Method and apparatus for UE handover in IAB network

Abstract

The embodiment of the invention relates to a method and equipment for switching UE in an IAB network. In accordance with some embodiments of the present disclosure, a UE may: communicate with a first BS via a wireless network node; receiving an RRC reconfiguration message for switching the UE from the first BS to a second BS together with the wireless network node; and in response to receiving the RRC reconfiguration message, maintaining an air interface between the UE and the wireless network node while performing the handover from the first BS to the second BS.

Description

Technical Field

[0001] Embodiments of the present disclosure relate generally to communication techniques, and more particularly, to user equipment (UE) handover in an integrated access and backhaul (IAB) network. Background Art

[0002] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcast, etc. Wireless communication systems may employ multiple access technologies capable of supporting communication with multiple users by sharing available system resources such as time, frequency, and power. Examples of wireless communication systems may include fourth generation (4G) systems such as long term evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may also be referred to as new radio (NR) systems.

[0003] In order to expand the coverage and availability of wireless communication systems (such as 5G systems), the Third Generation Partnership Project (3GPP) is envisioning an integrated access and backhaul (IAB) architecture to support multi-hop relays. In an IAB network, an IAB node may jump one or more IAB nodes before reaching a base station (also referred to as an "IAB donor" or "donor node"). A single hop may be considered a special case of a multi-hop. A multi-hop backhaul is beneficial because it provides a relatively larger coverage extension than a single-hop backhaul. In relatively high frequency radio communication systems (e.g., radio signals transmitted in frequency bands above 6 GHz), relatively narrow or small signal coverage may benefit from multi-hop backhaul technology.

[0004] The industry desires techniques for handling handover of UEs in an IAB network. Summary of the invention

[0005] Some embodiments of the present disclosure provide a user equipment (UE). The UE may include: a transceiver configured to: communicate with a first base station (BS) via a radio network node; and receive a radio resource control (RRC) reconfiguration message for switching the UE together with the radio network node from the first BS to a second BS; and a processor coupled to the transceiver and configured to: in response to receiving the RRC reconfiguration message, maintain an air interface between the UE and the radio network node while performing the switching from the first BS to the second BS.

[0006] In some embodiments of the present disclosure, the RRC reconfiguration message may include pre-allocated resources for an RRC reconfiguration complete message corresponding to the RRC reconfiguration message, or wherein resources for random access may not be configured in the RRC reconfiguration message, or both.

[0007] In some embodiments of the present disclosure, maintaining the air interface may be performed at a medium access control (MAC) entity or a radio link control (RLC) entity or a physical (PHY) layer of the UE.

[0008] Some embodiments of the present disclosure provide a first base station (BS). The BS may include: a processor; and a transceiver coupled to the processor. The transceiver may be configured to: transmit a handover (HO) request message for handing over a user equipment (UE) served by a radio network node together with the radio network node from the first BS to a second BS to the second BS; and receive a HO request confirmation message from the second BS in response to the HO request message.

[0009] Some embodiments of the present disclosure provide a method performed by a user equipment (UE). The method may include: communicating with a first base station (BS) via a radio network node; receiving a radio resource control (RRC) reconfiguration message for handing over the UE together with the radio network node from the first BS to a second BS; and in response to receiving the RRC reconfiguration message, maintaining an air interface between the UE and the radio network node while performing the handover from the first BS to the second BS.

[0010] Some embodiments of the present application provide a method performed by a first base station (BS). The method may include: transmitting a handover (HO) request message for handing over a user equipment (UE) served by a radio network node together with the radio network node from the first BS to a second BS to the second BS; and receiving a HO request confirmation message from the second BS in response to the HO request message.

[0011] Some embodiments of the present disclosure provide a device. According to some embodiments of the present disclosure, the device may include: at least one non-transitory computer-readable medium having computer-executable instructions stored thereon; at least one receiving circuit system; at least one transmitting circuit system; and at least one processor coupled to the at least one non-transitory computer-readable medium, the at least one receiving circuit system, and the at least one transmitting circuit system, wherein the at least one non-transitory computer-readable medium and the computer-executable instructions may be configured to cause the device to perform the method according to some embodiments of the present disclosure with the at least one processor.

[0012] Embodiments of the present disclosure provide technical solutions to facilitate and improve the implementation of various communication technologies such as 5G NR. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to describe the manner in which the advantages and features of the present disclosure can be obtained, the description of the present disclosure is presented by reference to specific embodiments of the present disclosure illustrated in the accompanying drawings. These drawings depict only exemplary embodiments of the present disclosure and therefore should not be considered limiting of its scope.

[0014] Figure 1 A schematic diagram illustrating a wireless communication system according to some embodiments of the present disclosure;

[0015] Figure 2 An example block diagram illustrating a protocol stack of an IAB network according to some embodiments of the present disclosure;

[0016] Figure 3 An example block diagram illustrating a protocol stack of an IAB network according to some embodiments of the present disclosure;

[0017] Figures 4 to 7 A flowchart illustrating an exemplary wireless communication procedure according to some embodiments of the present disclosure; and

[0018] Figure 8 A block diagram illustrating an exemplary apparatus according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0019] The detailed description of the accompanying drawings is intended as a description of the preferred embodiments of the present disclosure, and is not intended to represent the only form in which the present disclosure can be practiced. It should be understood that the same or equivalent functions can be completed by different embodiments that are intended to be included in the spirit and scope of the present disclosure.

[0020] Reference will now be made in detail to some embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided in specific network architectures and new service scenarios, such as the Third Generation Partnership Project (3GPP) 5G (NR), 3GPP Long Term Evolution (LTE) Release 8, etc. It is considered that with the development of network architectures and new service scenarios, all embodiments in the present disclosure are also applicable to similar technical problems; and in addition, the terms cited in the present disclosure may be changed, which should not affect the principles of the present disclosure.

[0021] Compared with 4G communication systems, 5G communication systems have put forward more stringent requirements on various network performance indicators, such as 1000 times capacity increase, wider coverage requirements, ultra-high reliability, ultra-low latency, etc. Considering the abundant frequency resources of high-frequency carriers, in order to meet the ultra-high capacity requirements of 5G, the use of high-frequency small base station deployment in hot spots has become more and more common. However, high-frequency carriers have poor propagation characteristics, severe attenuation due to obstacles, and limited coverage. Therefore, dense small base station deployment is required. In addition, fiber deployment may be difficult and expensive for these small base stations. Therefore, an economical and convenient backhaul solution is needed. The integrated backhaul (IAB) technology, in which both the access link and the backhaul link can use wireless transmission solutions to avoid fiber deployment, provides ideas for solving the above problems.

[0022] In an IAB network, a wireless network node such as a relay node (RN) or an IAB node or a wireless backhaul node / device may provide wireless access services for UEs. For example, a UE may be connected to an IAB donor relayed through one or more IAB nodes. An IAB donor may also be referred to as a donor node or a donor base station (e.g., DgNB, donor gNodeB). In addition, a wireless link between an IAB donor and an IAB node or a wireless link between different IAB nodes may be referred to as a "backhaul link". The wireless network nodes in an IAB node may be fixed or mobile.

[0023] An IAB node may include an IAB mobile terminal (MT) part and an IAB distributed unit (DU) part. When an IAB node is connected to its parent node (which may be another IAB node or an IAB donor), it may be considered as a UE, i.e., the role of an MT. When an IAB node provides services to its child node (which may be another IAB node or a UE), it may be considered as a network device, i.e., the role of a DU.

[0024] An IAB donor may be an access network element with complete base station functionality or an access network element with a separate form of a centralized unit (CU) and a distributed unit (DU). An IAB donor may be connected to a core network (e.g., to a 5G core (5GC) network) and provide wireless backhaul functionality for an IAB node. The CU of an IAB donor may be referred to as an "IAB donor CU" (or simply referred to as a "CU"), and the DU of an IAB donor may be referred to as an "IAB donor DU". An IAB donor CU may be divided into a control plane (CP) and a user plane (UP). For example, a CU may include one CU-CP and one or more CU-UPs.

[0025] Considering the limited coverage of high frequency bands and in order to ensure the coverage performance of the network, a multi-hop network may be adopted in the IAB network. Considering the requirements for service transmission reliability, the IAB node may support dual connectivity (DC) or multi-connectivity to improve transmission reliability in order to handle abnormal situations that may occur on the backhaul (BH) link, such as radio link failure (RLF) or congestion, load fluctuation, etc.

[0026] In the case where the IAB network supports multi-hop and dual-connectivity networking, there may be multiple transmission paths between the UE and the IAB donor. The transmission path may include multiple nodes, such as the UE, one or more IAB nodes, and the IAB donor (if the IAB donor is in the form of a separate CU and DU, it may also contain an IAB donor DU and an IAB donor CU). Each IAB node may regard the neighboring node that provides backhaul service for it as a parent node (or parent IAB node), and each IAB node may be regarded as a child node (or child IAB node) of its parent node.

[0027] Figure 1 A schematic diagram illustrating a wireless communication system 100 according to some embodiments of the present disclosure.

[0028] like Figure 1 As shown in FIG. 1 , the wireless communication system 100 may include some base stations (eg, IAB donors 110A and 110B), some IAB nodes (eg, IAB nodes 120A, 120B, and 120C), and some UEs (eg, UE 130A and UE 130B). Figure 1 A specific number of UEs, IAB nodes, and IAB donors are depicted in FIG. 1 , but it is contemplated that any number of UEs, IAB nodes, and IAB donors may be included in the wireless communication system 100 .

[0029] According to some other embodiments of the present disclosure, each of the IAB donor 110A, the IAB donor 110B, the IAB node 120A, the IAB node 120B, and the IAB node 120C may be directly connected to one or more IAB nodes. According to some other embodiments of the present disclosure, each of the IAB donor 110A, the IAB donor 110B, the IAB node 120A, the IAB node 120B, and the IAB node 120C may be directly connected to one or more UEs.

[0030] UE 130A and UE 130B may be any type of device configured to operate and / or communicate in a wireless environment. For example, UE 130A and UE 130B may include computing devices such as desktop computers, laptop computers, personal digital assistants (PDAs), tablet computers, smart TVs (e.g., TVs connected to the Internet), set-top boxes, game consoles, security systems (including security cameras), vehicle-mounted computers, network devices (e.g., routers, switches, and modems), or the like. According to some embodiments of the present disclosure, UE 130A and UE 130B may include portable wireless communication devices, smart phones, cellular phones, flip phones, devices with subscriber identity modules, personal computers, selective call receivers, or any other device capable of transmitting and receiving communication signals on a wireless network. In some embodiments of the present disclosure, UE 130A and UE 130B may include wearable devices such as smart watches, fitness bands, optical head-mounted displays, Internet of Things (IoT) devices, or the like. Furthermore, UE 130A and UE 130B may be referred to as subscriber units, mobile devices, mobile stations, users, terminals, mobile terminals, wireless terminals, fixed terminals, subscriber stations, user terminals or devices, or described using other terminology used in the art.

[0031] IAB donors 110A and 110B can communicate with the core network ( Figure 1 The core network (CN) may include multiple core network components, such as a mobility management entity (MME) ( Figure 1 not shown) or Access and Mobility Management Function (AMF) ( Figure 1 The CN can be used by the UE to access the Public Switched Telephone Network (PSTN) and / or other networks ( Figure 1 Gateway (not shown).

[0032] The wireless communication system 100 may be compatible with any type of network capable of transmitting and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular telephone network, a time division multiple access (TDMA) based network, a code division multiple access (CDMA) based network, an orthogonal frequency division multiple access (OFDMA) based network, an LTE network, a 3GPP based network, a 3GPP 5G network, a satellite communication network, a high altitude platform network, and / or other communication networks.

[0033] In some embodiments of the present disclosure, the wireless communication system 100 is compatible with 5G NR of the 3GPP protocol. For example, the IAB donors 110A and 110B may transmit data on the DL using an orthogonal frequency division multiplexing (OFDM) modulation scheme. The UE 130A and UE 130B may transmit data on the UL using a discrete Fourier spread orthogonal frequency division multiplexing (DFT-S-OFDM) or cyclic prefix OFDM (CP-OFDM) scheme. However, more generally, the wireless communication system 100 may implement some other open or proprietary communication protocols, such as WiMAX and other protocols.

[0034] It should be understood by those skilled in the art that, with the development and advancement of technology, the terms described in the present disclosure may change, but should not affect or limit the principle and spirit of the present application.

[0035] refer to Figure 1 , IAB node 120A can be directly connected to IAB donors 110A and 110B, and IAB node 120B can be directly connected to IAB donor 110A. IAB donors 110A and 110B are parent nodes of IAB node 120A, and IAB donor 110A is the parent node of IAB node 120B. In other words, IAB nodes 120A and 120B are child IAB nodes of IAB donor 110A, and IAB node 120A is also the child IAB node of IAB donor 110B. IAB node 120C can reach IAB donor 110A by skipping IAB node 120B. IAB node 120B is the parent IAB node of IAB node 120C. In other words, IAB node 120C is the child IAB node of IAB node 120B.

[0036] In some other embodiments of the present disclosure, the IAB node may be connected to the IAB node 120C so that it can reach the IAB donor 110A by skipping the IAB node 120C and the IAB node 120B. Such IAB node and the IAB node 120C may be referred to as descendant IAB nodes of the IAB node 120B.

[0037] UE 130A and 130B may be connected to IAB nodes 120A and 120C, respectively. An uplink (UL) packet (e.g., data or signaling) from UE 130A or UE 130B may be transmitted to an IAB donor (e.g., IAB donor 110A or 110B) via one or more IAB nodes, and then transmitted by the IAB donor to a mobile gateway device (e.g., a user plane function (UPF) in 5GC). A downlink (DL) packet (e.g., data or signaling) may be transmitted from an IAB donor (e.g., IAB donor 110A or 110B) after being received by a gateway device, and then transmitted to UE 130A or 130B through one or more IAB nodes.

[0038] For example, refer to Figure 1 , UE 130A may transmit UL data to IAB donor 110A or 110B or receive DL data therefrom via IAB node 120A. UE 130B may transmit UL data to IAB donor 110A or receive DL data therefrom via IAB node 120C and IAB node 120B.

[0039] In an IAB deployment such as the wireless communication system 100, an IAB donor (e.g. Figure 1 A radio link between an IAB donor 110A or 110B in FIG. 1 and an IAB node or between two IAB nodes may be referred to as a backhaul link (BL). Figure 1 The radio link between the IAB donor 110A or 110B in the example and the UE or between the IAB node and the UE may be referred to as an access link (AL). Figure 1 , radio links 140A to 140D are BL, and radio links 150A and 150B are AL.

[0040] A Backhaul Adaptation Protocol (BAP) layer, a protocol layer positioned above a Radio Link Control (RLC) layer, is introduced into the IAB system and may be used to implement packet routing, bearer mapping, and flow control on a wireless backhaul link.

[0041] An F1 interface may be established between an IAB node (e.g., a DU portion of an IAB node) and an IAB donor (e.g., an IAB donor CU). The F1 interface may support both a user plane protocol (e.g., F1-U) and a control plane protocol (e.g., F1-C). The user plane protocol of the F1 interface may include one or more of a general packet radio service (GPRS) tunneling protocol user plane (GTP-U), a user datagram protocol (UDP), an Internet protocol (IP), and other protocols. The control plane protocol of the F1 interface may include one or more of an F1 application protocol (F1AP), a stream control transmission protocol (SCTP), IP, and other protocols.

[0042] Through the control plane of the F1 interface, the IAB node and the IAB donor can perform functions such as interface management, IAB-DU management and UE context-related configuration. Through the user plane of the F1 interface, the IAB node and the IAB donor can perform functions such as user plane data transmission and downlink transmission status feedback.

[0043] Figure 2 An example block diagram illustrating a user plane (UP) protocol stack 200 of an IAB network according to some embodiments of the present disclosure. Figure 3 An example block diagram illustrating a control plane (CP) protocol stack 300 of an IAB network according to some embodiments of the present disclosure. Figure 2 and 3 In the embodiment, the UE may be connected to the IAB donor via the IAB node 2 and the IAB node 1. In some other embodiments of the present disclosure, the UE may be connected to the IAB donor via more or fewer IAB nodes.

[0044] refer to Figure 2 , the UP protocol stack of the UE may include a service data adaptation protocol (SDAP) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, a medium access control (MAC) layer, and a physical (PHY) layer. The UP protocol stack of the DU of the IAB node 2 may include a GTP-U layer, a UDP layer, an IP layer, an RLC layer, a MAC layer, and a PHY layer. The UP protocol stack of the MT of the IAB node 2 or the DU or MT of the IAB node 1 may include a BAP layer, an RLC layer, a MAC layer, and a PHY layer. The UP protocol stack of the DU of the IAB donor may include an IP layer, a BAP layer, an RLC layer, a MAC layer, and a PHY layer, wherein the PHY layer belongs to layer 1 (L1), and the BAP layer, the RLC layer, and the MAC layer belong to layer 2 (L2). The protocol stack of the CU-UP of the IAB donor may include a GTP-U layer, a UDP layer, an IP layer, a SDAP layer, a PDCP layer, an L2 layer, and an L1 layer.

[0045] refer to Figure 3, the CP protocol stack of the UE may include a radio resource control (RRC) layer, a PDCP layer, an RLC layer, a MAC layer, and a physical (PHY) layer. The CP protocol stack of the DU of the IAB node 2 may include a F1AP layer, a SCTP layer, an IP layer, an RLC layer, a MAC layer, and a PHY layer. The CP protocol stack of the MT of the IAB node 2 or the DU or MT of the IAB node 1 may include a BAP layer, an RLC layer, a MAC layer, and a PHY layer. The CP protocol stack of the DU of the IAB donor may include an IP layer, a BAP layer, an RLC layer, a MAC layer, and a PHY layer, wherein the PHY layer belongs to L1, and the BAP layer, the RLC layer, and the MAC layer belong to L2. The protocol stack of the CU-CP of the IAB donor may include an RRC layer, a PDCP layer, a F1AP layer, a SCTP layer, an IP layer, an L2 layer, and an L1 layer.

[0046] Figure 2 and 3 The protocol stack shown in is for illustrative purposes only. For example, Figure 2 and 3 The sequence of some of the protocol stacks in the protocol stack may be rearranged for illustrative purposes. For example, although the SDAP and PDCP layers belong to L2, Figure 2 In the protocol stack of the CU-UP of the IAB donor in , they are shown above the GTP-U layer, the UDP layer and the IP layer.

[0047] In some scenarios, a wireless network node (e.g., fixed or mobile) may migrate (or switch) from one BS (source BS or source IAB donor) to another BS (target BS or target IAB donor), or the wireless network node may migrate to another parent node under another BS. For example, return to reference Figure 1 , the IAB node 120C or the IAB node 120B may migrate from the IAB donor 110A to the IAB donor 110B.

[0048] In some embodiments, the descendant nodes of the radio network node (e.g., UEs served by the radio network node) may also migrate to the target BS. For example, the UE may migrate to the target BS together with the radio network node and may still be served by the radio network node after the migration. This may also be referred to as group mobility.

[0049] Embodiments of the present disclosure provide solutions for handling handover (or migration) of UEs served by a radio network node when the UE is handed over together with the radio network node. For example, an enhanced solution for handover of UEs is proposed. For example, a solution for minimizing the impact of handover on UEs is proposed. More details about embodiments of the present disclosure will be described in the following text in combination with the accompanying drawings.

[0050] Figure 4A flowchart illustrating an exemplary wireless communication procedure 400 according to some embodiments of the present disclosure. The details described in all the above embodiments of the present disclosure apply to Figure 4 For example, BS 410A and BS 410B may be used as the IAB donors described above, and wireless network node 420 may be used as the IAB node described above.

[0051] refer to Figure 4 , UE 430 may communicate with BS 410A (e.g., a cell of BS 510A) via radio network node 420. In operation 411, BS 410A (source BS) may determine to hand over radio network node 420 to a target cell (e.g., a cell of BS 410B) or a target BS (e.g., BS 410B).

[0052] In some embodiments of the present disclosure, at least one UE (e.g., UE 430) served by the radio network node 420 may also be handed over to a target cell or a target BS. For example, the BS 410A (e.g., the CU of the BS 410A) may trigger a handover (HO) of the UE 430, and may transmit a HO request message to the BS 410B (e.g., the CU of the BS 410B) in operation 413.

[0053] In some examples, BS 410A may transmit a corresponding HO request message to BS 410B for each of at least one UE served by radio network node 420. In some examples, the HO request for at least one UE served by radio network node 420 may be bundled with a HO request for radio network node 420 (e.g., a MT of radio network node 420), which is also referred to as group mobility.

[0054] In some embodiments of the present disclosure, the HO request for the UE 430 may indicate (eg, by including an indication) that a simplified HO procedure is supported at the UE 430. The simplified HO procedure may be different from a normal UE HO procedure. The indication may be used to distinguish the simplified HO procedure from a normal UE HO.

[0055] For example, during a normal HO procedure, the UE may perform a random access to the target cell, perform a MAC reset, refresh security and reestablishment of RLC and PDCP, and stop beam failure detection and recovery procedures. As will be described in more detail in the text below, the simplified HO procedure may maintain the air interface between the UE and its serving radio network node (e.g., between the UE and the serving cell of the radio network node), thereby minimizing the impact of the handover on the UE. For example, because the serving radio network node does not change during the handover of the UE and the migration of its serving radio network node, some configurations (e.g., lower layer configurations, such as PHY, MAC and / or RLC configurations, or serving beams) may be (partially) reusable after the handover. The simplified HO procedure may take this into account and introduce enhancements to the UE HO procedure.

[0056] In response to receiving the HO request message, BS 410B (e.g., a CU of BS 410B) may perform admission control for UE 430 and may transmit a HO request confirm message to BS 410A in operation 415. The HO request confirm message may include an RRC reconfiguration message for switching UE 430 together with (or in association with) the radio network node 420.

[0057] In some embodiments of the present disclosure, the RRC reconfiguration message may indicate (eg, explicitly or implicitly) to maintain the air interface between the UE 430 and the radio network node 420. In some embodiments of the present disclosure, maintaining the air interface may be performed at the MAC entity, RLC entity, or PHY layer of the UE 430.

[0058] In some embodiments of the present disclosure, maintaining the air interface between the UE 430 and the radio network node 420 may include at least one of the following: not resetting the MAC entity of the UE 430; not reestablishing the RLC entity of the UE 430; or not performing random access (e.g., to the cell of the BS 410B or the target cell) using the radio network node 420.

[0059] In some embodiments of the present disclosure, the RRC reconfiguration message may include an indication to maintain the air interface. For example, in some embodiments, the RRC reconfiguration message may include an information element (IE) for MAC reset or an IE for RLC reestablishment (e.g., resetMAC IE, re-establishRLC IE, or resetMAC / re-establishRLC IE) to indicate whether the MAC entity should be reset or whether the RLC entity should be reestablished. For example, the IE may be a Boolean type with a "true" or "false" value. In some other embodiments, an IE for no MAC reset or no RLC reestablishment (e.g., not-resetMAC IE, not-re-establishRLC IE, or not-resetMAC / re-establishRLC IE) may be used.

[0060] In some embodiments of the present disclosure, whether to maintain the air interface between the UE 430 and the radio network node 420 may be implicitly indicated in the RRC reconfiguration message. For example, in the case where the RRC reconfiguration message includes pre-allocated resources corresponding to the RRC reconfiguration complete message of the RRC reconfiguration message, the RRC reconfiguration message does not configure resources for random access, or both, the RRC reconfiguration message may implicitly indicate that the air interface between the UE 430 and the radio network node 420 should be maintained. For example, the above situation may indicate that the UE 430 should not use the radio network node 420 to perform random access (e.g., to the cell of the BS 410B or the target cell).

[0061] According to the above embodiment, the description of RRC reconfiguration (e.g., the purpose of the RRC reconfiguration procedure) may include the following (Note: the radio network node in the following text may be an IAB node, mobile or fixed):

[0062] - To modify the RRC connection, for example, to establish / modify / release a radio bearer (RB), to perform reconfiguration of synchronization, to set up / modify / release measurements, to add / modify / release secondary cells (SCells) and cell groups, to add / modify / release conditional handover configuration, to add / modify / release conditional primary secondary cell (PSCell) change configuration, to perform UE mobility associated with a serving radio network node (in which case the MAC may not be reset and / or the RLC may not be reestablished and / or the UE may not perform random access to a target cell). As part of the procedure, non-access stratum (NAS) specific information may be transmitted from the network to the UE.

[0063] According to the above embodiment, the RRC reconfiguration for synchronous execution reconfiguration may include but is not limited to the following (Note: the radio network node in the following text may be an IAB node, mobile or fixed):

[0064] -Reconfiguration with synchronization and security key refresh, involving random access (RA) to the primary secondary cell (PCell) / PSCell, MAC reset, security refresh and re-establishment of RLC and PDCP triggered by explicit L2 indicators; or for UEs served by a wireless network node, MAC may not be reset and / or RLC may not be re-established and / or UE does not perform random access to the target cell.

[0065] In some embodiments, whether to indicate (e.g., explicitly or implicitly) to maintain the air interface may be based on whether the UE switches with its serving radio network node. In some embodiments, whether to indicate (e.g., explicitly or implicitly) to maintain the air interface may be based on whether the simplified HO procedure is supported at the UE.

[0066] In response to receiving the HO request confirmation message, in operation 417, BS 410A (e.g., CU of BS 410A) may transmit a UE context modification request message to radio network node 420 (e.g., DU of radio network node 420). The UE context modification request message may include an RRC reconfiguration message from BS 410B. In operation 417', radio network node 420 may forward the RRC reconfiguration message to UE 430.

[0067] In operation 419, in response to receiving the RRC reconfiguration message, UE 430 may perform handover from BS 410A to BS 410B (e.g., from a source cell to a target cell) while maintaining an air interface between UE 430 and radio network node 420. For example, as described above, in some embodiments, UE 430 may not reset a MAC entity, may not reestablish an RLC entity, or may not perform random access (e.g., to a cell of BS 410B or a target cell) with radio network node 420.

[0068] In some embodiments of the present disclosure, the UE 430 may still perform a MAC reset or RLC re-establishment during a handover of the UE 430 or a migration of the radio network node 420. However, enhancements to the UE behavior on its MAC layer or MAC entity may be introduced.

[0069] For example, in some embodiments of the present disclosure, maintaining the air interface between the UE 430 and the radio network node 420 may include at least one of the following: (a) not initializing a token bucket parameter or a transmittable data amount (e.g., Bj specified in the 3GPP specification) for each logical channel (e.g., a logical channel of the UE 430 associated with the radio network node 420) during a logical channel prioritization procedure; (b) not resetting a new data indicator (NDI) for an uplink hybrid automatic repeat request (HARQ) process at the UE 430; (c) not canceling any triggered buffer status report (BSR) procedure; (d) not canceling any triggered timing advance report procedure; (e) not canceling any triggered suggested bit rate query procedure; or (f) not flushing a soft buffer for a DL HARQ process. In other words, in the event that an upper layer (e.g., an RRC layer) requests a reset of the MAC entity, the MAC entity of the UE 430 may perform at least one of operations (a) to (f).

[0070] In some embodiments, operation (a) may include not initializing the token bucket parameter to 0. Operation (a) is advantageous because UL transmissions at UE 430 may still be processed between UE 430 and radio network node 420 during handover of UE 430 and radio network node 420 together. It is not necessary to set the token bucket parameter to 0, and the MAC entity may keep the value unchanged during handover.

[0071] In some embodiments, operation (b) may include not setting the NDI of all UL HARQ processes to a value of 0. Operation (b) is advantageous because, for each UL HARQ process, UL transmissions may still be processed between the UE 430 and the radio network node 420 during a handover of the UE 430 and the radio network node 420 together. It is not necessary to set the token bucket parameter to 0, and the MAC entity may keep the value unchanged during the handover. The next transmission of a particular TB may be an initial transmission or a retransmission. It is not necessary to set the NDI of the corresponding HARQ process to 0.

[0072] Operation (c) is advantageous because the UL buffer in UE 430 has not been flushed during handover and UE 430 does not change serving radio network node (eg, IAB-DU), and therefore any triggered BSR procedure in the target cell does not have to be canceled.

[0073] Operation (d) is advantageous because UE 430 does not change serving radio network node (eg, IAB-DU), and thus the timing relationship between UE 430 and radio network node 420 may not need to be updated during handover. Therefore, any triggered timing advance reporting procedures in the target cell do not need to be cancelled.

[0074] Operation (e) is advantageous because UE 430 does not change serving radio network node (eg, IAB-DU), and thus the recommended bit rate of the physical layer may not need to be updated during handover. Therefore, any triggered recommended bit rate query procedure in the target cell does not need to be cancelled.

[0075] Operation (f) is advantageous because for each DL HARQ process, DL transmissions can still be processed between UE 430 and radio network node 420 during handover between UE 430 and radio network node 420. The next transmission for a particular TB may be an initial transmission or a retransmission. It is not necessary to flush the soft buffer. However, flushing the soft buffer may have some impact on the reliability of the DL transmission.

[0076] In some embodiments of the present disclosure, enhancements to UE behavior on its MAC layer or MAC entity may be introduced. Such enhancements may be suitable for various scenarios, including scenarios where UE 430 performs a MAC reset during a handover of UE 430 or a migration of a radio network node 420 or scenarios where UE 430 does not perform a MAC reset during a handover of UE 430 or a migration of a radio network node 420.

[0077] For example, in some embodiments of the present disclosure, in response to receiving an RRC reconfiguration message for handing over the UE 430 with the radio network node 420, the MAC entity of the UE 430 may perform at least one of the following:

[0078] - Stop the ongoing random access procedure (if any);

[0079] - a stop timer for random access (RA), such as a contention resolution timer for RA (e.g. ra-ContentionResolutionTimer specified in 3GPP specifications);

[0080] - discarding the explicitly signaled contention-free random access resources of 4-step RA type and 2-step RA type (if any);

[0081] -Flush Msg3 buffer;

[0082] -Flush MsgA buffer;

[0083] - cancel the triggered dispatch request procedure (if any);

[0084] - cancel the triggered power headroom reporting procedure (if any);

[0085] - cancel the triggered configured uplink grant confirmation (if any); or

[0086] - Release the temporary Cell Radio Network Temporary Identifier (C-RNTI), if any.

[0087] Regardless of whether or not a MAC reset is indicated, at least one of the above operations may be performed. In other words, in the case where the UE 430 performs a MAC reset during handover between the UE 430 and the radio network node 420 (e.g., the MAC reset is requested by an upper layer), at least one of the above operations may be performed by a MAC entity of the UE 430. For example, in the case where the cell ID of the radio network node 420 is changed during handover, the UE 430 may cancel any triggered power headroom reporting procedure. In the case where the UE 430 does not perform a MAC reset during handover between the UE 430 and the radio network node 420 (e.g., the upper layer does not request a MAC reset), at least one of the above operations may be performed by a MAC entity of the UE 430.

[0088] In some examples, UE 430 may determine to maintain the air interface when it is handed over with its serving radio network node. In some examples, UE 430 may determine to maintain the air interface based on an explicit or implicit indication of an RRC reconfiguration message.

[0089] In operation 421, the UE 430 may transmit an RRC reconfiguration complete message to the radio network node 420. In operation 421', the radio network node 420 may transmit a UL RRC messaging message to the BS 410B to express the received RRC reconfiguration complete message.

[0090] Those skilled in the art will appreciate that the sequence of operations in the exemplary process 400 may be changed and some operations in the exemplary process 400 may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0091] Figure 5 A flowchart illustrating an exemplary wireless communication procedure 500 according to some embodiments of the present disclosure. The details described in all the above embodiments of the present disclosure apply to Figure 5 For example, BS 510A and BS 510B may be used as the IAB donors described above, and wireless network node 520 may be used as the IAB node described above.

[0092] refer to Figure 5, UE 530 may communicate with BS 510A (e.g., a cell of BS 510A) via radio network node 520. In some embodiments of the present disclosure, beam failure detection and recovery procedures may be performed at UE 530. For example, UE 530 (e.g., a MAC entity) may start a timer for beam failure detection (BFD) (e.g., beamFailureDetectionTimer specified in the 3GPP specification) upon receiving a beam failure instance indication. For example, UE 530 (e.g., a MAC entity) may increment a counter for beam failure instances (e.g., BFI_COUNTER specified in the 3GPP specification) upon receiving a beam failure instance indication. UE 530 may trigger a beam failure recovery (BFR) procedure under certain conditions, including, for example, when a counter for a beam failure instance reaches a threshold.

[0093] In operation 511, BS 510A (source BS) may determine to hand over the radio network node 520 to a target cell (eg, a cell of BS 510B) or a target BS (eg, BS 510B).

[0094] In some embodiments of the present disclosure, at least one UE (e.g., UE 530) served by the radio network node 520 may also be handed over to a target cell or a target BS. For example, the BS 510A (e.g., the CU of the BS 510A) may trigger the HO of the UE 530, and may transmit a HO request message to the BS 510B (e.g., the CU of the BS 510B) in operation 513.

[0095] In some examples, BS 510A may transmit a corresponding HO request message to BS 510B for each of at least one UE served by the radio network node 520. In some examples, the HO request for at least one UE served by the radio network node 520 may be bundled with a HO request for the radio network node 520 (e.g., a MT of the radio network node 520), which is also referred to as group mobility.

[0096] In some embodiments of the present disclosure, the HO request for the UE 530 may indicate (eg, by including an indication) that the simplified HO procedure is supported at the UE 530. The above description about the simplified HO procedure is also applicable here and is therefore omitted herein.

[0097] In response to receiving the HO request message, BS 510B (e.g., a CU of BS 510B) may perform admission control for UE 530 and may transmit a HO request confirm message to BS 510A in operation 515. The HO request confirm message may include an RRC reconfiguration message for switching UE 530 together with (or in association with) the radio network node 520.

[0098] In some embodiments of the present disclosure, the RRC reconfiguration message may indicate (eg, explicitly or implicitly) to maintain the air interface between the UE 530 and the radio network node 520. The above description on maintaining the air interface is also applicable here and is therefore omitted herein.

[0099] In response to receiving the HO request confirmation message, in operation 517, the BS 510A (e.g., the CU of the BS 510A) may transmit a UE context modification request message to the radio network node 520 (e.g., the DU of the radio network node 520). The UE context modification request message may include an RRC reconfiguration message from the BS 510B. In operation 517', the radio network node 520 may forward the RRC reconfiguration message to the UE 530.

[0100] In operation 519, in response to receiving the RRC reconfiguration message, UE 530 may maintain the air interface between UE 530 and radio network node 520 while performing handover from BS 510A to BS 510B. For example, as described above, in some embodiments, UE 530 may not reset the MAC entity, may not reestablish the RLC entity, or may not perform random access (e.g., to a cell of BS 510B or a target cell) with radio network node 520. For example, as described above, in some embodiments, UE 530 may perform at least one of operations (a) to (f).

[0101] In some embodiments of the present disclosure, enhancements to UE behavior for beam failure detection and recovery procedures may be introduced.

[0102] For example, because the serving radio network node does not change during handover of a UE (e.g., UE 530) and its serving radio network node (e.g., radio network node 520) together, the serving beam of the UE for a source BS (e.g., BS 510A) or a source cell (e.g., a cell of BS 510A) may be the same as the serving beam of the UE for a target BS (e.g., BS 510B) or a target cell (e.g., a cell of BS 510B). In some embodiments, the serving beam may refer to a serving synchronization signal block (SSB) or a channel state information reference signal (CSI-RS) used for beam failure detection and recovery. In this scenario, maintaining the air interface between UE 530 and radio network node 520 may include at least one of: using the same serving beam for beam failure detection and recovery in the target BS (or cell) as in the source BS (or cell); pausing or not stopping the timer for BFD during handover of UE 530; maintaining or not resetting the counter for beam failure instances during handover of UE 530; canceling any triggered BFR procedure with BS 510A; or triggering a BFR procedure with BS 510B in response to connecting to BS 510B when the triggered BFR procedure with BS 510A was not canceled before the handover of UE 530 or there was an ongoing BFR procedure with BS 510A before the handover of UE 530. In some embodiments, the serving cell of UE 530 may be configured with more than one serving beam (e.g., two BFD-RS groups), and the above behavior may be applicable to each serving beam of the serving cell.

[0103] For example, if BFR has not been triggered in the source cell (e.g., BS 510A) or UE 530 is still performing beam failure detection for the source cell or a serving beam failure has not been declared when the handover occurs, then UE 530 (e.g., a MAC entity) may maintain a counter for beam failure instances and a timer for BFD during the handover. In some instances, UE 530 (e.g., a MAC entity) may suspend or not stop the timer for BFD and not reset the counter for beam failure instances during the handover.

[0104] For example, if BFR has been triggered in the source cell (e.g., BS 510A) and is not canceled or there is an ongoing BFR procedure in the source cell (e.g., BS 510A) or a serving beam failure has been declared when the handover occurs (e.g., an RRC reconfiguration message or a HO command may be received before the BFR procedure is triggered), then the UE 530 (e.g., a MAC entity) may maintain or not reset a counter for the beam failure instance. The UE 530 (e.g., a MAC entity) may maintain, not stop, or pause a timer for BFD during the handover. In some instances, the UE 530 may cancel the triggered BFR procedure of the source cell (e.g., with BS 510A). In some instances, in response to the UE 530 connecting to the target cell (e.g., with BS 510B), the UE 530 may trigger a BFR procedure in the target cell. For example, for a special cell (SpCell) (e.g., BFR is triggered for the SpCell), the UE 530 may trigger a random access procedure. For a SCell (eg, to trigger BFR for a SCell), the UE 530 may transmit a BFR MAC control element (CE).

[0105] As described above, the RRC reconfiguration message may indicate (e.g., explicitly or implicitly) that the air interface between the UE 530 and the radio network node 520 is maintained. In some embodiments of the present disclosure, the explicit indication may refer to an indication in the RRC reconfiguration message that the serving beam of the UE 530 for the source BS (e.g., BS 510A) or the source cell (e.g., the cell of BS 510A) is the same as the serving beam of the UE 530 for the target BS (e.g., BS 510B) or the target cell (e.g., the cell of BS 510B). The UE 530 may determine whether to maintain the air interface (e.g., perform the above-mentioned operations regarding the beam failure detection and recovery procedure) based on the indication. In some embodiments of the present disclosure, the implicit indication may be implemented as follows. For example, the RRC reconfiguration message may include beam information configured by the BS 510B. UE 530 may determine whether a serving beam of UE 530 for a source BS (e.g., BS 510A) or a source cell (e.g., a cell of BS 510A) is the same as a serving beam of UE 530 for a target BS (e.g., BS 510B) or a target cell (e.g., a cell of BS 510B) based on the beam information. UE 530 may determine whether to maintain an air interface (e.g., perform the above-described operations regarding beam failure detection and recovery procedures) based on the determination of whether the serving beam is changed. In some embodiments of the present disclosure, UE 530 may assume that an air interface should be maintained (e.g., perform the above-described operations regarding beam failure detection and recovery procedures) in a group mobility situation.

[0106] Those skilled in the art will appreciate that the sequence of operations in the exemplary process 500 may be changed and some operations in the exemplary process 500 may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0107] In some embodiments of the present disclosure, if the BS is aware that the serving beam of the UE has been declared failed, it would be beneficial for the BS to inform the target BS of the beam information when the BS decides to hand over the UE to the target cell.

[0108] For example, refer again to Figure 5 , the HO request message transmitted in operation 513 may include information about whether the serving beam of UE 530 for BS 510A or a source cell (e.g., a cell of BS 510A) has been declared faulty; or candidate beams (e.g., serving SSBs and / or CSI-RS) applicable to BS 510B or a target cell (e.g., a cell of BS 510B). The information may be used for SCell or SpCell. In the event that the serving beam of UE 530 for BS 510A or a source cell has been declared faulty, BS 510B may reconfigure the beam and include the reconfiguration information in an RRC reconfiguration message to UE 530. The reconfigured beam may be based on a candidate beam.

[0109] Those skilled in the art should understand that the above-mentioned embodiments regarding the indication of beam information between BSs may be applicable to any type of HO procedure, including, for example, the exemplary procedure 500, a normal HO procedure, a HO procedure in which the UE is directly connected to the source BS, a HO procedure in which the source cell and the target cell are co-located, etc.

[0110] Figure 6 A flowchart illustrating an exemplary wireless communication procedure 600 according to some embodiments of the present disclosure. The details described in all the above embodiments of the present disclosure apply to Figure 6 The embodiments shown in .

[0111] refer to Figure 6 In operation 611, the UE may communicate with the first BS (e.g., source BS) via the radio network node. In operation 613, the UE may receive an RRC reconfiguration message for switching the UE together with the radio network node from the first BS to the second BS (e.g., target BS). In some embodiments, the first BS and the second BS may be IAB donors, and the radio network node may be an IAB node.

[0112] In operation 615, the UE may maintain the air interface between the UE and the radio network node while performing handover from the first BS to the second BS in response to receiving the RRC reconfiguration message. The air interface between the UE and the radio network node may refer to an air interface between the UE and a serving cell of the radio network node.

[0113] The previous description regarding RRC reconfiguration messages and maintaining the air interface may apply here.

[0114] For example, in some embodiments of the present disclosure, the RRC reconfiguration message may include an indication to maintain the air interface between the UE and the radio network node.

[0115] For example, in some embodiments of the present disclosure, the RRC reconfiguration message may include pre-allocated resources for an RRC reconfiguration complete message corresponding to the RRC reconfiguration message, wherein resources for random access are not configured in the RRC reconfiguration message, or both.

[0116] For example, in some embodiments of the present disclosure, maintaining the air interface between the UE and the radio network node may include at least one of: not resetting the MAC entity of the UE; not reestablishing the RLC entity of the UE; or not performing random access with the radio network node.

[0117] For example, in some embodiments of the present disclosure, maintaining the air interface between the UE and the wireless network node may include at least one of the following: not initializing the token bucket parameters of each logical channel during the logical channel prioritization procedure (for example, initializing to 0); not resetting the new data indicator of the uplink HARQ process (for example, setting it to 0); not canceling any triggered buffer status reporting procedure; not canceling any triggered timing advance reporting procedure; not canceling any triggered recommended bit rate query procedure; or not refreshing the soft buffer of the downlink HARQ process.

[0118] For example, in some embodiments of the present disclosure, the indication may indicate that a serving beam for the UE of the first BS is the same as a serving beam for the second BS.

[0119] For example, in some embodiments of the present disclosure, maintaining an air interface between a UE and a wireless network node may include performing at least one of the following: using the same service beam for beam failure detection and recovery in the first BS as in the second BS; pausing or not stopping a timer for BFD during switching; maintaining or not resetting a counter for beam failure instances during switching; canceling any triggered BFR procedure with the first BS; or triggering a BFR procedure with the second BS in response to connecting to the second BS if a triggered BFR procedure with the first BS was not canceled before the switching or there was an ongoing BFR procedure with the first BS before the switching.

[0120] For example, in some embodiments of the present disclosure, maintaining the air interface is performed at a MAC entity or an RLC entity or a PHY layer of the UE.

[0121] Those skilled in the art will appreciate that the sequence of operations in the exemplary process 600 may be changed and some operations in the exemplary process 600 may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0122] Figure 7 A flowchart illustrating an exemplary wireless communication procedure 700 according to some embodiments of the present disclosure. The details described in all the above embodiments of the present disclosure apply to Figure 7 The embodiments shown in .

[0123] refer to Figure 7 In operation 711, the first BS (e.g., source BS) may transmit to the second BS (e.g., target BS) a HO request message for switching the UE served by the radio network node together with the radio network node from the first BS to the second BS. In some embodiments, the first BS and the second BS may be IAB donors and the radio network node may be an IAB node.

[0124] In operation 713, the first BS may receive an HO request confirm message from the second BS in response to the HO request message.

[0125] The previous description about the HO request message is applicable here.

[0126] For example, in some embodiments of the present disclosure, the HO request message may indicate that a simplified HO procedure is supported at the UE. In some embodiments, during the simplified HO procedure, the UE may maintain an air interface between the UE and the radio network node. The previous description about maintaining the air interface may apply here.

[0127] In some embodiments of the present disclosure, the HO request confirm message may include an RRC reconfiguration message for handing over the UE from the first BS to the second BS. The previous description about the RRC reconfiguration message may be applicable here.

[0128] For example, the RRC reconfiguration message may include an indication to maintain the air interface between the UE and the radio network node. For example, the RRC reconfiguration message may include pre-allocated resources for an RRC reconfiguration complete message corresponding to the RRC reconfiguration message, wherein resources for random access are not configured in the RRC reconfiguration message, or both.

[0129] For example, in some embodiments of the present disclosure, the indication may indicate at least one of the following: the UE does not reset the MAC entity of the UE; the UE does not reestablish the RLC entity of the UE; or the UE does not perform random access with the wireless network node.

[0130] For example, in some embodiments of the present disclosure, the indication may indicate at least one of the following: the UE does not initialize the token bucket parameters of each logical channel during the logical channel prioritization procedure; the UE does not reset the new data indicator of the uplink HARQ process; the UE does not cancel any triggered buffer status reporting procedure; the UE does not cancel any triggered timing advance reporting procedure; the UE does not cancel any triggered recommended bit rate query procedure; or the UE does not refresh the soft buffer of the downlink HARQ process.

[0131] For example, in some embodiments of the present disclosure, the indication may indicate that a serving beam for the UE of the first BS is the same as a serving beam for the second BS.

[0132] For example, in some embodiments of the present disclosure, the HO request message may include at least one of the following: information on whether a serving beam of the UE for the first BS has been declared failed; or a candidate beam applicable to the target BS.

[0133] Those skilled in the art will appreciate that the sequence of operations in the exemplary process 700 may be changed and some operations in the exemplary process 700 may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0134] Figure 8 A block diagram illustrating an exemplary apparatus 800 according to some embodiments of the present disclosure.

[0135] like Figure 8 8, the apparatus 800 may include at least one processor 806 and at least one transceiver 802 coupled to the processor 806. The apparatus 800 may be a wireless network node (eg, an IAB node), a BS (eg, an IAB donor, an IAB donor CU, or an IAB donor DU), or a UE.

[0136] Although elements such as at least one transceiver 802 and processor 806 are described in the singular in this figure, the plural form is contemplated unless limitation to the singular form is explicitly stated. In some embodiments of the present application, the transceiver 802 may be divided into two devices, such as a receive circuit system and a transmit circuit system. In some embodiments of the present application, the apparatus 800 may further include an input device, a memory, and / or other components.

[0137] In some embodiments of the present application, the device 800 may be a UE. The transceiver 802 and the processor 806 may interact with each other to perform Figures 1 to 7 In some embodiments of the present application, the device 800 may be a BS. The transceiver 802 and the processor 806 may interact with each other to perform Figures 1 to 7The operations of the BS, IAB donor, IAB donor CU or IAB donor DU described in the specification. In some embodiments of the present application, the device 800 may be a wireless network node. The transceiver 802 and the processor 806 may interact with each other to perform Figures 1 to 7 The operations of a wireless network node or an IAB node (mobile or fixed) are described in detail.

[0138] In some embodiments of the present application, the apparatus 800 may further include at least one non-transitory computer-readable medium.

[0139] For example, in some embodiments of the present disclosure, a non-transitory computer-readable medium may store computer-executable instructions to enable the processor 806 to implement the method described above with respect to the UE. For example, when the computer-executable instructions are executed, the processor 806 interacts with the transceiver 802 to perform Figures 1 to 7 The operations of the UE are described in .

[0140] In some embodiments of the present disclosure, a non-transitory computer-readable medium may store computer-executable instructions to enable the processor 806 to implement the method described above with respect to the BS, IAB donor, IAB donor CU, or IAB donor DU. For example, when the computer-executable instructions are executed, the processor 806 interacts with the transceiver 802 to perform Figures 1 to 7 The operations described in BS, IAB donor, IAB donor CU or IAB donor DU.

[0141] For example, in some embodiments of the present disclosure, a non-transitory computer-readable medium may store thereon computer-executable instructions to cause the processor 806 to implement the method described above with respect to a wireless network node or an IAB node (mobile or fixed). For example, when the computer-executable instructions are executed, the processor 806 interacts with the transceiver 802 to perform Figures 1 to 7 The operations of a radio network node or an IAB node (mobile or fixed) are described in detail in the accompanying drawings.

[0142] It should be understood by those of ordinary skill in the art that the operations or steps of the methods described in conjunction with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. In addition, in some aspects, the operations or steps of the methods may reside as one or any combination or set of codes and / or instructions on a non-transitory computer-readable medium that can be incorporated into a computer program product.

[0143] Although the present disclosure has been described with reference to specific embodiments of the present disclosure, it is apparent that many alternatives, modifications, and variations may be apparent to those skilled in the art. For example, the various components of the embodiments may be interchanged, added, or substituted in other embodiments. Moreover, all elements of each figure are not necessary for the operation of the disclosed embodiments. For example, a person of ordinary skill in the field of the disclosed embodiments will be able to make and use the teachings of the present disclosure by simply adopting the elements of the independent claims. Therefore, the embodiments of the present disclosure set forth herein are intended to be illustrative rather than restrictive. Various changes may be made without departing from the spirit and scope of the present disclosure.

[0144] In this document, the terms "switch", "path switching" and "migration" are used interchangeably. The term "include / including" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment containing the element list not only includes those elements but also may include other elements that are not explicitly listed or inherent to this process, method, article or equipment. Elements starting with "a / an" or the like do not exclude the presence of additional identical elements in the process, method, article or equipment containing the element without more constraints. Moreover, the term "another" is defined as at least one second or more. As used herein, the term "having" and the like are defined as "including". For example, the expression of "A and / or B" or "at least one of A and B" may include any and all combinations of the words enumerated together with the expression. For example, the expression "A and / or B" or "at least one of A and B" may include A, B or both A and B. The terms “first”, “second” or the like are merely used to clearly describe the embodiments of the present application but are not used to limit the essence of the present application.

Claims

1. A user equipment UE, comprising: A transceiver configured to: communicating with a first base station BS via a radio network node; and receiving a radio resource control (RRC) reconfiguration message for handing over the UE together with the radio network node from the first BS to a second BS; and a processor coupled to the transceiver and configured to: In response to receiving the RRC reconfiguration message, an air interface between the UE and the radio network node is maintained while performing the handover from the first BS to the second BS.

2. The UE of claim 1, wherein the RRC reconfiguration message includes an indication to maintain the air interface between the UE and the radio network node.

3. The UE of claim 1 or 2, wherein maintaining the air interface between the UE and the radio network node comprises at least one of: Not resetting the medium access control MAC entity of the UE; not reestablishing a radio link control, RLC, entity of the UE; or Random access is not performed using the radio network node.

4. The UE of claim 1 or 2, wherein maintaining the air interface between the UE and the radio network node comprises at least one of: The token bucket parameters for each logical channel are not initialized during the logical channel prioritization procedure; The new data indicator of the uplink hybrid automatic repeat request HARQ process is not reset; Do not cancel any triggered buffer status reporting process; No triggered timed advance reporting procedures will be cancelled; not cancel any triggered recommended bit rate query process; or The soft buffers of the downlink HARQ processes are not flushed. 5 . The UE of claim 2 , wherein the indication indicates that a serving beam of the UE for the first BS is the same as a serving beam for the second BS.

6. The UE of any one of claims 1, 2, and 5, wherein maintaining the air interface between the UE and the radio network node comprises performing at least one of: using, in the first BS, the same serving beam for beam failure detection and restoration as in the second BS; pausing or not stopping a timer for beam failure detection BFD during the switching; maintaining or not resetting a counter for beam failure instances during said switching; canceling any triggered beam failure recovery (BFR) procedure with the first BS; or In response to connecting to the second BS if the triggered BFR procedure with the first BS is not cancelled before the handover or there is an ongoing BFR procedure with the first BS before the handover, a BFR procedure with the second BS is triggered.

7. A first base station BS, comprising: processor; and a transceiver coupled to the processor, wherein the transceiver is configured to: transmitting a handover HO request message for handing over a user equipment UE served by a radio network node together with the radio network node from the first BS to a second BS to the second BS; and In response to the HO request message, a HO request confirm message is received from the second BS. 8 . The first BS of claim 7 , wherein the HO request message indicates that a simplified HO procedure is supported at the UE, and during the simplified HO procedure, the UE maintains an air interface between the UE and the radio network node.

9. The first BS according to claim 7, wherein the HO request confirm message includes a radio resource control (RRC) reconfiguration message for switching the UE from the first BS to the second BS; and The RRC reconfiguration message includes an indication to maintain an air interface between the UE and the radio network node.

10. The first BS according to claim 7, wherein the HO request confirm message includes a radio resource control (RRC) reconfiguration message for switching the UE from the first BS to the second BS; and wherein the RRC reconfiguration message includes pre-allocated resources for an RRC reconfiguration complete message corresponding to the RRC reconfiguration message, wherein resources for random access are not configured in the RRC reconfiguration message, or both.

11. The first BS of claim 9, wherein the indication indicates at least one of: The UE does not reset a medium access control MAC entity of the UE; The UE does not re-establish a radio link control, RLC, entity of the UE; or The UE performs random access without the radio network node.

12. The first BS of claim 9, wherein the indication indicates at least one of: The UE does not initialize token bucket parameters for each logical channel during the logical channel prioritization procedure; The UE does not reset a new data indicator of an uplink hybrid automatic repeat request HARQ process; The UE does not cancel any triggered buffer status reporting procedure; The UE does not cancel any triggered timing advance reporting procedure; The UE does not cancel any triggered recommended bit rate query procedure; or The UE does not flush the soft buffer of the downlink HARQ process. 13 . The first BS of claim 9 , wherein the indication indicates that the serving beam for the UE of the first BS is the same as a serving beam for the second BS.

14. The first BS according to claim 7, wherein the HO request message includes at least one of: information on whether a serving beam of the UE for the first BS has been declared failed; or Candidate beams applicable to the target BS.

15. A method performed by a user equipment UE, comprising: communicating with a first base station BS via a radio network node; receiving a radio resource control (RRC) reconfiguration message for handing over the UE together with the radio network node from the first BS to a second BS; and In response to receiving the RRC reconfiguration message, an air interface between the UE and the radio network node is maintained while performing the handover from the first BS to the second BS.

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