WO2023070554A1

WO2023070554A1 - Method and apparatus for mobility handling for mobile iab deployments

Info

Publication number: WO2023070554A1
Application number: PCT/CN2021/127573
Authority: WO
Inventors: Xiang Xu; Ömer BULAKCI; Rustam PIRMAGOMEDOV
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2021-10-29
Filing date: 2021-10-29
Publication date: 2023-05-04
Also published as: CN118202705A

Abstract

Methods and apparatus are disclosed for wireless communication. A method comprises, at a base station, receiving at least one handover tag of a first integrated access and backhaul (IAB) node, which includes a third group identity indicating a third group of terminal devices to be served or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the first IAB node; receiving at least one handover tag which includes a first group identity indicating a first group of terminal devices to be served or includes a second group identity indicating a second group of terminal devices not to be served by a second IAB node; matching the at least one handover tag of the IAB node with the at least one handover tag for the terminal device; and initiating a procedure related to a handover of the terminal device to the first IAB node or away from the first IAB node, based at least in part on the matching.

Description

METHOD AND APPARATUS FOR MOBILITY HANDLING FOR MOBILE IAB DEPLOYMENTS

Field of the Invention

Embodiments of the disclosure generally relate to wireless communication, and more particularly, to methods and apparatus for mobility handling for mobile integrated access and backhaul (IAB) deployments.

Background

Demand for improved 5G cellular coverage and connectivity continues to increase, which may be challenging in many outdoor and mobility scenarios. In New Radio (NR) , an integrated access and backhaul (IAB) technology is proposed to support a flexible extension of radio access network (RAN) . IAB enables wireless relaying in a radio access network. The relaying node, referred to as IAB-node, supports access and backhauling via NR. The RAN supports IAB by the IAB-node wirelessly connecting to a NR base station (gNB) capable of serving the IAB-nodes, named IAB-donor, which represents a normal gNB with additional functionality to support IAB.

A large quantity of IAB-nodes can be deployed to provide acceptable coverage (also referred to as IAB cell or cell of an IAB, hereinafter) to multiple user equipments (UEs) . A UE may be served by an IAB cell, or by a cell from an IAB-donor, or by a cell from a regular gNB.

There is a need for enhancement for mobility handling of a UE in IAB deployments, especially in mobile IAB deployments. For a mobile IAB-node installed on a vehicle (e.g., bus, train, airplane) , the IAB cell would be considered as an inside cell to mainly serve UEs inside of the vehicle. For UEs outside of the vehicle, the UEs would be served by other cells (also referred to as outside cell) . Then, when the UEs enter the vehicle or leave the vehicle, these UEs would be handed over between the IAB cell (or inside cell) and other cell (or an outside cell) . Due to the potentially large number of UEs entering or leaving the vehicle, it would be desirable to handover these UEs between an IAB cell and other cell efficiently and accurately.

Summary

This summary is provided to introduce simplified concepts of mobility handling for mobile IAB deployments. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

According to a first aspect of the disclosure, it is provided an apparatus. Said apparatus may comprise at least one processor, and at least one memory including computer program code, the at least one memory and the at least one computer program code configured to, working with the at least one processor, cause the apparatus to obtain at least one handover tag for a terminal device, which includes a first group identity indicating a first group of terminal devices to be served by an IAB node, or includes a second group identity indicating a second group of terminal devices not to be served by an IAB node; and transmit the at least one handover tag to at least one base station, so that a procedure related to a handover of the terminal device to the IAB node or away from the IAB node is enabled to be initiated by the at least one base station based at least in part on the at least one handover tag. The at least one base station may comprise a normal base station and/or an IAB donor.

In an embodiment, the at least one handover tag may comprise a first handover tag for the terminal device, which indicates the first group of terminal devices to be served by the IAB node. The at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to transmit the first handover tag to a first base station of the at least one base station, so that a procedure related to a handover of the terminal device to the IAB node is enabled to be initiated based at least in part on the first handover tag.

In an embodiment, the at least one handover tag may comprise a second handover tag for the terminal device, which indicates the second group of terminal devices not to be served by the IAB node. The at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to transmit the second handover tag to a second base station of the at least one base station, so that a procedure related to a handover of the terminal device from the IAB node is initiated based at least in part on the second handover tag.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to receive from the at least one base station, a request for the at least one handover tag. The at least one handover tag may be transmitted in response to the request for the at least one handover tag.

In another embodiment, transmitting the at least one handover tag may be transmitted without a request from the at least one base station.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to transmit the second handover tag by at least one of the following operations: transmitting the second handover tag to the first base station for forwarding the second handover tag to the second base station, when the terminal device is handed over to the second base station; transmitting the second handover tag to the second base station, upon a detection that the terminal device is in proximity of the second base station; and transmitting the second handover tag to the second base station, upon the terminal device detects a cell served by the second base station.

In an embodiment, the apparatus may be comprised in the terminal device.

In another embodiment, the apparatus may be comprised in a core network node. In an example, the core network node may comprise an access and mobility function. The first handover tag and/or the second handover tag may be transmitted in a context of the terminal device. In another example, the core network node may comprise a location management function, and the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to transmit to the at least one base station, a set of handover tags comprising a plurality of handover tags for a plurality of terminal devices. The set of handover tags includes the at least one handover tag for the terminal device.

In an embodiment, the at least one handover tag may further comprise: a first type indicator, indicative of whether the first group of terminal devices indicated by the first group identity of the handover tag are to be served by the IAB node or not; or a second type indicator indicative of whether the second group of terminal devices indicated by the second group identity are to be served by the IAB node or not.

In an embodiment, the at least one handover tag may further comprise: an identity of a cell; and/or an expiry time of the at least one handover tag.

According to a second aspect of the disclosure, it is provided an apparatus at a base station. Said apparatus may comprise at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, working with the at least one processor, cause the apparatus to receive at least one handover tag of a first IAB node, which includes a third group identity indicating indicates a third group of terminal devices to be served by the first IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the first IAB node; receive at least one handover tag for a terminal device, which includes a first group identity indicating a first group of terminal devices to be to be handed over to be served by a second IAB node, or includes a second group identity indicating a second group of terminal devices not to be served by a second IAB node; match the at least one handover tag of the first IAB with the at least one handover tag for the terminal device ; and initiate a procedure related to a handover of the terminal device to the first IAB node or away from the first IAB node, based at least in part on the matching of the at least one handover tag of the first IAB node and the at least one handover tag for the terminal device.

In an embodiment, the at least one handover tag of the first IAB node may be received from the first IAB node, or is received from another base station.

In an embodiment, the at least one handover tag for the terminal device may be received from the terminal device, or a core network node. In another embodiment, the at least one handover tag for terminal device may be received from another source base station.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to transmit to the terminal device or the core network node, a request for the at least one handover tag for the terminal device. The received at least one handover tag for the terminal device may be transmitted in response to the request.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to match the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device by at least one of following operations: determining whether the first group identity is included in the third group identity or is the same as the third group identity; and determining whether the second group identity is included in the fourth group identity or is the same as the fourth group identity.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to match the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device by at least one of the following operations: determining that the handover of the terminal device is a handover to the first IAB node, when the at least one handover tag of the terminal device indicates that the third group of terminal devices are to be served by the first IAB node and the at least one handover tag for the terminal device indicates that the first group of terminal devices are to be served by the second IAB node; and determining that the handover of the terminal device is a handover from the first IAB node, when the at least one handover tag of the first IAB node indicates that the fourth group of terminal devices are not to be served by the first IAB node and the at least one handover tag for the terminal device indicates that the second group of terminal devices are not to be served by the second IAB node.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to match the first handover tag with the second handover tag by: determining a target cell of the handover based on the at least one handover tag of the first IAB node and/or the at least one handover tag for the terminal device; and determining that the terminal device is an applicable terminal device of the handover based on the at least one handover tag of the first IAB node and/or the at least one handover tag for the terminal device.

In an embodiment, the at least one handover tag may further comprise: a third type indicator, indicative of whether the third group of terminal devices indicated by the third group identity are to be served by the first IAB node; or a fourth type indicator indicative of whether the fourth group of terminal devices indicated by the fourth group identity are not to be served by the first IAB node or not. The at least one handover tag for the terminal device may further comprise: a first type indicator, indicative of whether the first group of terminal devices indicated by the first group identity are to be served by the second IAB node or not; or a second type indicator indicative of whether the second group of terminal devices indicated by the second group identity are not to be served by the second IAB node or not.

In an embodiment, the procedure may comprise a preparation procedure of the handover of the terminal device.

According to a third aspect of the disclosure, it is provided an apparatus at an IAB node. Said apparatus may comprise at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, working with the at least one processor, cause the apparatus to obtain at least one handover tag of the IAB node, which includes a third group identity indicating a third group of terminal devices to be served by the IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the IAB node; and transmit the at least one handover tag to an IAB donor, so that a procedure is enabled to be initiated by the IAB donor based at least in part on the at least one handover tag, wherein the procedure is related to a handover of a terminal device in the third group of terminal devices or the fourth group of terminal devices to the IAB node or away from the IAB node.

In an embodiment, the at least one handover tag may comprise a third handover tag, which indicates the third group of terminal devices to be served by the IAB node. The third handover tag is transmitted to the IAB donor, so that the procedure is enabled to be initiated based at least in part on the third handover tag.

In an embodiment, the at least one handover tag may comprise a fourth handover tag, which indicates the fourth group of terminal devices not to be served by the IAB node. The fourth handover tag is transmitted to the IAB donor, so that the procedure is enabled to be initiated based at least in part on the fourth handover tag.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to, transmit to the terminal device, a request for reporting at least one handover tag for the terminal device to the IAB donor. The at least one handover tag for the terminal device may indicate a first group of terminal devices to be served by the IAB node, or a second group of terminal devices not to be served by the IAB node.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to receive from the terminal device, at least one handover tag for the terminal device, wherein the at least one handover tag for the terminal device indicates a first group of terminal devices to be served by the IAB node, or a second group of terminal devices not to be served by the IAB node; and forwarding the at least one handover tag for the terminal device to the IAB donor.

In an embodiment, the at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus to transmit the at least one handover tag of the IAB node to the IAB donor by transmitting the at least one handover tag of the IAB node to the IAB donor when the IAB node connects to the IAB donor.

According to a first aspect of the disclosure, it is provided a method. Said method comprises obtaining at least one handover tag for a terminal device, which includes a first group identity indicating a first group of terminal devices to be served by an IAB node, or includes a second group identity indicating a second group of terminal devices not to be served by an IAB node. The method further comprises transmitting the at least one handover tag to at least one base station, so that a procedure related to a handover of the terminal device to the IAB node or away from the IAB node is enabled to be initiated by the at least one base station based at least in part on the at least one handover tag. The base station may be a normal base station or an IAB donor.

According to fifth aspect of the disclosure, it is provided a method performed at a base station. Said method comprises: receiving at least one handover tag of a first IAB node, which includes a third group identity indicating a third group of terminal devices to be served by the first IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the first IAB node; receiving at least one handover tag for a terminal device, which includes a first group identity indicating a first group of terminal devices to be served by a second IAB node, or includes a second group identity indicating a second group of terminal devices not to be served by a second IAB node; matching the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device; and initiating a procedure related to a handover of the terminal device to the first IAB node or away from the first IAB node, based at least in part on the matching of the at least one handover tag of the first IAB node and the at least one handover tag for the terminal device. The base station may be a normal base station or an IAB donor.

According to sixth aspect of the disclosure, it is provided a method performed at an IAB node. Said method comprises: obtaining at least one handover tag of the IAB node which includes a third group identity indicating a third group of terminal devices to be served by the IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the IAB node; and transmitting the at least one handover tag to an IAB donor, so that a procedure is enabled to be initiated based at least in part on the handover tag, wherein the procedure is related to a handover of a terminal device in the third group of terminal devices or the fourth group of terminal devices to the IAB node or away from the IAB node.

According to seventh aspect of the present disclosure, it is provided a computer readable storage medium, on which instructions are stored, when executed by at least one processor, the instructions cause the at least one processor to perform any method according to the fourth, fifth and/or sixth aspects.

According to eighth aspect of the present disclosure, it is provided computer program product comprising instructions which when executed by at least one processor, cause the at least one processor to perform any method according to the first, second and/or third aspects.

These and other objects, features and advantages of the disclosure will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.

Brief Description of the Drawings

Some example embodiments will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates an example of IAB network architecture in which embodiments of the present disclosure can be implemented;

Figure 2 illustrates an exemplary scenario for mobile IAB deployments;

Figure 3 shows an exemplary procedure of mobility handling for mobile IAB deployments according to embodiments of the present disclosure;

Figure 4 shows another exemplary procedure of mobility handling for mobile IAB deployments according to embodiments of the present disclosure;

Figure 5 shows yet another exemplary procedure of mobility handling for mobile IAB deployments according to embodiments of the present disclosure;

Figure 6 is a flow chart depicting a method according to an embodiment of the present disclosure;

Figure 7 is a flow chart depicting a method according to an embodiment of the present disclosure;

Figure 8 is a flow chart depicting a method according to an embodiment of the present disclosure; and

Figure 9 shows a simplified block diagram of an apparatus according to an embodiment of the present disclosure.

Detailed Description

Some example embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the example embodiments may take many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout.

The terms “data, ” “content, ” “information, ” and similar terms may be used interchangeably, according to some example embodiments, to refer to data capable of being transmitted, received, operated on, and/or stored. Moreover, the term “exemplary” , as may be used herein, is not provided to convey any qualitative assessment, but instead merely to convey an illustration of an example. Thus, use of any such terms should not be taken to limit the spirit and scope of embodiments of the present invention.

The present disclosure is directed to mobility handling for mobile IAB deployments. In New Radio (NR) , IAB technology relies on splitting a gNB architecture consisting of Central Unit (CU) and Distributed Unit (DU) . Figure 1 illustrates an example of IAB network architecture 100 in which embodiments of the present disclosure can be implemented.

The architecture 100 comprises an IAB-donor (shown as 110 in Figure 1) , one or more IAB nodes (shown as 120, 130 in Figure 1) and one or more terminal devices (e.g., shown as

UEs

151, 152, 153 in Figure 1) . The IAB-donor 110 is a base station that provides network access to UEs (e.g., shown as UE 153 in Figure 1) . The IAB-donor 110 also provides network access to IAB node (e.g., shown as IAB 120 in Figure 1) via a network of backhaul and access links. The IAB-donor 110 is connected with a core network, such as a next generation core (NGC) network 140. IAB-

nodes

120, 130, are access nodes that support NR access links to UEs and use NR backhaul links for connecting to parent nodes and child nodes. In this architecture 100, the IAB-donor 110 consists of a CU (also referred to as IAB-donor-CU, shown as 112) and one or more DUs (also referred to as IAB-donor-DU, shown as 111) . An IAB-donor-CU 112 is a logical node hosting RRC (Radio Resource Control) , Service Data Adaptation Protocol (SDAP) and Packet Data Convergence Protocol (PDCP) protocols of a gNB, or RRC and PDCP protocols of an en-gNB that controls the operation of one or more IAB-donor-DUs. The IAB-donor-CU 112 terminates an F1 interface towards IAB-nodes and IAB-donor-DU.

A parent node is a next hop neighbour node of an IAB-MT. The parent node can be IAB-node or IAB-donor-DU. A child node is a next hop neighbour node of an IAB-node or IAB-donor-DU. The child node is also an IAB-node. The IAB-node are connected to an IAB-donor-DU via one or multiple hops. The direction toward the child node is referred to as downstream while the direction toward the parent node is referred to as upstream. The IAB-donor-CU performs centralized resource, topology and route management for the IAB topology.

An IAB-donor-DU 111 is a logical node hosting Radio Link Control (RLC) , Medium Access Control (MAC) and Physical (PHY) layers of the gNB or en-gNB. IAB-donor-DU 111 further hosts IAB Backhaul Adaptation Protocol (BAP) sublayer, providing wireless backhaul to IAB-nodes. Operations of an IAB-donor-DU are partly controlled by an IAB-donor-CU. One IAB-donor-DU supports one or multiple cells. One cell is supported by only one IAB-donor-DU. The IAB-donor-DU terminates the F1 interface connected with the IAB-donor-CU. The IAB-donor-DU provides wireless backhaul to the downstream IAB-nodes and UEs via the network functionalities of the NR Uu interface.

Each IAB-node holds DU functionality and Mobile Termination (MT) functionality. For example, as shown in Figure 1, the IAB-node 120 consists of a DU 121 (also referred to as IAB-DU) and a MT 122 (also referred to as IAB-MT) . The IAB-node 130 consists of a DU 131 and a MT 132. The function of IAB-DU is similar as that of IAB-donor-DU. An IAB-DU is a DU functionality supported by the IAB-node to terminate the NR access interface to UEs and next-hop IAB-nodes (i.e., child nodes) , and to terminate the F1 protocol to the IAB-donor-CU functionality on the IAB-donor. An IAB-node may contain one or more DUs and one or more MTs. Each DU part of the IAB-node has F1-C connection only with one control plane of one IAB-donor-CU. One IAB-DU supports one or multiple cells. One cell is supported by only one IAB-DU. These cells would be considered as a normal cell from the UE perspective. In other words, for the UE perspective, there is no difference between a cell provided by an IAB-DU and a cell provided by a normal gNB.

For communication with a parent node (which can be another IAB node or the IAB-donor) , an IAB-node hosts the mobile termination (MT) functionality corresponding to the UE operation or a part of the UE operation. IAB-MT is IAB-node functionality that terminates the Uu interface to the parent node using the procedures and behaviors specified for UEs unless stated otherwise. An IAB-node connects to an upstream IAB-node or an IAB-donor-DU via a subset of the UE functionalities of the NR Uu interface (i.e., IAB-MT function of IAB-node) . The IAB-MT supports a subset of the UE functionality, which includes, e.g., physical layer, layer-2, RRC and Non-Access Stratum (NAS) functionality to connect to the DU of another IAB-node or the IAB-donor, to connect to the CU on the IAB-donor, and to the core network.

In this architecture 100, the IAB-node 120 is a parent node of IAB-node 130. The IAB-node 110 is a parent node of IAB-

nodes

120 and 130. Via the IAB-MT 132, the IAB-node 130 connects to the upstream IAB-node 120. Via the IAB-DU 131, the IAB-node 130 establishes RLC-channels to UEs 151 and to MTs of its downstream IAB-nodes (not shown) . Via the IAB-MT 122, the IAB-node 120 connects to the IAB-donor 110. Via the IAB-DU 121, the IAB-node 120 establishes RLC-channels to UEs 152 and to MTs of its downstream IAB-nodes (e.g., IAB-node 130) . An IAB-DU provides wireless backhaul to its downstream IAB-nodes and UEs via network functionalities of a NR Uu interface.

The IAB-donor 110 holds a CU 112 for the DUs (e.g., 121, 131) of all IAB-nodes and for its own DU (111) . It is assumed that the DUs on an IAB-node are served by only one IAB-donor in the IAB architecture 100. This IAB-donor may change through topology adaptation. Each DU on an IAB-node connects to the CU in the IAB-donor using a F1 interface. F1 interface runs over the backhaul RLC channels on the wireless backhaul between a MT on an IAB-node and a DU on a parent IAB-node or an IAB-donor. A BAP sublayer is added, which holds routing information, enabling hop-by-hop forwarding.

The exemplary architecture 100 is shown as a two-hop chain of IAB-nodes underneath one IAB-donor, where IAB-node and UE connect in SA-mode to an NGC. However, it should be appreciated that IAB can support stand-alone (SA) and non-stand-alone (NSA) deployments. Embodiments of the present disclosure may be also implemented in an IAB architecture in NSA-mode. Furthermore, it should be appreciated that the IAB architecture 100 may be deployed with different IAB topology. For example, the chain of IAB-nodes may be of single hop or more than two hops. Multi-hop backhauling provides more range extension than single hop. One IAB-node may connect to more than one upstream IAB-node or IAB-donor DU. More than one downstream IAB-nodes may connect to one IAB-node or one IAB-donor DU.

Although the UEs, IAB-node and IAB-donor communicate via 5G in the exemplary architecture of Figure 1, embodiments of the present disclosure may also be implemented in an Long Term Evolution (LTE) or LTE-Advanced (LTE-A) network, or other networks supporting communications between these UEs, IAB-node and IAB-donor.

The

UEs

151, 152, 153 may be embodied as any suitable terminal device capable of cellular wireless communication, such as a mobile communication device, modem, cellular phone, gaming device, navigation device, media device, laptop computer, desktop computer, tablet computer, smart appliance, vehicle-based communication system, or an Internet-of-Things (IoT) device such as a sensor or an actuator. The IAB-

node

120, 130 and IAB-donor may be embodied as any suitable base station supporting IAB, for example, an Evolved Universal Terrestrial Radio Access Network Node B (E-UTRAN Node B) , evolved Node B, eNodeB (eNB) , Next Generation Node B, gNode B (gNB) .

IAB technology can support physically fixed relays where a location of an IAB-node is fixed, and mobile relays where an IAB-node is able to be mobile and its location is not fixed. For example, the IAB-node may be installed on vehicles, such as trains, trams or buses, etc., to provide cellular coverage and connectivity to users or devices inside the vehicle itself, in different environments, e.g., for passengers in the vehicles. Such kind of IAB deployments in which an IAB-node is able to be mobile, may be called as mobile IAB deployments.

Figure 2 illustrates an example scenario for mobile IAB deployments, where an IAB-node is installed on a train which is traversing multiple coverage areas of multiple IAB-donors. As shown in Figure 2, an IAB-node 250 (denoted as IAB1) traverses coverage areas (i.e., cells) of IAB-

donors

210, 220, 230, 240 in turn. These IAB-donors may be deployed along a railway of the train. For example, some of the IAB-

donors

210, 220, 230 and 240 may be deployed on separate stations of the railway.

At a train station, there are many platforms. There are many UEs that will leave different trains or enter different trains when respective trains arrive at the train station and stop at respective platforms. When a train arrives at a station, there may be a group of UEs (or all UEs, e.g., at a terminal station) of the passengers who will leave the train. There may be also another group of UEs (or all UEs, e.g., at an originating station) of the passengers who will enter the train. When the train has one or more mobile IAB-nodes deployed to serve the UEs fourth type indicator indicative of whether the fourth group of terminal devices indicated by the fourth group identity are not to be served by the second IAB node or nots inside of the train, handovers would be performed for UEs leaving the train, and for UEs entering the train. This may cause a large number of handovers in a short period. For example, in a festival season, it can be thousands of UEs entering/leaving the trains at a station per day. It is a challenge to a gNB (or an IAB-donor) to perform handover preparations and handover operations for such a significant number of UEs efficiently.

The legacy handover of a UE is based on a detection of one or more new target cells based on UE measurements. For example, when the UE enters the train, the UE may detect a cell of a mobile IAB-node installed on the train. UE reports information about the cell, including measured signal power, to a CU which is serving the UE. The CU can be a regular gNB-CU, or an IAB-donor-CU. The serving CU then initiates a handover from an outside cell to a cell served by the IAB-node. For the sake of brevity, a cell serving the UEs outside of the vehicle is referred to as an outside cell hereinafter, and a cell of a mobile IAB-node serving the UEs inside of the train is referred to as an inside cell or IAB cell. Similarly, a handover can be performed from the inside cell to the outside cell for a UE leaving the train.

The handover based on UE measurements may face some problems for mobile IAB deployments. Take a scenario of UEs entering a train (i.e., a handover from an outside cell to an IAB cell) for example. There may be a large number of UEs waiting at a platform at a station, and there may be multiple trains (equipped with respective mobile IAB-nodes) stopping at the station. UEs that are being served by an outside cell deployed at the station, may enter different trains (i.e., to be handed over to different mobile IAB-nodes installed on respective trains) soon later. For a specific UE, it is not possible (and unnecessary) for the serving CU to perform a handover preparation to all mobile IAB-nodes. Traditionally, the serving CU knows the potential target cell based on the measurement report from the UE. But this is a challenge in a deployment with mobile IAB. Due to a shield effect of a train carriage, a UE outside a train may not detect signals of the true target mobile IAB-node for the specific UE, or measurement reports may not provide an indication that the target mobile IAB is a good target. For example, a measurement report of the UE may indicate a weak signal of the inside cell from a mobile IAB-node and a strong signal of an outside cell. Further, the measurement reports may be delayed due to the shield effect and interferences among different IAB-nodes.

In another scenario in which UEs leave a train (i.e., handover from an inside cell of mobile IAB to an outside cell) , there are similar problems. The UEs inside of the train are served by the IAB-donor-CU which controls the mobile IAB deployed on the train. When the train arrives at a station, some of UEs which is being served by an IAB-node on a train will leave a train, while others of the UEs will stay at the train except the final destination. It is not possible (and unnecessary) to perform handover preparation for all UEs. The handover preparation is only needed for the target UEs, i.e., UEs which will leave the train. But the serving CU (i.e., the IAB-donor-CU) cannot know the target UEs, i.e., which UEs will leave the train.

So, an efficient handover preparation and handling method is needed. A possible enhancement to the legacy handover is to use Conditional Handover (CHO) . CHO is a handover procedure that is executed by a UE only when one or more execution conditions are met. In a CHO mechanism, a handover preparation is performed in advance and a handover command message is sent to UEs in advance. The handover command message contains a configuration of CHO candidate cell (s) generated by the candidate gNB (s) and execution condition (s) generated by the source gNB. The UE starts evaluating the execution condition (s) upon receiving the handover command message. If at least one CHO candidate cell satisfies the corresponding execution condition, the UE can handover to the target gNB/cell quickly by applying the stored corresponding configuration for that selected candidate gNB/cell.

However, it is not practical to use CHO for the above-mentioned mobile IAB deployments. In a CHO procedure, each candidate gNB/cell needs to reserve pre-configured resources so that the UE can be handed over to one candidate gNB/cell quickly upon execution conditions are met. However, for the above-mentioned scenario of mobile IAB, such as the scenario in which a large number of UEs are waiting at a platform at a station for entering different trains, multiple IAB-nodes installed on these different trains that are close to each other may become candidate base stations according to radio conditions. It is impossible and inefficient to reserve resources for all UEs on the platform on each of the IAB-nodes.

Meanwhile, several handover procedures for different cases are specified in current communication protocols, such as in the 3 ^rd Generation Partner Project (3GPP) specifications. However, none of them supports preparing the handover of a specific target UE in advance for the deployment with mobile IAB (s) , e.g., use CHO preparation before a UE enters (or leaves) a train. That is, the prior art mechanisms mainly rely on the radio conditions.

The present disclosure proposes a solution to perform the handover preparation in mobile IAB deployments, e.g., the above-mentioned scenarios, based on a handover tag indicating a group of UEs to be served or not to be served by an IAB-node. UE’s serving base station, which may be a normal gNB or an IAB-donor, may receive handover tags from UEs and an IAB-node. The handover tags are provided to UEs in advance (e.g., when buying a ticket to the train) . UEs may send the handover tags to the gNB or the IAB-donor before entering or leaving the train, which cause a serving base station (i.e., gNB-CU or IAB-donor-CU) to initiate a handover-related procedure accordingly.

In some embodiments, a UE may receive at least one handover tag including a group identity indicating a group of terminal devices to be served by an integrated access and backhaul (IAB) node, or indicating a group of terminal devices not to be served by an IAB node. The UE is a member of the group of terminal devices. The group of UEs may be devices carried by passengers who have bought tickets of a same train (or a same train cabin) with a same station (departure station or arrival station) . For example, when a train is equipped with one IAB cell, the group of UEs may be devices carried by passengers who will broad a same train with a same departure station, or will leave a same train with a same arrival station. In another example, when a train is equipped with multiple IAB cells (e.g. each train cabin is equipped with an IAB cell) , the group of UEs may be devices carried by passengers who will broad a same train cabin with a same departure station, or will leave a same train with a same arrival station. Handover tags may be provided to respective UEs when the passengers buy a ticket of the train, or when it is detected that the UEs are approaching the station or a platform for the train. In this case, the type of ticket can be the paper, plastic, electrical ticket, or application data. Naturally, there would be a predefined mapping between a handover tag and a target cell. For example, according to tickets of a train, it can be determined that a group of UEs would enter a coverage of a mobile IAB-node on the train from a specific departure station (or its specific platform) . Accordingly, the handover tag may be preconfigured for entering coverage of the mobile-IAB node, and indicates that the group of UEs are to be handed over to a target cell of the mobile-IAB node. According to tickets of a train, it can be also determined that a group of UEs would leave a coverage of a mobile IAB-node at a specific arrival station (or its specific platform) . Accordingly, the handover tag may be preconfigured for leaving coverage of the mobile IAB-node, and indicates that the group of UEs are to be handed over to a target cell of the arrival station.

In some embodiments, a UE may receive two handover tags. One handover tag includes a first group identity indicating a first group of UEs, to which the UE belongs, and to be served by a mobile IAB-node. For example, the first group of UEs enter the same train at the same station. The other handover tag includes a second group identity indicating a second group of UEs, to which the terminal device belongs, and not to be served by a mobile IAB-node. For example, the second group of UEs leave the same train at another same station.

In some embodiments, a UE may provide its handover tag to its serving base station (which may be a normal gNB or an IAB-donor) . In an example, a UE may provide a handover tag to the serving base station at a departure station, for example, when the UE entered the station and connected with the serving base station. A mobile IAB node installed on a train also provides one or more handover tags, each of which includes a group identity for a group of UEs to be served, to its IAB-donor-CU. Then, a handover preparation towards a target cell of a mobile IAB-node which is installed on a train staying at the station (e.g., from the IAB-donor) can be initiated based on the handover tag received from the UE, and the handover tag received from the IAB. The procedure of handover preparation is used to establish necessary resources in related nodes (including the target mobile IAB-node, the IAB-donor, etc. ) .

In another example, when a train enters a station, the IAB-node of the train has migrated or connected to the IAB-donor. The mobile IAB-node installed on a train provides one or more handover tags, each of which includes a group identity for a group of UEs not to be served, to its IAB-donor-CU. At that time, a UE which will leave the train may also provide a handover tag to an IAB-donor-CU at an arrival station, for example, when the UE is approaching or arrived at the arrival station. Then, via the IAB-node, UEs served by the IAB-node may connect with and be served by the IAB-donor. Then, a handover preparation from the mobile-IAB node to a target cell, which is an outside cell (e.g., a cell of the IAB-donor, or a cell of normal gNB) can be initiated based on the handover tag received from the UE, and the handover tag received from the IAB. The procedure of handover preparation is used to establish necessary resources in related nodes (including the outside cell, the CU of the outside cell, etc. ) .

In some embodiments, the handover tag may be provided by a UE to its serving base station (or CU) , in response to a request from its base station (or CU) . For example, the request may be sent in a unicast RRC message to a particular UE, or in a broadcast RRC message, e.g., a system information broadcast (SIB) . In some embodiments, the handover tag may also be sent by a UE to its serving base station (or CU) on its own initiative, e.g., without a request from the serving base station (or CU) .

In some embodiments, a UE would execute a handover command after entering or leaving a coverage (or cell) of an IAB-node, according to the handover preparation performed based on the handover tag.

In some embodiments, a serving base station (such as a normal gNB or an IAB-donor) may receive a handover tag of an IAB-node, which includes a group identity indicating a group of UEs to be or not to be served by the IAB-node. In an example, when the serving base station is the IAB-donor for the IAB node, the handover tag may be directly received from the IAB-node. In another example, when the serving base station is a neighbor base station of the IAB-donor for the IAB node, the handover tag may be received from a neighbor base station which is the IAB-donor for the IAB node. In this regard, the IAB-donor serving the IAB-node forwards the handover tag to the serving base station.

In some embodiments, the serving base station may further receive a handover tag for a particular UE. The handover tag includes a group identity indicating a group of UEs to be or not to be served by an IAB-node. It means that the particular UE belongs to the group of UEs.

In some embodiments, the handover tag for a particular UE may be received from the UE via a RRC message, e.g., in response to sending a request to the UE for providing the handover tag. In another embodiment, the handover tag for a particular UE may be also received from a core network, such as 5G core network (5GC) or evolved packet core network (EPC) or a future generation core network, e.g., 6G.

Based on a handover tag received from the mobile IAB-node, and a handover tag received for the particular UE, the serving base station may determine whether the UE is an applicable UE for handover and a target cell for initiating a handover preparation. In this regard, the serving base station may match the handover tag received for the particular UE with the handover tag received from the mobile IAB-node. For example, if the group identity indicated in the handover tag received for the particular UE matches (e.g., being included or identical with) a group identity indicated in the one or more handover tags received from the mobile IAB-node, the serving base station may determine that the particular UE is applicable for a handover involving the mobile IAB-node. It would mean that the particular UE is an applicable UE for the handover, while the mobile IAB-node is an association IAB-node that the particular UE is to be handed over to or away from. For example, according to a type of the handover tag, i.e. whether the handover tag is for a group of UEs to be served (for example, UEs entering or will enter coverage of a mobile IAB-node) or for a group of UEs not to be served (for example, UEs leaving or will leave coverage of a mobile IAB-node) , the serving base station may determine a direction of the handover (for example, the handover is a handover to a mobile IAB, or the handover is a handover away from a mobile IAB) , and consequently may determine the target cell of the handover of the target UE. Accordingly, the serving base station may initiate a handover preparation for the handover. In one example, when it is a handover to a mobile IAB-node, the serving base station may be a normal base station or an IAB-donor, and the handover is from an outside cell to a mobile IAB cell; when it is a handover from a mobile IAB-node, the serving base station may be an IAB-donor, and the handover is from a mobile IAB cell to an outside cell. The outside cell and IAB cell may belong to the same gNB-CU or different gNB-CUs.

In some embodiments, a mobile IAB-node may be configured with at least one handover tag, e.g., for each stop of a train in the above examples shown in Figure 2. For example, in an example that a mobile IAB-node is installed in a train, its handover tags for each stop indicate respective groups of UEs to enter or leave the train, i.e., to be handed over at each of its stop stations. The at least one handover tag for a particular station may include a handover tag indicating a group of UEs (i.e., UEs which will enter the train) to be served by the mobile IAB-node at the particular station. It means that this group of UEs are to be handed over to the mobile IAB-node. Alternatively or additionally, the at least one handover tag for a particular station may include a handover tag indicating a group of UEs (i.e. UEs which will leave the train) to be stopped serving by the mobile IAB-node at the particular station. It means that this group of UEs are to be handed over from the mobile IAB-node at the particular station. In some other embodiments, there may be multiple IAB cells installed on a train. For example, one IAB cell is installed in each train cabin. Multiple cells on the train may be served by one IAB-node, or by multiple IAB nodes (e.g., each IAB-node provide one cell) .

In the example where multiple cells are served by one IAB-node, the IAB-node may be configured with multiple handover tags, e.g., each IAB cell is associated with one different handover tag. In yet another example, an IAB node or an IAB cell may be associated with multiple sets of handover tags, for example, one handover tag for a specific set of UEs (e.g., when one IAB-node or one IAB cell is shared for multiple operators, the IAB node or IAB cell has one set of the handover tags for UEs from each operator) . In these examples, at a stop of the train, an IAB-node may provide multiple handover tags to its IAB-donor, each of which includes a group identity indicating a group of UEs to be served by the IAB-node. Alternatively or additionally, the IAB-node may provide multiple handover tags to its IAB-donor, each of which includes a group identity indicating a group of UEs not to be served by the IAB-node.

In some embodiments, a group of UEs indicated in a handover tag may comprise one or more UEs for only one passenger (i.e., corresponding to one ticket) . In other embodiments, a group of UEs indicated in a handover tag may comprise one or more UEs for only multiple passengers (i.e. corresponding to multiple ticket) , which are to be handed over to a same target cell.

In some embodiments, the mobile IAB-node may provide its handover tag to its serving IAB-donor. Taking a usage case that a mobile IAB-node is installed in a train for example, the mobile IAB-node may provide to an IAB-donor at a particular station, its handover tags configured for the particular station, including a handover tag which indicates a group of UEs (i.e. UEs which will enter the train) to be served by the mobile IAB-node when arriving at the particular station, and another handover tag which indicates another group of UEs (i.e. UEs which will leave the train) to be stopped serving by the mobile IAB-node when arriving at the particular station.

In some embodiments, a mobile IAB-node or IAB-donor may further generate and send a request for asking its associated UEs to report their handover tags to the serving IAB-donor. For example, when the mobile IAB-node provides to an IAB-donor at a station, a handover tag indicating a group of UEs to be stopped serving by the mobile IAB-node, the mobile IAB-node may request each UEs to report its own handover tag to the IAB-donor. The request may be carried in a broadcast RRC message generated by the IAB-node or by the IAB-donor, e.g., SIB. In another example, the IAB-donor of the mobile IAB-node may request each UEs to report its own handover tag to the IAB- donor. The request may be carried in a unicast RRC message generated by the IAB-donor. In yet another example, the IAB-donor may receive the handover tag of the UE when the UE is handover from its serving base station to the IAB-donor, for example, when the UE is handover from an outside cell to the IAB cell, or when the UE is handover from the first IAB-donor to the second IAB-donor during the IAB’s migration from the first IAB-donor to the second IAB-donor.

In this way, the present disclosure may support advanced handover of UEs from/to a cell of a mobile IAB-node. Figure 3 shows an example call flow for a proposed solution. This example may be implements in the scenario illustrated in Figure 2.

It assumes two railway stations along a railway of a train. IAB1 250 is an IAB-node installed on the train. The IAB-donor1 210 serves a first railway station, and DU1 211 is a DU of the IAB-donor1 210 for providing an outside cell #1. The IAB-donor4 240 serves a second railway station, and DU2 241 is a DU of the IAB-donor4 240 for providing an outside cell #2. It is assumed the same CU for the outside cells and IAB-nodes at a station. For example, CU1 212 controls the outside cell #1 and acts as IAB-donor-CU for IAB1 250 at the first station, and CU2 241 controls the outside cell #2 and acts as IAB-donor-CU at the second station.

At the first railway station, a terminal device (e.g., UE) UE1 301 may connect with the outside cell#1 of DU1 211, as shown at step 310. For example, the UE1 may be staying at the first train station or a platform thereof.

IAB1 250 is installed in a train. Per a train ticket, a user of UE1 will take the train. As shown at step 315, IAB1 250 may connect with IAB-donor1 210, e.g., when the train is approaching the first railway station, or after the train arrives at the first railway station. At that time, IAB1 250 may inform CU1 212 that it will start to serve UEs belonging to a specific group (e.g., called as Enter-group) identified by Enter-ID #E1. In this regard, IAB1 250 may transmit a handover tag (e.g., a third handover tag) including a group identity (e.g., a third group identity) , for example, Enter-ID #E1 indicating the specific group to the CU1 212. Additionally, IAB1 250 may further inform CU1 212 that it will stop to serve UEs belonging to another specific group (e.g., called as Leave-group) identified by Leave-ID #L1. In this regard, IAB1 250 may transmit another handover tag (e.g., a fourth handover tag) including another specific group identity (e.g., a fourth group identity) , for example, Leave-ID #L1 indicating said another specific group to the CU1 212. It can be predicted that if the first railway station is an originating station, there may be no UE belonging to the Leave-group. Then, the Leave-group may be empty, or the IAB1 250 may only inform CU1 212 of the Enter-group, without informing the Leave-group. The operation of step 315 may be implemented via Fl Application Protocol (F1AP) procedure (e.g., as defined in 3GPP specification TS 38.473) or an RRC procedure (e.g., as defined in 3GPP specification TS 38.331) .

An IAB-node may be provisioned with the information of the Enter-Group and Leave-Group for each station that the train will stop. In some examples, an IAB-node may have multiple cells installed at different train carriages; each cell may be associated with a specific Enter-ID. For example, the low 4-bit of Enter-ID can identify one out of total 16 cells installed on a train. Alternatively, the Enter-ID may include a cell ID of an IAB-node’s cell. The number of bits is merely an example, and the number of bits may be changed according to a capacity of a specific station.

In some embodiments, the IAB1 250 may determine that the train will arrive (or has arrived) at a specific station based on its location. In a further embodiment, the IAB1 250 may be connected to a train onboard computer, so that the information on the stations, speed, arrivals and departures can be communicated to the IAB1 250.

The Enter-ID and Leave-ID are respectively included in an Enter-type tag and a Leave-type tag, which are commonly referred as “handover tag” (also referred as “tag” ) in the present disclosure. An example for the structure of the handover tag is shown in Table 1, which will be described in detail later.

IAB-donor1 210 may request UEs served by IAB-donor1 210 to provide their handover tags. As shown at step 320, CU1 212 may transmit a message, requesting UE1 301 to provide its handover tag (e.g. Enter-type tag) . The message is delivered to UE1 301 via DU1 211, as UE1 is being served by the cell #1 of CU1. In an example, the request for a handover tag can be triggered when the UE1 301 connects with the cell #1, and/or when a new Enter-type tag (e.g., including a new Enter-ID) is received from an IAB1 250 (e.g., when its train just arrived at the station) . In yet another embodiment, DU1 may generate a SIB asking UEs to report its handover tag.

As shown at step 325, UE1 301 may provide its Enter-type handover tag (e.g., a first handover tag) including a group identity (e.g., a first group identity, for example an Enter-ID) for the first station to CU1 212. The UE1 301 may be provisioned with two handover tags (i.e., an Enter-type tag and a Leave type tag) in advance. In an example, when the user of UE1 301 purchases a train ticket via the UE application installed on UE1 301, the two handover tags may be configured and provided to UE1 301, e.g., by an operator. It should be appreciated that a user may have multiple communication devices (e.g., mobile phones, pad, wearables, etc. ) . In this case, same handover tags may be provided for all of the user’s communication devices. In this example, it is assumed the user of UE1 301 starts a journey in the first station, and stops the journey at the second station. So, for UE1 301, the Enter-type tag includes an Enter-ID #E1, and the Leave-type tag includes a Leave-ID #L2.

In some embodiments, the Enter-type handover tag may be transmitted from UE1 301 to CU1 212, in response to a reception of the request from CU1 212 at step 325. In other embodiments, the UE1 301 may send its at least one handover tag (e.g., the Enter-type handover tag including the Enter-ID, the Leave-type handover tag including the Leave-ID) to CU1 212 without the request from the CU1 212. For example, during an RRC establishment procedure, the UE1 301 may provide its at least one handover tag to the CU1 212. The CU1 212 then saves the information as part of a UE context of the UE1 301.

As shown at step 330, CU1 may determine applicable UEs and a target cell for the applicable UE (s) for a handover, based on the at least one handover tag received from respective UEs and the at least one handover tag received from IAB1 250. In this regard, based on the Enter-ID received from the UE1 301 and the Enter-ID received from IAB1 250, CU1 212 may determine that UE1 301 is one of the applicable UEs, i.e., UE1 301 needs to be handed over to the IAB1 250. For example, CU1 may check whether the first handover tag (including a first group identity) received from the UE1 301 matches the third handover tag (including a third group identity) received from IAB1 250 or not. If match, for example the two Enter-IDs are identical with each other (e.g., both are #E1) , then it can be determined that UE1 301 is to be handed over to the IAB1 250. In an example, based on the Enter-ID received from the IAB1 250, CU1 212 may determine the target cell for a group of UEs which have a same Enter-ID #E1. In another example, the target cell may be determined based on the Enter-ID from UE1 301.

It should be noted that, this procedure does not require CU1 212 to determine the UEs to be handover using a measurement report from the UEs (e.g., UE1) . It may be improper to ask all UEs staying at the first station to perform a measurement report, especially when the UE’s measurement report may not provide a correct indication. For example, the UE’s measurement report may indicate a weak signal from the IAB1 250 due to a window shield of the train.

Then, CU1 212 may initiate a handover or conditional handover procedure for the determined applicable UEs, e.g., UE1 301. In this example, as shown at step 335, CU1 212 may initiate a preparation procedure for the handover or conditional handover of UEs in a same Enter group (identified as #E1) , and the target cell is a cell of IAB1 250. This preparation procedure is used to establish necessary resources in the IAB1 250 and IAB-donor1 210 for the handover.

Next, UE1 250 may execute a handover, and connect with IAB1 250 (through a DU of IAB1 250) . In an example, when UE1 301 enters the train carriage, UE1 301 may execute the handover command. For example, UE1 301 may transmit an RRCReconfigurationComplete message to IAB1 250 to indicate that the handover procedure is completed, as shown at step 340. IAB1 250 may forward this message to CU1 212. The UE1 250 is now served by the IAB1 250 and IAB-donor1.

As the train travels along a railway line, it moves to a second railway station in coverage of IAB-donor4 240. As shown at step 345, IAB1 250 may migrate to the IAB-donor4 240. Similar as step 315, IAB1 250 may inform CU2 242 that it will stop to serve UEs belonging to another specific group (e.g., called Leave-group) identified by the Leave-ID #L2. In this regard, IAB1 250 may transmit a handover tag (e.g., a third handover tag) including a group identity (e.g., a third group identity) , for example, Leave-ID #L2 indicating the specific group to the CU2 242. Additionally, IAB1 250 may further inform CU2 242 that it will start to serve UEs belonging to a specific group (e.g., called as Enter-group) identified by the Enter-ID #E2. In this regard, IAB1 250 may transmit another handover tag (e.g., a fourth handover tag) including a group identity (e.g. a fourth group identity) , for example, Enter-ID #E2 indicating said another specific group to the CU2 242. It can be predicted that if the second railway station is a final station, there may be no UE belonging to the Enter-group. Then, the Enter-group may be empty, or the IAB1 250 may only inform CU2 242 of the Leave-group, without informing the Enter-group. The operation of step 345 may be implemented via F1AP procedure (e.g., as defined in 3GPP specification TS38.473) or an RRC procedure (e.g., as defined in 3GPP specification TS38.331) . IAB1 250 may perform the informing procedure of step 345 when IAB1 250 is migrate to CU2 (e.g., well before the train arrives the second railway station) , or later after the migration (e.g., when the train is approaching the second railway station) . During the informing procedure (step 345) , the IAB1 205 informs CU2 that it will serve the group #E2 of UEs and stop serve the group #L2 of UEs.

In some embodiments, IAB-donor4 240 may request UEs to provide their at least one handover tag. As shown at step 350, CU2 242 transmits a message, requesting UE1 301 to provide its at least one handover tag (e.g., including the Leave-ID) . The message is delivered to UE1 301 via a DU (not shown) of IAB1 250, as UE1 is being served by an inside cell of IAB1. In an example, this request may be triggered if CU2 242 detects that the IAB1 250 is approaching the second station, or may be triggered by an indication from the IAB1 250 when IAB1 250 detects that it is approaching the second station.

In some other embodiments, IAB1 250 may generate and send (e.g., by its DU) a request asking UEs within its coverage to provide their handover tags. For example, the DU (not shown) of IAB1 250 may generate a DU-owned SIB asking the UEs to provide its handover tag including the Leave-ID, and send the SIB to the UEs when or before the train is approaching the second station.

As shown at step 355, UE1 provides its Leave-type tag (e.g., a second group identity) including a group identity (e.g., a second group identity) , for example Leave-ID #L2, to CU2 242. In some embodiments, only UEs that will leave the train (i.e., leave IAB1 250) at the second station will provide their respective Leave-type tags.

In some other embodiments, a UE may send its handover tag (e.g., including the Leave-ID) without an explicit request from the network by using some predefined conditions. For example, UE may send its handover tag (e.g. including the Leave-ID) without an explicit request from the network using some predefined condition. In an example, the UE may detect it is near/entering the train station, and responsively send its handover tag (e.g. including the Leave-ID) . In another example, the UE may detect a cell served by IAB-donor4, and find that its cell ID is identical with a cell ID indicated by its handover tag, and then report its handover tag (e.g. including the Leave-ID) .

In a further embodiment, once the UE1 301 connects to a cell of IAB1 250, the UE1 may provide its handover tag (e.g. including the Leave-ID) . In an example, the handover tag (e.g. including the Leave-ID) may be integrated into the UE context, such that the handover tag (e.g. including the Leave-ID) can be communicated on Xn interface between neighboring CUs. Accordingly, instead of requesting the UE1 301 to communicate the handover tag (e.g. including the Leave-ID) , the handover tag (e.g. including the Leave-ID) may be exchanged among CUs of IAB-donors and/or gNB. For example, the UE1’s context may be delivered from IAB-donor1 to IAB-donor4. This embodiment may be valid for the cases where handover tag (e.g. including the Enter-IDs and/or Leave IDs) are pre-configured, e.g. by an operator of a communication system.

Then, based on the at least one handover tag received from respective UEs and at least one handover tag received from IAB1 250, CU2 242 may determine applicable UEs and a target cell for the applicable UE (s) for a handover. In this regard, based on the handover tag (including the Leave-ID) received from the UE1 301, CU2 242 may determine that UE1 301 is one of the applicable UEs, i.e. UE1 301 needs to be handed over from an inside cell (e.g. a cell of the IAB1 250) to an outside cell (e.g. a cell of IAB-donor1 240) . For example, CU2 242 may check whether the second handover tag (including the second group identity) received from the UE1 301 matches the fourth handover tag (including the fourth group identity) received from IAB1 250 or not. If match, for example the two Leave-IDs are identical with each other (e.g. both Leave-IDs are #L2) , then it can be determined that UE1 301 is to be handed over from the IAB1 250, e.g. to a target cell (denoted as outside cell #2) of the IAB-donor1 240.

In an example, the target cell may be determined at CU2 242, e.g. based on a preconfigured mapping from the Leave-ID to an outer cell. In another example, the target cell may be determined based on measurement reports of the MT (s) (not shown) of IAB1 250. For example, IAB1 250 may performs measurements (by its MT (s) ) on outside cells (e.g. including an outside cell #2) of IAB-donor4 240 when the train enters the second station.

Then, CU2 242 may initiate a handover or conditional handover procedure for the determined applicable UEs, e.g. UE1 301. In this example, as shown at step 365, CU2 242 may initiate a preparation procedure for the handover or conditional handover of UEs in a same Leave group (identified as #L2) from the IAB1 250 to the target cell #2. This preparation procedure is used to establish necessary resources in the DU2 241 and CU2 242 for the handover.

Next, UE1 301 may execute a handover, and connect with DU2 of IAB-donor 240. In an example, when UE1 301 leaves the train, UE1 301 may execute the handover command. For example, UE1 301 may transmit a RRCReconfigurationComplete message to DU2 241 to indicate that the handover procedure is completed, as shown at step 370. DU2 241 may forward this message to CU2 242. The UE1 250 is now served by the outside cell (i.e. a cell of DU2 241) and CU2 242.

It should be appreciated that for UEs of Enter group #E2 which will enter coverage of IAB1 250 at the second station, IAB-donor4 240 may handle their mobility from an outside cell (e.g. a cell of DU2 241) to an inside cell (e.g. a cell of IAB1 250) , in a similar procedure as those performed in steps 310 to 340. Similarly, for UEs of Leave group #L1 which will leave coverage of IAB1 250 at the first station, IAB-donor1 210 may handle their mobility from an inside cell (e.g. a cell of IAB1 250) to an outside cell (e.g. a cell of DU1 211) , in a similar procedure as those performed in steps 345 to 370.

An example structure for a handover tag is shown in Table 1.

Table 1. Structure of handover tag

1. Tag type, indicates a type of the handover tag, i.e. whether the group of UEs, Group ID, are to be served by an IAB-node (e.g. with one bit of value “1” ) , or not to be served by the IAB-node (e.g. with one bit of value “0” ) .

2. Optionally, the handover tag may have an identity of a cell (i.e., Cell ID) for a handover, which may be a NR cell global identifier (CGI) , for example. It indicates an IAB cell which will start/stop to serve a group of UEs identified with Group ID.

3. Group ID (identity) , indicates a group of UEs to be or not to be served by an IAB-node. For a handover tag of a particular UE, it explicitly indicates that the particular UE belongs to the group. For a handover tag of a particular IAB node, it explicitly indicates that the particular group of UEs are to be served or not to be served by the IAB cell of the particular IAB.

4. Optionally, the handover tag may have an expiry timer indicating when the handover tag will expire. This timer may be utilized to delete the handover tag after some time if it wasn’t used.

The Group ID may be defined per IAB-node. In the example discussed above with reference to Figure 3, the Group ID may be defined per train and per railway station. For example, a part of bits of the Group ID may be mapped to a train number, and another part of bits of the Group ID may be mapped to a railway station number. In some embodiments, the Cell ID may be mapped to the Group ID. For example, the Group ID includes a train number and the cell ID of an IAB cell installed on the train. So, the Cell ID can be derived from the Group ID. In this example, it is not necessary to include a Cell ID in a handover tag.

In some scenarios, the inside cell (e.g. a cell of IAB-node) and an outside cell may belong to two different CUs. The at least one handover tags may be exchanged between the two CUs, e.g. over Xn interface. Figure 4 illustrates an exemplary procedure of mobility handling for such scenarios, which can be taken as a variation of the procedure shown in Figure 3.

The variation lies in that, at the first station, IAB1 250 may connect with IAB-donor6 260, which is different from the gNB (e.g. gNB1 270) controlling the outside cell #4. In an embodiment, the gNB may be an IAB-donor. Then IAB1 250 may transmit information of handover tags for the first station to CU3 262 of IAB-donor6 260. As shown at step 415A, IAB1 250 may inform CU3 262 that it will start to serve UEs belonging to a specific group (e.g., called as Enter-group) identified by Enter-ID #E1. Additionally, IAB1 250 may further inform CU3 262 that it will stop to serve UEs belonging to another specific group (e.g. called as Leave-group) identified by Leave-ID #L1. Then, CU3 262 may inform its neighboring CUs of the handover tags. As shown at 415B, CU3 262 may transmit to CU4 272, handover tags indicating that IAB1 205 will serve group #E1, and will stop serve group #L1.

In another embodiment, IAB1 250 is connected with IAB-donor6 260, while UE1 301 is served by a normal gNB (e.g. gNB1 270) , e.g. when UE1 301 is waiting for train at the railway station. In this case, CU3 262 may forward the handover tags of IAB1 250 to the normal gNB (e.g. its gNB-CU) . The gNB may also receive a handover tag for UE1 301. Then, based on the handover tag from IAB-donor6 260 and the handover tag from UE1 301, the gNB may initiate a handover from its cell (outer cell) to the IAB1 250.

Operations at

steps

410, 420, 425, 430, 435 and 440 may be similar as

steps

310, 320, 325, 330, 335, and 340 shown in Figure 3, respectively.

In some embodiments, IAB-donor may obtain at least one handover tag of a UE from a core network, such as the 5GC or EPC. For example, the at least one handover tag is available in 5GC, where an application function (AF) may provide relevant information to a policy control function (PCF) , either directly or via a network exposure function (NEF) . The information on the at least one handover tag for the UE may be provided to an access and mobility function (AMF) via the AF or the PCF. A NG-RAN node can obtain the at least one handover tag of the UE from the AMF.

Figure 5 illustrates an exemplary procedure of mobility handling according to such embodiments, which can be taken as another variation of the procedure shown in Figure 3. That is, for procedures of UE1 entering coverage of IAB1, steps 510, 515, 530, 535 and 540 in Figure 5 are the same as

corresponding steps

310, 315, 330, 335 and 340 in Figure 3, respectively. The variation lies in that, the

steps

320 and 325 in Figure 3 are changed to

steps

520A and 525A, or

steps

520B and 525B performed between the CU1 and the 5GC. For procedures of UE1 leaving coverage of IAB1, the variation of such kind of embodiments is similar. For the sake of brevity, Figure 5 only shows procedures of UE1 entering coverage of IAB1.

In an example, AMF 501 may provide the at least one handover tag (e.g. including Enter-ID) of UE1 to CU1 212 as shown at step 525A, e.g. during a N2 procedure when providing the UE context to the CU1 212. N2 is an interface between AMF and a RAN node. In another example, CU1 212 may send a request (e.g. N2 request) to AMF 501 for providing the at least one handover tag (e.g. including Enter-ID) of UE1 as shown at step 520A, and in response, the CU1 212 may receive the handover tag (e.g. including Enter-ID #E1) from AMF 501 at step 525A. For example, the N2 request may be sent when the CU1 212 receives the handover tag (e.g. including an Enter-ID) from the IAB1 250. Accordingly, the handover tag information is obtained from the 5GC.

In another example, the at least one handover tags can be a part of UE context. In this regard, during the related UE context establishment or modification procedures, the 5GC (e.g. AMF 501) provide the RAN node with a UE context of a particular UE comprising the handover tags of the particular UE.

In a further embodiment, a location management function (LMF) may provide to an IAB-donor either directly or indirectly via other core network nodes (e.g. AMF) , handover tags of a list of UEs that are relevant for a handover scenario of mobile IAB. In an example, the UEs in the list could be the ones that are in the proximity of the first train or on a platform of the first station. For example, as shown at step 520B, CU1 121 may request LMF 502 to provide handover tags of a list of UEs. For example, the list of UEs may be denoted as UE1, UEi, UEj, …. Then, LMF 502 may provide at least one handover tag of the list of UEs, including their Enter-IDs {#E1, #Ei, #Ej, …} and/or Leave-IDs {#L1, #Li, #Lj, ... } , as shown at step 525B. This embodiment has an advantage of reducing the signaling overhead on requesting the handover tags for multiple UEs. This is particularly relevant for obtaining handover tags of UEs entering a train. In contrast, for obtaining handover tags of UEs leaving the train, the UEs are already connected to the IAB1 250, and the burden of signaling overhead is not too heavy.

Through embodiments of the present disclosure, the handover of the UEs entering/leaving the train can be prepared early, without requiring the measurement report from individual UE. Thus, mobility handling of the UEs may be performed efficiently and accurately, especially when measurement reports from the UEs may provide an incorrect indication.

Reference is now made to Figure 6, which illustrates a flowchart of a method 600 according to an embodiment of the present disclosure. The method can be performed at a UE, e.g. by UE1 301 as shown in Figures 3 and 4. Alternatively, the method can be performed at a core network entity, e.g. AMF 501 and LMF 502 as shown in Figure 5.

As shown at block 610, a method 600 comprises obtaining at least one handover tag for a terminal device, which includes a first group ID indicating a first group of terminal devices (e.g. UEs) to be served by an IAB node, or includes a second group ID indicating a second group of terminal devices not to be served by an IAB node. At block 620, the method 600 comprises transmitting the at least one handover tag to at least one base station (such as a gNB, an IAB-donor, e.g. IAB-donor1 210, IAB-donor4 240 as shown in Figures 3, 4, and 5) , so that a procedure related to a handover of the terminal device to the IAB node or away from the IAB node is enabled to be initiated by the at least one base station based at least in part on the at least one handover tag.

In some embodiments, the at least one handover tag may comprise a first handover tag (e.g. including Enter-ID) for the terminal device, which indicates the first group of terminal devices to be served by the IAB node (such as an IAB-node, e.g. IAB1 250 as shown in Figures 3, 4, 5) . Transmitting the at least one handover tag to the at least one base station may comprise, transmitting the first handover tag to a first base station (e.g. a gNB, the IAB-donor1 210) of the at least one base station, so that a procedure related to a handover of the terminal device to the IAB node is enabled to be initiated based at least in part on the first handover tag.

In some embodiments, the at least one handover tag comprises a second handover tag (e.g. including a Leave-ID) for the terminal device, which indicates the second group of terminal devices not to be served by the IAB node. Transmitting the at least one handover tag to the at least one base station may comprise, transmitting the second handover tag to a second base station (e.g. a gNB, the IAB-donor1 210, the IAB-donor4 240) of the at least one base station, so that a procedure related to a handover of the terminal device from the IAB node is enabled to be initiated based at least in part on the second handover tag.

In some embodiments, the method 600 may further comprise receiving from the at least one base station, a request for the at least one handover tag. Then, the at least one handover tag may be transmitted in response to the request for the at least one handover tag.

In some embodiments, the at least one handover tag may be transmitted without a request from the at least one base station.

In an embodiment that the method 600 is performed at a location managements function (e.g. LMF 502, the method 600 may further comprises transmitting to the at least one base station, a set of handover tags comprising a plurality of handover tags for a plurality of terminal devices. The set of handover tags includes the at least one handover tag for the terminal device.

Figure 7 is a flow chart depicting a method 700 according to an embodiment of the present disclosure. The method can be performed at an IAB-donor or a normal base station, e.g. by gNB1 270, the IAB-donor1 210 or IAB-donor4 240 as shown in Figures 3, 4 and 5.

As shown at block 710, the method 700 comprises receiving at least one handover tag of a first IAB node (such as an IAB-node, e.g. IAB1 250) . The at least one handover tag includes a third group ID indicating a third group of terminal devices (e.g. UEs) to be served by the first IAB node, or includes a fourth group ID indicating a fourth group of terminal devices not to be served by the first IAB node. At block 720, the method 700 comprises receiving at least one handover tag for a terminal device (e.g. UE1 301 as shown in Figures 3, 4 and 5) , which includes a first group ID indicating a first group of terminal devices to be served by a second IAB node, or includes a second group ID indicating a second group of terminal devices not to be served by a second IAB node. At block 730, the method 700 comprises matching the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device. At block 740, the method 700 comprises initiating a procedure related to a handover of the terminal device to the first IAB node or away from the first IAB node, based at least in part on the matching of at least one handover tag of the first IAB node and the at least one handover tag for the terminal device. In an example, the method 700 may comprises initiating a preparation of the handover of the terminal device.

In some embodiments, the at least one handover tag of the first IAB node is received from the first IAB node. In other embodiments, the at least one handover tag of the first IAB is received from another base station.

In some embodiments, the at least one handover tag for the terminal device may be received from the terminal device. In other embodiments, the at least one handover tag for the terminal device may be received from a core network node.

The method 700 may further comprise transmitting to the terminal device or the core network node, a request for the at least one handover tag for the terminal device. The received at least one handover tag for the terminal device may be transmitted in response to the request.

In some embodiments, the at least one handover tag for the terminal device may be received from another base station controlling the IAB node. In some embodiments, the at least one handover tag for the terminal device may be received from a source base station during the handover procedure performed from the source base station to current serving base station for the terminal device.

In some embodiments, matching the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device may comprises at least one of following: determining whether the first group ID is included in the third group ID or is the same as the third group ID; or determining whether the second group ID is included in the fourth group ID or is the same as the fourth group ID.

In some embodiments, matching the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device may further comprises at least one of following: determining that the handover of the terminal device is a handover to the first IAB node, when the at least one handover tag of the IAB node indicates that the third group of terminal devices are to be served by the first IAB node and the at least one handover tag for the terminal device indicates that the first group of terminal devices are to be served by the second IAB node; and determining that the handover of the terminal device is a handover from the first IAB node, when the at least one handover tag of the first IAB node indicates that the fourth group of terminal devices are not to be served by the first IAB node and the at least one handover tag for the terminal device indicates that the second group of terminal devices are not to be served by the second IAB node.

In some embodiments, the method 700 may further comprise determining a target cell of the handover based on the at least one handover tag of the first IAB node and/or the at least one handover tag for the terminal device; and determining that the terminal device is an applicable terminal device of the handover based on the at least one handover tag of the first IAB node and/or the at least one handover tag for the terminal device.

Figure 8 is a flow chart depicting a method 800 according to an embodiment of the present disclosure. The method can be performed at an IAB-node, e.g. by the IAB1 250 as shown in Figures 3, 4 and 5.

As shown at block 810, the method 800 comprises obtaining at least one handover tag of an IAB node which includes a third group identity indicating a third group of terminal devices (such as UEs) to be served by the IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the IAB node.

At block 820, the method 800 comprises transmitting the at least one handover tag of the IAB node to an IAB donor (such as an IAB-donor, e.g. IAB-donor1 and IAB-donor4 as shown in Figures 3, 4, 5) , so that a procedure is enabled to be initiated based at least in part on the at least one handover tag. The procedure is related to a handover of a terminal device in the third group of terminal devices or the fourth group of terminal devices to the IAB node or away from the IAB node.

In some embodiments, the at least one handover tag may comprise a third handover tag, which indicates the third group of terminal devices to be served by the IAB node. The third handover tag may be transmitted to the IAB donor, which may forward the third handover tag to other base station, so that a procedure is enabled to be initiated based at least in part on the third handover tag.

In some embodiments, the at least one handover tag may comprise a fourth handover tag, which indicates the fourth group of terminal devices not to be served by the IAB node. The fourth handover tag is transmitted to the IAB donor, which may forward the fourth handover tag to other base station, so that the procedure is enabled to be initiated based at least in part on the fourth handover tag.

The method 800 may further comprise transmitting, to the terminal device, a request for reporting at least one handover tag for the terminal device to the IAB donor, wherein the at least one handover tag for the terminal device includes a first group identity indicating a first group of terminal devices to be served by the IAB node, or includes a second group identity indicating a second group of terminal devices not to be served by the IAB node.

In some embodiments, the method 800 may further comprise receiving from the terminal device, at least one handover tag for the terminal device, wherein the at least one handover tag for the terminal device includes a first group identity indicating a first group of terminal devices to be served by the IAB node, or includes a second group identity indicating a second group of terminal devices not to be served by the IAB node; and forwarding the at least one handover tag for the terminal device to the IAB donor.

In some embodiments, the at least one handover tag of the IAB node may be transmitted to the IAB donor when the IAB node connects to the IAB donor.

Now reference is made to FIG. 9 illustrating a simplified block diagram of an apparatus 900 that may be embodied in/as a data processing device (such as UE, IAB-node, and IAB-done, shown in Figures 3, 4, 5) . The apparatus 900 may comprise at least one processor 901, such as a data processor (DP) and at least one memory (MEM) 902 coupled to the at least one processor 901. The apparatus 900 may further comprise one or more transmitters TX, one or more receivers RX 903, or one or more transceivers coupled to the one or more processors 901 to communicate wirelessly and/or through wireline.

The processors 901 may be of any type suitable to the local technical environment, 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 MEMs 902 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples.

The MEM 902 stores a program (PROG) 904. The PROG 904 may include instructions that, when executed on the associated processor 901, enable the apparatus 900 to operate in accordance with the embodiments of the present disclosure, for example to perform one of the

methods

600, 700 and 800. A combination of the at least one processor 901 and the at least one MEM 902 may form processing circuitry or means 905 adapted to implement various embodiments of the present disclosure.

Various embodiments of the present disclosure may be implemented by computer program executable by one or more of the processors 901, software, firmware, hardware or in a combination thereof.

In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, 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, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these 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.

As such, it should be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules. It should thus be appreciated that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit, where the integrated circuit may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor, a digital signal processor, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

It should be appreciated that at least some aspects of the exemplary embodiments of the inventions may be embodied in computer-executable instructions, such as in one or more program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. The computer executable instructions may be stored on a computer readable medium, for example, non-transitory computer readable medium, such as a hard disk, optical disk, removable storage media, solid state memory, RAM, etc. As will be appreciated by one of skills in the art, the function of the program modules may be combined or distributed as desired in various embodiments. In addition, the function may be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA) , and the like.

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.

Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of this disclosure.

The present invention includes any novel feature or combination of features disclosed herein either explicitly or any generalization thereof. Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this invention.

Claims

An apparatus for wireless communication, the apparatus comprising:

at least one processor; and

at least one memory including computer program code, the at least one memory and the computer program code configured to, working with the at least one processor, cause the apparatus to:

obtain at least one handover tag for a terminal device, which includes a first group identity indicating a first group of terminal devices to be served by an integrated access and backhaul (IAB) node, or includes a second group identity indicating a second group of terminal devices not to be served by an IAB node; and

transmit the at least one handover tag to at least one base station, so that a procedure related to a handover of the terminal device to the IAB node or away from the IAB node is enabled to be initiated by the at least one base station based at least in part on the at least one handover tag.
The apparatus according to claim 1, wherein the at least one handover tag comprises a first handover tag for the terminal device, which indicates the first group of terminal devices to be served by the IAB node, and

wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to transmit the first handover tag to a first base station of the at least one base station, so that a procedure related to a handover of the terminal device to the IAB node is enabled to be initiated based at least in part on the first handover tag.
The apparatus according to claim 1 or 2, wherein the at least one handover tag comprises a second handover tag for the terminal device, which indicates the second group of terminal devices not to be served by the IAB node, and

wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to transmit the second handover tag to a second base station of the at least one base station, so that a procedure related to a handover of the terminal device from the IAB node is enabled to be initiated based at least in part on the second handover tag.
The apparatus according to claim 1, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to,

receive from the at least one base station, a request for the at least one handover tag,

wherein the at least one handover tag is transmitted in response to the request for the at least one handover tag.
The apparatus according to claim 1, wherein the at least one handover tag is transmitted without a request from the at least one base station.
The apparatus according to claim 3, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to transmit the second handover tag by at least one of the following operations:

transmitting the second handover tag to the first base station for forwarding the second handover tag to the second base station, when the terminal device is handed over to the second base station;

transmitting the second handover tag to the second base station, upon a detection that the terminal device is in proximity of the second base station; and/or

transmitting the second handover tag to the second base station, upon the terminal device detects a cell served by the second base station.
The apparatus according to any of claims 1 to 6, wherein the apparatus is comprised in the terminal device.
The apparatus according to any of claims 1 to 6, wherein the apparatus is comprised in a core network node.
The apparatus according to claim 8, wherein the core network node comprises an access and mobility function.
The apparatus according to any of claims 7 to 9, wherein the first handover tag and/or the second handover tag are transmitted in a context of the terminal device.
The apparatus according to claim 8 or 9, wherein the core network node comprises a location management function, and wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to:

transmit to the at least one base station, a set of handover tags comprising a plurality of handover tags for a plurality of terminal devices,

wherein the set of handover tags includes the at least one handover tag for the terminal device.
The apparatus according to any of claims 1 to 11, wherein the at least one handover tag further comprises at least one of:

a first type indicator indicative of whether the first group of terminal devices indicated by the first group identity are to be served by the IAB node or not; or

a second type indicator indicative of whether the second group of terminal devices indicated by the second group identity are to be served by the IAB node or not.
The apparatus according to claim 12, wherein the at least one handover tag further comprises:

an identity of a cell; and/or

an expiry time of the at least one handover tag.
An apparatus for wireless communication at a base station, the method comprising:

at least one processor; and

at least one memory including computer program code, the at least one memory and the computer program code configured to, working with the at least one processor, cause the apparatus to:

receive at least one handover tag of a first integrated access and backhaul (IAB) node, which includes a third group identity indicating a third group of terminal devices to be served by the first IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the first IAB node;

receive at least one handover tag for a terminal device, which includes a first group identity indicating a first group of terminal devices to be served by a second IAB node, or includes a second group identity indicating a second group of terminal devices not to be served by a second IAB node;

match the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device; and

initiate a procedure related to a handover of the terminal device to the first IAB node or away from the first IAB node, based at least in part on the matching of the at least one handover tag of the first IAB node and the at least one handover tag for the terminal device.
The apparatus according to claim 14, wherein the at least one handover tag of the first IAB node is received from the first IAB node, or is received from another base station.
The apparatus according to claim 14 or 15, wherein the at least one handover tag for the terminal device is received from at least one of the following:

the terminal device;

a core network node; or

another base station.
The apparatus according to any of claims 14 to 16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to:

transmit, to the terminal device or the core network node, a request for the at least one handover tag for the terminal device,

wherein the received at least one handover tag for the terminal device is transmitted in response to the request.
The apparatus according to any of claims 14 to 17, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to match the at least one handover tag of the first IAB with the at least one handover tag for the terminal device by at least one of following operations:

determining whether the first group identity is included in the third group identity or is the same as the third identity; or

determining whether the second group identity is included in the fourth group identity or is the same as the fourth group identity.
The apparatus according to claim 18, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus match the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device by at least one of the following operations:

determining that the handover of the terminal device is a handover to the first IAB node, when the at least one handover tag of the first IAB node indicates that the third group of terminal devices are to be served by the first IAB node and the at least one handover tag indicates that the first group of terminal devices are to be served by the second IAB node; or

determining that the handover of the terminal device is a handover from the first IAB node, when the at least one handover tag of the first IAB node indicates that the fourth group of terminal devices are not to be served by the first IAB node and the at least one handover tag for the terminal device indicates that the second group of terminal devices are not to be served by the second IAB node.
The apparatus according to any of claims 14 to 18, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to match the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device by:

determining a target cell of the handover based on the at least one handover tag of the first IAB node and/or the at least one handover tag for the terminal device; and

determining that the terminal device is an applicable terminal device of the handover based on the at least one handover tag of the first IAB node and/or the at least one handover tag for the terminal device.
The apparatus according to any of claims 14 to 20, wherein the at least one handover tag of the first IAB node further comprises:

a third type indicator indicative of whether the third group of terminal devices indicated by the third group identity are to be served by the first IAB node or not; or

a fourth type indicator indicative of whether the fourth group of terminal devices indicated by the fourth group identity are not to be served by the first IAB node or not; and

wherein the at least one handover tag for the terminal device further comprises:

a first type indicator indicative of whether the first group of terminal devices indicated by the first group identity are to be served by the second IAB node or not; or

a second type indicator indicative of whether the second group of terminal devices indicated by the second group identity are not to be served by the second IAB node or not.
The apparatus according to claim 21, wherein at least one of the at least one handover tag of the first IAB node or the at least one handover tag for the terminal device further comprises:

an identity of a cell; and/or

an expiry time of the at least one handover tag of the first IAB node or the at least one handover tag for the terminal device.
The apparatus according to claim 14, wherein the procedure comprises a preparation procedure of the handover of the terminal device.
An apparatus for wireless communication at an integrated access and backhaul (IAB) node, the apparatus comprising:

at least one processor; and

at least one memory including computer program code, the at least one memory and the computer program code configured to, working with the at least one processor, cause the apparatus to:

obtain at least one handover tag of the IAB node which includes a third group identity indicating a third group of terminal devices to be served by the IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the IAB node; and

transmit the at least one handover tag to an IAB donor, so that a procedure is enabled to be initiated based at least in part on the at least one handover tag, wherein the procedure is related to a handover of a terminal device in the third group of terminal devices or the fourth group of terminal devices to the IAB node or away from the IAB node.
The apparatus according to claim 24, wherein the at least one handover tag comprises a third handover tag, which indicates the third group of terminal devices to be served by the IAB node, and

wherein the third handover tag is transmitted to the IAB donor, so that the procedure is enabled to be initiated based at least in part on the third handover tag.
The apparatus according to claim 24, wherein the at least one handover tag comprises a fourth handover tag, which indicates the fourth group of terminal devices not to be served by the IAB node, and

wherein the fourth handover tag is transmitted to the IAB donor, so that the procedure is enabled to be initiated based at least in part on the fourth handover tag.
The apparatus according to claim 26, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to,

transmit, to the terminal device, a request for reporting at least one handover tag for the terminal device to the IAB donor, wherein the at least one handover tag for the terminal device indicates a first group of terminal devices to be served by the IAB node, or a second group of terminal devices not to be served by the IAB node.
The apparatus according to claim 26, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to,

receive from the terminal device, at least one handover tag for the terminal device, wherein the at least one handover tag for the terminal device indicates a first group of terminal devices to be served by the IAB node, or a second group of terminal devices not to be served by the IAB node; and

forward the at least one handover tag for the terminal device to the IAB donor.
The apparatus according to claim 24, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus to transmit the at least one handover tag to the IAB donor by: transmitting the at least one handover tag to the IAB donor when the IAB node connects to the IAB donor.
The apparatus according to any of claims 24 to 29, wherein the at least one handover tag of the IAB node further comprises at least one of:

a third type indicator indicative of whether the third group of terminal devices indicated by the first group identity are to be served by the IAB node or not; or

a fourth type indicator indicative of whether the fourth group of terminal devices indicated by the second group identity are to be served by the IAB node or not.
The apparatus according to claim 29, wherein the at least one handover tag of the IAB node further comprises:

an identity of a cell; and/or

an expiry time of the at least one handover tag.
A method for wireless communication, the method comprising:

obtain at least one handover tag for a terminal device, which includes a first group identity indicating a first group of terminal devices to be served by an integrated access and backhaul (IAB) node, or includes a second group identity indicating a second group of terminal devices not to be served by an IAB node; and

transmit the at least one handover tag to at least one base station, so that a procedure related to a handover of the terminal device to the IAB node or away from the IAB node is enabled to be initiated by the at least one base station based at least in part on the at least one handover tag.
A method for wireless communication at a base station, the method comprising:

receiving at least one handover tag of a first integrated access and backhaul (IAB) node, which includes a third group identity indicating a third group of terminal devices to be served by the first IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the first IAB node;

receiving at least one handover tag for a terminal device, which includes a first group identity indicating a first group of terminal devices to be handed over to be served by a first IAB node, or includes a second group identity indicating a second group of terminal devices not to be served by a second IAB node;

matching the at least one handover tag of the first IAB node with the at least one handover tag for the terminal device; and

initiating a procedure related to a handover of the terminal device to the first IAB node or away from the first IAB node, based at least in part on the matching of the at least one handover tag of the first IAB node and the at least one handover tag for the terminal device.
A method for wireless communication at an integrated access and backhaul (IAB) node, the method comprising:

obtaining at least one handover tag of the IAB node which includes a third group identity indicating a third group of terminal devices to be served by the IAB node, or includes a fourth group identity indicating a fourth group of terminal devices not to be served by the IAB node; and

transmitting the at least one handover tag to an IAB donor, so that a procedure is enabled to be initiated based at least in part on the at least one handover tag, wherein the procedure is related to a handover of a terminal device in the third group of terminal devices or the fourth group of terminal devices to the IAB node or away from the IAB node.
A computer-readable storage medium having computer-executable program code instructions stored therein, when executed by a processor, the computer-executable program code instructions cause the processor to perform steps of the method of claim 32.
A computer-readable storage medium having computer-executable program code instructions stored therein, when executed by a processor, the computer-executable program code instructions cause the processor to perform steps of the method of claim 33.
A computer-readable storage medium having computer-executable program code instructions stored therein, when executed by a processor, the computer-executable program code instructions cause the processor to perform steps of the method of claim 34.