WO2025199695A1

WO2025199695A1 - Devices and methods of communication

Info

Publication number: WO2025199695A1
Application number: PCT/CN2024/083618
Authority: WO
Inventors: Da Wang; Gang Wang
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2024-03-25
Filing date: 2024-03-25
Publication date: 2025-10-02
Anticipated expiration: 2026-09-25

Abstract

Embodiments of the present disclosure relate to devices and methods of communication. In one aspect, upon determination that a LTM cell switch from a source PSCell to a target PSCell is to be executed, a first network device may transmit, to a terminal device, a command for the LTM cell switch, and transmit, to a second network device providing the target PSCell, a notification that the command is transmitted to the terminal device. Upon completion of the LTM cell switch, the terminal device may transmit, to a MN, a RRC reconfiguration complete message comprising an identity of a LTM candidate configuration associated with the target PSCell or an identity of the target PSCell. In this way, an inter-SN LTM PSCell switch may be performed.

Description

DEVICES AND METHODS OF COMMUNICATION

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication, and in particular, to devices and methods of communication for layer 1 (L1) or layer 2 (L2) triggered mobility (LTM) .

BACKGROUND

LTM as L2 based mobility is introduced to offer improvements in handover latency and interruption time compared to Layer 3 (L3) based mobility. However, the LTM still has some limitations compared to the L3 based mobility. It is expected to remove these limitations. For example, a LTM operation is only supported for mobility between cells of the same network device (i.e., same central unit (CU) ) . Depending on deployment of a network (NW) , this may significantly limit opportunities to use LTM. Thus, by enabling a LTM operation between cells of different network devices (i.e. inter-CU) , the NW may be able to gain benefits of LTM for a far greater number of handovers.

SUMMARY

In general, embodiments of the present disclosure provide methods, devices and computer storage media of communication for LTM.

In a first aspect, there is provided a first network device. The first network device comprises a processor configured to cause the first network device to: determine that a LTM cell switch from a source primary secondary cell (PSCell) to a target PSCell is to be executed; transmit, to a terminal device, a command for the LTM cell switch; and transmit, to a second network device providing the target PSCell, a notification that the command is transmitted to the terminal device.

In a second aspect, there is provided a second network device. The second network device comprises a processor configured to cause the second network device to: receive, from a first network device, a notification that a command for a LTM cell switch from a source PSCell to a target PSCell is transmitted to a terminal device, the target PSCell being provided by the second network device.

In a third aspect, there is provided a terminal device. The terminal device comprises a processor configured to cause the terminal device to: receive, from a source secondary node (SN) providing a source PSCell, a command for a LTM cell switch from the source PSCell to a target PSCell; and transmit, to a master node (MN) , a radio resource control (RRC) reconfiguration complete message comprising an identity of a LTM candidate configuration associated with the target PSCell or an identity of the target PSCell.

In a fourth aspect, there is provided a method of communication. The method comprises: determining, at a first network device, that a LTM cell switch from a source PSCell to a target PSCell is to be executed; transmitting, to a terminal device, a command for the LTM cell switch; and transmitting, to a second network device providing the target PSCell, a notification that the command is transmitted to the terminal device.

In a fifth aspect, there is provided a method of communication. The method comprises: receiving, at a second network device and from a first network device, a notification that a command for a LTM cell switch from a source PSCell to a target PSCell is transmitted to a terminal device, the target PSCell being provided by the second network device.

In a sixth aspect, there is provided a method of communication. The method comprises: receiving, at a terminal device and from a source SN providing a source PSCell, a command for a LTM cell switch from the source PSCell to a target PSCell; and transmitting, to a MN, a RRC reconfiguration complete message comprising an identity of a LTM candidate configuration associated with the target PSCell or an identity of the target PSCell.

In a seventh aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor, cause the at least one processor to perform the method according to any of the fifth to eighth aspects of the present disclosure.

Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein:

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

FIG. 2 illustrates a signaling chart illustrating an example process of a MN-initiated preparation of inter-SN LTM according to embodiments of the present disclosure;

FIG. 3 illustrates a signaling chart illustrating an example process of a SN-initiated preparation of inter-SN LTM according to embodiments of the present disclosure;

FIG. 4 illustrates a signaling chart illustrating an example process of a MN-initiated early sync of inter-SN LTM according to embodiments of the present disclosure;

FIG. 5 illustrates a signaling chart illustrating an example process of a SN-initiated early synchronization of inter-SN LTM according to embodiments of the present disclosure;

FIG. 6 illustrates a signaling chart illustrating an example process of a MN-initiated initial PSCell switch execution of inter-SN LTM according to embodiments of the present disclosure;

FIG. 7 illustrates a signaling chart illustrating an example process of a MN-initiated subsequent PSCell switch execution of inter-SN LTM according to embodiments of the present disclosure;

FIG. 8 illustrates a signaling chart illustrating example process of a SN-initiated initial or subsequent PSCell switch execution of inter-SN LTM according to embodiments of the present disclosure;

FIG. 9 illustrates a flowchart of an example method of communication implemented at a first network device in accordance with some embodiments of the present disclosure;

FIG. 10 illustrates a flowchart of an example method of communication implemented at a second network device in accordance with some embodiments of the present disclosure;

FIG. 11 illustrates a flowchart of an example method of communication implemented at a terminal device in accordance with some embodiments of the present disclosure; and

FIG. 12 illustrates a simplified block diagram of a device that is suitable for implementing 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 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 limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein, the term ‘terminal device’ refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, user equipment (UE) , personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs) , portable computers, tablets, wearable devices, Internet of things (IoT) devices, ultra-reliable and low latency communications (URLLC) devices, Internet of everything (IoE) devices, machine type communication (MTC) devices, device on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, devices for integrated access and backhaul (IAB) , small data transmission (SDT) , mobility, multicast and broadcast services (MBS) , positioning, dynamic/flexible duplex in commercial networks, reduced capability (RedCap) , space borne vehicles or air borne vehicles in non-terrestrial networks (NTN) including Satellites and high altitude platforms (HAPs) encompassing unmanned aircraft systems (UAS) , extended reality (XR) devices including different types of realities such as augmented reality (AR) , mixed reality (MR) and virtual reality (VR) , the unmanned aerial vehicle (UAV) commonly known as a drone which is an aircraft without any human pilot, devices on high speed train (HST) , or image capture devices such as digital cameras, sensors, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. The ‘terminal device’ can further has ‘multicast/broadcast’ feature, to support public safety and mission critical, V2X applications, transparent IPv4/IPv6 multicast delivery, IPTV, smart TV, radio services, software delivery over wireless, group communications and IoT applications. It may also incorporate one or multiple subscriber identity module (SIM) as known as multi-SIM. The term ‘terminal device’ can be used interchangeably with a UE, a mobile station, a subscriber station, a mobile terminal, a user terminal or a wireless device.

The term ‘network device’ refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a next generation NodeB (gNB) , a transmission reception point (TRP) , a remote radio unit (RRU) , a radio head (RH) , a remote radio head (RRH) , an IAB node, a low power node such as a femto node, a pico node, a reconfigurable intelligent surface (RIS) , network-controlled repeaters, and the like.

The terminal device or the network device may have artificial intelligence (AI) or machine learning capability. It generally includes a model which has been trained from numerous collected data for a specific function, and can be used to predict some information.

The terminal or the network device may work on several frequency ranges, e.g. FR1 (410 MHz to 7125 MHz) , FR2 (24.25GHz to 71GHz) , frequency band larger than 100GHz as well as Tera Hertz (THz) . It can further work on licensed/unlicensed/shared spectrum. The terminal device may have more than one connections with the network devices under MR-DC application scenario. The terminal device or the network device can work on full duplex, flexible duplex and cross division duplex modes.

The network device may have the function of network energy saving (NES) , SON or minimization of drive tests (MDT) . The terminal may have the function of power saving.

The embodiments of the present disclosure may be performed in test equipment, e.g. signal generator, signal analyzer, spectrum analyzer, network analyzer, test terminal device, test network device, channel emulator.

In one embodiment, the terminal device may be connected with a first network device and a second network device. One of the first network device and the second network device may be a master node and the other one may be a secondary node. The first network device and the second network device may use different radio access technologies (RATs) . In one embodiment, the first network device may be a first RAT device and the second network device may be a second RAT device. In one embodiment, the first RAT device is eNB and the second RAT device is gNB. Information related with different RATs may be transmitted to the terminal device from at least one of the first network device or the second network device. In one embodiment, first information may be transmitted to the terminal device from the first network device and second information may be transmitted to the terminal device from the second network device directly or via the first network device. In one embodiment, information related with configuration for the terminal device configured by the second network device may be transmitted from the second network device via the first network device. Information related with reconfiguration for the terminal device configured by the second network device may be transmitted to the terminal device from the second network device directly or via the first network device.

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. The term ‘includes’ and its variants are to be read as open terms that mean ‘includes, but is not limited to. ’ The term ‘based on’ is to be read as ‘at least in part based on. ’ The term ‘one embodiment’ and ‘an embodiment’ are to be read as ‘at least one embodiment. ’ The term ‘another embodiment’ is to be read as ‘at least one other embodiment. ’ The terms ‘first, ’ ‘second, ’ and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below.

In some examples, values, procedures, or apparatus are referred to as ‘best, ’ ‘lowest, ’ ‘highest, ’ ‘minimum, ’ ‘maximum, ’ or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, higher, or otherwise preferable to other selections.

In the context of the present disclosure, the term ‘a PSCell switch’ may be interchangeably used with ‘areconfiguration with sync for a secondary cell group (SCG) ’ or ‘PSCell change’ . The term ‘PSCell’ refers to a special cell (SpCell) of a SCG, the term ‘PCell’ refers to a SpCell of a MCG, and the term ‘SpCell’ refers to a primary cell of a SCG or MCG. The term ‘prepared PSCells’ may be interchangeably used with ‘candidate PSCells’ or ‘prepared candidate PSCells’ . The term ‘prepared PCells’ may be interchangeably used with ‘candidate PCells’ or ‘prepared candidate PCells’ .

Currently, it is proposed to specify support for inter-CU LTM, e.g., support the case when new radio (NR) -dual connectivity (DC) is configured and a CU is acting as a SN and a master cell group (MCG) is unchanged.

In view of this, embodiments of the present disclosure provide solutions of communication for inter-SN LTM so as to support an inter-SN LTM PSCell switch. In one aspect, upon determination that a LTM cell switch from a source PSCell to a target PSCell is to be executed, a first network device may transmit, to a terminal device, a command for the LTM cell switch, and transmit, to a second network device providing the target PSCell, a notification that the command is transmitted to the terminal device. Upon completion of the LTM cell switch, the terminal device may transmit, to a MN, a RRC reconfiguration complete message comprising an identity of a LTM candidate configuration associated with the target PSCell or an identity of the target PSCell. In this way, an inter-SN LTM PSCell switch execution may be performed.

Principles and implementations of the present disclosure will be described in detail below with reference to the figures.

EXAMPLE OF COMMUNICATION NETWORK

FIG. 1 illustrates a schematic diagram of an example communication environment 100 in which embodiments of the present disclosure can be implemented. As shown in FIG. 1, the communication environment 100 may comprise a network device 110 and a terminal device 120. The network device 110 provides a cell 111 and the terminal device 120 is located in the cell 111 and served by the network device 110.

The communication environment 100 may also comprise one or more other network devices such as network devices 130, 140 and 150. The network device 130 provides cells 131, 132 and 133. The network device 140 provides cells 141, 142 and 143, and the network device 150 provides cells 151, 152 and 153. It should be noted that the number of the cells are not limited to three, and more or less cells may be provided by the network devices 130, 140 and 150.

It is assumed that the terminal device 120 may establish a dual connection (i.e., simultaneous connection) with two network devices. For example, the network device 110 may serve as an MN (for convenience, also referred to as MN 110 below) , and the network device 130, 140 or 150 may serve as a SN (for convenience, also referred to as SN 130 or 140 or 150 below) . For convenience, it is assumed that the network device 130 serves as a SN initially.

Although only the cell 111 is shown, the MN 110 may provide multiple cells, and these cells may form a MCG for the terminal device 120. For example, the cell 111 is a primary cell (i.e., PCell) in the MCG. Further, the cells 131, 132 and 133 provided by the network device 130 may form a SCG for the terminal device 120. For example, the cell 131 is a primary cell (i.e., PSCell) in the SCG.

The SN 130 may communicate with the terminal device 120 via a channel such as a wireless communication channel. Similarly, the MN 110 may also communicate with the terminal device 120 via a channel such as a wireless communication channel. The SN 130 may communicate with the MN 110 via a Xn interface.

It is to be understood that the number of devices or cells in FIG. 1 is given for the purpose of illustration without suggesting any limitations to the present disclosure. The communication environment 100 may involve any suitable number of network devices and/or terminal devices and/or cells adapted for implementing implementations of the present disclosure.

The communications in the communication environment 100 may conform to any suitable standards including, but not limited to, global system for mobile communications (GSM) , long term evolution (LTE) , LTE-evolution, LTE-advanced (LTE-A) , new radio (NR) , wideband code division multiple access (WCDMA) , code division multiple access (CDMA) , GSM EDGE radio access network (GERAN) , machine type communication (MTC) and the like. The embodiments of the present disclosure may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G-advanced networks, or the sixth generation (6G) networks.

LTM is a procedure in which a network device (e.g., the network device 110) receives L1 measurement report (s) from a terminal device (e.g., the terminal device 120) , and based on the L1 measurement report (s) , the network device changes the terminal device’s serving cell by a cell switch command signaled via a medium access control (MAC) control element (CE) . The cell switch command indicates a LTM candidate cell configuration that the network device previously prepared and provided to the terminal device through a RRC signaling. Then the terminal device switches to a target cell according to the cell switch command.

In some embodiments, the terminal device 120 may receive, from the MN 110, a RRC reconfiguration comprising a LTM configuration for inter-SN PSCell switch. For example, the LTM configuration may indicate a set of candidate PSCells, e.g., cells of candidate SNs 130, 140 and 150.

In some embodiments, the terminal device 120 may perform an initial PSCell change or addition to the cell 131 of the SN 130. This procedure may be called as an initial execution of an inter-SN PSCell switch or an initial PSCell switch execution.

With reference to FIG. 1, in some embodiments, the terminal device 120 may perform a subsequent execution of subsequent LTM PSCell addition or change from the cell 131 of the SN 130 to the cell 142 of the SN 140, and a subsequent execution of subsequent LTM from the cell 142 of the SN 140 to the cell 151 of the SN 150. Any of these procedures may be called as a subsequent execution of an inter-SN PSCell switch or a subsequent PSCell switch execution.

Embodiments of the present disclosure provide solutions of communication for a preparation, an early synchronization and a cell switch execution of inter-SN LTM. In some embodiments, the preparation, early synchronization and/or cell switch execution of the inter-SN LTM may be initiated by a MN. In some embodiments, the preparation, early synchronization and/or cell switch execution of the inter-SN LTM may be initiated by a source SN. The solutions will be described in connection with FIGs. 2 to 8 below.

EXAMPLE IMPLEMENTATION OF PREPARATION OF INTER-SN LTM

For inter-SN LTM, it is still unclear which node triggers preparation of inter-SN LTM PSCell switch, and how does network devices coordinate with each other for the preparation of inter-SN LTM PSCell switch. Embodiments of the present disclosure provide solutions of preparation of inter-SN LTM PSCell switch.

FIG. 2 illustrates a signaling chart illustrating an example process 200 of a MN-initiated preparation of inter-SN LTM according to embodiments of the present disclosure. For the purpose of discussion, the process 200 will be described with reference to FIG. 1. The process 200 may involve the terminal device 120, the MN 110, the SNs 130, 140 and 150. In this example, the SNs 130, 140 and 150 are candidate SNs, and the terminal device 120 is served by the MN 110. The preparation of the inter-SN LTM is initiated by the MN 110.

As shown in FIG. 2, during the preparation of inter-SN LTM, the MN 110 may transmit 210, to a candidate SN (e.g., each candidate SN) in a set of candidate SNs, a request for resource allocation for a LTM cell switch comprising LTM information for a LTM cell switch (also referred to as first LTM information herein) . In some embodiments, the MN 110 may transmit, to each of the SNs 130, 140 and 150, an SN addition request message comprising the first LTM information. It is to be understood that any other suitable messages may also be feasible.

In some embodiments, the first LTM information may comprise at least one of the following: an indicator (also referred to as a LTM indicator herein) indicating that the request is for the LTM cell switch, a list (also referred to as a LTM configuration ID mapping list herein) of mappings between cell identities and LTM configuration identities, a channel state information (CSI) resource configuration, or early synchronization request information.

As shown in FIG. 2, upon reception of the request comprising the first LTM information, each candidate SN may transmit 220, to the MN 110, LTM information of a LTM candidate PSCell in a set of LTM candidate PSCells provided by the candidate SN (also referred to as second LTM information herein) . In some embodiments, the LTM information may comprise LTM configuration associated with the LTM candidate PSCell. In some embodiments, each of the SNs 130, 140 and 150 may transmit, to the MN 110, an SN addition request acknowledge message comprising the second LTM information. It is to be understood that any other suitable messages may also be feasible.

In some embodiments, the second LTM information may comprise at least one of the following: a synchronization signal block (SSB) configuration, a transmission configuration indication (TCI) related configuration, or an early synchronization related configuration.

In other words, the MN 110 may request the candidate SN (s) to allocate resources for the terminal device 120 by means of the SN addition procedure, indicating that the request is for the LTM cell switch, and comprising the first LTM information (including e.g., the LTM indicator, the LTM configuration ID mapping list, the CSI resource configuration, the early syn request information, etc. ) . The MN 110 may also provide candidate cells recommended by the MN 110 via the latest measurement results for the candidate SN (s) to choose and configure the SCG cell (s) , provide an upper limit for the number of PSCells that can be prepared by each candidate SN, and provide a list of secondary key (e.g., K_SN) and associated counter (e.g., sk-Counter) values for each candidate SN. In the SN addition procedure, the MN 110 may also include information of other candidate SN (s) , and for each candidate SN, a list of cells recommended by the MN 110 via the latest measurement results for the candidate SN to select the PSCell (s) for the following execution of subsequent LTM cell switch. Within the list of cells as indicated within the measurement results indicated by the MN 110, the candidate SN may decide the list of PSCell (s) to prepare (considering the maximum number indicated by the MN 110) and, for each prepared PSCell, the candidate SN may decide other SCG SCells and provide a corresponding SCG radio resource configuration to the MN 110 in a NR RRC reconfiguration message and a second LTM information (includes e.g., SSB configuration, TCI related configuration, and early synchronization configuration) for the prepared LTM candidate PSCell contained in the SN addition request acknowledge message with the prepared PSCell ID (s) . If data forwarding is needed, the candidate SN may provide data forwarding addresses to the MN 110. The candidate SN may also propose data forwarding to the MN 110 or other candidate SN (s) for LTM PSCell switch. The candidate SN may include an indication of a complete or delta RRC configuration with respect to a SCG reference configuration.

With reference to FIG. 2, in some embodiments, for SN terminated bearers using MCG resources, the MN 110 may provide 230 Xn-U DL transport network layer (TNL) address information in a Xn-U address indication message to each of the candidate SNs 130, 140 and 150.

Continuing to refer to FIG. 2, the MN 110 may transmit 240, to each candidate SN (also refer to as a first candidate SN herein) , LTM information of a LTM candidate PSCell in a further set of LTM candidate PSCells provided by other candidate SN (s) (also referred to as third LTM information herein) . In some embodiments, the MN 110 may transmit, to each of the SNs 130, 140 and 150, an SN modification request message comprising the third LTM information. It is to be understood that any other suitable messages may also be feasible.

In some embodiments, the third LTM information may comprise at least one of the following: a list of mappings between cell identities and LTM configuration identities, a CSI resource configuration, or an early synchronization related configuration for a candidate PSCell in the further set of LTM candidate PSCells.

As shown in FIG. 2, each candidate SN may transmit 250, to the MN 110, LTM information for an execution of a subsequent LTM cell switch or for updating configurations of candidate PSCells (also referred to as fourth LTM information herein) . In some embodiments, each of the SNs 130, 140 and 150 may transmit, to the MN 110, an SN modification request acknowledge message comprising the fourth LTM information. It is to be understood that any other suitable messages may also be feasible.

In some embodiments, the fourth LTM information may comprise a TCI related configuration. It is to be understood that the fourth LTM information may comprise any other suitable information.

In other words, for each candidate SN, the MN 110 may initiate the SN modification procedure towards the candidate SN to inform the third LTM information (including LTM configuration ID mapping list, early synchronization configuration, CSI resource configuration) of prepared PSCells in other candidate SN (s) . If requested, the candidate SN may send an SN modification request acknowledge message and if needed, provide the updated candidate SCG configuration (s) and/or the fourth LTM information (including e.g., TCI related configuration) for the following execution of subsequent LTM cell switch or for updating the configurations of candidate PSCell to the MN 110. For each candidate SN, the MN 110 may be required to initiate the SN modification procedure to the candidate SN only if the list proposed by the candidate SN is different from the prepared PSCells list. If all proposed PSCells by a candidate SN were prepared, the MN 110 may not be required to initiate the SN modification procedure to the candidate SN.

With reference to FIG. 2, the MN 110 may transmit 260, to the terminal device 120, a RRC reconfiguration message including a LTM configuration. The terminal device 120 may apply the RRC reconfiguration message received, and reply 270 to the MN 110 with a RRC reconfiguration complete message.

With the process 200, a MN-initiated preparation of inter-SN LTM PSCell switch may be carried out. It is to be understood that steps and an order of the steps in FIG. 2 are merely for illustration, and not for limitation. For example, the order of the steps may be changed. Some of the steps may be omitted or any other suitable steps may be added.

FIG. 3 illustrates a signaling chart illustrating an example process 300 of a SN-initiated preparation of inter-SN LTM according to embodiments of the present disclosure. For the purpose of discussion, the process 300 will be described with reference to FIG. 1. The process 300 may involve the terminal device 120, the MN 110, the SNs 130, 140 and 150. In this example, the SNs 130, 140 and 150 are candidate SNs and the SN 130 is a source SN serving the terminal device 120. The preparation of the inter-SN LTM is initiated by the SN 130.

As shown in FIG. 3, during the preparation of inter-SN LTM, the SN 130 (i.e., source SN) may transmit 310, to the MN 110, an indication (also referred to as a LTM initiation indication herein) for initiating a LTM. In some embodiments, the SN 130 may transmit a SN change required message containing the LTM initiation indication. The SN change required message may also contain candidate node ID (s) and may include a SCG reference configuration (to support delta configuration) , and contain measurements results which may include cells that are not LTM candidates. The SN change required message may also include a list of proposed PSCell candidates recommended by the source SN, an upper limit for the number of PSCells that can be prepared by each candidate SN, and may also include SCG measurement configurations for LTM.

With reference to FIG. 3, based on reception of the LTM initiation indication, the MN 110 may transmit 320, to a candidate SN (e.g., each candidate SN) in a set of candidate SNs, a request for resource allocation for a LTM cell switch comprising first LTM information for a LTM cell switch. In some embodiments, the MN 110 may transmit, to each of the SNs 130, 140 and 150, an SN addition request message comprising the first LTM information. It is to be understood that any other suitable messages may also be feasible.

As shown in FIG. 3, upon reception of the request comprising the first LTM information, each candidate SN may transmit 330, to the MN 110, second LTM information LTM information of a LTM candidate PSCell in a set of LTM candidate PSCells provided by the candidate SN. In some embodiments, each of the SNs 130, 140 and 150 may transmit, to the MN 110, an SN addition request acknowledge message comprising the second LTM information. It is to be understood that any other suitable messages may also be feasible.

With reference to FIG. 3, in some embodiments, for SN terminated bearers using MCG resources, the MN 110 may provide 340 Xn-U DL TNL address information in a Xn-U address indication message to each of the candidate SNs 130, 140 and 150.

Continuing to refer to FIG. 3, the MN 110 may transmit 350, to each candidate SN (i.e., the first candidate SN) , third LTM information of a LTM candidate PSCell in a further set of LTM candidate PSCells provided by other candidate SN (s) (i.e., second candidate SN(s) ) . In some embodiments, the MN 110 may transmit, to each of the candidate SNs 130, 140 and 150, an SN modification request message comprising the third LTM information. It is to be understood that any other suitable messages may also be feasible.

As shown in FIG. 3, each candidate SN may transmit 360, to the MN 110, fourth LTM information for an execution of a subsequent LTM cell switch or for updating configurations of candidate PSCells. In some embodiments, each of the candidate SNs 130, 140 and 150 may transmit, to the MN 110, an SN modification request acknowledge message comprising the fourth LTM information. It is to be understood that any other suitable messages may also be feasible.

With reference to FIG. 3, the MN 110 may transmit 370, to the terminal device 120, a RRC reconfiguration message including a LTM configuration. The terminal device 120 may apply the RRC reconfiguration message received, and reply 380 to the MN 110 with a RRC reconfiguration complete message. As shown in FIG. 3, if a SN RRC response message is included in the MN RRC reconfiguration complete message, the MN 110 may inform 390 the SN 130 (i.e., source SN) with the SN RRC reconfiguration complete message via a SN change confirm message. It is to be understood that any other suitable messages may also be feasible.

With the process 300, a SN-initiated preparation of inter-SN LTM PSCell switch may be carried out. It is to be understood that other details of the process 300 are the same as that described for the process 200, and thus are not repeated here for conciseness. It is also to be understood that steps and an order of the steps in FIG. 3 are merely for illustration, and not for limitation. For example, the order of the steps may be changed. Some of the steps may be omitted or any other suitable steps may be added.

EXAMPLE IMPLEMENTATION OF EARLY SYNCHRONIZATION OF INTER-SN LTM

For inter-SN LTM, it is still unclear which node triggers early synchronization of inter-SN LTM PSCell switch, and how does network devices coordinate with each other for the early synchronization of inter-SN LTM PSCell switch. Embodiments of the present disclosure provide solutions of early synchronization of inter-SN LTM PSCell switch.

FIG. 4 illustrates a signaling chart illustrating an example process 400 of a MN-initiated early synchronization of inter-SN LTM according to embodiments of the present disclosure. For the purpose of discussion, the process 400 will be described with reference to FIG. 1. The process 400 may involve the terminal device 120, the MN 110, the SNs 130 and 140. In this example, the SNs 130 and 140 are candidate SNs, and the SN 130 also is a serving or source SN. Early synchronization of inter-SN LTM is initiated by the MN 110.

As shown in FIG. 4, for a random access procedure towards a LTM candidate cell for early uplink (UL) timing advance (TA) acquisition, the MN 110 may transmit 410, to the terminal device 120, a physical downlink control channel (PDCCH) order comprising a contention free random access (CFRA) configuration, e.g., RA preamble assignment, ID of a candidate PSCell of a candidate SN (e.g., the SN 140) , SSB to be used, uplink carrier, PRACH mask index, etc. Based on reception of the PDCCH order, the terminal device 120 may transmit 420 a preamble (e.g., MSG1) towards the candidate PSCell of SN 140, without monitoring for a response from SN 140.

As shown in FIG. 4, the SN 140 may transmit 430, to the MN 110, TA information associated with the candidate PSCell, e.g., via a Xn message. In some embodiments, the TA information may include at least one of the following: a TA value, associated CFRA resource information, an ID of the candidate PSCell, validity time of the TA value (e.g., a time alignment timer) , an ID of the MN 110 (e.g., MN gNB-ID) , or an ID of a DU of the MN 110 (e.g., MN gNB-DU ID) .

With reference to FIG. 4, the MN 110 may transmit 440, to the terminal device 120, a TA command associated with the candidate PSCell of the candidate SN, e.g., via a medium access control (MAC) control element (CE) . In some embodiments, the TA command may be used to control the amount of timing adjustment for the candidate PSCell, and may be a 12-bits value or 6-bits value. In some embodiments, the MAC CE may be a LTM cell switch command MAC CE, a timing advance command MAC CE, an absolute timing advance command MAC CE or a newly defined MAC CE.

With the process 400, a MN-initiated early synchronization of inter-SN LTM PSCell switch may be carried out. It is to be understood that steps and an order of the steps in FIG. 4 are merely for illustration, and not for limitation. For example, the order of the steps may be changed. Some of the steps may be omitted or any other suitable steps may be added.

FIG. 5 illustrates a signaling chart illustrating an example process 500 of a SN-initiated early synchronization of inter-SN LTM according to embodiments of the present disclosure. For the purpose of discussion, the process 500 will be described with reference to FIG. 1. The process 500 may involve the terminal device 120, the MN 110, the SNs 130 and 140. In this example, the SNs 130 and 140 are candidate SNs, and the SN 130 also is a serving or source SN. Early synchronization of inter-SN LTM is initiated by the SN 130.

As shown in FIG. 5, for a random access procedure towards a LTM candidate cell for early UL TA acquisition, the SN 130 (i.e., source SN) may transmit 510, to the terminal device 120, a PDCCH order comprising a CFRA configuration, e.g., RA preamble assignment, ID of a candidate PSCell of a candidate SN (e.g., the SN 140) , SSB to be used, uplink carrier, PRACH mask index, etc. Based on reception of the PDCCH order, the terminal device 120 may transmit 520 a preamble (e.g., MSG1) towards the candidate PSCell of the SN 140, without monitoring for a response from the SN 140.

As shown in FIG. 5, the SN 140 may transmit 530, to the SN 130 via the MN 110, further TA information associated with the candidate PSCell. In some embodiments, the further TA information may comprise at least one of the following: a TA value, information of a CFRA resource associated with the candidate PSCell, an ID of the candidate PSCell, validity time of the TA value, an identity of the SN 130 (e.g., source-SN gNB-ID) , or an identity of a DU of the SN 130.

With reference to FIG. 5, in some embodiments, the SN 140 may transmit 531, to the MN 110, first TA information associated with the candidate PSCell, e.g., via a Xn message. In some embodiments, the first TA information may include at least one of the following: a TA value, associated CFRA resource information, an ID of the candidate PSCell, validity time of the TA value (e.g., a time alignment timer) , an ID of the SN 130 (e.g., source-SN gNB-ID) or an ID of a DU of the SN 130 (e.g., source SN gNB-DU ID) . Then the MN 110 may transmit 532, to the SN 130, second TA information associated with the candidate PSCell, e.g., via a Xn message. In some embodiments, the second TA information may include at least one of the following: a TA value, associated CFRA resource information, an ID of the candidate PSCell, validity time of the TA value (e.g., a time alignment timer) , or an ID of a DU of the SN 130 (e.g., source SN gNB-DU ID) .

Continuing to refer to FIG. 5, the SN 130 may transmit 540, to the terminal device 120, a TA command associated with the candidate PSCell of the candidate SN, e.g., via a MAC CE. In some embodiments, the TA command may be used to control the amount of timing adjustment for the candidate PSCell, and may be a 12-bits value or 6-bits value. In some embodiments, the MAC CE may be a LTM cell switch command MAC CE, a timing advance command MAC CE, an absolute timing advance command MAC CE or a newly defined MAC CE.

With the process 500, a SN-initiated early synchronization of inter-SN LTM PSCell switch may be carried out. It is to be understood that steps and an order of the steps in FIG. 5 are merely for illustration, and not for limitation. For example, the order of the steps may be changed. Some of the steps may be omitted or any other suitable steps may be added.

EXAMPLE IMPLEMENTATION OF CELL SWITCH EXECUTION OF INTER-SN LTM

For inter-SN LTM, it is still unclear which node triggers execution of inter-SN LTM PSCell switch, and how does network devices coordinate with each other for the execution of inter-SN LTM PSCell switch. Embodiments of the present disclosure provide solutions of execution of inter-SN LTM PSCell switch.

FIG. 6 illustrates a signaling chart illustrating an example process 600 of a MN-initiated initial PSCell switch execution of inter-SN LTM according to embodiments of the present disclosure. For the purpose of discussion, the process 600 will be described with reference to FIG. 1. The process 600 may involve the terminal device 120, the MN 110, the SNs 130, 140 and 150. The SNs 130, 140 and 150 are candidate SNs. In this example, the SN 130 is a target SN (also referred to as candidate target SN herein) providing a target PSCell (also referred to as a candidate target PSCell herein) . An initial PSCell switch of inter-SN LTM PSCell switch may be initiated by the MN 110. It is to be noted that the inter-SN LTM PSCell switch may be an MN-initiated or SN-initiated LTM PSCell switch.

As shown in FIG. 6, the MN 110 may determine 601 that a LTM cell switch to the target PSCell is to be executed. In other words, the MN 110 may decide to execute the LTM cell switch to the target PSCell.

With reference to FIG. 6, the MN 110 may transmit 602, to the terminal device 120, a command for the LTM cell switch. For example, the MN 110 may transmit the command via a MAC CE, e.g., LTM cell switch command MAC CE.

With reference to FIG. 6, the MN 110 may transmit 603, to the SN 130 (i.e., target SN) , a notification that the command is transmitted to the terminal device 120. In some embodiments, the MN 110 may transmit a Xn message to the SN 130 to indicate the initiation of the LTM cell switch command to the terminal device 120. In some embodiments, the notification or the Xn message may include an ID of the target PSCell, a TCI state ID, TA information of other candidate PSCells, and a secondary key (i.e., SN security key or K_SN) . The TA information of other candidate PSCells may include at least one of a TA value, or validly time of the TA value (e.g., a time alignment timer) .

As shown in FIG. 6, after reception of the LTM cell switch command, the terminal device 120 may apply a candidate configuration associated with the target PSCell, and transmit 604, to the MN 110, a MN RRC reconfiguration complete message (also referred to as RRC reconfiguration complete message to the MN in the disclosure) comprising a SN RRC reconfiguration complete message (also referred to as RRC reconfiguration complete message to the SN in the disclosure) and a security key counter (e.g., sk-counter) value.

Then the MN 110 may inform 605 the SN 130 of the target PSCell (i.e. the target SN) that the terminal device 120 has completed the reconfiguration procedure successfully via a SN reconfiguration complete message. The SN reconfiguration complete message may include the SN RRC reconfiguration complete message, a selected sk-counter value or a secondary key (i.e., SN security key or K_SN) .

With reference to FIG. 6, the terminal device 120 may perform 606 a random access procedure towards the target PSCell, if the terminal device 120 does not have valid TA of the target PSCell. It is to be noted that an order of transmitting the MN RRC reconfiguration complete message and performing the random access procedure towards the target PSCell or the SCG is not defined.

With reference to FIG. 6, if a packet data convergence protocol (PDCP) termination point is changed to the target SN for bearers using radio link control (RLC) acknowledgement mode (AM) , the MN 110 may transmit 607 a SN status transfer message to the SN 140 (i.e., the target SN) . The MN 110 may perform 608 data forwarding to the SN 140 (i.e., the target SN) from the MN 110.

Continuing to refer to FIG. 6, the MN 110 may transmit 609 a Xn-U address indication message to the SN 140 (i.e., the target SN) . The SN 130 (i.e., the target SN) may decide to perform early data forwarding for SN-terminated bearers, together with a transmission of an early status transfer message to the MN 110 (not shown) . As shown in FIG. 6, the SN 130 may perform 610 the early data forwarding to other candidate SNs (e.g., the SN 140 and 150) .

With the process 600, an execution of a MN-initiated initial PSCell switch of inter-SN LTM PSCell switch may be carried out. It is to be understood that steps and an order of the steps in FIG. 6 are merely for illustration, and not for limitation. For example, the order of the steps may be changed. Some of the steps may be omitted or any other suitable steps may be added.

FIG. 7 illustrates a signaling chart illustrating an example process 700 of a MN-initiated subsequent PSCell switch execution of inter-SN LTM according to embodiments of the present disclosure. For the purpose of discussion, the process 700 will be described with reference to FIG. 1. The process 700 may involve the terminal device 120, the MN 110, the SNs 130, 140 and 150. The SNs 130, 140 and 150 are candidate SNs. In this example, the SN 130 is a serving or source SN providing a source PSCell, and the SN 140 is a target SN providing a target PSCell. A subsequent PSCell switch of inter-SN LTM PSCell switch may be initiated by the MN 110. It is to be noted that the inter-SN LTM PSCell switch may be an MN-initiated or SN-initiated LTM PSCell switch.

As shown in FIG. 7, the MN 110 may determine 701 that a LTM cell switch from the source PSCell to the target PSCell is to be executed. In other words, the MN 110 may decide to execute the LTM cell switch to the target PSCell.

With reference to FIG. 7, the MN 110 may transmit 702, to the terminal device 120, a command for the LTM cell switch. For example, the MN 110 may transmit the command via a MAC CE.

With reference to FIG. 7, the MN 110 may transmit 703, to the SN 140 (i.e., target SN) , a notification that the command is transmitted to the terminal device 120. In some embodiments, the MN 110 may transmit a Xn message to the SN 140 to indicate the initiation of the LTM cell switch command to the terminal device 120. In some embodiments, the notification or the Xn message may include an ID of the target PSCell, a TCI state ID, TA information of other candidate PSCells, and a secondary key (i.e., SN security key, or K_SN) . The TA information of other candidate PSCells may include at least one of a TA value, or validly time of the TA value (e.g., a time alignment timer) .

As shown in FIG. 7, after reception of the LTM cell switch command, the terminal device 120 may apply a candidate configuration associated with the target PSCell, and transmit 704, a MN RRC reconfiguration complete message comprising a SN RRC reconfiguration complete message and a security key counter (e.g., sk-counter) value.

Then the MN 110 may inform 705 the SN 140 of the target PSCell (i.e. the target SN) that the terminal device 120 has completed the reconfiguration procedure successfully via a SN reconfiguration complete message. The SN reconfiguration complete message may include the SN RRC reconfiguration complete message, a selected sk-counter value or a secondary key (i.e., SN security key, or K_SN) .

With reference to FIG. 7, the terminal device 120 may perform 706 a random access procedure towards the target PSCell, if the terminal device 120 does not have valid TA of the target PSCell. It is to be noted that an order of transmitting the MN RRC reconfiguration complete message and performing the random access procedure towards the target PSCell or the SCG is not defined.

With reference to FIG. 7, the MN 110 may transmit 707, to the SN 130 (i.e., source SN) , a SN modification request to the last serving/source SN to inform the source SN to stop providing user data to the terminal device 120, to switch to a prepared state, and if applicable, to allow provisioning of new data forwarding addresses. The MN 110 may receive 708 a SN modification request acknowledge message from the source SN.

As shown in FIG. 7, the MN 110 may trigger 709 a Xn-U address indication procedure to inform the last serving/source SN of an address of the SN 140 of the target PSCell to start late data forwarding. If a PDCP termination point is changed for bearers using RLC AM, the SN 130 (i.e., source SN) may transmit 710 a SN status transfer message to the MN 110. As shown in FIG. 7, if a PDCP termination point is changed to the target SN for bearers using RLC AM, the MN 110 may transmit 711 a SN status transfer message to the SN 140 (i.e., the target SN) . The SN 130 (i.e., source SN) may perform 712, via the MN 110, data forwarding to the SN 140 (i.e., the target SN) from the last serving SN.

Continuing to refer to FIG. 7, the MN 110 may transmit 713 a Xn-U address indication message to the SN 140 (i.e., the target SN) . The SN 140 (i.e., the target SN) may decide to perform early data forwarding for SN-terminated bearers, together with a transmission of an early status transfer message to the MN 110 (not shown) . As shown in FIG. 7, the SN 140 may perform 714 the early data forwarding to other candidate SNs (e.g., the SN 130 and 150) .

With the process 700, a MN-initiated subsequent PSCell switch execution of inter-SN LTM PSCell switch may be carried out. It is to be understood that steps and an order of the steps in FIG. 7 are merely for illustration, and not for limitation. For example, the order of the steps may be changed. Some of the steps may be omitted or any other suitable steps may be added.

FIG. 8 illustrates a signaling chart illustrating an example process 800 of a SN-initiated initial or subsequent PSCell switch execution of inter-SN LTM according to embodiments of the present disclosure. For the purpose of discussion, the process 800 will be described with reference to FIG. 1. The process 800 may involve the terminal device 120, the MN 110, the SNs 130, 140 and 150. The SNs 130, 140 and 150 are candidate SNs. In this example, the SN 130 is a serving or source SN providing a source PSCell, and the SN 140 is a target SN providing a target PSCell. An initial or subsequent PSCell switch of inter-SN LTM PSCell switch may be initiated by the SN 130. It is to be noted that the inter- SN LTM PSCell switch may be an MN-initiated or SN-initiated LTM PSCell switch.

As shown in FIG. 8, the SN 130 may determine 801 that a LTM cell switch from the source PSCell to the target PSCell is to be executed. In other words, the SN 130 may decide to execute the LTM cell switch to the target PSCell.

With reference to FIG. 8, the SN 130 may transmit 802, to the terminal device 120, a command for the LTM cell switch. For example, the SN 130 may transmit the command via a MAC CE, e.g., LTM cell switch command MAC CE.

The SN 130 may transmit, to the SN 140 (i.e., target SN) via the MN 110, a notification that the command is transmitted to the terminal device 120. As shown in FIG. 8, in some embodiments, the SN 130 may transmit 803 a first Xn message to the MN 110 to indicate the initiation of the LTM cell switch command to the terminal device 120. Then the MN 110 may transmit 804 a second Xn message to the SN 140 to indicate the initiation of the LTM cell switch command to the terminal device 120. For example, the first Xn message may be a SN-MN cell switch notification message, and the second Xn message may be a MN-SN cell switch notification message. It is to be understood that any other suitable messages may also be feasible.

In some embodiments, the first Xn message may include an ID of the target PSCell, a TCI state ID, TA information of other candidate PSCells, and a secondary key (i.e., SN security key or K_SN) . The TA information of other candidate PSCells may include at least one of a TA value, or validly time of the TA value (e.g., a time alignment timer) .

In some embodiments, the second Xn message may include an ID of the target PSCell, a TCI state ID, TA information of other candidate PSCells, and a secondary key (i.e., SN security key) . The TA information of other candidate PSCells may include at least one of a TA value, or validly time of the TA value (e.g., a time alignment timer) .

As shown in FIG. 8, after reception of the LTM cell switch command, the terminal device 120 may transmit 805, to the MN 110, a RRC reconfiguration complete message comprising an ID of a LTM candidate configuration (e.g., LTM-CandidateId) associated with the target PSCell or an ID of the target PSCell (e.g., physical cell ID) . For example, upon reception of the LTM cell switch command, the terminal device 120 may apply a RRC reconfiguration in the LTM candidate configuration associated with the target PSCell, and transmit, to the MN 110, the RRC reconfiguration complete message comprising a SN RRC reconfiguration complete message and the ID of the LTM candidate configuration associated with the target PSCell or the ID of the target PSCell.

Then the MN 110 may inform 806 the SN 140 of the target PSCell (i.e. the target SN) that the terminal device 120 has completed the reconfiguration procedure successfully via a SN reconfiguration complete message. The SN reconfiguration complete message may include the SN RRC reconfiguration complete message, a selected sk-counter value or a secondary key (i.e., SN security key) .

With reference to FIG. 8, the terminal device 120 may perform 807 a random access procedure towards the target PSCell, if the terminal device 120 does not have valid TA of the target PSCell. It is to be noted that an order of transmitting the MN RRC reconfiguration complete message and performing the random access procedure towards the target PSCell or the SCG is not defined.

With reference to FIG. 8, the MN 110 may trigger 808 a Xn-U address indication procedure to inform the last serving/source SN of an address of the SN 140 of the target PSCell to start late data forwarding. If a PDCP termination point is changed for bearers using RLC AM, the SN 130 (i.e., source SN) may transmit 809 a SN status transfer message to the MN 110.

As shown in FIG. 8, if a PDCP termination point is changed to the target SN for bearers using RLC AM, the MN 110 may transmit 810 a SN status transfer message to the SN 140 (i.e., the target SN) . The SN 130 (i.e., source SN) may perform 811, via the MN 110, data forwarding to the SN 140 (i.e., the target SN) from the last serving SN.

Continuing to refer to FIG. 8, the MN 110 may transmit 812 a Xn-U address indication message to the SN 140 (i.e., the target SN) . The SN 140 (i.e., the target SN) may decide to perform early data forwarding for SN-terminated bearers, together with a transmission of an early status transfer message to the MN 110 (not shown) . As shown in FIG. 8, the SN 140 may perform 813 the early data forwarding to other candidate SNs (e.g., the SN 130 and 150) .

With the process 800, an execution of a SN-initiated initial or subsequent PSCell switch of an inter-SN LTM PSCell switch may be carried out. It is to be understood that steps and an order of the steps in FIG. 8 are merely for illustration, and not for limitation. For example, the order of the steps may be changed. Some of the steps may be omitted or any other suitable steps may be added.

It is to be understood that any of the processes 200 to 800 or operations of the processes 200 to 800 may be carried out separately or in any suitable combinations.

EXAMPLE IMPLEMENTATION OF METHODS

Accordingly, embodiments of the present disclosure provide methods of communication implemented at a first network device, a second network device and a terminal device. The first network device may be a MN or a source SN. The second network device may be a target or candidate SN. These methods will be described below with reference to FIGs. 9 to 11.

FIG. 9 illustrates a flowchart of an example method 900 of communication implemented at a first network device in accordance with some embodiments of the present disclosure. For example, the method 900 may be performed at the MN 110 or the SN 130 (source SN) as shown in FIG. 1. It is to be understood that the method 500 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard.

As shown in FIG. 9, at block 910, the first network device may determine that a LTM cell switch from a source PSCell to a target PSCell is to be executed.

At block 920, the first network device may transmit, to a terminal device (e.g., the terminal device 120) , a command for the LTM cell switch.

At block 930, the first network device may transmit, to a second network device providing the target PSCell, a notification that the command is transmitted to the terminal device.

In some embodiments, the first network device may be a MN (e.g., the MN 110) , and the second network device may be a target SN (e.g., the SN 140) . In this case, operations of the blocks 910 to 930 may be carried out as that described in the process 600 or 700. As such, a MN-initiated LTM PSCell switch execution may be carried out.

In some embodiments, the first network device may be a source SN (e.g., the SN 130) providing the source PSCell and the second network device is a target SN (e.g., the SN 140) providing the target PSCell. In these embodiments, the first network device may transmit the notification by transmitting the notification to the second network device via a MN (e.g., the MN 110) serving the terminal device 120. In this case, operations of the blocks 910 to 930 may be carried out as that described in the process 800. As such, a SN-initiated LTM PSCell switch execution may be carried out.

In some embodiments where the first network device is a MN and the second network device is a target SN, the first network device may transmit, to a first candidate SN providing a set of candidate PSCells, a request for resource allocation for the LTM cell switch, the request comprising first LTM information for the LTM cell switch; receive, from the first candidate SN, second LTM information of a LTM candidate PSCell in the set of LTM candidate PSCells; transmit, to the first candidate SN, third LTM information of a LTM candidate PSCell in a further set of LTM candidate PSCells provided by a second candidate SN in a set of second candidate SNs; and receive, from the first candidate SN, fourth LTM information for an execution of a subsequent LTM cell switch.

In some embodiments, the first LTM information may comprise at least one of an indicator indicating that the request is for the LTM cell switch, a list of mappings between cell identities and LTM configuration identities, a CSI resource configuration, or early sync request information. In some embodiments, the second LTM information may comprise at least one of a SSB configuration, a TCI related configuration, or an early sync related configuration. In some embodiments, the third LTM information may comprise at least one of a list of mappings between cell identities and LTM configuration identities, a CSI resource configuration, or an early sync related configuration for a candidate PSCell in the further set of LTM candidate PSCells. In some embodiments, the fourth LTM information may comprise the TCI related configuration. More details may be carried out as that described in the process 200. As such, a MN-initiated preparation of a LTM PSCell switch may be carried out.

In some embodiments where the first network device may be a source SN (e.g., the SN 130) providing the source PSCell and the second network device is a candidate/target SN (e.g., the SN 140) providing a candidate/target PSCell, the first network device may transmit to a MN (e.g., the MN 110) , an indication for initiating a LTM. Thereby, the MN may be caused to: transmit, to a first candidate SN providing a set of candidate PSCells, a request for resource allocation for the LTM cell switch, the request comprising first LTM information for the LTM cell switch; receive, from the first candidate SN, second LTM information of a LTM candidate PSCell in the set of LTM candidate PSCells; transmit, to the first candidate SN, third LTM information of a LTM candidate PSCell in a further set of LTM candidate PSCells provided by a second candidate SN in a set of second candidate SNs; and receive, from the first candidate SN, fourth LTM information for an execution of a subsequent LTM cell switch. More details may be carried out as that described in the process 300. As such, a SN-initiated preparation of a LTM PSCell switch may be carried out.

In some embodiments where the first network device is a MN and the second network device is a candidate SN providing a candidate PSCell, the first network device may receive, from the candidate SN, TA information associated with the candidate PSCell. In some embodiments, the TA information may comprise at least one of the following: a TA value, information of a CFRA resource associated with the candidate PSCell, an identity of the candidate PSCell, validity time of the TA value, an identity of the first network device, or an identity of a DU of the first network device. More details may be carried out as that described in the process 400. As such, a MN-initiated early synchronization of a LTM PSCell switch may be facilitated.

In some embodiments where the first network device may be a source SN (e.g., the SN 130) providing the source PSCell and the second network device is a candidate SN (e.g., the SN 140) providing a candidate PSCell, the first network device may receive, via a MN (e.g., the MN 110) , TA information associated with a candidate PSCell provided by the candidate SN. In some embodiments, the TA information may comprise at least one of the following: a TA value, information of a CFRA resource associated with the candidate PSCell, an identity of the candidate PSCell, validity time of the TA value, an identity of the first network device or an identity of a DU of the first network device. More details may be carried out as that described in the process 500. As such, a SN-initiated early synchronization of a LTM PSCell switch may be facilitated.

With the method 900, a behavior of an initiator of inter-SN LTM may be specified, and the inter-SN LTM may be enhanced.

FIG. 10 illustrates a flowchart of an example method 1000 of communication implemented at a second network device in accordance with some embodiments of the present disclosure. For example, the method 1000 may be performed at the SN 140 or 150 (target SN or candidate SN) as shown in FIG. 1. It is to be understood that the method 1000 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard.

As shown in FIG. 10, at block 1010, a second network device may receive, from a first network device, a notification that a command for a LTM cell switch from a source PSCell to a target PSCell is transmitted to a terminal device. The target PSCell is provided by the second network device.

In some embodiments, the first network device may be a MN (e.g., the MN 110) , and the second network device may be a target SN (e.g., the SN 140) . In this case, operations of the block 1010 may be carried out as that described in the process 600 or 700. As such, a MN-initiated LTM PSCell switch execution may be carried out.

In some embodiments, the first network device may be a source SN (e.g., the SN 130) providing the source PSCell and the second network device is a target SN (e.g., the SN 140) providing the target PSCell. In these embodiments, the second network device may receive the notification by receiving the notification from the first network device via a MN (e.g., the MN 110) serving the terminal device 120. In this case, operations of the block 1010 may be carried out as that described in the process 800. As such, a SN-initiated LTM PSCell switch execution may be carried out.

In some embodiments where the first network device is a MN and the second network device is a candidate SN (also referred to as a first candidate SN) providing a set of LTM candidate PSCells, the second network device may receive, from the first network device, a request for resource allocation for the LTM cell switch, the request comprising first LTM information for the LTM cell switch; transmit, to the first network device, second LTM information of a LTM candidate PSCell in the set of LTM candidate PSCells; receive, from the first network device, third LTM information of a LTM candidate PSCell in a further set of LTM candidate PSCells provided by a second candidate SN in a set of second candidate SNs; and transmit, to the first network device, fourth LTM information for an execution of a subsequent LTM cell switch.

In some embodiments where the first network device is a source SN and the second network device is a candidate SN (also referred to as a first candidate SN) providing a set of LTM candidate PSCells, the second network device may receive, from a MN, a request for resource allocation for the LTM cell switch, the request comprising first LTM information for the LTM cell switch; transmit, to the MN, second LTM information of a LTM candidate PSCell in the set of LTM candidate PSCells; receive, from the MN, third LTM information of a LTM candidate PSCell in a further set of LTM candidate PSCells provided by a second candidate SN in a set of second candidate SNs; and transmit, to the MN, fourth LTM information for an execution of a subsequent LTM cell switch. More details may be carried out as that described in the process 300. As such, a SN-initiated preparation of a LTM PSCell switch may be carried out.

In some embodiments where the first network device is a MN and the second network device is a candidate SN providing a candidate PSCell, the second network device may transmit, to the first network device, TA information associated with the candidate PSCell. In some embodiments, the TA information may comprise at least one of the following: a TA value, information of a CFRA resource associated with the candidate PSCell, an identity of the candidate PSCell, validity time of the TA value, an identity of the first network device, or an identity of a DU of the first network device. More details may be carried out as that described in the process 400. As such, a MN-initiated early synchronization of a LTM PSCell switch may be facilitated.

In some embodiments where the first network device may be a source SN (e.g., the SN 130) providing the source PSCell and the second network device is a candidate SN (e.g., the SN 140) providing a candidate PSCell, the second network device may transmit, to the first network device via a MN (e.g., the MN 110) , TA information associated with the candidate PSCell provided by the candidate SN. In some embodiments, the TA information may comprise at least one of the following: a TA value, information of a CFRA resource associated with the candidate PSCell, an identity of the candidate PSCell, validity time of the TA value, an identity of the first network device, or an identity of a DU of the first network device. More details may be carried out as that described in the process 500. As such, a SN-initiated early synchronization of a LTM PSCell switch may be facilitated.

With the method 1000, a behavior of a target or candidate SN of inter-SN LTM may be specified, and the inter-SN LTM may be enhanced.

FIG. 11 illustrates a flowchart of an example method 1100 of communication implemented at a terminal device in accordance with some embodiments of the present disclosure. For example, the method 1100 may be performed at the terminal device 120 as shown in FIG. 1. It is to be understood that the method 1100 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard.

As shown in FIG. 11, at block 1110, a terminal device (e.g., the terminal device 120) may receive, from a source SN (e.g., the SN 130) providing a source PSCell, a command for a LTM cell switch from the source PSCell to a target PSCell.

At block 1120, the terminal device may transmit, to a MN (e.g., the MN 110) , a RRC reconfiguration complete message comprising an identity of a LTM candidate configuration associated with the target PSCell or an identity of the target PSCell.

Operations of the blocks 1110 and 1120 may be carried out as that described in the process 800. As such, a SN-initiated LTM PSCell switch execution may be facilitated.

In some embodiments, the terminal device may receive a CFRA configuration from the MN, and transmit a preamble towards a candidate PSCell of a candidate SN. Other details may be carried out as that described in the process 400. As such, a MN-initiated early synchronization of a LTM PSCell switch may be facilitated.

In some embodiments, the terminal device may receive a CFRA configuration from the source SN, and transmit a preamble towards a candidate PSCell of a candidate SN. Other details may be carried out as that described in the process 500. As such, a SN-initiated early synchronization of a LTM PSCell switch may be facilitated.

With the method 1100, a behavior of a terminal device of inter-SN LTM may be specified, and the inter-SN LTM may be enhanced.

It is to be understood that operations of the methods 900 to 1100 correspond to that described with reference to FIGs. 2 to 8, and thus other details are not repeated here for conciseness.

EXAMPLE IMPLEMENTATION OF DEVICE

FIG. 12 is a simplified block diagram of a device 1200 that is suitable for implementing embodiments of the present disclosure. The device 1200 can be considered as a further example implementation of the terminal device 120 or the network device 110, 130, 140 or 150 as shown in FIG. 1. Accordingly, the device 1200 can be implemented at or as at least a part of the terminal device 120 or the network device 110, 130, 140 or 150.

As shown, the device 1200 includes a processor 1210, a memory 1220 coupled to the processor 1210, a suitable transceiver 1240 coupled to the processor 1210, and a communication interface coupled to the transceiver 1240. The memory 1210 stores at least a part of a program 1230. The transceiver 1240 may be for bidirectional communications or a unidirectional communication based on requirements. The transceiver 1240 may include at least one of a transmitter 1242 or a receiver 1244. The transmitter 1242 and the receiver 1244 may be functional modules or physical entities. The transceiver 1240 has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2/Xn interface for bidirectional communications between eNBs/gNBs, S1/NG interface for communication between a Mobility Management Entity (MME) /Access and Mobility Management Function (AMF) /SGW/UPF and the eNB/gNB, Un interface for communication between the eNB/gNB and a relay node (RN) , or Uu interface for communication between the eNB/gNB and a terminal device.

The program 1230 is assumed to include program instructions that, when executed by the associated processor 1210, enable the device 1200 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to FIGs. 1 to 11. The embodiments herein may be implemented by computer software executable by the processor 1210 of the device 1200, or by hardware, or by a combination of software and hardware. The processor 1210 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1210 and memory 1220 may form processing means 1250 adapted to implement various embodiments of the present disclosure.

The memory 1220 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 1220 is shown in the device 1200, there may be several physically distinct memory modules in the device 1200. The processor 1210 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1200 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.

In some embodiments, a first network device comprises a circuitry configured to: determine that a LTM cell switch from a source PSCell to a target PSCell is to be executed; transmit, to a terminal device, a command for the LTM cell switch; and transmit, to a second network device providing the target PSCell, a notification that the command is transmitted to the terminal device.

In some embodiments, a second network device comprises a circuitry configured to: receive, from a first network device, a notification that a command for a LTM cell switch from a source PSCell to a target PSCell is transmitted to a terminal device, the target PSCell being provided by the second network device.

In some embodiments, a terminal device comprises a circuitry configured to: receive, from a source SN providing a source PSCell, a command for a LTM cell switch from the source PSCell to a target PSCell; and transmit, to a MN, a RRC reconfiguration complete message comprising an identity of a LTM candidate configuration associated with the target PSCell or an identity of the target PSCell.

The term ‘circuitry’ used herein may refer to hardware circuits and/or combinations of hardware circuits and software. For example, the circuitry may be a combination of analog and/or digital hardware circuits with software/firmware. As a further example, the circuitry may be any portions of hardware processors with software including digital signal processor (s) , software, and memory (ies) that work together to cause an apparatus, such as a terminal device or a network device, to perform various functions. In a still further example, the circuitry may be hardware circuits and or processors, such as a microprocessor or a portion of a microprocessor, that requires software/firmware for operation, but the software may not be present when it is not needed for operation. As used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (s) or a portion of a hardware circuit or processor (s) and its (or their) accompanying software and/or firmware.

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

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to FIGs. 1 to 11. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

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

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine 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 machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

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

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

Claims

A first network device comprising:

a processor configured to cause the first network device to:

determine that a layer 1 or layer 2 triggered mobility (LTM) cell switch from a source primary secondary cell (PSCell) to a target PSCell is to be executed;

transmit, to a terminal device, a command for the LTM cell switch; and

transmit, to a second network device providing the target PSCell, a notification that the command is transmitted to the terminal device.
The first network device of claim 1, wherein the first network device is a master node (MN) , and the second network device is a target secondary node (SN) providing the target PSCell.
The first network device of claim 2, wherein the first network device is further caused to:

transmit, to a first candidate SN providing a set of candidate PSCells, a request for resource allocation for the LTM cell switch, the request comprising first LTM information for the LTM cell switch;

receive, from the first candidate SN, second LTM information of a LTM candidate PSCell in the set of LTM candidate PSCells;

transmit, to the first candidate SN, third LTM information of a LTM candidate PSCell in a further set of LTM candidate PSCells provided by a second candidate SN in a set of second candidate SNs; and

receive, from the first candidate SN, fourth LTM information for an execution of a subsequent LTM cell switch.
The first network device of claim 3, wherein the first LTM information comprises at least one of an indicator indicating that the request is for the LTM cell switch, a list of mappings between cell identities and LTM configuration identities, a channel state information (CSI) resource configuration, or early sync request information, or

wherein the second LTM information comprises at least one of a synchronization signal block (SSB) configuration, a transmission configuration indication (TCI) related configuration, or an early sync related configuration, or

wherein the third LTM information comprises at least one of a list of mappings between cell identities and LTM configuration identities, a channel state information (CSI) resource configuration, or an early sync related configuration for a candidate PSCell in the further set of LTM candidate PSCells, or

wherein the fourth LTM information comprises the TCI related configuration.
The first network device of claim 2, wherein the first network device is further caused to:

receive, from a candidate SN providing a candidate PSCell, timing advance (TA) information associated with the candidate PSCell.
The first network device of claim 1, wherein the first network device is a source secondary node (SN) providing the source PSCell, and the second network device is a target SN providing the target PSCell, and wherein the first network device is caused to transmit the notification by:

transmitting the notification to the second network device via a master node (MN) .
The first network device of claim 6, wherein the first network device is further caused to:

transmit, to a master node (MN) , an indication for initiating a LTM.
The first network device of claim 6, wherein the first network device is further caused to:

receive, via a master node (MN) , timing advance (TA) information associated with a candidate PSCell provided by a candidate SN.
The first network device of claim 5 or 8, wherein the TA information comprises at least one of the following:

a TA value,

information of a contention free random access (CFRA) resource associated with the candidate PSCell,

an identity of the candidate PSCell,

validity time of the TA value,

an identity of the first network device, or

an identity of a distributed unit (DU) of the first network device.
A second network device comprising:

a processor configured to cause the second network device to:

receive, from a first network device, a notification that a command for a layer 1 or layer 2 triggered mobility (LTM) cell switch from a source primary secondary cell (PSCell) to a target PSCell is transmitted to a terminal device, the target PSCell being provided by the second network device.
The second network device of claim 10, wherein the first network device is a master node (MN) , and the second network device is a target secondary node (SN) providing the target PSCell.
The second network device of claim 11, wherein the second network device also serves as a first candidate SN, and the second network device is further caused to:

receive, from the first network device, a request for resource allocation for the LTM cell switch, the request comprising first LTM information for the LTM cell switch;

transmit, to the first network device, second LTM information of a LTM candidate PSCell in a set of LTM candidate PSCells provided by the first candidate SN;

receive, from the first network device, third LTM information of a LTM candidate PSCell in a further set of LTM candidate PSCells provided by a second candidate SN in a set of second candidate SNs; and

transmit, to the first network device, fourth LTM information for an execution of a subsequent LTM cell switch.
The second network device of claim 12, wherein the first LTM information comprises at least one of an indicator indicating that the request is for the LTM cell switch, a list of mappings between cell identities and LTM configuration identities, a channel state information (CSI) resource configuration, or early sync request information, or

wherein the second LTM information comprises at least one of a synchronization signal block (SSB) configuration, a transmission configuration indication (TCI) related configuration, or an early sync related configuration, or

wherein the third LTM information comprises at least one of a list of mappings between cell identities and LTM configuration identities, a channel state information (CSI) resource configuration, or an early sync related configuration for a candidate PSCell in the further set of LTM candidate PSCells, or

wherein the fourth LTM information comprises the TCI related configuration.
The second network device of claim 11, wherein the second network device also serves as a candidate SN, and the second network device is further caused to:

transmit, to the first network device, timing advance (TA) information associated with a candidate PSCell provided by the candidate SN.
The second network device of claim 10, wherein the first network device is a source secondary node (SN) providing the source PSCell, and the second network device is a target SN providing the target PSCell, and wherein the second network device is caused to receive the notification by:

receiving the notification from the first network device via a master node (MN) .
The second network device of claim 15, wherein the second network device also serves as a candidate SN, and wherein the second network device is further caused to:

transmit, to the first network device via a master node (MN) , timing advance (TA) information associated with a candidate PSCell provided by the candidate SN.
The second network device of claim 14 or 16, wherein the TA information comprises at least one of the following:

a TA value,

information of a contention free random access (CFRA) resource associated with the candidate PSCell,

an identity of the candidate PSCell,

validity time of the TA value,

an identity of the first network device, or

an identity of a distributed unit (DU) of the first network device.
A terminal device comprising:

a processor configured to cause the terminal device to:

receive, from a source secondary node (SN) providing a source primary secondary cell (PSCell) , a command for a layer 1 or layer 2 triggered mobility (LTM) cell switch from the source PSCell to a target PSCell; and

transmit, to a master node (MN) , a radio resource control (RRC) reconfiguration complete message comprising an identity of a LTM candidate configuration associated with the target PSCell or an identity of the target PSCell.
The terminal device of claim 18, wherein the terminal device is further caused to:

receive, from the MN or the source SN, a contention free random access (CFRA) configuration; and

transmit a preamble towards a candidate PSCell of a candidate SN.
A method of communication comprising:

determining, at a first network device, that a layer 1 or layer 2 triggered mobility (LTM) cell switch from a source primary secondary cell (PSCell) to a target PSCell is to be executed;

transmitting, to a terminal device, a command for the LTM cell switch; and

transmitting, to a second network device providing the target PSCell, a notification that the command is transmitted to the terminal device.
A method of communication comprising:

receiving, at a second network device and from a first network device, a notification that a command for a layer 1 or layer 2 triggered mobility (LTM) cell switch from a source primary secondary cell (PSCell) to a target PSCell is transmitted to a terminal device, the target PSCell being provided by the second network device.
A method of communication comprising:

receiving, at a terminal device and from a source secondary node (SN) providing a source primary secondary cell (PSCell) , a command for a layer 1 or layer 2 triggered mobility (LTM) cell switch from the source PSCell to a target PSCell; and

transmitting, to a master node (MN) , a radio resource control (RRC) reconfiguration complete message comprising an identity of a LTM candidate configuration associated with the target PSCell or an identity of the target PSCell.