Method and apparatus for dual connectivity conditional handover recovery

Abstract

A method and apparatus for dual connectivity conditional handover recovery are presented. A user equipment (UE) is presented that supports dual connectivity and is configured for conditional handover CHO, where the UE is configured to establish a connection to a primary cell of a source master node and a primary secondary cell of a source secondary node. The UE is further configured to receive a plurality of CHOs, receive assistance information for CHO recovery, and determine a primary cell of a target master node and an associated CHO configuration from the plurality of CHO configurations based on the assistance information for CHO recovery. Finally, the UE is configured to perform CHO recovery to the primary cell of the target master node based on the determined associated CHO configuration. Methods, network nodes, and functional units of the network nodes involved in the presented dual connectivity conditional handover recovery process are also presented.

Description

[Technical Field]

[0001] The present disclosure relates generally to wireless communication systems, and more particularly to conditional handover in wireless communication systems. Even more particularly, the present disclosure provides a method and apparatus for dual connectivity conditional handover recovery. [Background technology]

[0002] Wireless telecommunications systems are continually being developed. Higher data rates and higher quality of service are required. The demand for reliability is constantly increasing, and methods and means are continually being developed to ensure reliable connections and data traffic while keeping transmission delays to a minimum.

[0003] Network developments enable new services for customers. One service is dual connectivity, where user equipment connects to a master node base station and a secondary node base station for communication. Dual connectivity improves data throughput and mobility robustness. Another service is conditional handover, which further improves mobility robustness. For conditional handover, the network may prepare multiple target cells, where conditional handover settings are associated with execution conditions that are evaluated by the user equipment. These settings can also be used to recover and re-establish connections in the event of a radio link failure.

[0004] The use of dual connectivity and conditional handover may require advanced techniques for dual connectivity conditional handover recovery. Summary of the Invention

[0005] According to a first aspect of the present disclosure, a user equipment (UE) is presented that is configured to support operation in dual connectivity with a primary cell of a source master node and a primary secondary cell of a source secondary node of a radio access network, and that is configured to support conditional handover (CHO). The user equipment includes at least one processor and at least one memory including computer program code that, when executed by the at least one processor, causes the user equipment to perform the processes described herein. Specifically, the UE is caused to establish a connection to the primary cell of the source master node and to establish a connection to the primary secondary cell of the source secondary node. Furthermore, the UE is caused to receive, from the source master node, a plurality of CHO configurations, including configurations for conditional handover to at least one target master node and at least one target secondary node, and to receive assistance information for CHO recovery from the source master node. In response to the user equipment experiencing a radio link failure in the primary cell of the source master node or experiencing a handover failure to the primary cell of the first target master node, the UE is caused to determine, based on the assistance information for CHO recovery, a primary cell of the second target master node and an associated CHO configuration among the plurality of CHO configurations, and further, perform CHO recovery to the primary cell of the second target master node based on the determined associated CHO configuration.

[0006] In an embodiment, the UE is further caused to perform CHO recovery to the primary secondary cell of the target secondary node in response to the determined CHO configuration being a dual connectivity CHO configuration having a primary secondary cell of the target secondary node different from the primary secondary cell of the source secondary node.

[0007] In some embodiments, the assistance information includes a single-dual connectivity prioritization flag for prioritizing single or dual connectivity for CHO recovery. In further embodiments, the assistance information includes information regarding the amount of pending traffic on secondary cell group bearers, and determining the CHO configuration includes prioritizing the single connectivity CHO configuration in response to the single connectivity CHO configuration having secondary cell group bearers mapped to the respective target master node, and prioritizing the dual connectivity CHO configuration in response to the dual connectivity CHO configuration having secondary cell group bearers mapped to the respective target secondary node.

[0008] In some embodiments, the assistance information indicates a preference for a dual connectivity CHO configuration in which a primary secondary cell of the source secondary node is maintained. In further embodiments, the assistance information includes a CHO recovery primary secondary cell selection condition, and determining the CHO configuration includes selecting a CHO configuration having a primary secondary cell that satisfies the primary secondary cell selection condition.

[0009] In an embodiment, determining the CHO configuration includes selecting a single connectivity CHO configuration in response to none of the at least one primary secondary cell satisfying a primary secondary cell selection condition. In some further embodiments, the user equipment is further caused to transmit cell selection information to the second target master node in response to selecting the single connectivity CHO configuration with the second target master node, the cell selection information including an indication that none of the at least one primary secondary cell associated with the second target master node satisfies the primary secondary cell selection condition. In some still other embodiments, the cell selection information further includes measurements related to at least one primary secondary cell associated with the second target master node.

[0010] In some embodiments, the cell selection information further includes measurements related to further cells performed by the user equipment. In further embodiments, the assistance information includes a single-dual connectivity indicator indicating whether the respective CHO configuration is a single or dual connectivity configuration. In embodiments, the assistance information includes a primary secondary cell identifier indicating which primary secondary cell is included in the respective CHO configuration.

[0011] According to a second aspect of the present disclosure, there is presented a source master node (source MN) configured to support establishment of a connection to a user equipment, where the user equipment supports operation in dual connectivity with a primary cell of the source master node and a primary secondary cell of a source secondary node, and configured to support conditional handover (CHO). The source MN comprises at least one processor and at least one memory including computer program code, which, when executed by the at least one processor, causes the source MN to perform the processes described herein. Specifically, the source MN is caused to transmit to the user equipment a plurality of CHO configurations, including configurations for conditional handover to at least one target master node and at least one target secondary node, and to transmit assistance information for CHO recovery to the user equipment, where the assistance information is used by the user equipment to determine a CHO configuration from the plurality of CHO configurations for CHO recovery.

[0012] In embodiments, the assistance information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery. In some embodiments, the single-dual connectivity preference flag is determined based on the amount of pending traffic on the secondary cell group bearers, to prioritize a single connectivity CHO configuration in response to the single connectivity CHO configuration having secondary cell group bearers mapped to the respective target master node, and to prioritize a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having secondary cell group bearers mapped to the respective target secondary node.

[0013] In some embodiments, the assistance information indicates that a dual connectivity CHO configuration in which a primary secondary cell of the source secondary node is maintained is preferred. In some embodiments, the assistance information includes a primary secondary cell selection condition for determining a CHO configuration having a primary secondary cell that satisfies the CHO recovery primary secondary cell selection condition. In further embodiments, the assistance information includes a single-dual connectivity indicator that indicates whether the respective CHO configuration is a single or dual connectivity configuration. In yet other embodiments, the assistance information includes a primary secondary cell identifier that indicates which primary secondary cell is included in the respective CHO configuration.

[0014] According to a third aspect of the present disclosure, there is provided a network node supporting at least one of a central unit control plane function of a radio access network or a Layer 3 protocol, the network node operating in dual connectivity with a primary cell of the network node and a primary secondary cell of a source secondary node, and configured to support connection with a user equipment configured for conditional handover (CHO). The network node comprises at least one processor and at least one memory including computer program code that, when executed by the at least one processor, causes the network node to perform the processes described herein. Specifically, the network node is caused to: generate a radio resource control (RRC) message including assistance information for CHO recovery; and transmit the RRC message including the assistance information to the user equipment, the assistance information being used by the user equipment to determine a CHO configuration from multiple CHO configurations including configurations for conditional handover to at least one target master node and at least one target secondary node for CHO recovery.

[0015] In embodiments, the assistance information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery. In some embodiments, the single-dual connectivity preference flag is determined based on the amount of pending traffic on the secondary cell group bearers, to prioritize a single connectivity CHO configuration in response to the single connectivity CHO configuration having secondary cell group bearers mapped to the respective target master node, and to prioritize a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having secondary cell group bearers mapped to the respective target secondary node.

[0016] In some embodiments, the assistance information indicates that a dual connectivity CHO configuration in which a primary secondary cell of the source secondary node is maintained is preferred. In some embodiments, the assistance information includes a primary secondary cell selection condition for determining a CHO configuration having a primary secondary cell that satisfies the CHO recovery primary secondary cell selection condition. In further embodiments, the assistance information includes a single-dual connectivity indicator that indicates whether the respective CHO configuration is a single or dual connectivity configuration. In yet other embodiments, the assistance information includes a primary secondary cell identifier that indicates which primary secondary cell is included in the respective CHO configuration.

[0017] According to a fourth aspect of the present disclosure, a method for conditional handover CHO recovery performed by a user equipment configured to operate in dual connectivity within at least one radio access network (RAN) is presented. The method includes: establishing a connection to a primary cell of a source master node; establishing a connection to a primary secondary cell of a source secondary node; receiving from the source master node a plurality of CHO configurations including configurations for conditional handover to at least one target master node and at least one target secondary node; and receiving assistance information for CHO recovery from the source master node. In response to the user equipment experiencing a radio link failure in the primary cell of the source master node or a handover failure to the primary cell of the first target master node, the method further includes determining a primary cell of a second target master node and an associated CHO configuration among the plurality of CHO configurations based on the assistance information for CHO recovery, and performing CHO recovery to the primary cell of the second target master node based on the determined associated CHO configuration.

[0018] In an embodiment, the method further includes, in response to the determined CHO configuration being a dual connectivity CHO configuration having a primary secondary cell of the target secondary node that is different from the primary secondary cell of the source secondary node, performing CHO recovery to the primary secondary cell of the target secondary node.

[0019] In some embodiments, the assistance information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery. In further embodiments, the assistance information includes information regarding the amount of pending traffic on secondary cell group bearers, and determining the CHO configuration includes prioritizing the single connectivity CHO configuration in response to the single connectivity CHO configuration having secondary cell group bearers mapped to the respective target master node, and prioritizing the dual connectivity CHO configuration in response to the dual connectivity CHO configuration having secondary cell group bearers mapped to the respective target secondary node.

[0020] In some embodiments, the assistance information indicates a preference for a dual connectivity CHO configuration in which a primary secondary cell of the source secondary node is maintained. In further embodiments, the assistance information includes a CHO recovery primary secondary cell selection condition, and determining the CHO configuration includes selecting a CHO configuration having a primary secondary cell that satisfies the primary secondary cell selection condition.

[0021] In an embodiment, determining the CHO configuration includes selecting a single connectivity CHO configuration in response to none of the at least one primary secondary cell satisfying a primary secondary cell selection condition. In some further embodiments, the user equipment is further caused to transmit cell selection information to the second target master node in response to selecting the single connectivity CHO configuration with the second target master node, the cell selection information including an indication that none of the at least one primary secondary cell associated with the second target master node satisfies the primary secondary cell selection condition. In some still other embodiments, the cell selection information further includes measurements related to at least one primary secondary cell associated with the second target master node.

[0022] In some embodiments, the cell selection information further includes measurements related to further cells performed by the user equipment. In further embodiments, the assistance information includes a single-dual connectivity indicator indicating whether the respective CHO configuration is a single or dual connectivity configuration. In embodiments, the assistance information includes a primary secondary cell identifier indicating which primary secondary cell is included in the respective CHO configuration.

[0023] According to a fifth aspect of the present disclosure, a method for conditional handover CHO recovery performed by a source master node connected to user equipment, where the user equipment operates in dual connectivity with a primary cell of the source master node and a primary secondary cell of a source secondary node, is presented. The method includes: transmitting, to the user equipment, a plurality of CHO configurations, each including a configuration for conditional handover to at least one target master node and at least one target secondary node; and transmitting, to the user equipment, assistance information for CHO recovery, where the assistance information is used by the user equipment to determine a CHO configuration from the plurality of CHO configurations for CHO recovery.

[0024] In embodiments, the assistance information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery. In some embodiments, the single-dual connectivity preference flag is determined based on the amount of pending traffic on the secondary cell group bearers, to prioritize a single connectivity CHO configuration in response to the single connectivity CHO configuration having secondary cell group bearers mapped to the respective target master node, and to prioritize a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having secondary cell group bearers mapped to the respective target secondary node.

[0025] In some embodiments, the assistance information indicates that a dual connectivity CHO configuration in which a primary secondary cell of the source secondary node is maintained is preferred. In some embodiments, the assistance information includes a primary secondary cell selection condition for determining a CHO configuration having a primary secondary cell that satisfies the CHO recovery primary secondary cell selection condition. In further embodiments, the assistance information includes a single-dual connectivity indicator that indicates whether the respective CHO configuration is a single or dual connectivity configuration. In yet other embodiments, the assistance information includes a primary secondary cell identifier that indicates which primary secondary cell is included in the respective CHO configuration.

[0026] The above aspects and features may be implemented in systems, apparatus, methods, articles, and non-transitory computer-readable media, depending on the desired configuration. The present disclosure may be implemented in and used with many types of devices, including, but not limited to, mobile phones, tablet computers, wearable computing devices, portable media players, and any of a variety of other computing devices.

[0027] This summary is intended to provide a brief overview of some of the aspects and features according to the present disclosure. It should therefore be understood that the above features are merely examples and should not be construed as narrowing the scope of the present disclosure in any way. Other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description, drawings, and claims.

[0028] List of Abbreviations In this disclosure, the following abbreviations are used and should be understood in accordance with the definitions provided: 3GPP 3rd Generation Partnership Project 5G 5th Generation (Mobile Communication Network) 5GC 5G Core Network NG-RAN Next Generation Radio Access Network NR New radio, 5G LTE Long Term Evolution, 4G BS base station UE User Equipment HO Handover CHO Conditional Handover DC Dual Connectivity gNB gNodeB(NR) eNB eNodeB(LTE) SCG Secondary Cell Group MCG Master Cell Group PCell Primary Cell PSCell Primary Secondary Cell MN Master / Main Node SN Secondary Node RRC Radio Resource Control Reconfiguration SRB Signaling Radio Bearer gNB-CU-CP gNodeB Central Unit Control Plane gNB-CU-UP gNodeB Central Unit User Plane gNB-DU gNodeB Distributed Unit CPC Conditional PSCell Change

[0029] The present disclosure can be better understood when considered in conjunction with the following detailed description of various embodiments in conjunction with the following drawings. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram of an exemplary communication system including a base station and multiple communication devices. [Figure 2] 1 is a schematic diagram of an exemplary mobile communication device. [Figure 3] FIG. 2 is a schematic diagram of an exemplary control device. [Figure 4A] FIG. 1 illustrates the NG-RAN architecture. [Figure 4B]FIG. 1 illustrates the NG-RAN architecture. [Figure 5] 1 is a flowchart of a dual connectivity conditional handover recovery performed by a user equipment. [Figure 6] 10 is a flowchart of dual connectivity conditional handover recovery performed by a source master node. [Figure 7] 1 is a flowchart of a dual connectivity conditional handover recovery performed by a network node supporting Layer 3 functionality. [Figure 8] FIG. 10 is a message flow diagram of an example overall dual connectivity conditional handover recovery. [Figure 9] FIG. 10 is another message flow diagram of an example overall dual connectivity conditional handover recovery. [Figure 10] 1 is a flow chart of one embodiment of overall dual connectivity conditional handover recovery. DETAILED DESCRIPTION OF THE INVENTION

[0031] Before describing the examples in detail, certain general principles of wireless communication systems and mobile communication devices will be briefly described with reference to Figures 1-3 to aid in understanding the technology underlying the examples described.

[0032] In a wireless communication system 100 as shown in FIG. 1, mobile communication devices, user devices, or user equipment (UE) 102, 104, 105 are provided with wireless access via at least one base station (e.g., a next generation NB, gNB), similar wireless transmitting and / or receiving node, or network node. The base station may be controlled or assisted by at least one suitable controller apparatus to enable operation of the base station and management of mobile communication devices communicating with the base station. The controller apparatus may be located in a Radio Access Network (RAN) (e.g., the wireless communication system 100) or a Core Network (CN) (not shown) and may be implemented as one central apparatus or its functionality may be distributed among several apparatuses. The controller apparatus may be part of a base station and / or may be provided by a separate entity, such as a Radio Network Controller (RNC). In FIG. 1, controllers 108 and 109 are shown for controlling macro-level base stations 106 and 107, respectively. The base station controllers may be interconnected with other control entities. The controller is typically provided with memory capacity and at least one data processor. The controls and functionality may be distributed across multiple control units, and in some systems the controls may additionally or alternatively be located within the RNC.

[0033] In Figure 1, base stations 106 and 107 are shown as connected to a wider communications network 113 via a gateway 112. Further gateway functions may be provided for connecting to other networks.

[0034] As used herein, the term “base station” has the full scope of its ordinary meaning and includes at least a wireless communication station installed at a fixed location and used to communicate as part of a wireless telephone or radio system. The communication area (or coverage area) of a base station may be referred to as a “cell.” The base station and UE may be configured to communicate over a transmission medium using any of a variety of radio access technologies (RATs), also referred to as wireless communication technologies, or telecommunications standards described below. As shown in FIG. 1, one of the base stations serves as a “serving cell” to the UE, and the UE may also be able to receive signals from (possibly within communication range of) one or more other cells, which may be referred to as “neighboring cells” (which may be provided by the base station and / or any other base stations).

[0035] Smaller base stations 116, 118, and 120 may also be connected to network 113, for example, by a separate gateway function and / or through a controller of a macro-level station. Base stations 116, 118, and 120 may be pico-level or femto-level base stations, etc. In this example, stations 116 and 118 are connected through gateway 111, and station 120 is connected through controller device 108. In some embodiments, smaller stations may not be provided. Smaller base stations 116, 118, and 120 may be part of a second network, for example, a wireless local area network (WLAN), and may be WLAN access points (APs). Communication devices 102, 104, 105 may access the communication system based on various access technologies, such as code division multiple access (CDMA) or wideband CDMA (WCDMA). Other non-limiting examples include Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and variations thereof, such as Interleaved Frequency Division Multiple Access (IFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), and Orthogonal Frequency Division Multiple Access (OFDMA), as well as Space Division Multiple Access (SDMA).

[0036] An example of a wireless communication system is the architecture standardized by the 3rd Generation Partnership Project (3GPP). The latest 3GPP-based development is often referred to as Long Term Evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio access technology. The various development stages of the 3GPP standard are called releases. More recent developments of LTE are often referred to as LTE-Advanced (LTE-A). LTE (or LTE-A) uses a radio mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a core network known as the Evolved Packet Core (EPC). The base station in such a system is known as the evolved or enhanced Node B (eNB) and provides E-UTRAN functions such as packet data convergence, radio link control, medium access control, and physical layer protocols (PDCP / RLC / MAC / PHY) in the user plane and Radio Resource Control (RRC) protocol termination in the control plane for communication devices. Other examples of wireless access systems are those provided by base stations in systems based on technologies such as WLAN and / or Worldwide interoperability for Microwave access (WiMax). A base station can provide coverage throughout a cell or similar wireless service area. Core network elements include a Mobility Management Entity (MME), a Serving Gateway (S-GW), and a Packet Gateway (P-GW).

[0037] An example of a suitable communication system is the 5G or NR concept. The network architecture of NR may be similar to LTE-A. Base stations in NR systems may also be known as next-generation Node Bs (gNBs). Changes to the network architecture may depend on the need to support various radio technologies and more granular Quality of Service (QoS) support, as well as on-demand requirements for QoS levels to support user-perspective Quality of Experience (QoE). Network-aware services and applications, as well as service- and application-enabled networks, may also bring about changes to the architecture. These are related to information-centric network (ICN) and user-centric content delivery network (UC-CDN) approaches. NR may use multiple input-multiple output (MIMO) antennas, many more base stations or nodes than LTE (the so-called small cell concept), including macro sites operating in conjunction with smaller stations and potentially using various radio technologies for better coverage and enhanced data rates.

[0038] Future networks may utilize Network Functions Virtualization (NFV), a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that can be operatively connected or linked together to provide services. A Virtualized Network Function (VNF) may include one or more virtual machines that run computer program code using standard or generic types of servers instead of customized hardware. Cloud computing or data storage may also be utilized. In wireless communications, this may mean that node operations are performed at least in part on a server, host, or node operatively coupled to a remote radio head. It is also possible that node operations may be distributed across multiple servers, nodes, or hosts. It should also be understood that the division of labor between core network operations and base station operations may differ from LTE and may even not exist.

[0039] An exemplary 5G Core Network (CN) includes functional entities. The CN is connected to the UE via a Radio Access Network (RAN). A User Plane Function (UPF) with a role called PDU Session Anchor (PSA) may be responsible for forwarding frames between the Data Network (DN) and a tunnel established over 5G for the UE that exchanges traffic with the DN.

[0040] The UPF is controlled by a Session Management Function (SMF), which receives policies from a Policy Control Function (PCF). The CN may also include an Access and Mobility Function (AMF).

[0041] A possible (mobile) communication device 200 will now be described in more detail with reference to FIG. 2 , which shows a schematic, partial cross-sectional view. Such a mobile communication device 200 is often referred to as user equipment (UE), user device, or terminal device. A suitable mobile communication device 200 may be provided by any device capable of transmitting and receiving radio signals. Non-limiting examples include a mobile station (MS) or mobile device, such as what is known as a mobile phone or smartphone, a computer equipped with a wireless interface card or other wireless interface facilities (such as a USB dongle), a personal data assistant (PDA) or tablet equipped with wireless communication capabilities, or any combination thereof. The communication device 200 may provide data communication, for example, to carry voice, electronic mail (e-mail), text messages, multimedia, and other communications. Various services may thereby be offered and provided to users via their communication device. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services, or simply access to a data communication network system such as the Internet. Broadcast or multicast data may also be provided to users. Non-limiting examples of content include downloads, television and radio programs, videos, advertisements, various alerts, and other information.

[0042] In industrial applications, the communication device may be a modem integrated into an industrial actuator (such as a robotic arm) and / or a modem acting as an Ethernet hub that serves as a connection point for one or several connected Ethernet devices (this connection may be wired or non-wired).

[0043] Communications device 200 is typically provided with at least one data processing entity 201, at least one memory 202, and possible other components 203 for use in software- and hardware-assisted execution of the tasks it is designed to perform, including controlling access to and communication with access systems and other communications devices. Data processing, storage, and other related controls may be provided on a suitable circuit board and / or within a chipset 204. A user may control the operation of communications device 200 using a suitable user interface, such as a keypad 205, voice commands, a touch-sensitive screen or pad, or a combination thereof. A display 208, a speaker, and a microphone may also be provided. Additionally, communications device 200 may include suitable connectors (wired or wireless) to other devices and / or for connecting external accessories, such as hands-free equipment.

[0044] The communication device 200 may receive signals over the air or wireless interface 207 via suitable receiving equipment and may transmit signals via suitable wireless signal transmitting equipment. In Figure 2, a transceiver unit is shown schematically by block 206. The transceiver unit 206 may be provided, for example, by a radio section and associated antenna equipment. The antenna equipment may be located inside or outside the communication device 200.

[0045] Additionally or alternatively, communications device 200 may be configured to communicate using one or more global navigation satellite systems (GNSS, such as GPS or GLONASS), one or more mobile television broadcast standards (such as ATSC-M / H or DVB-H), and / or any other wireless communications protocol, as desired. Other combinations of wireless communications standards (including two or more wireless communications standards) are possible.

[0046] 2 includes a set of components configured to perform core functions. For example, the set of components may be implemented as a system-on-chip (SoC) that may include portions for various purposes. Alternatively, the set of components may be implemented as individual components or groups of components for various purposes. The set of components may be communicatively coupled (e.g., directly or indirectly) to various other circuits of the communications device 200.

[0047] The communications device 200 may include at least one antenna in communication with a transmitter and a receiver (e.g., transceiver unit 206). Alternatively, the transmit and receive antennas may be separate. The communications device 200 may also include a processor (e.g., at least one data processing entity 201) configured to provide signals to the transmitter, receive signals from the receiver, and control functionality of the communications device 200. The processor may be configured to control functionality of the transmitter and receiver by generating control signaling via electrical leads to the transmitter and receiver. Similarly, the processor may be configured to control other elements of the communications device 200 by generating control signaling via electrical leads connecting the processor to other elements, such as a display (e.g., display 208) or memory (e.g., at least one memory 202). A processor may be embodied in various ways, such as, for example, a circuit, at least one processing core, one or more microprocessors with associated digital signal processors, one or more processors without associated digital signal processors, one or more coprocessors, one or more multi-core processors, one or more controllers, processing circuitry, one or more computers, various other processing elements including integrated circuits such as application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and / or the like, or combinations thereof. Thus, in some examples, a processor may include multiple processors or processing cores.

[0048] The communications device 200 may be operable with one or more air interface standards, communications protocols, modulation types, access types, and / or the like. Signals transmitted and received by the processor may include signaling information in accordance with applicable cellular system air interface standards and / or various wired or wireless network technologies, including, but not limited to, Wi-Fi, WLAN technologies, e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11, 802.16, 802.3, ADSL, DOCSIS, and / or the like. Additionally, these signals may include voice data, user-generated data, user-requested data, and / or the like.

[0049] For example, communication device 200 and / or the cellular modem therein may be capable of operating in accordance with various third-generation (3G), fourth-generation (4G), fifth-generation (5G), Internet Protocol Multimedia Subsystem (IMS) communication protocols, e.g., Session Initiation Protocol (SIP), and / or the like, or 5G or later. For example, communication device 200 may be capable of operating in accordance with 4G wireless communication protocols, e.g., LTE-A, 5G, and / or the like, as well as similar wireless communication protocols that may be developed in the future.

[0050] It is understood that the processor may include circuitry for implementing audio / video and logic functions of communication device 200. For example, the processor may include a digital signal processor device, a microprocessor device, an analog-to-digital converter, a digital-to-analog converter, and / or the like. Control and signal processing functions of communication device 200 may be allocated among these devices according to their respective capabilities. The processor may further include an internal audio coder, an internal data modem, and / or the like. Furthermore, the processor may include functionality for operating one or more software programs, which may be stored in memory. Generally, the processor and the stored software instructions may be configured to cause communication device 200 to perform actions. For example, the processor may be capable of operating a connectivity program, such as a web browser. The connectivity program may enable communication device 200 to send and receive web content, such as location-based content, according to protocols such as Wireless Application Protocol (WAP), Hypertext Transfer Protocol (HTTP), and / or the like.

[0051] Communications device 200 may also include a user interface, including, for example, an earpiece or speaker, a ringer, a microphone, a display, a user input interface, and / or the like, which may be operably coupled to the processor. The display may include a touch-sensitive display as described above, allowing a user to make selections, input values, and / or the like by touch and / or gestures. The processor may also include user interface circuitry configured to control at least some functionality of one or more elements of the user interface, such as the speaker, ringer, microphone, display, and / or the like. The processor and / or user interface circuitry including the processor may be configured to control one or more functions of one or more elements of the user interface through computer program instructions, such as software and / or firmware, stored in processor-accessible memory, such as volatile memory, non-volatile memory, and / or the like. Communications device 200 may include a battery for powering various circuits associated with the mobile terminal, such as, for example, circuitry for providing mechanical vibration as a detectable output. The user input interface may include devices that allow the communication device 200 to receive data, such as a keypad (e.g., keypad 206) and / or other input devices. The keypad may be a virtual keyboard displayed on a display or an externally coupled keyboard.

[0052] The communication device 200 may also include one or more mechanisms for sharing and / or obtaining data. For example, the communication device 200 may include a short-range radio frequency (RF) transceiver and / or interrogator, and data may be shared with and / or obtained from electronic devices according to RF technology. The communication device 200 may include other short-range transceivers, such as, for example, an infrared (IR) transceiver, a Bluetooth™ (BT) transceiver operating using Bluetooth™ wireless technology, a wireless universal serial bus (USB) transceiver, a Bluetooth™ low energy transceiver, a ZigBee transceiver, an ANT transceiver, a cellular device-to-device transceiver, a wireless local area link transceiver, and / or any other short-range wireless technology. The communication device 200, and more particularly, the short-range transceiver, may be capable of transmitting and / or receiving data to and from electronic devices in the vicinity of the device, such as within 10 meters. The communication device 200, which includes a Wi-Fi or WLAN modem, may also be capable of transmitting and / or receiving data to and from electronic devices according to various wireless network technologies, including 6LoWPAN, Wi-Fi, Wi-Fi low power, WLAN technologies, e.g., IEEE802.11 technologies, IEEE802.15 technologies, IEEE802.16 technologies, and / or the like.

[0053] Communications device 200 may include memory, such as one or more Subscriber Identity Modules (SIMs), one or more Universal Subscriber Identity Modules (USIMs), one or more Removable User Identity Modules (R-UIMs), one or more Embedded Universal Integrated Circuit Cards (eUICCs), one or more Universal Integrated Circuit Cards (UICCs), and / or the like, that may store information elements related to mobile subscribers. Additionally, communications device 200 may include other removable and / or fixed memory. Communications device 200 may include volatile and / or non-volatile memory. For example, volatile memory may include random access memory (RAM), e.g., dynamic RAM and / or static RAM, on-chip or off-chip cache memory, and / or the like. Non-volatile memory, which may be embedded and / or removable, may include, for example, read-only memory, flash memory, magnetic storage devices such as hard disks, floppy disk drives, magnetic tapes, optical disk drives and / or media, non-volatile random-access memory (NVRAM), and / or the like. Like volatile memory, non-volatile memory may include a cache area for temporarily storing data. At least a portion of the volatile and / or non-volatile memory may be embedded in the processor. The memory may store one or more software programs, instructions, information, data, and / or the like that may be used by the device to perform the operations disclosed herein.

[0054] The memory may include an identifier, such as an International Mobile Equipment Identification (IMEI) code, that can uniquely identify communication device 200. In an exemplary embodiment, the processor may be configured using computer code stored in the memory to cause the processor to perform the operations disclosed herein.

[0055] Some of the embodiments disclosed herein may be implemented in software, hardware, application logic, or a combination of software, hardware, and application logic. The software, application logic, and / or hardware may reside, for example, on memory, a processor, or electronic components. In some exemplary embodiments, the application logic, software, or instruction set is maintained on any one of a variety of conventional computer-readable media. In the context of this document, a "computer-readable medium" may be any non-transitory medium that can contain, store, communicate, propagate, or transfer instructions used by or in connection with an instruction execution system, apparatus, or device, such as a computer or data processor circuitry; in the example shown in FIG. 2, the computer-readable medium may include a non-transitory computer-readable storage medium, which may be any medium that can contain or store instructions used by or in connection with an instruction execution system, apparatus, or device, such as a computer.

[0056] In some embodiments, communications device 200 (i.e., a UE or user device in a network) includes a processor (e.g., at least one data processing entity 201) and memory (e.g., at least one memory 202). The memory includes computer program code that causes communications device 200 to perform processing according to the methods described below with reference to FIG.

[0057] FIG. 3 illustrates an exemplary embodiment of a controller for a communications system coupled to and / or controlling, for example, a base station, a station of an access system such as a RAN node such as an eNB or gNB, a relay node, a core network node such as an MME, an S-GW, or a P-GW, a core network function such as an AMF / SMF, a server, or a host. The controller may be incorporated into a single controller, or may be incorporated into two or more controllers. The controller may be integrated into a core network or RAN node or module, or may be external thereto. In some embodiments, a base station includes a separate controller unit or module. In other embodiments, the controller may be another network element, such as an RNC or a spectrum controller. In some embodiments, a base station may have such a controller in addition to a controller provided in an RNC. The controller 300 may be configured to provide control of communications within a service area of ​​the system. The controller 300 includes at least one memory 301, at least one data processing unit 302, 303, and an input / output interface 304. The controller 300 may be coupled to a receiver and a transmitter of the base station via an interface. The receiver and / or transmitter may be implemented as a radio front end or a remote radio head.

[0058] Generally, the control device 300 has an antenna for transmitting and receiving radio signals. A radio frequency (RF) transceiver module coupled to the antenna receives RF signals from the antenna, converts them into baseband signals, and transmits them to a processor (e.g., at least one data processing unit 302, 303). The RF transceiver also converts the baseband signals received from the processor, converts them into RF signals, and transmits them to the antenna. The processor processes the received baseband signals and invokes various function modules to perform functions within the control device 300. A memory (e.g., at least one memory 301) stores program instructions and data for controlling the operation of the control device 300. In the example of FIG. 3, the control device 300 also includes a protocol stack and a set of control function modules and circuits. A PDU session processing circuit processes PDU session establishment and modification procedures. A policy control module configures policy rules for the UE. A configuration and control circuit provides various parameters for related functions, including mobility management and session management, for configuring and controlling the UE. Suitable processors include, for example, special purpose processors, digital signal processors (DSPs), multiple microprocessors, one or more microprocessors associated with a DSP core, controllers, microcontrollers, ASICs, FPGA circuits, and other types of integrated circuits (ICs), and / or state machines.

[0059] In some embodiments, the controller 300 (i.e., a base station, a wireless transmitting and / or receiving point device, or a network node in a network) includes a processor (e.g., at least one data processing unit 302, 303) and a memory (e.g., at least one memory 301). The memory includes computer program code that causes the controller 300 to perform processing according to the methods described below with reference to FIG.

[0060] 4A and 4B illustrate a next-generation radio access network (NG-RAN) architecture 400 having a gNB 402 compliant with 3GPP TS38.401 V17.0.0. The gNB 402 serves UEs using NR user / control plane protocols and is connected to a 5GC 401 via an NG interface and to other gNBs 402 via an Xn interface. The gNB 402 in FIG. 4A includes a central unit (i.e., gNB-CU) 403 and one or more distributed units (i.e., gNB-DUs) 404. The gNB-CU is a logical node that hosts the RRC, SDAP, and PDCP protocols of a gNB or the RRC and PDCP protocols of an en-gNB, controlling the operation of one or more gNB-DUs 404. The gNB-CU 403 terminates the F1 interface connected to the gNB-DUs 404. The dNB-DU 404 is a logical node that hosts the RLC, MAC, and PHY layers of the gNB 402 or en-gNB, and its operation is partially controlled by the gNB-CU 403. One gNB-DU 404 supports one or more cells. One cell is supported by one gNB-DU 404. The gNB-DU 404 terminates the F1 interface connected to the gNB-CU 403.

[0061] One gNB-DU 404 is connected to one gNB-CU 403 via an F1 interface. NG, Xn, and F1 are logical interfaces. The Xn-C interface interconnects the gNB-CUs 403 of different gNBs 402. A gNB 402 may also include a gNB-CU control plane (gNB-CU-CP), multiple gNB-CU user planes (gNB-CU-UP), and multiple gNB-DUs, which are shown in more detail in Figure 4B.

[0062] Note that the NG-RAN may also include a set of ng-eNBs, which may include an ng-eNB-CU and one or more ng-eNB-DUs, which are connected via a W1 interface.

[0063] Figure 4B shows an architecture that separates the control plane and user plane of the gNB-CU 403 (i.e., the gNB-CU-CP and gNB-CU-UP). The gNB-CU-CP 405 is a logical node that hosts the control plane portion of the RRC and PDCP protocols of the gNB-CU 403 of the en-gNB or gNB 402. The gNB-CU-CP 405 terminates the E1 interface connected to the gNB-CU-UP 406 and the F1-C interface connected to the gNB-DU 404. The gNB-CU-UP 406 is a logical node that hosts the user plane portion of the PDCP protocol of the gNB-CU 403 of the en-gNB and the user plane portion of the PDCP protocol and the SDAP protocol of the gNB-CU 403 of the gNB 402. The gNB-CU-UP 406 terminates the E1 interface connected to the gNB-CU-CP 405 and the F1-U interface connected to the gNB-DU 404. The gNB-CU-UP406 is connected to one gNB-CU-CP405, multiple gNB-CU-UP406s, and multiple gNB-DU404s under the control of the same gNB-CU-CP405.

[0064] In some embodiments, the gNB-CU-CP 405 is associated with a processor and memory including computer program code that causes a gNB supporting the functionality of the gNB-CU-CP 405 to perform processing in accordance with the methods described below with reference to FIG.

[0065] The following description may provide further details of alternatives, modifications, and variations, and the gNB may include a node that provides NR user plane and control plane protocol termination to the UE and is connected to the 5GC via an NG interface, for example, in accordance with 3GPP TS38.300 V17.0.0, which is incorporated herein by reference.

[0066] The gNB central unit (gNB-CU) includes, for example, a logical node that hosts the RRC, SDAP, and PDCP protocols of a gNB or the RRC and PDCP protocols of an en-gNB, controlling the operation of one or more gNB-DUs. The gNB-CU terminates the F1 interface connected to the gNB-DU. The gNB distributed unit (gNB-DU) includes, for example, a logical node that hosts the RLC, MAC, and PHY layers of a gNB or en-gNB, and its operation is partially controlled by the gNB-CU. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU.

[0067] The gNB-CU control plane (gNB-CU-CP) includes, for example, logical nodes that host the control plane portions of the RRC and PDCP protocols of the en-gNB or the gNB-CU of the gNB. The gNB-CU-CP terminates the E1 interface connected to the gNB-CU-UP and the F1-C interface connected to the gNB-DU. The gNB-CU-user plane (gNB-CU-UP) includes, for example, logical nodes that host the user plane portion of the PDCP protocol of the gNB-CU of the en-gNB and the user plane portion of the PDCP protocol and the SDAP protocol of the gNB-CU of the gNB. The gNB-CU-UP terminates, for example, the E1 interface connected to the gNB-CU-CP and the F1-U interface connected to the gNB-DU in accordance with 3GPP TS38.401 V17.0.0, Section 3.1, which is incorporated herein by reference.

[0068] Various functional divisions, referred to as options, are possible between the central unit and the distributed units. In option 1 (1A-like division), the functional division resembles the 1A architecture of DC. RRC is located in the central unit. PDCP, RLC, MAC, physical layer, and RF are located in the distributed units. In option 2 (3C-like division), the functional division resembles the 3C architecture of DC. RRC and PDCP are located in the central unit. RLC, MAC, physical layer, and RF are located in the distributed units. In option 3 (intra-RLC division), low RLC (subfunctions of RLC), MAC, physical layer, and RF are located in the distributed units. PDCP and high RLC (other subfunctions of RLC) are located in the central unit. In option 4 (RLC-MAC division), MAC, physical layer, and RF are located in the distributed units. PDCP and RLC are located in the central unit. Alternatively, for example, according to Section 11 of 3GPP TR38.801 V14.0.0, which is incorporated by reference.

[0069] The gNB supports various protocol layers, including Layer 1 (L1)—the physical layer. NR Layer 2 (L2) is divided into the following sublayers: Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), and Service Data Adaptation Protocol (SDAP). The physical layer may provide transport channels to the MAC sublayer, which may provide logical channels to the RLC sublayer, which may provide RLC channels to the PDCP sublayer, which may provide radio bearers to the SDAP sublayer, and the SDAP sublayer may provide QoS flows to 5GC. Control channels include, for example, BCCH, PCCH, etc. Layer 3 (L3) includes Radio Resource Control (RRC), for example, in accordance with Section 6 of 3GPP TS38.300 V17.0.0, which is incorporated herein by reference.

[0070] A RAN (Radio Access Network) node or network node, e.g., a gNB, a base station, a gNB-CU, or a gNB-DU, or portions thereof, may be implemented using an apparatus having at least one processor and / or at least one memory (containing computer-readable instructions (computer programs)) configured to support and / or provide and / or process, e.g., CU and / or DU related functions and / or features, and / or at least one protocol (sub-)layer of the RAN (Radio Access Network), e.g., Layer 2 and / or Layer 3.

[0071] The gNB-CU and gNB-DU portions may be, for example, co-located or physically separated. The gNB-DU may be further divided, for example, into two portions, for example, a portion including processing equipment and a portion including antennas. The central unit (CU) may also be referred to as a BBU / REC / RCC / C-RAN / V-RAN, O-RAN, or a portion thereof. The distributed unit (DU) may also be referred to as an RRH / RRU / RE / RU, or a portion thereof. The gNB-DU may support one or more cells, thereby functioning, for example, as a serving cell to user equipment (UE).

[0072] User equipment (UE) may include wireless or mobile devices, devices having a radio interface for interacting with a radio access network (RAN), smartphones, automotive devices, IoT devices, M2M devices, etc. Such UEs or devices may include at least one processor and at least one memory containing computer program code configured by the at least one processor to cause the device to perform certain operations, such as an RRC connection to the RAN. The UE is configured, for example, to generate messages (e.g., including a cell ID) to be transmitted over the air toward the RAN (e.g., to reach and communicate with a serving cell). The UE may generate and transmit and receive RRC messages, including one or more RRC packet data units (PDUs).

[0073] A UE may have different states (e.g., according to 3GPP TS38.331 V17.0.0, sections 4.2.1 and 4.4, which are incorporated herein by reference). For example, when an RRC connection is established, the UE is in either an RRC_CONNECTED state or an RRC_INACTIVE state. In the RRC_CONNECTED state, the UE may store AS context, transfer unicast data to and from the UE, monitor a control channel associated with the shared data channel to determine whether data is scheduled on the data channel, provide channel quality and feedback information, and / or perform neighbor cell measurements and measurement reporting. The RRC protocol includes, for example, the following main functions: RRC connection control, measurement configuration and reporting, establishment / modification / release of measurement configuration (e.g., intra-frequency, inter-frequency, and inter-RAT measurements), setup and release of measurement gaps, and / or measurement reporting.

[0074] Before describing dual connectivity conditional handover recovery according to some embodiments of the present disclosure with reference to FIGS. 5-8, background information and aspects related to the present disclosure are provided.

[0075] For example, the present disclosure may be incorporated into a network that supports dual connectivity (DC) and conditional handover (CHO). The CHO procedure was introduced in 3GPP Rel. 16 to improve mobility robustness. For CHO, the network may prepare multiple target cells associated with CHO execution conditions for conditional handover reconfiguration, which are evaluated by the UE. The CHO execution conditions refer to a measurement ID (which associates measurement objects with a reporting configuration) configured by the source gNB. The reporting configuration defines a measurement event (e.g., measurement event A3 or A5 defined in the 3GPP standard) that triggers CHO execution. Each time the CHO execution condition is met, a corresponding target CHO configuration is selected, and handover is performed toward the selected target cell.

[0076] In CHO, the UE is served by the primary cell (PCell) of the source master node (MN) and the primary secondary cell (PSCell) of the source secondary node (SN). The UE sends a measurement report to its serving PCell to initiate CHO preparation for the PCell in the target MN. The source PCell prepares the target PCell and sends CHO preparation, i.e., CHO configuration for the target PCell and / or target PSCell, along with the CHO execution condition, to the UE in an RRC reconfiguration message. When the CHO execution condition for one of the target PCells is met, the UE disconnects from the source PCell, i.e., stops TX / RX with the source PCell. The UE initiates a random access procedure to the target PCell. Upon successful completion of the random access procedure, the target PCell of the target MN notifies the source PCell of the source MN that the handover procedure has been successfully completed. Upon receiving a handover success indication from the target MN, the source PCell in the source MN initiates data forwarding to the target PCell of the target MN. After the data forwarding procedure is completed, the UE continues data transmission / reception with the network.

[0077] However, even with CHO, the UE's radio link quality may degrade for a given period of time. Currently, the UE declares a failure and initiates a re-establishment procedure to reconnect to the network, which incurs additional signaling overhead and delay during the re-establishment procedure.

[0078] To overcome this issue, 3GPP introduced CHO recovery in Release 16 of the NR standard. CHO recovery (e.g., as described in 3GPP TS38.311 V17.0.0, Section 5.3.7.3) reduces the disruption time caused by a failure for a UE with conditional reconfiguration of multiple target cells. Although CHO minimizes the possibility of mobility failure, the UE may still detect a failure due to misconfiguration of mobility parameters or performing a handover to the wrong cell. Instead of performing a reestablishment, a UE supporting the CHO recovery feature can recover from the failure by utilizing the stored conditional reconfiguration of the prepared target cells.

[0079] After a failure is detected, the UE initiates a cell reselection procedure, and if the selected cell is one of the target cells prepared in CHO, the UE performs a handover to that cell using the CHO configuration previously provided by the network. Otherwise, if the UE does not have a corresponding CHO configuration, the UE initiates a re-establishment procedure to the selected cell. Therefore, with CHO recovery, the UE can start a CHO execution by leveraging the stored CHO configuration of the target cell instead of a costly re-establishment procedure, thereby reducing the interruption time after a failure.

[0080] The CHO recovery mechanism allows the UE to recover on a cell where the CHO configuration is stored. In the case of CHO over DC, i.e., CHO with multiple candidate Secondary Cell Groups (SCGs) and / or multiple CHO configurations for the target PCell and target PSCell, the UE may apply Dual Connectivity CHO (CHO-DC) configuration once the CHO conditions are met, but CHO recovery does not take into account which SCG to consider during CHO or whether to consider it at all. This may result in SCG failure and disruption of SCG bearers terminated at the MN / SN if CHO preparation with the appropriate SCG configuration is not selected.

[0081] Currently, the target CHO configuration is selected solely based on radio signal measurements of the target PCell that meet certain cell selection criteria, without considering the signal strength / quality of the target PSCell. If two or more CHO configurations are available for the same PCell, the UE does not further distinguish between different Dual Connectivity CHO (CHO-DC) and Single Connectivity CHO (CHO-SC) configurations during the CHO recovery procedure. To minimize performance impact and interruption of current bearers, it is essential to select the appropriate configuration with the same PCell.

[0082] Furthermore, if one of the CHO-DC configurations has both a suitable PCell and PSCell, the configuration details are not transparent to the UE, so the UE does not know which CHO configuration is DC or SC until it decodes the configuration. Furthermore, the UE does not know which CHO-DC configuration has a suitable PSCell configured until it decodes the configuration.

[0083] Solutions to these problems according to the present disclosure are summarized as follows: The network provides assistance information to the UE to improve the recovery procedure in the CHO-DC scenario.

[0084] In an embodiment, the network may provide an SC / DC preference flag to prioritize the CHO configuration of the same PCell during the recovery procedure. In additional or alternative embodiments, the criteria for prioritizing the SC or DC configuration may be based on the pending traffic volume of a particular SCG bearer rather than a direct indication of the DC / SC configuration. Thus, the network may indicate the pending traffic volume to the UE. Alternatively, if the SC configuration has a current SCG bearer mapped to the target SC configuration, the network may set the SC / DC preference flag and select the SC over the DC. If the current SCG bearer is only mapped to the target SCG, there is no benefit to switching to the SC, so the network may select the DC over the SC.

[0085] In a further embodiment, the network may additionally or alternatively indicate preferential selection of a target DC configuration with the same PSCell that minimizes interruption of current traffic (SCG-maintaining DC handover). In a further embodiment, the network may additionally or alternatively provide the UE with PSCell selection criteria to be met during cell selection for recovery. This enables the UE to select a target DC configuration with better radio conditions in the secondary cell group. In a further embodiment, the network may additionally or alternatively provide an SC / DC indication outside the CHO configuration to enable the UE to identify which CHO configuration is SC or DC. In a further embodiment, the network may additionally or alternatively provide a PSCell ID with or outside the CHO-DC configuration to enable the UE to identify which CHO-DC configuration the PSCell is configured in. Furthermore, if there is no suitable PSCell in the CHO-DC configuration, a fallback from CHO-DC to CHO-SC may be used, allowing the UE to remain on the PCell.

[0086] A flowchart of the dual connectivity conditional handover recovery performed by the UE is shown in Figure 5. The user equipment includes at least one processor and at least one memory containing computer program code that causes the UE to perform the processes described herein. In other words, the UE is configured to perform the processes described herein.

[0087] The UE operates in dual connectivity, i.e., connected to a source base station as a master node, also referred to as source MN, and a secondary base station, also referred to as source SN or SN. The process described with respect to FIG. 5 is performed during a conditional handover, e.g., after one or more possible target master nodes (also referred to as target MN) and / or target secondary nodes (also referred to as target SN) for CHO are configured in the UE. For example, the source MN may determine that a conditional handover with one or more target MNs is expected based on measurements performed by the UE and reported in a measurement report. The source MN may then send a CHO request to one or more target MNs. One or more (or at least some) target MNs may confirm the CHO request. In future communication systems, other steps may also be performed before or after the process described with respect to FIG. 5 is performed.

[0088] Starting from box 501, the UE receives multiple CHO configurations from the source master node. The CHO configurations relate to at least the primary cell of the target master node, but may also include primary secondary cells of the target master node. The CHO configurations may be transmitted to the UE in one message, such as an RRC reconfiguration message. Alternatively, the CHO configurations may be transmitted in at least two separate messages, i.e., one message per CHO configuration or one message per target master node containing one or more CHO configurations of this target master node. Instead of using Layer 3 RRC reconfiguration messages, other Layer 2 or 1 messages may be used, such as MAC signaling or signaling of CHO execution conditions via PDCCH.

[0089] In box 502, the UE receives assistance information for CHO recovery from the primary cell of the source master node. The assistance information may be any information that enables the UE to select a CHO configuration from multiple CHO configurations.

[0090] The assistance information may include a single-dual connectivity preference flag. Such a flag can be used to configure the UE to prioritize the single connectivity CHO configuration over the dual connectivity CHO configuration, or vice versa. For example, if the single-dual connectivity preference flag is set to 1, the UE prioritizes the dual connectivity (DC) CHO configuration over the single connectivity CHO configuration. Otherwise, if the single-dual connectivity preference flag is set to 0, the UE prioritizes the SC-CHO configuration over the DC-CHO configuration.

[0091] The assistance information may additionally or alternatively include information regarding the amount of pending traffic on the secondary cell group bearers, in which case the UE may be configured to prioritize a single connectivity CHO configuration in response to the single connectivity CHO configuration having the secondary cell group bearers mapped to the respective target master node, and to prioritize a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having the secondary cell group bearers mapped to the respective target secondary node.

[0092] The assistance information may additionally or alternatively include an indication to prefer a dual connectivity CHO configuration in which the primary secondary cell of the source secondary node is maintained. In such a configuration, the UE maintains a connection to the source SN. This reduces the required data transfer between nodes while having a stable connection to the source SN.

[0093] The assistance information may additionally or alternatively include primary secondary cell selection criteria, in which case the UE may be configured to select a CHO configuration having a primary secondary cell that satisfies the primary secondary cell selection criteria. For example, the primary secondary cell selection criteria may include a cell quality threshold and / or any selection criteria based on RSRP, RSRQ, or SINR criteria.

[0094] The assistance information may additionally or alternatively include information regarding which information is coded in which CHO configuration. For example, the assistance information may include a single-dual connectivity indicator indicating which type of CHO configuration is coded in the respective CHO configuration. In another additional or alternative example, the assistance information may include a primary secondary cell identifier indicating which primary secondary cell is coded in the CHO configuration. In alternative embodiments, the information regarding the CHO configuration may be indicated in a different manner, for example, by including the information in an additional field accompanying the CHO configuration or by signaling separately from the assistance information.

[0095] The UE then selects a CHO configuration from the multiple CHO configurations based on the assistance information for CHO recovery, as shown in box 503. Such a selection is typically performed in response to the user equipment experiencing a radio link failure with the primary cell of the source master node or a handover failure with the primary cell of the handover target master node. The selected CHO configuration relates to (at least) the primary cell of the target master node and may also relate to a possible primary secondary cell of the target secondary node that is used for DC in combination with the primary cell.

[0096] Finally, the UE performs CHO recovery using the primary cell of the target master node according to the selected CHO configuration, as shown in box 504. In an embodiment where the selected CHO is a dual connectivity CHO configuration with a primary secondary cell of the target secondary node that is different from the primary secondary cell of the source secondary node, the UE may also be configured to perform CHO recovery using the primary secondary cell of the target secondary node (in addition to the primary cell of the target master node to enable DC connectivity).

[0097] Furthermore, if none of the primary and secondary cells in the DC-CHO configuration are suitable, a fallback may be used, allowing the UE to remain with single connectivity on the primary cell. For example, if none of the at least one primary and secondary cells meets the above-mentioned primary and secondary cell selection conditions, the UE may be configured to select (or apply) the single connectivity CHO configuration of the target master node. In such an example, the UE may also be configured to transmit cell selection information to the target master node including an indication that none of the at least one primary and secondary cell configured for the target master node meets the primary and secondary cell selection conditions. In further embodiments, this cell selection information may also include measurements related to at least one primary and secondary cell configured for the target master node. This information may be used for root cause analysis by the network. In other additional or alternative embodiments, the cell selection information further includes measurements related to additional cells, such as all or at least a plurality of cells available for measurement by the user equipment.

[0098] The UE may also include means for performing the processes described herein. For example, the UE may include means for receiving multiple CHO configurations from a source master node and means for receiving assistance information for CHO recovery from a primary cell of the source master node. The UE may further include means for selecting a CHO configuration from the multiple CHO configurations based on the assistance information for CHO recovery in response to the user equipment experiencing a radio link failure on the primary cell of the source master node or a handover failure on the primary cell of a second target master node, the selected CHO configuration being associated with the primary cell of the target master node. Finally, the UE may include means for performing CHO recovery using the primary cell of the target master node. Means for other processes described herein may be provided as well.

[0099] A flowchart of dual connectivity conditional handover recovery performed by a source MN is shown in Figure 6. The source MN includes at least one processor and at least one memory containing computer program code that causes the source MN to perform the processes described herein. In other words, the source MN is configured to perform the processes described herein. The source MN operates in dual connectivity with a primary cell of a source master node and a primary secondary cell of a source secondary node and is connected to user equipment configured for conditional handover CHO.

[0100] To enable the improved CHO recovery mechanism described herein, the source MN transmits multiple CHO configurations to the user equipment, e.g., in response to measurements performed by the UE and reported in a measurement report indicating that a conditional handover with one or more target MNs is expected. This is shown in box 601 of FIG. 6. The CHO configurations relate to at least the primary cell of the target master node, but may also include primary secondary cells of the target master node. The CHO configurations may be transmitted to the UE in one message, such as an RRC reconfiguration message. Alternatively, the CHO configurations may be transmitted in at least two separate messages, i.e., one message per CHO configuration, or one message per target master node containing one or more CHO configurations for this target master node. Instead of using Layer 3 RRC reconfiguration messages, other Layer 2 or 1 messages may be used, such as MAC signaling or signaling of CHO execution conditions via PDCCH.

[0101] The source MN further transmits assistance information for CHO recovery to the user equipment, as shown in box 602. The assistance information is used by the user equipment to select a CHO configuration from multiple CHO configurations for CHO recovery, as described above with respect to FIG.

[0102] The assistance information may include a single-dual connectivity preference flag. Such a flag can be used to configure the UE to prioritize the single connectivity CHO configuration over the dual connectivity CHO configuration, or vice versa. For example, if the single-dual connectivity preference flag is set to 1, the UE prioritizes the dual connectivity (DC) CHO configuration over the single connectivity CHO configuration. Otherwise, if the single-dual connectivity preference flag is set to 0, the UE prioritizes the SC-CHO configuration over the DC-CHO configuration.

[0103] The single-dual connectivity preference flag may be determined based on the amount of pending traffic of the secondary cell group bearers, in which case the source MN may be configured to prioritize the single connectivity CHO configuration in response to the single connectivity CHO configuration having the secondary cell group bearers mapped to the respective target master nodes, and to prioritize the dual connectivity CHO configuration in response to the dual connectivity CHO configuration having the secondary cell group bearers mapped to the respective target secondary nodes.

[0104] The assistance information may additionally or alternatively include an indication to prefer a dual connectivity CHO configuration in which the primary secondary cell of the source secondary node is maintained. In such a configuration, the UE maintains a connection to the source SN. This reduces the required data transfer between nodes while having a stable connection to the source SN.

[0105] The assistance information may additionally or alternatively include primary secondary cell selection criteria, in which case the UE may be configured to select a CHO configuration having a primary secondary cell that satisfies the primary secondary cell selection criteria. For example, the primary secondary cell selection criteria may include a cell quality threshold and / or any selection criteria based on RSRP, RSRQ, or SINR criteria.

[0106] The assistance information may additionally or alternatively include information regarding which information is coded in which CHO configuration. For example, the assistance information may include a single-dual connectivity indicator indicating which type of CHO configuration is coded in the respective CHO configuration. In another additional or alternative example, the assistance information may include a primary secondary cell identifier indicating which primary secondary cell is coded in the CHO configuration. In alternative embodiments, the information regarding the CHO configuration may be indicated in a different manner, for example, by including the information in an additional field accompanying the CHO configuration or by signaling separately from the assistance information.

[0107] The source master node may also include means for performing the processes described herein. For example, the source master node may include means for transmitting a plurality of CHO configurations to a user equipment and means for transmitting assistance information for CHO recovery to the user equipment, where the assistance information is used by the user equipment to select a CHO configuration from the plurality of CHO configurations for CHO recovery. Means for other processes described herein may be provided as well.

[0108] The flowchart of dual connectivity conditional handover with on-time data transfer performed by a network node supporting the gNB-CU-CP functionality is shown in Figure 7.

[0109] The network node is configured to support at least one of a radio access network central unit control plane (gNB-CU-CP) function or a Layer 3 protocol and to support connection with user equipment operating in dual connectivity with a primary cell of the network node and a primary secondary cell of the source secondary node.

[0110] Starting from box 701, a network node, in particular a gNB-CU-CP of the network node, generates a radio resource control (RRC) message including assistance information for CHO recovery. The network node then transmits the RRC message including the assistance information to a user equipment. The assistance information is used by the user equipment to select a CHO configuration from multiple CHO configurations for CHO recovery. The RRC message is transmitted to the UE via a gNB-DU. The embodiments described with respect to the source MN may also be applied to the network nodes of FIG. 7, as will be understood by those skilled in the art.

[0111] An overall message flow diagram for one embodiment of dual connectivity conditional handover recovery is shown in Figure 8. The message flow diagram illustrates a UE 801, a source MN 802 associated with a primary cell PCell-0, a source SN 803 associated with n primary secondary cells PSCell-0, a first target MN 804 associated with a primary cell PCell-1, a first target SN 805 associated with primary secondary cells PCell-1 and PCell-3, a second target MN 806 associated with a primary cell PCell-2, and a second target SN 807 associated with a primary secondary cell PCell-2, operating during CHO recovery in accordance with the present disclosure.

[0112] The overall process of this exemplary embodiment is as follows: In numeral 1, a UE 801 is served by PCell-0 of a source MN 802 (S-MN) and a PSCell-0 of a source SN 803 (S-SN), i.e., the UE 801 operates in dual connectivity. In numeral 2, three CHO configurations for the same target PCell-1 of T-MN1 804 are configured in the UE 801. These CHO configurations are called Config 1a, Config 1b, and Config 1c. Config 1a contains CHO configuration information for CHO to PCell-1 and conditional PSCell change (CPC) to PSCell-1 of T-SN1 805 (MN+SN bearers, CHO-DC). Config 1b contains CHO configuration information for CHO to PCell-1 only (all MN bearers, CHO-SC). Config 1c includes CHO configuration information for CHO to PCell-1 and CPC to PSCell-3 of T-SN1 805 (MN+SN bearer, CHO-DC).

[0113] In addition to these three configurations for PCell-1, the UE 801 is configured with another CHO-DC configuration for PCell-2 in T-MN2 806 along with a CPC configuration for PSCell-2 in T-SN2 807. This is highlighted in box number 3. The configurations provided to the UE 801 in numbers 2 and 3 can also be provided in a single step (using a single RRC reconfiguration).

[0114] Numeral 4 indicates that the serving PCell-0 provides the UE 801 with assistance information for the CHO recovery procedure described with respect to the embodiments disclosed herein. In this example, the assistance information may include an SC / DC preference flag that configures the recovery behavior of the UE 801 and indicates the type of configuration preferred during the CHO recovery procedure. The assistance information may further include PSCell selection criteria for the CHO recovery procedure, which may be based on any one or all of RSRP, RSRQ, or SINR measurements. Furthermore, the assistance information may also include instructions related to the CHO-DC or CHO-SC, allowing the UE 801 to identify whether a configuration includes a PSCell, so that the UE can determine the configuration to consider / decode during the CHO recovery procedure. The assistance information also includes the ID of a PSCell outside the CHO-DC configuration configured with a PSCell ID, so that the UE 801 can select / decode the desired configuration. As will be appreciated by those skilled in the art, the assistance information may include some of this information as needed.

[0115] In number 5, UE 801 experiences either a radio link failure on source PCell-0 and / or a handover failure during CHO to the originally selected target PCell-2. In this example, it is assumed that UE 801 experiences a handover failure of PCell-2. UE 801 then selects one suitable cell for recovery, e.g., PCell-1. Suitable means, for example, that measurements indicate that the radio conditions of this cell are sufficient for a stable connection, or that other conditions for establishing a connection are met. In short, PCell-1 is one of the cells prepared for CHO and is suitable for recovering the connection.

[0116] According to the assistance information, as shown in number 7, UE 801 prioritizes the DC configuration over the SC configuration as configured by the serving PCell-0 in number 4. Then, in number 8, UE 801 detects the CHO-DC configuration associated with PCell-1 by using the SC / DC indicator provided in number 4. UE 801 identifies that Config 1a and Config 1c are the CHO-DC configurations associated with PCell-1.

[0117] In numeral 9, by using the assistance information provided in numeral 4, the UE 801 identifies that PSCell-1 and PSCell-3 are PSCells of the target SN configured together with the CHO configuration of PCell-1. In numeral 10, the UE 801 selects one of the CHO-DC configurations associated with PCell-1, namely, Config 1a and Config 1c. The selection criteria is based on the PSCell selection conditions provided in numeral 4. In this example, PSCell-3 meets the selection conditions during recovery, and the UE 801 selects Config 1c associated with PSCell-3.

[0118] Thereafter, as shown in numeral 11, UE 801 decodes Config 1c, which is selected as the appropriate configuration based on the assistance information of numeral 4 used in numerals 7 to 11. Finally, in numeral 12, UE 801 recovers on PCell-1 and PSCell-3 using the CHO configuration Config 1c selected in step 10 and decoded in step 11. As explained above, UE 801 is provided with and configured with sufficient information to minimize the interruption time of SCG bearers during the recovery procedure in the CHO-DC scenario.

[0119] An overall message flow diagram for one embodiment of dual connectivity conditional handover recovery is shown in Figure 9. The message flow diagram illustrates a UE 901, a source MN 902 associated with a primary cell PCell-0, a source SN 903 associated with n primary secondary cells PSCell-0, a first target MN 904 associated with a primary cell PCell-1, a first target SN 905 associated with primary secondary cells PCell-1 and PCell-3, a second target MN 906 associated with a primary cell PCell-2, and a second target SN 907 associated with a primary secondary cell PCell-2, operating during CHO recovery in accordance with the present disclosure.

[0120] The overall process of this exemplary embodiment is as follows: In numeral 1, a UE 901 is served by PCell-0 of a source MN 902 (S-MN) and a PSCell-0 of a source SN 903 (S-SN), i.e., the UE 901 operates in dual connectivity. In numeral 2, three CHO configurations for the same target PCell-1 of T-MN1 904 are configured in the UE 901. These CHO configurations are called Config 1a, Config 1b, and Config 1c. Config 1a contains CHO configuration information for CHO to PCell-1 and conditional PSCell change (CPC) to PSCell-1 of T-SN1 905 (MN+SN bearers, CHO-DC). Config 1b contains CHO configuration information for CHO to PCell-1 only (all MN bearers, CHO-SC). Config 1c includes CHO configuration information for CHO to PCell-1 and CPC to PSCell-3 of T-SN1 905 (MN+SN bearer, CHO-DC).

[0121] In addition to these three configurations for PCell-1, the UE 901 is configured with another CHO-DC configuration for PCell-2 in T-MN2 906 along with a CPC configuration for PSCell-2 in T-SN2 907. This is highlighted in box number 3. The configurations provided to the UE 901 in numbers 2 and 3 can also be provided in a single step (using a single RRC reconfiguration).

[0122] Numeral 4 indicates that the serving PCell-0 provides the UE 901 with assistance information for the CHO recovery procedure described with respect to the embodiments disclosed herein. In this example, the assistance information may include an SC / DC preference flag that configures the recovery behavior of the UE 901 and indicates the type of configuration preferred during the CHO recovery procedure. The assistance information may further include PSCell selection criteria for the CHO recovery procedure, which may be based on any one or all of RSRP, RSRQ, or SINR measurements. Furthermore, the assistance information may also include instructions related to the CHO-DC or CHO-SC, allowing the UE 901 to identify whether a configuration includes a PSCell, so that the UE can determine the configuration to consider / decode during the CHO recovery procedure. The assistance information also includes the ID of a PSCell outside the CHO-DC configuration configured with a PSCell ID, so that the UE 901 can select / decode the desired configuration. As will be appreciated by those skilled in the art, the assistance information may include some of this information as needed.

[0123] In number 5, UE 901 experiences either a radio link failure with source PCell-0 and / or a handover failure during CHO to the originally selected target PCell-2. In this example, it is assumed that UE 901 experiences a handover failure of PCell-2. Then, UE 901 selects one suitable cell for recovery, e.g., PCell-1. Suitable means, for example, that measurements indicate that the radio conditions of this cell are sufficient for a stable connection, or that other conditions for establishing a connection are met. In short, PCell-1 is one of the cells prepared for CHO and is suitable for recovering the connection.

[0124] According to the assistance information, as shown in number 7, UE 901 prioritizes the DC configuration over the SC configuration, as configured by the serving PCell-0 in number 4. Then, in number 8, UE 901 detects the CHO-DC configuration associated with PCell-1 by using the SC / DC indicator provided in number 4. UE 901 identifies that Config 1a and Config 1c are the CHO-DC configurations associated with PCell-1.

[0125] At number 9, UE 901 identifies that PSCell-1 and PSCell-3 are PSCells of the target SN configured together with the CHO configuration of PCell-1 by using the assistance information provided at number 4. At number 10, UE 901 does not select any of the CHO-DC configurations associated with PCell-1, i.e., does not select Config 1a or Config 1c, because neither of them satisfies the PSCell selection conditions.

[0126] Then, as shown in numeral 11, UE 901 selects CHO-SC configuration Config 1b as the appropriate configuration based on the assistance information provided in numeral 4 and used in numerals 7 to 11. Since there is an available CHO-SC configuration for PCell-1, the UE falls back from CHO-DC recovery to CHO-SC recovery. At numeral 12, UE 901 recovers on PCell-1 by using the CHO-SC configuration, i.e., Config 1b.

[0127] Finally, after the CHO recovery procedure is successful, the UE 901 reports to the T-MN1 904 that none of the PSCells configured in the CHO-DC configuration were suitable for the CHO recovery procedure. In one embodiment, the UE 901 also reports measurements related to PSCell-1 and PSCell-3, which were identified as PSCells associated with the CHO-DC configuration of PCell-1, which may be used for root cause analysis. In another embodiment, the UE 901 reports all available measurements that the network can use for root cause analysis.

[0128] Finally, FIG. 10 shows a flowchart of one embodiment of an overall dual connectivity conditional handover recovery illustrating the decision mechanism that the UE may follow.

[0129] Starting at box 1001, the UE determines (and self-declares) a radio quality impairment, such as RLF or HOF, as described with respect to the embodiments described herein. Then, as shown in box 1002, a PCell of the target master node is selected for CHO recovery, e.g., based on current measurements. PCell configurations, i.e., CHO configurations for this PCell, are available and are detected in box 1003. These CHO configurations are classified for SC and DC according to the information transmitted with the assistance information described above. If the assistance information indicates that DC is preferred over SC (as shown in box 1005), the UE proceeds to box 1006. Otherwise, the UE proceeds to box 1010 (described below).

[0130] In box 1006, the UE detects PSCells for each DC configuration. This may be done according to information transmitted together with the assistance information described above. Then, if any PSCell satisfies the PSCell selection condition (shown in box 1007), the UE proceeds to box 1008. Otherwise, the UE proceeds to box 1010 (described below). The PSCell selection condition may be one of the conditions described above for other embodiments, for example, the embodiment of FIG. 5. In box 1008, the UE selects a PSCell based on the PSCell condition, for example, selecting the PSCell for which the best condition is determined. Also, the PSCell condition may be included in the PSCell selection condition. If only one PSCell satisfies the selection condition, the processing of box 1008 may be skipped.

[0131] Finally, the UE selects the corresponding DC configuration in box 1009 and establishes a connection on the respective PCell and PSCell, or selects the corresponding SC configuration in box 1010 and establishes a connection only on the respective PCell.

[0132] It is to be understood that the apparatus described herein may include or be coupled to other units or modules, such as radio components or radio heads used in or for transmitting and / or receiving. Although the apparatus is described as one entity, the different modules and memories may be embodied in one or more physical or logical entities.

[0133] It should be noted that although the embodiments are described in the context of LTE and 5G NR, similar principles may be applied in connection with other networks and communication systems in which fast connection re-establishment needs to be performed. Accordingly, although particular embodiments are described above by way of example with reference to particular exemplary architectures of wireless networks, technologies, and standards, the embodiments may be applied to any other suitable form of communication system other than those illustrated and described herein.

[0134] Although exemplary embodiments have been described above, it should also be noted that there are several variations and modifications that can be made to the disclosed solution without departing from the scope of the present disclosure.

[0135] In general, various exemplary embodiments may be implemented in hardware or special-purpose circuits, software, logic, or any combination thereof. Some aspects of the present disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor, or other computing device, although the present disclosure is not limited thereto. While various aspects of the present disclosure may be illustrated and described using block diagrams, flowcharts, or other graphical representations, it is fully understood that these blocks, apparatus, systems, techniques, or methods described herein may be implemented in, by way of non-limiting example, hardware, software, firmware, special-purpose circuits or logic, general-purpose hardware or controller, or other computing device, or combinations thereof.

[0136] Exemplary embodiments of the present disclosure may be implemented by computer software executable by a data processor of a mobile device, such as a processor entity, or by hardware, or by a combination of software and hardware. Computer software or programs, also referred to as program products, including software routines, applets, and / or macros, may be stored on any device-readable data storage medium and include program instructions for performing specific tasks. A computer program product may include one or more computer-executable components configured to implement an embodiment when the program is executed. The one or more computer-executable components may be at least one software code or portion thereof.

[0137] Further, in this regard, it should be noted that the logic flow blocks as shown may represent program steps, or interconnected logic circuits, blocks, and functions, or a combination of program steps and logic circuits, blocks, and functions. The software may be stored on a physical medium such as a memory chip or memory block embodied in a processor, a magnetic medium such as a hard disk or floppy disk, or an optical medium such as a DVD and its data variants, a CD, etc. The physical medium is a non-transitory medium.

[0138] The memory may be of any type suitable for the local technology environment and may be implemented using any suitable data storage technology, e.g., semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, etc. The data processor may be of any type suitable for the local technology environment and may include, by way of non-limiting examples, one or more of: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), FPGAs, gate-level circuits, processors based on multi-core processor architectures, etc.

[0139] Exemplary embodiments of the present disclosure may be practiced in a variety of components, such as integrated circuit modules. The design of integrated circuits is generally a highly automated process. Complex and powerful software tools are available for converting logic-level designs into semiconductor circuit designs ready to be etched onto semiconductor substrates.

[0140] The foregoing description provides a complete and informative description of exemplary embodiments of the present disclosure, by way of non-limiting example. However, various modifications and adaptations may become apparent to those skilled in the relevant art upon reading the foregoing description in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of the present disclosure will still fall within the scope of the present disclosure as defined by the appended claims. Indeed, further embodiments exist that include combinations of one or more of the embodiments with any of the other embodiments described above.

Claims

1. 1. A user equipment configured to support operation in dual connectivity with a primary cell of a source master node and a primary secondary cell of a source secondary node of a radio access network, the user equipment configured to support conditional handover (CHO), the user equipment comprising: at least one processor; at least one memory containing computer program code; the computer program code, when executed by the at least one processor, causes the user equipment to: establishing a connection to a primary cell of the source master node; establishing a connection to a primary secondary cell of the source secondary node; receiving a plurality of CHO configurations from the source master node, the CHO configurations including conditional handover configurations to at least one target master node and at least one target secondary node; receiving assistance information for CHO recovery from the source master node; In response to the user equipment experiencing a radio link failure in the primary cell of the source master node or experiencing a handover failure to a primary cell of a first target master node, determining a primary cell of a second target master node and an associated CHO configuration among the plurality of CHO configurations based on the assistance information for CHO recovery; performing CHO recovery of the second target master node to the primary cell based on the determined associated CHO configuration; and A user device that executes the above.

2. 2. The user equipment of claim 1, further configured to perform CHO recovery to the primary secondary cell of the target secondary node in response to the determined CHO configuration being a dual connectivity CHO configuration having a primary secondary cell of the target secondary node that is different from the primary secondary cell of the source secondary node.

3. The user equipment of claim 1 or 2, wherein the assistance information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery.

4. 4. The user equipment of claim 1, wherein the assistance information includes information regarding a pending traffic volume on a secondary cell group bearer, and determining the CHO configuration includes: prioritizing a single connectivity CHO configuration in response to the single connectivity CHO configuration having a secondary cell group bearer mapped to a respective target master node; and prioritizing a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having the secondary cell group bearer mapped to a respective target secondary node.

5. The user equipment according to any one of claims 1 to 4, wherein the assistance information indicates that a dual connectivity CHO configuration in which the primary secondary cell of the source secondary node is maintained is preferred.

6. The user equipment according to any one of claims 1 to 5, wherein the support information includes a CHO recovery primary secondary cell selection condition, and determining the CHO configuration includes selecting a CHO configuration having a primary secondary cell that satisfies the primary secondary cell selection condition.

7. 7. The user equipment of claim 6, wherein determining a CHO configuration includes selecting a single connectivity CHO configuration in response to none of at least one primary secondary cell satisfying the primary secondary cell selection condition.

8. The user equipment: In response to selecting a single connectivity CHO configuration with the second target master node, transmitting cell selection information to the second target master node, the cell selection information including an indication that none of the at least one primary secondary cell associated with the second target master node satisfies the primary secondary cell selection condition. The user equipment of claim 7 , further configured to perform the following:

9. The user equipment of claim 8 , wherein the cell selection information further includes measurements related to the at least one primary secondary cell associated with the second target master node.

10. 10. The user equipment of claim 8 or 9, wherein the cell selection information further comprises measurements relating to further cells performed in the user equipment.

11. The user equipment of any one of claims 1 to 10, wherein the assistance information includes a single-dual connectivity indicator indicating whether the respective CHO configuration is a single or dual connectivity configuration.

12. The user equipment according to any one of claims 1 to 11, wherein the assistance information includes a primary secondary cell identifier indicating which primary secondary cell is included in the respective CHO configuration.

13. A source master node configured to support establishment of a connection to a user equipment, the user equipment supporting operation in dual connectivity with a primary cell of the source master node and a primary secondary cell of a source secondary node, and configured to support conditional handover (CHO), the source master node comprising: at least one processor; at least one memory containing computer program code; wherein the computer program code, when executed by the at least one processor, causes the source master node to: sending a plurality of CHO configurations to the user equipment, the CHO configurations including configurations for conditional handover to at least one target master node and at least one target secondary node; transmitting assistance information for CHO recovery to the user equipment, the assistance information being used by the user equipment to determine a CHO setting from the plurality of CHO settings for CHO recovery; The source master node.

14. The source master node of claim 13 , wherein the assistance information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery.

15. 15. The source master node of claim 14, wherein the single-dual connectivity preference flag is determined based on the amount of pending traffic on a secondary cell group bearer to prioritize a single connectivity CHO configuration in response to the single connectivity CHO configuration having a secondary cell group bearer mapped to a respective target master node, and to prioritize a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having the secondary cell group bearer mapped to a respective target secondary node.

16. The source master node according to any one of claims 13 to 15, wherein the support information indicates that a dual connectivity CHO configuration in which the primary secondary cell of the source secondary node is maintained is preferred.

17. The source master node of any one of claims 13 to 16, wherein the support information includes a primary secondary cell selection condition for determining a CHO configuration having a primary secondary cell that satisfies the CHO recovery primary secondary cell selection condition.

18. The source master node of any one of claims 13 to 17, wherein the support information includes a single-dual connectivity indicator that indicates whether each CHO configuration is a single or dual connectivity configuration.

19. The source master node according to any one of claims 13 to 18, wherein the support information includes a primary secondary cell identifier indicating which primary secondary cell is included in each CHO configuration.

20. A network node supporting at least one of a radio access network central unit control plane function or a Layer 3 protocol, the network node operating in dual connectivity with a primary cell of the network node and a primary secondary cell of a source secondary node, and configured to support a connection with a user equipment configured for conditional handover (CHO), the network node comprising: at least one processor; at least one memory containing computer program code; wherein the computer program code, when executed by the at least one processor, causes the network node to: generating a radio resource control (RRC) message including assistance information for CHO recovery; transmitting the RRC message including the assistance information to the user equipment, the assistance information being used by the user equipment to determine a CHO configuration from a plurality of CHO configurations including configurations of conditional handover to at least one target master node and at least one target secondary node for CHO recovery; A network node that runs

21. 21. The network node of claim 20, wherein the assistance information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery.

22. 22. The network node of claim 21, wherein the single-dual connectivity preference flag is determined based on an amount of pending traffic on a secondary cell group bearer to prioritize a single connectivity CHO configuration in response to the single connectivity CHO configuration having a secondary cell group bearer mapped to a respective target master node, and to prioritize a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having the secondary cell group bearer mapped to a respective target secondary node.

23. The network node according to any one of claims 20 to 22, wherein the assistance information indicates a preference for a dual connectivity CHO configuration in which the primary secondary cell of the source secondary node is maintained.

24. The network node according to any one of claims 20 to 23, wherein the assistance information includes a primary secondary cell selection condition for determining a CHO configuration having a primary secondary cell that satisfies the CHO recovery primary secondary cell selection condition.

25. The network node according to any one of claims 20 to 24, wherein the assistance information includes a single-dual connectivity indicator indicating whether the respective CHO configuration is a single or dual connectivity configuration.

26. 26. A network node according to any one of claims 20 to 25, wherein the assistance information comprises primary secondary cell identifiers indicating which primary secondary cells are included in the respective CHO configuration.

27. 1. A method of conditional handover CHO recovery performed by a user equipment configured to operate in dual connectivity in at least one radio access network RAN, comprising: Establishing a connection to the primary cell of the source master node; establishing a connection to a primary secondary cell of a source secondary node; receiving a plurality of CHO configurations from the source master node, the CHO configurations including conditional handover configurations to at least one target master node and at least one target secondary node; receiving assistance information for CHO recovery from the source master node; In response to the user equipment experiencing a radio link failure in the primary cell of the source master node or experiencing a handover failure to a primary cell of a first target master node, determining a primary cell of a second target master node and an associated CHO configuration among the plurality of CHO configurations based on the assistance information for CHO recovery; performing CHO recovery of the second target master node to the primary cell based on the determined associated CHO configuration; and A method comprising:

28. 28. The method of claim 27, further comprising: in response to the determined CHO configuration being a dual connectivity CHO configuration having a primary secondary cell of a target secondary node that is different from a primary secondary cell of the source secondary node, performing CHO recovery to the primary secondary cell of the target secondary node.

29. 29. The method of claim 27 or 28, wherein the aiding information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery.

30. 30. The method of claim 27, wherein the assistance information includes information regarding pending traffic volume on secondary cell group bearers, and determining the CHO configuration includes: prioritizing a single connectivity CHO configuration in response to the single connectivity CHO configuration having secondary cell group bearers mapped to respective target master nodes; and prioritizing a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having the secondary cell group bearers mapped to respective target secondary nodes.

31. The method of any one of claims 27 to 30, wherein the assistance information indicates a preference for a dual connectivity CHO configuration in which the primary secondary cell of the source secondary node is maintained.

32. The method of any one of claims 27 to 31, wherein the assistance information includes a CHO recovery primary secondary cell selection condition, and determining the CHO configuration includes selecting a CHO configuration having a primary secondary cell that satisfies the primary secondary cell selection condition.

33. 33. The method of claim 32, wherein determining a CHO configuration includes selecting a single connectivity CHO configuration in response to none of at least one primary secondary cell satisfying the primary secondary cell selection condition.

34. The user equipment: In response to selecting a single connectivity CHO configuration with the second target master node, transmitting cell selection information to the second target master node, the cell selection information including an indication that none of the at least one primary secondary cell associated with the second target master node satisfies the primary secondary cell selection condition.

34. The method of claim 33, further comprising:

35. 35. The method of claim 34, wherein the cell selection information further includes measurements related to the at least one primary secondary cell associated with the second target master node.

36. 36. The method of claim 34 or 35, wherein the cell selection information further comprises measurements relating to further cells performed in the user equipment.

37. The method of any one of claims 27 to 36, wherein the assistance information includes a single-dual connectivity indicator that indicates whether the respective CHO configuration is a single or dual connectivity configuration.

38. The method of any one of claims 27 to 37, wherein the assistance information includes primary secondary cell identifiers indicating which primary secondary cells are included in the respective CHO configurations.

39. 1. A method of conditional handover CHO recovery performed by a source master node connected to a user equipment, the user equipment operating in dual connectivity with a primary cell of the source master node and a primary secondary cell of a source secondary node, the method comprising: sending a plurality of CHO configurations to the user equipment, the CHO configurations including configurations for conditional handover to at least one target master node and at least one target secondary node; transmitting assistance information for CHO recovery to the user equipment, the assistance information being used by the user equipment to determine a CHO setting from the plurality of CHO settings for CHO recovery; A method comprising:

40. 40. The method of claim 39, wherein the aiding information includes a single-dual connectivity preference flag for prioritizing single or dual connectivity for CHO recovery.

41. 41. The method of claim 40, wherein the single-dual connectivity preference flag is determined based on the amount of pending traffic on secondary cell group bearers to prioritize a single connectivity CHO configuration in response to the single connectivity CHO configuration having a secondary cell group bearer mapped to a respective target master node, and to prioritize a dual connectivity CHO configuration in response to the dual connectivity CHO configuration having the secondary cell group bearer mapped to a respective target secondary node.

42. The method of any one of claims 39 to 41, wherein the assistance information indicates a preference for a dual connectivity CHO configuration in which the primary secondary cell of the source secondary node is maintained.

43. The method of any one of claims 39 to 42, wherein the assistance information includes a primary secondary cell selection condition for determining a CHO configuration having a primary secondary cell that satisfies the CHO recovery primary secondary cell selection condition.

44. The method of any one of claims 39 to 43, wherein the assistance information includes a single-dual connectivity indicator that indicates whether the respective CHO configuration is a single or dual connectivity configuration.

45. The method of any one of claims 39 to 44, wherein the assistance information includes primary secondary cell identifiers indicating which primary secondary cells are included in the respective CHO configurations.

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