Handover of a UE from a TRP common to a first and second network nodes

Abstract

A technique for changing a serving node is described. As to an aspect of the technique performed by a radio device (100; 1700; 2091; 2092) radio-connected to a radio access network, RAN (700), a method (400) comprises receiving (402), while radio-connected to a first network node (200; 1800; 2012) via a physical radio-access entity (702), a handover command to change a serving network node to a second network node (300; 1900; 2012), the physical radio-access entity (702) being shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012). The method (400) further comprises responsive to the received (402) handover command, changing (404) the serving network node of the radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012) while remaining radio-connected via the physical radio-access entity (702).

Description

[0001] Telefonaktiebolaget LM Ericsson (publ) 1 / 71

[0002] P112623WO01

[0003] Technique for changing a serving node

[0004] Technical Field

[0005] The present disclosure relates to a technique for serving-node change in a radio access network (RAN). More specifically, and without limitation, methods performed during a handover by a radio device and by source and target network nodes for handing over the radio device as well as corresponding devices in a RAN are provided.

[0006]

[0007] Communications technology has progressively evolved under global standardization efforts by organizations such as the Third Generation Partnership Project (3 GPP) and the O-RAN Alliance. These initiatives have introduced increasingly flexible radio-access architectures and multi-network connectivity to support the diverse demands on mobile communications.

[0008] Modem radio access technologies often leverage specialized front-end radio units, distributed computing resources, and real-time coordination to combine advanced features such as beamforming with distributed multi-antenna systems, e.g. in multiple Transmit / Receive Point (mTRP) operation introduced in 3 GPP Release 16. These features allow radio devices to maintain stable connectivity even under dynamic conditions imposed by user mobility and interference.

[0009] However, conventional approaches encounter challenges when a radio device is handed over across boundaries of serving-node responsibility within the RAN. The transition of serving-node control at cell boundaries can introduce unwanted delays, signaling overhead, and short intermptions, especially under challenging radio conditions or tight latency requirements.

[0010]

[0011] Accordingly, there is a need for a technique of changing a serving node for improved seamless mobility, reducing or avoiding disruption.

[0012] As to a first method aspect, a method performed by a radio device that is radioconnected to a radio access network (RAN) is provided according to claim 1. The methodTelefonaktiebolaget LM Ericsson (publ) 2 / 71

[0013] P112623WO01

[0014] comprises receiving a handover command. This reception occurs while the radio device is radio-connected via a physical radio-access entity to a first network node. The physical radio-access entity is shared between the first network node and a second network node. The method further comprises, e.g. in response to the handover command, changing the serving network node of the radio device from the first network node to the second network node. The radio device remains radio-connected via the physical radio-access entity during or after the change of the serving node.

[0015] By receiving the handover command while connected to the shared physical radioaccess entity, and by changing the serving network node without altering that physical entity, method embodiments enable the radio device to avoid a complete reorientation of physicallayer parameters. At least some embodiments maintain synchronization and / or reduce signaling overhead during or after the handover. These and further embodiments can reduce interruption times or improve radio-resource efficiency in transitions beyond conventional cell borders that were based on degraded radio link quality.

[0016] The first method aspect may further comprise any feature and / or any step disclosed in the context of below-mentioned further method aspects, or a feature and / or step corresponding thereto, e.g., a receiver counterpart to a transmitter feature or step.

[0017] As to a second method aspect, a method performed by a first network node of a radio access network (RAN) is provided according to claim 25. The method comprises sending, to a second network node of the radio access network, a request for a handover of a radio device from the first network node to the second network node. This request or subsequent inter-node signaling may be indicative of the radio device remaining connected to a physical radio-access entity shared between the first network node and the second network node. The method further comprises transmitting, to the radio device that is connected via the shared radio-access entity, a handover command to change the serving network node to the second network node.

[0018] By sending the request for handover between network nodes that share the physical radio-access entity, and by transmitting a handover command that allows the device to remain continuously connected to this same physical entity, method embodiments enable the first network node and the second network node to complete handover functionality with limited impact on the radio device. At least some embodiments of this coordinated approach enable a controlled transition of user-plane and / or control-plane functions, and / or mitigating data-flow interruptions, and / or allowing the network nodes to manage mobility more efficiently in terms of fronthaul signaling between the network nodes and / or downlink radioTelefonaktiebolaget LM Ericsson (publ) 3 / 71

[0019] P112623WO01

[0020] signaling to the radio device. Alternatively or in addition, method embodiments increase a time window for the first network node and / or the second network node to perform the handover, e.g. for inter-node signaling and / or control communication and / or data forwarding with a core network.

[0021] The second method aspect may further comprise any feature and / or any step disclosed in the context of the first method aspect or below-mentioned third method aspect, or a feature and / or step corresponding thereto, e.g., a receiver counterpart to a transmitter feature or step.

[0022] As to a third method aspect, a method of performed by a second network node in a radio access network (RAN) is provided according to claim 34. The method comprises receiving, from a first network node, a request to assume serving-node control of a radio device while maintaining a physical radio-access entity used by the radio device. The method further comprises, in response to the request, receiving a random access via the physical radio-access entity from the radio device and / or transmitting via the physical radioaccess entity to the radio device, optionally through the first network node, configuration information enabling continued communication for the radio device with the second node via the physical radio-access entity.

[0023] By receiving, from the first network node, a request to assume control of the radio device (e.g., any functionality of a serving network node) while that device remains on the same radio-access entity, and then facilitating a (e.g., contention-free or contention-based) random-access reception from the radio device via said physical entity and / or a configuration transmission to the radio device via that unchanged physical entity, the second network node keeps the radio link intact through the transition (handover). In other words, since the device need not alter its underlying radio access connection when switching to the second node’s control, the usual or potential conventional disruptions associated with re-establishing a new link can be eliminated or greatly reduced. For example, this directly addresses the problem of having to re-synchronize physical radio parameters upon serving-node change, thereby ensuring that communication continuity is preserved and seamless mobility is achieved.

[0024] The third method aspect may further comprise any feature and / or any step disclosed in the context of above-mentioned first and / or second method aspects, or a feature and / or step corresponding thereto, e.g., a receiver counterpart to a transmitter feature or step.

[0025] In any aspect, the first and second network nodes may be source and target network nodes, respectively, of the handover. Alternatively or in addition, any one of the three method aspects may be implemented as a serving-node change (e.g., a serving-node update)Telefonaktiebolaget LM Ericsson (publ) 4 / 71

[0026] P112623WO01

[0027] using a radio-access entity shared between the source and target network nodes, e.g. a shared cell and / or (e.g., for inter-RAT handover) a shared TRP.

[0028] The technique may be implemented in accordance with, or by amending, a technical specification of 3GPP or the Wi-Fi Alliance, e.g., for 3GPP release 20 or 21 or beyond WiFi 6. Embodiments may implement the technique for 3GPP New Radio (NR) or beyond, e.g. by modifying at least one of the 3GPP document TS 38.300, version 18.4.0; TS 38.331, version 18.4.0; and / or TS 38.413, version 18.4.0.

[0029] In any radio access technology (RAT), the technique may be implemented for a sidelink (SL) between radio devices. The SL may be implemented using proximity services (ProSe), e.g. according to a 3GPP specification. Further first and / or second radio devices may function as the first and / or second network node, e.g. in a radio mesh network as the RAN.

[0030] Any radio device may be a user equipment (UE), e.g., according to a 3 GPP specification. The radio device and the first and / or second network nodes (or the RAN) may be wirelessly connected in an uplink (UL) and / or a downlink (DL) through a Uu interface. Alternatively or in addition, the SL may enable a direct radio communication between proximal radio devices, e.g., a remote radio device and a relay radio device, optionally using a PC5 interface. Services provided using the SL or the PC5 interface may be referred to as proximity services (ProSe).

[0031] The radio device and / or the first network node and / or the second network node and / or the RAN may form, or may be part of, a radio network, e.g., according to the Third Generation Partnership Project (3GPP) or according to the standard family IEEE 802.11 (Wi-Fi). The first method aspect, the second method aspect, and the third method aspect may be performed by one or more embodiments of the radio device, the first network node (e.g., a first base station of the RAN), and the second network node (e.g., a second base station of the RAN), respectively.

[0032] The RAN may comprise one or more base stations, e.g., performing the second and / or third method aspects. Alternatively or in addition, the radio network may be a vehicular, ad hoc and / or mesh network comprising three or more radio devices, e.g., acting as the radio device and / or the first network node and / or the second network node.

[0033] Any of the radio devices may be a 3GPP user equipment (UE) or a Wi-Fi station (STA). The radio device may be a mobile or portable station, a device for machine-type communication (MTC), a device for narrowband Internet of Things (NB-IoT) or a combination thereof. Examples for the UE and the mobile station include a mobile phone, aTelefonaktiebolaget LM Ericsson (publ) 5 / 71

[0034] P112623WO01

[0035] tablet computer and a self-driving vehicle. Examples for the portable station include a laptop computer and a television set. Examples for the MTC device or the NB-IoT device include robots, sensors and / or actuators, e.g., in manufacturing, automotive communication and home automation. The MTC device or the NB-IoT device may be implemented in a manufacturing plant, household appliances and consumer electronics.

[0036] Whenever referring to the RAN, the RAN may be implemented by one or more network nodes (e.g., base stations) including at least one embodiment of the shared radioaccess entity.

[0037] The radio device may be wirelessly connected or connectable (e.g., according to a radio resource control, RRC, state or active mode) with the first network node and / or the second network node of the RAN. The first and second network node may or may not operate according to the same radio access technology (RAT). For example, one of the first and second network nodes may operate according to a fifth generation (5G) RAT. The other one of the first and second network nodes may operate according to a sixth generation (6G) RAT.

[0038] The first and / or second network node (e.g., a base station) may encompass any station that is configured to provide radio access to the radio device or any of the radio devices. The physical radio-access entity may be a base station, a cell, a transmission and reception point (TRP), a central unit (CU), a distributed unit (DU), a radio access node or an access point (AP). Optionally, the first and / or second network node may provide a data link to a host computer providing user data to the radio device or gathering user data from the radio device. Examples for the base stations may include a 3G base station or Node B (NB), 4G base station or eNodeB (eNB), a 5Gbase station or gNodeB (gNB), a 6Gbase station or xNB, a Wi-Fi AP, and a network controller (e.g., according to Bluetooth, ZigBee or Z-Wave).

[0039] The RAN may be implemented according to the Global System for Mobile Communications (GSM), the Universal Mobile Telecommunications System (UMTS), 3GPP Long Term Evolution (LTE), 3GPP New Radio (NR), and / or 6G RAT.

[0040] Any aspect of the technique may be implemented on a Physical Layer (PHY), a Medium Access Control (MAC) layer, a Radio Link Control (RLC) layer, a packet data convergence protocol (PDCP) layer, and / or a Radio Resource Control (RRC) layer of a protocol stack for the radio communication.

[0041] Herein, referring to a protocol of a layer may also refer to the corresponding layer in the protocol stack. Vice versa, referring to a layer of the protocol stack may also refer to theTelefonaktiebolaget LM Ericsson (publ) 6 / 71

[0042] P112623WO01

[0043] corresponding protocol of the layer. Any protocol may be implemented by a corresponding method.

[0044] As to another aspect, a computer program product is provided. The computer program product comprises program code portions for performing any one of the steps of the first and / or second and / or third method aspects disclosed herein when the computer program product is executed by one or more computing devices. The computer program product may be stored on a computer-readable recording medium. The computer program product may also be provided for download, e.g., via the radio network, the RAN, the Internet and / or the host computer. Alternatively, or in addition, the method may be encoded in a Field-Programmable Gate Array (FPGA) and / or an Application-Specific Integrated Circuit (ASIC), or the functionality may be provided for download by means of a hardware description language.

[0045] As to a first device aspect, a device (e.g., a radio device) according to claim 37 or 39 is provided. The device may be configured to perform any one of the steps of the first method aspect. As to a further first device aspect, the device comprises processing circuitry (e.g., at least one processor and a memory). Said memory comprises instructions executable by said at least one processor whereby the device is operative to perform any one of the steps of the first method aspect.

[0046] As to a second device aspect, a device (e.g., a first network node) according to claim 41 or 43 is provided. The device may be configured to perform any one of the steps of the second method aspect. As to a further second device aspect, the device comprises processing circuitry (e.g., at least one processor and a memory). Said memory comprises instructions executable by said at least one processor whereby the device is operative to perform any one of the steps of the second method aspect.

[0047] As to a third device aspect, a device (e.g., a second network node) according to claim 45 or 47 is provided. The device may be configured to perform any one of the steps of the third method aspect. As to a further third device aspect, the device comprises processing circuitry (e.g., at least one processor and a memory). Said memory comprises instructions executable by said at least one processor whereby the device is operative to perform any one of the steps of the third method aspect.

[0048] As to a still further aspect a communication system including a host computer is provided. The host computer comprises a processing circuitry configured to provide user data, e.g., included in user data of a transmission before and after the handover. The host computer further comprises a communication interface configured to forward the user dataTelefonaktiebolaget LM Ericsson (publ) 7 / 71

[0049] P112623WO01

[0050] to a cellular network (e.g., the RAN and / or the first and / or second network node) for transmission to a UE. A processing circuitry of the cellular network is configured to execute any one of the steps of the second and / or third method aspects. Alternatively or in addition, the UE comprises a radio interface and processing circuitry, which is configured to execute any one of the steps of the first method aspect.

[0051] The communication system may further include the UE. Alternatively or in addition, the cellular network may further include one or more physical radio-access entities (e.g., TRPs or base stations) configured for radio communication with the UE and / or to provide the data link between the UE and the host computer using the second and / or third method aspects.

[0052] The processing circuitry of the host computer may be configured to execute a host application, thereby providing the user data and / or any host computer functionality described herein. Alternatively, or in addition, the processing circuitry of the UE may be configured to execute a client application associated with the host application.

[0053] Any one of the devices, the radio device (e.g., UE), the first and / or second network nodes (e.g., base stations), the communication system or any node or station for embodying the technique may further include any feature disclosed in the context of the method aspect, and vice versa. Particularly, any one of the units and modules disclosed herein may be configured to perform or initiate one or more of the steps of the method aspect.

[0054] Brief Description of the Drawings

[0055] Further details of embodiments of the technique are described with reference to the enclosed drawings, wherein:

[0056] Fig. 1 shows a schematic block diagram of an embodiment of a device being handed over in terms of a serving network node within a radio access network;

[0057] Fig. 2 shows a schematic block diagram of an embodiment of a device for a source network node handing over a radio device within a radio access network;

[0058] Fig. 3 shows a schematic block diagram of an embodiment of a device for a target network node being handed over a radio device within a radio access network;

[0059] Fig. 4 shows a flowchart for a method of a radio device being handed over in terms of a serving network node within a radio access network, which method may be implementable by the device of Fig. 1;Telefonaktiebolaget LM Ericsson (publ) 8 / 71

[0060] P112623WO01

[0061] Fig. 5 shows a flowchart for a method of handing over a radio device at a source network node within a radio access network, which method may be implementable by the device of Fig. 2;

[0062] Fig. 6 shows a flowchart for a method of being handed over a radio device at a target network node within a radio access network, which method may be implementable may be implementable by the device of Fig. 3;

[0063] Fig. 7 schematically illustrates a first example of a radio network comprising embodiments of the devices of Figs. 1, 2, and 3 for performing the methods of Figs. 4, 5, and 6, respectively;

[0064] Fig. 8 schematically illustrates a second example of a radio network comprising embodiments of the devices of Figs. 1, 2, and 3 for performing the methods of Figs. 4, 5, and 6, respectively;

[0065] Fig. 9 schematically illustrates a third example of a radio network comprising embodiments of the devices of Figs. 1, 2, and 3 for performing the methods of Figs. 4, 5, and 6, respectively;

[0066] Fig. 10 schematically illustrates a signaling diagram resulting from embodiments of the devices of Figs. 1, 2, and 3 performing the methods of Figs. 4, 5, and 6, respectively, optionally using the same radio access technology by the devices of Figs. 5 and 6;

[0067] Fig. 11 schematically illustrates a signaling diagram resulting from embodiments of the devices of Figs. 1, 2, and 3 performing the methods of Figs. 4, 5, and 6, respectively, optionally using the different radio access technologies by the devices of Figs. 5 and 6;

[0068] Fig. 12 schematically illustrates a first example of a radio access procedures, which may be performed by the devices of the Figs. 1 and 3 in a step of the methods of Figs. 4 and 6;

[0069] Fig. 13 schematically illustrates a second example of a radio access procedures, which may be performed by the devices of the Figs. 1 and 3 in a step of the methods of Figs.

[0070] 4 and 6;

[0071] Fig. 14 schematically illustrates a third example of a radio access procedures, which may be performed by the devices of the Figs. 1 and 3 in a step of the methods of Figs. 4 and 6;

[0072] Fig. 15 schematically illustrates a fourth example of a radio access procedures, which may be performed by the devices of the Figs. 1 and 3 in a step of the methods of Figs. 4 and 6;Telefonaktiebolaget LM Ericsson (publ) 9 / 71

[0073] P112623WO01

[0074] Fig. 16 schematically illustrates a signaling diagram including optional steps that may be further performed by embodiments of the devices of Figs. 1, 2, and 3 according to embodiments of the methods of Figs. 4, 5, and 6, respectively;

[0075] Fig. 17 shows a schematic block diagram of a radio device embodying the device of Fig. 1;

[0076] Fig. 18 shows a schematic block diagram of a source network node embodying the device of Fig. 2;

[0077] Fig. 19 shows a schematic block diagram of a target network node embodying the device of Fig. 3; and

[0078] Fig. 20 schematically illustrates an example telecommunication network connected via an intermediate network to a host computer.

[0079] Detailed Description

[0080] In the following description, for purposes of explanation and not limitation, specific details are set forth, such as a specific network environment in order to provide a thorough understanding of the technique disclosed herein. It will be apparent to one skilled in the art that the technique may be practiced in other embodiments that depart from these specific details. Moreover, while the following embodiments are primarily described for a modification of a New Radio (NR) or 5G system, it is readily apparent that the technique described herein may also be implemented for any other radio communication technique, including a Wireless Local Area Network (WLAN) implementation according to the standard family IEEE 802.11, 6GRAT, 3GPP LTE, for Bluetooth according to the Bluetooth Special Interest Group (SIG), particularly Bluetooth Low Energy, Bluetooth Mesh Networking and Bluetooth broadcasting, for Z-Wave according to the Z-Wave Alliance or for ZigBee based on IEEE 802.15.4.

[0081] Moreover, those skilled in the art will appreciate that the functions, steps, units and modules explained herein may be implemented using software functioning in conjunction with a programmed microprocessor, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Digital Signal Processor (DSP) or a general-purpose computer, e.g., including an Advanced RISC Machine (ARM). It will also be appreciated that, while the following embodiments are primarily described in context with methods and devices, the invention may also be embodied in a computer program product as well as in a system comprising at least one computer processor and memory coupled toTelefonaktiebolaget LM Ericsson (publ) 10 / 71

[0082] P112623WO01

[0083] the at least one processor, wherein the memory is encoded with one or more programs that may perform the functions and steps or implement the units and modules disclosed herein.

[0084] As to a first method aspect, a method performed by a radio device radio-connected to a radio access network (RAN) is provided. The method comprises receiving, while radioconnected to a first network node via a physical radio-access entity, a handover command to change a serving network node to a second network node, wherein the physical radio-access entity is shared between the first network node and the second network node. The method comprises, responsive to the handover command, changing the serving network node of the radio device from the first network node to the second network node while remaining radioconnected via the physical radio-access entity.

[0085] Embodiments of the method allow the radio device to seamlessly change its serving network node without changing a physical access point or associated physical access parameters to the RAN, thereby enabling a faster and more efficient handover with minimal interruption to the connection.

[0086] Same or further embodiments allow to decouple the handover from changing the radio-access entity. For example, the handover may be performed while the physical radio link to the radio-access entity is still in a good state. Alternatively or in addition, a prior or subsequent change in the radio-access entity, to which the radio device is connected, may be controlled efficiently as an intra-network node handover.

[0087] Herein, “handover” may encompass a change of a serving network node (e.g., from the perspective of a radio device or relative to a radio device). “Mobility” (e.g., in a connected state of the radio device) may be used synonymously with handover. In other words, switching from the first network node to the second network node may be referred to as the handover.

[0088] Moreover, “network node” may encompass a physical and / or logical termination at the RAN for a core network.

[0089] Herein, remaining radio-connected (or maintaining a radio connection) via the radioaccess entity may mean that at least one physical access point (e.g., a TRP or cell or beam or section) used by the radio device prior to the handover is maintained after the handover. Herein, remaining radio-connected via the physical radio-access entity is also referred to as maintaining the physical radio-access entity.

[0090] The physical radio-access entity may encompass any piece of hardware for radio access to the RAN, e.g. any physical radio interface. For brevity, the shared physical radioaccess entity is also referred to as the radio-access entity.Telefonaktiebolaget LM Ericsson (publ) 11 / 71

[0091] P112623WO01

[0092] The shared radio-access entity may be further defined by one or more characteristics as set out in the following options.

[0093] Alternatively or additionally, the shared radio-access entity may comprise one physical entity for radio access to the RAN.

[0094] Alternatively or additionally, the shared radio-access entity may be associated with at least one physical access parameter for radio access to the RAN, and the at least one physical access parameter may be unchanged when changing the serving network node of the radio device from the first network node to the second network node.

[0095] Alternatively or additionally, the radio-access entity may comprise at least one of: one transmission and reception point (TRP) shared between and / or fronthaul -connected to both the first network node and the second network node; one radio unit (RU) shared between and / or fronthaul -connected to both the first network node and the second network node; one location where transmission and reception of radio signals of the RAN occurs; one radio-frequency transmitter chain and one radio-frequency receiver chain; and one collocated antenna system, optionally wherein the collocated antenna system comprising a plurality of antenna elements for multiple-input multiple-output (MIMO) transmission and reception.

[0096] Herein, “TRP” may encompass a physical radio-access point of the RAN. The shared radio-access entity may be related to a physical location for radio transmission and radio reception in the RAN.

[0097] Alternatively or in addition, the shared TRP may comprise a physical antenna system shared between the first network node and the second network node. The antenna system may be an antenna panel. The plurality of antenna elements may be coupled to the radio frequency transmitter chain and the radio frequency receiver chain of the TRP. The radiofrequency transmitter chain may comprise a precoder for multiple-input single-output (MISO) or MIMO transmission (e.g., beamforming transmission). The radio-frequency receiver chain may comprise a combiner for single-input multiple -output (SIMO) or MIMO reception (e.g., beamforming reception).

[0098] The radio-access entity (e.g., the TRP or the antenna system) comprising (e.g., representing) a location for transmission and reception in the RAN may mean that the first network node before the handover and the second network node after the handover are collocated from the perspective of the radio device.

[0099] More than one radio-access entity may be shared between the first and second network nodes an / or maintained during the handover, preferably meaning that each of theTelefonaktiebolaget LM Ericsson (publ) 12 / 71

[0100] P112623WO01

[0101] shared radio-access entities is maintained. Alternatively or in addition, more than one TRP or more than one RU may be shared between the network nodes and / or maintained during the handover, preferably meaning that each of the shared TRPs and / or shared RUs is maintained. In other words, maintaining more than one physical radio-access entity or maintaining more than one location, where transmission and reception of radio signals of the RAN occur, does not mean that (e.g., out of a set of radio-access entity or a set of locations) disjoint subsets are used before and after the handover. Rather, there is a non-empty (i.e., non-zero) overlap in terms of one or more radio-access entities (e.g., one or more locations) that are used by the radio device before and after the handover.

[0102] The shared radio-access entity may be associated with one or more of the alternatives set out in the following options.

[0103] Alternatively or additionally, the shared radio-access entity may be associated with a shared cell served by both the first network node and the second network node via the shared radio-access entity.

[0104] Alternatively or additionally, the shared radio-access entity may be associated with a shared carrier frequency used by both the first network node and the second network node via the shared radio-access entity. For example, the shared carrier frequency may be used in combination with different radio access techniques (RATs) provided by the first network node and the second network node via the shared radio-access entity.

[0105] Alternatively or additionally, a 5G Cell and a 6G cell can use the same shared carrier. Alternatively or additionally, the shared radio-access entity may be associated with a common radio access technique (RAT) used by both the first network node and the second network node via the shared radio-access entity.

[0106] The radio device may use one carrier frequency and one shared TRP on that carrier frequency.

[0107] The radio-access entity may be associated with a cell in terms of a cell identifier (cell ID or physical cell ID, PCI), e.g. periodically transmitted by the radio-access entity using a primary synchronization signal (PSS) and / or a secondary synchronization signal (SSS). The radio-access entity being “shared” may mean that the same cell ID is broadcast by the radioaccess entity when used by the first and second network nodes.

[0108] Alternatively or in addition, the radio-access entity may be associated with a cell in terms of a coverage area (e.g., a section) of the RAN covered by the radio-access entity. The radio-access entity being “shared” may mean that the coverage area of the first and second network nodes when using the radio-access entity overlaps or is essentially identical.Telefonaktiebolaget LM Ericsson (publ) 13 / 71

[0109] P112623WO01

[0110] Alternatively or in addition, the radio-access entity may comprise a radio unit (RU) and / or a physical layer (PHY) according to the RAT used by both the first network node and the second network node.

[0111] The radio device may remain connected via the radio-access entity reusing one or more physical access parameters before and after the handover, and / or the radio device may remain connected via the radio-access entity using or converting at least one parameter, entity, value, or information as set out in the following options.

[0112] Alternatively or additionally, the radio device may remain connected via the radioaccess entity reusing one or more physical access parameters before and after the handover.

[0113] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same cell before and after the handover.

[0114] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same radio spectrum before and after the handover. For example, the same carrier frequency may be used before and after the handover.

[0115] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same radio access technology (RAT) before and after the handover.

[0116] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same physical cell identifier (PCI) before and after the handover.

[0117] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same timing advance (TA) before and after the handover.

[0118] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same system frame number (SFN) before and after the handover.

[0119] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same search space for downlink control information (DCI) scheduling system information (SI) before and after the handover.

[0120] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same public land mobile network identifier (PLMN ID) before and after the handover.Telefonaktiebolaget LM Ericsson (publ) 14 / 71

[0121] P112623WO01

[0122] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same time-frequency position of a synchronization signal block (SSB) before and after the handover.

[0123] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same radio parameter values for a random-access channel (RACH) before and after the handover.

[0124] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same radio parameter values of a control resource set (CORESET) for monitoring a physical downlink control channel (PDCCH) before and after the handover.

[0125] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same radio access technology cell identifier (RAT cell ID) before and after the handover. For example, the same New Radio Cell Identifier (NCI) may be used before and after the handover.

[0126] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same radio parameter values of a transmission configuration indication (TCI) before and after the handover.

[0127] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same radio parameter values of a Quasi Co-Location (QCI) before and after the handover. For example, the same QCL source may be used before and after the handover.

[0128] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same values of beamforming weights before and after the handover. For example, the beamforming weights may be for a transmit beam to the radio-access entity or a receive beam from the radio-access entity.

[0129] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same channel state information (CSI) before and after the handover.

[0130] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same value of a precoding matrix indicator (PMI) before and after the handover.

[0131] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same link adaptation before and after the handover.Telefonaktiebolaget LM Ericsson (publ) 15 / 71

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[0133] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same modulation and coding scheme (MCS) before and after the handover.

[0134] Alternatively or additionally, the radio device may remain connected via the radioaccess entity using or converting the same radio network temporary identifier (RNTI) before and after the handover. For example, the same permanent cell RNTI (C-RNTI) and / or the same paging RNTI (P-RNTI) may be used before and after the handover.

[0135] Any of the above-listed maintained values (e.g., information) may be an example of the one or more physical access parameters re-used after the handover.

[0136] Herein, “using” (at least one of the above-listed entities, values or information) may also be referred to as re-using, e.g. by keeping the values used before the handover also after the handover.

[0137] Furthermore, “converting” (at least one of the above-listed entities, values or information) may comprise using or re-using values after converting the values from a format or scheme used by a source RAT performed by the first network node to a target RAT performed by the second network node. The converting may also be referred to as translation. The converting may or may not maintain an explicit value, e.g. but rather its physical meaning may be maintained, e.g. when changing the RAT. A translation from value to physical meaning may differ for different RATs (e.g. 5G and 6G).

[0138] The first and second network nodes may coordinate how they connect to the radio device via the same (i.e., shared) radio-access entity, e.g. to hand off control of the same shared cell (or TRP), so that the second network node keeps using an identical RNTI space without collision. For example, the first node may send the context of the radio device (optionally including the existing C-RNTI), and both first and second network nodes make use of a shared scheduling / arbitration scheme that ensures the same physical radio parameters and identifier remain valid when switching the “serving node.” This coordination entails exchanging information about ongoing uplink / downlink allocations, security / state parameters, and the UE’s MAC -lay er identity so that the second node can seamlessly assume radio control of the UE (optionally under the same RNTI) while the radio device remains on the same (i.e., shared) radio-access entity.

[0139] Re-using the RNTI may be applicable for a cell shared between the first and second network nodes. E.g., the same RAT (e.g. 6G) may be used before and after the handover in the shared cell.Telefonaktiebolaget LM Ericsson (publ) 16 / 71

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[0141] Optionally, each C-RNTI may be uniquely associated to one UE, or the C-RNTI may be unique within a cell amongst all RRC connected UE’s in a cell. Each of the first and second network nodes may make sure of this uniqueness per UE and cell. The uniqueness can be implemented in several ways. In case of a shared cell, the second network node may continue using the already unique association for C-RNTI, Cell, and UE; or it may select a new C-RNTI from a coordinated set of C-RNTIs between first and second network nodes, i.e. a network node-unique set of C-RNTIs to use for radio devices that is disjoint from the set of the other network node. In case of a shared carrier (e.g., when the handover includes a change from a 5G cell to a 6G cell), the C-RNTI may be a RAT-specific value (which can make it unique per RAT).

[0142] The shared radio-access entity may be controlled by at least one of the first network node and the second network node.

[0143] Alternatively or additionally, the shared radio-access entity may be controlled by the first network node.

[0144] Alternatively or additionally, the shared radio-access entity may be controlled by the second network node.

[0145] Each of the first network node and the second network node may have direct access to the radio radio-access entity.

[0146] Each of the first network node and the second network node may have logical access to radio resources of the shared radio-access entity.

[0147] At least one of the shared radio-access entity, the first network node, and the second network node may comprise a radio resource control entity for radio resources of the shared radio-access entity.

[0148] Alternatively or additionally, the shared radio-access entity may comprise the radio resource control entity for radio resources of the shared radio-access entity.

[0149] Alternatively or additionally, the first network node may comprise the radio resource control entity for radio resources of the shared radio-access entity.

[0150] Alternatively or additionally, the second network node may comprise the radio resource control entity for radio resources of the shared radio-access entity.

[0151] The radio resource control entity may be configured to share (e.g., schedule or coordinate scheduling) radio resources of the shared radio-access entity. In other words, the radio resource control entity may be a common radio resource control coordinator for the shared radio resources of the radio-access entity.Telefonaktiebolaget LM Ericsson (publ) 17 / 71

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[0153] Where the first and second network nodes share the radio-access entity (e.g., a cell or a TRP), they may use a shared arbitrator or scheduler, e.g. in the radio hardware (e.g., in a baseband unit). Embodiments including the arbitrator can ensure that only one of the first and second network nodes at a time performs Link Adaptation or HARQ scheduling for the radio device, preventing collisions in resource allocation while still allowing seamless transition from one controlling node to another.

[0154] The radio resource control entity may be further configured in accordance with one or more of the following options.

[0155] Alternatively or additionally, the radio resource control entity may be configured to distribute the radio resources of the shared radio-access entity between the first network node and the second network node.

[0156] Alternatively or additionally, the radio resource control entity may be configured to schedule the radio resources of the shared radio-access entity.

[0157] Alternatively or additionally, the radio resource control entity may be configured to coordinate scheduling of the radio resources of the shared radio-access entity.

[0158] Alternatively or additionally, the radio resource control entity may be configured to provide contention-free access to radio resources of the shared radio-access entity.

[0159] Alternatively or additionally, the radio resource control entity may comprise an arbitrator for radio resources of the radio-access entity shared between the first network node and the second network node.

[0160] Alternatively or additionally, the radio resource control entity may comprise a shared scheduler for radio resources of the radio-access entity shared between the first network node and the second network node.

[0161] Herein, “contention-free” may refer to a radio interface of the radio-access entity. “Contention-free” does not necessarily refer to a (e.g., wired) interface between the radioaccess entity and each of the first and second network nodes. That is, the first and second network nodes may use, free of contention, the radio resources of the radio-access entity, meaning that their transmissions over the radio interface of the radio-access entity do not experience contention. However, this does not necessarily imply contention-free procedures for requests (e.g., scheduling requests) of the network nodes to the radio-access entity.

[0162] The radio resources may be further defined in accordance with one or more of the following options.

[0163] Alternatively or additionally, the radio resources may comprise spectral resources for transmitting and / or receiving at the radio-access entity.Telefonaktiebolaget LM Ericsson (publ) 18 / 71

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[0165] Alternatively or additionally, the radio resources may comprise temporal resources for transmitting and / or receiving at the radio-access entity.

[0166] Alternatively or additionally, the radio resources may comprise spatial resources for transmitting and / or receiving at the radio-access entity.

[0167] Alternatively or additionally, the radio resources may be shared between the first network node and the second network node.

[0168] The radio-access entity and / or operation of the radio device may be further defined in accordance with one or more of the following options.

[0169] Alternatively or additionally, the radio-access entity may comprise multiple cells shared between and / or fronthaul-connected to both the first network node and the second network node.

[0170] Alternatively or additionally, the radio-access entity may comprise multiple TRPs shared between and / or fronthaul-connected to both the first network node and the second network node.

[0171] Alternatively or additionally, the radio device may be configured to use multiple TRPs before and after the handover.

[0172] While the technique is described for one shared physical radio-access entity, the first and second network node may share multiple physical radio-access entities or the shared physical radio-access entity may be defined to comprise multiple shared cells and / or multiple shared TRPs. These multiple shared cells may provide an area (e.g., between areas exclusively covered by only one of the first and second network nodes) for spatial hysteresis of the handover. Alternatively or in addition, a multi -connectivity of the radio device may be maintained by the handover.

[0173] The radio device may use the same set of multiple TRPs on the same one carrier frequency before and after the handover.

[0174] By virtue of the radio resource control entity, the radio device may reuse the one carrier frequency independent of with which one of the multiple TRP the radio device is communicating. Furthermore, the radio resource control entity may gradually allocate (e.g., schedule) less radio resources for the radio device at the first TRP of the multiple TRPs and more radio resource for the radio device at the second TRP of the multiple TRPs, e.g. as the radio device moves away from the first TRP and / or towards the second TRP.

[0175] The radio device may use the same set of carrier frequencies for the multiple TRPs, respectively, before and after the handover.Telefonaktiebolaget LM Ericsson (publ) 19 / 71

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[0177] Embodiments of the method can seamlessly handover the radio device while in a state of carrier aggregation (CA) and / or dual connectivity (DC) or multi-connectivity.

[0178] The radio-access entity may comprise multiple physical TRPs subsumed as one logical TRP.

[0179] A deployment may have at least two physical antenna sites but treat them as one logical shared TRP for the radio device. Moreover, both the first network node and the second network node may control these physical TRPs in a unified manner, allowing seamless handover while the radio device perceives no change in its serving multi-TRP coverage.

[0180] A first coverage area of the RAN may be covered by the first network node and a second coverage area of the RAN may be covered by the second network node, and a shared coverage area of the shared radio-access entity may be, or may be within, a partial overlap between the first coverage and the second coverage.

[0181] Alternatively or additionally, the shared coverage area of the shared radio-access entity may be a partial overlap between the first coverage and the second coverage.

[0182] Alternatively or additionally, the shared coverage area of the shared radio-access entity may be within a partial overlap between the first coverage and the second coverage.

[0183] The first and second coverage areas may be covered by the first and network nodes, respectively, e.g. using further first and second radio-access entities (e.g., TRPs) that are not shared between the first and network nodes.

[0184] For example, the shared radio-access entity may be associated with multiple shared cells served by both the first and the second network node via the shared radio-access entity. The shared coverage area of the multiple shared cells may correspond to, or may be within, the partial overlap of the first and second coverage area.

[0185] In other words, a shared cell coverage may comprise one or more cells at a mutual border of the first and second coverage areas of the first and second network nodes. The RAN (e.g., the serving first network node) may configure or comprise one or more cells, each spanning a coverage area (i.e., region) at or near the coverage border of the first and second network nodes. The radio device in shared cell coverage experiences the same cell identifier before and after the handover. Because the cell configuration (e.g., carrier frequency, synchronization signals) remains unchanged from the perspective of the radio device, handover interruptions are minimized.Telefonaktiebolaget LM Ericsson (publ) 20 / 71

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[0187] The shared coverage area may separate a non-shared first coverage area of the first network node and a non-shared second coverage area of the second network node by one or two or more layers of shared cells.

[0188] Alternatively or additionally, the shared coverage area may separate the non-shared first coverage area and the non-shared second coverage area by one layer of shared cells.

[0189] Alternatively or additionally, the shared coverage area may separate the non-shared first coverage area and the non-shared second coverage area by two or more layers of shared cells.

[0190] The handover from the first network node to the second network node when the radio device moves from the non-shared first coverage area in a first direction across the shared cells to the non-shared second coverage area may occur at a location farther in the first direction as compared to a location of the handover from the second network node to the first network node when the radio device moves from the non-shared second coverage area in a second direction opposite to the first direction across the shared cells to the non-shared second coverage area.

[0191] This may allow for a stable hysteresis in the handover, preventing frequent switching between the first and second network node as being the serving node. In other words, the one or more shared cells may enable a spatial hysteresis. For example, the shared cells as multiple adjacent coverage areas or “strip cells” may be jointly controlled by both the first and second network nodes. If the radio device enters or remains within one or more of these shared (strip) cells, switching the serving network node can be done under favorable radio conditions (rather than at a strict boundary point) reducing dropped calls or ping-pong handovers.

[0192] The first coverage area may be the union of the shared coverage area and the nonshared first coverage area. The shared coverage area and the non-shared first coverage area may be disjoint (non-overlapping, typically adjacent). The second coverage area may be the union of the shared coverage area and the non-shared second coverage area. The shared coverage area and the non-shared second coverage area may be disjoint.

[0193] The handover from the first network node to the second network node when the radio device moves from the non-shared first coverage area in a first direction across the two or more layers of shared cells to the non-shared second coverage area may occur farther in the first direction as compared to the handover from the second network node to the first network node when the radio device moves from the non-shared first coverage area in a second direction opposite to the first direction across the two or more layers of shared cells to theTelefonaktiebolaget LM Ericsson (publ) 21 / 71

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[0195] non-shared second coverage area. For example, the handover may occur within the shared cell that is neighboring the non-shared target coverage area. Thus, the handover can be performed in the good radio conditions of the shared cell, and still with clear hysteresis separated by the size of at least one cell.

[0196] The radio-access entity may correspond to a cell of the RAN and / or the radio device may receive the handover command while connected to a cell of the radio-access entity, and the serving network node may be changed while the radio device is connected to the cell of the radio-access entity.

[0197] Alternatively or additionally, the radio-access entity may correspond to a cell of the RAN.

[0198] Alternatively or additionally, the radio device may receive the handover command while connected to a cell of the radio-access entity, and the serving network node may be changed while the radio device is connected to the cell of the radio-access entity.

[0199] The first network node and the second network node may provide radio access via the radio-access entity according to the same radio access technology (RAT). For example, radio access may be provided via a TRP and / or in a cell.

[0200] Alternatively or additionally, the first network node and the second network node may provide radio access via the radio-access entity via a TRP.

[0201] Alternatively or additionally, the first network node and the second network node may provide radio access via the radio-access entity in a cell.

[0202] After receiving the handover command and prior to changing the serving network node, the radio device may determine that re-synchronization with the radio-access entity is to be omitted based on connectivity to the same radio-access entity, and / or the radio device may refrain from initiating a random-access procedure.

[0203] Alternatively or additionally, after receiving the handover command and prior to changing the serving network node, the radio device may determine that re-synchronization with the radio-access entity is to be omitted based on connectivity to the same radio-access entity.

[0204] Alternatively or additionally, after receiving the handover command and prior to changing the serving network node, the radio device may refrain from initiating a randomaccess procedure.

[0205] The radio device may stay synchronized to the same radio-access entity during the handover, thus saving signaling overhead and reducing delay associated with any additional random-access or re-synchronization procedure.Telefonaktiebolaget LM Ericsson (publ) 22 / 71

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[0207] Upon completion of the handover, the radio device may refrain from re-reading broadcast system information via the radio-access entity from the second network node. For example, this may be performed if the radio device previously received the system information while connected to the first network node.

[0208] By not having to re-read already valid broadcast information (e.g., in MIB or SIB1) for the same radio-access entity, the radio device can avoid unnecessary overhead and reduce latency right after the serving network node change, thus contributing to a more seamless handover.

[0209] The first network node and the second network node may provide radio access via the radio-access entity according to a first radio access technology (RAT) and a second RAT, respectively, wherein the second RAT is different from the first RAT.

[0210] The radio device may receive, from the second network node, at least one translation instruction for reusing link adaptation parameters previously applied by the radio device with the first network node under the first RAT. The radio device may apply the translation instruction to maintain a corresponding link adaptation via the shared radio-access entity under the second RAT.

[0211] By translating and reusing existing link adaptation parameters when changing to a different RAT, the radio device can reduce the need for further measurements or calibration after the serving network node change (i.e., the handover), thereby minimizing interruption and maintaining robust radio performance.

[0212] The radio device may receive an indication to reuse one or more physical access parameters after the handover and / or to retain or partially retain previously obtained channelstate information (CSI) after the handover and / or to transmit buffer status information when connecting to the second network node relative to a buffer status report sent to the first network node prior to the handover.

[0213] Alternatively or additionally, the radio device may receive an indication to reuse one or more physical access parameters after the handover.

[0214] Alternatively or additionally, the radio device may receive an indication to retain or partially retain previously obtained channel-state information (CSI) after the handover.

[0215] Alternatively or additionally, the radio device may receive an indication to transmit buffer status information when connecting to the second network node relative to a buffer status report sent to the first network node prior to the handover.

[0216] Having explicit permission to reuse or partially reuse internal measurements and status reports avoids re-initializing those procedures from scratch, thereby reducing the timeTelefonaktiebolaget LM Ericsson (publ) 23 / 71

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[0218] and signaling overhead needed to resume efficient uplink and downlink transmissions under the new serving network node.

[0219] The indication may be received receiving together with the handover command and / or from the first network node or from the network node.

[0220] In response to the handover command and / or after the handover, the radio device may transmit a previously determined buffer status report (BSR) to the second network node, optionally wherein the BSR is indicative of data awaiting uplink transmission at the time of switching from the first network node and / or wherein the BSR is a periodic BSR or not a regular BSR.

[0221] Alternatively or additionally, in response to the handover command, the radio device may transmit a previously determined buffer status report (BSR) to the second network node.

[0222] Alternatively or additionally, after the handover, the radio device may transmit a previously determined buffer status report (BSR) to the second network node.

[0223] Alternatively or additionally, the BSR may be indicative of data awaiting uplink transmission at the time of switching from the first network node.

[0224] Alternatively or additionally, the BSR may be a periodic BSR.

[0225] Alternatively or additionally, the BSR may not be a regular BSR.

[0226] By forwarding or re-sending the same BSR values to the second network node immediately after the serving node change, the radio device ensures accurate scheduling of uplink resources without requiring additional measurement or BSR re-calculation, thus reducing handover interruption and improving resource allocation efficiency.

[0227] Fig. 1 schematically illustrates a block diagram of an embodiment of a device for a handover, i.e., a change of a serving network node. The device is generally referred to by reference sign 100.

[0228] The device 100 comprises a handover command Rx (e.g., radio reception) module 102 that is configured to receive, while radio-connected to the network node via a physical radio-access entity, a handover command to change its serving network node to a second network node.

[0229] The device 100 further comprises a serving-node change module 104 that is configured to, in response to the received handover command, change the serving network node of the device 100 from the first network node to the second network node while remaining radio-connected via the physical radio-access entity.

[0230] Any of the modules of the device 100 may be implemented by units configured to provide the corresponding functionality.Telefonaktiebolaget LM Ericsson (publ) 24 / 71

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[0232] The device 100 may also be referred to as, or may be embodied by, a radio device (e.g., a user equipment or UE). The radio device 100 and the first network node may be in direct radio communication, e.g., at least for receiving the handover command from the first network node. Alternatively or in addition, the radio device 100 and the second network node may be in direct radio communication, e.g., at least for performing a random access to the second network node. The first network node and the second network node may be embodied by below-mentioned devices 200 and 300, respectively.

[0233] As to a second method aspect, a method performed by a first network node of a radio access network (RAN) is provided. The method comprises sending, to a second network node of the RAN, a request for a handover of a radio device from the first network node to the second network node while the radio device remains radio-connected via a physical radio-access entity shared between the first network node and the second network node. The method comprises transmitting, to the radio device connected via the physical radio-access entity, a handover command to change a serving network node to the second network node.

[0234] The handover of the radio device (e.g., from the first network node to the second network node) may be or may comprise a change of serving node control of the radio device (e.g., from the first network node to the second network node).

[0235] By separating a logical change of the serving node from a maintained (and optionally later changed) physical access point, the radio device remains radio-connected via the same radio-access entity (e.g., the same transmission and reception point, TRP) in at least some embodiments of the method, e.g., reducing interruptions and avoiding full radio reinitialization during the serving node change.

[0236] The handover command and / or a further control message may comprise at least one of the alternatives set out in the following options.

[0237] Alternatively or additionally, the handover command or the further control message may comprise an indication to reuse one or more physical access parameters after the handover and / or to retain or partially retain previously obtained channel-state information (CSI) after the handover and / or to transmit buffer status information when connecting to the second network node relative to a buffer status report sent to the first network node prior to the handover.

[0238] Alternatively or additionally, the handover command or the further control message may comprise an activation instruction triggering the radio device to re-establish mediumaccess control (MAC) or higher-layer controls with the second network node, without resynchronizing a physical link via the shared radio-access entity.Telefonaktiebolaget LM Ericsson (publ) 25 / 71

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[0240] Alternatively or additionally, the handover command or the further control message may comprise one or more configuration parameters received from the second network node for maintaining a radio-connection via the radio-access entity under serving node control of the second network node.

[0241] By allowing re-establishment at the MAC layer and / or higher protocol layers (e.g., of a radio protocol stack), while keeping the same physical synchronization, embodiments of the method can significantly decrease interruption time and resource usage during the node change.

[0242] The first network node may suspend scheduling and / or transmission of user-plane data flow at the first network node via the radio-access entity, optionally prior to forwarding buffered data to the second network node. The first network node may send a control signal indicative of a sequence number status to the second network node to synchronize the userplane data flow.

[0243] Alternatively or additionally, the first network node may suspend scheduling of userplane data flow at the first network node via the radio-access entity.

[0244] Alternatively or additionally, the first network node may suspend transmission of user-plane data flow at the first network node via the radio-access entity.

[0245] For example, suspending scheduling and / or transmission may be performed prior to forwarding buffered data to the second network node.

[0246] Alternatively or additionally, the first network node may send a control signal indicative of a sequence number status to the second network node to synchronize the userplane data flow.

[0247] By suspending the user-plane and transferring the corresponding sequence status to the second network node, embodiments of the method can avoid a duplication or a gap in data packets, ensuring reliable data continuity after the serving node change.

[0248] The first network node may forward user data of the radio device from the first network node to the second network node, optionally after transmission of the handover command and / or while the radio device transitions its serving node to the second network node, and / or the first network node may forward user data of the radio device from the second network node to the core network, optionally after transmission of the handover command and / or while the radio device transitions its serving node to the second network node.

[0249] Alternatively or additionally, the first network node may forward user data of the radio device from the first network node to the second network node.Telefonaktiebolaget LM Ericsson (publ) 26 / 71

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[0251] For example, forwarding user data from the first network node to the second network node may be performed after transmission of the handover command.

[0252] For example, forwarding user data from the first network node to the second network node may be performed while the radio device transitions its serving node to the second network node.

[0253] Alternatively or additionally, the first network node may forward user data of the radio device from the second network node to the core network.

[0254] For example, forwarding user data from the second network node to the core network may be performed after transmission of the handover command.

[0255] For example, forwarding user data from the second network node to the core network may be performed while the radio device transitions its serving node to the second network node.

[0256] By forwarding user data during the serving node transition, embodiments of the method can preserve end-to-end connectivity via the shared radio-access entity, and minimizes data loss or the need for providing user data at the end radio device.

[0257] At least one of the request sent to the second network node, the control signal sent to the second network node, and the user data forwarded to the second network node may be further indicative of one or more radio parameters of the radio device for reuse at the second network node when radio-connected via the radio-access entity.

[0258] Alternatively or additionally, the request sent to the second network node may be indicative of one or more radio parameters of the radio device for reuse at the second network node when radio-connected via the radio-access entity.

[0259] Alternatively or additionally, the control signal sent to the second network node may be indicative of one or more radio parameters of the radio device for reuse at the second network node when radio-connected via the radio-access entity.

[0260] Alternatively or additionally, the user data forwarded to the second network node may be indicative of one or more radio parameters of the radio device for reuse at the second network node when radio-connected via the radio-access entity.

[0261] The one or more radio parameters may comprise at least one of the alternatives set out in the following options.

[0262] Alternatively or additionally, the one or more radio parameters may comprise the same cell before and after the handover.Telefonaktiebolaget LM Ericsson (publ) 27 / 71

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[0264] Alternatively or additionally, the one or more radio parameters may comprise the same radio spectrum before and after the handover. For example, the same carrier frequency may be used before and after the handover.

[0265] Alternatively or additionally, the one or more radio parameters may comprise the same radio access technology (RAT) before and after the handover.

[0266] Alternatively or additionally, the one or more radio parameters may comprise the same physical cell identifier (PCI) before and after the handover.

[0267] Alternatively or additionally, the one or more radio parameters may comprise the same timing advance (TA) before and after the handover.

[0268] Alternatively or additionally, the one or more radio parameters may comprise the same system frame number (SFN) before and after the handover.

[0269] Alternatively or additionally, the one or more radio parameters may comprise the same search space for downlink control information (DCI) scheduling system information (SI) before and after the handover.

[0270] Alternatively or additionally, the one or more radio parameters may comprise the same public land mobile network identifier (PLMN ID) before and after the handover.

[0271] Alternatively or additionally, the one or more radio parameters may comprise the same time-frequency position of a synchronization signal block (SSB) before and after the handover.

[0272] Alternatively or additionally, the one or more radio parameters may comprise the same radio parameter values for a random-access channel (RACH) before and after the handover.

[0273] Alternatively or additionally, the one or more radio parameters may comprise the same radio parameter values of a control resource set (CORESET) for monitoring a physical downlink control channel (PDCCH) before and after the handover.

[0274] Alternatively or additionally, the one or more radio parameters may comprise the same radio access technology cell identifier (RAT cell ID) before and after the handover. For example, the same New Radio Cell Identifier (NCI) may be used before and after the handover.

[0275] Alternatively or additionally, the one or more radio parameters may comprise the same radio parameter values of a transmission configuration indication (TCI) before and after the handover.Telefonaktiebolaget LM Ericsson (publ) 28 / 71

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[0277] Alternatively or additionally, the one or more radio parameters may comprise the same radio parameter values of a Quasi Co-Location (QCI) before and after the handover. For example, the same QCL source may be used before and after the handover.

[0278] Alternatively or additionally, the one or more radio parameters may comprise the same values of beamforming weights for the radio-access entity before and after the handover. For example, the beamforming weights may be for a transmit beam to the radio device or a receive beam from the radio device.

[0279] Alternatively or additionally, the one or more radio parameters may comprise the same channel state information (CSI) before and after the handover.

[0280] Alternatively or additionally, the one or more radio parameters may comprise the same value of a precoding matrix indicator (PMI) for the radio-access entity before and after the handover.

[0281] Alternatively or additionally, the one or more radio parameters may comprise the same link adaptation before and after the handover.

[0282] Alternatively or additionally, the one or more radio parameters may comprise the same modulation and coding scheme (MCS) before and after the handover.

[0283] Alternatively or additionally, the one or more radio parameters may comprise the same radio network temporary identifier (RNTI) before and after the handover. For example, the same permanent cell RNTI (C-RNTI) and / or the same paging RNTI (P-RNTI) may be used before and after the handover.

[0284] The one or more radio parameters may comprise (or may be limited to) one or more physical access parameters (e.g., physical-layer adaptation parameters).

[0285] By reusing the one or more radio parameters at the second network node as the serving node can avoid re-establishing the link adaptation process from scratch, thereby reducing latency and signaling overhead.

[0286] The first network node may receive, from the radio device, a communication using a temporary device identifier assigned by the second network node. For example, the reception may be indicative of successful change of the serving node.

[0287] By detecting uplink transmissions tagged with a new identifier, embodiments of the first network node can confirm that the radio device has completed its transition to the second network node, ensuring a robust handover procedure.

[0288] The shared radio-access entity may comprise a radio resource control entity, optionally an arbitrator and / or a shared scheduler, for radio resources of the radio-access entity shared between the first network node and the second network node.Telefonaktiebolaget LM Ericsson (publ) 29 / 71

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[0290] Alternatively or additionally, the shared radio-access entity may comprise a radio resource control entity for radio resources of the radio-access entity shared between the first network node and the second network node.

[0291] For example, the radio resource control entity may comprise an arbitrator for radio resources of the radio-access entity shared between the first network node and the second network node.

[0292] For example, the radio resource control entity may comprise a shared scheduler for radio resources of the radio-access entity shared between the first network node and the second network node.

[0293] The radio resource control entity may be configured with a shared arbitration scheduler accessible by both the first network node and the second network node. The radio resource control entity may comprise exchanging scheduling information with the second network node to coordinate usage of common radio resources for the radio device.

[0294] The method may further comprise features and steps of any embodiment of the first method aspect, or features and steps in one-to-one correspondence thereto.

[0295] Fig.2 schematically illustrates a block diagram of an embodiment of a device for performing a handover. The device (e.g., a first network node) is generically referred to by reference sign 200.

[0296] The device 200 comprises a handover command Tx (e.g., radio transmission) module 202. This handover command Tx module 202 is configured to transmit to a radio device 100 connected via a radio-access entity 702 a handover command to change a serving network node to a second network node.

[0297] In addition, the device 200 comprises a handover request sending module 204. This handover request sending module 204 is configured to send, to the second network node, a request for a handover of the radio device 100 from the first network node to the second network node while the radio device 100 remains radio-connected via the radio-access entity shared between the first network node and the second network node.

[0298] Any of the modules 202 and 204 of the first network node 200 may be implemented by units configured to provide the corresponding functionalities.

[0299] The device 200 may also be referred to as, or may be embodied by, the first network node 200 or any source network node (e.g., a gNB). The radio device 100, in turn, may be in direct radio communication with the first network node 200, at least for transmitting the handover command from the first network node 200 to the radio device 100.Telefonaktiebolaget LM Ericsson (publ) 30 / 71

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[0301] As to a third method aspect, a method performed by a second network node in a radio access network (RAN) is provided. The method comprises receiving, from a first network node, a request to assume serving-node control of a radio device while maintaining a physical radio-access entity used by the radio device. The method comprises, in response to the request, receiving a random access via the physical radio-access entity from the radio device and / or transmitting via the physical radio-access entity to the radio device, through the first network node, configuration information enabling continued communication for the radio device via the physical radio-access entity with the second network node.

[0302] Alternatively or additionally, in response to the request, the second network node may receive a random access via the physical radio-access entity from the radio device.

[0303] Alternatively or additionally, in response to the request, the second network node may transmit via the physical radio-access entity to the radio device, through the first network node, configuration information enabling continued communication for the radio device via the physical radio-access entity with the second network node.

[0304] After providing the configuration information to the radio device, the second network node may send a path-switch request to a function of a core network (CN) serving the RAN, and the path-switch request may trigger the CN to route user-plane traffic via the second network node.

[0305] The third method may further comprise features and steps of any embodiments of the first or second method aspects, or features and steps in one-to-one correspondence thereto.

[0306] Fig.3 schematically illustrates a block diagram of an embodiment of a device for performing a handover in a radio access network, the device being generically referred to by reference sign 300. The device 300 may also be referred to as, or may be embodied by, a target or second network node of the handover.

[0307] The device 300 comprises a handover request receiving module 304 that is configured to receive, from a first network node 200, a request to assume serving-node control of a radio device 100 while maintaining a radio-access entity used by the radio device 100. In response to the request, the device 300 is further configured to receive or facilitate a random access from the radio device 100 via the radio-access entity and / or to transmit, via the radio-access entity to the radio device 100 (e.g., under scheduling control of the second network node), configuration information enabling continued communication for the radio device 100 after the handover.

[0308] The device 300 further comprises a configuration Tx (e.g., radio transmission) module 306. The configuration Tx module 306 is configured to facilitate a random access ofTelefonaktiebolaget LM Ericsson (publ) 31 / 71

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[0310] the radio device at the second network node via the radio-access entity and / or to transmit configuration information for continued communication.

[0311] Any of the modules 304 and 306 of the second network node 300 may be implemented by units configured to provide the corresponding functionalities.

[0312] The device 300 may also be referred to as, or may be embodied by, the second network node 300 or any target network node (e.g., a gNB). The radio device 100, in turn, may be in direct radio communication with the second network node 300, at least when performing the random access from the radio device 100 at the second network node 300 and / or transmitting the configuration information from the second network node 300 to the radio device 100.

[0313] Reference signs are optional indictors of features and steps. Especially, a description of a figure may refer to a reference sign shown in one of the previous figures as a clarification or an optional combination of features and steps.

[0314] As to a first device aspect, a radio device comprising memory operable to store instructions and processing circuitry operable to execute the instructions is provided. The radio device is operable to receive, while radio-connected to a first network node via a physical radio-access entity, a handover command to change a serving network node to a second network node, wherein the physical radio-access entity is shared between the first network node and the second network node. The radio device is operable to, responsive to the handover command, change the serving network node of the radio device from the first network node to the second network node while remaining radio-connected via the physical radio-access entity.

[0315] The radio device may be further operable to perform the steps of any embodiment of the first method aspect.

[0316] Fig. 4 schematically illustrates a flowchart of an embodiment of a method 400 performed by a radio device 100 that is radio-connected to a radio access network (RAN).

[0317] In a step 402, the method 400 comprises receiving, while the radio device 100 is radio-connected to a first network node 200 via a physical radio-access entity, a handover command to change a serving network node to a second network node 300, the physical radio-access entity being shared between the first network node 200 and the second network node 300.

[0318] In a subsequent step 404, the method 400 further comprises, responsive to the received handover command of step 402, changing the serving network node of the radioTelefonaktiebolaget LM Ericsson (publ) 32 / 71

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[0320] device 100 from the first network node 200 to the second network node 300 while remaining radio-connected via the physical radio-access entity.

[0321] The method 400 shown in Fig. 4 may be performed by the radio device 100 of Fig. 1. For example, a handover command Rx module 102 and a serving-node change module 104 of the radio device 100 may execute the step 402 and the step 404, respectively.

[0322] As to a second device aspect, a first network node in a radio access network (RAN), the first network node comprising memory operable to store instructions and processing circuitry operable to execute the instructions is provided. The first network node is operable to send, to a second network node of the RAN, a request for a handover of a radio device from the first network node to the second network node while the radio device remains radioconnected via a physical radio-access entity shared between the first network node and the second network node. The first network node is operable to transmit, to the radio device connected via the physical radio-access entity, a handover command to change a serving network node to the second network node.

[0323] The first network node may be further operable to perform the steps of any embodiment of the second method aspect.

[0324] Fig. 5 schematically illustrates a flowchart of an embodiment of a method 500 performed by a first network node 200 of a radio access network (RAN).

[0325] In a step 504-1, the method 500 comprises sending, to a second network node 300 of the radio access network 700, a request for a handover of a radio device 100 from the first network node 200 to the second network node 300 while the radio device 100 remains radioconnected via a radio-access entity shared between the first network node 200 and the second network node 300.

[0326] In a prior or subsequent step 502, the method 500 further comprises transmitting, to the radio device 100 connected via the radio-access entity, a handover command to change a serving network node to the second network node 300.

[0327] The method 500 shown in Fig. 5 may be performed by the first network node 200 of Fig. 2. For example, a handover request sending module 204 and a handover command Tx module 202 of the first network node 200 may execute the step 504-1 and the step 502, respectively.

[0328] As to a third device aspect, a second network node comprising memory operable to store instructions and processing circuitry operable to execute the instructions is provided. The second network node is operable to receive, from a first network node, a request to assume serving-node control of a radio device while maintaining a physical radio-accessTelefonaktiebolaget LM Ericsson (publ) 33 / 71

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[0330] entity used by the radio device. The second network node is operable to, in response to the request, receive a random access via the physical radio-access entity from the radio device and / or transmit via the physical radio-access entity to the radio device, through the first network node, configuration information enabling continued communication for the radio device via the physical radio-access entity with the second network node.

[0331] Alternatively or additionally, the second network node may be operable to, in response to the request, receive a random access via the physical radio-access entity from the radio device.

[0332] Alternatively or additionally, the second network node may be operable to, in response to the request, transmit via the physical radio-access entity to the radio device, through the first network node, configuration information enabling continued communication for the radio device via the physical radio-access entity with the second network node.

[0333] The second network node may be further operable to perform the steps of any embodiment of the third method aspect.

[0334] Fig. 6 schematically illustrates a flowchart of an embodiment of a method 600 performed by a second network node 300 in a radio access network (RAN).

[0335] In a step 604-1, the method 600 comprises receiving, from a first network node 200, a request to assume serving-node control of a radio device 100 while maintaining a radioaccess entity of the RAN previously used by the radio device 100.

[0336] In a subsequent step 606, the method 600 further comprises, responsive to the request, receiving a random access via the radio-access entity from the radio device 100 (which option is also referred to by 606-1) and / or transmitting configuration information via the radio-access entity to the radio device 100, e.g. while still under control of the first network node 200, to enable continued communication for the radio device 100 with the second network node 300 via the radio-access entity (which option is also referred to by 606-2). The latter option may enable the radio device 100 to continue the radio communication via the radio-access entity with the second network node 300 without a random access procedure with the second network node 300 after the handover.

[0337] The method 600 shown in Fig. 6 may be performed by the second network node 300 of Fig. 3. For example, the modules 304 and 306 of the second network node 300 may execute the steps 604-1 and 606, respectively.Telefonaktiebolaget LM Ericsson (publ) 34 / 71

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[0339] In any aspect, the technique may be applied to uplink (UL), downlink (DL) or direct communications between radio devices, e.g., device-to-device (D2D) communications or sidelink (SL) communications.

[0340] The radio-access entity may comprise any physical layer (PHY) component of a radio protocol stack of the RAN that is used by both the first network node 200 and the second network node 300.

[0341] Each of the first network node 200 and the second network node 300 may be a radio device or a base station. Herein, any radio device may be a mobile or portable station and / or any radio device wirelessly connectable to a base station or RAN, or to another radio device. For example, the radio device may be a user equipment (UE), a device for machine-type communication (MTC) or a device for (e.g., narrowband) Internet of Things (loT). Two or more radio devices may be configured to wirelessly connect to each other, e.g., in an ad hoc radio network or via a 3 GPP SL connection.

[0342] Furthermore, any base station may be a station providing radio access, may be part of a radio access network (RAN) and / or may be a node connected to the RAN for controlling the radio access. For example, the base station and / or the shared radio-access entity may be an access point, for example a Wi-Fi access point.

[0343] Herein, whenever referring to noise or a signal-to-noise ratio (SNR), a corresponding step, feature or effect is also disclosed for noise and / or interference or a signal-to-interference-and-noise ratio (SINR).

[0344] Furthermore, "predefined" may encompass stored in memory (e.g., in a Subscriber Identity Module, SIM) of the transmitting wireless device, or hard-coded or hard-wired in the transmitting wireless device, or preconfigured or configured by a network node or radio access network (RAN) for the transmitting wireless device (e.g., preconfigured while in coverage prior to performing the method out of coverage, or configured while in coverage when performing the method).

[0345] The radio spectrum shared by multiple RATs may be an unlicensed spectrum.

[0346] Herein, a list of the form A, B, and / or C (also written as A, B and / or C) may correspond to at least one or each of A, B, and C, i.e., A and / or B and / or C.

[0347] Fig. 7 shows schematically a radio access network (RAN) 700 in which a first network node 200 and a second network node 300 both radio-connect to a radio device 100. This arrangement provides a high-level architecture for an intra- or inter-radio access technology (RAT) mobility scenario. That is, the first network node 200 and a secondTelefonaktiebolaget LM Ericsson (publ) 35 / 71

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[0349] network node 300 may use the same or different RATs for their respective radio-connection to the radio device 100.

[0350] As an example of a shared radio-access entity 702, a transmission and reception point 702 is illustrated in a shared cell 704 at the center of the RAN 700. The shared transmission and reception point (TRP) 702 physically transmits and receives radio signals for the radio device 100 and belongs to, e.g. covers, the shared cell 704. Because the first network node 200 and the second network node 300 both access the shared TRP 702, the radio device 100 has continuity in its physical radio-access entity while switching between the serving nodes 200 and 300.

[0351] Optionally, a shared scheduler 706 is integrated into the RAN 700 (e.g., at one of the first network node 200 and the second network node 300) to coordinate scheduling for the shared TRP 702 among the first network node 200 and the second network node 300. The shared scheduler 706 has a control interface, e.g., at a medium access control (MAC) layer toward each of the first network node 200 and the second network node 300, ensuring that (e.g., uplink and / or downlink) radio resources are allocated without collisions between the first network node 200 and the second network node 300. This design allows precise timing and link adaptation to continue smoothly when the serving node changes.

[0352] The shared cell 704 is indicated around the radio device 100 to illustrate that the radio device 100 remains in the same coverage area before and after an inter-node handover. By not requiring the radio device 100 to change cells when switching between the first network node 200 and the second network node 300, embodiments can avoid re-synchronization delays and / or preserve the link conditions already established (e.g., as represented by initialized values of one or more maintained radio parameters).

[0353] The first network node 200 and the second network node 300 each comprise, or connect to, a radio protocol layer stack. The radio protocol layer stack may comprise functions for at least one of radio resource control (RRC), packet data convergence protocol (PDCP), and radio link control (RLC). These layers and / or the MAC layer may be implemented for each of the first network node 200 and the second network node 300.

[0354] The physical layer (PHY) and / or the MAC layer may be shared between the first network node 200 and the second network node 300. Optionally, the physical (PHY) layer and / or the MAC layer is implemented at the shared radio-access entity 702, which is exemplified by the TRP in Fig. 7. Alternatively or in addition, the PHY layer may include at least one of the shared scheduler 706 and the shared TRP.Telefonaktiebolaget LM Ericsson (publ) 36 / 71

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[0356] Since the radio connectivity of the radio device 100 maintains the radio-access entity 702 during (i.e., before and after) the handover, the first network node 200 and the second network node 300 can coordinate the inter-node handover (i.e., the change of the serving node control) according to the methods 500 and 600 while the radio device 100 is within the shared cell 704 covered by the shared physical radio-access entity 702, e.g. including exchanging control-plane data and / or user-plane data.

[0357] This approach achieves more robust mobility and efficiently uses the radio spectrum as the radio device moves through the shared cell. Optionally, the radio device 100 originates from a neighboring cell of the shared cell 704 (e.g., illustrated to the left in Fig. 7), which may be served by the first network node 200 or another network node (as indicated in Fig. 7). Alternatively or in addition, the radio device 100 may move towards a neighboring cell of the shared cell 704 (e.g., illustrated to the right in Fig. 7), which may be served by the second network node 300 or another network node (as indicated in Fig. 7).

[0358] In a variant of any embodiment of any aspect, at least one or each of the first and second network nodes 200 and 300 may a 5G or next generation Node B (gNB) and / or a distributed unit (DU) or a baseband (BB) unit.

[0359] In a variant of any embodiment of any aspect, the shared physical radio-access entity 702 may comprise a Transmission and Reception Point (TRP), e.g. in the context of 5G NR or beyond 5G. The TRP may encompass a logical and / or physical entity responsible for transmitting and receiving radio signals. For example, each TRP in a RAN 700 may encompass a distinct (e.g., discrete) transmission and / or reception point that may be coordinated for improved performance or coverage of the RAN 700.

[0360] Alternatively or in addition, the radio-access entity 702 may be an individual antenna system (e.g., an antenna panel), a sector, and / or a site (or location). In any embodiment, the radio-access entity 702 (e.g., a TRP) may comprise its own set of radios and / or antenna beams.

[0361] The sector, e.g. in cellular deployments (including 4G or LTE, 5G or NR, and beyond 5G) or any other RAT, may refer to a solid angle portion or slice of a coverage of the radioaccess entity 702, e.g. of a base station or of a TRP. The sector may be formed by using one or more directional antennas, e.g. that concentrate radio signals in a specific azimuth (horizontal) range and / or a specific elevation (vertical) range.

[0362] The site (e.g., a cell site a base station site or a TRP site) may comprise a physical infrastructure (e.g., a tower or roof-top installation plus equipment, i.e. one or more TRPs). The site may be subdivided into sectors, each covered by separate directional antennas aimedTelefonaktiebolaget LM Ericsson (publ) 37 / 71

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[0364] at different (e.g., solid or horizontal) angles. An arrangement of sectors may include a 3-sector (e.g., 120° each) or a 4-sector (e.g., 90° each), or more or fewer depending on design goals. Each cell or sector may correspond to a (distinct) TRP, e.g. for an inter-cell inter- TRP handover.

[0365] The radio-access entity 702 (e.g., a TRP and / or a cell 704) may be controlled by a (e.g., logical) network node (e.g., base station, particularly a gNB), e.g. as examples of the first network node 200 and / or the second network node 300. A single network node may control one or many TRPs. From a deployment standpoint, at least one TRP may belong to each network node. For example, the radio-access entity 702 (e.g., a transmitter and receiver site) being actually and / or currently under the control of a single network node (e.g., according to the shared scheduler 706) may be considered the TRP associated with that network node.

[0366] Herein, the scheduler may encompass an arbitrator.

[0367] Alternatively or in addition, the shared radio-access entity, e.g. a single cell or a single beam or a single sector, may be covered (and thus, shared) by multiple TRPs, e.g. for an intra-cell inter-TRP handover.

[0368] In a more advanced deployment, the shared radio-access entity 702, e.g. a single cell or single beam or single sector, may be covered by multiple TRPs all controlled by the first and second network nodes 200 and 300 based on the shared scheduler 706. Alternatively or in addition, the shared single cell 704 or the shared beam or the shared sector may be covered by the first and second network nodes 200 and 300 using the shared scheduler 706 for an intra-cell and / or inter-TRP and / or inter-beam and / or inter-sector handover between the network nodes 200 and 300.

[0369] Herein below, for concreteness and not limitation, the radio device 100 is referred to as aUE 100.

[0370] A first general embodiment that is implementable in each of the three aspects is an intra-RAT handover based on shared radio spectrum of the same radio-access entity 702 (e.g., the same cell and / or the same TRP) used for a more seamless change of serving-node for a UE 100. For example, the source network node 200 and the target network node 300 share the same cell, the same TRP, the same RAT, and share the same radio spectrum (e.g., as the radio resource asset allocatable to the UE 100). The dedicated UE radio resources allocations are controlled and coordinated with a common real time arbitrator and scheduler 706, and the one or more shared cells 704 are deployed at inter-node handover borders toTelefonaktiebolaget LM Ericsson (publ) 38 / 71

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[0372] make the serving-node change more seamless, e.g. as illustrated in Fig. 7 discussed above, and as shown in each of Fig. 8 and Fig. 9 for more detailed embodiments, respectively.

[0373] Instead of using spectrum sharing for different Radio Access Technologies (RATs), and / or for different cells as in legacy techniques (e.g. according to 4G or 5G sharing), the sharing is done between two network nodes 200 and 300 using same RAT and the same cell, i.e. a first 5G node 200 shares one or more some 5G cells 704 as an example of the physical radio-access entity 702 with one or more other second 5G nodes 300, or a first 6G network node 200 shares one or more 6G cells 704 with one or more other second 6G nodes 300. As a result, from a perspective of the UE 100, the same cell 704 and the same TRP 702 is used before and after the change of the serving RAN node. Typically, while the change is performed as an intra-cell handover, packet forwarding (i.e., UE data forwarding) is needed due to the change of the network node serving (from 200 to 300) serving the UE 100.

[0374] The change, as seen by the UE 100, is a type of intra-cell handover (HO), which is absent in the prior art, and re-synchronization is typically not needed. The reason for this is that, the UE position in relation to antenna (or antennas) used for the UE connection to the RAN (i.e., via the shared radio-access entity 702) are the same before and after the servingnode change.

[0375] Hence, at least one of radio propagation, DL and / or UL interference, and / or timing advance (TA) is the same (i.e., the values of the corresponding radio parameters may be kept), and / or the UE 100 does not need to change a QCL source and / or perform DL synchronization nor perform a re-synchronization between the UE 100 and the RAN 700.

[0376] This embodiment makes it possible to use the same link adaptation and / or the same beam weights (as examples of the maintained radio parameters) before and after the change (i.e., the handover) and / or may imply that re-initialization is typically not needed and / or may enable smaller or less reconfigurations for the UE 100. Thereby, shorter interruptions, and hence, a more seamless serving-node change can be achieved.

[0377] The UE 100 may or may not notice that a cell radio network temporary identifier (C-RNTI) changes and / or that a security key is changed. Embodiments of the methods 400, 500, and 600, collectively also referred to as serving-node change procedure, are more robust, since smaller reconfiguration messages typically are more reliable. In addition, the servingnode change procedure can be executed in good cell conditions, as opposed to a handover at the cell border, as in legacy handover techniques.

[0378] In a variant of any embodiment, the first network node 200 and / or the second network node 300 may inform the UE 100 that the UE 100 may or shall re-use some selected internalTelefonaktiebolaget LM Ericsson (publ) 39 / 71

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[0380] average estimations (e.g., channel state information, CSI; and / or a precoding matrix index, PMI), e.g., with no need for re-initiation due to the handover.

[0381] While at least some embodiments disclosed herein are based on one shared-cell 704 as an example of the shared physical radio-access entity 702, a variant of any of such embodiments can be expanded to multiple shared cells 704 and / or one or more shared TRPs.

[0382] Furthermore, a variant of any embodiment may comprise one or more carrier-aggregated cells and / or one or more carriers to be the same shared cells, or same shared TRPs or the same shared carriers before and after the node change.

[0383] A further variant of any method embodiment encompasses an inter-RAT handover method (e.g., using a concept similar as used for the serving-node change), which may be based a shared TRP 702 that is sharing radio spectrum for both a source cell and a target cell. The source cell and the target cell will be different cells, since they belong to different RATs.

[0384] Any embodiment of any aspect may support a separation (e.g., by virtue of the shared schedule 706 or a MAC layer) between the unchanged physical radio-connection (i.e., the radio connection via the shared physical radio-access entity 702) between the RAN 700 and the UE 100 and the changing first and second network nodes 200 and 300. For example, the scheduler 702 or the MAC layer may abstract the shared PHY layer for the higher layers.

[0385] Any embodiment may be configured to perform the serving-node change (i.e., the inter-node handover) when radio conditions via the shared radio-access entity 702 (e.g., to the source network node 200 and / or to the target network node 300) fulfill an inter-node intra-entity handover criterion (e.g., being below a threshold value for a handover threshold that triggers the handover). The inter-node intra-entity handover criterion may be more sensitive for a decay of the radio conditions (e.g., a threshold value that higher) compared to a handover criterion (e.g., a threshold value) for a cell-border handover. That is, the internode intra-entity handover may be triggered by, and / or performed in, better radio conditions than radio conditions that trigger a conventional cell-border handover.

[0386] Herein, intra-entity refers to the shared physical radio-access entity that is maintained by the handover (HO). In other words, any embodiment of the method 400, 500, and 600 may relate to or perform an intra-entity HO.

[0387] Furthermore, intra-RAT embodiments (e.g., for an inter-node intra-entity handover with source and target nodes using the same RAT) as well as inter-RAT embodiments (e.g., for an inter-node intra-entity handover with source and target nodes using the different RATs) allows changing the serving node for the UE 100 (e.g., a serving gNB) with asTelefonaktiebolaget LM Ericsson (publ) 40 / 71

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[0389] minimal impact as possible (e.g., in terms of UE configuration and / or UE radio connection interruption) by using a type of intra-entity (e.g., intra- TRP) handover that is part of a serving-node change procedure, and optionally includes packet forwarding between source and target network nodes 200 and 300.

[0390] The serving node 200 (before the HO) and the target node 300 may belong to the same RAT or different RAT (as examples of the inter-node intra-entity handover).

[0391] One or more shared cells 704 and / or one or more shared TRPs 702 may be used for an intra-RAT serving-node change (as an example of the intra-RAT inter-node intra-entity handover).

[0392] One or more shared TRPs may be used for an inter-RAT serving-node change (as an example of the inter-RAT inter-node intra-entity handover).

[0393] In any embodiment and any aspect, the shared physical radio-access entity 702 (e.g., the one or more shared TRPs 702) used for the inter-node handover may be located at a coverage border (or all coverage borders) between the first network node 200 and the second network node 300. As a result, the shared physical radio-access entity 702 may cover a buffer zone for the inter-node handover under improved radio conditions compared to the conventional border-based handover.

[0394] Any embodiment may be distinguished over conventional handover techniques by using at least one of the following features or steps.

[0395] One or more shared cells 704 and / or one or more shared TRPs may be deployed in borders between the first network node 200 and the second network node 300.

[0396] At least one or both of source network node 200 and target network node 300 may be made aware of and / or configured to use (e.g., by a core network serving the network nodes 200 and 300) the shared physical radio-access entity 702 (e.g., a shared cell deployment or shared TRP deployment).

[0397] For example, source network node 200 and target network node 300 may be made aware of and / or configured to use the intra-entity HO and / or that intra-entity (e.g., intrashared cell or an intra-shared TRP) inter-node serving-node HO is supported and used for a UE 100. For brevity, inter-node serving-node change is also referred to by inter-serving node change. Furthermore, change and HO may be used interchangeably.

[0398] The intra-entity HO (e.g., the intra-cell and / or intra-TRP HO) may comprise data packet forwarding between first and second network nodes 200 and 300.

[0399] The first (source) network node 200 may forward a (e.g., time dynamic LI) transmission and / or reception information to the second (target) network node 300. TheTelefonaktiebolaget LM Ericsson (publ) 41 / 71

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[0401] transmission and / or reception information may comprise one or more of the following: CSI, TA, DL beam weights, UL beam weights, Tx mode, beamforming mode, and a link adaptation (LA) mode.

[0402] The Tx mode may comprise at least one of: Orthogonal Frequency Division Multiplexing (OFDM), Discrete Fourier Transform-Spread-Orthogonal Frequency Division Multiplexing (DFT-S-OFDM), Single Carrier Frequency Division Multiple Access (SC-FDMA), Generalized Frequency Division Multiplexing (GFDM), Filter Bank Multi-Carrier (FBMC), Universal Filtered Multi-Carrier (UFMC), Zero Tail DFT-S-OFDM (ZT-DFT-S-OFDM), and Single Carrier (SC) Transmission.

[0403] The beamforming mode may comprise at least one of: channel reciprocity-based beamforming and code book-based beamforming.

[0404] The LA mode may comprise at least one of: open-loop LA (OLLA), and closed-loop LA (CLLA).

[0405] Any embodiment of the methods 400, 500, and 600 may, e.g. in case of inter-RAT serving-node change, comprise a step of translating a value (or a set of values) for the maintained radio parameters (e.g., physical information) from the source RAT of the first network node 200 to the target RAT of the second network node 300.

[0406] The second (target) network node 300 may select and / or use the (or at least some of the) (e.g., LI) transmission and / or reception information that is sent (e.g., forwarded) from the first network node 200 to the second network node 300.

[0407] In any embodiment, the UE 100 may be informed (e.g., by transmitting a configuration message) that it may or shall keep selected internal estimations and / or not reinitialize of one or more or all radio parameters related to the shared physical radio-access entity 702 and / or due to the intra-entity (e.g., intra-shared cell) inter-node serving-node change (i.e., HO). This information can be sent 502 to the UE 100 within the handover command.

[0408] In any embodiment, the handover command may be a radio resource control (RRC) reconfiguration message (and / or an RRC information element, RRC IE). In same or an alternative of any embodiment, the handover command may be a MAC Control Element (CE), e.g. a Long-Term Evolution for Machines (LTE-M) cell switch command.Telefonaktiebolaget LM Ericsson (publ) 42 / 71

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[0410] In same or an alternative of any embodiment, the handover command and / or the transmission and / or reception information may be part of a candidate cell configuration.

[0411] The UE 100 may be informed that it needs to translate (e.g., convert) conditions from a representation of a source RAT of the first network node 200 to representation of a target RAT of the second network node 300.

[0412] The UE 100 may be informed that it is not required to read system information (SI), e.g. not required to read a system information block (SIB) after the inter-serving node handover since source and target cell is the same. This information can be transmitted 502 to the UE 100 within the handover command. The handover command can be a RRC reconfiguration message. In an alternative embodiment, the handover command may be a MAC control element (CE), e.g. an LTE-M cell switch command. In yet another embodiment, the information is part of a candidate cell configuration.

[0413] In any embodiment, e.g., for intra-RAT HO, only one of the first and second network node 200 and 300 node may be in charge of configuring and / or signaling the shared physical radio-access entity, e.g. of a common cell configuration and signaling. The other network node (sharing the entity 702, e.g. the same cell and / or TRP) need only to be informed, e.g. via inter-node signaling of the common cell configurations, e.g. in a need-to-know fashion In any embodiment, the first and second network nodes 200 and 300 may page the UE 100 independently, optionally aligned to one node paging occasion configuration and / or connected-mode discontinuous reception (C-DRX) configuration.

[0414] Even if common random access radio resources are used for the shared cell access, arbitration of random-access responses may be done between the first and second network nodes 200 and 300, e.g. to distribute node load.

[0415] Alternatively or in addition, e.g. for an inter-RAT HO, each of the first network node 200 and the second network node 300 may or shall

[0416] provide a configuration for the shared physical radio-access entity 702 (e.g., for a common cell configuration) and / or

[0417] perform signaling to be used for the shared physical radio-access entity 702 (e.g., for the one or more shared TRPs 702) used by each cell belonging to different RATs.

[0418] The respective configuration may be provided to the UE 100 and / or the mutual other network node.

[0419] For example, random-access resources and / or paging and / or discontinuous reception (DRX) may be configured separately per cell and / or per network node.Telefonaktiebolaget LM Ericsson (publ) 43 / 71

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[0421] In contrast to embodiments of the methods 400, 500, and 600, conventional techniques use a TRP in the opposite way. While in embodiments one TRP, as an example of the shared radio-access entity 702, is connected to and used by at least two network node 200 and 300, conventional techniques use multiple TRPs (e.g. for a multi-TRP (mTRP) transmission and / or for a mTRP reception and / or for mobility and / or for inter-cell beam management) connected to the same network node, so that conventional inter Node mobility is executed, e.g. using Xn or NG signaling in a legacy way.

[0422] Embodiments of the methods 400, 500, and 600 can improve mobility in terms of resource-efficiency (e.g., in terms of radio spectrum) and signaling-efficiency (e.g., in terms of power consumption and latency) for allowing interruption free and a fast change of radio resources allocated to the radio device 100. For example, since radio parameters change in the conventional mobility technique, the inter-node handover typically cause longer preparation delays and longer interruptions and needs more radio device cooperation and reconfigurations than a typical intra-node handover (e.g., intra-gNB handover) where some intra-gNB resource changes are only partly implicitly visible to handed-over radio device, e.g. in terms of downlink (DL) synchronization (synch) and Quasi Co Location (QCL) source change.

[0423] Embodiments of the methods 400, 500, and 600 can achieves this conservation of one or more radio parameters also for the inter-node handover, i.e. the change of the servingnode control for the radio device 100 from first network node 200 to the second network node 300.

[0424] In embodiments of the methods 400, 500, and 600 for inter-RAT handover, the source cell and the target cell belong to different RATs, hence are always different cells. The first network node 200 as the source RAT node and the second network node 300 as the target RAT node are also different. However, the radio-access entity 702 (e.g., the TRP and the target TRP) is the same, e.g. by using multi-RAT spectrum sharing.

[0425] Conventional techniques for inter-node (e.g., inter-gNB 5G) mobility are based on changing UE-serving node and UE-serving cell at the same time. Radio device (i.e., UE) and radio access network (briefly: RAN or NW) re-synchronization after the change are typically achieved by using random access to the target cell. The conventional procedure that changes the current source serving cell to another target serving cell also makes the UE change configurations, DL synch, and QCL source. This implies more signaling and larger messages and that the change needs to be done when there is a better cell, and the current cell is notTelefonaktiebolaget LM Ericsson (publ) 44 / 71

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[0427] the best any longer which implies worse radio conditions for the UE connection and the signaling between NW and UE during the change.

[0428] Any aspect may be implemented, optionally in combination with afore-mentioned embodiments, using at least one feature and step of the following detailed embodiments. The skilled person understands that a description of such a feature or step from the perspective of one of the three aspects teaches a corresponding feature or step for the other aspects.

[0429] In a RAN 700, network nodes 200 and 300 are deployed, each covering and controlling a number of one or more cells. In the RAN 700, multiple network nodes need to be deployed each covering and controlling different cells, e.g. due to many different reasons such as node capacity, different vendors, different preferred spatial positions (e.g., sites), different sections (e.g., directions), e.g. from a performance or resilience perspective etc. In the border area between different network node 200 and 300, a radio device 100 may be connected to the same shared physical radio-access entity 702, e.g. one or more cells 704.

[0430] Herein below, for concreteness and not limitation of the described features, the physical radio-access entity 702 is embodied by one or more TRPs 702 and / or one or more cells 704. Furthermore, any scheduler and / or arbitrator described herein is to be understood as an example of a resource control entity configured to coordinate radio resource allocation at the physical radio-access entity 702.

[0431] To enable different nodes 200 and 300 to share the same cell 704 or TRP, a shared radio resource control entity arbitrator and / or scheduler 706 may be required, which is responsible for the distribution of the radio resources between the first and second network node 200 and 300. The arbitrator and / or scheduler 706 may be implemented in the radio or in baseband processing.

[0432] The sharing of radio resources between the nodes 200 and 300 is needed since each node runs its own radio resource scheduler, so there is a need to coordinate which actual physical resources can be used by which scheduler at a certain time instance. Using a shared and common radio resource control entity, i.e. arbitrator and / or physical scheduler, allows to decouple this coordination from the radio resource scheduling performed by the source and the target nodes. The physical scheduling may be done on symbol level or on slot level, e.g. in a round-robin resource fair scheme, optionally while arbitration uses a longer time scale for balancing against an actual resource need over time for each of the first and second network nodes 200 and 300.

[0433] When a UE 100 is connected to a first network node 200, e.g. as schematically illustrated Fig.8, node internal control (e.g., mTRP mobility and / or inter-cell beam forming)Telefonaktiebolaget LM Ericsson (publ) 45 / 71

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[0435] may be applied among the cells all controlled by the first network node 200 (illustrated as white cells in Fig. 8) as a low latency requirement (e.g., for the latency of controlling the cells, e.g. for scheduling radio resources therein) is fulfilled. However, as the UE 100 moves towards cells that is 100% black, the control latency becomes larger as these cells are controlled by another second network node 300, which makes it not possible towards these cells to fulfill the latency requirement.

[0436] When the UE 100 is in a shared cell 704 or radio-connected to the same (i.e., shared) TRP 702 (indicated by stripes in Fig. 8), the RAN 700 may, e.g. when feasible, move the control (e.g., scheduling or any other serving-node functionality) of the UE from the first network node 200 to a second network node 300, while the UE 100 remains in the same cell or TRP. Thereby, the connection now has low latency control fulfilled between all cells under the control of the second network node 300 (indicates a black cells in Fig. 8), and e.g. mTRP mobility and / or inter-cell beam management can be enabled.

[0437] Furthermore, the RAN 700 comprises one or more shared cells 704 and / or one or more shared TRPs 702 at an edge (or border) between cells served by different the nodes 200 and 300.

[0438] Fig. 8 schematically illustrates an example of shared cells 704 and / or corresponding one or more TRPs shared between the first network node 200 and the second network node 300.

[0439] While features are described for one radio-access entity 702, a variant of any embodiment may comprise one or more radio-access entities 702, e.g. one or more shared cells 704 and / or one or more shared TRPs 704. Deploying more than one radio-access entity 702 can achieve a stripe or other buffer area for more spatial hysteresis for the HO, i.e. the server-node change.

[0440] Fig. 9 schematically illustrates a wider strip of shared cells 704 for more spatial hysteresis in a RAN 700 as compared to the example of the RAN 700 illustrated in Fig. 8. In other words, Fig. 9 schematically illustrates an example of a deployment of one or more shared cells 704 and / or one or more shared TRPs 702, e.g. to allow spatial hysteresis.

[0441] Any embodiment of any of the methods 400, 500, and 600 may comprise at least one of the features and steps of the following sequence of an example intra-RAT serving-node change.

[0442] The first network node 200 is the source node in the examples of the RAN 700 of both Figs. 8 and 9. The second network node 300 is the target node. The UE 100 is moving from coverage of the first network node 200 to coverage of the second network node 300 inTelefonaktiebolaget LM Ericsson (publ) 46 / 71

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[0444] general via one or more of the shared cells 704. An example of a sequence is illustrated in Fig. 10 It is noted that the use of RRC and Xn interfaces, e.g. based on existing 5G RAT, is merely an example, which may be updated for future RAT generations.

[0445] Fig. 10 schematically illustrates an intra-RAT serving -node change using intra-RAT shared cell and / or shared TRP node handover. Any embodiment of the methods 400, 500, and 600 may comprise at least one of the following features and steps.

[0446] 1. The UE 100 sends a measurement report to the source node 200. E.g., the UE 100 is configured to evaluate and send a measurement report when radio conditions of the shared cell 704 are good to allow intra-shared cell and / or intra-shared TRP serving-node handover.

[0447] 2. The source node 200 sends in a step 504-1 an inter node message to a target node 300, requesting an intra-shared cell and / or intra-shared TRP serving-node handover, and optionally provides UE-capabilities and / or a current UE-configuration. The UE-configuration may forward one or more values of one or more radio parameters that are maintained during the HO, e.g. at least one of CSI, TA, QCL source, beam weights, and buffer status report (BSR) information.

[0448] 3. The target node 200 responds to the request by sending an acknowledge containing target configuration information to be forwarded to the UE (e.g., a target C-RNTI, a Nexthop ciphering key, and optionally pre-configured target resources to be used by the UE 100). The target configuration information can be contained within a RRC reconfiguration message. Transmitting this (target) configuration information from the second network node 300 (indirectly through the first network node 200, and of course via the shared radio-access entity 702) is an example of transmitting 606-2 configuration information according to the method 600.

[0449] 4. The source node 200 forwards the target configuration information to UE 100. This may also implement the step 502 of transmitting the HO command to the UE 100. Alternatively or in addition, this may conclude the step 606-2 initiated by the target network node 300.

[0450] 5. The source node 200 suspends 503 the user plane (UP) for the UE 100 and start forwarding 504-3 DL user data of the UE 100 from the source node 200 to the target node 300.

[0451] 6. A sequence number status is provided 504-2 to the target node 300. Optionally, this inter-node signaling may also contain at least one of CSI, TA, QCL source, beam weights, and buffer status report (BSR) information that was valid just before the userTelefonaktiebolaget LM Ericsson (publ) 47 / 71

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[0453] plane for the UE 100 was suspended at the source node 200. Forwarding this information from the source node 200 to the target node 300 can enable the target node 300 to use this information when scheduling the UE 100, and does not have to start link adaptation (LA) and / or beam refinement from scratch.

[0454] 7. TheUE 100 resets a MAC protocol and re-establish RLC andPDCP protocols to ensure no packets encrypted with the old security key are transmitted after the received target configuration (according to the target configuration information) is applied. The UE 100 changes the C-RNTI to the target C-RNTI and / or may re-use latest CSI and / or BSR, e.g. as sent to the source node 200 and / or may send the same or updated information (e.g., one or more values of the maintained radio parameters) to the target node 300.

[0455] 8. The UE 100 uses the target C-RNTI and / or latest CSI and BSR and / or transmits to the target node 300 directly on pre-allocated resources or transmits a scheduling request on configured resources using the target configuration or re-used control channel configurations from source node configuration.

[0456] The target node 300 may forward the (e.g., received UL) user data to the source node 200, which is received and forwarded 504-3 to the core network, e.g., while the source node 200 is still terminates an IP link of the UE 100 in the RAN 700.

[0457] 9. When the UE 100 get the first transmission using target C-RNTI acknowledged, the UE 100 consider the intra-shared cell and / or intra-shared TRP handover to have been successful and send an RRC complete to target node 300. In an alternative embodiment, the UE transmits the RRC complete message in the first UL grant received by the RAN 700 using the target C-RNTI and considers the intra-shared cell and / or intra-shared TRP handover to have been successful.

[0458] When receiving a UE transmission using the target C-RNTI and / or the RRC complete message the target node 300 can consider the intra-shared cell and / or the intra-shared TRP handover to have been successful.

[0459] In a variant of the method embodiment of Fig. 10, the first transmission from the UE 100 may be a transmission of a random access preamble, which may be received 606-1 at the second (target) network node 300. In particular, the control signaling previously signaled from the target network node 300 may be (e.g., in Radio Resource (RRC) signaling) indicative of a Preamble ID, which is used for by the UE 100 for the random access preamble.

[0460] 10. The target network node 300 sends a path switch request to the CN 710.Telefonaktiebolaget LM Ericsson (publ) 48 / 71

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[0462] 11. The target network node 300 sends forwarded user data to the UE 100 but now ciphered with the new ciphering key.

[0463] 12. The target node 300 receives last forwarded user data and an end marker from the source node 200.

[0464] 13. The target node 300 starts providing user data received from the CN 710 to the UE 100 and from the UE 100 to the CN 710 after the path switch.

[0465] 14. A path switch request acknowledge is received from the CN 710 concluding the path switch.

[0466] 15. The target node 300 sends UE release to inform the source node 200 that the UE 100 is now served by the target node 300.

[0467] Alternatively or in addition, any embodiment of the methods 400, 500, and 600 for inter-RAT serving-node change may comprise at least one feature or step of the following sequence, e.g. as shown in Fig. 11 and / or described below. As emphasized before, the shared TRP 702 is described as an example, which applies in general to the physical radio-access entity 702. Also as emphasized before, serving-node handover, serving-node change, and briefly "handover" (HO) are synonymous.

[0468] 1. The UE 100 sends a measurement report to the source node. UE is configured to evaluate and send a measurement report when the radio conditions of the shared cell are good to allow Inter RAT Intra shared TRP serving Node handover.

[0469] 2. The source node 200 sends 504-1 an inter-node message to a target node 300 requesting an inter-RAT intra-shared TRP serving-node handover an provides UE capabilities and current UE configuration (It may also contain CSI, TA, QCL source, Beam weights and BSR information).

[0470] 3. The target node 300 responds to the request by sending an acknowledge containing target 6G configuration information to be forwarded to the UE 100 (e.g. including at least one of Target 6G C-RNTI, Nexthop ciphering key, and optionally pre-configured target resources to be used by the UE 100) according to the step 606-2. The target configuration information may be contained within a RRC reconfiguration message.

[0471] This step 3 may initiate the transmitting 606-2 of configuration information according to the method 600.

[0472] 4. The source node 300 forwards the target configuration information to UE 100, thus concluding the step 606-2 initiated by the target network node 300. This may also implement the step 502 of transmitting the HO command to the UE 100.Telefonaktiebolaget LM Ericsson (publ) 49 / 71

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[0474] 5. The source node 300 suspends 503 the user plane (UP) and starts forwarding 504-3 DL user data from source node 200 to target node 300.

[0475] 6. A sequence number status is provided 504-2 to the target node 300. Optionally, it may also contain CSI, TA, QCL source, beam weights, and / or buffer status report (BSR) information that was valid just before source node user plane was suspended 503. Forwarding this information from the source node 200 to the target node 300 means that the target node 300, after translation (i.e., HO), may use this information when scheduling the UE 100, and does not have to start link adaptation and beam refinement from scratch.

[0476] 7. The UE 100 reset its MAC protocol and / or re-establishes RLC and / or PDCP protocols to ensure no packets encrypted with the old security key are transmitted after the target configuration is applied. The UE changes C-RNTI to the target 6G C-RNTI, and may re-use latest CSI and / or BSR as sent to the source node 200 and send the same or updated information to the target node 300.

[0477] 8. UE use Target 6G C-RNTI and latest CSI and BSR and send to target node directly on pre-allocated resources or sending a scheduling request on configured resources using the target configuration.

[0478] 9. When UE get the first transmission using target 6G C-RNTI acknowledged the UE consider the Intra shared cell / TRP Handover to have been successful and send RRC complete (Optional) to target. In an alternative embodiment, the UE transmits the 6G RRC complete message in the first UL grant received by the network using the target 6G C-RNTI and considers the Inter RAT intra shared TRP serving Node handover to have been successful. When receiving UE transmission using the target 6G C-RNTI and / or the 6G RRC complete message the target node can consider the Inter RAT Intra shared TRP serving Node Handover to have been successful.

[0479] 10. Target node sends a path switch request to CN 710.

[0480] 11. Target node 300 sends forwarded user data to UE 100 but now ciphered with the new ciphering key.

[0481] 12. Target node 300 receives last forwarded user data and an end marker from source node 200.

[0482] 13. Target node 300 starts providing user data received from CN 710 to UE 100 and from UE 100 to CN after the path switch.

[0483] 14. Path switch request acknowledge is received from CN 710 concluding the path switch.Telefonaktiebolaget LM Ericsson (publ) 50 / 71

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[0485] Target node sends UE release to inform source node 200 that the UE 100 is now served by the target node 300.

[0486] In one variant of any embodiment of the methods 400, 500, and 600, the UE 100 does not perform a random access procedure with the target network node 300, e.g. reusing values of radio parameters by virtue of the maintained radio link via the shared physical radio-access entity 702.

[0487] In another variant of any embodiment of the methods 400, 500, and 600, a random access (RA) procedure is performed, e.g. as illustrated in one of the Figs. 12 to 15. Fig. 12 shows a signaling diagram between the UE 100 and the target network node 300 for an example of a 4-Step contention-based random access (CBRA) procedure. Fig. 13 shows a signaling diagram between the UE 100 and the target network node 300 for a 2-Step CBRA procedure. Fig. 14 shows a signaling diagram between the UE 100 and the target network node 300 for a 4-Step contention-free random access (CFRA) procedure. The preamble ID may be signaled to the UE 100 according to the step 606-1 of the method 600. Fig. 15 shows a signaling diagram between the UE 100 and the target network node 300 for a 2-Step CFRA procedure.

[0488] Any one of these examples may implement the step 606-2 of the method 600, and corresponding steps in the method 400 performed by the UE 100.

[0489] Furthermore, any embodiment of the methods 400, 500, and 600 may further comprise at least one the steps of a typical sequence for inter-gNB handover, e.g. as is illustrated in Fig. 16 or described below. The embodiments may deviate from a conventional sequence for inter-cell HO in that the cell (e.g., the cell ID) remains the same after the handover. The embodiments may deviate from the typical sequence in that the source and target network node are not identical.

[0490] For an example of intra-cell handover, source and target cell as well source and target TRP are the same before and after the change. Embodiments replace coordination of the change using proprietary inter-node signaling (instead of the node-internal signaling for intra-gNB HO). Furthermore, packet forwarding over the backhaul between source and target gNB is needed. A re-synchronization between UE 100 and RAN 700 is not needed as the radio-access entity 702 is maintained, i.e. using a random access to the same entity 702 is optional.

[0491] In any embodiment the handover may be triggered due to a change of ciphering key and / or to support unambiguous sequence number wrap around.Telefonaktiebolaget LM Ericsson (publ) 51 / 71

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[0493] Fig. 16 schematically illustrates an intra-core network (e.g. maintaining Access and Mobility Management Function (AMF) and / or User Plane Function (UPF). The existing technique for inter-gNB handover is replaced by proprietary or future O-RAN-defined signaling between the source and target network nodes 200 and 300.

[0494] At step 1 in Fig. 16, a measurement configuration cause UE 100 to send measurement reports to source gNB 200 when event conditions are fulfilled. At step 6 in Fig. 16, a handover trigger is done by source gNB 200 sending RRC reconfiguration with mobility information to UE 100 according to the step 502. The UE 100 is also informed to use a new ciphering key since that is required for the gNB handover that cause RAN User Plane termination change for security reasons according to the step 606-2.

[0495] At an optional step 8 in Fig. 16, the UE 100 synchronizes to the target network node 300 although the same cell 704 is reused via the same TRP 702. The UE 100 completes RRC handover procedure. Synchronization can be done in several ways, e.g. contention-based random access (CBRA) according to Fig. 12 and Fig. 13 and contention free random access (CFRA) according to Fig. 14 and Fig. 15. After successful random access, the UE 100 sends RRC reconfiguration complete to the target gNB 200.

[0496] Fig. 17 shows a schematic block diagram for an embodiment of the device 100. The device 100 comprises processing circuitry, e.g., one or more processors 1704 for performing the method 400 and memory 1706 coupled to the processors 1704. For example, the memory 1706 may be encoded with instructions that implement at least one of the modules 102 and 104.

[0497] The one or more processors 1704 may be a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, microcode and / or encoded logic operable to provide, either alone or in conjunction with other components of the device 100, such as the memory 1706, radio device functionality. For example, the one or more processors 1704 may execute instructions stored in the memory 1706. Such functionality may include providing various features and steps discussed herein, including any of the benefits disclosed herein. The expression "the device being operative to perform an action" may denote the device 100 being configured to perform the action.

[0498] As schematically illustrated in Fig. 17, the device 100 may be embodied by a radio device 1700, e.g., functioning as a UE. The radio device 1700 comprises a radio interfaceTelefonaktiebolaget LM Ericsson (publ) 52 / 71

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[0500] 1702 coupled to the device 100 for radio communication with the shared radio-access entity 702, e.g., functioning as a TRP or cell or beam.

[0501] Fig. 18 shows a schematic block diagram for an embodiment of the device 200. The device 200 comprises processing circuitry, e.g., one or more processors 1804 for performing the method 500 and memory 1806 coupled to the processors 1804. For example, the memory 1806 may be encoded with instructions that implement at least one of the modules 202 and 204.

[0502] The one or more processors 1804 may be a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, microcode and / or encoded logic operable to provide, either alone or in conjunction with other components of the device 100, such as the memory 1806, source node functionality. For example, the one or more processors 1804 may execute instructions stored in the memory 1806. Such functionality may include providing various features and steps discussed herein, including any of the benefits disclosed herein. The expression "the device being operative to perform an action" may denote the device 200 being configured to perform the action.

[0503] As schematically illustrated in Fig. 18, the device 200 may be embodied by a first (e.g., source) network node 1800, e.g., functioning as a base station or central unit of a base station or a gNB. The first network node 1800 comprises a radio interface 1802 coupled to the device 200 for radio communication with one or more radio devices, e.g., functioning as aUE.

[0504] Fig. 19 shows a schematic block diagram for an embodiment of the device 300. The device 300 comprises processing circuitry, e.g., one or more processors 1904 for performing the method 600 and memory 1906 coupled to the processors 1904. For example, the memory 1906 may be encoded with instructions that implement at least one of the modules 304 and 306.

[0505] The one or more processors 1904 may be a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, microcode and / or encoded logic operable to provide, either alone or in conjunction with other components of the device 200, such as the memory 1906, target node functionality. For example, the one or more processors 1904 may execute instructions stored in the memory 1906. Such functionality may includeTelefonaktiebolaget LM Ericsson (publ) 53 / 71

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[0507] providing various features and steps discussed herein, including any of the benefits disclosed herein. The expression "the device being operative to perform an action" may denote the device 300 being configured to perform the action.

[0508] As schematically illustrated in Fig. 19, the device 200 may be embodied by a second (e.g., target) network node 1900, e.g., functioning as a target base station of the handover. The second network node 1900 comprises a radio interface 1902 coupled to the device 300 for radio communication with one or more radio device being handed over, e.g., functioning as a UE.

[0509] With reference to Fig- 20, in accordance with an embodiment, a communication system 2000 includes a telecommunication network 2010, such as a 3 GPP -type cellular network, which comprises an access network 2011, such as a radio access network, and a core network 2014. The access network 2011 comprises a plurality of base stations 2012a, 2012b, 2012c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 2013a, 2013b, 2013c. Each base station 2012a, 2012b, 2012c is connectable to the core network 2014 over a wired or wireless connection 2015. A first user equipment (UE) 2091 located in coverage area 2013c is configured to wirelessly connect to, or be paged by, the corresponding base station 2012c. A second UE 2092 in coverage area 2013a is wirelessly connectable to the corresponding base station 2012a. While a plurality of UEs 2091, 2092 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 2012.

[0510] Any of the base stations 2012 may embody the devices 200 and / or 300. The UEs 2091 and 2092 may embody the device 100.

[0511] The telecommunication network 2010 is itself connected to a host computer 2030, which may be embodied in the hardware and / or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer 2030 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections 2021, 2022 between the telecommunication network 2010 and the host computer 2030 may extend directly from the core network 2014 to the host computer 2030 or may go via an optional intermediate network 2020. The intermediate network 2020 may be one of, or a combination of more than one of, a public, private or hosted network; the intermediate network 2020, if any, may be a backbone network or the Internet; in particular, the intermediate network 2020 may comprise two or more sub-networks (not shown).Telefonaktiebolaget LM Ericsson (publ) 54 / 71

[0512] P112623WO01

[0513] The communication system 2000 of Fig. 20 as a whole enables connectivity between one of the connected UEs 2091, 2092 and the host computer 2030. The connectivity may be described as an over-the-top (OTT) connection 2050. The host computer 2030 and the connected UEs 2091, 2092 are configured to communicate data and / or signaling via the OTT connection 2050, using the access network 2011, the core network 2014, any intermediate network 2020 and possible further infrastructure (not shown) as intermediaries. The OTT connection 2050 may be transparent in the sense that the participating communication devices through which the OTT connection 2050 passes are unaware of routing of uplink and downlink communications. For example, a base station 2012 need not be informed about the past routing of an incoming downlink communication with data originating from a host computer 2030 to be forwarded (e.g., handed over) to a connected UE 2091. Similarly, the base station 2012 need not be aware of the future routing of an outgoing uplink communication originating from the UE 2091 towards the host computer 2030.

[0514] By virtue of the method 400 being performed by any one of the UEs 2091 or 2092 and / or the method 500 by any one of the base stations 2012 and / or the method 600 by any one of the base stations 2012, the performance or range of the OTT connection 2050 can be improved, e.g., in terms of increased throughput and / or reliability and / or radio resource efficiency and / or energy efficiency. More specifically, the host computer 2030 may indicate to the RAN 700 or the radio device 100 or the first and / or second network node 200 or 300 (e.g., on an application layer) a QoS of the traffic of the radio device 100.

[0515] As has become apparent from above description, at least some embodiments of the technique (e.g., for an intra-RAT serving node change) can continue (e.g., maintain a value of) at least one of the following radio parameters:

[0516] UE measurements,

[0517] DL synch,

[0518] QCL source,

[0519] Timing Advance (TA),

[0520] link adaptation, and

[0521] beam weights.

[0522] For example, embodiments of the radio device or the second network node or the core network do not need re-initialize at least one of these radio parameters during or after the handover of the radio device.

[0523] The maintained radio-access entity may be a cell. In other words, the serving node change may be an intra-cell handover. Beneficially, one or more control channels do notTelefonaktiebolaget LM Ericsson (publ) 55 / 71

[0524] P112623WO01

[0525] need to be reconfigured and / or re-initialized at the serving node change (i.e., during or after the handover).

[0526] Same of further embodiments can perform the handover using less configuration signaling and / or shorter connection interruptions for a faster and / or a more spectrumefficient serving node change.

[0527] Same of further embodiments can require, e.g. due to above-mentioned more seamless serving node change, less care to be spent or less measurement time on planning RAN node coverage borders between the first and the second network node.

[0528] In addition, same or further embodiments of the proposed procedure enable

[0529] a relocation of one or all user plane layer 2 (L2, e.g., MAC) buffers from the first (source) network node 200 to the second (target) network node 300 (e.g., by forwarding DL and / or UL user data); or / and (e.g., simultaneously)

[0530] a change of one or more security keys

[0531] to occur not at a cell border (as in a regular handover) but instead within the shared cell 704 (e.g., in good cell coverage), which can greatly improve reliability of the handover procedure.

[0532] Further embodiments of any aspect, or a variant of any of the embodiments, allow multi-TRP (mTRP) and / or carrier aggregation (CA) and / or usage of one or more shared cells before and after the change of the serving node (i.e., the handover).

[0533] Same or further embodiments can improve inter-node handover by avoiding that at least one of

[0534] - a UE configuration changes,

[0535] - a serving RAN node changes,

[0536] - a serving cell changes, and

[0537] - a serving TRP changes

[0538] at the same time with the handover. Furthermore, the embodiments can avoid the need for coordination of such changes via inter-node signaling via fronthaul midhaul or backhaul and / or can avoid re-synchronization between radio device and RAN.

[0539] As a result, the embodiments can use shorter messages and / or achieve shorter interruptions when the radio device crosses a border of a serving network node of the RAN.

[0540] Same or further embodiments can perform the serving-node change without or with shorter radio interruptions, e.g. since the handover is not between different radio-access entities (e.g., in the same cells and / or the same TRP. Thereby, radio propagation changes before and after the connection may be kept unchanged for the radio device 100. ForTelefonaktiebolaget LM Ericsson (publ) 56 / 71

[0541] P112623WO01

[0542] example, radio parameter values for at least one of UE DL synch, UE UL synch, and QCL source may be maintained during the handover, and / or link adaptation and / or beam weights may be kept and / or not re-initiated.

[0543] Same or further embodiments can achieve a serving -node change (i.e., the inter-node handover) that is robust and avoids a ping-pong behavior by applying sufficiently large (e.g., larger than in conventional cell-border-trigged handover) handover hysteresis margins, e.g. because the handover within the shared radio-access entity (e.g., the shared cell) does not lead to higher radio resource cost. In other words, within the shared cell there is room for handover hysteresis margins.

[0544] Same or further embodiments can avoid a multi-TRP type of serving-node change. The shared TRP type serving-node change is advantageous over the multi-TRP type of serving-node change, since the same radio-access entity enables the required level of (e.g., TRP) time synchronization, e.g., by a shared scheduler 706 for the network nodes 200 and 300, e.g. for two radio units (RU) or two baseband unit (BBU) serving through the shared TRP.

[0545] While above embodiments and advantages are primarily described for an intra-RAT serving node change, further embodiments (e.g., analogously to the embodiments for an intra-RAT handover) for an inter-RAT handover may further comprise a translation (e.g., when maintaining the radio parameters of the shared radio-access entity) from one RAT representation of the information to the other RAT representation.

[0546] Many advantages of the present invention will be fully understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the units and devices without departing from the scope of the invention and / or without sacrificing all of its advantages. Since the invention can be varied in many ways, it will be recognized that the invention should be limited only by the scope of the following claims.

Claims

Telefonaktiebolaget LM Ericsson (publ) 57 / 71P112623WO01Claims1. A method (400) performed by a radio device (100; 1700; 2091; 2092) radioconnected to a radio access network, RAN (700), the method (400) comprising:receiving (402), while radio-connected to a first network node (200; 1800; 2012) via a physical radio-access entity (702), a handover command to change a serving network node to a second network node (300; 1900; 2012), the physical radio-access entity (702) being shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012); andresponsive to the received (402) handover command, changing (404) the serving network node of the radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012) while remaining radio-connected via the physical radio-access entity (702).

2. The method (400) of claim 1, wherein the shared radio-access entity (702) comprises one physical entity for radio access to the RAN (700); and / orwherein the shared radio-access entity (702) is associated with at least one physical access parameter for radio access to the RAN (700), the at least one physical access parameter being unchanged when changing (404) the serving network node of the radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012); and / orwherein the radio-access entity (702) comprises at least one of:one transmission and reception point, TRP, shared between and / or fronthaul-connected to both the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012);one radio unit, RU, shared between and / or fronthaul -connected to both the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012);one location where transmission and reception of radio signals of the RAN (700) occurs;one radio-frequency transmitter chain and one radio-frequency receiver chain; one collocated antenna system, optionally wherein the collocated antenna system comprising a plurality of antenna elements for multiple-input multiple-output, MIMO, transmission and reception.Telefonaktiebolaget LM Ericsson (publ) 58 / 71P112623WO013. The method (400) of claim 1 or 2, wherein the shared radio-access entity (702) is associated with at least one of:a shared cell (704) served by both the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012) via the shared radio-access entity (702);a shared carrier frequency used by both the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012) via the shared radio-access entity (702), optionally in combination with different radio access techniques, RATs, provided by the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012) via the shared radio-access entity (702); anda 5G Cell and a 6G cell can use the same shared carrier.; anda common radio access technique, RAT, used by both the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012) via the shared radio-access entity (702).

4. The method (400) of any one of claims 1 to 3, wherein the radio device (100; 1700; 2091; 2092) remains connected via the radio-access entity (702) reusing one or more physical access parameters before and after the handover; and / or wherein the radio device (100; 1700; 2091; 2092) remains connected via the radio-access entity (702) using or converting at least one of:the same cell (704) before and after the handover;the same radio spectrum, optionally the same carrier frequency, before and after the handover;the same radio access technology, RAT, before and after the handover;the same physical cell identifier, PCI, before and after the handover;the same timing advance, TA, before and after the handover;the same system frame number, SFN, before and after the handover;the same search space for downlink control information, DCI, scheduling system information, SI, before and after the handover;the same public land mobile network identifier, PLMN ID, before and after the handover;the same time-frequency position of a synchronization signal block, SSB, before and after the handover;Telefonaktiebolaget LM Ericsson (publ) 59 / 71P112623WO01the same radio parameter values for a random-access channel, RACH, before and after the handover;the same radio parameter values of a control resource set, CORESET, for monitoring a physical downlink control channel, PDCCH, before and after the handover;the same radio access technology cell identifier, RAT cell ID, optionally New Radio Cell Identifier, NCI, before and after the handover;the same radio parameter values of a transmission configuration indication, TCI, before and after the handover;the same radio parameter values of a Quasi Co-Location, QCI, optionally of a QCL source, before and after the handover;the same values of beamforming weights, optionally for a transmit beam to the radioaccess entity (702) or a receive beam from the radio-access entity (702), before and after the handover;the same channel state information, CSI, before and after the handover;the same value of a precoding matrix indicator, PMI, before and after the handover; the same link adaptation before and after the handover;the same modulation and coding scheme, MCS, before and after the handover; and the same radio network temporary identifier, RNTI, before and after the handover, optionally the same permanent cell RNTI, C-RNTI, and / or the same paging RNTI, P-RNTI.Any of the above-listed maintained values (e.g., information) may be an example of the one or more physical access parameters re-used after the handover.

5. The method (400) of any one of claims 1 to 4, wherein the shared radio-access entity (702) is controlled by at least one of the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012).

6. The method (400) of any one of claims 1 to 5, wherein each of the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012) has logical access to radio resources of the shared radio-access entity (702).

7. The method (400) of any one of claims 1 to 6, wherein at least one of the shared radio-access entity (702), the first network node (200; 1800; 2012), and the second network node (300; 1900; 2012) comprises a radio resource control entity for radio resources of the shared radio-access entity (702).Telefonaktiebolaget LM Ericsson (publ) 60 / 71P112623WO018. The method (400) of claim 7, wherein the radio resource control entity is configured to distribute the radio resources of the shared radio-access entity (702) between the first network node (200; 1800; 2012) and second network node (300; 1900; 2012) or to schedule or to coordinate scheduling of the radio resources of the shared radio-access entity (702); and / orwherein the radio resource control entity is configured to provide contention-free access to radio resources of the shared radio-access entity (702); and / orwherein the radio resource control entity comprises at least one of an arbitrator and a shared scheduler (706) for radio resources of the radio-access entity (702) shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012).Herein, "contention-free" may refer to a radio interface of the radio-access entity. "Contention-free" does not necessarily refer to a (e.g., wired) interface between the radioaccess entity and each of the first and second network nodes. That is, the first and second network nodes may use, free of contention, the radio resources of the radio-access entity, meaning that their transmissions over the radio interface of the radio-access entity do not experience contention. However, this does not necessarily imply contention-free procedures for requests (e.g., scheduling requests) of the network nodes to the radio-access entity.

9. The method (400) of any one of claims 6 to 8, wherein the radio resources comprise spectral, temporal, and / or spatial resources for transmitting and / or receiving at the radio-access entity (702); and / or wherein the radio resources are shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012).

10. The method (400) of any one of claims 1 to 9, wherein the radio-access entity (702) comprises multiple cells and / or multiple TRPs shared between and / or fronthaul-connected to both the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012), and / orwherein the radio device (100; 1700; 2091; 2092) is configured to use multiple TRPs before and after the handover.While the technique is described for one shared physical radio-access entity, the first and second network node may share multiple physical radio-access entities or the shared physical radio-access entity may be defined to comprise multiple shared cells and / or multiple shared TRPs. These multiple shared cells may provide an area (e.g., between areasTelefonaktiebolaget LM Ericsson (publ) 61 / 71P112623WO01exclusively covered by only one of the first and second network nodes) for spatial hysteresis of the handover. Alternatively or in addition, a multi -connectivity of the radio device may be maintained by the handover.

11. The method (400) of any one of claims 1 to 10, wherein the radio device (100; 1700; 2091; 2092) uses the same set of multiple TRPs on the same one carrier frequency before and after the handover.

12. The method (400) of any one of claims 1 to 10, wherein the radio device (100; 1700; 2091; 2092) uses the same set of carrier frequencies for the multiple TRPs, respectively, before and after the handover.

13. The method (400) of any one of claims 1 to 12, wherein the radio-access entity (702) comprises multiple physical TRPs subsumed as one logical TRP.

14. The method (400) of any one of claims 1 to 13, wherein a first coverage area of the RAN (700) is covered by the first network node (200; 1800; 2012) and a second coverage area of the RAN (700) is covered by the second network node (300; 1900; 2012), and wherein a shared coverage area of the shared radio-access entity (702) is, or is within, a partial overlap between the first coverage and the second first coverage.

15. The method (400) of claim 14, wherein the shared coverage area separates a non-shared first coverage area of the first network node (200; 1800; 2012) and a non-shared second coverage area of the second network node (300; 1900; 2012) by one or two or more layers of shared cells.

16. The method (400) of claim 14 or 15, wherein the handover from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012) when the radio device (100; 1700; 2091; 2092) moves from the non-shared first coverage area in a first direction across the shared cells to the non-shared second coverage area occurs at a location farther in the first direction as compared to a location of the handover from the second network node (300; 1900; 2012) to the first network node (200; 1800; 2012) when the radio device (100; 1700; 2091; 2092) moves from the non-shared second coverage areaTelefonaktiebolaget LM Ericsson (publ) 62 / 71P112623WO01in a second direction opposite to the first direction across the shared cells to the non-shared second coverage area.

17. The method (400) of any one of claims 1 to 16, wherein the radio-access entity (702), (702) corresponds to a cell (704) of the RAN (700); and / orwherein the radio device (100; 1700; 2091; 2092) receives (402) the handover command while connected to a cell (704) of the radio-access entity (702), and wherein the serving network node is changed (404) while the radio device (100; 1700; 2091; 2092) is connected to the cell (704) of the radio-access entity (702).

18. The method (400) of any one of claims 1 to 17, wherein the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012) provide radio access via the radio-access entity (702), optionally via a TRP (702) and / or in a cell (704), according to the same radio access technology, RAT.

19. The method (400) of any one of claims 1 to 18, further comprising, after the receiving (402) of the handover command and prior to the changing (404) of the serving network node, determining that re-synchronization with the radio-access entity (702) is to be omitted based on connectivity to the same radio-access entity (702), and / or refraining from initiating a random-access procedure.

20. The method (400) of any one of claims 1 to 19, wherein the radio device (100; 1700; 2091; 2092), upon completion of the handover (404), refrains from re-reading broadcast system information via the radio-access entity (702) from the second network node (300; 1900; 2012), optionally if previously received the system information while connected to the first network node (200; 1800; 2012).

21. The method (400) of any one of claims 1 to 20, wherein the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012) provide radio access via the radio-access entity (702) according to a first radio access technology, RAT, and a second RAT, respectively, wherein the second RAT is different from the first RAT.

22. The method (400) of claim 21, further comprising receiving, from the second network node (300; 1900; 2012), at least one translation instruction for reusing linkTelefonaktiebolaget LM Ericsson (publ) 63 / 71P112623WO01adaptation parameters previously applied by the radio device (100; 1700; 2091; 2092) with the first network node (200; 1800; 2012) under the first RAT, and applying said translation instruction to maintain a corresponding link adaptation via the shared radio-access entity (702) under the second RAT.

23. The method (400) of any one of claims 1 to 22, further comprising: receiving an indication to reuse one or more physical access parameters after the handover and / or to retain or partially retain previously obtained channel-state information, CSI, after the handover and / or to transmit buffer status information when connecting to the second network node (300; 1900; 2012) relative to a buffer status report sent to the first network node (200; 1800; 2012) prior to the handover.

24. The method (400) of any one of claims 1 to 23, further comprising:in response to the handover command and / or after the handover, transmitting a previously determined buffer status report, BSR, of the radio device (100; 1700; 2091; 2092) to the second network node (300; 1900; 2012), optionally wherein the BSR is indicative of data awaiting uplink transmission at the time of switching from the first network node (200; 1800; 2012) and / or wherein the BSR is a periodic BSR or not a regular BSR.

25. A method (500) performed by a first network node (200; 1800; 2012) of a radio access network, RAN (700), the method (500) comprising:sending (504-1), to a second network node (300; 1900; 2012) of the RAN (700), a request for a handover of a radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012) while the radio device (100; 1700; 2091; 2092) remains radio- connected via a physical radio-access entity (702) shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012); andtransmitting (502), to the radio device (100; 1700; 2091; 2092) connected via the physical radio-access entity (702), a handover command to change a serving network node to the second network node (300; 1900; 2012).

26. The method (500) of claim 25, wherein the transmitted (502) handover command or a further control message transmitted to the radio device (100; 1700; 2091; 2092) comprises at least one of:Telefonaktiebolaget LM Ericsson (publ) 64 / 71P112623WO01an indication to reuse one or more physical access parameters after the handover and / or to retain or partially retain previously obtained channel-state information, CSI, after the handover and / or to transmit buffer status information when connecting to the second network node (300; 1900; 2012) relative to a buffer status report sent to the first network node (200; 1800; 2012) prior to the handover;an activation instruction triggering the radio device (100; 1700; 2091; 2092) to reestablish medium-access control, MAC, or higher-layer controls with the second network node (300; 1900; 2012), without re-synchronizing a physical link via the shared radio-access entity (702); andone or more configuration parameters received from the second network node (300; 1900; 2012) for maintaining a radio-connection via the radio-access entity (702) under serving node control of the second network node (300; 1900; 2012).

27. The method (500) of claim 25 or 26, further comprising:suspending (503) scheduling and / or transmission of user-plane data flow at the first network node (200; 1800; 2012) via the radio-access entity (702), optionally prior to forwarding (504-3) buffered data to the second network node (300; 1900; 2012), and sending (504-2) a control signal indicative of a sequence number status to the second network node (300; 1900; 2012) to synchronize the user-plane data flow.

28. The method (500) of any one of claims 25 to 27, further comprising: forwarding (504-3) user data of the radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012), optionally after the transmission (502) of the handover command and / or while the radio device (100; 1700; 2091; 2092) transitions its serving node to the second network node (300; 1900; 2012); and / orforwarding (504-3) user data of the radio device (100; 1700; 2091; 2092) from the second network node (300; 1900; 2012) to the core network (710), optionally after the transmission (502) of the handover command and / or while the radio device (100; 1700; 2091; 2092) transitions its serving node to the second network node (300; 1900; 2012).

29. The method (500) of any one of claim 25 to 28, wherein at least one of the request sent (504-1) to the second network node (300; 1900; 2012), the control signal sent (504-2) to the second network node (300; 1900; 2012), and the user data forwarded (504-3)Telefonaktiebolaget LM Ericsson (publ) 65 / 71P112623WO01to the second network node (300; 1900; 2012) is further indicative of one or more radio parameters of the radio device (100; 1700; 2091; 2092) for reuse at the second network node (300; 1900; 2012) when radio-connected via the radio-access entity (702).

30. The method (500) of claim 29, wherein the one or more radio parameters comprise at least one of:the same cell (704) before and after the handover;the same radio spectrum, optionally the same carrier frequency, before and after the handover;the same radio access technology, RAT, before and after the handover;the same physical cell identifier, PCI, before and after the handover;the same timing advance, TA, before and after the handover;the same system frame number, SFN, before and after the handover;the same search space for downlink control information, DCI, scheduling system information, SI, before and after the handover;the same public land mobile network identifier, PLMN ID, before and after the handover;the same time-frequency position of a synchronization signal block, SSB, before and after the handover;the same radio parameter values for a random-access channel, RACH, before and after the handover;the same radio parameter values of a control resource set, CORESET, for monitoring a physical downlink control channel, PDCCH, before and after the handover;the same radio access technology cell identifier, RAT cell ID, optionally New Radio Cell Identifier, NCI, before and after the handover;the same radio parameter values of a transmission configuration indication, TCI, before and after the handover;the same radio parameter values of a Quasi Co-Location, QCI, optionally of a QCL source, before and after the handover;the same values of beamforming weights for the radio-access entity (702), optionally for a transmit beam to the radio device (100; 1700; 2091; 2092) or a receive beam from the radio device (100; 1700; 2091; 2092), before and after the handover;the same channel state information, CSI, before and after the handover;Telefonaktiebolaget LM Ericsson (publ) 66 / 71P112623WO01the same value of a precoding matrix indicator, PMI, for the radio-access entity (702) before and after the handover;the same link adaptation before and after the handover;the same modulation and coding scheme, MCS, before and after the handover; and the same radio network temporary identifier, RNTI, before and after the handover, optionally the same permanent cell RNTI, C-RNTI, and / or the same paging RNTI, P-RNTI.The one or more radio parameters may comprise (or may be limited to) one or more physical access parameters (e.g., physical-layer adaptation parameters).By reusing the one or more radio parameters at the second network node as the serving node can avoid re-establishing the link adaptation process from scratch, thereby reducing latency and signaling overhead.

31. The method (500) of any one of claim 25 to 30, further comprising: receiving (506), from the radio device (100; 1700; 2091; 2092), a communication using a temporary device identifier assigned by the second network node (300; 1900; 2012), optionally wherein the reception (506) is indicative of successful change of the serving node.

32. The method (500) of any one of claim 25 to 31, wherein the shared radioaccess entity (702) comprises a radio resource control entity, optionally an arbitrator and / or a shared scheduler (704), for radio resources of the radio-access entity (702) shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012).

33. The method (500) of any one of claim 25 to 32, further comprising features and steps of any one of the claims 2 to 24, or features and steps in one-to-one correspondence thereto.

34. A method (600) performed by a second network node (300; 1900; 2012) in a radio access network, RAN (700), the method (600) comprising:receiving (604-1), from a first network node (200; 1800; 2012), a request to assume serving-node control of a radio device (100; 1700; 2091; 2092) while maintaining a physical radio-access entity (702) used by the radio device (100; 1700; 2091; 2092); andin response to the request, receiving (606-1) a random access via the physical radioaccess entity (702) from the radio device (100; 1700; 2091; 2092) and / or transmitting (606-2) via the physical radio-access entity (702) to the radio device (100; 1700; 2091; 2092),Telefonaktiebolaget LM Ericsson (publ) 67 / 71P112623WO01through the first network node (200; 1800; 2012), configuration information enabling continued communication for the radio device (100; 1700; 2091; 2092) via the physical radio-access entity (702) with the second node (300; 1900; 2012).

35. The method (600) of claim 34, further comprising sending a path-switch request to a function of a core network, CN (710), serving the RAN (700) after providing the configuration information to the radio device (100; 1700; 2091; 2092), the path-switch request triggering the CN to route user-plane traffic via the second network node (300; 1900; 2012).

36. The method (600) of claim 34 or 35, further comprising features and steps of any one of the claims 2 to 24 or any one of claims 26 to 33, or features and steps in one-to-one correspondence thereto.

37. A radio device (100; 1700; 2091; 2092) comprising memory (1706) operable to store instructions and processing circuitry (1704) operable to execute the instructions, such that the radio device (100; 1700; 2091; 2092) is operable to:receive, while radio-connected to a first network node (200; 1800; 2012) via a physical radio-access entity (702), a handover command to change a serving network node to a second network node (300; 1900; 2012), the physical radio-access entity (702) being shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012); andresponsive to the received handover command, change the serving network node of the radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012) while remaining radio-connected via the physical radio-access entity (702).

38. The radio device (100; 1700; 2091; 2092) of claim 37, further operable to perform the steps of any one of claims 2 to 24.

39. A radio device (100; 1700; 2091; 2092) configured to:receive, while radio-connected to a first network node (200; 1800; 2012) via a physical radio-access entity (702), a handover command to change a serving network node to a second network node (300; 1900; 2012), the physical radio-access entity (702) beingTelefonaktiebolaget LM Ericsson (publ) 68 / 71P112623WO01shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012); andresponsive to the received handover command, change the serving network node of the radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012) while remaining radio-connected via the physical radio-access entity (702).

40. The radio device (100; 1700; 2091; 2092) of claim 39, further configured to perform the steps of any one of claims 2 to 24.

41. A first network node (200; 1800; 2012) in a radio access network, RAN (700), the first network node (200; 1800; 2012) comprising memory (1806) operable to store instructions and processing circuitry (1804) operable to execute the instructions, such that the network node (200; 1800; 2012) is operable to:send, to a second network node (300; 1900; 2012) of the RAN (700), a request for a handover of a radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012) while the radio device (100; 1700; 2091; 2092) remains radio-connected via a physical radio-access entity (702) shared between the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012); andtransmit, to the radio device (100; 1700; 2091; 2092) connected via the physical radio-access entity (702), a handover command to change a serving network node to the second network node (300; 1900; 2012).

42. The first network node (200; 1800; 2012) of claim 41, further operable to perform any one of the steps of any one of claims 26 to 33.

43. A first network node (200; 1800; 2012) in a radio access network, RAN (700), the first network node (200; 1800; 2012) being configured to:send, to a second network node (300; 1900; 2012) of the RAN (700), a request for a handover of a radio device (100; 1700; 2091; 2092) from the first network node (200; 1800; 2012) to the second network node (300; 1900; 2012) while the radio device (100; 1700; 2091; 2092) remains radio-connected via a physical radio-access entity (702) shared betweenTelefonaktiebolaget LM Ericsson (publ) 69 / 71P112623WO01the first network node (200; 1800; 2012) and the second network node (300; 1900; 2012); andtransmit, to the radio device (100; 1700; 2091; 2092) connected via the physical radio-access entity (702), a handover command to change a serving network node to the second network node (300; 1900; 2012).

44. The first network node (200; 1800; 2012) of claim 43, further configured to perform the steps of any one of claim 26 to 33.

45. A second network node (300; 1900; 2012) comprising memory operable to store instructions and processing circuitry operable to execute the instructions, such that the network node (200; 1800; 2012) is operable to:receive, from a first network node (200; 1800; 2012), a request to assume servingnode control of a radio device (100; 1700; 2091; 2092) while maintaining a physical radioaccess entity (702) used by the radio device (100; 1700; 2091; 2092); andin response to the request, receive a random access via the physical radio-access entity (702) from the radio device (100; 1700; 2091; 2092) and / or transmit via the physical radio-access entity (702) to the radio device (100; 1700; 2091; 2092), through the first network node (200; 1800; 2012), configuration information enabling continued communication for the radio device (100; 1700; 2091; 2092) via the physical radio-access entity (702) with the second node (300; 1900; 2012).

46. The second network node (300; 1900; 2012) of claim 45, further operable to perform any one of the steps of any one of claims 35 to 36.

47. A second network node (300; 1900; 2012) in a radio access network, RAN (700), configured to:receive, from a first network node (200; 1800; 2012), a request to assume servingnode control of a radio device (100; 1700; 2091; 2092) while maintaining a physical radioaccess entity (702) used by the radio device (100; 1700; 2091; 2092); andin response to the request, receive a random access via the physical radio-access entity (702) from the radio device (100; 1700; 2091; 2092) and / or transmit via the physical radio-access entity (702) to the radio device (100; 1700; 2091; 2092), through the first network node (200; 1800; 2012), configuration information enabling continuedTelefonaktiebolaget LM Ericsson (publ) 70 / 71P112623WO01communication for the radio device (100; 1700; 2091; 2092) via the physical radio-access entity (702) with the second node (300; 1900; 2012).

48. The second network node (300; 1900; 2012) of claim 47, further configured to perform the steps of any one of claims 35 to 36.

49. A computer program product comprising program code portions for performing the steps of any one of the claims 1 to 24 and / or 25 to 33 and / or 34 to 36 when the computer program product is executed on one or more computing devices (1704; 1804; 1904), optionally stored on a computer-readable recording medium.

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