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; sending 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, an acknowledgement message to confirm CPC preparation for the UE, the acknowledgement message including a full secondary cell group (SCG) configuration.

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 for target differential SCG configuration and avoidance of double resource reservation 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 with DC preparation; and receiving, from the target secondary node, an acknowledgement message to confirm CPC preparation for the UE, wherein the acknowledgement message includes a complete secondary cell group (SCG) configuration.

[0008] The target master node and target secondary node are informed about the ongoing CPC preparation. In response, the target secondary does not reserve duplicate resources for the same UE. Furthermore, a full SCG configuration is provided instead of a differential SCG configuration, thereby preventing SCG configuration validity issues in case of a serving secondary node change.

[0009] In an embodiment of the first aspect, a handover request acknowledgement message is sent to the source master node, the handover request acknowledgement message including data representing an indication that the DC-with-CHO includes a full SCG configuration and an indication that the provided configuration will be maintained by the UE after execution of the UE's ongoing CPC configuration.

[0010] The method may further include receiving, from the source master node, a confirmation of the UE handover from the source secondary node 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.

[0011] In an example, the complete SCG configuration may be valid before and after a UE handover from a source secondary node to a target secondary node.

[0012] A second aspect of the present disclosure provides a source master node in a wireless network, the source 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 source master node to: send a CHO request message to a target master node of the wireless network, the 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; and receive, from the target master node of the wireless network, a handover request acknowledgement message including data representing an indication that the CHO configuration includes a full SCG configuration and an indication that the provided configuration will be maintained by the UE after execution of an ongoing CPC configuration of the UE.

[0013] In an embodiment of the second aspect, the program code may further include one or more instructions for causing the source master node to send a confirmation of the UE handover to the target master node. The program code may further include one or more instructions for causing the source master node to send data to the UE including an indication that the DC-with-CHO configuration is maintained after execution of the CPC.

[0014] 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: receive, from the source master node, a conditional handover (CHO) request 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; send the unique identifier of the UE as part of a secondary node addition request for CHO preparation with DC to the target secondary node; and receive, from the target secondary node, an acknowledgement message to confirm CPC preparation for the UE, the acknowledgement message including a full secondary cell group (SCG) configuration.

[0015] 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 send a handover request acknowledgement message to the source master node, the handover request acknowledgement message including data representing an indication that the DC-with-CHO includes a full SCG configuration and an indication that the provided configuration will be maintained by the UE after execution of the UE's ongoing CPC configuration.

[0016] The machine-readable storage may be further encoded with instructions executable by a processor of the target master node to cause the target master node to receive, from the source master node, a confirmation of the UE handover from the source secondary node to the target secondary node.

[0017] 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 receive, from the target secondary node, a confirmation of the UE handover from the source secondary node to the target secondary node.

[0018] A fourth 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: receive a conditional handover (CHO) request message from a source master node, the conditional handover request 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; send the unique identifier of the UE to the target secondary node as part of a secondary node addition request for CHO with DC preparation; and receive an acknowledgement message from the target secondary node to confirm CPC preparation for the UE, the acknowledgement message including a full secondary cell group (SCG) configuration.

[0019] The program code may further include one or more instructions that cause the target master node to send a handover request acknowledgement message to the source master node that includes data representing an indication that the DC-with-CHO includes a full SCG configuration and that the provided configuration is to be maintained by the UE after execution of an ongoing CPC configuration of the UE.

[0020] The program code may further include one or more instructions that cause the target master node to receive, from the source master node, a confirmation of the UE handover from the source secondary node to the target secondary node.

[0021] Embodiments will now be described, by way of example only, with reference to the drawings, in which: [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic representation of the message flow through the example. [Figure 2] 1 is a schematic representation of an example machine. [Figure 3] 1 is a flowchart of a method according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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."

[0029] The terms "system" and "network" may be used interchangeably.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Examples of some terms used in this disclosure are as follows:

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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).

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] According to an example, to prevent differential configuration and thereby avoid the CHO-CPC coexistence validity issue, the source MN provides existing CPC-related information to the target MN as part of the CHO request. That is, the source master node provides the existing CPC-related information to the target master node as part of the CHO request. The existing CPC-related information may be relayed to the target secondary node, so that the target master node and the target secondary node are aware of the ongoing CPC configuration. Thus, the target secondary node can configure a complete SCG configuration that is effective before and after the execution of the CPC prepared by the source master node. This prevents double reservation of resources.

[0067] Figure 1 is a schematic representation of the message flow according to an example, in which a source master node first prepares a CPC and then initiates target master node preparation in CHO-DC, and the target master node provides a full SCG configuration rather than a differential SCG configuration to prevent SCG configuration validity issues in case of a serving secondary node change. In the example, the target master node and the target secondary node are notified about the ongoing CPC preparation, so that the target secondary node does not reserve duplicate resources for the same UE.

[0068] Referring 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 to the target master node 109 (4).

[0069] 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).

[0070] 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)).

[0071] The target secondary node SN-2 (107) recognizes 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 add an SN by the target master node 109, via the SN-2 UE XnAP ID provided as part of the SN Addition Request message (5). Thus, the target secondary node SN-2, 107 will not reserve resources twice for the same UE 101 if the bearer configuration allows for optimization. Furthermore, the target secondary node SN-2, 107 provides a full SCG configuration rather than a differential configuration, since a differential configuration may become invalid once CPC is performed by the UE 101, whereas a full SCG configuration will not.

[0072] The target secondary node SN-2, 107 acknowledges (7) its readiness for the requested UE 101 and transmits (7) the generated full SCG configuration. The target master node 109 then generates (8) a CHO-DC configuration, including an MCG configuration for the target master node 109 and a full SCG configuration for the target secondary node 107.

[0073] The target master node 109 sends a handover request acknowledgement message (9) to the source master node 103, which also indicates that the CHO-DC configuration will be valid even if the CPC-1 prepared by the source master node 103 is executed by the UE 101. This allows the source master node 103 to avoid canceling the CHO if the CPC is executed first.

[0074] 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). As indicated in message 10, the UE 101 retains the CHO-DC configuration because the CHO-DC configuration is still valid due to the full SCG configuration.

[0075] 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).

[0076] 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 a CHO to the 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 the target master node 109 to the source master node 103 and from the source master node to the target secondary node 107. In an 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 the source master node 103 to the target secondary node SN-2, 107 to prevent the UE context from being released (28).

[0077] 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.

[0078] 2 is a schematic representation of a machine according to an example. Machine 200 may be, for example, a node in a wireless network. For example, machine 200 may be source master node 103 or target master node 109 in wireless network 201. Machine 200 includes a processor 203 and memory 205 storing instructions 207 executable by processor 203. The machine includes storage 209 that may be used to store data 211 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. In an example, instructions 207 executable by processor 203 may cause machine 200 to receive, from a 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, and to send the unique identifier of the UE to the target secondary node as part of a request to add a secondary node for CHO with DC preparation.

[0079] In an example, instructions 207 executable by processor 203 may cause machine 200 to receive an acknowledgement message from a target secondary node to confirm CPC preparation for the UE, where the acknowledgement message includes a complete secondary cell group (SCG) configuration.

[0080] The machine 200 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.

[0081] 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.

[0082] 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.

[0083] 3 is a flowchart of a method according to an example. In the example of FIG. 3, the method is suitable for preparing a handover of a user equipment (UE) in dual connectivity (DC), where 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. In block 301, a conditional handover (CHO) request message is received by a target master node from a source master node, the conditional handover request 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.

[0084] In block 303, the unique identifier of the UE is sent to the target secondary node as part of a secondary node addition request for CHO with DC preparation. In block 305, an acknowledgement message is received (by the target master node) from the target secondary node to confirm CPC preparation for the UE, the acknowledgement message including the complete secondary cell group (SCG) configuration.

[0085] 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, an acknowledgement message to confirm CPC preparation for the UE, the acknowledgement message including a complete secondary cell group (SCG) configuration; Sending a handover request acknowledgement message to the source master node, the handover request acknowledgement message including data representing an indication that the DC-with-CHO includes a full SCG configuration and that the provided configuration will be maintained by the UE after execution of the UE's ongoing CPC configuration; A method comprising:

2. 2. The method of claim 1, further comprising receiving, from the source master node, a confirmation of the UE handover from the source SN to the target SN.

3. The method of claim 1 , further comprising receiving, from the target SN, a confirmation of the UE handover from the source secondary node to the target secondary node.

4. The method according to any one of claims 1 to 3, wherein the complete SCG configuration is valid before and after a UE handover from the source secondary node to the target secondary node.

5. A source 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 source master node to: sending a CHO request message to the target master node of the wireless network, the CHO request 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; and receiving a handover request acknowledgement message from the target master node of the wireless network, the handover request acknowledgement message including data representing an indication that a CHO configuration includes a full SCG configuration and that the provided configuration will be maintained by the UE after execution of an ongoing CPC configuration of the UE; [0023] The source master node includes one or more instructions to execute.

6. The source master node of claim 5 , wherein the program code further comprises one or more instructions that cause the source master node to send a confirmation of UE handover to the target master node.

7. 7. The source master node of claim 5 or 6, wherein the program code further includes one or more instructions that cause the source master node to execute transmitting data to the UE including an indication that the DC-with-CHO configuration is maintained after execution of the CPC.

8. 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: 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, an acknowledgement message to confirm CPC preparation for the UE, the acknowledgement message including a complete secondary cell group (SCG) configuration; Sending a handover request acknowledgement message to the source master node, the handover request acknowledgement message including data representing an indication that the DC-with-CHO includes a full SCG configuration and that the provided configuration will be maintained by the UE after execution of the UE's ongoing CPC configuration, to the target master node; A machine-readable storage medium that causes the

9. 9. The machine-readable storage medium of claim 8, further encoded with instructions executable by the processor of the target master node that cause the target master node to receive, from the source master node, a confirmation of a UE handover from the source SN to the target SN.

10. 10. The machine-readable storage medium of claim 8, further encoded with instructions executable by the processor of the target master node to cause the target master node to receive, from the target SN, a confirmation of UE handover from the source secondary node to the target secondary node.

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; and receiving, from the target secondary node, an acknowledgement message to confirm CPC preparation for the UE, the acknowledgement message including a complete secondary cell group (SCG) configuration; The program code sends a handover request acknowledgement message to the source master node, the handover request acknowledgement message including data representing an indication that the DC-with-CHO includes a full SCG configuration and that the provided configuration will be maintained by the UE after execution of an ongoing CPC configuration of the UE; a target master node including one or more instructions to execute the

12. 12. The target master node of claim 11, wherein the program code further comprises one or more instructions that cause the target master node to receive, from the source master node, a confirmation of a UE handover from the source SN to the target SN.

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