WO2022160249A1

WO2022160249A1 - Methods, devices, and computer readable medium for communication

Info

Publication number: WO2022160249A1
Application number: PCT/CN2021/074416
Authority: WO
Inventors: Zhe Chen; Da Wang; Gang Wang
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2021-01-29
Filing date: 2021-01-29
Publication date: 2022-08-04
Anticipated expiration: 2023-07-29

Abstract

According to embodiments of the present disclosure, solutions on dual transmission handover have been proposed. According to embodiments of the present disclosure, an IAB node receives a first packet in a BAP layer from a first communication device. The first packet comprises an indication of a dual transmission handover between the first communication device and a second communication device. The first packet also comprises a first sequence number which is determined based on a second sequence number which is configured by a donor CU of the first communication device to a donor DU of the donor CU. In this way, the dual transmission handover can be achieved and it can ensure communication reliability.

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 recent communication networks, network speed has been improved. The communication networks are expected to provide low latency and reliability for consumers and industries. In order to achieve super-fast data rates and ultra-low latency, higher frequency electromagnetic waves (for example, millimeter waves) are introduced into the communication networks. However, signals transmitted with higher frequency electromagnetic waves are easily blocked by objects. In this situation, a technology of Integrated Access and Backhaul (IAB) has been introduced. Further, handover procedures are very important to ensure communication qualities. In cellular telecommunication, the term “handover (HO) ” refers to a process of transferring an ongoing cell or data session from one channel to another channel. The handover procedures may be different in different scenarios. Therefore, applying the handover to the IAB scenario is worth studying.

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 receiving, at an integrated access backhaul (IAB) node and from a first communication device, a first packet in a backhaul adaptation protocol (BAP) layer, the first packet comprising: an indication of a dual transmission handover between the first communication device and a second communication device, and a first sequence number which is determined based on a second sequence number, wherein the second sequence number is configured by a first donor centralized unit (CU) of the first communication device to a first donor distributed unit (DU) of the first donor CU.

In a second aspect, there is provided a method for communication. The method comprises receiving, at a first donor distributed unit (DU) and from a first donor centralized unit (CU) , a backhaul adaptation protocol (BAP) data forwarding start message comprising a second sequence number configured by the first donor CU; receiving, from the first donor CU, a packet in a data unit to be forwarded to an integrated access backhaul (IAB) node by the first donor DU with a first sequence number; and transmitting, to the IAB node, a first packet in the BAP layer generated based on the packet in the data unit, the first packet comprising: an indication of a dual transmission handover between the first donor CU and a second donor CU, and the first sequence number which is determined based on the second sequence number.

In a third aspect, there is provided a method for communication. The method comprises transmitting, at a first donor centralized unit (CU) and to a first donor distributed unit (DU) , a backhaul adaptation protocol (BAP) data forwarding start message comprising a second sequence number which is used for determining a first sequence number by the first donor DU; and transmitting, to the first donor DU, a packet in a data unit to forwarded to an integrated access backhaul (IAB) node by the first donor DU with the first sequence number.

In a fourth aspect, there is provided a method for communication. The method comprises receiving, at an integrated access backhaul (IAB) node and from a first communication device, a first packet in a backhaul adaptation protocol (BAP) layer, the first packet comprising a packet data convergence protocol (PDCP) sequence number; transmitting, to a third communication device, the first packet in a first cell related to the first communication device; receiving, from a second communication device, a second packet in the BAP layer, the second packet comprising the PDCP sequence number; and transmitting, to a third communication device, a second packet in a second cell related to the second communication device.

In a fifth aspect, there is provided a method for communication. The method comprises receiving, at a source donor centralized unit (CU) and from an integrated access backhaul (IAB) node, a measurement report regarding a radio link control channel between the IAB node and a source donor DU of the source donor CU; determining, based on the measurement, a dual transmission handover between the source donor CU and a target donor CU; and transmitting, to the target donor CU, a dual transmission handover request indicating an identity of the radio link control channel and an identity of the IAB node.

In a sixth aspect, there is provided an IAB node. The 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 IAB node device to perform method according the first aspect.

In a seventh aspect, there is provided a donor DU. The donor DU 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 donor DU to perform method according the second aspect.

In an eighth aspect, there is provided a donor CU. The donor CU 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 donor CU to perform method according the third aspect.

In a ninth aspect, there is provided a IAB node. The 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 IAB node device to perform method according the fourth aspect.

In a tenth aspect, there is provided a donor CU. The donor CU 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 donor CU to perform method according the fifth aspect.

In an eleventh 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, second, third, fourth, or fifth 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 illustrates a schematic diagram of an IAB architecture;

Fig. 2 illustrates a schematic diagram of an IAB architecture;

Figs. 3A and 3B illustrate schematic diagrams of a F1 interface;

Fig. 4 is a schematic diagram of a communication environment in which embodiments of the present disclosure can be implemented;

Fig. 5 is a flowchart of an example method for handover/load balancing according to some embodiments of the present disclosure;

Figs. 6A and 6B illustrate simplified block diagrams of structures of messages according to some embodiments of the present disclosure, respectively;

Fig. 7 is a flowchart of an example method for handover/load balancing according to some embodiments of the present disclosure;

Fig. 8 is a flowchart of an example method for handover/load balancing according to some embodiments of the present disclosure;

Fig. 9 illustrates a signaling flow for handover/load balancing according to some embodiments of the present disclosure;

Fig. 10 illustrates a signaling flow for handover/load balancing according to some embodiments of the present disclosure;

Fig. 11 is a flowchart of an example method for handover according to some embodiments of the present disclosure;

Fig. 12 is a flowchart of an example method for handover according to some embodiments of the present disclosure;

Fig. 13 illustrates a signaling flow for handover according to some embodiments of the present disclosure; and

Fig. 14 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.

As mentioned above, handover procedures are very important to ensure communication qualities. For example, in release 16 mobility enhancement, a Dual Active Protocol Stack (DAPS) handover has been introduced to reduce handover failure and minimize service interruption. The term “DAPS handover” used herein can refer to a handover procedure that maintains a source gNB connection after reception of radio resource control (RRC) message for handover and until releasing a source cell after successful random access to a target gNB. For data radio bearers configured with DAPS, the source gNB does not stop transmitting downlink packets until it receives a handover success message from the target gNB. The term “data radio bearer” used herein can refer to a bearer that can transport packets of an evolved packet system (EPS) bearer between a UE and a network device. Further, for DRBs configured with DAPS, the source gNB may send the EARLY STATUS TRANSFER message. The source gNB does not stop assigning sequence numbers (SNs) to downlink packet data convergence protocol (PDCP) service data units (SDUs) until it sends the SN STATUS TRANSFER message to the target gNB. The UE synchronizes to the target cell and completes the RRC handover procedure by sending RRCReconfigurationComplete message to target gNB. In case of DAPS handover, the UE does not detach from the source cell upon receiving the RRCReconfiguration message. In case of DAPS handover, the target gNB sends the HANDOVER SUCCESS message to the source gNB to inform that the UE has successfully accessed the target cell. In return, the source gNB sends the SN STATUS TRANSFER message for DRBs configured with DAPS and the normal data forwarding.

In a scenario of downlink (DL) , during HO preparation, a forwarding tunnel is always established. The source gNB is responsible for allocating downlink packet data convergence protocol (PDCP) SNs until the SN assignment is handed over to the target gNB and data forwarding takes place. That is, the source gNB does not stop assigning PDCP SNs to downlink packets until it receives the HANDOVER SUCCESS message and sends the SN STATUS TRANSFER message to the target gNB. Upon allocation of downlink PDCP SNs by the source gNB, it starts scheduling downlink data on the source radio link and also starts forwarding downlink PDCP SDUs along with assigned PDCP SNs to the target gNB. For security synchronization, hyper frame number (HFN) is maintained for the forwarded downlink SDUs with PDCP SNs assigned by the source gNB. The source gNB sends the EARLY STATUS TRANSFER message to convey the DL COUNT value, indicating PDCP SN and HFN of the first PDCP SDU that the source gNB forwards to the target gNB. HFN and PDCP SN are maintained after the SN assignment is handed over to the target gNB. The SN STATUS TRANSFER message indicates the next DL PDCP SN to allocate to a packet which does not have a PDCP sequence number yet. During handover execution period, the source and target gNBs separately perform robust header compression (ROHC) header compression, ciphering, and adding PDCP header. During handover execution period, the UE continues to receive downlink data from both source and target gNBs until the source gNB connection is released by an explicit release command from the target gNB. During handover execution period, the UE DAPS PDCP maintains separate security and ROHC header decompression associated with each gNB, while maintaining common reordering function, duplicate detection, discard function, and PDCP SDUs in-sequence delivery to upper layers. PDCP SN continuity is supported for both radio link control (RLC) acknowledgment mode (AM) and unacknowledgment mode (UM) DRBs configured with DAPS.

In a scenario of uplink (UL) , the UE transmits UL data to the source gNB until the random access procedure toward the target gNB has been successfully completed. Afterwards the UE switches its UL data transmission to the target gNB. Even after switching its UL data transmissions, the UE continues to send UL layer 1 channel state information (CSI) feedback, hybrid automatic repeat request (HARQ) feedback, layer 2 RLC feedback, ROHC feedback, HARQ data re-transmissions, and RLC data re-transmission to the source gNB. During handover execution period, the UE maintains separate security context and ROHC header compressor context for uplink transmissions towards the source and target gNBs. The UE maintains common UL PDCP SN allocation. PDCP SN continuity is supported for both RLC AM and UM DRBs configured with DAPS. During handover execution period, the source and target gNBs maintain their own security and ROHC header decompressor contexts to process UL data received from the UE. The establishment of a forwarding tunnel is optional. HFN and PDCP SN are maintained in the target gNB. The SN STATUS TRANSFER message indicates the first missing UL COUNT that the target should start delivering to the 5GC, even for RLC-UM.

As mentioned above, IAB is an important feature in 5G New Radio (NR) that enables rapid and cost-effective millimeter wave deployments through self-backhauling in the same spectrum. The term “wireless self-backhauling” used herein refers to a technology that uses the same wireless channel for coverage and backhaul connectivity to other base stations. It can achieve greater performance, more efficient use of spectrum resources and lowers equipment costs, while also reduce the reliance on the availability of wired backhaul at each access node location. In an IAB system, there are two types of network devices, IAB node and IAB donor. In other words, IAB is a multi-hop approach to network deployment and allows deployment of millimeter wave base stations with or without fiber backhaul transport. It works by having a fraction of the deployed network device act as donor nodes, using a fiber/wired connection. The remainder without a wired connection is called IAB nodes. Both types of BSs generate an equivalent cellular coverage area and appear identical to user equipment (UE) in its coverage area. The Donor distributed unit (DU) is a conventional fiber-fed BS connected to the centralized unit (CU) using an F1 interface. The IAB node may serve as a first hop or second hop node. Both donor and IAB nodes also directly support UEs multiplexed with the backhaul Ur interface. The Uu interface is directly between a UE and an IAB or donor node. The channel between two IAB nodes can be called radio link control (RLC) channel.

When IAB node is serving a UE, it works as a distributed unit (DU) to the UE, and a mobile terminal (MT) to its parent IAB node. PDCP is from UE to CU through the intermediate IAB node. Fig. 1 illustrates a schematic diagram of an IAB architecture. As shown in Fig. 1, the IAB node 120-1 and the IAB node 120-2 are the intermediate IAB nodes between the UE 110 and the IAB donor 130 which comprises the DU 130-1 and the CU 130-2. The UE 110 can comprise a service data adaptation protocol (SDAP) layer 1110, a PDCP layer 1120, a RLC layer 1130 and a medium access control (MAC) layer 1140. When the IAB node 120-2 works as a DU to the UE 110, it can comprise the RLC layer 1221 and the MAC layer 1222. When the IAB node 120-2 works as a MT to the IAB node 120-1, it can comprise a General Packet Radio Service (GPRS) Tunnelling Protocol User (GTP-U) layer 1223, a user datagram protocol (UDP) layer 1224, an internet protocol (IP) layer 1225, an adaptation layer 1226, a RLC layer 1227 and a MAC layer 1228. Since the IAB node 120-1 is between the IAB node 120-2 and the IAB donor 130, when the IAB node 120-1 works as the DU to the IAB node 120-2, the IAB node 120-1 can comprise an IP layer 1211, an adaptation layer 1212, a RLC layer 1213 and a MAC layer 1214. When the IAB node 120-1 works as the MT to the IAB donor 130, the IAB node 120-1 can comprise an IP layer 1215, an adaptation layer 1216, a RLC layer 1217 and a MAC layer 1218. The donor DU 130-1 can comprise an IP layer 1311, an adaptation layer 1312, a RLC layer 1313 and a MAC layer 1314. The donor CU 130-2 can comprise a SDAP layer 1321, a PDCP layer 1322, a GTP-U layer 1323, a UDP layer 1324 and an IP layer 1325. There can be backhaul (BH) RLC channels between the IAB node 120-2 and the IAB node 120-1. There can be an intra-donor F1-U interface between the donor DU 130-1 and the donor CU 130-2. It can be seen that the IAB nodes 120-1 and 120-2 do not comprise SDAP layers and PDCP layers.

Since IAB node doesn’t have PDCP entity, so IAB node can’t perform PDCP PDU duplication detection, dual stack for PDCP encryption, ROHC header compression. Fig. 2 illustrates a schematic diagram of an IAB architecture. When the IAB node 220-2 works as a DU, it can comprise a GTP-U layer 2221, a UDP layer 2222 and an IP layer 2223. When the IAB node 220-2 works as a MT, it can comprise a BAP layer 2224, a RLC layer 2225, a MAC layer 2226 and a physical (PHY) layer 2227. When the IAB node 220-1 works as a DU, it can comprise a BAP layer 2211, a RLC layer 2212, a MAC layer 2213 and a PHY layer 2214. When the IAB node 220-1 works as a MT, it can comprise a BAP layer 2215, a RLC layer 2216, a MAC layer 2217 and a PHY layer 2218. The IAB donor CU 240 can comprise a GTP-U layer 2401, a UDP layer 2402, an IP layer 2403, a L2 layer 2405 and a L1 layer 2406. When the IAB donor DU 230 connects with an IAB node, it can comprise an IP layer 2304, a BAP layer 2305, a RLC layer 2306, a MAC layer 2307 and a PHY layer 2308. When the IAB donor DU 230 connects with the IAB donor CU 240, it can comprise an IP layer 2301, a L2 layer 2302 and a L1 layer 2303. Backhaul RLC channel (s) are setup between the MT part and the parent nodes DU part and adaptation layer called Backhaul Adaptation Protocol (BAP) is agreed to be on top of the RLC layer. The IAB-node DU part connects to the IAB-donor CU with F1 interface which is enhanced to support IAB functions. F1 packets (GTP-U/UDP/IP for user plane (UP) and F1AP/SCTP/IP for control plane (CP) ) are transported on top of the adaptation layer. IAB thus implements L2 relaying. An IAB node represents a co-located resource providing NR access coverage and backhauling over the air interface. As such, an IAB node may take on both the personality of UE (MT part) for transferring backhaul traffic or that of gNB (or gNB-DU) serving connected UEs and forwarding backhaul traffic to the next hop. There can be BH RLC channels between the IAB node 220-2 and the IAB node 220-1. There can be an intra-donor F1-U interface between the donor DU 230 and the donor CU 240.

Figs. 3A and 3B illustrate schematic diagrams of a F1 interface. As shown in Fig. 3A, in a control plane, there can be a F1 AP layer 310 in the radio network layer and there can be a Stream Control Transmission Protocol (SCTP) layer 320, an IP layer 330, a data link layer 340, a physical layer 350 in the transport network layer. As shown in Fig. 3B, in a user plane, there can be a GTP-U layer 311, a UDP layer 321, an IP layer 331, a data link layer 341, a physical layer 351 in the transport network layer.

As illustrated in Figs 1-3, there is no PDCP entity in IAB nodes. A parent IAB DAPS handover cannot work due to lack of PDCP entity. For example, when an immigrating IAB node is required to handover from source parent IAB node to target parent IAB node, since the immigrating IAB node doesn’t have PDCP entity, source Donor CU1 can’t configure DAPS DRB for the immigrating IAB node. The data forwarding can be done for the RLC channel of the immigrating IAB node, as the immigrating IAB node can’t decode the duplicated PDCP PDU. If the immigrating IAB node can perform part of the DAPS HO function, its descendant node IAB still need instruction of the immigrating IAB node.

Therefore, new solutions on dual transmission handover (or DAPS like handover) on IAB nodes are needed. According to embodiments of the present disclosure, an IAB node receives a first packet in a BAP layer from a first communication device. The first packet comprises an indication of a dual transmission handover between the first communication device and a second communication device. The first packet also comprises a first sequence number which is determined based on a second sequence number which is configured by a donor CU of the first communication device to a donor DU of the donor CU. In this way, the dual transmission handover can be achieved and it can ensure communication reliability. The term “dual transmission handover” used herein can refer to a handover where the IAB node can establishing a connection with a target device while maintaining a connection with a source device, which means the IAB node can receive information/data from the source and target devices at the same time.

Fig. 4 illustrates a schematic diagram of a communication system in which embodiments of the present disclosure can be implemented. The communication system 400, which is a part of a communication network, comprises a terminal device 410-1, a terminal device 410-2, ..., a terminal device 410-N, which can be collectively referred to as “terminal device (s) 410. ” The number N can be any suitable integer number.

The communication system 400 further comprises an IAB node 420-1, an IAB node 420-2, an IAB node 420-3, an IAB node 420-4, ..., a network device 420-M (not shown) which can be collectively referred to as “IAB node (s) 420. ” In some embodiments, the IAB node can be any suitable device. The number M can be any suitable integer number. As shown in Fig. 4, the communication system 400 may also a donor DU 430-1 and its donor CU 440-1, a donor DU 430-2 and its donor CU 440-2. It should be noted that the number of donor DUs and donor CUs shown in Fig. 4 is only an example. In the communication system 400, the IAB nodes 420 and the terminal devices 410 can communicate data and control information to each other. The IAB nodes 420 can communicate with each other. The donor DUs can also communicate with the IAB nodes 420. According to the topology shown in Fig. 4, the IAB node 420-2 node can be regarded an ancestor/parent node of the IAB node 420-1 and the terminal devices 410. In other words, the IAB node 420-1 and the terminal devices 410 can be regarded as descendant/child node of the network device 420-2. The term “parent node” used herein can refer to an IAB node which is between the current IAB node and the donor. The term “descendant/child node” used herein can refer to an IAB node which is between the current IAB node and a terminal device. The numbers of devices shown in Fig. 4 are given for the purpose of illustration without suggesting any limitations.

Communications in the communication system 400 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.

As shown in Fig. 4, the IAB node 420-2 can connect with the donor DU 430-1 directly. Alternatively, the IAB node 420-2 can connect with the donor DU 430-1 through the IAB node 420-3. Similarly, the IAB node 420-2 can connect with the donor DU 430-2 directly. Alternatively, the IAB node 420-2 can connect with the donor DU 430-2 through the IAB node 420-4. In some embodiments, the IAB node 420-2 can perform DAPS-like handover between the IAB nodes 420-3 and 420-4, or between the donor DUs 430-1 and 430-2. In other words, the IAB node 420-2 can receive data from the IAB nodes 420-3 and 420-4 (or from the donor DUs 430-1 and 430-2) simultaneously. The DRB 440-2 of the terminal device 410-2 can be mapped to the RLC channel 450-2. The DRB 440-1 of the terminal device 410-1 can be mapped to the RLC channel 450-1 and the RLC channel 450-1 can be mapped to the RLC channel 450-2. The RLC channel 450-2 between the IAB node 420-2 and the IAB node 420-3 (or the donor DU 430-1) can be mapped between the IAB node 420-2 and the IAB node 420-4 (or the donor DU 430-2) .

Only for the purpose of illustrations, embodiments of the present disclosure are described with the reference to a scenario where the IAB node 420-2 can connect with the donor DUs 430-1 and 430-2 directly. Embodiments of the present disclosure can also be applied to a scenario where the IAB node 420-2 can connect with the donor DUs through other IAB nodes. It should be noted that embodiments of the present disclosure are not limited in this aspect.

Fig. 5 shows a flowchart of an example method 500 in accordance with an embodiment of the present disclosure. The method 500 can be implemented at any suitable devices. Only for the purpose of illustrations, the method 500 is described to be implemented at the IAB node 420-2.

In some embodiments, the IAB node 420-2 can measure link quality between the IAB node 420-2 and the donor DU 430-1. For example, the IAB node 420-2 can measure a reference signal received power (RSRP) which is from the donor DU 430-1. In other embodiments, the IAB node 420-1 can also measure RSRP from the donor DU 430-2. The IAB node 420-2 can transmit a measurement report to the donor CU 440-1. The donor CU 440-1 can determine whether to perform DAPS-like handover or dual transmission handover based on the measurement report, which will be described in details later.

At block 510, the IAB node 420-1 receives a first packet in a BAP layer from a first communication device. In some embodiments, the first communication device can be an IAB node, for example, the IAB node 420-3 or the IAB node 420-4. Alternatively, the first communication device can be a donor DU, for example, the donor DU 430-1 or the donor DU 430-2.

The first packet comprises an indication of a dual transmission handover between the first communication device and a second communication device. In some embodiments, the second communication device can be an IAB node. Alternatively, the second communication device can be a donor DU. Only for the purpose of illustrations, the first communication device can be regarded as a source IAB node or a source donor DU and the second communication device can be regarded as a target IAB node or a target donor DU. The first packet also comprises a first sequence number which is determined based on a second sequence number. The second sequence number is configured by the donor CU 440-1 to the donor DU 430-1. In some embodiments, the second sequence number can be a GTP-U sequence number. Alternatively, the second sequence number can be a PDCP sequence number.

Fig. 6A shows a simplified block diagram of a BAP PDU according to some embodiments of the present disclosure. The BAP PDU 600 can comprise a bit field 610 which indicate the BAP PDU is related to data or control information. The bit fields 620-1 and 620-2 can be reserved bits. The bit fields 630-1 and 630-2 can be used to indicate destination of the BAP PDU. The bit fields 640-1 and 640-2 can be used to indicate a path identity of the BAP PDU. The bit field 650 can be used to indicate a dual transmission handover between the first communication device and the second communication device. The bit fields 660-1 and 660-2 can be used for the first sequence number. The bit field 670 can be used to carry data. Only as an example, if the bit field 650 is “1” , it means that there is a dual transmission handover (or DAPS-like handover) for the IAB node 420-2 between its source IAB node and target IAB node (or between its source donor DU and target donor DU) .

In some embodiments, there can be a plurality of DRBs mapped to one RLC channel. For example, as shown in Fig. 4, the DRBs 410-1 and 410-2 are mapped to the RLC channel 450-2. In this situation, the first packet can comprise an identity of a terminal device (for example, the terminal device 410-2) and an identity of a DRB of the terminal device. For example, as shown in Fig. 6A, the bit field 670 can comprise the identity of the terminal device 410-2 and the identity of the DRB 440-2. In some embodiments, the identity of the terminal device 410-2 and the identity of the DRB 440-2 can be more than one octet. In some embodiments, the identity of the terminal device can be an international mobile subscriber identity (IMSI) . Alternatively, the identity of the terminal device can be an F1-AP identity. It should be noted that the identity of the terminal device can be any suitable identities which can identify the terminal device. In some embodiments, the tunnel endpoint identifier (TEID) can comprise the identity of the terminal device and the identity of the DRB.

In some embodiments, at block 520, the IAB node 420-2 can transmit a second packet associated with the first packet to a terminal device or another IAB node. For example, the IAB node 420-2 can transmit the second packet to the terminal device 410-2. In this situation, the IAB node 420-2 can process the first packet by removing the first sequence number from the first packet. The IAB node 420-2 can generate the second packet based on the processed first packet. The second packet can be transmitted to the terminal device 410-2 in a cell related to the donor CU 440-1.

In other embodiments, the IAB node 420-2 can transmit the second packet to the IAB node 420-1. In this situation, the IAB node 420-2 can process the first packet by removing the first sequence number form the first packet. The IAB node 420-2 can generate the second packet based on the first packet and add an indication to indicate that the first packet is received from the donor CU 440-1 in the second packet.

Fig. 6B shows a simplified block diagram of a BAP PDU according to some embodiments of the present disclosure. The BAP PDU 605 can comprise a bit field 615 which indicate the BAP PDU is related to data or control information. The bit fields 625-1, 625-2 and 685 can be reserved bits. The bit fields 635-1 and 635-2 can be used to indicate destination of the BAP PDU. The bit fields 645-1 and 645-2 can be used to indicate a path identity of the BAP PDU. The bit field 655 can be used to indicate a dual transmission handover between the first communication device and the second communication device. The bit field 665 can be used as source/target indicator (STI) . The bit field 675 can be used to indicate whether the BAP PDU is from a source donor CU or a target donor CU. The bit field 695 can be used to carry data. Only as an example, if the bit field 655 is “1” , it means that there is a dual transmission handover (or DAPS-like handover) for the IAB node 420-2 between its source IAB node and target IAB node (or between its source donor DU and target donor DU) . Only as an example, if the bit field 675 is set to “0” , it means that the BAP PDU 605 is from the source donor CU. If the bit field 675 is set to “1” , it means that the BAP PDU 605 is from the target donor CU.

In other embodiments, the IAB node 420-1 receives a third packet in a BAP layer from the second communication device. In some embodiments, the second communication device can be an IAB node, for example, the IAB node 420-3 or the IAB node 420-4. Alternatively, the second communication device can be a donor DU, for example, the donor DU 430-1 or the donor DU 430-2.

The third packet can comprise an indication of a dual transmission handover between the first communication device and the second communication device. Only for the purpose of illustrations, the first communication device can be regarded as a source IAB node or a source donor DU and the second communication device can be regarded as a target IAB node or a target donor DU. The third packet can also comprise a third sequence number which is determined based on a fourth sequence number. The fourth sequence number is configured by the donor CU 440-2 to the donor DU 430-2.

The IAB node 420-2 can perform duplication detection based on the first and second sequence numbers. For example, the IAB node 420-2 can compare the first sequence number in the first packet with the third sequence number in the third packet. If the first sequence number is same as the third sequence number, the IAB node 420-2 can discard the third packet. As discussed above, the first packet can be received from the source donor DU or source IAB node and the third packet can be received from the target donor DU or target IAB node. Alternatively, the third packet can be received from the source donor DU or source IAB node and the first packet can be received from the target donor DU or target IAB node.

If the third sequence number is different from the first sequence number, the IAB node 420-2 can transmit a fourth packet associated with the third packet to a terminal device or another IAB node. For example, the IAB node 420-2 can transmit the fourth packet to the terminal device 410-2. In this situation, the IAB node 420-2 can process the third packet by removing the third sequence number from the third packet. The IAB node 420-2 can generate the fourth packet based on the processed third packet. The fourth packet can be transmitted to the terminal device 410-2 in a cell related to the donor CU 440-2.

In other embodiments, the IAB node 420-2 can transmit the fourth packet to the IAB node 420-1. In this situation, the IAB node 420-2 can process the third packet by removing the third sequence number form the third packet. The IAB node 420-2 can generate the fourth packet based on the third packet and add an indication to indicate that the third packet is received from the donor CU 440-2 in the fourth packet.

In some embodiments, if the IAB node 420-2 is performing handover, when receiving GTP PDU from source/target Donor CU, the PDCP SN in the GTP PDU can be used for duplication detection. If the IAB node 420-1 is performing handover, the IAB node 420-1 can eavesdrop the GTP SN/PDCP SN to perform duplication detection.

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. For example, the method 700 can be implemented at the donor DU 430-1. Alternatively, the method 700 can be implemented at the donor DU 430-2. Only for the purpose of illustrations, the method 700 is described to be implemented at the donor DU 430-1.

At block 710, the donor DU 430-1 receives a BAP data forwarding start message from the donor CU 440-1. The BAP data forwarding start message comprises a second sequence number configured by the donor CU 440-4. In some embodiments, the second sequence number can be a GTP-U sequence number. Alternatively, the second sequence number can be a PDCP sequence number. In some embodiments, the BAP data forwarding start message can indicate an identity of a DRB of a terminal device is required. In this situation, the donor DU 430-1 can add the identity of the DRB of the terminal device in the first packet.

At block 720, the donor DU 430-1 receives a packet in a data unit from the donor CU 440-1. For example, the packet can be transmitted in a GTP-U PDU. In some embodiments, the PDU can comprise a fifth sequence number. For example, if the fifth sequence number in the data unit matches with the second sequence number in the BAP data forwarding start message, the donor DU 430-1 can determine the firs sequence number to be an initial number. Only as an example, the second sequence number in the BAP data forwarding start message is “0010, ” which means that packets with the sequence number which is not smaller than “0010” should be forwarded. If the fifth sequence number in the GTP-U PDU is also “0010” , the donor DU 430-1 can determine that the firth sequence number matches with the second sequence number. In this situation, the donor DU 430-1 can determine the first sequence number to be the initial number, for example “00. ”

At block 730, the donor DU 430-1 transmits a first packet in the BAP layer to the IAB node 420-2. The first packet is generated based on the packet in the data unit. Tables 1 and 2 below show an example of GTP-U SN or PDCP SN in the GTP-U PDU which can be used to generate the BAP SN.

Table 1

Table 2

The first packet comprises an indication of a dual transmission handover between the first communication device and a second communication device. In some embodiments, the second communication device can be an IAB node. Alternatively, the second communication device can be a donor DU. Only for the purpose of illustrations, the first communication device can be regarded as a source IAB node or a source donor DU and the second communication device can be regarded as a target IAB node or a target donor DU. The first packet also comprises a first sequence number which is determined based on the second sequence number.

In some embodiments, the donor DU 430-1 can receive a data forwarding stop message from the donor CU 440-1. In this situation, the donor DU 430-1 can stop generating BAP sequence numbers for the BAP PDU.

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. For example, the method 800 can be implemented at the donor CU 440-1. Alternatively, the method 800 can be implemented at the donor CU 440-2. Only for the purpose of illustrations, the method 800 is described to be implemented at the donor CU 440-1.

In some embodiments, if the donor CU 440-1 is a source donor CU, the IAB node 420-2 can transmit a measurement report to the donor CU 440-1. The donor CU 440-1 can determine whether to perform DAPS-like handover or dual transmission handover based on the measurement report. If the dual transmission handover between the donor CU 440-1 and the donor CU 440-2 which can be regarded as a target donor CU is needed, the donor CU 440-1 can transmit a dual transmission handover request to the donor CU 440-2. The dual transmission handover request can indicate an identity of the DRB and an identity of the IAB node. Alternatively, if the donor CU 440-1 is a source donor CU, the donor CU 440-1 can receive flow control feedback from the IAB node 420-2. In this situation, the donor CU 440-1 can determine that a load balancing is needed based on the flow control feedback.

In some embodiments, the donor CU 440-1 can transmit a dual transmission start message to the donor CU 440-2. For example, the dual transmission start message can comprise the identity of the IAB node and the identity of the RLC channel.

In some embodiments, the donor CU 440-2 can respond a DUAL TRANSMISSION START ACK message to the donor CU 440-1. The DUAL TRANSMISSION START ACK message can comprise the identity of the IAB node and the identity of the RLC channel.

In some embodiments, the donor CU 440-1 can also transmit an early status transfer request to the donor CU 440-2. The early status transfer request can indicate the identity of the radio link control channel and an identity of the IAB node.

At block 810, the donor CU 440-1 transmits a BAP data forwarding start message to the donor DU 430-1. The BAP data forwarding start message comprises a second sequence number configured by the donor CU 440-4. In some embodiments, the second sequence number can be a GTP-U sequence number. Alternatively, the second sequence number can be a PDCP sequence number. In some embodiments, the BAP data forwarding start message can indicate an identity of a DRB of a terminal device is required. The second sequence number can be used to determine a first sequence number by the donor DU 430-1.

At block 820, the donor CU 440-1 transmits a packet in a data unit to the donor DU 430-1. For example, the packet can be transmitted in a GTP-U PDU. In some embodiments, the PDU can comprise a fifth sequence number.

In some embodiments, the donor CU 440-1 can transmit a DAPS handover request to the donor CU 440-2. The DAPS handover request can comprise one or more of: an identity of a terminal device, an identity of a data radio bearer of the terminal device, or an indication regarding whether the identity of the data radio bearer is required. In this situation, the donor CU 440-2 can transmit a BAP data forwarding start message which comprise an indication regarding whether the identity of the data radio bearer is required to its donor DU 430-2.

In some embodiments, if the donor CU 440-1 is the source donor CU and the donor CU 440-2 is the target donor CU, the donor CU 440-1 can receive a handover success message from the donor CU 440-2. In this situation, the donor CU 440-1 can transmit a data forwarding stop message to the donor DU 430-1. Alternatively, if the donor CU 440-1 is the target donor CU, the donor CU 440-1 can transmit the data forwarding stop message to the donor DU 430-1 after completion of the handover.

Alternatively, the donor CU 440-1 can transmit a dual transmission stop message to the donor CU 440-2. For example, the dual transmission stop message can comprise the identity of the IAB node and the identity of the RLC channel.

In some embodiments, the donor CU 440-2 can respond a DUAL TRANSMISSION STOP ACK message to the donor CU 440-1. The DUAL TRANSMISSION STOP ACK message can comprise the identity of the IAB node and the identity of the RLC channel.

In the circumstance of dual transmission caused by a load balancing, the donor CU 440-1 (source donor CU) could send RRCReconfiguration to the IAB node 420-2 to disconnect the donor CU 440-2 (target Donor CU) .

In some embodiments, the donor CU 440-2 can transmit a dual transmission handover stop message to the donor CU 440-1. For example, the dual transmission handover stop message can comprise the identity of the IAB node and the identity of the RLC channel.

In some embodiments, the donor CU 440-1 could respond a DUAL TRANSMISSION HANDOVER STOP ACK message to the donor CU 440-2. The DUAL TRANSMISSION HANDOVER STOP ACK message can comprise the identity of the IAB node and the identity of the RLC channel.

Alternatively, in the circumstance of dual transmission handover caused by a load balancing, donor CU 440-2 (target Donor CU) could send RRCReconfiguration to the IAB node 420-2 to disconnect the donor CU 440-1 (source donor CU) .

Embodiments of the present disclosure will be described in detail below. Reference is first made to Fig. 9, which shows a signaling chart illustrating process 900 among devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 900 may involve the terminal device 410-2, the IAB node 420-2, the donor DU 430-1, the donor DU 430-2, the donor CU 440-1 and the donor CU 440-2. It should be noted that the process can involve any proper devices.

The IAB node 420-2 can measure link quality between the IAB node 420-2 and the donor DU 430-1. For example, the IAB node 420-2 can measure a reference signal received power (RSRP) which is from the donor DU 430-1. In other embodiments, the IAB node 420-1 can also measure RSRP from the donor DU 430-2. The IAB node 420-2 can transmit 9001 a measurement report to the donor CU 440-1. The donor CU 440-1 can determine whether to perform DAPS-like handover or dual transmission handover based on the measurement report. Alternatively, the donor CU 440-1 can receive flow control feedback from the IAB node 420-2. In this situation, the donor CU 440-1 can determine that a load balancing is needed based on the flow control feedback.

The donor CU 440-1 can transmit 9002 a dual transmission handover request which comprises the identity of the IAB node 420-2 and the identity of the RLC 440-2 to the donor CU 440-2. In return, the donor CU 440-2 can respond a Handover Request ACK to the donor CU 440-1.

The donor CU 440-1 can transmit 9003 the EARLY STATUS TRANSFER which comprises RLC 440-2 and BAP SN to the donor CU 440-2. EARLY STATUS TRANSFER may not be needed for IAB RLC channel if the data forwarding is done in UE DRB granularity.

The donor CU 440-1 can transmit 9004 a RRCReconfiguration to the IAB node 420-2. The IAB node 420-2 can establish a connection to the donor CU 440-2. The connection to the donor CU 440-1 is maintained.

The donor CU 440-1 can transmit 9006 a Handover Request which comprises the identity of the terminal device 410-2, the identity of the DRB 440-2, and an indication whether the identity of the DRB 440-2 is required, to the donor CU 440-2.

The donor CU 440-1 can transmit 9007 a RRCReconfiguration to the terminal device 410-2, by which the terminal device 410-2 can establish dual connection to the donor CU 440-1 (cell1 of the IAB node 420-2) and donor CU 440-2 (cell2 of the IAB node 420-2) .

The donor CU 440-1 can transmit 9008 an EARLY STATUS TRANSFER which comprises the identity of the terminal device 410-2, the identity of the DRB 440-2 and a PDCP count, to the donor CU 440-2.

The donor CU 440-1 can transmit 9009 an F1-AP message BAP data forwarding start message to the donor DU 430-1. Upon the reception of this message, the donor DU 430-1 can add BAP SN from the GTP SN/PDCP SN received from donor CU 440-1.

The donor CU 440-1 can transmit 9010 a GTP PDU with GTP SN/PDCP SN in the BAP data forwarding start message to the donor DU 430-1. The donor DU 430-1 can add BAP SN from 0 if the GTP/PDCP SN of the GTP PDU from donor CU 440-1 matches the GTP SN/PDCP SN. If DRB id required is present in BAP data forwarding start message, the donor DU 430-1 can add UE ID+DRB ID accordingly.

The donor DU 430-1 can transmit 9011 the BAP PDU to the IAB node 420-2. Since the IAB node 420-2 knows this BAP PDU is sent from the donor CU 440-1, the IAB node 420-2 can transmit 9012the packet to the terminal device 410-2 via the cell associated with the donor CU 440-1.

The donor CU 440-2 can transmit 9013 an F1-AP message BAP data forwarding start message which comprises GTP SN /PDCP SN, DRB id required to the donor DU 430-2. Upon the reception of this message, the donor DU 430-2 may add BAP SN from the GTP SN/PDCP SN received from donor CU 440-2.

The donor CU 440-2 can transmit 9014 a GTP PDU to the donor DU 430-2. If the GTP SN/PDCP SN in the GTP PDU matches in the BAP data forwarding start (GTP SN/PDCP SN) , the donor DU 430-2 may add BAP SN from 0. If DRB id required is present in BAP data forwarding start message, the donor DU 430-2 may add UE ID+DRB ID accordingly.

If the IAB node 420-2 receives 9015 the BAP PDU from the donor DU 430-2 has the same BAP SN as the BAP PDU from the donor DU 430-1, the IAB node 420-2 can discard this BAP PDU from the donor DU 430-2.

The donor CU 440-2 can transmit 9016 a Handover Success message to the donor CU 440-1. The donor CU 440-1 can transmit 9017 a BAP data forwarding stop message to the donor DU 430-1 and the donor CU 440-2 can transmit 9018 the BAP data forwarding stop message to the donor DU 430-2. Upon the reception of this message, the donor DU 430-1 and the donor DU 430-1 may not add BAP SN in the BAP header any longer.

Reference is first made to Fig. 10, which shows a signaling chart illustrating process 1000 among devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 1000 may involve the terminal device 410-2, the IAB node 420-2, the IAB node 420-1, the donor DU 430-1, the donor DU 430-2, the donor CU 440-1, the donor CU 440-2 and the terminal device 410-1. It should be noted that the process can involve any proper devices.

The IAB node 420-2 can measure link quality between the IAB node 420-2 and the donor DU 430-1. For example, the IAB node 420-2 can measure a reference signal received power (RSRP) which is from the donor DU 430-1. In other embodiments, the IAB node 420-1 can also measure RSRP from the donor DU 430-2. The IAB node 420-2 can transmit 10001 a measurement report to the donor CU 440-1.

The donor CU 440-1 can transmit 10002 a dual transmission handover request which comprises the identity of the IAB node 420-2 and the identity of the RLC 440-2 to the donor CU 440-2. In return, the donor CU 440-2 can respond a Handover Request ACK to the donor CU 440-1.

The donor CU 440-1 can transmit 10003 the EARLY STATUS TRANSFER which comprises RLC 440-2 and BAP SN to the donor CU 440-2. EARLY STATUS TRANSFER may not be needed for IAB RLC channel if the data forwarding is done in UE DRB granularity.

The donor CU 440-1 can transmit 10004 a RRCReconfiguration to the IAB node 420-2. The IAB node 420-2 can establish a connection to the donor CU 440-2. The connection to the donor CU 440-1 is maintained.

The donor CU 440-1 can transmit 10006 a Handover Request which comprises the identity of the terminal device 410-2, the identity of the DRB 440-2, and an indication whether the identity of the DRB 440-2 is required, to the donor CU 440-2.

The donor CU 440-1 can transmit 10007 a RRCReconfiguration to the terminal device 410-2, by which the terminal device 410-2 can establish dual connection to the donor CU 440-1 (cell1 of the IAB node 420-2) and donor CU 440-2 (cell2 of the IAB node 420-2) .

The donor CU 440-1 can transmit 10008 an EARLY STATUS TRANSFER which comprises the identity of the terminal device 410-2, the identity of the DRB 440-2 and a PDCP count, to the donor CU 440-2.

The donor CU 440-1 can transmit 10009 an F1-AP message BAP data forwarding start message to the donor DU 430-1. Upon the reception of this message, the donor DU 430-1 can add BAP SN from the GTP SN/PDCP SN received from donor CU 440-1.

The donor CU 440-1 can transmit 10010 a GTP PDU with GTP SN/PDCP SN in the BAP data forwarding start message to the donor DU 430-1. The donor DU 430-1 can add BAP SN from 0 if the GTP/PDCP SN of the GTP PDU from donor CU 440-1 matches the GTP SN/PDCP SN. If DRB id required is present in BAP data forwarding start message, the donor DU 430-1 can add UE ID+DRB ID accordingly.

The donor DU 430-1 can transmit 10011 the BAP PDU to the IAB node 420-2. Since the IAB node 420-2 knows this BAP PDU is sent from the donor CU 440-1, the IAB node 420-2 can transmit 10012 the packet to the IAB node 420-1. The packet can comprise an indication that the packet is received from the donor CU 440-1. The IAB node 420-1 can transmit 10112 the packet to the terminal device 410-1.

The donor CU 440-2 can transmit 10013 an F1-AP message BAP data forwarding start message which comprises GTP SN /PDCP SN, DRB id required to the donor DU 430-2. Upon the reception of this message, the donor DU 430-2 may add BAP SN from the GTP SN/PDCP SN received from donor CU 440-2.

The donor CU 440-2 can transmit 10014 a GTP PDU to the donor DU 430-2. If the GTP SN/PDCP SN in the GTP PDU matches in the BAP data forwarding start (GTP SN/PDCP SN) , the donor DU 430-2 may add BAP SN from 0. If DRB id required is present in BAP data forwarding start message, the donor DU 430-2 may add UE ID+DRB ID accordingly.

If the IAB node 420-2 receives 10015 the BAP PDU from the donor DU 430-2 has the same BAP SN as the BAP PDU from the donor DU 430-1, the IAB node 420-2 can discard this BAP PDU from the donor DU 430-2.

The donor CU 440-2 can transmit 10016 a Handover Success message to the donor CU 440-1. The donor CU 440-1 can transmit 10017 a BAP data forwarding stop message to the donor DU 430-1 and the donor CU 440-2 can transmit 10018 the BAP data forwarding stop message to the donor DU 430-2. Upon the reception of this message, the donor DU 430-1 and the donor DU 430-1 may not add BAP SN in the BAP header any longer.

Fig. 11 shows a flowchart of an example method 1100 in accordance with an embodiment of the present disclosure. The method 1100 can be implemented at any suitable devices. Only for the purpose of illustrations, the method 1100 is described to be implemented at the IAB node 420-2.

At block 1110, the IAB node 420-2 receives a first packet in a backhaul adaptation protocol (BAP) layer from a first communication device. The first packet comprises a packet data convergence protocol (PDCP) sequence number.

At block 1120, the IAB node 420-2 transmits, to a third communication device, the first packet in a first cell related to the first communication device. In some embodiments, the third communication device can be a terminal device. Alternatively, the third communication device can be another IAB node.

At block 1130, the IAB node 420-2 receives, from a second communication device, a second packet in the BAP layer, the second packet comprising the PDCP sequence number.

At block 1120, the IAB node 420-2 transmits, to the third communication device, a second packet in a second cell related to the second communication device.

Fig. 12 shows a flowchart of an example method 1200 in accordance with an embodiment of the present disclosure. The method 1200 can be implemented at any suitable devices. Only for the purpose of illustrations, the method 1200 is described to be implemented at the donor CU 440-1.

At block 1210, the donor CU 440-1 receives, from the IAB node 420-2, a measurement report regarding a radio link control channel between the IAB node 420-2 and the donor DU 430-1.

At block 1220, the donor CU 440-1 determines, based on the measurement, a dual transmission handover between the donor CU 440-1 and the donor CU 440-2.

At block 1230, the donor CU 440-1 transmits, to the donor CU 440-2, a dual transmission handover request indicating an identity of the radio link control channel and an identity of the IAB node.

In some embodiments, the donor CU 440-1 transmits, to the donor CU 440-2, an early status transfer request indicating an identity of the radio link control channel and an identity of the IAB node. In other embodiments, the donor CU 440-1 transmits, to the donor CU 440-2, a dual active protocol stack (DAPS) handover request comprising one or more of: an identity of a terminal device, an identity of a data radio bearer of the terminal device, an indication regarding whether the identity of the data radio bearer is required, or an identity of a radio control channel corresponding to the identity of the data radio bearer of the terminal device.

Reference is first made to Fig. 13, which shows a signaling chart illustrating process 1300 among devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 1300 may involve the terminal device 410-2, the IAB node 420-2, the donor DU 430-1, the donor DU 430-2, the donor CU 440-1, and the donor CU 440-2. It should be noted that the process can involve any proper devices.

The IAB node 420-2 can measure link quality between the IAB node 420-2 and the donor DU 430-1. For example, the IAB node 420-2 can measure a reference signal received power (RSRP) which is from the donor DU 430-1. In other embodiments, the IAB node 420-1 can also measure RSRP from the donor DU 430-2. The IAB node 420-2 can transmit 13001 a measurement report to the donor CU 440-1.

The donor CU 440-1 can transmit 13002 a dual transmission handover request which comprises the identity of the IAB node 420-2 and the identity of the RLC 440-2 to the donor CU 440-2. In return, the donor CU 440-2 can respond a Handover Request ACK to the donor CU 440-1.

The donor CU 440-1 can transmit 13003 the EARLY STATUS TRANSFER which comprises RLC 440-2 and BAP SN to the donor CU 440-2. EARLY STATUS TRANSFER may not be needed for IAB RLC channel if the data forwarding is done in UE DRB granularity.

The donor CU 440-1 can transmit 13004 a RRCReconfiguration to the IAB node 420-2. The IAB node 420-2 can establish a connection to the donor CU 440-2. The connection to the donor CU 440-1 is maintained.

The donor CU 440-1 can transmit 13006 a Handover Request which comprises the identity of the terminal device 410-2, the identity of the DRB 440-2, and an indication whether the identity of the DRB 440-2 is required, to the donor CU 440-2.

The donor CU 440-1 can transmit 13007 a RRCReconfiguration to the terminal device 410-2, by which the terminal device 410-2 can establish dual connection to the donor CU 440-1 (cell1 of the IAB node 420-2) and donor CU 440-2 (cell2 of the IAB node 420-2) .

The donor CU 440-1 can transmit 13008 an EARLY STATUS TRANSFER which comprises the identity of the terminal device 410-2, the identity of the DRB 440-2 and a PDCP count, to the donor CU 440-2.

The donor CU 440-1 can transmit 13009 a packet to the IAB node 420-2 through the donor DU 430-1. Since the IAB node 420-2 knows this packet is sent from the donor CU 440-1, the IAB node 420-2 can transmit 13012 the packet to the terminal device 410-2 in the cell associated with the donor CU 440-1.

The donor CU 440-2 can transmit 13014 a packet to the IAB node 420-2 through the donor DU 430-2. Since the IAB node 420-2 knows this packet is sent from the donor CU 440-2, the IAB node 420-2 can transmit 13016 the packet to the terminal device 410-2 in the cell associated with the donor CU 440-2.

Since the terminal device 410-2 can determine which donor CU the packet comes from, the terminal device 410-2 can perform duplication detection and discarding. For example, the PDCP entity at the terminal device 410-2 can perform duplication detection and discarding.

Fig. 14 is a simplified block diagram of a device 1400 that is suitable for implementing embodiments of the present disclosure. The device 1400 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 1400 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 1400 includes a processor 1410, a memory 1420 coupled to the processor 1410, a suitable transmitter (TX) and receiver (RX) 1440 coupled to the processor 1410, and a communication interface coupled to the TX/RX 1440. The memory 1420 stores at least a part of a program 1440. The TX/RX 1440 is for bidirectional communications. The TX/RX 1440 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 1440 is assumed to include program instructions that, when executed by the associated processor 1410, enable the device 1400 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to Fig. 5 to 13. The embodiments herein may be implemented by computer software executable by the processor 1410of the device 1000, or by hardware, or by a combination of software and hardware. The processor 1410may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1410and memory 1420 may form processing means 1450 adapted to implement various embodiments of the present disclosure.

The memory 1420 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 1420 is shown in the device 1400, there may be several physically distinct memory modules in the device 1400. The processor 1410may 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 1400 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, an IAB node comprises circuitry configured to: receive, from a first communication device, a first packet in a backhaul adaptation protocol (BAP) layer, the first packet comprising: an indication of a dual transmission handover between the first communication device and a second communication device, and a first sequence number which is determined based on a second sequence number, wherein the second sequence number is configured by a first donor centralized unit (CU) of the first communication device to a first donor distributed unit (DU) of the first donor CU.

In some embodiments, the first packet comprises an identity of a terminal device and an identity of a radio data bearer of the terminal device.

In some embodiments, the IAB node comprises circuitry configured to: process the first packet by removing the first sequence number from the first packet; and transmit, to a terminal device, a second packet generated based on the processed first packet in a cell related to the first communication device.

In some embodiments, the IAB node comprises circuitry configured to: process the first packet by removing the first sequence number from the first packet; add an indication to indicate that the first packet is received from the first donor CU in a second packet generated based on the processed first packet; and transmit the second packet to another IAB node.

In some embodiments, the IAB node comprises circuitry configured to: receive, from the second communication device, a third packet in the BAP layer, the third packet comprising: the indication of the dual transmission handover between the first communication device and the second communication device, and a third sequence number which is determined based on a fourth sequence number, wherein the fourth sequence number is configured by a second donor CU of the second communication device to a second donor DU of the second donor CU; in accordance with a determination that the third sequence number is same as the first sequence number, discard the third packet; or in accordance with a determination that the third sequence number is different from the first sequence number, transmit, to a terminal device, a fourth packet generated based on the third packet in a cell related to the second communication device; or transmit, to another IAB node, the fourth packet generated based on the third packet, wherein the fourth packet comprises an indication to indicate that the third packet is received from the second donor CU.

In some embodiments, the first communication device is an IAB node or a donor distributed unit (DU) , and the second communication device is an IAB node or a donor DU.

In some embodiments, the second sequence number is a General Packet Radio Service (GPRS) Tunnelling Protocol-User (GTP-U) sequence number, or a Packet Data Convergence Protocol (PDCP) sequence number.

In some embodiments, a donor DU comprises circuitry configured to: receive from a first donor centralized unit (CU) , a backhaul adaptation protocol (BAP) data forwarding start message comprising a second sequence number configured by the first donor CU; receive, from the first donor CU, a packet in a data unit to be forwarded to an integrated access backhaul (IAB) node by the first donor DU with a first sequence number; and transmit, to the IAB node, a first packet in the BAP layer generated based on the packet in the data unit, the first packet comprising: an indication of a dual transmission handover between the first donor CU and a second donor CU, and the first sequence number which is determined based on the second sequence number.

In some embodiments, the donor DU comprises circuitry configured to: in accordance with a determination that the BAP data forwarding start message indicates an identity of a radio data bearer of a terminal device is required, add an identity of the terminal device and the identity of the radio data bearer in the first packet.

In some embodiments, the donor DU comprises circuitry configured to: in accordance with a determination that a fifth sequence number in the data unit matches with the second sequence number in the BAP data forwarding start message, determine the first sequence number to be an initial number.

In some embodiments, the donor DU comprises circuitry configured to: receive, from the first donor CU, a data forwarding stop message.

In some embodiments, a donor CU comprises circuitry configured to: transmit, to a first donor distributed unit (DU) , a backhaul adaptation protocol (BAP) data forwarding start message comprising a second sequence number which is used for determining a first sequence number by the first donor DU; and transmit, to the first donor DU, a packet in a data unit to forwarded to an integrated access backhaul (IAB) node by the first donor DU with the first sequence number.

In some embodiments, wherein the first donor CU is a source donor CU of the IAB node, and the donor CU comprises circuitry configured to: receive, from the IAB node, a measurement report regarding a radio link control channel between the IAB node and a first donor DU of the first donor CU; determine, based on the measurement, a dual transmission handover between the first donor CU and a second donor CU which is a target donor CU of the IAB node; and transmit, to the second donor CU, a dual transmission handover request indicating an identity of the radio link control channel and an identity of the IAB node.

In some embodiments, the donor CU comprises circuitry configured to: transmit, to the second donor CU, an early status transfer request indicating an identity of the radio link control channel and an identity of the IAB node.

In some embodiments, the donor CU comprises circuitry configured to: transmit, to the second donor CU, a dual active protocol stack (DAPS) handover request comprising at least one of: an identity of a terminal device, an identity of a data radio bearer of the terminal device, or an indication regarding whether the identity of the data radio bearer is required.

In some embodiments, the donor CU comprises circuitry configured to: transmit, to the first donor DU, a data forwarding stop message.

In some embodiments, the donor CU comprises circuitry configured to: transmit the BAP data forwarding start message indicates an identity of a data radio bearer of a terminal device is required.

In some embodiments, an IAB node comprises circuitry configured to: receive, from a first communication device, a first packet in a backhaul adaptation protocol (BAP) layer, the first packet comprising a packet data convergence protocol (PDCP) sequence number; transmit, to a third communication device, the first packet in a first cell related to the first communication device; receive, from a second communication device, a second packet in the BAP layer, the second packet comprising the PDCP sequence number; and transmit, to a third communication device, a second packet in a second cell related to the second communication device.

In some embodiments, wherein the first and second communication devices are donor distributed units (DUs) , or the first and second communication devices are IAB nodes, and the third communication device is an IAB node or a terminal device.

In some embodiments, a donor CU comprises circuitry configured to: receive, from an integrated access backhaul (IAB) node, a measurement report regarding a radio link control channel between the IAB node and a source donor DU of the source donor CU; determine, based on the measurement, a dual transmission handover between the source donor CU and a target donor CU; and transmit, to the target donor CU, a dual transmission handover request indicating an identity of the radio link control channel and an identity of the IAB node.

In some embodiments, the donor CU comprises circuitry configured to: transmit, to the target donor CU, an early status transfer request indicating an identity of the radio link control channel and an identity of the IAB node.

In some embodiments, a donor CU comprises circuitry configured to: transmit, to the target donor CU, a dual active protocol stack (DAPS) handover request comprising at least one of: an identity of a terminal device, an identity of a data radio bearer of the terminal device, an indication regarding whether the identity of the data radio bearer is required, or an identity of a radio control channel corresponding to the identity of the data radio bearer of the terminal device.

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:

receiving, at an integrated access backhaul (IAB) node and from a first communication device, a first packet in a backhaul adaptation protocol (BAP) layer, the first packet comprising: an indication of a dual transmission handover between the first communication device and a second communication device, and a first sequence number which is determined based on a second sequence number, wherein the second sequence number is configured by a first donor centralized unit (CU) of the first communication device to a first donor distributed unit (DU) of the first donor CU.
The method of claim 1, wherein the first packet comprises an identity of a terminal device and an identity of a radio data bearer of the terminal device.
The method of claim 1, further comprising:

processing the first packet by removing the first sequence number from the first packet; and

transmitting, to a terminal device, a second packet generated based on the processed first packet in a cell related to the first communication device.
The method of claim 1, further comprising:

processing the first packet by removing the first sequence number from the first packet;

adding an indication to indicate that the first packet is received from the first donor CU in a second packet generated based on the processed first packet; and

transmitting the second packet to another IAB node.
The method of claim 1, further comprising:

receiving, from the second communication device, a third packet in the BAP layer, the third packet comprising: the indication of the dual transmission handover between the first communication device and the second communication device, and a third sequence number which is determined based on a fourth sequence number, wherein the fourth sequence number is configured by a second donor CU of the second communication device to a second donor DU of the second donor CU;

in accordance with a determination that the third sequence number is same as the first sequence number, discarding the third packet; or

in accordance with a determination that the third sequence number is different from the first sequence number,

transmitting, to a terminal device, a fourth packet generated based on the third packet in a cell related to the second communication device; or

transmitting, to another IAB node, the fourth packet generated based on the third packet, wherein the fourth packet comprises an indication to indicate that the third packet is received from the second donor CU.
The method of claim 1, wherein the first communication device is an IAB node or a donor distributed unit (DU) , and the second communication device is an IAB node or a donor DU.
The method of claim 1, wherein the second sequence number is a General Packet Radio Service (GPRS) Tunnelling Protocol-User (GTP-U) sequence number, or a Packet Data Convergence Protocol (PDCP) sequence number.
A communication method, comprising:

receiving, at a first donor distributed unit (DU) and from a first donor centralized unit (CU) , a backhaul adaptation protocol (BAP) data forwarding start message comprising a second sequence number configured by the first donor CU;

receiving, from the first donor CU, a packet in a data unit to be forwarded to an integrated access backhaul (IAB) node by the first donor DU with a first sequence number; and

transmitting, to the IAB node, a first packet in the BAP layer generated based on the packet in the data unit, the first packet comprising: an indication of a dual transmission handover between the first donor CU and a second donor CU, and the first sequence number which is determined based on the second sequence number.
The method of claim 8, further comprising:

in accordance with a determination that the BAP data forwarding start message indicates an identity of a radio data bearer of a terminal device is required, adding an identity of the terminal device and the identity of the radio data bearer in the first packet.
The method of claim 8, further comprising:

in accordance with a determination that a fifth sequence number in the data unit matches with the second sequence number in the BAP data forwarding start message, determining the first sequence number to be an initial number.
The method of claim 8, wherein the second sequence number is a General Packet Radio Service (GPRS) Tunnelling Protocol-User (GTP-U) sequence number, or a Packet Data Convergence Protocol (PDCP) sequence number.
The method of claim 8, further comprising:

receiving, from the first donor CU, a data forwarding stop message.
A communication method, comprising:

transmitting, at a first donor centralized unit (CU) and to a first donor distributed unit (DU) , a backhaul adaptation protocol (BAP) data forwarding start message comprising a second sequence number which is used for determining a first sequence number by the first donor DU; and

transmitting, to the first donor DU, a packet in a data unit to forwarded to an integrated access backhaul (IAB) node by the first donor DU with the first sequence number.
The method of claim 13, wherein the first donor CU is a source donor CU of the IAB node, and the method further comprising:

receiving, from the IAB node, a measurement report regarding a radio link control channel between the IAB node and a first donor DU of the first donor CU;

determining, based on the measurement, a dual transmission handover between the first donor CU and a second donor CU which is a target donor CU of the IAB node; and

transmitting, to the second donor CU, a dual transmission handover request indicating an identity of the radio link control channel and an identity of the IAB node.
The method of claim 14, further comprising:

transmitting, to the second donor CU, an early status transfer request indicating an identity of the radio link control channel and an identity of the IAB node.
The method of claim 14, further comprising:

transmitting, to the second donor CU, a dual active protocol stack (DAPS) handover request comprising at least one of: an identity of a terminal device, an identity of a data radio bearer of the terminal device, or an indication regarding whether the identity of the data radio bearer is required.
The method of claim 13, further comprising:

transmitting, to the first donor DU, a data forwarding stop message.
The method of claim 13, wherein transmitting the BAP data forwarding start message comprises:

transmitting the BAP data forwarding start message indicates an identity of a data radio bearer of a terminal device is required.
A communication method, comprising:

receiving, at an integrated access backhaul (IAB) node and from a first communication device, a first packet in a backhaul adaptation protocol (BAP) layer, the first packet comprising a packet data convergence protocol (PDCP) sequence number;

transmitting, to a third communication device, the first packet in a first cell related to the first communication device;

receiving, from a second communication device, a second packet in the BAP layer, the second packet comprising the PDCP sequence number; and

transmitting, to a third communication device, a second packet in a second cell related to the second communication device.
The method of claim 19, wherein the first and second communication devices are donor distributed units (DUs) , or the first and second communication devices are IAB nodes, and the third communication device is an IAB node or a terminal device.
A communication method, comprising:

receiving, at a source donor centralized unit (CU) and from an integrated access backhaul (IAB) node, a measurement report regarding a radio link control channel between the IAB node and a source donor DU of the source donor CU;

determining, based on the measurement, a dual transmission handover between the source donor CU and a target donor CU; and

transmitting, to the target donor CU, a dual transmission handover request indicating an identity of the radio link control channel and an identity of the IAB node.
The method of claim 21, further comprising:

transmitting, to the target donor CU, an early status transfer request indicating an identity of the radio link control channel and an identity of the IAB node.
The method of claim 21, further comprising:

transmitting, to the target donor CU, a dual active protocol stack (DAPS) handover request comprising at least one of: an identity of a terminal device, an identity of a data radio bearer of the terminal device, an indication regarding whether the identity of the data radio bearer is required, or an identity of a radio control channel corresponding to the identity of the data radio bearer of the terminal device.
An integrated access and backhaul (IAB) node comprising:

a processor configured to perform the method according to any of claims 1 to 7, or 19-20.
A donor distributed unit comprising:

a processor configured to perform the method according to any of claims 8-12.
A donor centralized unit comprising:

a processor configured to perform the method according to any of claims 13 to 18 or any of claims 21-23.
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 of claims 1 to 7, or any of claims 8 to 12, or any of claims 13 to 18, or claims 19-20, or any of claims 21 to 23.