Conditional Handover

Abstract

In some examples, a method for preparing a handover of a user equipment (UE) in dual connectivity (DC), performed in a target master node (MN) of a wireless network, where the handover is between primary cells (PCells) of a source MN and a target MN and between primary secondary cells (PSCells) between a source secondary node (SN) and a target SN, includes: transmitting to the source MN a secondary cell group (SCG) delta configuration config1 of a CHO and a target SN having a DC configuration including a unique identifier of the UE defined between the source master node and the target secondary node; receiving from the source MN an indication representing a CPC procedure configured after transmitting the CHO having the DC configuration, the unique identifier of the UE, and an identifier of the target SN; and transmitting to the target SN a request to prepare a second delta SCG configuration config2 to be used by the UE when a source MN-initiated CPC procedure is performed.

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] The fifth-generation (5G) New Radio (NR) system is designed to provide flexibility and configurability to optimize network services and types for various 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 traditional handover procedures, which leave the decision of whether to perform a handover to the network. Consequently, handovers are reactive processes that are prone to 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 can start evaluating the execution conditions when it receives a CHO configuration, and can finish 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 the CHO-DC configuration over the target delta SCG configuration and the avoidance of double resource reservations in the context of CHO-CPC coexistence.

[0005] These and other objects are achieved by 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 for preparing a handover of a user equipment (UE) in dual connectivity (DC), performed in a target master node (MN) of a wireless network, the handover being between primary cells (PCells) of a source MN and a target MN and between primary secondary cells (PSCells) between a source secondary node (SN) and a target SN, the method including: transmitting to the source MN a secondary cell group (SCG) delta configuration config1 of a CHO and a target SN having a DC configuration including a unique identifier of the UE defined between the source master node and the target secondary node; receiving from the source MN an indication representing a CPC procedure configured after transmission of the CHO having the DC configuration, the unique identifier of the UE, and the identifier of the target SN; and transmitting to the target SN a request to prepare a second delta SCG configuration, config2, to be used by the UE when a source MN-initiated CPC procedure is performed.

[0008] In an embodiment of the first aspect, the method may further include receiving config2 from the target SN, where the second delta SCG configuration is valid when the UE applies the SCG configuration after the CPC procedure is performed. The method may further include generating a second CHO having a DC configuration using the second delta SCG configuration. The method may further include transmitting a handover request update message to the source MN to update the existing CHO having the DC configuration. The second CHO having the DC configuration can be maintained and used by the UE when the CPC procedure is performed. The method may further include providing the second CHO having the DC configuration to the UE and instructing the UE to maintain the second CHO with the DC configuration after the CPC procedure is performed.

[0009] A second aspect of the present disclosure provides a source master node in a wireless network, the source master node comprising: 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 receive from a target MN a secondary cell group (SCG) delta configuration config1 of a CHO and a target SN having a DC configuration including a unique identifier of a UE defined between the source master node and the target SN; send to the target MN an indication comprising a CPC procedure configured after sending the CHO having the DC configuration, the unique identifier of the UE, and the identifier of the target SN; and receive from the target MN a handover request update message including the CHO having a second DC configuration.

[0010] In an embodiment of the second aspect, the program code may comprise one or more further instructions to cause the source master node to update an existing CHO with DC configuration with a second CHO with DC configuration. The program code may comprise one or more further instructions to cause the source master node to send the second CHO with DC configuration to the UE and to instruct the UE to maintain the second CHO with DC configuration after a CPC procedure has been performed. The program code may comprise one or more further instructions to cause the source master node to send a CHO Condition ID associated with the second CHO with DC settings to the UE.

[0011] A third aspect of the present disclosure provides a user equipment UE comprising: 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, thereby causing the UE to receive a second CHO having a DC configuration from a source MN; and maintain the second CHO having the DC configuration after a CPC procedure is performed.

[0012] In an embodiment of the third aspect, the program code may comprise one or more further instructions to cause the UE to receive, from the source MN, a CHO Condition ID associated with a second CHO having a DC configuration.

[0013] A fourth aspect of the present disclosure provides a machine-readable storage medium encoding instructions for preparing a handover of a user equipment (UE) in dual connectivity (DC), the handover being between a primary cell (PCell) of a source MN and a primary cell (PCell) of a target MN, and between a primary secondary cell (PSCell) between a source secondary node (SN) and a target SN, the instructions being executable by a processor of a target master node to cause the target master node to send to the source MN a secondary cell group (SCG) delta configuration config1 of a CHO and a target SN having a DC configuration including a unique identifier of the UE defined between the source master node and the target secondary node, receive from the source MN an indication indicating a CPC procedure configured after sending the CHO having the DC configuration, the unique identifier of the UE, and the identifier of the target SN, and send to the target SN a request to prepare a second delta SCG configuration, config2, to be used by the UE when a source MN-initiated CPC procedure is performed.

[0014] In an embodiment of the fourth aspect, the machine-readable storage medium may further be encoded with instructions executable by a processor of the target master node to cause the target master node to receive config2 from the target SN, where the second delta SCG configuration is valid when the UE applies the SCG configuration after the CPC procedure is executed. The machine-readable storage medium may further be encoded with instructions executable by a processor of the target master node to cause the target master node to generate a second CHO having a DC configuration using the second delta SCG configuration.

[0015] Embodiments will now be described, by way of example only, with reference to the drawings in which: [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram of a message flow according to one embodiment. [Figure 2] FIG. 2 is a schematic diagram of a message flow according to one embodiment. [Figure 3] 1 is a schematic diagram of a machine according to one embodiment; [Figure 4] 1 is a flowchart of a method according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Exemplary embodiments are described below in sufficient detail to enable those skilled in the art to embody and practice the systems and methods described herein. It is important to understand that embodiments may be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

[0018] Accordingly, while the embodiments may be modified in various ways and may take various alternative forms, specific embodiments thereof are shown by way of example in the drawings and will be described in detail below. There is no intention to be limited to the particular forms disclosed. Rather, the inclusion of all modifications, equivalents, and alternatives falling within the scope of the appended claims is intended. Elements of exemplary embodiments will, where appropriate, be consistently designated by the same reference numerals throughout the drawings and detailed description.

[0019] The terms used herein to describe embodiments are not intended to limit the scope of the present invention. The articles "a," "an," and "the" are singular in the sense that they have a single referent; however, the use of the singular herein should not exclude the presence of more than one referent. In other words, elements referred to in the singular may refer to one or more than one, unless the context clearly indicates otherwise. Furthermore, as used herein, the terms "comprises," "comprising," "including," and / or "comprising" will be understood to specify the presence of stated features, items, steps, operations, elements, and / or components, but not to 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 correlation for describing related objects, and represents a three-way relationship, where A and / or B can indicate A alone, A and B together, or B alone. The character " / " generally indicates an "or" relationship between related objects.

[0020] Unless otherwise specified, all terms (including technical and scientific terms) used herein should be interpreted as customary in the art. Furthermore, it will be understood that commonly used terms should also be interpreted as customary in the relevant art, and should not be interpreted in an idealized or overly formal sense, unless expressly defined herein.

[0021] The following contains specific information related to embodiments of the present disclosure. The drawings and the 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.

[0022] The phrases "in one embodiment" or "in some embodiments" can each refer to one or more of the same or different embodiments. The term "coupled" is defined as connected 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."

[0023] The terms "system" and "network" may be used interchangeably.

[0024] For purposes of explanation and not limitation, specific details are set forth such as functional entities, techniques, protocols, and standards 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.

[0025] Those skilled in the art will readily recognize that any network function or algorithm disclosed can be implemented by hardware, software, or a combination of software and hardware. The disclosed functions can correspond to modules that can be software, hardware, firmware, or a combination thereof.

[0026] Software implementations may include machine-readable and / or computer-readable and / or executable instructions stored on a machine-readable 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 capabilities can be programmed with the corresponding executable instructions to perform the disclosed network functions or algorithms.

[0027] A microprocessor or general-purpose computer may include 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 as hardware, or as 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 device, or any other equivalent medium capable of storing computer-readable instructions.

[0028] 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 the one or more BSs.

[0029] A UE may include, but is not limited to, a mobile station, a mobile terminal or device, or a user communication wireless terminal. A UE may be a portable wireless 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. A UE is configured to receive and transmit signals over the air interface to one or more cells in a RAN.

[0030] The BS may provide communication services according to at least one radio access technology (RAT), such as Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM), often referred to as 2G, GSM Enhanced Data rates for GSM Evolution (EDGE) RAN (GERAN), General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), often referred to as 3G based on basic wideband code division multiple access (W-CDMA), 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.

[0031] The BS may include, but is not limited to, a Node B (NB) in UMTS, an Evolved Node B (eNB) in LTE or LTE-A, a Radio Network Controller (RNC) in UMTS, a BS Controller (BSC) in GSM / GERAN, a Next Generation (ng)-eNB of an Evolved Universal Terrestrial Radio Access (E-UTRA) BS connected to 5G-RAN, a Next Generation Node B (gNB) of a 5G-RAN, or any other device capable of controlling radio communication and managing radio resources within a cell. The BS may provide service to one or more UEs over an air interface.

[0032] A BS can provide radio coverage for a particular geographic area using multiple cells, which form a RAN. The BS supports the operation of the cells, and each cell operates to serve at least one UE within its radio coverage.

[0033] Each cell (often called a serving cell) can 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 uplink (UL) packet transmissions. A BS can communicate with one or more UEs in a wireless communication system via multiple cells.

[0034] Cells can allocate sidelink (SL) resources to support proximity services (ProSe) or vehicle-to-everything (V2X) services. Each cell may have overlapping coverage areas with other cells.

[0035] The NR frame structure supports flexible configuration to accommodate various next-generation (e.g., 5G) communication requirements, such as enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC), meeting high reliability, high data rates, and low latency requirements. The 3rd Generation Partnership Project (3GPP) orthogonal frequency division multiplexing (OFDM) technology can serve as the baseline for NR waveforms. Scalable OFDM arithmetic processing, such as adaptive subcarrier spacing, channel bandwidth, and cyclic prefix (CP), can also be used.

[0036] Examples of some terms used in this disclosure are as follows:

[0037] Primary Cell (PCell): A PCell is a Master Cell Group (MCG) cell operating 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.

[0038] Primary SCG Cell (PSCell): In dual connectivity (DC) operation, a PSCell is a secondary cell group (SCG) cell that a UE randomly accesses when performing a Reconfiguration with Sync procedure. A PSCell is an SpCell of an SCG. In some implementations, the term PSCell can refer to a primary secondary cell. The terms "primary SCG cell" and "primary secondary cell" can be used interchangeably in this disclosure.

[0039] Special Cell (SpCell): In DC operation, the term special cell (SpCell) refers to a PCell of an MCG or a PSCell of an SCG, or the term special cell refers to a PCell.

[0040] Secondary Cell (SCell): In a UE configured with Carrier Aggregation (CA), a SCell is a cell that provides additional radio resources above a special cell.

[0041] Serving Cell: For a UE in RRC_CONNECTED without CA / DC configured, there is only one serving cell comprising the primary cell. For a UE in RRC_CONNECTED with CA / DC configured, the term "serving cell" is used to refer to the collection of cells comprising the special cell and all secondary cells.

[0042] Master Cell Group (MCG): In MR-DC, an MCG is a group of serving cells associated with a master node, comprising an SpCell (PCell) and optionally one or more SCells.

[0043] 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. The MN may be a master eNB (EN-DC), a master ng-eNB (NGEN-DC), or a master gNB (NR-DC and NE-DC). In some embodiments, the MN or primary node may comprise a source node or a target node for the UE.

[0044] Secondary Cell Group (SCG): In MR-DC, an SCG is a group of serving cells associated with a secondary node, comprising an SpCell (PSCell) and optionally one or more SCells.

[0045] Secondary Node (SN): In MR-DC, an SN is a radio access node that does not have a control plane connection to the core network and provides additional resources to the UE. It is the en-gNB (in EN-DC), the secondary ng-eNB (in NE-DC), or the secondary gNB (in NR-DC and NGEN-DC). In some embodiments, the SN or secondary node may comprise the source node or target node of the UE.

[0046] 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 a serving cell is below a preset threshold and the quality (e.g., signal strength and / or service quality) of a neighboring cell is above a preset threshold, the UE can 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 can 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 can select and send a handover command message (which may be included in a handover acknowledgement message from one of the target base stations) to the UE so that the UE can connect to the target cell.

[0047] The success of the entire handover procedure depends on several factors. One of these factors is that the serving cell quality does not deteriorate rapidly in a short time, which may be determined by the latency of the backhaul (e.g., the X2 / Xn / Xx interface), the processing time of the target base station, and the signaling transmission time. However, in real-world situations, the serving cell quality may deteriorate rapidly in a short time, and the UE may not successfully receive the handover command message before the serving cell quality deteriorates significantly. As a result, the UE may detect a radio link failure. As a result, in response to the detected radio link failure, the UE may initiate a radio resource control (RRC) connection re-establishment procedure, resulting in a significant service interruption.

[0048] In next-generation wireless networks (e.g., 5G NR networks), with massive antenna beamforming in higher frequency bands, the quality of the serving cell may degrade even faster, especially if narrow beams are used to serve the UE. Shadowing is another issue in NR deployments.

[0049] 3GPP introduced the concept of Conditional Handover (CHO) to improve the reliability of the entire handover procedure. The CHO procedure can be seen as a complementary procedure to the conventional handover procedure to reduce the handover failure rate.

[0050] 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) of the conditional reconfiguration command are met. If the UE determines that the trigger condition is met, it may apply a 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.

[0051] CHO may help improve the reliability of the entire handover procedure. Applying a concept similar to CHO may also be beneficial to a PSCell addition procedure, a PSCell modification procedure, an SN addition procedure, or an SN modification procedure in MR-DC mode, since the preparation between the MN and the SN and the RRC signaling for adding the SN may be completed in advance.

[0052] 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, the UE may behave differently. For example, if the executed conditional reconfiguration command is for a PSCell addition / modification, the UE may not need to release the link to the current PCell (or MN). Some information or guidelines (e.g., implicitly) may be required for the UE to decide what to do when a conditional reconfiguration command is executed. Also, the principles for applying CHO (or conditional configuration) to a PCell modification and those for applying CHO (or conditional configuration) to a PSCell addition / modification may differ due to the different purposes.

[0053] A conditional reconfiguration procedure may be a reconfiguration procedure that is 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).

[0054] 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 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.

[0055] In the context of the CHO-CPC coexistence framework, there are two configurations: one that is provided to the UE and one that runs in parallel, i.e., the UE monitors both measurements for both configurations: one is the CHO configuration with CHO execution conditions (including DC connection and / or SN connection), and the other is the Conditional PSCell Change (CPC) configuration and CPC execution conditions that are provided to the UE and also run in parallel.

[0056] In a CHO-CPC coexistence scenario, the issue of CPC validity arises when the target MN prepares a CHO-DC with an SN delta configuration. Thus, the UE is served by a source MN and a source SN (i.e., DC setup). The source MN can initiate a CHO preparation for the target MN, in which the target MN prepares the target SN with the target SN delta configuration (i.e., CHO-DC preparation). The target SN delta configuration will be retained during the CHO preparation and execution of the target MN, and will be applied when the UE applies the target SN delta configuration to the source SN configuration to obtain the complete configuration required for the target SN connection.

[0057] However, if the source SN is changed after CHO preparation (before CHO execution), the delta configuration becomes invalid because the UE's serving SN changes, and the delta configuration cannot be applied to the new SN configuration. This invalidity is observed when the source MN prepares CPC between the source SN and target SN after CHO-DC preparation, and CPC is executed before CHO-DC execution. In this case, i.e., if the source SN is changed before CHO-DC execution, the delta SN configuration in CHO-DC preparation becomes invalid. Therefore, CHO preparation must be repeated.

[0058] In some cases, both the serving MN and the target MN may prepare the same target SN for the UE, i.e., the target MN prepares the target SN for CHO-DC handover, and the source MN prepares a CPC towards the same target SN. In this case, the target SN will be unaware that the same UE for CHO-DC preparation has also been prepared as part of the CPC preparation initiated by the source MN. Thus, the target SN will reserve resources twice, even though the bearer configuration is the same.

[0059] Therefore, in a CHO-CPC coexistence scenario, the serving MN can initiate CHO preparation toward the target MN. The target MN can prepare CHO-DC, i.e., CHO-DC for the target SN with the delta configuration. Then, the target MN can prepare a CPC for the UE toward the same target SN. In this case, the serving MN prepares the same SN that the target MN has already prepared for CHO-DC configuration, so the same target SN reserves resources twice for the same UE. Furthermore, the target SN delta configuration included in the CHO-DC configuration becomes invalid if the serving SN is changed (by a CPC prepared after CHO-DC preparation) before CHO-DC execution, because the delta configuration is prepared for the initial serving SN. To avoid SN failure (due to the use of an invalid configuration), CHO-DC preparation is initiated again at the expense of extra signaling overhead and a delay in CHO-DC configuration imposed on the UE.

[0060] In this given scenario, the source MN first prepares a CHO for the target MN, and then prepares a CPC for the target SN. When the target MN prepares a CHO-DC (with SN connection), if the CPC configured by the source MN is executed first, the delta SCG configuration of the CHO-DC configuration of the target MN becomes invalid. The reason for this invalidity is that the delta SCG configuration of the target MN is configured to be used when the serving SN does not change before and after CHO-DC preparation. However, the solution is different from the perspective of signaling sequence because CPC preparation comes after CHO preparation and CHO preparation needs to be updated after CPC preparation is completed.

[0061] According to one example, in a case where a source MN first prepares a CHO-DC and then prepares a target SN with a CPC, if the CPC preparation is handled after the CHO-DC preparation, the CHO-DC of the target MN can be updated. Furthermore, the target SN can provide information related to the previous CHO-DC or CPC preparation for the same UE so that the target SN does not reserve resources for the same UE twice.

[0062] Figure 1 is a schematic diagram of a message flow according to one embodiment. In the example of Figure 1, the message flow relates to a method executed in a target master node (MN) of a wireless network for preparing a handover of a user equipment (UE) in dual connectivity (DC), where the handover is between primary cells (PCells) of a source MN and a target MN and between primary secondary cells (PSCells) of a source secondary node (SN) and a target secondary node (SN).

[0063] The UE 101 sends a measurement report (1) to the source master node 103 and initiates CHO preparation of the target master node 109. After that, the source master node 103 sends a CHO request (2) to the target master node 109.

[0064] The target MN 109 prepares the target SN 107 for CHO-DC preparation and generates a CHO-DC configuration config1 containing the delta SCG configuration 1 of the target SN 107 in block 5. A handover request acknowledgement message (6) is sent from the target MN 109 to the source MN 103 and includes the CHO-DC configuration prepared by the target MN 109.

[0065] According to one embodiment, as part of message (6), the target MN 109 also includes the SN UE XnAP ID that was defined between the target secondary node 107 and the source MN 103 during CPC-1 preparation of the UE for communication over the Xn interface.

[0066] Now that the CHO-DC configuration of the UE 101 is complete, the UE 101 monitors the CHO status towards the target PCell of the target MN 109 in block 10. The UE 101 sends another measurement report (11) to the source MN 103 to initiate CPC preparation of the target PSCell in the target SN 107.

[0067] The source MN 109 sends an SN change request (12) to prepare CPC-1 between the source SN 105 and the target SN 107. This request is sent to the target SN 107 indicated above (i.e., specified by the SN ID), so that the source MN 103 transfers the SN UE XnAP ID to the target SN 107, allowing the target SN to identify the UE that has already been prepared by the target MN 109 in the CHO-DC preparation.

[0068] Since the target SN 107 will be aware that a CPC is being requested for the UE 101 that was already prepared by the target MN in the CHO-DC preparation, it can optimize the resource allocation (13) if the bearer configuration allows it, i.e. no duplicate resources are allocated in the target SN 107.

[0069] The target SN 107 replies with an acknowledgement (14) to the source MN's SN change request (12). In one example, the target SN 107 also indicates that the same UE 101 is prepared for CHO-DC operation with the target MN 109.

[0070] The CPC preparation configuration and conditions are provided to the UE, and CPC preparation is completed (15-17) between the UE 101, the source MN 103, and the target SN 107. Therefore, the UE starts monitoring the CPC-1 conditions to execute CPC-1 (18).

[0071] The source MN 105 notifies the target MN 109 of the UE's conditional PSCell change CPC-1 preparation so that the target MN knows that if CPC is executed before CHO is executed, the delta secondary cell group SCG configuration of the target MN's CHO-DC configuration may become invalid (12). To this end, the source MN 103 indicates CPC-1 together with the SN ID and SN UE XnAP ID sent from the target MN 109 in message 6 of the source MN 103.

[0072] The target MN 109 requests the target SN 107 to prepare a second delta SCG configuration to be used by the UE 101 when CPC-1 is executed (20).

[0073] The target SN 107 transmits to the target MN 109 a target delta SCG configuration configu2 that will become effective when the UE 101 applies SCG configuration 2 after CPC-1 is executed (21).

[0074] The target MN 109 generates a second CHO-DC configuration using the target delta SCG configuration 2 (block 22) and sends a handover request update message (23) to the source MN 103 to update the previous CHO-DC configuration. That is, the target MN 109 sends the second CHO-DC configuration to be maintained and used by the UE 101 when CPC-1 is performed.

[0075] The source MN 103 relays the second CHO-DC configuration to the UE 101 (24) along with the CHO condition ID that is bound to the CHO-DC configuration, and instructs the UE 101 to maintain the second CHO-DC configuration after CPC-1 is executed.

[0076] The UE 101 notifies the source MN 103 about the RRC reconfiguration completion (25), and the source MN 103 relays this information to the target MN 109 (26).

[0077] FIG. 2 is a schematic diagram of a message flow according to one embodiment, which is a continuation of the message flow described above with reference to FIG.

[0078] In block 27, the CPC-1 condition is met and the UE 101 hands over from the source SN 105 to the target SN 107 (CPC execution, 28-31) without changing the source MN from the source MN 103. The target SN 107 becomes the new serving SN for the UE 101 (SN changed). The target MN 109 is notified about the CPC-1 execution, i.e., that the PSCell has been changed from the source SN 105 to the target SN 107 (32).

[0079] After execution of CPC-1, UE 101 retains CHO-DC Config 2 as instructed (24) in block 33, and therefore has a valid Delta SCG Configuration 2 after execution of CPC-1 (Delta SCG Configuration 2 is generated for the case where target SN 107 becomes UE 101's serving SN).

[0080] The UE 101 continues to monitor the CHO conditions towards the target PCell of the target MN 109, and when the conditions are satisfied, the UE performs CHO-DC towards the target MN 109 and the target SN 107, and the handover procedure is completed (34-41).

[0081] Embodiments 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 a general-purpose computer, a platform comprising a smart device, user equipment, such as a smartphone, and / or a network entity, such as a base station or node of a wireless network. Modules of the apparatus (e.g., modules for generating a CHO configuration, a CHO with a DC configuration, a CPC configuration, etc.) may be implemented by a generator that executes machine-readable instructions stored in a memory, or a processor that operates according to instructions embodied in logic circuitry. The methods and modules may all be executed by a single processor, or may be divided among multiple processors.

[0082] 3 is a schematic diagram of a machine according to one embodiment. The machine 300 may be, for example, a node of a wireless network. For example, the machine 300 may be a source master node 103 or a target master node 109 in the wireless network 301. The machine 300 comprises a processor 303 and a memory 305 storing instructions 307 executable by the processor 303. The machine comprises storage 309 operable to store data 311 representing any one or more of the CHO configuration, the CHO with DC configuration, the CPC configuration, UE and / or node identifiers, etc., as described above. In one example, the instructions 307 executable by the processor 303 may cause the machine 300 to perform a method for preparing a handover of a user equipment, UE, in dual connectivity (DC), where the handover is between primary cells (PCells) of a source MN and a target MN and between primary secondary cells (PSCells) between a source secondary node (SN) and a target SN. When executed by the processor 303, the instructions can cause a machine such as a target master node to perform the following steps: sending to the source MN a secondary cell group (SCG) delta configuration config1 of the CHO and target SN having a DC configuration including a unique identifier of the UE defined between the source master node and the target secondary node; receiving from the source MN an indication representing a CPC procedure configured after sending the CHO having the DC configuration, the unique identifier of the UE, and the identifier of the target SN; and sending to the target SN a request to prepare a second delta SCG configuration config2 to be used by the UE when a source MN-initiated CPC procedure is performed.

[0083] In an embodiment, the machine may be a target master node or a source master node, and the instructions may be executable by a processor of the target master node or a processor of the source master node.

[0084] 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 accessed, for example, through a web browser or other remote interface on a user's device. Various features described herein may be provided through a remote desktop environment or other cloud-based computing environment.

[0085] Although various embodiments have been described and / or illustrated herein in the context of a fully functional computer system, one or more of these exemplary embodiments may be deployed as a program product in various forms, regardless of the particular type of computer-readable storage medium actually used to implement the deployment. The embodiments disclosed herein may also be implemented using software modules that perform particular 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 computer system. In some embodiments, these software modules may configure a computer system to execute one or more of the exemplary embodiments disclosed herein. Furthermore, one or more of the modules described herein may transform data, physical devices, and / or representations of physical devices from one form to another.

[0086] FIG. 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), where the handover is between a primary cell (PCell) of a source MN and a primary cell (PCell) of a target MN, and between primary secondary cells (PSCells) between a source secondary node (SN) and a target SN. In block 401, a secondary cell group (SCG) delta configuration config1 of a CHO and a target SN having a DC configuration including a unique identifier of the UE defined between the source master node and the target secondary node is transmitted from the target MN to the source MN. In block 403, the target MN receives an indication from the source MN indicating a CPC procedure configured after transmission of the CHO having the DC configuration, the unique identifier of the UE, and the identifier of the target SN. In block 405, a request is transmitted to the target SN to prepare a second delta SCG configuration config2 to be used by the UE when a source MN-initiated CPC procedure is performed.

[0087] The foregoing 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. [Explanation of symbols]

[0088] 103 Source MN 105 Source SN 107 Target SN 109 Target MN 1 Send the measurement report 2 CHO request 3 SN addition request 4 SN additional request ACK 5 Config1: Generate a CHO configuration consisting of MCG configuration 1 + target delta SCG configuration 1 (delta to source SCG) 6 Handover Request Acknowledgement Message (CHO Configuration) 7 RRC Reconfiguration 8 RRC reconfiguration completed 9 RRC reconfiguration completed 10 UE evaluates CHO conditions 11 Measurement Report 12 SN Change (CPC-1) Request 13 Duplicate resources are not allocated 14 SN Change (CPC-1) Request ACK (CHO-DC in progress) 15 RRC Reconfiguration (CPC-1) 16 RRC reconfiguration completed 17 SN reconfiguration completed 18 UE evaluates CPC-1 conditions 20 SN change request SN-2 UE XnAP ID, SCG configuration of CPC-1 21 SN change request ACK Target delta SCG configuration 2 22 Config2: Generate a CHO configuration consisting of MCG configuration 1 + target delta SCG configuration 2 (delta to applied target SCG) (if CPC-1 is executed) 23 Handover Request Update (Previous SCG configured for CPC-1) 24 RRC Reconfiguration Maintain configuration 2 after executing CPC-1 25 RRC reconfiguration completed 26 RRC reconfiguration completed

Claims

1. 1. A method for preparing a handover of a user equipment (UE) in dual connectivity (DC), the method being performed in a target master node (MN) of a wireless network, the handover being between primary cells (PCells) of a source MN and a target MN, and between primary secondary cells (PSCells) between a source secondary node (SN) and a target SN; Sending to the source MN a secondary cell group (SCG) delta configuration config1 of the CHO and the target SN having a DC configuration including a unique identifier of a UE defined between the source master node and the target secondary node; Receive an indication from the source MN indicating a configured CPC procedure after sending a CHO having the DC configuration, a unique identifier of the UE, and an identifier of the target SN; sending a request to the target SN to prepare a second delta SCG configuration, config2, to be used by the UE when a source MN initiated CPC procedure is performed; A method comprising:

2. 2. The method of claim 1, further comprising receiving config2 from the target SN, wherein the second delta SCG configuration is valid when the UE applies the SCG configuration after the CPC procedure is performed.

3. 3. The method of claim 1 or 2, further comprising using the second delta SCG configuration to generate a second CHO having a DC configuration.

4. The method of claim 3 , further comprising: sending a handover request update message to the source MN to update the existing CHO with DC configuration.

5. The method of claim 4, wherein the second CHO having a DC configuration is maintained and used by the UE when the CPC procedure is performed.

6. providing the second CHO having a DC configuration to the UE; Instructing the UE to maintain the second CHO with a DC configuration after the CPC procedure is performed; The method of claim 5 further comprising:

7. A source master node in a wireless network, comprising: a processor; a memory coupled to the processor, the memory configured to store program code executable by the processor; Equipped with The program code includes one or more instructions that cause the source master node to: receiving, from a target MN, a CHO having a DC configuration including a unique identifier of a UE defined between a source master node and the target SN and a secondary cell group (SCG) delta configuration config1 of the target SN; Sending an indication to the target MN indicating a CHO with DC configuration, a unique identifier of the UE, and a configured CPC procedure after sending an identifier of the target SN; receiving a handover request update message from the target MN, the handover request update message including a second CHO having a DC configuration; The source master node.

8. The program code may comprise one or more further instructions, which cause the source master node to: updating the existing CHO having the DC configuration with the second CHO having the DC configuration; The source master node of claim 7.

9. The program code may comprise one or more further instructions, which cause the source master node to: transmitting a second CHO having the DC configuration to the UE; Instructing the UE to maintain a second CHO having the DC configuration after the CPC procedure is performed; to carry out A source master node according to claim 7 or 8.

10. The program code may comprise one or more further instructions, which cause the source master node to: transmitting to the UE a CHO condition ID associated with a second CHO having the DC configuration; The source master node of claim 9.

11. A user equipment (UE), a processor; a memory coupled to the processor, the memory configured to store program code executable by the processor; Equipped with The program code includes one or more instructions that cause the UE to: receiving a second CHO having a DC configuration from a source MN; maintaining the second CHO with a DC configuration after the CPC procedure has been performed; A user equipment (UE) that causes the

12. The program code comprises one or more further instructions, which cause the UE to: receiving from the source MN a CHO Condition ID associated with the second CHO having a DC configuration; The UE of claim 11.

13. 1. A machine-readable storage medium encoding instructions for preparing a handover of a user equipment (UE) in dual connectivity (DC), the handover being between primary cells (PCells) of a source MN and a target MN, and between primary secondary cells (PSCells) between a source secondary node (SN) and a target SN; The instructions are executable by a processor of the target master node, thereby causing the target node to: causing the source MN to send a secondary cell group (SCG) delta configuration config1 of the target SN and a CHO having a DC configuration including a unique identifier of a UE defined between the source master node and the target secondary node; Receive an indication from the source MN indicating a configured CPC procedure after sending a CHO having the DC configuration, a unique identifier of the UE, and an identifier of the target SN; causing the target SN to send a request to prepare a second delta SCG configuration, config2, to be used by the UE when a source MN initiated CPC procedure is performed; Machine-readable storage medium.

14. and further encoding instructions executable by a processor of the target master node, whereby the target master node: a machine-readable storage medium for receiving config2 from the target SN, wherein the second delta SCG configuration is valid when the UE applies the SCG configuration after the CPC procedure is performed; 14. The machine-readable storage medium of claim 13.

15. and further encoding instructions executable by a processor of the target master node, whereby the target master node: generating a second CHO having a DC configuration using the second delta SCG configuration; 15. The machine-readable storage medium according to claim 13 or 14.

Images