WO2025060001A1

WO2025060001A1 - Handover in scenario when both source distributed unit and target distributed unit are co-located

Info

Publication number: WO2025060001A1
Application number: PCT/CN2023/120477
Authority: WO
Inventors: Xiang Xu; Jeroen Wigard; Jedrzej STANCZAK
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Priority date: 2023-09-21
Filing date: 2023-09-21
Publication date: 2025-03-27
Anticipated expiration: 2026-03-21

Abstract

Embodiments of the present disclosure relate to apparatuses, methods, devices and computer readable storage medium for handover in scenario when both source distributed unit and target distributed unit are co-located. The method comprising: at a first apparatus, the first apparatus transmits, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of downlink data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

Description

HANDOVER IN SCENARIO WHEN BOTH SOURCE DISTRIBUTED UNIT AND TARGET DISTRIBUTED UNIT ARE CO-LOCATED

FIELDS

Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for a handover in a scenario when both source distributed unit (DU) and target DU are co-located.

BACKGROUND

The Third Generation Partnership Project (3GPP) had proposed a regenerative Non-Terrestrial Network (NTN) architecture with gNB-DU on the satellite. The satellite may also embark Centralized Unit-User Plane (CU-UP) , User Plane Function (UPF) , etc. In this architecture, three types of service links are supported, namely earth-fixed, quasi-earth-fixed and earth-moving.

SUMMARY

In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: transmit, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In a second aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: receive, from a first apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus; and perform the delayed handover for the handover the third apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In a third aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third apparatus at least to: receive, from a second apparatus performing a delayed handover for a handover of the third apparatus from the second apparatus to a fourth apparatus, DL data buffered at the second apparatus; and perform the handover based on at least one of a trigger condition of the handover or buffered DL data delivery status.

In a fourth aspect of the present disclosure, there is provided a method. The method comprises: transmitting, at a first apparatus, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In a fifth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a first apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus; and performing the delayed handover for the handover the third apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In a sixth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a second apparatus performing a delayed handover for a handover of the third apparatus from the second apparatus to a fourth apparatus, DL data buffered at the second apparatus; and performing the handover based on at least one of a trigger condition of the handover or buffered DL data delivery status.

In a seventh aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for transmitting, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In an eighth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for receiving, from a first apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus; and means for performing the delayed handover for the handover the third apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In a ninth aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises means for receiving, from a second apparatus performing a delayed handover for a handover of the third apparatus from the second apparatus to a fourth apparatus, DL data buffered at the second apparatus; and means for performing the handover based on at least one of a trigger condition of the handover or buffered DL data delivery status.

In a tenth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourth aspect.

In an eleventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fifth aspect.

In a twelfth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the sixth 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 communication environment in which example embodiments of the present disclosure can be implemented;

FIG. 2 illustrates a signaling chart of an example process based on normal handover according to some example embodiments of the present disclosure;

FIG. 3 illustrates a signaling chart of an example process based on conditional handover according to some example embodiments of the present disclosure;

FIG. 4 illustrates an example scenario of mobile Integrated Access &Backhaul (IAB) full migration according to some example embodiments of the present disclosure;

FIG. 5 illustrates a flowchart of a method implemented at a first apparatus according to some example embodiments of the present disclosure;

FIG. 6 illustrates a flowchart of a method implemented at a second apparatus according to some example embodiments of the present disclosure;

FIG. 7 illustrates a flowchart of a method implemented at a third apparatus according to some example embodiments of the present disclosure;

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

FIG. 9 illustrates a block diagram of an example computer readable medium in accordance with some 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. Embodiments 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, ” “second, ” …, etc. in front of noun (s) and the like 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 and they do not limit the order of the noun (s) . 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.

As used herein, “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” and similar wording, where the list of two or more elements are joined by “and” or “or” , mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

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 New Radio (NR) , Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) , the 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, for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , an NR NB (also referred to as a gNB) , a Distributed Unit of a gNB (gNB-DU) , or a Central Unit of a gNB (gNB-CU) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a relay, an Integrated Access and Backhaul (IAB) node, 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. In some example embodiments, radio access network (RAN) maybe based on split architecture. A network device may comprises a Central Unit (CU) and one or more Distributed Unit (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 (IoT) 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. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node) . In the following description, the terms “terminal device” , “communication device” , “terminal” , “user equipment” and “UE” may be used interchangeably.

As used herein, the term “resource, ” “transmission resource, ” “resource block, ” “physical resource block” (PRB) , “uplink resource, ” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and/or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. In the communication environment 100, the communication environment 100 may include a first apparatus 110-1 and a first apparatus 110-2. Hereinafter the first apparatus 110-1 and the first apparatus 110-2 may also be referred to as a first apparatus 110 collectively. In some scenarios, the first apparatus 110-1 and the first apparatus 110-2 may communicate with each other. In some example embodiments, the first apparatus 110 may comprise a network device (e.g., a gNB-CU) .

As shown in FIG. 1, the communication environment 100 may further include a second apparatus 120 and a fourth apparatus 140. The second apparatus 120 or the fourth apparatus 140 may comprise a network device (e.g., a gNB-DU) , respectively. In some scenarios, the second apparatus 120 and the fourth apparatus 140 are co-located, e.g., deployed at a same satellite, which may be referred to as a Non-Terrestrial Network (NTN) regenerative architecture.

The second apparatus 120 may communicate with the first apparatus 110-1, and the fourth apparatus 140 may communicate with the first apparatus 110-2. For example, the second apparatus 120 may communicate with the first apparatus 110-1 and/or the fourth apparatus 140 may communicate with the first apparatus 110-2 via a transport network node, e.g., a gateway (GW) , respectively.

The communication environment 100 may further include a third apparatus 130, which may comprise a terminal device (e.g., a UE) . In some scenarios, the third apparatus 130 may perform an inter-DU handover, e.g., from the second apparatus 120 to the fourth apparatus 140. For example, when the second apparatus 120 may be incapable of serving the third apparatus 130.

In the following, for the purpose of illustration, some example embodiments are described with the first apparatus 110-1 operating as a source CU, the second apparatus 120 operating as a source DU for the handover of third apparatus 130, and the first apparatus 110-2 operating as a target CU and the fourth apparatus 140 operating as a target DU for the handover of third apparatus 130.

However, in some example embodiments, operations described in connection with the first apparatus 110-1 may be implemented at the first apparatus 110-2, and operations described in connection with the second apparatus 120 may be implemented at the fourth apparatus 140.

It is to be understood that the number of the terminal devices and network devices shown in FIG. 1 is given for the purpose of illustration without suggesting any limitations. The communication environment 100 may include any suitable number of the terminal devices and network devices.

In some example embodiments, a link from a network device to a terminal device is referred to as a downlink (DL) , and a link from a terminal device to a network device is referred to as an uplink (UL) . In DL, the network device is a transmitting (TX) device (or a transmitter) and the terminal device is a receiving (RX) device (or a receiver) . In UL, the terminal device is a TX device (or a transmitter) and the network device is a RX device (or a receiver) .

Communications in the communication environment 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) , the fifth generation (5G) , the sixth generation (6G) , and 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 described above, the handover may occur in the scenario when the second apparatus 120 and the fourth 140 are co-located. One example scenario is NTN regenerative architecture with DU on the satellite.

NTN regenerative architecture may support some types of service links. For example, the NTN regenerative architecture may support earth-fixed which may be provisioned by beam (s) continuously covering the same geographical areas all the time (e.g., the case of Geostationary Earth Orbit (GSO) satellites) . For another example, the NTN regenerative architecture may support quasi-Earth-fixed which may be provisioned by beam (s) covering one geographic area for a limited period and a different geographic area during another period (e.g., the case of Non-Geostationary Earth Orbit (NGSO) satellites generating steerable beams) . For still another example, the NTN regenerative architecture may support earth-moving which may be provisioned by beam (s) whose coverage area slides over the earth surface (e.g., the case of NGSO satellites generating fixed or non-steerable beams) .

The NTN regenerative architecture may support Feeder Link SwitchOver (FLSO) . During NTN operation, it may become necessary to switch the feeder link for a satellite from one NTN GW to another NTN. This may be due to e.g., maintenance, traffic offloading, or (for NGSO) due to the NGSO satellite moving out of visibility with respect to the current NTN GW.

The FLSO may include the soft FLSO and the hard FLSO. For the soft FLSO, an NTN payload is able to connect to more than one NTN Gateway during a given period, i.e., a temporary overlap may be ensured during the transition between the feeder links. For the NTN regenerative architecture with DU on satellite, the FLSO may change the CU. In this case, when CU is changed, all connected UEs in the cell need to be handed over from a CU1 (e.g., a source CU) to a CU2 (e.g., a target CU) .

For the hard FLSO, an NTN payload may connect to only one NTN Gateway at any given time, i.e., a radio link interruption may occur during the transition between the feeder links.

With reference to FIG. 1, for the NTN regenerative with gNB-DU on satellite, when the soft FLSO is performed and the CU is changed (e.g., from the first apparatus 110-1 to the first apparatus 110-2) , the satellite needs to host at least 2 gNB-DUs (e.g., the second apparatus 120 and the fourth apparatus 140) . The second apparatus 120 (considered as a source DU) may connect with the first apparatus 110-1 (considered as a source CU) , the F1 transport network connection between the second apparatus 120 and the first apparatus 110-1 may use a GW or NTN GW. The first apparatus 110-2 (considered as the target CU) may connect with the fourth apparatus 140 (considered as the target DU) , the F1 transport network connection between the fourth apparatus 140 and the first apparatus 110-2 may use a further GW or NTN GW.

During the soft FLSO, the third apparatus 130 (e.g., UE) may hand over from the second apparatus 120 connecting the first apparatus 110-1 to the fourth apparatus 140 connecting the first apparatus 110-2. In this case, both second apparatus 120 (e.g., source cell) and fourth apparatus 140 (e.g., target cell) may have similar footprint.

In this NTN regenerative architecture, there are problems for the scenario when a third apparatus 130 connected with a physical node, which has co-located the second apparatus 120 acting as the source serving device for the third apparatus 130 and the fourth apparatus 140 to be acted as the target serving device for the third apparatus 130 connecting different first apparatuses, need to be handed over from the second apparatus 120 to the co-located fourth apparatus 140.

For example, during the inter-gNB-DU Handover (HO) /Conditional (CHO) , untransmitted DL data buffered in the source DU, i.e. the second apparatus 120, will be discarded, and the first apparatus 110 has to re-forward the DL data (which are already buffered in the second apparatus 120) to the fourth apparatus 140 (which is co-located with the source second apparatus 120) based on the Downlink Data Delivery Status (DDDS) received from the second apparatus 120. This is inefficient.

In case of Radio Link Control Unacknowledged Mode (RLC UM) , the third apparatus 130 will not receive those DL data that have been transmitted to the second apparatus 120 but not sent to the third apparatus 130, since the first apparatus 110 does not keep them. This leads to the DL data missing.

During the FLSO with CU change, even if the second apparatus 120 may forward untransmitted DL data (received from the first apparatus 110-1) to the fourth apparatus 140, then the fourth apparatus 140 sends them to the third apparatus 130. The fourth apparatus 140 may also transmit the DL data received from the first apparatus 110-2. The third apparatus 130 will receive both DL data originated from the first apparatus 110-1 (and ciphered by the first apparatus 110-1) , and DL data originated from the first apparatus 110-2 (and ciphered by the first apparatus 110-2) . However, the third apparatus 130 cannot differentiate them. The third apparatus 130 will not be able to decipher the received DL data before its application layer can remove the duplicated data.

Considering the above issues, the example embodiments of the present disclosure propose a new solution for handover scenario when both source DU and target DU are co-located. In this solution, the first apparatus 110 transmits, to the second apparatus 120 an indication for requesting the second apparatus 120 to use a delayed handover for a handover of the third apparatus 130 from the second apparatus 120 to the fourth apparatus 140 that is co-located with the second apparatus 120. By using the delayed handover, at least a portion of DL data buffered at the second apparatus 120 is to be transmitted to the third apparatus 130 before an execution of the handover of the third apparatus 130. In other words, the delayed handover means the third apparatus 130 does not immediately execute or perform the handover after the first apparatus 110 make the decision for the handover of the third apparatus 130. Depends on whether third apparatus 130 support conditional handover or not, the delayed handover may be implemented by enhancement to normal handover where the RRCReconfiguration message to the third apparatus 130 is first buffered in the second apparatus 120 then delivered to the third apparatus 130 when at least a portion of DL data buffered at the second apparatus 120 has been transmitted to the third apparatus 130, or enhancement to conditional handover where the third apparatus 130 performs or executes a conditional handover when at least a portion of DL data buffered at the second apparatus 120 has been transmitted to the third apparatus 130.

In this way, the untransmitted DL data buffered in the source DU can be transmitted to the UE instead of discarding them no matter in normal handover or conditional handover. Moreover, sending duplicated data from the CU to the target DU is avoided when the UE needs to be handed over from the source DU to the co-located target DU, while the source DU and the target DU may connect with different CUs.

Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

Reference is now made to FIG. 2, which illustrates a signaling chart 200 of an example process based on normal handover according to some example embodiments of the present disclosure. As shown in FIG. 2, the signaling chart 200 involves the first apparatus 110, the second apparatus 120, the third apparatus 130 and the fourth apparatus 140. For the purposes of discussion, the signaling chart 200 will be discussed with reference to FIG. 1.

In some scenarios of the FIG. 1, The second apparatus 120 and the fourth apparatus 140 are co-located. The second apparatus 120 may connect with the first apparatus 110-1. The fourth apparatus 140 may connect with the first apparatus 110-2. For sake of clarity, the XnAP signaling between the first apparatus 110-1 and the first apparatus 110-2 may be omitted. In FIG. 2, only a single first apparatus 110 is shown.

As shown in FIG. 2, in an inter DU HO, in a case the first apparatus 100 determines that e.g., a handover from the second apparatus 120 to the fourth apparatus 140 is to be initiated for the third apparatus 130, the first apparatus 110 may transmit (210) an indication to the second apparatus 120 of requesting the second apparatus 120 to use a delayed handover for the handover of the third apparatus 130. The delayed handover may indicate the second apparatus 120 to continue the transmission of the buffered DL data to the third apparatus 130, before the third apparatus 130 executes or performs the handover.

For example, the first apparatus 110 may transmit the indication to the second apparatus via a message, for example, a F1 application protocol (F1AP) message, such as a UE CONTEXT MODIFICATION REQUEST message, or a downlink radio resource control message transfer (DL RRC MESSAGE TRANSFER) message, or other F1AP message. The first apparatus 110 may transmit the F1AP message, e.g., UE CONTEXT MODIFICATION REQUEST message, including a generated a radio resource control (RRC) Reconfiguration message.

As an example, a new information element (IE) may be introduced to the F1AP message, e.g., UE CONTEXT MODIFICATION REQUEST message, indicating the delayed handover to be used by the second apparatus 120. The indication of the delayed handover may indicate the second apparatus 120 to buffer the RRCReconfiguration message until all or an amount of DL data buffered at the second apparatus 120 has been transmitted to the third apparatus 130.

In case the first apparatus 110 intends to use the delayed handover, in addition to the IE for the “delayed handover” indication, in some embodiment, the F1AP message, e.g., UE CONTEXT MODIFICATION REQUEST message, may further include other IEs, such as an IE for timing information of handover, e.g., indicating the handover of the third apparatus 130 is to be performed before a time point. That is, the RRCReconfiguration message buffered at the second apparatus 120 is to be sent to the third apparatus 130 before this timing.

In some other embodiments, the UE CONTEXT MODIFICATION REQUEST message may further include an IE for location information of handover e.g., indicating the handover of the third apparatus 130 is to be performed before the second apparatus moves to a location. That is, the RRCReconfiguration message buffered at the second apparatus 120 is to be sent to the third apparatus 130 before the second apparatus 120 (e.g., the satellite which host the second apparatus 120) arrives at this location at which the second apparatus 120 is incapable of serving the third apparatus 130.

After receiving the delayed handover indication from the first apparatus 110, the second apparatus 120 buffers (220) the RRCReconfiguration message and transmits (230) the DL data buffered at the second apparatus 120 to the third apparatus 130.

Based on the delayed handover indication, in some embodiments, the second apparatus 120 may transmit (240) the RRCReconfiguration message to the third apparatus 130 when the last buffered DL data or all buffered DL data or a specific buffered DL data has been transmitted to the third apparatus 130. In some other embodiments, the second apparatus 120 may transmit (240) the RRCReconfiguration message to the third apparatus 130 when a certain amount of buffered DL data has been transmitted to the third apparatus 130. It is to be understood that a minimum amount of buffered DL data may be transmitted to the third apparatus 130 before the transmission of the RRCReconfiguration message. The certain amount of buffered DL data and/or a minimum amount of buffered DL data may also be configured by the first apparatus 110 and be part of the delayed handover indication.

Furthermore, a radio link connection may be guaranteed for the third apparatus 130. That is, the second apparatus 120 may determine whether the RRCReconfiguration message should be transmitted to the third apparatus 130 based on other condition (s) indicated by the delayed handover indication.

In some example embodiments, the second apparatus 120 may transmit the buffered RRCReconfiguration message to the third apparatus 130 before a time point at which the second apparatus 120 is incapable of serving the third apparatus 130, e.g., even there is still a portion of DL data buffered at the second apparatus 120 that has not been transmitted to the third apparatus 130.

In other example embodiments, the second apparatus 120 may transmit the buffered RRCReconfiguration message to the third apparatus 130 before the second apparatus 120 moves to a location at which the second apparatus 120 is incapable of serving the third apparatus 130, e.g., even there is still a portion of DL data buffered at the second apparatus 120 that has not been transmitted to the third apparatus 130.

The second apparatus 120 may transmit (250) a DDDS message to the first apparatus 110 to indicate a status of DL data currently still buffered at the second apparatus 120 but will be transmitted to the third apparatus 130 before the third apparatus 130 executes the handover. For example, the second apparatus 120 may indicate, via the DDDS message, the highest sequence number of a packet data convergence protocol, PDCP, protocol data unit that will be successfully delivered to the third apparatus 130 before the third apparatus 130 executes the handover.

For example, in a case where the second apparatus 120 has successfully transmitted DL up to PDCP SN#10, and the second apparatus 120 still have untransmitted DL packet from PDCP SN #11 to #20, in this case, the second apparatus 120 may indicate the highest sequence number of PDCP protocol data unit that will be successfully delivered, i.e., the sequence number #20, before the third apparatus 130 executes the handover.

Additionally, the first apparatus 110 may continue the downlink transmission after receiving the DDDS message, the second apparatus 120 may inform the first apparatus 110 for those DL data that have not been successfully transmitted to the third apparatus 130 but will be transmitted to the third apparatus 130 before the third apparatus 130 executes the handover.

Then the second apparatus 120 may transmit (260) a message, for example, a F1AP message, e.g., UE CONTEXT MODIFICATION RESPONSE message, to the first apparatus 110.

Reference is now made to FIG. 3, which illustrates a signaling chart 300 of an example process based on conditional handover according to some example embodiments of the present disclosure. As shown in FIG. 3, the signaling chart 300 involves the first apparatus 110, the second apparatus 120, the third apparatus 130 and the fourth apparatus 140. For the purposes of discussion, the signaling chart 300 will be discussed with reference to FIG. 1.

The difference between the example of FIG. 2 and the example of FIG. 3 is that the third apparatus 110 may support conditional handover. As shown in FIG. 3, the first apparatus 110 may transmit (310) , to the second apparatus 120, a RRCReconfiguration message via a message, for example, a F1AP message, such as a DL RRC MESSAGE TRANSFER message. In case the first apparatus 110 may desire to use the delayed handover, the F1AP message may include an indication for requesting the second apparatus 120 to use the delayed handover.

The RRCReconfiguration message may also include a new trigger condition for a conditional handover of the third apparatus 130, for example, the third apparatus 130 may execute the handover, for example, execute the RRCReconfiguration, when the last DL data or a certain amount of DL data has been received from the second apparatus 120 or the source cell. That is, the third apparatus 130 may determine whether execute a conditional handover by considering buffered DL data delivery status of the second apparatus 120.

In addition, this trigger condition may be used in combination with other trigger condition (e.g., timing-based trigger condition, or location-based trigger condition, etc. ) , to ensure the handover is triggered before the source cell disappear.

Continue to refer to FIG. 3, the second apparatus 120 may forward (320) the RRC reconfiguration message including the above-mentioned trigger condition (s) to the third apparatus 130. The third apparatus 130 may response (330) a RRC reconfiguration complete message to the second apparatus 120. Then the second apparatus 120 may continue (350) the DL transmission until all buffered DL data or an amount of buffered DL data has been sent.

Optionally or additionally, the second apparatus 120 may transmit (360) the buffered DL data to the third apparatus 130 and indicate (370) the last buffered DL data to the third apparatus 130.

In some example embodiments, the second apparatus 120 may indicate a DL data is the last buffered DL data when the second apparatus 120 transmits the last buffered DL data, e.g., via a new flag in the header of PDCP protocol data.

In some other embodiments, the second apparatus 120 may indicate to the third apparatus 130 beforehand of the packet number or the sequence number of the last buffered DL data packet. Therefore, the third apparatus 130 may be aware of the last buffered DL data when third apparatus 130 receives it, e.g., receive a DL data with a specific packet number or sequence number.

The third apparatus 130 does not execute the received RRCReconfiguration message until the trigger condition for a conditional handover has been fulfilled. The third apparatus 130 may determine (380) whether the trigger condition for a conditional handover has been fulfilled. In some example embodiments, the third apparatus 130 may determine the trigger condition for a conditional handover has been fulfilled, for example, when the last buffered DL data from the source cell has been received. That is, a trigger condition of a conditional handover may include whether the last DL data buffered in the second apparatus 120 has been received, or whether a certain amount of buffered DL data has been received from the second apparatus 120, whether a buffered DL data having a specific sequence number has been received from the second apparatus 120, whether a time point, at which the second apparatus 120 is incapable of serving the third apparatus 130, is passed, or whether the second apparatus 120 is moving to a location. If so, the third apparatus 130 may execute the conditional handover.

In some other example embodiments, the third apparatus 130 may determine whether the conditional handover is to be initiated based on other trigger condition (s) , such as whether a time point, at which the second apparatus 120 is incapable of serving the third apparatus, is passed and/or whether the second apparatus 120 is moving to a location incapable of serving the third apparatus 130.

After determining the trigger condition for a conditional handover has been fulfilled, the third apparatus 130 may execute the buffered RRCReconfiguration message, detach from the second apparatus 120 and connect to the fourth apparatus 140.

In this way, the untransmitted DL data buffered in the second apparatus 120 can be transmitted to the third apparatus 130 instead of discarding them no matter in normal handover or conditional handover.

Furthermore, the embodiments of the present disclosure may be used in a scenario is that the UE performs the handover in the case of the mobile Integrated Access &Backhaul (IAB) migration (i.e., IAB-DU migration) as described in FIG. 4.

Reference is now made to FIG. 4, which illustrates an example scenario of mobile IAB full migration according to some example embodiments of the present disclosure. As shown in FIG. 4, the scenario 400 involves an IAB-donor-CU 410-1 (referred to as source CU) , an IAB-donor-CU 410-2 (referred to as target CU) and an IAB 450. The mobile IAB or Mobile Base Station Relay (MBSR) 440 have 2 co-located IAB-DU, i.e., a DU 420 (referred to as source DU) and a DU 440 (referred to as target DU) . The source F1 is established between the IAB-donor-CU 410-1 (source CU) and DU 420. The target F1 is established between the IAB-donor-CU 410-2 (source CU) and DU 440.

A handover of the UE 430 may be performed from the source CU/DU pair to the target CU/DU pair, during the IAB-DU migration. The F1 serving the UE is switched from the source F1 to the target F1. The operations described with reference to FIGS. 2-3 may also be suitable for the handover occurs at the scenario 400. The detail will be omitted here.

FIG. 5 shows a flowchart of an example method 500 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 500 will be described from the perspective of the first apparatus 110 in FIG. 1.

At block 510, the first apparatus 110 transmits, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In some example embodiments, the method 500 further comprises: the first apparatus 110 transmits, to the second apparatus, the indication by an information element via a message, for example, a F1AP message, such as a UE CONTEXT MODIFICATION REQUEST message or a DOWNLINK RADIO RESOURCE CONTROL MESSAGE TRANSFER message.

In some example embodiments, the indication comprises at least one further information element indicating at least one of: the handover of the third apparatus is to be performed before a time point, the handover of the third apparatus is to be performed before the second apparatus moves to a location, all downlink data buffered in the second apparatus has been sent to the third apparatus, a certain amount of downlink data buffered in the second apparatus has been sent to the third apparatus, or a downlink data having a specific sequence number buffered in the second apparatus has been sent to the third apparatus.

In some example embodiments, the method 500 further comprises: the first apparatus 110 receives, from a second apparatus, an indication indicating the highest sequence number of a packet data convergence protocol, PDCP, protocol data unit to be successfully delivered to the third apparatus, before the execution of the handover of the third apparatus.

In some example embodiments, the method 500 further comprises: the first apparatus 110 transmits the radio resource control reconfiguration message to the third apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following: whether the last buffered DL data has been received from the second apparatus, whether a certain amount of buffered DL data has been received from the second apparatus, whether a buffered DL data having a specific sequence number has been received from the second apparatus, whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or whether the second apparatus is moving to a location.

In some example embodiments, the first apparatus comprises a centralized unit, the second apparatus comprises a source distributed unit in the handover, the third apparatus comprises a terminal device and the fourth apparatus comprises a target distributed unit in the handover.

FIG. 6 shows a flowchart of an example method 600 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 600 will be described from the perspective of the second apparatus 120 in FIG. 1.

At block 610, the second apparatus 120 receives, from a first apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus; and

At block 620, the second apparatus 120 performs the delayed handover for the handover the third apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In some example embodiments, the method 600 further comprises: the second apparatus 120 receives, from the first apparatus, the indication by an information element via a message, for example, a F1AP UE context modification request message or a F1AP downlink radio resource control message transfer message.

In some example embodiments, the indication comprises at least one further information element indicating at least one of: the handover of the third apparatus is to be performed before a time point; the handover of the third apparatus is to be performed before the second apparatus moves to a location, all downlink data buffered in the second apparatus has been sent to the third apparatus, a certain amount of downlink data buffered in the second apparatus has been sent to the third apparatus, or a downlink data having a specific sequence number buffered in the second apparatus has been sent to the third apparatus.

In some example embodiments, the method 600 further comprises: the second apparatus 120 buffers a radio resource control reconfiguration message until all or a certain amount of DL data or a downlink data having a specific sequence number buffered at the second apparatus has been transmitted to the third apparatus and/or based on the at least one further information element.

In some example embodiments, the method 600 further comprises: the second apparatus 120 transmits, to the third apparatus, the radio resource control reconfiguration message before the time point and/or before the second apparatus moves to the location.

In some example embodiments, the method 600 further comprises: the second apparatus 120 transmits, to the first apparatus, an indication indicating the highest sequence number of a packet data convergence protocol, PDCP, protocol data unit to be successfully delivered to the third apparatus, before the execution of the handover of the third apparatus.

In some example embodiments, the method 600 further comprises: the second apparatus 120 transmits, to the third apparatus, the DL data buffered at the second apparatus after the transmission of the radio resource control reconfiguration message.

In some example embodiments, the radio resource control reconfiguration message is transmitted from the first apparatus to the third apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following: whether the last buffered DL data has been received from the second apparatus, whether a certain amount of buffered DL data has been received from the second apparatus, whether a buffered DL data having a specific sequence number has been received from the second apparatus, or whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or whether the second apparatus is moving to a location.

In some example embodiments, the method 600 further comprises: the second apparatus 120 indicate, to third apparatus, a data packet transmitted to the third apparatus is the last data packet buffered at the second apparatus or the sequence number of the last data packet to be transmitted from the second apparatus, before the third apparatus execute the handover.

FIG. 7 shows a flowchart of an example method 700 implemented at a third apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 700 will be described from the perspective of the third apparatus 130 in FIG. 1.

At block 710, the third apparatus 130 receives, from a second apparatus performing a delayed handover for a handover of the third apparatus from the second apparatus to a fourth apparatus, DL data buffered at the second apparatus.

At block 720, the third apparatus 130 performs the handover based on at least one of a trigger condition of the handover or buffered DL data delivery status.

In some example embodiments, the method 700 further comprises: the third apparatus 130 receives a radio resource control reconfiguration message from a first apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following: whether the last buffered DL data has been received from the second apparatus, whether a certain amount of buffered DL data has been received from the second apparatus, whether a buffered DL data having a specific sequence number has been received from the second apparatus, whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or whether the second apparatus is moving to a location.

In some example embodiments, the method 700 further comprises: the third apparatus 130 receives, from the second apparatus, the DL data buffered at the second apparatus after the reception of the radio resource control reconfiguration message.

In some example embodiments, the method 700 further comprises: the third apparatus 130 indicate, by the second apparatus, the data packet transmitted to the third apparatus is the last data packet or the sequence number of the last data packet to be transmitted from the second apparatus, before the third apparatus execute the handover.

In some example embodiments, the method 700 further comprises: the third apparatus 130 executes the conditional handover based on at least one of: when the last downlink data has been received from the second apparatus, when a certain amount of downlink data has been received from the second apparatus, when a downlink data having a specific sequence number has been received from the second apparatus, when a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or when the second apparatus has arrived at the location.

In some example embodiments, a first apparatus capable of performing any of the method 500 (for example, the first apparatus 110 in FIG. 1) may comprise means for performing the respective operations of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 110 in FIG. 1.

In some example embodiments, the first apparatus comprises means for transmitting, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In some example embodiments, the first apparatus further comprises means for transmitting, to the second apparatus, the indication by an information element via a message, for example, a F1AP UE context modification request message or a F1AP downlink radio resource control message transfer message.

In some example embodiments, the first apparatus further comprises means for receiving, from a second apparatus, an indication indicating the highest sequence number of a packet data convergence protocol, PDCP, protocol data unit to be successfully delivered to the third apparatus, before the execution of the handover of the third apparatus.

In some example embodiments, the first apparatus further comprises means for transmitting the radio resource control reconfiguration message to the third apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following: whether the last buffered DL data has been received from the second apparatus, whether a certain amount of buffered DL data has been received from the second apparatus, or whether a buffered DL data having a specific sequence number has been received from the second apparatus, whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or whether the second apparatus is moving to a location..

In some example embodiments, the first apparatus further comprises means for performing other operations in some example embodiments of the method 500 or the first apparatus 110. In some example embodiments, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the first apparatus.

In some example embodiments, a second apparatus capable of performing any of the method 600 (for example, the second apparatus 120 in FIG. 1) may comprise means for performing the respective operations 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. The second apparatus may be implemented as or included in the second apparatus 120 in FIG. 1.

In some example embodiments, the second apparatus comprises means for receiving, from a first apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus; and means for performing the delayed handover for the handover the third apparatus, wherein at least a portion of DL data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.

In some example embodiments, the second apparatus further comprises means for receiving, from the first apparatus, the indication by an information element via a message, for example, a F1AP UE context modification request message or a F1AP downlink radio resource control message transfer message.

In some example embodiments, the second apparatus further comprises means for buffering a radio resource control reconfiguration message until all or a certain amount of DL data or a downlink data having a specific sequence number buffered at the second apparatus has been transmitted to the third apparatus and/or based on the at least one further information element.

In some example embodiments, the second apparatus further comprises means for transmitting, to the third apparatus, the radio resource control reconfiguration message before the time point and/or before the second apparatus moves to the location.

In some example embodiments, the second apparatus further comprises means for transmitting, to the first apparatus, an indication indicating the highest sequence number of a packet data convergence protocol, PDCP, protocol data unit to be successfully delivered to the third apparatus, before the execution of the handover of the third apparatus.

In some example embodiments, the second apparatus further comprises means for transmitting, to the third apparatus, the DL data buffered at the second apparatus after the transmission of the radio resource control reconfiguration message.

In some example embodiments, the radio resource control reconfiguration message is transmitted from the first apparatus to the third apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following: whether the last buffered DL data has been received from the second apparatus, whether a certain amount of buffered DL data has been received from the second apparatus, or whether a buffered DL data having a specific sequence number has been received from the second apparatus, whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or whether the second apparatus is moving to a location.

In some example embodiments, the second apparatus further comprises means for indicating, to third apparatus, a data packet transmitted to the third apparatus is the last data packet buffered at the second apparatus or the sequence number of the last data packet to be transmitted from the second apparatus, before the third apparatus execute the handover.

In some example embodiments, a third apparatus capable of performing any of the method 700 (for example, the third apparatus 130 in FIG. 1 may comprise means for performing the respective operations of the method 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the third apparatus 130 in FIG. 1.

In some example embodiments, the third apparatus comprises: means for receiving, from a second apparatus performing a delayed handover for a handover of the third apparatus from the second apparatus to a fourth apparatus, DL data buffered at the second apparatus; and means for performing the handover based on at least one of a trigger condition of the handover or buffered DL data delivery status.

In some example embodiments, the third apparatus further comprises means for receiving a radio resource control reconfiguration message from a first apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following: whether the last buffered DL data has been received from the second apparatus, whether a certain amount of buffered DL data has been received from the second apparatus, whether a buffered DL data having a specific sequence number has been received from the second apparatus, whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or whether the second apparatus is moving to a location.

In some example embodiments, the third apparatus further comprises means for receiving, from the second apparatus, the DL data buffered at the second apparatus after the reception of the radio resource control reconfiguration message.

In some example embodiments, the third apparatus further comprises means for indicating, by the second apparatus, the data packet transmitted to the third apparatus is the last data packet or the sequence number of the last data packet to be transmitted from the second apparatus, before the third apparatus execute the handover.

In some example embodiments, the third apparatus further comprises means for initiate the conditional handover based on at least one of: when the last downlink data has been received from the second apparatus, when a certain amount of downlink data has been received from the second apparatus, when a downlink data having a specific sequence number has been received from the second apparatus, when a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or when the second apparatus has arrived at the location.

FIG. 8 is a simplified block diagram of a device 800 that is suitable for implementing example embodiments of the present disclosure. The device 800 may be provided to implement a communication device, for example, the first apparatus 110, the second apparatus 120 or the third apparatus 130 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 modules 840 coupled to the processor 810.

The communication module 840 is for bidirectional communications. The communication module 840 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 840 may include at least one antenna.

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) , an optical disk, a laser disk, 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 instructions of the program 830 may include instructions for performing operations/acts of some example embodiments of the present disclosure. The program 830 may be stored in the memory, e.g., the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

The example 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 FIG. 2 to FIG. 7. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some example 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. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory, ” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM) .

FIG. 9 shows an example of the computer readable medium 900 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 900 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, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although 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.

Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. 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. The program code 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 code, 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 code 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, although 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, although 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. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of 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 apparatus comprising:

at least one processor; and

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

transmit, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of downlink data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.
The first apparatus of claim 1, wherein the first apparatus is caused to:

transmit, to the second apparatus, the indication by an information element via a UE context modification request message or a downlink radio resource control message transfer message.
The first apparatus of claim 1 or 2, wherein the indication comprises at least one further information element indicating at least one of:

the handover of the third apparatus is to be performed before a time point,

the handover of the third apparatus is to be performed before the second apparatus moves to a location,

all downlink data buffered in the second apparatus has been sent to the third apparatus,

a certain amount of downlink data buffered in the second apparatus has been sent to the third apparatus, or

a downlink data having a specific sequence number buffered in the second apparatus has been sent to the third apparatus.
The first apparatus of any of claims 1-3, wherein the first apparatus is caused to:

receive, from a second apparatus, an indication indicating the highest sequence number of a packet data convergence protocol, PDCP, protocol data unit to be successfully delivered to the third apparatus, before the execution of the handover of the third apparatus.
The first apparatus of any of claim 1 or 2, wherein first apparatus is caused to:

transmit the radio resource control reconfiguration message to the third apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following:

whether the last buffered downlink data has been received from the second apparatus,

whether a certain amount of buffered downlink data has been received from the second apparatus,

whether a buffered downlink data having a specific sequence number has been received from the second apparatus,

whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or

whether the second apparatus is moving to a location.
The first apparatus of any of claims 1-5, wherein the first apparatus comprises a centralized unit, the second apparatus comprises a source distributed unit in the handover, the third apparatus comprises a terminal device and the fourth apparatus comprises a target distributed unit in the handover.
A second apparatus comprising:

at least one processor; and

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

receive, from a first apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus; and

perform the delayed handover for the handover the third apparatus, wherein at least a portion of downlink data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.
The second apparatus of claim 7, wherein the second apparatus is caused to:

receive, from the first apparatus, the indication by an information element via a UE context modification request message or a downlink radio resource control message transfer message.
The second apparatus of claim 7 or 8, wherein the indication comprises at least one further information element indicating at least one of:

the handover of the third apparatus is to be performed before a time point;

the handover of the third apparatus is to be performed before the second apparatus moves to a location,

all downlink data buffered in the second apparatus has been sent to the third apparatus,

a certain amount of downlink data buffered in the second apparatus has been sent to the third apparatus, or

a downlink data having a specific sequence number buffered in the second apparatus has been sent to the third apparatus.
The second apparatus of claim 9, wherein the second apparatus is caused to:

buffer a radio resource control reconfiguration message until all or a certain amount of downlink data or a downlink data having a specific sequence number buffered at the second apparatus has been transmitted to the third apparatus and/or based on the at least one further information element.
The second apparatus of claim 10, wherein the second apparatus is caused to:

transmit, to the third apparatus, the radio resource control reconfiguration message before the time point and/or before the second apparatus moves to the location.
The second apparatus of any of claims 7-11, wherein the second apparatus is caused to:

transmit, to the first apparatus, an indication indicating the highest sequence number of a packet data convergence protocol, PDCP, protocol data unit to be successfully delivered to the third apparatus, before the execution of the handover of the third apparatus.
The second apparatus of claim 7 or 8, wherein the second apparatus is caused to:

transmit, to the third apparatus, the downlink data buffered at the second apparatus after the transmission of the radio resource control reconfiguration message.
The second apparatus of claim 13, wherein the radio resource control reconfiguration message is transmitted from the first apparatus to the third apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following:

whether the last buffered downlink data has been received from the second apparatus,

whether a certain amount of buffered downlink data has been received from the second apparatus,

whether a buffered downlink data having a specific sequence number has been received from the second apparatus,

whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or

whether the second apparatus is moving to a location.
The second apparatus of claim 14, wherein the second apparatus is caused to:

indicate, to third apparatus, a data packet transmitted to the third apparatus is the last data packet buffered at the second apparatus or the sequence number of the last data packet to be transmitted from the second apparatus, before the third apparatus execute the handover.
The second apparatus of any of claims 7-15, wherein the first apparatus comprises a centralized unit, the second apparatus comprises a source distributed unit in the handover, the third apparatus comprises a terminal device and the fourth apparatus comprises a target distributed unit in the handover.
A third apparatus comprising:

at least one processor; and

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

receive, from a second apparatus performing a delayed handover for a handover of the third apparatus from the second apparatus to a fourth apparatus, downlink data buffered at the second apparatus; and

perform the handover based on at least one of a trigger condition of the handover or buffered downlink data delivery status.
The third apparatus of claim 17, wherein the third apparatus is caused to:

receive a radio resource control reconfiguration message from a first apparatus via the second apparatus, and wherein the radio resource control reconfiguration message indicates a trigger condition of a conditional handover of the third apparatus comprising at least one of the following:

whether the last downlink data has been received from the second apparatus,

whether a certain amount of downlink data has been received from the second apparatus,

whether a downlink data having a specific sequence number has been received from the second apparatus,

whether a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or

whether the second apparatus is moving to a location.
The third apparatus of claim 18, wherein the third apparatus is caused to:

receive, from the second apparatus, the downlink data after the reception of the radio resource control reconfiguration message.
The third apparatus of claim 18 or 19, wherein the third apparatus is caused to:

indicate, by the second apparatus, the data packet transmitted to the third apparatus is the last data packet or the sequence number of the last data packet to be transmitted from the second apparatus, before the third apparatus execute the handover.
The third apparatus of claim 18, wherein the third apparatus is caused to:

execute the conditional handover based on at least one of:

when the last downlink data has been received from the second apparatus,

when a certain amount of downlink data has been received from the second apparatus,

when a downlink data having a specific sequence number has been received from the second apparatus, or

when a time point, at which the second apparatus is incapable of serving the third apparatus, is passed, or

when the second apparatus has arrived at the location.
The third apparatus of any of claims 17-21, wherein the first apparatus comprises a centralized unit, the second apparatus comprises a source distributed unit in the handover, the third apparatus comprises a terminal device and the fourth apparatus comprises a target distributed unit in the handover.
A method comprising:

transmitting, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of downlink data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.
A method comprising:

receiving, from a first apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus; and

performing the delayed handover for the handover the third apparatus, wherein at least a portion of downlink data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.
A method comprising:

receiving, from a second apparatus performing a delayed handover for a handover of the third apparatus from the second apparatus to a fourth apparatus, downlink data buffered at the second apparatus; and

performing the handover based on at least one of a trigger condition of the handover or buffered downlink data delivery status.
A first apparatus comprising:

means for transmitting, to a second apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus co-located with the second apparatus, wherein at least a portion of downlink data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.
A second apparatus comprising:

means for receiving, from a first apparatus, an indication of requesting the second apparatus to use a delayed handover for a handover of a third apparatus from the second apparatus to a fourth apparatus; and

means for performing the delayed handover for the handover the third apparatus, wherein at least a portion of downlink data buffered at the second apparatus, by using the delayed handover, is to be transmitted to the third apparatus before an execution of the handover of the third apparatus.
A third apparatus comprising:

means for receiving, from a second apparatus performing a delayed handover for a handover of the third apparatus from the second apparatus to a fourth apparatus, downlink data buffered at the second apparatus; and

means for performing the handover based on at least one of a trigger condition of the handover or buffered downlink data delivery status.
A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform the method of claim 23, the method of claim 24 or the method of claim 25.