WO2021092766A1

WO2021092766A1 - Enhanced handover and timing advance alignment

Info

Publication number: WO2021092766A1
Application number: PCT/CN2019/117598
Authority: WO
Inventors: Wenjian Wang; Pingping Wen; Kai Zhu
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2019-11-12
Filing date: 2019-11-12
Publication date: 2021-05-20
Also published as: CN114731542A

Abstract

Embodiments of the present disclosure relate to enhanced handover and timing advance alignment. According to embodiments of the present disclosure, the first device receives the measurement report which comprises the information specific to the second device from the second device. The first device selects a third device for handover based on the signal strength of the target device and new criteria. The third device determines whether the current timing advance is valid and performs the TA pre-compensation. In this way, the frequency of handover is reduced and fast data transmission is achieved.

Description

ENHANCED HANDOVER AND TIMING ADVANCE ALIGNMENT

FIELD

Embodiments of the present disclosure generally relate to the field of communications, especially in non-terrestrial network and in particular, to a method, device, apparatus and computer readable storage medium for enhanced handover and timing advance alignment.

BACKGROUND

Since resources and infrastructure are limited in remote area, it is very difficult for terrestrial network to provide 5G coverage. The main benefits of introducing Non-Terrestrial Network (NTN) is to enable ubiquitous 5G services to terminal devices by extending connectivity in less densely populated areas with extremely low density of devices and the overall cost of deployment may be much less than providing permanent infra-structure on the ground. A new solution for new radio (NR) to support NTN has been proposed. However, it has also brought some problems in other aspects.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for enhanced handover and timing advance alignment and corresponding communication devices.

In a first aspect, there is provided a method. The method comprises receiving, at a first device, a measurement report from a second device served by the first device, the measurement report comprising information specific to the second device. The method also comprises selecting a third device for handover of the second device at least partially based on a rule associated with signal strength of one or more candidate devices, the one or more candidate devices comprising the third device. The method further comprises transmitting to a third device a handover request comprising a first timing advance value of the second device and the information specific to the second device. The method also comprises receiving information of the handover from the third device, the information of the handover concerning an applicable timing advance value to the third device. The method yet comprises transmitting to the second device an indication of the handover from the first device to the third device.

In a second aspect, there is provided a method. The method comprises transmitting, at a second device, a measurement report to a first device serving the second device, the measurement report comprising information specific to the second device. The method further comprises receiving, from the first device, an indication of a handover from the first device to a third device. The method also comprises obtaining information concerning a timing advance value applicable to the third device. The method yet comprises performing an uplink transmission with the third device based on the timing advance value.

In a third aspect, there is provided a method. The method comprises receiving, at a third device, a handover request from a first device, the handover request comprising a first timing advance value of the second device and information specific to a second device served by the first device. The method also comprises determining whether the first timing advance value is applicable to the third device based on the information specific to the second device. The method further comprises generating, based on the determination, information of the handover from the first device to the third device. The method yet comprises transmitting the information to the first device.

In a fourth 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 second device to receive a measurement report from a second device served by the first device, the measurement report comprising information specific to the second device. The first device is also caused to select a third device for handover of the second device at least partially based on a rule associated with signal strength of one or more candidate devices, the one or more candidate devices comprising the third device. The first device is further caused to transmit to a third device a handover request comprising a first timing advance value of the second device and the information specific to the second device. The first device is also caused to receive information of the handover from the third device, the information of the handover concerning an applicable timing advance value to the third device. The first device is yet caused to transmit to the second device an indication of the handover from the first device to the third device.

In a fifth aspect, there is provided a second device. The second 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 second device to transmit a measurement report to a first device serving the second device, the measurement report comprising information specific to the second device. The second device is also caused to receive, from the first device, an indication of a handover from the first device to a third device. The second device is further caused to obtain information concerning a timing advance value applicable to the third device. The second device is yet caused to perform an uplink transmission with the third device based on the timing advance value.

In a sixth aspect, there is provided a third device. The third 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 third device to receive a handover request from a first device, the handover request comprising a first timing advance value of the second device and information specific to a second device served by the first device. The third device is also caused to determine whether the first timing advance value is applicable to the third device based on the information specific to the second device. The third device is further caused to generate, based on the determination, information of the handover from the first device to the third device. The third device is yet caused to transmit the information to the first device.

In a seventh aspect, there is provided an apparatus. The apparatus comprises means for receiving, at a first device, a measurement report from a second device served by the first device, the measurement report comprising information specific to the second device; means for selecting a third device for handover of the second device at least partially based on a rule associated with signal strength of one or more candidate devices, the one or more candidate devices comprising the third device; means for transmitting to a third device a handover request comprising a first timing advance value of the second device and the information specific to the second device; means for receiving information of the handover from the third device, the information of the handover concerning an applicable timing advance value to the third device; and means for transmitting to the second device an indication of the handover from the first device to the third device.

In an eighth aspect, there is provided an apparatus. The apparatus comprises means for transmitting, at a second device, a measurement report to a first device serving the second device, the measurement report comprising information specific to the second device; means for receiving, from the first device, an indication of a handover from the first device to a third device; means for obtaining information concerning a timing advance value applicable to the third device; and means for performing an uplink transmission with the third device based on the timing advance value.

In a ninth aspect, there is provided an apparatus. The apparatus comprises means for receiving, at a third device, a handover request from a first device, the handover request comprising a first timing advance value of the second device and information specific to a second device served by the first device; means for determining whether the first timing advance value is applicable to the third device based on the information specific to the second device; means for generating, based on the determination, information of the handover from the first device to the third device; and means for transmitting the information to the first device.

In a tenth 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 first to third aspects.

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 communication network in which embodiments of the present disclosure may be implemented;

Fig. 2 illustrates a schematic diagram of interactions among communication devices according to embodiments of the present disclosure;

Fig. 3 illustrates a schematic diagram of handover criteria according to embodiments of the present disclosure;

Fig. 4 illustrates a schematic diagram of beam footprint and differential propagation according to embodiments of the present disclosure;

Fig. 5 illustrates a flowchart of a method implemented at a first device according to embodiments of the present disclosure;

Fig. 6 illustrates a flowchart of a method implemented at a second device according to embodiments of the present disclosure;

Fig. 7 illustrates a flowchart of a method implemented at a third device according to embodiments of the present disclosure;

Fig. 8 illustrates a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure; and

Fig 9 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

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) , Narrow Band Internet of Things (NB-IoT) , New Radio (NR) , Non-terrestrial network (NTN) 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, 2.85G, 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 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 NB (also referred to as a gNB) , 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.

As mentioned above, the NTN has also brought some problems in other aspects. For the NTN, the round-trip time (RTT) to the terminal device can be much larger than that in the terrestrial networks. Therefore, it is necessary to consider its impact for different aspects of new radio (NR) design, including cell search, handover, Timing Advance (TA) adjustment.

For systems of Medium Earth orbit (MEO) , Low-Earth Orbit (LEO) and High-Altitude Pseudo-Satellite (HAPS) in NTN network, there are strong varying delays because satellites and terminal devices are fast-moving and are not relatively static.

It has approved a solution evaluation for NR to support Non-Terrestrial Network. The objectives for physical-layer and high-layer are reported as follows respectively.

Physical layer:

● Physical layer control procedures (for example, channel state information (CSI) feedback, power control) ;

● Uplink Timing advance/random access channel (RACH) procedure including PRACH sequence/format/message;

● Making retransmission mechanisms at the physical layer more delay-tolerant as appropriate. This may also include capability to deactivate the Hybrid Automatic Repeat reQuest (HARQ) mechanisms.

Layer 2 and higher lays, and RAN architecture:

● Study the following aspects and identify related solutions if needed: Propagation delay: Identify timing requirements and solutions on layer 2 aspects, medium access channel (MAC) , radio link control (RLC) , radio resource control (RRC) , to support NTN propagation delays considering frequency division duplex (FDD) and time division duplex (TDD) duplexing mode. This includes radio link management;

● Handover: Study and identify mobility requirements and necessary measurements that may be needed for handovers between some non-terrestrial space-borne vehicles (such as Non Geo stationary satellites) that move at much higher speed but over predictable paths;

● Architecture: Identify needs for the 5G’s Radio Access Network architecture to support non-terrestrial networks (e.g. handling of network identities) ;

● Paging: procedure adaptations in case of moving satellite foot prints or cells.

It is known that the handover and RACH procedures are important issues for the non-terrestrial network. The problem is there is a strong varying delay because the satellite and terminal devices are fast-moving and are not relatively static. As a result, the duration of staying in a given spot beam for a given terminal device is very short, which may lead to frequent handover problems from the serving spot beam or satellite to the new target spot beam or new target satellite. The individual timing advances of the terminal devices also have to be fast updated dynamically and appropriate TA index values are needed. In addition to these, there is agreement on Link-Level and System-Level Evaluations as shown in Table 1 below:

Table 1

Besides the ground terminal devices, the aerial terminal devices are also not excluded for some scenario. So seamless mobility service and efficient handover is a significant especially for those aerial terminal devices applicable to the purpose of military, industry such as delivery service or disaster warning and so on, which could be fully controlled and even a little of disconnection is able to become a serious operation problem. Actually, handover failure and radio link failure may additionally lead to latency upon the already long RTT in NTN network. When the aerial terminal device generates message just before reception of handover command, it may fail to transmit the message at a source cell. Then, the terminal device needs to delay transmission of the message until RRC Connection Re-establishment successfully completes at a cell.

Because the transmission channel is line of sight without obstructions at flying altitude, and generally a drone terminal device may move at very fast speed, and the strongest signal may come from a different spot beam or from different satellite at a short period of time.

However, in conventional technologies, when the NTN terminal device satisfies the handover condition, the random access and RRC re-establish process is still needed, which may cause a lot of latencies. Furthermore, the frequent handover problem is still not solved.

According to embodiments of the present disclosure, the first device receives the measurement report which comprises the information specific to the second device from the second device. The first device selects a third device for handover based on the signal strength of the target device and new criteria. The third device determines whether the current timing advance is valid and performs the TA pre-compensation. In this way, the frequency of handover is reduced and fast data transmission is achieved.

Principle and embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Reference is first made to Fig. 1, which illustrates an example communication system 100 in which embodiments of the present disclosure may be implemented.

Fig. 1 illustrates a schematic diagram of a communication system 100 in which embodiments of the present disclosure can be implemented. For the purpose of illustrations, the devices 110 may be referred to as the network device 110 and the device 120 may be referred to as the terminal device 120 hereinafter. It should be noted that the first devices and the second devices are interchangeable. For example, the procedures which are described to be implemented at the terminal device may also be able to be implemented at the network device and the procedures which are described to be implemented at the network device may also be able to be implemented at the terminal device.

The link from the device 120 to the devices 110 may be referred to as the “uplink” and the link from the devices 110 to the device 120 may be referred to as the “downlink” .

The communication system 100, which is a part of a communication network, comprises devices 110-1, 110-2, ..., 110-N (collectively referred to as “device (s) 110” where N is an integer number) . The device 110 may be air-bone network devices, for example, satellite.

The communication system 100 comprises devices 120-1, 120-2, ..., 120-M (collectively referred to as “device (s) 120” where M is an integer number) . The device 120 may be ground terminal device or aerial terminal device.

It should be understood that the communication system 100 may also comprise other elements which are omitted for the purpose of clarity. It is to be understood that the numbers of devices shown in Fig. 1 are given for the purpose of illustration without suggesting any limitations.

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.

As shown in Fig. 1, the spot beams 140-1, 140-2 and 140-3 are from the device 110-1. The spot beams 150-1, 150-2 and 150-3 are from the device 110-2. It should be noted that device may have any suitable number of beams. The device 120-1 may be an aerial terminal device which flies in circle or “8” shaped across different devices. Only for the purpose of illustrations, the device 110-1 refers to the first device hereinafter, the device 120 refers to the second device herein after, and the device 110-2 refers to the third device hereinafter. The first device and the third device can be interchangeable.

Fig. 2 illustrates a schematic diagram of interactions 200 in contention-free system in accordance with embodiments of the present disclosure. The interactions 200 may be implemented at any suitable devices. Only for the purpose of illustrations, the interactions 200 are described to be implemented at the first device 110-1, the second device 120 and the third device 110-2.

The second device 120-1 may perform 2005 a measurement for handover. For example, the second device 120-1 may measure the signal strength of the first device 110-1. The first device 110-1 is currently serving the second device 120-1. The second device 120-1 may receive the measurement configuration from the first device 110-1. The measurement configuration may comprise measurement objects and/or reporting configurations. The measurement objects may refer to the objects on which the UE shall perform the measurements, i.e. what to measure. The reporting configurations may refer to a list of reporting configurations which comprises reporting criteria and reporting format.

The second device 120-1 transmits 2010 the measurement report to the first device 110-1. The measurement report comprises the information specific to the second device 120-1. For example, the information specific to the second device 120-1 may comprise identification information of the second device 120-1. The information specific to the second device 120-1 may also comprise a speed of the second device 120-1. Alternatively or in addition, the information specific to the second device 120-1 may comprise the moving direction of the second device 120-1. In some embodiments, if the second device 120-1 is the GNSS terminal device. The information specific to the second device 120-1 may also comprise the location of the second device 120-1. In other embodiments, the information specific to the second device 120-1 may comprise an altitude of the second device 120-1. The information specific to the second device 120-1 may also comprise an altitude range of the second device 120-1.

The first device 110-1 may obtain 2015 signal strengths of other devices, for example, the third device 110-2. For example, the first device 110-1 may obtain the reference signal received power (RSRP) of the candidate devices which indicate the signal strengths. In some embodiments, the second device 120-1 may measure the RSRP of one or more candidate devices and transmit the RSRP to the first device 110-1. It should be noted that the signal strength may be any suitable measurement values.

The first device 110-1 selects 2020 the third device 110-2 at least partially based on the rule associated with signal strength of at least one candidate device. The first device 110-1 may receive the signal strength of one or more candidate devices from the second device 120-1. In some embodiments, the first device 110-1 determines weighted factors of the other candidate devices. The first device 110-10 may determine threshold signal strength based on the signal strengths and the weighted factors. If the signal strength of the third device 110-2 exceeds the threshold signal strength, the first device 110-1 may select the third device. The first device 110-1 may collect RSRP and the weighted factors (τ ₁＞τ ₂＞τ ₃＞τ _n) based on the descending RSRPs of devices in sequence except the serving cell. Then the first device 110-1 may determine about combination of devices according to the collected RSRPs.

In some embodiments, the first device 110-1 may determine a duration within which the signal strength of the third device 110-2 exceeds the threshold signal strength. If the duration exceeds a threshold duration, the first device 110-1 may select the third device.

In some embodiments, the first device 110-1 may select the third device 110-2 in accordance with the rule associated with the signal strength with the one or more candidate devices (shown below) :

where the RSRP _{targetcandidatesm} expresses the signal RSRP received from the candidate device-m, N expresses the number of candidate target devices. τ ₁＞τ ₂＞τ ₃＞τ _n are weighted factors to be used as weighted average of all the candidate target devices. The definition of τ depends on the RSRP proportion from the candidate target devices, H _margin is handover margin, which are used as the index to connect to the device with higher electric power. T _TTT is used to stop the excessive handover in a short time.

Fig. 3 shows a schematic diagram of handover process procedures with the movement of the second device and the fluctuations of a weighted average value of RSRPs from the candidate devices. As shown in Fig. 3, the line 350 represents the signal strength of the first device 110-1 varying with time and the line 360 represents the signal strength of the third device 110-2 varying with the time. The line 370 represents the threshold signal strength determined based on the signal strength and the weighted factors. T310 shown in Fig. 3 is the starting time of the trigger-to-time (TTT) measurement of conventional scheme and T320 shown in Fig. 3 means that the RSRP of the target device is H _margin larger than the first device 110-1 with the time duration of TTT. According to the conventional technologies, if the duration 390 between T210 and T320 exceeds the threshold duration, the first device 110-1 may determine to handover to the third device 110-2. As shown in Fig. 3, T330 is the starting time of the TTT measurement and T340 means the RSRP of the third device 110-2 is H _margin larger than the threshold signal strength with the time duration of TTT. If the duration 380 between T330 and T340 exceeds the threshold duration, the first device 110-1 may determine to handover to the third device 110-2. Thereby, the excessive handover times is reduced.

In some embodiments, the threshold duration may be adjusted to adapt to the NTN. For example, it can set an adjusted factor δ _threshold, if RSRP _serving-H _margin≥δ _threshold, the serving device can be regarded as still having sufficient RSRP to maintain the network connection, then the TTT is increased to T _TTT+T _δ. If T' _duration≥T _TTT+T _δ, handover can be performed and the handover trigger timing is delayed. Through this way, the system will delay the handover occurrence thereby reducing the handover frequency by adjusting the TTT.

The first device 110-1 transmits 2025 the handover request to the third device 110-2. The handover request comprises the information specific to the second device 120. The handover request further comprises the first timing advance value of the second device 120-1. The information specific to the second device 120 may indicate that the second device 120 is a NTN terminal device which should avoid frequent handover and have fast data transmission.

The third device 110-2 determines 2030 whether the first timing advance is applicable to the third device 110-2 based on the information specific to the second device 120. The third device 110-2 generates 2035 the information of the handover based on the determination. If the first timing advance value is applicable, the third device 110-2 may generate an indication that the first timing advance can be reused. The information of the handover may comprise the indication.

If the first timing advance value is not applicable, the third device 110-2 may generate an indication that the first timing advance is inapplicable. The indication can be included in the information of the handover.

In some embodiments, if the first timing advance value is not applicable, the third device 110-2 may determine a second advance timing which is applicable. In some embodiments, if the second device 120 is a non-GNSS terminal device, the third device 110-2 may indicate the common propagation delay d1/c and the differential delay compensation with d _compensation/c so that the residual differential delay could be controlled within the 200km/c, where c is the speed of light. In this way, the uplink reception from different terminal devices are synchronized at the network devices within the accuracy of CP length, as a results, the current NR preamble do not have to be changed in the handover procedure to reduce the handover overhead and improve the efficiency.

Fig. 4 illustrates a schematic diagram of satellite beam footprint and differential propagation. As shown in Fig. 4, within the satellite footprint, the beam of the device 110-2 can broadcast a common timing advance corresponding to the shortest distance in the footprint which is shown as d410. If the differential delay d430=d420-d410 is controlled within 200km, which could be supported in current NR, the conventional NR PRACH format can be re-used. Table 2 below shows the relationship between differential delays and the device elevation angle.

Table 2

α440 [degree]	cell radius (S460/2) [km]	d430 [km]
10	200	390
20	200	372
30	200	343
40	200	303

50	200	254
60	200	197
70	200	134
80	200	67

From Table 2 above, the differential delay d ₃=d ₂-d ₁ may exceed the maximum cell coverage supported by the NR preamble format for device elevation angles which are smaller than 60 degrees. In this situation, pre-compensation in advance can be made according to the rule of

in the target device, so that the residual differential delay is located within maximum cell coverage supported by the NR preamble. Considering the different elevation angel, it can be known that 190≤d _compensation≤267. In one example embodiment, assuming d _compensation = 200, and then the differential delay d3' after compensation is shown in Table 3 as below. It can see that the absolute values of compensated d3, denoted as d3’, fall into the range of 0～200km.

Table 3

α440 [degree]	cell radius (S460/2) [km]	d3’ [km]
10	200	190
20	200	172
30	200	143
40	200	103
50	200	54
60	200	-3
70	200	-66
80	200	-133

In some embodiments, after compensation, for the terminal devices of which the CP length is inefficient to address the uncertainties of the differential delay corresponding to the minus values in Table 3. In this situation, it may cause severe inter-carrier interference (ICI) and inter-symbol interference (ISI) , and it needs to redesign or extend the NR preamble format considering different footprint. In order to keep timing advance error within the cyclic prefix of Orthogonal Frequency Division Multiplexing (OFDM) , the effect of the residual differential delay may be mitigated as follows: case 1: NTN differential delay ≤ Max currently specified NR PRACH CP duration. In this case no change is required to the specified NR RACH procedure; case 2: NTN differential delay > Max currently specified NR PRACH CP duration. In this case different solutions are possible which are for further study.

In the above case 2, currently there are two types of PRACH format in NR, which are long preambles with L _RA=839 and short preambles length L _RA=139 as shown in Table 4-1 and Table 4-2.

Table 4-1 PRACH preamble formats for L _RA=839 and Δf ^RA∈ {1.25, 5} kHz

Table 4-2 Preamble formats for L _RA=139 and Δf ^RA=15·2 ^μ kHz where μ∈ {0, 1, 2, 3}

The PRACH sequence and CP lengths in time are detailed in Table 4-3. It can be seen that the CP length is no more than 684.37 us while the max differential delay within a beam is 1.6 ms in GEO and 0.65ms in LEO, which is much larger than 684.37 us or approximating this value. Therefore, the current NR preamble formats may not be sufficient for all NTN scenarios.

Table 4-3 Preamble parameters in different formats

To compensate the large differential delay in NTN, conventional CP length could be considered. Currently supported sub-carrier spacing (SCS) for preamble format 0, 1, 2 and 3 may be not adequate in systems with high residual frequency uncertainties. In some embodiments, if the first timing advance value is not applicable, the third device 110-2 may generate the information of the handover indicating at least one of a physical random access channel format. To mitigate RA detection impairments caused by large delays, path-loss and frequency uncertainties, here the new formats 4 and 5 may be introduced based on the conventional long preamble formats with proper scaling factor μ. The format 4 could be used in LEO scenarios and the format 5 could be used in GEO system. Table 5 shows the proposed preamble format for the NTN.

Table 5

Format 4 has approximately 2ms CP length and format 6 has 0.79ms CP length, which are sufficient for the maximum differential delay in NTN scenarios as mentioned above. Moreover, these new PRACH formats could be signaling from third device to first device for the preparation of terminal device handover. For example, if the a delay of the second device 120-1 with a compensation range of a cyclic prefix length and the second device 120-1 fails to perform the uplink transmission with the third device 110-2, the second device 120-1 may perform the retransmission using the physical random access channel format. In this way, it addresses the uncertainties of the differential delay.

In some embodiments, the third device 110-2 may determine the resource allocation for the second device 120 and generate the information of the handover comprising the resource allocation.

The third device 110-2 transmits 2040 the information of the handover to the first device 110-1. The information of the handover may comprise the second timing advance value. Alternatively or in addition, the information of the handover may comprise the indication that the first timing advance value is inapplicable to the third device. In other embodiments, the information of the handover may comprise the indication that the first timing advance value is reused. In further embodiments, the information of the handover may indicate at least one of a physical random access channel format. In some embodiments, the information of the handover may comprise the resource allocation.

The first device 110-1 transmits 2045 the indication of the handover to the second device 120-1. In some embodiments, the indication of the handover may comprise resource allocation. Alternatively or in addition, the indication of the handover may comprise an uplink procedure avoidance indication assigned by the third device 110-1. In other embodiments, the indication of the handover may comprise an indication to reuse the first timing advance value. In a further embodiment, the indication of the handover may comprise an indication of the second timing advance value.

The second device 120-1 obtains 2050 the information concerning the timing advance. In some embodiments, the second device 120-1 may obtain the indication to reuse the first timing advance value from the indication of the handover. In other embodiments, the second device 120-1 may obtain the indication of the second timing advance value from the indication of the handover. In other embodiments, the second device 120-1 may obtain the indication that the first timing advance is not applicable and receive the ephemeris of the third device 110-2 from the first device 110-1. The second device 120-1 may estimate the required timing advance value of the third device 110-2.

The second device 120-1 performs 2055 the uplink transmission with the third device 110-2. For example, the second device 120-1 may perform the uplink transmission based on the resource allocation with required timing advance. If the second device 120-1 fails in performing the uplink transmission with the third device 110-1, the second device 120-1 may compare then the delay of the second device 120-1 with the compensation range of the cyclic prefix length. If the delay exceeds the compensation range, the second device 120-1 may perform the retransmission using the physical random access channel format.

Fig. 5 shows a flowchart of an example method 500 implemented at a terminal device in accordance with some embodiments of the present disclosure. The method 500 may be implemented at any suitable devices. For the purpose of discussion, the method 500 will be described from the perspective of the first device 110-1 with reference to Fig. 1.

At block 510, the first device 110-1 receives the measurement report to the first device 110-1. The measurement report comprises the information specific to the second device 120-1. For example, the information specific to the second device 120-1 may comprise identification information of the second device 120-1. The information specific to the second device 120-1 may also comprise a speed of the second device 120-1. Alternatively or in addition, the information specific to the second device 120-1 may comprise the moving direction of the second device 120-1. In some embodiments, if the second device 120-1 is the GNSS terminal device. The information specific to the second device 120-1 may also comprise the location of the second device 120-1. In other embodiments, the information specific to the second device 120-1 may comprise an altitude of the second device 120-1. The information specific to the second device 120-1 may also comprise an altitude range of the second device 120-1.

The first device 110-1 may obtain signal strengths of other devices, for example, the third device 110-2. For example, the first device 110-1 may obtain, from the second device 120-1, the reference signal received power (RSRP) of the candidate devices which indicate the signal strengths. It should be noted that the signal strength may be any suitable measurement values.

At block 520, the first device 110-1 selects the third device 110-2 at least partially based on a rule associated with signal strength of the one or more candidate devices. In some embodiments, the first device 110-1 determines weighted factors of the other candidate devices. The first device 110-10 may determine threshold signal strength based on the signal strength of the one or more candidate devices and the weighted factors. If the signal strength of the third device 110-2 exceeds the threshold signal strength, the first device 110-1 may select the third device.

In some embodiments, the first device 110-1 may determine a duration within which the signal strength of the third device 110-2 exceeds the threshold signal strength. If the duration exceeds a threshold duration, the first device 110-1 may select the third device. In some embodiments, the first device 110-1 may select the third device 110-2 in accordance with predetermined criteria.

At block 530, the first device 110-1 transmits the handover request to the third device 110-2. The handover request comprises the information specific to the second device 120. The handover request further comprises the first timing advance value of the second device 120-1. The information specific to the second device 120 may indicate that the second device 120 is a NTN terminal device which should avoid frequent handover and have fast data transmission.

At block 540, the first device 110-1 receives the information of the handover from the third device. The information of the handover may be about an applicable timing advance value to the third device 110-2. The information of the handover may comprise one of: a second timing advance, an indication that the first timing advance is applicable, or an indication that the first timing advance in inapplicable.

At block 550, the first device 110-1 transmits the indication of the handover to the second device 120-1. In some embodiments, the indication of the handover may comprise resource allocation. Alternatively or in addition, the indication of the handover may comprise an uplink procedure avoidance indication assigned by the third device 110-1. In other embodiments, the indication of the handover may comprise an indication to reuse the first timing advance value. In a further embodiment, the indication of the handover may comprise an indication of the second timing advance value.

Fig. 6 shows a flowchart of an example method 600 implemented at a terminal device in accordance with some embodiments of the present disclosure. The method 600 may be implemented at any suitable devices. For the purpose of discussion, the method 600 will be described from the perspective of the second device 120-1 with reference to Fig. 1.

At block 610, the second device 120-1 transmits the measurement report to the first device 110-1. The measurement report comprises the information specific to the second device 120-1. For example, the information specific to the second device 120-1 may comprise identification information of the second device 120-1. The information specific to the second device 120-1 may also comprise a speed of the second device 120-1. Alternatively or in addition, the information specific to the second device 120-1 may comprise the moving direction of the second device 120-1. In some embodiments, if the second device 120-1 is the GNSS terminal device. The information specific to the second device 120-1 may also comprise the location of the second device 120-1. In other embodiments, the information specific to the second device 120-1 may comprise an altitude of the second device 120-1. The information specific to the second device 120-1 may also comprise an altitude range of the second device 120-1.

In some embodiments, the second device 120-1 may perform a measurement for handover. For example, the second device 120-1 may measure the signal strength of the first device 110-1. The first device 110-1 is currently serving the second device 120-1. The second device 120-1 may receive the measurement configuration from the first device 110-1. The measurement configuration may comprise measurement objects and/or reporting configurations. The measurement objects may refer to the objects on which the UE shall perform the measurements, i.e. what to measure. The reporting configurations may refer to a list of reporting configurations which comprises reporting criteria and reporting format. In some embodiments, the second device 120-1 may measure the RSRP of one or more candidate devices and transmit the RSRP to the first device 110-1.

At block 620, the second device 120-1 receives the indication of the handover from the first device 110-1. In some embodiments, the indication of the handover may comprise resource allocation. Alternatively or in addition, the indication of the handover may comprise an uplink procedure avoidance indication assigned by the third device 110-1. In other embodiments, the indication of the handover may comprise an indication to reuse the first timing advance value. In a further embodiment, the indication of the handover may comprise an indication of the second timing advance value.

At block 630, the second device 120-1 obtains the information concerning the timing advance. In some embodiments, the second device 120-1 may obtain the indication to reuse the first timing advance value from the indication of the handover. In other embodiments, the second device 120-1 may obtain the indication of the second timing advance value from the indication of the handover. In other embodiments, the second device 120-1 may obtain the indication that the first timing advance is not applicable and receive the ephemeris of the third device 110-2 from the first device 110-1. The second device 120-1 may estimate the required timing advance value of the third device 110-2.

At block 640, the second device 120-1 performs the uplink transmission with the third device 110-2. For example, the second device 120-1 may perform the uplink transmission based on the resource allocation with required timing advance. If the second device 120-1 fails in performing the uplink transmission with the third device 110-1, the second device 120-1 may compare then the delay of the second device 120-1 with the compensation range of the cyclic prefix length. If the delay exceeds the compensation range, the second device 120-1 may perform the retransmission using the physical random access channel format.

Fig. 7 shows a flowchart of an example method 800 implemented at a terminal device in accordance with some embodiments of the present disclosure. The method 800 may be implemented at any suitable devices. For the purpose of discussion, the method 800 will be described from the perspective of the third device 110-2 with reference to Fig. 1.

At block 710, the third device 110-2 receives the handover request from the first device 110-1. The handover request comprises the information specific to the second device 120. The handover request further comprises the first timing advance value of the second device 120-1. The information specific to the second device 120 may indicate that the second device 120 is a NTN terminal device which should avoid frequent handover and have fast data transmission.

At block 720, the third device 110-2 determines whether the first timing advance is applicable to the third device 110-2 based on the information specific to the second device 120.

At block 730, the third device 110-2 generates the information of the handover based on the determination. If the first timing advance value is applicable, the third device 110-2 may generate an indication that the first timing advance can be reused. The information of the handover may comprise the indication.

In some embodiments, the third device 110-2 may determine the resource allocation for the second device 120 and generate the information of the handover comprising the resource allocation. In further embodiments, the third device 110-2 may generate the information of the handover indicating at least one of a physical random access channel format.

At block 740, the third device 110-2 transmits the information of the handover to the first device 110-1. The information of the handover may comprise the second timing advance value. Alternatively or in addition, the information of the handover may comprise the indication that the first timing advance value is inapplicable to the third device. In other embodiments, the information of the handover may comprise the indication that the first timing advance value is reused. In further embodiments, the information of the handover may indicate at least one of a physical random access channel format. In some embodiments, the information of the handover may comprise the resource allocation.

In some embodiments, an apparatus for performing the method 500 (for example, the first device 110-1) may comprise respective means for performing the corresponding steps in the method 500. These means may be implemented in any suitable manners. For example, it can be implemented by circuitry or software modules.

In some embodiments, the apparatus comprises means for receiving, at a first device, a measurement report from a second device served by the first device, the measurement report comprising information specific to the second device; means for selecting a third device for handover of the second device at least partially based on a rule associated with signal strength of one or more candidate devices, the one or more candidate devices comprising the third device; means for transmitting to a third device a handover request comprising a first timing advance value of the second device and the information specific to the second device; means for receiving information of the handover from the third device, the information of the handover concerning an applicable timing advance value to the third device; and means for transmitting to the second device an indication of the handover from the first device to the third device.

In some embodiments, the means for selecting the third device comprises: means for obtaining, from the second device, the signal strength of the one or more candidate devices; means for determining one or more weighted factors of the one or more candidate devices; means for determining a threshold signal strength based at least in part on the signal strength and the one or more weighted factors; and means for in accordance with a determination that signal strength of the third device exceeds the threshold signal strength, selecting the third device.

In some embodiments, the means for selecting the third device comprises: means for determining a duration within which the signal strength exceeds the threshold signal strength; means for comparing the duration with a threshold duration; and means for in accordance with a determination that the duration exceeds the threshold duration, selecting the third device.

In some embodiments, the means for transmitting the indication of the handover comprises: receiving, from the third device, a resource allocation for the second device; and means for transmitting the indication comprising the resource allocation to the second device.

In some embodiments, the means for transmitting the indication of the handover comprises: means for in accordance with the information of the handover comprising a second timing advance value of the first device, transmitting the indication comprising the second timing advance value to the second device.

In some embodiments, the means for transmitting the indication of the handover comprises: means for in accordance with the information of the handover comprising a further indication that the first timing advance value is applicable to the third device, transmitting the indication to the second device to reuse the first timing advance value.

In some embodiments, the apparatus comprises means for in accordance with the information of the handover comprising a further indication that the first timing advance value is inapplicable to the third device and a physical random access channel format, transmitting ephemeris information of the third device to the second device and the physical random access channel format.

In some embodiments, wherein the information specific to the second device comprises at least one of: identification information of the second device, a speed of the second device, a moving direction of the second device, a location of the second device, an altitude of the second device, or an altitude range of the second device.

In some embodiments, wherein the first device comprises a network device, the second device comprises a terminal device, the third device comprises a further network device.

In some embodiments, an apparatus for performing the method 600 (for example, the second device 120-1) may comprise respective means for performing the corresponding steps in the method 600. These means may be implemented in any suitable manners. For example, it can be implemented by circuitry or software modules.

In some embodiments, the apparatus comprises: means for transmitting, at a second device, a measurement report to a first device serving the second device, the measurement report comprising information specific to the second device; means for receiving, from the first device, an indication of a handover from the first device to a third device; means for obtaining information concerning a timing advance value applicable to the third device; and means for performing an uplink transmission with the third device based on the timing advance value.

In some embodiments, the means for receiving the indication of the handover comprises: means for receiving the indication comprising a resource allocation used for the uplink transmission with the third device.

In some embodiments, the means for obtaining the information concerning the timing advance value comprises: means for obtaining the timing advance value applicable to the third device from the indication received from the first device.

In some embodiments, the means for obtaining the information concerning the timing advance comprises: means for receiving ephemeris information of the third device from the first device; and means for determining the timing advance based on the ephemeris information.

In some embodiments, the apparatus further comprises means for receiving information of a physical random access channel format from the first device; means for in accordance with a failure in performing the uplink transmission, comparing a delay of the second device with a compensation range of a cyclic prefix length; and means for in accordance with the delay exceeding the compensation range, performing a retransmission using the physical random access channel format.

In some embodiments, the information specific to the second device comprises at least one of: identification information of the second device, a speed of the second device, a moving direction of the second device, a location of the second device, an altitude of the second device, or an altitude range of the second device.

In some embodiments, the first device comprises a network device, the second device comprises a terminal device, the third device comprises a further network device.

In some embodiments, an apparatus for performing the method 700 (for example, the third device 110-2) may comprise respective means for performing the corresponding steps in the method 700. These means may be implemented in any suitable manners. For example, it can be implemented by circuitry or software modules.

In some embodiments, the apparatus comprises: means for receiving, at a third device, a handover request from a first device, the handover request comprising a first timing advance value of the second device and information specific to a second device served by the first device; means for determining whether the first timing advance value is applicable to the third device based on the information specific to the second device; means for generating, based on the determination, information of the handover from the first device to the third device; and means for transmitting the information to the first device.

In some embodiments, the means for generating the information of the handover comprises: means for in accordance with a determination that the first timing advance value is inapplicable to the third device, determining a second timing advance value applicable to the third device based on the information specific to the second device; and means for generating the information of the handover comprising the second timing advance value.

In some embodiments, the means for generating the information of the handover comprises: means for in accordance with a determination that the first timing advance value is inapplicable to the third device, generating an indication that the first timing advance value is inapplicable to the third device; and means for generating the information of the handover comprising the indication.

In some embodiments, the means for generating the information of the handover comprises: means for in accordance with a determination that the first timing advance value is applicable to the third device, generating an further indication that the first timing advance value is reused; and means for generating the information of the handover comprising the further indication.

In some embodiments, the means for generating the information of the handover comprises: means for generating a resource allocation for the second device; and means for generating the information comprising the resource allocation.

In some embodiments, the means for generating the information of the handover comprises: means for in accordance with a determination that the first timing advance value is inapplicable to the third device, generating the information of the handover indicating at least one of a physical random access channel format.

FIG. 8 is a simplified block diagram of a device 800 that is suitable for implementing embodiments of the present disclosure. The device 800 may be provided to implement the communication device, for example, the first device 110-1, the second device 120-1 or the third device 110-2 as shown in Fig. 1. As shown, the device 800 includes one or more processors 810, one or more memories 820 coupled to the processor 810, and one or more communication module (for example, transmitters and/or receivers (TX/RX) ) 840 coupled to the processor 810.

The communication module 840 is for bidirectional communications. The communication module 840 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 810 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 800 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 820 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) 824, 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) 822 and other volatile memories that will not last in the power-down duration.

A computer program 830 includes computer executable instructions that are executed by the associated processor 810. The program 830 may be stored in the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

The embodiments of the present disclosure may be implemented by means of the program 830 so that the device 800 may perform any process of the disclosure as discussed with reference to Figs. 2 to 7. 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 830 may be tangibly contained in a computer readable medium which may be included in the device 800 (such as in the memory 820) or other storage devices that are accessible by the device 800. The device 800 may load the program 830 from the computer readable medium to the RAM 822 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. 9 shows an example of the computer readable medium 900 in form of CD or DVD. The computer readable medium has the program 830 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 methods 200-400 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.

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 method comprising:

receiving, at a first device, a measurement report from a second device served by the first device, the measurement report comprising information specific to the second device;

selecting a third device for handover of the second device at least partially based on a rule associated with signal strength of one or more candidate devices, the one or more candidate devices comprising the third device;

transmitting to a third device a handover request comprising a first timing advance value of the second device and the information specific to the second device;

receiving information of the handover from the third device, the information of the handover concerning an applicable timing advance value to the third device; and

transmitting to the second device an indication of the handover from the first device to the third device.
The method of claim 1, wherein selecting the third device based on the rule comprises:

obtaining, from the second device, the signal strength of the one or more candidate devices;

determining one or more weighted factors of the one or more candidate devices;

determining a threshold signal strength based at least in part on the signal strength and the one or more weighted factors; and

in accordance with a determination that signal strength of the third device exceeds the threshold signal strength, selecting the third device.
The method of claim 2, wherein selecting the third device comprises:

determining a duration within which the signal strength exceeds the threshold signal strength;

comparing the duration with a threshold duration; and

in accordance with a determination that the duration exceeds the threshold duration, selecting the third device.
The method of claim 1, wherein transmitting the indication of the handover comprises:

receiving, from the third device, a resource allocation for the second device; and

transmitting the indication comprising the resource allocation to the second device.
The method of claim 1, wherein transmitting the indication of the handover comprises:

in accordance with the information of the handover comprising a second timing advance value of the first device, transmitting the indication comprising the second timing advance value to the second device.
The method of claim 1, wherein transmitting the indication of the handover comprises:

in accordance with the information of the handover comprising a further indication that the first timing advance value is applicable to the third device, transmitting the indication to the second device to reuse the first timing advance value.
The method of claim 1, further comprising:

in accordance with the information of the handover comprising a further indication that the first timing advance value is inapplicable to the third device and a physical random access channel format, transmitting ephemeris information of the third device to the second device and the physical random access channel format.
The method of claim 1, wherein the information specific to the second device comprises at least one of: identification information of the second device, a speed of the second device, a moving direction of the second device, a location of the second device, an altitude of the second device, or an altitude range of the second device.
The method of claim 1, wherein the first device comprises a network device, the second device comprises a terminal device, the third device comprises a further network device.
A method comprising:

transmitting, at a second device, a measurement report to a first device serving the second device, the measurement report comprising information specific to the second device;

receiving, from the first device, an indication of a handover from the first device to a third device;

obtaining information concerning a timing advance value applicable to the third device; and

performing an uplink transmission with the third device based on the timing advance value.
The method of claim 10, wherein receiving the indication of the handover comprises:

receiving the indication comprising a resource allocation used for the uplink transmission with the third device.
The method of claim 10, wherein obtaining the information concerning the timing advance value comprises:

obtaining the timing advance value applicable to the third device from the indication received from the first device.
The method of claim 10, wherein obtaining the information concerning the timing advance comprises:

receiving ephemeris information of the third device from the first device; and

determining the timing advance based on the ephemeris information.
The method of claim 10, further comprising:

receiving information of a physical random access channel format from the first device;

in accordance with a failure in performing the uplink transmission, comparing a delay of the second device with a compensation range of a cyclic prefix length; and

in accordance with the delay exceeding the compensation range, performing a retransmission using the physical random access channel format.
The method of claim 10, wherein the information specific to the second device comprises at least one of: identification information of the second device, a speed of the second device, a moving direction of the second device, a location of the second device, an altitude of the second device, or an altitude range of the second device.
The method of claim 10, wherein the first device comprises a network device, the second device comprises a terminal device, the third device comprises a further network device.
A method comprising:

receiving, at a third device, a handover request from a first device, the handover request comprising a first timing advance value of the second device and information specific to a second device served by the first device;

determining whether the first timing advance value is applicable to the third device based on the information specific to the second device;

generating, based on the determination, information of the handover from the first device to the third device; and

transmitting the information to the first device.
The method of claim 17, wherein generating the information of the handover comprises:

in accordance with a determination that the first timing advance value is inapplicable to the third device, determining a second timing advance value applicable to the third device based on the information specific to the second device; and

generating the information of the handover comprising the second timing advance value.
The method of claim 17, wherein generating the information of the handover comprises:

in accordance with a determination that the first timing advance value is inapplicable to the third device, generating an indication that the first timing advance value is inapplicable to the third device; and

generating the information of the handover comprising the indication.
The method of claim 17, wherein generating the information of the handover comprises:

in accordance with a determination that the first timing advance value is applicable to the third device, generating an further indication that the first timing advance value is reused; and

generating the information of the handover comprising the further indication.
The method of claim 17, wherein generating the information of the handover comprises:

generating a resource allocation for the second device; and

generating the information comprising the resource allocation.
The method of claim 17, wherein generating the information of the handover comprises:

in accordance with a determination that the first timing advance value is inapplicable to the third device, generating the information of the handover indicating at least one of a physical random access channel format.
The method of claim 17, wherein the information specific to the second device comprises at least one of: identification information of the second device, a speed of the second device, a moving direction of the second device, a location of the second device, an altitude of the second device, or an altitude range of the second device.
The method of claim 17, wherein the first device comprises a network device, the second device comprises a terminal device, the third device comprises a further network device.
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 to perform the method according to any one of claims 1-9.
A second 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 second device to perform the method according to any one of claims 10-16.
A third 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 third device to perform the method according to any one of claims 17-24.
A computer readable medium storing instructions thereon, the instructions, when executed by at least one processing unit of a machine, causing the machine to perform the method according to any one of claims 1-9.
A computer readable medium storing instructions thereon, the instructions, when executed by at least one processing unit of a machine, causing the machine to perform the method according to any one of claims 10-16.
A computer readable medium storing instructions thereon, the instructions, when executed by at least one processing unit of a machine, causing the machine to perform the method according to any one of claims 17-24.
An apparatus comprising means for performing a method according to any of claims 1-9.
An apparatus comprising means for performing a method according to any of claims 10-16.
An apparatus comprising means for performing a method according to any of claims 17-24.