WO2025208637A1

WO2025208637A1 - Reduction of uncertainty in satellite switching

Info

Publication number: WO2025208637A1
Application number: PCT/CN2024/086258
Authority: WO
Inventors: Jedrzej STANCZAK; Enric Juan; Ping Yuan; Rafhael MEDEIROS DE AMORIM
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Priority date: 2024-04-05
Filing date: 2024-04-05
Publication date: 2025-10-09
Anticipated expiration: 2026-10-05

Abstract

Embodiments of the present disclosure disclose devices, methods and apparatuses for reduction of uncertainty in satellite switching. In the embodiments, a terminal device starts a timer based on determining that a cell provided by a first satellite stops serving the terminal device. Then, the terminal device performs an operation based on the timer. In this way, the uncertainty in satellite switching is able to be reduced.

Description

REDUCTION OF UNCERTAINTY IN SATELLITE SWITCHING

FIELD

Various example embodiments relate to the field of communications and in particular, to devices, methods, apparatuses and a computer readable storage medium for the reduction of uncertainty in satellite switching.

BACKGROUND

A communication network can be seen as a facility that enables communications between two or more communication devices, or provides communication devices access to a data network. A mobile or wireless communication network is one example of a communication network.

Such communication networks operate in accordance with standards, such as those promulgated by 3GPP (Third Generation Partnership Project) or ETSI (European Telecommunications Standards Institute) . Examples of such standards include the so-called 5G (5th Generation) standard or other standards promulgated by 3GPP.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for the reduction of uncertainty in satellite switch, especially for reducing the uncertainty of the satellite switching with resynchronization completion.

In a first aspect, there is provided a terminal device. The terminal device comprises at least one processor and at least one memory including computer program codes. The at least one memory and the computer program codes are configured to, with the at least one processor, cause the terminal device to start a timer based on determining that a cell provided by a first satellite stops serving the terminal device. The terminal device is further caused to perform an operation based on the timer.

In a second aspect, there is provided a network device. The network device comprises at least one processor and at least one memory including computer program codes. The at least one memory and the computer program codes are configured to, with the at least one processor, cause the network device to start a timer based on determining that a cell provided by a first satellite stops serving a terminal device. The network device is further caused to perform an operation related to the terminal device based on the timer.

In a third aspect, there is provided a method implemented at a terminal device. The method comprises: starting, by a terminal device, a timer based on determining that a cell provided by a first satellite stops serving the terminal device. The method further comprises performing an operation based on the timer.

In a fourth aspect, there is provided a method implemented at a network device. The method comprises: starting, by a network device, a timer based on determining that a cell provided by a first satellite stops serving a terminal device. The method further comprises performing an operation related to the terminal device based on the timer.

In a fifth aspect, there is provided an apparatus comprising means for starting, by a terminal device, a timer based on determining that a cell provided by a first satellite stops serving a terminal device; and means for performing an operation based on the timer.

In a sixth aspect, there is provided an apparatus comprising means for starting, by a network device, a timer based on determining that a cell provided by a first satellite stops serving a terminal device; and means for performing an operation related to the terminal device based on the timer.

In a seventh aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method according to any one of the above fourth to fifth aspect.

In an eighth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: start a timer based on determining that a cell provided by a first satellite stops serving a terminal device. The apparatus is further caused to perform an operation based on the timer.

In a ninth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: start a timer based on determining that a cell provided by a first satellite stops serving the terminal device. The apparatus is further caused to perform an operation related to the terminal device based on the timer.

In a tenth aspect, there is provided a terminal device. The terminal device comprises starting circuitry configured to start a timer based on determining that a cell provided by a first satellite stops serving the terminal device. The terminal device further comprises performing circuitry configured to perform an operation based on the timer.

In an eleventh aspect, there is provided a network device. The network device comprises starting circuitry configured to start a timer based on determining that a cell provided by a first satellite stops serving a terminal device. The network device further comprises performing circuitry configured to perform an operation related to the terminal device based on the timer.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1A illustrates an example communication network in which embodiments of the present disclosure may be implemented;

FIG. 1B illustrates an example architecture of a non-terrestrial network;

FIG. 1C illustrates an example of resynchronization switching of a UE from a source satellite (SAT) -1 to a target satellite (SAT) -2;

FIG. 2A illustrates an example signaling process for the reduction of uncertainty in resynchronization switch according to example embodiments of the present disclosure;

FIG. 2B illustrates an example signaling process for the reduction of uncertainty in resynchronization switch under the successful satellite switching according to example embodiments of the present disclosure;

FIG. 2C illustrates another example signaling process for the reduction of uncertainty in resynchronization switch under the successful satellite switching according to example embodiments of the present disclosure;

FIG. 2D illustrates a further example signaling process for the reduction of uncertainty in resynchronization switch under the unsuccessful satellite switching according to example embodiments of the present disclosure;

FIG. 3A illustrates an example process for the reduction of uncertainty in the resynchronization switch in the case that the resynchronization switch is successful according to some embodiments of the present disclosure;

FIG. 3B illustrates another example process for the reduction of uncertainty in the resynchronization switch in the case that the resynchronization switch is successful according to some embodiments of the present disclosure;

FIG. 3C illustrates an example process for the reduction of uncertainty in the resynchronization switch in the case that the resynchronization switch is unsuccessful according to some embodiments of the present disclosure;

FIG. 4 illustrates a flowchart of a method implemented at a terminal device according to some embodiments of the present disclosure;

FIG. 5 illustrates a flowchart of a method implemented at a network device according to some embodiments of the present disclosure;

FIG. 6 illustrates a simplified block diagram of an apparatus that is suitable for implementing embodiments of the present disclosure; and

FIG. 7 illustrates a block diagram of an example computer readable medium in accordance with some embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principles of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

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 skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes 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 affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof. As used herein, “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” and similar wording, where the list of two or more elements are joined by “and” or “or” , mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

(i) a combination of analog and/or digital hardware circuit (s) with software/firmware and

(ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

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

As used herein, the term “communication network” refers to a network following any suitable communication standards, such as 5G New Radio (NR) , Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the future fifth generation (5G) communication protocols, and/or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned systems.

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 therefrom. The network device may refer to a base station (BS) or an access point (AP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR NB (also referred to as a gNB, a base station of a 5G system) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology.

The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, 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 not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA) , portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) , an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD) , a vehicle, a drone, a medical device and applications (e.g., remote surgery) , an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts) , a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. In the following description, the terms “terminal device” , “communication device” , “terminal” , “user equipment” and “UE” may be used interchangeably.

In some wireless communication systems, satellite communication is involved. Using 5G NR standards to support non-terrestrial networks (NTN) has been studied during 3GPP releases 15 and 16. In an approved work item for Non Terrestrial Network (NTN) in release 17, the UEs supporting NTN are assumed to have Global Navigation Satellite System (GNSS) capability. In an NTN system, 5G base stations (gNB) or gNB functionality are deployed on board satellites or relayed by gNBs in a transparent way to provide communication coverage over a very large area that may be otherwise unreachable by cellular networks. Such functionality can be used to connect IoT devices globally as well as provide personal communication in remote areas and in disaster relief. There are different types of satellite orbits that have been studied for New Radio (NR) access including Low Earth Orbit (LEO) satellites which orbit at approximately 600 km above the earth. During the Rel-16 study item the typical beam footprint size for a LEO satellite was assumed to be between 100-1000 km radiuses. Thus, one LEO satellite can cover a very large area on the Earth which may include multiple countries.

In some embodiments of the disclosure, the terms “resynchronization switching” , “satellite switch with resynchronization” , “satellite switch” and “satellite switching” may be used interchangeably without any limitation.

In Rel-18, the topic of unchanged physical cell identification (PCI) is addressed, with the goal of reducing the signaling overhead and simplifying RRC procedures for the UE. In some embodiments of the disclosure, the term “unchanged PCI” may be also referred to as “satellite switch with resynchronization” or “resynchronization switching” .

The working principle is that after a satellite switching, the serving gNB and the cell (on ground) does not change and, therefore, the (majority of the) cell configuration can be kept without changing the PCI, frequency, and other cell configuration parameters (e.g., servingCellconfigCommon) . Then, the satellite switching is almost transparent for the UE, that is, it is not required to perform layer 3 (L3) mobility (i.e., handover procedure) , thus it can avoid flushing buffers, and it does not need to update the security key.

The satellite switching can be broken down in two additional scenarios, i.e., a hard satellite switching and a soft satellite switching. The soft satellite switching considers a certain cell overlapping between the NTN cell radiated by Satellite-1 and Satellite-2, while the hard satellite switching considers no overlapping between the old and the new cell (note that the UE should consider certain interruption time to pre-compensate frequency and timing of the new cell) . For the soft satellite switching it is assumed that Satellite-1 and Satelllite-2 are transmitting SSBs offset in time, thereby allowing (in theory) a UE to gracefully switch to the new (incoming) satellite. Only to discuss clarity, the satellite switching is further discussed with reference to FIG. 1B.

The conditions for the above mechanism to work are: (i) NTN cells must be deployed as quasi-Earth fixed cells (EFC) since the cell coverage’s area should not change; (ii) the network (NW) should indicate the UE how/when to re-synchronize after satellite switching; (iii) target satellite information should be provided before satellite switching and via broadcast signaling (no RRC dedicated signaling shall be used to reduce the 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 the fixed PCI is provided by the same gNB, so only the satellite node is changed. However, theoretically, this could also work with different gNB and potentially even for the regenerative case.

In some solutions, UE actions upon satellite switch are contained. For example, upon receiving System Information Block 19 (SIB19) in an NTN cell, the UE in RRC_CONNECTED shall: start or restart T430 for serving cell with the timer value set to ntn-UlSyncValidityDuration for the serving cell from the subframe indicated by epochTime for the serving cell; if SatSwitchWithReSync and t-Service are included, and the UE supports satellite switch with resynchronization. In addition, UE performs the satellite switch with resynchronization not before t-Service for the serving cell.

It should be noted that UE should attempt to re-acquire SIB19 before the end of the duration indicated by ntn-UlSyncValidityDuration and epochTime by UE implementation. For satellite switch with re-synchronization in RRC_CONNECTED UE, the UE shall stop timer T430 if running; inform lower layers that uplink (UL) synchronization is lost due to satellite switch with re-synchronization; start re-synchronising to the downlink (DL) of the SpCell served by the satellite indicated by ntn-Config in SatSwitchWithReSync; start timer T430 with the timer value set to ntn-UlSyncValidityDuration from the subframe indicated by epochTime in ntn-Config in SatSwitchWithReSync; inform lower layers when UL synchronisation is obtained.

A definition of SIB19 above is contained in Clause 6.3 (RRC information elements) in TS38.331. Specifically, the SIB19 is a NTN-specific SIB used to signal satellite assistance information (including target satellite information for the satellite switch) . In SIB 19, optionally, some fields, such as ntn-Config, satSwitchWithReSync, t-Service, ssb-TimeOffset and t-ServiceStart are contained.

The t-Service indicates the time information on when a cell provided via NTN system is going to stop serving the area it is currently covering. This field applies for both service link switches in NTN quasi-Earth fixed system and feeder link switches for both NTN quasi-Earth fixed and Earth moving system. The field indicates a time in multiples of 10 ms after 00: 00: 00 on Gregorian calendar date 1 January, 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. The reference point for t-Service is the uplink time synchronization reference point of the cell. This field is only present in an NTN cell.

The t-ServiceStart indicates the time information on when the target satellite is going to start serving the area currently covered by the serving satellite. 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 ntn-Config provides parameters needed for the UE to access NR via NTN access such as Ephemeris data, common Timing Advance (TA) parameters, k_offset, validity duration for UL sync information and epoch. In a Terrestrial Network (TN) cell, this field is only present in ntn-NeighCellConfigList and ntn-NeighCellConfigListExt.

The satSwitchWithReSync provides parameters for the target satellite required to perform satellite switch with re-synchronization. This field is present in an NTN cell and its presence indicates that satellite switch without Physical Cell Identification (PCI) change is supported in the cell.

The ssb-TimeOffset indicates the time offset between the SSB from source and target satellite at the uplink time synchronization reference point. It is given in number of subframes. The t-ServiceStart indicates the time information on when the target satellite is going to start serving the area currently covered by the serving satellite. 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.

Some solutions of a RACH-less access process during the satellite switch with resynchronization involves a UE and source satellites (e.g. a source SAT-1) . The UE will conduct the following steps: UE receives SIB19 in source SAT-1, containing the information required for RACH-less satellite switch to the target satellite, e.g. NTN-configuration of target satellite, SSB index (optional) , SSB time offset (optional) .

Then, UE operations are as followings. At radio resource control (RRC) layer, UE decides the satellite switch time (i.e. T-switch) . No matter for hard switch or soft switch, the T-switch is not before the T-service. UE considers T430 expiry, and a new trigger of T430 expiry should be specified. Then, UE indicates MAC to start satellite switch procedure.

At the media access control (MAC) layer, upon a reception of satellite switch start indication from upper layer, there is no impact on TA Timer and UE flushes the hybrid automatic repeat request hybrid (HARQ) buffer without waiting the expiry of the timer T430. UE suspends UL transmission without waiting the expiry of the timer T430.

In addition, UE detects the DL synchronization of target satellite (e.g., a target SAT-2) based on the provided SSB time offset. UE performs SSB-based RRM Measurement Timing Configuration (SMTC) adjustment based on PDD. For soft satellite switch, the SMTC adjustment also considers the SSB time offset (if configured) . UE detects the target satellite’s SSB within the adjusted SMTC window. If SSB information of target satellite is not provided in SIB19 by network, source’s SSB is used. When UE acquires DL sync of target satellite, UE operation is as follows: at RRC layer, acquire SIB19; start T430; and indicate to lower layer that UL sync for satellite switch is restored.

At MAC layer, UE sets NTA value = 0 and clears UE specific Koffset. UE allows UL transmission without waiting an expiry of the timer T430. UE may trigger TAR and TAR-SR. Then, UE may initiate the TA reporting transmission as the 1st UL transmission.

In view of the above, it was agreed that for satellite switching with resynchronization, a UE shall start accessing the target satellite not before T-service, irrespectively of the type of satellite switching (i.e. hard-or soft-switching) . Thus, even though the UE can measure the target satellite and acquire DL timing before (in case of soft-switching) , it will not apply the new timing and frequency pre-compensation until after t-Service. After the UE successfully finishes the resynchronization towards the target satellite, the UE is able to communicate with the gNB via the target satellite, for example in the case of the transparent architecture.

In the handover procedure, when the UE has successfully completed the target cell access (i.e., UE is ready to TX/RX) , UE may transmit an RRC Reconfiguration Complete message to confirm the network that the handover (or switch) procedure was successful completed. Then, the network may schedule the UE without uncertainty. However, in the satellite switching with resynchronization, there is no explicit UL transmission for confirming a successful switching.

A solution for eliminating the uncertainty may be mandating UEs to access the target satellite via RACH procedure. However, it has been agreed that all UEs supporting satellite switch with (re-) synchronization shall be able to perform satellite switching with re-synchronization without RACH. Thus, if UE performs the satellite switching with resynchronization, the network still has no means to confirm whether the UE successfully resynchronization or UE cannot access via the RACH procedure.

Moreover, the satellite switch with (re-) synchronization was a feature proposed during the normative phase of Rel-18 to reduce the signaling overhead. Thus, an explicit confirmation message immediately transmitted after the successful resynchronization switching may be contrary to the intentions of the resynchronization switch. Furthermore, if every UE has to explicitly confirm the successful switching, it is a waste of UL air interface resources. Another potential solution could be an implicit confirmation. That is, if the UE has UL data to transmit, the NW could confirm the switching based on that first UL transmission. However, if the UE has no UL data to transmit, the network has no means to acknowledge whether the UE did switch or not. Similarly, if the network has DL data for UE, the network does not know if it should risk scheduling resources for a UE which has not confirmed its effective switch (even though the UE stays in theory in the same cell) .

In view of these analysis and considerations, a new solution is proposed in some embodiments of the present disclosure. In some aspects, a terminal device starts a timer based on determining that a cell provided by a first satellite stops serving the terminal device. Then, the terminal device performs an operation based on the timer. On the other hand, a network device starts a timer based on determining that a cell provided by a first satellite stops serving the terminal device. Then, the network device performs an operation related to the terminal device based on the timer.

In this way, a timer is introduced for the resynchronization switching, the timer may define how long the terminal device can stay under the inbound target network device without performing any actions. In some embodiments of the disclosure, if the terminal device performs some operations during the timer is running, the resynchronization switching may be determined as successful implicitly. In some embodiments, if the timer expires, the terminal device may be triggered to perform some other operations to confirm the successful resynchronization switching or unsuccessful resynchronization switching. In this way, the uncertainty in the resynchronization switching is able to be eliminated without increasing the signaling significantly.

Principles and embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Reference is first made to FIG. 1A, which illustrates an example communication system 100A (or referred to as communication network) in which embodiments of the present disclosure may be implemented. The system 100A, for example, a communication network, includes a plurality of terminal device (s) and network device (s) , such as a terminal device 110 and a network device 120. The system 100A further includes satellites 122 and 124, for example, SAT-1 and SAT-2, respectively. In some embodiments of the disclosure, the terrestrial network device 120 provides a cell coverage for the terminal device 110 via the satellites 122 and 124. In some embodiments, the satellites 122 and 124 may act as a “repeater” of the network device 120. For example, the satellites 122 and 124 may forward the signals from the network device 120 to the terminal device 110 and forwards the signals from the terminal device 110 to the network device 120. In some embodiments, the network device 120 may provide the cell coverage via the satellites 122 and 124 in a relay manner. For example, the satellite 122 may provide the cell A at first. With the movement of the satellite 122, the satellite is not able to provide the cell A anymore. In this case, the network device 120 may provide the cell coverage via the satellite 124, for example, the cell B. In some embodiments, the cells A and B are the same cell identified with the same physical cell identity (PCI) in NTN. In some embodiments of the disclosure, the above architecture may be also referred to as a “transparent architecture” . In some embodiments of the disclosure, the satellite 122 may be also referred to as a source satellite and the satellite 124 may be also to as a target satellite, since the terminal device may perform a switching with resynchronization from the satellite 122 to the satellite 124.

Alternatively, in some embodiments of the disclosure, the network devices may be also located on the satellites (which are not shown in FIG. 1A) . Assuming that the satellite 122 may include a first network device and the satellite 124 may include a second network device. In this case, the terminal device 110 may perform a switching with resynchronization from the first network device on the satellite 122 to the second network device on the satellite 124. In some embodiments of the disclosure, the above architecture may be also referred to as a “regenerative architecture” .

In NR NTN scenarios, the satellites 122 and 124 may be NTN devices. In some examples, the satellites 122 and 124 may be a low earth orbiting (LEO) satellite, a medium earth orbiting (MEO) satellite, or a geostationary earth orbiting (GEO) satellite. The terminal device 110 may communicate with the satellites 122 or 124.

Thus, the satellites 122 or 124 (e.g. the NTN device) may function as a transmission relay node between the network device 120 and the terminal device 110 in a transparent manner. Alternatively, in the regenerative case, the satellites 122 or 124 may be the network device (e.g., base station) themselves, and the network device 120 may be a core network (CN) device in the regenerative manner.

Only for discussion purposes, assuming that a cell A provided by the satellite 124 is going to stop serving due to the movement of the satellite 122, and a cell B provided by the satellite 124 is going to provide communication service for the related area. The cell A and B are identified with the same physical cell identity (PCI) in an NTN system. In turn, the terminal device 110 is able to switch from the satellite 122 to the satellite 124 with resynchronization. As an example, since the satellite 122 moves away from the terminal device 110 and the satellite 124 gets closer, the network (e.g. the base station 120 under the transparent case or a base station on the satellite 122 under regenerative case) may indicate, via the satellite 122, when the satellite switching will occur and how to perform re-synchronization to the new cell. Once the satellite 124 takes over serving the area (i.e. a cell B) , the terminal device 110 performs DL/UL synchronization operations to re-connect. In some example embodiments of the disclosure, the terminal device 110 may communicate with the network device 120 via the satellite 124 after the satellite 124 takes over serving the area. For example, the terminal device 110 may transmit UL transmission to the network device 120 via the satellite 124. Without any limitation, the terminal device 110 may also communicate with the network device 120 via the satellite 122, for example, before the cell A stops serving the terminal device. In such examples, even though the terminal device 110 is being served by a new satellite, i.e., the satellite 124, the serving base station is not changed so it can keep the cell configuration. In some embodiments, in the transparent architecture, the network device 120 is configured with the same PCI, same UE context and same protocol stack (including SSB generation, coding/decoding, modulation/demodulation, same CORESET configuration, and switch routing) . Alternatively, in the regenerative architecture, the network devices on the satellite 122 and the satellite 124 may be configured with the same PCI, same UE context and same protocol stack (including SSB generation, coding/decoding, modulation/demodulation, same CORESET configuration, and switch routing) . However, from the terminal device’s reference, the satellites 122 and 124 introduce different frequency (i.e., Doppler) and timing drifts (the propagation paths towards Satellite-1 and Satellite-2 are different) . Thus, the terminal device is required to perform the resynchronization for the satellite 124 in order to access the satellite 124 “gracefully” .

In some embodiments of the disclosure, the satellite 122 may be also referred to as a first satellite 122 or a source satellite 122. The satellite 124 may be also referred to as a second satellite 124 or a target satellite 124. The switching between the satellites 122 and 124 may be also referred to as the satellite switching.

Some examples of satellite switching may be described with reference to FIG. 1A. As mentioned above, PCI is kept unchanged in a transparent-based EFC deployment. During the satellite switching, a UE (an example of the terminal device 110) , which is stationary, is being served by the satellite-1 (an example of the network device 115, providing a cell A) .

It is to be understood that the number of network devices and terminal devices is only for the purpose of illustration without suggesting any limitations. The system 100 may include any suitable number of network devices and terminal devices adapted for implementing embodiments of the present disclosure.

Communications in the communication system 100 may be implemented according to any proper communication protocol (s) , comprising, but not limited to, cellular communication protocols of the first generation (1G) , the second generation (2G) , the third generation (3G) , the fourth generation (4G) and the fifth generation (5G) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising 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 Multiple (OFDM) , Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and/or any other technologies currently known or to be developed in the future.

FIG. 1B illustrates an example architecture 100B of a non-terrestrial network. As shown in FIG. 1B, the example architecture 100B, may include a plurality of network device (s) and terminal device (s) , such as a terminal device 125 and network devices 127 and 129. In some examples, the network device 129 may be a satellite or a UAS platform. The network device 127 may be a gateway. The terminal device 125 is in a beam footprint among a plurality of beam footprints. One of the plurality of beam footprints may be shown at 125. There is a service link between the terminal device 125 and the network device 129. There is a feeder link between the network device 129 and the network device 127. In some examples, the system 100B may also include a data network 130. The network device 127 and the data network 130 (e.g., the Internet, an intranet, a wide area network, etc. ) may connect to each other over a wired and/or wireless network. Additionally or alternatively, the network device 127 may be connected to other core network elements not shown in FIG. 1B, such as servers, access points, switches, routers, nodes, etc.

FIG. 1C illustrates an example of resynchronization switching of a UE from a source satellite (SAT) -1 to a target satellite (SAT) -2. In FIG. 1C, UE 110 may be an example of the terminal device 110 in FIG. 1A, the source SAT-1 122 may be an example of the first satellite 122, and the target SAT-2 124 may be an example of the second satellite 124.

As mentioned above, the network (for example, the base station 120 in the transparent situation) may transmit, via the source satellite122, a system information block 19 (SIB19) 145 to UE 110 to inform how and when to perform re-synchronization to the new cell, such that to access the next network device, i.e., target SAT-2. The SIB 19 may include a field “T-service” that indicates the time information on when a cell provided via NTN system is going to stop serving the area it is currently covering. In addition, the SIB 19 may include a field “t-ServiceStart” that indicates the time information on when the target satellite is going to start serving the area currently covered by the serving satellite. In the soft satellite switching, the (first) T-service start (which may be also referred to as T-start in some embodiments) may be earlier than the T-service, and thus there is overlapping between the cell provided by the source network device and the cell provided by the target network device. In turn, UE 110 may perform the resynchronization acquisition 150-1 for the target SAT-2 124. Alternatively, in the hard satellite switching, the (second) T-start may be equal to or later than the T-service. Similarly, UE 110 may perform the resynchronization acquisition 150-2 for the target SAT-2 124. Irrespectively of the type of satellite switching (i.e. hard-or soft-switching) , UE 110 should perform (160) the switching not before the T-service. For example, UE 120 shall apply the acquired DL timing and start accessing the target satellite with related operations (for example, restart T430, reset N_TA, resume UL operations) not before t-Service.

However, as mentioned above, no matter the terminal device completes the switching with resynchronization or fails to access the target SAT-2 120, there is no means for the network to confirm whether the terminal device completed the satellite switching with resynchronization. Thus, the network may be faced with a situation in which the terminal device is in an idle state while the network still schedules resources for this terminal device.

Reference is now made to FIG. 2A, which illustrates an example signaling process 200 for the reduction of uncertainty in resynchronization switch according to example embodiments of the present disclosure. As shown in FIG. 2A, in the process 200A, a terminal device and a network device are involved. For the purpose of discussions, the signaling process 200A will be described with reference to FIG. 1A. The terminal device may be the terminal device 110 as shown. In some examples, the terminal device 110 may be a UE or another terminal device. The network device 120 may be a base station or a gNB, etc. Alternatively, the network device may be also another network device included in the target satellite 124, which is not shown in FIG. 1A. Only for discussion simplicity, the embodiments are mainly discussed with reference to the terrestrial network device 120 as shown by FIG. 1A. It is to be understood that the similar or same steps performed by the terrestrial network device 120 in the embodiments of the disclosure may be also performed by another network device on the target satellite 124, which is not shown in FIG. 1A. It would be appreciated that although the signaling process 200 has been described in the communication environment 100 of Fig. 1A, this flowchart 200 may be likewise applied to other communication scenarios.

In the process 200A, the terminal device 110 starts (210) a timer based on determining that a cell provided by a first satellite 122 (i.e., the source satellite) stops serving. In addition, the network device 120 (or another network device on the target satellite 124) also starts (220) this timer based on determining that the cell provided by the first satellite 122 stops serving. As mentioned above, in some embodiments, the field “T-service” in SIB 19 indicates the time information on when a cell provided via NTN system is going to stop serving the area it is currently covering. Thus, the terminal device 110 and the network device 120 may start the timer at the time occasion “T-service” .

In some embodiments, the timer may define the maximum allowed duration for a successful satellite switching of the terminal device 110. For example, the terminal device 110 may be allowed to perform no action (for example, transmitting no acknowledge message or non-acknowledge message) during the timer running. In other words, the timer may define how long the terminal device can stay under the inbound satellite without performing any actions, such as UL transmission. In some embodiments, during the timer running, some predefined operations (if any) of the terminal device may facilities the network to determine the resynchronization switching of the terminal device 110 is successful. In this case, the terminal device 110 and the network device 120 may terminate or cancel the timer accordingly. In turn, in some other embodiments, if there are no predefined operations required to be performed during the timer running, the terminal device should be triggered to perform some other operations upon the timer expiry to inform the state of the resynchronization switching to the network. As such, the uncertainty at the network device may be eliminated.

In some embodiments, the configuration information for the timer is indicated by the network, such as, by the network device 120 (or a further network device on the source satellite 122) . For example, the network device 120 may transmit (202) configuration information 203 for the timer to the terminal device 110. This configuration information 203 may be carried in a broadcast message, for example, the SIB 19. In addition or alternatively, the configuration information 203 may be carried in a message specific to the terminal device 110, for example, a UE-specific message. In addition or alternatively, the configuration information 203 may be carried in a message specific to cell, for example, a cell-specific message. Without any limitation, the configuration information 203 may be also carried in any new signaling, dedicated message or broadcast message. Then, the terminal device 110 may receive (205) the configuration information 203 accordingly. In addition, in some embodiments, the configuration information 203 may be preconfigured in NTN or indicated with each other in NTN devices. Thus, in the case of regenerative architecture, the network device on the target satellite is also aware the information on the timer.

In addition, based on determining that the cell provided by the first satellite 122 stops serving, the terminal device 110 may perform (230) a resynchronization switching from the first satellite 122 to the second satellite 124. Meanwhile, the timer continues running when the terminal device 110 performs the resynchronization switching. Then, the terminal device 110 may perform (233) operations based on the timer to eliminate the uncertainty at the network. Correspondingly, the network device 120 performs (236) operations related to the terminal device 110 based on the timer, to determine the state of the resynchronization switching of the terminal device 110. To discuss clarity, the operations performed by the terminal device 110 and network device 120 are further discussed with reference to FIGS. 2B to 2D. FIG. 2B illustrates the operations based on the timer in the case that the satellite switching with the resynchronization is successful and the terminal device 110 performs UL transmission before the timer expires. FIG. 2C illustrates the operations based on the timer in the case that the satellite switching with the resynchronization is successful and the terminal device 110 performs no UL transmission before the timer expires. FIG. 2D illustrates the operations based on the timer in the case that the satellite switching with the resynchronization is unsuccessful.

FIG. 2B illustrates an example signaling process 200B for the reduction of uncertainty in resynchronization switch under the successful satellite switching according to example embodiments of the present disclosure.

In the process 200B, in some embodiments, assuming that the resynchronization switching is successful. In this case, if the terminal device 110 has data to be transmitted, the terminal device 110 may transmit (240) uplink (UL) transmission 245 including the data to the network device 120 before the expiry of the timer. As an example, the terminal device 110 may transmit the data in a physical uplink shared channel (PUSCH) . If the UL transmission is completed or received by the network device 120 successfully, the network (for example, the network device 120) may determine (251) that the terminal device 110 has completed the resynchronization to the second satellite 124. In addition, in some embodiments, upon receiving (250) the uplink transmission 245, the network device 120 may further transmit (252) an acknowledge (ACK) 253 for the uplink transmission 245 to the terminal device 110, such that the terminal device 110 to be aware that the uplink transmission 245 is successful.

Alternatively, during the timer running, the network device 120 may transmit DL information to the terminal device 120, for example, downlink control information (DCI) . In turn, if the terminal device 110 transmits the UL transmission including UL feedback for the DL information to the network device 120 successfully. The network (for example, the network device 120) and may also determine (255) that the terminal device 110 has completed the resynchronization to the second satellite 124. Thus, during the timer running period, the network may decide scheduling the terminal device 110 if there is any DL traffic to be scheduled.

In addition or alternatively, the terminal device 110 may also transmit the UL transmission including a scheduling request (SR) or a random access channel (RACH) to the network device 120 before the expiry of the timer. Similarly, the network may determine (255) that the terminal device 110 has completed the resynchronization to the second satellite 124 accordingly. To discuss clarity, the SR transmitted before the expiry of the timer may be also referred to as the first SR, and RACH transmitted before the expiry of the timer may be also referred to as the first RACH. Thus, the terminal device 110 may also trigger an SR or RACH if UL transmission is needed (for example, UL buffer of the terminal device 110 needs to be emptied) .

As such, before the expiry of the timer, the terminal device 110 may transmit UL transmission including data in buffer, SR and/or RACH to the network device 120 to eliminate the uncertainty. In addition, if the terminal device is not mandated to confirm a successful switching, has no UL data to transmit and does not trigger an SR/RACH, the network may also use e.g., PDSCH/PDCCH feedback or a buffer status report (BSR) from the terminal device 110 to determine that the resynchronization is completed.

In addition, if the resynchronization has been determined as successful, the terminal device 110 and the network device 120 may stop, terminate or cancel (255 and 256) the running timer. In addition, in the embodiment where the network device 120 further transmits the ACK for the uplink transmission, the terminal device 110 may terminate (255) the timer upon receiving (254) this ACK 253. In turn, after receiving (250) the uplink transmission 245, the network device 120 may directly terminate (256) the timer, and transmit (252) the ACK 253 accordingly.

In this way, based on the UL transmission before the expiry of the timer, the network device may determine that the terminal device 110 has completed the resynchronization switching to the network device 120. As such, the network may schedule the radio resources for the terminal device 110 without wondering about the waste of the resources.

FIG. 2C illustrates another example signaling process 200C for the reduction of uncertainty in resynchronization switch under the successful satellite switching according to example embodiments of the present disclosure.

In the process 200C, assuming that the terminal device 110 transmits no UL transmission to the network device 120 during the timer running. In this case, before the expiry of the timer, the network is not able to determine whether the terminal device 110 has switched using resynchronization to the second satellite 124 successfully. In some embodiments, based on the expiry of the timer, the terminal device 110 should be triggered to perform respective operations to help the network confirm the state of the terminal device 110. For example, if the terminal device 110 has completed the resynchronization to the network device 120 successfully but transmitted no UL transmission before the expiry of the timer, the terminal device 110 may trigger, based on the expiry of timer, an UL transmission to inform the network about its presence related to the network device 120. As such, the terminal device 110 and the network device 120 may have the common understandings on the switch status, and the network can continue to schedule this terminal device without uncertainty.

In some embodiments, assuming that the terminal device 110 has completed the synchronization switching from the first satellite 122 to the second satellite 124 successfully and the terminal devices transmits no UL transmission during the timer running. In this case, once the timer expires, the terminal device 110 may transmit (261) another SR 263 (which may be also referred to as a second SR) to the network device 120. In addition or alternatively, the terminal device 110 may transmit (261) another RACH 263 (which may be also referred to as a second RACH) to the network device 120 based on the expiry of the timer. In addition or alternatively, the terminal device 110 may transmit (261) a media access control (MAC) control element (CE) to the network device 120 based on the expiry of the timer. By receiving the second SR, second RACH and/or MAC CE based on the expiry of the timer, the network device 120 may determine (267) that the terminal device 110 has completed the resynchronization.

In some embodiments, the indication of successful satellite switching may be an SR having a dedicated SR configuration, a RACH including a preamble having a dedicated RACH configuration and/or a new MAC CE (e.g., this MAC CE may include new LCID or new elements in its payload) . As an example, the second SR may be determined based on a dedicated SR configuration associated with a resynchronization switching. Thus, upon the timer expiry, the network device 120 may determine (267) that the resynchronization switching is successful if receiving the second SR determined based on a dedicated SR configuration.

As another example, the second RACH may include a preamble that is determined based on a dedicated RACH configuration associated with the resynchronization switching. Thus, upon the timer expiry, the network device 120 may determine that the resynchronization switching is successful if receiving the second SR that includes this preamble complying with the dedicated RACH configuration. In turn, if an RACH without the preamble determined based on the dedicated RACH configuration is received after the expiry of the timer, the network device 120 may determine that the resynchronization switching is unsuccessful. In some embodiments, the second RACH may be the RACH including the preamble determined based on the dedicated RACH configuration. The above third RACH may be the RACH includes other preambles. That is, the network device 120 may distinguish the RACH (i.e., the second RACH or the third RACH) indicating the successful resynchronization or another RACH indicating the unsuccessful resynchronization based on the preamble included in RACHs.

As a further example, the MAC CE indicating the successful resynchronization switching may include a logical channel identifier (LCID) and/or an element associated with the resynchronization switching. Similarly, the network device 120 may determine that the resynchronization switching is successful when receiving this MAC CE.

In some embodiments, the terminal device 110 and the network device 120 may initiate (257 and 259) another timer based on the expiry of the above timer. To discuss clarity, the timer started when the cell provided by the first satellite 122 stops serving the terminal device 110 is referred to the first timer. The other timer started when the first timer expires is referred to as a second timer. In some embodiments, upon the expiry of the first timer, the terminal device 110 may start the second timer. Before the second timer expires, the terminal device 110 is required to send the UL indication of its presence to the target satellite 124. Otherwise (if no such UL transmission is made) , the terminal device 120 may be considered as lost by the network device. Alternatively, the network device 120 may also directly release the radio resources allocated to the terminal device 110 upon the first timer expires without waiting any further tolerance duration.

FIG. 2D illustrates a further example signaling process 200D for the reduction of uncertainty in resynchronization switch under the unsuccessful satellite switching according to example embodiments of the present disclosure.

In the process 200D, assuming that the terminal device 110 fails to complete the synchronization switching from the first network device 115 to the network device 120. In this case, based on the expiry of timer, the terminal device 110 may transition to an idle state. For example, the terminal device 110 has no communication requirement currently. In addition or alternatively, the terminal device 110 may perform a cell reselection and a connection reestablishment to the network device 120 based on expiry of the timer. In addition or alternatively, the terminal device 110 may transmit (269) a further RACH 271 (which may be also referred to as “a third RACH” ) to the network device 120, and the third RACH may indicate that the synchronization switching from the first network device 115 to the network device 120 is unsuccessful. In some embodiments, the third RACH may be the RACH which is not determined based on the dedicated RACH configuration as mentioned above. In turn, if the network device 120 receives no UL transmission from the terminal device 110 after the expiry of the (first) timer, or the network device 120 receives (265) the third SR 271, or the network device 120 receives a request associated with the cell reselection and the connection reestablishment, then the network device 120 may determine (275) that the synchronization switching of the terminal device is unsuccessful. Furthermore, the network device 120 may release (277) the radio resources allocated to the terminal device 110. In this way, the preconfigured resources will be not preserved for the terminal device 110 for a longer time if the resynchronization switching is unsuccessful.

At the network side, in some embodiments, the network device 120 may directly determine the resynchronization switching of terminal device 110 is unsuccessful upon the expiry of the timer. Then, the network device 120 may release the set of radio resources allocated for the terminal device 110.

In addition or alternatively, as mentioned above, the network device 120 may wait for the UL transmission from the terminal device 110 after the expiry of the timer, and the UL transmission is triggered by the expiry of the timer. Then, the network device 120 may determine whether the resynchronization switching is successful based on the received UL transmission within a predetermined duration after the expiry of the first timer. For example, the network device 120 may determine whether the resynchronization switching is successful based on the second SR, second RACH, third RACH received within the predetermined duration after the expiry of the first timer.

Similarly, the terminal device 110 and the network device 120 may initiate (257 and 259) the second timer based on the expiry of the above timer. In some embodiments, upon the expiry of the first timer, the terminal device 110 may start the second timer. Before the second timer expires, the terminal device 110 is required to send the UL indication of its presence to the target satellite 124. Otherwise (if no such UL transmission is made) , the terminal device 120 may be considered as lost by the network device.

In an example, if the terminal device transmits no UL transmission until the expiry of the first timer, the terminal device 110 should perform respective operations during the second timer running. As mentioned above, the terminal device 110 may perform the transmission of the second SR, second RACH, MAC CE, third RACH, or perform cell reselection and a connection reestablishment and so on before the second timer expires. Then, the network device 120 may determine the status of the resynchronization switching based on the received UL transmission before the expiry of the second timer. As an example, if the network device 120 receives the second RACH before the second timer expires, the network device 120 may determine that the resynchronization switching is successful. If the network device 120 receives the third RACH during the second timer running or receives no UL transmission until the expiry of the second timer, the network device 120 may determine (267) that the resynchronization switching is successful and release the set of radio resources.

In this way, the terminal device and network are able to have the common understanding of satellite switching status with limited signaling/overhead in air interface (i.e., not all UEs need to trigger a dedicated UL transmission for satellite switch confirmation) . For discussion purposes, some example situations are further discussed below with reference to FIGS. 3A to 3C.

FIG. 3A illustrates an example process 300A for the reduction of uncertainty in the resynchronization switch in the case that the resynchronization switch is successful according to some embodiments of the present disclosure. In FIG. 3A, the terminal device may be the terminal device 110 in FIG. 1A. The network device may be the network device 120 in FIG. 1A or another network device on the second satellite 124. Only for discussion simplicity, the embodiments are mainly discussed with reference to the terrestrial network device 120. It is to be understood that the similar of same steps performed by the terrestrial network device 120 in the embodiments of the disclosure may be also performed by another network device on the target satellite 124.

FIG. 3A presents a successful switching and confirmation case. Specifically, FIG. 3A illustrates the terminal device 110 behaviors in the case that the terminal device 110 is provided with a timer for controlling “how long the switching can take” after the time occasion “T-service” .

In the process 300A, in some embodiments, the (first) timer may be a common setting for all terminal devices that support satellite switching with resynchronization. Thus, the timer may be provided in SIB (e.g. SIB19, see reference number 301 in FIG. 3A) . It is to be understood that it does not exclude the possibility to provide the (first) timer using the terminal device-dedicated signaling (for example, UE-specific signaling) . In addition, the first timer may be configured together with the configuration of the other RRC timers. Then, at 303, the terminal device 110 may be configured for satellite switching with resynchronization based on the information obtained from SIB19 (RRC IE SatSwitchWithReSync) . In some embodiments, the terminal device 110 may perform the resynchronization switching after t-Service.

At 305, upon t-Service, the terminal device 110 may start the (first) timer. Meanwhile, the terminal device 110 may change (307) the communicated satellite via satellite switching with resynchronization procedure. However, the terminal device 110 may not confirm the success of this procedure. Before the expiry of the timer expiry, it may happen that the terminal device performs (309) an UL transmission 311 to the network device 120 via the second satellite 124.

In turn, this is a clear proof for the network (e.g., the network device 120) that the terminal device 110 has successfully managed to resynchronize to a new satellite. It also implies the (first) timer can be stopped (313) for the terminal device 110 and the network is aware of the terminal device 110 being ready to be served.

FIG. 3B illustrates another example process 300B for the reduction of uncertainty in the resynchronization switch in the case that the resynchronization switch is successful according to some embodiments of the present disclosure. In FIG. 3B, the terminal device may be the terminal device 110 in FIG. 1A. The network device may be the network device 120 in FIG. 1A or another network device on the second satellite 124. Only for discussion simplicity, the embodiments are mainly discussed with reference to the terrestrial network device 120. It is to be understood that the similar of same steps performed by the terrestrial network device 120 in the embodiments of the disclosure may be also performed by another network device on the target satellite 124.

FIG. 3B presents a successful switching and confirmation case. Compared to the situation of FIG. 3A, the terminal device 110 has no UL data during the (first) timer running. Thus, the terminal device 110 transmits no UL transmission before the expiry of the timer.

In the process 300B, similarly, the (first) timer may be provided in SIB (e.g. SIB19, see reference number 315 in FIG. 3B) . It is to be understood that it does not exclude the possibility to provide the (first) timer using the terminal device-dedicated signaling (for example, UE-specific signaling) . In addition, the first timer may be configured together with the configuration of the other RRC timers. Then, at 317, the terminal device 110 may be configured for satellite switching with resynchronization based on the information obtained from SIB19 (RRC IE SatSwitchWithReSync) . In some embodiments, the terminal device 110 may perform the resynchronization switching after t-Service.

At 319, upon t-Service, the terminal device 110 may start the (first) timer. Meanwhile, the terminal device 110 may change (321) the communicated satellite via satellite switching with resynchronization procedure. However, the terminal device 110 may not confirm the success of this procedure. Before the expiry of the timer expiry, the terminal device 110 has no UL data or UL feedback for DL transmission to be transmitted, as shown by 323. Then, the (first) timer expires at 325.

At 327, the terminal device 110 may perform an UL transmission to the network device 120 via the second satellite 124 to indicate the satellite switching was actually successful. Actually, the network device does not know switching status until such UL transmission.

FIG. 3C illustrates an example process 300C for the reduction of uncertainty in the resynchronization switch in the case that the resynchronization switch is unsuccessful according to some embodiments of the present disclosure. In FIG. 3C, the terminal device may be the terminal device 110 in FIG. 1A. The network device may be the network device 120 in FIG. 1A or another network device on the second satellite 124. Only for discussion simplicity, the embodiments are mainly discussed with reference to the terrestrial network device 120. It is to be understood that the similar of same steps performed by the terrestrial network device 120 in the embodiments of the disclosure may be also performed by another network device on the target satellite 124.

FIG. 3C presents a case where the satellite switching was not successful. The steps shown by 329, 331 and 333 may be similar as the steps shown by 301, 303 and 305 as shown in FIG. 3A.

In addition, in the process 300C, the terminal device 110 attempts (335) to access a new satellite (e.g., the second satellite 124. However, as shown by 337, this attempt is not successful before timer T expires. Then, the terminal device 110 may transition to the idle state, perform (341) a transmission of the third RACH or the cell reselection and so on. Then, the network may assume the UE has not managed to switch, based on the operations upon the expiry of the timer, e.g. the received third RACH.

FIG. 4 illustrates a flowchart 400 of a method implemented at a terminal device according to some embodiments of the present disclosure. The terminal device performing the method 400 may be an example of the terminal device 110 above.

At 410, the terminal device 110 starts a timer based on determining that a cell provided by a first satellite stops serving the terminal device 110. At 420, the terminal device 110 performs an operation based on the timer.

In some embodiments, the terminal device 110 may further perform, based on determining that the cell provided by the first satellite stops serving the terminal device, a resynchronization switching from the first satellite to a second satellite.

In some embodiments, the first satellite and the second satellite provide the same serving cell identified with the same physical cell identity (PCI) in a non-terrestrial network (NTN) . In some embodiments, the first satellite and the second satellite are associated with the same network device. In some embodiments, the first satellite is associated with a first network device and the second satellite is associated with a second network device.

In some embodiments, the terminal device may perform the operation by the following: transmitting, to a network device associated with a second satellite, an uplink transmission before the expiry of the timer; and terminating the timer.

In some embodiments, the terminal device may perform the operation by the following: transmitting, to a network device associated with a second satellite, an uplink transmission before the expiry of the timer; receiving, from the network device, an acknowledgement for the uplink transmission; and terminating the timer.

In some embodiments, a resynchronization switching from the first satellite to the second satellite is determined as successful based on the uplink transmission. In some embodiments, the uplink transmission comprises at least one of a physical uplink shared channel (PUSCH) for uplink data, a first random access channel (RACH) or a first scheduling request (SR) .

In some embodiments, a resynchronization switching is determined as successful, and the terminal device may perform the operation by at least one of the following: transmitting, to a network device associated with a second satellite, a second SR based on expiry of the timer; transmitting, to the network device, a second RACH based on the expiry of the timer; or transmitting, to the network device, a media access control (MAC) control element (CE) based on the expiry of the timer.

In some embodiments, the second SR is determined based on a dedicated SR configuration associated with a resynchronization switching. In some embodiments, the second RACH comprises a preamble that is determined based on a dedicated RACH configuration associated with the resynchronization switching. In some embodiments, the MAC CE comprises at least one of a logical channel identifier (LCID) or an element associated with the resynchronization switching.

In some embodiments, the timer is a first timer, and wherein the terminal device may further start a second timer based on the expiry of the first timer. At least one of the second SR, the second RACH or the MAC-CE is transmitted before the second timer expires.

In some embodiments, a resynchronization switching is determined as unsuccessful, and the terminal device may perform the operation by at least one of the following: transitioning to an idle state based on expiry of the timer; performing a cell reselection and a connection reestablishment with a network device associated with a second satellite based on expiry of the timer; or transmitting, to the network device, a third RACH to access the network device based on the expiry of the timer.

In some embodiments, the third RACH is transmitted after a second timer expires, and wherein the second timer starts based on the expiry of the first timer. In some embodiments, the terminal device may further receive configuration information for the timer.

FIG. 5 illustrates a flowchart of a method 500 implemented at a network device according to some embodiments of the present disclosure. The network device performing the method 500 may be an example of the network device 120 above.

At 510, the network device 120 starts a timer based on determining that a cell provided by a first satellite stops serving a terminal device. At 520, the network device 120 performs an operation related to the terminal device based on the timer.

In some embodiments, the terminal device is to perform a resynchronization switching from the first satellite to a second satellite based on the cell provided by the first satellite stopes serving the terminal device. In some embodiments, the first satellite and a second satellite provide the same cell identified with the same physical cell identity (PCI) in a non-terrestrial network (NTN) ; the first satellite and the second satellite are associated with the network device; or the network device is a second network device, the first satellite is associated with a first network device and the second satellite is associated with the second network device.

In some embodiments, the network device 120 may perform the operation by: receiving, from the terminal device, an uplink transmission before the expiry of the timer; and terminating the timer.

In some embodiments, the network device 120 may perform the operation by: receiving, from the terminal device, an uplink transmission before the expiry of the timer; transmitting, to the terminal device, an acknowledgement for the uplink transmission; and terminating the timer.

In some embodiments, the network device 120 may further determine, based on the uplink transmission, that a resynchronization switching of the terminal device from the first satellite to a second satellite is successful. In some embodiments, the uplink transmission comprises at least one of a physical uplink shared channel (PUSCH) for uplink data, a first random access channel (RACH) or a first scheduling request (SR) .

In some embodiments, the network device may perform the operation by at least one of the following: receiving, from the terminal device, a second SR based on the expiry of the timer; receiving, from the terminal device, a second RACH based on the expiry of the timer; or receiving, from the terminal device, a media access control (MAC) control element (CE) based on the expiry of the timer.

In some embodiments, the timer is a first timer, and the network device 120 may further start a second timer based on the expiry of the first timer, and at least one of the second SR, the second RACH or the MAC-CE is received before the second timer expires.

In some embodiments, the network device 120 may further determine that a resynchronization switching of the terminal device from the first satellite to a second satellite is successful.

In some embodiments, the timer is a first timer, and the network device 120 may perform the operation by at least one of the following: releasing a set of radio resources allocated to the terminal device based on the expiry of the first timer; or releasing the set of radio resources allocated to the terminal device based on an expiry of a second timer and determining that the network device receives no second SR, second RACH or MAC CE during the second timer running, wherein the second timer starts based on the expiry of the first timer.

In some embodiments, the network device 120 may further determine that a resynchronization switching of the terminal device from the first satellite to a second satellite is unsuccessful.

In some embodiments, the first satellite is a source satellite and the second satellite is a target satellite.

In some embodiments, an apparatus capable of performing any of the method 400 (for example, the terminal device) may comprise means for starting a timer based on determining that a cell provided by a first satellite stops serving the terminal device; and means for performing an operation based on the timer. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some embodiments, the apparatus may further include means for performing, based on determining that the cell provided by the first satellite stops serving the terminal device, a resynchronization switching from the first satellite to a second satellite.

In some embodiments, the means for performing the operation includes: means for transmitting, to a network device associated with a second satellite, an uplink transmission before the expiry of the timer; and means for terminating the timer.

In some embodiments, a resynchronization switching is determined as successful, and the means for performing the operation includes at least one of the following: means for transmitting, to a network device associated with a second satellite, a second SR based on expiry of the timer; means for transmitting, to the network device, a second RACH based on the expiry of the timer; or means for transmitting, to the network device, a media access control (MAC) control element (CE) based on the expiry of the timer.

In some embodiments, the timer is a first timer, and the apparatus may further include means for starting a second timer based on the expiry of the first timer. At least one of the second SR, the second RACH or the MAC-CE is transmitted before the second timer expires.

In some embodiments, a resynchronization switching is determined as unsuccessful, and the means for performing the operation may include at least one of the following: means for transitioning to an idle state based on expiry of the timer; means for performing a cell reselection and a connection reestablishment with a network device associated with a second satellite based on expiry of the timer; or means for transmitting, to the network device, a third RACH to access the network device based on the expiry of the timer.

In some embodiments, an apparatus capable of performing any of the method 500 (for example, the network device) may comprise means for starting a timer based on determining that a cell provided by a first satellite stops serving a terminal device; and means for performing an operation related to the terminal device based on the timer. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some embodiments, the means for performing the operation may include: means for receiving, from the terminal device, an uplink transmission before the expiry of the timer; and terminating the timer.

In some embodiments, the apparatus may further include means for determining, based on the uplink transmission, that a resynchronization switching of the terminal device from the first satellite to a second satellite is successful. In some embodiments, the uplink transmission comprises at least one of a physical uplink shared channel (PUSCH) for uplink data, a first random access channel (RACH) or a first scheduling request (SR) .

In some embodiments, the means for performing the operation may include at least one of the following: means for receiving, from the terminal device, a second SR based on the expiry of the timer; means for receiving, from the terminal device, a second RACH based on the expiry of the timer; or means for receiving, from the terminal device, a media access control (MAC) control element (CE) based on the expiry of the timer.

In some embodiments, the timer is a first timer, and the apparatus may further include means for starting a second timer based on the expiry of the first timer, and at least one of the second SR, the second RACH or the MAC-CE is received before the second timer expires.

In some embodiments, the apparatus may further include means for determining that a resynchronization switching of the terminal device from the first satellite to a second satellite is successful.

In some embodiments, the timer is a first timer, and the means for performing the operation may include at least one of the following: means for releasing a set of radio resources allocated to the terminal device based on the expiry of the first timer; or means for releasing the set of radio resources allocated to the terminal device based on an expiry of a second timer and determining that the network device receives no second SR, second RACH or MAC CE during the second timer running, wherein the second timer starts based on the expiry of the first timer.

In some embodiments, the apparatus may further include means for determining that a resynchronization switching of the terminal device from the first satellite to a second satellite is unsuccessful.

FIG. 6 is a simplified block diagram of a device 600 that is suitable for implementing embodiments of the present disclosure. The device 600 may be provided to implement the communication device, for example the terminal device or the network device. As shown, the device 600 includes one or more processors 610, one or more memories 620 coupled to the processor 610, and one or more communication modules 640 coupled to the processor 710.

The communication modules 640 is for bidirectional communications. The communication modules 640 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements.

The processor 610 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 700 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 620 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 624, an electrically programmable read only memory (EPROM) , a flash memory, a hard disk, a compact disc (CD) , a digital video disk (DVD) , and other magnetic storage and/or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 722 and other volatile memories that will not last in the power-down duration.

A computer program 630 includes computer executable instructions that are executed by the associated processor 610. The program 730 may be stored in the ROM 624. The processor 610 may perform any suitable actions and processing by loading the program 630 into the RAM 622.

The embodiments of the present disclosure may be implemented by means of the program 630 so that the device 600 may perform any process of the disclosure as discussed with reference to FIGS. 2 to 5. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some embodiments, the program 630 may be tangibly contained in a computer readable medium which may be included in the device 600 (such as in the memory 620) or other storage devices that are accessible by the device 600. The device 600 may load the program 730 from the computer readable medium to the RAM 622 for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. FIG. 7 shows an example of the computer readable medium 700 in form of CD or DVD. The computer readable medium has the program 630 stored thereon.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

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 those included in program modules, being executed in a device on a target real or virtual processor, to carry out the method 500 or 600 as described above with reference to Figs. 2-6. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. The term “non-transitory, ” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM) .

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A terminal device comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to:

start a timer based on determining that a cell provided by a first satellite stops serving the terminal device; and

perform an operation based on the timer.
The terminal device of claim 1, wherein the terminal device is further caused to:

perform, based on determining that the cell provided by the first satellite stops serving the terminal device, a resynchronization switching from the first satellite to a second satellite.
The terminal device of claim 2, wherein at least one of the following:

the first satellite and the second satellite provide the same serving cell identified with the same physical cell identity (PCI) in a non-terrestrial network (NTN) ;

the first satellite and the second satellite are associated with the same network device; or

the first satellite is associated with a first network device and the second satellite is associated with a second network device.
The terminal device of any claims 1 to 3, wherein the terminal device is caused to perform the operation by the following:

transmitting, to a network device associated with a second satellite, an uplink transmission before the expiry of the timer; and

terminating the timer.
The terminal device of any claims 1 to 3, wherein the terminal device is caused to perform the operation by the following:

transmitting, to a network device associated with a second satellite, an uplink transmission before the expiry of the timer;

receiving, from the network device, an acknowledgement for the uplink transmission; and

terminating the timer.
The terminal device of claim 4 or 5, wherein:

a resynchronization switching from the first satellite to the second satellite is determined as successful based on the uplink transmission, and

the uplink transmission comprises at least one of a physical uplink shared channel (PUSCH) for uplink data, a first random access channel (RACH) or a first scheduling request (SR) .
The terminal device of any of claims 1 to 6, wherein a resynchronization switching is determined as successful, and wherein the terminal device is caused to perform the operation by at least one of the following:

transmitting, to a network device associated with a second satellite, a second SR based on expiry of the timer;

transmitting, to the network device, a second RACH based on the expiry of the timer; or

transmitting, to the network device, a media access control (MAC) control element (CE) based on the expiry of the timer.
The terminal device of claim 7, wherein at least one of the following:

the second SR is determined based on a dedicated SR configuration associated with a resynchronization switching;

the second RACH comprises a preamble that is determined based on a dedicated RACH configuration associated with the resynchronization switching; or

the MAC CE comprises at least one of a logical channel identifier (LCID) or an element associated with the resynchronization switching.
The terminal device of claim 7 or 8, wherein the timer is a first timer, and wherein the terminal device is further caused to:

start a second timer based on the expiry of the first timer, and

wherein at least one of the second SR, the second RACH or the MAC-CE is transmitted before the second timer expires.
The terminal device of any of claims 1 to 3, wherein a resynchronization switching is determined as unsuccessful, and wherein the terminal device is caused to perform the operation by at least one of the following:

transitioning to an idle state based on expiry of the timer;

performing a cell reselection and a connection reestablishment with a network device associated with a second satellite based on expiry of the timer; or

transmitting, to the network device, a third RACH to access the network device based on the expiry of the timer.
The terminal device of claim 10, wherein the third RACH is transmitted after a second timer expires, and wherein the second timer starts based on the expiry of the first timer.
The terminal device of any of claims 1 to 11, wherein the terminal device is further caused to:

receive configuration information for the timer.
The terminal device of any of claims 1 to 12, wherein the first satellite is a source satellite and the second satellite is a target satellite for a satellite switching operation.
A network device comprising:

at least one memory storing instructions that, when executed by the at least one processor, cause the network device at least to:

start a timer based on determining that a cell provided by a first satellite stops serving a terminal device; and

perform an operation related to the terminal device based on the timer.
The network device of claim 13, wherein the terminal device is to perform a resynchronization switching from the first satellite to a second satellite based on the cell provided by the first satellite stopes serving the terminal device, and wherein at least one of the following:

the first satellite and a second satellite provide the same cell identified with the same physical cell identity (PCI) in a non-terrestrial network (NTN) ;

the first satellite and the second satellite are associated with the network device; or

the network device is a second network device, the first satellite is associated with a first network device and the second satellite is associated with the second network device.
The network device of claim 13 or 14, wherein the network device is caused to perform the operation by:

receiving, from the terminal device, an uplink transmission before the expiry of the timer; and

terminating the timer.
The network device of claim 13 or 14, wherein the network device is caused to perform the operation by the following:

receiving, from the terminal device, an uplink transmission before the expiry of the timer;

transmitting, to the terminal device, an acknowledgement for the uplink transmission; and

terminating the timer.
The network device of claim 16 or 17, wherein the network device is further caused to:

determine, based on the uplink transmission, that a resynchronization switching of the terminal device from the first satellite to a second satellite is successful, and

wherein the uplink transmission comprises at least one of a physical uplink shared channel (PUSCH) for uplink data, a first random access channel (RACH) or a first scheduling request (SR) .
The network device of claim 14 or 15, wherein the network device is caused to perform the operation by at least one of the following:

receiving, from the terminal device, a second SR based on the expiry of the timer;

receiving, from the terminal device, a second RACH based on the expiry of the timer; or

receiving, from the terminal device, a media access control (MAC) control element (CE) based on the expiry of the timer.
The network device of claim 19, wherein least one of the following:

the second SR is determined based on a dedicated SR configuration associated with a resynchronization switching;

the second RACH comprises a preamble that is determined based on a dedicated RACH configuration associated with the resynchronization switching; or

the MAC CE comprises at least one of a logical channel identifier (LCID) or an element associated with the resynchronization switching.
The network device of any of claim 19 or 20, wherein the timer is a first timer, wherein the network device is further caused to:

start a second timer based on the expiry of the first timer, and

wherein at least one of the second SR, the second RACH or the MAC-CE is received before the second timer expires.
The network device of any of claims 19 to 21, wherein the network device is further caused to:

determine that a resynchronization switching of the terminal device from the first satellite to a second satellite is successful.
The network device of claim 14 or 15, wherein the timer is a first timer, and wherein the network device is caused to perform the operation by at least one of the following:

releasing a set of radio resources allocated to the terminal device based on the expiry of the first timer; or

releasing the set of radio resources allocated to the terminal device based on an expiry of a second timer and determining that the network device receives no second SR, second RACH or MAC CE during the second timer running, wherein the second timer starts based on the expiry of the first timer.
The network device of claim 23, wherein the network device is further caused to:

determine that a resynchronization switching of the terminal device from the first satellite to a second satellite is unsuccessful.
The network device of any of claims 14 to 24, wherein the first satellite is a source satellite and the second satellite is a target satellite.
A method comprising:

starting, by a terminal device, a timer based on determining that a cell provided by a first satellite stops serving the terminal device; and

performing an operation based on the timer.
A method comprising:

starting, by a network device, a timer based on determining that a cell provided by a first satellite stops serving a terminal device; and

performing an operation related to the terminal device based on the timer.
An apparatus comprising:

means for starting, by a terminal device, a timer based on determining that a cell provided by a first satellite stops serving the terminal device; and

means for performing an operation based on the timer.
An apparatus comprising:

means for starting, by a network device, a timer based on determining that a cell provided by a first satellite stops serving a terminal device; and

means for performing an operation related to the terminal device based on the timer.
A non-transitory computer readable medium comprising program instructions stored thereon for performing at least the method of claim 26 or 27.