computer-readable storage medium. In particular, other implementations provide non-temporary computer-readable recording media. When executed by one or more processors, the recording media stores a program that causes one or more processors to perform the steps of the method according to this disclosure.

[0201] As an unrestricted example, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage devices, magnetic disk storage devices, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and can be accessed by a computer. Any connection is also referred to as computer-readable media, as appropriate. For example, if instructions are transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of media. However, it should be understood that computer-readable storage media and data storage media do not include connections, carriers, signals, or other temporary media, but instead refer to non-temporary tangible storage media. As used herein, the terms "disk" and "disc" include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs (Blu-ray® discs), where a disk typically reproduces data magnetically, while a disc reproduces data optically using a laser. Any combination of the above should also be included within the scope of computer-readable media.

[0202] Furthermore, it should be noted that individual features of several different embodiments can be the subject of other embodiments, individually or in any combination. Those skilled in the art will understand that various changes and / or modifications can be made to the specific embodiments of this disclosure without departing from the broadly defined concept or scope of the invention. Therefore, the embodiments described herein are illustrative in all respects and are not intended to limit the invention.

[0203] <Further aspects> According to the first embodiment, user equipment (UE) is provided. When operating, the UE includes a transceiver that receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell, and a cell switching command indicating one of the at least one LTM candidate cell as the target cell to switch to. When operating, the UE further includes a circuit that performs an LTM operation to switch from a source cell servicing the UE to the target cell in accordance with the cell switching command, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects the source cell as a recovery cell, or selects one of at least one candidate recovery cells including one or more of the at least one LTM candidate cells indicated by the LTM candidate setting as a recovery cell, and performs an LTM operation to switch to the selected recovery cell.

[0204] According to a second aspect, the UE described in the first aspect is provided, wherein the cell switching command indicates whether the source cell is permitted to be selected as the recovery cell, and the circuit, when operating, selects the source cell as the recovery cell if the cell switching command indicates that the source cell is permitted to be selected as the recovery cell, and performs a cell selection and radio resource control (RRC) connection re-establishment procedure if the cell switching command indicates that the source cell is not permitted to be selected as the recovery cell.

[0205] According to a third aspect, if the UE described in the second aspect is provided and the source cell is selected as the recovery cell, the transmitting / receiving unit, in operation, performs a first UL transmission after switching to the source cell as the recovery cell, the first UL transmission includes at least one of a UL channel state information (CSI) report, a sounding reference signal (SRS), a cell switching error indicator, and an RRC reconfiguration error message.

[0206] According to a fourth aspect, if the UE described in the second or third aspect is provided and the source cell is selected as the recovery cell, the circuit, in operation, after switching to the source cell selected as the recovery cell, reuses the downlink (DL) and uplink (UL) synchronization characteristics and bearer settings that were applied to transmission and reception with the source cell before receiving the cell switching command.

[0207] According to the fifth aspect, a UE is provided as described in any one of the second to fourth aspects, wherein the circuit determines, during operation, whether the LTM operation to switch to the source cell was successful or not, and if it is determined that the LTM operation to switch to the source cell was unsuccessful, it performs a cell selection and radio resource control (RRC) connection re-establishment procedure.

[0208] According to the sixth aspect, the UE described in the first aspect is provided, wherein the transmitting / receiving unit receives a recovery setting indicating the at least one candidate recovery cell from among the at least one LTM candidate cell during operation.

[0209] According to the seventh aspect, the UE described in the sixth aspect is provided, wherein the recovery setting indicates a single candidate recovery cell, and the circuit, in operation, selects the single candidate recovery cell as the recovery cell.

[0210] According to the eighth aspect, the UE described in the sixth aspect is provided, wherein the recovery setting indicates a plurality of candidate recovery cells, the transmitting / receiving unit receives a priority indicator indicating the priority of the plurality of candidate recovery cells during operation, and the circuit selects a recovery cell from the plurality of candidate recovery cells according to the priority during operation.

[0211] According to the ninth aspect, the UE described in the sixth aspect is provided, wherein the recovery setting indicates a plurality of candidate recovery cells, and the circuit, during operation, performs a channel state measurement and selects a recovery cell from the plurality of candidate recovery cells according to the result of the channel state measurement.

[0212] According to the tenth aspect, a UE is provided as described in any one of the sixth to ninth aspects, wherein, during operation, if any of the LTM operations to switch to the candidate recovery cell are unsuccessful, the circuit performs a cell selection and radio resource control (RRC) connection re-establishment procedure.

[0213] According to the eleventh aspect, the UE described in the first aspect is provided, wherein the transmitting / receiving unit receives a recovery setting indicating the at least one candidate recovery cell from among the at least one LTM candidate cell during operation, the cell switching command indicates that the source cell is permitted to be selected as the recovery cell, and the circuit selects the recovery cell from among the source cell and the at least one candidate recovery cell during operation according to predetermined conditions.

[0214] According to the twelfth aspect, the UE described in the eleventh aspect is provided, wherein, during operation, if the cell switching command indicates that the source cell is permitted to be selected as the recovery cell, the circuit determines whether the LTM operation to select the source cell as the recovery cell and switch to the selected recovery cell (source cell) was successful, and if the LTM operation to switch to the recovery cell (source cell) was unsuccessful, the circuit selects one of the at least one candidate recovery cells as the next recovery cell and performs an LTM operation to switch to the selected next recovery cell.

[0215] According to the 13th aspect, the UE described in the 11th aspect is provided, wherein the circuit, during operation, measures the channel state of the source cell and the at least one candidate recovery cell, and selects the recovery cell from the source cell and the at least one candidate recovery cell according to the results of the channel state measurement.

[0216] According to the 14th aspect, a UE is provided as described in any one of the first to 13 aspects, wherein the circuit, during operation, activates an LTM monitoring timer upon receiving the cell switching command, and determines that the LTM operation to switch from the source cell to the target cell was unsuccessful if a synchronization error occurs, if the LTM monitoring timer expires before receiving a UL grant or a Physical Uplink Shared Channel (PUSCH) resource, and / or if the number of transmission errors for UL data or Random Access Channel (RACH) messages to the target cell exceeds a threshold.

[0217] According to the 15th aspect, a method is provided for a user device that receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell, receives a cell switching command indicating one of the at least one LTM candidate cell as the target cell to switch to, performs an LTM operation to switch from a source cell serving the UE to the target cell in accordance with the cell switching command, determines whether the LTM operation to switch from the source cell to the target cell was successful, and if it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, selects the source cell as a recovery cell, or selects one of at least one candidate recovery cells including one or more of the at least one LTM candidate cells indicated by the LTM candidate setting as a recovery cell, and performs an LTM operation to switch to the selected recovery cell.

[0218] According to the 16th aspect, a method of the 15th aspect is provided, wherein the cell switching command indicates whether the source cell is permitted to be selected as the recovery cell, and the method includes selecting the source cell as the recovery cell if the cell switching command indicates that the source cell is permitted to be selected as the recovery cell, and performing a cell selection and radio resource control (RRC) connection re-establishment procedure if the cell switching command indicates that the source cell is not permitted to be selected as the recovery cell.

[0219] According to the 17th aspect, the method of the 16th aspect is provided, wherein if the source cell is selected as the recovery cell, a first UL transmission is performed after switching to the source cell as the recovery cell, the first UL transmission includes at least one of a UL channel state information (CSI) report, a sounding reference signal (SRS), a cell switching error indicator, and an RRC reconfiguration error message.

[0220] According to the 18th aspect, the method of the 16th or 17th aspect is provided, wherein if the source cell is selected as the recovery cell, the downlink (DL) and uplink (UL) synchronization characteristics and bearer settings that were applied to transmission and reception with the source cell before receiving the cell switching command are reused after switching to the source cell selected as the recovery cell.

[0221] According to the 19th aspect, a method is provided in any one of the 16th to 18th aspects, wherein it is determined whether the LTM operation to switch to the source cell was successful, and if it is determined that the LTM operation to switch to the source cell was unsuccessful, a cell selection and radio resource control (RRC) connection re-establishment procedure is performed.

[0222] According to the 20th aspect, the method of the 15th aspect is provided, which includes receiving a recovery setting indicating the at least one candidate recovery cell from among the at least one LTM candidate cell.

[0223] According to a 21st aspect, the method of the 20th aspect is provided, wherein the recovery setting indicates a single candidate recovery cell, and the single candidate recovery cell is selected as the recovery cell.

[0224] According to the 22nd aspect, a method of the 20th aspect is provided, wherein the recovery setting indicates a plurality of candidate recovery cells, and the method includes receiving a priority indicator indicating the priority of the plurality of candidate recovery cells, and selecting a recovery cell from the plurality of candidate recovery cells according to the priority.

[0225] According to the 23rd aspect, a method of the 20th aspect is provided, wherein the recovery setting indicates a plurality of candidate recovery cells, and the method includes performing a channel state measurement and selecting a recovery cell from the plurality of candidate recovery cells according to the results of the channel state measurement.

[0226] According to the 24th aspect, a method of any one of the 20th to 23rd aspects is provided, which includes performing a cell selection and radio resource control (RRC) connection re-establishment procedure if none of the LTM operations to switch to the candidate recovery cell are successful.

[0227] According to the 25th aspect, a method of the 15th aspect is provided, comprising receiving a recovery setting indicating the at least one candidate recovery cell from among the at least one LTM candidate cell, wherein the cell switching command indicates that the source cell is permitted to be selected as the recovery cell, and the method comprises selecting the recovery cell from among the source cell and the at least one candidate recovery cell according to predetermined conditions.

[0228] According to the 26th aspect, the method of the 25th aspect is provided, wherein if the cell switching command indicates that the source cell is permitted to be selected as the recovery cell, the source cell is selected as the recovery cell, and it is determined whether the LTM operation to switch to the selected recovery cell, the source cell, has been successfully executed. If the LTM operation to switch to the recovery cell, the source cell, has not been successful, one of the at least one candidate recovery cells is selected as the next recovery cell, and the LTM operation to switch to the selected next recovery cell is executed.

[0229] According to the 27th aspect, the method of the 25th aspect is provided, which includes measuring the channel state of the source cell and the at least one candidate recovery cell, and selecting the recovery cell from the source cell and the at least one candidate recovery cell according to the results of the channel state measurement.

[0230] According to the 28th aspect, a method is provided according to any one of the 15th to 27th aspects, which includes activating an LTM monitoring timer upon receipt of the cell switching command, and determining that the LTM operation to switch from the source cell to the target cell was unsuccessful if a synchronization error occurs, the LTM monitoring timer expires before receiving a UL grant or a Physical Uplink Shared Channel (PUSCH) resource, and / or the number of transmission errors for UL data or Random Access Channel (RACH) messages to the target cell exceeds a threshold.

[0231] According to the 29th aspect, a base station is provided. The base station comprises a circuit that, when in operation, determines at least one lower-layer triggered mobility (LTM) candidate cell, and a transceiver that, when in operation, transmits an LTM candidate setting indicating at least one LTM candidate cell. The circuit further determines one of the at least one LTM candidate cell as the target cell to which user equipment (UE) will switch. The transceiver transmits a cell switching command indicating the target cell.

[0232] According to the 30th aspect, a base station as described in the 29th aspect is provided, wherein the cell switching command indicates whether or not the source cell is permitted to be selected as the recovery cell.

[0233] According to the 31st aspect, a base station as described in the 30th aspect is provided, wherein the transceiver unit receives a first UL transmission during operation, which includes at least one of a UL channel state information (CSI) report, a sounding reference signal (SRS), a cell switching error indicator, and an RRC reconfiguration error message.

[0234] According to the 32nd aspect, a base station as described in the 30th or 31st aspect is provided, and when the source cell is selected as the recovery cell, the circuit, in operation, reuses the downlink (DL) and uplink (UL) synchronization characteristics and bearer settings that were applied to transmission and reception with the source cell before receiving the cell switching command, after the UE has switched to the source cell selected as the recovery cell.

[0235] According to the 33rd aspect, a base station as described in the 29th aspect is provided, wherein the circuit, when in operation, determines the at least one candidate recovery cell from among the at least one LTM candidate cell, and the transceiver unit, when in operation, transmits a recovery setting indicating the at least one candidate recovery cell from among the at least one LTM candidate cell.

[0236] According to the 34th aspect, a base station as described in the 33rd aspect is provided, wherein the recovery setting indicates a single candidate recovery cell.

[0237] According to the 35th aspect, a base station as described in the 33rd aspect is provided, wherein the recovery setting indicates a plurality of candidate recovery cells, the circuit determines the priority of the plurality of candidate recovery cells, and the transmitting / receiving unit transmits a priority indicator indicating the priority of the plurality of candidate recovery cells when in operation.

[0238] According to the 36th aspect, a base station as described in the 33rd aspect is provided, wherein the recovery setting indicates a plurality of candidate recovery cells.

[0239] According to the 37th aspect, a base station as described in the 29th aspect is provided, wherein the circuit, when in operation, determines the at least one candidate recovery cell from among the at least one LTM candidate cell, the transceiver, when in operation, transmits a recovery setting indicating the at least one candidate recovery cell from among the at least one LTM candidate cell, and the cell switching command indicates that the source cell is permitted to be selected as the recovery cell.

[0240] According to the 38th aspect, a method for a base station is provided. The method includes determining at least one lower-layer triggered mobility (LTM) candidate cell, transmitting an LTM candidate setting indicating at least one LTM candidate cell, determining one of the at least one LTM candidate cell as a target cell to which user equipment (UE) will switch, and transmitting a cell switching command indicating the target cell.

[0241] According to the 39th aspect, the method of the 38th aspect is provided, wherein the cell switching command indicates whether or not the source cell is permitted to be selected as the recovery cell.

[0242] According to the 40th aspect, a method of the 39th aspect is provided, which includes receiving a first UL transmission including at least one of a UL Channel State Information (CSI) report, a sounding reference signal (SRS), a cell switching error indicator, and an RRC reconfiguration error message.

[0243] According to the 41st aspect, a method of the 39th or 40th aspect is provided, which includes reusing the downlink (DL) and uplink (UL) synchronization characteristics, as well as the bearer settings, that were applied to transmission and reception with the source cell before receiving the cell switching command, after switching to the source cell selected as the recovery cell.

[0244] According to the 42nd aspect, a method of the 38th aspect is provided, which includes determining the at least one candidate recovery cell from among the at least one LTM candidate cell, and transmitting a recovery setting indicating the at least one candidate recovery cell from among the at least one LTM candidate cell.

[0245] According to the 43rd aspect, a base station as described in the 42nd aspect is provided, wherein the recovery setting indicates a single candidate recovery cell.

[0246] According to the 44th aspect, a base station as described in the 42nd aspect is provided, wherein the recovery setting indicates a plurality of candidate recovery cells, and the method includes determining the priority of the plurality of candidate recovery cells and transmitting a priority indicator indicating the priority of the plurality of candidate recovery cells.

[0247] According to the 45th aspect, a base station as described in the 42nd aspect is provided, wherein the recovery setting indicates a plurality of candidate recovery cells.

[0248] According to the 46th aspect, a base station as described in the 38th aspect is provided, comprising determining the at least one candidate recovery cell from among the at least one LTM candidate cell, and transmitting a recovery setting indicating the at least one candidate recovery cell from among the at least one LTM candidate cell, wherein the cell switching command indicates that the source cell is permitted to be selected as the recovery cell.

[0249] In summary, the present invention provides a user device (UE), a base station, and a corresponding method for the user device and base station. The UE includes a transceiver that, when in operation, receives an LTM candidate setting indicating at least one lower-layer triggered mobility (LTM) candidate cell, and a cell switching command indicating one of the at least one LTM candidate cell as the target cell to switch to. The UE further includes a circuit that, when in operation, performs an LTM operation to switch from a source cell servicing the UE to the target cell in accordance with the cell switching command, and determines whether the LTM operation to switch from the source cell to the target cell was successful. If the circuit determines that the LTM operation to switch from the source cell to the target cell was unsuccessful, the circuit selects the source cell as a recovery cell, or selects one of at least one candidate recovery cells, including one or more of the at least one LTM candidate cell indicated by the LTM candidate setting, as a recovery cell, and performs an LTM operation to switch to the selected recovery cell.

Claims

1. During operation, Receive an LTM candidate configuration indicating at least one lower-layer triggered mobility (LTM) candidate cell. A transmitting and receiving unit that receives a cell switching command indicating one of the at least one LTM candidate cells as the target cell to be switched to, During operation, In accordance with the aforementioned cell switching command, the LTM operation is executed to switch from the source cell serving user equipment (UE) to the target cell. Determine whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, Select the aforementioned source cell as a recovery cell, or select one of at least one candidate recovery cell that includes one or more of the at least one LTM candidate cells indicated by the LTM candidate setting as a recovery cell. A circuit that performs an LTM operation to switch to the selected recovery cell, A UE equipped with [unclear] features.

2. The cell switching command indicates whether or not it is permitted to select the source cell as the recovery cell. The circuit, when in operation, If the cell switching command indicates that it is permitted to select the source cell as the recovery cell, then the source cell is selected as the recovery cell. If the cell switching command indicates that the source cell is not permitted to be selected as the recovery cell, the cell selection and Radio Resource Control (RRC) connection re-establishment procedure is performed. The UE according to claim 1.

3. When the source cell is selected as the recovery cell, the transmitting / receiving unit, during operation, performs a first UL transmission after switching to the source cell as the recovery cell, and the first UL transmission includes at least one of the following: a UL channel state information (CSI) report, a sounding reference signal (SRS), a cell switching error indicator, and an RRC reset error message. The UE according to claim 2.

4. When the source cell is selected as the recovery cell, the circuit, during operation, after switching to the source cell selected as the recovery cell, reuses the downlink (DL) and uplink (UL) synchronization characteristics and bearer settings that were applied to transmission and reception with the source cell before receiving the cell switching command. The UE according to claim 2 or 3.

5. The circuit, when in operation, Determine whether the LTM operation to switch to the source cell was successful or not. If it is determined that the LTM operation to switch to the source cell was unsuccessful, the cell selection and Radio Resource Control (RRC) connection re-establishment procedure is executed. The UE according to any one of claims 2 to 4.

6. The transmitting and receiving unit, during operation, receives a recovery setting indicating at least one candidate recovery cell from among the at least one LTM candidate cell. The UE according to claim 1.

7. The recovery setting indicates a single candidate recovery cell. The circuit, during operation, selects the single candidate recovery cell as the recovery cell. The UE according to claim 6.

8. The recovery setting indicates multiple candidate recovery cells, The transmitting and receiving unit receives a priority indicator that shows the priority of the plurality of candidate recovery cells during operation. The circuit, during operation, selects a recovery cell from among the plurality of candidate recovery cells according to the priority order. The UE according to claim 6.

9. The recovery setting indicates multiple candidate recovery cells, The circuit, during operation, measures the channel state and selects a recovery cell from among the multiple candidate recovery cells according to the results of the channel state measurement. The UE according to claim 6.

10. The circuit, when operating, executes a cell selection and Radio Resource Control (RRC) connection re-establishment procedure if none of the LTM operations to switch to the candidate recovery cell are successful. The UE according to any one of claims 6 to 9.

11. During operation, the transmitting and receiving unit receives a recovery setting indicating at least one candidate recovery cell from among the at least one LTM candidate cell. The cell switching command indicates that the source cell is permitted to be selected as the recovery cell. The circuit, during operation, selects a recovery cell from the source cell and the at least one candidate recovery cell according to predetermined conditions. The UE according to claim 1.

12. The circuit, when in operation, If the cell switching command indicates that it is permitted to select the source cell as the recovery cell, then the source cell is selected as the recovery cell. Determine whether the LTM operation to switch to the selected recovery cell, which is the source cell, was successful. If the LTM operation to switch to the source cell which is the recovery cell is unsuccessful, one of the at least one candidate recovery cells is selected as the next recovery cell. The LTM operation is performed to switch to the next selected recovery cell. The UE according to claim 11.

13. The circuit, during operation, measures the channel state of the source cell and the at least one candidate recovery cell, and selects the recovery cell from the source cell and the at least one candidate recovery cell according to the results of the channel state measurement. The UE according to claim 11.

14. The circuit, when in operation, When the aforementioned cell switching command is received, the LTM monitoring timer is activated. If a synchronization error occurs, If the LTM monitoring timer expires before a UL grant or Physical Uplink Shared Channel (PUSCH) resource is allocated, and / or, If the number of transmission errors for UL data or Random Access Channel (RACH) messages to the target cell exceeds a threshold, It is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful. The UE according to any one of claims 1 to 13.

15. A method performed by user equipment (UE), Receive an LTM candidate configuration indicating at least one lower-layer triggered mobility (LTM) candidate cell. A cell switching command is received that indicates one of the at least one LTM candidate cells as the target cell to be switched to. In accordance with the aforementioned cell switching command, the LTM operation is executed to switch from the source cell serving the UE to the target cell. Determine whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, Select the aforementioned source cell as a recovery cell, or select one of at least one candidate recovery cell that includes one or more of the at least one LTM candidate cells indicated by the LTM candidate setting as a recovery cell. The LTM operation is performed to switch to the selected recovery cell. method.

16. An integrated circuit configured to control user equipment (UE), During operation, Receive an LTM candidate configuration indicating at least one lower-layer triggered mobility (LTM) candidate cell. A transceiver circuit that receives a cell switching command indicating one of the at least one LTM candidate cells as the target cell to be switched to, During operation, In accordance with the aforementioned cell switching command, the LTM operation is executed to switch from the source cell serving the UE to the target cell. Determine whether the LTM operation to switch from the source cell to the target cell was successful. If it is determined that the LTM operation to switch from the source cell to the target cell was unsuccessful, Select the aforementioned source cell as a recovery cell, or select one of at least one candidate recovery cell that includes one or more of the at least one LTM candidate cells indicated by the LTM candidate setting as a recovery cell. The system includes a control circuit that performs an LTM operation to switch to the selected recovery cell, Integrated circuit.

17. During operation, a circuit determines at least one lower-layer triggered mobility (LTM) candidate cell, A base station comprising: a transceiver unit that transmits an LTM candidate setting indicating at least one LTM candidate cell during operation, During operation, the circuit determines one of the at least one LTM candidate cell as the target cell to which the user equipment (UE) will switch. The transmitting / receiving unit transmits a cell switching command indicating the target cell during operation. Base station.

18. A method performed by a base station, Determine at least one lower-layer triggered mobility (LTM) candidate cell, Send an LTM candidate setting that indicates at least one LTM candidate cell, One of the at least one LTM candidate cells is determined to be the target cell to which the user equipment (UE) will switch. Send a cell switching command indicating the target cell. method.

19. An integrated circuit configured to control a base station, A control circuit that determines at least one lower-layer triggered mobility (LTM) candidate cell during operation, The system includes a transmit / receive circuit that transmits an LTM candidate setting indicating at least one LTM candidate cell during operation, During operation, the control circuit determines one of the at least one LTM candidate cell as the target cell to which the user equipment (UE) will switch. The transmitting and receiving circuit transmits a cell switching command indicating the target cell when in operation. Integrated circuit.

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