Conditional Handover and Dual Connectivity Coexistence

Abstract

In some examples, a method performed in a target master node of a wireless network for preparing a handover of a user equipment (UE) in dual connectivity (DC), the handover being performed between respective primary cells (PCells) of a source master node and a target master node, and between respective primary secondary cells (PSCells) of a source secondary node and a target secondary node, the method including: receiving, from the source master node, a conditional handover (CHO) request message including a unique identifier of the UE and an identifier of the target secondary node defined between the source master node and the target secondary node; transmitting the unique identifier of the UE to the target secondary node as part of a secondary node addition request for CHO preparation with DC; and receiving, from the target secondary node, a first differential secondary cell group (SCG) configuration and a second differential SCG configuration, each of the first differential SCG configuration and the second differential SCG configuration being generated to correspond to a different CPC execution state.

Description

[Technical Field]

[0001] The present invention relates generally to fifth generation (5G) New Radio (NR) systems. Aspects relate to conditional handover in 5G NR systems. [Background technology]

[0002] Fifth-generation (5G) New Radio (NR) systems are designed to provide flexibility and configurability to optimize network services and types to accommodate a variety of use cases. A new handover procedure, provided as part of the 5G NR system, allows a user equipment (UE) to decide to perform a handover when certain conditions are met. This NR handover procedure, called conditional handover (CHO), contrasts with legacy handover procedures, in which the network was responsible for making the decision as to whether or not a handover would be performed. Legacy handovers were thus reactive processes, resulting in handover failures.

[0003] On the other hand, CHO is a handover that is executed by the UE when one or more handover execution conditions are met. Specifically, the UE may start evaluating the execution conditions when it receives a CHO configuration and may stop evaluating the execution conditions when the handover is executed. Summary of the Invention

[0004] The objective of this disclosure is to enable the effectiveness of CHO-DC configuration and avoidance of double resource reservation for a target delta SCG configuration in the context of CHO-CPC coexistence.

[0005] The above and other objects are achieved by means of the features of the independent claims.

[0006] Further embodiments are evident from the dependent claims, the description and the drawings.

[0007] A first aspect of the present disclosure provides a method, performed in a target master node of a wireless network, for preparing a handover of a user equipment (UE) in dual connectivity (DC), wherein the handover is performed between respective primary cells (PCells) of a source master node and a target master node, and between respective primary secondary cells (PSCells) of a source secondary node and a target secondary node, the method including: receiving, from the source master node, a conditional handover (CHO) request message including a unique identifier of the UE and an identifier of the target secondary node defined between the source master node and the target secondary node; transmitting the unique identifier of the UE to the target secondary node as part of a secondary node addition request for CHO preparation with DC; and receiving, from the target secondary node, a first differential secondary cell group (SCG) configuration and a second differential SCG configuration, wherein each of the first differential SCG configuration and the second differential SCG configuration is generated to correspond to a different CPC execution state.

[0008] In an embodiment of the first aspect, the first differential SCG configuration may be generated for an execution state in which an ongoing CPC configuration is not performed. The second differential SCG configuration may be generated for an execution state in which an ongoing CPC configuration is performed. The method may further include generating a first CHO with DC configuration based on the first differential SCG configuration and using the first CHO with DC configuration when an ongoing CPC configuration, configured by the source master node, defining a handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node, is not performed. The method may further include generating a second CHO with DC configuration based on the second differential SCG configuration and using the second CHO with DC configuration when an ongoing CPC configuration, configured by the source master node, defining a handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node, is performed. The method may further include transmitting at least one of the first DC-with CHO configuration and the second DC-with CHO configuration to the source master node, and providing an indication to the source primary node that the second DC-with CHO configuration includes a temporary SCG configuration to be used when the UE executes a CPC prepared by the source master node for handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node. The method may further include receiving, from the source master node, a confirmation of the UE handover from the source secondary to the target secondary node. The method may further include receiving, from the target secondary node, a confirmation of the UE handover from the source secondary node to the target secondary node. The method may further include providing respective conditions for selecting one of the first DC-with CHO configuration and the second DC-with CHO configuration. The method may further include selecting one of the first DC-with CHO configuration and the second DC-with CHO configuration based on the condition.

[0009] A second aspect of the present disclosure provides a target master node in a wireless network, the target master node including: a processor; and a memory coupled to the processor, the memory configured to store program code executable by the processor, the program code including one or more instructions that cause the target master node to perform the following: receiving a conditional handover (CHO) request message from a source master node, the message including a unique identifier of a UE defined between the source master node and the target secondary node and an identifier of the target secondary node; sending the unique identifier of the UE to the target secondary node as part of a secondary node addition request for DC-with-CHO preparation; and receiving from the target secondary node a first differential secondary cell group (SCG) configuration and a second differential SCG configuration, each of the first differential SCG configuration and the second differential SCG configuration being generated to correspond to a different CPC execution state.

[0010] In an embodiment of the second aspect, the program code may further include one or more instructions for causing the target master node to generate a first DC-with-CHO configuration based on a first differential SCG configuration configured by the source master node that defines a handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node to use when an ongoing CPC configuration is not performed.The program code may further include one or more instructions for causing the target master node to generate a second DC-with-CHO configuration based on a second differential SCG configuration configured by the source master node that defines a handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node to use when an ongoing CPC configuration is performed.

[0011] A third aspect of the present disclosure provides a machine-readable storage medium encoded with instructions for preparing a handover of a user equipment (UE) in dual connectivity (DC), the handover occurring between respective primary cells (PCells) of a source master node and a target master node, and between respective primary secondary cells (PSCells) of a source secondary node and a target secondary node, the instructions being executable by a processor of the target master node to cause the target master node to: transmit at least one of a first DC-with-CHO configuration and a second DC-with-CHO configuration to the source master node; and provide an indication to the source primary node that the second DC-with-CHO configuration includes a temporary SCG configuration to be used when the UE executes a CPC prepared by the source master node for handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node.

[0012] In an embodiment of the third aspect, the machine-readable storage medium may be further encoded with instructions executable by a processor of the target master node to cause the target master node to generate respective conditions for selecting one of the first DC-with CHO configuration and the second DC-with CHO configuration.

[0013] Embodiments will now be described, by way of example only, with reference to the drawings, in which: [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic representation of the message flow through the example. [Figure 2] 1 is a schematic representation of the message flow through the example. [Figure 3] 1 is a schematic representation of an example machine. [Figure 4] 1 is a flowchart of a method according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Exemplary embodiments are described below in sufficient detail to enable those skilled in the art to embody and practice the systems and processes described herein. It is important to understand that embodiments may be provided in many alternative forms and should not be construed as limited to the examples presented herein.

[0016] Accordingly, while the embodiments may be modified in various ways and take various alternative forms, specific embodiments thereof are shown in the drawings and will be described in detail below by way of example. There is no intention to limit the invention to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims are to be covered. Elements of exemplary embodiments will be consistently designated by the same reference numerals throughout the drawings and detailed description, where appropriate.

[0017] The terminology used herein to describe embodiments is not intended to limit the scope. The articles “a,” “an,” and “the” are singular in that they have a single referent, but the use of the singular in this document should not exclude the presence of more than one referent. In other words, elements referred to in the singular may include one or more unless the context clearly dictates otherwise. It should be further understood that the terms “comprises,” “comprising,” “includes,” and / or “including,” as used herein, specify the presence of stated features, items, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, items, steps, operations, elements, components, and / or groups thereof. The term “and / or” is merely a relation of association for describing related objects and indicates that a three-way relationship may exist, such as A and / or B may indicate that A is present alone, that A and B are present simultaneously, or that B is present alone. The " / " character generally indicates that the related objects are in an "or" relationship.

[0018] Unless otherwise defined, all terms (including technical and scientific terms) used herein shall be interpreted in the manner customary in the art. It should be further understood that terms of common usage should also be interpreted in the manner customary in the relevant art, and should not be interpreted in an idealized or overly formal sense unless expressly defined as such in this specification.

[0019] The following contains specific information related to embodiments of the present disclosure. The drawings and their accompanying detailed disclosure are directed to embodiments only. However, the present disclosure is not limited to these embodiments. Other variations and embodiments of the present disclosure will be apparent to those skilled in the art.

[0020] The phrases "in one embodiment" or "in some embodiments" may refer to one or more of the same or different embodiments, respectively. The term "coupled" is defined as connected, either directly or indirectly through intervening components, and is not necessarily limited to a physical connection. The phrase "at least one of A, B, and C" or "at least one of the following A, B, and C" means "A only, or B only, or C only, or any combination of A, B, and C."

[0021] The terms "system" and "network" may be used interchangeably.

[0022] For purposes of explanation and not limitation, specific details such as functional entities, techniques, protocols, and standards are presented to provide an understanding of the present disclosure. In other instances, detailed disclosure of well-known methods, techniques, systems, and architectures is omitted so as not to obscure the present disclosure with unnecessary detail.

[0023] Those skilled in the art will readily recognize that any disclosed network function or algorithm can be implemented by hardware, software, or a combination of software and hardware. The disclosed functions may correspond to modules that can be software, hardware, firmware, or any combination thereof.

[0024] Software implementations may include machine- and / or computer-readable and / or executable instructions stored on a machine- and / or computer-readable medium, such as a memory or other type of storage device. One or more microprocessors or general-purpose computers with communications processing capability may be programmed with the corresponding executable instructions to perform the disclosed network functions or algorithms.

[0025] A microprocessor or general-purpose computer may include the use of an application-specific integrated circuit (ASIC), a programmable logic array, and / or one or more digital signal processors (DSPs). While some of the disclosed embodiments are directed to software installed and executed on computer hardware, alternative embodiments implemented as firmware or hardware or a combination of hardware and software are well within the scope of this disclosure. Computer-readable media include, but are not limited to, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, compact disc read-only memory (CD-ROM), magnetic cassette, magnetic tape, magnetic disk storage, or any other equivalent medium capable of storing computer-readable instructions.

[0026] A wireless communication network architecture, such as a Long Term Evolution (LTE) system, an LTE-Advanced (LTE-A) system, an LTE-Advanced Pro system, or a 5G NR radio access network (RAN), typically includes at least one base station (BS), at least one user equipment (UE), and one or more optional network elements that provide connectivity within the network. The UE communicates with a network, such as a Core Network (CN), an Evolved Packet Core (EPC) network, an Evolved Universal Terrestrial RAN (E-UTRAN), a 5G Core (5GC), or the Internet, via the RAN established by one or more BSs.

[0027] A UE may include, but is not limited to, a mobile station, a mobile terminal or device, or a user communication radio terminal. A UE may also be a portable radio device, including, but not limited to, a mobile phone, a tablet, a wearable device, a sensor, a vehicle, or a personal digital assistant (PDA) with wireless communication capabilities. The UE is configured to receive and transmit signals over the air interface to one or more cells in the RAN.

[0028] The BS may provide communication services according to at least a radio access technology (RAT), such as Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM), often referred to as 2G, Enhanced Data rates for GSM Evolution RAN (GERAN), General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), based on basic Wideband Code Division Multiple Access (W-CDMA) and often referred to as 3G, High Speed ​​Packet Access (HSPA), LTE, LTE-A, evolved LTE (eLTE), which is LTE connected to 5GC, NR (often referred to as 5G), and / or LTE-A Pro. However, the scope of this disclosure is not limited to these protocols.

[0029] The BS may include, but is not limited to, a Node B (NB) for UMTS, an Evolved Node B (eNB) for LTE or LTE-A, a Radio Network Controller (RNC) for UMTS, a BS Controller (BSC) for GSM / GERAN, a Next Generation (ng)-eNB for Evolved Universal Terrestrial Radio Access (E-UTRA) BS in connection with 5G-RAN, a Next Generation Node B (gNB) for 5G-RAN, or any other device capable of controlling radio communications and managing radio resources within a cell. The BS may serve one or more UEs over an air interface.

[0030] A BS may provide radio coverage to a particular geographic area using multiple cells forming a RAN. The BS supports the operation of the cells, each operable to serve at least one UE within its radio coverage.

[0031] Each cell (often also referred to as a serving cell) may serve one or more UEs within its radio coverage, such that each cell schedules downlink (DL) and optionally uplink (UL) resources to at least one UE within its radio coverage for DL ​​and optionally UL packet transmissions. A BS may communicate with one or more UEs in a wireless communication system via multiple cells.

[0032] A cell may allocate sidelink (SL) resources to support proximity services (ProSe) or vehicle-to-everything (V2X) services. Each cell may have a coverage area that overlaps with other cells.

[0033] The frame structure for NR supports flexible configuration to meet high reliability, high data rate, and low latency requirements while accommodating various next-generation (e.g., 5G) communication requirements, such as evolved mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC). Third Generation Partnership Project (3GPP) orthogonal frequency division multiplexing (OFDM) technology may serve as the baseline for NR waveforms. Scalable OFDM numerology, such as adaptive subcarrier spacing, channel bandwidth, and cyclic prefix (CP), may also be used.

[0034] Examples of some terms used in this disclosure are as follows:

[0035] Primary Cell (PCell): A PCell is a Master Cell Group (MCG) cell that operates on a primary frequency on which a UE performs an initial connection establishment procedure or initiates a connection re-establishment procedure. The PCell is a Special Cell (SpCell) of the MCG.

[0036] Primary SCG Cell (PSCell): In the case of dual connectivity (DC) operation, a PSCell is a secondary cell group (SCG) cell in which a UE performs random access when performing a reconfiguration procedure with synchronization. A PSCell is an SpCell of an SCG. In some embodiments, the term PSCell may be referred to as a primary secondary cell. The terms "primary SCG cell" and "primary secondary cell" may be used interchangeably in this disclosure.

[0037] Special Cell (SpCell): In case of DC operation, the term special cell (SpCell) refers to a PCell of an MCG or a PSCell of an SCG; otherwise, the term special cell refers to a PCell.

[0038] Secondary Cell (SCell): For a UE configured with Carrier Aggregation (CA), a SCell is a cell that provides additional radio resources above the special cell.

[0039] Serving cell: For a UE in RRC_CONNECTED state that is not configured with CA / DC, there is only one serving cell, which includes the primary cell. For a UE in RRC_CONNECTED state that is configured with CA / DC, the term "serving cell" is used to denote the set of cells that includes the special cell and all secondary cells.

[0040] Master Cell Group (MCG): In MR-DC, an MCG is a group of serving cells associated with a master node, including an SpCell (PCell) and optionally one or more SCells.

[0041] Master Node (MN): In MR-DC, the MN or primary node is the radio access node that provides the control plane connection to the core network. It may be the master eNB (in EN-DC), the master ng-eNB (in NGEN-DC), or the master gNB (in NR-DC and NE-DC). In some embodiments, the MN or primary node may include the source or target node for the UE.

[0042] Secondary Cell Group (SCG): In MR-DC, an SCG is a group of serving cells associated with a secondary node, consisting of an SpCell (PSCell) and optionally one or more SCells.

[0043] Secondary Node (SN): In MR-DC, an SN is a radio access node without a control plane connection to the core network that provides additional resources to the UE. It may be an en-gNB (in EN-DC), a secondary ng-eNB (in NE-DC), or a secondary gNB (in NR-DC and NGEN-DC). In some embodiments, the SN, i.e., the secondary node, may comprise a source or target node for the UE.

[0044] In wireless communication networks such as E-UTRAN, one of the main causes of handover (HO) failure is that a UE does not receive a handover command message from a source base station (e.g., a source eNB or a source gNB) or a serving base station (e.g., a serving eNB or a serving gNB). Conventional handover procedures are typically triggered by a measurement report from the UE. For example, if the quality (e.g., signal strength and / or service quality) of the serving cell is below a preconfigured threshold and the quality (e.g., signal strength and / or service quality) of a neighboring cell exceeds a preconfigured threshold, the UE may send a measurement report to the source base station under the serving cell based on the received measurement configuration. Upon receiving the measurement report, the source base station may send a handover request message to multiple target base stations (e.g., eNBs or gNBs) for admission control and receive a handover acknowledgement message from the target base station. The source base station may select and send a handover command message (which may be included in the handover acknowledgement message from one of the target base stations) to the UE, thereby allowing the UE to connect to the target cell.

[0045] The success of the entire handover procedure depends on several factors. One of the factors is that the serving cell quality does not degrade rapidly in a short period of time, which may depend on backhaul latency (e.g., for the X2 / Xn / Xx interface), target base station processing time, and signaling transmission time. However, in real-world situations, the serving cell quality may degrade rapidly in a short period of time, and the UE may not successfully receive the handover command message before the serving cell quality degrades significantly. As a result, the UE may detect a radio link failure. As a result, the UE may initiate a radio resource control (RRC) connection re-establishment procedure in response to the detected radio link failure, which in turn leads to a significant service interruption time.

[0046] In next-generation wireless networks (e.g., 5G NR networks), large-scale antenna beamforming in higher frequency bands may cause the serving cell quality to degrade even faster, especially when narrow beams are used to serve the UE. Obstructions are another issue in NR deployments.

[0047] 3GPP introduced the concept of Conditional Handover (CHO) to improve the reliability of the overall handover procedure. The CHO procedure may be seen as a complementary procedure to the conventional handover procedure to help reduce the handover failure rate.

[0048] To execute a conditional reconfiguration command, the UE may evaluate a trigger condition associated with the conditional reconfiguration command to determine whether one or more trigger conditions (or execution conditions) for the conditional reconfiguration command are met. If the UE determines that the trigger condition is met, the UE may apply the corresponding conditional reconfiguration command to connect to the target cell. Existing measurement events (e.g., A3 and A5) may be used to determine whether the trigger condition of the conditional reconfiguration command is met.

[0049] CHO may help to improve the reliability of the entire handover procedure. Applying a similar concept to CHO may also be beneficial to the PSCell addition procedure, PSCell modification procedure, SN addition procedure, or SN modification procedure for MR-DC mode, because the preparation between the MN and the SN and the RRC signaling for adding the SN may be completed in advance.

[0050] A UE may behave differently when the concept of CHO (or conditional configuration) is applied to a normal HO (e.g., PCell modification) procedure or a PSCell addition / modification (or SN addition / modification) procedure. For example, the UE may not need to release the link to the current PCell (or MN) if the executed conditional reconfiguration command is for a PSCell addition / modification. Some information or guidelines (e.g., in an implicit manner) may be required for the UE to determine what to do when a conditional reconfiguration command is executed. In addition, the principles for applying CHO (or conditional configuration) to a PCell modification and the principles for applying CHO (or conditional configuration) to a PSCell addition / modification may differ for different reasons.

[0051] A conditional reconfiguration procedure may be a reconfiguration procedure executed by a UE when one or more execution conditions (also called trigger conditions) are met. There are three types of conditional reconfiguration. The first type is conditional reconfiguration for PCell change, also called conditional reconfiguration for handover or conditional handover (CHO). The second type is conditional reconfiguration for PSCell change, also called conditional PSCell change (CPC). The third type is conditional reconfiguration for PSCell addition, also called conditional PSCell addition (CPA).

[0052] CHO may be a handover procedure executed by a UE when one or more handover execution conditions are met. The UE may start evaluating the execution conditions upon receiving the CHO configuration and may stop evaluating the execution conditions when the execution conditions are met. In some embodiments, the execution conditions may include, for example, A3 / A5 events. In some embodiments, the execution conditions may consist of one or two trigger conditions.

[0053] In the context of the CHO-CPC coexistence framework, there are two configurations provided to the UE and operating in parallel, i.e. the UE in question monitors both measurements for both configurations: one configuration is the CHO configuration with CHO execution conditions (with or without DC connection, i.e. SN connection), the other configuration is the Conditional PSCell Change (CPC) configuration and CPC execution conditions provided to the UE, which also operate in parallel.

[0054] When a UE is connected to a PCell under an MN and a PSCell under an SN (i.e., in DC setup), it is possible for the UE to hand over to a target cell of another MN and to request that this target cell remain the UE's serving PSCell.

[0055] However, if the source MN first prepares the UE's CPC from the source SN to the target SN, the source MN initiates CHO preparation for the target MN, and the target MN provides CHO-DC configuration, i.e., it prepares the target SN (which the source MN also prepared for CPC) with differential (i.e., partial) configuration for CHO preparation. In such a case, a CHO-CPC coexistence validity issue occurs because the CHO-DC configuration becomes invalid when the CPC is first executed, i.e., the CPC execution leads to a serving SN change, and the SN differential configuration of the CHO-DC configuration cannot be applied to the new serving SN. To avoid SN failure, the CHO-DC preparation is restarted at the expense of additional signaling overhead and a delay in CHO-DC configuration imposed on the UE.

[0056] Furthermore, both the serving and target MNs prepare the same target SN for UE switching. Thus, the source MN first prepares a CPC for the target SN, and the target MN prepares the same target SN for CHO-DC handover. In that case, the target SN is not aware that the same UE is prepared during the CHO-DC of the target MN, and therefore the target SN double-reserves the requested resources even though the bearer configurations are identical.

[0057] In a given scenario, it is assumed that the source MN first configures the UE with a CPC from the source SN to the target SN, and then the source MN initiates CHO preparation to the target MN, where the target MN prepares a CHO-DC configuration.

[0058] According to an example, the target primary node and the target secondary node may be notified about the ongoing CPC preparation of the source primary node. The target secondary node may provide two differential SCG configurations. The first configuration is valid before CPC execution and the second configuration is valid after CPC execution. The UE may be configured to maintain the second configuration when CPC is executed, since the second configuration was generated by taking CPC execution into account and is valid after CPC execution.

[0059] In an embodiment, the target secondary node and the target primary node may prepare two differential SCG configurations. However, the target primary node may also configure two conditions (one for each differential SCG configuration). Thus, the UE may check the serving PSCell and determine which CHO-DC configuration should be selected. This ensures that the UE uses the correct configuration before and after CPC execution. That is, the target secondary node is not prevented from providing a differential configuration in the case of CHO-CPC coexistence. Instead, the target secondary node may provide two differential configurations. One differential SCG configuration may be provided for the secondary node currently serving the UE, and another (provisional) differential SCG configuration may be provided for the candidate target secondary node that will become the serving secondary node in the future (e.g., when CPC is executed).

[0060] Figure 1 is a schematic representation of an example message flow. In blocks 1 and 2, the source master node 103 prepares a CPC, CPC-1, for the UE 101 to change its serving SN from source secondary node SN-1, 105 to target secondary node SN-2, 107. The UE 101 evaluates the conditions of CPC-1 in block 2. The UE 101 sends a measurement report (3) to its source master node 103 to initiate CHO preparation of the target master node 109. The source master node 103 then sends a CHO request (4) to the target master node 109.

[0061] By way of example, as part of the CHO request message (4), the source master node also includes the SN UE XnAP ID defined with the target secondary node SN-2, 107 during the UE's CPC-1 preparation for communication over the Xn interface to the source master node 103. The source master node 103 also sends the ID of SN-2 (107) to the target master node 109 to indicate between which source master node 103 and secondary node the UE's 101 XnAP ID was defined. The target secondary node (107) is the same secondary node for which the source master node configures the CPC for the target secondary node (i.e., it is not any secondary node identifier).

[0062] The target master node 109 sends an Add Secondary Node Request to target SN-2 (107) to prepare target SN-2 in the CHO-DC (5). The target master node 109 includes the UE XnAP ID of target SN-2 in its message because it knows that target secondary node 107 needed this information (the SN-2 ID was sent in message (4)).

[0063] The target secondary node SN-2 (107) recognizes, via the SN-2 UE XnAP ID provided as part of the SN Addition Request message (5), that the UE 101 configured for CPC from the source secondary node SN-1, 105 to the target secondary node SN-2, 107 is being requested to be SN added by the target master node 109. Therefore, the target secondary node SN-2, 107 will not reserve resources twice for the same UE 101 if the bearer configuration allows for optimization (6). That is, the target secondary node 107 can optimize resource allocation because it recognizes that the UE 101 is the same UE that it has already prepared for CPC.

[0064] The target secondary node 107 then provides (7) the two differential configurations to the target master node 109. In an example, the two differential configurations may be provided as part of an add secondary node request message acknowledgment sent from the target secondary node 107 to the target master node 109.

[0065] The first differential configuration, Differential SCG Configuration 1 (default), may be the configuration applied during CHO-DC when the CPC of the source master node 103 is not running, i.e., when the serving secondary node (of the UE 101) is still the source secondary node 105. This is valid when CPC-1 is not running (Block 1).

[0066] The second differential configuration, differential SCG configuration 2, may be the configuration applied during CHO-DC when the CPC of the source master node 103 is running, i.e., when the serving secondary node (of the UE 101) is the target secondary node 107. This is valid when CPC-1 is running.

[0067] Therefore, the target master node 109 compiles two CHO-DC configurations in block 8. The first configuration is based on differential SCG configuration 1, and the second configuration is based on differential SCG configuration 2. Thus, there are two configurations on the UE side. In this way, the UE 101 always has a valid configuration before or after the CPC of the source master node runs. That is, in the example, when the CPC of the source master node is not running, the first CHO-DC configuration is valid, and when the CPC of the source master node is running, the second CHO-DC configuration is valid.

[0068] The target master node sends two CHO-DC configurations to the source master node 103 (9), indicating that the second configuration contains a tentative SCG configuration to be used if the source master node's CPC, CPC-1, is executed.

[0069] The source master node 103 then forwards (10) the RRC reconfiguration of the target master node 109 to the UE 101, indicating to the UE 101 that the second configuration should be maintained and activated only after execution of CPC-1.

[0070] The UE 101 sends an RRC reconfiguration complete message to the source master node 103 (11), which relays this information to the target master node 109 (12). After receiving the CHO-DC, the UE 101 starts monitoring the CHO execution conditions in block 13. If the CPC-1 conditions are met in block 14, the UE 101 executes CPC-1. That is, the UE 101 hands over from the source secondary node SN-1, 105 (old secondary node 16) to the target secondary node SN-2, 107 (new secondary node 17) without changing its source master node (15).

[0071] After the serving secondary node is changed from source SN-1, 105 to target SN-2, 107 by executing CPC-1 of the source master node, the UE 101 retains a second CHO-DC configuration, which is prepared for the UE by the target master node and is used after executing CPC for the target SN-2, 107.

[0072] According to an example, the source master node 103 may notify the target master node 109 (19) because the target master node 109 needs to be notified about the change in serving secondary node. In another example, the target secondary node SN-2, 107 (here, the new secondary node 17) may notify the target master node 109 (20).

[0073] Because the CHO-DC configuration is valid after CPC-1 execution, UE 101 may continue monitoring the CHO-DC condition (21). If the condition is met (22), UE 101 may perform CHO to target master node 109, apply the full SCG configuration, and connect to target secondary node SN-2 with the new configuration (22-28). During UE context release (27), secondary node 107 may be notified not to release the UE context if the CHO has the same target SN. Such an instruction may be sent from target master node 109 to source master node 103 and from the source master node to target secondary node 107. In the example, this may be an alternative to 4-5 to prevent the UE context from being released by the target secondary node. Alternatively, this instruction may be sent from source master node 103 to target secondary node SN-2, 107 to prevent the UE context from being released (28). UE 101 uses the second CHO-DC configuration during CHO execution. This is because this is the configuration that the UE has and that is valid after CPC-1 is executed.

[0074] Depending on the CPC execution state, the UE 101 is thus instructed to select one of the provided CHO-DC configurations that is valid at CHO-DC execution time.

[0075] In an embodiment, the target master node may prepare two differential SCG configurations as described above, but the selection criteria for the configurations may be based on the serving PCCell of the UE when CHO-DC is executed.

[0076] Figure 2 is a schematic representation of an example message flow. Similar to Figure 1, in blocks 1 and 2, the source master node 103 prepares a CPC, CPC-1, for the UE 101 to change its serving SN from source secondary node SN-1, 105 to target secondary node SN-2, 107. The UE 101 evaluates the conditions of CPC-1 in block 2. The UE 101 sends a measurement report (3) to its source master node 103 to initiate CHO preparation of the target master node 109. The source master node 103 then sends a CHO request (4) to the target master node 109.

[0077] By way of example, as part of the CHO request message (4), the source master node also includes the SN UE XnAP ID assigned in the target secondary node SN-2, 107 during the UE's CPC preparation for communication over the Xn interface to the source master node 103. The source master node 103 also sends the ID of SN-2 (107) to the target master node 109 to indicate to which secondary node the UE's 101 XnAP ID was assigned. The target secondary node (107) is the same secondary node for which the source master node configures the CPC for the target secondary node (i.e., it is not any secondary node identifier).

[0078] The target master node 109 sends an Add Secondary Node Request to target SN-2 (107) to prepare target SN-2 in the CHO-DC (5). The target master node 109 includes the UE XnAP ID of target SN-2 in its message because it knows that target secondary node 107 needed this information (the SN-2 ID was sent in message (4)).

[0079] The target secondary node SN-2 (107) recognizes, via the SN-2 UE XnAP ID provided as part of the SN Addition Request message (5), that the UE 101 configured for CPC from the source secondary node SN-1, 105 to the target secondary node SN-2, 107 is being requested to be SN added by the target master node 109. Therefore, the target secondary node SN-2, 107 will not reserve resources twice for the same UE 101 if the bearer configuration allows for optimization (6). That is, the target secondary node 107 can optimize resource allocation because it recognizes that the UE 101 is the same UE that it has already prepared for CPC.

[0080] The target secondary node 107 then provides (7) the two differential configurations to the target master node 109. In an example, the two differential configurations may be provided as part of an add secondary node request message acknowledgment sent from the target secondary node 107 to the target master node 109.

[0081] The first differential configuration, Differential SCG Configuration 1 (default), may be the configuration applied during CHO-DC when the CPC of the source master node 103 is not running, i.e., when the serving secondary node (of the UE 101) is still the source secondary node 105. This is valid when CPC-1 is not running (Block 1).

[0082] The second differential configuration, differential SCG configuration 2, may be the configuration applied during CHO-DC when the CPC of the source master node 103 is running, i.e., when the serving secondary node (of the UE 101) is the target secondary node 107. This is valid when CPC-1 is running.

[0083] The target master node compiles two CHO-DC configurations in block 8, as described above, where the first configuration is based on differential SCG configuration 1 and the second configuration is based on differential SCG configuration 2. In the example, the target master node further defines additional conditions for each configuration, such that when a CHO-DC condition is met, UE 101 checks the serving PSCell to select one of the CHO-DC configurations.

[0084] By way of example, if the serving PSCell is the PSCell of the source master node 103 where the UE 101 is served before CPC-1 execution, the UE 101 selects the first CHO-DC configuration, and if the serving PSCell is the PSCell of the target secondary node 107 (SN-2) after CPC-1 execution, the UE 101 selects the second CHO-DC configuration.

[0085] The CHO-DC configuration generated by the target master node 109 is sent to the source master node 103 (9), for example as part of a handover request acknowledgement message, and forwarded to the UE 101 (10). It includes a CHO-DC configuration selection condition based on the serving PSCell at the time of CHO-DC execution. The condition also indicates to the UE 101 that it should retain the CHO-DC configuration that is valid after CPC-1 is executed. An RRC reconfiguration complete message (11) is sent from the UE 101 to the source master node 103 and forwarded to the target master node 109 (12).

[0086] The UE 101 evaluates (13) both the CHO condition and the CPC-1 condition and executes CPC-1 to change its serving master node from the source secondary node 105 to the target secondary node 107 without changing its serving master node, and notifies the target master node 109 accordingly about the secondary node change.

[0087] The UE 101 starts monitoring the CPC-1 execution condition in block 13. If the CPC-1 condition is met in block 14, the UE 101 executes CPC-1, i.e., the UE 101 hands over from the source secondary node SN-1, 105 (old secondary node 16) to the target secondary node SN-2, 107 (new secondary node 17) (15) without changing its source master node.

[0088] The source master node 103 notifies the target master node 109 that the execution of CPC-1 is complete (18). Upon completion of CPC-1 execution, the UE 101 retains the valid CHO-DC configuration, i.e., configuration 2, as instructed in message 10. The UE 101 may delete CHO-DC configuration 1 because CHO-DC configuration 1 is no longer valid after CPC-1 execution.

[0089] After the execution of CPC-1 is completed, the UE 101 continues to monitor the CHO condition for the target PCell of the target master node in block 20. If the CHO condition for the target PCell of the target master node 109 is met (block 21), the UE 101 initiates the CHO execution procedure. The UE 101 evaluates the CHO-DC configuration selection criteria to determine which of the CHO-DC configurations to select. In the example of FIG. 2, the serving PSCell has changed due to the execution of CPC-1 at the time the CHO condition is met, and therefore the UE 101 selects the second CHO-DC configuration (configuration 2), where the differential SCG configuration of configuration 2 is effective for the current serving PSCell. The final part of the process shown in FIG. 2 is the same as that described above with reference to FIG. 1.

[0090] Examples of the present disclosure may be provided as a method, system, or machine-readable instructions, such as any combination of software, hardware, firmware, etc. The machine-readable instructions may be executed by a machine, such as, for example, a general-purpose computer, a platform including a smart device, user equipment such as a smartphone, and / or a network entity such as a base station or node in a wireless network. Modules of the apparatus (e.g., modules that generate a CHO configuration, a CHO with DC configuration, a CPC configuration, etc.) may be implemented by a processor executing machine-readable instructions stored in memory or by a processor operating according to instructions embedded in logic circuitry. The methods and modules may all be performed by a single processor or may be divided among several processors.

[0091] 3 is a schematic representation of an example machine. Machine 300 may be, for example, a node in a wireless network. For example, machine 300 may be target master node 109 in wireless network 301. Machine 300 includes a processor 303 and a memory 305 that stores instructions 307 executable by processor 303. The machine includes storage 309 that may be used to store data 311 representing any one or more of a CHO configuration, a CHO with DC configuration, a CPC configuration, UE and / or node identifiers, etc., as described above. Instructions 307 executable by the processor 303 may cause the machine 300 to send at least one of the first DC-with-CHO configuration and the second DC-with-CHO configuration to the source master node and provide an indication to the source primary node that the second DC-with-CHO configuration includes a temporary SCG configuration to be used when the UE executes a CPC prepared for the UE by the source master node for handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node.

[0092] Thus, the machine 300 may implement a method for preparing a handover of a user equipment (UE) in dual connectivity (DC). The handover occurs between respective primary cells (PCells) of a source master node and a target master node, and between respective primary secondary cells (PSCells) of a source secondary node and a target secondary node. In an embodiment, the machine is a target master node, and the instructions are executable by a processor of the target master node.

[0093] In some examples, some methods may be performed in a cloud computing environment or a network-based environment. A cloud computing environment may provide various services and applications over the Internet. These cloud-based services (e.g., software as a service, platform as a service, infrastructure as a service, etc.) may be accessible, for example, through a web browser or other remote interface of a user device. Various functions described herein may be provided through a remote desktop environment or any other cloud-based computing environment.

[0094] While various embodiments are described and / or illustrated herein in the context of a fully functional computing system, one or more of these exemplary embodiments may be distributed in a variety of forms as a program product, regardless of the particular type of computer-readable storage medium used to actually perform the distribution. The embodiments disclosed herein may also be implemented using software modules that perform certain tasks. These software modules may include script, batch, or other executable files that may be stored on a computer-readable storage medium or within a computing system. In some embodiments, these software modules may configure a computing system to execute one or more of the exemplary embodiments disclosed herein. Additionally, one or more of the modules described herein may convert data, physical devices, and / or representations of physical devices from one format to another.

[0095] 4 is a flowchart of a method according to an example. In the example of FIG. 4, the method is suitable for preparing a handover of a user equipment (UE) in dual connectivity (DC), the handover being performed between respective primary cells (PCells) of a source master node and a target master node, and between respective primary secondary cells (PSCells) of a source secondary node and a target secondary node.

[0096] In block 401, a conditional handover (CHO) request message is received by a target master node from a source master node, the message including a unique identifier of the UE defined between the source master node and the target secondary node and an identifier of the target secondary node. The target secondary node in question is a secondary node that has already configured a CPC with the source master node.

[0097] In block 403, a unique identifier of the UE is sent to the target secondary node as part of a secondary node addition request for DC-with-CHO preparation. In block 405, a first differential secondary cell group (SCG) configuration and a second differential SCG configuration are received from the target secondary node, and each of the first differential SCG configuration and the second differential SCG configuration is generated to correspond to a different CPC execution state.

[0098] The above description is provided to enable those skilled in the art to best utilize various aspects of the exemplary embodiments disclosed herein. This exemplary description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible without departing from the spirit and scope of the present disclosure. The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. Reference should be made to the appended claims and their equivalents in determining the scope of the present disclosure.

Claims

1. 1. A method, performed in a target master node of a wireless network, for preparing a handover of a user equipment (UE) in dual connectivity (DC), the handover being performed between respective primary cells (PCells) of a source master node and a target master node, and between respective primary secondary cells (PSCells) of a source secondary node and a target secondary node, the method comprising: receiving a conditional handover (CHO) request message from the source master node, the message including a unique identifier of the UE defined between the source master node and the target secondary node and an identifier of the target secondary node; Sending the unique identifier of the UE to the target secondary node as part of a secondary node addition request for DC-enabled CHO preparation; receiving, from the target secondary node, a first differential Secondary Cell Group (SCG) configuration and a second differential SCG configuration, each of the first differential SCG configuration and the second differential SCG configuration being generated to correspond to a different Conditional PSCell Change (CPC) execution state; A method comprising:

2. The method of claim 1 , wherein the first differential SCG configuration is generated for a running state in which no ongoing CPC configuration is performed.

3. The method of claim 1 , wherein the second differential SCG configuration is generated for a running state in which an ongoing CPC configuration is performed.

4. generating a first DC-with CHO configuration based on the first differential SCG configuration; using the first CHO with DC configuration when an ongoing CPC configuration configured by the source master node defining a handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node is not performed; The method of claim 2 further comprising:

5. generating a second DC-with CHO configuration based on the second differential SCG configuration; using the second CHO with DC configuration when an ongoing CPC configuration configured by the source master node is performed, the CPC configuration defining a handover from a source PSCell of the source secondary node to a target PSCell of the target secondary node; The method of claim 3 further comprising:

6. transmitting at least one of the first DC-with CHO configuration and a second DC-with CHO configuration to the source master node; Providing an indication to the source master node that the second DC-with CHO configuration includes a temporary SCG configuration to be used when the UE executes a CPC prepared by the source master node for the UE to handover from a source PSCell of the source secondary node to the target PSCell of a target secondary node; The method of claim 4 further comprising:

7. The method of any one of claims 1 to 6, further comprising receiving, from the source master node, a confirmation of the UE handover from the source secondary node to the target secondary node.

8. The method of any one of claims 1 to 6, further comprising receiving, from the target secondary node, a confirmation of the UE handover from the source secondary node to the target secondary node.

9. 7. The method of claim 6, further comprising providing respective conditions for selecting one of the first DC-plus CHO configuration and the second DC-plus CHO configuration.

10. 10. The method of claim 9, further comprising selecting one of the first DC-plus CHO configuration and the second DC-plus CHO configuration based on the condition.

11. A target master node in a wireless network, a processor; a memory coupled to the processor; The memory is configured to store program code executable by the processor, the program code causing the target master node to: receiving a conditional handover (CHO) request message from a source master node, the message including a unique identifier of a UE defined between the source master node and a target secondary node and an identifier of the target secondary node; Sending the unique identifier of the UE to the target secondary node as part of a secondary node addition request for DC-enabled CHO preparation; receiving, from the target secondary node, a first differential secondary cell group (SCG) configuration and a second differential SCG configuration, each of the first differential SCG configuration and the second differential SCG configuration being generated to correspond to a different CPC execution state; a target master node including one or more instructions to execute the

12. The program code causes the target master node to:

12. The target master node of claim 11, further comprising one or more instructions that cause the target master node to execute: generating a first DC-with-CHO configuration based on the first differential SCG configuration to be used when an ongoing CPC configuration configured by the source master node that defines a handover from a source PSCell of a source secondary node to a target PSCell of the target secondary node is not executed.

13. The program code causes the target master node to: The target master node of claim 11 or 12, further comprising one or more instructions that cause the target master node to generate a second DC-with-CHO configuration based on the second differential SCG configuration to be used when an ongoing CPC configuration configured by the source master node that defines a handover from a source PSCell of a source secondary node to a target PSCell of the target secondary node is performed.

14. 1. A machine-readable storage medium encoded with instructions for preparing a handover of a user equipment (UE) in dual connectivity (DC), the handover occurring between respective primary cells (PCells) of a source master node and a target master node, and between respective primary secondary cells (PSCells) of a source secondary node and a target secondary node, the instructions being executable by a processor of the target master node, the medium comprising: transmitting at least one of a first DC-with CHO configuration and a second DC-with CHO configuration to the source master node; Providing an indication to the source master node that the second DC-with-CHO configuration includes a temporary SCG configuration to be used when the UE executes a CPC prepared for the UE by the source master node for handover from a source PSCell of the source secondary node to a target PSCell of a target secondary node; A machine-readable storage medium that causes the

15. 15. The machine-readable storage medium of claim 14, further encoded with instructions executable by the processor of the target master node to cause the target master node to generate respective conditions for selecting one of the first DC-with CHO configuration and the second DC-with CHO configuration.

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