Satellite handover with resynchronization

Abstract

The embodiment of the invention relates to satellite switching with resynchronization. In one aspect, a terminal device receives, from a network device, an indication for determining a time of at least one operation associated with a handover from a first satellite to a second satellite. The at least one operation includes at least one of (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite. The terminal device performs at least one operation based on the received indication. According to the embodiment of the invention, scheduling request (SR) burst at t-Service and NW overload caused by scheduling a large number of PUSCH transmissions can be avoided. Thus, the UE may suffer less risk of long-term interruption, and the NW may schedule the first UL transmission of the UE through the target satellite in a distributed manner.

Description

Technical Field

[0001] Various example embodiments relate to the field of communications, and in particular, to devices, methods, apparatus, and computer-readable storage media for satellite handoff with resynchronization. Background Art

[0002] In the field of communications, there is a constant development to provide efficient and reliable solutions for utilizing wireless communication networks. Each new generation of products has its own technical challenges in dealing with the different situations and processes required to connect and serve devices connected to wireless networks. In order to meet the demand for wireless data services that has increased since the deployment of the fourth generation (4G) communication system, people have been working hard to develop improved fifth generation (5G), pre-5G communication systems, sixth generation (6G) communication systems, or higher versions. The new communication system can support various types of service applications for terminal devices.

[0003] In some wireless communication systems, satellite communication is involved. In such a system, artificial satellites are used to provide communication links between various locations on the earth. Due to the low altitude, the moving speed of the satellite relative to the earth is about 7.5km / s. In the Third Generation Partnership Project (3GPP), Earth Fixed Cell (EFC) and Earth Mobile Cell (EMC) are considered. EFC means that the satellite constantly adjusts the satellite beam pointing direction to fix the new radio (NR) cell and NR beam to a specific location on the earth, while EMC means that the satellite beam pointing direction is fixed, and therefore the beam footprint (i.e., NR cell) moves on the earth. In non-terrestrial networks (NTNs) based on EMC, mobility is mainly due to satellite movement because they move much faster than user equipment (UE) on the ground. Summary of the invention

[0004] In general, example embodiments of the present disclosure provide a solution for satellite handover with resynchronization.

[0005] In a first aspect, a terminal device is provided. The terminal device includes: at least one processor, and at least one memory including computer program code. The at least one memory and the computer program code are configured to, together with the at least one processor, enable the terminal device to: receive an indication from a network device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation includes at least one of the following items: (i) initiating a resynchronization process to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and based on the received indication, perform the at least one operation.

[0006] In a second aspect, a network device is provided. The network device includes: at least one processor, and at least one memory including computer program code. The at least one memory and the computer program code are configured to, together with the at least one processor, enable the network device to: send an indication to a terminal device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation includes at least one of the following items: (i) initiating a resynchronization process to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and receiving an uplink transmission from the terminal device via the second satellite.

[0007] In a third aspect, a method is provided. The method includes: receiving, at a terminal device, an indication from a network device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation includes at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and performing the at least one operation based on the received indication.

[0008] In a fourth aspect, a method is provided. The method includes: sending, at a network device, to a terminal device, an indication for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation includes at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and receiving the uplink transmission from the terminal device via the second satellite.

[0009] In a fifth aspect, an apparatus is provided, comprising: a component for receiving, at a terminal device, an indication from a network device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization process to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and a component for performing the at least one operation based on the received indication.

[0010] In a sixth aspect, an apparatus is provided, comprising: a component for sending an indication at a network device to a terminal device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization process to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and a component for receiving an uplink transmission from the terminal device via the second satellite.

[0011] In a seventh aspect, a non-transitory computer-readable medium is provided, the non-transitory computer-readable medium comprising: program instructions for causing an apparatus to execute a method according to at least any one of the third and fourth aspects above.

[0012] In an eighth aspect, a computer program is provided comprising instructions which, when executed by an apparatus, cause the apparatus to at least: receive an indication from a network device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization process to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and perform at least one operation based on the received indication.

[0013] In a ninth aspect, there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to at least: send to a terminal device an indication for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization process to a network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and receiving an uplink transmission from the terminal device via the second satellite.

[0014] In a tenth aspect, a terminal device is provided. The terminal device includes: a receiving circuit system configured to: receive an indication from a network device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation includes at least one of the following items: (i) initiating a resynchronization process to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and an executing circuit system configured to: perform the at least one operation based on the received indication.

[0015] In an eleventh aspect, a network device is provided. The network device includes: a transmitting circuit system configured to: transmit to a terminal device an indication for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation includes at least one of the following items: (i) initiating a resynchronization process to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and a receiving circuit system configured to: receive the uplink transmission from the terminal device via the second satellite.

[0016] It should be understood that the invention summary is not intended to determine the key or essential features of the embodiments of the present disclosure, nor is it intended to limit the scope of the present disclosure. Other features of the present disclosure will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Some example embodiments will now be described with reference to the accompanying drawings, in which:

[0018] Figure 1A illustrates an example communication network in which embodiments of the present disclosure may be implemented;

[0019] Figure 1B illustrates an example architecture of a non-terrestrial network;

[0020] Figure 2 illustrates a flow chart illustrating a process for satellite handoff with resynchronization according to some embodiments of the present disclosure;

[0021] Figure 3 illustrates an example process of satellite switching with resynchronization according to some embodiments of the present disclosure;

[0022] Figure 4 illustrates another example process of satellite handoff with resynchronization according to some embodiments of the present disclosure;

[0023] Figure 5 A flowchart of a method implemented at a terminal device according to some embodiments of the present disclosure is illustrated;

[0024] Figure 6 A flowchart of a method implemented at a network device according to some embodiments of the present disclosure is illustrated;

[0025] Figure 7 illustrates a simplified block diagram of an apparatus suitable for implementing embodiments of the present disclosure; and

[0026] Figure 8 A block diagram of an example computer-readable medium is illustrated in accordance with some embodiments of the present disclosure.

[0027] Throughout the drawings, the same or similar reference numerals refer to the same or similar elements. DETAILED DESCRIPTION

[0028] The principle of the present disclosure will now be described with reference to some example embodiments. It should be understood that these embodiments are described only to illustrate and help those skilled in the art understand and implement the present disclosure, and do not represent any limitation on the scope of the present disclosure. The disclosure described herein can be implemented in various other ways except the way described below.

[0029] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0030] In this disclosure, references to "one embodiment," "an embodiment," and "an example embodiment" indicate that the described embodiment may include a particular feature, structure, or characteristic, but not every embodiment must include the particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, those skilled in the art recognize that it is within the knowledge of those skilled in the art to affect such feature, structure, or characteristic in conjunction with other embodiments, whether or not explicitly described.

[0031] It should be understood that although the terms "first" and "second" etc. can be used to describe various elements in this article, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the scope of the exemplary embodiment, the first element can be referred to as the second element, and similarly, the second element can be referred to as the first element. As used herein, the term "and / or" includes any and all combinations of one or more of the listed terms.

[0032] The term used herein is only used to describe specific embodiments, but is not intended to limit exemplary embodiments. As used herein, unless the context clearly states otherwise, the singular form "one", "one" and "the" also include plural forms. It is further understood that the term "includes", "comprising", "having", "having", "containing", and / or "containing" specifies the existence of the features, elements, and / or components when used in this article, but does not exclude the existence or addition of one or more other features, elements, components, and / or their combinations. As used herein, "at least one of the following: <list of two or more elements>" and "at least one of <list of two or more elements>" and similar wording (wherein the list of two or more elements is connected by "and" or "or") refer to at least any one element in these elements, or at least any two or more elements in these elements, or at least all these elements.

[0033] As used in this application, the term "circuitry" may refer to one, more, or all of the following:

[0034] (a) a pure hardware circuit implementation (such as an implementation using only analog and / or digital circuitry), and

[0035] (b) a combination of hardware circuitry and software such as (where applicable):

[0036] (i) a combination of analog and / or digital hardware circuits and software / firmware, and

[0037] (ii) any portion of a hardware processor(s) with software, including digital signal processor(s), software, and memory(s), which work together to enable a device (such as a mobile phone or server) to perform various functions,

[0038] as well as

[0039] (c) Hardware circuits and / or processor(s), such as microprocessor(s) or portions of microprocessor(s), that require software (e.g., firmware) to operate, but which may not be present when the software is not required for operation.

[0040] This definition of circuitry applies to all uses of the term in this application, including in any claims. As another example, as used in this application, the term circuitry also covers an implementation of only a hardware circuit or processor (or multiple processors) or a portion of a hardware circuit or processor and its accompanying software and / or firmware. For example, if applicable to a particular claim element, the term circuitry also covers a baseband integrated circuit or processor integrated circuit for a mobile device, or a similar integrated circuit in a server, cellular network device, or other computing or network device.

[0041] As used herein, the term "communication network" refers to a network that complies with any suitable communication standard, such as 5G New Radio (NR), Long Term Evolution (LTE), Advanced LTE (LTE-A), Wideband Code Division Multiple Access (WCDMA), High Speed ​​Packet Access (HSPA), Narrowband Internet of Things (NB-IoT), etc. In addition, the communication between the terminal equipment and the network equipment in the communication network can be performed according to any suitable generation of communication protocols, including but not limited to the first generation (1G), second generation (2G), 2.5G, 2.75G, third generation (3G), fourth generation (4G), 4.5G, future fifth generation (5G) communication protocols, and / or any other protocols currently known or to be developed in the future. The embodiments of the present disclosure can be applied to various communication systems. In view of the rapid development of communication, there will certainly be future types of communication technologies and systems that can embody the present disclosure. The scope of the present disclosure should not be limited to the above-mentioned systems.

[0042] As used herein, the term "network device" refers to a node in a communication network, via which a terminal device accesses the network and receives services from the network. Depending on the terminology and technology applied, a network device may refer to a base station (BS) or an access point (AP), such as a NodeB (NodeB or NB), an evolved NodeB (eNodeB or eNB), a NR NB (also known as a gNB, a base station for a 5G system), a remote radio unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, a low-power node (such as a femto BS, a pico BS), etc.

[0043] The term "terminal device" refers to any terminal device capable of wireless communication. As an example and not limitation, a terminal device may also be referred to as a communication device, a user equipment (UE), a subscriber station (SS), a portable subscriber station, a mobile station (MS), or an access terminal (AT). The terminal device may include, but is not limited to, a mobile phone, a cellular phone, a smart phone, a voice over IP (VoIP) phone, a wireless local loop phone, a tablet computer, a wearable terminal device, a personal digital assistant (PDA), a portable computer, a desktop computer, an image acquisition terminal device such as a digital camera, a game terminal device, a music storage and playback device, a vehicle-mounted wireless terminal device, a wireless endpoint, a mobile station, a laptop embedded device (LEE), a laptop mounted device (LME), a USB dongle, a smart device, a wireless customer premises equipment (CPE), an Internet of Things (IoT) device, a watch or other wearable device, a head mounted display (HMD), a vehicle, a drone, medical equipment and applications (e.g., remote surgery), industrial equipment and applications (e.g., robots and / or other wireless devices operating in the context of an industrial and / or automated processing chain), consumer electronic devices, equipment operating on a commercial and / or industrial wireless network, etc. In the following description, the terms "terminal device", "communication device", "terminal", "user equipment", and "UE" may be used interchangeably.

[0044] In 3GPP Release 15 and Release 16, the use of 5G NR standards to support non-terrestrial networks has been studied. In the work item for non-terrestrial networks (NTN) approved in Release 17, it is assumed that UEs supporting NTN have global navigation satellite system (GNSS) capabilities. In NTN systems, 5G base stations (gNBs) or gNB functions are deployed on satellites or relayed by gNBs in a transparent manner to provide communication coverage over very large areas that may not be reached by cellular networks. This functionality can be used to connect IoT devices around the world and provide personal communications in remote areas and disaster relief. To achieve new radio (NR) access, different types of satellite orbits have been studied, including low earth orbit (LEO) satellites operating at about 600km above the earth. In the Rel-16 study project, the typical beam footprint size of LEO satellites is assumed to be between 100-1000km radius. Therefore, one LEO satellite can cover a very large area on the earth, which can include multiple countries.

[0045] In Rel-18, the topic of unchanged physical cell identity (PCI) is addressed with the goal of reducing signaling overhead and simplifying the RRC procedures for the UE. The working principle is that after a satellite handover, the serving gNB and the cell (on the ground) do not change, and therefore (most of) the cell configuration can be maintained without changing the PCI, frequency, and other cell configuration parameters (e.g., servingCellconfigCommon). Then, the satellite handover is almost transparent to the UE, i.e., no L3 mobility (i.e., handover procedure) needs to be performed, so flushing the buffer can be avoided and no security keys need to be updated.

[0046] The conditions for this mechanism to work are: (i) NTN cells must be deployed as quasi-Earth Fixed Cells (EFCs) since the cell coverage area should not change; (ii) the network (NW) should instruct the UE how / when to resynchronize after satellite handover; (iii) the target satellite information should be provided via broadcast signaling before satellite handover (no RRC dedicated signaling should be used to reduce Uu interface overhead). In Rel-18, the focus is on transparent architecture, and the most obvious case is when the cells are provided by the same gNB, i.e. the same cell with fixed PCI is provided by the same gNB, so only the satellite node is changed. However, in theory, this can also apply to different gNBs, and potentially even to regeneration cases.

[0047] In some solutions, the UE's actions at satellite handover are included. For example, according to TS 38.331 clauses 5.2.2.4.21 and 5.7.19, after receiving System Information Block 19 (SIB19) in the NTN cell, the UE in RRC_CONNECTED shall: start or restart T430 of the serving cell from the subframe indicated by the epochTime of the serving cell, where the timer value is set to the ntn-UlSyncValidityDuration of the serving cell; if SatSwitchWithReSync and t-Service are included, and the UE supports hard satellite handover with resynchronization. If t-ServiceStart is included, and the UE supports soft satellite handover with resynchronization: between the time indicated by t-ServiceStart and the time indicated by t-Service of the serving cell, perform satellite handover with resynchronization as specified in 5.7.19; otherwise: at the time indicated by t-Service of the serving cell, perform satellite handover with resynchronization as specified in 5.7.19.

[0048] It should be noted that the UE shall attempt to reacquire SIB19 before the end of the duration indicated by ntn-UlSyncValidityDuration and epochTime implemented by the UE. For satellite switching with resynchronization in RRC_CONNECTED UE, the UE shall stop timer T430 if running; notify lower layers that uplink (UL) synchronization is lost due to satellite switching and resynchronization; start resynchronization of the downlink (DL) with the SpCell served by the satellite indicated by ntn-Config in SatSwitchWithReSync; start timer T430 from the subframe indicated by epochTime in ntn-Config in SatSwitchWithReSync, where the timer value is set to ntn-UlSyncValidityDuration; notify lower layers when UL synchronization is acquired.

[0049] The definition of SIB19 described above is included in Section 6.3 (RRC Information Elements) of TS38.331. Specifically, SIB19 is an NTN-specific SIB used to signal satellite assistance information (including target satellite information for satellite switching). In SIB 19, some fields such as ntn-Config, satSwitchWithReSync, t-Service, ssb-TimeOffset, and t-ServiceStart are optionally included. ntn-Config provides the parameters required for the UE to access NR via NTN access, such as ephemeris data, common timing advance (TA) parameters, k_offset, validity period and epoch of UL synchronization information. In the terrestrial network (TN) cell, this field only exists in ntn-NeighCellConfigList and ntn-NeighCellConfigListExt. SatSwitchWithReSync provides parameters for the target satellite required to perform satellite switching with resynchronization.

[0050] This field is present in the NTN cell, and its presence indicates that satellite switching without physical cell identity (PCI) change is supported in the cell. t-Service indicates time information about when the cell provided via the NTN system will stop serving the area currently covered. This field is applicable to both service link switching in the NTN quasi-terrestrial fixed system and feeder link switching of the NTN quasi-earth fixed and earth mobile systems. This field indicates the time in multiples of 10ms after 00:00:00 on the Gregorian calendar date January 1, 1900 (midnight between Sunday, December 31, 1899 and Monday, January 1, 1900). The exact stop time is between the time indicated by the value of this field minus 1 and the time indicated by the value of this field.

[0051] The reference point of t-Service is the uplink time synchronization reference point of the cell. This field only exists in NTN cells. ssb-TimeOffset indicates the time offset between the SSBs of the source satellite and the target satellite at the uplink time synchronization reference point. It is given in the number of subframes. t-ServiceStart indicates time information about when the target satellite starts serving the area currently covered by the service satellite. This field indicates the time in multiples of 10ms after 00:00:00 on the Gregorian calendar date January 1, 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 date indicated by the value of this field.

[0052] Some solutions for RACH-free access procedures involve the UE and source satellites (e.g., source SAT-1 and source SAT-2) during satellite switching with resynchronization. The UE will perform the following steps during soft satellite switching: At t-switch (i.e., any time between t-ServiceStart and t-Service), the UE suspends UL operation to the source satellite (i.e., UL synchronization is lost), after DL synchronization acquisition, the UE applies new timing, and restores UL synchronization to the target satellite (this can happen before, at, or after t-Service). For the first (1st) UL transmission, the UE triggers a TA Report Scheduling Request (TAR-SR) via a PUCCH Scheduling Request (SR) or a configured grant (CG) / DG. If the TimeAlignmentTimer (TAT) expires, the UE falls back to RACH-based access.

[0053] In soft satellite handover, the UE can apply the timing of the target satellite and start physical downlink control channel (PDCCH) monitoring of the scheduling grant before t-Service. In fact, it only defines that the UE performs satellite resynchronization between t-ServiceStart and t-Service (see Section 5.2.2.4.21 in TS38.331). The problem with this process is that when the UE triggers resynchronization depends on the UE implementation, because the NW does not know when this will happen specifically. The NW does not know when the UE will resynchronize (i.e., resynchronize) with the target satellite, so it cannot know whether the UE should be scheduled via the source satellite or the target satellite within the time window between t-ServiceStart and t-Service. This problem may lead to inefficient use of scheduling resources and may increase downlink interference (i.e., the source satellite and target satellite coverage overlap, and the NW cannot coordinate resources because it cannot control when the UE resynchronizes). Normal network implementations will not schedule any UE at all during the overlap, resulting in resource waste and performance degradation.

[0054] Some other solutions propose that all UEs resume UL operation at t-Service, so the NW will know exactly when uplink transmission will start towards the target satellite. This can be an effective solution, but may not be sufficient because it will result in scheduling request (SR) bursts. To alleviate this problem, the NW can disperse the SR resources, so the UEs send SRs in a more distributed manner, however, bursts are difficult to avoid. In addition to this, another problem is the overload of physical uplink shared channel (PUSCH) allocations used for, for example, TA reports. The UE needs to trigger a TA report for the first UL transmission. If a group of UEs sends SRs to request UL transmissions (e.g., for TA reports), the NW will overload the TA report by allocating PUSCH transmissions. Resuming all UL transmissions at t-Service may overload the NW that schedules PUSCH transmissions and may cause UEs to experience longer interruption times (i.e., the NW cannot schedule all UEs immediately after t-Service and needs to spread them out over a longer period of time).

[0055] In this solution, all UEs resume uplink operation at t-service, it being unclear before t-service which downlink they monitor. It may be logical for them to monitor the source satellite. However, this leads to a disadvantage, namely that all UEs are scheduled between t-serviceStart and t-service by the source satellite, which means that only the transmit power of one satellite can be used. When the service can be distributed on 2 satellites, not all PRBs may be used due to interference reasons, but all power can be used when coordinating resources. However, this requires some UEs to switch earlier than others, i.e. not all UEs are at t-service.

[0056] In view of these analyses and considerations, a new solution is proposed in some embodiments of the present disclosure. In some aspects, the NW and the UE can benefit from a more flexible solution, where both parts know when the first UL transmission will occur, but the transmission is distributed over time (between t-ServiceStart and t-Service) to reduce the scheduling load and enhance the UE experience. It is worth noting that the time between t-ServiceStart and t-Service can be quite long, so good utilization of resources during this period can significantly increase capacity.

[0057] The principles and embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Figure 1A , which illustrates an example communication system 100 (or communication network) in which embodiments of the present disclosure may be implemented. System 100 (e.g., a communication network) includes a plurality of network devices and terminal devices, such as terminal device 101, and network devices 103 and 105. In the NR NTN scenario, network devices 103 and 105 may be NTN devices, such as satellite 1 and satellite 2, respectively. In some examples, satellite 1 or satellite 2 may be a low earth orbit (LEO) satellite, a medium earth orbit (MEO) satellite, or a geostationary orbit (GEO) satellite. Terminal device 101 may communicate with network device 103 or 105. In some examples, system 100 may further include network device 107, such as a ground station, such as a gateway (GW) or a gNB. Network device 103 or 105 (e.g., an NTN device) may be used as a transmission relay node between network device 107 and terminal device 101 in a transparent manner.

[0058] It should be understood that the number of network devices and terminal devices is for illustration purposes only and does not represent any limitation. System 100 may include any suitable number of network devices and terminal devices suitable for implementing the embodiments of the present disclosure.

[0059] The communication in the communication system 100 can be implemented according to any appropriate (multiple) communication protocols, including but not limited to cellular communication protocols such as the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G), and the fifth generation (5G), such as wireless local area network communication protocols such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11, and / or any other protocol currently known or developed in the future. In addition, the communication can utilize any appropriate wireless communication technology, including but not limited to: code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), frequency division duplex (FDD), time division duplex (TDD), multiple input multiple output (MIMO), orthogonal frequency division multiplexing (OFDM), discrete Fourier transform spread OFDM (DFT-s-OFDM), and / or any other technology currently known or developed in the future.

[0060] Some examples of satellite switching can be found in Figure 1A Description. In a transparent EFC-based deployment, the PCI remains unchanged. During a satellite handover, a stationary UE (an example of terminal device 101) is served by satellite 1 (an example of network device 103 providing cell A). As satellite 1 moves away from the UE and satellite 2 (an example of network device 105) gets closer, the NW (e.g., network device 107) indicates when the satellite handover occurs and how to perform resynchronization with the new cell. After satellite 2 takes over serving the area (i.e., cell B), the UE performs DL / UL synchronization operations to reconnect. In such an example, even though the UE is served by a new satellite, it does not change the serving gNB, so the cell configuration can be maintained. Satellite 1 and satellite 2 are configured with the same PCI, the same UE context, and the same protocol stack (including SSB generation, encoding / decoding, modulation / demodulation, the same CORESET configuration, and switching routing).

[0061] However, satellite 1 and satellite 2 introduce different frequency (i.e. Doppler) and timing drifts (propagation paths towards satellite 1 and 2 are different) from the UE's reference. Satellite handover can be divided into two additional scenarios: i) hard satellite handover, and ii) soft satellite handover. Soft satellite handover considers some cell overlap between the NTN cells radiated by satellite 1 and satellite 2, while hard satellite handover considers no overlap between the old and new cells (note that the UE should consider some interruption time to pre-compensate the frequency and timing of the new cell). For soft satellite handover, it is assumed that satellite 1 and satellite 2 are sending time-shifted SSBs, thereby (theoretically) allowing the UE to switch gracefully to the new (incoming) satellite.

[0062] Figure 1B Figure 2 shows an example architecture of a non-terrestrial network. Figure 1BAs shown in , example architecture 100-1 may include multiple network devices and terminal devices, such as terminal device 102, and network devices 104 and 106. In some examples, network device 104 may be a satellite or UAS platform. Network device 106 may be a gateway. Terminal device 102 is located within a beam footprint of multiple beam footprints. One of the multiple beam footprints can be shown at 112. There is a service link between terminal device 102 and network device 104. There is a feeder link between network device 104 and network device 106. In some examples, system 100-1 may also include a data network 108. Network device 106 and data network 108 (e.g., the Internet, an intranet, a wide area network, etc.) can be connected to each other via a wired and / or wireless network. Additionally or alternatively, network device 106 can be connected to Figure 1B Other core network elements not shown, such as servers, access points, switches, routers, nodes, etc.

[0063] Reference now Figure 2 , which illustrates the process of satellite switching with resynchronization according to some embodiments of the present disclosure. Figure 2 As shown in FIG. 2 , in process 200, terminal device 210 and network device 220 are involved. Terminal device 210 may be Figure 1A The network device 220 may be an example of the terminal device 101 mentioned in Figure 1A In some examples, the terminal device 210 may be a UE or another terminal device. The network device 220 may be a base station or a gNB, etc.

[0064] In process 200, network device 220 may send (202) to terminal device 210 an indication 205 for determining a time for at least one operation associated with switching from a first satellite to a second satellite. In some examples, the first satellite may be referred to as a source satellite (see Figure 1A , network device 103), and the second satellite may be referred to as a target satellite (reference Figure 1A, network device 105). The at least one operation may include: (i) initiating a resynchronization process to the network device via the second satellite, and / or (ii) performing an uplink transmission via the second satellite. On the terminal device 210 side, the terminal device 210 may receive (204) an indication 205 for determining a time for the at least one operation from the network device 220. After receiving the indication 205, the terminal device 210 may initiate (206) a resynchronization process to the network device 220 via the second satellite, and may send (208) an uplink transmission 215 to the network device 220 via the second satellite. On the network device 220 side, the network device 220 may receive (212) an uplink transmission 215 from the terminal device 210 via the second satellite. Details of the process 200 will be further described below.

[0065] In some examples, the timing of at least one of the above operations is during the overlapping time between the first time point and the second time point. For example, time T may exist in the space [t-ServiceStart, t-Service). t-Service may represent the second time point, and the second time point is the time point for the first satellite to stop serving the terminal device 210 in the area covered by the service satellite of the terminal device 210. t-ServiceStart may represent the first time point, and the first time point is the time point for the second satellite to start serving the area covered by the service satellite of the terminal device 210. In some examples, the switch from the first satellite to the second satellite may be a soft satellite switch during the overlapping time. In some examples, before the first time point, the network device 220 may exchange data with the terminal device 210 via the first satellite, and may determine the optimal resynchronization time for the terminal device 210.

[0066] In some examples, the time of the at least one operation may be calculated based on the indication 205. In such an example, the time may be referred to as time T. In some examples, the time T may be specific to the terminal device 210, or specific to a terminal device group including the terminal device 210. For example, the time T may be UE-specific or UE-group-specific. Some details of an example for determining the time T will be given below.

[0067] In some examples, the indication may include: a parameter indicating a function in a preconfigured function set. In some examples, the parameter may be part of a system information block (SIB) broadcast from the network device 220. After receiving the indication 205, the terminal device 210 may use the identification (ID) of the terminal device 210 as an input, based on the function, to determine the time (i.e., time T). For example, time T may be calculated based on the NW indication X, which is a parameter broadcast as part of SIB19. In a soft satellite switching scenario, the SatSwitchWithReSync IE and the t-ServiceStart IE may be broadcast as part of SIB19. The parameter may be a pointer to a function (in a preconfigured function set) (e.g., point-T in some examples below), which uses the UE ID (an example of the ID of the terminal device 210) as an input. In some examples, the network device 220 may send the indication 205 before the first time point mentioned above. Therefore, the terminal device 210 may receive the indication 205 before the first time point. Alternatively, the network device 220 may send the indication 205 after the first time point, and on the terminal device 210 side, the terminal device 210 may receive the indication 205 after the first time point. Both the terminal device 210 and the network device 220 know the function and the ID of the terminal device 210. On the network device 220 side, the network device 220 may determine the time T based on the function using the identification (ID) of the terminal device as input.

[0068] In some examples, indication 205 may include: a group number of a terminal device group including terminal device 210. Terminal device 210 may determine the time (i.e., time T) based on the group number and the ID of terminal device 210. In some examples, terminal device 210 may determine time T using a formula for calculating time T. In some examples, the formula may be T=floor((t-Service-t-ServiceStart) / N)*(UE-ID mod N), where T represents the time to be calculated. t-Service represents the above-mentioned second time point. t-ServiceStart represents the above-mentioned first time point. N represents the group number. UE-ID represents the ID of terminal device 210. Function floor() represents the floor function. mod represents a modulus operation. For example, NW indicates group number N, where each UE is distributed in a group, and time T is calculated using the above formula. In some examples, the ID of terminal device 210 may be C-RNTI, IMSI, or any unique identifier of terminal device 210. On the network device 220 side, the network device 220 can determine the time T in the same manner (based on the group number and the ID of the terminal device). For example, the network device 200 can calculate the time T based on the above formula.

[0069] In some examples, terminal device 210 may perform at least one operation based on received indication 205. As described above, in some examples, terminal device 210 may calculate time T based on indication 205. In such examples, at least one operation may include an uplink transmission via a second satellite. Terminal device 210 may perform the following operations: prior to time T, initiate (206) a resynchronization procedure to network device 220 via the second satellite, and at that time, perform (e.g., send) (208) an uplink transmission 215 to network device 220. On the network device 220 side, network device 220 may receive (212) an uplink transmission 215 from terminal device 210 at that time.

[0070] Different from calculating the time T based on a pointer to a function or based on the group number N, in some other examples, during the time between a first time point (e.g., t-ServiceStart) and a second time point (e.g., t-Service), NW may indicate over-scheduling information of when to perform resynchronization. Some details of such an example will be given later.

[0071] In some examples, indication 205 may be included in the scheduling information and indicate that the scheduled transmission will be the last transmission via the first satellite. In some examples, indication 205 may be a single bit indication. For example, a single bit indication of a DCI format carried on a PDCCH may indicate that the resource allocation is the last resource allocation on the source satellite (and therefore, the UE must initiate a resynchronization procedure via the target satellite). In such an example, terminal device 210 may perform the following operations: after the scheduled transmission, initiate (206) a resynchronization procedure to network device 220 via the second satellite; and perform (e.g., send) (208) an uplink transmission 215 to network device 220 via the second satellite. On the network device 220 side, based on the scheduled transmission, network device 220 may determine that terminal device 210 will initiate a resynchronization procedure to network device 220 via the second satellite and that the uplink transmission will be received from terminal device 210 via the second satellite.

[0072] In some examples, the indication 205 may be included in the scheduling information and indicate a satellite identification (ID) of the second satellite. In some examples, the indication 205 may be a multi-bit indication. In such examples, the terminal device 210 may perform operations such as initiating (206) a resynchronization procedure to the network device 220 via the second satellite based on receiving a satellite ID different from the identification of the first satellite, and performing (e.g., sending) (208) an uplink transmission 215 to the network device 220 via the second satellite. For example, the multi-bit indication in the TA DCI format on the PDCCH may indicate the satellite ID, such that when the UE obtains an assignment with a satellite ID different from the satellite ID belonging to the source satellite, the UE initiates the resynchronization procedure.

[0073] Figure 3 An example process of satellite switching with resynchronization according to some embodiments of the present disclosure is illustrated. Figure 3 As shown in , process 300 may involve UE 310, satellite (i.e., SAT1) 320, satellite (i.e., SAT2) 330, and gNB 340. In some examples, UE 310 may be an example of terminal device 101. Satellite (i.e., SAT1) 320 may be a source satellite and may be an example of network device 103. Satellite (i.e., SAT2) 330 may be a target satellite and may be an example of network device 105. gNB 340 may be an example of network device 107.

[0074] In process 300, at 301, before t-ServiceStart 302, UE 310 exchanges data with NW (e.g., gNB 340) via source satellite SAT1 320. During this period, NW determines the optimal resynchronization time for each connected UE. After t-ServiceStart and before t-Service, and close to the optimal resynchronization time determined above, at 303, NW sends scheduling information (downlink control information (DCI) on PDCCH) including an indication that the scheduled transmission will be the last transmission on source satellite SAT1 320 (i.e., there will be no subsequent transmissions on source satellite SAT 1 320). At 304, via source satellite SAT1 320, the last scheduled transmission (UL / DL data transmission) is performed. After the last scheduled transmission, at 305, UE 310 performs resynchronization. At 306, 307, and 309, UE 310 resumes UL operation through target satellite SAT2 330. t-ServiceStart 302 may indicate time information about when the target satellite (e.g., SAT2 330) starts serving the area currently covered by the serving satellite. t-Service 308 may indicate time information about when a cell provided via the NTN system (e.g., a cell provided by SAT1 320) will stop serving the area currently covered by it.

[0075] Based on some of the above embodiments, the NW can control when the UE will perform resynchronization. Scheduling request (SR) bursts at the t-Service can be avoided. NW overload due to scheduling a large number of PUSCH transmissions can also be avoided. The risk of a long interruption that the UE may suffer is less. The NW and the UE have a common understanding of the time when the UE resumes UL transmission through the target satellite in a soft satellite handover with resynchronization scenario. The advantage is that the NW can schedule the UE's first UL transmission through the target satellite in a distributed manner. At the same time, this will also allocate downlink transmissions and has the associated advantage of more transmission power available on the satellite.

[0076] Figure 4 Another example process of satellite handover with resynchronization according to some embodiments of the present disclosure is illustrated. In process 400, UE 410, satellite (i.e., SAT1) 420, satellite (i.e., SAT2) 430, and gNB 440 are involved. In some examples, UE 410 can be an example of terminal device 101. Satellite (i.e., SAT1) 420 can be a source satellite and can be an example of network device 103. Satellite (i.e., SAT2) 430 can be a target satellite and can be an example of network device 105. gNB 440 can be an example of network device 107.

[0077] In process 400, the steps or operations for allocating UE access to a target satellite are as follows. At 401, before t-ServiceStart 404, UE 410 exchanges data with the NW (e.g., gNB 440) via the source satellite SAT1 420. During this period, at 402, the NW determines the optimal resynchronization time for each connected UE and includes point-T as part of SIB19. Before or after t-ServiceStart 404, at 403, UE 410 acquires SIB19. At 405, UE 410 determines the time T for access based on pointer-T and UE ID (e.g., IMSI of UE 410). Before time T, at 406, UE 410 initiates a resynchronization process. Referring to 407, 408, and 411, UE 410 resumes UL operation via the target satellite SAT2 430, where UE 410 performs a first UL transmission via SAT2 430 at time T.

[0078] Figure 5 The flowchart of the method implemented at the terminal device according to some embodiments of the present disclosure is illustrated. The terminal device executing the method 500 may be an example of the terminal device 210 described above.

[0079] At block 510, the terminal device may receive an indication from the network device for determining a time for at least one operation associated with switching from a first satellite to a second satellite. The at least one operation may include at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite. At block 520, the terminal device may perform at least one operation based on the received indication.

[0080] In some embodiments, the indication may include: indicating a parameter of a function in the set of preconfigured functions. The terminal device may determine the time based on the function using an identification (ID) of the terminal device as an input.

[0081] In some embodiments, the parameter may be part of a system information block (SIB) broadcast from a network device.

[0082] In some embodiments, the indication may be received before or after a first point in time at which the second satellite begins serving an area covered by the terminal device's serving satellite.

[0083] In some embodiments, the indication may include: a group number of a terminal device group including the terminal device. The terminal device may determine the time based on the group number and the ID of the terminal device.

[0084] In some embodiments, the terminal device may determine the time based on a formula for calculating the time. The formula may be: T = floor ((t-Service-t-ServiceStart) / N) * (UE-ID mod N), where T represents the time, t-Service represents the second time point at which the first satellite stops serving the terminal device in the area covered by the service satellite of the terminal device, t-ServiceStart represents the first time point at which the second satellite starts serving the area, N represents the group number, UE-ID represents the ID of the terminal device, floor() represents the floor function, and mod represents the modulus operation.

[0085] In some embodiments, the at least one operation may include an uplink transmission via the second satellite.The terminal device may perform the at least one operation by initiating a resynchronization process to the network device via the second satellite before the time, and performing an uplink transmission to the network device at the time.

[0086] In some embodiments, the time may be specific to a terminal device, or specific to a group of terminal devices including the terminal device.

[0087] In some embodiments, the indication may be included in the scheduling information and indicates that the scheduled transmission will be the last transmission via the first satellite.

[0088] In some embodiments, the indication may be a single-bit indication.

[0089] In some embodiments, the terminal device may perform at least one of the following operations: after the scheduled transmission, initiating a resynchronization process to the network device via the second satellite; and performing an uplink transmission to the network device via the second satellite.

[0090] In some embodiments, the indication may be included in the scheduling information and indicate a satellite identification (ID) of the second satellite.

[0091] In some embodiments, the indication may be a multi-bit indication.

[0092] In some embodiments, the terminal device may perform at least one of the following operations: initiating a resynchronization process to the network device via the second satellite based on receiving a satellite ID different from the identification of the first satellite; and performing an uplink transmission to the network device via the second satellite.

[0093] In some embodiments, the time is during an overlapping time between a first time point and a second time point, wherein the first time point is used for the second satellite to start serving the terminal device in an area covered by a service satellite of the terminal device, and the second time point is used for the first satellite to stop serving the terminal device in the area.

[0094] In some embodiments, the handover may be a soft satellite handover during an overlap time.

[0095] Figure 6 The flowchart of the method implemented at the network device according to some embodiments of the present disclosure is illustrated. The network device executing the method 600 may be an example of the network device 220 described above.

[0096] At block 610, the network device may send an indication to the terminal device for determining a time for at least one operation associated with switching from the first satellite to the second satellite, wherein the at least one operation includes at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite. At block 620, the network device may receive the uplink transmission from the terminal device via the second satellite.

[0097] In some embodiments, the indication may include: indicating a parameter of a function in a set of preconfigured functions. The network device may determine the time based on the function using an identification (ID) of the terminal device as an input.

[0098] In some embodiments, the parameter may be part of a system information block 19 (SIB 19) broadcast from a network device.

[0099] In some embodiments, the indication may be sent before or after a first point in time at which the second satellite begins serving the area covered by the terminal device's serving satellite.

[0100] In some embodiments, the indication may include: a group number of a terminal device group including the terminal device. The network device may determine the time based on the group number and the ID of the terminal device.

[0101] In some embodiments, the network device can determine the time by: calculating the time based on the formula T = floor((t-Service-t-ServiceStart) / N)*(UE-ID mod N), where T represents the time, t-Service represents the second time point when the first satellite stops serving the terminal device in the area covered by the service satellite of the terminal device, t-ServiceStart represents the first time point when the second satellite starts serving the area, N represents the group number, UE-ID represents the ID of the terminal device, floor() represents the floor function, and mod represents the modulo operation.

[0102] In some embodiments, at least one operation may include: an uplink transmission via a second satellite.The network device may receive the uplink transmission from the terminal device at the time.

[0103] In some embodiments, the time may be specific to a terminal device, or specific to a group of terminal devices including the terminal device.

[0104] In some embodiments, the indication may be included in the scheduling information and indicates that the scheduled transmission will be the last transmission via the first satellite.

[0105] In some embodiments, the indication may be a single-bit indication.

[0106] In some embodiments, the network device may determine based on the scheduled transmission that the terminal device is to initiate a resynchronization procedure with the network device via the second satellite and that an uplink transmission is to be received from the terminal device via the second satellite.

[0107] In some embodiments, the indication may be included in the scheduling information and indicate a satellite identification (ID) of the second satellite.

[0108] In some embodiments, the indication may be a multi-bit indication.

[0109] In some embodiments, the time may be during an overlapping time between a first time point and a second time point. The first time point is for the second satellite to start serving the terminal device in an area covered by the serving satellite of the terminal device, and the second time point is for the first satellite to stop serving the terminal device in the area.

[0110] In some embodiments, the handover may be a soft satellite handover during an overlap time.

[0111] In some embodiments, the network device may exchange data with the terminal device via the first satellite before a first point in time when the second satellite starts serving an area covered by a serving satellite of the terminal device; and determine an optimal resynchronization time for the terminal device.

[0112] In some embodiments, an apparatus (e.g., a terminal device) capable of performing any of the methods 500 may include a component for performing the corresponding steps of the method 500. The component may be implemented in any suitable form. For example, the component may be implemented in a circuit system or a software module.

[0113] In some embodiments, the apparatus includes: means for receiving an indication from a network device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation includes at least one of: (i) initiating a resynchronization process to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and means for performing the at least one operation based on the received indication.

[0114] In some embodiments, the indication comprises a parameter indicating a function from a set of preconfigured functions, and the apparatus further comprises: means for using an identification (ID) of the terminal device as input to determine the time based on the function.

[0115] In some embodiments, the parameter is part of a system information block (SIB) broadcast from the network device.

[0116] In some embodiments, the indication is received before or after a first point in time at which the second satellite begins serving an area covered by the terminal device's serving satellite.

[0117] In some embodiments, the indication includes a group number of a terminal device group, the terminal device group includes the terminal device, and the apparatus further includes: a component for determining the time based on the group number and an ID of the terminal device.

[0118] In some embodiments, the component for determining the time includes a component for calculating the time based on the following formula: T = floor((t-Service-t-ServiceStart) / N)*(UE-ID mod N), where T represents the time, t-Service represents the second time point when the first satellite stops serving the terminal device in the area covered by the service satellite of the terminal device, t-ServiceStart represents the first time point when the second satellite starts serving the area, N represents the group number, UE-ID represents the ID of the terminal device, floor() represents the floor function, and mod represents the modulo operation.

[0119] In some embodiments, at least one operation includes an uplink transmission via a second satellite, and the components for performing the at least one operation include: a component for initiating a resynchronization process to the network device via the second satellite before the time; and a component for performing the uplink transmission to the network device at the time.

[0120] In some embodiments, the time is specific to a terminal device, or specific to a group of terminal devices including the terminal device.

[0121] In some embodiments, the indication is included in the scheduling information and indicates that the scheduled transmission will be the last transmission via the first satellite.

[0122] In some embodiments, the indication is a single bit indication.

[0123] In some embodiments, means for performing at least one operation includes means for initiating a resynchronization procedure to the network device via the second satellite after the scheduled transmission; and means for performing an uplink transmission to the network device via the second satellite.

[0124] In some embodiments, the indication is included in the scheduling information and indicates a satellite identification (ID) of the second satellite.

[0125] In some embodiments, the indication is a multi-bit indication.

[0126] In some embodiments, means for performing at least one operation includes means for initiating a resynchronization procedure to the network device via the second satellite based on receiving a satellite ID different from an identification of the first satellite; and means for performing an uplink transmission to the network device via the second satellite.

[0127] In some embodiments, the time is during an overlapping time between a first time point and a second time point, the first time point being used for the second satellite to start serving the terminal device in an area covered by the terminal device's service satellite, and the second time point being used for the first satellite to stop serving the terminal device in the area.

[0128] In some embodiments, the handover is a soft satellite handover during an overlapping time.

[0129] In some embodiments, the apparatus further comprises means for performing other steps of some embodiments of method 500. In some embodiments, the apparatus comprises: at least one processor, and at least one memory comprising computer program code, the at least one memory and the computer program code being configured to, together with the at least one processor, enable the performance of the apparatus.

[0130] In some embodiments, an apparatus (e.g., a network device) capable of performing any of the methods 600 may include a component for performing the corresponding steps of the method 600. The component may be implemented in any suitable form. For example, the component may be implemented in a circuit system or a software module.

[0131] In some embodiments, the apparatus includes: components for sending an indication to a terminal device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation includes at least one of: (i) initiating a resynchronization process to a network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and components for receiving the uplink transmission from the terminal device via the second satellite.

[0132] In some embodiments, the indication comprises a parameter indicating a function from a set of preconfigured functions.The apparatus further comprises means for using an identification (ID) of the terminal device as input to determine the time based on the function.

[0133] In some embodiments, the parameter is part of a system information block 19 (SIB 19) broadcast from the network device.

[0134] In some embodiments, the indication is sent before or after a first point in time when the second satellite begins serving an area covered by the terminal device's serving satellite.

[0135] In some embodiments, the indication includes a group number of a terminal device group, the terminal device group including the terminal device. The apparatus further includes a component for determining the time based on the group number and an ID of the terminal device.

[0136] In some embodiments, the component for determining the time includes a component for calculating the time based on the following formula: T = floor((t-Service-t-ServiceStart) / N)*(UE-ID mod N), where T represents the time, t-Service represents the second time point when the first satellite stops serving the terminal device in the area covered by the service satellite of the terminal device, t-ServiceStart represents the first time point when the second satellite starts serving the area, N represents the group number, UE-ID represents the ID of the terminal device, floor() represents the floor function, and mod represents the modulo operation.

[0137] In some embodiments, at least one operation comprises an uplink transmission via a second satellite.The apparatus also includes means for receiving an uplink transmission from a terminal device at the time.

[0138] In some embodiments, the time is specific to a terminal device or specific to a group of terminal devices including the terminal device.

[0139] In some embodiments, the indication is included in the scheduling information and indicates that the scheduled transmission will be the last transmission via the first satellite.

[0140] In some embodiments, the indication is a single bit indication.

[0141] In some embodiments, the apparatus further comprises a component for determining, based on the scheduled transmission, that the terminal device will initiate a resynchronization process to the network device via the second satellite, and that an uplink transmission will be received from the terminal device via the second satellite.

[0142] In some embodiments, the indication is included in the scheduling information and indicates a satellite identification (ID) of the second satellite.

[0143] In some embodiments, the indication is a multi-bit indication.

[0144] In some embodiments, the time is during an overlapping time between a first time point and a second time point, the first time point being used for the second satellite to start serving the terminal device in an area covered by the terminal device's service satellite, and the second time point being used for the first satellite to stop serving the terminal device in the area.

[0145] In some embodiments, the handover is a soft satellite handover during an overlapping time.

[0146] In some embodiments, the apparatus further comprises means for exchanging data with the terminal device via the first satellite before a first point in time when the second satellite starts serving an area covered by a serving satellite of the terminal device; and means for determining an optimal resynchronization time for the terminal device.

[0147] In some embodiments, the apparatus further comprises means for performing other steps of some embodiments of method 600. In some embodiments, the apparatus comprises: at least one processor, and at least one memory comprising computer program code, the at least one memory and the computer program code being configured to, together with the at least one processor, enable the performance of the apparatus.

[0148] Figure 7 700 is a simplified block diagram of a device 700 suitable for implementing an embodiment of the present disclosure. The device 700 may be provided to implement a communication device, such as a terminal device or a network device. As shown in the figure, the device 700 includes: one or more processors 710, one or more memories 720 coupled to the processor 710, and one or more communication modules 740 coupled to the processor 710.

[0149] The communication module 740 is used for two-way communication. The communication module 740 has at least one antenna to facilitate communication. The communication interface may represent any interface necessary for communication with other network elements.

[0150] Processor 710 may be of any type suitable for the local technology network, and may include, as non-limiting examples, one or more of a general purpose computer, a special purpose computer, a microprocessor, a digital signal processor (DSP), and a processor based on a multi-core processor architecture. Device 700 may have multiple processors, such as application specific integrated circuit chips that are time slaved to a clock synchronized with a main processor.

[0151] The memory 720 may include one or more non-volatile memories and one or more volatile memories. Examples of non-volatile memories include, but are not limited to, read-only memory (ROM) 724, electrically programmable read-only memory (EPROM), flash memory, hard disk, compact disk (CD), digital video disk (DVD) and other magnetic storage devices, and / or optical storage devices. Examples of volatile memories include, but are not limited to, random access memory (RAM) 722 and other volatile memories that do not persist during power outages.

[0152] The computer program 730 includes computer executable instructions that are executed by the associated processor 710. The program 730 may be stored in the ROM 724. The processor 710 may perform any suitable actions and processes by loading the program 730 into the RAM 722.

[0153] The embodiments of the present disclosure can be implemented by means of program 730, so that device 700 can execute reference Figures 2 to 6 Any process of the present disclosure discussed. The embodiments of the present disclosure may also be implemented by hardware or a combination of software and hardware.

[0154] In some embodiments, the program 730 may be tangibly contained in a computer-readable medium, which may be included in the device 700 (such as in the memory 720), or in other storage devices accessible to the device 700. The device 700 may load the program 730 from the computer-readable medium to the RAM 722 for execution. The computer-readable medium may include any type of tangible non-volatile memory, such as ROM, EPROM, flash memory, hard disk, CD, DVD, etc. Figure 8 An example of a computer readable medium 800 in the form of a CD or DVD is shown. The computer readable medium has a program 730 stored thereon.

[0155] Generally, various embodiments of the present disclosure may be implemented using hardware or dedicated circuits, software, logic, or any combination thereof. Some aspects may be implemented using hardware, while other aspects may be implemented using firmware or software that may be executed by a controller, microprocessor, or other computing device. Although various aspects of the embodiments of the present disclosure are illustrated and described as block diagrams, flow charts, or using some other graphical representations, it should be understood that, as non-limiting examples, the blocks, devices, systems, techniques, or methods described herein may be implemented using hardware, software, firmware, dedicated circuits or logic, general hardware or controllers or other computing devices, or some combination thereof.

[0156] The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer executable instructions, such as instructions included in a program module, which are executed in a device on a target real or virtual processor to perform the above reference Figure 2-Figure 6 The described method 500 or 600. Typically, a program module includes a routine, program, library, object, class, component, data structure, etc. that performs a specific task or implements a specific abstract data type. In various embodiments, the functions of the program modules can be combined or split between program modules as needed. The machine executable instructions of the program modules can be executed in a local or distributed device. In a distributed device, the program modules can be located in both local and remote storage media.

[0157] The program code for executing the method of the present disclosure can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device so that the program code, when executed by the processor or controller, enables the function / operation specified in the flow chart and / or block diagram to be realized. The program code can be executed completely on the machine, partially on the machine, as an independent software package, partially on the machine and partially on a remote machine, or completely on a remote machine or server.

[0158] In the context of the present disclosure, computer program codes or related data may be carried by any suitable carrier to enable a device, apparatus, or processor to perform various processes and operations as described above. Examples of carriers include signals, computer-readable media, etc.

[0159] Computer readable medium can be a computer readable signal medium or a computer readable storage medium. Computer readable medium can include but is not limited to electronic, magnetic, optical, electromagnetic, infrared or semiconductor systems, devices or equipment, or any suitable combination of the foregoing. More specific examples of computer readable storage medium will include electrical connections with one or more wires, portable computer floppy disks, hard disks, random access memories (RAM), read-only memories (ROM), erasable programmable read-only memories (EPROM or flash memory), optical fibers, portable compact disk read-only memories (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing. The term "non-transient" used herein is a restriction on the medium itself (i.e., tangible, rather than signal), rather than a restriction on data storage persistence (e.g., RAM and ROM).

[0160] In addition, although the operations are described in a specific order, this should not be understood as requiring such operations to be performed in the specific order shown or in order or performing all the operations shown to obtain the desired result. In some cases, multitasking and parallel processing may be advantageous. Similarly, although several specific implementation details are included in the above discussion, these should not be interpreted as limitations on the scope of the present disclosure, but rather descriptions of features that may be specific to a particular embodiment. Certain features described in the context of a separate embodiment may also be implemented in combination in a single embodiment. On the contrary, the various features described in the context of a single embodiment may also be implemented in multiple embodiments individually or in any suitable sub-combination.

[0161] Although the present disclosure has been described in language specific to structural features and / or methodological actions, it should be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or actions described above. Instead, the specific features or actions described above are disclosed as example forms of implementing the claims.

Claims

1. A terminal device, comprising: at least one processor; as well as At least one memory stores instructions, which, when executed by the at least one processor, cause the terminal device to at least: receiving, from a network device, an indication for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; as well as Based on the received indication, the at least one operation is performed.

2. The terminal device according to claim 1, wherein the indication comprises a parameter, the parameter indicating a function in a set of preconfigured functions, and the terminal device is further caused to: The time is determined based on the function using an identification (ID) of the terminal device as an input.

3. The terminal device of claim 2, wherein the parameter is part of a system information block (SIB) broadcast from the network device.

4. The terminal device according to claim 2 or 3, wherein: The indication is received before or after a first point in time at which the second satellite starts serving an area covered by a serving satellite of the terminal device.

5. The terminal device according to claim 1, wherein the indication comprises a group number of a terminal device group, the terminal device group comprises the terminal device, and the terminal device is further caused to: Based on the group number and the ID of the terminal device, the time is determined.

6. The terminal device according to claim 5, wherein the terminal device is caused to determine the time by: The time is calculated based on the formula T=floor((t-Service-t-ServiceStart) / N)*(UE-ID mod N), where T represents the time, t-Service represents the second time point when the first satellite stops serving the terminal device in the area covered by the service satellite of the terminal device, t-ServiceStart represents the first time point when the second satellite starts serving the area, N represents the group number, UE-ID represents the ID of the terminal device, floor() represents floor function, and mod represents modulo operation.

7. The terminal device according to any one of claims 2 to 6, wherein the at least one operation comprises the uplink transmission via the second satellite, and the terminal device is caused to perform the at least one operation by: before the time, initiating the resynchronization process to the network device via the second satellite; and The uplink transmission is performed to the network device at the time.

8. The terminal device according to claim 7, wherein the time is specific to the terminal device or specific to a terminal device group including the terminal device.

9. The terminal device of claim 1, wherein the indication is included in scheduling information and indicates that the scheduled transmission will be the last transmission via the first satellite.

10. The terminal device according to claim 9, wherein the indication is a single-bit indication.

11. The terminal device according to claim 9 or 10, wherein the terminal device is configured to perform the at least one operation by: initiating the resynchronization process to the network device via the second satellite after the scheduled transmission; and The uplink transmission is performed to the network device via the second satellite. 12 . The terminal device according to claim 1 , wherein the indication is included in scheduling information and indicates a satellite identification (ID) of the second satellite.

13. The terminal device according to claim 12, wherein the indication is a multi-bit indication.

14. The terminal device according to claim 12 or 13, wherein the terminal device is caused to perform the at least one operation by: initiating the resynchronization process to the network device via the second satellite based on receiving the satellite ID that is different from the identification of the first satellite; and The uplink transmission is performed to the network device via the second satellite.

15. The terminal device according to any one of claims 1 to 14, wherein: The time is during the overlapping time between the first time point and the second time point, The first time point is for the second satellite to start serving the terminal device in an area covered by the serving satellite of the terminal device, and The second time point is used for the first satellite to stop serving the terminal device in the area.

16. The terminal device of claim 15, wherein the handover is a soft satellite handover during the overlap time.

17. A network device comprising: at least one processor; as well as at least one memory storing instructions, which, when executed by the at least one processor, cause the network device to at least: sending an indication to a terminal device for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and The uplink transmission is received from the terminal device via the second satellite.

18. The network device of claim 17, wherein the indication comprises a parameter indicating a function from a set of preconfigured functions, and the network device is further caused to: The time is determined based on the function using an identification (ID) of the terminal device as an input.

19. The network device of claim 18, wherein the parameter is part of a system information block 19 (SIB19) broadcast from the network device.

20. The network device according to claim 18 or 19, wherein: The indication is sent before or after a first point in time when the second satellite starts serving an area covered by a serving satellite of the terminal device.

21. The network device according to claim 17, wherein the indication comprises a group number of a terminal device group, the terminal device group comprising the terminal device, and the network device is further caused to: Based on the group number and the ID of the terminal device, the time is determined.

22. The network device of claim 21, wherein the network device is caused to determine the time by: The time is calculated based on the formula T=floor((t-Service-t-ServiceStart) / N)*(UE-ID mod N), where T represents the time, t-Service represents the second time point when the first satellite stops serving the terminal device in the area covered by the service satellite of the terminal device, t-ServiceStart represents the first time point when the second satellite starts serving the area, N represents the group number, UE-ID represents the ID of the terminal device, floor() represents floor function, and mod represents modulo operation.

23. The network device of any one of claims 18 to 21, wherein the at least one operation comprises the uplink transmission via the second satellite, and the network device is further caused to: At the time, the uplink transmission is received from the terminal device.

24. The network device according to claim 23, wherein the time is specific to the terminal device, or specific to a group of terminal devices including the terminal device.

25. The network device of claim 17, wherein the indication is included in scheduling information and indicates that the scheduled transmission will be the last transmission via the first satellite.

26. The network device of claim 25, wherein the indication is a single-bit indication.

27. The network device according to claim 25 or 26, wherein the network device is further caused to: It is determined based on the scheduled transmission that the terminal device will initiate the resynchronization process to the network device via the second satellite and that the uplink transmission will be received from the terminal device via the second satellite.

28. The network device of claim 17, wherein the indication is included in scheduling information and indicates a satellite identification (ID) of the second satellite.

29. The network device of claim 28, wherein the indication is a multi-bit indication.

30. The network device according to any one of claims 17 to 29, wherein: The time is during the overlapping time between the first time point and the second time point, The first time point is for the second satellite to start serving the terminal device in an area covered by the serving satellite of the terminal device, and The second time point is used for the first satellite to stop serving the terminal device in the area.

31. The network device of claim 30, wherein the handover is a soft satellite handover during the overlap time.

32. The network device according to any one of claims 17 to 31, wherein the network device is further configured to: exchanging data with the terminal device via the first satellite before a first point in time when the second satellite starts serving an area covered by a serving satellite of the terminal device; and An optimal resynchronization time for the terminal device is determined.

33. A method for communication, comprising: receiving, at a terminal device, from a network device, an indication for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; as well as Based on the received indication, the at least one operation is performed.

34. A method for communication, comprising: sending, at a network device, to a terminal device, an indication for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; and The uplink transmission is received from the terminal device via the second satellite.

35. An apparatus for use in a communication network, comprising: means for receiving, at a terminal device, from a network device, an indication for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; as well as Means for performing the at least one operation based on the received indication.

36. An apparatus for use in a communication network, comprising: means for sending, at a network device, to a terminal device, an indication for determining a time for at least one operation associated with switching from a first satellite to a second satellite, wherein the at least one operation comprises at least one of: (i) initiating a resynchronization procedure to the network device via the second satellite, or (ii) performing an uplink transmission via the second satellite; as well as Means for receiving the uplink transmission from the terminal device via the second satellite.

37. A non-transitory computer-readable medium comprising program instructions, which, when executed by a device, cause the device to at least perform the method according to any one of claims 33 to 34.

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