WO2023133705A1

WO2023133705A1 - Enhancements on uplink synchronization

Info

Publication number: WO2023133705A1
Application number: PCT/CN2022/071452
Authority: WO
Inventors: Konstantinos MANOLAKIS; Frank Frederiksen; Ping Yuan
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2022-01-11
Filing date: 2022-01-11
Publication date: 2023-07-20

Abstract

Embodiments of the present disclosure relate to methods, devices, apparatuses, and computer readable medium of enhancements on uplink synchronization. The method comprises: prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, receiving, at a first device and from a second device serving the first device, a message at least comprising second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information; determining, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer; and synchronizing, based on the first assistance information and/or the second assistance information, with the second device for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.

Description

ENHANCEMENTS ON UPLINK SYNCHRONIZATION

FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to devices, methods, apparatus and computer readable storage media of enhancements on uplink (UL) synchronization.

BACKGROUND

With the arrival of fifth generation New Radio (5G NR) , a target for Non-Terrestrial Network (NTN) is to provide 5G NR services to the users on earth, for example, through Low-Earth Orbit (LEO) satellites, GEO satellites and High Altitude Platforms (HAPS) . In addition, the NB-IoT/eMTC (Narrow band Internet of Things/Enhanced Machine Type Communication) can also be supported in NTN for 5G NR.

As one of the widely used satellites in NTN scenarios, the Low Earth Orbit (LEO) satellite is flying at an altitude of 500-1500 km. Each LEO satellite may provide NR services on earth through one or more satellite beams that create NR cells. Due to the low altitude, the satellites move with a speed of about 7.5 km/srelative to earth. When considering a change of distance between the satellite and the UE on the ground, it is necessary to control and update frequency and time synchronization as the satellite moves time and frequency synchronization needs to be adjusted along with the satellite’s movement. In order words, the UE has to obtain an understanding of the time/frequency relations between itself and the satellite/NTN RAN in order to synchronize and keep the synchronization with the network. Therefore, enhancements on uplink synchronization are needed for the NTN architecture for both NR and NB-IoT/eMTC.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for UL transmission.

In a first aspect, there is provided a first device. The first 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 first device to: prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, receive a message from a second device serving the first device, the message at least comprising second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information; determine, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer; and synchronize, based on the first assistance information and/or second assistance information, with the second device for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.

In a second aspect, there is provided a method. The method comprises: prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, receiving, at a first device and from a second device serving the first device, a message at least comprising second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information; determining, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer; and synchronizing, based on the first assistance information and/or the second assistance information, with the second device for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.

In a third aspect, there is provided a first apparatus. The first apparatus comprises: means for prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, receiving, from a second apparatus serving the first apparatus, a message at least comprising second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information; means for determining, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer; and means for synchronizing, based on the first assistance information and/or the second assistance information, with the second apparatus for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.

In a fourth aspect, there is provided a non-transitory computer readable medium. The non-transitory computer readable medium comprises program instructions for causing an apparatus to perform the method according to the second aspect.

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, where:

FIG. 1 illustrates an example network environment in which embodiments of the present disclosure can be implemented;

FIG. 2 shows a timing diagram of an example uplink synchronization procedure;

FIG. 3 shows a signaling chart illustrating an example UL synchronization procedure according to some example embodiments of the present disclosure;

FIG. 4 shows a timing diagram of the example uplink synchronization procedure in FIG. 3 according to some example embodiments of the present disclosure;

FIG. 5 illustrates an example time evolution of TA component due to the feeder link during a satellite flyover where the change of the TA is symmetrical in time;

FIG. 6 illustrates a flowchart of an example method implemented at a first device according to example embodiments of the present disclosure;

FIG. 7 illustrates a simplified block diagram of an apparatus that is suitable for implementing example embodiments of the present disclosure; and

FIG. 8 illustrates a block diagram of an example computer readable medium in accordance with example embodiments of the present disclosure.

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

DETAILED DESCRIPTION

Principle 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 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 Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , Non-terrestrial network (NTN) , Narrow Band Internet of Things (NB-IoT) , IoT over NTN (Internet of Things over Non-terrestrial network) 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 fifth generation (5G) , a further sixth generation (6G) 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 system.

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 Next Generation NodeB (gNB) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , Integrated Access and Backhaul (IAB) node, a relay, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. The network device is allowed to be defined as part of a gNB such as for example in CU/DU split in which case the network device is defined to be either a gNB-CU or a gNB-DU.

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.

FIG. 1 illustrates an example network environment in which embodiments of the present disclosure can be implemented. The network environment 100 includes a NTN device 102, a first device 110, a second device 120, and a third device 112. In the following description, the network environment 100 is described as an NTN system for NR. However, it should be understood that the network environment 100 is also applicable for the NTN system for NB-IoT/eMTC.

As shown in FIG. 1, the first device 110 and the third device 112 may be implemented as terminal devices, such as, UEs or NB-IoT devices. The second device 120 may be implemented as a network device, such as, an eNB or a gNB. The NTN device 102 may be implemented as a satellite. In the context of the example embodiments, the first device 110 and the third device 112 may be also referred to as UEs or

terminal devices

110 and 112, and the second device 120 may be also referred to as the network device 120.

The NTN device 102 provides coverage enhancement and relay functions, which may be the LEO satellite. The NTN system 100 is a transparent architecture in which the second device 120 (e.g., a gNB) may be on the ground as shown in FIG. 1, or alternatively, in some cases, the gNB or parts of it may be onboard the satellite. The signals between the first device 110 and the second device 120 are routed through the NTN device 102. In the NTN system, a wireless link between the satellite and the NTN gateway (NTN-GW) is referred to as “feeder link” , and a wireless link between the satellite and the UE is referred to as “service link.

In particular, the second device 120 communicates with the second NTN device 102 via a feeder link and provides radio coverage in a cell 104 where the first device 110, the second device 120 and the third device 112 may communicate with each other via a UL or DL channel. The direction from the first device 110 to the second device 120 may refer to UL, and the direction from the second device 120 to the first device 110 may refer to DL. Moreover, the first device 110 may communicate with the third device 112.

In the NTN scenario, the network device (e.g., gNB) may be deployed either on the ground or on a satellite. In the example shown in FIG. 1, the second device 120 is deployed on the ground and connected to the NTN device 102. As previously described, the LEO satellite has a speed relative to Earth, as about 7.56 km/second, and thus the radio coverage is discontinuous. The location and speed of the satellite at given time may be referred to as ephemeris data, and obtained from information broadcasted by the network, for example, in SIB (system information block) . The ephemeris data may be in format of either state vectors or orbital elements.

In order to ensure that the first device 110 is well time-synchronized with the network, it needs to adjust UL synchronization information at a specific time instant or at a specific frequency. The UL synchronization information may include, but not limited to, the timing advance (TA) in time domain and the frequency Doppler shift in frequency domain. The TA applied by the UE in a NTN system can be given as below.

T _TA= (N _TA+N _{TA, UE-specific}+N _TA, common+N _TA, offset) ×T _c (1)

where T _TA represents the TA, N _TA is defined as 0 for PRACH (Physical random-access channel) and updated based on the TA command field in MSG2/MSGB and the MAC CE TA command; N _{TA, UE-specific} represents a UE self-estimated TA to pre-compensate for the service link delay; N _TA, common represents a network controlled common TA, and may include any timing offset considered necessary by the network; N _TA, offset is a fixed offset used for calculating T _TA. T _c represents a number of time units in seconds that defines a size of fields in time domain.

In particular, the UE self-estimated TA, N _{TA, UE-specific}, is derived based on GNSS (Global Navigation Satellite System) information and satellite ephemeris data, and the common TA, N _TA, common, is provided by the network that is common to all the UEs in a cell/beam. In NR NTN scenarios, it is assumed that the UEs have access to GNSS that provides the GNSS location (i.e., geographical location of the UE) and/or the GNSS time. GNSS may be supported by another satellite not shown in FIG. 1.

Accordingly, before performing UL transmissions, the first device 110 acquires the ephemeris data associated with the NTN device 102 by reading system broadcast information, such as, SIB transmitted from the second device 120. Additionally, the first device 110 acquires its location information by reading system broadcast information from GNSS. The first device 110 may then determine the TA, and synchronize in UL based on the TA.

It should be understood that the number of the devices as shown in FIG. 1 is given only for illustrative purpose without suggesting any limitations. For example, the network environment 100 may include any suitable number of terminal devices and network devices adapted for implementing embodiments of the present disclosure. The present disclosure is not limited in this regard.

The communications in the network environment 100 may conform to any suitable standards including, but not limited to, LTE, LTE-evolution, LTE-advanced (LTE-A) , wideband code division multiple access (WCDMA) , code division multiple access (CDMA) and global system for mobile communications (GSM) and the like. Furthermore, the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, 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 fifth generation (5G) , a future sixth generation (6G) and/or any further communication protocols.

Similar to a legacy timeAlignmentTimer is used for closed loop TA update, there are also validity timers used for open loop TA update. The reasons for introducing such timers are that the information used for updating UE-specific and common TAs, i.e., the ephemeris data and the assistance information including common TA and potentially common TA drift rate as well as higher order derivatives of common TA, respectively, will be valid only during a period, which is mainly due to the satellite movement. In this way, it is ensured that the UE is not using ephemeris information or common TA related information which is outdated and not valid any more for UL synchronization.

It has been agreed that a single validity timer is used for both serving satellite ephemeris and common TA related parameters. The validity duration is broadcasted in the SIB, and is defined as a maximum time during which the UE can apply the acquired information without having to acquire new one. The validity timer should be started or restarted with configured validity duration at an epoch time of the serving satellite ephemeris and assistance information. The epoch time is the time when the information can be first applied, and which is also called an application time in the context of embodiments of the present disclosure.

In a case where new or additional assistance information (i.e., serving satellite ephemeris data or common TA parameters) is not available within the associated validity duration, the UE assumes that it has lost UL synchronization with the network. The serving satellite ephemeris and common TA related parameters may be signaled in the same SIB message and have the same epoch time. The reference point for the epoch time of the serving satellite ephemeris and common TA related parameters is the UL time synchronization reference point, i.e., the point where multiple UL signals align with each other and also align with the DL signals.

FIG. 2 shows a timing diagram of an example uplink synchronization procedure. As shown, the satellite 102 updates ephemeris data in

messages

201 and 202. The second device 120 may convert the ephemeris data to the right format and derive the common TA related parameters. The second device 120 then broadcasts multiple SIBs 211 to 214 including the ephemeris data and common TA related parameters updated by the satellite 102. The ephemeris data and common TA related parameters may be also referred to as assistance information for UL synchronization hereinafter. The epoch times associated with the broadcasted SIBs will be after the SIB broadcast times. Depending on the SIB location in a radio frame, and how the epoch time is defined (e.g., implicitly or explicitly) , the epoch time may be up to 10s later than the SIB.

In particular, the

SIBs

211 and 212 may include the assistance information for UL synchronization updated at t ₀, while the

SIBs

213 and 214 may include the assistance information for UL synchronization updated at t ₂. As can be seen that, the broadcast rate of the SIB may be higher than the updating rate of ephemeris information, in order to provide sufficient opportunities to UEs that attempt random access or handover and to the new power-on UEs to read the SIB and avoid large delays in connection establishment.

Accordingly, the UE may acquire assistance information for UL synchronization by reading the SIB 211 at time instant t ₀ and consider the information valid from the epoch time t ₁. In addition, the validity timer will be started or restarted at the epoch time t ₁ and with the configured validity duration, which is indicated as the duration from t ₁ to t ₃, that is, he the validity timer will be expired at t ₃. Hence, from the epoch time and for the following validity duration, the UE is able to use the acquired assistance information and its own propagator model to track the UE-specific TA and the common TA based on the satellite movement and its own location. Before the validity duration expires, the UE has to read the SIB again to acquire new assistance information and restart the validity timer at the new epoch time, which are indicated as SIB reading at time instant t ₂ preceding the expiration time t ₃.

In the conventional NR NTN, there is no mechanism that mandates the UE to read the ephemeris data or common TA at specific time instants or with a specific frequency. In fact, some of the UEs may have a more advanced propagator model, and hence would read the SIB less frequently than other UEs which may have less accurate models for the tracking and predicting of the satellite movement. Anyhow, the UE will need to read the SIB at least not too late, so that it can restart the validity timer before the validity duration from the previous SIB reading expires.

However, there is a risk that although the UE reads the SIB within the duration of the validity timer, i.e., “on time” , the UE is not able to restart the validity timer before the current timer expires. This may happen if the epoch time associated with the SIB reading lies in a time instant which is after the expiration of the timer which is still running. This can be explained be referring to FIG. 2. As shown, the UE reads the SIB 213 at t ₂, so as to acquire new assistance information before the validity timer expires. The next epoch time associated with the new assistance information corresponds to time instant t ₄ that is later than the expiration time t ₃. As a result, there is time gap between time instants t ₃ and t ₄. In this case, the validity timer expires before the next epoch time is reached. Due to the time gap, the UE will assume that it has lost UL synchronization with the network.

There are several reasons why this may happen. First, the UE is unaware of when the epoch time associated with a SIB reading is. The epoch time as applied at the gNB may change over time. The location of the epoch time within the radio frame may change, if the way this is defined by the gBN changes. If the gNB provides the SIB more often than the ephemeris data is updated, practically the same information will be provided in several consecutive SIBs. In this case, several SIBs in the same radio frame will be associated with the same epoch time, which will be towards the end of the radio frame. The gNB may start providing more common TA related assistance information (e.g. higher order derivatives) , which allow the UE to perform a more accurate tracking, and in contrast to this, the gNB may provide information less frequently (e.g., not in every SIB) , or prolong the epoch time.

Second, the UE may fail to read the SIB one or more times, and when finally reading the SIB, this may be already too late to restart the validity timer and maintain UL synchronization.

Last but not least, the gNB does not know the validity timer status at each UE, i.e. when each UE has read the SIB and when the validity timer will expire, and thus has no way to adjust the epoch time in order to assist UEs in this way.

In order to solve the above and other potential problems, embodiments of the present disclosure provide an enhanced UL synchronization mechanism. In the mechanism, the validity timer running at the UE side is prevented from expiration, in a case that the UE has read a SIB including updated assistance information for UL synchronization that has not yet been valid when the validity timer expires. Additionally or alternatively, the UE is capable of expanding the validity duration associated with a given SIB, without any cost in the accuracy of this information at the UE.

Principle and implementations of the present disclosure will be described in detail below with reference to FIGs. 3 to 5. FIG. 4 shows a signaling chart illustrating an example UL synchronization procedure 300 according to some example embodiments of the present disclosure. FIG. 4 shows a timing diagram 400 of the example uplink synchronization procedure 300. For the purpose of discussion, the process 300 will be described with reference to FIGs. 1 and 4. The process 300 may involve the first device 110, the second device 120 and the NTN device 102.

As shown, the NTN device 102 provides ephemeris data to the second device 120 in message 401 at time instant t ₀. Upon receipt of the message 401, the second device 120 may convert the ephemeris data in a corresponding format and derive a corresponding common TA related parameters. The second device 120 may generate a SIB 411 including the ephemeris data and the common TA related parameters as first assistance information for UL synchronization.

The second device 120 broadcasts 205 the SIB 411. In addition to the first assistance information for UL synchronization, the SIB 411 may include at least a first configuration for a validity timer corresponding to the first assistance information. The first configuration may indicate a first application time t ₁ (i.e., the epoch time) and a first validity duration T1 of the validity timer, where the first validity duration T1 starts from the first application time t1 and ends at the expiration time t3.

In some cases, the assistance information for UL synchronization may be provided by a terminal device instead of the gNB, for example, the third device 112 as shown in FIG. 1. All the steps and operations in process 300 are also suitable for such cases.

Upon receiving and reading the SIB 411, the first device 110 determines that the first assistance information for UL synchronization will be valid for TA estimation from the first application time t ₁ and for the first validity duration T1.

In order to provide sufficient opportunity for acquiring the assistance information for UL synchronization, the second device 120 may transmit SIB 412 that includes the same first assistance information for UL synchronization and the first configuration as the SIB 411. The receipt and reading of SIB 412 would not change the TA estimation or the determination of UL synchronization at the first device 110.

As time goes by and the NTN device 102 moves, it provides updated ephemeris data to the second device 120 in message 402 at time instant t ₂. Similarly, after receiving the message 402, the second device 120 may convert the updated ephemeris data in a corresponding format and derive an updated common TA related parameters. The second device 120 then generates a SIB 413 including the updated ephemeris data and common TA related parameters as second assistance information for UL synchronization.

The second device 120 broadcasts 310 the SIB 413. In addition to the second assistance information for UL synchronization, the SIB 413 may include at least a second configuration for a validity timer corresponding to the second assistance information. The second configuration is different from the first configuration, which may indicate a second application time t ₄ and a second validity duration T2 of the validity timer, where the second validity duration T2 starts from the second application time t ₄ and ends at the expiration time t ₅.

The second device 120 may transmit SIB 414 that includes the same second assistance information for UL synchronization and the second configuration as the SIB 413. It should be understood that the transmission of the SIBs including the same assistance information are not necessary for the UL synchronization procedure. In some cases, the broadcast rate of SIB may be equal to the updating rate of ephemeris data.

Since the validity timer with the first configuration is to expire at time instant t ₃, the first device 110 should read SIB to acquire the updated assistance information and configuration of the validity timer before it expires. Upon receiving and reading the SIB 413, the first device 110 determines that the second assistance information for UL synchronization will be valid for TA estimation from the second application time t ₄ and for the second validity duration T2.

The first device 110 then determines 315, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer. In this case, the first device 110 should not regard its UL synchronization lost during the time gap stating from t ₃ and ending at t ₄.

To this end, in the case where new assistance information has been acquired while the new epoch time is later than the expiration of the validity timer, the first device 110 may restart 320 the validity timer before the new epoch time t ₄. In other words, the validity timer will be restarted ahead of the originally indicated time instant t ₄.

In some example embodiments, the first device 110 may advance the restarting point of the validity timer within a target time window up to the updated validity duration as indicated in the later SIB 413. The target time window is defined based on symmetry of the aging effect of the serving satellite ephemeris and common TA related parameters. In particular, the aging of this information from the moment it is generated and into the future depends on the satellite’s location and relative speed vector to the NTN-GW/gNB and to the UE. Although the model used for tracking the satellite location and/or the derived parameters is up to the UE implementation, the validity duration provides an upper bound for ensuring that UE would not use information that is significantly outdated.

FIG. 5 illustrates an example time evolution of TA component due to the feeder link during a satellite flyover where the change of the TA is symmetrical in time, where the TA component is the common TA, and an elevation angle is 40 degree at t=0. As shown, the aging effect of the ephemeris data and derived parameters is symmetrical with respect to the time when the information is generated. In other words, the change of the TA is symmetrical in time. Considering the movement of the satellite on the orbit, it can be safely regarded as observation window in the order of magnitude of the validity timer. The expected deviation of a satellite’s location at time t0 + Δ from its location at reference time t0 is the same as the expected deviation at time t0 -Δ from its location at reference time t0.

The change of the ephemeris data and derived parameter should be symmetrical for both of the durations T2 with a reference point of t ₄ corresponding to the updated epoch time. Therefore, the target time window for advancing the restarting point of the validity timer can be determined to start from a specific time instant, which may be referred to as the first time t ₅’, and end at the second epoch time t ₄, and the specific time instant t ₅’ is defined in a way that a time difference between the specific time instant t ₅’ and the second application time is equal to the second validity duration T2.

The length of the target time window defines the maximum time interval from the updated epoch time, during which the UE can consider the assistance information for UL synchronization as valid. In the above embodiments, the length of the target time window corresponds to the second validity duration T2. Alternatively, in some other embodiments, the length of the target time window may correspond to half of the second validity duration T2. That is, the target time window may start from another specific time instant, which may be referred to as the second time t ₆, and end at the second epoch time t ₄, and the second time t ₆ is defined in a way that a time difference between the second application time t ₄ and the second time is equal to a half of the second validity duration T2. In this way, the UE may receive the SIB and thus update the ephemeris data and common TA related parameters more frequently.

After determining the target time window based on the second application time and the second duration, the first device 110 may determine whether the validity timer expires during the target time window. For example, if the expiration time t ₃ is later than the specific time instant t ₅’, then the validity timer will expire during the target time window. In this case, the first device 110 may restart the validity timer within the target time window. In this way, the restarting point of the validity timer is advanced. The first device 110 may then synchronize 330 with the second device 120 based on the second assistance information before the restarted validity timer is expired.

In some example embodiments where the restarting of the validity timer is advanced, the expiration time of the restarted validity timer may be the same as an expiration time based on the second configuration. That is, the restarted validity timer may expire at time instant t ₅.

Otherwise, if the expiration time t ₃ is earlier than the specific time instant t ₅’, then the validity timer will not expire during the target time window. In this case, the restarting of the validity timer cannot be advanced to the target time window. The first device 110 synchronizes with the second device 120 based on the first assistance information before the validity timer is expired.

Additionally and alternatively, in order to avoid losing UL synchronization in a case that the updated assistance information is to be applied after the expiration of the validity timer, the first device 110 may stop 325 the running validity timer during the time gap from t ₃ to t ₄. As such, the validity timer will not expire, and the first assistance information will be regarded as valid during this time gap. In this case, the first device 110 may then synchronize 330 with the second device 120 based on the first assistance information for at least a time period from the expiration time t ₃ that is determined based on the first configuration to the second application time t ₄ that is determined based on the second configuration.

Accordingly, the first device 110 synchronizes 330, based on the first assistance information and/or second assistance information, with the second device 120 for at least the time gap starting from the expiration time based on the first configuration and ending at the application time of the second assistance information based on the second configuration.

It should be noted that the description above considers parameters and variables associated to time instants in absolute time, while the proposed UL synchronization mechanism can be also suitable for relative time, where time is internal to system clocks in a device or internal to the time of the system (relative to symbols, slots, frames and so on) . Therefore, the example embodiments are not limited in this regard.

Additionally, it should be noted that the timing sequence and numbers of messages as well as parameters shown in FIGs. 4 and 5 are given as illustrative purpose, without limitations of the present disclosure. Any other suitable configurations and settings are also applicable for implementations of the proposed UL synchronization mechanism.

According to the example embodiments, there is provided an enhanced mechanism for UL synchronization. Such a mechanism is especially beneficial to NTN scenarios. In the enhanced mechanism, the UE is able to apply the ephemeris and assistance information before a corresponding epoch time, which minimizes the probability that the UE loses UL synchronization with the network due to the expiration of the validity timer preceding the updated epoch time. Therefore, the UL synchronization in NTN can be ensured, and the system performance can be improved.

FIG. 6 illustrates a flowchart of an example method 600 implemented at a first device according to example embodiments of the present disclosure. The method 600 can be implemented by a terminal device, such as, the first device 110 shown in FIG. 1. Additionally or alternatively, the method 600 can be implemented by any other terminal device. For the purpose of discussion, the method 600 will be described with reference to FIG. 1. It is to be understood that method 600 may further include additional blocks not shown and/or omit some shown blocks, and the scope of the present disclosure is not limited in this regard.

Prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, the first device 110 receives, at 610, a message from the second device 120 serving the first device 110. The message at least comprises second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information. In some example embodiments, the message may include a system information block (SIB) .

In some example embodiments, the first configuration may include a first application time of the first assistance information and a first duration of the validity timer in which the first assistance information is available for uplink synchronization. The second configuration may include a second application time of the second assistance information and a second duration of the validity timer in which the second assistance information is available for uplink synchronization.

At 620, the first device 110 determines, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer.

At 630, the first device 110 synchronizes, based on the first assistance information and/or second assistance information, with the second device 120 for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.

In some example embodiments, if the second assistance information is to be applied after the expiration of the validity timer, the first device 110 may restart the validity timer before the expiration of the validity timer.

A target time window may be defined for determining whether the validity timer can be restarted in advance. In some example embodiments, the first device 110 may determine a target time window based on the second application time and the second duration. If the validity timer is expired during the target time window, the first device 110 may restart the validity timer.

In the above embodiments, the target time window may be determined to start from a first time and end at the second application time, and the first time is defined in a way that a time difference between the second application time and the first time is equal to the second duration.

In the above embodiments, the target time window may be determined to start from a second time and end at the second application time, and the second time is defined in a way that a time difference between the second application time and the second time is equal to the second duration.

Additionally, the validity timer is restarted no earlier than a corresponding one of the first time or the second time, and no later than the expiration time based on the second configuration. In some example embodiments, if the expiration time based on the first configuration is within the target time window, the first device 110 may synchronize with the second device 120 based on the second assistance information before the restarted validity timer is expired.

In some example embodiments, an expiration time of the restarted validity timer may be the same as an expiration time based on the second configuration. In this case, the end time of the validity timer keeps unchanged as indicated by the second configuration.

In some example embodiments, the validity timer is restarted no earlier than a corresponding one of the first time or the second time, and no later than the expiration time based on the second configuration. If the expiration time based on the first configuration precedes the target time window, the first device 110 may synchronize with the second device 120 based on the first assistance information before the restarted validity timer is expired.

In some example embodiments, if the second assistance information is to be applied after the expiration of the validity timer, the first device 110 may stop the validity timer during the time period.

In the above embodiments, the first device 110 may synchronize with the second device 120 based on the first assistance information during the time period.

In some example embodiments, the first assistance information and the second assistance information may include at least one of ephemeris data associated with the second device 120 and common timing advance information controlled by the second device 120.

In some example embodiments, the first device 110 may transmit, to the second device 120 and based on second assistance information, a data transmission during the timer period.

In some example embodiments, the first device 110 may be a terminal device, such as, a UE. The second device 120 may be a network device, such as, a network device deployed either on the ground or on the satellite. Alternatively, in some example embodiments, the second device 120 may be another terminal device.

According to the example embodiments, there is provided a method for UL synchronization. In the method, the UE is able to advance the restarting of the validity timer or stop it before its expiration. In this way, the UE can apply the ephemeris and assistance information before a corresponding epoch time and thus avoid losing UL synchronization with the network due to the expiration of the validity timer preceding the updated epoch time. As such, the UL synchronization in NTN can be ensured, and the system performance can be improved.

In some example embodiments, a first apparatus capable of performing any of the method 600 (for example, the first device 110) may comprise means for performing the respective steps of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the first apparatus comprises: means for prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, receiving, from a second apparatus serving the first apparatus, a message at least comprising second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information; means for determining, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer; and means for synchronizing, based on the first assistance information and/or the second assistance information, with the second apparatus for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.

In some example embodiments, the first configuration comprises a first application time of the first assistance information and a first duration of the validity timer in which the first assistance information is available for uplink synchronization, and the second configuration comprises a second application time of the second assistance information and a second duration of the validity timer in which the second assistance information is available for uplink synchronization.

In some example embodiments, the first apparatus further comprises: means for in accordance with a determination that the second assistance information is to be applied after the expiration of the validity timer, restarting the validity timer before the expiration of the validity timer.

In some example embodiments, the means for restarting the validity timer comprises: means for determining a target time window based on the second application time and the second duration; and means for in accordance with a determination that the validity timer is expired during the target time window, restarting the validity timer.

In some example embodiments, the target time window is determined to start from a first time and end at the second application time, and the first time is defined in a way that a time difference between the second application time and the first time is equal to the second duration.

In some example embodiments, the target time window is determined to start from a second time and end at the second application time, and the second time is defined in a way that a time difference between the second application time and the second time is equal to the second duration.

In some example embodiments, the validity timer is restarted no earlier than a corresponding one of the first time or the second time, and no later than the expiration time based on the second configuration. In these embodiments, the means for synchronizing with the second apparatus comprises: means for in accordance with a determination that the expiration time based on the first configuration is within the target time window, synchronizing with the second apparatus based on the second assistance information before the restarted validity timer is expired.

In some example embodiments, an expiration time of the restarted validity timer is the same as an expiration time based on the second configuration.

In some example embodiments, the validity timer is restarted no earlier than a corresponding one of the first time or the second time, and no later than the expiration time based on the second configuration. In these embodiments, the means for synchronizing with the second apparatus comprises: means for in accordance with a determination that the expiration time based on the first configuration precedes the target time window, synchronizing with the second apparatus based on the first assistance information before the restarted validity timer is expired.

In some example embodiments, the first apparatus further comprises: means for in accordance with a determination that the second assistance information is to be applied after the expiration of the validity timer, stopping the validity timer during the time period.

In some example embodiments, the means for synchronizing with the second apparatus comprises: means for synchronizing with the second apparatus based on the first assistance information during the time period.

In some example embodiments, the first assistance information and the second assistance information comprise at least one of ephemeris data associated with the second apparatus and common timing advance information controlled by the second apparatus.

In some example embodiments, the message comprises a system information block, SIB.

In some example embodiments, the first apparatus further comprises: means for transmitting, to the second apparatus and based on second assistance information, a data transmission during the timer period.

In some example embodiments, the first apparatus comprises a terminal device, and a second apparatus comprises a network device.

FIG. 7 is a simplified block diagram of a device 700 that is suitable for implementing embodiments of the present disclosure. The device 700 may be provided to implement the communication device, for example the first device 110 and the second device 120 as shown in FIG. 2. As shown, the device 700 includes one or more processors 710, one or more memories 720 coupled to the processor 710, and one or more transmitters and/or receivers (TX/RX) 740 coupled to the processor 710.

The TX/RX 740 may be configured for bidirectional communications. The TX/RX 740 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 710 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 720 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) 724, 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 media. 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 730 includes computer executable instructions that may be executed by the associated processor 710. The program 730 may be stored in the ROM 724. The processor 710 may perform any suitable actions and processing by loading the program 730 into the RAM 722.

The embodiments of the present disclosure may be implemented by means of the program 730 so that the device 700 may perform any process of the disclosure as discussed with reference to FIG. 3. 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 730 may be tangibly contained in a computer readable medium which may be included in the device 700 (such as in the memory 720) or other storage devices that are accessible by the device 700. The device 700 may load the program 730 from the computer readable medium to the RAM 722 for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. FIG. 8 shows an example of the computer readable medium 800 in form of CD or DVD. The computer readable medium has the program 730 stored thereon.

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, device, 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 600 as described above with reference to FIG. 6. Generally, program modules may 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 device, 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, device 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, device, 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.

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 first device, comprising:

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 first device at least to:

prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, receive a message from a second device serving the first device, the message at least comprising second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information;

determine, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer; and

synchronize, based on the first assistance information and/or second assistance information, with the second device for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.
The first device of Claim 1, wherein the first configuration comprises a first application time of the first assistance information and a first duration of the validity timer in which the first assistance information is available for uplink synchronization, and the second configuration comprises a second application time of the second assistance information and a second duration of the validity timer in which the second assistance information is available for uplink synchronization.
The first device of Claim 2, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, further cause the first device to:

in accordance with a determination that the second assistance information is to be applied after the expiration of the validity timer, restart the validity timer before the expiration of the validity timer.
The first device of Claim 3, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, further cause the first device to restart the validity timer by:

determining a target time window based on the second application time and the second duration; and

in accordance with a determination that the validity timer is expired during the target time window, restarting the validity timer.
The first device of Claim 4, wherein the target time window is determined to start from a first time and end at the second application time, wherein the first time is defined in a way that a time difference between the second application time and the first time is equal to the second duration.
The first device of Claim 4, wherein the target time window is determined to start from a second time and end at the second application time, wherein the second time is defined in a way that a time difference between the second application time and the second time is equal to a half of the second duration.
The first device of Claim 5 or 6, wherein the validity timer is restarted no earlier than a corresponding one of the first time or the second time, and no later than the expiration time based on the second configuration, and wherein the at least one memory and the computer program codes are configured to, with the at least one processor, cause the first device to synchronize with the second device by:

in accordance with a determination that the expiration time based on the first configuration is within the target time window, synchronizing with the second device based on the second assistance information before the restarted validity timer is expired.
The first device of Claim 5 or 6, wherein the validity timer is restarted no earlier than a corresponding one of the first time or the second time, and no later than the expiration time based on the second configuration, and wherein the at least one memory and the computer program codes are configured to, with the at least one processor, cause the first device to synchronize with the second device by:

in accordance with a determination that the expiration time based on the first configuration precedes the target time window, synchronizing with the second device based on the first assistance information before the restarted validity timer is expired.
The first device of Claim 3, wherein an expiration time of the restarted validity timer is the same as an expiration time based on the second configuration.
The first device of Claim 1, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, further cause the first device to:

in accordance with a determination that the second assistance information is to be applied after the expiration of the validity timer, stop the validity timer during the time period.
The first device of Claim 10, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, cause the first device to synchronize with the second device by:

synchronizing with the second device based on the first assistance information during the time period.
The first device of Claim 1, wherein the first assistance information and the second assistance information comprise at least one of ephemeris data associated with the second device and common timing advance information controlled by the second device.
The first device of Claim 1, wherein the message comprises a system information block, SIB.
The first device of Claim 1, wherein the at least one memory and the computer program codes are configured to, with the at least one processor, further cause the first device to:

transmit, to the second device and based on second assistance information, a data transmission during the timer period.
The first device of Claim 1, wherein the first device comprises a terminal device, and a second device comprises a network device.
A method comprising:

prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, receiving, at a first device and from a second device serving the first device, a message at least comprising second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information;

determining, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer; and

synchronizing, based on the first assistance information and/or the second assistance information, with the second device for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.
The method of Claim 16, wherein the first configuration comprises a first application time of the first assistance information and a first duration of the validity timer in which the first assistance information is available for uplink synchronization, and the second configuration comprises a second application time of the second assistance information and a second duration of the validity timer in which the second assistance information is available for uplink synchronization.
The method of Claim 17, further comprising:

in accordance with a determination that the second assistance information is to be applied after the expiration of the validity timer, restarting the validity timer before the expiration of the validity timer.
The method of Claim 18, wherein restarting the validity timer comprises:

determining a target time window based on the second application time and the second duration; and

in accordance with a determination that the validity timer is expired during the target time window, restarting the validity timer.
The method of Claim 19, wherein the target time window is determined to start from a first time and end at the second application time, wherein the first time is defined in a way that a time difference between the second application time and the first time is equal to the second duration.
The method of Claim 19, wherein the target time window is determined to start from a second time and end at the second application time, wherein the second time is defined in a way that a time difference between the second application time and the second time is equal to a half of the second duration.
The method of Claim 20 or 21, wherein the validity timer is restarted no earlier than a corresponding one of the first time or the second time, and no later than the expiration time based on the second configuration, and wherein synchronizing with the second device comprises:

in accordance with a determination that the expiration time based on the first configuration is within the target time window, synchronizing with the second device based on the second assistance information before the restarted validity timer is expired.
The method of Claim 20 or 21, wherein the validity timer is restarted no earlier than a corresponding one of the first time or the second time, and no later than the expiration time based on the second configuration, and wherein synchronizing with the second device comprises:

in accordance with a determination that the expiration time based on the first configuration precedes the target time window, synchronizing with the second device based on the first assistance information before the restarted validity timer is expired.
The method of Claim 18, wherein an expiration time of the restarted validity timer is the same as an expiration time based on the second configuration.
The method of Claim 16, further comprising:

in accordance with a determination that the second assistance information is to be applied after the expiration of the validity timer, stopping the validity timer during the time period.
The method of Claim 25, wherein synchronizing with the second device comprises:

synchronizing with the second device based on the first assistance information during the time period.
The method of Claim 16, wherein the first assistance information and the second assistance information comprise at least one of ephemeris data associated with the second device and common timing advance information controlled by the second device.
The method of Claim 16, wherein the message comprises a system information block, SIB.
The method of Claim 16, further comprising:

transmitting, to the second device and based on second assistance information, a data transmission during the timer period.
The method of Claim 16, wherein the first device comprises a terminal device, and a second device comprises a network device.
A first apparatus comprising:

means for prior to expiration of a validity timer with a first configuration corresponding to first assistance information for uplink synchronization, receiving, from a second apparatus serving the first apparatus, a message at least comprising second assistance information for uplink synchronization and a second configuration for the validity timer corresponding to the second assistance information;

means for determining, based on the first configuration and the second configuration, that the second assistance information is to be applied after the expiration of the validity timer; and

means for synchronizing, based on the first assistance information and/or the second assistance information, with the second apparatus for at least a time period from an expiration time based on the first configuration to an application time of the second assistance information based on the second configuration.
A non-transitory computer readable medium comprising program instructions for causing an apparatus to perform the method of any of Claims 16 to 30.