Patent Publication Number: US-2022217586-A1

Title: Systems and methods for releasing candidate target cell resources in multi-connectivity operation

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority under 35 U.S.C. § 120 as a continuation of PCT Patent Application No. PCT/CN2019/109011, filed on Sep. 29, 2019, the disclosure of which is incorporated herein by reference in its entirety 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of telecommunications, and in particular, to the release, cancelation, or deletion of communication resources of candidate conditional handover (CHO) primary secondary cell (PScell)/secondary cell group (SCG) in multi-connectivity operation. 
     BACKGROUND 
     The land-based 5th Generation Mobile Communication Technology (5G) cellular mobile communication system includes two subsystems—the next-generation core network referred to as the 5th Generation Core (5GC) and the next-generation wireless access network referred to as the Next Generation Radio Access Network (NG-RAN). The 5GC includes, for example, an Access Mobility Function (AMF), a Session Management Function (SMF), a User Plane Function (UPF), and other network entities/nodes. The AMF provides for mobility access. The SMF provides for session management. The UPF provides for user plane functionalities. The NG-RAN includes base stations providing service via at least two different Radio Access Technologies (RATs). The next generation eNodeB (ng-eNB), the air interface of which can support the Evolved Universal Terrestrial Radio Access (E-UTRA) RAT system, is evolved from the 4G eNB. The gNB with the new physical layer air interface design supports the New Radio (NR) RAT system. Logical interfaces have been developed for related network element node entities. NG-RAN base station (e.g., gNB or ng-eNB), via a standardized NG interface, connects to the 5GC bidirectionally, including an NG-Control Plane (NG-C) connection for signaling transmission and an NG-User Plane (NG-U) connection for user data transmission. The NG-RAN base stations (e.g., gNB or ng-eNB) are bidirectionally connected to each other through the Xn interface, which includes the Xn-Control Plane (Xn-C) connection and the Xn-User Plane (Xn-U) connection. 
     SUMMARY 
     The example embodiments disclosed herein are directed to solving the issues relating to one or more of the problems presented in the prior art, as well as providing additional features that will become readily apparent by reference to the following detailed description when taken in conjunction with the accompany drawings. In accordance with various embodiments, example systems, methods, devices and computer program products are disclosed herein. It is understood, however, that these embodiments are presented by way of example and are not limiting, and it will be apparent to those of ordinary skill in the art who read the present disclosure that various modifications to the disclosed embodiments can be made while remaining within the scope of this disclosure. 
     In some embodiments, a master node (MN) determines that a candidate target PScell/SCG in a candidate target secondary node (SN) needs to be released, canceled, or deleted. The candidate target SN is involved in a conditional SN addition or change multi-RAT dual connectivity (MR-DC) procedure of a wireless communication device. The MN and a source SN are currently configured to provide communication services to the wireless communication device. The MN requests to release, cancel, or delete the at least one candidate target PScell/SCG in the candidate target SN using a first signaling procedure. In response to the candidate target PScell/SCG being successfully released, canceled, or deleted, the MN notifies the source SN via a second signaling procedure that the concerned candidate target PScell/SCG in the candidate target SN has been released, canceled, or deleted. 
     In some embodiments, a candidate target SN is involved in a conditional SN addition or change MR-DC procedure of a wireless communication device. The candidate target SN determines that a candidate target PScell/SCG in the candidate target SN needs to be released, canceled, or deleted. A MN and a source SN are currently configured to provide communication services to the wireless communication device. The candidate target SN requests to release, cancel, or delete the at least one candidate target PScell/SCG in the candidate target SN itself using a first signaling procedure. In response to the candidate target PScell/SCG being successfully released, canceled, or deleted, the MN notifies the source SN via a second signaling procedure that the concerned candidate target PScell/SCG in the candidate target SN has been released, canceled, or deleted. 
     In some embodiments, a source SN determines that a candidate target PScell/SCG in a candidate target SN needs to be released, canceled, or deleted. The candidate target SN is involved in a conditional SN addition or change MR-DC procedure of a wireless communication device. A MN and the source SN are currently configured to provide communication services to the wireless communication device. The source SN requests the MN to release, cancel, or delete the at least one candidate target PScell/SCG in the candidate target SN using a first signaling procedure. In response to the candidate target PScell/SCG being successfully released, canceled, or deleted, the MN notifies the source SN via a second signaling procedure that the concerned candidate target PScell/SCG in the candidate target SN has been released, canceled, or deleted. 
     The above and other aspects and their implementations are described in greater detail in the drawings, the descriptions, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various example embodiments of the present solution are described in detail below with reference to the following figures or drawings. The drawings are provided for purposes of illustration only and merely depict example embodiments of the present solution to facilitate the reader&#39;s understanding of the present solution. Therefore, the drawings should not be considered limiting of the breadth, scope, or applicability of the present solution. It should be noted that for clarity and ease of illustration, these drawings are not necessarily drawn to scale. 
         FIG. 1  is a block diagram illustrating an example communication system including an aggregated NG-RAN node, in accordance with some embodiments of the present disclosure; 
         FIG. 2  is a block diagram illustrating an example communication system including a disaggregated NG-RAN node, in accordance with some embodiments of the present disclosure; 
         FIG. 3  illustrates a system that manages CHO preconfigured resources using a single base station, in accordance with some embodiments of the present disclosure; 
         FIG. 4  illustrates a system that manages CHO preconfigured resources using a multiple base stations, in accordance with some embodiments of the present disclosure; 
         FIG. 5  illustrates a system capable of performing NG-RAN multi-connectivity operations, in accordance with some embodiments of the present disclosure; 
         FIG. 6  illustrates a system supporting multi-connectivity operation of a UE, in accordance with some embodiments of the present disclosure; 
         FIG. 7  is a signal diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 8  is a signal diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 9  is a signal diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 10  is a signal diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 11  is a signal diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 12  is a signal diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 13  is a signal diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 14A  is a flow diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 14B  is a flow diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 14C  is a flow diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure; 
         FIG. 15A  illustrates a block diagram of an example base station, in accordance with some embodiments of the present disclosure; and 
         FIG. 15B  illustrates a block diagram of an example UE, in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Various example embodiments of the present solution are described below with reference to the accompanying figures to enable a person of ordinary skill in the art to make and use the present solution. As would be apparent to those of ordinary skill in the art, after reading the present disclosure, various changes or modifications to the examples described herein can be made without departing from the scope of the present solution. Thus, the present solution is not limited to the example embodiments and applications described and illustrated herein. Additionally, the specific order or hierarchy of steps in the methods disclosed herein are merely example approaches. Based upon design preferences, the specific order or hierarchy of steps of the disclosed methods or processes can be re-arranged while remaining within the scope of the present solution. Thus, those of ordinary skill in the art will understand that the methods and techniques disclosed herein present various steps or acts in a sample order, and the present solution is not limited to the specific order or hierarchy presented unless expressly stated otherwise. 
       FIG. 1  is a block diagram illustrating an example communication system  100  including an aggregated NG-RAN node  110 , in accordance with some embodiments of the present disclosure. Referring to  FIG. 1 , the communication system  100  corresponds to a network architecture in which CU/DU air interface protocol stack is unseparated. As shown, the aggregated NG-RAN node  110  includes a first network node entity  120  and a second network node entity  130 . Each of the network node entities  120  and  130  can be a gNB or a ng-eNB (unseparated). 
       FIG. 2  is a block diagram illustrating an example communication system  200  including a disaggregated NG-RAN node  210 , in accordance with some embodiments of the present disclosure. Referring to  FIGS. 1-2 , the communication system  200  corresponds to a network architecture in which gNB CU/DU air interface protocol stack is separated. As shown in the communication system  200 , a single gNB  220  can be separated into network node entities including a single gNB-CU  222  and multiple gNB-DUs (e.g., gNB-DU  224  and  226 ). Likewise, the gNB  230  can be separated into network node entities including a single gNB-CU  232  and multiple gNB-DUs (e.g., gNB-DU  234  and  236 ). The gNB-CUs  222  and  232  can be bidirectionally connected to respective ones of the gNB-DUs  224 ,  226 ,  234 , and  236  via standardized F1 interfaces, each of which includes F1-Control Plane (F1-C) connections and F1-User Plane (F1-U) connections. 
     In the communication systems  100  in which the gNB CU/DU air interface protocol stack is unseparated and in the communication systems  200  in which the gNB CU/DU air interface protocol stack is separated, the logical interfaces externally presented are NG and Xn interfaces. For example, the network node entities  120  and  130  are connected to each other via the Xn interface and connected to a 5GC  102  (including the AMF, SMF, UPF, and so on) via the NG interfaces. The gNBs  220  and  230  are connected to each other via the Xn interface and connected to the 5GC  102  via the NG interfaces. 
     The Control Plane (CP) connections of the network-side logical interfaces (e.g., NG, Xn, and F1) are used for transmitting control signaling messages between network entities/nodes. 
     User Plane (UP) connections are used for transmitting user service data (packets). NG Application Protocol (NGAP), Xn Application Protocol (XnAP), and F1 Application Protocol (F1AP) are logical network application layer protocols for CP of NG-C, Xn-C, and F1-C Radio Network Layer (RNL), respectively. The NGAP, XnAP, and F1AP standardize signaling flow messages for each logical interface. 
     In some examples, the UE is only served by one serving base station (e.g., an eNB, an ng-eNB, or a gNB) at a given time, as in the case of a single-connection operation. In a single-connection operation, a current NG-RAN serving base station maintains the continuity of the terminal user communication service (session) using the handover (HO) procedure. IN the HO procedure, the communication context of the UE is smoothly migrated from a source serving node or cell to a target node or cell. The HO procedure typically includes three stages: an HO preparation stage, an HO execution stage, and an HO completion stage. In the HO preparation stage, the source serving base station, node, or cell (hereinafter referred to as the source node or the source cell) and the target serving base station, node, or cell (hereinafter referred to as the target node or the target cell) negotiate using the signaling flow of the network logical interface to determine the reservation configurations and air interface HO Command of the target-side communication resources. In the HO execution phase, the source node sends the air interface HO Command to the UE using the Radio Resource Control RRC) air interface signaling. The UE attempts to perform a HO operation for obtaining communication services from the designated target node. In the HO completion phase, the source node and the target node negotiate using suitable signaling procedures to notify the HO result and to release the communication resources that are no longer needed and the UE communication context from the source-side. 
     In a traditional unconditional or immediate HO procedure, the HO preparation stage and the HO execution stage are executed continuously in time. That is, the time interval between these two stages is minimal or non-existent. The source node initiates the HO preparation stage based on wireless Measurement Report and local Radio Resource Management (RRM) policy of the UE. Responsive to the designated target node (typically there is only one target primary node and one target primary serving cell in the traditional unconditional HO procedure) completing target-side resource reservation configuration related to the HO preparation stage, the source node immediately initiates HO execution. The UE then executes the HO command, attempting to switch to the target node. Therefore, the “actual HO moment” of the UE and receiving the air interface switching command occur continuously in time. The source node typically sends the air interface switching command to the UE in response to determining that the UE and the network-side satisfy actual switching conditions at the same time. Here, the actual switching conditions refer to the radio signal quality of the designated target node is sufficiently strong, and the reserved communication resource is sufficient and reasonably configured. After the UE successfully switches to the target node, at least part of the service continuity can be maintained. 
     The described traditional unconditional or immediate HO mechanism is originally designed for low-frequency band, sparse cell deployment. As the network capacity expands, heterogeneous networks (HetNets) are deployed over the homogeneous network. For example, a number of Small Cells are deployed within the coverage of the cellular macro cell. In the 5G system, aside from using low-frequency band resources, high-frequency band resources up to 100 GHz can be used. Such high-frequency cells can usually be deployed in the form of dense small cells referred to as Small Cell Clusters. In the 5G system, the CHO has been introduced. In the CHO process, a CHO handover preparation stage and a CHO handover execution stage are discontinuous in time, e.g., a large time interval exists between the CHO handover preparation stage and the CHO handover execution stage. The source node initiates the CHO preparation stage based on wireless Measurement Report and local RRM policy of the UE. In the CHO preparation stage, the source node requests multiple potential/candidate target base stations, cells, or nodes (referred to as potential/candidate target nodes/cells) to complete the CHO handover preparation process. For example, the candidate target nodes are requested to complete the target-side resource reservation configurations and to send the CHO pre-configuration or prepared information to the UE in advance through the air interface RRC signaling. 
     Then, the source node does not immediately initiate the CHO execution stage, and the UE does not immediately perform a CHO operation to a suitable target node. Instead, the UE stands by until the UE locally determines that actual HO conditions have been satisfied. In response to the UE determining that the actual HO conditions have been satisfied, the terminal UE performs a CHO operation to a suitable target node. Therefore, the actual HO moment of the UE and receiving the air interface CHO command are discontinuous in time. Through the CHO mechanism, the source node can perform reservation configuration for multiple target-side (cell) resources in advance when the source-side radio link status is still sufficient (e.g., when the UE is not at the edge of the source node cell). The UE selects the most suitable candidate target node according to local conditions that are dynamic. The target cell performs the HO, thus reducing the probability of HO failure and improving the user service experience. 
       FIG. 3  illustrates a system  300  that manages CHO preconfigured or prepared resources using a single base station (e.g., a source node  302 ), in accordance with some embodiments of the present disclosure. The system  300  does not involve inter-base station interfaces. As shown in  FIG. 3 , the source node  302  is a source base station providing wireless communication services in local cells  311 - 317 . The cell  311  is the current primary serving cell for UE  301 . As the UE  301  moves, the neighboring cells  312 - 317  may become potential/candidate target cells of the UE  301 . In order to enhance mobile robustness and to improve user experience, the source node  302  can, through the CHO mechanism, preconfigure cells  312 - 317  as potential/candidate target cells of the UE  301 . Responsive to the UE  301  locally determining that a target cell satisfies the actual HO conditions while the UE  301  is moving, the UE  301  performs the CHO on that target cell. 
     In the scenario in which the CHO involves different base stations or nodes, the source node needs to perform CHO pre-configuration or prepared negotiation and CHO preparation with a neighboring node using a suitable interface signaling procedure.  FIG. 4  illustrates a system  400  that manages CHO preconfigured or prepared resources using a multiple base stations (e.g., nodes  402 ,  404 , and  406 ), in accordance with some embodiments of the present disclosure. As shown in  FIG. 4 , the source node  402  administers communication services within local cells  411 ,  412 , and  417 . A neighboring base station  404  administers communication services within local cells  413  and  414 . A neighboring base station  406  administers communication services within local cells  416  and  416 . The cell  411  is the current primary serving cell of the UE  401 . As the UE  401  moves, the cells  412 - 417  may also become a potential/candidate target cell of the UE  401 . In order to enhance mobile robustness and to improve user experience, the source node  402  can preconfigure cells  413 - 416  as potential/candidate target cells of the UE  401  by negotiating the with the neighboring base stations  404  and  406  through the CHO mechanism. 
     With respect to the candidate target cells  413 - 416 , in addition to a CHO Add (initial pre-configuration or prepared)” operation for each of the candidate target cells  413 - 416 , CHO Modify (re-pre-configured) operation and CHO Release (cancel, delete pre-configuration or prepared) operation can also be performed. In some examples, the CHO Add and CHO Modify operations allow the CHO mechanism to function because a target node reserves configurations for the communication resources for the UE  401 . The CHO release (or CHO cancellation) operation significantly affects the efficiency of the CHO mechanism and the occupation of system resources given that when a preconfigured or prepared candidate target cell is no longer suitable, a base station should release or cancel such a candidate target cell as soon as possible in time. The UE no longer locally evaluates whether that candidate target cell satisfies the actual HO conditions and is no longer ready to perform CHO with respect to that candidate target cell. In some examples, the candidate target cell is no longer suitable if the UE has gradually moved away from the candidate target cell such that subsequent access is unlikely, or if the candidate target cell is suffering from load congestion. 
       FIG. 5  illustrates a system  500  capable of performing NG-RAN multi-connectivity operations, in accordance with some embodiments of the present disclosure. Referring to  FIG. 5 , under network and terminal multi-connectivity operation, a UE  501  can be served by two or more serving base stations at the same time. As shown in  FIG. 5 , the UE  501  can be simultaneously and uniquely connected to a MN  502  and two SNs  508  and  510 . 
     The MN  502  is a primary anchor base station that determines the RRC state of the UE  501 . The MN  502  has an NG-C connection with the 5GC (e.g., AMF/SMF  504 , which is connected to UPF  506 ). The MN  502  also has a master NG-U connection with the UPF  506 . The SNs  508  and  510  data offloads the MN  502  and are controlled by the MN  502 . Each of the SN  508  and  510  is connected to the MN  502  via a Xn-C connection and a Xn-U connection. Each of the SNs  508  and  510  is connected to the 5GC (e.g., the UPF  506 ) via a second NG-U connection. The UE  501  can establish a master Uu-User Plane (Uu-U) radio link (RL) and a Uu-Control Plane (Uu-C) RL with the MN  502  and a secondary Uu-U RL with reach of the SNs  508  and  510  for transmitting uplink and downlink user service data simultaneously. 
     In the 5G NG-RAN system, each of the MN  502  and SNs  508  and  510  can be a gNB or a ng-eNB. Each of the MN  502  and SNs  508  and  510  independently allocates and schedules radio resources for providing wireless communication services to the UE  501 . As the UE  501  moves, a change of the MN may occur, for example, if the UE  501  moves from the coverage of the source MN to the coverage of a target MN. At this time, the traditional HO or CHO mobility procedure flow for the single-connection operation as described herein can be executed. Mobility management of the serving cell on the MN side can be performed. 
     In addition, the multi-connectivity operation has a unique mobility scenario—as the UE moves, the MN connected to the UE remains unchanged, and the SN changes. That is, the UE is within the coverage of the same MN while moving away from the coverage of the source SN to the coverage of a target SN. In that regard,  FIG. 6  illustrates a system  600  supporting multi-connectivity operation of a UE  601 , in accordance with some embodiments of the present disclosure. Referring to  FIG. 6  illustrates a mobile scenario in which a SN is changed. The system  600  involving a MN  612 , a source SN  614 , and a target SN  616 . As shown in  FIG. 6 , a UE  601  is originally in multi-connectivity operation (e.g., MR-DC operation) in the joint coverage of the MN  612  and the source SN  614 . The MN  612  and the source SN  614  are currently configured to provide communication services to the UE  601 . As the UE  601  moves toward the target SN  616 , the UE  601  enters the joint coverage of the anchor MN  612  and the target SN  616 . In this case, to manage mobility of the UE  601 , the SN can be changed using the traditional SN change mobility flow in multi-connectivity operation, or the SN can be changed using conditional SN change mobility flow. 
     While the UE  601  is already in the multi-connectivity operation, the currently serving MN  612  and the source SN  614  can preconfigure the candidate conditional target SN on the secondary-SN side, and perform related addition, modification, and release management. In this case, the UE  601  does not immediately access the candidate CHO PScell/SCG on the SN side and stands by until the UE  601  locally determines that the actual conditions are satisfied before accessing the PScell/SCG. A wireless communication link is established after the UE  601  access the PScell/SCG of the target SN. Similarly, the candidate conditional target SN facing the SN side also performs the SN-side CHO addition (e.g., initial pre-configuration or prepared) operation associated with each candidate CHO PScell/SCG, the SN-side CHO modification (e.g., re-provisioning) operation, and SN-side CHO release (e.g., preconfiguring cancelation, deletion, and so on). 
     Some aspects of the present disclosure relate to improvements to the release, cancelation and deletion of the candidate target SN on the SN side that can effectively reduce the long-term reservation or occupation of related communication resources, thus realizing timely recovery and reuse of such communication resources. Some described features provide a method for releasing, canceling, and deleting a SN-side candidate condition target cell (candidate CHO PScell/SCG) resources in multi-connectivity operation. 
     The disclosed features can be implemented in or applicable to a scenario or environment in which all of the UE, the primary base station, and the secondary base stations support multi-connectivity conditional SN change mobile scenario and related flow. Due to mobility features, the UE can move across coverages of different secondary base stations. At any given time, at least one source secondary base station (e.g., a source SN) and at least one candidate target base station (e.g., a candidate target SN or target SN) exist simultaneously. The UE is currently operating in a multi-connectivity mode, meaning that a master base station (e.g., a MN) and a source secondary base station (e.g., a source SN) are currently providing wireless communication services to the UE. For the sake of clarity, although described with respect to dual-connectivity operations, the methods and systems of the present disclosure can be implemented in any multi-connectivity operations. 
       FIG. 7  is a signal diagram illustrating a method  700  for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 1-7 , the UE (not shown) is currently in dual-connectivity operation in which a MN  704  and a source SN  702  are simultaneously serving the UE by providing wireless communication services thereto. In that regard, the UE is connected to both the MN  704  and the SN  702  simultaneously. The UE reports, to the MN  704  and the source SN  702 , relevant RRM measurements as the UE moves. Based on such RRM measurements, the MN  704  elects and conditionally preconfigures one or more candidate target SNs (including a first target SN  706 , at  712 ) for the conditional SN change for the UE. On the other hand, based on such RRM measurements, the source SN  702  selects and conditionally preconfigures one or more candidate target SNs (including a second target SN  708 , at  714 ) for the conditional SN change for the UE. 
     As used herein, conditionally preconfiguring a candidate target SN (e.g., the target SNs  706  and  708 ) refers to providing or preconfiguring conditions used for determining mobility operations for the UE, such that in response to the UE determining that such preconfigured or prepared conditions are satisfied, the UE performs mobility operations with respect to the candidate target SN (e.g., to connect to the candidate target SN). For example, the UE subsequently evaluates “actual conditions” locally to determine whether the preconfigured or prepared conditions are satisfied. Responsive to determining that a target SN (of the candidate target SNs selected and preconfigured or prepared by the MN  704  and the candidate target SNs selected and preconfigured or prepared by the source SN  702 ) satisfies the preconfigured or prepared conditions, the UE attempts to access candidate target PScell/SCG (and resources thereof) of that target SN. 
     Accordingly, the disclosed features apply mechanisms and principles of CHO to multi-connectivity conditional SN change and MR-DC scenarios. Through the use of signaling procedures such as but not limited to, the SN Release signaling flow, the Conditional PScell Cancel signaling flow, and so on, the cancelation or deletion of the communication resources of the candidate target secondary base station cell (group) can be realized in a flexible and efficient manner, thus effectively reducing long-term reservation and occupation of the communication resources and providing timely recovery and reuse of the communication resources. 
       FIG. 8  is a signal diagram illustrating a method  800  for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 6-8 , the method  800  involves a source secondary gNB (SgNB)  802 , a master eNB (MeNB)  804 , a first target SgNB  806 , and a second target SgNB  808 . The MeNB  804  corresponds to a MN. The source SgNB  802  corresponds to source SN. The target SgNBs  806  and  808  correspond to candidate target SNs. 
     A UE (not shown) is currently in a dual-connectivity operation (e.g., E-UTRA-NR Dual Connectivity (EN-DC) operation). That is, the MeNB  804  and the source SgNB  802  are currently configured to provide communication services for the UE. The MeNB  804  selects and conditionally preconfigures two candidate target secondary base stations (e.g., the target SgNBs  806  and  808 ) according to the UE mobility and RRM measurement report received from the UE. The first target SgNB  806  includes first candidate target secondary cell (group) PScell/SCG (referred to herein as PScell1/SCG1). The second target SgNB  808  includes second candidate target secondary cell (group) PScell/SCG (referred to herein as PScell2/SCG2). 
     As the UE gradually moves away from the first target SgNB  806 , the first target SgNB  806  being the actual secondary base station for the UE becomes increasingly unlikely. In response to the MeNB  804  determining that the first target SgNB  806  cannot be the actual SN for the UE, the MeNB  804  timely releases, cancels, or deletes the communication resources of the first target SgNB  806  and timely recycles the communication resources. The MeNB  804  has established UE-associated signaling connections with the source SgNB  802 , the first target SgNB  806 , and the second target SgNB  808  to carry or otherwise communicate UE-specific signaling in the manner described herein. 
     For example, at  812 , the MeNB  804  sends to the first target SgNB  806 , a request message requesting the first target SgNB  806  to release, cancel, or delete indication information and Cause of the conditionally preconfigured or prepared PScell1/SCG1. In some implementations, the message is an X2AP:SgNB Release Request UE-associated message. In response to determining that PScell1/SCG1 is uniquely associated with the MeNB UE X2AP ID and the SgNB UE X2AP ID associated with the UE-specific message, an identifier of the PScell1/SCG1 is not needed. On the other hand, in response to determining that PScell1/SCG1 cannot be uniquely associated with the MeNB UE X2AP ID or the SgNB UE X2AP ID associated with the UE-specific message, the PScell1/SCG1 identifier needs to be included to identify PScell1/SCG1. 
     Responsive to the request received at  812 , the first target SgNB  806  releases, cancels, or deletes PScell1/SCG1 and communication resources associated therewith. At  814 , the target SgNB  806  replies to the request received at  812  by sending a request acknowledge message (e.g., a X2AP:SgNB Release Request Acknowledge UE-associated message) to the MeNB  804 . 
     At  816 , the MeNB  804  sends a cancel message to the source SgNB  802 , informing the source SgNB  802  that the preconfigured or prepared PScell1/SCG1 and communication resources associated therewith have been successfully released, canceled, or deleted. In some examples, the cancel message is X2AP: Conditional PScell Cancel UE-associated message. Responsive to receiving the cancel message at  816 , the source SgNB  802  refrains from conditionally preconfiguring PScell1/SCG1 within a predefined time interval. 
       FIG. 9  is a signal diagram illustrating a method  900  for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 6-9 , the method  900  involves the source SgNB  802 , the MeNB  804 , the first target SgNB  806 , and the second target SgNB  808 . A UE (not shown) is currently in a dual-connectivity operation (e.g., EN-DC operation). That is, the MeNB  804  and the source SgNB  802  are currently configured to provide communication services for the UE. The MeNB  804  selects and conditionally preconfigures the first target SgNB  806  according to the UE mobility and RRM measurement report received from the UE. The first target SgNB  806  includes PScell1/SCG1. The SgNB  802  selects and conditionally preconfigures the second target SgNB  808  according to the UE mobility and RRM measurement report received from the UE. The second target SgNB  808  includes PScell2/SCG2. 
     As the second target SgNB  808  locally experiences load congestion of its communication resources or policy adjustment, the second target SgNB  808  can no longer be a candidate target SN for the UE. In response to the second target SgNB  808  determining that the second target SgNB  808  itself cannot be the candidate target SN for the UE, the second target SgNB  808  timely releases, cancels, or deletes the communication resources of the second target SgNB  808  itself, and timely recycles the communication resources. The MeNB  804  has established UE-associated signaling connections with the source SgNB  802 , the first target SgNB  806 , and the second target SgNB  808  to carry or otherwise communicate UE-specific signaling in the manner described herein. 
     For example, at  912 , the second target SgNB  808  sends to the MeNB  804 , a request message containing indication information of and Cause for the second target SgNB  808  releasing, canceling, or deleting of the conditionally preconfigured or prepared PScell2/SCG2. In some implementations, the request message is an X2AP:SgNB Release Required UE-associated message. In response to determining that PScell2/SCG2 is uniquely associated with the MeNB UE X2AP ID and the SgNB UE X2AP ID associated with the UE-specific message, an identifier of the PScell2/SCG2 is not needed. On the other hand, in response to determining that PScell2/SCG2 cannot be uniquely associated with the MeNB UE X2AP ID or the SgNB UE X2AP ID associated with the UE-specific message, the PScell2/SCG2 identifier needs to be included to identify PScell2/SCG2. 
     Responsive to the request message received at  912 , the MeNB  804  confirms the releasing, canceling, or deleting of the conditionally preconfigured or prepared PScell2/SCG2 and communication resources associated therewith by sending a release confirm message to the second target SgNB  808 , at  914 . In some examples, the release confirm message is a X2AP: SgNB Release Confirm UE-associated message. 
     At  916 , the MeNB  804  sends a cancel message to the source SgNB  802 , informing the source SgNB  802  that the preconfigured or prepared PScell2/SCG2 and communication resources associated therewith have been successfully released, canceled, or deleted. In some examples, the cancel message is X2AP: Conditional PScell Cancel UE-associated message. Responsive to receiving the cancel message at  916 , the source SgNB  802  refrains from conditionally preconfiguring PScell2/SCG2 within a predefined time interval. 
       FIG. 10  is a signal diagram illustrating a method  1000  for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 6-10 , the method  1000  involves the source SgNB  802 , the MeNB  804 , the first target SgNB  806 , and the second target SgNB  808 . A UE (not shown) is currently in a dual-connectivity operation (e.g., EN-DC operation). That is, the MeNB  804  and the source SgNB  802  are currently configured to provide communication services for the UE. The MeNB  804  selects and conditionally preconfigures the first target SgNB  806  according to the UE mobility and RRM measurement report received from the UE. The first target SgNB  806  includes PScell1/SCG1. The source SgNB  802  selects and conditionally preconfigures the second target SgNB  808  according to the UE mobility and RRM measurement report received from the UE. The second target SgNB  808  includes PScell2/SCG2. 
     As the source SgNB  802  locally experiences policy adjustment, the source SgNB  802  determines to cancel the second target SgNB  808  and communication resources associated therewith, where the second target SgNB  808  had been selected and conditionally preconfigured or prepared by the source SgNB  802 . In response to the source SgNB  802  determining that the second target SgNB  808  cannot be the candidate target SN for the UE, the source SgNB  802  timely releases, cancels, or deletes the communication resources of the second target SgNB  808 , and timely recycles the communication resources. The MeNB  804  has established UE-associated signaling connections with the source SgNB  802 , the first target SgNB  806 , and the second target SgNB  808  to carry or otherwise communicate UE-specific signaling in the manner described herein. 
     For example, at  1012 , the source SgNB  802  sends to the MeNB  804 , a request message requesting the MeNB  804  to release, cancel, or delete the conditionally preconfigured or prepared PScell2/SCG2 and communication resources associated therewith. In some implementations, the request message is an X2AP: Conditional PScell Cancel UE-associated message. In response to determining that PScell2/SCG2 is uniquely associated with the MeNB UE X2AP ID and the SgNB UE X2AP ID associated with the UE-specific message, an identifier of the PScell2/SCG2 is not needed. On the other hand, in response to determining that PScell2/SCG2 cannot be uniquely associated with the MeNB UE X2AP ID or the SgNB UE X2AP ID associated with the UE-specific message, the PScell2/SCG2 identifier needs to be included to identify PScell2/SCG2. 
     Responsive to the request message received at  1012 , the MeNB  804  sends to the second target SgNB  808 , a request message requesting the second target SgNB  808  to release, cancel, or delete indication information and Cause of the conditionally preconfigured or prepared PScell2/SCG2, at  1014 . In some implementations, the request message is an X2AP:SgNB Release Request UE-associated message. In response to determining that PScell2/SCG2 is uniquely associated with the MeNB UE X2AP ID and the SgNB UE X2AP ID associated with the UE-specific message, an identifier of the PScell2/SCG2 is not needed. On the other hand, in response to determining that PScell2/SCG2 cannot be uniquely associated with the MeNB UE X2AP ID or the SgNB UE X2AP ID associated with the UE-specific message, the PScell2/SCG2 identifier needs to be included to identify PScell2/SCG2. 
     Responsive to the request received at  1014 , the second target SgNB  808  releases, cancels, or deletes PScell2/SCG2 and communication resources associated therewith. At  1016 , the second target SgNB  808  replies to the request received at  1014  by sending a request acknowledge message (e.g., a X2AP:SgNB Release Request Acknowledge UE-associated message) to the MeNB  804 . Responsive to receiving the cancel message at  1016 , the source SgNB  802  refrains from conditionally preconfiguring PScell2/SCG2 within a predefined time interval. 
       FIG. 11  is a signal diagram illustrating a method  1100  for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 6-11 , the method  1100  involves the source SgNB  802 , a master gNB (MgNB)  1104 , the first target SgNB  806 , and the second target SgNB  808 . The MgNB  1104  corresponds to a MN. 
     A UE (not shown) is currently in a dual-connectivity operation (e.g., Intra-NR Dual Connectivity (NR-DC)@5GC operation). That is, the MgNB  1104  and the source SgNB  802  are currently configured to provide communication services for the UE. The MgNB  1104  selects and conditionally preconfigures two candidate target secondary base stations (e.g., the target SgNBs  806  and  808 ) according to the UE mobility and RRM measurement report received from the UE. The first target SgNB  806  includes PScell1/SCG1. The second target SgNB  808  includes PScell2/SCG2. 
     As the UE gradually moves away from the first target SgNB  806 , the first target SgNB  806  being the actual SN for the UE becomes increasingly unlikely. In response to the MgNB  1104  determining that the first target SgNB  806  cannot be the actual SN for the UE, the MgNB  1104  timely releases, cancels, or deletes the communication resources of the first target SgNB  806  and timely recycles the communication resources. The MgNB  1104  has established UE-associated signaling connections with the source SgNB  802 , the first target SgNB  806 , and the second target SgNB  808  to carry or otherwise communicate UE-specific signaling in the manner described herein. 
     For example, at  1112 , the MgNB  1104  sends to the first target SgNB  806 , a request message requesting the first target SgNB  806  to release, cancel, or delete indication information and Cause of the conditionally preconfigured or prepared PScell1/SCG1. In some implementations, the request message is an XnAP:S-Node Release Request UE-associated message. In response to determining that PScell1/SCG1 is uniquely associated with the M-NG-RAN node UE XnAP ID and the S-NG-RAN node UE XnAP ID associated with the UE-specific message, an identifier of the PScell1/SCG1 is not needed. On the other hand, in response to determining that PScell1/SCG1 cannot be uniquely associated with the M-NG-RAN node UE XnAP ID or the S-NG-RAN node UE XnAP ID associated with the UE-specific message, the PScell1/SCG1 identifier needs to be included to identify PScell1/SCG1. 
     Responsive to the request received at  1112 , the first target SgNB  806  releases, cancels, or deletes PScell1/SCG1 and communication resources associated therewith. At  1114 , the target SgNB  806  replies to the request received at  1112  by sending a request acknowledge message (e.g., a XnAP:S-Node Release Request Acknowledge UE-associated message) to the MgNB  1104 . 
     At  1116 , the MgNB  1104  sends a cancel message to the source SgNB  802 , informing the source SgNB  802  that the preconfigured or prepared PScell1/SCG1 and communication resources associated therewith have been successfully released, canceled, or deleted. In some examples, the cancel message is XnAP: Conditional PScell Cancel UE-associated message. 
     Responsive to receiving the cancel message at  1116 , the source SgNB  802  refrains from conditionally preconfiguring PScell1/SCG1 within a predefined time interval. 
       FIG. 12  is a signal diagram illustrating a method  1200  for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to FIGS.  6 - 12 , the method  1200  involves the source SgNB  802 , the MgNB  1104 , the first target SgNB  806 , and the second target SgNB  808 . A UE (not shown) is currently in a dual-connectivity operation (e.g., NR-DC@5GC operation operation). That is, the MgNB  1104  and the source SgNB  802  are currently configured to provide communication services for the UE. The MgNB  1104  selects and conditionally preconfigures the first target SgNB  806  according to the UE mobility and RRM measurement report received from the UE. The first target SgNB  806  includes PScell1/SCG1. The SgNB  802  selects and conditionally preconfigures the second target SgNB  808  according to the UE mobility and RRM measurement report received from the UE. The second target SgNB  808  includes PScell2/SCG2. 
     As the second target SgNB  808  locally experiences load congestion of its communication resources or policy adjustment, the second target SgNB  808  can no longer be a candidate target SN for the UE. In response to the second target SgNB  808  determining that the second target SgNB  808  itself cannot be the candidate target SN for the UE, the second target SgNB  808  timely releases, cancels, or deletes the communication resources of the second target SgNB  808  itself, and timely recycles the communication resources. The MgNB  1104  has established UE-associated signaling connections with the source SgNB  802 , the first target SgNB  806 , and the second target SgNB  808  to carry or otherwise communicate UE-specific signaling in the manner described herein. 
     For example, at  1212 , the second target SgNB  808  sends to the MgNB  1104 , a request message containing indication information of and Cause for the second target SgNB  808  releasing, canceling, or deleting of the conditionally preconfigured or prepared PScell2/SCG2. In some implementations, the request message is an XnAP:S-Node Release Required UE-associated message. In response to determining that PScell2/SCG2 is uniquely associated with the M-NG-RAN node UE XnAP ID and the S-NG-RAN node UE XnAP ID associated with the UE-specific message, an identifier of the PScell2/SCG2 is not needed. On the other hand, in response to determining that PScell2/SCG2 cannot be uniquely associated with the M-NG-RAN node UE XnAP ID or the S-NG-RAN node UE XnAP ID associated with the UE-specific message, the PScell2/SCG2 identifier needs to be included to identify PScell2/SCG2. 
     Responsive to the request message received at  1212 , the MgNB  1104  confirms the releasing, canceling, or deleting of the conditionally preconfigured or prepared PScell2/SCG2 and communication resources associated therewith by sending a release confirm message to the second target SgNB  808 , at  1214 . In some examples, the release confirm message is a XnAP:S-Node Release Confirm UE-associated message. 
     At  1216 , the MgNB  1104  sends a cancel message to the source SgNB  802 , informing the source SgNB  802  that the preconfigured or prepared PScell2/SCG2 and communication resources associated therewith have been successfully released, canceled, or deleted. In some examples, the cancel message is XnAP: Conditional PScell Cancel UE-associated message. Responsive to receiving the cancel message at  1216 , the source SgNB  802  refrains from conditionally preconfiguring PScell2/SCG2 within a predefined time interval. 
       FIG. 13  is a signal diagram illustrating a method  1300  for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 6-13 , the method  1300  involves the source SgNB  802 , the MgNB  1104 , the first target SgNB  806 , and the second target SgNB  808 . A UE (not shown) is currently in a dual-connectivity operation (e.g., NR-DC@5GC operation). That is, the MgNB  1104  and the source SgNB  802  are currently configured to provide communication services for the UE. The MgNB  1104  selects and conditionally preconfigures the first target SgNB  806  according to the LIE mobility and RRM measurement report received from the UE. The first target SgNB  806  includes PScell1/SCG1. The source SgNB  802  selects and conditionally preconfigures the second target SgNB  808  according to the UE mobility and RRM measurement report received from the UE. The second target SgNB  808  includes PScell2/SCG2. 
     As the source SgNB  802  locally experiences policy adjustment, the source SgNB  802  determines to cancel the second target SgNB  808  and communication resources associated therewith, where the second target SgNB  808  had been selected and conditionally preconfigured or prepared by the source SgNB  802 . In response to the source SgNB  802  determining that the second target SgNB  808  cannot be the candidate target SN for the UE, the source SgNB  802  timely releases, cancels, or deletes the communication resources of the second target SgNB  808 , and timely recycles the communication resources. The MgNB  1104  has established UE-associated signaling connections with the source SgNB  802 , the first target SgNB  806 , and the second target SgNB  808  to carry or otherwise communicate UE-specific signaling in the manner described herein. 
     For example, at  1312 , the source SgNB  802  sends to the MgNB  1104 , a request message requesting the MgNB  1104  to release, cancel, or delete the conditionally preconfigured or prepared PScell2/SCG2 and communication resources associated therewith. In some implementations, the request message is an XnAP: Conditional PScell Cancel UE-associated message. In response to determining that PScell2/SCG2 is uniquely associated with the M-NG-RAN node UE XnAP ID and the S-NG-RAN node UE XnAP ID associated with the UE-specific message, an identifier of the PScell2/SCG2 is not needed. On the other hand, in response to determining that PScell2/SCG2 cannot be uniquely associated with the M-NG-RAN node UE XnAP ID or the S-NG-RAN node UE XnAP ID associated with the UE-specific message, the PScell2/SCG2 identifier needs to be included to identify PScell2/SCG2. 
     Responsive to the request message received at  1312 , the MgNB  1104  sends to the second target SgNB  808 , a request message requesting the second target SgNB  808  to release, cancel, or delete indication information and Cause of the conditionally preconfigured or prepared PScell2/SCG2, at  1314 . In some implementations, the request message is an XnAP:S-Node Release Request UE-associated message. In response to determining that PScell2/SCG2 is uniquely associated with the M-NG-RAN node UE XnAP ID and the S-NG-RAN node UE XnAP ID associated with the UE-specific message, an identifier of the PScell2/SCG2 is not needed. On the other hand, in response to determining that PScell2/SCG2 cannot be uniquely associated with the M-NG-RAN node UE XnAP ID or the S-NG-RAN node UE XnAP ID associated with the UE-specific message, the PScell2/SCG2 identifier needs to be included to identify PScell2/SCG2. 
     Responsive to the request received at  1314 , the second target SgNB  808  releases, cancels, or deletes PScell2/SCG2 and communication resources associated therewith. At  1316 , the second target SgNB  808  replies to the request received at  1314  by sending a request acknowledge message (e.g., a XnAP:S-Node Release Request Acknowledge UE-associated message) to the MgNB  1104 . Responsive to receiving the cancel message at  1316 , the source SgNB  802  refrains from conditionally preconfiguring PScell2/SCG2 within a predefined time interval. 
       FIG. 14A  is a flow diagram illustrating a method  1400   a  for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 6-8, 11, and 14A , in some implementations, a MN as described herein can actively trigger/initiate the release, cancelation, or deletion of the candidate target PScell/SCG resources in the candidate target SN. 
     At  1410   a , the MN determines that a candidate target PScell/SCG in a candidate target SN needs to be released, canceled, or deleted. The candidate target SN is involved in a conditional SN addition or change MR-DC procedure of a UE. The MN and a source SN are currently configured to provide communication services to the UE. 
     The UE is in a multi-connectivity MR-DC operation. The first signaling procedures is a Class1 MN-initiated SN Release Request/Acknowledge signaling procedure. The candidate target SN is selected and conditionally preconfigured and prepared by the MN, or the candidate target SN is selected and conditionally preconfigured and prepared by the source SN. 
     At  1420   a , the MN requests to release, cancel, or delete the at least one candidate target PScell/SCG in the candidate target SN using a first signaling procedure. The candidate target PScell/SCG is identified using a PScell/SCG-related cell (group) ID, an ID List, or a UE-associated interface application protocol ID. The UE-associated interface application protocol ID corresponds to a UE-dedicated signaling connection used by SN release signaling procedure specific to the UE. In the embodiments in which a single message in the first signaling procedure can be used to release, cancel, or delete multiple different candidate PScells/SCGs in the same target candidate SN (e.g., the PScell/SCG includes multiple PScells/SCGs), the ID List includes the IDs corresponding to the different candidate PScell/SCG in the same target candidate SN. In some examples, the UE-associated interface application protocol ID comprises a UE X2AP ID or a UE XnAP ID. 
     At  1430   a , in response to the candidate target PScell/SCG being successfully released, canceled, or deleted, the MN notifies the source SN via a second signaling procedure that the concerned candidate target PScell/SCG in the candidate target SN has been released, canceled, or deleted. The second signaling procedure is a Class2 Conditional PScell Cancel signaling procedure. The Class2 Conditional PScell Cancel signaling procedure carrying a concerned PScell/SCG-related cell (group) ID, an ID List (identifying multiple PScells/SCGs), or a UE-associated interface application protocol ID. Responsive to being notified, the source SN learns a status and cause for releasing the candidate target PScell/SCG. 
       FIG. 14B  is a flow diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 6, 7, 9, 12, and 14B , in some implementations, the candidate target SN actively triggers/initiates the release, cancelation, or deletion of the candidate target PScell/SCG resources of the candidate target SN itself. The candidate target SN is involved in a conditional SN addition or change MR-DC procedure of a UE. A MN and a source SN are currently configured to provide communication services to the UE. The UE is in a multi-connectivity MR-DC operation. 
     At  1410   b , the candidate target SN determines that a candidate target PScell/SCG in the candidate target SN needs to be released, canceled, or deleted. The candidate target SN is selected and conditionally preconfigured and prepared by the MN, or the candidate target SN is selected and conditionally preconfigured and prepared by the source SN. 
     The candidate target PScell/SCG is identified using a PScell/SCG-related cell (group) ID, an ID List, or a UE-associated interface application protocol ID. The UE-associated interface application protocol ID corresponding to the UE-dedicated signaling connection used by SN release signaling procedure specific to the UE. In the embodiments in which a single message in the first signaling procedure can be used to release, cancel, or delete multiple different candidate PScells/SCGs in the same target candidate SN (e.g., the PScell/SCG includes multiple PScells/SCGs), the ID List includes the IDs corresponding to the different candidate PScell/SCG in the same target candidate SN. In some examples, the UE-associated interface application protocol ID comprises a UE X2AP ID or a UE XnAP ID. 
     At  1420   b , the candidate target SN requests to release, cancel, or delete the at least one candidate target PScell/SCG in the candidate target SN itself using a first signaling procedure. The first signaling procedures is a Class1 target SN-initiated SN Release Required/Confirm signaling procedure. 
     In some embodiments, in response to the candidate target PScell/SCG being successfully released, canceled, or deleted, the MN notifies the source SN via a second signaling procedure that the concerned candidate target PScell/SCG in the candidate target SN has been released, canceled, or deleted. The second signaling procedure is a Class2 Conditional PScell Cancel signaling procedure. The Class2 Conditional PScell Cancel signaling procedure carrying a concerned PScell/SCG-related cell (group) ID, an ID List (identifying multiple PScells/SCGs), or a UE-associated interface application protocol ID. Responsive to being notified, the source SN learns a status and cause for releasing the candidate target PScell/SCG. 
       FIG. 14C  is a flow diagram illustrating a method for performing a conditional SN change, in accordance with some embodiments of the present disclosure. Referring to  FIGS. 6, 7, 10, 13, and 14C , in some implementations, the source SN actively triggers/initiates the release, cancelation, or deletion of the candidate target PScell/SCG resources in the candidate target SN. The candidate target SN is involved in a conditional SN addition or change MR-DC procedure of a UE. A MN and a source SN are currently configured to provide communication services to the UE. The UE is in a multi-connectivity MR-DC operation. 
     At  1410   c , the source SN determines that a candidate target primary secondary cell (PScell)/secondary cell group (SCG) in a candidate target secondary node (SN) needs to be released, canceled, or deleted. The candidate target SN is selected and conditionally preconfigured and prepared by the source SN 
     At  1420   c , the source SN requests the MN to release, cancel, or delete the at least one candidate target PScell/SCG in the candidate target SN using a first signaling procedure. The first signaling procedures is a Class2 source SN-initiated Conditional PScell Cancel signaling procedure. The candidate target PScell/SCG is identified using a PScell/SCG-related cell (group) ID, an ID List, or a UE-associated interface application protocol ID, the UE-associated interface application protocol ID corresponding to a UE-dedicated signaling connection used by Conditional PScell Cancel signaling procedure specific to the UE. The UE-associated interface application protocol ID comprises a UE X2AP ID or a UE XnAP ID. 
     In some embodiments, in response to the candidate target PScell/SCG being successfully released, canceled, or deleted, the MN notifies the source SN via a second signaling procedure that the concerned candidate target PScell/SCG in the candidate target SN has been released, canceled, or deleted. The second signaling procedure is a Class2 Conditional PScell Cancel signaling procedure. The Class2 Conditional PScell Cancel signaling procedure carrying a concerned PScell/SCG-related cell (group) ID, an ID List (identifying multiple PScells/SCGs), or a UE-associated interface application protocol ID. Responsive to being notified, the source SN learns a status and cause for releasing the candidate target PScell/SCG. 
       FIG. 15A  illustrates a block diagram of an example base station  1502 , in accordance with some embodiments of the present disclosure.  FIG. 15B  illustrates a block diagram of an example UE  1501 , in accordance with some embodiments of the present disclosure. Referring to  FIGS. 1-15B , the UE  1501  (or a wireless communication device) is an example implementation of the UEs described herein, and the base station  1502  is an example implementation of the base stations and nodes described herein. 
     The base station  1502  and the UE  1501  can include components and elements configured to support known or conventional operating features that need not be described in detail herein. In one illustrative embodiment, the base station  1502  and the UE  1501  can be used to communicate (e.g., transmit and receive) data symbols in a wireless communication environment, as described above. For instance, the base station  1502  can be a base station (e.g., gNBs, eNBs, and so on), a server, a node, or any suitable computing device used to implement various network functions. 
     The base station  1502  includes a transceiver module  1510 , an antenna  1512 , a processor module  1514 , a memory module  1516 , and a network communication module  1518 . The module  1510 ,  1512 ,  1514 ,  1516 , and  1518  are operatively coupled to and interconnected with one another via a data communication bus  1520 . The UE  1501  includes a UE transceiver module  1530 , a UE antenna  1532 , a UE memory module  1534 , and a UE processor module  1536 . The modules  1530 ,  1532 ,  1534 , and  1536  are operatively coupled to and interconnected with one another via a data communication bus  1540 . The base station  1502  communicates with the UE  1501  or another base station via a communication channel, which can be any wireless channel or other medium suitable for transmission of data as described herein. 
     As would be understood by persons of ordinary skill in the art, the base station  1502  and the UE  1501  can further include any number of modules other than the modules shown in  FIGS. 15A and 15B . The various illustrative blocks, modules, circuits, and processing logic described in connection with the embodiments disclosed herein can be implemented in hardware, computer-readable software, firmware, or any practical combination thereof. To illustrate this interchangeability and compatibility of hardware, firmware, and software, various illustrative components, blocks, modules, circuits, and steps are described generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware, or software can depend upon the particular application and design constraints imposed on the overall system. The embodiments described herein can be implemented in a suitable manner for each particular application, but any implementation decisions should not be interpreted as limiting the scope of the present disclosure. 
     In accordance with some embodiments, the UE transceiver  1530  includes a radio frequency (RF) transmitter and a RF receiver each including circuitry that is coupled to the antenna  1532 . A duplex switch (not shown) may alternatively couple the RF transmitter or receiver to the antenna in time duplex fashion. Similarly, in accordance with some embodiments, the transceiver  1510  includes an RF transmitter and a RF receiver each having circuitry that is coupled to the antenna  1512  or the antenna of another base station. A duplex switch may alternatively couple the RF transmitter or receiver to the antenna  1512  in time duplex fashion. The operations of the two transceiver modules  1510  and  1530  can be coordinated in time such that the receiver circuitry is coupled to the antenna  1532  for reception of transmissions over a wireless transmission link at the same time that the transmitter is coupled to the antenna  1512 . In some embodiments, there is close time synchronization with a minimal guard time between changes in duplex direction. 
     The UE transceiver  1530  and the transceiver  1510  are configured to communicate via the wireless data communication link and cooperate with a suitably configured RF antenna arrangement  1512 / 1532  that can support a particular wireless communication protocol and modulation scheme. In some illustrative embodiments, the UE transceiver  1510  and the transceiver  1510  are configured to support industry standards such as the Long Term Evolution (LTE) and emerging 5G standards, and the like. It is understood, however, that the present disclosure is not necessarily limited in application to a particular standard and associated protocols. Rather, the UE transceiver  1530  and the base station transceiver  1510  may be configured to support alternate, or additional, wireless data communication protocols, including future standards or variations thereof. 
     The transceiver  1510  and the transceiver of another base station (such as but not limited to, the transceiver  1510 ) are configured to communicate via a wireless data communication link and cooperate with a suitably configured RF antenna arrangement that can support a particular wireless communication protocol and modulation scheme. In some illustrative embodiments, the transceiver  1510  and the transceiver of another base station are configured to support industry standards such as the LTE and emerging 5G standards, and the like. It is understood, however, that the present disclosure is not necessarily limited in application to a particular standard and associated protocols. Rather, the transceiver  1510  and the transceiver of another base station may be configured to support alternate, or additional, wireless data communication protocols, including future standards or variations thereof. 
     In accordance with various embodiments, the base station  1502  may be a base station such as but not limited to, an eNB, gNB, ng-eNB, a femto station, or a pico station, for example. In some embodiments, the UE  1501  may be embodied in various types of user devices such as a mobile phone, a smart phone, a personal digital assistant (PDA), tablet, laptop computer, wearable computing device, etc. The processor modules  1514  and  1536  may be implemented, or realized, with a general-purpose processor, a content addressable memory, a digital signal processor, an application specific integrated circuit, a field programmable gate array, any suitable programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof, designed to perform the functions described herein. In this manner, a processor may be realized as a microprocessor, a controller, a microcontroller, a state machine, or the like. A processor may also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a digital signal processor core, or any other such configuration. 
     Furthermore, the method or algorithm disclosed herein can be embodied directly in hardware, in firmware, in a software module executed by processor modules  1514  and  1536 , respectively, or in any practical combination thereof. The memory modules  1516  and  1534  may be realized as 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 this regard, memory modules  1516  and  1534  may be coupled to the processor modules  1510  and  1530 , respectively, such that the processors modules  1510  and  1530  can read information from, and write information to, memory modules  1516  and  1534 , respectively. The memory modules  1516  and  1534  may also be integrated into their respective processor modules  1510  and  1530 . In some embodiments, the memory modules  1516  and  1534  may each include a cache memory for storing temporary variables or other intermediate information during execution of instructions to be executed by processor modules  1510  and  1530 , respectively. Memory modules  1516  and  1534  may also each include non-volatile memory for storing instructions to be executed by the processor modules  1510  and  1530 , respectively. 
     The network communication module  1518  generally represents the hardware, software, firmware, processing logic, and/or other components of the base station  1502  that enable bi-directional communication between the transceiver  1510  and other network components and communication nodes in communication with the base station  1502 . For example, the network communication module  1518  may be configured to support internet or WiMAX traffic. In a deployment, without limitation, the network communication module  1518  provides an 802.3 Ethernet interface such that the transceiver  1510  can communicate with a conventional Ethernet based computer network. In this manner, the network communication module  1518  may include a physical interface for connection to the computer network (e.g., Mobile Switching Center (MSC)). In some embodiments in which the base station  1502  is an IAB donor, the network communication module  1518  includes a fiber transport connection configured to connect the base station  1502  to a core network. The terms “configured for,” “configured to” and conjugations thereof, as used herein with respect to a specified operation or function, refer to a device, component, circuit, structure, machine, signal, etc., that is physically constructed, programmed, formatted and/or arranged to perform the specified operation or function. 
     While various embodiments of the present solution have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. Likewise, the various diagrams may depict an example architectural or configuration, which are provided to enable persons of ordinary skill in the art to understand example features and functions of the present solution. Such persons would understand, however, that the solution is not restricted to the illustrated example architectures or configurations, but can be implemented using a variety of alternative architectures and configurations. Additionally, as would be understood by persons of ordinary skill in the art, one or more features of one embodiment can be combined with one or more features of another embodiment described herein. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described illustrative embodiments. 
     It is also understood that any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations can be used herein as a convenient means of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements can be employed, or that the first element must precede the second element in some manner. 
     Additionally, a person having ordinary skill in the art would understand that information and signals can be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits and symbols, for example, which may be referenced in the above description can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     A person of ordinary skill in the art would further appreciate that any of the various illustrative logical blocks, modules, processors, means, circuits, methods and functions described in connection with the aspects disclosed herein can be implemented by electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two), firmware, various forms of program or design code incorporating instructions (which can be referred to herein, for convenience, as “software” or a “software module), or any combination of these techniques. To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. Skilled artisans can implement the described functionality in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure. 
     Furthermore, a person of ordinary skill in the art would understand that various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, modules, and circuits can further include antennas and/or transceivers to communicate with various components within the network or within the device. A general purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein. 
     If implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method or algorithm disclosed herein can be implemented as software stored on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. 
     In this document, the term “module” as used herein, refers to software, firmware, hardware, and any combination of these elements for performing the associated functions described herein. Additionally, for purpose of discussion, the various modules are described as discrete modules; however, as would be apparent to one of ordinary skill in the art, two or more modules may be combined to form a single module that performs the associated functions according embodiments of the present solution. 
     Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the present solution. It will be appreciated that, for clarity purposes, the above description has described embodiments of the present solution with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processing logic elements or domains may be used without detracting from the present solution. For example, functionality illustrated to be performed by separate processing logic elements, or controllers, may be performed by the same processing logic element, or controller. Hence, references to specific functional units are only references to a suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization. 
     Various modifications to the implementations described in this disclosure will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other implementations without departing from the scope of this disclosure. Thus, the disclosure is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with the novel features and principles disclosed herein, as recited in the claims below.