Transient non-cell-defining synchronization signal block for soft satellite switching

Abstract

Methods and systems for transient non-cell-defining synchronization signal block usage for soft satellite switching are provided. A user equipment is presented, which receives satellite switching information for soft satellite switching in a cell from a source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining synchronization signal block (NCD-SSB) of the target satellite, acquires synchronization with the target satellite using at least one NCD-SSB between the first point in time and the second point in time, and switches to the target satellite for continued service of the cell based on the acquired synchronization. Satellites are also presented that support the soft satellite switching of the user equipment accordingly.

Description

[0001] TRANSIENT NON-CELL-DEFINING SYNCHRONIZATION SIGNAL BLOCK FOR SOFT SATELLITE SWITCHING TECHNICAL FIELD

[0002] The subject disclosure generally relates to wireless communication systems and, in particular, to transient non-cell-defining synchronization signal block usage for soft satellite switching.

[0003] BACKGROUND

[0004] Wireless telecommunication systems, also referred to mobile communication systems, are under constant development. In 3GPP (3rd Generation Partnership Project) mobile communication systems, such as in new radio (NR) / 5th generation (5G) mobile communication systems and beyond, the basic earth-bound mobile communication become now enhanced with non-terrestrial networks (NTN). In an NTN system, 5G base stations (g NBs) are deployed on board of satellites and / or satellites may act as a kind of relay for ground-based gNBs to provide communication coverage over a large area that may be otherwise unreachable by cellular networks. Such functionality can, e.g., be used to connect UEs or Internet-of-Things (loT) devices globally as well as provide personal communication in remote areas and in disaster relief.

[0005] Since satellites move in space, a cell that covers an area on the globe may be switched or handed over from one serving satellite to another from time to time. This procedure can be transparent to a user equipment (UE) to a far extent on the logical level because the serving gNB or the corresponding gateway to the network (on ground) does not change and, therefore, the majority of the cell configuration can be maintained. However, the UE still need to synchronize with the new serving satellite on the physical level. First suggestions how to achieve such a synchronization have been discussed recently in 3GPP, which all require fundamental changes in the cell timing and / or transmission the synchronization signal block (SSB) of the target cell. Therefore, all options currently discussed face difficulties and improvements are needed.

[0006] SUMMARY

[0007] According to a first aspect of the disclosure, a user equipment, UE, is provided which comprises at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to receive satellite switching information for soft satellite switching in a cell from a source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD,synchronization signal block, SSB, of the target satellite, acquire synchronization with the target satellite using at least one NCD-SSB between the first point in time and the second point in time, and switch to the target satellite for continued service of the cell based on the acquired synchronization.

[0008] In some embodiments, the UE is further caused to perform NCD-SSB measurements according to the satellite switching information for acquiring synchronization. In some embodiment, the UE is further caused to partially acquire and / or maintain synchronization with the target satellite based on at least one cell-defining SSB transmitted by the target satellite after the second point in time. In some embodiments, the first point in time indicates when the target satellite starts service of the cell, wherein the second point in time indicates when the source satellite stops service of the cell.

[0009] In some embodiments, the NCD-SSB configuration comprises a time offset with respect to a cell-defining SSB of the source satellite and / or a frequency location of the NCD-SSB. In some embodiments, the satellite switching information is transmitted within a system information block of the source satellite. In some embodiments, the at least one NCD-SSB of the target satellite is allocated in orthogonal resources with respect to a cell-defining SSB of the source satellite.

[0010] According to a second aspect of the disclosure, a satellite in a non-terrestrial communication network being a source satellite for soft satellite switching in a cell is provided, which comprises at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the satellite at least to transmit satellite switching information for the soft satellite switching from the source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite, and stop transmission of cell-defining SSBs and stop provision of service of the cell at the second point in time.

[0011] In some embodiments, the first point in time indicates when the target satellite starts service of the cell, wherein the second point in time indicates when the source satellite stops service of the cell. In some embodiments, the NCD-SSB configuration comprises a time offset with respect to a cell-defining SSB of the source satellite and / or a frequency location of the NCD-SSB. In some embodiments, the satellite switching information is transmitted within a system information block. In some embodiments, the at least one NCD-SSB of the target satellite is allocated in orthogonal resources with respect to a cell-defining SSB of the source satellite.

[0012] According to a third aspect of the disclosure, a satellite in a non-terrestrial communication network being a target satellite for soft satellite switching in a cell is provided, which comprises at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the satellite at least to transmit at least one non-cell-defining, NCD, synchronization signal block, SSB, between a first point in time and a second point in time, suspend transmission of cell-defining SSBsbetween the first point in time and the second point in time, and stop transmission of the at least one NCD-SSB, resume transmission of the cell-defining SSBs, and start provision of service of the cell at the second point in time.

[0013] In some embodiments, the first point in time indicates when the target satellite starts service of the cell, wherein the second point in time indicates when the source satellite stops service of the cell. In some embodiments, the at least one NCD-SSB is allocated in orthogonal resources with respect to a celldefining SSB of the source satellite.

[0014] According to a fourth aspect of the disclosure, a method executed by a user equipment, UE, is presented, which comprises receiving satellite switching information for soft satellite switching in a cell from a source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite, acquiring synchronization with the target satellite using at least one NCD-SSB between the first point in time and the second point in time, and switching to the target satellite for continued service of the cell based on the acquired synchronization.

[0015] In some embodiments, the method further comprises performing NCD-SSB measurements according to the satellite switching information for acquiring synchronization. In some embodiments, the method further comprises partially acquiring and / or maintaining synchronization with the target satellite based on at least one cell-defining SSB transmitted by the target satellite after the second point in time. In some embodiments, the first point in time indicates when the target satellite starts service of the cell, wherein the second point in time indicates when the source satellite stops service of the cell.

[0016] In some embodiments, the NCD-SSB configuration comprises a time offset with respect to a cell-defining SSB of the source satellite and / or a frequency location of the NCD-SSB. In some embodiments, the satellite switching information is transmitted within a system information block of the source satellite. In some embodiments, the at least one NCD-SSB of the target satellite is allocated in orthogonal resources with respect to a cell-defining SSB of the source satellite.

[0017] According to a fifth aspect of the disclosure, a method executed by a satellite in a non-terrestrial communication network, the satellite being a source satellite for soft satellite switching in a cell, is presented, which comprises transmitting satellite switching information for the soft satellite switching from the source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite, and stopping transmission of cell-defining SSBs and stopping provision of service of the cell at the second point in time.

[0018] In some embodiments, the first point in time indicates when the target satellite starts service of the cell, wherein the second point in time indicates when the source satellite stops service of the cell. In someembodiments, the NCD-SSB configuration comprises a time offset with respect to a cell-defining SSB of the source satellite and / or a frequency location of the NCD-SSB. In some embodiments, the satellite switching information is transmitted within a system information block. In some embodiments, the at least one NCD-SSB of the target satellite is allocated in orthogonal resources with respect to a cell-defining SSB of the source satellite.

[0019] According to a sixth aspect of the disclosure, a method executed by a satellite in a non-terrestrial communication network, the satellite being a target satellite for soft satellite switching in a cell, is presented, which comprises transmitting at least one non-cell-defining, NCD, synchronization signal block, SSB, between a first point in time and a second point in time, suspending transmission of celldefining SSBs between the first point in time and the second point in time, and stopping transmission of the at least one NCD-SSB, resuming transmission of the cell-defining SSBs, and starting provision of service of the cell at the second point in time.

[0020] In some embodiments, the first point in time indicates when the target satellite starts service of the cell, wherein the second point in time indicates when the source satellite stops service of the cell. In some embodiments, the at least one NCD-SSB is allocated in orthogonal resources with respect to a celldefining SSB of the source satellite.

[0021] The above-noted aspects and features may be implemented in systems, apparatuses, methods, articles and non-transitory computer-readable media depending on the desired configuration. The subject disclosure may be implemented in and used with a number of different types of devices, including but not limited to cellular phones, tablet computers, wearable computing devices, portable media players, and any of various other computing devices.

[0022] This summary is intended to provide a brief overview of some of the aspects and features according to the subject disclosure. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope of the subject disclosure in any way. Other features, aspects, and advantages of the subject disclosure will become apparent from the following detailed description, drawings and claims.

[0023] TERMINOLOGY

[0024] To facilitate understanding on the terminologies in the subject disclosure, the following list of the most relevant abbreviations is provided:

[0025] 3GPP 3rd Generation Partnership Program

[0026] AMF Access and Mobility Management Function

[0027] AS Access Stratum

[0028] ON Core NetworkeNB LTE Base Station, E-Utran NodeB

[0029] gNB 5G Base Station, 5G NodeB

[0030] GW Gateway

[0031] ID Identifier

[0032] loT Internet of Things

[0033] ISL Inter Satellite Link

[0034] 5G / NG 5thGeneration, Next Generation

[0035] NTN Non-Terrestrial Networks

[0036] PDU Processing Data Unit

[0037] RAN Radio Access Network

[0038] RNTI Radio Network Temporary Identifier

[0039] RRC Radio Resource Control

[0040] RRM Radio Resource Management

[0041] SAT Satellite

[0042] SIB System Information Block

[0043] SMTC SSB-based RRM Measurement Timing Configuration

[0044] SSB Synchronization Signal Block

[0045] UE User Equipment

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] A better understanding of the subject disclosure can be obtained when the following detailed description of various embodiments is considered in conjunction with the following drawings, in which:

[0048] FIG. 1 shows a schematic diagram of an example wireless earth-bound network;

[0049] FIG. 2 shows a schematic diagram of an example wireless device;

[0050] FIG. 3 shows a schematic diagram of an example network node;

[0051] FIG. 4 shows a schematic diagram of an example non-terrestrial-network (NTN);

[0052] FIG. 5 illustrates a situation of satellite switching according to this disclosure.

[0053] FIG. 6 highlights options discussed in the prior art and the solution according to this disclosure.

[0054] FIG. 7A is a flow chart of the basic method executed by a UE according to this disclosure. FIG. 7B is a flow chart of the basic method executed by a source satellite according to this disclosure. FIG. 70 is a flow chart of the basic method executed by a target satellite according to this disclosure.

[0055] FIG. 8 depicts a message flow diagram of a satellite switching according to the disclosure.DETAILED DESCRIPTION

[0056] The examples and embodiments set forth below represent information to enable those skilled in the art to practice the subject disclosure. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the description and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the description.

[0057] In the following description, numerous specific details are set forth. However, it is understood that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of the description. Those of ordinary skill in the art, with the included description, will be able to implement appropriate functionality without undue experimentation.

[0058] References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0059] As used herein, "plurality" means two or more. As used herein, a "set" of items may include one or more of such items. As used herein, whether in the subject disclosure or the claims, the terms "comprising", "including", "carrying", "having", "containing", "involving", and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of' and "consisting essentially of', respectively, are closed or semi-closed transitional phrases with respect to claims. Use of ordinal terms such as "first", "second", "third", etc., in the claims or the subject disclosure to modify an element does not by itself connote any priority, precedence, or order of one element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the elements. As used herein, "and / or" and "at least one of" means that the listed items are alternatives, but the alternatives also include any combination of the listed items. Before explaining the examples according to the subject disclosure in detail, certain general principles of a wireless communication system are briefly explained with reference to FIGS. 1 to 4 to assist in understanding the technology underlying the described examples.FIG. 1 illustrates an example of an earth-bound wireless network 100 that may be used for wireless communications. It is noted that - although this example relates to earth bound wireless communication, many principles also apply to the non-terrestrial setup, which is further explained in FIG. 4.

[0060] Wireless network 100 includes wireless devices, such as UEs 110 (e.g., 110A-110B), and network nodes, such as radio access nodes 120 (e.g., 120A-120B) (e.g., eNBs, gNBs, etc.), connected to one or more network nodes 130 over an interconnecting network 125. The network 100 may use any suitable deployment scenarios. UEs 110 within coverage area 115 may each be capable of communicating directly with radio access nodes 120 over a wireless or air interface. In some embodiments, UEs 110 may also be capable of communicating with each other via D2D communication.

[0061] As an example, UE 110A may communicate with radio access node 120A over a wireless or air interface. That is, UE 110A may transmit wireless signals to and / or receive wireless signals from radio access node 120A. The wireless signals may contain voice traffic, data traffic, control signals, and / or any other suitable information. If a UE moves in the area, it may start communication (or more generally connection) with radio access node 120B and terminate communication (or more generally connection) with radio access node 120B. In such cases, radio access node 120A may be denoted as source base station or last serving base station and radio access node 120B may be denoted as target base station or new serving base station.

[0062] As used herein, the term "user equipment" (UE) has the full breadth of its ordinary meaning and may refer to any type of wireless device which can communicate with a network node and / or with another UE in a cellular or mobile or wireless communication system. Examples of UE are target device, D2D UE, machine type UE or UE capable of machine-to-machine (M2M) communication, personal digital assistant, tablet, mobile terminal, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, ProSe UE, vehicle-to-vehicle (V2V) UE, V2X UE, MTC UE, eMTC UE, FeMTC UE, UE Cat 0, UE Cat Ml, narrow band loT (NB-loT) UE, UE Cat NB1, etc. Example embodimentsof a UE are described in more detail below with respect to FIG. 2.

[0063] In some embodiments, an area of wireless signal coverage 115 associated with a radio access node 120 may be referred to as a cell. However, particularly with respect to the 5thgeneration (5G) / New Radio (NR) mobile communication concepts, beams, may be used within cells for communication. This principle is also applied for NTN, as can be seen in FIG. 4.

[0064] With respect to a beam-based mobile communication system, the radio access node 120 (base station) may transmit a beamformed signal to the UE 110 in one or more transmit directions (transmission beam, Tx beam). The UE 110 may receive the beamformed signal from the base station 120 in one or more receive directions (reception beam, Rx beam). The UE 110 may also transmit a beamformed signal to the base station 120 in one or more directions and the base station 120 may receive the beamformed signalfrom the UE 110 in one or more directions. The base station 120 and the UE 110 may determine the best receive and transmit directions, e.g., best in the sense of these directions leading to the highest link quality or fulfilling other quality conditions in the most suitable manner, for each of the base station / UE pairs. The interconnecting network 125 may refer to any interconnecting system capable of transmitting audio, video, signals, data, messages, etc., or any combination of the preceding. The interconnecting network 125 may include all or a portion of a public switched telephone network (PSTN), a public or private data network, a local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a local, regional, or global communication or computer network such as the Internet, a wireline or wireless network, an enterprise intranet, or any other suitable communication link, including combinations thereof. In some embodiments, the network node 130 may be a core network node, managing the establishment of communication sessions and other various other functionalities for UEs 110. Examples of network node 130 may include mobile switching center (MSC), MME, serving gateway (SGW), packet data network gateway (PGW), operation and maintenance (O&M), operations support system (OSS), SON, positioning node (e.g., Enhanced Serving Mobile Location Center, E-SMLC), location server node, MDT node, etc. UEs 110 may exchange certain signals with the network node 130 using the non-access stratum (NAS) layer. In non-access stratum signaling, signals between UEs 110 and the network node 130 may be transparently passed through the radio access network. In some embodiments, radio access nodes 120 may interface with one or more network nodes 130 over an internode interface.

[0065] As used herein, the term "network node" has the full breadth of its ordinary meaning and may correspond to any type of radio access node (or radio network node) or any network node, which can communicate with a UE and / or with another network node in a cellular or mobile or wireless communication system. Examples of network nodes are NodeB, MeNB, SeNB, a network node may belonging to MCG or SCG, base station (BS), multi-standard radio (MSR) radio access node such as MSR BS, eNodeB, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission point, transmission node, RRU, RRH, node in distributed antenna system (DAS), core network node (e.g., MSC, MME, etc.), O&M, OSS, Self-organizing Network (SON), positioning node (e.g., E-SMLC), MDT, test equipment, etc. Example embodiments of a network node are described in more detail below with respect to FIG. 3.

[0066] In some embodiments, radio access node 120 may be a distributed radio access node. The components of the radio access node 120, and their associated functions, may be separated into two main units (or sub-radio network nodes) which may be referred to as the central unit (CU) and the distributed unit (DU). Different distributed radio network node architectures are possible. For instance, in some architectures, a DU may be connected to a CU via dedicated wired or wireless link (e.g., an optical fiber cable) while in other architectures, a DU may be connected a CU via a transport network. Also, how the various functionsof the radio access node 120 are separated between the CU(s) and DU(s) may vary depending on the chosen architecture.

[0067] In some embodiments, radio access nodes 120 may communicate with each other over terrestrial or other connections. The communication between the radio access nodes 120 may, e.g., in a 5G / NR communication system may be achieved by using an Xn interface connecting the radio access nodes 120.

[0068] Exemplary wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A 3GPP based development is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology (RAT). The various development stages of the 3GPP specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE (LTE-A) employs a radio mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a core network known as the Evolved Packet Core (EPC). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features such as user plane Packet Data Convergence / Radio Link Control / Medium Access Control / Physical layer protocol (PDCP / RLC / MAC / PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other RAT examples comprise those provided by base stations of systems that are based on technologies such as WLAN and / or Worldwide Interoperability for Microwave Access (WiMax). A base station can provide coverage for an entire cell or similar radio service area. Core network elements include Mobility Management Entity (MME), Serving Gateway (S-GW) and Packet Gateway (P-GW).

[0069] An example of a suitable communications system is the 5G or NR concept. Network architecture in NR may be similar to that of LTE-A. Base stations of NR systems may be known as next generation Node Bs (gNBs). Changes to the network architecture may depend on the need to support various radio technologies and finer Quality of Service (QoS) support, and some on-demand requirements for QoS levels to support Quality of Experience (QoE) of user point of view. Also network aware services and applications, and service and application aware networks may bring changes to the architecture. Those are related to Information Centric Network (ICN) and User-Centric Content Delivery Network (UC-CDN) approaches. NR may use multiple input-multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates. It is noted that the concepts disclosed herein are not limited to LTE or, in particular, with respect to NTN to 5G or NR but may also be applied similarly in future networks, e.g., 6G as currently discussed by 3GPP and beyond.Future networks may utilize network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes, or hosts. It should also be understood that the distribution of labor between core network operations and base station operations may differ from that of the LTE or even be non-existent.

[0070] An example 5G core network (CN) comprises functional entities. The CN is connected to a UE via the radio access network (RAN). An UPF (User Plane Function) whose role is called PSA (PDU Session Anchor) may be responsible for forwarding frames back and forth between the DN (data network) and the tunnels established over the 5G towards the UEs exchanging traffic with the data network (DN). The UPF is controlled by an SMF (Session Management Function) that receives policies from a PCF (Policy Control Function). The CN may also include an AMF (Access & Mobility Function).

[0071] Generally, all concepts disclosed herein may be applicable to different communication networks, comprising but not limited to LTE, LTE-A, 5G, 5G advanced, 6G, and other future or already implemented networks.

[0072] FIG. 2 is a schematic diagram of an apparatus for the UE. In an embodiment, the apparatus may comprise the UE, in yet another embodiment the apparatus is comprised in the UE, and in another embodiment the apparatus is the UE. The apparatus may comprise a wireless device. The apparatus may comprise at least one processor 220 and at least one memory 230 storing computer program instructions that, when executed by the at least one processor 220, cause the apparatus to carry out the embodiments of the UE 110 described herein. UE 110 includes a transceiver 210, processor 220, memory 230, and a network interface 240. In some embodiments, the transceiver 210 facilitates transmitting wireless signals to and receiving wireless signals from radio access node 120 (e.g., via transmitter(s) (Tx), receiver(s) (Rx) and antenna(s)). The processor 220 executes instructions to provide some or all of the functionalities described herein as being provided by UE 110, and the memory 230 stores the instructions executed by the processor 220. In some embodiments, the processor 220 and the memory 230 form processing circuitry.

[0073] The processor 220 may include any suitable combination of hardware to execute instructions and manipulate data to perform some or all of the described functions of UE 110 described herein. In some embodiments, the processor 220 may include, for example, one or more computers, one or more centralprocessing units (CPUs), one or more microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs) and / or other logic.

[0074] The memory 230 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and / or other instructions capable of being executed by a processor 220. Examples of memory 230 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or or any other volatile or non-volatile, non- transitory computer-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by the processor 220 of UE 110. For example, the memory 230 includes computer program code causing the processor 220 to perform processing according to the methods described herein.

[0075] The network interface 240 is communicatively coupled to the processor 220 and may refer to any suitable device operable to receive input for UE 110, send output from UE 110, perform suitable processing of the input or output or both, communicate to other devices, or any combination thereof. The network interface 240 may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network. Other embodiments of UE 110 may include additional components beyond those shown in FIG. 2 that may be responsible for providing certain aspects of the wireless device’s functionalities, including any of the functionalities described herein and / or any additional functionalities (including any functionality necessary to support the mechanisms according to the subject disclosure). As an example, UE 110 may include input devices and circuits, output devices, and one or more synchronization units or circuits, which may be part of the processor 220. Input devices include mechanisms for entry of data into UE 110. For example, input devices may include input mechanisms, such as a microphone, input elements, a display, etc. Output devices may include mechanisms for outputting data in audio, video and / or hard copy format. For example, output devices may include a speaker, a display, etc.

[0076] In some embodiments, the wireless device UE 110 may comprise a series of modules configured to implement the functionalities of the wireless device described herein. Moreover, in some embodiments, the UE 110 may also comprise means for the functionalities described herein.

[0077] It will be appreciated that the various modules may be implemented as combination of hardware and software, for instance, the processor, memory, and transceiver(s) of UE 110 shown in FIG. 2. Some embodiments may also include additional modules to support additional and / or optional functionalities. FIG. 3 is a schematic diagram of an example of an apparatus for a radio access node 120, in particular, an NTN node as described herein, or network node 130. The apparatus may comprise at least one processor 320 and at least one memory 330 storing computer program instructions that, when executedby the at least one processor 320, cause the apparatus to carry out the embodiments of the network node 130 or radio access node 120 described herein. The example radio access node 120 or network node 130 may include one or more of a transceiver 310, processor 320, memory 330, and network interface 340. In some embodiments, the transceiver 310 facilitates transmitting wireless signals to and receiving wireless signals from wireless devices, such as UE 110 (e.g., via transmitter(s) (Tx), receiver(s) (Rx), and antenna(s)). The processor 320 executes instructions to provide some or all of the functionalities described herein as being provided by the radio access node 120 or the network node 130, the memory 330 stores the instructions executed by the processor 320. In some embodiments, the processor 320 and the memory 330 form processing circuitry. The network interface 340 can communicate signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), core network nodes or radio network controllers, etc.

[0078] The processor 320 can include any suitable combination of hardware to execute instructions and manipulate data to perform some or all of the described functions of the radio access node 120 or the network node 130, such as those described herein. In some embodiments, the processor 320 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs) and / or other logic.

[0079] The memory 330 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and / or other instructions capable of being executed by a processor 320. Examples of memory 330 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or or any other volatile or non-volatile, non- transitory computer-readable and / or computer-executable memory devices that store information. For example, the memory 330 includes computer program code causing the processor 320 to perform processing according to the methods described herein.

[0080] In some embodiments, the network interface 340 is communicatively coupled to the processor 320 and may refer to any suitable device operable to receive input for the radio access node 120 or the network node 130, send output from the radio access node 120 or the network node 130, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. The network interface 340 may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.Other embodiments of the radio access node 120 or the network node 130 can include additional components beyond those shown in FIG. 3 that may be responsible for providing certain aspects of the node’s functionalities, including any of the functionalities described herein and / or any additional functionalities (including any functionality necessary to support the solutions described herein). The various different types of radio access nodes or network nodes may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

[0081] Processors, interfaces, and memory similar to those described with respect to FIG. 3 may be included in other nodes (such as UE 110, radio access node 120, etc.). Other nodes may optionally include or not include a wireless interface (such as the transceiver described in FIG. 3).

[0082] In some embodiments, the radio access node 120 or the network node 130 may comprise a series of modules configured to implement the functionalities of the radio access node 120 or the network node 130 described herein. Moreover, in some embodiments, the radio access node 120 or the network node 130 may also comprise means for the functionalities described herein.

[0083] It will be appreciated that the various modules may be implemented as combination of hardware and software, for instance, the processor, memory, and transceiver(s) of the radio access node 120 or the network node 130 shown in FIG. 3. Some embodiments may also include additional modules to support additional and / or optional functionalities.

[0084] FIG. 4 now presents a further development of the earth-bound wireless communication system of FIG. 1, namely, a wireless non-terrestrial network (NTN). An NTN refers to a network, or a segment of networks, using radio frequency (RF) resources on board of a satellite or UAS platform.

[0085] Practically speaking, an NTN refers to at least one UE 110 or loT device which is interfaced to a radio access node via a satellite 401 (also referred to herein as NTN node 401) via a service link 421. The NTN node 401 is interfaced to an NTN gateway 402 (also referred to as ground gNB 402) via a feeder link 422, and the NTN gateway 402 is interfaced to a core network node 130 for accessing a data network 403. The combination of the NTN node 401 and the NTN gateway 402 may be considered to be functionally equal to an earth-bound radio access node 120 as shown in FIG. 1. Particularly, the components described with respect to FIG. 3 can be equally present in NTN node 401 and / or NTN gateway 402. There are different types of satellites that can be used for deployment and differ by the orbit, in which they are located. The geostationary earth orbit (GEO) has an altitude of about 36,000 km. GEO satellites match the rotation of the earth as they travel, and so remain above the same point on the ground. Hundreds of GEO satellites are in orbit today and already serving different purposes. The medium earth orbit (MEO) has an altitude of about 7,000 to 25,000 km. MEO satellites have historically been used for geographicpositioning and other navigation applications. The low earth orbit (LEO) has an altitude of about 300 to 1,500 km. LEO is densely populated with thousands of LEO satellites in operation.

[0086] A cell 411 of an NTN node 401 may, thus, be quite large. A cell may be composed of one or more beams 412, similar to what has been described above for the earth-bound wireless setup. The beam footprint size, i.e., size of the footprint of all beams 412 of the cell 411, thereby reflects the whole coverage area of the cell, which is, e.g., 100 to 1 ,000 km for a LEO satellite, 100 to 1 ,000 km for a MEO satellite, and 200 to 3,500 km for a GEO satellite. There exist two type of NTN cells, namely, Earth Fixed Cells (EFC) and Earth Moving Cells (EMC). The EFC stick to the same area on the earth, i.e., the satellites use steerable beams and hand over or switch the cell to other satellites when moving too far away from the serviced area (which is particularly the case for LEO and MEO satellites). The EMC moves with its respective satellite. In this disclosure, EFCs are mainly considered although some aspects - as apparent to the skilled person - are at least partially also applicable to EMCs.

[0087] FIG. 5 now illustrates a situation of satellite switching of a cell 411 from a source satellite 401 A to a target satellite 401 B. Arrow 501 shows the movement direction of the satellites 401 A, 401 B and arrow 502 the handover or switching direction. The UE 110 receives information from the source satellite 401 A over service link 421 A and from the target satellite 401 B over service link 421 B.

[0088] In Release 18, 3GPP has introduced the concept of satellite switching with re-synchronization (re-sync), which is explained with respect to Fig. 5 now further. The basic concept is that a cell 411 that covers an area on the earth is switched from one satellite to another (i.e., from the source satellite 401 Ato the target satellite 402B) without changes of the current Physical Cell Indicator (PCI), i.e., the cell identity remains the same. A working principle is that after a satellite switching, the serving gNB 402 (on ground) does not change and, therefore, the (majority of the) cell configuration can be maintained without changing the PCI, frequency, and / or other cell configuration parameters, such as the information element (IE) servingCellconfigCommon. This means that the satellite switching is almost transparent for the UE 110 on a logical level, except for some re-synchronization needed on the physical level.

[0089] A change of satellite 401 A, 401 B without PCI modification may only achievable if certain conditions are met. Moreover, interruption at the UE side may not be avoidable. However, it is advantageous for transparent architectures, especially for cases where the gNB on the ground 402 is maintained the same before and after the change on the serving satellite (gNB on ground 401 is expected to have feeder links to both current satellite 401 A that is serving the UE 110 and to the new satellite 401 B that is going to serve the UE for the next period of time (according to the satellite’s movement around the globe)). FIG. 5 shows an example of satellite switching where most of the cell configuration can be kept unchanged in a transparent-based EFC deployment. The following steps may take place during the satellite switching: 1) The UE 110, which is considered to be (almost) stationary, is being served by source satellite 401 A incell 411. 2) As the source satellite 401 A moves away from the UE 110 and the served cell 411 and the target satellite 401 B gets closer, the network indicates to the UE 110 when the satellite switching will occur and how to perform re-synchronization to the new satellite 401 B. It is noted that the cell areas of the satellites 401 A, 401 B likely have a large overlap but may not be completely identical as shown in FIG.

[0090] 5 with cell 411. 3) Once the target satellite 401 B takes over the cell 411, the UE 110 performs DL / UL synchronization operations towards the target satellite 401 B to re-connect.

[0091] Even though the UE 110 is being served by a new satellite, i.e., the target satellite 401 B, the serving gNB on ground 402 does not change, which allows to keep the cell configuration. The satellites 401 A, 401 B are configured with the same PCI, same UE context and / or same protocol stack (including SSB generation, system timing, coding / decoding, modulation / demodulation, same CORESET configuration, switch routing, and the like). However, the two satellites 401 A, 401 B introduce, from a UE’s perspective, different frequency (i.e., Doppler effect) and timing drifts and offsets.

[0092] In general, satellite switching can be broken down in two scenarios: i) hard satellite switching and ii) soft satellite switching. The latter considers a certain (areal) overlap of the NTN cell 411 radiated by the source satellite 401 A and the target satellite 401 B, while the former considers no overlapping between an old and a new cell of the UE 110. For the hard satellite switching, the UE 110 will anyway observe a certain interruption time to pre-compensate frequency and timing of the new cell. For the soft satellite switching, in which the configuration of the cell 411 remains the same, it may be assumed that - during a transition period of time - the source satellite 401 A and the target satellite 401 B are transmitting synchronization signal blocks (SSBs) at the same time but with a different propagation delay. In theory, since the SSBs are sent with same PCI but with different time / frequency offsets from the two satellites 401 A, 401 B, a UE 110 may be enabled to gracefully switch to a new (incoming) satellite. However, there are difficulties as is explained in the following

[0093] In current deployments and as non-limiting example, all the parameters needed for the UE 110 to perform the satellite switching with re-sync (new synchronization to the target satellite 401 B) are provided in system information block SIB19. SIB19 defines a time until the source satellite provides service of the area (i.e., the cell 411) in parameter t-Service and the satSwitchWithReSync information element (IE), which contains further relevant information for the switch. The UE 110 is thereby provided with the configuration of the target satellite 401 B such that UE 110 can perform relevant time and frequency synchronization to switch to the target satellite 401 B. More specifically, the satSwitchWithReSync IE contains the ephemeris information of the target satellite 401 B (e.g., satellite position and directional velocity vector in space) as well as information on the feeder link 422 (e.g., needed for doing timing advance calculations at the UE side).The satSwitch With ReSync IE also provides parameters t-ServiceStart and ssb-timeOffset. The parameter ssb-timeOffset indicates the time offset of the SSB from target satellite 401 B at its uplink time synchronization reference point with respect to the SSB from source satellite 401 A at its uplink time synchronization reference point. It is given in number of subframes. The parameter t-ServiceStart indicates the time information on when the target satellite 401 B is going to start serving the area currently covered by the serving satellite 401 A. The field indicates a time in multiples of 10 ms after 00:00:00 on Gregorian calendar date 1st January 1900 (midnight between Sunday, December 31, 1899, and Monday, January 1 , 1900). The exact start time is between the time indicated by the value of this field minus 1 and the time indicated by the value of this field. The reference point for t-ServiceStart is the uplink time synchronization reference point of the serving satellite 401 A.

[0094] At t-ServiceStart, the UE 110 knows that the target satellite 401 B is available, and therefore initiates measurements to acquire relevant timing information of the target satellite 401 B. The UE 110 then has to finish the measurements and be connected to the target satellite 401 B (as defined in 3GPP Technical Specifications). Particularly, it is defined that, during the time period from t-ServiceStart to t-Service, scheduling restriction is allowed, with the exception that the locations of SSB symbols of target satellite 401 B, where scheduling restriction applies, are determined by the periodicity and location of SSB of the source satellite 401 A, the ssb-TimeOffset and the difference between propagation delay of the serving satellite 401 A and the target satellite 401 B counted from the ssb-TimeOffset reference point as defined in 3GPP Technical Specifications to the UE 110. This indicates that the UE 110 shall consider the difference in the propagation delay between the UE 110 and the two different satellites 401 A, 401 B, and that the ssb-TimeOffset is needed for the UE to track the SSBs of the target satellite 401 B and perform the measurements before moving to the target cell.

[0095] FIG. 6 highlights options for re-sync as discussed in the prior art and the solution according to this disclosure for enabling a soft satellite switch. Three options and different understandings of the ssb-TimeOffset application were currently discussed in the RAN2 meeting #128 (of November 2024) and have been summarized in 3GPP R2-2410971 (Huawei, HiSilicon). These three options are now explained with respect to FIG. 6 and compared to the solution presented herein.

[0096] FIG. 6 depicts in 601 the timing of the source satellite 401 A (starting with subframe number 0 on the left) and the transmission of the usual, i.e., the cell-defining SSBs 611. The transmission of the SSBs are standardized with respect to the timing of a cell, i.e., with respect to the subframe number 0. In this example, the SSBs 611 are transmitted at the beginning of subframes 1, 5, 9 etc., meaning that they have a periodicity of 4 subframes. Therefore, the transmission timing of the SSBs 611 can usually not be changed. However, for acquiring synchronization with a new satellite 401 B, it is necessary that the SSBs 611 of the old satellite 401 A and the SSBs of the new satellite 401 B can be distinguished during the timeperiod between t-ServiceStart and t-Service, i.e., they cannot be transmitted at the same time and the same frequency.

[0097] The first option for transmitting the SSB 612 from the target satellite 401 B discussed is presented in 602. In this option, a shifted cell timing is suggested. The ssb-TimeOffset is assumed to indicate a shift in the real transmission timing (shown with arrow 622) of the target satellite 401 B. The goal is to ensure the SSBs 611 and 612 do not overlap at the UE 110. After the satellite switching is complete, the UE 110 has to adjust its own SSB-based RRM Measurement Timing Configuration window (SMTC window) to follow the new timing of the cell 411 provided now by the target satellite 401 B. Hence, after every satellite switching, the UE 110 has to adapt its SMTC window.

[0098] The second option for transmitting the SSB 613 from the target satellite 401 B discussed is presented in 603. In this option, a shifted SSB pattern is suggested. The ssb-TimeOffset is assumed to indicate a shift in the position of the SSBs 613 (shown with arrow 623) in relation to subframe 0 within a frame. In this case, after the resynchronization, the UE 110 would still need to update the SMTC configuration, in order to adapt to the modified SSB position which is affected by both, the SSB location in the frame and the total propagation time.

[0099] The third option for transmitting the SSB 614 from the target satellite 401 B discussed is presented in 604. In this option, a temporarily shifted SSB pattern is suggested. The SSB is only shifted (shown with arrow 624) for the interval between t-ServiceStart (when the target satellite 401 B initiates the transmission of SSBs 614) and t-Service (when the source satellite 401 A stops transmitting SSBs 611 for the same geographical area). Although this indicates that there may be no need of SMTC adjustment after t-Service, this is not entirely true. There will be a difference between source and target satellite timing due to the propagation delay from the different satellites to the UE 110. Moreover, there is a need for the target satellite 401 B to adapt its SSB transmission timing for SSBs 614’ after t-Service (shown with arrow 624’). Options two and three face a similar problem, namely, that SSBs can usually not be moved within a frame. They have pre-defined positions according to specification (e.g., defined in 3GPP Technical Specifications), which are hard-coded and not a matter of configuration. It is, thus, currently not possible to implement these two options.

[0100] The solution presented herein for re-synchronization with the target satellite 401 B overcomes these issues and is presented in 605. This solution is based on non-cell-defining SSBs (NCD-SSB) 635 and temporarily muting of (common, i.e., cell-defining) SSBs 615 coming from the target satellite 401 B.

[0101] NCD-SSBs are transmission of synchronization signal blocks similar to the original, cell-defining SSBs but which are not associated with Remaining Minimum System Information (RMSI). This means that there is no SIB1 transmission associated to these NCD-SSBs and that they are only used to identify the cell or to facilitate initial cell search, i.e., usually being configured only for UEs 110 in connected mode. Themain purpose of NCD-SSBs is to be capable of providing DL synchronization reference through synchronization signals, for example, in bandwidth parts that do not contain the cell-defining SSBs. Their initial intent of NCD-SSBs was to facilitate connectivity for REDCAP UEs (whose monitoring bandwidth might be limited) outside of the initial BWP.

[0102] The use of NCD-SSBs in soft satellite switching may be as follows. A source satellite 401 A provides a modified satellite switching information, which contains the configuration of the transient NCD-SSBs 635. Since the source satellite 401 A and the target satellite 401 B may be co-located, they both have all information of the satellite switching information at hand (this is also sensible as the target satellite 401 B is about to take all operation over, e.g., including security context, HARQ operation, etc.).Those NCD-SSBs 635 are to be broadcasted by the target satellite 401 B and are implicitly (between the given first and second points in time as pre-defined in standard documents / technical specifications) and / or explicitly (by defining another time period) defined to be valid only between a first point in time and a second point in time, e.g., between t-ServiceStart and t-Service.

[0103] This may be implemented by establishing a first point in time (e.g., t-serviceStart), when the target satellite 401 B starts the transmission using NCD-SSBs 635, either in pre-configured positions / frequencies or configured by indicating a timing offset (shown with arrow 625) and / or a frequency for transmission. The transmission of regular SSBs 615 is suspended (or not initiated yet) in the target satellite 401 B during the time period of transmission of NCD-SSBs 635.

[0104] The UE 110 may acquire the NCD-SSB 635 for synchronizing into the target satellite 401 B and finalize the switching according to specified requirements, e.g., when the synchronization was successful. At the second point in time, e.g., t-Service, the source satellite 401 A stops broadcasting in this cell, whereas the transmission coming from the target satellite stops the NCD-SSB 635 transmission and initiates transmission of regular (cell-defining) SSB 615’. The UE’s SMTC configuration does not need to be changed but UE 110 adjusts the timing of the SMTC window according to the synchronization. Hence, the herein presented solution does neither require a reconfiguration of the SMTC window at the UE 110 nor a change in transmission timing of regular cell-defining SSBs.

[0105] The target satellite 401 B initiates the transmission of cell information at t-serviceStart but with muted / suspended SSBs 615 and NCD-SSBs 635 being transmitted. Only after the source satellite 401 A ceases serving the cell (t-Service), the target satellite 401 B initiates the transmission of the cell-defining SSBs 615’ and ceases the (now unnecessary) NCD-SSB 635 transmissions.

[0106] One advantage of this deployment is that it minimizes the interruption time at the UE 110, as the NCD-SSBs 635 can be allocated in orthogonal resources (in frequency domain) to the cell-defining SSBs 611 of the source satellite 401 A, which alleviates any concern of the collision between SSBs with same identity transmitted by the source satellite 401 A and target satellite 401 B.The expected change of operation at the UE side is that a UE 110 targeting soft satellite switch with resynchronization and being connected to a source satellite 401 A, observes that a satellite switch will be imminent (by detecting / receiving t-ServiceStart and other satellite switching information), starts monitoring for and synchronizing according to the configured NCD-SSBs 635 at the expected locations (derived from NCD-SSB configuration, e.g., in the satellite switching information, as well as the ephemeris of the target satellite 401 B), and updates its receive (and transmit) timing parameters att-Service without interruption of service.

[0107] FIG. 7A is a flow chart of the basic method executed by a UE 110 according to this disclosure. Moreover, the method may be implemented by a user equipment, UE 110, comprising at least one processor and at least one memory (e.g., as described with respect to FIG. 2) storing instructions that, when executed by the at least one processor, cause the UE 110 at least to execute the method as described herein. The method starts in box 701 with receiving satellite switching information for soft satellite switching in a cell 411 from a source satellite 401 A to a target satellite 401 B , wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for an NCD-SSB 635 of the target satellite 401 A. The first point in time may indicate when the target satellite 401 B starts service of the cell 411 (e.g., t-ServiceStart), wherein the second point in time may indicate when the source satellite 401 A stops service of the cell 411 (e.g., t-Service). In some embodiments, the NCD-SSB configuration may comprise a time offset with respect to a cell-defining SSB 611 of the source satellite 401 A and / or a frequency location of the NCD-SSB 635. The satellite switching information may be transmitted within a system information block of the source satellite 401 A, e.g., within SIB 19 as described above.

[0108] The method proceeds in box 702 to acquiring synchronization with the target satellite 401 B using at least one NCD-SSB 635 between the first point in time and the second point in time. In some embodiments, the UE 110 may perform NCD-SSB measurements according to the satellite switching information for acquiring synchronization. The at least one NCD-SSB 635 of the target satellite 401 B may be allocated in orthogonal resources with respect to a cell-defining SSB 611 of the source satellite 401 A.

[0109] The methods ends in box 703 with switching to the target satellite 401 B for continued service of the cell 411 based on the acquired synchronization. In some embodiments, the UE 110 may partially acquire synchronization also based on based on at least one cell-defining SSB 615’ (e.g., because full resynchronization could not be finished in the transition time period between the first and the second point in time based solely on the NCD-SSBs 635). In some embodiments, the UE 110 may maintain synchronization with the target satellite 401 B based on at least one cell-defining SSB 615’ transmitted by the target satellite after the second point in time.In some embodiments, the UE 110 comprises means for receiving satellite switching information for soft satellite switching in a cell from a source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite, means for acquiring synchronization with the target satellite using at least one NCD-SSB between the first point in time and the second point in time, and means for switching to the target satellite for continued service of the cell based on the acquired synchronization.

[0110] FIG. 7B is a flow chart of the basic method executed by a source satellite 401 A according to this disclosure. The method may be implemented by satellite in a non-terrestrial communication network being a source satellite 401 A for soft satellite switching in a cell 411, which comprises at least one processor and at least one memory (e.g., as described with respect to FIG. 3) storing instructions that, when executed by the at least one processor, cause the satellite at least to execute the method as described herein.

[0111] The method starts in box 711 with transmitting satellite switching information to a UE 110 (the information is for the soft satellite switching from the source satellite 401 A to a target satellite 401 B), wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a NCD- SSB 635 of the target satellite 401 B. The first point in time may indicate when the target satellite 401 B starts service of the cell 411 (e.g., t-ServiceStart), wherein the second point in time may indicate when the source satellite 401 A stops service of the cell 411 (e.g., t-Service).

[0112] In some embodiments, the NCD-SSB configuration may comprise a time offset with respect to a celldefining SSB 611 of the source satellite 401 A and / or a frequency location of the NCD-SSB 635. The satellite switching information may be transmitted within a system information block of the source satellite 401 A, e.g., within SIB 19 as described above. The at least one NCD-SSB 635 of the target satellite 401 B may be allocated in orthogonal resources with respect to a cell-defining SSB 611 of the source satellite 401 A. The method proceeds in box 712 to stopping transmission of cell-defining SSBs 611 and stopping provision of service of the cell 411 at the second point in time. Hence, the source satellite 401 A hands over the cell 411 to the target satellite 401 B.

[0113] In some embodiments, the satellite comprises means for transmitting satellite switching information for the soft satellite switching from the source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite, and means for stopping transmission of cell-defining SSBs and stopping provision of service of the cell at the second point in time. FIG. 7C is a flow chart of the basic method executed by a target satellite according to this disclosure. The method may be implemented by satellite in a non-terrestrial communication network being a targetsatellite 401 B for soft satellite switching in a cell 411, which comprises at least one processor and at least one memory (e.g., as described with respect to FIG. 3) storing instructions that, when executed by the at least one processor, cause the satellite at least to execute the method as described herein.

[0114] The method starts in box 721 with transmitting at least one NCD-SSB 635 between a first point in time and a second point in time and in box 722 with suspending transmission of cell-defining SSBs 615 between the first point in time and the second point in time.

[0115] At the second point in time, the method proceeds to stopping transmission of the at least one NCD-SSB 635, resuming transmission of the cell-defining SSBs 615’, and starting provision of service of the cell 411 at the second point in time.

[0116] The first point in time may indicate when the target satellite 401 B starts service of the cell 411 (e.g., t-ServiceStart), wherein the second point in time may indicate when the source satellite 401 A stops service of the cell 411 (e.g., t-Service). In some embodiments, the at least one NCD-SSB 635 may be allocated in orthogonal resources with respect to a cell-defining SSB 611 of the source satellite 401 A.

[0117] In some embodiments, the satellite comprises means for transmitting at least one non-cell-defining, NCD, synchronization signal block, SSB, between a first point in time and a second point in time, means for suspending transmission of cell-defining SSBs between the first point in time and the second point in time, and means for stopping transmission of the at least one NCD-SSB, resuming transmission of the celldefining SSBs, and starting provision of service of the cell at the second point in time.

[0118] FIG. 8 depicts a message flow diagram of a satellite switching according to the disclosure. The UE 110 is in connected mode with the source satellite 401 A (as shown with arrow 801) and receives satellite switch information (e.g., in SIB19 as described above), which defines a transient NCD-SSB configuration for the transition phase between a first point in time 811, e.g., indicated by t-ServiceStart, and a second point in time 812, e.g., indicated by t-Service. The transmission of the satellite switch information is shown with arrow 802.

[0119] The UE 110 then knows that satellite switching will occur and NCD-SSB measurements are configured by the network at the UE 110 (shown with rectangle 803). After the first point of time 811, the target satellite 401 B transmits one or more NCD-SSBs 635 and mutes at the same time common, i.e., celldefining SSBs, which is shown with arrow 804. The UE 110 searches and detects the one or more NCD-SSBs 635 as is shown with rectangle 805. Moreover, as indicated with arrow 806, the connected mode exchange is still between the source satellite 401 A and the UE 110 during this time. Hence, cell-defining SSBs 611 are still transmitted from the source satellite 401 A.

[0120] After the second point in time 812, the target cell 401 B resumes / starts transmission of cell-defining SSBs 615’ and mutes the transmission of the NCD-SSBs 635 (shown with arrow 807). The connected modeexchange would then occur between the target satellite 401 B and the UE 110 (not shown) since the source satellite 401 A then has terminated service of the cell 411.

[0121] The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of the subject disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this disclosure will still fall within the scope of the subject disclosure as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

Claims:

1. A user equipment, UE, comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to:- receive satellite switching information for soft satellite switching in a cell from a source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite;- acquire synchronization with the target satellite using at least one NCD-SSB between the first point in time and the second point in time; and- switch to the target satellite for continued service of the cell based on the acquired synchronization.

2. The UE of claim 1 , wherein the UE is further caused to perform NCD-SSB measurements according to the satellite switching information for acquiring synchronization.

3. The UE of claim 1 or claim 2, wherein the UE is further caused to partially acquire and / or maintain synchronization with the target satellite based on at least one cell-defining SSB transmitted by the target satellite after the second point in time.

4. The UE of any one of claims 1 to 3, wherein the first point in time indicates when the target satellite starts service of the cell, and wherein the second point in time indicates when the source satellite stops service of the cell.

5. The UE of any one of claims 1 to 4, wherein the NCD-SSB configuration comprises a time offset with respect to a cell-defining SSB of the source satellite and / or a frequency location of the NCD- SSB.

6. The UE of any one of claims 1 to 5, wherein the satellite switching information is transmitted within a system information block of the source satellite.

7. The UE of any one of claims 1 to 6, wherein the at least one NCD-SSB of the target satellite is allocated in orthogonal resources with respect to a cell-defining SSB of the source satellite.

8. A satellite in a non-terrestrial communication network being a source satellite for soft satellite switching in a cell comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the satellite at least to:- transmit satellite switching information for the soft satellite switching from the source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite; and- stop transmission of cell-defining SSBs and stop provision of service of the cell at the second point in time.

9. The satellite of claim 8, wherein the first point in time indicates when the target satellite starts service of the cell, and wherein the second point in time indicates when the source satellite stops service of the cell.

10. The satellite of claim 8 of claim 9, wherein the NCD-SSB configuration comprises a time offset with respect to a cell-defining SSB of the source satellite and / or a frequency location of the NCD-SSB.

11. The satellite of any one of claims 8 to 10, wherein the satellite switching information is transmitted within a system information block.

12. The satellite of any one of claims 8 to 11 , wherein the at least one NCD-SSB of the target satellite is allocated in orthogonal resources with respect to a cell-defining SSB of the source satellite.

13. A satellite in a non-terrestrial communication network being a target satellite for soft satellite switching in a cell comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the satellite at least to:- transmit at least one non-cell-defining, NCD, synchronization signal block, SSB, between a first point in time and a second point in time;- suspend transmission of cell-defining SSBs between the first point in time and the second point in time; and- stop transmission of the at least one NCD-SSB, resume transmission of the cell-defining SSBs, and start provision of service of the cell at the second point in time.

14. The satellite of claim 13, wherein the first point in time indicates when the target satellite starts service of the cell, and wherein the second point in time indicates when the source satellite stops service of the cell.

15. The satellite of claim 13 of claim 14, wherein the at least one NCD-SSB is allocated in orthogonal resources with respect to a cell-defining SSB of the source satellite.

16. A method executed by a user equipment, UE, comprising:- receiving satellite switching information for soft satellite switching in a cell from a source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite;- acquiring synchronization with the target satellite using at least one NCD-SSB between the first point in time and the second point in time; and- switching to the target satellite for continued service of the cell based on the acquired synchronization.

17. A method executed by a satellite in a non-terrestrial communication network, the satellite being a source satellite for soft satellite switching in a cell, the method comprising:- transmitting satellite switching information for the soft satellite switching from the source satellite to a target satellite, wherein the satellite switching information indicates a first point in time and a second point in time and comprises a configuration for a non-cell-defining, NCD, synchronization signal block, SSB, of the target satellite; and- stopping transmission of cell-defining SSBs and stopping provision of service of the cell at the second point in time.

18. A method executed by a satellite in a non-terrestrial communication network, the satellite being a target satellite for soft satellite switching in a cell, the method comprising:- transmitting at least one non-cell-defining, NCD, synchronization signal block, SSB, between a first point in time and a second point in time;- suspending transmission of cell-defining SSBs between the first point in time and the second point in time; and- stopping transmission of the at least one NCD-SSB, resuming transmission of the celldefining SSBs, and starting provision of service of the cell at the second point in time.26

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