Data Transfer for Dual Connectivity

Abstract

The present subject matter relates to a method comprising: transmitting, by an apparatus, to a user equipment, a message for conditional handover, referred to herein as a reconfiguration message, indicating a set of one or more candidate target master nodes and associated candidate target secondary nodes; receiving, by the apparatus, from the user equipment, a message indicating at least one particular candidate target secondary node among the candidate target secondary nodes in response to transmitting the reconfiguration message; and performing, by the apparatus, a data transfer to the at least one particular candidate target secondary node and to a subset of the candidate target master nodes associated with the at least one particular candidate target secondary node.

Description

[Technical Field]

[0001] Various exemplary embodiments relate to telecommunications systems, and more particularly to data transfer to facilitate handovers and secondary cell changes. [Background technology]

[0002] Fifth-generation wireless networks (5G) refer to a new generation of radio systems and network architectures. 5G is expected to offer higher bit rates and coverage than current Long Term Evolution (LTE) systems. 5G is also expected to increase network scalability to hundreds of thousands of connections. However, there is a need to improve the communication services offered by these systems, particularly to enable dual connectivity. Some aspects of dual connectivity are described in standards such as TS 36.300, TS 36.423, and TS 36.413 for LTE and TS 38.300, TS 37.340, and TS 38.423 for NR. Summary of the Invention

[0003] An example embodiment provides an apparatus configured as a master node for serving user equipment in dual connectivity. The apparatus comprises means configured for: transmitting a message for conditional handover, referred to herein as a reconfiguration message, to the user equipment, indicating a set of one or more candidate target master nodes and associated candidate target secondary nodes; receiving a message from the user equipment in response to transmitting the reconfiguration message, indicating at least one particular one of the candidate target secondary nodes; and performing data transfer to the at least one particular candidate target secondary node and to a subset of the candidate target master nodes associated with the at least one particular candidate target secondary node.

[0004] An example embodiment provides a user equipment in dual connectivity with an apparatus that functions as a source master node and a source secondary node. The user equipment comprises means configured for receiving, from the apparatus, a reconfiguration message for conditional handover indicating a condition for a conditional handover (CHO) to a set of candidate target master nodes, referred to herein as a CHO condition, and another condition for a conditional primary secondary cell change (CPC) to the candidate target secondary nodes, referred to herein as a CPC condition; evaluating the CHO condition and the CPC condition; and, in response to determining that the CPC condition is satisfied by at least one particular candidate target secondary node among the candidate target secondary nodes, transmitting a message to the apparatus indicating the at least one particular candidate target secondary node.

[0005] An example embodiment provides a method comprising: transmitting, by an apparatus, to a user equipment, a message for conditional handover, referred to herein as a reconfiguration message, indicating a set of one or more candidate target master nodes and associated candidate target secondary nodes; receiving, by the apparatus, from the user equipment, a message indicating at least one particular candidate target secondary node among the candidate target secondary nodes in response to transmitting the reconfiguration message; and performing, by the apparatus, a data transfer to the at least one particular candidate target secondary node and to a subset of the candidate target master nodes associated with the at least one particular candidate target secondary node.

[0006] An example embodiment provides a computer program comprising instructions to cause an apparatus to transmit to a user equipment a message for conditional handover, herein referred to as a reconfiguration message, indicating at least a set of one or more candidate target master nodes and associated candidate target secondary nodes; receive from the user equipment, in response to transmitting the reconfiguration message, a message indicating at least one particular candidate target secondary node of the candidate target secondary nodes; and perform a data transfer to the at least one particular candidate target secondary node and to a subset of the candidate target master nodes associated with the at least one particular candidate target secondary node.

[0007] An example embodiment provides a method comprising receiving, from a device, a reconfiguration message for conditional handover indicating a condition for conditional handover to a set of candidate target master nodes, referred to herein as a CHO condition, and another condition for conditional primary secondary cell change (CPC) to one or more candidate target secondary nodes, referred to herein as a CPC condition, evaluating the CHO condition and the CPC condition, and, in response to determining that the CPC condition is satisfied by at least one particular candidate target secondary node among the candidate target secondary nodes, transmitting a message to the device indicating the at least one particular candidate target secondary node.

[0008] An example embodiment provides a computer program comprising instructions for causing a user equipment to receive from the device a reconfiguration message for conditional handover indicating at least a condition for conditional handover to a set of candidate target master nodes, referred to herein as a CHO condition, and another condition for conditional primary secondary cell change (CPC) to one or more candidate target secondary nodes, referred to herein as a CPC condition; evaluate the CHO condition and the CPC condition; and, in response to determining that the CPC condition is satisfied by at least one particular candidate target secondary node among the candidate target secondary nodes, send a message to the device indicating the at least one particular candidate target secondary node.

[0009] In one embodiment, the at least one specific candidate target secondary node that satisfies the CPC condition may be one specific candidate target secondary node.

[0010] The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated into and constitute a part of this specification. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 illustrates a portion of an exemplary radio access network. [Figure 2] 1 is a schematic diagram of a wireless communication system. [Figure 3] 1 is a flowchart of a method used in a master node according to an embodiment of the present subject matter. [Figure 4] 1 is a flowchart of a method used in a user equipment according to an embodiment of the present subject matter. [Figure 5] 1 is a flowchart of a method used in a master node according to an embodiment of the present subject matter. [Figure 6] 1 is a flowchart of a method used in a user equipment according to an embodiment of the present subject matter. [Figure 7] 1 is a flow diagram of a signaling method for conditional handover according to an embodiment of the present subject matter. [Figure 8] 1 is a flow diagram of a signaling method for conditional handover according to an embodiment of the present subject matter. [Figure 9A] FIG. 1 illustrates a process for monitoring CPC and CHO conditions by a user equipment according to an embodiment of the present subject matter. [Figure 9B] FIG. 1 illustrates a process for monitoring CPC and CHO conditions by a user equipment according to an embodiment of the present subject matter. [Figure 9C] FIG. 1 illustrates a process for monitoring CPC and CHO conditions by a user equipment according to an embodiment of the present subject matter. [Figure 10] 1 is a block diagram illustrating an embodiment of an apparatus according to an embodiment of the present subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the following description, for purposes of explanation and without limitation, specific details are set forth, such as particular architectures, interfaces, techniques, etc., to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that the disclosed subject matter may be practiced in other exemplary embodiments that depart from these specific details. In some instances, detailed descriptions of well-known devices and / or methods are omitted so as not to obscure the description with unnecessary detail.

[0013] A communication system may be provided. The communication system may include nodes, such as base stations, each serving user equipment (UE) located within the node's geographic area or cell of service. The communication system may support one or more radio access technologies (RATs). These radio access technologies may be, for example, but are not limited to, Evolved Universal Terrestrial Radio Access (E-UTRA) or 5G New Radio (NR), and those skilled in the art may apply the present subject matter to other communication systems having the required characteristics.

[0014] The communication system may enable dual connectivity. During dual connectivity operation, a user equipment (UE) may couple to a first node and further couple to a second node. Thus, dual connectivity may encompass a user equipment (UE) and two nodes. One of the two nodes may function as a master node (MN), and the other node may function as a secondary node (SN). The master node and the secondary node may be connected via a network interface, and at least the master node is connected to a core network of the communication system. The nodes of the communication system may include multiple nodes configured to operate as master nodes and multiple nodes configured to operate as secondary nodes during dual connectivity operation. Communication between two nodes of the communication system may be via an ideal or non-ideal backhaul. Dual connectivity may enable a user equipment (UE) to consume radio resources provided by two nodes. In particular, dual connectivity allows a user equipment to communicate with two nodes simultaneously by sending and receiving data from the two nodes on two completely separate streams.

[0015] The geographical area served by the master node may be referred to as a primary cell. The geographical area served by the secondary node may be referred to as a primary-secondary cell. In one embodiment, the two nodes and user equipment may communicate with each other via multiple component carriers. For example, the master node may communicate with user equipment via a first set of component carriers that provide coverage to a first set of cells forming a so-called master cell group (MCG). The secondary node may communicate with user equipment via a second set of component carriers that provide coverage to a second set of cells forming a so-called secondary cell group (SCG). The cell of the first set of cells used to initiate initial access may be referred to as a primary cell (PCell), and the remaining cells may be named secondary cells (SCells). Similarly, the second set of cells comprises a primary cell (PSCell), which can be understood as a cell from which initial access is initiated under an SCG, and a secondary cell (SCell).

[0016] Nodes of a communication system may comprise low-power nodes and high-power nodes. The low-power nodes may be configured to transmit with lower power and less processing / hardware capacity than the high-power nodes. The low-power nodes may comprise miniature, micro, or pico base stations, or femto base stations. The low-power nodes may be able to handle explosive growth in mobile traffic, especially in hotspot deployments in indoor and outdoor scenarios. The master node may be, for example, a high-power node. The secondary nodes may be, for example, high-power or low-power nodes.

[0017] The present subject matter may improve dual connectivity operation to enhance mobility robustness in a communication system. To that end, an apparatus may be provided. The apparatus may be configured as a master node in dual connectivity involving a user equipment and a secondary node. After dual connectivity is established, the apparatus may be configured as the master node. In this specification, the user equipment may be referred to as a dual connectivity user equipment, and the secondary node may be referred to as a serving secondary node. The dual connectivity user equipment may be served by an apparatus in a primary cell, such as a PCell. The dual connectivity user equipment may be served by a serving secondary node in a primary secondary cell, such as a PSCell.

[0018] A movement of the dual connectivity user equipment may trigger a handover of the dual connectivity user equipment from a primary cell to a target primary cell served by a target master node. If this handover is performed conditionally, it is referred to as a conditional handover (CHO). A movement of the dual connectivity user equipment may trigger a change of the primary secondary cell to a target primary secondary cell served by a target secondary node. If this primary secondary cell change is performed conditionally, it may be referred to as a conditional primary secondary cell (PSCell) change (CPC).

[0019] The dual connectivity user equipment may be configured to perform cell measurements in connected, inactive, or idle mode of the primary cell. Measurements of a cell, such as the primary cell, may be performed, for example, by measuring at least one beam of the cell (e.g., its power). The beam measurement results may be combined (e.g., averaged) to derive the signal quality or cell quality of the cell. The signal quality may be, for example, a measurement of Reference Signal Received Power (RSRP) or Reference Signal Received Quality (RSRQ). The cell measurements may be advantageously used to perform a conditional handover (CHO) procedure. For example, the dual connectivity user equipment may be configured to use the cell measurements of the primary cell to check whether an initial handover criterion is met. The initial handover criterion may comprise, for example, a condition for a radio resource management (RRM) event A3. If the initial handover condition is met, the dual connectivity user equipment may be triggered to send a measurement report to the device. Based on the measurement reports, the device may determine whether a handover is necessary, and if so, the device may select M sets of candidate target master nodes, e.g., from a neighbor list of the target master node.

[0020]

number

number

number

[0021]

number

number

[0022]

number

[0023]

number

number

number

[0024]

number

[0025]

number

number

[0026]

number

number

number

number

[0027] A set of candidate target master nodes

number

number

number

number

number

[0028] The reconfiguration message is sent to a set of candidate target master nodes.

number

[0029]

number

[0030] Upon receiving the reconfiguration message, the dual connectivity user equipment may determine whether the CHO condition is met and whether the CPC condition is met, for example, using cell measurements of the primary cell and cell measurements of the primary secondary cell. Alternatively, the dual connectivity user equipment may be configured to automatically check the CHO condition and the CPC condition without relying on the reconfiguration message. In other words, triggering the dual connectivity user equipment to check the CHO condition and the CPC condition with the reconfiguration message may be optional. The dual connectivity user equipment may repeatedly check the CPC condition and the CHO condition.

[0031] The CPC condition may require that a signal value indicative of a signal received from a candidate target secondary node exceed another signal value indicative of a signal received from a serving secondary node by at least an offset value of a time-to-trigger (TTT) interval.

number

[0032] The CHO condition may require that a signal value indicating a signal received from a candidate target master node exceeds another signal value indicating a signal received from the device by at least an offset value of the TTT interval. Each signal value may be an RSRP or an RSRQ. The CHO condition may require that a user equipment selects a set of candidate target master nodes.

number

[0033] At least one candidate target secondary node may satisfy the CPC condition. In one embodiment, one candidate target secondary node may satisfy the CPC condition. One jth candidate target secondary node may satisfy the CHO condition before the CHO condition is satisfied.

number

number

[0034]

number

[0035] In response to receiving the CPC message, the device

number

number

number

[0036]

number

[0037]

number

[0038] Data forwarding is done by forwarding buffered packets to candidate target secondary nodes.

number

number

number

[0039]

number

[0040] After the CPC condition is satisfied, if the CHO condition is satisfied by a specific candidate target master node, the dual connectivity user equipment may stop exchanging data with the device and synchronize to the specific candidate target master node. The dual connectivity user equipment may detach from the device and apply a configuration to the specific candidate target master node before synchronizing to the specific candidate target master node. The dual connectivity user equipment may detach from the device and apply a configuration to the specific candidate target secondary node.

[0041]

number

[0042]

number

number

[0043]

number

[0044]

number

[0045] A specific candidate target master node is a candidate target secondary node that meets the CPC conditions.

number

number

[0046]

number

[0047] The present subject matter may enable a faster data forwarding process than so-called late data forwarding. When so-called early data forwarding is not required, the present subject matter may achieve low interruption time with low data forwarding overhead. Thus, the present subject matter may enable uninterrupted availability and high reliability of communication between devices and base stations of a communication system. This may meet the requirements of ultra-reliable and low-latency communication (URLLC) during user equipment handover procedures.

[0048] According to one embodiment, the device is configured to:

number

[0049]

number

[0050]

number

number

number

[0051] In one embodiment, the dual connectivity user equipment may select a candidate target secondary node if the CHO condition is not yet satisfied.

[0052]

number

[0053]

number

[0054]

number

[0055]

number

[0056] If multiple candidate target secondary nodes satisfy the CPC condition, a CPC departure condition may be checked for the multiple candidate target secondary nodes. If the CPC departure condition is satisfied by multiple candidate target secondary nodes, the device may stop forwarding data to a subset of the multiple candidate target secondary nodes and all associated candidate target nodes. If the CPC departure condition is satisfied by only a portion of the multiple candidate target secondary nodes, the device may stop forwarding data to those portions of the candidate target secondary nodes and associated candidate target master nodes, and may continue forwarding data to other portions of the candidate target secondary nodes and associated candidate target master nodes.

[0057] In one embodiment, upon receiving a handover success message from a particular candidate target master node by the device, the device may stop forwarding data to candidate target master nodes of a subset of candidate target master nodes different from the particular candidate target master node. In addition, the device may stop forwarding data to the particular candidate target master node if path switching to the particular candidate target master node is completed.

[0058] For example, an apparatus APP is provided. The apparatus APP includes at least one processor and at least one memory including computer program code, the at least one memory and the computer program code being configured by the at least one processor to cause the apparatus to: transmit a message for conditional handover, referred to herein as a reconfiguration message, to user equipment UE1, indicating a set of one or more candidate target master nodes and associated candidate target secondary nodes; receive a message from the user equipment indicating a particular candidate target secondary node among the candidate target secondary nodes in response to transmitting the reconfiguration message; and perform data transfer to the particular candidate target secondary node and to a subset of candidate target master nodes associated with the particular candidate target secondary node. In one embodiment, the apparatus APP may serve user equipment UE1 during dual connectivity operation of user equipment UE1. User equipment UE1 may be connected to the apparatus APP. User equipment UE1 may further be connected to a secondary node during dual connectivity operation.

[0059] 1 depicts an example of a simplified system architecture, illustrating only some elements and functional entities, all of which are logical units and whose implementation may differ from those shown. The connections illustrated in FIG. 1 are logical connections, and the actual physical connections may differ. It is clear to those skilled in the art that a system typically includes functions and structures other than those illustrated in FIG. 1.

[0060] However, the embodiment is not limited to the system given as an example, and a person skilled in the art can apply this solution to other communication systems with the required characteristics.

[0061] The example of FIG. 1 illustrates a portion of an example radio access network. FIG. 1 illustrates a device 110 and a device 112. The device 110 and the device 112 may be, for example, user devices. The device 110 and the device 112 are configured to be wirelessly connected to a node 114 over one or more communication channels. The node 114 is further connected to a core network 120. In one example, the node 114 may be an access node (e.g., an (e / g)NodeB) 114 that provides or serves devices in a cell. In one example, the node 114 may be a non-3GPP access node. The physical link from a device to the (e / g)NodeB is referred to as an uplink or reverse link, and the physical link from the (e / g)NodeB to the device is referred to as a downlink or forward link. It should be appreciated that the (e / g)NodeB or its functionality may be implemented using any node, host, server, or access point, or other entity suitable for such use.

[0062] A communication system typically includes multiple (e / g)NodeBs, which may be configured to communicate with each other via wired or wireless links designed for that purpose. These links may be used for signaling purposes. An (e / g)NodeB is a computing device configured to control radio resources of the communication system to which it is coupled. A NodeB may also be referred to as a base station, an access point, or another type of interface device, including a relay station operable in a wireless environment. An (e / g)NodeB includes or is coupled to a transceiver. The transceiver of the (e / g)NodeB provides a connection to an antenna unit that establishes a bidirectional radio link to the device. The antenna unit may include multiple antennas or antenna elements. The (e / g)NodeB is further connected to a core network 20 (CN or Next Generation Core NGC). For example, an (e / g)NodeB may connect to an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) in the control plane and the user plane, respectively. Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, responsible for routing and forwarding user data packets), a packet data network gateway (P-GW) for providing connectivity of the device (UE) to an external packet data network, or a mobile management entity (MME), etc.

[0063] A device (also referred to as a user device, UE, user equipment, user terminal, terminal device, etc.) illustrates one type of apparatus to which resources over the air interface are allocated and assigned, and therefore any functionality described herein with respect to a device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a Layer 3 relay (self-backhaul relay) to a base station.

[0064] A device generally refers to a device (e.g., a portable or non-portable computing device), including wireless mobile communication devices that operate with or without a subscriber identity module (SIM), including, but not limited to, types of devices such as mobile stations (mobile phones), smartphones, personal digital assistants (PDAs), handsets, devices that use wireless modems (such as alarm or measurement devices), laptop and / or touchscreen computers, tablets, game consoles, notebooks, and multimedia devices. It should be recognized that a device may almost exclusively be an uplink-only device, an example of which is a camera or video camera that loads images or video clips onto a network. A device may also be capable of operating in an Internet of Things (IoT) network, a scenario in which objects are provided with the ability to transfer data over a network without the need for human-to-human or human-to-computer interaction, such as in smart power grids and connected vehicles. A device may also utilize the cloud. In some applications, a device may comprise a user-portable device (such as a watch, earphones, or glasses) with a radio section, and computations are performed in the cloud. The device (or in some embodiments, a Layer 3 relay node) is configured to perform one or more of the user equipment functions. The device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal, or user equipment (UE), to name but a few.

[0065] The various techniques described herein may also be applied to cyber-physical systems (CPS), systems of cooperating computational elements that control physical entities. CPS may enable the implementation and utilization of a large number of interconnected ICT devices (sensors, actuators, processor microcontrollers, etc.) embedded in physical objects in different locations. Mobile cyber-physical systems are a subcategory of cyber-physical systems due to the inherent mobility of the physical systems in question. Examples of mobile physical systems include mobile robots and electronic devices carried by humans or animals.

[0066] Additionally, while depicted as a single entity, the device may be implemented with different units, processors, and / or memory units (not all of which are shown in FIG. 1 ). 5G enables many more base stations or nodes than existing LTE systems, including macro sites operating in conjunction with small sites using multiple-input-multiple-output (MIMO) antennas (the so-called small cell concept), applying various radio technologies depending on service needs, use cases, and / or available spectrum. 5G mobile communications support a wide range of use cases and related applications, including video streaming, augmented reality, different data sharing techniques, and various forms of machine-type applications (vehicle safety, different sensors, and (massive) machine-type communications (mMTC) including real-time control). 5G has multiple air interfaces, including sub-6 GHz, cmWave, and mmWave, and is expected to be integrable with existing legacy radio access technologies such as LTE. Integration with LTE, at least initially, will likely involve macro coverage provided by LTE, with 5G air interface access provided by LTE aggregation. 5G may be implemented as a system delivered from small cells. In other words, 5G is planned to support both inter-RAT interoperability (e.g., LTE-5G) and inter-RI interoperability (inter-air interface interoperability, e.g., sub-6 GHz to cmWave, sub-6 GHz to cmWave to mmWave). One concept being considered for use in 5G networks is network slicing, where multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services with different requirements regarding latency, reliability, throughput, and mobility.

[0067] The current architecture of LTE networks is fully distributed over the air and fully centralized in the core network. Low-latency applications and services in 5G require content to be closer to the air, which brings about local breakout and multi-access edge computing (MEC). 5G enables analytics and knowledge generation at the source of data. This approach must leverage resources that may not be continuously connected to the network, such as laptops, smartphones, tablets, and sensors. MEC provides a distributed computing environment for hosting applications and services. It also has the ability to store and process content closer to cellular subscribers for faster response times. Edge computing covers a wide range of technologies, including wireless sensor networks, mobile data acquisition, mobile signature analysis, collaborative, distributed peer-to-peer ad-hoc networking, local cloud / fog computing and grid / mesh computing, dew computing, mobile edge computing, cloudlets, distributed data storage and acquisition, autonomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, and processing that can also be classified as Internet of Things (massive connectivity and / or latency critical), critical communications (autonomous vehicles, road safety, real-time analytics, time-critical control, healthcare applications).

[0068] The communications system may also communicate with or utilize services provided by other networks, such as the public switched telephone network or the Internet, as exemplified by the component referenced by reference numeral 122. The communications network may also be capable of supporting the use of cloud services, e.g., at least a portion of the core network operations may be performed as cloud services (depicted in FIG. 1 by "cloud" 124). The communications system may also comprise a central control entity that provides the ability for networks of different operators to cooperate, e.g., in spectrum sharing.

[0069] Edge cloud technology can be introduced into the Radio Access Network (RAN) by utilizing Network Function Virtualization (NVF) and Software-Defined Networking (SDN). Using edge cloud technology may mean that access node operations are performed at least in part in a server, host, or node that is operationally coupled to a remote radio head or base station that comprises the radio components. It is also possible for node operations to be distributed among multiple servers, nodes, or hosts. The application of cloudRAN architecture allows RAN real-time functions to be performed on the RAN side (in distributed units, DU 114) and non-real-time functions to be performed in a centralized manner (in centralized units, CU 118).

[0070] It should also be understood that the distribution of load between core network operations and base station operations may be different from that in LTE, and in some cases may not even exist. Some other technological advances that will likely be used are big data and all-IP, which could change the way networks are built and managed. 5G is designed to support multiple hierarchies, where MEC servers can be located between the core and base stations or Node Bs (gNBs). It should be recognized that MEC is equally applicable to 4G networks.

[0071] 5G may utilize satellite communications to extend or complement 5G service coverage, for example, by providing backhaul. Possible use cases include providing service continuity to machine-to-machine (M2M) or Internet of Things (IoT) devices or passengers on board vehicles, or ensuring service availability for critical communications and future rail, maritime, and aviation communications. Satellite communications may utilize not only geostationary orbit (GEO) satellite systems but also low-earth orbit (LEO) satellite systems, especially megaconstellations (systems in which hundreds of (nano)satellites are deployed). Each satellite 116 in a megaconstellation may cover multiple satellite-enabled network entities, creating ground cells. Ground cells may be created via terrestrial relay nodes 114 or by gNBs located on the ground or within the satellite.

[0072] Those skilled in the art will understand that the depicted system is only a few examples of a wireless access system, and that in practice, the system may include multiple (e / g)NodeBs, a device may have access to multiple wireless cells, and the system may also include other devices such as physical layer relay nodes or other network elements. One of the (e / g)NodeBs may be a Home(e / g)NodeB. In addition, a geographic area of ​​a wireless communication system may be provided with multiple wireless cells as well as multiple different types of wireless cells. A wireless cell may be a macrocell (or umbrella cell), which is typically a large cell with a diameter of tens of kilometers, or a smaller cell such as a microcell, femtocell, or picocell. The (e / g)NodeB in FIG. 1 may provide any of these types of cells. A cellular wireless system may be implemented as a multi-layer network including multiple types of cells. Typically, in a multi-layer network, one access node provides one type of cell, and therefore multiple (e / g)NodeBs are required to provide such a network structure.

[0073] To meet the need to improve the deployment and performance of communication systems, the concept of "Plug and Play" (e / g) NodeB was introduced. Typically, a network that can use "Plug and Play" (e / g) NodeBs includes a Home NodeB Gateway, or HNB-GW (not shown in FIG. 1), in addition to Home (e / g) NodeBs (H(e / g)NodeBs). The HNB Gateway (HNB-GW), which is typically installed inside an operator's network, can aggregate traffic from multiple HNBs back to the core network.

[0074] 2 is a schematic diagram of a wireless communication system 200. The communication system 200 may be configured to use time division duplex (TDD) techniques for data transmission.

[0075] For simplicity, communication system 200 is illustrated as including four master nodes MN1, MN2, MN3, and MN4, three secondary nodes SN1, SN2, and SN3, and user equipment 201. Each of master nodes MN1-MN4 and secondary nodes SN1-SN3 may be, for example, an eNodeB or a gNB, as described with reference to FIG. 1. That is, communication system 200 may support the same RAT or different RATs.

[0076] Each of the master nodes MN1 to MN4 may serve UEs within a respective geographic coverage area of ​​the service, i.e., cells 203.1 to 203.4. Each of the secondary nodes SN1 to SN3 may serve UEs within a respective geographic coverage area of ​​the service, i.e., cells 205.1 to 205.3.

[0077] In this particular embodiment, master node MN1 is associated with secondary nodes SN1 and SN2. That is, master node MN1 may be configured with dual connectivity with secondary node SN1 and user equipment such as UE 201. Alternatively, master node MN1 may be configured with dual connectivity with secondary node SN2 and user equipment such as UE 201. Master node MN2 is associated with secondary nodes SN1, SN2, and SN3. Master node MN3 is associated with secondary nodes SN2 and SN3. Master node MN4 is associated with secondary node SN3.

[0078] In this particular example, UE 201 is moving, for example, from left to right. Initially, UE 201 has dual connectivity with master node MN1 and secondary node SN1. Therefore, master node MN1 may be referred to as source master node MN1, and secondary node SN1 may be referred to as source secondary node SN1.

[0079] While user equipment 201 is moving from left to right, it is configured to perform neighbour cell measurements of cells 203.2-3 and cells 205.2-3.

[0080] 3 is a flowchart of a method according to an embodiment of the present subject matter. For illustrative purposes, the method described in FIG. 3 may be implemented in, but is not limited to, the system illustrated in FIG. 2. The method may be performed, for example, by a source master node MN1.

[0081] The method starts in step 301, when a source master node MN1 may send a reconfiguration message for conditional handover to the user equipment 201. The reconfiguration message indicates a set of one or more candidate target master nodes and associated candidate target secondary nodes. Following the example of FIG. 2, the reconfiguration message indicates a set of candidate target master nodes MN2, MN3, and MN4 and associated candidate target secondary nodes SN2 and SN3. For example, the source master node MN1 may select master nodes MN2, MN3, and MN4 as candidate target master nodes for the moving user equipment 201 because the master nodes MN2, MN3, and MN4 are neighboring nodes of the source master node MN1. For example, the reconfiguration message may comprise a data structure with the following pair entries of candidate target secondary nodes associated with the candidate target master nodes: {MN2, SN2}, {MN2, SN3}, {MN3, SN2}, {MN3, SN3}, and {MN4, SN3}. The reconfiguration message may further comprise a CPC configuration and a CHO configuration. The CPC configuration may indicate CPC conditions that may be checked by the UE 201 and a configuration to be applied to a target secondary node that satisfies the CPC conditions. The CPC configuration may further indicate a CPC departure condition. The CHO configuration may indicate CHO conditions that may be checked by the UE 201 and a configuration to be applied to a target master node that satisfies the CHO conditions.

[0082] In response to sending the reconfiguration message, the source master node MN1 may receive a message (named a CPC message) indicating a candidate target secondary node among the candidate target secondary nodes SN2, SN3 from the user equipment 201 in step 303. For example, assume that the candidate target secondary node SN2 being indicated in the CPC message means that the target secondary node SN2 satisfies the CPC conditions.

[0083] Upon receiving the CPC message, the method proceeds to step 305, where the source master node MN1 may perform a data transfer to the candidate target secondary node SN2 and to a subset of candidate primary target nodes associated with the candidate target secondary node SN2. For example, the source master node MN1 may use the received data structure to select an entry comprising the candidate target secondary node SN2. This may result in the following entries {MN2,SN2} and {MN3,SN2} being selected. Thus, the subset of candidate primary target nodes may comprise master nodes MN2 and MN3, as shown in the selected entries. The data transfer performed by the device may relate to data that enables serving the user equipment 201.

[0084] 4 is a flowchart of a method used in user equipment according to an embodiment of the present subject matter. For illustrative purposes, the method described in FIG. 4 may be implemented in, but is not limited to, the system illustrated in FIG. 2. The method may be performed by, for example, user equipment 201.

[0085] The method begins in step 401, when the user equipment 201 receives a reconfiguration message for conditional handover from the source master node MN1. The reconfiguration message indicates a set of one or more candidate target master nodes and associated candidate target secondary nodes. According to the example of FIG. 2, the reconfiguration message indicates a set of candidate target master nodes MN2, MN3, and MN4 and associated candidate target secondary nodes SN2 and SN3. For example, the reconfiguration message may comprise a data structure comprising pair entries of candidate target master nodes and associated candidate target secondary nodes: {MN2, SN2}, {MN2, SN3}, {MN3, SN2}, {MN3, SN3}, and {MN4, SN3}. The reconfiguration message may further comprise a CPC configuration and a CHO configuration. The CPC configuration may indicate CPC conditions that may be checked by the UE 201 and configurations to be applied to target secondary nodes that satisfy the CPC conditions. The CPC configuration may further indicate a CPC departure condition. The CHO configuration may indicate the CHO conditions that may be checked by the UE 201 and the configuration that will be applied to target master nodes that meet the CHO conditions.

[0086] Upon receiving the reconfiguration message, the user equipment 201 may check the CHO condition and the CPC condition in step 403. The user equipment 201 may check whether the CPC condition is satisfied by any of the candidate target secondary nodes SN2, SN3, and may check whether the CHO condition is satisfied by any of the set of candidate target master nodes MN2, MN3, MN4. For example, checking whether the CPC condition is satisfied by a given target SN, e.g., SN2, may require that a signal value indicative of a signal received from SN2 exceeds another signal value indicative of a signal received from SN1 by at least a first offset value. Similarly, checking whether the CHO condition is satisfied by a given target MN, e.g., MN2, may require that a signal value indicative of a signal received from MN2 exceeds another signal value indicative of a signal received from MN1 by at least a second offset value.

[0087] If the CPC condition is met, for example by candidate target secondary node SN2, before the CHO condition is met (query step 404), the method proceeds to step 405, where user equipment 201 sends a message (CPC message) to source master node MN1 informing source master node MN1 that candidate target secondary node SN2 has met the CPC condition. If the CPC condition is not met before the CHO condition is met, user equipment 201 may continue checking the CPC condition until it is met.

[0088] 5 is a flowchart of a method according to an embodiment of the present subject matter. For illustrative purposes, the method described in FIG. 5 may be implemented in, but is not limited to, the system illustrated in FIG. 2. The method may be performed, for example, by a source master node MN1.

[0089] The method starts in step 501, where a source master node MN1 may send a reconfiguration message for conditional handover to the user equipment 201. The reconfiguration message indicates a set of one or more candidate target master nodes and associated candidate target secondary nodes. According to the example of FIG. 2, the reconfiguration message indicates a set of candidate target master nodes MN2, MN3, and MN4 and associated candidate target secondary nodes SN2 and SN3. For example, the source master node MN1 may select master nodes MN2, MN3, and MN4 as candidate target master nodes for the moving user equipment 201, for example, because the master nodes MN2, MN3, and MN4 are neighboring nodes of the source master node MN1. For example, the reconfiguration message may comprise a data structure comprising the following pair entries of candidate target master nodes and associated candidate target secondary nodes: {MN2, SN2}, {MN2, SN3}, {MN3, SN2}, {MN3, SN3}, and {MN4, SN3}. The reconfiguration message may further comprise a CPC configuration and a CHO configuration. The CPC configuration may indicate CPC conditions that may be checked by the UE 201 and a configuration to be applied to a target secondary node that satisfies the CPC conditions. The CPC configuration may further indicate a CPC departure condition. The CHO configuration may indicate CHO conditions that may be checked by the UE 201 and a configuration to be applied to a target master node that satisfies the CHO conditions.

[0090] In response to sending the reconfiguration message, the source master node MN1 may receive a message (named a CPC message) indicating a candidate target secondary node among the candidate target secondary nodes SN2, SN3 from the user equipment 201 in step 503. For example, assume that the candidate target secondary node SN2 being indicated in the CPC message means that the target secondary node SN2 satisfies the CPC conditions.

[0091] Upon receiving the CPC message, the method proceeds to step 505, where the source master node MN1 may perform a data transfer to the candidate target secondary node SN2 and to a subset of candidate primary target nodes associated with the candidate target secondary node SN2. For example, the source master node MN1 may use the received data structure to select an entry comprising the candidate target secondary node SN2. This may result in the following entries {MN2,SN2} and {MN3,SN2} being selected. Thus, the subset of candidate primary target nodes may comprise master nodes MN2 and MN3, as shown in the selected entries. The data transfer performed by the device may relate to data that enables serving the user equipment 201.

[0092] The source master node MN1 may receive a message from the user equipment 201 in step 507 indicating that the candidate target secondary node SN2 (which previously met the CPC condition) has met the CPC departure condition.

[0093] Upon receiving the message, the source master MN1 may stop data forwarding in step 509 to the candidate target secondary node SN2 and to the subset of candidate primary target nodes MN2, MN3 associated with the candidate target secondary node SN2.

[0094] 6 is a flowchart of a method for use in user equipment according to an embodiment of the present subject matter. For illustrative purposes, the method described in FIG. 6 may be implemented in the system illustrated in FIG. 2, but is not limited to this implementation. The method may be performed by user equipment 201, for example.

[0095] The method begins in step 601, when the user equipment 201 receives a reconfiguration message for a conditional handover from the source master node MN1. The reconfiguration message indicates a set of one or more candidate target master nodes and associated candidate target secondary nodes. According to the example of FIG. 2, the reconfiguration message indicates a set of candidate target master nodes MN2, MN3, and MN4 and associated candidate target secondary nodes SN2 and SN3. For example, the reconfiguration message may comprise a data structure comprising candidate target master node and associated candidate target secondary node pair entries {MN2, SN2}, {MN2, SN3}, {MN3, SN2}, {MN3, SN3}, and {MN4, SN3}. The reconfiguration message may further comprise a CPC configuration and a CHO configuration. The CPC configuration may indicate a CPC condition that may be checked by the UE 201 and a configuration to be applied to target secondary nodes that satisfy the CPC condition. The CPC configuration may further indicate a CPC departure condition. The CHO configuration may indicate the CHO conditions that may be checked by the UE 201 and the configuration that will be applied to target master nodes that meet the CHO conditions.

[0096] Upon receiving the reconfiguration message, the user equipment 201 may check the CHO condition and the CPC condition in step 603. The user equipment 201 may check whether the CPC condition is satisfied by any of the candidate target secondary nodes SN2, SN3, and may check whether the CHO condition is satisfied by any of the set of candidate target master nodes MN2, MN3, MN4. For example, checking whether the CPC condition is satisfied by a given target SN, e.g., SN2, may require that a signal value indicative of a signal received from SN2 exceeds another signal value indicative of a signal received from SN1 by at least a first offset value. Similarly, checking whether the CHO condition is satisfied by a given target MN, e.g., MN2, may require that a signal value indicative of a signal received from MN2 exceeds another signal value indicative of a signal received from MN1 by at least a second offset value.

[0097] If the CPC condition is met, for example by candidate target secondary node SN2, before the CHO condition is met (query step 604), the method then proceeds to step 605, where user equipment 201 sends a message (CPC message) to source master node MN1 informing the source master node of candidate target secondary node SN2 that has met the CPC condition. If the CPC condition is not met before the CHO condition is met, user equipment 201 may continue checking the CPC condition until the CPC condition is met.

[0098] After the CPC conditions are satisfied, the user equipment 201 may continue to monitor the CPC conditions and the CHO conditions. Monitoring the CPC conditions may comprise checking whether the candidate target secondary node SN2 satisfies the CPC leave conditions; for example, if the CPC conditions are no longer satisfied by SN2, this indicates that SN2 has satisfied the CPC leave conditions. If the CPC leave conditions are satisfied by the candidate target secondary node SN2 (inquiry step 607), the user equipment 201 may send a message to the source master node MN1 in step 609 indicating that the candidate target secondary node SN2 (which previously satisfied the CPC conditions) has satisfied the CPC leave conditions. If the CPC leave conditions are not satisfied, the user equipment 201 may continue checking the CPC leave conditions until the CPC leave conditions are satisfied.

[0099] FIG. 7 depicts an example signaling diagram between a user equipment 701, a source master node 702, a source secondary node 703, one or more candidate target secondary nodes 704, one or more candidate target master nodes 705, a first core network node 707 (e.g., a User Plane Function (UPF)), and a second core network node 708 (e.g., an Access and Mobility Management Function (AMF)) in accordance with an embodiment of the present subject matter. In the example of FIG. 7, initially, the user equipment 701 is configured with dual connectivity with the source master node 702 and the source secondary node 703. At 1, the source master node 702 may send a handover request to each of the candidate target master nodes 705. At 2, each of the candidate target master nodes 705 may send an SN addition request to a respective candidate target secondary node 704. At 3, each of the candidate target secondary nodes 704 may respond with an SN addition request acknowledgment to a respective candidate target master node 705. At 4, each candidate target MN 705 may send an Xn-U address indication message to each candidate target SN 704, the Xn-U address indication message comprising address information of the interface Xn-U between the candidate target MN 705 and each candidate target SN 704. In particular, the Xn-U address indication message may comprise address information of the downlink (DL) transport network layer (TNL). At 5, each candidate target MN 705 may send a handover request acknowledgement message to the source MN 702. The request acknowledgement message may comprise the TEID for each direct tunnel (e.g., DRB tunnel) that may be established by the source MN 702 and each candidate target MN 705 or candidate target SN 704 to perform data forwarding. At 6, the source MN 702 may send an XN-U address indication message to the source SN 703 to forward data forwarding information. At 7, the source MN 702 may trigger the UE 701 to perform handover and cell change and apply configuration.In particular, the source MN 702 may send an RRC connection reconfiguration message to enable timely data transfer. At the same time, the source MN 702 may provide a flag to the UE 701 to configure the UE 701 to send a notification message when the CPC condition is met (7). The source MN 702 may also configure the UE 701 to include PCell measurements and a CHO condition status (such as whether the TTT for the CHO condition is running) in the CPC message (8). The UE 701 may monitor the CHO condition and the CPC condition (8). The CPC condition may also be referred to as the CPAC condition. The UE 701 may check whether the candidate target MN 705 meets the CHO condition and whether the candidate target SN 704 meets the CPC condition (9). Even if the CHO condition is not met, the CPC condition may be met by the candidate target SN (named target SN-1). The target SN-1 may serve the primary secondary cell PSCell-1. Target SN-1 may be associated with only a subset of candidate target MNs 705. At 10, the UE 701 may send a message (CPC message) to the source MN 702 indicating that the CPC condition is met by target SN-1. Optionally, this CPC message may further comprise the current CHO measurements and the status of the CHO condition. At 11, the UE 701 continues checking the CHO and CPC conditions. The CHO condition may be checked for each candidate target MN of the candidate target MNs 705. The CPC condition may be checked for each candidate target SN 704. At 12, the source MN 702 may select a subset of candidate target MNs associated with target SN-1. For example, at 12, the source MN 702 may select the TEIDs of the DRBs of target PSCell-1 and of the corresponding subset of PCells. The subset of PCells may be further reduced by selecting a portion of the subset of PCells based on the CHO PCell measurements. The source MN 702 may establish direct tunnels with a subset of the candidate target MNs and with target SN-1 using the selected TEIDs.The source MN 702 may transmit the sequence number status, including the sequence number status received at 13 from the source SN 703, to a subset of candidate target MNs 705 at 14. Each of the subset of candidate target MNs 705 may forward the sequence number status to an associated candidate target SN 704 at 15. Data forwarding occurs at 16 and 17. The source MN 702 may perform data forwarding to the subset of candidate target MNs 705 and associated candidate target SN-1. At 18, the CHO condition is satisfied by one candidate target node (named target MN-1) of the subset of candidate target MNs 705.

[0100] The UE may perform a RACH procedure at 19 to synchronize to Target MN-1, and then perform an RRC completion procedure between the UE 701 and Target MN-1 705 at 20. At 21, Target MN-1 705 may send a handover success message to Source MN 702. At 22, Source MN 702 may send an SN release request to Source SN 703. At 23, Source SN 703 may send an SN release request acknowledgement to Source MN 702. At 24, Source SN 703 may perform a sequence number status transfer to Source MN 702. At 25, Source MN 702 may perform a sequence number status transfer to Target MN-1 705. At 26, Target MN-1 705 may perform a sequence number status transfer to Target SN-1 704. At 27, UE 701 may perform a RACH procedure to synchronize to Target SN-1 704. At 28, target MN-1 705 may send an SN reconfiguration complete message to target SN-1 704. At 29, source SN 703 may send a secondary RAT usage report to source MN 702. At 30, source MN 702 may send a secondary RAT usage report to AMF 708. At 31, target MN-1 705 may send a path switch request to AMF 708. At 32, AMF 708 may send a bearer modification request to UPF 707. At 33, UPF 707 may send a new path to target MN-1 705. At 34, UPF 707 may send a new path to target SN-1 704. At 35, AMF 708 may send a path switch request acknowledgment to target MN-1 705. At 36, the target MN-1 may initiate a UE context release procedure toward the source MN 702. At 37, upon receiving the UE context release message from the source MN 702, the source SN 703 may release C-plane related resources associated with the UE context toward the source MN 702.

[0101] FIG. 8 depicts an example signaling diagram between a user equipment 801, a source master node 802, a source secondary node 803, one or more candidate target secondary nodes 804, one or more candidate target master nodes 805, a first core network node 807 (e.g., User Plane Function (UPF)), and a second core network node 808 (e.g., Access and Mobility Management (AMF)) in accordance with an example embodiment of the present subject matter. In the example of FIG. 8, the user equipment 801 is initially configured with dual connectivity with the source master node 802 and the secondary node 803. At 1, the source master node 802 may send a handover request to each of the candidate target master nodes 805. At 2, each of the candidate target master nodes 805 may send an SN Addition Request to a respective candidate target secondary node 804. At 3, each of the candidate target secondary nodes 804 may respond with an SN Addition Request Acknowledgement to a respective candidate target master node 805. At 4, each candidate target MN 805 may send an Xn-U address indication message to each candidate target SN 804, the Xn-U address indication message comprising address information of the interface Xn-U between the candidate target MN 805 and each candidate target SN 804. In particular, the Xn-U address indication message may comprise address information of a downlink (DL) transport network layer (TNL). At 5, each candidate target MN 805 may send a handover request acknowledgment message to the source MN 802. The request acknowledgment message may comprise a TEID for each direct tunnel (e.g., DRB tunnel) that may be established by the source MN 802 and each candidate target MN 805 or candidate target SN 804 to perform data transfer. At 6, the source MN 802 may send an XN-U address indication message to the source SN 803 to transfer data transfer information. At 7, the source MN 802 may trigger the UE 801 to perform handover and cell change and apply configuration.In particular, the source MN 702 may send an RRC connection reconfiguration message to enable on-time data transfer. At the same time, the source MN 702 may provide a flag to the UE 701 in 7 to configure the UE 701 to send a notification message when the CPC condition is met. The source MN 702 may also configure the UE 701 to include PCell measurements and a CHO condition status (such as whether the TTT for the CHO condition is running) in the CPC message. In 8, the UE 801 may monitor the CHO condition and the CPC condition. The UE 801 may check whether the candidate target MN 805 meets the CHO condition and whether the candidate target SN 804 meets the CPC condition. In 9, the CPC condition may be met by a candidate target SN (named target SN-1) even if the CHO condition is not met. The target SN-1 may serve the primary secondary cell PSCell-1. The target SN-1 may be associated with only a subset of the candidate target MNs 805. At 10, the UE 801 may send a message to the source MN 802 indicating that the CPC condition is met by the target SN-1. Optionally, this message may further comprise the current CHO measurement values ​​and the status of the CHO condition. At 11, the UE 801 continues checking the CHO condition and the CPC condition. The CHO condition may be checked for each candidate target MN of the candidate target MNs 805. The CPC condition may be checked for each candidate target SN of the candidate target SNs 804. At 12, the source MN 802 may select a subset of candidate target MNs associated with the target SN-1. For example, at 12, the source MN 802 may select TEIDs of the DRBs of the target PSCell-1 and of the corresponding subset of PCells. The subset of PCells may be further reduced by selecting a portion of the subset of PCells based on the CHO PCell measurements. The source MN 802 may use the selected TEIDs to establish direct tunnels with the subset of candidate target MNs and with the target SN-1.The source MN 802 may transmit sequence number status, including the sequence number status received at 13 from the source SN 803, to a subset of candidate target MNs 805 at 14. Each of the subset of candidate target MNs 805 may forward the sequence number status to an associated candidate target SN 804 at 15. Data forwarding occurs at 16 and 17. The source MN 802 may perform data forwarding to the subset of candidate target MNs 805 and associated candidate target SN-1.

[0102] At 18, the CPC leave condition is met. At 19, the UE 801 uses the connection to the source MN 802 to notify the source MN 802 about the fact that the CPC leave condition of the target SN-1 804 (or PSCell-1) is met. At 20, the source MN 802 may stop data transfer to each of the target MN 805 and the target SN-1. At 21, the UE 801 may perform monitoring of the CHO condition and the CPC condition. The CPC leave condition may also be referred to as a CPAC leave condition.

[0103] FIG. 9A is a diagram illustrating a process for monitoring CPC and CHO conditions by user equipment in a communication system 900 according to an embodiment of the present subject matter.

[0104] In the example of Figure 9A, user equipment 901 is initially configured with dual connectivity with a source master node and a source secondary node (not shown). User equipment 901 is served by the source master node in primary cell 903.1. User equipment 901 is served by the source secondary node in primary secondary cell 905.1. Communication system 900 further comprises two primary secondary cells 905.2, 905.3 served by respective secondary nodes, and two primary cells 903.2, 903.3 served by respective master nodes.

[0105] In this particular example, user equipment 901 is moving along trajectory 907. Figure 9A illustrates three positions 910.1, 910.2, and 910.3 of user equipment 901 along trajectory 907. Initially, user equipment 901 is at position 910.1, where user equipment 901 receives a reconfiguration message from the source master node indicating CHO and CPC configurations. While moving, user equipment 901 may check the CPC and CHO conditions. At user equipment 901's position 910.2, the CPC condition is met by primary secondary cell 905.2. Accordingly, user equipment 901 notifies the source master node, which may then initiate data transfer to the secondary node serving cell 905.2 and to the other two master nodes, since these nodes are both associated with primary secondary cell 905.2, i.e., each of the serving cells 903.2-3 overlaps with primary secondary cell 905.2. While the data transfer is in progress and user equipment 901 is at location 910.3, the CHO condition is satisfied by primary cell 903.3 because user equipment 901 is within primary cell 903.3. Thus, user equipment 901 may synchronize to the master node serving primary cell 903.3 and to the secondary node serving primary secondary cell 905.2.

[0106] FIG. 9B is a diagram illustrating a process for monitoring CPC and CHO conditions by user equipment in a communication system 900 according to an embodiment of the present subject matter.

[0107] In the example of Figure 9B, user equipment 901 is initially configured with dual connectivity with a source master node and a secondary node (not shown). User equipment 901 is served by a source master node in a primary cell 903.1. User equipment 901 is served by a source secondary node in a primary secondary cell 905.1. Communication system 900 further comprises two primary secondary cells 905.2, 905.3 served by respective secondary nodes, and two primary cells 903.2, 903.3 served by respective master nodes.

[0108] In this particular example, user equipment 901 is moving along trajectory 917. Figure 9B illustrates three positions 920.1, 920.2, and 920.3 of user equipment 901 along trajectory 917. Initially, user equipment 901 is at position 920.1, where user equipment 901 receives a reconfiguration message from the source master node indicating the CHO configuration and the CPC configuration. While moving, user equipment 901 may check the CPC and CHO conditions. At user equipment 901's position 920.2, the CPC condition is met by the primary secondary cell 905.2. Thus, user equipment 901 may notify the source master node, which may initiate data transfer to the secondary node serving cell 905.2 and to the other two master nodes, since these nodes are both associated with primary secondary cell 905.2, i.e., each of the serving cells 903.2-3 overlaps with primary secondary cell 905.2. However, while the data transfer is in progress and user equipment 901 is at location 920.3, the CPC leave condition is satisfied by primary secondary cell 905.2, since user equipment 901 is approaching primary secondary cell 905.3 and, in principle, the CPC condition could be satisfied when UE 901 is at location 920.3. Therefore, user equipment 901 may notify the source master node so that the source master node can stop the data transfer.

[0109] FIG. 9C is a diagram illustrating a process for monitoring CPC and CHO conditions by user equipment in a communication system 900 according to an embodiment of the present subject matter.

[0110] In the example of Figure 9C, user equipment 901 is initially configured with dual connectivity with a source master node and a secondary node (not shown). User equipment 901 is served by a source master node in a primary cell 903.1. User equipment 901 is served by a source secondary node in a primary secondary cell 905.1. Communication system 900 further comprises two primary secondary cells 905.2, 905.3 served by respective secondary nodes, and two primary cells 903.2, 903.3 served by respective master nodes.

[0111] In this particular example, user equipment 901 is moving along trajectory 927. Figure 9C illustrates three positions 930.1, 930.2, and 930.3 of user equipment 901 along trajectory 907. Initially, user equipment 901 is at position 930.1, where user equipment 901 receives a reconfiguration message from the source master node indicating the CHO configuration and the CPC configuration. While moving, user equipment 901 may check the CPC and CHO conditions. At user equipment 901's position 930.2, the CPC condition is met by the primary secondary cell 905.2. Thus, user equipment 901 may notify the source master node, which may initiate data transfer to the secondary node serving cell 905.2 and to the other two master nodes, because these nodes are both associated with primary secondary cell 905.2, i.e., each of the serving cells 903.2-3 overlaps with primary secondary cell 905.2. However, while the data transfer is in progress and user equipment 901 moves to location 930.3, the CPC leave or exit condition is satisfied by primary secondary cell 905.2 because user equipment 901 is now within primary cell 903.1. Therefore, user equipment 901 may notify the source master node so that the source master node can stop the data transfer.

[0112] FIG. 10 illustrates a block circuit diagram of an apparatus 1070 configured to implement at least a portion of the present subject matter. It should be noted that the apparatus 1070 illustrated in FIG. 10 may include additional elements or functions beyond those described hereinafter; however, these are not essential for understanding and are omitted herein for simplicity. Furthermore, the apparatus may be another device having similar functionality, such as a chipset, a chip, or a module, which may also be part of the apparatus or may be attached to the apparatus 1070 as a separate element. The apparatus 1070 may include a processing function or processor 1071, such as a central processing unit (CPU), that executes instructions provided by a program associated with a flow control mechanism. The processor 1071 may include one or more processing units dedicated to a specific process, as described below, or the process may be performed by a single processor. The portions for performing such specific processes may be provided as separate elements or in one or more additional processors or processing units, e.g., within a single physical processor, such as a CPU, or within multiple physical entities. Reference numeral 1072 denotes a transceiver or input / output (I / O) unit (interface) connected to the processor 1071. The I / O unit 1072 may be used to communicate with one or more other network elements, entities, terminals, etc. The I / O unit 1072 may be a composite unit comprising communication equipment to multiple network elements or may comprise a distributed structure comprising multiple different interfaces to different network elements. Reference numeral 1073 denotes a memory usable for example for storing data and programs executed by the processor 1071 and / or as working storage for the processor 1071.

[0113] The processor 1071 is configured to perform processing related to the subject matter described above. In particular, the device 1070 may be configured to perform the methods described in connection with Figure 3, Figure 4, Figure 5, or Figure 6.

[0114] For example, processor 1071 is configured for: transmitting a reconfiguration message for conditional handover to user equipment indicating a set of one or more candidate target master nodes and associated candidate target secondary nodes; receiving, by the device, a message from the user equipment indicating a particular candidate target secondary node among the candidate target secondary nodes in response to transmitting the reconfiguration message; and performing, by the device, a data transfer to the particular candidate target secondary node and to a subset of the candidate target master nodes associated with the particular candidate target secondary node.

[0115] Alternatively, processor 1071 is configured for receiving from the device a reconfiguration message for conditional handover indicating a condition for conditional handover to a set of candidate target master nodes, referred to herein as a CHO condition, and another condition for conditional primary secondary cell change (CPC) to the candidate target secondary node, referred to herein as a CPC condition; evaluating the CHO condition and the CPC condition; and, in response to determining that the CPC condition is satisfied by the particular candidate target secondary node, sending a message to the device indicating the particular candidate target secondary node.

[0116] As will be appreciated by those skilled in the art, aspects of the present invention may be embodied as an apparatus, a method, a computer program, or a computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, all of which may be referred to generally herein as a "circuit," "module," or "system." Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer-readable medium(s) having computer-executable code embodied therein. A computer program comprises computer-executable code or "program instructions."

[0117] Any combination of one or more computer-readable media may be utilized. A computer-readable medium may be a computer-readable storage medium. As used herein, "computer-readable medium" encompasses any tangible storage medium that can store instructions executable by a processor of a computing device. A computer-readable storage medium may also be referred to as a computer-readable non-transitory storage medium. A computer-readable storage medium may also be referred to as a tangible computer-readable medium. In some embodiments, a computer-readable storage medium may be capable of storing data accessible by a processor of a computing device.

[0118] "Computer memory" or "memory" is an example of a computer-readable storage medium. Computer memory is any memory that is directly accessible to a processor. "Computer storage" or "storage" is a further example of a computer-readable storage medium. Computer storage is any non-volatile computer-readable storage medium. In some embodiments, computer storage may also be computer memory, or vice versa.

[0119] As used herein, a "processor" encompasses an electronic component that can execute a program or machine-executable instructions, or computer-executable code. References to a computing device comprising a "processor" should be interpreted as potentially encompassing multiple processors or processing cores. A processor may be, for example, a multi-core processor. A processor may also refer to a collection of processors within a single computer system or distributed across multiple computer systems. The term computing device should also be interpreted as sometimes referring to a collection or network of computing devices, each comprising one or more processors. Computer-executable code may be executed by multiple processors, which may be within the same computing device or even distributed across multiple computing devices.

[0120] Computer-executable code may comprise machine-executable instructions or programs that cause a processor to perform aspects of the present invention. Computer-executable code for performing operations for aspects of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and traditional procedural programming languages ​​such as the "C" programming language, or similar programming languages, and may be compiled into machine-executable instructions. In some cases, the computer-executable code may be in the form of a high-level language or in a pre-compiled form and may be used in conjunction with an interpreter that generates the machine-executable instructions on the fly.

[0121] Typically, program instructions may be executed by one processor or by multiple processors. In the case of multiple processors, the multiple processors may be distributed among multiple different entities, with each processor being capable of executing some of the instructions intended for that entity. Thus, when referring to a system or process involving multiple entities, it is understood that the computer program or program instructions are adapted to be executed by processors associated with or related to the respective entities.

Claims

1. 1. An apparatus configured as a master node for serving user equipment in dual connectivity, the apparatus comprising: sending a message for conditional handover, referred to herein as a reconfiguration message, to the user equipment indicating a set of one or more candidate target master nodes and associated candidate target secondary nodes; receiving a message from the user equipment indicating at least one particular candidate target secondary node among the candidate target secondary nodes in response to transmitting the reconfiguration message; performing data transfer to the at least one particular candidate target secondary node and to a subset of the candidate target master nodes associated with the at least one particular candidate target secondary node; 12. An apparatus comprising: means configured for:

2. The means comprises: receiving measurement reports from the user equipment; In response to receiving the measurement reports, evaluating the measurement reports and sending a handover request to the set of candidate target master nodes based on the evaluation; receiving handover request acknowledgments from the set of candidate target master nodes indicating the candidate target secondary nodes; performing the submission of the reconfiguration message in response to receiving the handover request acknowledgment; and The apparatus of claim 1 configured for:

3. The means comprises: receiving a message from the user equipment indicating that the at least one particular candidate target secondary node satisfies a disassociation condition while performing the data forwarding; In response to receiving the message, stopping the data forwarding to the at least one particular candidate target secondary node and to the subset of the candidate target master nodes.

3. The device according to claim 1 or 2, configured for:

4. 4. The apparatus of claim 1, wherein the reconfiguration message indicates a condition for a conditional handover to the set of candidate target master nodes and another condition for a conditional primary secondary cell change (CPC) to the candidate target secondary node.

5. The apparatus of claim 1 , wherein the received message further indicates that the at least one particular candidate target secondary node satisfies a CPC condition defined in the reconfiguration message.

6. 6. The apparatus of claim 1, wherein the received message comprises cell measurements performed by the user equipment for cells served by the set of one or more candidate target master nodes, and wherein the means is further configured to select the subset of the candidate target master nodes based on the cell measurements.

7. 7. The apparatus of claim 2, wherein the handover request acknowledgment comprises data indicating endpoints of direct tunnels, and wherein the means is configured to use the data to establish direct tunnels between the apparatus, the at least one particular candidate target secondary node, and the subset of candidate target master nodes to perform the data transfer using the endpoints.

8. The apparatus of claim 7 , wherein the data comprises a tunnel endpoint identifier (TEID) of the direct tunnel.

9. The apparatus of any one of claims 2 to 8, wherein the means is configured to receive a handover success from a particular candidate target master node of the set of candidate target master nodes, and in response to receiving the handover success, stop the data forwarding to the candidate target nodes that are not the particular candidate target master node.

10. 10. The apparatus of claim 1, wherein the means comprises at least one processor and at least one memory containing computer program code, the at least one memory and the computer program code being configured to effect performance of the apparatus using the at least one processor.

11. A user equipment having dual connectivity with an apparatus that functions as a source master node and a source secondary node, the user equipment comprising: receiving from the device a reconfiguration message for conditional handover indicating conditions for a conditional handover CHO to a set of candidate target master nodes, referred to herein as CHO conditions, and another condition for a conditional primary secondary cell change (CPC) to a candidate target secondary node, referred to herein as CPC conditions; assessing the CHO condition and the CPC condition; In response to determining that the CPC condition is satisfied by at least one particular candidate target secondary node among the candidate target secondary nodes, sending a message to the device indicating the at least one particular candidate target secondary node; 11. A user equipment comprising: means configured for:

12. The user equipment of claim 11 , wherein the means is configured to transmit the message if the CHO condition is not met.

13. The means comprises:

13. The user equipment of claim 11 or 12, configured to, in response to determining that the CHO condition is satisfied for a particular candidate target master node, synchronize the user equipment to the particular candidate target master node and synchronize the user equipment to a selected particular candidate target secondary node of the at least one particular candidate target secondary node.

14. 14. The user equipment of claim 11, wherein the transmitted message comprises cell measurements performed by the user equipment for cells served by the set of one or more candidate target master nodes.

15. The means comprises: determining whether the at least one particular candidate target secondary node satisfies a CPC departure condition; if the CPC departure condition is satisfied by the at least one particular candidate target secondary node, sending another message to the device indicating that the CPC departure condition is satisfied by the at least one particular candidate target secondary node; A user equipment according to any one of claims 11 to 14, configured for:

16. 16. A user equipment according to any one of claims 11 to 15, wherein the means comprises at least one processor and at least one memory containing computer program code, the at least one memory and the computer program code being configured to effect performance of the user equipment using the at least one processor.

17. 1. A method comprising: transmitting, by the apparatus, to the user equipment, a message for conditional handover, referred to herein as a reconfiguration message, indicating a set of one or more candidate target master nodes and associated candidate target secondary nodes; receiving, by the apparatus, from the user equipment a message indicating at least one particular one of the candidate target secondary nodes in response to transmitting the reconfiguration message; performing, by the device, a data transfer to the at least one particular candidate target secondary node and to a subset of the candidate target master nodes associated with the at least one particular candidate target secondary node; A method comprising:

18. 18. The method of claim 17, wherein the received message comprises cell measurements performed by the user equipment for cells served by the set of one or more candidate target master nodes, the method further comprising selecting the subset of the candidate target master nodes based on the cell measurements.

19. For the device, at least transmitting a message for conditional handover, referred to herein as a reconfiguration message, to the user equipment indicating a set of one or more candidate target master nodes and associated candidate target secondary nodes; receiving a message from the user equipment indicating at least one particular candidate target secondary node among the candidate target secondary nodes in response to transmitting the reconfiguration message; performing data transfer to the at least one particular candidate target secondary node and to a subset of the candidate target master nodes associated with the at least one particular candidate target secondary node; A computer program comprising instructions for causing the computer to execute:

20. receiving, from the device, a reconfiguration message for conditional handover indicating conditions for a conditional handover to a set of candidate target master nodes, referred to herein as CHO conditions, and another condition for a conditional primary-secondary cell change (CPC) to the candidate target secondary nodes, referred to herein as CPC conditions; assessing the CHO condition and the CPC condition; In response to determining that the CPC condition is satisfied by at least one particular candidate target secondary node among the candidate target secondary nodes, sending a message to the device indicating the at least one particular candidate target secondary node; A method comprising:

21. For user equipment, at least receiving, from the device, a reconfiguration message for conditional handover indicating conditions for a conditional handover to a set of candidate target master nodes, referred to herein as CHO conditions, and another condition for a conditional primary-secondary cell change (CPC) to the candidate target secondary nodes, referred to herein as CPC conditions; assessing the CHO condition and the CPC condition; In response to determining that the CPC condition is satisfied by at least one particular candidate target secondary node among the candidate target secondary nodes, sending a message to the device indicating the at least one particular candidate target secondary node; A computer program comprising instructions for causing the computer to execute:

Images