WO2022252130A1

WO2022252130A1 - Methods, devices, and computer readable medium for communication

Info

Publication number: WO2022252130A1
Application number: PCT/CN2021/097781
Authority: WO
Inventors: Zhe Chen; Gang Wang
Original assignee: Nec Corporation
Priority date: 2021-06-01
Filing date: 2021-06-01
Publication date: 2022-12-08

Abstract

Embodiments of the present disclosure relates to communications. The migrating integrated access and backhaul (IAB) node performs a condition handover (CHO) to handover from a source IAB node to a target IAB node. The migrating IAB node transmits, to a descendant IAB node of the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU). The first BAP PDU indicates routing information to identify a CHO path. In this way, it minimizes service interruption during handover. It also offloads uplink traffic congestion caused by a default routing and bearer mapping configuration.

Description

METHODS, DEVICES, AND COMPUTER READABLE MEDIUM FOR COMMUNICATION

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication, and in particular, to methods, devices, and computer readable medium for communication.

BACKGROUND

In communication networks, a base station generally has a limited reach, to achieve connectivity between mobile devices. A technology of handover has been proposed, which is a process in telecommunication and mobile communication in which cellular transmission is transferred from one base station to another base station without losing connectivity to the cellular transmission. Handover is a core element in deploying mobile transmission as it creates data sessions or connects phone calls between mobile devices which are constantly on the move.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for communication.

In a first aspect, there is provided a method for communication. The method comprises performing, at a migrating integrated access and backhaul (IAB) node, a condition handover (CHO) to handover from a source IAB node to a target IAB node; and transmitting, to a descendant IAB node of the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) , the first BAP PDU indicating routing information to identify a CHO path.

In a second aspect, there is provided a method for communication. The method comprises in accordance with a determination that a migrating integrated access and backhaul (IAB) performs a condition handover (CHO) to handover from a source IAB node to a target IAB node, receiving, at a descendant IAB node of the migrating IAB node and from the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) , the first BAP PDU indicating routing information to identity a CHO path.

In a third aspect, there is provided a method for communication. The method comprises transmitting, at a source donor centralized unit (CU) and to a target donor CU, a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity; receiving, from the target donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node; transmitting, to the target donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity; and receiving, from the target donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.

In a fourth aspect, there is provided a method for communication. The method comprises receiving, at a target donor centralized unit (CU) and from a source donor CU, a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity; transmitting, to the source donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node; receiving, from the source donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity; and transmitting, to the source donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.

In a fifth aspect, there is provided a migrating integrated access and backhaul (IAB) node. The migrating IAB node comprises a processing unit; and a memory coupled to the processing unit and storing instructions thereon, the instructions, when executed by the processing unit, causing the migrating IAB node to perform acts comprising: performing, at a migrating integrated access and backhaul (IAB) node, a condition handover (CHO) to handover from a source IAB node to a target IAB node; and transmitting, to a descendant IAB node of the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) , the first BAP PDU indicating routing information to identify a CHO path.

In a sixth aspect, there is provided a descendant IAB node. The descendant IAB node comprises a processing unit; and a memory coupled to the processing unit and storing instructions thereon, the instructions, when executed by the processing unit, causing the descendant IAB node to perform acts comprising: in accordance with a determination that a migrating integrated access and backhaul (IAB) performs a condition handover (CHO) to handover from a source IAB node to a target IAB node, receiving, at a descendant IAB node of the migrating IAB node and from the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) , the first BAP PDU indicating routing information to identity a CHO path.

In a seventh aspect, there is provided a source donor centralized unit (CU) . The source donor CU comprises a processing unit; and a memory coupled to the processing unit and storing instructions thereon, the instructions, when executed by the processing unit, causing the source donor CU to perform acts comprising: transmitting, to a target donor CU, a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity; receiving, from the target donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node; transmitting, to the target donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity; and receiving, from the target donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.

In an eighth aspect, there is provided a target centralized unit (CU) . The target donor CU comprises a processing unit; and a memory coupled to the processing unit and storing instructions thereon, the instructions, when executed by the processing unit, causing the target donor CU to perform acts comprising: receiving, from a source donor CU, a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity; transmitting, to the source donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node; receiving, from the source donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity; and transmitting, to the source donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.

In a ninth aspect, there is provided a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to carry out the method according to any one of the first aspect, second, third or fourth aspect.

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

BRIEF DESCRIPTION OF THE DRAWINGS

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

Fig. 1 is a schematic diagram of a communication environment in which embodiments of the present disclosure can be implemented;

Fig. 2 illustrates a signaling flow for handover according to some embodiments of the present disclosure;

Figs. 3A and 3B illustrate simplified block diagrams of structures of messages according to some embodiments of the present disclosure, respectively;

Fig. 4 illustrates a signaling flow for rerouting according to some embodiments of the present disclosure;

Fig. 5 illustrates a signaling flow for handover according to some embodiments of the present disclosure;

Fig. 6 is a flowchart of an example method in accordance with an embodiment of the present disclosure;

Fig. 7 is a flowchart of an example method in accordance with an embodiment of the present disclosure;

Fig. 8 is a flowchart of an example method in accordance with an embodiment of the present disclosure;

Fig. 9 is a flowchart of an example method in accordance with an embodiment of the present disclosure; and

Fig. 10 is a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

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

As used herein, the term “network device” refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB) , an Evolved NodeB (eNodeB or eNB) , a NodeB in new radio access (gNB) a Remote Radio Unit (RRU) , a radio head (RH) , a remote radio head (RRH) , a low power node such as a femto node, a pico node, a satellite network device, an aircraft network device, and the like. For the purpose of discussion, in the following, some example embodiments will be described with reference to eNB as examples of the network device.

As used herein, the term “terminal device” refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, user equipment (UE) , personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs) , portable computers, tablets, wearable devices, internet of things (IoT) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, device on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, or image capture devices such as digital cameras, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. In the following description, the terms “terminal device” , “communication device” , “terminal” , “user equipment” and “UE” may be used interchangeably.

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

Communications discussed herein may use conform to any suitable standards including, but not limited to, New Radio Access (NR) , Long Term Evolution (LTE) , LTE-Evolution, LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , Code Division Multiple Access (CDMA) , cdma2000, and Global System for Mobile Communications (GSM) and the like. Furthermore, the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.85G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) , and the sixth (6G) communication protocols. The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies.

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

As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “includes” and its variants are to be read as open terms that mean “includes, but is not limited to. ” The term “based on” is to be read as “based at least in part on. ” The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ” The terms “first, ” “second, ” and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below.

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

According to conventional technologies, conditional handover (CHO) has been introduced to reduce the service interruption and reduce the radio link failure (RLF) possibility. The network provides CHO triggering criteria, with the radio configuration of potential target gNBs. When the UE evaluates the criteria of the target gNB is fulfilled, the UE may complete the handover on its own, with a notification to the target gNB by RRCReconfigurationComplete message.

Further, the introduction of inter-donor Integrated Access Backhaul (IAB) -node migration increases robustness and allows for more refined load-balancing and topology management. Reduction of service interruption time caused by IAB-node migration and backhaul (BH) RLF recovery improves network performance and allows network deployments to undergo more frequent topology changes, and provides stable backhaul performance.

According to conventional technologies, after the handover is completed, the donor centralized unit (CU) can reconfigure a routing table and bearer mapping afterwards. But when to reconfigure the routing table and the bearer mapping is up to network implementation. Congestion occurs during this handover/reconfiguration gap. For example, default UL routing and bearer mapping configuration can cause congestion due to multi-hop IAB architecture.

In order to solve at least part of above and potential problems, a solution of handover is proposed. The migrating IAB node performs a condition handover (CHO) to handover from a source IAB node to a target IAB node. The migrating IAB node transmits, to a descendant IAB node of the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) . The first BAP PDU indicates routing information to identify a CHO path. In this way, it minimizes service interruption during handover. It also offloads uplink traffic congestion caused by a default routing and bearer mapping configuration.

Fig. 1 illustrates a schematic diagram of a communication system in which embodiments of the present disclosure can be implemented. The communication system 100, which is a part of a communication network, comprises a terminal device 110-1, a terminal device 110-2, ..., a terminal device 110-N, which can be collectively referred to as “terminal device (s) 110. ” The number N can be any suitable integer number.

The communication system 100 further comprises a IAB node 120-1, a IAB node 120-2, a IAB node 120-3, a IAB node 120-4, a IAB node 120-5, ..., a IAB node 120-M which can be collectively referred to as “IAB node (s) 120. ” In some embodiments, the IAB node may be any suitable network device. The number M can be any suitable integer number. As shown in Fig. 1, the communication system 100 may also a donor CU 130-1, a donor CU 130-2 and a donor 130-3. It should be noted that the number of donors shown in Fig. 1 is only an example. In the communication system 100, the IAB node 120 and the terminal devices 110 can communicate data and control information to each other. The IAB nodes 120 can communicate with each other. The donor CUs can also communicate with the IAB nodes 120. Only for the purpose of illustrations, the IAB node 120-2 can be handed over from the IAB node 120-3 to the IAB node 120-4. In some embodiments, the IAB node 120-2 can be handed over from the IAB node 120-3 to the IAB node 120-5. Thus, the IAB node 120-3 can be regarded as a source IAB node and the IAB node 120-4 or the IAB node 120-4 can be regarded as a target IAB node. The donor 130-1 connects with the IAB node 120-3. In some embodiments, the donor 130-1 can also connect with the IAB node 120-4. In this case, the handover between the IAB node 120-3 and the IAB node 120-4 can be referred to as intra-donor CU handover. In other embodiments, the donor 130-2 can connect with the IAB node 120-4 and the donor 130-3 can connect with the IAB node 120-5. In this case, the handover between the IAB node 120-3 and the IAB node 120-4 can be referred to as inter-donor CU handover. According to the topology shown in Fig. 1, the IAB node 120-2 can be regarded an ancestor/parent node of the IAB node 120-1 and the terminal devices 110. In other words, the IAB node 120-1 can be regarded as descendant/child node of the IAB node 120-2. The numbers of devices shown in Fig. 1 are given for the purpose of illustration without suggesting any limitations.

Communications in the communication system 100 may be implemented according to any proper communication protocol (s) , comprising, but not limited to, cellular communication protocols of the first generation (1G) , the second generation (2G) , the third generation (3G) , the fourth generation (4G) , the fifth generation (5G) and the sixth generation (6G) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Divided Multiple Address (CDMA) , Frequency Divided Multiple Address (FDMA) , Time Divided Multiple Address (TDMA) , Frequency Divided Duplexer (FDD) , Time Divided Duplexer (TDD) , Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Divided Multiple Access (OFDMA) and/or any other technologies currently known or to be developed in the future.

Embodiments of the present disclosure can be applied to any suitable scenarios. For example, embodiments of the present disclosure can be implemented at reduced capability NR devices. Alternatively, embodiments of the present disclosure can be implemented in one of the followings: NR multiple-input and multiple-output (MIMO) , NR sidelink enhancements, NR systems with frequency above 52.6GHz, an extending NR operation up to 71GHz, narrow band-Internet of Thing (NB-IOT) /enhanced Machine Type Communication (eMTC) over non-terrestrial networks (NTN) , NTN, UE power saving enhancements, NR coverage enhancement, NB-IoT and LTE-MTC, Integrated Access and Backhaul (IAB) , NR Multicast and Broadcast Services, or enhancements on Multi-Radio Dual-Connectivity.

The term “slot” used herein refers to a dynamic scheduling unit. One slot comprises a predetermined number of symbols. The term “downlink (DL) sub-slot” may refer to a virtual sub-slot constructed based on uplink (UL) sub-slot. The DL sub-slot may comprise fewer symbols than one DL slot. The slot used herein may refer to a normal slot which comprises a predetermined number of symbols and also refer to a sub-slot which comprises fewer symbols than the predetermined number of symbols.

In some embodiments, the donor 130-1 can only provide CHO configuration to the IAB node 120-2 only if donor 130-1 hasn’t received any measurement reports from any descendant node/UE of the IAB node 120-2 during the past T period. If the IAB node 120-4 has a connection to the donor 130-1, the IAB node 120-2 may transmit data through the path from the IAB node 120-4 to the donor 130-1. In some embodiments, the terminal device 110-1 may transmit data to the IAB node 120-2. Before the IAB node 120-2 transmits the data to the IAB node 120-3, the IAB node 120-2 may handover to the IAB node 120-4. The IAB node 120-2 may transmit the data to the IAB node 120-4 and the IAB node may transmit the data to the donor 130-1.

Embodiments of the present disclosure will be described in detail below. Reference is first made to Fig. 2, which shows a signaling chart illustrating process 200 among devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 200 will be described with reference to Fig. 1. The process 200 may involve the terminal device 110-1, the IAB node 120-1, the IAB node 120-2, the IAB node 120-3, the IAB node 120-4, the donor 130-1 and the donor 130-2 in Fig. 1.

The IAB node 120-2 may perform 2005 measurements for the IAB node 120-3 (i.e., the source IAB node) and the IAB node 120-4 (i.e., the target IAB node) . The IAB node 120-2 may transmit 2010 the measurement report about the IAB nodes 120-3 and 120-4 to the IAB node 120-3. For example, the measurement report can be transmitted via Radio Resource Control signaling. The IAB node 120-2 may perform any suitable measurement events. For example, the IAB node 120-2 may perform Event A3 where a neighbor cell becomes offset better than a serving cell. Alternatively, the IAB node 120-2 may perform any one of: Event A1 where a serving cell becomes better than a threshold, Event A2 where the serving cell becomes worse than a threshold, Event A4 where the neighbor cell becomes better than a threshold, Event A5 wherein the serving cell becomes worse than threshold 1 and the neighbor cell becomes better than threshold A2, Event B1 wherein inter RAT neighbor becomes better than a threshold, and Event B2 where the serving cell becomes worse than threshold 1 and inter RAT neighbor becomes better than threshold 2. In some embodiments, the IAB node 120-2 may measure a reference signal received power. Alternatively, the IAB node 120-2 may measure a reference signal receiving quality. The IAB node 120-2 may measure any suitable parameters.

The IAB node 120-2 may encapsulate the RRC message into a F1-AP message. The IAB node 120-3 may transfer 2012 the F1-AP message which comprises the RRC container which contains the measurement report to the donor 130-1. The donor 130-1 may make 2015 the conditional handover decision. For example, the donor 130-1 may determine that the IAB node 120-2 needs to be handed over from the IAB node 120-3 to the IAB node 120-4. Further, the donor 130-1 may also determine that one or more descendant nodes (for example, the IAB node 120-1) of the IAB node 120-2 need to be handed over from the IAB node 120-3 to the IAB node 120-4.

The donor 130-1 may transmit 2020 a first handover request for the IAB node 120-2 to the donor 130-2. The first handover request can comprise an identity of the IAB node 120-2. The first handover request can also comprise a routing identity for the IAB node 120-2. The donor 130-2 may transmit 2025 a first handover request acknowledgment to the donor 130-1 for the IAB node 120-2. The first handover request acknowledgment can comprise an identity of the IAB node 120-2. The first handover request acknowledgment can also comprise bearer mapping for the IAB node 120-2. Alternatively or in addition, the first handover request acknowledgment can comprise routing table information for the IAB node 120-2.

The donor 130-1 may transmit 2030 a second handover request for the IAB node 120-1 to the donor 130-2. The second handover request can comprise an identity of the IAB node 120-1. The second handover request can also comprise a routing identity for the IAB node 120-1. The donor 130-2 may transmit 2035 a second handover request acknowledgment to the donor 130-1 for the IAB node 120-1. The second handover request acknowledgment can comprise an identity of the IAB node 120-3. The second handover request acknowledgment can also comprise bearer mapping for the IAB node 120-3. Alternatively or in addition, the second handover request acknowledgment can comprise routing table information for the IAB node 120-3. It should be noted that the donor 130-1 can transmit the second handover request after receiving the first handover request acknowledgment. Alternatively, the donor 130-1 can transmit the second handover request before receiving the first handover request acknowledgement. In this way, it avoids routing identity collision between donor CUs.

In other embodiments, the bearer mapping in the first or second handover request acknowledgement can refer to a traffic IE. In this way, it can offload UL traffic congestion. Table 1 below shows an example of the bearer mapping.

Table 1

The donor CU 130-1 may transmit 2040 downlink RRC message transfer to the IAB node 120-3. The IAB node 120-3 may transmit 2045 a RRC Reconfiguration to the IAB node 120-2. The RRCReconfiguration may comprise the CHO execution condition. The IAB node 120-2 may transmit 2050 a RRC Reconfiguration complete message to the IAB node 120-3. The IAB node 120-3 may transfer 2055 UL RRC message to the donor CU 130-1.

The donor CU 130-1 may transmit 2060 a first BAP mapping configuration to the IAB node 120-1. The first BAP mapping configuration can comprise the identity of the IAB node 120-1. The first BAP mapping configuration can also comprise BH routing information added list of the CHO. The donor CU 130-1 may transmit 2065 a second BAP mapping configuration to the IAB node 120-2. The second BAP mapping configuration can comprise the identity of the IAB node 120-2. The second BAP mapping configuration can also comprise BH routing information added list of the CHO. It should be noted that the first BAP mapping configuration can be transmitted before or after the transmission of the second BAP mapping configuration.

In some embodiments, the routing table information can refer to backhaul (BH) routing information. A target IAB node cell identity (for example, the IAB node 120-4 or the IAB node 120-5) can be added in backhaul adaptation protocol (BAP) mapping configuration message. In this way, the routing table information indicates that which target IAB node the migrating IAB node is handed over to. Alternatively, a network device identity (i.e., CU identity) can replace the target IAB node cell identity. In other embodiments, a condition reconfiguration identity can replace the target IAB node cell identity. Table 2 below shows an example of the routing information in Routing information element (IE) .

Table 2

The donor CU 130-1 may transmit 2070 a first UE context modification request to the IAB node 120-1. The first UE context modification request can comprise the identity of the IAB node 120-1. The first UE context modification request can comprise also a BH radio link control (RLC) channel to be modified list for the CHO. The donor CU 130-1 may transmit 2075 a second UE context modification request the IAB node 120-2. The second UE context modification request can comprise the identity of the IAB node 120-2. The second UE context modification request can also a BH radio link control (RLC) channel to be modified list for the CHO. It should be noted that the first UE context modification request can be transmitted before or after the transmission of the second UE context modification request. Table 3 below shows an example of the UE context modification request.

Table 3

The IAB node 120-2 performs 2080 the CHO to handover from the source IAB node to the target IAB node. For example, the IAB node 120-2 is handed over from the IAB node 120-3 to the IAB node 120-4.

The IAB node 120-2 transmits 2085 a CHO complete message in a BAP protocol data unit (PDU) to the IAB node 120-1. The BAP PDU indicates routing information to identify a CHO path. In some embodiments, the donor CU 130-1 may include the routing information in a header of the BAP PDU which is sent to the IAB node 120-2.

In some embodiments, the CHO path can be identified by a routing identity of the target donor DU (for example, the donor DU of the IAB node 120-4) . For example, the routing information can comprise a first routing identity. The first routing identity can comprise the destination identity and a path identity. The first routing identity can be used to find all descendant IAB nodes. In addition, the routing information can comprise a second routing identity. The second routing identity can indicate which path is executed for the CHO. Fig. 3A shows a simplified block diagram of a BAP PDU according to some embodiments of the present disclosure. The BAP PDU 300 can comprise a bit field 301 which indicate the BAP PDU is related to data or control information. The bit field 302 can be used to indicate the PDU type. The bit fields 303-1, 303-2, 303-4, 303-5, 303-6, 303-7, 303-8, 303-9, 303-10 and 303-11 can be reserved bits. The bit fields 304-1 and 304-2 can be used to indicate a destination of the BAP PDU. The bit fields 305-1 and 305-2 can be used to indicate a path identity of the BAP PDU. The bit fields 306-1, 306-2 and 306-3 can indicate the routing identity used after the CHO.

Alternatively, the CHO path can be identified by a CHO reconfiguration identity. Fig. 3B shows a simplified block diagram of a BAP PDU according to some embodiments of the present disclosure. The BAP PDU 310 can comprise a bit field 311 which indicate the BAP PDU is related to data or control information. The bit field 312 can be used to indicate the PDU type. The bit fields 313-1, 313-2, 313-4, 313-5, 313-6, 313-7, 313-8, 313-9, 313-10, 313-11 and 303-12 can be reserved bits. The bit fields 314-1 and 314-2 can be used to indicate a destination of the BAP PDU. The bit fields 315-1 and 315-2 can be used to indicate a path identity of the BAP PDU. The bit field 316 can comprise the CHO reconfiguration identity.

Table 4 below shows an example of PDU type. It should be noted that the numbers shown in Table 4 are only examples not limitations.

Table 4

Bit	Description
0000	Flow control feedback per BH RLC channel

0001	Flow control feedback per routing ID
0010	Flow control feedback polling
0011	BH RLF indication
0100	CHO complete indication
0101-1111	Reserved

For example, if the bit field 302 indicates “0100” , it means that the BAP PDU 300 comprises a CHO complete message. Similarly, if the bit field 312 indicates “0100” , it means that the BAP PDU 310 comprises a CHO complete message.

After receiving the CHO complete message, the IAB node 120-1 can apply the new routing table and/or bearer mapping. The IAB node 120-1 can forward the CHO complete message based on the destination identity in the BAP PDU. For example, if the IAB node 120-1 determines that the destination identity in the BAP PDU is not the IAB node 120-1, the IAB node 120-2 may forward the CHO complete message based on the routing identity, for example, a descendant IAB node of the IAB node 120-1. Upon reception of the CHO complete message, the descendant IAB node of the IAB node 120-1 can find the destination identity in the CHO complete message is the identity of itself, and then the descendant IAB node of the IAB node 120-1 will not forward the CHO complete message.

Before the IAB node 120-1 transmits a RRC reconfiguration to the terminal device 110-1 to apply the handover, the terminal device 110-1 may transmit 2090 UL data with PDCP configuration of the donor CU 130-1 to the IAB node 120-1.

In some embodiments, the IAB node 120-1 is configured with two routing tables with the source donor CU. For example, in some embodiments, the IAB node 120-4 may also connect with the donor CU 130-1. In this situation, there are two routing tables with the donor CU 130-1, i.e., one is through the IAB node 120-3 and the other is through the IAB node 120-4. In this case, the IAB node 120-1 can transmit 2095 the UL data to the IAB node 120-4. The IAB node 120-4 may then transmit 2100 the UL data to the donor CU 130-1.

Alternatively, the UL BAP PDU cannot be routed to the donor CU 130-1. For example, the IAB node 120-1 may be only configured with the routing table of the target donor CU (for example, the donor CU 130-2) . In other embodiments, the IAB node 120-1 may be configured with two routing tables of the source donor CU (for example, the IAB node 120-4 may also connect with the donor CU 130-1) and the IAB node 120-2 executed the CHO to the IAB node 120-5. In this case, in some embodiments, the IAB node 120-1 can transmit 2110 a RLC non-acknowledgment (NACK) to the terminal device 110-1. The IAB node 120-1 can transmit 2105 the RRC reconfiguration to the terminal device 110-1. The terminal device 110-1 may retransmit 21110 the RLC PDUC with a same PDCP sequence number by the re-established PDCP entity. Alternatively, in such case, the IAB node 120-2 may transmit 2115 the PDCP PDU with source donor CU PDCP configuration to the IAB node 120-3. The IAB node 120-4 can forward 2120 the PDCP PDU to the donor CU 130-2. If the donor CU 130-2 is able to decode the PDCP PDU based on the PDCP configuration of the donor CU 130-1, the donor CU 130-2 can decode the PDCP PDU. If the donor CU 130-2 is not able to decode the PDCP PDU, the donor CU 130-2 can transmit 2125 the PDCP PDU to the donor CU 130-1. The PDCP PDU can be transmitted with an indication to request the donor CU 130-1 to decode the PDCP PDU. The donor CU 130-1 can decode the PDCP PDU to obtain a PDCP service data unit (SDU) . The donor CU 130-1 can transmit 2130 the PDCP SDU to the donor CU 130-2.

Embodiments of the present disclosure will be described in detail below. Reference is first made to Fig. 4, which shows a signaling chart illustrating process 400 among devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 400 will be described with reference to Fig. 1. The process 400 may involve the IAB node 120-1, the IAB node 120-2, and the donor 130-1in Fig. 1.

In some embodiments, the donor CU 130-1 may transmit 4010 a reroute configuration in a RRC reconfiguration to the IAB node 120-2. The reroute configuration can comprise an old routing identity, an old CU identity, a new routing identity, and a new CU identity. The CU identity can be an identity which can uniquely identify a target parent node of a target donor CU. Alternatively, the CU identity may be a gNB identity associated with the target donor CU. In other embodiments, the CU identity can be a condition reconfiguration identity. In this way, it can reduce the number of bits. Table 5 shows an example of the reroute configuration. It should be noted that the Table 5 is only an example not limitation. Details of how to utilize the reroute configuration are described later.

Table 5

As shown in Table 5, the old CU ID is associated with the old routing ID, and the new CU ID is associated with the new routing ID.

The IAB node 120-2 can store 4015 a previous routing table after the CHO is executed. The IAB node 120-1 may transmit 4020 a BAP PDU to the IAB node 120-2. The BAP PDU comprises a previous routing identity which is no longer valid. The IAB node 120-2 may change 4025 the old routing identity which corresponds to the old CU ID to a new routing identity which corresponds to the new CU ID. In some embodiments, the IAB node 120-2 can select the new routing identity based on an implementation of the IAB node 120-2. Alternatively, the IAB node 120-2 may determine the new routing identity based on the reroute configuration received (4010) from the donor CU 130-1. For example, after the IAB node 120-2 is handed over to the donor CU 130-2, the IAB node 120-2 may determine the new routing identity which corresponds to the CU ID of the donor CU 130-2 based on the reroute configuration shown as Table 5. The IAB node 120-2 may transmit 4027 the BAP PDU with the new routing identity to the target donor CU (i.e., the donor CU 130-2) . In this way, the buffered BAP PDU can be rerouted correctly after the CHO.

In some embodiments, the donor CU 130-1 may transmit 4030 the reroute configuration to descendant IAB node (s) of the IAB node 120-2, for example, the IAB node 120-1. The IAB node 120-1 may transmit 4035 the BAP PDU with the new routing identity to the IAB node 120-2. For example, the IAB node 120-1 can determine the new routing identity which corresponds to the CU ID of the donor CU 130-2 based on the reroute configuration shown as Table 5. The IAB node 120-1 can replace the old routing identity corresponding to the donor CU 130-1 to the new routing identity corresponding to the donor CU 130-2. The IAB node 120-2 can forward 4040 the BAP PDU to the donor CU 130-2. In this way, the buffered BAP PDU can be rerouted correctly after the CHO.

In an example embodiment, both the IAB node 120-4 and the IAB node 120-5 may be configured to the IAB node 120-1 and the IAB node 120-2. After the configuration, the IAB node 120-1 may hold RCK acknowledgment when a RLC PDU is received from the terminal device 110-1. If the IAB node 120-2 indicates that the CHO to the IAB node 120-4 is executed, the IAB node 120-1 may send the RLC ACK to the terminal device 110-1 and change the routing identity to the new routing identity.

Alternatively, if the IAB node 120-2 indicates that the CHO to the IAB node 120-5 is executed, the IAB node 120-1 may not transmit any RLC ACK to the terminal device 110-1. The IAB node 120-1 may drop UL data from the terminal device 110-1. The terminal device 110-1 may ensure lossless by PDCP status report.

In other embodiments, if the IAB node 120-2 indicates that the CHO to the IAB node 120-5 is executed, the IAB node 120-1 may change the routing identity to an identity associated with the target donor CU, i.e., the donor CU of the IAB node 120-5. In order to indicate that the BAP PDU is encoded/encrypted by the source CU PDCP configuration (i.e., the PDCP configuration of the donor CU 130-1) , the IAB node 120-1 can add an indication associated with the source donor CU. For example, the IAB node 120-1 can add a source CU BAP PDU indicator (for example, one bit) in the BAP PDU. When the donor CU 130-3 (i.e., the donor CU of the IAB node 120-5) receives a BAP PDU for the terminal device 110-1 with a source CU BAP PDU indicator, the PDCP entity of the donor CU 130-3 may decode or decrypt the PDCP PDU based on the PDCP configuration of the donor CU 130-1. If the donor CU 130-3 cannot decode the PDCP PDU based on the PDCP configuration of the donor CU 130-1, the donor CU 130-3 may transmit the PDCP PDU to the donor CU 130-1 with an indication to request the donor CU 130-1 to decode the PDCP PDU. The donor CU 130-1 may decode the PDCP PDU and obtain the PDCP SDU. The donor CU 130-1 can transmit the PDCP SDU to the donor CU 130-3.

Embodiments of the present disclosure will be described in detail below. Reference is first made to Fig. 5, which shows a signaling chart illustrating process 500 among devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 500 will be described with reference to Fig. 1. The process 500 may involve the terminal device 110-1, the IAB node 120-1, the IAB node 120-2, the IAB node 120-3, the IAB node 120-4, the donor 130-1 and the donor 130-2 in Fig. 1. Fig. 5 shows the process 500 according to embodiments of the present disclosure where intra-donor CU CHO is executed. In other words, the donor CU of the IAB nodes 120-3, 120-4 and 120-5 is the donor CU 130-1.

The IAB node 120-2 may perform 5005 measurements for the IAB node 120-3 (i.e., the source IAB node) and the IAB node 120-4 (i.e., the target IAB node) . The IAB node 120-2 may transmit 5010 the measurement report about the IAB nodes 120-3 and 120-4 to the IAB node 120-3. For example, the measurement report can be transmitted via Radio Resource Control signaling. The IAB node 120-2 may perform any suitable measurement events. For example, the IAB node 120-2 may perform Event A3 where a neighbor cell becomes offset better than a serving cell. Alternatively, the IAB node 120-2 may perform any one of: Event A1 where a serving cell becomes better than a threshold, Event A2 where the serving cell becomes worse than a threshold, Event A4 where the neighbor cell becomes better than a threshold, Event A5 wherein the serving cell becomes worse than threshold 1 and the neighbor cell becomes better than threshold A2, Event B1 wherein inter RAT neighbor becomes better than a threshold, and Event B2 where the serving cell becomes worse than threshold 1 and inter RAT neighbor becomes better than threshold 2. In some embodiments, the IAB node 120-2 may measure a reference signal received power. Alternatively, the IAB node 120-2 may measure a reference signal receiving quality. The IAB node 120-2 may measure any suitable parameters.

The IAB node 120-2 may encapsulate the RRC message into a F1-AP message. The IAB node 120-3 may transfer 5012 the F1-AP message which comprises the RRC container which contains the measurement report to the donor 130-1. The donor 130-1 may make 2015 the conditional handover decision. For example, the donor 130-1 may determine that the IAB node 120-2 needs to be handed over from the IAB node 120-3 to the IAB node 120-4. Further, the donor 130-1 may also determine that one or more descendant nodes (for example, the IAB node 120-1) of the IAB node 120-2 need to be handed over from the IAB node 120-3 to the IAB node 120-4.

The donor CU 130-1 may transmit 5040 downlink RRC message transfer to the IAB node 120-3. The IAB node 120-3 may transmit 5045 a RRC Reconfiguration to the IAB node 120-2. The RRCReconfiguration may comprise the CHO execution condition. The IAB node 120-2 may transmit 5050 a RRC Reconfiguration complete message to the IAB node 120-3. The IAB node 120-3 may transfer 5055 UL RRC message to the donor CU 130-1.

The donor CU 130-1 may transmit 5060 a first BAP mapping configuration to the IAB node 120-1. The first BAP mapping configuration can comprise the identity of the IAB node 120-1. The first BAP mapping configuration can also comprise BH routing information added list of the CHO in addition to each BH routing information added list item. The donor CU 130-1 may transmit 5065 a second BAP mapping configuration to the IAB node 120-2. The second BAP mapping configuration can comprise the identity of the IAB node 120-2. The second BAP mapping configuration can also comprise BH routing information added list of the CHO. It should be noted that the first BAP mapping configuration can be transmitted before or after the transmission of the second BAP mapping configuration.

In other embodiments, the bearer mapping in the first or second handover request acknowledgement can refer to a traffic IE. In this way, it can offload UL traffic congestion. Table 6 below shows an example of the bearer mapping.

Table 6

In some embodiments, the routing table information can refer to backhaul (BH) routing information. A target IAB node cell identity (for example, the IAB node 120-4 or the IAB node 120-5) can be added in backhaul adaptation protocol (BAP) mapping configuration message. In this way, the routing table information indicates that which target IAB node the migrating IAB node is handed over to. Alternatively, a network device identity (i.e., CU identity) can replace the target IAB node cell identity. In other embodiments, a condition reconfiguration identity can replace the target IAB node cell identity. Table 7 below shows an example of the routing information in Routing information element (IE) . Table 8 below shows an example of BAP layer BH RLC channel mapping information list. It should be noted that Tables 7 and 8 are only examples not limitations.

Table 7

Table 8

The donor CU 130-1 may transmit 5070 a first UE context modification request to the IAB node 120-1. The first UE context modification request can comprise the identity of the IAB node 120-1. The first UE context modification request can comprise also a BH radio link control (RLC) channel to be modified list for the CHO. The donor CU 130-1 may transmit 5075 a second UE context modification request the IAB node 120-2. The second UE context modification request can comprise the identity of the IAB node 120-2. The second UE context modification request can also a BH radio link control (RLC) channel to be modified list for the CHO. It should be noted that the first UE context modification request can be transmitted before or after the transmission of the second UE context modification request. Table 9 below shows an example of the UE context modification request.

Table 9

The IAB node 120-2 performs 5080 the CHO to handover from the source IAB node to the target IAB node. For example, the IAB node 120-2 is handed over from the IAB node 120-3 to the IAB node 120-4. When the IAB node 120-2 executes the CHO to the IAB node 120-4, the IAB node 120-2 can apply 5085 the preconfigured bearer mapping and routing information for the IAB node 120-4.

The IAB node 120-2 transmits 5090 a CHO complete message in a BAP protocol data unit (PDU) to the IAB node 120-1. The CHO complete message can comprise BH routing information added for CHO. For example, if the IAB node 120-2 executes CHO to the IAB node 120-4, the CHO complete message can comprise the routing information for the IAB node 120-4.

After receiving the CHO complete message, the IAB node 120-1 can apply 5100 the new routing table and/or bearer mapping. The IAB node 120-2 can transmit 5105 a RRC reconfiguration complete message to the donor CU 130-1 after the CHO is executed.

Fig. 6 shows a flowchart of an example method 600 in accordance with an embodiment of the present disclosure. The method 600 can be implemented at any suitable devices. Only for the purpose of illustrations, the method 600 can be implemented at a migrating IAB node, for example the IAB node 120-2.

At block 610, the IAB node 120-2 performs a condition handover (CHO) to handover from a source IAB node (for example, the IAB node 120-3) to a target IAB node (for example, the IAB node 120-4) .

At block 610, the IAB node 120-2 transmits, to a descendant IAB node (for example, the IAB node 120-1) , a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) . The first BAP PDU indicates routing information to identify a CHO path.

In some embodiments, the routing information comprises: a first routing identity comprising a destination identity and a path identity, and a second routing identity indicating which path is executed for the CHO.

In some embodiments, the routing information comprises: a first routing identity which comprises a destination identity and a path identity, and a CHO reconfiguration identity.

In some embodiments, the source IAB node is connecting with a first donor centralized unit (CU) (for example, the donor CU 130-1) and the target IAB node is connecting with a second donor centralized unit (CU) (for example, the donor CU 130-2) .

In some embodiments, the IAB node 120-2 may receive, from the first donor CU, a BAP mapping configuration indicating: an identity of the migrating IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.

In some embodiments, the routing table information comprises one of: a cell identity of the target IAB node, a network identity associated with the target IAB node, or a gNB ID associated with the target CU; a condition reconfiguration identity.

In some embodiments, the IAB node 120-2 may stores, at the migrating IAB node, a previous routing table after the CHO. The IAB node 120-2 may receive, from the descendant IAB node, a second BAP PDU comprising a previous routing identity and replace the previous routing identity with a new routing identity.

In some embodiments, the IAB node 120-2 may receive a reroute configuration in a radio resource control reconfiguration from the first donor CU, the reroute configuration comprising: the previous routing identity, an old CU identity, a new routing identity, and a new CU identity.

In some embodiments, the source IAB node and the target IAB node are connecting with a third donor centralized unit (CU) .

In some embodiments, the IAB node 120-2 may receive, from the third donor CU, a BAP mapping configuration comprising a backhaul routing information added list for the CHO.

In some embodiments, the IAB node 120-2 may receive, from the third donor CU, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.

In some embodiments, the IAB node 120-2 may apply a preconfigured bearer mapping based on the UE context modification request and routing information for the target IAB node based on the BAP mapping configuration after the CHO is executed.

In some embodiments, the first BAP PDU indicates routing information for the target IAB node.

Fig. 7 shows a flowchart of an example method 700 in accordance with an embodiment of the present disclosure. The method 700 can be implemented at any suitable devices. Only for the purpose of illustrations, the method 700 can be implemented at a descendant IAB node, for example, the IAB node 120-1.

In some embodiments, at block 710, the IAB node 120-1 may receive, from a first donor CU, a BAP mapping configuration indicating: an identity of the descendant IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.

At block 720, in accordance with a determination that a migrating IAB (for example, the IAB node 120-2) performs a CHO to handover from a source IAB node (for example, the IAB node 120-3) to a target IAB node (for example, the IAB node 120-4) , the IAB node 120-1 receives from the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) . The first BAP PDU indicates routing information to identity a CHO path.

In some embodiments, the routing information comprises: a first routing identity which comprises a destination identity and a path identity, and a second routing identity which indicates which path is executed for the CHO.

In some embodiments, the source IAB node is connecting with a first donor CU (for example, the donor CU 130-1) and the target IAB node is connecting with a second donor CU (for example, the donor CU 130-2) .

In some embodiments, the IAB node 120-1 may receive, from the first donor CU, a BAP mapping configuration indicating: an identity of the descendant IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.

In some embodiments, the routing table information comprises one of: a cell identity of the target IAB node, a network identity associated with the target IAB node, or a condition reconfiguration identity.

In some embodiments, the IAB node 120-1 may receive, from a terminal device connecting with the descendant IAB node, uplink data with a packet data convergence protocol (PDCP) configuration of the first donor CU.

In some embodiments, if the descendant IAB node is configured with more than one routing table with the first donor CU, the IAB node 120-1 may forward the UL data to the target IAB node, wherein the UL data is forwarded to the first donor CU by the target IAB node.

In some embodiments, if the descendant IAB node is configured with one routing table with a third donor CU or that the descendant IAB node is configured with a routing table of the first donor CU and a routing table of the second donor CU, the IAB node 120-1 may transmit, to a terminal device, a radio link control (RLC) non-acknowledgment. The IAB node 120-1 may transmit, to the terminal device, a radio resource control (RRC) reconfiguration. The IAB node 120-1 may receive, from the terminal device, a RLC PDU with a same PDCP sequence number (SN) .

In some embodiments, if the descendant IAB node is configured with one routing table with a third donor CU or that the descendant IAB node is configured with a routing table of the first donor CU and a routing table of the second donor CU, the IAB node 120-1 may transmit, to the second donor CU, a PDCP PDU with a PDCP configuration of the first donor CU.

In some embodiments, the IAB node 120-1 may receive a reroute configuration in a radio resource control reconfiguration from the first donor CU. The reroute configuration comprises the previous routing identity, an old CU identity, a new routing identity, and a new CU identity. In some embodiments, the IAB node 120-1 may transmit a second BAP PDU comprising the new routing identity.

In some embodiments, the IAB node 120-1 may receive uplink data from a terminal device. The IAB node 120-1 may hold a radio link control (RLC) acknowledgment to the uplink data. The IAB node 120-1 may drop the uplink data from the terminal device.

In some embodiments, the IAB node 120-1 may receive uplink data from a terminal device. The IAB node 120-1 may transmit to the second donor CU, a BAP PDU comprising the uplink data and an indication associated with the first donor CU BAP PDU.

In some embodiments, the source IAB node and the target IAB node are connecting with a third CU, for example, the donor CU 130-1.

In some embodiments, the IAB node 120-1 may receive, from the third donor CU, a BAP mapping configuration comprising a backhaul routing information added list for the CHO.

In some embodiments, the IAB node 120-1 may receive, from the third donor CU, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO. The IAB node 120-1 may apply a preconfigured bearer mapping based on the UE context modification request and routing information for the target IAB node based on the BAP mapping configuration during the CHO.

Fig. 8 shows a flowchart of an example method 800 in accordance with an embodiment of the present disclosure. The method 800 can be implemented at any suitable devices. Only for the purpose of illustrations, the method 800 can be implemented at a source donor CU, for example, the donor CU 130-1..

At block 810, the donor CU 130-1 transmits, to a target donor CU (for example, the donor CU 130-2) , a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity.

At block 820, the donor CU 130-1 receives, from the target donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node.

At block 830, the donor CU 130-1 transmits, to the target donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity.

At block 840, the donor CU 130-1 receives, from the target donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.

In some embodiments, the donor CU 130-1 may receive, from the target donor CU, a packet data convergence protocol (PDCP) protocol data unit (PDU) with an indication for decoding. The donor CU 130-2 may decode the PDCP PDU to obtain a PDCP service data unit (SDU) . The donor CU 130-2 may transmit the PDCP SDU to the target donor CU.

In some embodiments, the donor CU 130-1 may transmit, to the migrating IAB node, a first BAP mapping configuration indicating: an identity of the migrating IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU. The donor CU 130-1 may transmit, to the descendant IAB node, a second BAP mapping configuration indicating: an identity of the descendant IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.

In some embodiments, the donor CU 130-1 may transmit, to at least one of: the migrating IAB node or the descendant IAB node, a reroute configuration in a radio resource control reconfiguration. The reroute configuration may comprise the previous routing identity, an old CU identity, a new routing identity, and a new CU identity.

In some embodiments, the donor CU 130-1 may transmit, transmitting, to the migrating IAB node, a BAP mapping configuration comprising a backhaul routing information added list for the CHO. In some embodiments, the donor CU 130-1 may transmit, to the migrating IAB node, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.

In some embodiments, the donor CU 130-1 may transmit, to the descendant IAB node, a BAP mapping configuration comprising a backhaul routing information added list for the CHO. In some embodiments, the donor CU 130-1 may transmit, to the descendant IAB node, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.

Fig. 9 shows a flowchart of an example method 900 in accordance with an embodiment of the present disclosure. The method 900 can be implemented at any suitable devices. Only for the purpose of illustrations, the method 900 can be implemented at a target donor CU, for example, the donor CU 130-2.

At block 910, the donor CU 130-2 receives from a source donor CU (for example, the donor CU 130-1) , a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity.

At block 920, the donor CU 130-2 transmits, to the source donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node.

At block 930, the donor CU 130-2 receives, from the source donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity.

At block 940, the donor CU 130-2 transmits, to the source donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.

In some embodiments, the donor CU 130-2 may receive, from the descendant IAB node, a packet data convergence protocol (PDCP) protocol data unit (PDU) with a PDCP configuration of the first donor CU. The donor CU 130-2 may decode the PDCP PDU.

In some embodiments, ift the target donor CU fails in decoding the PDCP PDU, the donor CU 130-2 may transmit, to the source donor CU, the PDCP PDU with an indication for decoding. The donor CU 130-2 may receive, from the source donor CU, a PDCP service data unit (SDU) which is obtained based on the PDCP PDU by the source donor CU.

Fig. 10 is a simplified block diagram of a device 1000 that is suitable for implementing embodiments of the present disclosure. The device 1000 can be considered as a further example implementation of the terminal device, the IAB node 120 or the donor as shown in Fig. 1. Accordingly, the device 1000 can be implemented at or as at least a part of the terminal device, the IAB node 120 or the donor.

As shown, the device 1000 includes a processor 1000, a memory 1020 coupled to the processor 1000, a suitable transmitter (TX) and receiver (RX) 1040 coupled to the processor 1000, and a communication interface coupled to the TX/RX 1040. The memory 1020 stores at least a part of a program 1030. The TX/RX 1040 is for bidirectional communications. The TX/RX 1040 has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2 interface for bidirectional communications between eNBs, S1 interface for communication between a Mobility Management Entity (MME) /Serving Gateway (S-GW) and the eNB, Un interface for communication between the eNB and a relay node (RN) , or Uu interface for communication between the eNB and a terminal device.

The program 1030 is assumed to include program instructions that, when executed by the associated processor 1000, enable the device 1000 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to Fig. 2 to 9. The embodiments herein may be implemented by computer software executable by the processor 1000 of the device 1000, or by hardware, or by a combination of software and hardware. The processor 1000 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1000 and memory 1020 may form processing means adapted to implement various embodiments of the present disclosure.

The memory 1020 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 1020 is shown in the device 1000, there may be several physically distinct memory modules in the device 1000. The processor 1000 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1000 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

In some embodiments, a migrating integrated access and backhaul (IAB) node comprises circuitry configured to: perform a condition handover (CHO) to handover from a source IAB node to a target IAB node; and transmit, to a descendant IAB node of the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) , the first BAP PDU indicating routing information to identify a CHO path.

In some embodiments, the source IAB node is connecting with a first donor centralized unit (CU) and the target IAB node is connecting with a second donor centralized unit (CU) .

In some embodiments, the migrating IAB node comprises circuitry further configured to: receive, from the first donor CU, a BAP mapping configuration indicating: an identity of the migrating IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.

In some embodiments, the migrating IAB node comprises circuitry further configured to: store, at the migrating IAB node, a previous routing table after the CHO; receive, from the descendant IAB node, a second BAP PDU comprising a previous routing identity; and replace the previous routing identity with a new routing identity.

In some embodiments, the migrating IAB node comprises circuitry further configured to: receive a reroute configuration in a radio resource control reconfiguration from the first donor CU, the reroute configuration comprising: the previous routing identity, an old CU identity, a new routing identity, and a new CU identity.

In some embodiments, the migrating IAB node comprises circuitry further configured to: receive, from the third donor CU, a BAP mapping configuration comprising a backhaul routing information added list for the CHO.

In some embodiments, the migrating IAB node comprises circuitry further configured to: receive, from the third donor CU, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.

In some embodiments, the migrating IAB node comprises circuitry further configured to: apply a preconfigured bearer mapping based on the UE context modification request and routing information for the target IAB node based on the BAP mapping configuration after the CHO is executed.

In some embodiments, a descendant IAB node comprises circuitry configured to in accordance with a determination that a migrating IAB performs a CHO to handover from a source IAB node to a target IAB node, receive, at a descendant IAB node of the migrating IAB node and from the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) , the first BAP PDU indicating routing information to identity a CHO path.

In some embodiments, the descendant IAB node comprises circuitry further configured to receive, from the first donor CU, a BAP mapping configuration indicating: an identity of the descendant IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.

In some embodiments, the descendant IAB node comprises circuitry further configured to receive, from a terminal device connecting with the descendant IAB node, uplink data with a packet data convergence protocol (PDCP) configuration of the first donor CU.

In some embodiments, the descendant IAB node comprises circuitry further configured to: in accordance with a determination that the descendant IAB node is configured with more than one routing table with the first donor CU, forward the UL data to the target IAB node, wherein the UL data is forwarded to the first donor CU by the target IAB node.

In some embodiments, the descendant IAB node comprises circuitry further configured to: in accordance with a determination that the descendant IAB node is configured with one routing table with a third donor CU or that the descendant IAB node is configured with a routing table of the first donor CU and a routing table of the second donor CU, transmit, to a terminal device, a radio link control (RLC) non-acknowledgment; transmit, to the terminal device, a radio resource control (RRC) reconfiguration; and receive, from the terminal device, a RLC PDU with a same PDCP sequence number (SN) .

In some embodiments, the descendant IAB node comprises circuitry further configured to in accordance with a determination that the descendant IAB node is configured with one routing table with a third donor CU or that the descendant IAB node is configured with a routing table of the first donor CU and a routing table of the second donor CU, transmit, to the second donor CU, a PDCP PDU with a PDCP configuration of the first donor CU.

In some embodiments, the descendant IAB node comprises circuitry further configured to receive a reroute configuration in a radio resource control reconfiguration from the first donor CU, the reroute configuration comprising: the previous routing identity, an old CU identity, a new routing identity, and a new CU identity; and transmitting a second BAP PDU comprising the new routing identity.

In some embodiments, the descendant IAB node comprises circuitry further configured to receive uplink data from a terminal device; hold a radio link control (RLC) acknowledgment to the uplink data; and drop the uplink data from the terminal device.

In some embodiments, the descendant IAB node comprises circuitry further configured to receive uplink data from a terminal device; and transmit, to the second donor CU, a BAP PDU comprising the uplink data and an indication associated with the first donor CU BAP PDU.

In some embodiments, the descendant IAB node comprises circuitry further configured to receive, from the third donor CU, a BAP mapping configuration comprising a backhaul routing information added list for the CHO.

In some embodiments, the descendant IAB node comprises circuitry further configured to receive, from the third donor CU, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO; and apply a preconfigured bearer mapping based on the UE context modification request and routing information for the target IAB node based on the BAP mapping configuration during the CHO.

In some embodiments, a source CU comprises circuitry configured to: transmit, to a target donor CU, a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity; receive, from the target donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node; transmit, to the target donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity; and receive, from the target donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.

In some embodiments, the source CU comprises circuitry further configured to: receive, from the target donor CU, a packet data convergence protocol (PDCP) protocol data unit (PDU) with an indication for decoding; decode the PDCP PDU to obtain a PDCP service data unit (SDU) ; and transmit the PDCP SDU to the target donor CU.

In some embodiments, the source CU comprises circuitry configured to: transmit, to the migrating IAB node, a first BAP mapping configuration indicating: an identity of the migrating IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU; and transmit, to the descendant IAB node, a second BAP mapping configuration indicating: an identity of the descendant IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.

In some embodiments, the source CU comprises circuitry configured to: transmit transmitting, to at least one of: the migrating IAB node or the descendant IAB node, a reroute configuration in a radio resource control reconfiguration, the reroute configuration comprising: the previous routing identity, an old CU identity, a new routing identity, and a new CU identity.

In some embodiments, the source CU comprises circuitry configured to: transmit to the migrating IAB node, a BAP mapping configuration comprising a backhaul routing information added list for the CHO; and transmit, to the migrating IAB node, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.

In some embodiments, a source CU comprises circuitry configured to: transmit, to the descendant IAB node, a BAP mapping configuration comprising a backhaul routing information added list for the CHO; and transmit, to the descendant IAB node, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.

In some embodiments, a target CU comprises circuitry configured to: receive, from a source donor CU, a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity; transmit, to the source donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node; receive, from the source donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity; and transmit, to the source donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.

In some embodiments, the target CU comprises circuitry further configured to: receive, from the descendant IAB node, a packet data convergence protocol (PDCP) protocol data unit (PDU) with a PDCP configuration of the first donor CU; and decode the PDCP PDU.

In some embodiments, the target CU comprises circuitry further configured to: in accordance with a determination that the target donor CU fails in decoding the PDCP PDU, transmit, to the source donor CU, the PDCP PDU with an indication for decoding; and receive, from the source donor CU, a PDCP service data unit (SDU) which is obtained based on the PDCP PDU by the source donor CU.

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

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to any of Figs. 4-10. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

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

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

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

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

Claims

A communication method, comprising:

performing, at a migrating integrated access and backhaul (IAB) node, a condition handover (CHO) to handover from a source IAB node to a target IAB node; and

transmitting, to a descendant IAB node of the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) , the first BAP PDU indicating routing information to identify a CHO path.
The method of claim 1, wherein the routing information comprises:

a first routing identity comprising a destination identity and a path identity, and

a second routing identity indicating which path is executed for the CHO.
The method of claim 1, wherein the routing information comprises:

a first routing identity which comprises a destination identity and a path identity, and

a CHO reconfiguration identity.
The method of claim 1, wherein the source IAB node is connecting with a first donor centralized unit (CU) and the target IAB node is connecting with a second donor centralized unit (CU) .
The method of claim 4, further comprising:

receiving, from the first donor CU, a BAP mapping configuration indicating: an identity of the migrating IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.
The method of claim 5, wherein the routing table information comprises one of:

a cell identity of the target IAB node,

a network identity associated with the target IAB node, or

a gNB ID associated with the target CU;

a condition reconfiguration identity.
The method of claim 4, further comprising:

storing, at the migrating IAB node, a previous routing table after the CHO;

receiving, from the descendant IAB node, a second BAP PDU comprising a previous routing identity; and

replacing the previous routing identity with a new routing identity.
The method of claim 7, further comprising:

receiving a reroute configuration in a radio resource control reconfiguration from the first donor CU, the reroute configuration comprising:

the previous routing identity,

an old CU identity,

a new routing identity, and

a new CU identity.
The method of claim 1, wherein the source IAB node and the target IAB node are connecting with a third donor centralized unit (CU) .
The method of claim 9, further comprising:

receiving, from the third donor CU, a BAP mapping configuration comprising a backhaul routing information added list for the CHO.
The method of claim 9, further comprising:

receiving, from the third donor CU, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.
The method of claim 11, further comprising:

applying a preconfigured bearer mapping based on the UE context modification request and routing information for the target IAB node based on the BAP mapping configuration after the CHO is executed.
The method of claim of claim 9, wherein the first BAP PDU indicates routing information for the target IAB node.
A communication method, comprising:

in accordance with a determination that a migrating integrated access and backhaul (IAB) node performs a condition handover (CHO) to handover from a source IAB node to a target IAB node, receiving, at a descendant IAB node of the migrating IAB node and from the migrating IAB node, a CHO complete message in a first backhaul adaptation protocol (BAP) protocol data unit (PDU) , the first BAP PDU indicating routing information to identity a CHO path.
The method of claim 14, wherein the routing information comprises:

a first routing identity which comprises a destination identity and a path identity, and

a second routing identity which indicates which path is executed for the CHO.
The method of claim 14, wherein the routing information comprises:

a first routing identity which comprises a destination identity and a path identity, and

a CHO reconfiguration identity.
The method of claim 14, wherein the source IAB node is connecting with a first donor centralized unit (CU) and the target IAB node is connecting with a second donor centralized unit (CU) .
The method of claim 17, further comprising:

receiving, from the first donor CU, a BAP mapping configuration indicating: an identity of the descendant IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.
The method of claim 18, wherein the routing table information comprises one of:

a cell identity of the target IAB node,

a network identity associated with the target IAB node, or

a condition reconfiguration identity.
The method of claim 17, further comprising:

receiving, from a terminal device connecting with the descendant IAB node, uplink data with a packet data convergence protocol (PDCP) configuration of the first donor CU.
The method of claim 20, further comprising:

in accordance with a determination that the descendant IAB node is configured with more than one routing table with the first donor CU, forwarding the UL data to the target IAB node, wherein the UL data is forwarded to the first donor CU by the target IAB node.
The method of claim 20, further comprising:

in accordance with a determination that the descendant IAB node is configured with one routing table with a third donor CU or that the descendant IAB node is configured with a routing table of the first donor CU and a routing table of the second donor CU, transmitting, to a terminal device, a radio link control (RLC) non-acknowledgment;

transmitting, to the terminal device, a radio resource control (RRC) reconfiguration; and

receiving, from the terminal device, a RLC PDU with a same PDCP sequence number (SN) .
The method of claim 20, further comprising:

in accordance with a determination that the descendant IAB node is configured with one routing table with a third donor CU or that the descendant IAB node is configured with a routing table of the first donor CU and a routing table of the second donor CU, transmitting, to the second donor CU, a PDCP PDU with a PDCP configuration of the first donor CU.
The method of claim 17, further comprising:

receiving a reroute configuration in a radio resource control reconfiguration from the first donor CU, the reroute configuration comprising:

the previous routing identity,

an old CU identity,

a new routing identity, and

a new CU identity; and

transmitting a second BAP PDU comprising the new routing identity.
The method of claim 17, further comprising:

receiving uplink data from a terminal device;

holding a radio link control (RLC) acknowledgment to the uplink data; and

dropping the uplink data from the terminal device.
The method of claim 17, further comprising:

receiving uplink data from a terminal device; and

transmitting, to the second donor CU, a BAP PDU comprising the uplink data and an indication associated with the first donor CU BAP PDU.
The method of claim 14, wherein the source IAB node and the target IAB node are connecting with a third donor centralized unit (CU) .
The method of claim 27, further comprising:

receiving, from the third donor CU, a BAP mapping configuration comprising a backhaul routing information added list for the CHO.
The method of claim 27, further comprising:

receiving, from the third donor CU, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO; and

applying a preconfigured bearer mapping based on the UE context modification request and routing information for the target IAB node based on the BAP mapping configuration during the CHO.
The method of claim of claim 14, wherein the first BAP PDU indicates routing information for the target IAB node.
A communication method, comprising:

transmitting, at a source donor centralized unit (CU) and to a target donor CU, a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity;

receiving, from the target donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node;

transmitting, to the target donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity; and

receiving, from the target donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.
The method of claim 31, further comprising:

receiving, from the target donor CU, a packet data convergence protocol (PDCP) protocol data unit (PDU) with an indication for decoding;

decoding the PDCP PDU to obtain a PDCP service data unit (SDU) ; and

transmitting the PDCP SDU to the target donor CU.
The method of claim 31, further comprising:

transmitting, to the migrating IAB node, a first BAP mapping configuration indicating: an identity of the migrating IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU; and

transmitting, to the descendant IAB node, a second BAP mapping configuration indicating: an identity of the descendant IAB node, bearer mapping information of the second donor CU, and routing table information of the second donor CU.
The method of claim 33, wherein the routing table information comprises one of:

a cell identity of the target IAB node,

a network identity associated with the target IAB node, or

a condition reconfiguration identity.
The method of claim 31, further comprising:

transmitting, to at least one of: the migrating IAB node or the descendant IAB node, a reroute configuration in a radio resource control reconfiguration, the reroute configuration comprising:

the previous routing identity,

an old CU identity,

a new routing identity, and

a new CU identity.
The method of claim 31, further comprising:

transmitting, to the migrating IAB node, a BAP mapping configuration comprising a backhaul routing information added list for the CHO; and

transmitting, to the migrating IAB node, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.
The method of claim 31, further comprising:

transmitting, to the descendant IAB node, a BAP mapping configuration comprising a backhaul routing information added list for the CHO; and

transmitting, to the descendant IAB node, a UE context modification request indicating a backhaul radio link control (RLC) channel to be modified list for the CHO.
A communication method, comprising:

receiving, at a target donor centralized unit (CU) and from a source donor CU, a first handover request indicating: a first identity of a migrating integrated access and backhaul (IAB) node and a routing identity;

transmitting, to the source donor CU, a first handover request acknowledgment indicating: the first identity, bearer mapping for the migrating IAB node, and routing information for the migrating IAB node;

receiving, from the source donor CU, a second handover request indicating: a second identity of a descendant IAB node and the routing identity; and

transmitting, to the source donor CU, a second handover request acknowledgment indicating: the second identity, bearer mapping for the descendant IAB node, and routing information for the descendant IAB node.
The method of claim 38, further comprising:

receiving, from the descendant IAB node, a packet data convergence protocol (PDCP) protocol data unit (PDU) with a PDCP configuration of the first donor CU; and

decoding the PDCP PDU.
The method of claim 39, further comprising:

in accordance with a determination that the target donor CU fails in decoding the PDCP PDU, transmitting, to the source donor CU, the PDCP PDU with an indication for decoding; and

receiving, from the source donor CU, a PDCP service data unit (SDU) which is obtained based on the PDCP PDU by the source donor CU.
An integrated access and backhaul (IAB) node, comprising:

circuitry, configured to perform the method according to any one of claims 1-13, or any one of claims 14-30.
A donor centralized unit, comprising:

circuitry, configured to perform the method according to any one of claims 31-37, or any one of claims 38-40.
A computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to perform the method according to any one of claims 1-13, or any one of claims 14-30, or any one of claims 31-37, or any one of claims 38-40.