User Equipment and Base Stations Involved in Mobility Procedures

Abstract

The present disclosure relates to a base station central unit (BS-CU) comprising: a transmitter that transmits a mobility request to a distributed unit (mobility candidate BS-DU) of a base station that is a candidate for participating in user equipment (UE) mobility; a receiver of the BS-CU that receives, from the mobility candidate BS-DU, a reference signal (RS) resource configuration of the mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU; a processing circuit of the BS-CU that generates an updated list, the updated RS resource configuration list including information on the received RS resource configuration of the mobility candidate BS-DU and information on the RS resource configuration of at least a serving BS-DU that serves the UE; and a transmitter that transmits the contents of the updated RS resource configuration list to the serving BS-DU for further forwarding to the UE.

Description

[Technical Field]

[0001] The present disclosure is directed to methods, apparatus, and articles in communication systems, such as 3GPP communication systems. [Background technology]

[0002] Currently, the 3rd Generation Partnership Project (3GPP) is working on technical specifications for a new radio access technology, 5G New Radio (NR), also referred to as fifth generation (5G) or NR, which are used interchangeably herein.

[0003] One objective is to provide a single technical framework that addresses all usage scenarios, requirements, and deployment scenarios (see, for example, Section 6 of Non-Patent Document 1), including at least enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine-type communications (mMTC). For example, deployment scenarios for eMBB may include indoor hotspots, dense urban areas, suburban areas, and urban macro-high-speed environments. Deployment scenarios for URLLC may include industrial control systems, mobile health management (remote monitoring, remote diagnosis, and remote treatment), real-time vehicle control, and wide-area monitoring and control systems for smart grids. Deployment scenarios for mMTC may include scenarios using a large number of devices, such as smart wearables and sensor networks, where the impact of data transmission latency is small. While eMBB and URLLC services are similar in that both require very high bandwidth, URLLC services differ in that they preferably require ultra-low latency.

[0004] A second goal is to achieve forward compatibility, which facilitates the introduction of entirely new system designs and / or new features. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] 3GPP TR 38.913 v16.0.0 / v17.0.0 [Non-patent document 2] 3GPP TS 38.300 v17.2.0 [Non-patent document 3] 3GPP TS 38.211 v17.4.0 [Non-patent document 4] ITU-R M.20183 [Non-patent document 5] 3GPP TS 23.501 [Non-patent document 6] 3GPP TS 38.214 v17.3.0 [Non-Patent Document 7] 3GPP TS 38.401 v17.3.0 [Non-patent document 8] 3GPP TS 38.473 v17.3.0 [Non-Patent Document 9] 3GPP TS 38.213 v17.4.0 [Non-Patent Document 10] 3GPP TS 38.212 v17.4.0 [Non-Patent Document 11] 3GPP TS 38.331 Summary of the Invention

[0006] One non-limiting exemplary embodiment facilitates a Base Station-Central Unit (BS-CU) to perform improved mobility procedures.

[0007] In one embodiment, the technology disclosed herein features a base station central unit (BS-CU) including: a transmitter that transmits a mobility request to a distributed unit (mobility candidate BS-DU) of a base station that is a candidate for participating in user equipment (UE) mobility; a receiver of the BS-CU that receives, from the mobility candidate BS-DU, a reference signal (RS) resource configuration of the mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU; a processing circuit of the BS-CU that generates an updated list, the updated RS resource configuration list including information regarding the received RS resource configuration of the mobility candidate BS-DU and information regarding the RS resource configuration of at least a serving BS-DU that serves the UE; and a transmitter that transmits the contents of the updated RS resource configuration list to the serving BS-DU for further forwarding to the UE.

[0008] One non-limiting, exemplary embodiment facilitates a UE performing an improved mobility procedure. In one aspect, the disclosed technology features a user equipment (UE) comprising: a receiver that receives, from a distributed unit (i.e., serving BS-DU) of a base station serving the UE, communication configurations of BS-DUs that are candidates for participating in the UE's mobility; a processing circuit in the UE that decodes the received mobility candidate BS-DU communication configurations to obtain Reference Signal (RS) resource configurations of the mobility candidate BS-DUs for candidate cells of the mobility candidate BS-DU; and a processing circuit that updates a current list that includes information regarding at least the RS resource configurations of the serving BS-DUs based on the decoded RS resource configurations of the mobility candidate BS-DUs.

[0009] Further benefits and advantages of the disclosed embodiments and various implementations will become apparent from the specification and drawings. Such benefits and / or advantages may be provided by some of the embodiments and features described in the specification and drawings, respectively, but not necessarily all of them may be provided to obtain one or more identical features.

[0010] The following exemplary embodiments are described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 illustrates an example architecture of a 3GPP NR system to which the improved procedures of the present disclosure can be applied. [Figure 2] 1 is a schematic diagram illustrating the functional division between the NG Radio Access Network (NG-RAN) and the 5G Core Network (5GC), to which the improved procedures of the present disclosure may be applied; [Figure 3] 1 is a sequence diagram of a Radio Resource Control (RRC) connection setup / reconfiguration procedure to which the improved procedures of the present disclosure may be applied. [Figure 4] FIG. 1 is a schematic diagram illustrating eMBB, mMTC, and URLLC usage scenarios in which the improved procedures of the present disclosure may be applied. [Figure 5] Block diagram illustrating an example 3GPP NR system architecture for a non-roaming scenario [Figure 6] Diagram showing a split gNB architecture where the gNB is split into a gNB central unit and one or more gNB distributed units. [Figure 7] FIG. 1 illustrates a simplified exemplary implementation of a set of synchronization signal blocks distributed within one half-frame. [Figure 8] Diagram showing multiple beams and corresponding SSB indices (SSB1-SSB8) and how the beams are transmitted by the gNB in ​​a beam-sweeping manner. [Figure 9] Simplified signaling diagram of lower layer cell switch within DU [Figure 10] FIG. 1 shows an exemplary simplified structure of a UE and a gNB. [Figure 11] FIG. 1 shows an example of basic mobility procedures and cell switch preparation, to which various solutions and variants are applied. [Figure 12]FIG. 1 shows the structure of a base station central unit according to an embodiment of the first solution of the improved mobility procedure. [Figure 13] FIG. 1 is a flow diagram illustrating the behavior of a BS-CU according to an embodiment of a first solution for improved mobility procedures. [Figure 14] FIG. 1 is a signaling diagram illustrating an exemplary and simplified embodiment of an improved mobility procedure according to a first solution. [Figure 15] Further signaling diagram according to the first variant of the first solution of the improved mobility procedure [Figure 16] Further signaling diagram of a scenario involving a second candidate gNB-DU-2 according to the first variant of the first solution of the improved mobility procedures [Figure 17] Further signaling diagram of the second variant of the first solution of the improved mobility procedure [Figure 18] FIG. 1 is a flow diagram illustrating the behavior of a UE according to an embodiment of the second solution of the improved mobility procedure. [Figure 19] Flow diagram of UE behavior according to an embodiment of the second solution of the improved mobility procedure [Figure 20] 1 is a signaling diagram illustrating a simplified embodiment of an example of a second solution for improved mobility procedures; [Figure 21] FIG. 1 shows a more detailed signaling diagram according to a simplified embodiment of an example of a second solution for improved mobility procedures. DETAILED DESCRIPTION OF THE INVENTION

[0012] <5G NR system architecture and protocol stack> 3GPP is working on the next release of fifth-generation cellular technology (known simply as "5G"), which includes the development of a new radio access technology (NR) that will operate in frequencies up to 100 GHz. The first version of the 5G standard was completed at the end of 2017, allowing for the testing and commercial deployment of smartphones compliant with the 5G NR standard.

[0013] In particular, the overall system architecture assumes an NG-RAN (Next Generation - Radio Access Network) with gNBs, which terminate NG radio access user plane (SDAP / PDCP / RLC / MAC / PHY) protocols and control plane (Radio Resource Control (RRC) protocols) towards UEs. The gNBs are interconnected with each other by an Xn interface. The gNBs are also connected to 5GC by a Next Generation (NG) interface, more specifically to the Access and Mobility Management Function (AMF) (e.g., a specific core entity running AMF) by an NG-C interface and to the User Plane Function (UPF) (e.g., a specific core entity running UPF) by an NG-U interface. The NG-RAN architecture is shown in Figure 1 (see, for example, section 4 of v17.2.0 of Non-Patent Document 2).

[0014] The user plane protocol stack in NR (see, for example, Section 4.4.1 of Non-Patent Document 2) includes a PDCP (Packet Data Convergence Protocol; see, for example, Section 6.4 of Non-Patent Document 2) sublayer, a RLC (Radio Link Control; see, for example, Section 6.3 of Non-Patent Document 2) sublayer, and a MAC (Medium Access Control; see, for example, Section 6.2 of Non-Patent Document 2) sublayer, and these sublayers terminate at the gNB on the network side. In addition, a new access stratum (AS) sublayer (SDAP, Service Data Adaptation Protocol) is introduced above PDCP (see, for example, Section 6.5 of Non-Patent Document 2). NR also defines a control plane protocol stack (see, for example, Section 4.4.2 of Non-Patent Document 2). An overview of Layer 2 functions is described in Section 6 of Non-Patent Document 2. The functions of the RRC layer are described in Section 7 of Non-Patent Document 2.

[0015] For example, the Medium-Access-Control (MAC) layer handles scheduling and scheduling-related functions, including multiplexing logical channels and handling various numerologies.

[0016] The physical layer (PHY) is responsible for, for example, coding, PHY HARQ processing, modulation, multi-antenna processing, and mapping of signals to appropriate physical time-frequency resources. The physical layer also handles 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 specific transport channel, and each transport channel is mapped to a corresponding physical channel. For example, physical channels are the PRACH (Physical Random Access Channel), PUSCH (Physical Uplink Shared Channel), and PUCCH (Physical Uplink Control Channel) for the uplink, and the PDSCH (Physical Downlink Shared Channel), PDCCH (Physical Downlink Control Channel), and PBCH (Physical Broadcast Channel) for the downlink.

[0017] NR use cases / deployment scenarios include enhanced mobile broadband (eMBB), ultra-reliable and low-latency communications (URLLC), and / or massive machine-type communications (mMTC), which have diverse requirements for data rates, latency, and coverage. For example, eMBB is expected to support peak data rates (20 Gbps downlink and 10 Gbps uplink) and user-perceived data rates on the order of three times those offered by IMT-Advanced. In contrast, URLLC has more stringent requirements, including extremely low latency (user plane latency of 0.5 ms for both UL and DL) and high reliability (1-10 Mbps within 1 ms). -5 ) and mMTC requires high connection density (1 km in urban environments).2 1,000,000 devices per second), wide coverage in harsh environments, and extremely long battery life (15 years) to lower device costs may be preferably required.

[0018] Therefore, an OFDM numerology (e.g., subcarrier spacing, OFDM symbol length, cyclic prefix (CP) length, number of symbols per scheduling interval) suitable for one use case may not work well for another use case. For example, low-latency services may preferably require a shorter symbol length (and therefore a larger subcarrier spacing) and / or fewer symbols per scheduling interval (also referred to as TTI) than mMTC services. Furthermore, deployment scenarios with large channel delay spreads may preferably require a longer CP length than scenarios with small delay spreads. To maintain a similar CP overhead, the subcarrier spacing should be optimized depending on the delay spread. In NR, more than one value of subcarrier spacing may be supported. Therefore, subcarrier spacings of 15 kHz, 30 kHz, 60 kHz, ... are currently being considered. The symbol length T u and the subcarrier spacing Δf is given by the formula (Δf=1 / T u ) As in LTE systems, the term "resource element" can be used to denote the smallest resource unit consisting of one subcarrier for the length of one OFDM / SC-FDMA symbol.

[0019] In the new radio 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 3). For example, downlink transmission and uplink transmission are set in a frame having a time length of 10 ms. Each frame consists of 10 subframes each having a time length of 1 ms. 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 subcarrier spacing of 15 kHz, the subframe has 14 OFDM symbols (assuming a normal cyclic prefix, similar to an LTE-compliant implementation). On the other hand, in the case of a subcarrier spacing of 30 kHz, the subframe has two slots, and each slot contains 14 OFDM symbols.

[0020] <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.

[0021] In particular, gNB and ng-eNB process 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 the downlink - IP header compression, encryption, and integrity protection of data - Selection of AMF at the time of UE attachment when the routing to AMF cannot be determined from the information provided by the UE - Routing of user plane data to the UPF - Routing of control plane information to AMF - Establishing and releasing connections - scheduling and transmission of paging messages - Scheduling and transmission of system broadcast information (sent from AMF or OAM) - Configuring measurements and measurement reporting for mobility and scheduling - Transport-level packet marking in the uplink - Session Management - Network slicing support - QoS flow management and mapping to data radio bearers - Support for UEs in RRC_INACTIVE state - Non-Access Stratum (NAS) message delivery function - Radio Access Network Sharing - Dual Connectivity - Close cooperation between NR and E-UTRA

[0022] The Access and Mobility Management Function (AMF) handles the following main functions: - Termination of Non-Access Stratum (NAS) signaling - NAS signaling security - Access Stratum (AS) security control - Core Network (CN) inter-node signaling for mobility between 3GPP access networks - Reachability for idle mode UEs (including control and execution of paging retransmissions) - Registration Area Management - Support for intra-system and inter-system mobility - Access Authentication - Access authentication, including roaming rights checks - Mobility management controls (subscriptions and policies) - Network slicing support - Selection of Session Management Function (SMF)

[0023] Additionally, the User Plane Function (UPF) handles the following main functions: - Anchor points for intra-RAT / inter-RAT mobility (when applicable) - External PDU session points for interconnection with data networks - Packet routing and forwarding - User plane part of packet inspection and policy rule enforcement - Traffic Usage Report - Uplink classifier to support routing of traffic flows to the data network - Branching points to support multi-homed PDU sessions - User plane QoS processing (e.g., packet filtering, gating, UL / DL rate enforcement) - Verification of uplink traffic (mapping from SDF to QoS flow) - Downlink packet buffering and downlink data notification triggering

[0024] Finally, the Session Management Function (SMF) handles the following main functions: - Session Management - UE IP address allocation and management - UP function selection and control - Traffic steering configuration in the User Plane Function (UPF) to route traffic to the correct destination - Policy enforcement and QoS control part - Downlink Data Notification

[0025] <Procedures for Establishing and Reconfiguring 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 2).

[0026] 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 by the gNB sending an RRCReconfiguration message to the UE and the gNB 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.

[0027] Accordingly, the present disclosure provides a fifth generation core (5GC) entity (e.g., AMF, SMF, etc.) having: circuitry for, in operation, establishing a next generation (NG) connection with a gNodeB such that a signaling radio bearer is established between the gNodeB and a user equipment (UE); and a transmitter for, in operation, transmitting an initial context setup message to the gNodeB via the NG connection. In particular, the gNodeB transmits radio resource control (RRC) signaling including a resource allocation configuration information element (IE) to the UE via the signaling radio bearer. The UE then performs uplink transmission or downlink reception based on the resource allocation configuration.

[0028] <IMT usage scenarios after 2020> Figure 4 shows some use cases for 5G NR. The 3GPP NR (3rd Generation Partnership Project New Radio) is considering three use cases envisioned for IMT-2020 to support a wide variety of services and applications. Phase 1 specifications for enhanced mobile broadband (eMBB) have been finalized. Current and future work includes standardization for ultra-reliable and low-latency communications (URLLC) and massive machine-type communications (mMTC), in addition to further extending eMBB support. Figure 4 shows some examples of IMT usage scenarios envisioned for 2020 and beyond (see, for example, Figure 2 in Non-Patent Document 4).

[0029] URLLC use cases have stringent requirements for capabilities such as throughput, latency, and availability, and are envisioned as one of the enablers for future vertical applications, such as wireless control of industrial manufacturing or production processes, remote medical surgery, power distribution automation in smart grids, and transportation safety. URLLC's ultra-high reliability is supported by identifying technologies to meet the requirements set by NR URLLC in Release 15. For NR URLLC in Release 15, key requirements include a user plane target latency of 0.5 ms for the uplink (UL) and 0.5 ms for the downlink (DL). A typical URLLC requirement for a single packet transmission is a block error rate (BLER) of 1E-5 for a 32-byte packet size with a user plane latency of 1 ms.

[0030] From a physical layer perspective, there are several possible ways to improve reliability. Current scope for improving reliability includes defining a separate CQI table for URLLC, a more compact DCI format, PDCCH repetition, etc. However, as NR becomes more stable and developed (a key requirement 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.

[0031] Furthermore, technology enhancements targeted at NR URLLC target latency improvement and reliability enhancement. Technology enhancements for latency improvement include configurable numerology, non-slot-based scheduling with flexible mapping, grant-free (configured grant) uplink, slot-level repetition of data channels, and downlink preemption. Preemption means that a transmission for which resources have already been allocated is aborted and the already allocated resources are used for another transmission requested later with smaller latency / higher priority requirements. Thus, an already granted transmission 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). Technology enhancements for reliability improvement include dedicated CQI / MCS tables for a target BLER of 1E-5.

[0032] The mMTC (Massive Machine Type Communication) use case is characterized by a very large number of connected devices transmitting relatively small amounts of data that are generally latency sensitive. The devices need to be low cost and have extremely long battery life. From an NR perspective, utilizing very narrow bandwidth portions is one possible solution to achieve power savings from the UE perspective, enabling long battery life.

[0033] As mentioned above, it is expected that the reliability range in NR will expand. One important requirement for all cases, especially for URLLC and mMTC, is high or ultra-high reliability. Several mechanisms can be considered to improve reliability from a radio perspective and a network perspective. In general, there are several key areas that can help improve reliability. These areas include compact control channel information, data channel / control channel repetition, and diversity related to the frequency, time, and / or spatial domains. These areas are generally applicable to reliability, regardless of the specific communication scenario.

[0034] For NR URLLC, additional use cases with more stringent requirements are envisioned, such as factory automation, transportation, and power distribution. The more stringent requirements include higher reliability (up to 10 times faster), depending on the use case. 6 level), higher availability, packet size up to 256 bytes, time synchronization on the order of a few microseconds (values ​​range from 1 to a few microseconds depending on the frequency range), and short latency on the order of 0.5 to 1 ms (target latency for the user plane in particular is 0.5 ms).

[0035] Furthermore, for NR URLLC, several technical enhancements are possible 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 enhancements of HARQ (Hybrid Automatic Repeat Request) and CSI feedback. In addition, enhancements of PUSCH related to mini-slot level hopping and retransmission / repetition have also been recognized. The term "mini-slot" refers to a transmission time interval (TTI: Transmission Time Interval) that contains fewer symbols than a slot (a slot has 14 symbols).

[0036] <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, a QoS flow is the finest granularity for QoS differentiation in a PDU session. A QoS flow is identified within a PDU session by a QoS flow ID (QFI) carried in a capsule header through the NG-U interface.

[0037] The 5GC establishes one or more PDU sessions for each UE. The NG-RAN establishes at least one Data Radio Bearer (DRB) for each UE along with the PDU session, and can then configure additional DRBs for the QoS flows of that PDU session (as determined by the NG-RAN, e.g., as described above with reference to Figure 3). The NG-RAN maps packets belonging to different PDU sessions to different DRBs. NAS-level packet filters in the UE and 5GC associate 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.

[0038] Figure 5 shows the 5G NR non-roaming reference architecture (see also, for example, Section 4.2.3 of v16.9.0, v17.5.0, or v18.0.0 of Non-Patent Document 5). Application Functions (AFs) (e.g., external application servers handling 5G services as exemplarily illustrated in Figure 4) interact with the 3GPP Core Network to provide services. For example, they support application influence on traffic routing, access Network Exposure Functions (NEFs), or interact with a policy framework (see Policy Control Function (PCF)) for policy control (e.g., QoS control). Based on the operator's deployment, Application Functions (AFs) deemed trusted by the operator can be allowed to interact directly with the associated Network Functions. Application Functions not permitted by the operator to directly access Network Functions interact with the associated Network Functions using an external exposure framework via the NEF.

[0039] Figure 5 shows further functional units of the 5G architecture: 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 part of the core network functions and application services may be located and executed in a cloud computing environment.

[0040] Therefore, the present disclosure provides an application server (e.g., an AF in a 5G architecture) having: a transmitter that, when operated, sends a request including QoS requirements for at least one of a URLLC service, an eMBB service, and an mMTC service to at least one of 5GC functions (e.g., an NEF, an AMF, an SMF, a PCF, an UPF, etc.) to establish a PDU session including a radio bearer between a gNodeB and a UE in accordance with the QoS requirements; and a circuit that, when operated, performs a service using the established PDU session.

[0041] <Transmission setting indicator status and QCL> According to Non-Patent Document 6, "Physical Layer Procedures for Data (Release 17)" (September 2022), two reference signals can have a Quasi-Co-Located (QCL) relationship. Two antenna ports are said to be QCL if the characteristics of the channel through which symbols on one antenna port are carried can be inferred from the channel through which symbols on the other antenna port are carried.

[0042] In 5G NR systems, the state of the Transmission Configuration Indication (TCI) is used to establish a Quasi Co-Location (QCL) connection between a target Reference Signal (RS) and a source RS. The QCL types of antenna ports are defined below.

[0043] [Table 1]

[0044] The TCI state is set for the PDCCH, PDSCH, and channel state information reference signal (CSI-RS) and conveys the QCL indication for each RS. In frequency range 1 (FR1, below 7.125 GHz), QCL types A to C are applied, and in frequency range 2 (FR2, above 24.250 GHz), QCL types A to D are applied. QCL type D in FR2 indicates that the PDCCH / PDSCH / CSI-RS is transmitted with the same spatial filter as the reference signal associated with that TCI. In FR2, the network can indicate a change in the transmit beam of the PDSCH or PDCCH by switching the TCI state.

[0045] Each TCI state may include a TCI state identifier, a TCI state ID, and a set of RSs used for QCL reference, or one or more individual RSs. Each RS within a TCI state may be associated with one or more sets of Tx (transmit) beams and / or Rx (receive) beams.

[0046] <Split gNB architecture> In the 3GPP standard, a gNB may be divided into a gNB-CU (Central Unit) and one or more gNB-DUs (Distributed Units), as shown in Figure 6.

[0047] The gNB-CU is a logical node that provides support for the upper layers of the protocol stack, such as SDAP, PDCP, and RRC, while the gNB-DU is a logical node that provides support for the lower layers of the protocol stack, such as RLC, MAC, and the physical layer. It should also be noted that the SDAP layer is not present when the CU is connected to a 4G core network, as a 5G core network is required to support it.

[0048] Therefore, the PHY layer and MAC layer are terminated in the gNB-DU, and Layer 3 (RRC) is terminated in the gNB-CU.

[0049] Each gNB has one CU. That is, one gNB-DU is connected to only one gNB-CU. Alternatively, for fault tolerance, a gNB-DU may be connected to multiple gNB-CUs. One gNB-CU can control multiple gNB-DUs; for example, more than 100 gNB-DUs can be connected to one gNB-CU. Each gNB-DU can support one or more cells, so one gNB can control hundreds of cells, unlike a 4G BTS. One cell is supported by only one gNB-DU.

[0050] Also, note that the interface between the CU and DU is named F1 and should be an open interface according to 3GPP. In the case of NG-RAN, the NG interface and Xn-C interface for a gNB consisting of a gNB-CU and a gNB-DU are terminated at the gNB-CU. In the case of EN-DC, the S1-U interface and X2-C interface for a gNB consisting of a gNB-CU and a gNB-DU are terminated at the gNB-CU. The gNB-CU and the connected gNB-DU are recognized only as a gNB to other gNBs and 5GC.

[0051] Details of the gNB-CU / DU architecture are specified, for example, in section 6.1 of Non-Patent Document 7. The F1 interface is specified in more detail, for example, in Non-Patent Document 8.

[0052] <Synchronization signal block measurement timing setting - SMTC-PSS / SSS, PBCH> NR introduces so-called synchronization signal blocks (SSBs), which include a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a physical broadcast channel (PBCH) (actually, PBCH DMRS and PBCH data). The PSS and SSS can be used by UEs to discover, synchronize to, and identify networks. The PBCH carries a minimal amount of system information, including an indication of where the remaining broadcast system information is transmitted.

[0053] In LTE, these three signals (PSS, SSS, and PBCH) were used, although they were not called SSBs. The three SSB elements are always transmitted together in NR, e.g., they have the same period. A given SSB may be repeated within an SS burst set, which may potentially be used for gNB beam-sweeping transmission. An SS burst set may be limited to a specific time period, such as a 5 ms window (half frame). For initial cell selection, the UE may assume a default SS burst set period of 20 ms.

[0054] The 5G NR PSS is a physical layer specific signal for identifying radio frame boundaries and is a type of m-sequence. The 5G NR SSS is a physical layer specific signal for identifying subframe boundaries and is also an m-sequence. The PSS / SSS sequence consists of complex values ​​used by each element / sample of the sequence. Information about a current example 5G implementation of PSS and SSS is available in sections 7.4.2.2 and 7.4.2.3 of 3GPP TS 26.2014-01-01 10:24 AM - 25:24 AM, including their respective sequence generation and mapping to physical resources.

[0055] The time-frequency structure of the SS / PBCH block carrying the SSS is described in Section 7.4.3.1 of 3GPP TS 36.254. In one such example 5G implementation, in the time domain, the SS / PBCH block consists of four OFDM symbols numbered in increasing order from 0 to 3. The distribution of the PSS, SSS, and PBCH signals within the SS / PBCH block is defined by Table 7.4.3.1-1 of 3GPP TS 36.254.

[0056] In the frequency domain, an SS / PBCH block consists of 240 consecutive subcarriers indexed from 0 to 239. The exact subcarriers used for each PSS, SSS, and PBCH signal within the SS / PBCH block are also defined by Table 7.4.3.1-1 of 3GPP TS 2.0.

[0057] A simplified exemplary diagram of an SSB according to the above definition is shown in FIG. 7, with the bottom portion of FIG. 7 showing the PSS, SSS, and PBCH in the time and frequency domains.

[0058] The timing (OFDM symbol) at which the SS block (see Figure 7) is transmitted by the gNB can be defined in various ways. In particular, the first symbol index (within each half-frame having SSBs) at which the candidate SSBs start is determined according to Section 4.1 "Cell search" of 3GPP TS 35.210.1000, TS 35.210.1000, and TS 35.210.1000. Figure 7 shows an example set of SSBs. In Figure 7, it is assumed to start from 2, 8, 16, 22, 30, 36, 44, and 50 OFDM symbols (for SCS = 30 kHz and frequencies > 3 GHz). The numbering of related OFDM symbols starts from 0 in a half-frame. The number of SSBs in the set of SSBs may also be limited to a maximum Lmax. As an example, the SSB set may include 4, 8, or 64 SSBs.

[0059] The candidate SS / PBCH blocks in a half-frame (e.g., referred to as a set of SSBs) are indexed in time in ascending order from 0 to Lmax-1. Correspondingly, each SSB in the set of SSBs is assigned a unique number that starts from 0 and increases by 1.

[0060] The SSB set shown in Figure 7 indicates a case where all candidate SSBs that may be transmitted by the base station are actually transmitted. However, it is not necessary to transmit all SSBs. Rather, the gNB may select only some of the SSBs in the set of SSBs based on certain requirements and transmit only those. The SSBs actually transmitted by the SSBs can be referred to as an SSB pattern. An SSB pattern has essentially the same characteristics as the corresponding SSB set, including periodicity.

[0061] The gNB informs the UE of the SSB pattern, e.g., which SSBs are actually transmitted and which are not. This can be done, for example, by the gNB transmitting an SSB bitmap that defines the SSB pattern, where each bit in the SSB bitmap is associated with one SSB and identifies whether the SSB is transmitted or not. The length of the SSB bitmap depends on the applicable SSB set and can be, for example, 4, 8, or 64 bits.

[0062] Simply put, a set of candidate SSBs to be used by a gNB in ​​a cell is configured, and from the set of candidate SSBs, the gNB can select all or fewer of the candidate SSBs for actual transmission, which is called an SSB pattern.

[0063] All SSBs can be transmitted on all beams in the system. Alternatively, SSBs can be transmitted on different beams, for example, if SSB beamforming is enabled. In that case, as shown in Figure 8, each SSB is transmitted on a different spatial beam. Similar to the exemplary scenario in Figure 7, there are eight SSBs (0 to 7) that can be transmitted on different beams, each beam being transmitted in a different beam direction. Therefore, beam-swept transmission of SSBs is realized. In other words, the beam (and SSB) sweep transmission is time-division multiplexed and occurs at different times. Two UEs, UE1 and UE2, receive different SSBs at different times. Each beam is assigned a beam index, e.g., the beam index corresponds to the SSB index transmitted through that beam.

[0064] The UE uses SSB signals (eg, PSS, SSS, PBCH) in different mechanisms, such as serving cell measurements, time / frequency synchronization, among others.

[0065] <Beam management> Beam management is a set of Layer 1 (PHY) and Layer 2 (MAC) procedures to establish and maintain optimal beam pairs for good connectivity. A beam pair consists of, for example, a transmit beam and a corresponding receive beam in one link direction.

[0066] Before a UE can communicate with the network, it must perform a cell search and selection procedure to acquire initial cell synchronization and system information. The first steps in that process are to acquire frame synchronization, find the cell identifier, and decode MIB and SIB1.

[0067] For multi-antenna systems transmitting multiple beams, detecting the beam from the gNB is also part of the initial procedure (e.g., when a UE typically detects all beams in its search space).

[0068] Beam management is mainly divided into three procedures: Initial beam establishment, Beam conditioning (also known as beam tracking and beam refinement), Beam fault recovery

[0069] <Layer 1-Layer 2 Triggered Mobility (LTM)> When a UE moves from the coverage area of ​​one cell to another, it will need to change its serving cell at some point. According to one possibility, the serving cell change is performed by a reconfiguration triggered by L3 measurements, with synchronization triggered by RRC signaling for the PCell and PSCell change, and the release and addition of SCells, if applicable. Such a procedure may involve a complete L2 (and L1) reset, resulting in longer latency, higher overhead, and longer disruption times than beam-switched mobility.

[0070] One of the topics currently under consideration in the mobility extensions of 3GPP Rel. 18 is support for Layer 1-Layer 2 (also called lower layer) triggered mobility (LTM). A UE is first configured with a set of candidate cells by RRC (L3). Then, L1 or L2 signaling (e.g., MAC CE (and / or DCI)) is used to trigger a switch of the UE's serving cell among the candidate cells without RRC reconfiguration. In other words, to facilitate sequential cell switches, the cell switch must be prepared in advance so that no RRC reconfiguration is required for the UE after the cell switch, regardless of which candidate cell becomes the new serving cell. The goal is to reduce the latency, overhead, and interruption time associated with a serving cell change. Both intra-DU cell switches and inter-DU cell switches within a CU are within the scope of this specification. Figure 6 illustrates an intra-DU switch between two cells of the same gNB-DU and an inter-DU switch between two cells of different gNB-DUs.

[0071] Figure 9 shows a simplified exemplary message exchange for an intra-DU lower layer cell switch according to the proposed 3GPP Rel. 18. Accordingly, it is assumed by way of example that the gNB-DU controls multiple cells, including the UE's current serving cell. The gNB-DU is connected to the gNB-CU.

[0072] As can be seen from the figure, the cell switch decision is based on lower layer (e.g., Layer 1 RSRP) measurements performed by the UE and reported to the gNB-DU (see "Lower Layer Measurement Reporting"). More specifically, the UE measures reference signals from one or more candidate cells of the gNB-DU and reports the results to the gNB-DU. The gNB-DU can use the received measurement results to decide whether to perform LTM for the candidate target cell. A lower layer cell switch trigger is sent to the UE, allowing the UE to perform a switch from the current cell to another cell of the gNB-DU.

[0073] The advantage achieved by performing measurements and reporting over Layer 1 is low latency.

[0074] As mentioned above, the lower layer mobility procedure is based on the premise that the UE performs measurements and reports the results to the serving gNB (gNB-DU and / or gNB-CU). For this purpose, the UE may be configured with the necessary parameters and information by the serving gNB. For example, the configuration of the UE to perform measurements and report the measurement results conceptually includes the following: The quantity or set of quantities to be reported. The downlink resources of each cell on which measurements should be performed to derive the quantities to be reported. How the actual reporting is performed, e.g., timing of reporting and uplink channel to use for reporting.

[0075] According to one example, the measurement and reporting may be based on, for example, a CSI reporting framework, which may be generally considered to consist of two parts: a part relating to the configuration of CSI reporting and a part for triggering CSI reporting.

[0076] The CSI-MeasConfig IE is the top-level IE for CSI configuration, and configures not only L1-RSRP-related measurements / reports for beam management, but also conventional CSI-related measurements / reports (e.g., CQI) for determining appropriate MIMO precoding, modulation and coding, etc.

[0077] The CSI-MeasConfig IE mainly sets the following three types of lists:

[0078] (1) List of RS resource sets Each RS resource set in the list contains one or more RS resources. For example, multiple CSI-RS resources may be configured by the NZP-CSI-RS-Resource IE and then grouped into an RS resource set by the NZP-CSI-RS-ResourceSet IE. Other possible RS resources are defined by the IEs "CSI-IM-Resource" and "SSB-Index".

[0079] (2) List of CSI-ResourceConfig IEs Different CSI-ResourceConfigs in the list may include one or more different RS resource sets selected from list element (1), which may include NZP-CSI-RS-ResourceSet, CSI-IM-ResourceSet, and / or CSI-SSB-ResourceSet, each identified by an appropriate ID (e.g., NZP-CSI-RS-ResourceSetId, CSI-IM-ResourceSetId, and / or CSI-SSB-ResourceSetId).

[0080] (3) A list of CSI-ReportConfig IEs. Different CSI-ReportConfigs in the list configure different CSI reporting instances. This is an information element that links the reporting configuration (e.g., by PUCCH or PUSCH) of this CSI-ReportConfig to a measurement resource set (i.e., one CSI-ResourceConfig in list element 2 above). The CSI-ResourceConfigID is included in the CSI-ReportConfig IE and identifies the CSI-ResourceConfig IE to be used.

[0081] Measurement and reporting can be performed periodically, semi-periodically, or aperiodically. Measurement results are reported from the UE to the gNB, for example, as uplink control information in the PUCCH or PUSCH. In one 5G-compliant example, CSI reporting is performed by the UE based on the definition given in Section 6.3 of 3GPP TS 36.210.

[0082] In current 3GPP 5G systems, there are two types of reference signals that can be used for measurements: SSB (see SSB-Index above) and CSI-RS (Channel State Information Reference Signal; see NZP-CSI-RS-Resource IE and CSI-IM-Resource IE above). SSB is always transmitted by the network and is not specific to the UE, which means it lacks flexibility. For example, SSB can be used in association with a relatively wide beam. On the other hand, CSI-RS can be individually configured for a specific UE, allowing for great flexibility in terms of when and how often it is transmitted (time domain) and the resources in the frequency domain. CSI-RS can be configured for only one or a few UEs, so it can be used in association with a relatively narrow beam.

[0083] CSI reporting in 5G NR has several reporting components (i.e., several different types of CSI) based on, for example, section 5.2.1 of 3GPP TS 2013-01-10 20:20:45 Channel Quality Information (CQI) Precoding Matrix Indicator (PMI) CSI-RS Resource Indicator (CRI) SS / PBCH Resource Block Indicator (SSBRI) Layer Indicator (LI) Rank Indicator (RI) L1-RSRP, and / or Capability Index

[0084] One or more or a combination of different indicators may be reported by the UE. Generally, these indicators can be classified into two types: - Quantities related to L1-RSRP (e.g., cri-RSRP, ssb-Index-RSRP, see IE "CSI-ReportConfig" below) - CSI-related quantities (e.g., remaining items of the IE "CSI-ReportConfig") L1-RSRP-related quantities are new and were first introduced in NR (Rel-15), and one of their purposes is to facilitate beam management. In contrast, CSI-related quantities (e.g., CQI) are traditional and already exist in LTE. These traditional CSI-related quantities can be used by the base station to select appropriate MIMO precoding, modulation schemes, and coding sizes to adapt to channel conditions.

[0085] An embodiment may follow the current definition of the 5G 3GPP standard as defined in 3GPP TS 36.112.1, and may include, for example, the following information elements (IEs): CellGroupConfig, CSI-MeasConfig, CSI-ReportConfig, CSI-ResourceConfig, NZP-CSI-RS-Resource, and NZP-CSI-RS-ResourceSet.

[0086] In short, the measurement and reporting of the LTM can be based on the 5G CSI reporting framework. In particular, the information element (IE) "CSI-MeasConfig" and the information element "CSI-ReportConfig" indicate parameters of the CSI reporting framework that the UE can use to measure and then report the measurement results.

[0087] One possible subsequent sequence of IEs to define measurements and reporting according to the CSI framework is shown below: [Table 2] The following exemplary definition of the IE "CellGroupConfig" is taken from section 6.3.2 of 3GPP TS 2.0:

[0088] - CellGroupConfig The CellGroupConfig IE is used to configure a Master Cell Group (MCG) or a Secondary Cell Group (SCG). A cell group consists of one MAC entity, a set of logical channels with associated RLC entities, a primary cell (SpCell) and one or more secondary cells (SCells).

[0089] [Table 3-1] [Table 3-2] [Table 3-3] The definitions of the above fields and parameters of the CellGroupConfig IE are described in Non-Patent Document 11. Relevant ones therein include ServingCellConfig and ServingCellConfigCommon.

[0090] [Table 4]

[0091] The following exemplary definition of the IE “CSI-MeasConfig” is taken from section 6.3.2 of 3GPP TS 2.0:

[0092] - CSI-MeasConfig The IE "CSI-MeasConfig" is used to configure CSI-RS (Reference Signal) belonging to the serving cell containing the CSI-MeasConfig, the channel state information report transmitted on the PUCCH in the serving cell containing the CSI-MeasConfig, and the channel state information report on the PUSCH triggered by DCI received in the serving cell containing the CSI-MeasConfig. See also Section 5.2 of Non-Patent Document 6

[19] .

[0093] [Table 5] The definitions of the above fields and parameters of the CSI-MeasConfig IE are given in Non-Patent Document 11. Relevant ones include:

[0094] [Table 6]

[0095] The following example definition of the IE “CSI-ReportConfig” is taken from Non-Patent Document 11:

[0096] - CSI-ReportConfig The IE "CSI-ReportConfig" is used to configure periodic or semi-persistent reports transmitted on the PUCCH in the cell in which the CSI-ReportConfig is included, or to configure semi-persistent or aperiodic reports transmitted on the PUSCH triggered by DCI received in the cell in which the CSI-ReportConfig is included (in this case the cell from which the report is transmitted is determined by the received DCI), see section 5.2.1 of 3GPP TS 26.2006

[19] .

[0097] [Table 7-1] [Table 7-2] [Table 7-3] The definitions of the above fields and parameters of the CSI-ReportConfig IE are given in Non-Patent Document 11. Relevant ones include:

[0098] [Table 8]

[0099] The following exemplary definition of the IE “CSI-ResourceConfig” is taken from section 6.3.2 of 3GPP TS 26.2006.02.

[0100] - CSI-ResourceConfig The IE "CSI-ResourceConfig" defines a group of one or more NZP-CSI-RS-ResourceSet, CSI-IM-ResourceSet, and / or CSI-SSB-ResourceSet.

[0101] [Table 9] The definitions of the above fields and parameters of the CSI-ResourceConfig IE are given in Non-Patent Document 11. Relevant ones include:

[0102] [Table 10]

[0103] <Further improvements> In Rel.15 / 16, Layer 1 (L1) measurements are performed by the UE on the reference signals of the serving cell. In Rel.17, to support Inter-Cell Beam Management (ICBM), a new mechanism was introduced that allows the UE to perform L1 measurements on the reference signals of neighboring cells, as described below.

[0104] This mechanism essentially involves including the RS of neighboring cells in the measurement resource set configured by the serving cell, but the way this is done differs between SSB and CSI-RS.

[0105] In the case of SSB, the IE "CSI-SSB-ResourceSet" has a parameter "ServingAdditionalPCIIndex-r17" that provides the non-serving cell ID for the SSB. Details are described in Non-Patent Document 11.

[0106] In the case of CSI-RS, the UE needs to be configured with the CSI-RS of the serving cell that has a QCL relationship to the SSB of the neighboring cell. This is done by providing the QCL source using the TCI-State. More specifically, the IE "NZP-CSI-RS-Resource" has a field called TCI-StateID, which points to additionalPCI-r17, where a non-serving cell ID can be indicated for the SSB used as the QCL source for the related CSI-RS. For details, see 3GPP TS 2013-01-10 20:29:49.

[0107] However, this Rel.17-ICBM has an important condition that neighboring cells and serving cells are provided by the same gNB-DU. In particular, the gNB-DU needs to have knowledge of the resource signal configurations of neighboring cells. The gNB-DU may include the resource signal configuration for one of the neighboring cells in the measurement resource set configuration for the UE. In response, the UE has the necessary information about the resource signals of neighboring cells to perform L1 measurements for Rel.-17-ICBM. This condition can be achieved by intra-DU cell switching by the gNB-DU, as shown in Figure 9.

[0108] On the other hand, for L1-L2 triggered mobility (LTM) between different gNB-DUs, i.e., inter-DU LTM, it is unclear how a UE can be configured to measure reference signals of cells of other gNB-DUs, since the source gNB-DU of the UE's serving cell does not know the resource signal configuration of this other gNB-DU.

[0109] The inventors have thus identified the possibility of defining improved mobility procedures that tend to avoid one or more of the drawbacks mentioned above. The present invention relates to various solutions and variants for such improved mobility procedures.

[0110] <Embodiment> In the following, UEs, base stations, and procedures for meeting these needs are described for new radio access technologies envisioned for 5G mobile communication systems, but may also be used in previous LTE-based mobile communication systems or future (e.g., 6G) mobile communication systems. Various implementations and variations are also described. The following disclosure is facilitated by, and may be based, for example, at least in part on, the above discussion and findings.

[0111] In general, it should be noted that many assumptions have been made herein and will be made hereinafter in order to be able to explain the principles underlying the present disclosure in a clear, concise, and understandable manner. However, these assumptions should be understood as merely examples made herein for illustrative purposes, and they are not necessarily essential to the present invention, and therefore should not limit the scope of the present disclosure. Those skilled in the art will understand that the principles described in the following disclosure and claims can be applied to different scenarios and in ways not explicitly described herein.

[0112] Furthermore, although specific terminology used in the context of new radio access technologies for upcoming communication systems has not yet been fully determined or may eventually change, some of the terms used below, such as procedures, entities, and layers, are closely related to the terms used in LTE / LTE-A systems or in the current 3GPP 5G standardization. Therefore, the terms may change in the future without affecting the functionality of each feature and solution. As a result, those skilled in the art will recognize that the solutions and their scope of protection should not be limited to the specific terms used illustratively in this specification, which lack newer or final agreed-upon terms, but should be more broadly understood by the underlying functions and concepts of the solutions described in this disclosure.

[0113] For example, a mobile station or mobile node or user terminal or user equipment (UE) is a physical entity (physical node) in a communication network. A node may have several functional entities. A functional entity refers to a software or hardware module that implements and / or provides a set of functions to other functional entities of the same node or other nodes or the network. A node may have one or more interfaces that attach the node to communication facilities or media over which the node can communicate. Similarly, a network entity may have logical interfaces that attach the functional entity to communication facilities or media over which the functional entity may communicate with other functional entities or corresponding nodes.

[0114] The term "base station" or "radio base station" in this specification refers to a physical entity in 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 set of predetermined functions to other functional entities of the same node or other nodes or networks. A physical entity performs several control tasks for communication devices, including one or more of scheduling and configuration. It should be noted that base station functions and communication device functions may 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. A base station may also be a gNB in ​​a Non-Terrestrial Network (NTN) NR system.

[0115] Communication between a UE and a base station is typically standardized and may be defined by different layers, eg, PHY, MAC, RRC, etc. (see background discussion above).

[0116] 10 shows a general and simplified exemplary block diagram of a user equipment (also referred to as a communication device) and a scheduling device (here assumed for purposes of illustration to be located in a base station such as an LTE eNB (also known as an ng-eNB) or a gNB in ​​5G NR). The UE and the eNB / gNB communicate with each other via a (wireless) physical channel using their respective transceivers.

[0117] A communication device may include a transceiver and a processing circuit. The transceiver may include and / or function as a receiver and a transmitter. The processing circuit may be one or more hardware components, such as one or more processing units or any LSI. An input / output point (or node) exists between the transceiver and the processing circuit, and the processing circuit can control the transceiver through the input / output point during operation, i.e., control the receiver and / or transmitter to exchange receive / transmit data. The transceiver may include an RF front end, including one or more antennas, amplifiers, RF modulators / demodulators, etc., as the transmitter and receiver. The processing circuit may control the transceiver to perform control tasks, such as transmitting user data and control data provided by the processing circuit and / or receiving user data and control data that are further processed by the processing circuit. The processing circuit may also be responsible for performing other processes, such as judgment, decision, calculation, measurement, etc. The transmitter may be responsible for performing the transmission process and other processes related thereto. The receiver may be responsible for performing the reception process and other processes related thereto, such as monitoring the channel. The present invention relates to various solutions and variants for improved mobility procedures. A simplified example of one mobility procedure is given below based on Figure 11.

[0118] In particular, a split gNB architecture with one gNB-CU and multiple gNB-DUs is exemplarily assumed. The UE is located in the cell of the serving gNB-DU and exchanges user data via the serving gNB-DU and gNB-CU. Furthermore, the UE may be configured to perform measurements on the cell of its serving gNB-DU and report the measurement results to the gNB-DU (and possibly the gNB-CU). For example, the UE already has configuration information for the serving gNB-DU, including the measurement configuration of the serving gNB-DU. Such communication configuration of the gNB-DU may include, for example, configuration parameters of the gNB-DU's lower layers, such as downlink and uplink channel information. The UE is also already provided with higher layer parameters related to RRC required for connection to and operation with the gNB-CU.

[0119] The gNB-CU shall determine a new cell for a new gNB-DU (i.e., a new gNB-DU different from the current serving gNB-DU) to which the UE may eventually switch. In one example, the gNB-CU maintains a list of candidate cells (and their corresponding gNB(-DUs)) for the UE. For example, the candidate cell list indicates the candidate cells associated with each cell and the corresponding communication configuration for that gNB(-DU).

[0120] In preparation for such a cell switch, the gNB-CU requests the new gNB-DU whether it will participate in the UE's mobility (see Mobility Request). In this way, the new gNB-DU and its cell become candidates for the UE's subsequent cell switch.

[0121] To facilitate a subsequent switch to the cell of this new gNB-DU, the UE is provided by the gNB-CU with appropriate configuration information of the new candidate gNB-DU, which the gNB-CU obtains from the Mobility Confirm message received from the new gNB-DU. The configuration information of the new candidate gNB-DU may include information necessary for the UE when connecting to the gNB-DU, such as information about downlink and uplink channels. The UE continues to perform measurements to support lower layer mobility (e.g., see the 5G LTM described above), including on the new candidate cell of the new gNB-DU. At this point, the UE should have been provided with information about the reference signals transmitted by the new candidate cell of the new candidate gNB-DU. In this way, the UE can measure the reference signals of the cell of the serving gNB-DU and also measure the reference signals of the candidate cell of the new candidate gNB-DU (and possibly reference signals of further candidate cells of other existing gNB-DUs). The lower layer measurement reports are sent to the serving gNB-DU, which may at some point decide to perform a cell switch for the UE from the serving gNB-DU's current serving cell to the candidate gNB-DU's cell, i.e., an inter-DU cell switch is performed. This procedure may include, for example, the serving gNB-DU informing the new gNB-DU and possibly the gNB-CU about the cell switch.

[0122] In either case, a lower layer cell switch trigger is sent by the serving gNB-DU to the UE, indicating the determined candidate cell of the new candidate gNB-DU as the target for a cell switch. The UE then performs a cell switch to the indicated candidate cell. User data is then exchanged between the UE and the gNB-CU via the new serving gNB-DU (previous candidate gNB-DU).

[0123] Also, providing the UE with appropriate information about the reference signals of candidate cells of new candidate gNB-DUs, thereby enabling it to perform lower layer measurements to support lower layer mobility, is part of and an objective of the cell switch preparation as illustrated in Figure 11. Furthermore, to facilitate sequential cell switches, the cell switch must be prepared in such a way that the UE does not need to reconfigure higher layers (e.g., RRC) after the cell switch, regardless of which candidate cell becomes the new serving cell.

[0124] The present invention provides several solutions and respective variants to improve the provisioning of cell switches and therefore the overall mobility procedure.

[0125] In summary, the first solution involves the gNB-CU being primarily responsible for obtaining necessary information regarding reference signals (RS) for any candidate gNB-DUs and maintaining updated lists of RS resource configurations for the UE's current serving gNB-DU as well as all candidate gNB-DUs that may support a possible cell switch. The first solution distinguishes between two variants. One variant involves each gNB-DU (including the serving gNB-DU and all candidate gNB-DUs) including a measurement configuration that includes a list of the most recent and complete RS resource configurations (e.g., including the configuration of the UE's current serving gNB-DU and the configurations of all candidate gNB-DUs for a possible cell switch). Meanwhile, the second variant of the first solution uses a new measurement configuration that does not necessarily include the RS resource configurations of each gNB-DU. Rather, the RS resource configurations of the gNB-DUs are provided separately from the measurement configurations of the gNB-DUs. Furthermore, the list of the most recent and complete RS resource configurations is separate from the measurement configurations of the gNB-DUs, and they can be used together.

[0126] The second solution is based primarily on the UE being responsible for maintaining an updated list of complete RS resource configurations, for example for the UE's current serving gNB-DU as well as all candidate gNB-DUs for a possible cell switch.

[0127] In relation to the first and second solutions, an improved UE, an improved base station (here, for example, a base station distributed unit and a central unit), and an improved integrated circuit participate separately or together in an improved mobility procedure. Corresponding methods of the UE behavior and the base station behavior are also provided. The integrated circuit can correspond to the UE and the base station and their respective behaviors.

[0128] The first and second solutions below can be based on some or a combination of the various mechanisms described above in the context of a 3GPP 5G-NR implementation example, including, for example, signaling mechanisms (e.g., new F1 interface signaling mechanisms for split gNB architectures using information elements for measurement configuration and reporting) or how L1-L2 triggered mobility (LTM) is defined (as currently discussed in 3GPP).

[0129] According to an embodiment, improved mobility procedures according to the following first and second solutions may be provided in accordance with the 3GPP standard, where the communication configuration mentioned for the improved mobility procedures may be implemented in the same or similar manner as the IE "CellGroupConfig", and the measurement configuration may be implemented in the same or similar manner as the IE "CSI-MeasConfig".

[0130] According to one embodiment, the above candidate list for a UE may have the following structure:

[0131] [Table 11] And the LTM cell switching command may indicate one of the configuration IDs. When the UE receives such an LTM cell switching command, the corresponding CellGroupConfig IE becomes the new serving cell.

[0132] First Solution - gNB-CU maintains an updated RS resource configuration list As mentioned above, the first solution involves the gNB-CU being primarily responsible for obtaining the necessary reference signal (RS) information for any candidate gNB-DUs and maintaining an updated list of RS resource configurations for the UE's current serving gNB-DU as well as all candidate gNB-DUs to support possible cell switches.

[0133] More specifically, a first solution for improved mobility procedures provides at least an improved base station central unit (BS-CU), as described below.

[0134] Figure 12 shows a simplified exemplary structure of a base station central unit according to one embodiment of the improved mobility procedure according to the first solution, which can be implemented based on the general base station structure described in relation to Figure 10. The various structural elements of the base station central unit shown in Figure 12 can be connected to each other, for example, by corresponding input / output nodes (not shown) for exchanging control and user data and other signals. Although not shown for illustrative purposes, the base station central unit may include further structural elements.

[0135] As can be seen from the figure, the base station central unit includes a mobility request sending unit, a reference signal resource configuration receiving unit, a reference signal resource configuration updating circuit, and a reference signal resource configuration sending unit.

[0136] In this case, as will become apparent from the disclosure below, the receiver of the base station central unit may be configured to at least partially perform one or more of, for example, receiving reference signal resource configuration, receiving communication configuration, etc.

[0137] In this case, as will become apparent from the disclosure below, the processing circuitry of the base station central unit may be configured to at least partially perform, for example, the generation of an updated list of RS resource configurations.

[0138] In this case, which will become clear from the disclosure below, the transmitter of the base station central unit may be configured, as an example, to at least partially perform one or more of the following: transmitting a mobility request, transmitting an updated RS resource configuration list, etc.

[0139] An example procedure, as disclosed in more detail below, is implemented by a base station central unit, including: a transmitter transmits a mobility request to a base station distributed unit (mobility candidate BS-DU) that is a candidate for participating in user equipment (UE) mobility; a receiver of the BS-CU receives, from the mobility candidate BS-DU, the mobility candidate BS-DU's reference signal (RS) resource configuration for the mobility candidate BS-DU's candidate cell; a processing circuit of the BS-CU generates an updated list, where the updated RS resource configuration list includes information about the received RS resource configuration of the mobility candidate BS-DU and information about the RS resource configuration of at least the serving BS-DU serving the UE; and a transmitter transmits the contents of the updated RS resource configuration list to the serving BS-DU for further forwarding to the UE.

[0140] The corresponding method comprises the following steps, which are carried out by a base station central unit: sending a mobility request to a base station distributed unit (mobility candidate BS-DU) that is a candidate for participating in the mobility of the user equipment (UE); receiving a reference signal (RS) resource configuration from a mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU; generating an updated list, the updated RS resource configuration list comprising information of the received RS resource configuration of the mobility candidate BS-DU and at least the RS resource configuration of the serving BS-DU serving the UE; and sending the content of the updated RS resource configuration list to the serving BS-DU for further forwarding to the UE.

[0141] A corresponding sequence diagram for the operation of an example of a base station central unit in accordance with the above-described base station central unit and corresponding method is shown in Figure 13. This sequence diagram shows an example simplified implementation of the above-described method.

[0142] Figure 14 is a signaling diagram of a simplified embodiment of an example of an improved mobility procedure according to the first solution, illustrating the exchange of messages between the different participating entities (here, the UE, the gNB-DU, and the gNB-CU) and the steps performed by these entities. As is clear from Figure 14, the contents of the RS resource configuration list updated by the gNB-CU are eventually transferred from the gNB-CU to the UE via the serving gNB-DU.

[0143] Therefore, according to the above embodiment of the first solution, an up-to-date list of RS resource configurations for different gNB-DUs can be maintained, and a cell switch to a cell controlled by a gNB-DU different from the current serving gNB-DU can be supported. The UE can be easily provided with the contents of such an up-to-date RS resource configuration list, i.e., the contents including necessary information on the RS resources used by the serving gNB-DU and at least the RS resources used by a different gNB-DU. This allows the UE to perform measurements on cells of a gNB-DU different from the serving gNB-DU. This facilitates cell switches between gNB-DUs.

[0144] Below we present two different variants of the first solution.

[0145] <First Modification> As described above, in the first variant, each gNB-DU (including the serving gNB-DU and all candidate gNB-DUs) generates a measurement configuration that includes a list of the most recent and complete RS resource configurations (e.g., including the configuration of the UE's current serving gNB-DU and the configurations of all possible candidate gNB-DUs for a cell switch).

[0146] A more detailed embodiment of the first solution of the improved mobility procedure is described for a first variant with reference to Figure 15, which is intended to show how the cell switch preparation initially described with reference to Figure 11 can be performed. More specifically, it shows how the lower layer mobility of a UE can be extended to a new candidate gNB-DU and its cells. The cells added to the UE's candidate cell list belong to a candidate gNB-DU that is different from the serving gNB-DU. One of the goals of the cell switch preparation is to provide the UE with appropriate information about the reference signals of the candidate cells of the new candidate gNB-DU.

[0147] For simplicity, it is exemplarily assumed that the new candidate gNB-DU has one cell that needs to be prepared. However, the first variant of the first solution is equally applicable to a scenario in which the new candidate gNB-DU has two or more cells to be prepared. In such a case, the cell switch preparation targets multiple candidate cells of the candidate gNB-DU (a subset or the full set of cells of the candidate gNB-DU).

[0148] In order for the new candidate gNB-DU to participate in the UE's lower layer mobility, the gNB-CU sends a mobility request message to the new candidate gNB-DU (step 1).

[0149] According to this example, it is assumed that the mobility request may already include a current RS resource configuration list, including the RS resource configuration of the serving gNB-DU. To enable this, the gNB-CU may have previously obtained the RS resource configuration of the serving gNB-DU.

[0150] Furthermore, the current RS resource configuration list may also be provided to the candidate gNB-DU in a message other than the mobility request.

[0151] It is assumed that the candidate gNB-DU will confirm that it will participate in the UE's lower layer mobility.

[0152] In step 2, the candidate gNB-DU generates a communication configuration for the candidate gNB-DU for the candidate cell. This candidate gNB-DU communication configuration may include an RS resource configuration for its own candidate cell, but may also include an RS resource configuration for the serving gNB-DU (if received from the gNB-CU). The two RS resource configurations may, for example, be included in the measurement configuration of the communication configuration and thus may be mapped (also referred to as "linked") to the measurement configuration of the candidate gNB-DU.

[0153] Additionally, the candidate gNB-DU separately generates an RS resource configuration for the candidate gNB-DU (and its candidate cell) and transmits it to the gNB-CU. By separating the RS resource configuration information from the communication configuration information, the gNB-CU can decode only the RS resource configuration without decoding the candidate gNB-DU's communication configuration, which the gNB-CU can simply forward to the UE via the serving gNB-DU without interpretation, as described below.

[0154] In step 3, the candidate gNB-DU sends an appropriate Mobility Confirm message to the gNB-CU containing the generated items: candidate gNB-DU communication configuration and separate candidate gNB-DU RS resource configuration.

[0155] In step 4, the gNB-CU obtains the RS resource configuration of the candidate gNB-DU, and then in step 5, the gNB-CU updates its list of current RS resource configurations to include the received RS resource configuration of the candidate gNB-DU. The updated and current complete list thus obtained will include the RS resource configurations for the cells for the serving gNB-DU and the candidate gNB-DU.

[0156] According to a first variant of the first solution, the serving gNB-DU is required to generate a communication configuration, in particular a measurement configuration as part of the communication configuration, that includes an updated RS resource configuration list. This is because this updated communication configuration of the serving gNB-DU is to be provided to and followed by UEs that remain connected to the serving gNB-DU, and therefore the communication configuration must include the latest RS resource configuration. To this end, the gNB-CU requests the serving gNB-DU to change the communication configuration and provides the serving gNB-DU with the updated RS resource configuration list (step 6).

[0157] In accordance with the request, the serving gNB-DU updates its measurement configuration to include the updated RS resource configuration list (step 7). The serving gNB-DU then updates its communication configuration based on the updated measurement configuration (step 8). In the updated communication configuration obtained in this way, the contents of the updated RS resource configuration list are mapped (also referred to as "linked") to the measurement configuration of the serving gNB-DU. The serving gNB-DU's communication configuration, updated to include this latest RS resource configuration list, is then sent to the gNB-CU as part of a change confirmation message (step 9).

[0158] The gNB-CU may forward the received updated communication configuration of the serving gNB-DU and the communication configuration of the candidate gNB-DU to the serving gNB-DU (step 10). The serving gNB-DU forwards the received information to the UE (step 11).

[0159] Thus, the communication configurations of both the serving gNB-DU and the candidate gNB-DU include the updated RS resource configuration, thus providing the UE with a complete picture of the RS resources to be measured by the UE, respectively. While the UE is still connected to the serving gNB-DU, the UE follows the measurement configuration of the serving gNB-DU communication configuration, in particular the RS resource configuration that has information on the RS resource configurations for all mobility candidate cells.

[0160] Accordingly, in step 12, the UE may perform measurements as configured, for example, on the cells of the serving gNB-DU and the new candidate gNB-DU (and, if possible, all previously added candidate gNB-DUs).

[0161] Furthermore, when the UE finally performs a cell switch to a cell of the candidate gNB-DU, it will follow the measurement configuration of the candidate gNB-DU communication configuration, in particular the RS resource configuration, which also includes information on the RS resource configuration for all mobility candidate cells.

[0162] As described above, steps 6, 7, 8, and 9 of the first variant are provided so that the gNB-CU obtains an updated communication configuration of the serving gNB, which would normally be generated by the serving gNB-DU. This updated communication configuration of the serving gNB includes the contents of an updated RS resource configuration list. The UE may be provided with the RS resource configurations of cells in both the serving gNB-DU and the candidate gNB-DU in steps 10 and 11. This facilitates mobility procedures because the UE knows the reference signals of all candidate cells in the serving gNB-DU and candidate gNB-DU.

[0163] Meanwhile, steps 10 and 11 are also provided to convey the communication configuration of the new candidate gNB-DU to the UE, which facilitates the mobility procedure because when the UE eventually switches to a candidate cell of the candidate gNB-DU, it already has all the information to connect to that candidate cell and candidate gNB-DU without involving higher layers terminating in the gNB-CU.

[0164] In the improved mobility procedure according to the first variant of the first solution above, we have described how the serving gNB-DU updates its measurement and communication configurations to include the RS resource configurations of both its own and the candidate gNB-DU in steps 7 and 8. In one example implementation, which can be combined with any of the other described implementations, these update processes can be implemented in the same or similar manner as known for Inter-Cell Beam Management (ICBM) in 3GPP Rel. 17.

[0165] According to one example of Rel.17 ICBM, neighbor cell reference signals are included in the measurement resource set configuration by the serving cell in different ways, for example, between reference signals SSB and CSI-RS.

[0166] For SSB, the IE "CSI-SSB-ResourceSet" has a parameter "ServingAdditionalPCIIndex-r17" that provides the non-serving cell ID for the SSB. An example taken from 3GPP TS 23.2006, section 6.3.2 is shown below:

[0167] CSI-SSB-ResourceSet The IE "CSI-SSB-ResourceSet" is used to configure one SS / PBCH block resource set that references the SS / PBCH as indicated in "ServingCellConfigCommon" and "ServingCellConfig".

[0168] [Table 12]

[0169] [Table 13]

[0170] For CSI-RS, a UE can configure CSI-RS under a serving cell that has a Quasi Co-located (QCL) relationship with the SSB beam of a neighboring cell. This can be done by providing QCL resources using the parameter "TCI-State". As an example, the IE "NZP-CSI-RS-Resource" has a field called TCI-StateID, which can point to additionalPCI-r17 and indicate the non-serving cell ID for the SSB used as the QCL source for the related CSI-RS.

[0171] An example of the NZP-CSI-RS-Resource IE and the TCI-State IE taken from section 6.3.2 of 3GPP TS 2.0, 2011, is shown below:

[0172] - NZP-CSI-RS-Resource The IE "NZP-CSI-RS-Resource" is used to configure the Non-Zero-Power (NZP) CSI-RS transmitted in the cell in which the IE is included, and the UE may be configured to measure it (see section 5.2.2.3.1 of 3GPP

[19] ). Configuration changes between periodic, semi-persistent, or aperiodic configurations for NZP-CSI-RS-Resource are not supported without release and addition.

[0173] [Table 14]

[0174] -TCI-State The IE "TCI-State" associates one or two DL reference signals with the corresponding QCL type.

[0175] [Table 15]

[0176] In the improved mobility procedure according to the first variant of the first solution, a method for transmitting an updated communication configuration of the serving gNB-DU to the gNB-CU in step 9 has been described. In one embodiment, which can be combined with other embodiments, this transmission can be performed by transmitting an IE "CellGroupConfig" defined in 3GPP, generated by the serving gNB-DU. The updated CellGroupConfig IE of the serving gNB-DU is then signaled to the UE transparently (transparently to the gNB-CU, meaning that the gNB-CU does not need to interpret the CellGroupConfig IE) via steps 10 and 11. For example, in step 10, a message is transmitted based on a higher layer (e.g., RRC) that terminates between the gNB and the UE. In step 11, a higher layer message including the updated CellGroupConfig IE is simply forwarded from the serving gNB-CU to the UE. As an example, the RRC message can be an RRC reconfiguration message.

[0177] As mentioned above, steps 10 and 11 are also provided to convey the communication configuration of the new candidate gNB-DU to the UE. Similarly, the communication configuration can be implemented by the IE "CellGroupConfig" obtained from the new candidate gNB-DU via step 3. The advantage of such an implementation is that the gNB-CU can simply forward such a container without having to interpret the contents of the CellGroupConfig.

[0178] It should be noted that the above description of Figure 15 exemplarily assumes that the RS resource configuration of the serving gNB-DU is already available in the gNB-CU. Such information may be obtained before step 1 of Figure 15, for example, when communication is established between the serving gNB-DU and the gNB-CU.

[0179] Alternatively, such information regarding the serving gNB-DU's RS resource configuration can be obtained in step 9 of FIG. 15. Similar to step 3 of FIG. 15, this involves the serving gNB-DU separately generating an RS resource configuration for its own cell and transmitting such information to the gNB-CU. In the latter case, the list of currently available RS resource configurations (if any) in step 1 does not include the serving gNB-DU's RS configuration. Furthermore, the updated list of RS resource configurations transmitted from the gNB-CU to the serving gNB-DU in step 6 also does not include the serving gNB-DU's RS configuration. This is not an issue for updating the serving gNB-DU communication configuration in step 8, because the serving gNB-DU is responsible for the RS configuration of its own cell and therefore has all the necessary information for its cell's RS configuration.

[0180] Figure 16 shows a first variant of the first solution when an additional cell (e.g., a cell of yet another candidate gNB-DU-2) is added to the candidate cell list of the UE. More specifically, one cell of another candidate gNB-DU-2 is detected as a potential candidate for a cell switch. The gNB-DU-2 is different from the conventional gNB-DU (gNB-DU-1 in the example of Figure 15) and also different from the serving gNB-DU. Figure 16 is an expanded diagram based on the previous Figure 15 to show the new candidate gNB-DU-2.

[0181] Figure 16 shows how steps 1 to 5 are performed again for a new candidate gNB-DU-2, as described in detail above. Steps 1, 2, and 3 are provided to obtain the communication configuration of the new candidate gNB-DU-2, which is then forwarded to the UE (content (c)) in step 10. This facilitates the mobility procedure, as when the UE eventually switches to a candidate cell of the new candidate gNB-DU-2, it already has all the information to connect to that candidate cell and candidate gNB-DU-2.

[0182] Figure 16 also shows that after updating the RS resource configuration list in the gNB-CU, the updated RS resource configuration list must be further propagated to the remaining two gNB-DUs, i.e., in this case, the serving gNB-DU and candidate gNB-DU-1. In particular, steps 6-1 to 9-1 are provided to again update the communication configuration for the serving gNB-DU, similar to Figure 15. Furthermore, steps 6-2 to 9-2 are added to update the communication configuration of gNB-DU-1.

[0183] The reason is that each gNB-DU involved in lower layer mobility according to the first variant of the first solution is required to generate a communication configuration, in particular a measurement configuration that is part of the communication configuration, that includes an up-to-date RS resource configuration list. The communication configuration already obtained from the new candidate gNB-DU-2 can be prepared by gNB-DU-2 to include an up-to-date RS resource configuration list, since it has been received at the time gNB-DU-2 generates its own communication configuration.

[0184] All of these updated communication settings are then provided to the UE (see steps 10 and 11).

[0185] As a result, whenever the RS resource configuration list is changed (e.g., due to the addition of a new candidate cell), the updated RS resource configuration list needs to be propagated to the remaining gNB-DUs as described above. Steps 6 to 9 need to be repeated frequently, which results in a lot of signaling overhead on the gNB-DU interface, the gNB-CU interface, and the interface towards the UE. This drawback worsens as the number of gNB-DUs participating in the UE's lower layer mobility increases.

[0186] As described above for the first variant of the first solution, each gNB-DU (including the serving gNB-DU and all candidate gNB-DUs) has the capability to create an up-to-date and complete list of RS resource configurations by receiving a list of RS resource configurations from the gNB-CU and then adding its own RS resource configurations for new candidate cells participating in mobility. This complete list of RS resource configurations is then used to create a measurement configuration, and then a communication configuration for the gNB-DU.

[0187] Furthermore, the gNB-DU according to the first variant of the first solution has the function of participating in cell switch preparation by transmitting its own RS resource configuration to the gNB-CU, which is responsible for maintaining an up-to-date and complete RS resource configuration list. Alternatively, instead of transmitting only its own RS resource configuration, the gNB-DU can transmit to the gNB-CU an updated RS resource configuration list prepared for generating its own measurement configuration. In this alternative case, the gNB-CU does not need to perform the update process itself, but simply adopts the received updated RS resource configuration list as is.

[0188] Thus, the first variant of the improved mobility procedure provides at least an improved base station distribution unit (e.g., serving BS-DU or candidate BS-DU), as described below.

[0189] An example BS-DU includes: a receiver of the BS-DU receives a mobility request for participating in user equipment (UE) mobility from a central unit of a base station; the mobility request or other message received by the receiver includes a list having information about RS resource configurations of the serving BS-DU serving at least the UE, where the RS resource configurations of the serving BS-DU are associated with candidate cells of the serving BS-DU; a processing circuit of the BS-DU updates the RS resource configurations of the BS-DU for the candidate cells of the BS-DU with the received RS resource configuration list; and a transmitter of the BS-DU transmits the RS resource configurations of the BS-DU or the updated RS resource configuration list to the BS-CU.

[0190] Furthermore, each gNB-DU has the capability to regenerate measurement and communication configurations using the latest and complete list of RS resource configurations, even after initial configuration. Accordingly, the improved BS-DU is provided such that a receiver of the BS-DU receives a modification request from a BS-CU, the modification request including an updated list of RS resource configurations, including the RS resource configurations of the serving BS-DU and the BS-DU as well as the RS resource configurations of other mobility candidate BS-DUs. A processing circuit of the BS-DU generates an updated communication configuration for the BS-DU based on the updated RS resource configuration list received from the BS-CU in the modification request. A transmitter of the BS-DU transmits the generated updated BS-DU communication configuration to the BS-CU.

[0191] <Second Modification> As already mentioned above, a second variant of the first solution uses a new measurement configuration that does not necessarily include the RS resource configuration of the respective gNB-DU. Rather, the RS resource configuration of the gNB-DU is provided separately from the measurement configuration of the gNB-DU. Also, a list of the most recent and complete RS resource configurations is separate from the measurement configuration of the gNB-DU, and they can be used together. According to one example of the second variant, the communication configuration of the gNB-DU (in one example, the measurement configuration) includes a pointer to another external RS resource configuration. This pointer facilitates mapping the measurement configuration of the gNB-DU (contained in the communication configuration of the gNB-DU) to a separate RS resource configuration or list of RS resource configurations.

[0192] This new measurement configuration, and therefore also the new communication configuration (including the measurement configuration), can be used for all gNBs involved in the UE's mobility. Therefore, the serving gNB-DU's communication configuration, and in particular its measurement configuration, does not include the RS resource configuration for its cell. Instead, the serving gNB-DU's RS resource configuration is provided separately and can then be used by the UE, along with the measurement configuration, in the process of measuring the serving gNB-DU's cell and reporting the measurement results to the serving gNB-DU. Therefore, in the following discussion regarding FIG. 17, it is exemplarily assumed that the UE is already configured for operation with the serving gNB-DU and therefore includes a new type of measurement configuration that does not include a usable RS resource configuration. Instead, the UE has separate access to the RS resource configuration for the serving gNB-DU's cell.

[0193] A more detailed embodiment of the first solution of the improved mobility procedure is described for a second variant of the improved mobility procedure with respect to Figure 17, which is believed to illustrate how the cell switch preparation initially described with respect to Figure 11 may be performed. More specifically, it illustrates how the lower layer mobility of a UE can be extended to a new candidate gNB-DU and its cells. The cells added to the UE's candidate cell list belong to a candidate gNB-DU that is different from the serving gNB-DU. One of the goals of the cell switch preparation is to provide the UE with appropriate information regarding the reference signals of the candidate cells of the new candidate gNB-DU.

[0194] For simplicity, it is again exemplary assumed that the new candidate gNB-DU has one cell for which preparation needs to be performed. However, the second variant of the first solution is equally applicable to scenarios in which the new candidate gNB-DU has two or more cells for which preparation needs to be performed. In such cases, the cell switch preparation targets multiple candidate cells of the candidate gNB-DU (a subset or the full set of cells of the candidate gNB-DU).

[0195] In step 1, the gNB-CU sends a mobility request message to the new candidate gNB-DU requesting that it participate in the UE's lower layer mobility. Compared to the first variant, there is no need to provide the new candidate gNB-DU with a list of current RS resource configurations, since the communication configuration prepared by the new candidate gNB-DU will not include RS resource configurations anyway.

[0196] In step 2, the candidate gNB-DU generates a communication configuration that differs from the first variant in that it does not include the candidate gNB-DU's RS resource configuration (e.g., the candidate gNB-DU's RS resource configuration for one cell). However, the candidate gNB-DU generates, for example, an RS resource configuration for the candidate cell outside of the communication configuration.

[0197] In step 3, the candidate gNB-DU sends an appropriate confirmation message to the gNB-CU containing the generated items: a new type of candidate gNB-DU communication configuration and a separate candidate gNB-DU RS resource configuration.

[0198] In step 4, the gNB-CU obtains the RS resource configuration of the candidate gNB-DU, and then in step 5, the gNB-CU updates its list of current RS resource configurations to include the received RS resource configuration of the candidate gNB-DU. The updated and current complete list thus obtained will include the RS resource configurations for the cells for the serving gNB-DU and the candidate gNB-DU.

[0199] In step 6, the gNB-CU forwards the received communication configuration of the candidate gNB-DU and the generated updated RS resource configuration list to the serving gNB-DU, which then forwards the received information to the UE (step 7).

[0200] Thus, in step 8, the UE receives the RS resource configuration list and has the necessary information about reference signals transmitted in the new candidate cell of the candidate gNB-DU. For example, the previous RS resource configuration list in the UE may have only included information about reference signals of the serving gNB-DU. The UE creates a link between the received updated RS resource configuration and the measurement configuration of the serving gNB-DU.

[0201] This updated RS resource configuration list can then be used together with the measurement configuration of the serving gNB-DU to perform measurements on cells configured, for example, as the serving gNB-DU and new candidate gNB-DU (steps 9 and 10).

[0202] Although not shown in FIG. 17, the UE may report the results of the measurements to the serving BS-DU as part of lower layer mobility, as already described with respect to FIG.

[0203] As described with respect to the exemplary implementation above, to use the updated RS resource configuration list with the serving gNB-DU's measurement configuration, the UE links the serving gNB-DU's measurement configuration to the updated RS resource configuration list. This can be achieved, for example, by ignoring the previous RS resource configuration list and using the updated RS resource configuration list instead. In other words, the previous RS resource configuration of the serving gNB-DU's measurement configuration is overwritten by the new updated RS resource configuration list newly generated by the UE.

[0204] In one example, the measurement configuration of the serving gNB-DU includes a pointer to an external RS resource configuration, in this case an RS resource configuration list that is kept updated by the gNB-CU (the gNB-CU is also responsible for sending the updated RS resource configuration list to the UE).

[0205] As can be seen, steps 3, 4, and 5 of the second variant are provided so that the gNB-CU generates an updated RS resource configuration list for the UE. The UE can be provided with the RS resource configurations of cells in both the serving gNB-DU and the candidate gNB-DU in steps 6 and 7. This facilitates mobility procedures because the UE knows the reference signals of all candidate cells in the serving gNB-DU and the candidate gNB-DU.

[0206] Steps 6 and 7 are provided to convey the communication configuration of the new candidate gNB-DU to the UE, which ultimately facilitates the mobility procedure since when switching to a candidate cell of the candidate gNB-DU, the UE will follow the communication configuration of the candidate gNB-DU and will therefore have all the information to connect to that candidate cell and candidate gNB-DU without involving higher layers terminating in the gNB-CU.

[0207] The second variant has the advantage over the first variant in that by introducing a separation between the RS resource configuration of the gNB-DU and the measurement configuration of the gNB-DU, the gNB-CU can continue to update the RS resource configuration without having to request each gNB-DU to regenerate its respective measurement configuration and communication configuration.

[0208] Compared with the first variant of the first solution, the second variant has the advantage that the above-mentioned propagation problem does not occur. In particular, according to the second variant, when an additional cell (e.g., a cell of another candidate gNB-DU-2) is added to the candidate cell list of the UE, conceptually, similar steps 1 to 9 are performed. More specifically, a cell of another candidate gNB-DU-2, which is different from both the previous candidate gNB-DU (see FIG. 17, e.g., candidate gNB-DU-1) and the serving gNB-DU, is detected as a potential candidate for cell switch. By performing steps 1 to 5 again, the gNB-CU is provided with a separate RS resource configuration for the new candidate cell of gNB-DU-2 and the current RS resource configuration list is updated to include the just-received RS resource configuration for the new candidate cell of gNB-DU-2. This updated RS resource configuration list is transmitted to the serving gNB-DU of the UE and further transmitted to the UE according to steps 6 and 7.

[0209] In parallel, the communication configuration of the new candidate gNB-DU-2 cell is provided to the gNB-CU and then to the UE, and steps 2 to 7 are executed.

[0210] The UE obtains and uses the updated RS resource configuration list according to step 10 instead of the previous RS resource configuration list, particularly in mobility procedures for performing measurements on the cell of the serving gNB-DU, the cell of the candidate gNB-DU-1, and the cell of the candidate gNB-DU-2.

[0211] As explained, the second variant is based on using the communication configuration of the gNB-DU, and the measurement configuration itself does not include the (available) RS resource configuration of each gNB-DU (and its associated cells). Instead, an external and separate list of RS resource configurations is maintained, kept up to date, and then flexibly used by the UE in combination with this modified measurement configuration.

[0212] Therefore, each new candidate gNB-DU-1 and gNB-DU-2 generates its respective communication configuration using the changed measurement configuration (without the available RS resource configuration), and the communication configuration does not depend on the (updated) contents of the RS resource configuration list.

[0213] Compared to the first variant of the first solution, there is no need to propagate the latest RS resource configuration list to existing gNB-DUs participating in the UE's mobility every time a new cell is added to the RS resource configuration list. In particular, the steps corresponding to steps 6, 7, 8, and 9 of the first solution in Fig. 16 according to the second solution are not required.

[0214] As described above for the second variant of the first solution, each gNB-DU (including the serving gNB-DU and all candidate gNB-DUs) has the capability to create a new type of measurement configuration that does not necessarily include the RS resource configuration of the respective gNB-DU.

[0215] Therefore, the second variant of the first solution for the improved mobility procedure provides at least an improved distribution unit of the base station (e.g., serving BS-DU or candidate BS-DU), as described below.

[0216] An example BS-DU includes: a receiver of the BS-DU receives a mobility request from a central unit of a base station to participate in user equipment (UE) mobility; a processing circuit of the BS-DU generates a communication configuration of the BS-DU, where the communication configuration of the BS-DU does not include a reference signal (RS) resource configuration of the BS-DU; and a transmitter of the BS-DU transmits the BS-DU communication configuration to the BS-CU.

[0217] As described above for the second variant of the first solution, the UE has the capability to repeatedly receive an updated list of RS resource configurations and then use the last received list of RS resource configurations instead of the old list of RS resource configurations together with the measurement configuration to perform measurements for different cells. Furthermore, the UE can handle new measurement configurations according to this second variant, which do not necessarily include the RS resource configuration for each gNB-DU.

[0218] Therefore, the second variant of the first solution for improved mobility procedures provides at least an improved UE.

[0219] An example UE includes: A processing circuit in the UE has access to a communication configuration of a base station serving the UE, i.e., a serving BS-DU. The serving BS-DU communication configuration includes a measurement configuration of the serving BS-DU that does not include a reference signal (RS) resource configuration of the serving BS-DU. The processing circuit in the UE has access to a list of one or more RS resource configurations including at least the RS resource configuration of the serving BS-DU, where the RS resource configuration is associated with a candidate cell for the serving BS-DU. A receiver in the UE receives an updated list of one or more RS resource configurations from the serving BS-DU. The updated RS resource configuration list includes the RS resource configuration of the serving BS-DU and the RS resource configurations of BS-DUs that are candidates for participating in the UE's mobility. The processing circuit in the UE uses the updated RS resource configuration list together with the measurement configuration of the serving BS-DU.

[0220] The improved UE according to the second variant has the capability to process a pointer contained in the communication configuration of the gNB-DU (in one example, contained in the measurement configuration of the communication configuration), which pointer points to an external RS resource configuration such as an RS resource configuration list that is continually updated as described above.

[0221] In the above embodiments of the improved mobility procedure according to the first and second variants of the first solution, it has been described how a list of RS resource configurations can be maintained by the gNB-CU. In further embodiments, further embodiments of the improved mobility procedure, which can be combined with any of the other embodiments, describe how the RS resource configuration list can be exemplarily implemented.

[0222] The RS resource configuration list may be implemented, for example, as an information element denoted as "LTM-L1-MeasResourceSetList" and may include at least a set of SSBs (and optionally a set of CSI-RSs) for L1 measurements for each candidate cell of the gNB-DU. The LTM-L1-MeasResourceSetList information element may be defined, for example, as follows:

[0223] [Table 16]

[0224] The above IE "LTM-L1-MeasResourceSetList" is also written as "RS resource setting list", specifically, ● In the first variant of the first solution ○ In step 6 of Figure 15, ● In the second variant of the first solution o It can be sent in steps 6 and 7 of Figure 17.

[0225] In a second variant of the first solution above, the updated RS resource configuration list is forwarded from the gNB-CU to the UE's serving gNB-DU and then forwarded to the UE (see steps 6 and 7 in Figure 17). In one example, the updated RS resource configuration list can be included in a higher layer message such as an RRCReconfiguration message.

[0226] According to the example below, the updated RS resource configuration can be defined as follows: [Table 17] Thus, the LTM-L1-MeasResourceSetList can indicate one or more LTM-L1-ResourceSets identified by LTM-L1-ResourceSetID, and each LTM-L1-ResourceSet can be defined, for example, as follows:

[0227] [Table 18] In a second variant of the first solution above, the measurement configuration does not contain the RS resource configuration, but may for example contain a pointer that is used to point to a separate RS resource configuration list (see for example LTE-L1-MeasResourceSetList above). For this purpose, a new IE "CSI-ResourceConfig-r18" can be used as follows:

[0228] [Table 19] As can be seen, we define a resource configuration for CSI with an ID (here "CSI-ResourceConfigID") and with a pointer that allows to establish a link to a separate RS resource configuration list, namely LTE-L1-MeasResourceSetList.

[0229] <Second Solution - UE Maintaining Updated RS Resource Configuration List> As mentioned above, the second solution is based on the UE being primarily responsible for maintaining an updated and complete list of RS resource configurations, e.g., for its current serving gNB-DU and all candidate gNB-DUs for a possible cell switch. Thus, the UE has all the necessary information regarding RS resource configurations to proceed with lower layer mobility, including, in particular, performing measurements by the UE on the cell of the current serving gNB-DU and on the cells of other (candidate gNB-DUs).

[0230] More specifically, the second solution of the improved mobility procedures provides an improved UE, as described below.

[0231] Figure 18 shows a simplified example UE structure according to one embodiment of a second solution for improved mobility procedures, which can be implemented based on the general UE structure described in relation to Figure 10. The various structural elements of the UE shown in Figure 18 may be connected to each other using corresponding input / output nodes (not shown), for example, to exchange control data and user data and other signals. Although not shown for illustrative purposes, the UE may include further structural elements.

[0232] As is apparent from FIG. 18, the UE may include a communication setting receiver, a communication setting decoder, and a reference signal resource setting update circuit.

[0233] In this case, the receiver of the UE may be configured, as an example, to at least partially receive communication settings from the BS-DU or the like.

[0234] In this case, as will become apparent from the disclosure below, the processing circuitry of the UE may be configured, as an example, to at least partially perform one or more of the following: decode the received communication configuration, update the list of reference signal resource configurations, etc.

[0235] In this case, as will become apparent from the disclosure below, the transmitter of the UE may be configured to at least partially perform one or more of, for example, measurement reporting.

[0236] As will be described in more detail below, the procedure disclosed as an example in this disclosure is performed by a UE, including: a receiver receiving, from a distributed unit of a base station serving the UE, i.e., a serving BS-DU, a communication configuration of a BS-DU that is a candidate for participating in the UE's mobility; a processing circuit in the UE decoding the received mobility candidate BS-DU communication configuration to obtain a reference signal (RS) resource configuration of the mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU; and, based on the decoded RS resource configuration of the mobility candidate BS-DU, updating a current list having information on at least the serving BS-DU's RS resource configuration.

[0237] A corresponding exemplary method includes the following steps by a UE: receiving, from a distributed unit of a base station serving the UE, i.e., a serving BS-DU, communication configurations of BS-DUs that are candidates for participating in the UE's mobility; decoding the received mobility candidate BS-DU communication configuration to obtain a reference signal (RS) resource configuration for the mobility candidate BS-DU's candidate cell; and updating the current list, which includes information of at least the RS resource configuration of the serving BS-DU, based on the decoded RS resource configuration of the mobility candidate BS-DU.

[0238] FIG. 19 shows a corresponding sequence diagram for UE operation in one embodiment in accordance with the UE and UE operation described above.

[0239] Figure 20 shows a signaling diagram of an exemplary and simplified embodiment of an improved mobility procedure relating to the second solution, illustrating the exchange of messages between different participating entities (here, the UE and its serving gNB-DU) and the steps performed by these entities.

[0240] Thus, the above mobility procedure achieves the objectives and overcomes some of the drawbacks mentioned above. The second solution is simple and can provide the UE with the necessary information about the reference signals of cells of other BS-DUs.

[0241] A more detailed embodiment of the second solution for the improved mobility procedure is described with reference to Figure 21. Figure 21 can be thought of as illustrating how to perform the cell switch preparation first described with reference to Figure 11. More specifically, it shows how the lower layer mobility of a UE can be extended to cover a new candidate gNB-DU and its cells. The cells added to the UE's candidate cell list belong to a candidate gNB-DU that is different from the serving gNB-DU. One of the purposes of cell switch preparation is to provide the UE with appropriate information about the reference signals of the candidate cells of the new candidate gNB-DU.

[0242] For simplicity, it is exemplarily assumed that the new candidate gNB-DU has one cell that needs to be prepared.

[0243] However, the second solution is equally applicable in scenarios where the new candidate gNB-DU has more than one cell to prepare, in which case the cell switch preparation targets multiple candidate cells of the candidate gNB-DU (a subset or the full set of cells of the candidate gNB-DU).

[0244] In order for the new candidate gNB-DU to participate in the UE's lower layer mobility, the gNB-CU sends a mobility request message to the new candidate gNB-DU (Step 1). It is assumed that the candidate gNB-DU confirms that it will participate in the UE's lower layer mobility. In this way, the new candidate gNB-DU generates a communication configuration that the UE can later use to connect to the candidate gNB-DU's cell (Step 2). This candidate gNB-DU communication configuration includes the candidate gNB-DU's measurement configuration, which includes the candidate gNB-DU's reference signal resource configuration that the candidate gNB-DU uses to transmit reference signals in its own cell.

[0245] The candidate gNB-DU communication configuration thus generated is then sent, together with its contents, to the gNB-CU as part of an appropriate mobility confirmation message (Step 3).

[0246] Furthermore, the gNB-CU transmits the communication configuration of the candidate gNB-DU to the UE's serving gNB-DU (step 4.), which then further forwards the received communication configuration of the candidate gNB-DU to the UE (step 5.).

[0247] The UE is responsible for maintaining an up-to-date list of RS resource configurations for the cells of the serving gNB-DU and new candidate gNB-DU, as well as maintaining an up-to-date list of RS resource configurations for the cells of other previously added candidate gNB-DUs.

[0248] Therefore, the UE decodes the received communication configuration of the new candidate gNB-DU (step 6.) and obtains therefrom the RS resource configuration of the new candidate gNB-DU (particularly its cell).The UE updates its current RS resource configuration list to include the RS resource configuration of the new candidate gNB-DU (step 7.).

[0249] This updated RS resource configuration list is used together with the measurement configuration of the serving gNB-DU to perform measurements, for example, on the cells of the serving gNB-DU and the new candidate gNB-DU, according to that configuration (steps 8 and 9).

[0250] Although not shown in FIG. 21, the UE may report the results of the measurements to the serving BS-DU as part of lower layer mobility, as already described with respect to FIG.

[0251] According to one embodiment, to use the updated RS resource configuration list together with the measurement configuration of the serving gNB-DU, the UE links the measurement configuration of the serving gNB-DU to the updated RS resource configuration list. This can be achieved, for example, by ignoring the previous RS resource configuration list and using the updated RS resource configuration list instead. In other words, the previous RS resource configuration of the serving gNB-DU measurement configuration is overwritten by the new updated RS resource configuration list newly generated by the UE.

[0252] The second solution has the advantage that the mobility procedure is simple. Furthermore, the second solution relies on signaling and mechanisms already defined in mobility procedures, such as obtaining the communication configuration of the BS-DU and transferring the communication configuration of the BS-DU to the UE. Therefore, there is no need to define new signaling and mechanisms in the various gNB-DUs and gNB-CUs and the interfaces between them (such as the F1 interface in 3GPP).

[0253] Compared with the first variant of the first solution, the second solution also has the advantage that the above-mentioned propagation problem does not occur. In particular, according to the second solution, when another cell (e.g., a cell of another candidate gNB-DU-2) is added to the candidate cell list of the UE, conceptually, similar steps 1 to 8 are performed. More specifically, one cell of the other candidate gNB-DU-2 is detected as a potential candidate for cell switch, and the candidate gNB-DU-2 is different from the previous candidate gNB-DU (see FIG. 21, e.g., candidate gNB-DU-1) and also different from the serving gNB-DU. By performing steps 1 to 5 again, the communication configuration of the other new candidate gNB-DU-2 for the new candidate cell is provided to the UE. In steps 6, 7, and 8, the UE decodes the corresponding RS resource configuration for the new candidate cell of candidate gNB-DU-2, and then updates its current RS resource configuration list accordingly to include the RS resource configuration for the new candidate cell of candidate gNB-DU-2 in addition to the existing RS resource configurations for the cell of the serving gNB-DU and the cell of the conventional candidate gNB-DU-1.

[0254] Finally, the UE continues to perform measurements according to step 9, but this time for the cell of candidate gNB-DU-1, the cell of candidate gNB-DU-2, and the cell of the serving gNB-DU, using the most recent and complete list of RS resource configurations maintained in the UE.

[0255] Therefore, each new candidate gNB-DU-1 and gNB-DU-2 generates communication configurations such that the communication configurations include only the RS resource configurations of its own cell (unlike the first variant of the first solution) and do not depend on the contents of the (updated) RS resource configuration list.

[0256] Compared to the first variant of the first solution, there is no need to propagate the latest RS resource configuration list to existing gNB-DUs participating in the UE's mobility every time a new cell is added to the RS resource configuration list. In particular, according to the second solution, steps corresponding to steps 6, 7, 8, and 9 of the first variant of the first solution in Fig. 16 are not necessary.

[0257] On the other hand, the second solution requires the UE to perform steps to maintain an up-to-date list of RS resource configurations, which increases the computational complexity of the UE. For example, the UE needs to decode the communication configurations of all candidate cells (gNB-DUs) to obtain complete information on the RS resource configurations. According to the first solution, the UE only needs to decode one communication configuration to obtain the up-to-date list of RS resource configurations (prepared by the gNB-CU).

[0258] Further Aspects According to a first aspect, there is provided a base station central unit (BS-CU) comprising: a transmitter unit that transmits a mobility request to a base station distributed unit (BS-DU) that is a candidate for participating in user equipment (UE) mobility, i.e., a mobility candidate BS-DU; a receiver unit of the BS-CU that receives, from the mobility candidate BS-DU, reference signal (RS) resource configurations for candidate cells of the mobility candidate BS-DU; a processing circuit of the BS-CU that generates an updated RS resource configuration list that includes information on the received RS resource configurations of the mobility candidate BS-DU and the RS resource configurations of at least a serving BS-DU that serves the UE; and a transmitter unit that transmits the updated RS resource configuration list to the serving BS-DU for further forwarding to the UE.

[0259] According to a second aspect provided in addition to the first aspect, a transmitter transmits an updated RS resource configuration list to a serving BS-DU of a UE. A receiver receives an updated communication configuration of the serving BS-DU from the serving BS-DU. The updated communication configuration of the serving BS-DU has content of the updated RS resource configuration list mapped to a measurement configuration of the serving BS-DU. Transmitting the content of the updated RS resource configuration list includes forwarding the updated communication configuration of the serving BS-DU to the serving BS-DU.

[0260] According to a third aspect provided in addition to the second aspect, a mobility request or other message transmitted to a mobility candidate BS-DU includes a list having information on at least the RS resource configuration of the serving BS-DU. A receiver receives communication configurations of the mobility candidate BS-DU from the mobility candidate BS-DU. A transmitter forwards the received communication configurations of the mobility candidate BS-DU to the serving BS-DU for further forwarding to the UE. In one optional implementation, the communication configurations of the mobility candidate BS-DU have the contents of the RS resource configuration list mapped to measurement configurations of the mobility candidate BS-DU. The contents of the mapped RS resource configuration list include the RS resource configuration of the serving BS-DU and the RS resource configuration of the mobility candidate BS-DU.

[0261] According to a fourth aspect provided in addition to the second or third aspect, a transmitter transmits an other mobility request to another mobility candidate BS-DU participating in the UE's mobility. Optionally, the other mobility request or further message includes an RS resource configuration list for at least the serving BS-DU and the mobility candidate BS-DU. The receiver receives, from the other mobility candidate BS-DU, an RS resource configuration of the other mobility candidate BS-DU for a candidate cell of the other mobility candidate BS-DU. The processing circuit updates the RS resource configuration list based on the received RS resource configuration of the other mobility candidate BS-DU. The transmitter transmits the updated RS resource configuration list to the serving BS-DU. The receiver receives, from the serving BS-DU, an updated communication configuration of the serving BS-DU. The updated communication configuration of the serving BS-DU includes the contents of the updated RS resource configuration list mapped to the measurement configuration of the serving BS-DU. The transmitter forwards the received communication configuration of the serving BS-DU to the serving BS-DU for forwarding to the UE. In one optional implementation, the transmitter transmits an updated RS resource configuration list to the mobility candidate BS-DU. The receiver, in operation, receives updated communication configurations of the mobility candidate BS-DU from the mobility candidate BS-DU, and the transmitter, in operation, forwards the received updated communication configurations of the mobility candidate BS-DU to the serving BS-DU for forwarding to the UE. In one optional implementation, the receiver receives communication configurations of other mobility candidate BS-DUs from other mobility candidate BS-DUs. The transmitter transmits the received communication configurations of the other mobility candidate BS-DUs to the serving BS-DU for further forwarding to the UE.

[0262] According to a fifth aspect provided in addition to the first aspect, a receiver receives a communication configuration of the mobility candidate BS-DU in response to a mobility request from the mobility candidate BS-DU. A transmitter forwards the received communication configuration of the mobility candidate BS-DU to a serving BS-DU for further forwarding to the UE. The communication configuration of the mobility candidate BS-DU does not include an RS resource configuration of the mobility candidate BS-DU. In one optional implementation, the communication configuration of the mobility candidate BS-DU includes a pointer to an updated RS resource configuration list sent to the serving BS-DU to map the updated RS resource configuration list to the measurement configuration of the mobility candidate BS-DU included in the communication configuration of the mobility candidate BS-DU.

[0263] According to a sixth aspect provided in addition to the fifth aspect, a transmitter transmits an other mobility request to an other BS-DU to become a candidate for participating in the mobility of the UE. A receiver receives an RS resource configuration of the other mobility candidate BS-DU for a candidate cell of the other mobility candidate BS-DU for the other mobility request from the other mobility candidate BS-DU. A processing circuit updates a current RS resource configuration list based on the received RS resource configuration of the other mobility candidate BS-DU. The transmitter transmits the updated RS resource configuration list to a serving BS-DU for further forwarding to the UE. In one optional implementation, the receiver receives a communication configuration of the other mobility candidate BS-DU for the other mobility request. The transmitter forwards the received communication configuration of the other mobility candidate BS-DU to the serving BS-DU for further forwarding to the UE. The communication configuration of the other mobility candidate BS-DU does not include the RS resource configuration of the other mobility candidate BS-DU.

[0264] According to a seventh aspect, the steps performed by a central unit of a base station, namely: sending a mobility request to a base station distributed unit (BS-DU) that is a candidate to participate in the mobility of the user equipment (UE), i.e., a mobility candidate BS-DU; receiving, from the mobility candidate BS-DU, a reference signal (RS) resource configuration of the mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU; generating an updated RS resource configuration list having information of the received RS resource configuration of the mobility candidate BS-DU and the RS resource configuration of at least the serving BS-DU serving the UE; sending the content of the updated RS resource configuration list to the serving BS-DU for further forwarding to the UE.

[0265] According to an eighth aspect, there is provided an integrated circuit that, in operation, controls the processing of a base station central unit (BS-CU), the processing comprising the following steps performed by the BS-CU: sending a mobility request to a base station distributed unit (BS-DU) that is a candidate to participate in the mobility of the user equipment (UE), i.e., a mobility candidate BS-DU; receiving, from the mobility candidate BS-DU, a reference signal (RS) resource configuration of the mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU; generating an updated RS resource configuration list having information of the received RS resource configuration of the mobility candidate BS-DU and the RS resource configuration of at least the serving BS-DU serving the UE; and sending the content of the updated RS resource configuration list to the serving BS-DU for further forwarding to the UE.

[0266] According to a ninth aspect, there is provided a base station distributed unit (BS-DU) comprising: a receiver of the BS-DU receives a mobility request for participating in user equipment (UE) mobility from a central unit of the base station; the mobility request or other message received by the receiver includes a list having information on RS resource configuration of a serving BS-DU serving at least the UE, the serving BS-DU's RS resource configuration relating to candidate cells of the serving BS-DU; a processing circuit of the BS-DU updates the received RS resource configuration list with the BS-DU's RS resource configuration relating to the BS-DU's candidate cells; and a transmitter of the BS-DU transmits the BS-DU's RS resource configuration or alternatively the updated RS resource configuration list to a BS-CU.

[0267] According to a tenth aspect provided in addition to the ninth aspect, a receiver receives, from a BS-CU, a modification request including an updated RS resource configuration list including RS resource configurations of other mobility candidate BS-DUs in addition to the serving BS-DU and the RS resource configuration of the BS-DU. A processing circuit generates an updated communication configuration for the BS-DU based on the updated RS resource configuration list received from the BS-CU in the modification request. A transmitter transmits the generated updated communication configuration for the BS-DU to the BS-CU.

[0268] According to an eleventh aspect, there is provided a base station distributed unit (BS-DU) comprising: a receiver of the BS-DU receives a mobility request for participating in user equipment (UE) mobility from a base station central unit; a processing circuit generates a communication configuration of the BS-DU, where the communication configuration of the BS-DU does not include a reference signal (RS) resource configuration of the BS-DU; and a transmitter transmits the communication configuration of the BS-DU to a BS-CU.

[0269] According to a twelfth aspect provided in addition to the eleventh aspect, the communication configuration of the BS-DU includes a pointer to a current list of one or more RS resource configurations that can be used to map the current list of one or more RS resource configurations to the measurement configuration of the BS-DU included in the communication configuration of the BS-DU.

[0270] According to a thirteenth aspect provided in addition to the eleventh or twelfth aspect, a transmitter transmits an RS resource configuration of the BS-DU for a candidate cell of the BS-DU to a BS-CU.

[0271] According to a fourteenth aspect, there is provided a user equipment (UE) comprising: a processing circuit in the UE has access to a communication configuration of a base station (serving BS-DU) serving the user equipment (UE); the communication configuration of the serving BS-DU includes a measurement configuration of the serving BS-DU that does not include a reference signal (RS) resource configuration of the serving BS-DU; the processing circuit has access to a list of one or more RS resource configurations including at least an RS resource configuration of the serving BS-DU, the RS resource configuration associated with a candidate cell of the serving BS-DU; a receiver in the UE receives an updated RS resource configuration list of one or more RS resource configurations from the serving BS-DU; the updated RS resource configuration list includes RS resource configurations of the serving BS-DU and BS-DUs that are candidates to participate in the UE's mobility; the processing circuit uses the updated RS resource configuration list together with the measurement configuration of the serving BS-DU.

[0272] According to a fifteenth aspect provided in addition to the fourteenth aspect, the measurement configuration of the serving BS-DU includes a pointer to an updated RS resource configuration list. In one optional implementation, a receiver receives communication configurations of mobility candidate BS-DUs from the serving BS-DU. In one optional implementation, a processing circuit performs measurements based on the updated RS resource configuration list and the measurement configuration of the serving BS-DU. In a further optional implementation, the UE includes a transmitter that transmits a measurement report to the serving BS-DU that includes a result of the measurement.

[0273] According to a sixteenth aspect, the following steps are performed by a user equipment (UE): accessing a communication configuration of a base station serving the UE, i.e., a serving BS-DU, where the communication configuration of the serving BS-DU includes a measurement configuration of the serving BS-DU but does not include a reference signal (RS) resource configuration of the serving BS-DU; accessing a list of one or more RS resource configurations including at least an RS resource configuration of a serving BS-DU, the RS resource configurations being associated with candidate cells of the serving BS-DU; receiving, from a serving BS-DU, an updated RS resource configuration list of one or more RS resource configurations, including RS resource configurations of the serving BS-DU and BS-DUs that are candidates for participating in the UE's mobility; and using the updated RS resource configuration list together with the measurement configuration of the serving BS-DU.

[0274] According to a seventeenth aspect, there is provided an integrated circuit that, in operation, controls processing of a user equipment (UE), the processing comprising the following steps performed by the UE: accessing a communication configuration of a base station serving the UE, i.e., a serving BS-DU, where the communication configuration of the serving BS-DU includes a measurement configuration of the serving BS-DU but does not include a reference signal (RS) resource configuration of the serving BS-DU; accessing a list of one or more RS resource configurations including at least an RS resource configuration of a serving BS-DU, the RS resource configurations being associated with candidate cells of the serving BS-DU; receiving, from a serving BS-DU, an updated RS resource configuration list of one or more RS resource configurations, including RS resource configurations of the serving BS-DU and BS-DUs that are candidates for participating in the UE's mobility; and using the updated RS resource configuration list together with the measurement configuration of the serving BS-DU.

[0275] According to an eighteenth aspect, there is provided a user equipment (UE) comprising: a receiver unit receives, from a distributed unit of a base station serving the user equipment (UE), a serving BS-DU, a communication configuration of a BS-DU that is a candidate for participating in the mobility of the UE; a processing circuit decodes the received communication configuration of the mobility candidate BS-DU to obtain a reference signal (RS) resource configuration of the mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU; and the processing circuit updates a current list having information of at least the RS resource configuration of the serving BS-DU based on the decoded RS resource configuration of the mobility candidate BS-DU.

[0276] According to a 19th aspect provided in addition to the 18th aspect, the processing circuit maps the updated RS resource configuration list to a measurement configuration of the serving BS-DU. In one optional implementation, the mapping includes ignoring the current RS resource configuration list and instead using the updated RS resource configuration list for the measurement configuration of the serving BS-DU.

[0277] According to a twentieth aspect, provided in addition to the eighteenth or nineteenth aspect, a receiver receives a communication configuration of another mobility candidate BS-DU from a serving BS-DU. A processing circuit decodes the received communication configuration of the other mobility candidate BS-DU to obtain an RS resource configuration of the other mobility candidate BS-DU for a candidate cell of the other mobility candidate BS-DU. The processing circuit updates a current RS resource configuration list based on the decoded RS resource configuration of the other mobility candidate BS-DU. In one optional implementation, the processing circuit maps the updated RS resource configuration list to a measurement configuration of the serving BS-DU.

[0278] According to a 21st aspect provided in addition to any one of the 18th to 20th aspects, the processing circuit performs measurements based on the updated RS resource configuration list. In one optional implementation, the UE includes a transmitter configured to transmit a measurement report including a result of the measurements to the serving BS-DU.

[0279] According to a 22nd aspect provided in addition to any one of the 14th, 15th, and 18th to 21st aspects, a receiver receives a cell switch trigger from a serving BS-DU indicating a cell of a mobility candidate BS-DU as a target for a cell switch. The processing circuit controls a switch from a current cell of the serving BS-DU to the indicated cell of the mobility candidate BS-DU. In one optional implementation, the communication configuration of the mobility candidate BS-DU further includes configuration parameters of lower layers of the BS-DU related to facilitating UE communication with the cell of the mobility candidate BS-DU. In a further optional implementation, an RS resource configuration of the BS-DU is associated with one cell of the BS-DU, and another RS ​​resource configuration of the BS-DU is associated with another cell of the BS-DU.

[0280] According to a 23rd aspect, the following steps are performed by a user equipment (UE): receiving, from a distributed unit of a base station serving the UE, i.e., a serving BS-DU, communication configurations of BS-DUs that are candidates for participating in the UE's mobility; decoding the received communication configuration of the mobility candidate BS-DU to obtain a reference signal (RS) resource configuration for the candidate cell of the mobility candidate BS-DU; updating a current list having information about at least the RS resource configuration of the serving BS-DU based on the decoded RS resource configuration of the mobility candidate BS-DU.

[0281] According to a twenty-fourth aspect, there is provided an integrated circuit that, in operation, controls processing of a user equipment (UE), the processing comprising the following steps performed by the UE: receiving, from a distributed unit of a base station serving the UE, i.e., a serving BS-DU, communication configurations of BS-DUs that are candidates for participating in the UE's mobility; decoding the received communication configuration of the mobility candidate BS-DU to obtain a reference signal (RS) resource configuration for the candidate cell of the mobility candidate BS-DU; and updating a current list having information about at least the RS resource configuration of the serving BS-DU based on the decoded RS resource configuration of the mobility candidate BS-DU.

[0282] Further variations including hardware and software implementations of the present disclosure The present disclosure may be implemented by software, hardware, or software operating in conjunction with hardware. Each functional block used in the above-described embodiments may be implemented, in whole or in part, by an LSI such as an integrated circuit. Each process described in each embodiment may be controlled, in whole or in part, by the same LSI or a combination of LSIs. An LSI may be formed as an individual chip, or a single chip may be formed to include some or all of the functional blocks. An LSI may include a data input / output unit coupled thereto. Depending on the level of integration, an LSI may also be referred to as an IC (integrated circuit), system LSI, super LSI, or ultra LSI. However, the technology for implementing an integrated circuit is not limited to LSI, and may be implemented using dedicated circuits, general-purpose processors, or dedicated processors. Furthermore, an FPGA (field programmable gate array), which can be programmed after LSI fabrication, or a reconfigurable processor, which can reconfigure the connections and settings of circuit cells arranged within an LSI, may also be used. The present disclosure may be implemented using digital or analog processing. If, as a result of advances in semiconductor technology or other derivative technologies, LSI is replaced by future integrated circuit technology, that future integrated circuit technology can be used to integrate functional blocks. Biotechnology can also be applied.

[0283] The present disclosure can be implemented by any kind of apparatus, device, or system having a communication capability (referred to as a communication apparatus).

[0284] A communications device may include a radio transceiver (transceiver unit) and processing / control circuitry. The transceiver unit may include and / or function as a receiver and a transmitter. The transceiver unit as a transmitter and a receiver may include an RF (radio frequency) module including an amplifier, an RF modulator / demodulator, etc., and one or more antennas.

[0285] Some non-limiting 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, smart watches, tracking devices), game consoles, e-readers, telehealth / telemedicine devices, vehicles (e.g., automobiles, airplanes, ships) that provide communication capabilities, and various combinations thereof.

[0286] Communication devices are not limited to portable or mobile devices, but can also include any type of equipment, device, or system that is non-portable or fixed, such as smart home devices (e.g., appliances, lights, smart meters, control panels), vending machines, and any other "thing" in an "Internet of Things" (IoT) network.

[0287] Communications include data communications via cellular systems, wireless LAN systems, communications satellite systems, etc., as well as data communications via combinations of these.

[0288] A communications device may include devices such as a controller or a sensor coupled to the communications device to perform the communications functions described in this disclosure. For example, a communications device may include a controller or a sensor that generates control or data signals used by the communications device to perform the communications functions of the communications device.

[0289] The communications apparatus may further include infrastructure facilities, such as base stations, access points, and any other apparatus, device, or system that communicate with or control apparatuses such as the apparatuses in the non-limiting examples above.

[0290] (control signal) In the present disclosure, the downlink control signal (information) according to the present disclosure may be a signal (information) transmitted via a PDCCH of a physical layer, or may be a signal (information) transmitted via a MAC Control Element (CE) of a higher layer or an RRC. The downlink control signal may be a predefined signal (information).

[0291] The uplink control signal (information) according to the present disclosure may be a signal (information) transmitted via a PUCCH of a physical layer, or may be a signal (information) transmitted via a MAC CE of a higher layer or RRC. The uplink control signal may also be a predefined signal (information). The uplink control signal may be uplink control information (UCI), first-stage sidelink control information (SCI), or second-stage SCI.

[0292] (base station) In the present 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. Furthermore, in sidelink communication, a terminal may be used instead of a base station. The base station may be a relay device that relays communication between an upper node and a terminal. The base station may be a roadside unit.

[0293] (Uplink / Downlink / Sidelink) The present disclosure may be applied to any of the uplink, downlink, and sidelink.

[0294] For example, the present disclosure may be applied to uplink channels such as PUSCH, PUCCH, and PRACH, downlink channels such as PDSCH, PDCCH, and PBCH, and sidelinks such as PSSCH (Physical Sidelink Shared Channel), PSCCH (Physical Sidelink Control Channel), and PSBCH (Physical Sidelink Broadcast Channel).

[0295] The PDCCH, PDSCH, PUSCH, and PUCCH are examples of a downlink control channel, a downlink data channel, an uplink data channel, and an uplink control channel, respectively. The PSCCH and PSSCH are examples of a sidelink control channel and a sidelink data channel, respectively. The PBCH and PSBCH are examples of a broadcast channel, and the PRACH is an example of a random access channel. (Data channel / Control channel) The present disclosure may be applied to both data channels and control channels. The channels in the present disclosure may be replaced with data channels including PDSCH, PUSCH, and PSSCH, and / or control channels including PDCCH, PUCCH, PBCH, PSCCH, and PSBCH.

[0296] (reference signal) In this disclosure, a reference signal is a signal known to both a base station and a mobile station, and each reference signal may be referred to as a reference signal (RS) or a pilot signal. A reference signal may be any of a demodulation reference signal (DMRS), a channel state information - reference signal (CSI-RS), a tracking reference signal (TRS), a phase tracking reference signal (PTRS), a cell-specific reference signal (CRS), and a sounding reference signal (SRS).

[0297] (time interval) In the present disclosure, the time resource unit is not limited to one or a combination of a slot and a symbol, and may be a time resource unit such as a frame, a superframe, a subframe, a slot, a subslot of a time slot, a minislot, or a symbol, an Orthogonal Frequency Division Multiplexing (OFDM) symbol, a Single Carrier-Frequency Division Multiplexing Access (SC-FDMA) symbol, or other time resource unit. The number of symbols included in one slot is not limited to the number of symbols exemplified in the above-mentioned embodiments, and may be other numbers of symbols.

[0298] (frequency band) The present disclosure may be applied to both licensed and unlicensed bands.

[0299] (communication) The present disclosure may be applied to communication between a base station and a terminal (Uu link communication), communication between terminals (sidelink communication), and vehicle-to-everything (V2X) communication. The channels in the present disclosure may be replaced with PSCCH, PSSCH, physical sidelink feedback channel (PSFCH), PSBCH, PDCCH, PUCCH, PDSCH, PUSCH, and PBCH.

[0300] The present disclosure may also be applied to a terrestrial network or a network other than a terrestrial network (a non-terrestrial network (NTN)) that uses a satellite or a high altitude pseudo satellite (HAPS). The present disclosure may also be applied to a network with a large cell size or a terrestrial network in which the delay is large compared to the symbol length or slot length, such as an ultra-wideband transmission network.

[0301] (antenna port) An antenna port refers to a logical antenna (antenna group) formed by one or more physical antennas (multiple antennas are possible). That is, an antenna port does not necessarily refer to one physical antenna, but may refer to an array antenna formed by multiple antennas. For example, the number of physical antennas forming an antenna port is not defined, and instead, an antenna port is defined as the smallest unit by which a terminal can transmit a reference signal. An antenna port may also be defined as the smallest unit for multiplying a weight of a precoding vector.

[0302] Furthermore, the various embodiments may also be implemented by means of software modules, which are executed by a processor or directly in hardware. A combination of software modules and hardware implementation is also possible. The software modules may be stored on any kind of computer-readable storage medium, for example RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. Furthermore, it should be noted that individual features of the different embodiments may also be the subject of another embodiment, individually or in any combination.

[0303] It will be appreciated by those skilled in the art that various changes and / or modifications may be made to the present disclosure set forth in the specific embodiments without departing from the concept or scope of the invention as broadly described, and the embodiments set forth herein are therefore to be considered in all respects as illustrative and not restrictive.

Claims

1. A base station central unit (BS-CU), a transmitter that, during operation, transmits a mobility request to Base Station-Distributed Units (BS-DUs) that are candidates to participate in User Equipment (UE) mobility, i.e., mobility candidate BS-DUs; a receiver configured to receive, in operation, from the mobility candidate BS-DU, a Reference Signal (RS) resource configuration of the mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU; a processing circuit that, during operation, generates an updated list having information regarding the received RS resource configuration of the mobility candidate BS-DU and at least an RS resource configuration of a serving BS-DU serving the UE; the transmitter, in operation, transmits the contents of the updated list to the serving BS-DU for further forwarding to the UE; BS-CU.

2. The transmitter, upon operation, transmits the updated list to the serving BS-DU of the UE; The receiver, in operation, receives from the serving BS-DU an updated communication configuration of the serving BS-DU; the updated communication configuration of the serving BS-DU has the contents of the updated list mapped to a measurement configuration of the serving BS-DU; transmitting the contents of the updated list includes forwarding the updated communication configuration of the serving BS-DU to the serving BS-DU. The BS-CU according to claim 1.

3. the mobility request or other message sent to the mobility candidate BS-DU includes the list having information regarding at least the serving BS-DU's RS resource configuration; The receiver, when operating, receives a communication configuration of the mobility candidate BS-DU from the mobility candidate BS-DU; The transmitter, in operation, forwards the received communication configuration of the mobility candidate BS-DU to the serving BS-DU for further forwarding to the UE; Optionally, the communication configuration of the mobility candidate BS-DU comprises the contents of an RS resource configuration list mapped to a measurement configuration of the mobility candidate BS-DU; The content of the mapped RS resource configuration list includes the RS resource configuration of the serving BS-DU and the RS resource configuration of the mobility candidate BS-DU; The BS-CU according to claim 2.

4. The transmitter, in operation, transmits other mobility requests to other mobility candidate BS-DUs participating in the mobility of the UE; Optionally, the other mobility request or further message includes an RS resource configuration list for at least the serving BS-DU and the mobility candidate BS-DU; The receiver, in operation, receives from the other mobility candidate BS-DU an RS resource configuration of the other mobility candidate BS-DU for a candidate cell of the other mobility candidate BS-DU; The processing circuitry, in operation, updates the RS resource configuration list based on the received RS resource configuration of the other mobility candidate BS-DU; The transmitter, upon operation, transmits the updated RS resource configuration list to the serving BS-DU; The receiver, in operation, receives from the serving BS-DU an updated communication configuration of the serving BS-DU; the updated communication configuration of the serving BS-DU has the contents of the updated RS resource configuration list mapped to a measurement configuration of the serving BS-DU; The transmitter, in operation, forwards the received communication configuration of the serving BS-DU to the serving BS-DU for forwarding to the UE; Optionally, the transmitter, in operation, transmits the updated RS resource configuration list to the mobility candidate BS-DU; the receiver, in operation, receives the updated communication configuration of the mobility candidate BS-DU from the mobility candidate BS-DU; and the transmitter, in operation, forwards the received updated communication configuration of the mobility candidate BS-DU to the serving BS-DU for forwarding to the UE; Optionally, the receiver, in operation, receives a communication configuration of the other mobility candidate BS-DU from the other mobility candidate BS-DU, and the transmitter, in operation, transmits the received communication configuration of the other mobility candidate BS-DU to the serving BS-DU for further forwarding to the UE. The BS-CU according to claim 2 or 3.

5. The receiver, during operation, receives from the mobility candidate BS-DU a communication configuration of the mobility candidate BS-DU in response to the mobility request; The transmitter, in operation, forwards the received communication configuration of the mobility candidate BS-DU to the serving BS-DU for further forwarding to the UE; the communication configuration of the mobility candidate BS-DU does not include an RS resource configuration of the mobility candidate BS-DU; Optionally, the communication configuration of the mobility candidate BS-DU includes a pointer to the updated list, which is sent to the serving BS-DU to map the updated list to a measurement configuration of the mobility candidate BS-DU included in the communication configuration of the mobility candidate BS-DU. The BS-CU according to claim 1.

6. The transmitter, in operation, transmits another mobility request to another BS-DU to become a candidate for participating in the mobility of the UE; The receiver, during operation, receives from the other mobility candidate BS-DU an RS resource configuration of the other mobility candidate BS-DU for a candidate cell of the other mobility candidate BS-DU in response to the other mobility request; The processing circuitry, in operation, updates a current RS resource configuration list based on the received RS resource configuration of the other mobility candidate BS-DU; The transmitter, in operation, transmits the updated RS resource configuration list to the serving BS-DU for further forwarding to the UE; Optionally, the receiver, in operation, receives a communication configuration of the other mobility candidate BS-DU for the other mobility request, and the transmitter forwards the received communication configuration of the other mobility candidate BS-DU to the serving BS-DU for further forwarding to the UE, wherein the communication configuration of the other mobility candidate BS-DU does not include an RS resource configuration of the other mobility candidate BS-DU. The BS-CU according to claim 5.

7. The steps performed by the central unit of the base station, namely: sending a mobility request to base station distributed units (BS-DUs) that are candidates to participate in the mobility of a user equipment (UE), i.e., mobility candidate BS-DUs; receiving, from the mobility candidate BS-DU, a reference signal (RS) resource configuration of the mobility candidate BS-DU for the mobility candidate BS-DU's candidate cell; generating an updated list having information of the received RS resource configuration of the mobility candidate BS-DU and at least the RS resource configuration of a serving BS-DU serving the UE; sending the contents of the updated list to the serving BS-DU for further forwarding to the UE; A method comprising:

8. An integrated circuit that, in operation, controls the processing of a base station central unit (BS-CU), said processing comprising the following steps performed by said BS-CU: sending a mobility request to base station distributed units (BS-DUs) that are candidates to participate in the mobility of a user equipment (UE), i.e., mobility candidate BS-DUs; receiving, from the mobility candidate BS-DU, a reference signal (RS) resource configuration of the mobility candidate BS-DU for the mobility candidate BS-DU's candidate cell; generating an updated list having information of the received RS resource configuration of the mobility candidate BS-DU and at least the RS resource configuration of a serving BS-DU serving the UE; transmitting the contents of the updated list to the serving BS-DU for further forwarding to the UE. Integrated circuit.

9. A base station distributed unit (BS-DU), comprising: a receiver that, during operation, receives a mobility request from a base station central unit (BS-CU) for participating in mobility for a user equipment (UE), the mobility request or other message received by the receiver including a list having information on RS resource configuration of a serving BS-DU serving at least the UE, the RS resource configuration of the serving BS-DU being associated with a candidate cell of the serving BS-DU; a processing circuit that, during operation, updates the received list with the BS-DU's RS resource configuration for the BS-DU's candidate cells; a transmitter that, in operation, transmits the BS-DU's RS resource configuration or alternatively the updated list to the BS-CU; The BS-DU comprises:

10. The receiver, in operation, receives from the BS-CU a change request including an updated list of RS resource configurations including RS resource configurations of the serving BS-DU and the BS-DU as well as RS resource configurations of other mobility candidate BS-DUs; The processing circuitry, in operation, generates an updated communication configuration for the BS-DU based on the list of updated RS resource configurations received from the BS-CU in the change request; the transmitter, in operation, transmits the generated updated communication configuration of the BS-DU to the BS-CU; The BS-DU of claim 9.

11. A base station distributed unit (BS-DU), comprising: a receiver for receiving, in operation, a mobility request from a base station central unit (BS-CU) for participating in mobility of a user equipment (UE); a processing circuit that, during operation, generates a communication configuration for the BS-DU that does not include a reference signal (RS) resource configuration for the BS-DU; a transmitter that, in operation, transmits the communication configuration of the BS-DU to the BS-CU; The BS-DU comprises:

12. the communication configuration of the BS-DU includes a pointer to the current list of one or more RS resource configurations that can be used to map the current list of one or more RS resource configurations to a measurement configuration of the BS-DU included in the communication configuration of the BS-DU; The BS-DU of claim 11.

13. The transmitter, in operation, transmits to the BS-CU an RS resource configuration of the BS-DU for a candidate cell of the BS-DU.

13. The BS-DU according to claim 11 or 12.

14. A processing circuit having, in operation, access to a communication configuration of a distributed unit (BS-DU) of a base station serving a user equipment (UE), the processing circuit comprising: the communication configuration of the serving BS-DU includes a measurement configuration of the serving BS-DU that does not include a reference signal (RS) resource configuration of the serving BS-DU; the processing circuitry, in operation, has access to a list of one or more RS resource configurations including at least an RS resource configuration of the serving BS-DU, the RS resource configurations associated with candidate cells of the serving BS-DU; a processing circuit; a receiver that, during operation, receives from the serving BS-DU an updated list of one or more RS resource configurations including the RS resource configurations of the serving BS-DU and BS-DUs that are candidates for participating in the UE's mobility; the processing circuitry, in operation, uses the updated list together with the measurement configuration of the serving BS-DU. UE.

15. the measurement configuration of the serving BS-DU includes a pointer to the updated list; Optionally, the receiver, in operation, receives from the serving BS-DU a communication configuration for the mobility candidate BS-DU; Optionally, the processing circuitry, during operation, performs measurements based on the updated list and the measurement configuration of the serving BS-DU; Optionally, the UE comprises a transmitter configured, in operation, to transmit a measurement report to the serving BS-DU, the measurement report including a result of the measurement.

15. The UE of claim 14.

16. The following steps are performed by a User Equipment (UE): accessing a communication configuration of a base station serving the UE, i.e., a serving BS-DU, wherein the communication configuration of the serving BS-DU includes a measurement configuration of the serving BS-DU that does not include a reference signal (RS) resource configuration of the serving BS-DU; accessing a list of one or more RS resource configurations including at least an RS resource configuration of the serving BS-DU, the RS resource configurations being associated with candidate cells of the serving BS-DU; receiving, from the serving BS-DU, an updated list of one or more RS resource configurations including the RS resource configurations of the serving BS-DU and BS-DUs that are candidates to participate in the UE's mobility; using the updated list together with the measurement configuration of the serving BS-DU; A method comprising:

17. An integrated circuit that, in operation, controls the processing of a user equipment (UE), said processing comprising the following steps performed by said UE: accessing a communication configuration of a base station serving the UE, i.e., a serving BS-DU, wherein the communication configuration of the serving BS-DU includes a measurement configuration of the serving BS-DU that does not include a reference signal (RS) resource configuration of the serving BS-DU; accessing a list of one or more RS resource configurations including at least an RS resource configuration of the serving BS-DU, the RS resource configurations being associated with candidate cells of the serving BS-DU; receiving, from the serving BS-DU, an updated list of one or more RS resource configurations including the RS resource configurations of the serving BS-DU and BS-DUs that are candidates to participate in the UE's mobility; and using the updated list together with the measurement configuration of the serving BS-DU. Integrated circuit.

18. a receiver for receiving, in operation, from a distributed unit of a base station serving a user equipment (UE), a serving BS-DU, communication configurations of BS-DUs that are candidates to participate in the mobility of said UE; a processing circuit that, during operation, decodes the received communication configuration of the mobility candidate BS-DU to obtain a reference signal (RS) resource configuration of the mobility candidate BS-DU for a candidate cell of the mobility candidate BS-DU, and that, during operation, updates a current list having information of at least an RS resource configuration of the serving BS-DU based on the decoded RS resource configuration of the mobility candidate BS-DU; A UE comprising:

19. The processing circuitry, in operation, maps the updated list to a measurement configuration of the serving BS-DU; Optionally, said mapping includes ignoring the current list and instead using the updated list in association with the measurement configuration of the serving BS-DU.

19. The UE of claim 18.

20. The receiver, in operation, receives communication configurations of other mobility candidate BS-DUs from the serving BS-DU; In operation, the processing circuitry decodes the received communication configuration of the other mobility candidate BS-DU to obtain an RS resource configuration of the other mobility candidate BS-DU with respect to a candidate cell of the other mobility candidate BS-DU; The processing circuitry, in operation, updates the current list based on the decoded RS resource configurations of the other mobility candidate BS-DUs; Optionally, the processing circuitry, upon operation, maps the updated list to the measurement configuration of the serving BS-DU.

19. The UE of claim 18.

21. The processing circuitry, in operation, performs measurements based on the updated list; Optionally, the UE comprises a transmitter configured, in operation, to transmit a measurement report to the serving BS-DU, the measurement report including a result of the measurement.

21. The UE according to any one of claims 18 to 20.

22. The receiver, in operation, receives a cell switch trigger from the serving BS-DU indicating a cell of the mobility candidate BS-DU as a target for a cell switch; The processing circuitry, in operation, controls a switch from a current cell of the serving BS-DU to the indicated cell of the mobility candidate BS-DU; Optionally, the communication configuration of the mobility candidate BS-DU further includes lower layer configuration parameters of the BS-DU related to facilitating communication of the UE with the cell of the mobility candidate BS-DU; Optionally, an RS resource configuration of a BS-DU is associated with one cell of the BS-DU, and another RS ​​resource configuration of the BS-DU is associated with another cell of the BS-DU; 21. The UE according to any one of claims 14, 15 and 18 to 20.

23. The following steps are performed by a User Equipment (UE): receiving, from a distributed unit of a base station serving the UE, i.e., a serving BS-DU, communication configurations of BS-DUs that are candidates to participate in the mobility of the UE; decoding the received communication configuration of the mobility candidate BS-DU to obtain a reference signal (RS) resource configuration for a candidate cell of the mobility candidate BS-DU; updating a current list, which includes information about at least the serving BS-DU's RS resource configuration, based on the decoded RS resource configuration of the mobility candidate BS-DU; A method comprising:

24. An integrated circuit that, in operation, controls the processing of a user equipment (UE), said processing comprising the following steps performed by said UE: receiving, from a distributed unit of a base station serving the UE, i.e., a serving BS-DU, communication configurations of BS-DUs that are candidates to participate in the mobility of the UE; decoding the received communication configuration of the mobility candidate BS-DU to obtain a reference signal (RS) resource configuration for a candidate cell of the mobility candidate BS-DU; and updating a current list, which includes information about at least the serving BS-DU's RS resource configuration, based on the decoded RS resource configuration of the mobility candidate BS-DU. Integrated circuit.

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