User equipment and base stations involved in handover

Abstract

This document provides methods, devices, and articles for improving handover procedures. [Solution] In a communication system, a user device (UE) receives a common timing advance value for a target radio cell from the source base station of a source radio cell in a first handover message that includes a timing instruction for sending a second handover message from the UE to the target base station. Based on the common timing advance value and the timing instruction, the UE determines a first uplink timing for an uplink transmission to the target base station with respect to a downlink transmission from the target base station. Based on the determined uplink timing, the UE sends a second handover message to the target base station. Based on the UE's location, ephemeris information, and the common timing advance value, the UE determines a UE-specific timing advance value unique to the UE and the target radio cell.

Description

[Technical Field]

[0001] This disclosure covers methods, devices, and articles in communication systems, such as 3GPP communication systems. [Background technology]

[0002] Currently, the 3rd Generation Partnership Project (3GPP®) is working on the technical specifications for next-generation cellular technology (also known as 5G).

[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, eMBB deployment scenarios may include indoor hotspots, densely populated urban areas, suburbs, urban wide areas, and high speeds. URLLC deployment scenarios may include industrial control systems, mobile healthcare (remote monitoring, remote diagnosis, and remote treatment), real-time vehicle control, and wide-area monitoring and control systems for smart grids. mMTC deployment scenarios may include scenarios using a large number of devices that perform low-latency data transmission, such as smart wearables and sensor networks. While both eMBB and URLLC services require extremely wide bandwidths, URLLC services differ in that they preferably require extremely low latency.

[0004] The second objective is to achieve forward compatibility. Backward compatibility with Long-Term Evolution (LTE, LTE-A) cellular systems is not required, which facilitates the design of entirely new systems and / or the introduction of new features. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] TR 38.913 version 15.0.0 [Non-Patent Document 2] 3GPP TS 38.300 v15.6.0 [Non-Patent Document 3] 3GPP TR 38.801 v14.0.0 [Non-Patent Document 4] 3GPP TS 38.211 v15.6.0 [Non-Patent Document 5] TS 23.501 v16.1.0 [Non-Patent Document 6] 3GPP TS 38.321 v15.6.0 [Non-Patent Document 7] TS 38.213 version 15.6.0 [Non-Patent Document 8] TR 38.821 v0.3.0 [Non-Patent Document 9] TS 38.401 [Non-Patent Document 10] 3GPP standard TS 38.331 version 15.6.0 [Overview of the project]

[0006] One non-limiting and exemplary embodiment facilitates the provision of a procedure that facilitates improvements to handover procedures.

[0007] One of the primary aspects of this disclosure is a user device (UE), A receiving unit that receives a common timing advance value for a target radio cell from a source base station of a source radio cell, wherein the UE is connected to the source radio cell and participates in a handover procedure that hands over the UE from the source radio cell to the target radio cell, the common timing advance value is received from the source base station in a first handover message of the handover procedure, and the first handover message of the handover procedure further includes a timing instruction for transmitting a second handover message of the handover procedure from the UE to the target base station, A processing unit that determines a first uplink timing for uplink transmission to the target base station with respect to downlink transmission from the target base station, based on the received common timing advance value and the timing instruction, The system includes a transmitting unit that transmits the second handover message of the handover procedure to the target base station based on the determined uplink timing, The processing unit determines, based on the location of the UE, the ephemeris information, and the common timing advance value, a UE-specific timing advance value that is specific to the UE and the target radio cell and used by the UE to perform uplink transmission in the target radio cell. It is a user device.

[0008] In one embodiment, the technology disclosed herein features a user device (UE) having a receiver, the receiver of the UE receiving a common timing advance value for a target radio cell from a source base station of a source radio cell. The UE is connected to the source radio cell and participates in a handover procedure that hands over the UE from the source radio cell to the target radio cell. The common timing advance value is also received from the source base station in a first message of the handover procedure, which also includes a timing instruction for transmitting a second message from the UE to the target base station. The processor of the UE then determines a first uplink timing for an uplink transmission to the target base station with respect to a downlink transmission from the target base station, based on the received common timing advance value and the timing instruction. The transmitter of the UE transmits the second message of the handover procedure to the target base station based on the determined uplink timing. The processor determines a UE-specific timing advance value, which is specific to the UE and the target radio cell, and is used by the UE to perform uplink transmission in the target radio cell.

[0009] It should be noted that general or specific embodiments may be implemented as systems, methods, integrated circuits, computer programs, storage media, or any selective combination thereof.

[0010] Further benefits and advantages of the disclosed embodiments and various implementations will become apparent from this specification and the drawings. These benefits and / or advantages can be obtained individually by the various embodiments and features of this specification and the drawings; however, it is not necessary to provide all of them in order to obtain one or more of such benefits and / or advantages. [Brief explanation of the drawing]

[0011] Hereinafter, exemplary embodiments will be described in more detail with reference to the accompanying drawings.

[0012] [Figure 1] Figure showing an exemplary architecture of a 3GPP NR system [Figure 2] Figure showing an exemplary user and control plane architecture for LTE eNB, gNB, and UE [Figure 3] Schematic diagram showing the functional split between NG-RAN and 5GC [Figure 4] Sequence diagram of RRC connection setup / reconfiguration procedure [Figure 5] Schematic diagram showing usage scenarios of enhanced mobile broadband (eMBB), massive machine type communication (mMTC), and ultra-reliable and low-latency communication (URLLC) [Figure 6] Block diagram showing an exemplary 5G system architecture for non-roaming scenarios [Figure 7] Figure showing messages exchanged between eNB and UE when performing contention-based RACH procedure [Figure 8] Figure showing messages exchanged between eNB and UE when performing RACH procedure without contention [Figure 9] Figure showing timing misalignment of uplink transmissions from two mobile terminals received at a base station when uplink timing alignment is not performed [Figure 10] Figure showing the effect of performing uplink timing alignment for uplink transmissions from two mobile terminals [Figure 11] Figure showing an exemplary NG RAN architecture based on transparent satellites [Figure 12] Figure showing an exemplary NG RAN architecture based on regenerative satellites [Figure 13] Figure showing the regenerative satellite scenario together with the corresponding propagation delay and reference points for common TA calculation [Figure 14]This figure shows a transparent satellite scenario along with the corresponding propagation delay and reference points for common TA calculations. [Figure 15] Diagram showing signaling exchange for legacy handover procedure [Figure 16] Diagram showing signaling exchange for RACH-less handover procedure [Figure 17] Diagram showing simplified exemplary structures of UE and gNB. [Figure 18] Diagram showing the structure of the UE with an exemplary implementation of the improved handover procedure. [Figure 19] Flowchart of UE operation with an exemplary implementation of the improved handover procedure. [Figure 20] Flowchart of base station operation with an exemplary implementation of the improved handover procedure. [Figure 21] Signaling and processing diagrams with exemplary implementations of improved handover procedures. [Figure 22] Signaling and processing diagrams with exemplary implementations of improved handover procedures. [Figure 23] Signaling and processing diagrams with an exemplary implementation of an improved handover procedure, based on a first option for how the UE determines the UE-specific TA value of the target radio cell. [Figure 24] Signaling and processing diagrams with an exemplary implementation of an improved handover procedure, based on a second option for how the UE determines the UE-specific TA value of the target radio cell. [Figure 25] Signaling and processing diagrams with an exemplary implementation of an improved handover procedure based on a third option for how a GNSS-equipped UE determines the UE-specific TA value of a target radio cell. [Figure 26] A diagram showing feeder link delays and processing delays caused by a transparent satellite scenario and communications. [Modes for carrying out the invention]

[0013] 5G NR system architecture and protocol stack

[0014] 3GPP is working on the next release of fifth-generation cellular technology (simply called 5G), which will include the development of a new radio access technology (NR) that will operate at frequencies up to 100 GHz. The first version of the 5G standard will be completed at the end of 2017, which will allow for testing and commercial deployment of smartphones compliant with the 5G NR standard.

[0015] In particular, the overall system architecture envisions an NG-RAN (Next Generation Radio Access Network) with gNBs, which terminate the NG Radio Access User Plane (SDAP / PDCP / RLC / MAC / PHY) protocols and the Control Plane (RRC) protocol. The gNBs are interconnected with each other via the Xn interface. Furthermore, the gNBs are connected to the NGC (Next Generation Core) via the Next Generation (NG) interface, more specifically to the AMF (Access and Mobility Management Function) (e.g., a specific core entity that performs the AMF) via the NG-C interface, and to the UPF (User Plane Function) (e.g., a specific core entity that performs the UPF) via the NG-U interface. The NG-RAN architecture is shown in Figure 1 (see, for example, Section 4 of Non-Patent Document 2).

[0016] It can support a variety of different deployment scenarios (see, for example, Non-Patent Document 3). This document presents, for example, decentralized deployment scenarios (see, for example, Section 5.2 of Non-Patent Document 3; a centralized deployment is shown in Section 5.4) in which base stations supporting 5G NR can be deployed. Figure 2 shows an exemplary decentralized deployment scenario (see, for example, Figure 5.2-1 of Non-Patent Document 3), further showing an LTE eNB and user equipment (UE), the user equipment (UE) is connected to both a gNB and an LTE eNB. A new eNB for NR 5G can be exemplary referred to as a gNB. The eLTE eNB is an evolution of the eNB and supports connectivity to the Evolved Packet Core (EPC) and Next Generation Core (NGC).

[0017] The user plane protocol stack in NR (see, for example, section 4.4.1 of Non-Patent Document 2) includes the PDCP (Paper Data Convergence Protocol, see section 6.4 of Non-Patent Document 2) sublayer, the RLC (Radio Link Control, see section 6.3 of Non-Patent Document 2) sublayer, and the MAC (Medium Access Control, see section 6.2 of Non-Patent Document 2) sublayer, which are terminated at the gNB on the network side. In addition, a new access layer (AS) sublayer (SDAP, Service Data Adaptation Protocol) is introduced on top of PDCP (see, for example, section 6.5 of Non-Patent Document 2). A control plane protocol stack is also defined in NR (see, for example, section 4.4.2 of Non-Patent Document 2). An overview of the Layer 2 functions is described in section 6 of Non-Patent Document 2. The functions of the PDCP sublayer, RLC sublayer, and MAC sublayer are described in sections 6.4, 6.3, and 6.2 of Non-Patent Document 2, respectively. The function of the RRC layer is described in section 7 of Non-Patent Document 2.

[0018] For example, the media access control layer handles scheduling and scheduling-related functions, including logical channel multiplexing and processing of various numerologies.

[0019] The Physical Layer (PHY) is responsible for tasks such as coding, PHY HARQ processing, modulation, multi-antenna processing, and mapping signals to appropriate physical time-frequency resources. The Physical Layer also handles the mapping of transport channels to physical channels. It serves the MAC layer in the form of transport channels. A physical channel corresponds to a set of time-frequency resources used for transmitting a particular transport channel, and each transport channel is mapped to a corresponding physical channel. One physical channel is the PRACH (Physical Random Access Channel) used for random access.

[0020] NR use cases / deployment scenarios include Enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and Massive Machine-Type Communications (mMTC), and these services have diverse requirements regarding data rate, latency, and coverage. For example, eMBB is expected to support peak data rates of the order of three times that provided by IMT-Advanced (20 Gbps downlink and 10 Gbps uplink) and user-perceived data rates. 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 ms within 1 ms). -5 ) and are imposed. Furthermore, in mMTC, a high connection density (1km in urban environments) is required. 2 Preferably, a capacity of 1,000,000 devices per unit, wide coverage in harsh environments, and extremely long-life batteries (15 years) to reduce device costs may be required.

[0021] Therefore, OFDM numerology suitable for one use case (e.g., subcarrier spacing, OFDM symbol duration, cyclic prefix (CP) duration, number of symbols per scheduling interval) may not work well for another use case. For example, low-latency services may prefer shorter symbol durations (and thus larger subcarrier spacings) and / or fewer symbols per scheduling interval (also known as TTI) than mMTC services. Furthermore, in configuration scenarios with large channel delay spreads, longer CP durations may be preferred than in scenarios with smaller delay spreads. To maintain a similar level of CP overhead, the subcarrier spacing should be optimized according to the delay spread. NR may support two or more values ​​for subcarrier spacing. Therefore, currently, subcarrier spacings of 15kHz, 30kHz, 60kHz, ... are being considered. Symbol duration T u The subcarrier spacing Δf is given by the equation (Δf = 1 / T u This is directly related. As with LTE systems, the term "resource element" can be used to represent the smallest resource unit consisting of one subcarrier for the length of one OFDM / SC-FDMA symbol.

[0022] In the new 5G-NR wireless system, resource grids for subcarriers and OFDM symbols are defined for each numerology and carrier, both in the uplink and downlink. Each element within the resource grid is called a resource element and is identified based on its frequency index in the frequency domain and its symbol position in the time domain (see Non-Patent Literature 4).

[0023] Splitting of 5G NR functionality between NG-RAN and 5GC

[0024] Figure 3 shows the functional division 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.

[0025] In particular, gNB and ng-eNB handle the following main functions: - Radio Resource Management functions such as Radio Bearer Control, Radio Admission Control, Connection Mobility Control, and dynamic resource allocation (scheduling) to UEs in both uplink and downlink directions. - IP header compression, encryption, and data integrity protection - Selection of AMF when UE attaches if routing to AMF cannot be determined from the information provided by the UE. - Routing user plane data to UPF - Routing of control plane information to AMF - Establishing and releasing connections - Scheduling and sending paging messages - Scheduling and transmission of system broadcast information (sent from AMF or OAM) - Setting up measurements and measurement reporting for mobility and scheduling. - Transport-level packet marking in uplink - Session management - Support for network slicing - QoS flow management and mapping to data radio bearers - Support for UEs in RRC_INACTIVE state - NAS message delivery function - Wireless access network sharing - Dual connectivity - Close interworking between NR and E-UTRA

[0026] The Access and Mobility Management Function (AMF) handles the following key functions: - Termination of Non-Access Stratum (NAS) signaling - NAS signaling security - Security control at the Access Layer (AS) - Core Network (CN) node-to-node signaling for mobility between 3GPP access networks - Reachability of idle mode UE (including control and execution of paging retransmissions) - Registration Area Management - Support for intra-system and inter-system mobility - Access Authentication - Access authentication including roaming rights check - Mobility management and control (subscriptions and policies) - Support for network slicing - Selection of Session Management Function (SMF)

[0027] Furthermore, the User Plane Function (UPF) handles the following key functions: - Anchor points for mobility within / between RATs (when applicable) - External PDU session points for interconnection with the data network - Packet routing and forwarding - User plane portion of packet inspection and policy rule enforcement - Traffic usage report - Uplink classifier to support routing of traffic flow to the data network. - Branching points to support multi-homed PDU sessions - User plane QoS processing (e.g., packet filtering, gating, UL / DL rate enforcement) - Uplink traffic verification (mapping from SDF to QoS flow) - Downlink packet buffering and downlink data notification triggering

[0028] Finally, the Session Management Function (SMF) handles the following main functions: - Session management - Assignment and management of UE IP addresses - Selection and control of UP function - Configuring traffic steering in User Plane Functions (UPF) to route traffic to the correct destination. - Policy enforcement and QoS control section - Downlink data notification

[0029] RRC connection establishment and reconfiguration procedure

[0030] Figure 4 shows the interaction between the UE, gNB, and AMF (5GC entity) in the NAS portion when the UE transitions from RRC_IDLE to RRC_CONNECTED (see Non-Patent Literature 2).

[0031] RRC is a higher-layer signaling protocol used for configuring UEs and gNBs. Specifically, in this transition, the AMF prepares UE context data (including, for example, PDU session context, security key, UE radio capability, and UE security capability) and sends it to the gNB via an Initial Context Setup Request. The gNB then activates AS security with the UE, which is done by the gNB sending a SecurityModeCommand message to the UE, and the UE responding to the gNB with a SecurityModeComplete message. Subsequently, the gNB performs reconfiguration to establish the Signaling Radio Bearer 2 (SRB2) and Data Radio Bearer (DRB), which is done by the gNB sending an RRCReconfiguration message to the UE, and the gNB receiving an RRCReconfigurationComplete from the UE in response. In the case of a signaling-only connection, SRB2 and DRB are not established, so these steps related to RRCReconfiguration are skipped. Finally, the gNB notifies the AMF that the establishment procedure is complete by sending an Initial Context Setup Response.

[0032] Accordingly, this disclosure provides a fifth-generation core (5GC) entity (e.g., AMF, SMF, etc.) having a control circuit that establishes a next-generation (NG) connection with a gNodeB during operation so that a signaling radio bearer is established between the gNodeB and the user equipment (UE), and a transmitter that sends an initial context setup message to the gNodeB via the NG connection during operation. In particular, the gNodeB transmits radio resource control (RRC) signaling, including resource allocation setting information elements, to the UE via the signaling radio bearer. The UE then performs uplink transmission or downlink reception based on this resource allocation setting.

[0033] Usage scenarios for IMT-2020 and later

[0034] Figure 5 illustrates some use cases for 5G NR. The 3rd Generation Partnership Project NR (3GPP NR) considers three use cases where IMT-2020 is expected to support a wide variety of services and applications. Phase 1 specifications for Enhanced Mobile Broadband (eMBB) have been finalized. Current and future work will include further expanding eMBB support, as well as standardization for Ultra-Reliable Low-Latency Communications (URLLC) and Massive Machine-Type Communications. Figure 5 shows some examples of anticipated use scenarios for IMT beyond 2020.

[0035] URLLC use cases have stringent requirements regarding capabilities such as throughput, latency, and availability, and are envisioned as one means of realizing future vertical applications such as wireless control of industrial manufacturing or production processes, telemedicine surgery, power distribution automation in smart grids, and transportation safety. The ultra-high reliability of URLLC is supported by identifying the technology to meet the requirements set out in Non-Patent Document 1. For NR URLLC in Release 15, key requirements include a target user plane latency of 0.5 ms for UL (uplink) and 0.5 ms for DL ​​(downlink). Typical URLLC requirements for a single packet transmission are a BLER (block error rate) of 1E-5 with a user plane latency of 1 ms and a packet size of 32 bytes.

[0036] From a RAN1 perspective, reliability can be improved in many possible ways. The current range of ways to improve reliability includes defining separate CQI tables for URLLC, a more compact DCI format, and PDCCH iterations. However, as NR becomes more stable and development progresses (regarding key requirements for NR URLLC), the range 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.

[0037] Furthermore, the technical enhancements targeted by NR URLCC aim to improve latency and reliability. Technical enhancements for improving latency include configurable numerology, non-slot-based scheduling using flexible mapping, grant-free (configured grant) uplinks, slot-level iteration on data channels, and downlink preemption. Preemption means that a transmission for which resources have already been allocated is aborted, and the allocated resources are used for another transmission requested later with lower latency / higher priority requirements. Thus, a transmission that has already been permitted is preempted by a later transmission. Preemption applies regardless of the specific service type. For example, a transmission of service type A (URLCC) can be preempted by a transmission of service type B (e.g., eMBB). Technical enhancements for improving reliability include a dedicated CQI / MCS table for the 1E-5 target BLER.

[0038] The use case for mMTC (Massive Machine Type Communication) is characterized by a very large number of connected devices transmitting relatively small amounts of data, which are generally less affected by latency. These devices need to be low-cost and have extremely long battery life. From a noise reduction (NR) perspective, utilizing a very narrow bandwidth segment is one possible solution to achieve power savings from a UE perspective and enable long battery life.

[0039] As described above, the range of reliability in NR is expected to broaden. One important requirement in all cases, especially for URLLC and mMTC, is high or very high reliability. Several mechanisms can be considered to improve reliability from both a radio and network perspective. In general, there are several important areas that can help improve reliability. These areas include compact control channel information, data channel / control channel repetition, and diversity related to the frequency domain, time domain, and / or spatial domain. These areas are generally applicable to reliability regardless of the specific communication scenario.

[0040] For NR URLLC, further use cases with more stringent requirements have been identified, such as factory automation, the transportation industry, and power supply. These stringent requirements, depending on the use case, include higher reliability (up to 10⁻⁶ levels), higher availability, a packet size of up to 256 bytes, time synchronization on the order of a few microseconds (values ​​ranging from 1 to a few microseconds depending on the frequency range), and low latency on the order of 0.5 to 1 ms (with a target latency of 0.5 ms specifically for the user plane).

[0041] Furthermore, in the case of NR URLLC, several technical enhancements have been recognized from a RAN1 perspective. In particular, enhancements to the PDCCH (Physical Downlink Control Channel) are mentioned, related to a more compact DCI, PDCCH repetition, and increased PDCCH monitoring. In addition, enhancements to the UCI (Uplink Control Information) are related to enhancements to HARQ (Hybrid Automatic Repeat Request) and CSI feedback. Enhancements to PUSCH related to minislot level hopping and retransmission / repetition have also been recognized. The term "minislot" refers to a Transmission Time Interval (TTI) containing fewer symbols than a slot (a slot containing 14 symbols).

[0042] QoS control

[0043] The 5G QoS (Quality of Service) model is based on QoS flows and supports both QoS flows that require a guaranteed flow bitrate (GBR QoS flows) and QoS flows that do not require a guaranteed flow bitrate (non-GBR QoS flows). Therefore, at the NAS level, QoS flows are the finest granularity of QoS differentiation within a PDU session. Within a PDU session, QoS flows are identified by a QoS flow ID (QFI) transmitted in the encapsulation header via the NG-U interface.

[0044] The 5GC establishes one or more PDU sessions for each UE. The NG-RAN establishes at least one Data Radio Bearer (DRB) with each PDU session for each UE, and can then configure additional DRBs for the QoS flow of that PDU session, as described above, for example with reference to Figure 4 (the NG-RAN decides when to configure them). 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.

[0045] Figure 6 shows the 5G NR non-roaming standard architecture (see Section 4.23 of Non-Patent Literature 5). Application Functions (AFs) (e.g., external application servers handling 5G services as illustrated in Figure 5) interact with the 3GPP Core Network for the purpose of providing services. For example, they support application influence on traffic routing, access Network Exposure Functions (NEFs), or interact with policy frameworks for policy control (e.g., QoS control) (see Policy Control Function PCF). Based on operator deployment, application functions (AFs) that are considered trusted by the operator may be allowed to interact directly with the relevant Network Functions. Application functions (AFs) that are not permitted by the operator to directly access Network Functions interact with the relevant Network Functions using external exposure frameworks via NEFs.

[0046] Figure 6 shows further functional units of the 5G architecture, including the Network Slice Selection Function (NSSF), Network Repository Function (NRF), Unified Data Management (UDM), Authentication Server Function (AUSF), Access and Mobility Management Function (AMF), Session Management Function (SMF), and Data Network (DN) (e.g., operator services, internet access, or third-party services).

[0047] Random access procedure

[0048] Similar to LTE, 5G NR provides a RACH (Random Access Channel) procedure (or simply a random access procedure). For example, the RACH procedure can be used by a UE to access a cell it has found. The RACH procedure is used in other contexts within NR, for example, • In the case of a handover, when establishing synchronization for a new cell, • Re-establishing uplink synchronization to the current cell if synchronization is lost due to too long a period of time without uplink transmission from the device. • Requesting uplink scheduling when a dedicated scheduling request resource is not configured on the device. It can also be used in other contexts.

[0049] There are numerous events that can cause the UE to execute a random access procedure (see, for example, section 9.2.6 of Non-Patent Document 2).

[0050] The RACH procedure will be described in more detail below with reference to Figures 7 and 8. A mobile terminal can be scheduled for uplink transmission if its uplink transmission is time-synchronized. Therefore, the Random Access Channel (RACH) procedure serves as an interface between asynchronous mobile terminals (UEs) and orthogonal transmission of uplink radio access. For example, random access is used to achieve uplink time synchronization for user equipment that has not yet achieved or has lost uplink synchronization. Once user equipment achieves uplink synchronization, the base station can schedule uplink transmission resources for it. One scenario related to random access is when user equipment in the RRC_CONNECTED state that is handing over from its current serving cell to a new target cell performs the random access procedure to achieve uplink time synchronization in the target cell.

[0051] There can be two types of random access procedures: those that allow access to be either competition-based, meaning implying an inherent risk of conflict, or non-competition-based. An exemplary definition of a random access procedure can be found in Section 5.1 of Non-Patent Document 6.

[0052] The following describes the conflict-based random access procedure in more detail with reference to Figure 7. This procedure consists of four "steps" and can therefore also be called the four-step RACH procedure. First, the user device sends a random access preamble to the base station on the Physical Random Access Channel (PRACH) (i.e., message 1 of the RACH procedure). After the base station detects the RACH preamble, it uses the Random Access RA-RNTI (RA-RNTI) which identifies the time-frequency and slot in which the preamble was detected, to send a Random Access Response (RAR) message (message 2 of the RACH procedure) on the Physical Downlink Shared Channel (PDSCH) addressed on the PDCCH. If multiple user devices send the same RACH preamble on the same PRACH resource (this is also called a collision), those multiple user devices will receive the same random access response message. A RAR message can convey the detected RACH preamble, a timing alignment command (TA command) for synchronizing subsequent uplink transmissions based on the timing of the received preamble, an initial uplink resource allocation (grant) for sending the first scheduled transmission, and the allocation of a Temporary Cell Radio Network Temporary Identifier (T-CRNTI). This T-CRNTI is used by the base station to address the mobile station from which the RACH preamble was detected until the RACH procedure is completed, because the mobile station's "true" identity at this point is not yet known to the base station.

[0053] User equipment monitors the PDCCH to receive Random Access Response messages within a given time window (e.g., called the RAR reception window) (which can be set by the base station). In response to the RAR message received from the base station, user equipment first sends a scheduled uplink transmission using the radio resources allocated by the grant in the Random Access Response. This scheduled uplink transmission carries actual messages with specific functions, such as RRC Connection Request, RRC Resume Request, or buffer status report.

[0054] If a preamble collision occurs in the first message of the RACH procedure, that is, if multiple user devices send the same preamble on the same PRACH resource, the colliding user devices will receive the same T-CRNTI in the random access response and will also collide on the same uplink resource when sending their own scheduled transmissions in the third step of the RACH procedure. If the base station successfully decodes the scheduled transmission from one user device, the conflict remains unresolved for the other user devices. To resolve this type of conflict, the base station sends a conflict resolution message (the fourth message) addressed to C-RNTI or Temporary C-RNTI. The procedure then ends.

[0055] Figure 8 shows a condensed, non-conflict random access procedure compared to a conflict-based random access procedure. In the first step, the base station provides the user equipment with a dedicated preamble for random access to avoid the risk of collisions, i.e., the risk of multiple user equipment transmitting the same preamble. The user equipment then transmits the preamble signaled by the base station over the uplink on the PRACH resource. Since non-conflict random access avoids the case where multiple UEs transmit the same preamble, the non-conflict random access procedure essentially terminates after the UE has successfully received the random access response.

[0056] Furthermore, 3GPP is also considering a two-step (competition-based) RACH procedure for 5G NR, in which message 1 (which can also be called msgA) is sent first, corresponding to messages 1 and 3 in the four-step LTE RACH procedure. The gNB then responds with message 2 (which can also be called msgB), corresponding to messages 2 and 4 in the LTE RACH procedure. This msgB can include, for example, a success random access response (RAR), a fallback RAR, and optionally a backoff instruction. For the two-step RACH procedure, several further assumptions are made, for example, that the UE, after determining the RACH type (e.g., two-step RACH), continues to retry that same RACH type until it fails. However, it is also possible that the UE may fall back to the four-step RACH procedure after a certain period of time.

[0057] Furthermore, the network can semi-statically determine the mutually exclusive radio resources used to execute the two-step and four-step RACH procedures. The radio resources used to send the first message in the RACH procedure include at least the RACH occasion and preamble. For example, in the two-step RACH procedure, the first message msgA uses not only the PRACH resources (e.g., the RACH occasion and preamble) but also the associated PUSCH resources.

[0058] One of the primary objectives of the random access procedure is to obtain timing advance values ​​used by the UE to measure the time of uplink transmission to the base station. Uplink orthogonality is maintained by ensuring that transmissions from different user equipment within the cell are time-aligned at the base station's receiver. This avoids the occurrence of intra-cell interference both between user equipment assigned to transmit on consecutive subframes and between user equipment transmitting on adjacent subcarriers. Time alignment of uplink transmissions is achieved by applying a timing advance at the user equipment's transmitter to the received downlink timing, as illustrated in Figures 9 and 10. Its main role is to cancel out the varying propagation delays between different user equipment within the cell.

[0059] Figure 9 illustrates a misalignment of uplink transmissions from two UEs when uplink timing alignment is not performed, causing the base station (assumed here to be an eNodeB) to receive uplink transmissions from the two UEs at different times. The propagation delays PD_eNB-UE1 and PD_UE1-eNB for UE1 and PD_UE1-eNB for UE2 are significantly different from those for UE2, resulting in the uplink transmissions from UE1 and UE2 being received by the eNodeB at different times.

[0060] In contrast, Figure 10 shows synchronized uplink transmissions to two UEs. Uplink timing alignment (TA) is performed by each UE and applied to the uplink transmissions so that the uplink transmissions from the two UEs arrive at the base station at approximately the same time.

[0061] Therefore, the user-specific timing advance determines the uplink transmission timing from the user's equipment's perspective. The criterion for the timing advance is the downlink subframe boundary timing from the user's equipment's perspective, as shown in Figure 10.

[0062] Timing adjustment for uplink transmission is described in detail in Section 4.2 of Non-Patent Document 7 and Section 5.2 of Non-Patent Document 6.

[0063] The Timing Advance Command MAC CE is identified by a MAC subheader having the LCID shown in Table 6.2.1-1 of Non-Patent Literature 6. This has a fixed size and consists of a single octet defined as follows: - TAG Identity (Timing Advance Group ID): This field indicates the TAG identity of the addressed TAG. TAGs containing SpCells have a TAG identity of 0. The field length is 2 bits. - Timing Advance Command: This field indicates an index value TA (0, 1, 2, ..., 63) used to control the amount of timing adjustment required by the MAC entity. The field length is 6 bits.

[0064] [Table 1]

[0065] If uplink time matching is not performed during the random access procedure, the UE sends a preamble according to the DL synchronization timing. The base station then responds with a timing advance value in the RAR message, where the timing advance value is, for example, 2 × PD(P D =P U (Assume that) (P D is the downlink propagation time, and P U (This is the uplink propagation time). The UE applies the received timing advance value to perform the uplink transmission.

[0066] Non-Terrestrial Network (NTN)

[0067] Satellites will continue to be the most effective means of reaching areas beyond ground coverage, not only for passengers on trains, aircraft, and ships. Therefore, including satellites as an integral part of the 5G ecosystem adds resilience. The satellite industry has participated in various committees, including 3GPP, EC, and ITU-T, to ensure that satellite systems are integrated as an essential part of the 5G ecosystem. The goals are: 1) to support highly available and reliable connectivity using satellites for use cases such as ubiquitous coverage, disaster relief, public safety requirements, emergency response, remote sensor connectivity, and broadcast services; 2) to support air interfaces with a one-way latency of up to 275 ms when accompanied by satellite connectivity; and 3) to support seamless mobility between ground and satellite-based networks with varying latencies. The role and benefits of satellites in 5G have been studied in 3GPP Release 14, leading to specific requirements for supporting satellite access.

[0068] Figure 11 shows an exemplary NG RAN architecture based on a transparent satellite. According to one exemplary implementation (see Section 5.1 of Non-Patent Literature 8), the satellite payload implements frequency converters and radio frequency amplifiers in both the uplink and downlink directions. This corresponds to an analog RF repeater. Thus, the satellite relays the NR-Uu radio interface from the feeder link (between the NTN gateway and the satellite) to the service link (between the satellite and the UE), and vice versa. The satellite radio interface (SRI) on the feeder link is the NR-Uu. That is, the satellite does not terminate the NR-Uu.

[0069] Figure 12 shows an exemplary NG-RAN architecture based on a regenerative satellite. According to one exemplary implementation (see Section 5.2 of Non-Patent Document 8), the NG-RAN logic architecture described in Non-Patent Document 9 is used as a baseline for the NTN scenario. The satellite payload implements the regeneration of signals received from Earth. The NR-Uu radio interface is on the service link between the UE and the satellite. The satellite radio interface (SRI) is on the feeder link between the NTN gateway and the satellite. The SRI (Satellite Radio Interface) is the transport link between the NTN GW and the satellite.

[0070] Furthermore, satellite payloads also provide inter-satellite links (ISLs) between satellites. Inter-satellite links (ISLs) are transport links between satellites.

[0071] NTN Timing Advance

[0072] To support long delays in NTN scenarios, it is possible to specify the total timing advance based on two components: a common timing advance value and an individual (i.e., UE-specific) timing advance value. Together, the common TA value and the individual TA value constitute the total TA value. The common TA is used to compensate for round-trip delay (RTD) at the reference point location within the radio cell / beam (e.g., at the nearest point of the cell) and may be determined to be twice the transmission delay between the satellite and the reference point. The individual TA, on the other hand, is used to control the timing for each UE and varies, for example, based on the location of a specific UE.

[0073] Two different satellite scenarios are shown in Figures 13 and 14, with Figure 13 showing the deployment of a regenerative satellite and Figure 14 showing the deployment of a transparent satellite. The delay corresponding to the illustrated delay d1 can be compensated by a common TA value calculated at the illustrated reference point. On the other hand, for different positions within the cell (with a total delay d2), the differential delay corresponding to d3 (d3 = d2 - d1) can be further compensated by individual TAs. Thus, the common TA value is the same as the total TA value when the UE is located at the reference point.

[0074] We exemplify the assumption that the gNB responds with individual TAs in random access response messages during the RACH procedure. The common TA value can be broadcast, for example, in the system information of the wireless cell. Thus, the UE, having obtained values ​​for both parameters, can determine the total TA value.

[0075] In response to this, the UE can use a common TA when sending the random access preamble, and then obtain individual TAs in the RAR. If a common TA is not applied when sending the RACH preamble, the Guard Period (GP) in the PRACH transmission must be long enough to accommodate the NTN RTD (which is very long), and therefore may not be easily achievable. This differs from the non-NTN scenario, where, when performing the RACH procedure, the UE typically does not apply timing advance when sending the RACH preamble, but rather follows downlink timing.

[0076] In addition, common TAs can be specified per radio cell or per beam. Hereinafter, we will exemplify the assumption that common TAs are valid for the entire cell. However, if common TA values ​​are per beam of a radio cell, multiple common TA values ​​can be provided, each corresponding to one of several beams. The UE then selects one of the beam-specific common TA values ​​based, for example, on SSB selection (Synchronization Signal Block selection).

[0077] As a further exemplary implementation, the common TA should be understood as a parameter that can be signaled as a time offset value to compensate for the Round Trip Time (RTT). It can also be used for other purposes (e.g., not necessarily in the same form as the "common TA") and may be referred to differently.

[0078] Handover procedure

[0079] A typical, simplified handover is shown in Figure 15 and briefly explained below. UE handover involves the source base station deciding whether or not to hand over the UE to an adjacent radio cell. The decision to hand over the UE from the source cell to the target cell is typically made by the source gNB, for example, based on measurement results from the UE (conveyed by one or more measurement reports).

[0080] Subsequently, a handover is prepared between the two involved base stations (source base station and target base station) by the source gNB sending a handover request message to the target base station, and the target gNB responding with a handover request acknowledgment message (preparation phase). Then, in the execution phase, the UE is instructed to switch from the source cell to the target cell via a handover command message (RRCReconfiguration message), which includes, for example, reconfiguring the UE's radio resources to establish a connection with the target base station of the target radio cell. Thus, the UE performs the reconfiguration and attaches to the new target base station. This includes performing synchronous and (conflict-free) random access procedures. For example, synchronization may include the UE obtaining synchronization signals (e.g., Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS)) typically used to obtain the cell identity and frame timing of the target cell, thereby achieving time and frequency synchronization. The random access procedure is performed by the UE, for example, to obtain timing advance values ​​and uplink resources for uplink transmission in a RAR message. This consists of at least sending a RACH preamble (as instructed by the preamble in a RACH handover command message without conflicts), receiving a random access response (e.g., including an uplink grant), and finally, as a third and final step of the random access procedure, the UE confirming that the reconfiguration and access to the target cell are complete by sending a handover confirmation message (RRCReconfigurationComplete message) to the target gNB.

[0081] An exemplary implementation of such a handover procedure is defined for 5G NR in section 9.2.3 of Non-Patent Document 2.

[0082] RACH-less handover for NTN

[0083] Discussions are underway to enhance NTN's mobility. The inventors have recognized that round-trip delay (RTD) can be considerably larger in non-terrestrial communications than in terrestrial communications. For example, NTN's maximum RTD is 541.1 ms in GEO (Geostationary Earth Orbiting, e.g., at an altitude of 35786 km) and 25.76 / 41.76 ms in LEO (Low Earth Orbiting, e.g., at an altitude of 600 / 1200 km). In terrestrial communications, the RTD can be as low as, for example, 5 ms.

[0084] Long RTDs can lead to increased handover latency. Therefore, specific solutions are needed to minimize or reduce latency during handover for mobile UEs, especially for real-time applications.

[0085] One possible solution is a RACH-less handover, as described below.

[0086] One exemplary assumption for a RACH-less handover procedure is that the source and target cells are time-synchronized so that the subframe boundaries between them are aligned. For example, according to the strictest time synchronization, the subframe boundaries are synchronized up to the symbol timing, for example, up to the same system frame number, the same slot number, and the same symbol number. However, less strict time synchronization is also possible, for example, up to the same system frame number or the same slot number.

[0087] RACH-less handover may be similar to the legacy handover described above in relation to Figure 15, for example, but there are some important differences, as explained with reference to Figure 16.

[0088] First, the UE needs to know whether to perform a RACH-less handover or another type of handover (e.g., the legacy handover procedure in Figure 15). One possibility is to configure the UE appropriately to perform a RACH-less handover. In this case, for example, the source base station can provide the corresponding configuration information to the UE. Another possibility is that the handover command message provides the UE with the corresponding instruction on whether to perform a RACH-less handover procedure (or not, e.g., a legacy handover including a random access procedure). For example, to coordinate the uplink transmission of a handover acknowledgment message to the target base station, the handover command message may include an instruction for the uplink resource used by the UE to transmit the handover acknowledgment message. This resource instruction is not necessarily required for the legacy handover procedure because the appropriate UL grant is usually communicated by the Random Access Response message in the RACH procedure. Therefore, if the UE determines that the handover command message contains a UL grant, the UE may determine that the source base station instructed the UE to perform a RACH-less handover. Otherwise, if the UL grant is not present in the handover command message, the UE will determine to perform another type of handover, such as the legacy handover procedure shown in Figure 15. Alternatively or additionally, the handover command message may simply contain one or more bits that encode the type of handover procedure the UE must perform.

[0089] The UL grant in a handover command message can be understood as indicating a specific time (e.g., a specific SFN) that can be mutually agreed upon between the source base station and the target base station. For example, the target base station provides UL grant information in a handover confirmation message to the source gNB.

[0090] After receiving a command to hand over to the target cell, the UE can proceed to synchronize with the target gNB. On the other hand, assuming the source and target gNBs are (perfectly) synchronized, the UE may not even need to obtain PSS and SSS for time and frequency synchronization. Furthermore, the UE does not initiate a normal RACH procedure and therefore does not send a random access preamble. Correspondingly, the UE does not need to perform a random access procedure (or at least a fully random access procedure).

[0091] Instead, at the mutually agreed-upon time described above, the UE will hand over from the source radio cell to the target radio cell. Thus, the RACH procedure is not initiated, and the handover procedure proceeds with the UE confirming the handover to the target cell by sending a handover confirmation message using the UL resources indicated in the handover command message.

[0092] Eliminating RACH delays during the handover procedure significantly reduces data interruptions during handover, greatly improving the user experience. This is particularly important in NTN scenarios where RTD is assumed to be long.

[0093] However, one of the main purposes of the RACH procedure during handover is to match target and uplink timing by performing a random access procedure and obtaining the target cell timing advance value (target cell TA value) used by the UE for uplink transmission in the target cell. However, if the RACH procedure is not present, the UE will not obtain the timing advance value in the RAR message. Therefore, the UE must determine the target cell TA value in a different way.

[0094] According to one possible solution, the UE can estimate the required TA value of the gNB based on the satellite ephemeris and the UE's location. For example, the UE must estimate the target cell TA value before sending the RRCReconfigurationComplete message to the target cell in order to ensure that the message is correctly received at the target node. First, the UE observes the DL propagation delay difference between the source cell and the target cell, e.g., T2-T1 (or T1-T2), where T1 is the DL propagation delay between the UE and the source gNB, and T2 is the DL propagation delay between the UE and the target gNB. It is also assumed that the UL propagation delay is the same as the DL propagation delay. Under these assumptions, the UE can derive the target cell timing advance based on the source cell timing advance as follows:

[0095]

number

[0096] However, the inventors have confirmed that, particularly for NTN scenarios, there is a general need to improve time synchronization and RACH-less handover procedures.

[0097] The above-mentioned estimation of the target TA value (see Equation 1) has drawbacks when applied to NTN's RACH-less handover procedure.

[0098] Conventional RACH-less HOs with normal TA estimation can cause the following problems due to the lack of timing advance corrections (e.g., common TA and individual TA). First, the UE cannot perform a RACH immediately after the HO to the target cell because the common TA of the target cell is not yet available. Second, the UE may not be able to fall back to using a conflict-based HO if the conflict-free HO fails because the common TA of the target cell is not yet known. Therefore, after the handover is complete and the updated common TA of the target cell is received (e.g., in system information), the UE does not know how to adjust the TA while performing the UL transmission because the individual TA is not yet known to the UE.

[0099] Furthermore, the UE may not be able to observe the true DL timing difference between the source and target cells because, due to the large RTD, a "larger difference than SFN" situation can exist in NTN. For example, if the synchronization signal from the source cell is from SFN n and the synchronization signal from the target cell is from SFN n-1, these two synchronization signals arrive at the UE very close together in time. The UE then perceives the DL timing difference between these two cells as very small, even though the actual DL timing difference is already as large as 10ms. This scenario is possible if the distance between the source cell and the UE is considerably longer than the distance between the target cell and the UE, or vice versa.

[0100] Furthermore, such solutions are not optimal for GNSS-equipped UEs.

[0101] Furthermore, feeder link delays and satellite processing delays in transparent satellite scenarios must be considered.

[0102] Furthermore, the assumption that DL and UL propagation delays are the same may be incorrect. Especially in the transparent satellite case, DL and UL propagation delays can differ because propagation delays cover both feeder link delays and satellite processing delays, which can differ between DL and UL cases.

[0103] Therefore, the inventors have identified the possibility of improving the handover procedure that should be performed to hand over a UE from a source base station to a target base station. Such an improved handover procedure may facilitate the overcoming of one or more of the problems described above.

[0104] The following describes UEs, base stations, and procedures that meet these needs for new radio access technologies envisioned for 5G mobile communication systems, but which may also be used for LTE mobile communication systems. Various implementations and examples of modifications are also described. The following disclosures are facilitated by and may be based, for example, on the above discussions and findings, or at least in part thereof.

[0105] It should be noted that this specification makes many assumptions in order to clearly and easily explain the principles underlying this disclosure. However, these assumptions should be understood as merely illustrative examples made herein for illustrative purposes and not limiting the scope of this disclosure. Those skilled in the art will recognize that the principles of the following disclosure and the principles described in the claims can be applied to various scenarios in ways not expressly described herein.

[0106] Furthermore, some of the terms used below, such as procedures, entities, and layers, are closely related to those used in LTE / LTE-A systems or in current 3GPP 5G standardization, even though specific terms to be used in the context of new radio access technologies for upcoming 3GPP 5G communication systems have not yet been fully determined or may ultimately change. Therefore, the terminology may change in the future without affecting the functionality of the embodiments. Those skilled in the art will therefore recognize that embodiments and their scope of protection should not be limited to specific terms used exemplary herein because there are no other newer or ultimately agreed-upon terms, but should be understood more broadly in terms of the underlying functionalities and concepts of the functionality and principles of this disclosure.

[0107] For example, a mobile station, mobile node, user terminal, or user equipment (UE) is a physical entity (physical node) within a communication network. A single node may have several functional entities. A functional entity refers to a software or hardware module that implements and / or provides a predetermined set of functions to the same or other nodes or other functional entities in the network. A node may have one or more interfaces connecting it to communication equipment or media that enable it to communicate. Similarly, a network entity may have logical interfaces connecting its functional entities to communication equipment or media that enable it to communicate with other functional entities or corresponding nodes.

[0108] In this specification, the terms “base station” or “radio base station” refer to a physical entity within a communication network. Similar to a mobile station, a base station may have several functional entities. A functional entity refers to a software or hardware module that implements and / or provides a predetermined set of functions to the same or other nodes or other functional entities in the network. The physical entity performs several control tasks related to communication devices, including one or more scheduling and configuration tasks. It should also be noted that base station functions and communication device functions may 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.

[0109] Figure 17 shows a general, simplified, illustrative block diagram of user equipment (also called communication devices) and scheduling devices (here, illustratively, assumed to be located within a base station, e.g., within an eLTE eNB (alternatively called an ng-eNB) or a 5G NR gNB). The UE and eNB / gNB communicate with each other via (radio) physical channels using transceivers.

[0110] A communication device may have a transceiver and a processing circuit. The transceiver may have a receiver and a transmitter, and / or function as both. The processing circuit may be one or more pieces of hardware, such as one or more processors or any LSI. Between the transceiver and the processing circuit are input / output points (or nodes), through which the processing circuit can control the transceiver during operation, i.e., control the receiver and / or transmitter, and exchange received / transmitted data. The transceiver may include an RF (radio frequency) front, such as one or more antennas, amplifiers, RF modulators / demodulators, etc., as both transmitter and receiver. The processing circuit may implement control tasks, such as controlling the transceiver to transmit user data and control data provided by the processing circuit, and / or to receive user data and control data that is further processed by the processing circuit. The processing circuit may also be responsible for performing other processes, such as judgment, decision, calculation, and measurement. The transmitter may be responsible for performing the process of transmitting and other related processes. A receiver may be responsible for performing the receiving process and other related processes (such as monitoring the channel).

[0111] The following describes the improved procedure for performing the handover procedure.

[0112] Figure 18 shows a simplified exemplary UE structure with one solution for an improved handover procedure, which can be implemented based on the general UE structure described in relation to Figure 17. The various structural elements of the UE shown in this figure can be interconnected with each other, for example, using corresponding input / output nodes (not shown) to exchange control data, user data, and other signals. Although not shown for illustrative purposes, the UE may include further structural elements.

[0113] As is clear from Figure 18, the UE may include a common timing advance value receiver, a handover procedure circuit, a first uplink timing determination circuit, a second message timing instruction receiver, a UE-specific timing advance value determination circuit, and a second handover message transmitter.

[0114] Therefore, in this case, as will become apparent from the following disclosure, the processing circuit can be exemplary configured to perform at least partially one or more of the following: determining a first uplink timing for uplink transmission to a target base station; determining a UE-specific timing advance value for a target cell; determining a second uplink timing for sending a message for a random access procedure; and determining a third uplink timing for sending uplink data.

[0115] Therefore, the receiver can be exemplary configured to perform at least partially one or more of the following: receiving a first message from the source base station of the handover procedure, which includes a common timing advance value and timing instructions for sending a second message of the handover procedure; and receiving a third message from the target base station of the handover procedure, which includes information regarding UE-specific timing advance values ​​for the UE and target cell.

[0116] Therefore, the transmitter can be exemplary configured to perform at least partially one or more of the following: sending a second message for the handover procedure to the target base station based on a predetermined uplink transmission timing; sending a message for the random access procedure to the target base station at a second uplink timing; and sending uplink data to the target base station at a third uplink timing.

[0117] One solution, disclosed in more detail below, is implemented by a UE, which includes: The UE's receiver receives a common timing advance value for the target radio cell from the source base station of the source radio cell. The UE is connected to the source radio cell and participates in a handover procedure that hands over the UE from the source radio cell to the target radio cell. The common timing advance value is also received from the source base station in the first message of the handover procedure, which also includes timing instructions for the UE to send a second message to the target base station. The UE's processor then determines the first uplink timing for an uplink transmission to the target base station with respect to a downlink transmission from the target base station, based on the received common timing advance value and timing instructions. The UE's transmitter sends the second message of the handover procedure to the target base station based on the determined uplink timing. The processor determines a UE-specific timing advance value, specific to the UE and the target radio cell, which is used by the UE to perform the uplink transmission in the target radio cell.

[0118] As a further exemplary implementation, the common TA may be signaled as a time offset value to compensate for the Round Trip Time (RTT). The RTT can be used for other purposes (for example, not necessarily in the same form as the "common TA").

[0119] In response to this, the UE already possesses knowledge of the common TA that must be used for communication in the target cell while still connected to the source BS. This makes it easier to overcome the above problem related to the fact that the UE does not obtain the common TA value if it does not read the target base station's system information. For example, messages sent later (e.g., of the handover procedure) are more likely to be correctly received by the target base station if they are time-matched based on the common TA value. Since the common target TA is already obtained during the handover procedure, the UE can execute a random access procedure immediately after completing the handover procedure.

[0120] Furthermore, this solution involves determining UE-specific TA values ​​for the UE used in the target cell, which facilitates communication in the target cell. Also, since the individual TA values ​​are known, it allows for adjustment and updating of the total TA.

[0121] Overall, the advantages of the RACH-less handover procedure—that it speeds up handovers by eliminating random access procedures and thus significantly reduces handover interruption time—are maintained. At the same time, the acquired common TA values ​​and determined UE-specific TA values ​​are used to match uplink communications at the target cell, thereby maintaining a high success rate for handovers even when RACH is not performed.

[0122] The above solution, as well as variations and further improvements of the above solution, will be described in more detail below.

[0123] For the following explanation of the improved handover procedure solution, we will make some illustrative basic assumptions. First, we assume the NTN scenario. In this case, the UE communicates via satellite in the source radio cell, and the adjacent radio cell as a possible handover target is a non-land network as described above. Furthermore, we assume that the UE supports handovers that do not perform random access procedures and performs such handovers, for example, a RACH-less handover as described above.

[0124] An exemplary implementation of this solution is illustrated with reference to Figures 19, 20, and 21.

[0125] Figure 19 is a sequence diagram of exemplary UE operation, Figure 20 is a sequence diagram of exemplary source base station operation, and Figure 21 shows the message exchange between the UE, source BS, and target BS implementing the improved handover procedure. The handover procedure is improved by providing a common TA value for the target cell in the first handover message sent from the source base station to the UE. The common TA value is valid in the target cell to which the UE is handing over. For example, the common TA value is common to all UEs in the target cell and is calculated with respect to a reference point within the target radio cell (e.g., the shortest distance to the satellite or the center of the radio cell). On the other hand, UE-specific TA values ​​(also called individual TA values), which will be discussed later, are specific to a particular UE and its location and should be considered in addition to the common TA value. Exemplarily, the common TA value and individual TA value should be understood as described above in relation to Figures 13 and 14.

[0126] Furthermore, the first handover message also conveys a timing instruction for the UE to send a second handover message to the target base station, thus providing the UE with a specific time to send that second handover message and thus proceed with the execution of the handover procedure to the target base station. The timing instruction can be provided to the UE in the form of an uplink grant that schedules the uplink resources to be used to send the second handover message. Both the timing instruction and the common TA value are used to determine the actual time when the UE sends the second handover message. For example, the timing based on the timing instruction for sending the second handover message is corrected based on the common TA value to align the UE's uplink transmission with (at least partially) other uplink transmissions from other UEs to the target base station.

[0127] Therefore, by providing a common TA value and uplink transmission timing for sending a second handover message, the handover procedure facilitates the correct reception of the second handover message at the target base station.

[0128] For example, timing instructions can implement the same or similar uplink grants provided in random access response messages (see Figures 7 and 8) during random access procedures.

[0129] Next, the UE can send a second handover message to the target base station at a predetermined uplink transmission timing.

[0130] Following the transmission of the second handover message, the UE may determine a UE-specific TA value for the target cell to enable more precise matching of the uplink transmission timing for the next uplink transmission. The UE-specific TA value is more important for correct uplink transmission time matching when the UE is located far from the reference point for calculating the common TA value. Conversely, if the UE is located near or at the reference point for calculating the common TA value, the UE may not even need to determine a UE-specific TA value for the target cell, because the UE-specific TA value is very small or zero, and the common TA value is almost the same as the total TA value in the target cell. Therefore, the UE may decide not to determine a UE-specific TA value if it is informed, for example, that it is located near or at the reference point for calculating the common TA value in the target cell. The corresponding information may be provided, for example, by the source base station. However, below we assume that the UE determines a UE-specific TA value to further improve the timing advance matching of its uplink transmission.

[0131] In either case, by determining the timing advance values ​​in this way (for example, determining the common TA value and the UE-specific TA value), the UE can synchronize its uplink transmit timing and thus improve uplink transmits during the handover procedure (using only the common TA value) and after the handover procedure (using the common TA value and possibly the UE-specific TA value as well).

[0132] More specifically, the UE may perform a random access procedure with the target base station at some point after completing the handover procedure. To enable the target base station to properly determine the required UE-specific timing advance values, the UE may send messages for the RACH procedure based solely on common timing advance values, without using, for example, previously determined UE-specific TA values.

[0133] Furthermore, the UE may use common TA values ​​and UE-specific TA values ​​when determining uplink transmission timing related to transmitting uplink data to the target base station. For example, the target base station schedules uplink radio resources to the UE that the UE can use to transmit data uplink. The UE then aligns the transmission time given by the scheduled UL radio resources based on the common TA values ​​and UE-specific TA values.

[0134] In the above description, the first and second handover messages are referred to as part of the solution presented with reference to Figures 19, 20, and 21. The first handover message can be considered a handover command message instructing the UE how to reconfigure the UE's radio resource configuration to establish a connection to the target radio cell. Thus, from the UE's perspective, the handover command message is the first message in the handover procedure. In an exemplary implementation of the solution in a 5G NR standardization scenario, the handover command message may be implemented as an RRCReconfiguration message as defined in section 6.2.2 of the corresponding Non-Patent Document 10 (see also Figure 15 and the corresponding description). When reusing an already defined RRCReconfiguration message, its content must be extended to convey additional information regarding timing instructions (uplink grant) and common TA values. For example, the RRCReconfiguration message may be extended to convey the Timing Advance Command (MAC CE) described above, the value of which is then taken by the UE as the common TA value of the target cell. For example, the TAC MAC CE value can be placed in the secondaryCellGroup information element of the RRCReconfiguration message. Similarly, the uplink grant can also be placed in the secondaryCellGroup information element of the RRCReconfiguration message.

[0135] On the other hand, the second handover message sent from the UE to the target base station can be considered a handover confirmation message indicating to the target base station that the establishment of the UE's connection to the target base station is complete. In an exemplary implementation of the solution in a 5G NR standardization scenario, the handover confirmation message can be implemented as the RRCReconfigurationComplete message defined in the corresponding Non-Patent Document 10. No additional modifications to the RRCReconfigurationComplete already defined in the 3GPP standard appear to be necessary for the implementation of handover confirmation described as part of the above solution.

[0136] As explained above, the UE receives the common TA value of the target cell from the source cell in the handover message. The source base station can then determine the common TA value of the target cell. This can be done in several ways. According to one solution, the target base station provides its neighboring base stations with information about the common TA value it uses and broadcasts in its own radio cell. For example, a target BS can provide the common TA value when it is asked to become the target of a handover, for example, in a handover acknowledgment message sent from the target base station to the source base station in response to a handover request message. According to another solution, the target base station periodically and proactively broadcasts its common TA to its neighboring base stations as part of background information exchange.

[0137] In a further exemplary implementation of the improved handover procedure described above, the handover can be determined by the source base station based on measurements performed by the UE, in the same or similar manner as described above for the legacy handover procedure in Figure 15 and the RACH-less handover in Figure 16. This exemplary variation of the improved handover procedure is reflected in Figure 22, which shows the measurement report from the UE to the source base station and the subsequent decision by the source base station to hand over the UE to the target base station. Correspondingly, the source base station sends a handover request message to the target base station. It is assumed that the target base station acknowledges the handover and responds with a handover acknowledgment message. In this exemplary implementation of Figure 22, it is assumed that a common TA value is sent by the target base station to the source base station in the handover acknowledgment message. In addition, the handover acknowledgment message also indicates the radio resources that the UE is to use to send a second handover message to the target base station (see UL grant). These radio resources should be understood as mutually agreed-upon times when the UE will send a handover confirmation message to the target base station. These radio resources are then forwarded to the UE by the source base station with a handover command message, as already described above.

[0138] The operation of the source base station shown in Figure 20 demonstrates that the source base station participates in the improved handover procedure, as is already clear from the above description. In particular, the source base station determines the common timing advance value and the UL timing for the UE to send the second handover message, based at least, for example, on the corresponding information contained in the handover acknowledgment message received from the target base station. The source base station then forwards the information to the UE in the first handover message, as already described above.

[0139] As is clear from Figure 22, and in accordance with what has already been explained in relation to Figure 21, the source base station proceeds with the handover by sending a handover command message to the UE, and the UE switches its connection to the target cell.

[0140] Furthermore, the improved handover procedure may also include, exemplarily, a further step in which the UE decides whether to perform the improved handover procedure or another type of handover (e.g., the legacy handover procedure in Figure 15). This can be implemented, for example, in a similar manner to that described for the RACH-less handover procedure in Figure 16, i.e., based on the content of the handover command message. For example, the UE decides to perform the improved handover procedure if the handover command message contains one or more of the UL grant and common TA values. On the other hand, the UE may decide to perform the legacy handover procedure (see Figure 15) if the handover command message contains neither a UL grant nor a common TA value. In yet another implementation, the UE may decide to perform the RACH-less handover procedure (see Figure 16) if the handover command contains a UL grant but does not contain a common TA value.

[0141] Therefore, although not shown in Figure 20, the source base station can control which type of handover procedure the UE should perform and then adapt the content of the handover command message according to that decision. The source base station may decide to perform an improved handover procedure or a legacy handover procedure, for example, depending on the location of the UE. If the UE is far from the reference point where the common TA value is calculated, the source base station may decide to perform the legacy handover procedure instead, because the source base station wants to ensure that the target base station can correctly decode the handover confirmation message.

[0142] The source base station can determine the location of the UE based on one or more of the following: the base station's location information, the UE's current serving beam, the beam angle of the UE's serving beam, and the UE's measurement report.

[0143] Furthermore, UE operations after the handover procedure may include the UE updating the common TA value based on system information broadcast in the target radio cell, for example. Therefore, if the UE obtains system information in the target cell that has the updated common TA value, the UE will use the updated common TA value, rather than the previously obtained common TA value, to perform further operations. For example, when performing a random access procedure, the UE may use the updated common TA value, and when transmitting uplink data, the UE may use the updated common TA value plus the UE-specific TA value.

[0144] Further exemplary implementations of the improved handover procedure present several different solutions regarding how the UE implements the process of determining UE-specific timing advance values ​​unique to the UE and the target radio cell (see, for example, the last step in Figures 19, 21, and 22).

[0145] According to the first solution shown in FIG. 23, after the UE establishes a connection to the target base station, the UE directly obtains information regarding the UE-specific TA value from the target base station in a further message of the handover procedure. Correspondingly, the UE can determine the UE-specific TA value based on the received information. According to one exemplary solution, the UE-specific TA value can be conveyed in an additional message of an improved handover procedure, for example, a message called the RRCReconfigurationCompleteACK message. The RRCReconfigurationCompleteACK message is a message transmitted by the target base station to the UE after receiving the RRCReconfigurationComplete message from the UE. For example, the RRCReconfigurationCompleteACK message is transmitted by the target base station to acknowledge the reception of the RRCReconfigurationComplete message from the UE and may convey an individual TA value. According to an exemplary implementation of the improved handover procedure in the 5G NR standard, the RRCReconfigurationCompleteACK message includes the above-mentioned Timing Advance Command MAC CE, thereby ending the improved handover procedure. The value shown in the TAC MAC CE becomes the individual TA (ITA target ) of the UE.

[0146] Before transmitting the UE-specific TA value to the UE, the target base station must determine the UE-specific TA value. Note that the RRCReconfigurationComplete message is transmitted by the UE based on the previously obtained common TA value and using the radio resources instructed by the UL grant. According to one exemplary implementation, if the target base station can decode the RRCReconfigurationComplete message and find that the start position of the RRCReconfigurationComplete message is Tms later than the start position instructed to the UE by the UL grant, then the target base station knows that the UE-specific TA value is equal to Tms.

[0147] Furthermore, according to other exemplary implementations, the target base station can configure a UL grant (in the time domain) that is larger than the size required to send the RRCReconfigurationComplete message. This facilitates the target base station so that the RRCReconfigurationComplete message does not overlap with other messages from other UEs in the time domain, thereby facilitating the correct decoding of the message by the target base station.

[0148] As is clear from the explanations given in relation to Figures 13 and 14 above, the individual TA value becomes more relevant the further the UE is from the reference point for calculating the common TA value. Therefore, if the UE is located close to the reference point, the individual TA value may not even be necessary to successfully perform a handover, and the RRCReconfigurationCompleteACK message may be optional. On the other hand, if the UE is located far from the reference point, the individual TA value is necessary to correct uplink time matching and facilitate the correct reception of further messages at the target base station. In such cases, the RRCReconfigurationCompleteACK message is indeed necessary.

[0149] Compared to the second solution (see below), the first solution has the advantage that the UE does not need to observe the DL timing difference (DL propagation time difference) between the source cell and the target cell, and does not need to estimate the individual timing advance of the target cell based on the observed timing difference (which would consume time and processor resources).

[0150] According to a second solution for determining the UE-specific TA value in the UE, the UE does not receive information about the UE-specific TA value from the target base station, but rather calculates the UE-specific TA value of the target cell by making several assumptions and taking into account the information available in the UE. For this purpose, the UE uses the following parameters: • Common timing advance values ​​for target wireless cells • UE-specific timing advance value of the source wireless cell • Common timing advance value of source wireless cell • Downlink propagation time difference between source base station and target base station

[0151] Based on these parameters, the UE can determine the UE-specific TA value of the target cell. The common TA value of the target cell is obtained, for example, in the handover command message from the source base station, as described above. Furthermore, the common TA value and UE-specific TA value of the source radio cell are known to the UE from previous communications in the source radio cell. Additionally, the downlink propagation time difference between the source base station and the target base station can be observed by the UE based on signals received from the source and target base stations, respectively. Based on the interrelationships of these parameters, Equation 1(TA) above can be used to determine the TA value. target =TA source Similar to -2 × (T1 - T2)), UE can determine the UE-specific TA value. target It is CTA_target + ITA_target, and TA source It is CTA_source + ITA_source.

[0152] In one exemplary embodiment, the calculation of the UE-specific timing advance value for the UE and target radio cell is based on the following formula.

[0153]

number

[0154] The parameter ITA_target is the UE-specific timing advance value for the UE and target radio cell being calculated. The parameter CTA_source is the common timing advance value for the source radio cell, which is known to the UE from communication with the source base station.

[0155] ITA_source is the UE-specific timing advance value of the source radio cell, CTA_target is the common timing advance value received by the target radio cell, and (T1-T2) is the downlink propagation time difference between the source base station and the target base station.

[0156] The second solution described above, which determines the UE-specific timing advance value for the target cell, can be performed, for example, as shown in Figures 21 and 22, i.e., after the transmission of the handover acknowledgment message. On the other hand, since this second solution does not depend on the transmission of a message from the target base station, as the first solution does, the second solution allows the UE-specific TA value to be determined at a much earlier time. According to a further modification of the improved handover procedure shown in Figure 24, the UE performs the step of determining the UE-specific TA value according to the second solution before the UL transmission time for sending the handover acknowledgment message. Thus, the UE can determine the UL transmission timing of the second handover message (here, for example, the handover acknowledgment message) based on the UE-specific TA value in addition to the UL grant information and the common TA value of the target cell.

[0157] The second solution has the advantage that the final TA applied to the handover complete message transmission (the RRCReconfigurationComplete message in other exemplary implementations) can be very close to the actual TA experienced by the UE, because the determination of the individual TA values ​​is based on detailed measurements performed by the UE and is already applicable to determining time-matched uplink transmission timing. Thus, the handover complete message transmitted by the UE at this time-matched uplink transmission timing is likely to be successfully decoded by the target base station.

[0158] One possible drawback of the second solution is that observing the DL propagation time difference may not provide accurate results. For example, the DL timing difference between the source and target cells may be larger than the SFN (system frame number) difference (e.g., larger than 10 ms), in which case the UE may misinterpret the actual DL timing difference because it does not know the SFN of the target cell when performing the corresponding measurement (or observation).

[0159] A possible way to avoid the above drawbacks is for the source base station to instruct the UE to perform the legacy handover procedure instead of the improved handover procedure in such cases. The source base station can determine whether this "greater than SFN difference" situation occurs, for example, according to the approximate distance from the source base station to the UE and the approximate distance from the target base station to the UE. These approximate distances can be roughly obtained based on the positions of the satellite and the UE, and possibly also based on beam angle information of the beam that the source base station uses to serve the UE. Therefore, when the source base station confirms such a situation, it provides a corresponding instruction in the handover command message to the UE to perform the legacy handover procedure (e.g., one of those described in relation to Figure 15 or Figure 16) instead of the improved handover procedure. This can be done by appropriately generating the content of the handover command message so that the UE can derive which type of handover to perform. As described above, this can be encoded in the handover command message based on one or more bits, or it can be encoded by the presence or absence of the uplink grant and / or common TA value.

[0160] Furthermore, the following exemplary modifications of the improved handover procedure facilitate overcoming the above shortcomings by enabling the UE to determine whether such a "greater than SFN difference" situation exists. According to the first modification, the UE can compare the common TA values ​​of the source and target cells to determine whether such a "greater than SFN difference" situation exists. For example, if the common TA value of the source radio cell is greater than the common TA value of the target radio cell, but the observed DL time difference is negative (i.e., CTA_source > CTA_target and T1-T2 < 0), the observed DL propagation difference is likely incorrect because the common TA value indicates that the source radio cell is farther away than the target radio cell, while the observed DL timing difference indicates that the target radio cell is farther away than the source radio cell.

[0161] According to a second variation of determining whether a "greater than SFN difference" situation exists, the UE obtains system information from the target radio cell (e.g., one or more of the SIB, MIB, and PBCH) to obtain the system frame number (SFN) of the target radio cell. Based on the obtained SFN_target, the UE can determine that a "greater than SFN difference" situation exists if SFN_target is not the same as SFN_source. Otherwise, there is no "greater than SFN difference" situation.

[0162] According to this second modification, the UE obtains system information from the target cell. Therefore, assuming a solution in which the common TA value is broadcast by the base station in its radio cell with system information, the UE may obtain the common TA value of the target cell in this manner, in addition to obtaining it in the handover command message from the source base station, or instead. In such a case, the handover command message sent from the source base station to the UE may not need to include the common TA value of the target cell.

[0163] If the UE determines that such a situation is "greater than the SFN difference," the UE may decide not to perform the improved handover procedure (even though it may have been instructed to do so) but instead use another type of handover procedure (e.g., one of the legacy handover procedures described in relation to Figures 15 and 16).

[0164] In the third solution regarding how the UE determines its own UE-specific TA value, we assume that the UE is equipped with Global Navigation Satellite System (GNSS) hardware. As described above, the improved handover procedure solution does not utilize the capabilities of the GNSS-equipped UE. However, since the GNSS hardware allows the UE to acquire its own Earth position information, the UE can determine the total timing advance of the target cell (here, for example, called GNSS_TA_target) based on the UE's position and the ephemeris information of the target satellite known to the UE.

[0165] Furthermore, we assume that the source base station provides a common TA value for the target radio cell in the first handover message (as adequately explained in the previous solution). The UE can then determine the UE-specific TA value for the target radio cell based on these two parameters, for example, ITA_target = GNSS_TA_target - CTA_target. As presented in relation to the second solution, this determination of GNSS_TA_target, and the determination of the UE-specific TA for the target cell, can be performed before the UL transmission timing specified in the handover confirmation message. Therefore, the UE can time-align the UL transmission timing based on GNSS_TA_target more accurately than if it were based on CTA_target alone.

[0166] Furthermore, although the ITA_target value is not used to determine the time-coordinated UL transmission timing of the handover confirmation message, by determining the ITA_target value in this way, the UE has enough information to determine the updated total TA value if it receives an update to the target radio cell's common TA value (e.g., through system information) after completing the handover to the target radio cell. The determined ITA_target value can then be updated, for example, by performing a RACH procedure and receiving the updated ITA_target value in a random access response message.

[0167] A specific implementation is shown in Figure 25. As illustratively assumed in the figure, the UE obtains the common TA value of the target cell. Then, illustratively, the UE may determine the GNSS_TA_target value (see above). Based on the GNSS_TA_target and the common TA value of the target cell, the UE can determine the UE-specific TA value of the target radio cell. In this illustrative implementation, the UE uses the previously determined GNSS_TA_target and UL grant to determine a time-matched uplink transmission timing for sending a second handover message (here, a handover acknowledgment message) to the target base station.

[0168] However, determining the GNSS_TA_target value is not always possible for a GNSS-equipped UE. For example, if there are no visible satellites (e.g., fewer than four satellites are visible), the UE cannot accurately determine the GNSS_TA_target value. If this situation is confirmed by the UE, the UE may resort to determining the ITA_target by using a second option, which involves observing the DL propagation time difference and calculating the ITA_target using Equation 2, in a manner different from the third GNSS-based solution described above.

[0169] The improved handover procedure described above did not distinguish whether the handover was performed in a regenerative satellite scenario or a transparent satellite scenario. As explained in more detail with reference to Figures 11-14, in a regenerative satellite, the gNB is located on the satellite, while in a transparent satellite scenario, the gNB is located on the ground and the satellite acts as a repeater. Therefore, for timing advance matching, the transparent satellite scenario must also take into account the feeder link delay (FD_target) between the satellite (repeater) and the ground-based gNB, and the satellite processing delay (PD_target) for processing incoming UL messages from the UE and further forwarding such messages to the ground-based gNB. The additional delays (FD_target and PD_target) to be considered for timing advance are shown in Figure 26.

[0170] In response, the target gNB broadcasts a common TA value in its system information that also takes these two additional delays into account. In such a transparent satellite scenario, the common TA value takes into account not only the delay d1 but also the processing delay PD_target and the feeder link delay FD_target. That is, CTA_target = 2 × (d1 + PD_target + FD_target).

[0171] In other words, the common TA value for the transparent satellite scenario is twice the common TA value for the regenerative satellite, as well as twice the additional delays FD_target and PD_target for the transparent satellite.

[0172]

number

[0173] Therefore, in all of the improved handover procedures described above, the common TA values ​​to be used depend on the specific satellite scenario. For example, in a transparent satellite scenario like that shown in Figure 26, the common TA values ​​(e.g., CTA_target or CTA_source sent to the UE in the handover command message) further take into account processing delays and feeder link delays. In other words, the parameters CTA_target_transS and CTA_source_transS, which are specific to the transparent satellite (transS) scenario, should be used instead of CTA_target_regS and CTA_source_regS, which are specific to the regenerative satellite (regS) scenario, respectively.

[0174] On the other hand, in an alternative variation, the timing advance for the transparent satellite scenario is instructed to the UE based on three different parameters: a common TA value (considering only the d1 delay, referred to as CTA_source_regS or CTA_target_regS above), a feeder link delay (FD_source or FD_target), and a satellite processing delay (PD_source or PD_target). These three parameters for the target cell can then be provided to the UE from the source base station in a handover command message, while the source base station determines these three parameters from information received, for example, in an HO-requested acknowledgment message sent to the source base station by the target base station.

[0175] In response to this, the UE then needs to calculate the common TA value for the transparent satellite scenario itself, for example, using the following formula already mentioned above.

[0176]

number

[0177] For some of the above solutions for the improved handover procedure, it was assumed that the DL delay (e.g., gNB → satellite → UE) is the same as the UL delay (UE → satellite → gNB). For example, equations 1 and 2 above are based on this assumption. However, this is not necessarily true for several reasons, such as the DL delay and UL delay not being the same. For example, downlink and uplink transmissions may use different frequency bands, and / or satellite processing may differ between uplink and downlink.

[0178] Therefore, such a solution based on the assumption that "DL delay = UL delay" cannot be used when the UL delay and DL delay are different. To overcome this constraint, according to the modified version of the improved handover procedure described above, the difference between the downlink delay and the uplink delay is further considered. For example, Equation 1(TA) target =TA source -2 × (T1 - T2)) needs to be adjusted.

[0179] The parameter Off_source is the time offset between the DL delay and UL delay in the source radio cell. This parameter can be obtained by the UE in the source radio cell, for example, through system information in the appropriate System Information Block. A positive value of Off_source can be understood as meaning, for example, that the UL delay is longer than the DL delay by the indicated value of Off_source in the source radio cell. Conversely, a negative value of Off_source can be understood as meaning, for example, that the UL delay is shorter than the DL delay by the indicated value of Off_source in the source radio cell.

[0180] Similarly, the parameter Off_target is the time offset between the DL delay and UL delay in the target radio cell. This parameter can be obtained by the UE in the source radio cell, for example, by the first handover message (e.g., a handover command message in some implementations, or an RRCReconfiguration message in other implementations), along with the common TA value of the target radio cell. A positive value of Off_target can be understood as meaning, for example, that the UL delay is longer than the DL delay in the target radio cell by the indicated value of Off_target. Conversely, a negative value of Off_target can be understood as meaning, for example, that the UL delay is shorter than the DL delay in the target radio cell by the indicated value of Off_target.

[0181] Based on the additional parameters Off_source and Off_target, Equation 1 can be modified to obtain the following Equation 3.

[0182]

number

[0183] Accordingly, in scenarios where the uplink delay and downlink delay are not the same in a wireless cell, Equation 3 should be used instead of Equation 1.

[0184] Therefore, Equation 2 is changed to Equation 4. Here, the parameters TA_target and TA_source in Equation 3 are replaced with (CTA_target + ITA_target) and (CTA_source + ITA_source), respectively.

[0185]

number

[0186] In the above solution based on Equation 2, the UE can use Equation 4 instead of Equation 2 to determine the UE-specific TA value of the target cell. As already explained with respect to Equation 2, the UE must be able to obtain all the parameters of Equation 4 in order to determine the UE-specific TA value ITA_target of the target radio cell. For example, as already mentioned in relation to Equation 3, Off_target can be obtained by the UE through the first handover message.

[0187] In response to this, the UE may first determine whether the downlink propagation delay in the source radio cell is the same as the uplink propagation delay in the source radio cell, and whether the downlink propagation delay in the target radio cell is the same as the uplink propagation delay in the target radio cell. According to one exemplary implementation, the UE is notified of this by the source base station. For example, if the parameters Off_source and Off_target are included in the handover command message, the UE determines that the assumption UL delay = DL delay is not true and that a different formula must be used.

[0188] In particular, depending on the outcome of the decision, the appropriate formula 1, 2, 3, or 4 is used as described above. Specifically, formulas 1 and 2 can be used when the UL delay and DL delay are substantially the same in the source radio cell and the target radio cell. On the other hand, formulas 3 and 4 can be used when the UL delay and DL delay are different in the source radio cell or the target radio cell.

[0189] Further aspects

[0190] According to a first embodiment, user equipment (UE) has a receiver that receives a common timing advance value for a target radio cell from a source base station of a source radio cell. The UE is connected to the source radio cell and participates in a handover procedure that hands over the UE from the source radio cell to the target radio cell. The common timing advance value is also received from the source base station in a first message of the handover procedure, the first message of the handover procedure further includes a timing instruction for sending a second message from the UE to the target base station. The processor of the UE then determines a first uplink timing for an uplink transmission to the target base station with respect to a downlink transmission from the target base station, based on the received common timing advance value and the timing instruction. The transmitter of the UE transmits the second message of the handover procedure to the target base station based on the determined uplink timing. The processor determines a UE-specific timing advance value, which is specific to the UE and the target radio cell, and is used by the UE to perform the uplink transmission in the target radio cell.

[0191] In addition to the first embodiment, according to a second embodiment provided, the processor determines a second uplink timing for sending a random access procedure message to the target base station based on the common timing advance value and not based on the UE-specific timing advance value. The processor also determines a third uplink timing for sending uplink data to the target base station based on the common timing advance value and the UE-specific timing advance value.

[0192] According to a third embodiment provided in addition to the first or second embodiment, the receiver receives a third message of the handover procedure from the target base station, which includes information relating to the UE-specific timing advance values ​​for the UE and the target radio cell, and the processor determines the UE-specific timing advance values ​​for the UE and the target radio cell from the received information relating to the UE-specific timing advance values.

[0193] According to a fourth aspect provided in addition to any one of the first to third aspects, the processor is: The received common timing advance value of the target radio cell, • UE-specific timing advance value of the aforementioned source wireless cell, • Common timing advance value of the aforementioned source wireless cell, • Downlink propagation time difference between the source base station and the target base station, Based on calculations using this method, the UE-specific timing advance values ​​for the UE and the target radio cell are determined. Furthermore, the calculation is performed before determining the first uplink timing for uplink transmission to the target base station, and the determination of the first uplink timing is further based on the calculated UE-specific timing advance value. In an optional implementation, the calculation of the UE-specific timing advance value for the UE and the target radio cell is based on the following formula:

number

[0194] According to a fifth aspect provided in addition to the fourth aspect, if the downlink propagation delay between the UE and the source base station is not the same as the uplink propagation delay between the UE and the source base station, the determination of the UE-specific timing advance value further takes into account the time offset between the downlink delay and the uplink delay in the source radio cell and the time offset between the downlink delay and the uplink delay in the target radio cell. In an optional implementation, the calculation of the UE-specific timing advance value for the UE and the target radio cell is based on the following formula:

number

[0195] According to a sixth embodiment provided in addition to any one of the first to fifth embodiments, the UE is equipped with a Global Navigation Satellite System (GNSS) circuit that determines the total timing advance value of the target radio cell. Determining the UE-specific timing advance value for the target radio cell is based on the total timing advance value for the target radio cell and the received common timing advance value for the target radio cell. In an optional implementation, the UE-specific timing advance value for the target radio cell is the total timing advance value for the target radio cell minus the received common timing advance value for the target radio cell.

[0196] According to a seventh aspect provided in addition to the sixth aspect, the processor determines whether it is possible to determine the total timing advance value of the target radio cell using the GNSS circuit. If it is not possible, the processor determines to determine the UE-specific timing advance value of the target radio cell as described in the third or fourth aspect, rather than determining the UE-specific timing advance value for the target radio cell based on the total timing advance value of the target radio cell using the GNSS circuit.

[0197] According to an eighth aspect provided in addition to any one of the first to seventh aspects described above, a common timing advance value is common to all UEs in the source / target radio cell and is calculated with respect to a reference point in the source / target radio cell. A UE-specific timing advance value is specific to one UE in the source / target radio cell and is based on the location of the UE in the source / target radio cell.

[0198] According to a ninth aspect provided in addition to any one of the first to eighth aspects, the processor determines that the first message of the handover procedure instructs the UE to participate in the handover without performing a random access procedure with the target base station. In an optional implementation, the processor determines that if the first message includes the timing instruction, the handover will be performed without performing the random access procedure.

[0199] According to a tenth aspect provided in addition to any one of the first to ninth aspects, the first message of the handover procedure, including the common timing advance value and the timing instruction of the target radio cell, is a handover command message of the handover procedure. The handover command message instructs the UE how to reconfigure the radio resource configuration of the UE to establish a connection to the target radio cell. The second message of the handover procedure is an RRCReconfigurationComplete message indicating to the target base station that the UE has completed the reconfiguration of the radio resources to establish a connection of the UE to the target base station.

[0200] According to an eleventh embodiment provided in addition to any one of the first to tenth embodiments, the UE is connected to the source base station located on the ground via a source satellite, and the common timing advance value of the source radio cell takes into account a first delay that occurs in the communication while it is being transmitted from the source satellite and the source base station located on the ground, and a second delay that occurs in the communication while it is being processed by the source satellite.

[0201] According to a twelfth aspect, a base station is provided having a transmitter that transmits a common timing advance value for a target radio cell to a user device (UE). The UE is connected to the radio cell of the base station. The base station, as a source base station, is involved in a handover procedure that causes the UE to be handed over from the radio cell, which is a source radio cell, to the target radio cell. The common timing advance value is transmitted by the base station, as a source base station, in a first message of the handover procedure. The first message of the handover procedure further includes a timing instruction for the UE to transmit a second message to the target base station.

[0202] In addition to the twelfth embodiment provided, according to a thirteenth embodiment, the base station has a processor that determines the common timing advance value of the target radio cell and the timing instruction for transmitting a second message from the UE to the target base station. In an optional implementation, the base station has a receiver that receives from the target base station of the target radio cell information regarding the common timing advance value of the target radio cell and information regarding the timing instruction for transmitting a second message from the UE to the target base station.

[0203] According to a 14th aspect provided in addition to the 12th or 13th aspects, the base station, as a target base station, is involved in other handover procedures that hand over another UE from another source radio cell to the radio cell as the target radio cell. As the target base station, the base station has a transmitter that, while operating, transmits a common timing advance value of the base station's radio cell to the other source radio station controlling the other source radio cell in a first message of the other handover procedure. The first message of the other handover procedure further includes a timing instruction for the other UE to transmit another message to the base station. As the target base station, the base station has a receiver that receives the other message of the other handover procedure transmitted from the other UE based on the common timing advance value of the radio cell and the timing instruction for transmitting the other message.

[0204] According to the 15th aspect, a method comprising the following steps performed by a user device (UE): A step of receiving a common timing advance value for a target radio cell from a source base station of a source radio cell, wherein the UE is connected to the source radio cell and participates in a handover procedure that hands over the UE from the source radio cell to the target radio cell, the common timing advance value is received from the source base station in a first message of the handover procedure, and the first message of the handover procedure further includes timing instructions for sending a second message from the UE to the target base station. The steps include determining a first uplink timing for an uplink transmission to the target base station with respect to a downlink transmission from the target base station, based on the received common timing advance value and the timing instruction, The steps include transmitting the second message of the handover procedure to the target base station based on the uplink timing determined above, A step of determining a UE-specific timing advance value, which is specific to the UE and the target radio cell, and is used by the UE to perform uplink transmission in the target radio cell. A method is provided that includes this.

[0205] Hardware and software implementations of this disclosure

[0206] This disclosure can be implemented as software, hardware, or software in conjunction with hardware. Each functional block used in the description of each embodiment above can be implemented partially or entirely by an LSI such as an integrated circuit, and each process described in each embodiment may be controlled partially or entirely by the same LSI or combination of LSIs. The LSI may be formed individually as chips, or a single chip may be formed to include some or all of the functional blocks. The LSI may include data inputs and data outputs connected thereto. Here, LSIs may be referred to as ICs, system LSIs, super LSIs, or ultra LSIs depending on the degree of integration. However, the technology for realizing integrated circuits is not limited to LSIs and may be implemented using dedicated circuits, general-purpose processors, or dedicated processors. Alternatively, an FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that allows for the reconfiguration of the connections and settings of circuit cells located inside the LSI, may be used. This disclosure can be implemented as digital or analog processing. If future integrated circuit technologies replace LSIs as a result of advances in semiconductor technology or other derivative technologies, functional blocks can be integrated using those future integrated circuit technologies. Biotechnology is also applicable.

[0207] This disclosure can be implemented by any kind of device, apparatus, or system having communication capabilities, which is referred to as a communication apparatus.

[0208] Some non-exclusive examples of such communication devices include telephones (e.g., mobile phones, smartphones), tablets, personal computers (PCs) (e.g., laptops, desktops, notebooks), cameras (e.g., digital still / video cameras), digital players (digital audio / video players), wearable devices (e.g., wearable cameras, smartwatches, tracking devices), game consoles, digital book readers, telehealth / telemedicine devices, vehicles providing communication capabilities (e.g., automobiles, airplanes, ships), and various combinations thereof.

[0209] Communication devices are not limited to portable or mobile devices, but may include all kinds of non-portable or fixed devices, devices, or systems, such as smart home devices (e.g., appliances, lighting, smart meters, control panels), vending machines, and any other "things" in the "Internet of Things (IoT)" network.

[0210] Communication can include, for example, the exchange of data via cellular systems, wireless LAN systems, and communication satellite systems, as well as the exchange of data through various combinations thereof.

[0211] A communication device may have devices such as controllers and sensors that are connected to a communication device that performs the communication functions described in this disclosure. For example, a communication device may have a controller or sensor that generates control signals or data signals used by the communication device that performs the communication functions of the communication device.

[0212] Furthermore, communication equipment may include infrastructure facilities, such as base stations, access points, and any other devices, devices, or systems, that communicate with or control the equipment in the non-limiting examples described above.

[0213] Furthermore, various embodiments may be implemented by software modules, which are executed by a processor or directly in hardware. Combinations of software modules and hardware implementations are also possible. Software modules can be stored in any type of computer-readable storage medium, such as RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROMs, DVDs, etc. It should also be noted that individual features of multiple different embodiments, individually or in any combination, can be the subject of other embodiments.

[0214] Those skilled in the art will understand that various changes and / or modifications can be made to the embodiments of this disclosure shown herein. Accordingly, the embodiments shown herein are illustrative in all respects and are not intended to limit the invention.

Claims

1. User equipment (UE), A receiving unit that receives a common timing advance value for a target radio cell from a source base station of a source radio cell, wherein the UE is connected to the source radio cell and participates in a handover procedure that hands over the UE from the source radio cell to the target radio cell, the common timing advance value is received from the source base station in a first handover message of the handover procedure, and the first handover message of the handover procedure further includes a timing instruction for transmitting a second handover message of the handover procedure from the UE to the target base station, A processing unit that determines a first uplink timing for uplink transmission to the target base station with respect to downlink transmission from the target base station, based on the received common timing advance value and the timing instruction, The system includes a transmitting unit that transmits the second handover message of the handover procedure to the target base station based on the determined uplink timing, The processing unit determines a UE-specific timing advance value, which is specific to the UE and the target radio cell, and is used by the UE to perform uplink transmission in the target radio cell, based on the position of the UE, ephemeris information, and the common timing advance value. User equipment.

2. The processing unit determines a second uplink timing for sending a random access procedure message to the target base station based on the common timing advance value and not based on the UE-specific timing advance value. The processing unit determines a third uplink timing for transmitting uplink data to the target base station based on the common timing advance value and the UE-specific timing advance value. The user device according to claim 1.

3. The receiving unit receives a third message of the handover procedure from the target base station, which includes information relating to the UE and the UE-specific timing advance value for the target radio cell, and the processing unit determines the UE-specific timing advance value for the UE and the target radio cell from the received information relating to the UE-specific timing advance value. The user device according to claim 1.

4. The aforementioned processing unit, - The received common timing advance value of the target radio cell, - UE-specific timing advance value of the aforementioned source wireless cell, - Common timing advance value of the aforementioned source wireless cell, - Downlink propagation time difference between the source base station and the target base station, Based on calculations using the above, the UE-specific timing advance values ​​for the UE and the target radio cell are determined. The calculation is performed before determining the first uplink timing for uplink transmission to the target base station, and the determination of the first uplink timing is further based on the calculated UE-specific timing advance value. The calculation of the UE-specific timing advance value for the UE and the target radio cell is based on the following formula: [Math 1] Here, ITA_target is the UE-specific timing advance value for the UE and the target radio cell, CTA_source is the common timing advance value of the source radio cell, ITA_source is the UE-specific timing advance value of the source radio cell, CTA_target is the received common timing advance value of the target radio cell, and (T2-T1) is the downlink propagation time difference between the source base station and the target base station. The user device according to claim 1.

5. If the downlink propagation delay between the UE and the source base station is not the same as the uplink propagation delay between the UE and the source base station, the determination of the UE-specific timing advance value further takes into account the time offset between the downlink propagation delay and the uplink propagation delay in the source radio cell and the time offset between the downlink propagation delay and the uplink propagation delay in the target radio cell. The calculation of the UE-specific timing advance value for the UE and the target radio cell is based on the following formula: [Math 2] Here, Off_source is the time offset between the downlink propagation delay and the uplink propagation delay in the source radio cell, and Off_target is the time offset between the downlink propagation delay and the uplink propagation delay in the target radio cell. The user device according to claim 4.

6. The aforementioned UE is equipped with a Global Navigation Satellite System (GNSS) circuit that determines the total timing advance value of the target radio cell. Determining the UE-specific timing advance value for the target radio cell is based on the total timing advance value for the target radio cell and the received common timing advance value for the target radio cell, wherein the UE-specific timing advance value for the target radio cell is obtained by subtracting the received common timing advance value for the target radio cell from the total timing advance value for the target radio cell. The user device according to claim 1.

7. The processing unit determines whether it is possible to determine the total timing advance value of the target radio cell using the GNSS circuit. If not possible, the processing unit does not use the GNSS circuit to determine the UE-specific timing advance value for the target radio cell based on the total timing advance value of the target radio cell, The receiving unit receives a third message of the handover procedure from the target base station, which includes information regarding the UE and the UE-specific timing advance value for the target radio cell, and decides to determine the UE-specific timing advance value for the target radio cell from the received information regarding the UE-specific timing advance value. The user device according to claim 6.

8. The common timing advance value is common to all UEs in the source radio cell and the target radio cell, and is calculated with respect to the reference point in the source radio cell and the target radio cell. The UE-specific timing advance value is specific to one UE in the source radio cell and the target radio cell, and is based on the position of the UE in the source radio cell and the target radio cell. The user device according to claim 1.

9. The processing unit determines that the first handover message of the handover procedure instructs the UE to participate in the handover without performing a random access procedure with the target base station, The processing unit decides to perform the handover without executing the random access procedure if the first handover message includes the timing instruction. The user device according to claim 1.

10. The first handover message of the handover procedure, including the common timing advance value and timing instruction of the target radio cell, is a handover command message of the handover procedure, which instructs the UE how to reconfigure the UE's radio resource configuration to establish a connection to the target radio cell. The second handover message of the handover procedure is an RRCReconfigurationComplete message that indicates to the target base station that the reconfiguration of the UE to establish a connection of the UE to the target base station is complete. The user device according to claim 1.

11. The aforementioned UE is connected to the aforementioned source base station located on the ground via the source satellite, The common timing advance value of the source radio cell takes into account a first delay that occurs in the communication while it is being transmitted from the source satellite and the source base station located on the ground, and a second delay that occurs in the communication while it is being processed by the source satellite. The user device according to claim 1.

12. A method comprising the following steps performed by a user device (UE): A step of receiving a common timing advance value for a target radio cell from a source base station of a source radio cell, wherein the UE is connected to the source radio cell and participates in a handover procedure that hands over the UE from the source radio cell to the target radio cell, the common timing advance value is received from the source base station in a first handover message of the handover procedure, and the first handover message of the handover procedure further includes a timing instruction for sending a second handover message of the handover procedure from the UE to the target base station. The steps include determining a first uplink timing for an uplink transmission to the target base station with respect to a downlink transmission from the target base station, based on the received common timing advance value and the timing instruction, Based on the uplink timing determined above, the second handover message of the handover procedure is transmitted to the target base station. A step of determining a UE-specific timing advance value, which is specific to the UE and the target radio cell, used by the UE to perform uplink transmission in the target radio cell, based on the location of the UE, ephemeris information, and the common timing advance value. Methods that include...

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