WO2025124795A1

WO2025124795A1 - Controlling timing advance acquisition

Info

Publication number: WO2025124795A1
Application number: PCT/EP2024/080930
Authority: WO
Inventors: Umur KARABULUT; Panagiotis SPAPIS; Shehzad Ali ASHRAF; Andres ARJONA; Anastasios KAKKAVAS
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2023-12-15
Filing date: 2024-11-01
Publication date: 2025-06-19
Anticipated expiration: 2026-06-15
Also published as: GB202319310D0; GB2636585A

Abstract

The disclosure relates to source distributed unit (S-DU) controlled timing advance (TA) acquisition. In particular, it proposes a solution that enables the network to know whether the TA of the S-DU can be used when the UE of the S-DU or source cell needs to execute handover towards the T-DU or target cell. In particular, the S-DU determines whether the TA value of the S-DU is same as that of the T-DU. If the S-DU and the T-DU share the same TA value, the S-DU informs the CU of the S-DU that the S-DU and the T-DU share the same TA value. The CU informs the T- DU to release resources for acquiring the TA value. The S-DU does not trigger the UE to obtain the TA for the T-DU. In this way, it avoids interruption on the UE side for each unnecessary TA acquisition and performance degradation.

Description

CONTROLLING TIMING ADVANCE ACQUISITION

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 timing advance acquisition.

BACKGROUND

When a user equipment (UE) moves from the coverage area of one cell to another cell, a serving cell change needs to be performed at some point. Currently serving cell change is triggered by Layer 3 (L3) measurements and is done by downlink radio resource control (RRC) signaling, i.e., RRC Reconfiguration message with Synchronization for change of Primary Cell (PCell) and Primary Secondary Cell (PSCell), as well as release and add for Secondary Cells (SCell)s when applicable. However, the current procedure is not optimal.

SUMMARY

In a first aspect of the present disclosure, there is provided a source distributed unit. The source distributed unit comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source distributed unit to: determine whether a timing advance value between a source cell of the source distributed unit and a terminal device is same as that between a target cell of a target distributed unit and the terminal device, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device; and based on a determination that the timing advance value is same as that between the target cell and the terminal device, transmit, to a central unit of the source distributed unit, first information indicating that the source cell and the target cell share a same timing advance value.

In a second aspect of the present disclosure, there is provided a central unit. The central unit comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the central unit to: receive, from a source distributed unit of the central unit, first information indicating that a source cell of the source distributed unit and a target cell of a target distributed unit share a same timing advance value, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device.

In a third aspect of the present disclosure, there is provided a target distributed unit. The target distributed unit comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the target distributed unit to: receive, from a central unit of the target distributed unit, an indication for releasing timing acquisition resources at the target distributed unit, wherein the target distributed unit is associated with a potential handover of a terminal device; and release the timing acquisition resources based on the indication.

In a fourth aspect of the present disclosure, there is provided a source distributed unit. The source distributed unit comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source distributed unit to: receive, from a central unit of the source distributed unit, an indication of a potential handover of a terminal device from a source cell of the source distributed unit to a target cell of a target distributed unit; determine if it can be considered that a timing advance value between the source cell and the terminal device is the same as that between the target cell and the terminal device; and based on a determination that the distributed unit cannot consider that the timing advance value is the same as that between the target cell and the terminal device, trigger the terminal device for acquisition of a timing advance for the target cell.

In a fifth aspect of the present disclosure, there is provided a central unit. The central unit comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the central unit to: obtain a predetermined criterion useable for determining whether a timing advance value between a terminal device and a first cell is the same as a timing advance between the terminal device and a second cell; transmit, to a source distributed unit, a first message indicating the predetermined criterion ; and transmit, to a target distributed unit or a central unit of the target distributed unit, a second message indicating the predetermined criterion, wherein the source distributed unit and target distributed unit are associated with a potential handover of a terminal device. In a sixth aspect of the present disclosure, there is provided a method. The method comprises: determining, at a source distributed unit, whether a timing advance value between a source cell of the source distributed unit and a terminal device is same as that between a target cell of a target distributed unit and the terminal device, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device; and based on a determination that the timing advance value is same as that between the target cell and the terminal device, transmitting, to a central unit of the source distributed unit, first information indicating that the source cell and the target cell share a same timing advance value.

In a seventh aspect of the present disclosure, there is provided a method. The method comprises: receiving, at a central unit and from a source distributed unit of the central unit, first information indicating that a source cell of the source distributed unit and a target cell of a target distributed unit share a same timing advance value, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device.

In an eighth aspect of the present disclosure, there is provided a method. The method comprises: receiving, a target distributed unit and from a central unit of the target distributed unit, an indication for releasing timing acquisition resources at the target distributed unit, wherein the target distributed unit is associated with a potential handover of a terminal device; and releasing the timing acquisition resources based on the indication.

In a ninth aspect of the present disclosure, there is provided a method. The method comprises: receiving, at a source distributed unit and from a central unit of the source distributed unit, an indication of a potential handover of a terminal device from a source cell of the source distributed unit to a target cell of a target distributed unit; determining if it can be considered that a timing advance value between the source cell and the terminal device is the same as that between the target cell and the terminal device; and based on a determination that the distributed unit cannot consider that the timing advance value is the same as that between the target cell and the terminal device, triggering the terminal device for acquisition of a timing advance for the target cell. In a tenth aspect of the present disclosure, there is provided a method. The method comprises: obtaining, at a central unit, a predetermined criterion useable for determining whether a timing advance value between a terminal device and a first cell is the same as a timing advance between the terminal device and a second cell; transmitting, to a source distributed unit, a first message indicating the predetermined criterion; and transmitting, to a target distributed unit or a central unit of the target distributed unit, a second message indicating the predetermined criterion, wherein the source distributed unit and target distributed unit are associated with a potential handover of a terminal device.

In an eleventh aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for determining whether a timing advance value between a source cell of a source distributed unit and a terminal device is same as that between a target cell of a target distributed unit and the terminal device, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device; and means for based on a determination that the timing advance value is same as that between the target cell and the terminal device, transmitting, to a central unit of the source distributed unit, first information indicating that the source cell and the target cell share a same timing advance value.

In a twelfth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for receiving, from a source distributed unit of a central unit, first information indicating that a source cell of the source distributed unit and a target cell of a target distributed unit share a same timing advance value, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device.

In a thirteenth aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises means for receiving, from a central unit of the target distributed unit, an indication for releasing timing acquisition resources at the target distributed unit, wherein the target distributed unit is associated with a potential handover of a terminal device; and means for releasing the timing acquisition resources based on the indication. In a fourteenth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for receiving, from a central unit of a source distributed unit, an indication of a potential handover of a terminal device from a source cell of the source distributed unit to a target cell of a target distributed unit; means for determining if it can be considered that a timing advance value between the source cell and the terminal device is the same as that between the target cell and the terminal device; and means for based on a determination that the distributed unit cannot consider that the timing advance value is the same as that between the target cell and the terminal device, triggering the terminal device for acquisition of a timing advance for the target cell. In a fifteenth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for obtaining a predetermined criterion useable for determining whether a timing advance value between a terminal device and a first cell is the same as a timing advance between the terminal device and a second cell; means for transmitting, to a source distributed unit, a first message indicating the predetermined criterion ; and means for transmitting, to a target distributed unit or a central unit of the target distributed unit, a second message indicating the predetermined criterion, wherein the source distributed unit and target distributed unit are associated with a potential handover of a terminal device.

In a sixteenth 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, seventh, eighth, ninth or tenth 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 flow chart of collecting timing advance values according to example embodiments of the present disclosure;

FIG. 3 illustrates a flow chart of providing a predetermined threshold according to example embodiments of the present disclosure;

FIG. 4A illustrates a flow chart of collecting timing advance values in intra-central unit (CU) according to example embodiments of the present disclosure;

FIG. 4B illustrates a flow chart of collecting timing advance values in inter-CU according to example embodiments of the present disclosure;

FIG. 5 illustrates a flow chart of handover without timing advance acquisition according to example embodiments of the present disclosure;

FIG. 6 illustrates a flow chart of providing timing advance values according to example embodiments of the present disclosure;

FIG. 7A illustrates a flow chart of handover without timing advance acquisition in intra-CU scenario according to example embodiments of the present disclosure;

FIG. 7B illustrates a flow chart of handover without timing advance acquisition in inter-CU scenario according to example embodiments of the present disclosure;

FIG. 8A illustrates a flow chart of handover without timing advance acquisition in intra-CU scenario according to other example embodiments of the present disclosure; FIG. 8B illustrates a flow chart of handover without timing advance acquisition in inter-CU scenario according to other example embodiments of the present disclosure; FIG. 9 illustrates a flowchart of a method implemented at a source distributed unit (DU) according to some example embodiments of the present disclosure;

FIG. 10 illustrates a flowchart of a method implemented at a CU according to some example embodiments of the present disclosure;

FIG. 11 illustrates a flowchart of a method implemented at a target DU according to some example embodiments of the present disclosure;

FIG. 12 illustrates a flowchart of a method implemented at a terminal device according to some example embodiments of the present disclosure;

FIG. 13 illustrates a flowchart of a method implemented at a source DU device according to some example embodiments of the present disclosure;

FIG. 14 illustrates a flowchart of a method implemented at a CU according to some example embodiments of the present disclosure;

FIG. 15 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

FIG. 16 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 (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), 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) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node. 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. 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.

The term “timing advance (TA)”/ “TA value” used herein may refer to a parameter used to synchronize the transmission timing of a mobile device with that of the serving cell in a cellular network. The term “TA acquisition” used herein may refer to a procedure to obtain/measure the TA value. The term “TA resources” used herein may refer to resources that are used to obtain/measure TA value, for example, a physical random access channel (PRACH) preamble.

The term “handover” used herein may refer to a process in communications where a connected call or a data session is transferred from one cell to another cell without disconnecting the session. The term “source cell” used herein may refer to a current serving cell during the handover procedure. The term “target cell” used herein may refer to a cell to which a UE is handed over to.

A network device/base station may be divided into two entities including a central/centralized unit (CU) and a distributed unit (DU). The CU may provide support for higher layers of the protocol stack such as service data adaptation protocol (SDAP), packet data convergence protocol (PDCP) and radio resource control (RRC) while DU provides support for the lower layers of the protocol stack such as radio link control (RLC), medium access control (MAC) and physical layer. One CU may correspond to one or more DUs. The term “source DU (S-DU)” used herein may refer to a DU that provides the source cell. The term “target DU (T-DU)” used herein may refer to a DU that provides the target cell. If the S-DU and the T-DU belong to different CUs, the CU of the S-DU may be referred to as “source CU (S-CU)” and the CU of the T-DU may be referred to as “target CU (T-CU).”

As mentioned above, the serving cell change is triggered by Layer 3 (L3) measurements and is done by downlink radio resource control (RRC) signaling, which involves complete Layer 2 (L2) and Layer 1 (LI) resets, leading to longer latency, larger overhead, and longer interruption time than beam switch mobility. The goal of L1/L2 mobility enhancements is to enable a serving cell change via L1/L2 signaling, to reduce the latency, overhead and interruption time.

In some solutions, it proposes that a candidate gNB-DU may provide information about same TA value as source DU in L1/L2 triggered mobility (LTM) configuration phase. However, in order for a candidate gNB-DU to provide such information, it has to know two things in advance, the source cell TA and target cell TA. The source cell TA is known only by the source DU, hence it cannot be assumed that the T-DU knows it. Besides, the T-DU does not know the value of the TA between the UE and the T- DU/cell until the UE sends the PRACH preamble to the T-DU. The UE sends the PRACH preamble to the T-DU after the preparation. Considering that, at the time of the preparation, T-DU knows neither the S-DU TA nor T-DU TA.

In some other solutions, it proposes to provide TA group (TAG) information for LTM, for example adding TAG ID include UE context setup response. TAG ID just indicates the ID of the TAG that the cell belongs to. However, it does not indicate the value of the TA by itself. Even if the TAG ID is shared along with the TA value, the shared TA value of the S-DU may change over time and at the time of TA acquisition or execution, the S-DU/cell TA and T-DU/cell TA may be same/or different.

Further, as it is agreed, the S-DU does not trigger an early TA acquisition of the T- DU/cell if the T-DU/cell and S-DU/cell share the same TA value. TA is not a configuration of a cell, but it is a value that is measured between each UE and cell, i.e., it is the timing of the received signal on the cell when a UE transmit its signal to the cell. In some cell borders, the TA value for the same UE can be the same between both pairs, 1) the UE and the source cell and 2) the UE and the target cell. However, the S-DU does not know whether the source and target cell shares the same TA value, since, as it is mentioned above, it is not a network parameter configuration, but rather a measured value between each UE and the cell, i.e., S-DU/cell is not aware of the TA value between the UE and the T-DU/cell. Eventually, this leads the S-DU to trigger the TA acquisition unnecessarily. Ultimately, this causes interruption on the UE side for each unnecessary early TA acquisition and leads performance degradation. Besides, it causes signaling overhead as each TA acquisition requires UL signaling from the UE to target cell, as well as the signaling in the Fl interface for forwarding the TA value from T-DU/cell to S-DU/cell.

In addition, when the source and the target cells share the same TA, the early TA acquisition is not triggered. Therefore, resources that are needed for the early TA acquisition procedure does not need to be reserved as they will not be used. Considering that fact that the CU does not know whether the source and target cell shares the same TA value, the CU needs to request and reserve TA Acquisition resources at the T-DU. This leads unnecessary reservation of resources used for early TA acquisition. Besides, both the S-DU and the UE will be configured with early TA acquisition, unnecessarily that causes additional processing of the configurations at the receiving nodes.

According to example embodiments of the present disclosure, it proposes a solution that enables the network to know whether the TA of the S-DU can be used when the UE of the S-DU or source cell needs to execute handover towards the T-DU or target cell. In particular, the S-DU determines whether the TA value of the S-DU is same as that of the T-DU. If the S-DU and the T-DU share the same TA value, the S-DU informs the CU of the S-DU that the S-DU and the T-DU share the same TA value. The CU informs the T-DU to release resources for acquiring the TA value. The S-DU does not trigger the UE to obtain the TA for the T-DU. In this way, it avoids interruption on the UE side for each unnecessary TA acquisition and performance degradation. Moreover, it saves signaling overheads and resources.

FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. In the communication environment 100, there may be a terminal device 150-1, a terminal device 150-2, ..., a terminal device 150-N (collectively referred to as “terminal device 150”), where N is an integer number. The terminal devices 150 are in a current serving cell 101 (also referred to as “source cell 101”) which is provided by the DU 110 (also referred to as “source DU 110”). There may be candidate target cells to which the terminal devices 150 may be handed over to, for example, the cell 103 (also referred to as “target cell 103”) and the cell 104. As shown in FIG. 1, the target cell 103 may be provided by the DU 130 (also referred to as “target DU 130”). In some example embodiments, in an intra-CU scenario, the source DU 110 and the target DU 130 may share or belong to the same CU 120. In some other example embodiments, in an inter-CU scenario, the source DU 110 belongs to the CU 120 (referred to as “source CU 120” in the inter- CU scenario) and the target DU 130 belongs to the CU 140 (referred to “target CU 140” in the inter-CU scenario). The source DU and the source CU may form a source base station and the target DU and the target CU may form a target base station of a handover of a terminal device.

In some example embodiments, a link from the source DU 110 or the target DU 130 to the terminal device 150 is referred to as a downlink (DL), and a link from the terminal device 150 to the source DU 110 or the target DU 130 is referred to as an uplink (UL). In DL, the source DU 110 or the target DU 130 is a transmitting (TX) device (or a transmitter) and the terminal device 150 is a receiving (RX) device (or a receiver). In UL, the terminal device 150 is a TX device (or a transmitter) and the source DU 110 or the target DU 130 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.

Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It is noted that one or more example embodiments described with reference to different drawings can be combined in any suitable manner. Moreover, one or more example embodiments described with reference to the same drawing can be implemented separately or in combinations.

Reference is made to FIG. 2, which illustrates a signaling flow 200 in accordance with some embodiments of the present disclosure. For the purposes of discussion, the signaling flow 200 will be discussed with reference to FIG. 1, for example, by using the source DU 110 and the CU 120. The signaling flow 200 may be implemented in the intra-CU scenario or the inter-CU scenario. It is noted that FIG. 2 is only a brief signaling flow of the present disclosure and details of example embodiments are described later with reference to other drawings.

The CU 120 transmits (2010) to the source DU 110 an indication of a potential handover of the terminal device 150-1 from the source cell 101 to the target cell 102. In other words, the source DU 110 receives (2010) the indication of the potential handover from the CU 120.

The source DU 110 determines (2020) if the source DU 110 is aware of whether a TA value between the source cell 101 and the terminal device 150-1 is same as that between the target cell 102 and the terminal device 150-1. In other words, the source DU 110 determines (2020) if the source DU 110 can/is able to consider that the TA value between the source cell 101 and the terminal device 150-1 is the same as a TA value between the target cell 102 and the terminal device 150-1. In this case, if the source DU 110 is unaware of whether (or cannot consider that) the TA value is same as that between the target cell 102 and the terminal device 150-1, the source DU 110 triggers (2030) the terminal device 150-1 for a TA acquisition for the target cell 102. Alternatively, if the source DU 110 is aware that the TA value is different from that between the target cell 102 and the terminal device 150-1, the source DU 110 may also trigger the terminal device 150-1 for a TA acquisition for the target cell 102. In some other embodiments, if the source DU 110 considers that the TA value is the same as that between the target cell 102 and the terminal device 150-1, the source DU 110 may refrain from triggering the terminal device 150-1 for acquisition of TA value for the target cell 102.

The source DU 110 obtains (2040) from the CU 120 a number of TA values between the target cell 102 and a set of terminal devices that is served by the source cell 101, based on the triggering. For example, the source DU 110 may need to perform the TA acquisitions of the target DU 130 for several times before reaching to the conclusion whether the TA between any two cell is same or different. For example, the source DU 110 may obtain the TA values between the target cell 102 and each of the terminal devices 150. By way of example, the source DU 110 may obtain the TA value between the target cell 102 and the terminal device 150-1, the TA value between the target cell 102 and the terminal device 150-2, ... , the TA value between the target cell 102 and the terminal device 150-N. The source DU 110 may store (2050) the number of TA values between the target cell 102 and the set of terminal devices.

In some example embodiments, the source DU 110 may collect the same number of TA values for each cell pair between the source DU 110 and the target DU 130. For example, the source DU 110 may collect number X of TA values for the cell pair of the source cell 101 and the target cell 102 and may also collect number X of TA values for the cell pair of the source cell 101 and the target cell 103, where X may be any suitable integer number.

Alternatively, the source DU 110 may collect different numbers of TA values for different cell pairs between the source DU 110 and the target DU 130. For example, the source DU 110 may collect number X of TA values for the cell pair of the source cell 101 and the target cell 102 and may collect number Y of TA values for the cell pair of the source cell 101 and the target cell 103, where X and Y may be different integer numbers. In some embodiments, the number(s) of TA values to be collected may be preconfigured or determined at the source DU 110. Alternatively, the number(s) of TA values to be collected may be configured by the CU 120.

The source DU 110 may derive statistics of TA value comparison between the source DU 110 and the target DU 130 based on the number of TA values collected by the source DU 110 for the target cell / target DU. For example, the source DU 110 may determine (or consider) the timing advance value of the source cell 101 is same as that of the target cell 102 based on the number of timing advance values for the target cell 102 meeting a predetermined criterion. Alternatively, the source DU may determine/consider the TA value of the source cell 101 is not the same as the TA value of the target cell. The predetermined criterion may include one or more of a threshold value for the number of required TA acquisitions, or another threshold value representing the hit rate or accuracy of the shared TA values out of all collected TA values, or a combination of the above mentioned threshold values.

In some example embodiments, the predetermined criterion may require a predetermined number of TA values for the target cell 102 are the same as that between the source cell 101 and the terminal device 150-1. In this case, in some example embodiment, if the source DU 110 collects the number X of TA values of the target cell 102 and the number of TA values that is equal to the TA value for the source cell 101 is equal to or larger than the number A (i.e., the predetermined number) , the source DU 110 may determine that the source cell 101 and the target cell 102 share the same TA value, where A is an integer number which is less than or equal to X. For example, if the source DU 110 collects 10 TA values of the target cell 102 and the number of TA values for the target cell 102 which are substantially equal to the TA value for the source cell 101 is equal to or larger than 8, the source DU 110 may determine that the source cell 101 and the target cell 102 share the same TA value. Alternatively, if the source DU 110 collects the number X of TA values of the target cell 102 and the number of TA values that is equal to the TA value of the source cell is less than the number A, the source DU 110 may determine that the source cell 101 and the target cell 102 does not share the same TA value. For example, if the source DU 110 collects 10 TA values of the target cell 102 and 7 TA values out of the 10 TA values have the same value as the TA value of the source cell, the source DU 110 may determine that the source cell 101 and the target cell 102 does not share the same TA value. In some embodiments, the number A may be preconfigured or determined at the source DU 110. Alternatively, the number A may be configured by the CU 120. Alternatively, or in addition, the predetermined criterion may include a predetermined ratio of TA values for the target cell 102 are the same as that between the source cell 101 and the terminal device 150-1. For example, if the source DU 110 collects the number X of TA values of the target cell 102 and B% (i.e, the predetermined ratio) of the collected TA values are equal to the TA value for the source cell 101, the source DU 110 may determine that the source cell 101 and the target cell 102 share the same TA value. Alternatively, if less than B% of the collected TA values are equal to the TA value for the source cell 101, the source DU 110 may determine that the source cell 101 and the target cell 102 does not share the same TA value.

In some other example embodiments, the source DU 110 may determine that the source DU 110 is unaware of whether the TA value of the source cell is same as that between the target cell 102 and the terminal device 150-1 based on that the TA acquisition is triggered less than the predetermined number.

In some example embodiments, the predetermined criterion may be preconfigured at source DU 110. For example, the predetermined criterion may be a default parameter that is specified to for the target DU 130.

Alternatively, the predetermined criterion may be configured by the CU 120. For example, the source DU 110 may receive the predetermined criterion from the CU 120. As shown in FIG. 3, the CU 120 may transmit (3020) a first message including the predetermined criterion to the source DU 110. The CU 120 may transmit (3030) a second message including the predetermined criterion to target DU 130. For example, the predetermined criterion may be transmitted in Fl setup requests for the source DU 110 and the target DU 130. The source DU 110 may transmit (3040) an Fl setup response to the CU 120. The target DU 130 may transmit (3050) an Fl setup response to the CU 120.

In some example embodiments, the CU 120 may determine the predetermined criterion used for determining whether the TA value between the terminal device 150- 1 and a first cell (i.e., the source cell 101 in this embodiment) is the same as a timing advance between the terminal device 150-1 and a second cell (i.e., the target cell 102 in this embodiment). For example, the CU 120 may determine the predetermined criterion based on one or more of propagation property for mobility, or transmission failures and the like. It is noted that the predetermined criterion may be determined based on any proper characteristics. The CU 120 may update the predetermined criterion for one or more DUs via gNB DU Configuration Update procedures. Alternatively, a core network device 310 (for example, operations, administration, and maintenance (0AM)) may provide the predetermined criterion to the CU 120.

In some example embodiments, the predetermined criterion is a global parameter for all target DUs. For example, the predetermined criterion may be the same for all target DUs associated with the CU 120. Alternatively, the predetermined criterion may be a DU pair parameter. For example, the predetermined criterion may be same for a pair of DUs associated with the CU 120. In some other example embodiment, the predetermined criterion may be a parameter per DU. For example, the predetermined criterion may be different for different DUs associated with the CU 120. In some other example embodiment, the predetermined criterion may be a parameter per cell pair. For example, the predetermined criterion for the cell pair including the source cell 101 and the target cell 102 may be different from the predetermined criterion for the cell pair including the source cell 101 and the target cell 103.

FIG. 4A illustrates a signaling flow 400 of collecting timing advance values in intra- CU according to example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 400 will be discussed with reference to FIG. 1, for example, by using the source DU 110, the target DU 130, the CU 120, and the terminal device 150-1.

The terminal device 150-1 may transmit (4001) an L3 measurement report that includes the L3 measurements of the source cell 101 and neighbor cells (for example, cells 102 and 103) to the source DU 110. The L3 measurement report means that L3 at the terminal device 150-1 does filtering on values and does the final reporting. Filtering is done to remove the effect of fast fading and ignore short-term variations. Though LI may collect measurements more often, L3 might report them at a larger configured periodicity. The source DU 110 may forward (4002) the L3 measurement report to the CU 120.

The CU 120 may perform (4003) a handover (HO) decision. For example, the CU 120 may decide to prepare the target DU 130 or the target cell 102 for handover of the terminal device 150-1. The CU 120 may also decide to prepare the physical downlink control channel (PDCCH) ordered random access channel (RACH) configuration for a TA acquisition of the prepared cell (i.e., the target cell 102).

The CU 120 may transmit (4004) a UE context setup request to the target DU 130 to prepare it for handover. The CU 120 may also request the target DU 130 to provide the TA acquisition configuration. For example, the UE context setup request may include a TA acquisition configuration request. The target DU 130 may transmit (4005) a UE context setup response to the CU 120. For example, the target DU 130 may provide the TA acquisition configuration along with the handover configuration in the UE context setup response.

The CU 120 may transmit (4006) a UE context modification request to the source DU 110. For example, the CU 120 may inform the source DU 110 or the cell 101 about the handover preparation (i.e., the indication of a potential handover) and ask the source DU 110 or the cell 101 to provide further configurations that are needed for LTM handover preparation along with the information on the prepared cells (i.e., the cell 102).

In some example embodiments, the source DU 110 may determine (4006.5) whether the source DU 110 knows whether the source cell 101 and the target cell 102 share the same TA value. For example, the source DU 110 may check whether the cell 101 to cell 102 TA relation is known, i.e., if the TA value of the source cell 101 is same as (or can be considered to be the same as) the TA value of the target cell 102. For example, the source DU 110 may make the decision (4006.5) based on the previous number of TA acquisitions that are observed as explained above in connection of FIGs 2 and 3. For example, if the TA acquisition was never triggered before or if the TA acquisition was triggered one or more times but the number of obtained TA values for the target cell detected to be substantially the same as that of the source cell is less than the predetermined number, then it may be determined that the TA values cannot be considered to be the same. The source DU 110 may transmit (4007) a UE context modification response.

The CU 120 may generate (4008) a handover configuration including a measurement configuration and a cell configuration. The handover configuration may also include the TA acquisition configuration of the target DU 130 or the target cell 102. The CU 120 may transmit (4009) the handover configuration including the TA acquisition configuration in RRC message to the source DU 110. Alternatively, instead of determining (4006.5) whether the source DU 110 knows whether the source cell 101 and the target cell 102 share the same TA value right after 4006, the source DU 110 may determine (4010) whether the source DU 110 knows whether the source cell 101 and the target cell 102 share the same TA value in step 4010. The source DU 110 may store (4011) the TA acquisition configuration.

The source DU 110 may forward (4012) the handover configuration including the TA acquisition configuration in RRC message to the terminal device 150-1. After receiving the handover configuration in the RRC configuration, the terminal device 150-1 may transmit (4013) a RRC reconfiguration completion message to the source DU 110. The source DU 110 may forward (4014) the RRC reconfiguration completion message to the CU 120.

The terminal device 150-1 may transmit (4015) an LI measurement report including one or more candidate cells to the source DU 110. For example, the LI measurement report may indicate reference signal received power (RSRP) values.

Since the source DU 110 is unaware of whether the source cell 101 and the target cell 102 share the same TA value, the source DU 110 may trigger (4016) the physical downlink control channel (PDCCH) ordered TA acquisition.

The terminal device 150-1 may transmit (4017) a preamble (for example, PRACH preamble) to the target DU 130. The target DU 130 may evaluate (4018) the TA value between the target DU 130 and the terminal device 150-1 based on the preamble. The target DU 130 may inform (4019) the source DU 110 of the evaluated TA value via the CU 120. The source DU 110 may store (4020) the received TA value of the target cell 102. In this way, the source DU can understand whether the source cell and the target cell share the same TA value based on the stored TA value(s) of the target cell, which facilitates the handover without TA acquisition at later stage.

The terminal device 150-1 may transmit (4021) the LI measurement report regarding the target cell 102 to the source DU 110. The source DU 110 may trigger (4022) a cell change indicating the TA value of the target cell 102. For example, the source DU 110 may transmit (4022) a medium access control control element (MAC CE) for triggering the cell change (i.e., changing to the target cell 102) to the terminal device 150-1. The MAC CE may further include the TA value of the target cell 102. The terminal device 150-1 may perform (4023) a RACHless access to the target DU 130 when executing the HO by using the TA value that is provided in the MAC CE. In this way, it can reduce the latency for accessing the target DU and avoid UE interruption.

FIG. 4B illustrates a signaling flow 400’ of collecting timing advance values in inter- CU according to example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 400’ will be discussed with reference to FIG. 1, for example, by using the source DU 110, the target DU 130, the CU 120, the CU 140, and the terminal device 150-1.

The terminal device 150-1 may transmit (4001’) an L3 measurement report that includes the L3 measurements of the source cell 101 and neighbor cells (for example, cells 102 and 103) to the source DU 110. The L3 measurement report means that L3 at the terminal device 150-1 does filtering on values and does the final reporting. Filtering is done to remove the effect of fast fading and ignore short-term variations. Though LI may collect measurements more often, L3 might report them at a larger configured periodicity. The source DU 110 may forward (4002’) the L3 measurement report to the CU 120.

The CU 120 may perform (4003’) a handover (HO) decision. For example, the CU 120 may decide to prepare the target DU 130 or the target cell 102 for handover of the terminal device 150-1. The CU 120 may also decide to prepare the physical downlink control channel (PDCCH) ordered random access channel (RACH) configuration for a TA acquisition of the prepared cell (i.e., the target cell 102). The CU 120 may transmit (4003.5) a handover request to the CU 140.

The CU 140 may transmit (4004’) a UE context setup request to the target DU 130 to prepare it for handover. The CU 150 may also request the target DU 130 to provide the TA acquisition configuration. For example, the UE context setup request may include a TA acquisition configuration request. The target DU 130 may transmit (4005’) a UE context setup response to the CU 140. For example, the target DU 130 may provide the TA acquisition configuration along with the handover configuration in the UE context setup response. The CU 140 may transmit (4005.5) a handover request acknowledgement to the CU 120.

The CU 120 may transmit (4006’) a UE context modification request to the source DU 110. For example, the CU 120 may inform the source DU 110 or the cell 101 about the handover preparation (i.e., the indication of a potential handover) and ask the source DU 110 or the cell 101 to provide further configurations that are needed for LTM handover preparation along with the information on the prepared cells (i.e., the cell 102).

In some example embodiments, the source DU 110 may determine (4006.5’) whether the source DU 110 knows whether the source cell 101 and the target cell 102 share the same TA value. For example, the source DU 110 may check whether the cell 101 to cell 102 TA relation is known, as explained above in connection of FIGs 2 and 3. For example, if the TA acquisition was never triggered before or if the TA acquisition was triggered one or more times but the number of obtained TA values for the target cell detected to be substantially the same as that of the source cell is less than the predetermined number, then it may be determined that the TA values cannot be considered to be the same. The source DU 110 may transmit (4007’) a UE context modification response.

The CU 120 may generate (4008’) a handover configuration including a measurement configuration and a cell configuration. The handover configuration may also include the TA acquisition configuration of the target DU 130 or the target cell 102. The CU 120 may transmit (4009’) the handover configuration including the TA acquisition configuration in RRC message to the source DU 110.

Alternatively, instead of determining (4006.5’) whether the source DU 110 knows whether the source cell 101 and the target cell 102 share the same TA value right after 4006, the source DU 110 may determine (4010’) whether the source DU 110 knows whether the source cell 101 and the target cell 102 share the same TA value. The source DU 110 may store (4011’) the TA acquisition configuration. The source DU 110 may forward (4012’) the handover configuration including the TA acquisition configuration in RRC message to the terminal device 150-1. After receiving the handover configuration in the RRC configuration, the terminal device 150-1 may transmit (4013’) a RRC reconfiguration completion message to the source DU 110. The source DU 110 may forward (4014’) the RRC reconfiguration completion message to the CU 120.

The terminal device 150-1 may transmit (4015’) an LI measurement report including one or more candidate cells to the source DU 110. For example, the LI measurement report may indicate reference signal received power (RSRP) values.

Since the source DU 110 is unaware of whether the source cell 101 and the target cell 102 share the same TA value, the source DU 110 may trigger (4016’) the physical downlink control channel (PDCCH) ordered TA acquisition.

The terminal device 150-1 may transmit (4017’) a preamble (for example, physical random access channel (PRACH) preamble) to the target DU 130. The target DU 130 may evaluate (4018’) the TA value between the target DU 130 and the terminal device 150-1 based on the preamble. The target DU 130 may inform (4019’) the source DU 110 of the evaluated TA value via the CU 120 and the CU 140. The source DU 110 may store (4020’) the received TA value of the target cell 102. In this way, the source DU can understand whether the source cell and the target cell share the same TA value based on the stored TA value(s) of the target cell, which facilitates the handover without TA acquisition at later stage.

The terminal device 150-1 may transmit (4021’) the LI measurement report regarding the target cell 102 to the source DU 110. The source DU 110 may trigger (4022’) a cell change indicating the TA value of the target cell 102. For example, the source DU 110 may transmit (4022’) a medium access control control element (MAC CE) for triggering the cell change (i.e., changing to the target cell 102) to the terminal device 150-1. The MAC CE may further include the TA value of the target cell 102. The terminal device 150-1 may perform (402’3) a RACHless access to the target DU 130 when executing the HO by using the TA value that is provided in the MAC CE. In this way, it can reduce the latency for accessing the target DU and avoid UE interruption.

Reference is made to FIG. 5, which illustrates a signaling flow 500 in accordance with some embodiments of the present disclosure. For the purposes of discussion, the signaling flow 500 will be discussed with reference to FIG. 1, for example, by using the source DU 110, the CU 120, the target DU 130 and the terminal device 150-1. The signaling flow 500 may be implemented in the intra-CU scenario or the inter-CU scenario. It is noted that FIG. 5 is only a brief signaling flow of the present disclosure and details of example embodiments are described later with reference to other drawings.

The source DU 110 determines (5010) whether a TA value between the source cell 101 of the source DU 110 and the terminal device 150-1 is same as a TA value between the target cell 102 of the target DU 130 and the terminal device 150-1. In other words, the source DU 110 may determine whether the source cell 101 and the target cell 102 share the same TA value. In some example embodiments, the source DU 110 may determine whether the source cell 101 and the target cell 102 share the same TA value based on historical TA information. For example, the information regarding whether the source cell 101 and the target cell 102 may be previously stored at the source DU 110 and the source DU 110 may make the determination (5010) based on the stored information.

In an example embodiment, the source DU 110 may determine a list of cell pairs that shares same timing advance values. In this case, the determined list of cell pairs may include a pair of the source cell 101 and the target cell 102. In this case, the list of cell pairs may be determined before the LTM procedure. Detailed description of this example embodiment is provided with reference to FIG. 6 later.

Alternatively, the CU 120 may transmit, to the source DU 110, an indication of potential handover of the terminal device 150-1 from the source cell 101 to the target cell 102. In other words, the source DU 110 may receive the indication of the potential handover from the CU 120. The source DU 110 may determine whether the source cell 101 and the target cell 102 share the same TA value, after receiving the indication of the potential handover. The source DU 110 transmits (5020) first information indicating that the source cell 101 and the target cell 102 share the same timing advance value to the CU 120. In other words, the CU 120 receives the first information indicating that the source cell 101 and the target cell 102 share the same timing advance from the source DU 110. In this way, it can avoid necessary TA acquisitions and achieve lower signaling.

In some example embodiments, the first information may be transmitted in an information element (IE). For example, the first information may be transmitted in the IE in an Fl application protocol (F1AP) message to the CU 120. By way of example, the first information may be LTM group information which indicates a group of target cells (including the target cell 102) that shares the same timing advance with the source cell 101.

The CU 120 may transmit (5030) an indication for releasing TA acquisition resources to the target DU 130. In other words, the target DU 130 may receive (5030) the indication for releasing TA acquisition resources from the CU 120. In some example embodiments, in the intra-CU scenario, the CU 120 may directly transmit the indication for releasing TA acquisition resources to the target DU 130. Alternatively, in the inter-CU scenario, the CU 120 may transmit the indication for releasing TA acquisition resources to the CU 140 and the CU 140 may then forward the indication for releasing TA acquisition resources to the target DU 130. The target DU 130 may release (5040) the TA acquisition resources based on the indication. In this way, it can prevent unnecessary reservation of resources and avoid wasting resources.

The source DU 110 may transmit (5050) second information indicating the timing advance value as that of the target cell 102, without triggering a timing advance acquisition. In this way, it can decrease UE interruption and achieve lower signaling. FIG. 6 illustrates a signaling flow 600 of providing timing advance values according to example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 600 will be discussed with reference to FIG. 1, for example, by using the source DU 110, the CU 120, and a core network device 610 (for example, operations, administration, and maintenance (0AM)). The signaling flow 600 may be implemented in the intra-CU scenario or the inter-CU scenario. The source DU 110 may determine (6010) a list of cell pairs that share the same TA value. For example, if the source cell 101 and the target cell 102 share the same TA value, the source DU 110 may determine a cell pair including the source cell 101 and the target cell 102. Alternatively, or in addition, if the source cell 101 and the target cell 103 also share the same TA value, the source DU 110 may determine another cell pair including the source cell 101 and the target cell 103. In this case, the list of cell pairs may include the cell pair of the source cell 101 and the target cell 102 and the cell pair of the source cell 101 and the target cell 103.

The source DU 110 may transmit (6020) the list of cell pairs to the CU 120. In other words, the CU 120 may receive the list of cell pairs from the source DU 110. For example, the list of cell pairs may be transmitted via gNB-DU configuration update procedure. In some example embodiments, the CU 120 may then transmit (6030), to the 0AM 610, the list of cell pairs that does not require the TA acquisition.

According to example embodiment described with reference to FIG. 6, the CU does not need to request the target DU to provide the early TA acquisition configurations and the source DU 110 does not need to indicate whether the TA of the source cell 101 and target DU cell 102 are same. Hence, the signaling overhead and unnecessary reservation will be solved with single signaling.

FIG. 7A illustrates a signaling flow 700 of handover without timing advance acquisition in intra-CU scenario according to example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 700 will be discussed with reference to FIG. 1, for example, by using the source DU 110, the target DU 130, the CU 120, and the terminal device 150-1.

The terminal device 150-1 may transmit (7001) an L3 measurement report that includes the L3 measurements of the source cell 101 and neighbor cells (for example, cells 102 and 103) to the source DU 110. The L3 measurement report means that L3 at the terminal device 150-1 does filtering on values and does the final reporting. Filtering is done to remove the effect of fast fading and ignore short-term variations. Though LI may collect measurements more often, L3 might report them at a larger configured periodicity. The source DU 110 may forward (7002) the L3 measurement report to the CU 120.

The CU 120 may perform (7003) a handover (HO) decision. For example, the CU 120 may decide to prepare the target DU 130 or the target cell 102 for handover of the terminal device 150-1. The CU 120 may also decide to prepare the physical downlink control channel (PDCCH) ordered random access channel (RACH) configuration for a TA acquisition of the prepared cell (i.e., the target cell 102).

The CU 120 may transmit (7004) a UE context setup request to the target DU 130 to prepare it for handover. The CU 120 may also request the target DU 130 to provide the TA acquisition configuration. For example, the UE context setup request may include a TA acquisition configuration request. The target DU 130 may transmit (7005) a UE context setup response to the CU 120. For example, the target DU 130 may provide the TA acquisition configuration along with the handover configuration in the UE context setup response.

The CU 120 may transmit (7006) a UE context modification request to the source DU 110. For example, the CU 120 may inform the source DU 110 or the cell 101 about the handover preparation (i.e., the indication of a potential handover) and ask the source DU 110 or the cell 101 to provide further configurations that are needed for LTM handover preparation along with the information on the prepared cells (i.e., the cell 102).

The source DU 110 may determine (7007) whether the TA value of the source cell 101 is the same as that of the target cell 102. For example, the source DU 110 may check whether the cell 101 to cell 102 TA relation is known, i.e., if the TA value of the source cell 101 is same as the TA value of the target cell 102, based on the previous events that are observed at the source DU 110 side.

If the TA value of the source cell 101 is the same as that of the target cell 102, the source DU 110 may indicate the TA value of the source cell 101 is the same as that of the target cell 102. For example, the source DU 110 may transmit (7008) a UE context modification response including an IE indicating the TA value of the source cell 101 is the same as that of the target cell 102 to the CU 120. For example, the source DU 110 may indicate the TA value of the source cell 101 is the same as that of the target cell 102 by LTM group information.

The CU 120 may generate (7009) a handover configuration including a measurement configuration and a cell configuration. During the generation of the handover configuration, the CU 120 may exclude the TA acquisition configuration from the handover configuration. For example, although the CU 120 has acquired the TA acquisition configuration of the target DU 130 or the target cell 102, the CU 120 may exclude the TA acquisition configuration (received from the target DU 130 during UE context setup) from the RRC Reconfiguration of the LTM preparations.

The CU 120 may transmit (7010) the handover configuration without the TA acquisition configuration in RRC message to the source DU 110. The source DU 110 may forward (7013) handover configuration without the TA acquisition configuration in RRC message to the terminal device 150-1. In this way, it can save signaling overheads.

The CU 120 may transmit (7011) an indication for releasing the TA acquisition resources to the target DU 130. For example, the CU 120 may transmit (7011) a UE context modification request indicating releasing the TA acquisition resources/configurations of the target DU 130, after the reception (7008) of the indication from source DU 110 that the “No Early TA acquisition configuration Needed”. The target DU 130 may transmit (7012) a UE context modification response to the CU 120. The target DU 130 may release the resources based on the indication. In this way, it can prevent unnecessary reservation of resources and avoid wasting resources.

After receiving the handover configuration in the RRC configuration, the terminal device 150-1 may transmit (7014) a RRC reconfiguration completion message to the source DU 110. The source DU 110 may forward (7015) the RRC reconfiguration completion message to the CU 120.

The terminal device 150-1 may transmit (7016) an LI measurement report including one or more candidate cells to the source DU 110. For example, the LI measurement report may indicate reference signal received power (RSRP) values.

Since the source DU 110 is aware that the source cell 101 and the target cell 102 share the same TA value, the source DU 110 may not trigger the PDCCH ordered TA acquisition. The source DU 110 may determine (7017) that the terminal device 150- 1 is to be handed over to the target cell 102. The terminal device 150-1 may also transmit (7018) the LI measurement report regarding the target cell 102 to the source DU 110.

The source DU 110 may trigger (7019) a cell change without TA acquisition. For example, the source DU 110 may transmit (7019) a medium access control control element (MAC CE) for triggering the cell change (i.e., changing to the target cell 102) to the terminal device 150-1. The MAC CE may further include the TA value of the target cell 102. For example, the source DU 110 may provide the TA value of the source cell 101 as that of the target cell 102 to the terminal device 150-1. The terminal device 150-1 may perform (7020) a RACHless access to the target DU 130 when executing the HO by using the TA value that is provided in the MAC CE. In this way, it can reduce the latency for accessing the target DU and avoid UE interruption.

FIG. 7B illustrates a signaling flow 700’ of handover without timing advance acquisition in inter-CU scenario according to example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 700’ will be discussed with reference to FIG. 1, for example, by using the source DU 110, the target DU 130, the CU 120, and the terminal device 150-1.

The terminal device 150-1 may transmit (7001’) an L3 measurement report that includes the L3 measurements of the source cell 101 and neighbor cells (for example, cells 102 and 103) to the source DU 110. The L3 measurement report means that L3 at the terminal device 150-1 does filtering on values and does the final reporting. Filtering is done to remove the effect of fast fading and ignore short-term variations. Though LI may collect measurements more often, L3 might report them at a larger configured periodicity. The source DU 110 may forward (7002’) the L3 measurement report to the CU 120. The CU 120 may perform (7003’) a handover (HO) decision. For example, the CU 120 may decide to prepare the target DU 130 or the target cell 102 for handover of the terminal device 150-1. The CU 120 may also decide to prepare the physical downlink control channel (PDCCH) ordered random access channel (RACH) configuration for a TA acquisition of the prepared cell (i.e., the target cell 102). The CU 120 may transmit (7003.5) a handover request to the CU 140 which is the CU of the target DU 130.

The CU 140 may transmit (7004’) a UE context setup request to the target DU 130 to prepare it for handover. The CU 140 may also request the target DU 130 to provide the TA acquisition configuration. For example, the UE context setup request may include a TA acquisition configuration request. The target DU 130 may transmit (7005’) a UE context setup response to the CU 140. For example, the target DU 130 may provide the TA acquisition configuration along with the handover configuration in the UE context setup response.

The CU 120 may transmit (7006’) a UE context modification request to the source DU 110. For example, the CU 120 may inform the source DU 110 or the cell 101 about the handover preparation (i.e., the indication of a potential handover) and ask the source DU 110 or the cell 101 to provide further configurations that are needed for LTM handover preparation along with the information on the prepared cells (i.e., the cell 102).

The source DU 110 may determine (7007’) whether the TA value of the source cell 101 is the same as that of the target cell 102. For example, the source DU 110 may check whether the cell 101 to cell 102 TA relation is known, i.e., if the TA value of the source cell 101 is same as the TA value of the target cell 102, based on the previous events that are observed at the source DU 110 side. The CU 140 may transmit (7007.5) the handover request acknowledgement (ACK) to the CU 120.

If the TA value of the source cell 101 is the same as that of the target cell 102, the source DU 110 may indicate the TA value of the source cell 101 is the same as that of the target cell 102. For example, the source DU 110 may transmit (7008’) a UE context modification response including an IE indicating the TA value of the source cell 101 is the same as that of the target cell 102 to the CU 120. For example, the source DU 110 may indicate the TA value of the source cell 101 is the same as that of the target cell 102 by LTM group information.

The CU 120 may generate (7009’) a handover configuration including a measurement configuration and a cell configuration. During the generation of the handover configuration, the CU 120 may exclude the TA acquisition configuration from the handover configuration. For example, although the CU 120 has acquired the TA acquisition configuration of the target DU 130 or the target cell 102, the CU 120 may exclude the TA acquisition configuration (received from the target DU 130 during UE context setup) from the RRC Reconfiguration of the LTM preparations.

The CU 120 may transmit (7010’) the handover configuration without the TA acquisition configuration in RRC message to the source DU 110. The source DU 110 may forward (7013’) handover configuration without the TA acquisition configuration in RRC message to the terminal device 150-1. In this way, it can save signaling overheads.

The CU 120 may transmit (7010.5) a handover update request which indicates that TA acquisition is not needed to the CU 140. The CU 140 may transmit (7011’) an indication for releasing the TA acquisition resources to the target DU 130. For example, the CU 140 may transmit (7011’) a UE context modification request indicating releasing the TA acquisition resources/configurations of the target DU 130, after the reception (7010.5) of the handover update request from the CU 120 that the “No Early TA acquisition configuration Needed”. The target DU 130 may transmit (7012’) a UE context modification response to the CU 140. The target DU 130 may release the resources based on the indication. In this way, it can prevent unnecessary reservation of resources and avoid wasting resources. The CU 140 may transmit (7012.5) a handover update ACK to the CU 120.

After receiving the handover configuration in the RRC configuration, the terminal device 150-1 may transmit (7014’) a RRC reconfiguration completion message to the source DU 110. The source DU 110 may forward (7015’) the RRC reconfiguration completion message to the CU 120. The terminal device 150-1 may transmit (7016’) an LI measurement report including one or more candidate cells to the source DU 110. For example, the LI measurement report may indicate reference signal received power (RSRP) values.

Since the source DU 110 is aware that the source cell 101 and the target cell 102 share the same TA value, the source DU 110 may not trigger the PDCCH ordered TA acquisition. The source DU 110 may determine (7017’) that the terminal device 150- 1 is to be handed over to the target cell 102. The terminal device 150-1 may also transmit (7018’) the LI measurement report regarding the target cell 102 to the source DU 110.

The source DU 110 may trigger (7019’) a cell change without TA acquisition. For example, the source DU 110 may transmit (7019’) a medium access control control element (MAC CE) for triggering the cell change (i.e., changing to the target cell 102) to the terminal device 150-1. The MAC CE may further include the TA value of the target cell 102. For example, the source DU 110 may provide the TA value of the source cell 101 as that of the target cell 102 to the terminal device 150-1. The terminal device 150-1 may perform (7020’) a RACHless access to the target DU 130 when executing the HO by using the TA value that is provided in the MAC CE. In this way, it can reduce the latency for accessing the target DU and avoid UE interruption.

FIG. 8A illustrates a signaling flow 800 of handover without timing advance acquisition in intra-CU scenario according to other example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 800 will be discussed with reference to FIG. 1, for example, by using the source DU 110, the target DU 130, the CU 120, and the terminal device 150-1.

The terminal device 150-1 may transmit (8001) an L3 measurement report that includes the L3 measurements of the source cell 101 and neighbor cells (for example, cells 102 and 103) to the source DU 110. The L3 measurement report means that L3 at the terminal device 150-1 does filtering on values and does the final reporting. Filtering is done to remove the effect of fast fading and ignore short-term variations. Though LI may collect measurements more often, L3 might report them at a larger configured periodicity. The source DU 110 may forward (8002) the L3 measurement report to the CU 120.

The CU 120 may perform (8003) a handover (HO) decision. For example, the CU 120 may decide to prepare the target DU 130 or the target cell 102 for handover of the terminal device 150-1. The CU 120 may also decide to prepare the physical downlink control channel (PDCCH) ordered random access channel (RACH) configuration for a TA acquisition of the prepared cell (i.e., the target cell 102).

The CU 120 may transmit (8004) a UE context modification request to the source DU 110. For example, the CU 120 may inform the source DU 110 or the cell 101 about the handover preparation (i.e., the indication of a potential handover) and ask the source DU 110 or the cell 101 to provide further configurations that are needed for LTM handover preparation along with the information on the prepared cells (i.e., the cell 102).

The source DU 110 may determine (8005) whether the TA value of the source cell 101 is the same as that of the target cell 102. For example, the source DU 110 may check whether the cell 101 to cell 102 TA relation is known, i.e., if the TA value of the source cell 101 is same as the TA value of the target cell 102, based on the previous events that are observed at the source DU 110 side.

If the TA value of the source cell 101 is the same as that of the target cell 102, the source DU 110 may indicate the TA value of the source cell 101 is the same as that of the target cell 102. For example, the source DU 110 may transmit (8006) a UE context modification response including an IE indicating the TA value of the source cell 101 is the same as that of the target cell 102 to the CU 120. For example, the source DU 110 may indicate the TA value of the source cell 101 is the same as that of the target cell 102 by LTM group information.

The CU 120 may transmit (8007) a UE context setup request to the target DU 130 to prepare it for handover. In this case, the CU 120 does not request the target DU 130 to provide the TA acquisition configuration. For example, the UE context setup request does not include a TA acquisition configuration request. The target DU 130 may transmit (8008) a UE context setup response to the CU 120. Since the CU 120 does not request the TA acquisition configuration, the target DU 130 does not provide the TA acquisition configuration to the CU 120. In this way, it can reduce the signaling overheads.

The CU 120 may generate (8009) a handover configuration including a measurement configuration and a cell configuration. During the generation of the handover configuration, since the CU 120 does not receive the TA acquisition configuration from the target DU 130, the handover configuration does not include the TA acquisition configuration.

The CU 120 may transmit (8010) the handover configuration without the TA acquisition configuration in RRC message to the source DU 110. The source DU 110 may forward (8011) the handover configuration without the TA acquisition configuration in RRC message to the terminal device 150-1. In this way, it can save signaling overheads.

After receiving the handover configuration in the RRC configuration, the terminal device 150-1 may transmit (8012) a RRC reconfiguration completion message to the source DU 110. The source DU 110 may forward (8013) the RRC reconfiguration completion message to the CU 120.

The terminal device 150-1 may transmit (8014) an LI measurement report including one or more candidate cells to the source DU 110. For example, the LI measurement report may indicate reference signal received power (RSRP) values.

Since the source DU 110 is aware that the source cell 101 and the target cell 102 share the same TA value, the source DU 110 may not trigger the PDCCH ordered TA acquisition. The source DU 110 may determine (8015) that the terminal device 150- 1 is to be handed over to the target cell 102. The terminal device 150-1 may also transmit (8016) the LI measurement report regarding the target cell 102 to the source DU 110.

The source DU 110 may trigger (8017) a cell change without TA acquisition. For example, the source DU 110 may transmit (8017) a medium access control control element (MAC CE) for triggering the cell change (i.e., changing to the target cell 102) to the terminal device 150-1. The MAC CE may further include the TA value of the target cell 102. For example, the source DU 110 may provide the TA value of the source cell 101 as that of the target cell 102 to the terminal device 150-1. The terminal device 150-1 may perform (8018) a RACHless access to the target DU 130 when executing the HO by using the TA value that is provided in the MAC CE. In this way, it can reduce the latency for accessing the target DU and avoid UE interruption.

FIG. 8B illustrates a signaling flow 800’ of handover without timing advance acquisition in inter-CU scenario according to other example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 800’ will be discussed with reference to FIG. 1, for example, by using the source DU 110, the target DU 130, the CU 120, the CU 140, and the terminal device 150-1.

The terminal device 150-1 may transmit (8001’) an L3 measurement report that includes the L3 measurements of the source cell 101 and neighbor cells (for example, cells 102 and 103) to the source DU 110. The L3 measurement report means that L3 at the terminal device 150-1 does filtering on values and does the final reporting. Filtering is done to remove the effect of fast fading and ignore short-term variations. Though LI may collect measurements more often, L3 might report them at a larger configured periodicity. The source DU 110 may forward (8002’) the L3 measurement report to the CU 120.

The CU 120 may perform (8003’) a handover (HO) decision. For example, the CU 120 may decide to prepare the target DU 130 or the target cell 102 for handover of the terminal device 150-1. The CU 120 may also decide to prepare the physical downlink control channel (PDCCH) ordered random access channel (RACH) configuration for a TA acquisition of the prepared cell (i.e., the target cell 102).

The CU 120 may transmit (8004’) a UE context modification request to the source DU 110. For example, the CU 120 may inform the source DU 110 or the cell 101 about the handover preparation (i.e., the indication of a potential handover) and ask the source DU 110 or the cell 101 to provide further configurations that are needed for LTM handover preparation along with the information on the prepared cells (i.e., the cell 102).

The source DU 110 may determine (8005’) whether the TA value of the source cell 101 is the same as that of the target cell 102. For example, the source DU 110 may check whether the cell 101 to cell 102 TA relation is known, i.e., if the TA value of the source cell 101 is same as the TA value of the target cell 102, based on the previous events that are observed at the source DU 110 side.

If the TA value of the source cell 101 is the same as that of the target cell 102, the source DU 110 may indicate the TA value of the source cell 101 is the same as that of the target cell 102. For example, the source DU 110 may transmit (8006’) a UE context modification response including an IE indicating the TA value of the source cell 101 is the same as that of the target cell 102 to the CU 120. For example, the source DU 110 may indicate the TA value of the source cell 101 is the same as that of the target cell 102 by LTM group information.

The CU 120 may transmit (8006.5) a handover request which indicates that TA acquisition is not needed to the CU 140. The CU 140 may transmit (8007’) a UE context setup request to the target DU 130 to prepare it for handover. In this case, the CU 140 does not request the target DU 130 to provide the TA acquisition configuration. For example, the UE context setup request does not include a TA acquisition configuration request. The target DU 130 may transmit (8008’) a UE context setup response to the CU 140. Since the CU 140 does not request the TA acquisition configuration, the target DU 130 does not provide the TA acquisition configuration to the CU 140. In this way, it can reduce the signaling overheads. The CU 140 may transmit (8009.5) a handover request ACK to the CU 120.

The CU 120 may generate (8009’) a handover configuration including a measurement configuration and a cell configuration. During the generation of the handover configuration, since the CU 120 does not obtain the TA acquisition configuration, the handover configuration does not include the TA acquisition configuration.

The CU 120 may transmit (8010’) the handover configuration without the TA acquisition configuration in RRC message to the source DU 110. The source DU 110 may forward (8011’) the handover configuration without the TA acquisition configuration in RRC message to the terminal device 150-1. In this way, it can save signaling overheads.

After receiving the handover configuration in the RRC configuration, the terminal device 150-1 may transmit (8012’) a RRC reconfiguration completion message to the source DU 110. The source DU 110 may forward (8013’) the RRC reconfiguration completion message to the CU 120.

The terminal device 150-1 may transmit (8014’) an LI measurement report including one or more candidate cells to the source DU 110. For example, the LI measurement report may indicate reference signal received power (RSRP) values.

Since the source DU 110 is aware that the source cell 101 and the target cell 102 share the same TA value, the source DU 110 may not trigger the PDCCH ordered TA acquisition. The source DU 110 may determine (8015’) that the terminal device 150- 1 is to be handed over to the target cell 102. The terminal device 150-1 may also transmit (8016’) the LI measurement report regarding the target cell 102 to the source DU 110.

The source DU 110 may trigger (8017’) a cell change without TA acquisition. For example, the source DU 110 may transmit (8017’) a medium access control control element (MAC CE) for triggering the cell change (i.e., changing to the target cell 102) to the terminal device 150-1. The MAC CE may further include the TA value of the target cell 102. For example, the source DU 110 may provide the TA value of the source cell 101 as that of the target cell 102 to the terminal device 150-1. The terminal device 150-1 may perform (8018’) a RACHless access to the target DU 130 when executing the HO by using the TA value that is provided in the MAC CE. In this way, it can reduce the latency for accessing the target DU and avoid UE interruption.

FIG. 9 shows a flowchart of an example method 900 implemented at a source DU in accordance with some example embodiments of the present disclosure. For example, the method 900 may be implemented at the source DU 110 in FIG. 1. At block 910, the source DU determines whether a timing advance value between a source cell of the source distributed unit and a terminal device is same as that between a target cell of a target distributed unit and the terminal device. The source distributed unit and target distributed unit are associated with a potential handover of the terminal device.

At block 920, if the timing advance value is same as that between the target cell and the terminal device, the source DU transmits, to a central unit of the source distributed unit, first information indicating that the source cell and the target cell share a same timing advance value.

In some example embodiments, the first information is layerl/layer2 triggered mobility group information which indicates a group of target cells that shares the same timing advance value with the source cell.

In some example embodiments, the method 900 includes: determining, at the source distributed unit, a list of cell pairs sharing same timing advance values, the list of cell pairs comprising a pair of the source cell and the target cell; and transmitting, to the central unit, the first information comprising the list of cell pairs.

In some example embodiments, the method 900 includes: receiving, from the central unit, an indication of potential handover of the terminal device from the source cell to the target cell; and transmitting, to the central unit, the first information after the reception of the indication of the potential handover.

In some example embodiments, the method 900 includes: transmitting, to the terminal device, second information indicating the timing advance value as that of the target cell, without triggering a timing advance acquisition.

In some example embodiments, the source distributed unit and the target distributed unit share the central unit, or wherein the source distributed unit and the target distributed unit belong to different central units.

FIG. 10 shows a flowchart of an example method 1000 implemented at a CU device in accordance with some example embodiments of the present disclosure. For example, the method 1000 may be implemented at the CU 120 in FIG. 1.

At block 1010, the CU receives, from a source distributed unit of the central unit, first information indicating that a source cell of the source distributed unit and a target cell of a target distributed unit share a same timing advance value. A timing advance value between the source cell and the terminal device is same as that between the target cell and the terminal device. The source distributed unit and target distributed unit are associated with a potential handover of the terminal device.

In some example embodiments, the method 1000 includes: transmitting, to the target distributed unit or a target central unit of the target distributed unit, a timing advance acquisition configuration request; receiving, from the target distributed unit or the target central unit, a timing advance acquisition configuration; transmitting, to the source distributed unit, an indication indicating a potential handover of the terminal device from the source cell to the target cell, after the reception of the timing advance acquisition configuration; and receiving, from the source distributed unit, the first information.

In some example embodiments, the method 1000 includes: generating a handover configuration comprising a measurement configuration and a cell configuration; excluding the timing advance acquisition configuration from the handover configuration; transmitting, to the source distributed unit, the handover configuration without the timing advance acquisition configuration; and transmitting, to the target distributed unit or the target central unit, an indication for releasing timing acquisition resources at the target distributed unit.

In some example embodiments, the method 1000 includes: transmitting, to the source distributed unit, an indication of a potential handover of the terminal device from the source cell to the target cell; receiving, from the source distributed unit, the first information; transmitting, to the target distributed unit or the target central unit, a user context setup request without a timing advance acquisition configuration request, after the reception of the first information; and receiving, from the target distributed unit or the target central unit, a user context setup response without a timing advance acquisition configuration.

In some example embodiments, the method 1000 includes: generating a handover configuration comprising a measurement configuration and a cell configuration without the timing advance acquisition configuration, and transmitting, to the source distributed unit, the handover configuration without the timing advance acquisition configuration.

In some example embodiments, the first information comprises a list of cell pairs sharing same timing advance values, the list of cell pairs comprising a pair of the source cell and the target cell, and transmitting, to a core network device, the list of cell pairs.

In some example embodiments, the method 1000 includes: transmitting, to the source distributed unit, an indication of a potential handover of the terminal device from the source cell to the target cell; transmitting, to the target distributed unit or a target central unit of the target distributed unit, a user context setup request without a timing advance acquisition configuration request; and receiving, from the target distributed unit or the target central unit, a user context setup response without a timing advance acquisition configuration.

FIG. 11 shows a flowchart of an example method 1100 implemented at a third device in accordance with some example embodiments of the present disclosure. For example, the method 1100 may be implemented at the target DU 130 in FIG. 1.

At block 1110, the target DU receives, from a central unit of the target distributed unit, an indication for releasing timing acquisition resources at the target distributed unit. The target distributed unit is associated with a potential handover of a terminal device.

At block 1120, the target DU releases the timing acquisition resources based on the indication.

FIG. 12 shows a flowchart of an example method 1200 implemented at a terminal device in accordance with some example embodiments of the present disclosure. For example, the method 1200 may be implemented at the terminal device 150 in FIG. 1.

At block 1210, the terminal device transmits, to a source distributed unit, a measurement report that comprising measurements of a source cell of a source distributed unit and a set of neighbor cells.

At block 1220, the terminal device receives, from the source distributed unit, an indication of a target cell of a target distributed unit, the target cell being from the set of neighbor cells. The source distributed unit and target distributed unit are associated with a potential handover of the terminal device.

At block 1230, the terminal device receives, from the source distributed unit, information indicating the timing advance value as that of the target cell, without triggering a timing advance acquisition.

FIG. 13 shows a flowchart of an example method 1300 implemented at a source DU device in accordance with some example embodiments of the present disclosure. For example, the method 1300 may be implemented at the source DU 110 in FIG. 1.

At block 1310, the source DU receives, from a central unit of the source distributed unit, an indication of a potential handover of a terminal device from a source cell of the source distributed unit to a target cell of a target distributed unit.

At block 1320, the source DU determines if it can be considered that a timing advance value between the source cell and the terminal device is same as that between the target cell and the terminal device.

At block 1330, if the source distributed unit cannot consider that the timing advance value is same as that between the target cell and the terminal device, the source DU trigger the terminal device for acquisition of a timing advance for the target cell.

In some embodiments, at block 1340, the source DU may obtain, from the central unit and based on the triggering, a number of timing advance values between the target cell and a set of terminal devices that is served by the source cell.

In some example embodiments, the method 1300 includes: determining that the timing advance value is the same based on a number of timing advance values obtained for the target cell meeting a predetermined criterion; and determining that the timing advance value is not the same based on the number of time advance values obtained for the target cell not meeting the predetermined criterion.

In some example embodiments, the predetermined criterion requires that at least one of: a predetermined number or a predetermined ratio of timing advance values for the target cell are the same as that between the source cell and the terminal device.

In some example embodiments, the method 1300 includes: receiving, from the central unit, a message indicating the predetermined criterion.

In some example embodiments, the predetermined criterion is a default parameter configured at the source distributed unit.

In some example embodiments, the predetermined criterion is a global parameter for all target distributed units, or wherein the predetermined criterion is a target distributed unit pair parameter, or wherein the predetermined criterion is a parameter per target distributed unit, or wherein the predetermined criterion is a parameter per cell pair.

In some example embodiments, the method 1300 includes based on a determination that the source distributed unit can consider that the timing advance value is the same as that between the target cell and the terminal device, refraining from triggering the terminal device for acquisition of a timing advance for the target cell.

FIG. 14 shows a flowchart of an example method 1400 implemented at a CU device in accordance with some example embodiments of the present disclosure. For the example, the method 1400 may be implemented at the CU 120 in FIG. 1.

At block 1410, the CU 120 obtains a predetermined criterion useable for determining whether a timing advance value between a terminal device and a first cell is the same as (or can be considered to be the same as) a timing advance value between the terminal and a second cell.

At block 1420, the CU 120 transmits, to a source distributed unit, a first message indicating the predetermined criterion.

At block 1430, the CU 120 transmits, to a target distributed unit or a central unit of the target distributed unit, a second message indicating the predetermined criterion. The source distributed unit and target distributed unit are associated with a potential handover of a terminal device.

In some example embodiments, the method 1400 includes: obtaining the predetermined criterion for timing advance acquisitions from a core network device; or generating the predetermined criterion for timing advance acquisitions.

In some example embodiments, a first apparatus capable of performing any of the method 900 (for example, the source DU 110 in FIG. 1) may comprise means for performing the respective operations of the method 900. 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 source DU 110 in FIG. 1.

In some example embodiments, the first apparatus comprises means for determining whether a timing advance value between a source cell of the source distributed unit and a terminal device is same as that between a target cell of a target distributed unit and the terminal device, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device; and means for based on a determination that the timing advance value is same as that between the target cell and the terminal device, transmitting, to a central unit of the source distributed unit, first information indicating that the source cell and the target cell share a same timing advance value.

In some example embodiments, the first apparatus comprises means for determining, at the source distributed unit, a list of cell pairs sharing same timing advance values, the list of cell pairs comprising a pair of the source cell and the target cell; and means for transmitting, to the central unit, the first information comprising the list of cell pairs.

In some example embodiments, the first apparatus comprises means for receiving, from the central unit, an indication of potential handover of the terminal device from the source cell to the target cell; and means for transmitting, to the central unit, the first information after the reception of the indication of the potential handover. In some example embodiments, the first apparatus comprises means for transmitting, to the terminal device, second information indicating the timing advance value as that of the target cell, without triggering a timing advance acquisition.

In some example embodiments, the first apparatus further comprises means for performing other operations in some example embodiments of the method 900 or the source DU 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 1000 (for example, the CU 120 in FIG. 1) may comprise means for performing the respective operations of the method 1000. 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 CU 120 in FIG. 1.

In some example embodiments, the second apparatus comprises means for receiving, from a source distributed unit of the central unit, first information indicating that a source cell of the source distributed unit and a target cell of a target distributed unit share a same timing advance value, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device.

In some example embodiments, the second apparatus comprises means for transmitting, to the target distributed unit or a target central unit of the target distributed unit, a timing advance acquisition configuration request; means for receiving, from the target distributed unit or the target central unit, a timing advance acquisition configuration; means for transmitting, to the source distributed unit, an indication indicating a potential handover of the terminal device from the source cell to the target cell, after the reception of the timing advance acquisition configuration; and means for receiving, from the source distributed unit, the first information.

In some example embodiments, the second apparatus comprises means for generating a handover configuration comprising a measurement configuration and a cell configuration; means for excluding the timing advance acquisition configuration from the handover configuration; means for transmitting, to the source distributed unit, the handover configuration without the timing advance acquisition configuration; and means for transmitting, to the target distributed unit or the target central unit, an indication for releasing timing acquisition resources at the target distributed unit.

In some example embodiments, the second apparatus comprises means for transmitting, to the source distributed unit, an indication of a potential handover of the terminal device from the source cell to the target cell; means for receiving, from the source distributed unit, the first information; means for transmitting, to the target distributed unit or the target central unit, a user context setup request without a timing advance acquisition configuration request, after the reception of the first information; and means for receiving, from the target distributed unit or the target central unit, a user context setup response without a timing advance acquisition configuration.

In some example embodiments, the second apparatus comprises means for generating a handover configuration comprising a measurement configuration and a cell configuration without the timing advance acquisition configuration, and means for transmitting, to the source distributed unit, the handover configuration without the timing advance acquisition configuration.

In some example embodiments, the first information comprises a list of cell pairs sharing same timing advance values, the list of cell pairs comprising a pair of the source cell and the target cell, and means for transmitting, to a core network device, the list of cell pairs. In some example embodiments, the second apparatus comprises means for transmitting, to the source distributed unit, an indication of a potential handover of the terminal device from the source cell to the target cell; means for transmitting, to the target distributed unit or a target central unit of the target distributed unit, a user context setup request without a timing advance acquisition configuration request; and means for receiving, from the target distributed unit or the target central unit, a user context setup response without a timing advance acquisition configuration.

In some example embodiments, the second apparatus further comprises means for performing other operations in some example embodiments of the method 1000 or the CU 120. 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 second apparatus.

In some example embodiments, a third apparatus capable of performing any of the method 1100 (for example, the target DU 130 in FIG. 1) may comprise means for performing the respective operations of the method 1100. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The third apparatus may be implemented as or included in the target DU 130 in FIG. 1.

In some example embodiments, the third apparatus comprises means for receiving, from a central unit of the target distributed unit, an indication for releasing timing acquisition resources at the target distributed unit, wherein the target distributed unit is associated with a potential handover of a terminal device; and means for releasing the timing acquisition resources based on the indication.

In some example embodiments, the third apparatus further comprises means for performing other operations in some example embodiments of the method 1100 or the target DU 130. 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 third apparatus.

In some example embodiments, a fourth apparatus capable of performing any of the method 1200 (for example, the terminal device 150 in FIG. 1) may comprise means for performing the respective operations of the method 1200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The fourth apparatus may be implemented as or included in the terminal device 150 in FIG. 1.

In some example embodiments, the fourth apparatus comprises means for transmitting, to a source distributed unit, a measurement report that comprising measurements of a source cell of a source distributed unit and a set of neighbor cells; means for receiving, from the source distributed unit, an indication of a target cell of a target distributed unit, the target cell being from the set of neighbor cells, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device; and means for receiving, from the source distributed unit, information indicating the timing advance value as that of the target cell, without triggering a timing advance acquisition.

In some example embodiments, the fourth apparatus further comprises means for performing other operations in some example embodiments of the method 1200 or the terminal device 150. 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 fourth apparatus.

In some example embodiments, a fifth apparatus capable of performing any of the method 1300 (for example, the source DU 110 in FIG. 1) may comprise means for performing the respective operations of the method 1300. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The fifth apparatus may be implemented as or included in the source DU 110 in FIG. 1.

In some example embodiments, the fifth apparatus comprises means for receiving, from a central unit of the source distributed unit, an indication of a potential handover of a terminal device from a source cell of the source distributed unit to a target cell of a target distributed unit; means for determining if it can be considered that a timing advance value between the source cell and the terminal device is the same as that between the target cell and the terminal device; and means for based on a determination that the source distributed unit cannot consider the timing advance value is same as that between the target cell and the terminal device, triggering the terminal device for acquisition of a timing advance for the target cell.

In some example embodiments, the fifth apparatus comprises: means for determining that the timing advance value is the same based on a number of timing advance values obtained for the target cell meeting a predetermined criterion; or means for determining that the timing advance value is not the same based on the number of time advance values obtained for the target cell not meeting the predetermined criterion.

In some example embodiments, the predetermined criterion requires that at least one of a predetermined number of a predetermined ratio of timing advance values for the target cell are the same as that between the source cell and the terminal device.

In some example embodiments, the fifth apparatus comprises: means for receiving, from the central unit, a message indicating the predetermined criterion.

In some example embodiments, the fifth apparatus comprises: means for based on a determination that the source distributed unit can consider that the timing advance value is the same as that between the target cell and the terminal device, refraining from triggering the terminal device for acquisition of a timing advance for the target cell.

In some example embodiments, the fifth apparatus further comprises means for performing other operations in some example embodiments of the method 1300 or the source DU 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 fifth apparatus.

In some example embodiments, a sixth apparatus capable of performing any of the method 1400 (for example, the CU 120 in FIG. 1) may comprise means for performing the respective operations of the method 1400. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The sixth apparatus may be implemented as or included in the CU 120 in FIG. 1.

In some example embodiments, the sixth apparatus comprises means for obtaining a predetermined criterion useable for determining whether a timing advance value between a terminal device and a first cell is the same as a timing advance between the terminal device and a second cell; means for transmitting, to a source distributed unit, a first message indicating the predetermined criterion; and means for transmitting, to a target distributed unit or a central unit of the target distributed unit, a second message indicating the predetermined criterion, wherein the source distributed unit and target distributed unit are associated with a potential handover of a terminal device. In some example embodiments, the sixth apparatus comprises means for obtaining the predetermined criterion for timing advance acquisitions from a core network device; or means for generating the predetermined criterion for timing advance acquisitions.

In some example embodiments, the sixth apparatus further comprises means for performing other operations in some example embodiments of the method 1400 or the CU 120. 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 sixth apparatus.

FIG. 15 is a simplified block diagram of a device 1500 that is suitable for implementing example embodiments of the present disclosure. The device 1500 may be provided to implement a communication device, for example, the source DU 110, the CU 120, the target DU 130, the CU 140 and the terminal device 150 as shown in FIG. 1. As shown, the device 1500 includes one or more processors 1510, one or more memories 1520 coupled to the processor 1510, and one or more communication modules 1540 coupled to the processor 1510.

The communication module 1540 is for bidirectional communications. The communication module 1540 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 1540 may include at least one antenna.

The processor 1510 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 1500 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 1520 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) 1524, 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) 1522 and other volatile memories that will not last in the power-down duration.

A computer program 1530 includes computer executable instructions that are executed by the associated processor 1510. The instructions of the program 1530 may include instructions for performing operations/acts of some example embodiments of the present disclosure. The program 1530 may be stored in the memory, e.g., the ROM 1524. The processor 1510 may perform any suitable actions and processing by loading the program 1530 into the RAM 1522.

The example embodiments of the present disclosure may be implemented by means of the program 1530 so that the device 1500 may perform any process of the disclosure as discussed with reference to FIG. 2 to FIG. 14. 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 1530 may be tangibly contained in a computer readable medium which may be included in the device 1500 (such as in the memory 1520) or other storage devices that are accessible by the device 1500. The device 1500 may load the program 1530 from the computer readable medium to the RAM 1522 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. 16 shows an example of the computer readable medium 1600 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 1600 has the program 1530 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

Claims:

1. A source distributed unit comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source distributed unit to: determine whether a timing advance value between a source cell of the source distributed unit and a terminal device is same as that between a target cell of a target distributed unit and the terminal device, wherein the source distributed unit and target distributed unit are associated with a potential handover of the terminal device; and based on a determination that the timing advance value is same as that between the target cell and the terminal device, transmit, to a central unit of the source distributed unit, first information indicating that the source cell and the target cell share a same timing advance value.

2. The source distributed unit of claim 1, wherein the first information is layerl/layer2 triggered mobility group information which indicates a group of target cells that shares the same timing advance value with the source cell.

3. The source distributed unit of claim 1, wherein the source distributed unit is caused to: determine, at the source distributed unit, a list of cell pairs sharing same timing advance values, the list of cell pairs comprising a pair of the source cell and the target cell; and transmit, to the central unit, the first information comprising the list of cell pairs.

4. The source distributed unit of any of claims 1 to 3, wherein the source distributed unit is caused to: receive, from the central unit, an indication of potential handover of the terminal device from the source cell to the target cell; and transmit, to the central unit, the first information after the reception of the indication of the potential handover.

5. The source distributed unit of any of claims 1-4, wherein the source distributed unit is caused to: transmit, to the terminal device, second information indicating the timing advance value as that of the target cell, without triggering a timing advance acquisition.

6. A central unit comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the central unit to: receive, from a source distributed unit of the central unit, first information indicating that a source cell of the source distributed unit and a target cell of a target distributed unit share a same timing advance value, wherein the source distributed unit and target distributed unit are associated with a potential handover of a terminal device.

7. The central unit of claim 6, wherein the first information is layerl/layer2 triggered mobility group information which indicates a group of target cells that shares the same timing advance value with the source cell.

8. The central unit of any of claims 6 to 7, wherein the central unit is caused to: transmit, to the target distributed unit or a target central unit of the target distributed unit, a timing advance acquisition configuration request; receive, from the target distributed unit or the target central unit, a timing advance acquisition configuration; transmit, to the source distributed unit, an indication indicating a potential handover of the terminal device from the source cell to the target cell, after the reception of the timing advance acquisition configuration; and receive, from the source distributed unit, the first information.

9. The central unit of claim 8, wherein the central unit is caused to: generate a handover configuration comprising a measurement configuration and a cell configuration; exclude the timing advance acquisition configuration from the handover configuration; transmit, to the source distributed unit, the handover configuration without the timing advance acquisition configuration; and transmit, to the target distributed unit or the target central unit, an indication for releasing timing acquisition resources at the target distributed unit.

10. The central unit of any of claims 6 to 7, wherein the central unit is caused to: transmit, to the source distributed unit, an indication of a potential handover of the terminal device from the source cell to the target cell; receive, from the source distributed unit, the first information; transmit, to the target distributed unit or the target central unit, a user context setup request without a timing advance acquisition configuration request, after the reception of the first information; and receive, from the target distributed unit or the target central unit, a user context setup response without a timing advance acquisition configuration.

11. The central unit of claim 10, wherein the central unit is caused to: generate a handover configuration comprising a measurement configuration and a cell configuration without the timing advance acquisition configuration, and transmit, to the source distributed unit, the handover configuration without the timing advance acquisition configuration.

12. The central unit of any of claims 6 to 11, wherein the first information comprises a list of cell pairs sharing same timing advance values, the list of cell pairs comprising a pair of the source cell and the target cell, and wherein the central unit is caused to: transmit, to a core network device, the list of cell pairs.

13. The central unit of claim 12, wherein the central unit is caused to: transmit, to the source distributed unit, an indication of a potential handover of the terminal device from the source cell to the target cell; transmit, to the target distributed unit or a target central unit of the target distributed unit, a user context setup request without a timing advance acquisition configuration request; and receive, from the target distributed unit or the target central unit, a user context setup response without a timing advance acquisition configuration.

14. A target distributed unit comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the target distributed unit to: receive, from a central unit of the target distributed unit, an indication for releasing timing acquisition resources at the target distributed unit, wherein the target distributed unit is associated with a potential handover of a terminal device; and release the timing acquisition resources based on the indication.

15. A source distributed unit comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source distributed unit to: receive, from a central unit of the source distributed unit, an indication of a potential handover of a terminal device from a source cell of the source distributed unit to a target cell of a target distributed unit; determine if it can be considered that a timing advance value between the source cell and the terminal device is the same as that between the target cell and the terminal device; and based on a determination that the source distributed unit cannot consider that the timing advance value is the same as that between the target cell and the terminal device, trigger the terminal device for acquisition of a timing advance for the target cell.

16. The source distributed unit of claim 15, wherein the source distributed unit is caused to: determine that the timing advance value is the same based on a number of timing advance values obtained for the target cell meeting a predetermined criterion; or determine that the timing advance value is not the same based on the number of time advance values obtained for the target cell not meeting the predetermined criterion.

17. The source distributed unit of claim 15, wherein the predetermined criterion requires that at least one of a predetermined number or a predetermined ratio of timing advance values for the target cell are the same as that between the source cell and the terminal device.

18. The source distributed unit of any of claims 16-17, wherein the source distributed unit is caused to: receive, from the central unit, a message indicating the predetermined criterion.

19. The source distributed unit of any of claims 16-17, wherein the predetermined criterion is a default parameter configured at the source distributed unit.

20. The source distributed unit of any of claims 15-19, wherein the source distributed unit is caused to: based on a determination that the source distributed unit can consider that the timing advance value is the same as that between the target cell and the terminal device, refrain from triggering the terminal device for acquisition of a timing advance for the target cell.

21. The source distributed unit of any of claims 15-20, wherein the source distributed unit and the target distributed unit share the central unit, or wherein the source distributed unit and the target distributed unit belong to different central units.

22. A central unit comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the central unit to: obtain a predetermined criterion useable for determining whether a timing advance value between a terminal device and a first cell is the same as a timing advance value between the terminal and a second cell; transmit, to a source distributed unit, a first message indicating the predetermined criterion; and transmit, to a target distributed unit or a central unit of the target distributed unit, a second message indicating the predetermined criterion, wherein the source distributed unit and target distributed unit are associated with a potential handover of a terminal device.

23. The central unit of claim 22, wherein the central unit is caused to: obtain the predetermined criterion for timing advance acquisitions from a core network device; or generate the predetermined criterion for timing advance acquisitions.