NTN handover timing improvements

Abstract

One embodiment relates to system information for supporting handover in a non-terrestrial network, for example, a terminal receiving system information of a non-terrestrial network, and determining from the system information an information element including indication of coverage of one or more neighboring cells adjacent to a serving cell of the UE, and determining whether to handover depending on the coverage of at least one of the one or more neighboring cells and a location of the UE.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to transmitting system information for non-terrestrial based networks. In particular, the present disclosure relates to apparatus and methods for generating, signaling, receiving, and / or utilizing system information for non-terrestrial based networks. [Background technology]

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

[0003] One objective is to provide a single technical framework that addresses all usage scenarios, requirements, and deployment scenarios, including at least enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine-type communications (mMTC). For example, deployment scenarios for eMBB may include indoor hotspots, high-density urban areas, rural areas, and urban macro and high-speed environments. Deployment scenarios for URLLC may include industrial control systems, mobile healthcare (remote monitoring, diagnosis, and treatment), real-time vehicle control, and wide-area monitoring and control systems for smart grids. Deployment scenarios for mMTC may include scenarios involving many devices with non-time-critical data transfer, such as smart wearables and sensor networks. While eMBB and URLLC services are similar in that they both require extremely high bandwidth, URLLC services differ in that they may preferably require ultra-low latency.

[0004] A second objective is to achieve forward compatibility: backward compatibility to 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.

[0005] One of the hallmarks of 5G is the introduction of non-terrestrial networks (NTNs), which include satellites in the communication path between user equipment and the network. Due to their broad service coverage and reduced vulnerability to space and airborne physical attacks and natural disasters, NTNs can facilitate the deployment of NR services in underserved areas (e.g., isolated and remote areas, on aircraft and ships) and unserved areas (e.g., suburban and rural areas) that cannot be covered by terrestrial NR networks. Furthermore, NTNs can enhance the reliability of NR services by providing service continuity for passengers on moving platforms and ensuring service availability everywhere, especially for critical communications.

[0006] These benefits relate to either standalone non-terrestrial networks or integrated terrestrial and non-terrestrial networks, which may impact coverage, user bandwidth, system capacity, service reliability or availability. Further improvements to NTNs are desirable to increase the coverage and efficiency of communication systems. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] 3GPP TS 38.300 v16.3.0 [Non-patent document 2] 3GPP TS 38.211 v16.3.0 [Non-patent document 3] ITU-R M.20183 [Non-patent document 4] 3GPP TR 38.913 v16.0.0 [Non-Patent Document 5] 3GPP TS 23.501 v16.6.0 [Non-patent document 6] 3GPP TR 38.811 v15.4.0 [Non-Patent Document 7] 3GPP TR 38.821 v16.1.0 [Non-patent document 8] 3GPP TS 38.321 v17.3.0 [Non-Patent Document 9] 3GPP TS 38.401 v17.3.0 Summary of the Invention

[0008] One of several non-limiting exemplary embodiments contributes to efficient performance of handovers in non-terrestrial based networks.

[0009] In one embodiment, the disclosed technology features a UE including a transceiver unit and circuitry, wherein the transceiver unit, in operation, receives system information of a non-terrestrial network, and the circuitry, in operation, determines from the system information an information element including an indication of coverage of one or more neighboring cells adjacent to a serving cell of the UE, and determines whether to hand over depending on the coverage of at least one of the one or more neighboring cells and a location of the UE.

[0010] It should be noted that the general or specific embodiments may be implemented as a system, a method, an integrated circuit, a computer program, a storage medium, or any selective combination thereof.

[0011] For example, the integrated circuit may control processing of a UE or a network node.

[0012] Further advantages and benefits of an embodiment of the present disclosure will become apparent from the specification and drawings. Such advantages and / or benefits may be provided by some of the embodiments and features described in the specification and drawings, but not all of them necessarily need to be provided to obtain one or more identical features. [Brief explanation of the drawings]

[0013] The following exemplary embodiments are described in more detail with reference to the accompanying drawings. [Figure 1] 1 is a block diagram illustrating an example architecture of a 3GPP NR system. [Figure 2] Block diagram showing the functional division between NG-RAN and 5GC. [Figure 3] Message sequence diagram for RRC connection setup / reconfiguration procedure. [Figure 4] Schematic diagram showing usage scenarios for enhanced Mobile Broadband (eMBB), massively multi-mode telecommunications (mMTC), and ultra-reliable, low-latency communications (URLLC). [Figure 5] 1 is a block diagram illustrating an example 5G system architecture for a non-roaming scenario. [Figure 6] FIG. 1 is a block diagram illustrating an exemplary NG RAN architecture based on transparent relay satellites. [Figure 7] FIG. 1 is a block diagram illustrating an exemplary NG RAN architecture based on regenerative satellites. [Figure 8] 1 is a block diagram illustrating an example scenario in which several UEs are served by satellites. [Figure 9] 1 is a schematic diagram illustrating an example scenario of received signal strength characteristics of a terrestrial network and a non-terrestrial based network. [Figure 10] Schematic diagram showing a moving serving cell and its surrounding neighboring cells. [Figure 11] 1 is a block diagram showing the structure of a UE and a BS that can communicate with each other. [Figure 12]1 is a block diagram illustrating the functional structure of a memory module containing code instructions executed by a circuit including one or more processors for a UE and a BS. [Figure 13] Schematic showing the effect of satellite beam aperture angle on cell coverage. [Figure 14] Schematic diagram showing the effect of satellite beam aperture and tilt angles on cell coverage. [Figure 15] Schematic showing a scenario for generating elliptical cell shapes. [Figure 16] Schematic diagram illustrating an example scenario of non-terrestrial cell mobility including a serving cell and three handover candidate cells. [Figure 17] Schematic diagram illustrating an example scenario of non-terrestrial cell mobility including a serving cell and three handover candidate cells defined by cell center and radius. [Figure 18] 1 is a flow diagram illustrating a method performed at a UE side for performing a handover based on neighbor cell coverage signaling. [Figure 19] 1 is a flow diagram illustrating a method performed on the UE side for performing a handover without neighbor cell coverage signaling. [Figure 20] 10 is a flow diagram illustrating another method performed on the UE side for performing a handover without neighbor cell coverage signaling. DETAILED DESCRIPTION OF THE INVENTION

[0014] <5G NR system architecture and protocol stack> In particular, the system architecture as a whole assumes an NG-RAN (Next Generation - Radio Access Network) comprising gNBs. The gNBs provide UE-side termination of NG radio access user plane (SDAP / PDCP / RLC / MAC / PHY) and control plane (RRC) protocols. The gNBs are connected to each other via an Xn interface. The gNBs are also connected to an NGC (Next Generation Core) via a Next Generation (NG) interface, more specifically to an AMF (Access and Mobility Management Function) (e.g., a specific core entity that performs AMF) via an NG-C interface, and to a UPF (User Plane Function) (e.g., a specific core entity that performs UPF) via an NG-U interface. The NG-RAN architecture is shown in Figure 1 (see, for example, Non-Patent Document 1, Section 4).

[0015] The NR user plane protocol stack (see, for example, Section 4.4.1 of Non-Patent Document 1) includes a Packet Data Convergence Protocol (PDCP) sublayer (see, for example, Section 6.4 of Non-Patent Document 1), a Radio Link Control (RLC) sublayer (see, for example, Section 6.3 of Non-Patent Document 1), and a Medium Access Control (MAC) sublayer (see, for example, Section 6.2 of Non-Patent Document 1), which are terminated on the network side at the gNB. A new Access Stratum (AS) sublayer (Service Data Adaptation Protocol (SDAP)) is introduced on top of PDCP (see, for example, Section 6.5 of Non-Patent Document 1). A control plane protocol stack is also defined for NR (see, for example, Section 4.4.2 of Non-Patent Document 1). An overview of Layer 2 functions is described in Section 6 of Non-Patent Document 1. RRC layer functions are listed in Section 7 of Non-Patent Document 1.

[0016] For example, the Medium-Access-Control layer handles logical channel multiplexing and scheduling and scheduling-related functions, including handling various numerologies.

[0017] For example, the physical layer (PHY) is responsible for coding, PHY HARQ processing, modulation, multi-antenna processing, and mapping of signals to appropriate physical time-frequency resources. The physical layer also handles mapping of transport channels to physical channels. The physical layer provides services to the MAC layer in the form of transport channels. A physical channel corresponds to a set of time-frequency resources used for transmitting a specific transport channel, and each transport channel is mapped to a corresponding physical channel. For example, physical channels include the Physical Random Access Channel (PRACH), the Physical Uplink Shared Channel (PUSCH), and the Physical Uplink Control Channel (PUCCH) as uplink physical channels, and the Physical Downlink Shared Channel (PDSCH), the Physical Downlink Control Channel (PDCCH), and the Physical Broadcast Channel (PBCH) as downlink physical channels.

[0018] NR use cases / deployment scenarios may include enhanced mobile broadband (eMBB), ultra-reliable and low-latency communications (URLLC), and massively multiplexed communications (mMTC), which have diverse requirements in terms of data rate, latency, and coverage. For example, eMBB is expected to support peak data rates (20 Gbps in the downlink and 10 Gbps in the uplink) and effective (user-experienced) data rates approximately three times higher than those offered by IMT-Advanced. Meanwhile, URLLC imposes more stringent requirements for ultra-low latency (0.5 ms user-plane latency for both UL and DL) and high reliability (1-10-5 within 1 ms). Finally, mMTC may require preferably high connection density (1,000,000 devices / km2 in urban environments), wide coverage in adverse environments, and extremely long battery life (15 years) for low-cost devices.

[0019] Therefore, OFDM numerology (e.g., subcarrier spacing, OFDM symbol length, cyclic prefix (CP) length, number of symbols per scheduling interval) suitable for one use case may not be valid for another use case. For example, low-latency services may preferably require a shorter symbol length (and therefore a larger subcarrier spacing) and / or fewer symbols per scheduling interval (also known as TTI) than mMTC services. Furthermore, deployment scenarios with large channel delay spreads may preferably require a longer CP length than scenarios with small delay spreads. Subcarrier spacing should be optimized accordingly to maintain similar CP overhead. NR may support one or more subcarrier spacing values. Therefore, subcarrier spacings of 15 kHz, 30 kHz, 60 kHz, etc. are currently considered. The symbol length Tu and subcarrier spacing Δf are directly related by the formula Δf = 1 / Tu. Similar to LTE systems, the term "resource element" can be used to mean the smallest resource unit consisting of one subcarrier for the length of one OFDM / SC-FDMA symbol.

[0020] In the new radio system 5G-NR, a resource grid of subcarriers and OFDM symbols is defined for each numerology and each carrier in the uplink and downlink, respectively. Each element of the resource grid is called a resource element and is identified based on a frequency index in the frequency domain and a symbol position in the time domain (see Non-Patent Document 2 (e.g., Section 4)). For example, downlink and uplink transmissions are configured as frames with a time length of 10 ms. Each frame consists of 10 subframes, each with a time length of 1 ms. In a 5G NR implementation, the number of consecutive OFDM symbols per subframe depends on the subcarrier spacing setting. For example, with a subcarrier spacing of 15 kHz, a subframe has 14 OFDM symbols (similar to an LTE-compliant implementation, assuming a normal cyclic prefix). On the other hand, with a subcarrier spacing of 30 kHz, a subframe has two slots, each with 14 OFDM symbols.

[0021] <Function division between NG-RAN and 5GC in 5G NR> Figure 2 shows the functional division between NG-RAN and 5GC. The logical node of NG-RAN is gNB or ng-eNB. 5GC has logical nodes AMF, UPF, and SMF.

[0022] In particular, the gNB and ng-eNB host the following main functions: - Radio Resource Management functions such as Radio Bearer Control, Radio Admission Control, Connection Mobility Control, dynamic allocation (scheduling) of resources to UEs in both uplink and downlink; - IP header compression, encryption, and integrity protection of data; - AMF selection at UE attach time if routing to the AMF cannot be determined from information provided by the UE; - Routing of user plane data towards UPF; - Routing of control plane information towards AMF; - Connection setup and release; - scheduling and sending of paging messages; - Scheduling and transmission of system broadcast information (originating from AMF or Operation, Admission, and Maintenance Function (OAM)); - Setting up measurements and reporting of measurements for mobility and scheduling; - Transport level packet marking in the uplink; - Session management; - Network slicing support; - QoS flow management and mapping to data radio bearers; - Support for UEs in RRC_INACTIVE state; - Non-Access Stratum (NAS) message delivery functions; - Sharing of radio access networks; - Dual connectivity; - Close cooperation between NR and E-UTRA.

[0023] The Access and Mobility Management Function (AMF) hosts the following main functions: - Terminating Non-Access Stratum (NAS) signaling; - NAS signaling security; - Access Stratum (AS) security controls; - 3GPP Core Network (CN) inter-node signaling for mobility between access networks; - Reachability to idle mode UEs (including control and execution of paging retransmissions); - Managing the registration area; - Support for intra-system and inter-system mobility; - Access authentication; - Access authorization, including checking roaming privileges; - Mobility management control (subscription and policy); - Network slicing support; - Selection of Session Management Function (SMF).

[0024] Additionally, the User Plane Function (UPF) hosts the following main functions: - Anchor points for intra-RAT / inter-RAT mobility (if applicable); - External PDU (Protocol Data Unit) session points for interconnection with data networks; - Packet routing and forwarding; - Packet inspection and policy rule enforcement for the user plane; - Traffic usage reporting; - uplink classifier that supports routing of traffic flows to the data network; - Branching Point to support multi-homed PDU sessions; - QoS processing for the user plane (e.g., packet filtering, gating, UL / DL rate enforcement); - Uplink traffic validation (mapping of SDF to QoS flows); - Buffer management of downlink packets and trigger function of downlink data notification.

[0025] Finally, the Session Management Function (SMF) hosts the following main functions: - Session management; - IP address allocation and management for the UE; - Selection and control of the UPF; - Traffic steering setting function in the User Plane Function (UPF) for routing traffic to the appropriate destination; - Policy enforcement and QoS of the control part; - Notification of downlink data.

[0026] <RRC connection setup and reconfiguration procedures> Figure 3 shows some of the interactions between the UE, gNB, and AMF (5GC entity) when the UE transitions from RRC_IDLE to RRC_CONNECTED in the NAS part (see Non-Patent Document 1).

[0027] RRC is a higher layer signaling protocol used to configure the UE and the gNB. In particular, with this transition, the AMF prepares UE context data (including, for example, PDU session context, security keys, UE radio capabilities, and UE security capabilities) and sends it to the gNB with an INITIAL CONTEXT SETUP REQUEST. The gNB then activates AS security together with the UE. This is done by the gNB sending a SecurityModeCommand message to the UE, and the UE responding with a SecurityModeComplete message. The gNB then sends an RRCReconfiguration message to the UE, and upon receiving an RRCReconfigurationComplete from the UE, the gNB reconfigures the UE to set up a Signaling Radio Bearer 2 (SRB2) and a Data Radio Bearer (DRB). For signaling-only connections, the RRCReconfiguration steps are omitted because SRB2 and DRB are not set up. Finally, the gNB notifies the AMF that the setup procedure is complete with an INITIAL CONTEXT SETUP RESPONSE.

[0028] The present disclosure provides a 5th Generation Core (5GC) entity (e.g., AMF, SMF, etc.) including: a control circuit that, in operation, establishes a Next Generation (NG) connection with a gNB; and a transmitter that, in operation, transmits an initial context setup message to the gNB via the NG connection so that a signaling radio bearer between the gNB and a user equipment (UE) is set up. Specifically, the gNB transmits Radio Resource Control (RRC) signaling including a resource allocation configuration information element (IE) to the UE via the signaling radio bearer. Then, the UE performs uplink transmission or downlink reception based on the resource allocation configuration.

[0029] <IMT usage scenarios from 2020 onwards> Figure 4 shows some use cases for 5G NR. The 3rd Generation Partnership Project New Radio (3GPP NR) is considering three use cases envisioned by IMT-2020 to support a wide variety of services and applications. The first phase of specifications for enhanced mobile broadband (eMBB) has been completed. Current and future work includes standardization for ultra-reliable, low-latency communications (URLLC) and massively multiplexed communications (mMTC), in addition to expanding support for eMBB. Figure 4 shows some examples of expected usage scenarios for IMT beyond 2020 (see, for example, Figure 2 in Non-Patent Document 3).

[0030] URLLC use cases have stringent performance requirements such as throughput, latency, and availability, and are envisioned as one of the enablers of future applications such as wireless control of industrial production or manufacturing processes, remote medical surgery, automated power transmission and distribution in smart grids, and road safety. URLLC's ultra-high reliability is supported by identifying technologies that meet the requirements set by [Non-Patent Document 4]. Key requirements for NR URLLC in Release 15 include a target user plane latency of 0.5 ms on the uplink (UL) and 0.5 ms on the downlink (DL). A typical URLLC requirement for a single packet transmission is a block error rate (BLER) of 1E-5 for a 32-byte packet size with a user plane latency of 1 ms.

[0031] From a physical layer perspective, reliability can be improved in many possible ways. Current reliability improvement room includes defining a separate CQI table for URLLC, a more compact DCI format, repeated transmission of PDCCH, etc. However, this room can be expanded to achieve ultra-high reliability as NR (with respect to the key requirements of NR URLLC) becomes more stable and developed. Specific use cases for NR URLLC in Release 15 include augmented reality / virtual reality (AR / VR), e-health, e-safety, and mission-critical applications.

[0032] Additionally, technology enhancements targeted by NR URLLC aim to improve latency and reliability. Technology enhancements for latency improvement include configurable numerology, non-slot-based scheduling with flexible mapping, grant-free (configured grant) uplink, slot-level repeated transmission in the data channel, and preemption in the downlink. Preemption means that a transmission with already allocated resources is stopped and the allocated resources are used for another transmission with a later requested lower latency / higher priority. Thus, a previously allowed transmission is preempted by a later transmission. Preemption is applicable regardless of the specific service type. For example, a transmission of service type A (URLLC) can be preempted by a transmission of service type B (eMBB, etc.). Technology enhancements for reliability improvement include dedicated CQI / MCS tables for a target BLER of 1E-5.

[0033] The use case for massive machine-type communication (mMTC) is characterized by a very large number of connected devices that typically transmit relatively small amounts of data that are not sensitive to latency. These devices are required to be low cost and have very long battery life. From an NR perspective, using very narrow bandwidth portions is one solution that saves power and allows for long battery life for the UE.

[0034] As mentioned above, the scope of reliability improvement in NR is expected to become broader. One of the key requirements for all cases, especially for URLLC and mMTC, is high or ultra-high reliability. Several mechanisms can improve reliability from a radio perspective and a network perspective. Generally, there are two to three key areas that can help improve reliability. These areas include compact control channel information, data channel / control channel repetition, and diversity in the frequency, time, and / or spatial domains. These areas are generally applicable to reliability improvement regardless of the specific communication scenario.

[0035] For NR URLLC, further use cases with more stringent requirements are envisioned, such as factory automation, transportation, and power distribution: high reliability (up to the power of 10 reliability), high availability, packet sizes up to 256 bytes, and time synchronization down to a few microseconds (depending on the use case, the value can be 1 microsecond or a few microseconds depending on the frequency range and low latency in the order of 0.5ms-1ms, especially for targeted user plane latency of 0.5ms).

[0036] Furthermore, for NR URLLC, several technical extensions may be possible from the perspective of the physical layer. These technical extensions include the extension of the Physical Downlink Control Channel (PDCCH) related to compact DCI, the repeated transmission of PDCCH, and the increased monitoring of PDCCH. Also, the extension of UCI (Uplink Control Information) is related to the extension of enhanced HARQ (Hybrid Automatic Repeat Request) and CSI feedback. In addition, extensions of PUSCH related to mini-slot level hopping, and extensions of retransmission / repeated transmission may be possible. The term "mini-slot" refers to a transmission time interval (TTI: Transmission Time Interval) that contains fewer symbols than a slot (a slot has 14 symbols).

[0037] <QoS Control> The QoS (Quality of Service) model of 5G is based on QoS flows and supports both QoS flows that require a guaranteed flow bit rate (GBR (Granteed Bit Rate) QoS flows) and QoS flows that do not require a guaranteed flow bit rate (non-GBR QoS flows). Therefore, at the NAS level, a QoS flow is the finest granularity QoS differentiation in a PDU session. A QoS flow is identified within a PDU session by a QoS flow ID (QFI: QoS Flow ID) that is carried in an encapsulation header via the NG-U interface.

[0038] For each UE, the 5GC establishes one or more PDU sessions. For each UE, the NG-RAN establishes at least one Data Radio Bearer (DRB) for each PDU session, e.g., as shown above with reference to Figure 3. Additional DRBs for the QoS flows of that PDU session can be configured later (when this is up to the NG-RAN). The NG-RAN maps packets belonging to different PDU sessions to different DRBs. NAS-level packet filters in the UE and the 5GC associate UL and DL packets with QoS flows, while AS-level mapping rules in the UE and the NG-RAN associate UL and DL QoS flows with DRBs.

[0039] Figure 5 shows the non-roaming reference architecture for 5G NR (see Section 4.2.3 of Non-Patent Document 5). An Application Function (AF) (e.g., an external application server hosting 5G services as illustrated in Figure 4) interacts with the 3GPP core network to provide services, for example, to support application influence on traffic routing, access to a Network Exposure Function (NEF), or interact with a policy framework for policy control (e.g., QoS control) (see Policy Control Function (PCF)). Based on the operator's deployment, Application Functions that are considered trusted by the operator can interact directly with the relevant Network Functions. Application Functions that are not permitted by the operator to directly access Network Functions interact with the relevant Network Functions using an external exposure framework via the NEF.

[0040] Figure 5 further illustrates further functional units of the 5G architecture, namely, 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-provided services, Internet access, or third-party services). All or part of the core network functions and application services may be deployed and run in a cloud computing environment.

[0041] Therefore, the present disclosure provides an application server (e.g., an AF in a 5G architecture) including: a transmitter configured to, in operation, transmit a request including QoS requirements for at least one of a URLLC service, an eMBB service, and an mMTC service to at least one of 5GC functions (e.g., an NEF, an AMF, an SMF, a PCF, an UPF, etc.) to establish a PDU session including a radio bearer between a gNB and a UE according to the QoS requirements; and a control circuit configured, in operation, to perform a service using the established PDU session. <Send system information> System information is downlink broadcast information sent by a base station (gNB in ​​5G, or network node in general). System information contains information for a UE to establish a connection with a base station. In 5G, a UE reads system information for cell camping when it powers on, and for cell selection and reselection when it is in RRC_IDLE mode. System information provides all the details needed to access the network, such as system frame number, system bandwidth, PLMN, cell selection and reselection thresholds, etc.

[0042] The system information is structured into a Master Information Block (MIB) and a System Information Block (SIB). Various information is contained in the SIB. In the present disclosure, the relevant information may be information about NTN transmission, which will be described later. The MIB information is transmitted (broadcast) via the BCH and PBCH channels, and the SIB is transmitted via the DL-SCH and PDSCH channels.

[0043] Generally, system information is transmitted periodically (so that newly connecting terminals can acquire it) or on demand. The periodic schedule for the transmission of system information can be configured by RRC. In particular, SIB1 (referenced by the MIB) conveys scheduling information that specifies, for example, the system information window (repetition period of the system information transmission pattern), some transmission parameters (e.g., physical layer parameters) for receiving the system information, and the mapping (transmission pattern) of SIBs within the system information window.

[0044] <Non-terrestrial network (NTN)> A non-terrestrial network refers to a network or segment of a network that uses RF resources onboard an airborne or space-based entity for transmission. Space-based vehicles include, for example, satellites (including low Earth orbiting (LEO), medium Earth orbiting (MEO), geostationary Earth orbiting (GEO), and highly elliptical orbiting (HEO) satellites). Airborne vehicles include, for example, high altitude platforms (HAPs) and unmanned aerial systems (UAS), including lighter-than-air unmanned aerial systems (LTA) and heavier-than-air unmanned aerial systems (HTA), all of which typically operate quasi-routinely at altitudes between 8 km and 50 km.

[0045] 3GPP has been studying and explaining NR-based operation in non-terrestrial networks (NTNs) (see, for example, Non-Patent Document 6, "Study on New Radio (NR) to support non-terrestrial networks," and Non-Patent Document 7, "Solutions for NR to support non-terrestrial networks").

[0046] An NTN typically comprises the following system elements: an NTN terminal, which refers to a 3GPP UE or a terminal specific to the satellite system if the satellite does not directly serve the 3GPP UE; a service link, which refers to the radio link between the user equipment and the space / airborne platform; an airborne platform carrying the payload; a gateway connecting the space / airborne platform with the core network; and a feeder link, which refers to the radio link between the gateway and the space / airborne platform.

[0047] A platform can implement either transparent repeater payload transmission or regenerative repeater payload transmission. In transparent repeater payloads, the payload remains unchanged, and the platform acts as a repeater by filtering, converting, and amplifying the radio signal. In regenerative repeater payloads, the platform has some or all base station functionality. In addition to radio frequency filtering, conversion, and amplification, the platform may perform demodulation / modulation, switching / routing, and encoding / decoding. Inter-Satellite Links (ISLs) can optionally be used to form constellations of satellites. An ISL is a transport link between satellites.

[0048] Figure 6 shows a non-terrestrial network scenario, in which transmission to and from a terminal (UE) is via a remote radio unit (RRU) including a satellite and an NTN gateway. A gNB is located in the gateway as a scheduling device. The satellite payload performs frequency conversion and radio frequency amplification in both the uplink and downlink directions. Thus, the satellite relays the NR 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 NR-Uu. In other words, the satellite does not terminate the NR-Uu. A satellite with this configuration is called a transparent relay satellite.

[0049] Figure 7 illustrates a non-terrestrial network scenario, in which transmission to and from a terminal (UE) is performed via a satellite including a gNB as a scheduling device. A satellite with this configuration is called a regenerative satellite. According to one embodiment (see Non-Patent Document 8, Section 5.2 "NR; Medium Access Control (MAC) protocol specification"), the logical architecture of NG-RAN described in Non-Patent Document 9, "NG-RAN; Architecture description", is used as a baseline for the NTN scenario. The satellite payload performs 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, and the SRI is the transport link between the NTN gateway and the satellite.

[0050] Because LEO, MEO, and HEO satellites do not have fixed locations relative to a given point on Earth, the satellite beams corresponding to the cells or Physical Cell IDs (PCIs) or Synchronization Signal Block (SSB) beams of an NR radio system may move around the Earth.

[0051] An NTN scenario providing cells that move continuously on the Earth (e.g., LEO-, MEO-, or HEO-based NTN) is called an Earth-moving cell scenario. The continuous cell movement on the Earth is due to the operation of satellite beams that are fixed relative to the NTN platform. Therefore, the footprint of a cell corresponding to multiple satellite beams or a single satellite beam slides across the Earth's surface in accordance with the movement of the NTN platform (e.g., a LEO satellite). This is shown in FIG. 8. A satellite 810 moves at a speed of, for example, 7.6 km / s (indicated by the moving arrow 820). The satellite 810 may provide one or more cells (here, three cells) 890. A service link 840 exists between the UE 850 and the satellite 810. System information, particularly a system information block (SIB), carries NTN information and is sometimes referred to as an NTN-SIB. Currently, SIB19 carries NTN information in 3GPP NTN-NR. The system information is broadcast by the satellite 810. The present disclosure is not limited to any particular network configuration. In some communication systems that may benefit from the present disclosure, satellites may be controlled by the gNB 860 to broadcast system information. There is a feeder link 830 delay between the satellite 810 and the gNB 860.

[0052] <Handover between cells belonging to non-terrestrial networks (NTN)> Handover in non-terrestrial cells involves some additional challenges compared to handover in terrestrial cells: for example, handover may be necessary not only due to the movement of the UE, but also due to the movement of the non-terrestrial base station, depending on the type of cell, or the cell itself due to the movement of the Earth.

[0053] One challenge is the potentially large number of UEs (up to approximately 20,000 UEs / second) that may need to be handed over from one cell (e.g., a serving cell) to a neighboring cell, or roughly from one cell to another. Cell movement can result in a large number of UEs, and all UEs in such a cell need to be handed over. Such handovers typically need to be performed within a short time period to ensure seamless connectivity.

[0054] Below is Table 7.3.2.1.6-1 taken from Non-Patent Document 7, which shows, among other things, the average handover (hand-out and / or hand-in) rate (number of UEs / second) as a function of the cell diameter / area of ​​the satellite cell and an exemplary UE density.

[0055] [Table 1]

[0056] For latency reasons, it may be useful to allow a connected UE to initiate a handover based on conditions pre-set by the network, sometimes referred to as a Conditional Handover (CHO).

[0057] Currently, there are three types of conditional events available for handover from a serving cell to a neighboring cell: events based on radio frequency (RF) measurements, events based on time thresholds, and events based on location thresholds.

[0058] Conditional events based on RF measurements (serving cell and / or neighboring cells) are, for example:

[0059] CondEvent A3: Conditional reconfiguration candidate is an offset amount superior to the PCell / PSCell. For example, the UE measures the signal strength of the candidate cell higher than the signal strength (received power) measured for the current serving cell, which must be higher by a pre-configured or defined amount.

[0060] CondEvent A4: Conditional reconfiguration candidate is better than absolute threshold, e.g., the UE measures a signal strength higher than a pre-configured or defined threshold.

[0061] CondEvent A5: PCell / PSCell is worse than absolute threshold 1 and conditional reconfiguration candidate is better than another (different from threshold 1) absolute threshold 2. For example, the UE measures the signal strength of the serving cell and some more cells. The signal strength of the serving cell is below a first threshold (threshold 1) and the signal strength of the candidate cell is above a second threshold (threshold 2).

[0062] Examples of conditional events based on time thresholds are:

[0063] CondEvent T1: A time measured at the UE is greater than the configured threshold t1-Threshold and less than t1-Threshold+duration. For example, the time instance t1-Threshold indicates the start of a time window whose duration is indicated as "duration." Therefore, the UE may perform a handover within the time window.

[0064] A conditional event based on a location threshold may be:

[0065] CondEvent D1: The distance between the UE and the reference location referenceLocation1 becomes greater than the set threshold distanceThreshFromReference1, and the distance between the UE and the reference location referenceLocation2 of a conditional reconfiguration candidate (e.g., a cell other than the current serving cell) becomes less than the set threshold distanceThreshFromReference2.

[0066] Regarding the RF measurements mentioned above, in terrestrial systems, a UE can determine that it is near the cell edge due to a clear difference in RSRP compared to the cell center. This is shown in Figure 9(a). This effect may not be as pronounced in non-terrestrial deployments, where the difference in signal strength between the two beams in the overlapping region is smaller, as shown in Figure 9(b). Because the Release 15 handover mechanism is based on RF measurement events (e.g., A3), the UE may have difficulty distinguishing between the better cell. Due to this field (signal) strength situation, RF measurements alone may not be sufficient to initiate a conditional handover (see CondEvents A3-A5).

[0067] FIG. 10 illustrates the coverage of multiple cells, each represented by a circle. A UE (shown as a black dot) is located in serving cell 100. The serving cell is surrounded by six neighboring cells, denoted A, B, C, a, b, and c. There is an overlap region 150 between the coverage of the serving cell and neighboring cell a. Circle 110 within serving cell 100 indicates the region between the boundary of the serving cell and the boundary of the portion of the serving cell area that is located less than 90% away from the cell center, corresponding to the use of CondEvent D1. Here, 90% is merely an example. In general, such a location threshold can be high (e.g., 95%) or low (e.g., 88%).

[0068] However, the location threshold, i.e., CondEvent D1, currently does not adapt well to the shape of the RF overlap of neighboring cells, which can result in unnecessarily forcing a large number of UEs to handover in a short period of time. Figure 10 illustrates the challenge assuming the criteria distanceThreshFromReference1 = 0.8distanceThresh (80% of the radius of the serving cell's coverage area) and distanceTreshFromReference2 = 0.8distanceTresh (80% of the radius of the neighboring cell's coverage area). There is a clear discrepancy between the outer "donut" segment 160 that meets the above criteria and the actual overlap region 150 where handover is possible.

[0069] Here, the "donut" refers to the area between two concentric circles, for example, the circle defined by distanceThresh (the coverage of the serving cell) and the circle defined by distanceThreshFromReference1, which in this example is 0.8 × distanceThresh (generally a preset value). For neighboring cells, the donut also refers to the area between two concentric circles, namely, the circle defined by distanceThresh (the coverage of the neighboring cell, which in this example is the same as the coverage of the serving cell) and the circle defined by distanceThreshFromReference2 (also 0.8 × distanceThresh in this example). In principle, distanceThreshFromReference2 does not have to correspond to distanceThreshFromReference1 and may be different.

[0070] The current CondEvent D1 in combination with CondEvents A3, A4, or A5 may not be optimal as the sole criteria for handover because the donut-shaped region 160 outside the serving cell's coverage area does not well represent the overlap region 150 between that serving cell and neighboring cells.

[0071] Regarding the time threshold, indicating a time window, as can be achieved with CondEvent T1, is a somewhat inefficient approach since it is unlikely to be the same for all UEs in the serving cell, as it may depend on the location of the UE in the serving cell, the speed of the UE's movement, and / or the direction of the UE's movement.

[0072] This disclosure recognizes that it may be desirable to prevent, or at least reduce the number of, unnecessary handovers and to spread out unavoidable handovers over the entire time that a UE is located within an overlap region between adjacent cells. Furthermore, the above conditions may not be sufficient for improved handover efficiency.

[0073] <Signaling of coverage areas of neighboring cells> According to one embodiment, in addition to indicating the coverage area of ​​the serving cell, the coverage area of ​​each neighboring cell that may be a potential target cell within a certain time frame is also indicated.

[0074] 11 illustrates a user equipment (UE) 210 including a transceiver 240 and circuitry 220. The transceiver 240 is configured to receive system information for a non-terrestrial network. The circuitry 220 is configured to determine, from the system information, an information element including an indication of coverage of one or more neighboring cells adjacent to a serving cell of the UE. The circuitry 220 is further configured to determine whether to perform a handover depending on the coverage of at least one of the one or more neighboring cells and the location of the UE.

[0075] For example, a non-terrestrial network may include a base station (BS) 290. Also shown in FIG. 11 is the base station 290. The base station may be mounted on a non-terrestrial airframe, and the base station (not itself entirely mounted on the non-terrestrial airframe) may control such a non-terrestrial airframe to provide / irradiate one or more non-terrestrial cells. The base station 290 includes a transceiver 260 and circuitry 280. The circuitry 280 is configured to determine coverage of one or more neighboring cells adjacent to the BS's own cell and generate system information including an information element containing an indication of the coverage of the one or more neighboring cells. The transceiver 260 is configured to transmit the system information.

[0076] In general, the term "information element" refers to an element of a protocol syntax (such as the RRC protocol mentioned above) that may (but need not) encapsulate additional information elements. UE 210 may use non-terrestrial cells to access a communication network, such as 5G NR. Base station 290 may be located directly on a serving non-terrestrial airframe (e.g., a satellite) and may control the serving non-terrestrial airframe as described above with reference to Figures 6 and 7. In the context of 5G NR, the base station may be a gNB. The present disclosure is readily applicable to 5G NR systems, but is not limited thereto. Any current or future communication system using non-terrestrial cells may benefit from the present disclosure.

[0077] 11, UE 210 and BS 290 may communicate over channel 250. In particular, BS 290 may transmit system information to UE 210 over channel 250, which may include a wireless channel between a non-terrestrial airframe and a UE.

[0078] The transceivers (e.g., UE transceiver 240 and BS transceiver 260) may be any receiver and / or transmitter including, for example, one or more antennas and corresponding amplifiers and modulators / demodulators (upconversion to / downconversion from the system carrier). The transceivers may be controlled by a control module to transmit and / or receive specific data at specific times and on specific resources. Such a control module may be part of the circuits 220, 280.

[0079] The circuitry (such as the UE circuitry 220 and the BS circuitry 280) may include one or more processors, one or more memory modules, one or more programmable or application-specific hardware, and / or several additional electronic elements.

[0080] For example, as shown in FIG. 13 for BS 290, circuit 280 may include processing circuit 288 and memory circuit 285. Processing circuit 288 may be controlled by program code stored in memory circuit 285. The program code may include functional modules 281, 282, and 283 that configure processing circuit 288 to perform the functions of the BS described above. In particular, coverage determination module 281 configures the processing circuit to determine coverage of one or more neighboring cells adjacent to the BS's own cell, and system information (SI) generation module 282 configures the processing circuit to generate system information including information elements that include indications of the coverage of the one or more neighboring cells. Tx / Rx control module 283 controls transceiver 260 via interface 270 to transmit system information in resources scheduled for transmission. For example, Tx / Rx control module 283 outputs system information to be transmitted to transceiver 260. Note that memory circuit 285 may include additional modules that implement additional functions of BS 290.

[0081] For example, as shown in FIG. 12 for a UE 210, the circuit 220 may include a processing circuit 228 and a memory circuit 225. The processing circuit 228 may be controlled by program code stored in the memory circuit 225. The program code may include functional modules 221, 222, and 223 that configure the processing circuit 228 to perform the functions of the UE described above. In particular, the coverage acquisition module 221 configures the processing circuit to acquire, from system information, an information element including an indication of the coverage of one or more neighboring cells adjacent to the UE's serving cell, and the handover control module 222 configures the processing circuit to determine whether to perform a handover depending on the coverage of at least one of the one or more neighboring cells (and further depending on the location of the UE). The transceiver control module 223 controls the transceiver 240 via the interface 230 to receive the system information in resources scheduled for transmission. For example, the transceiver control module 223 receives a received signal including the system information from the transceiver 240. It should be noted that the memory circuitry 225 may include additional modules for implementing additional functionality of the UE 210. The circuitry 220 may further be configured to initiate a handover if it is determined that the UE should hand over.

[0082] The memory circuitry may be on the same chip as the processing circuitry, or may be integrated into one or more chips separate from the integration of the processing circuitry.

[0083] For example, the coverage indication may include, for one or more neighboring cells, an indication of the center of the neighboring cell and the radius of the neighboring cell. Such indication may allow the coverage to be modeled as a circular region. It may be desirable to indicate the coverage in the same format (e.g., as a center and a radius) for each of the one or more neighboring cells. However, the present disclosure is not limited to such indication, and the coverage may be indicated differently for some of the one or more neighboring cells. For example, it is possible to indicate all information for some cells and indicate identity (e.g., an indication that the radius is the same as a reference cell already included in the system information) or difference (e.g., a difference in location relative to the reference cell and / or a difference in radius relative to the radius of the reference cell) for the remaining cells.

[0084] In one embodiment, the neighbor coverage information can represent the coverage of neighbor cells in a similar manner as for the serving cell, i.e., using similar parameters as referenceLocation-r17 and distanceThresh-r17. The referenceLocation-r17 may convey the location of the center of the cell, and the distanceThresh-r17 may convey the radius.

[0085] In particular, currently in NR, SIB19 conveys the following elements: [Table 2]

[0086] It can be seen that referenceLocation and distanceThresh are indicated for the cell providing the system information (e.g., the primary cell PCell or the serving cell). According to the above exemplary embodiment, these parameters may be included for one or more (or each) of the neighbor cells listed in the IE container ntn-NeighCellConfigList or ntn-NeighCellConfigListExt. Note that the suffix "-r17" in the names of the IEs simply indicates the release of the standard in which the respective IE is available. Therefore, these elements are used herein without this suffix, since it is not important for the present disclosure which version of the standard the elements are incorporated into. referenceLocation and distanceThresh may be indicated in existing IEs for neighbor cells in the list of neighbor cells. Alternatively, referenceLocation and distanceThresh may be indicated in separate IEs, which may be separate lists signaling the coverage of one or more cells included in the ntn-NeighCellConfigList or ntn-NeighCellConfigListExt list. However, the present disclosure is not limited to providing coverage indications in the form of reference positions and radii.

[0087] According to one embodiment, the indication of coverage includes, for a neighboring cell of the one or more neighboring cells, an indication of the aperture angle of a satellite beam forming the neighboring cell and / or the tilt of the satellite beam from vertical.

[0088] FIG. 13 illustrates a beam aperture angle 630 for an example cell served by a satellite 610 and a beam aperture angle 640 for another example cell served by a satellite 620, both of which orbit the Earth 690 in an orbit 600. The two aperture angles 630 and 640 are different from each other; in this example, angle 630 is 80 degrees and angle 640 is 30 degrees. Because both satellites 610 and 620 are in the same orbit 600, the angular separation has a dominant effect on the cell coverage (cell size). The example in FIG. 13 shows the cells beamed to the Earth's surface via the shortest path. In other words, the beam axis is perpendicular to the Earth's surface. In such a deployment scenario, it may be sufficient to indicate the aperture angle per cell as an indication of coverage. A UE may use this indication, in conjunction with knowledge of the orbital height and possibly the location of non-terrestrial vehicles (e.g., satellites as shown in FIG. 13), to determine the location of the cells. The orbital height and / or non-terrestrial vehicle position may be known from system information about neighboring cells.

[0089] FIG. 14 illustrates another exemplary case, in which the aperture angle 750 of the cell beam provided by the satellite 710 is tilted relative to the direction of shortest distance (vertical). In other words, the beam has an azimuth, i.e., a non-zero tilt angle. FIG. 14 illustrates a 10-degree tilt relative to vertical (tilt from the satellite 710 in orbit 700 to Earth 790). In such cases, it may be advantageous to indicate coverage not only by aperture angle 750 but also by angular tilt. Thus, in this example case, the IE conveying the coverage indication may indicate the satellite beam's azimuth (tilt angle) and aperture angle indication (e.g., as two separate IEs). As mentioned above, the orbital altitude is known from the position indication of a reference satellite (which may be the serving satellite). One advantage of signaling the coverage area by aperture angle and tilt is that, unlike the radius and reference point signaling described above, it can indicate non-circular coverage.

[0090] However, the signaling of the reference point (center) and radius can be adapted to enable indication of the elliptical shape of the cell's coverage area. In particular, the information element containing the coverage indication can specify the coverage as an ellipse. Such an information element may include two parameters, the major and minor radii (or the major and minor radii), instead of a single radius. Such signaling can convey more accurate information of the cell coverage, especially when a non-terrestrial aircraft generates a non-vertical beam. This is shown in FIG. 15. In particular, UE 950 is located in an area above Earth 990. Satellite 910 is located directly above UE 950 (vertically) and therefore forms a substantially circular cell 915 (ignoring the effects of terrain). Meanwhile, satellite 920 (and satellite 930) are located only 10 degrees above the ground. This results in an elliptical illumination area 960. It can be seen that the coverage of region 960 is substantially different from the coverage of region 925 obtained from signaling only one radius. In particular, for quasi-earth fixed cells, out-of-circular coverage situations can arise, especially as one approaches the minimum elevation angle (see image below).

[0091] As shown above, the center of the cell (or generally the reference location) and its radius may be signaled using referenceLocation-r17 and distanceThresh-r17. To provide signaling suitable for elliptical cells, two parameters may be introduced in addition to referenceLocation-r17: shortDistanceTresh-r18 and longDistanceTresh-r18. These may have the same range of values ​​as distanceThresh-r17.

[0092] Neighbor cells are listed in the system information transmitted by a primary cell (PCell), which may be the serving cell. Generally, there is no limit to the number of cells that must be included in the list. FIG. 16 shows a serving cell 100 where a UE is located. The serving cell is surrounded by neighboring cells A, B, C, and a, b, and c. Among these neighboring cells, cells a, b, and c are potential candidates for handover of the UE. This is because the cell is moving leftward, as indicated by the left arrow in FIG. 16. When the cell moves so that the UE is located in overlapping areas 150 (with neighboring cell a), 160 (with neighboring cell b), and 170 (with neighboring cell c), it may be advantageous to perform handover. Note that if the cell moves in the opposite direction (to the right in FIG. 16), neighboring cells A, B, and C would be more suitable candidates for handover.

[0093] Accordingly, the one or more neighboring cells for which coverage is indicated are at least one of the following:

[0094] Neighboring cells that are on the same orbit as the serving cell, as exemplified by cell a in Figure 16.

[0095] A neighboring cell whose orbit is adjacent to the orbit of the serving cell on a first side of the orbit of the serving cell, as exemplified in Figure 16 by cell b located above the orbit of the serving cell.

[0096] A neighboring cell whose orbit is adjacent to the orbit of the serving cell on a second side opposite to the first side of the orbit of the serving cell, as exemplified in Figure 16 by cell c located below the orbit of the serving cell.

[0097] In practice, if all three cells a, b, and c are available, it may be desirable to include all three of these cells in the one or more neighboring cells and signal their coverage. In FIG. 16, these three cells a, b, and c located to the right of the serving cell 100 follow the serving cell 100 in the direction of movement of the serving cell. Cells further to the right (cells following cells a, b, and c in the direction of movement of the serving cell) may be indicated in the system information. This may be beneficial, for example, when the cell coverage area is small (e.g., approximately 50 km in diameter).

[0098] <Handover decision execution> The signaling of coverage provided by neighboring cells may be used by the UE to determine whether to perform a handover to a neighboring cell (and to which neighboring cell). In particular, the UE may detect whether it is located within an overlapping area of ​​neighboring cells (e.g., areas 150, 160, 170). If the UE is located in one of the overlapping areas, it may decide to handover to a neighboring cell.

[0099] Specifically, the determination of whether to perform handover in the UE includes the following processes.

[0100] · Estimating, based on the coverage indication, whether the UE is located within the coverage of a neighboring cell among the one or more neighboring cells and whether the UE is located within the coverage of a serving cell.

[0101] · Determining whether to hand over to a neighboring cell based on a first condition that requires the UE to be located within an overlapping coverage area for the UE to hand over.

[0102] Note that this estimation may be based on the coverage of neighboring cells determined based on system information, or on the coverage of a serving cell determined based on system information. Furthermore, the UE knows its location. For example, the UE may determine its location based on Global Navigation Satellite Systems (GNSS) or any other method known in the art.

[0103] The first condition may be the only condition for determining to perform a handover. However, the present disclosure is not limited thereto, and the condition may include additional requirements. Also, the decision on whether to perform a handover may be separate from the decision on when to perform the handover. For example, when the first condition is met, the UE may determine when to perform a handover and perform the handover at the determined time.

[0104] In one example of signaling implementation, the system information includes an information element specifying a handover condition for the UE to decide whether to hand over from a set of predetermined handover conditions including the first condition. In other words, the UE can be configured by the network to decide whether to hand over based on certain conditions. This set of predetermined conditions may correspond to the currently available set mentioned above, i.e., may include one or more of the above conditions (conditions A to A5, T1, and D1) in addition to the first condition.

[0105] Figure 17 shows a portion of Figure 16, namely, a serving cell 100 and neighboring cells a, b, and c following the serving cell in its direction of movement 101 (here considered to be equivalent to the direction of the satellite generating the cell). In this example, the serving cell has coverage obtained by an indication including a reference location referenceLocation-r17 (e.g., the center point of the serving cell) and a radius distanceTresh-r17. Neighboring cell a has coverage obtained by corresponding parameters indicating a reference location referenceLocationNeighbour-r18 (e.g., the center point of neighboring cell a) and a radius distanceTreshNeighbour-r18. The overlapping area between serving cell 100 and neighboring cell a is indicated by 150.

[0106] The new location-based CondEvent D2 may be an example of the above-mentioned condition, and may require that the distance between the UE and the reference location referenceLocation1 is smaller than the set threshold distanceThreshFromReference1 and that the distance between the UE and the conditional reconfiguration candidate reference location referenceLocation2 is shorter than the set threshold distanceThreshFromReference2, i.e., the UE reaches the overlap area between coverage area 1 and coverage area 2.

[0107] Here, to describe the overlap region (150, 160, or 170) of the serving cell with each neighboring cell (a, b, or c), parameters referenceLocation1 and distanceThreshFromReference1 represent the reference location (e.g., center) and radius of the serving cell. Parameters referenceLocation2 and distanceTreshFromReference2 represent the reference location (e.g., center) and radius of the neighboring cell (e.g., a, b, or c).

[0108] The new CondEvent D2 can be extended for elliptical cell coverage areas as already described with reference to Figure 15. The logic of the new CondEvent D2 remains the same in this case. The only difference from the previous example is that instead of one radius distanceTreshNeighbor-r18, two radius parameters shortDistanceTreshNeighbor-r18 and longDistanceTreshNeighbor-r18 are indicated in the system information of the neighboring cell and used to test whether the UE is in the overlap area. Additionally or alternatively, the coverage of the serving cell may also be indicated to have an elliptical shape in the system information, for example by providing two radius parameters shortDistanceTresh-r18 and longDistanceTresh-r18, which are then used to test whether the UE is in the overlap area.

[0109] Based on knowledge of the coverage of neighboring cells, unnecessary handovers can be reduced. For example, a handover from the serving cell to neighboring cell b and then immediately to neighboring cell a in quick succession can be prevented by the presence of cell coverage area information for both neighboring cells, since the UE is in a position to more accurately estimate the time it will be in the overlap regions 150 and 160.

[0110] To reduce the excessive number of handovers simultaneously performed by all UEs in a cell, in one example applicable to any of the above embodiments and examples, the UE randomly determines where or when to switch to a neighboring cell within the overlap area. The randomization may be performed according to any one of known mechanisms for generating random numbers. Specifically, determining whether to handover includes determining the timing of the handover based on the randomly generated number.

[0111] Here, randomization is not necessarily part of the configurable first condition. The UE may first determine that a handover is to be performed if it is detected to be located in an overlapping area (e.g., 150). The UE may then determine when to handover (which can be considered as determining whether to perform a handover for different time instances while the UE is in the overlapping area). However, the present disclosure is not limited to such a two-stage approach. In general, the first condition may include an additional requirement that the random number generated at that instant be greater than a predetermined threshold.

[0112] The randomization may be configurable by the base station. Specifically, the base station may set the probability distribution or predefined threshold of the random number generator and may provide individual UEs or groups of UEs with random values ​​to make decisions.

[0113] For example, the decision whether to perform a handover to a neighboring cell may be made on the UE side by: Determine the UE's own location; Estimating a time interval during which the UE is within the coverage of a neighboring cell and within the coverage of a serving cell; This involves randomly determining at what point within that time interval the UE will hand over.

[0114] The time interval may be estimated based on the speed and / or direction of travel of the UE itself, or the speed and / or direction of travel of a cell (e.g., a satellite carrying the cell), which may be obtained by any known method.

[0115] The use of velocity information may be particularly suitable when the aperture and tilt angles of the satellite relative to neighboring cells are given, and when the coverage area indication by center point and radius is not updated frequently.

[0116] Generally, to estimate the period during which a handover from the serving cell 100 to a neighboring cell a is possible, the UE may know the geographic extent of the overlap area at its current location. This is provided based on system information indicating the coverage of the serving cell and / or neighboring cells, as described above. The UE also knows its location, for example, based on GNSS (GPS, GALILEO, or other navigation systems). The satellite velocity is provided by the serving cell's velocity indication and / or the neighboring cell's orbit indication (or the serving cell's orbit, if it is in the same orbit as the serving cell) in the system information. Generally, for some satellites, an altitude indication may be sufficient to determine the velocity, since the satellite's velocity depends on A) the radius of its orbit relative to the center of the Earth, B) the Earth's mass, and C) the gravitational constant. The UE's velocity and direction of movement may also be taken into account. These parameters are available to the UE based on the UE's GNSS capabilities. However, since the UE's velocity is much slower than the satellite's velocity, the UE's velocity and direction are usually not required.

[0117] FIG. 18 shows an example flowchart of a method that may be performed in a UE, combining several of the above approaches. In step 1810, the UE (using the circuitry described above) detects its location. In step 1820, the UE compares its location with the coverage areas of the next neighboring cells stored in its database (previously received in system information, e.g., SIB19 in NR). In step 1830, the UE determines whether its location is within the location of the neighboring cell. If so ("Yes" in step 1830), the UE calculates the duration of the UE's presence in the overlapping area between the serving cell and the neighboring cell in step 1840. In step 1850, the UE randomizes the calculated duration, i.e., randomly determines at what point in the calculated duration to perform handover (handover time).

[0118] The UE then periodically checks whether that point has been reached in a loop that includes step 1860, which tests whether that point has been reached, and step 1890, which increments the clock. Step 1890 is a delay between checks.

[0119] In this exemplary flowchart, in addition to the first condition (tested in step 1830) and randomization (step 1850) described above, an additional condition regarding the neighboring cell's radio frequency (RF) parameters is tested in step 1870. Specifically, step 1870 tests whether the neighboring cell's field strength exceeds an RF strength threshold. If so ("Yes" in step 1870), the UE initiates a handover to the neighboring cell in which it is located in step 1880. If not ("No" in step 1870), the method returns to step 1810. If the UE's location is not within the neighboring cell's location ("No" in step 1830), the method also returns to step 1810.

[0120] Field strength is one possible condition. In general, any radio frequency measurement may be used to determine whether the UE has or is expected to have sufficient reception quality in neighboring cells. Figure 18 shows a method performed for one cell. However, the method may also be performed for multiple neighboring cells, such as cells a, b, and c above. For example, if after a "No" in step 1870 there are more neighboring cells to test, the method may continue for the same UE location and the next cell in the list of neighboring cells of step 1820.

[0121] In this way, a reliable handover approach can be achieved with limited gNB / network load. In summary, such an approach combines neighbor cell coverage information (and in this case, identifying overlap areas between the serving cell and neighbor cells) with RF measurements, a suitable combination for a proper, ideally seamless, conditional handover. Since the UE knows the available area and distance for the handover, as well as the satellite velocity, it can determine the time to perform the handover based on a randomized approach. For example, time instance of handover location = current time + (random(0,1) × time required for the overlap area to pass at the UE location). Random(0,1) means that the random number generator is configured to output values ​​of 0 or 1 randomly (pseudo-randomly). For greater accuracy, the UE's speed and direction of movement must also be taken into account.

[0122] <Coverage estimation without explicit signaling> In the previous embodiment, the coverage of neighboring cells was signaled, however, there is also the possibility to improve handover decisions for non-terrestrial cells and make signaling of neighboring cell coverage unnecessary.

[0123] For example, a user equipment (UE) is provided, the UE comprising a transceiver and circuitry as described above with reference to Figure 11. The transceiver is configured to receive radio frequency signals of a non-terrestrial cell other than the serving cell. The circuitry comprises: determining whether the received radio frequency signal satisfies a predetermined condition; Estimate a remaining serving cell coverage period during which the serving cell can cover the UE; The device is configured to determine whether and / or when to perform a handover depending on whether a preset condition is met and based on the estimated serving cell coverage time.

[0124] The pre-defined condition may be set, for example, by system information or RRC signaling from the base station to the UE, but may also be specified by a standard, etc. Also, as described in some embodiments above, the decision on when to hand over may be randomized.

[0125] The decision on whether and / or when to perform a handover may include, for example, deciding not to perform a handover if a preset condition is not met, where the preset condition requires that the radio signal of another cell be stronger than a threshold.

[0126] In particular, after the UE detects a neighboring cell based on RF, the UE can initiate handover based on its knowledge of the time it takes for the currently serving cell to disappear. Here, for example, RF-based means field strength-based. If the measured field strength exceeds a threshold, the neighboring cell is suitable for handover. If the measured field strength does not exceed the threshold, the neighboring cell is not suitable for handover, and handover is not performed.

[0127] FIG. 19 illustrates an exemplary method using a flowchart. Specifically, in step 1910, the UE monitors the received field strength (signal strength) of a neighboring cell. In step 1920, it is determined whether the monitored (measured) field strength of the neighboring cell exceeds a threshold. If so ("Yes" in step 1920), the UE further determines when to perform a handover. Specifically, it determines the serving cell's coverage time (also referred to as a time window, or more descriptively, the remaining serving cell coverage period) and a randomization factor. The UE then determines whether to perform a handover based on the serving cell's coverage time (also referred to as a time window) and the randomization factor. Specifically, it tests whether the time window length x the randomization factor reaches a predetermined value. If so ("Yes" in step 1930), the UE initiates a handover to the neighboring cell in step 1950. If the field strength of the neighboring cell does not exceed the threshold ("No" in step 1950), the UE waits in step 1940 (with a delay and possibly a timer increase) and returns to step 1930 to check again whether to hand over.

[0128] Here, randomization performed by multiplying a random number by a time window is not a limitation of this disclosure, and any randomization of handover time may work as long as the handover time is within the time window.

[0129] The time window until the serving cell disappears can be determined based on information already available to the UE. For example, the cell speed may be determined based on system information of the primary cell (serving cell), such as SIB19. Furthermore, the serving cell coverage is signaled by a reference position (e.g., center) and radius. In this case, the coverage information of the target cell is not explicitly given but is implied by timing information (how long the serving cell coverage will last). However, the remaining features of the above-described embodiments and examples may be applied in a similar manner. For example, the serving cell coverage may be indicated by two radius parameters that enable an ellipsoidal cell shape, and the above-described events A1 to A5, T1, and D1 may be applied within the above-described preset conditions, and randomization may be applied, etc.

[0130] Handovers can occur at random times within the coverage period of the serving cell, with different UEs being able to handover at different times within said period.

[0131] Below is another example of a reliable handover approach with limited gNB / network load without explicit signaling of neighbor cell coverage. Figure 20 shows the corresponding method performed by the UE. In step 2010, a condition for leaving the serving cell is met. The condition may be, for example, one of the above conditions A1-A5, D1, or T1 (referred to as Release 17, R17 conditions) for neighbor cells. If the condition is not met ("No" in step 2010), the test for the condition is repeated. If the condition is met ("Yes" in step 2010), a test is performed in step 2020 to see if the time or location window length times a randomization factor has been reached. Generally, a test is performed to see if a randomly selected point in time (within the above time window) for handover has arrived. If not ("No" in step 2020), step 2020 is repeated after a delay imposed by a timer in step 2030. Otherwise (“Yes” in step 2020), in step 2040 the UE initiates a handover to a neighboring cell.

[0132] In this example, the condition of leaving the serving cell before the expiration of the time window and the random determination of the time point of handover within the window still apply. In other words, the handover is randomized by a timer. The randomization of leaving the serving cell can be achieved as follows:

[0133] The location within the serving cell is randomized, and / or The time after the location-based exit condition is randomized.

[0134] By setting randomized leaving conditions before handover, different UEs can be handed over at different times. Randomizing the location within the serving cell means that the UE randomly selects a location within the serving cell to which it performs handover.

[0135] Hardware and Software Implementations of the Disclosure The present disclosure can be realized by software, hardware, or software in conjunction with hardware. Each functional block described in the above embodiments may be partially or entirely realized as an LSI, which is an integrated circuit. Each process described in the above embodiments may be partially or entirely controlled by a single LSI or a combination of LSIs. The LSI may be composed of individual chips, or may be composed of a single chip that includes some or all of the functional blocks. The LSI may have data inputs and outputs. Depending on the level of integration, the LSI may be referred to as an IC, system LSI, super LSI, or ultra LSI. The integration method is not limited to LSIs; it may also be realized by dedicated circuits, general-purpose processors, or dedicated processors. Furthermore, FPGAs (Field Programmable Gate Arrays), which can be programmed after LSI fabrication, or reconfigurable processors, which allow the connections and settings of circuit cells within the LSI to be reconfigured, may also be used. The present disclosure may be realized as digital or analog processing. Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, it is natural that such technology can be used to integrate functional blocks. The application of biotechnology is also a possibility.

[0136] The present disclosure may be implemented in any type of apparatus, device, or system having a communication function (collectively referred to as a communication apparatus).

[0137] A communications device may include a wireless transceiver (transmitter / receiver) and processing / control circuitry. The wireless transceiver may include a receiver and a transmitter, or both. The wireless transceiver (transmitter and receiver) may include an RF (Radio Frequency) module and one or more antennas. The RF module may include an amplifier, an RF modulator / demodulator, or the like.

[0138] Non-limiting examples of communication devices include telephones (e.g., cell phones, smartphones), tablets, personal computers (PCs) (e.g., laptops, desktops, netbooks), cameras (e.g., digital still / video cameras), digital players (e.g., digital audio / video players), wearable devices (e.g., wearable cameras, smartwatches, tracking devices), game consoles, digital book readers, telehealth / telemedicine devices, communication-enabled vehicles or mobile transportation (e.g., cars, airplanes, ships), and combinations of the above devices.

[0139] Communications equipment is not limited to portable or mobile equipment, but also includes non-portable or fixed equipment, devices, and systems of any kind, such as smart home devices (appliances, lighting equipment, smart meters or metering devices, control panels, etc.), vending machines, and any other "things" that may exist on an Internet of Things (IoT) network.

[0140] Communications include data communications via cellular systems, wireless LAN systems, communications satellite systems, etc., as well as data communications via combinations of these.

[0141] A communications apparatus also includes devices such as controllers and sensors connected or coupled to a communications device that performs the communications functions described in this disclosure, such as controllers and sensors that generate control and data signals used by the communications device to perform the communications functions of the communications apparatus.

[0142] The communication apparatus also includes infrastructure facilities, such as base stations, access points, and any other apparatus, device, or system that communicates with or controls the various apparatuses listed above, but are not limited to these.

[0143] Furthermore, various embodiments may also be implemented by software modules. These software modules are executed by a processor or directly in hardware. A combination of software modules and hardware implementation is also possible. The software modules may be stored on any type of computer-readable storage medium. In particular, according to another implementation, a non-transitory computer-readable storage medium is provided. The storage medium stores a program that, when executed by one or more processors, causes the one or more processors to perform the steps of a method according to the present disclosure.

[0144] By way of non-limiting example, such computer-readable storage media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is referred to as a computer-readable medium, as appropriate. For example, if instructions are transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included within the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but instead cover non-transitory tangible storage media. As used herein, a disc includes a compact disc (CD), a laser disc, an optical disc, a digital versatile disc (DVD), a floppy disk, and a Blu-ray disc, where a "disk" typically reproduces data magnetically, while a "disc" reproduces data optically with a laser. Combinations of the above should also be included within the scope of computer-readable media.

[0145] Furthermore, it should be noted that individual features of different embodiments may be the subject of other embodiments, individually or in any combination. Those skilled in the art will appreciate that the present disclosure, as set forth in the specific embodiments, may be subject to various changes and / or modifications without departing from the concept or scope of the invention as broadly described. The embodiments described herein are therefore to be considered in all respects as illustrative and not restrictive.

[0146] <Summary of the embodiment> According to a first aspect, there is provided a user equipment (UE), the user equipment comprising: a transceiver unit configured, in operation, to receive system information of a non-terrestrial network; and a circuit configured, in operation, to determine from the system information an information element comprising an indication of coverage of one or more neighboring cells adjacent to a serving cell of the UE, and to decide whether to hand over depending on the coverage of at least one of the one or more neighboring cells and a location of the UE.

[0147] According to a second aspect, in addition to the first aspect, the indication of coverage includes, for a neighboring cell of the one or more neighboring cells, an indication of a center of the neighboring cell and a radius of the neighboring cell.

[0148] According to a third aspect, in addition to the first aspect, the indication of coverage includes, for a neighboring cell of the one or more neighboring cells, an indication of the opening angle of a satellite beam forming the neighboring cell and the inclination of the satellite beam from the vertical.

[0149] According to a fourth aspect, in addition to any one of the first to third aspects, the one or more neighboring cells include at least one of a neighboring cell in the same orbit as the orbit of the serving cell, a neighboring cell in an orbit adjacent to the orbit of the serving cell on a first side of the orbit of the serving cell, and a neighboring cell in an orbit adjacent to the orbit of the serving cell on a second side opposite the first side of the orbit of the serving cell.

[0150] According to a fifth aspect, in addition to any one of the first to fourth aspects, the decision on whether to hand over includes estimating whether the UE is located within the coverage of a neighboring cell among the one or more neighboring cells and within the coverage of the serving cell based on the indication of coverage, and deciding whether to hand over to the neighboring cell based on a first condition requiring the UE to be located within the overlapping coverage area in order for the UE to hand over.

[0151] According to a sixth aspect, in addition to the fifth aspect, the system information includes an information element that identifies a handover condition from a set of predefined handover conditions, including the first condition, for the UE to decide whether to perform a handover.

[0152] According to a seventh aspect, in addition to the fifth or sixth aspect, the decision on whether to hand over includes determining the timing of the handover further based on a randomly generated number.

[0153] According to an eighth aspect, in addition to the seventh aspect, the decision of whether to hand over to the neighboring cell includes determining the UE's own location, estimating a time interval in which the UE is located within the coverage of the neighboring cell and within the coverage of the serving cell, and randomly determining at what point within the time interval the UE will hand over.

[0154] According to a ninth aspect, in addition to any one of the first to eighth aspects, the information element including an indication of coverage enables the coverage to be specified as an ellipse.

[0155] According to a tenth aspect, there is provided a user equipment (UE), the user equipment comprising: a transceiver unit configured, in operation, to receive a radio frequency signal of a non-terrestrial cell other than a serving cell; and a circuit configured, in operation, to determine whether the received radio frequency signal satisfies a preset condition, to estimate a remaining serving cell coverage time during which the serving cell can cover the UE, and to decide whether to perform a handover and / or a timing of the handover depending on whether the preset condition is satisfied and based on the estimated serving cell coverage time.

[0156] According to an eleventh aspect, in addition to the tenth aspect, the determination of the timing of handover is randomized.

[0157] According to a twelfth aspect, in addition to the tenth or eleventh aspects, the decision on whether to hand over and / or the timing of hand over includes deciding not to hand over if the preset condition requiring the radio signal of the other cell to be stronger than a threshold is not met.

[0158] According to a thirteenth aspect, there is provided a base station (BS) for a non-terrestrial network, the base station comprising: circuitry for, in operation, determining coverage of one or more neighbouring cells adjacent to an own cell of the BS, and generating system information including information elements containing an indication of the coverage of the one or more neighbouring cells; and a transceiver for, in operation, transmitting the system information.

[0159] It should be noted that the above aspects specifying the format and content of the signaling (eg, coverage) apply equally to base stations, as base stations may generate and transmit the signaling.

[0160] According to a fourteenth aspect, there is provided a method for handover, the method comprising: receiving system information of a non-terrestrial network; determining from the system information an information element comprising an indication of coverage of one or more neighboring cells adjacent to a serving cell of the UE; and deciding whether to handover depending on the coverage of at least one of the one or more neighboring cells and a location of the UE.

[0161] According to a 15th aspect, a method for transmitting system information of a non-terrestrial network includes determining coverage of one or more neighboring cells adjacent to the BS's own cell, generating system information including information elements containing an indication of the coverage of the one or more neighboring cells, and transmitting the system information.

[0162] According to a sixteenth aspect, a method is provided for a UE, the method including: receiving a radio frequency signal of a non-terrestrial cell other than a serving cell; determining whether the received radio frequency signal satisfies a predetermined condition; estimating a remaining serving cell coverage time during which the serving cell can cover the UE; and determining whether to perform a handover and / or a timing of the handover depending on whether the predetermined condition is satisfied and based on the estimated serving cell coverage time.

[0163] It should be noted that these methods may include further limitations corresponding to the steps performed by the exemplary embodiments, particularly the circuits described above.

[0164] According to a seventeenth aspect, there is provided program code stored on a computer readable and non-transitory medium and comprising program code instructions that, when executed by one or more processors, cause the one or more processors to perform any of the methods set forth above.

Claims

1. A communication device, a transceiver unit configured to receive system information of a non-terrestrial network during operation; When in operation, determining from the system information an information element comprising an indication of coverage of one or more neighboring cells adjacent to a serving cell of the communications device; and a circuit for determining whether to hand over depending on the coverage of at least one of the one or more neighboring cells and a location of the communication device. Communication equipment.

2. the indication of coverage includes, for a neighboring cell among the one or more neighboring cells, an indication of a center of the neighboring cell and a radius of the neighboring cell. The communication device according to claim 1 .

3. the indication of coverage includes, for a neighboring cell of the one or more neighboring cells, an indication of an aperture angle of a satellite beam forming the neighboring cell and an inclination of the satellite beam from a vertical line; The communication device according to claim 1 .

4. The one or more neighboring cells: a neighboring cell that is on the same orbit as the orbit of the serving cell; a neighbor cell in an orbit adjacent to the orbit of the serving cell on a first side of the orbit of the serving cell; a neighboring cell located on an orbit adjacent to the orbit of the serving cell on a second side opposite the first side of the orbit of the serving cell; The communication device according to claim 1 .

5. The decision whether to hand over is made by: estimating whether the communication device is located within a coverage of a neighboring cell among the one or more neighboring cells and within a coverage of the serving cell based on the coverage indication; determining whether to hand over to the neighboring cell based on a first condition requiring the communication device to be located within an overlapping coverage area in order for the communication device to hand over; The communication device according to claim 1 .

6. the system information includes an information element that identifies a handover condition for determining whether or not the communication device should perform a handover, from among a set of predefined handover conditions including the first condition; The communication device according to claim 5 .

7. determining whether to hand over includes determining timing of handover further based on a randomly generated number; The communication device according to claim 5 .

8. The decision whether to hand over to the neighboring cell comprises: determining a self-location of the communication device; estimating a time interval in which the communication device is located within the coverage of the neighboring cell and within the coverage of the serving cell; and randomly determining at what point within the time interval the communication device will hand over. The communication device according to claim 7.

9. the information element containing the indication of coverage allows the coverage to be specified as an ellipse, The communication device according to claim 1 .

10. A communication device, a transceiver unit that, in operation, receives radio frequency signals of non-terrestrial cells other than the serving cell; When in operation, determining whether the received radio frequency signal satisfies a preset condition; Estimating a remaining serving cell coverage period during which a serving cell can cover the communication device; a circuit for determining whether and / or when to perform a handover depending on whether the predetermined condition is met and based on the estimated serving cell coverage duration. Communication equipment.

11. The determination of the timing of handover is randomized. The communication device according to claim 10.

12. The decision of whether and / or when to hand over includes deciding not to hand over if the predetermined condition requiring that the radio frequency signal of a non-terrestrial cell other than the serving cell be stronger than a threshold is not met.

12. A communication device according to claim 10 or 11.

13. A base station (BS) of a non-terrestrial network, comprising: When in operation, determining coverage of one or more neighboring cells adjacent to the BS's own cell; a circuit for generating system information including an information element including an indication of the coverage of the one or more neighboring cells; a transceiver unit that, in operation, transmits the system information. B.S.

14. receiving system information of a non-terrestrial network; determining from the system information an information element comprising an indication of coverage of one or more neighboring cells adjacent to a serving cell of the communications device; determining whether to hand over depending on the coverage of at least one neighboring cell of the one or more neighboring cells and a location of the communication device; Handover method.

15. 1. A method for transmitting system information of a non-terrestrial network, comprising: determining coverage of one or more neighboring cells adjacent to the BS's own cell; generating the system information including an information element including an indication of the coverage of the one or more neighboring cells; transmitting the system information. method.

16. 1. A method for a communication device, comprising: receiving radio frequency signals of non-terrestrial cells other than the serving cell; determining whether the received radio frequency signal satisfies a preset condition; estimating a remaining serving cell coverage period during which a serving cell can cover the communication device; and determining whether and / or when to hand over depending on whether the predetermined condition is met and based on the estimated serving cell coverage duration. method.

17. comprising program code instructions that, when executed by one or more processors, cause said one or more processors to perform the method of any one of claims 14 to 16; Program code stored on a computer readable and non-transitory medium.

18. An integrated circuit for controlling processing of a communication device, the processing comprising: receiving system information of a non-terrestrial network; and determining from the system information an information element comprising an indication of coverage of one or more neighboring cells adjacent to a serving cell of the communication device; and determining whether to hand over depending on the coverage of at least one neighboring cell of the one or more neighboring cells and a location of the communication device. Integrated circuit.

19. 1. An integrated circuit for controlling processing of a base station (BS) of a non-terrestrial network, the processing comprising: determining the coverage of one or more neighboring cells adjacent to the BS's own cell; generating system information including an information element including an indication of the coverage of the one or more neighboring cells; configured to transmit the system information; Integrated circuit.

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