WO2025201693A1

WO2025201693A1 - Handling concurrent handover configurations at ue

Info

Publication number: WO2025201693A1
Application number: PCT/EP2025/051498
Authority: WO
Inventors: Marvin Manalastas; Rakash SIVASIVA GANESAN; Hans Thomas HÖHNE; Xin Zhang; Aritra CHATTERJEE
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2024-03-26
Filing date: 2025-01-22
Publication date: 2025-10-02
Anticipated expiration: 2026-09-26
Also published as: GB2639869A; GB202404278D0

Abstract

There is provided a solution for handling multiple handover configurations at user equipment According to an aspect, a method for the user equipment comprises: receiving, by the user equipment, an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receiving, by the user equipment, an inter-centralized-unit handover configuration from the centralized unit; based on a determined criterion, executing by the user equipment a handover according to only one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration.

Description

HANDLING CONCURRENT HANDOVER CONFIGURATIONS AT UE

TECHNICAL FIELD

Various example embodiments relate generally to cellular communication system with multiple handover scenarios.

BACKGROUND

In a modern cellular communication system, user equipment (UE) is provided with various options for mobility control. As the UE moves, its connection with a radio access network is transferred (handed over) from one radio access network node to another. There are multiple options for the handover, such as a ‘conventional’ Layer 3 handover where handover execution is commanded by the network, a conditional handover where the network sets up conditions under which the UE can autonomously trigger the handover execution, and Layerl/Layer2-triggered mobility (LTM) where the serving cell switch is brought below Layer 3 and the handover (or serving cell switch) execution may be triggered via medium access control (MAC) signalling.

BRIEF DESCRIPTION

According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. The embodiments that do not fall under the scope of the claims are to be interpreted as examples useful for understanding the disclosure.

According to an aspect, there is provided an apparatus for user equipment, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receive an inter-centralized-unit handover configuration from the centralized unit; based on a determined criterion, execute a handover according to only one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration.

In an embodiment, the apparatus is configured to receive the determined criterion in a radio resource control configuration message.

In an embodiment, the determined criterion is such that the handover configuration received earlier than the other shall be executed.

In an embodiment, the determined criterion is such that a handover configuration for an unconditional handover prevails over a handover configuration for a conditional handover.

In an embodiment, the determined criterion is such that the inter-cen- tralized-unit handover configuration prevails over the intra-centralized-unit handover configuration.

In an embodiment, the determined criterion is such that the intra-cen- tralized-unit handover configuration prevails over the inter-centralized-unit handover configuration.

In an embodiment, a handover configuration associated with a stronger signal strength measured by the user equipment shall prevail over a handover configuration associated with a weaker signal strength.

In an embodiment, the apparatus is configured to send a configuration complete message for the other one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration, wherein the configuration complete message comprises a notification that said one of the intra-central- ized-unit handover configuration and inter-centralized-unit handover configuration has been discarded.

According to an aspect, there is provided a method comprising: receiving, by user equipment, an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receiving, by the user equipment, an inter-centralized-unit handover configuration from the centralized unit; based on a determined criterion, executing by the user equipment a handover according to only one of the intra-centralized-unit handover configuration and inter-central- ized-unit handover configuration.

In an embodiment, the user equipment receives the determined criterion in a radio resource control configuration message.

In an embodiment, the determined criterion is such that the intra-cen- tralized-unit handover configuration prevails over the inter-centralized-unit handover configuration. In an embodiment, a handover configuration associated with a stronger signal strength measured by the user equipment shall prevail over a handover configuration associated with a weaker signal strength.

In an embodiment, the user equipment sends a configuration complete message for the other one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration, wherein the configuration complete message comprises a notification that said one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration has been discarded.

According to an aspect, there is provided a computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the method according to any of the above-described embodiments.

Some embodiments of the invention are defined in the dependent claims.

LIST OF THE DRAWINGS

In the following, the invention will be described in greater detail with reference to the embodiments and the accompanying drawings, in which

Figures 1A and IB illustrates a network and a communication scenario to which one or more embodiments are applicable;

Figures 2 and 3 shows an example of a process for managing concurrent handover configurations according to an embodiment;

Figures 4A and 4B illustrate embodiments of notification-based prevention of concurrent handover configurations in a radio access network;

Figures 5A and 5B illustrate embodiments for acknowledgment-based prevention of concurrent handover configurations in a radio access network;

Figure 6 illustrates a process for managing concurrent handover configurations in user equipment according to an embodiment;

Figure 7 illustrates an embodiment of a procedure for modifying an execution condition of a handover configuration of concurrent handover configurations;

Figures 8A and 8B illustrate embodiments for indicating a selected handover configuration to a radio access network by user equipment;

Figures 9 and 10 illustrate apparatuses, according to some embodiments.

DESCRIPTION OF EMBODIMENTS

The following embodiments are exemplary. Although the specification may refer to “an”, “one”, or “some” embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment's), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. For the purposes of the present disclosure, the phrases “at least one of A or B”, “at least one of A and B”, “A and/or B” means (A), (B), or (A and B). For the purposes of the present disclosure, the phrases “A or B” and “A and/or B” means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments.

Embodiments described may be implemented in a radio system, such as one comprising at least one of the following radio access technologies (RATs): Worldwide Interoperability for Micro-wave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, and enhanced LTE (eLTE). Term ‘eLTE’ here denotes the LTE evolution that connects to a 5G core. LTE is also known as evolved UMTS terrestrial radio access (EUTRA) or as evolved UMTS terrestrial radio access network (EUTRAN). A term “resource” may refer to radio resources, such as a physical resource block (PRB), a radio frame, a subframe, a time slot, a subband, a frequency region, a sub-carrier, a beam, etc. The term “transmission” and/or “reception” may refer to wirelessly transmitting and/or receiving via a wireless propagation channel on radio resources.

The embodiments are not, however, restricted to the systems/RATs given as an example but a person skilled in the art may apply the solution to other communication systems/networks provided with necessary properties. Some examples of a suitable communication networks include a 5G network and/or a 6G network. The 3GPP solution to 5G is referred to as New Radio (NR). 6G is envisaged to be a further development of 5G. NR has been envisaged to use multiple-input- multiple-output (M1M0) multi-antenna transmission techniques, more base stations or nodes than the current network deployments of LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller local area access nodes and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates. 5G will likely be comprised of more than one radio access technology / radio access network (RAT /RAN), each optimized for certain use cases and/or spectrum. 5G mobile communications may have a wider range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications, including vehicular safety, different sensors and real-time control. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and being integrable with existing legacy radio access technologies, such as the LTE.

The current architecture in LTE networks is distributed in the radio and centralized in the core network. The low latency applications and services in 5G may require to bring the content close to the radio which leads to local break out and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach requires leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC provides a distributed computing environment for application and service hosting. It also has the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing covers a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer- to-peer ad hoc networking and processing also classifiable as local cloud/fog computing and grid/mesh computing, dew computing, mobile edge computing, cloudlet, distributed data storage and retrieval, autonomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications). Edge cloud may be brought into RAN by utilizing network function virtualization (NVF) and software defined networking (SDN). Using edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head or base station comprising radio parts. Network slicing allows multiple virtual networks to be created on top of a common shared physical infrastructure. The virtual networks are then customised to meet the specific needs of applications, services, devices, customers or operators.

In radio communications, node operations may in be carried out, at least partly, in a central/centralized unit, CU, (e.g. server, host or node) operationally coupled to distributed unit, DU, (e.g. a radio head/node). It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of work between core network operations and base station operations may vary depending on implementation. Thus, 5G networks architecture may be based on a so-called CU-DU split. One gNB- CU controls several gNB-DUs. The term ‘gNB’ may correspond in 5G to the eNB in LTE. The gNBs (one or more) may communicate with one or more UEs. The gNB- CU (central node) may control a plurality of spatially separated gNB-DUs, acting at least as transmit/receive (Tx/Rx) nodes. In some embodiments, however, the gNB- DUs (also called DU) may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the gNB-CU (also called a CU) may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layers. Other functional splits are possible too. It is considered that skilled person is familiar with the OS1 model and the functionalities within each layer.

In an embodiment, the server or CU may generate a virtual network through which the server communicates with the radio node. In general, virtual networking may involve a process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Such virtual network may provide flexible distribution of operations between the server and the radio head/node. In practice, any digital signal processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may be selected according to implementation.

Some other possible technology advancements to be used are Software- Defined Networking (SDN), Big Data, and all-lP, to mention only a few non-limiting examples. For example, network slicing may be a form of virtual network architecture using the same principles behind software defined networking (SDN) and network functions virtualisation (NFV) in fixed networks. SDN and NFV may deliver greater network flexibility by allowing traditional network architectures to be partitioned into virtual elements that can be linked (also through software). Network slicing allows multiple virtual networks to be created on top of a common shared physical infrastructure. The virtual networks are then customised to meet the specific needs of applications, services, devices, customers or operators.

The plurality of gNBs (access points/nodes), each comprising the CU and one or more DUs, may be connected to each other via the Xn interface over which the gNBs may negotiate. The gNBs may also be connected over next generation (NG) interfaces to a 5G core network (5GC), which may be a 5G equivalent for the core network of LTE. Such 5G CU-DU split architecture may be implemented using cloud/server so that the CU having higher layers locates in the cloud and the DU is closer to or comprises actual radio and antenna unit. There are similar plans ongoing for LTE/LTE-A/eLTE as well. When both eLTE and 5G will use similar architecture in a same cloud hardware (HW), the next step may be to combine software (SW) so that one common SW controls both radio access networks/technol- ogies (RAN /RAT). This may allow then new ways to control radio resources of both RANs. Furthermore, it may be possible to have configurations where the full protocol stack is controlled by the same HW and handled by the same radio unit as the CU.

It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent. Some other technology advancements probably to be used are Big Data and all-lP, which may change the way networks are being constructed and managed. 5G (or new radio, NR) networks are being designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or nodeB (gNB). It should be appreciated that MEC can be applied in 4G networks as well.

5G may also utilize satellite communication to enhance or complement the coverage of 5G service, for example by providing backhauling. Possible use cases are providing service continuity for machine-to-machine (M2M) or Internet of Things (loT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future rail-way/maritime/aeronauti- cal communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano) satellites are deployed). Each satellite in the mega-constellation may cover several satellite- enabled network entities that create on-ground cells. The on-ground cells may be created through an on-ground relay node or by a gNB located on-ground or in a satellite.

The embodiments may be also applicable to narrow-band (NB) Inter- net-of-things (loT) systems which may enable a wide range of devices and services to be connected using cellular telecommunications bands. NB-loT is a narrowband radio technology designed for the Internet of Things (loT) and is one of technologies standardized by the 3rd Generation Partnership Project (3GPP). Other 3GPP loT technologies also suitable to implement the embodiments include machine type communication (MTC) and eMTC (enhanced Machine-Type Communication). NB-loT focuses specifically on low cost, long battery life, and enabling a large number of connected devices. The NB-loT technology is deployed “in-band” in spectrum allocated to Long Term Evolution (LTE) - using resource blocks within a normal LTE carrier, or in the unused resource blocks within a LTE carrier’s guard-band - or “standalone” for deployments in dedicated spectrum.

The embodiments may be also applicable to device-to-device (D2D), machine-to-machine, peer-to-peer (P2P) communications. The embodiments may be also applicable to vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V21), in- frastructure-to-vehicle (12V), or in general to V2X or X2V communications.

Figure 1 illustrates an example of a communication system to which embodiments of the invention may be applied. The system may comprise a control node 110 providing one or more cells, such as cell 100, and a control node 112 providing one or more other cells, such as cell 102. Each cell may be, e.g., a macro cell, a micro cell, femto, or a pico cell, for example. In another point of view, the cell may define a coverage area or a service area of the corresponding access node. The control node 110, 112 may be an evolved Node B (eNB) as in the LTE and LTE-A, ng-eNB as in eLTE, gNB of 5G, or any other apparatus capable of controlling radio communication and managing radio resources within a cell. The control node 110, 112 may be called a base station, network node, or an access node.

The system may be a cellular communication system composed of a radio access network of access nodes, each controlling a respective cell or cells. The access node 110 may provide user equipment (UE) 120 (one or more UEs) with wireless access to other networks such as the Internet. The wireless access may comprise downlink (DL) communication from the control node to the UE 120 and uplink (UL) communication from the UE 120 to the control node.

Additionally, although not shown, one or more local area access nodes may be arranged such that a cell provided by the local area access node at least partially overlaps the cell of the access node 110 and/or 112. The local area access node may provide wireless access within a sub-cell. Examples of the sub-cell may include a micro, pico and/or femto cell. Typically, the sub-cell provides a hot spot within a macro cell. The operation of the local area access node may be controlled by an access node under whose control area the sub-cell is provided. In general, the control node for the small cell may be likewise called a base station, network node, or an access node.

There may be a plurality of UEs 120, 122 in the system. Each of them may be served by the same or by different control nodes 110, 112. The UEs 120, 122 may communicate with each other, in case D2D communication interface is established between them.

The term “terminal device” or “UE” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station CSS}, a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

In the case of multiple access nodes in the communication network, the access nodes may be connected to each other with an interface. LTE specifications call such an interface as X2 interface. For IEEE 802.11 network (i.e. wireless local area network, WLAN, WiFi), a similar interface may be provided between access points. An interface between an LTE access point and a 5G access point, or between two 5G access points may be called Xn. Other communication methods between the access nodes may also be possible. The access nodes 110 and 112 may be further connected via another interface to a core network 116 of the cellular communication system. The LTE specifications specify the core network as an evolved packet core (EPC), and the core network may comprise a mobility management entity (MME) and a gateway node. The MME may handle mobility of terminal devices in a tracking area encompassing a plurality of cells and handle signalling connections between the terminal devices and the core network. The gateway node may handle data routing in the core network and to/from the terminal devices. The 5G specifications specify the core network as a 5G core (5GC), and there the core network may comprise e.g. an access and mobility management function (AMF) and a user plane function/gateway (UPF), to mention only a few. The AMF may handle termination of non-access stratum (NAS) signalling, NAS ciphering & integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. The UPF node may support packet routing & forwarding, packet inspection and QoS handling, for example.

There has been envisaged a new configuration for responsibilities of the CU and DU in a control plane. Such a configuration is disclosed in patent publication W02023/222190. In this configuration, there are two separate radio resource control (RRC) entities that establish a control plane for UE, one RRC entity in the CU that establishes a CU control plane (CU-CP) and one RRC entity in the DU that establishes a local control plane (L-CP). The L-CP may handle the "local" mobility functions of the UE e.g., forwarding of NAS messages to CU-CP and intra-gNB- based mobility operation, and is assigned with its own UE identity which may include RRC handling for selected UEs. This may include performing L-CP functions at a UE level or data radio bearer or packet data unit (DRB/PDU) session level. This may allow for transferring some of the CU-CP tasks (such as LTM) related to RRC to the L-CP, while maintaining the overall connection control and RRC termination at CU-CP. The L-CP may be completely transparent to the core network. Additionally, this may require that the RRC message and/or the packet data convergence protocol (PDCP) layer indicates the RRC entity to the UE to enable (de) ciphering the RRC message with the correct security key.

The CU-CP may synchronize with the L-CP after/during inter-gNB procedures, e.g. UE context release. The L-CP may coordinate/notify the CU-CP before or after mobility events, such as intra-CU handover. The CU-CP may fetch the latest UE RRC configuration from the L-CP while initiating inter-gNB procedures or, alternatively, the L-CP can sync with the CU-CP after completion of each RRC procedure, such as Layer 3 handover.

However, using two different entities of the radio access network for the same or substantially similar procedures on the same protocol layer, such as the handovers, may create confusing situations. Let us refer to Figure IB that illustrates a situation where the UE 120 is served by the DU 210 and CU 200 and is moving towards DU 212 and DU 214 where DU 214 (and DU 216) is controlled by CU 202. The DU 210 and CU 200 may both receive measurement reports from the UE 120: one measurement report for intra-CU handover handled by the DU and another measurement report for inter-CU handover handled by the CU. Accordingly, both DU 210 and CU 200 may start concurrent Layer 3 handover preparations (to DU 212 and DU 214) and even both issue a handover command to the UE 120. As another example, the UE may receive two conditional handover (CHO) configurations: one from the DU 210 and the other from the CU 200. Using two CHO configurations may cause unnecessary processing and power consumption in the UE and may cause unpredictable behaviour in the UE.

For the sake of clarity, the following description uses the terms “intra- CU measurements” and “intra-CU handover” which include both of the following scenarios: intra-DU (cells under the same DU and same CU) measurements and handover and inter-DU intra-CU (cells under different DUs but under one CU) measurements and handover, respectively. Further, the description uses terms “in- ter-CU measurements” and “inter-CU handover” which cover inter-DU inter-CU (cells under different DUs that belong to different CUs) measurements and handover, respectively. All intra-CU measurements may be directed to the L-CP and intra- CU handovers may be handled by the L-CP. All inter-CU measurements may be directed to the CU-CP and inter-CU handovers may be handled by the CU-CP. Terms DU and L-CP may be used interchangeably. Similarly, the terms CU and CU-CP may be used interchangeably in the context of the present description because the description has a focus on the control plane functions. Furthermore, in the following description, the context is that the described DU is under the control of the CU with which the DU communicates in connection with the handover preparation for the UE.

Figure 2 illustrates an embodiment for handling concurrent handover procedures in the above-described context. The method may be performed by an apparatus for the DU. The apparatus may be the DU or comprised in the DU. The apparatus may manage the L-CP of the DU and communicate with the UE over the L-CP.

Referring to Figure 2, the method comprises: receiving (block 220), for UE, a measurement report; determining (block 222) to initiate an intra-central- ized-unit handover procedure based on the received measurement report, wherein said initiation comprises transmitting to a centralized unit controlling the distributed unit, a message for preventing concurrent intra-centralized-unit handover procedure and inter-centralized-unit handover procedure for the user equipment; and based on transmitting the message, executing the intra-centralized-unit handover procedure with the user equipment or cancelling the initiated intra-central- ized-unit handover procedure (block 224).

The process of Figure 2 establishes coordination between the DU and the CU in connection with initiating the intra-CU handover procedure. The coordination in the form of the message then provides the outcome that the DU determines whether or not to execute the intra-CU handover procedure and to avoid overlapping intra-CU and inter-CU handover procedures. Embodiments described below illustrate further details of how the concurrent handover procedures can be reduced or prevented.

Figure 3 illustrates another embodiment for handling the concurrent handover procedures. The method of Figure 3 may be performed by an apparatus for the CU. The apparatus may be the CU or comprised in the CU. The apparatus may manage the CU-CP and communicate with the UE over the CU-CP. The method of Figure 3 is related to the method of Figure 2 in the sense that the message described above and transmitted by the DU is the same message received by the CU in the method of Figure 3.

Referring to Figure 3, the method comprises: receiving (block 300), from a distributed unit controlled by the centralized unit, a message indicating that the distributed unit intends to execute an intra-centralized-unit handover procedure with user equipment; receiving (block 302), for the user equipment, a measurement report indicating inter-centralized-unit handover procedure; based on timings of the message and the measurement report (determined in block 304), executing (block 306) an inter-centralized-unit handover procedure based on the received measurement report and transmitting to the distributed unit a second message for preventing concurrent intra-centralized-unit handover procedure and inter-centralized-unit handover procedure for the user equipment, or determining not to execute the inter-centralized-unit handover procedure to allow execution of the intra-centralized-unit handover procedure indicated by the message.

The embodiment of Figure 3 provides the same advantage as the embodiment of Figure 2, in reduction or even elimination of the concurrent handover procedures at the CU and DU for the UE. This results from the coordination between the CU and DU in the form of the message(s).

In the embodiments of Figures 2 and 3, the measurement report is received for the UE. The measurement report may be received from the UE, e.g. in the form of a neighbour cell measurement report. In another embodiment, the measurement report is based on positioning of the UE and, as known in the art, the UE may be measured by the UE itself or by anchor nodes in the proximity of the UE and capable of exchanging positioning signals with the UE. In such a case, the measurement report for the UE may be received from such an anchor node.

In an embodiment, the initiation of the handover procedure is performed based on another criterion than the received measurement report. For example, the handover procedure may be initiated based on knowledge of the network layout. Upon the UE entering a cell, a certain set of neighbour cells may be prepared for the handover of the UE by default. The set of prepared neighbour cells may comprise cells under the same CU and/or cells under multiple CUs. The set of prepared cells may also vary, e.g. depending on a source cell from which the UE entered the cell. Therefore, in some situations only intra-CU cells may be prepared while in other situations the set of prepared cells may also include cell(s) controlled by another CU.

Let us then describe embodiments of the methods of Figures 2 and 3 in greater detail with reference to Figures 4A to 5B. Figures 4A and 4B are describe embodiments where a network node (DU or CU), upon determining to initiate the handover procedure for the UE, notifies the initiation to the other network node (DU or CU) and then proceeds with the initiation. The other network node receiving the notification may disable the initiation of the handover procedure(s) for the UE based on reception of the notification, thus preventing the concurrent handover procedures for the UE. In other words, the network node determining to initiate the handover procedure and sending the message may execute the handover procedure without a response to the message from the other network node.

Referring to Figure 4A, the CU may configure the UE with a measurement configuration for performing neighbour cell measurements for the purposes of the handover. The measurement configuration may be a RRC configuration. The measurement configuration may instruct the UE about how measurement reporting shall be made. The measurement configuration may indicate, for example, that intra-CU measurements shall be reported to the DU/L-CP while measurement reports for inter-CU measurement shall be reported to the CU/CU-CP. The measurement configuration may comprise an intra-CU measurement configuration and an inter-CU measurement configuration. The intra-CU measurement configuration may indicate, for example, cell(s) of DU(s) of the CU that the UE shall measure for the purpose of the intra-CU handover. The inter-CU measurement configuration may indicate, for example, cell(s) of other CU(s) the UE shall measure for the purpose of the inter-CU handover. The measurement configuration(s) may further indicate timing of the respective measurement report(s). The measurement configuration may indicate any other measurement parameters. The measurement configuration is transmitted from the CU 200 to the UE 120 in step 400.

In block 402, the UE 120 performs both inter-CU measurements and in- tra-CU measurements by measuring the respective neighbour cells. Because of different reporting intervals configured in the measurement configuration, or because of other factors, the UE 120 may report the intra-CU measurements and in- ter-CU measurements at different times. In the embodiment of Figure 4A, the UE reports the intra-CU measurements in step 404 to the DU 210, the measurements indicating the need for initiating the intra-CU handover procedure. Upon determining to initiate the intra-CU handover procedure in 406, the DU 210 sends the abovedescribed message indicating the initiation to the CU 200 (step 408). The DU may start the handover preparations in step 410 without waiting for any response from the CU 200. In other words, the DU 210 does not need a confirmation from the CU 200 to start the handover procedure and related handover preparations. The CU may still acknowledge at least the reception of the message. Depending on the type of the handover, the handover preparation performed in step 410 may be different. It may include at least sending UE context parameters to the neighbouring DU(s) 212 in step 410.

Upon receiving the notification in step 408, the CU 200 may disable the handover initiation for the UE 120. As a consequence, upon receiving from the UE 120 a measurement report comprising inter-CU measurements in step 412, even if the measurements indicate the need for the inter-CU handover, the CU 200 may omit the initiation of the handover procedure for the UE 120 (block 414).

Figure 4B illustrates a procedure where the CU starts the initiation of the handover for the UE before the DU 210 and, hence, the situation is reversed in view of the embodiment of Figure 4A. Referring to Figure 4B, upon receiving the measurement report comprising the inter-CU measurements indicating the need for the inter-CU handover in step 412, the CU may determined to initiate the inter- CU handover procedure (block 420). Upon determining to initiate the inter-CU handover procedure in 420, the CU 200 sends a message that may be similar to the message transferred in step 408 indicating the initiation to the DU 210 (step 422). The CU may start the handover preparations in step 424 with a neighbour CU 202 without waiting for any response from the DU 210. Similar to the procedure of Figure 4A, the CU 200 does not need a confirmation from the DU 210 to start the handover procedure and related handover preparations. Depending on the type of the handover, the handover preparation performed in step 424 may be different. It may include at least sending UE context parameters to the neighbouring CU(s) 202 in step 424.

Upon receiving the notification in step 422, the DU 210 may disable the handover initiation for the UE 120. As a consequence, upon receiving from the UE 120 a measurement report comprising intra-CU measurements in step 404, even if the measurements indicate the need for the intra-CU handover, the DU 210 may omit the initiation of the handover procedure for the UE 120 (block 426).

In both embodiments of Figures 4A and 4B, the handover preparation for the UE 120 may again be enabled after a certain event. The event may be an indication from the network node that has the active handover procedure that the handover procedure has been released or the handover has been executed. As a consequence, whenever the UE returns to the cell, the procedure of Figure 4A or 4B may be executed again.

Following the embodiment of Figure 4B, the CU may equally execute the process of Figure 2, with the exception that the considered handover procedure is inter-CU handover procedure and that the message is transmitted by the CU to the DU and other DU(s) controlled by the CU. Accordingly, the process of Figure 2 may be adapted to the following form: receiving, by the CU from the UE, a measurement report; determining to initiate an inter-CU handover procedure based on the received measurement report, wherein said initiation comprises transmitting to each distributed unit controlled by the CU, a message for preventing concurrent intra- centralized-unit handover procedure and inter-centralized-unit handover procedure for the user equipment; and based on transmitting the message, executing the inter-centralized-unit handover procedure with the user equipment. According to this embodiment, the DU may receive from the CU the message for preventing the concurrent intra-CU handover procedure and inter-CU handover procedure, and cancel/disable the intra-CU handover procedure(s) for the UE 120.

The embodiments of Figures 4A and 4B define the handover preparation priority on the basis of which type of measurement report is transferred first and which network node (DU or CU) serving the UE first initiates the handover procedure. Accordingly, from the perspective of the CU, the timing of the message (step 408) before the timing of the measurement report (step 412) causes the disabling of the handover procedure initiation in the CU 200. On the other hand, the timing of the message (step 408) after the timing of the measurement report (step 412) causes the initiation of the handover procedure at the CU 200.

Figures 5A and 5B illustrate a procedure where the CU 200 controls the initiation of the handover procedures at the DU(s) 210, 212 controlled by the CU 200. In these embodiments, the DU(s) 210, 212 have to wait for the approval from the CU 200 before initiating the handover procedure. In other words, the DU may upon transmitting the message, wait for an acknowledgment from the CU and, upon determining that the acknowledgment indicates that the centralized unit approves the intra-centralized-unit handover procedure, execute the intra-centralized-unit handover procedure. The execution in this context may mean starting the handover preparations for the UE. On the other hand, upon determining that the acknowledgment indicates that the CU rejects the intra-CU handover procedure, the DU may cancel the intra-CU handover procedure.

In Figures 5A and 5B, the same reference numbers as in Figures 4A and 4B represent the same or substantially similar actions.

Referring to Figure 5A, upon receiving the measurement report comprising the intra-CU measurements (measurement data) in 404, the DU 210 may determine to initiate the handover procedure for the UE 120 and, as a consequence, request for the handover preparation from the CU 200 in 500. The message transferred in 500 may thus differ from the message transferred in step 408 that it is a request mandating a response from the CU 200. The DU may thus wait for the response before starting the handover preparations. In this case, let us assume that there is no active handover procedure for the UE 120 at the CU 200 and, as a consequence, the CU 200 may approve the request and send a corresponding acknowledgement message to the DU 210 in 502. (Only) upon receiving the approval, the DU may proceed with the intra-CU handover preparation in 410. Meanwhile, the CU 200 may have disabled the inter-CU handover procedure(s) for the UE 120. It means that if the CU 200 receives the measurement report in 412 indicating the need for the inter-CU handover, the CU 200 may omit the handover preparations (414).

In the embodiment of Figure 5B, the timing of the measurement reports and associated order of handover procedure initiations is opposite. As a consequence, the CU 200 may receive the measurement report comprising the inter-CU measurements in 412 and, as a consequence, trigger the inter-CU handover preparation in 420. A later transmitted and received measurement report comprising the intra-CU measurements (404) may also trigger the handover initiation in the DU 210 and transmission of the request in step 500. However, since the CU 200 already has an active handover procedure for the UE 120, the CU may reject the request and transmit the rejection (negative acknowledgment, NACK) in 504. As a consequence, the DU may cancel the intra-CU handover procedure for the UE 120 (426).

To summarize, if the CU receives the measurement report comprising the inter-CU measurements before the message indicating that the DU intends to execute the handover procedure, the CU may execute the inter-CU handover procedure based on the received measurement report. As a consequence, the CU may transmit the message comprising an indication of the handover procedure initiation to the DU(s), thus preventing the DU(s) from initiating a concurrent intra-cen- tralized-unit handover procedure. This may be applied also to the embodiment of Figures 5A and 5B, thus reducing the need for the DU 210 to request for the intra- CU handover preparation unnecessarily. If the CU receives the message before the measurement report comprising the inter-CU measurements, the CU may determine not to execute the inter-CU handover procedure based on the received measurement report. In this embodiment, the CU may respond to the request from the DU with the acknowledgment indicating that the intra-CU handover procedure is approved.

In an embodiment, the UE 120 is configured to associate the measurement report with a time stamp and to include the time stamp in the message. The time stamp may indicate the timing of the performed measurements. A respective time stamp may be added to both measurement reports 412, 404. The DU may propagate the time stamp to the request sent in 500. In the event that the CU 200 receives the measurement report 412 and the message 500 substantially at the same time or at least so that the inter-CU handover procedure has not yet been initiated, and in the event that the inter-CU measurements indicate the need for the inter-CU handover, the CU may compare the time stamp of the received inter-CU measurements with the time stamp in the request received in 500 and make the decision on which handover procedure to initiate on the basis of the comparison. For example, the CU may prefer the handover procedure based on the latest measurements and, accordingly, the handover procedure associated with a time stamp indicating later timing will be initiated. If the request 500 indicates a later timing of the intra-CU measurements, the procedure may follow Figure 5A. If the request indicates an earlier timing of the intra-CU measurements, the procedure may follow Figure 5B.

In an embodiment, the above-described procedures may be applied per type of handover. It means that the procedures are performed within each handover type, e.g. a conditional handover (CHO) procedure, a Layer 3 handover procedure, or a Layer 1/2 triggered mobility (LTM). In other words, the intra-CU handover procedure and inter-CU handover procedure in each embodiment may both be of the same type of handovers. As a consequence, a concurrent Layer 3 intra-CU handover procedure and a CHO inter-CU handover procedure may be allowed. In another embodiment, the concurrent handover procedures of the same handover type may be allowed while the concurrent handovers of the different types may be prevented according to any one of the embodiments described herein.

Preventing the concurrent handover procedures at the network side simplifies the procedure at the UE because the UE has to consider a reduced number of handover procedures. According to another aspect, the above-described problem may be solved at the UE side. In other words, the CU and DU may be allowed to initiate concurrent intra-CU and inter-CU handover procedures. Figure 6 illustrates an embodiment of a process for the UE in such a case. Referring to Figure 6, the method performed by the UE comprises: receiving an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit (block 600); receiving an inter-centralized-unit handover configuration from the centralized unit (block 602); based on a determined criterion (604), execute (block 606 or 608) a handover according to only one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration.

In an embodiment, the UE receives from the centralized unit a radio resource control configuration message indicating the criterion.

In an embodiment, the UE enables the intra-CU handover configuration and disables the inter-CU handover configuration. Accordingly, the determined criterion is such that the intra-centralized-unit handover configuration prevails over the inter-centralized-unit handover configuration. In another embodiment, the UE enables the inter-CU handover configuration and disables the intra-CU handover configuration.

Figures 7 to 8B illustrate embodiments of the various criteria and configurations for handling the concurrent handover procedures at the UE 120. Figure 7 illustrates an embodiment for the CHOs where there are separate execution conditions for the intra-CU handover and inter-CU handover. Therefore, the criterion in 604 may be one of the execution conditions becoming fulfilled, and the respective handover will be executed in 606 or 608. Furthermore, the CU may determine to prioritize one of the intra-CU and inter-CU by configuring a conditional modification for one of the execution conditions.

Referring to Figure 7, the method performed by the UE may comprise: receiving (702) an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receiving (704) an inter-centralized-unit handover configuration from the centralized unit; receiving (700), from the centralized unit, a configuration for conditional modification of an execution condition of one of the intra-centralized-unit handover configuration and inter-centralized- unit handover configuration; based on the configuration for conditional modification, changing (706) at least one parameter of the execution condition of said one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration; and after said changing, execute (708) a handover of whichever of the intra-centralized-unit handover configuration and intra-central- ized-unit handover has the respective execution condition becoming fulfilled.

The method may further comprise steps 400, 402, 404, and 412 but it should be noted that this embodiment may in principle be performed without the measurement reporting. For example, when the UE enters a cell, the neighbour cell(s) may be prepared for the handover of the UE without any measurements. The network may utilize, for example, the knowledge of the network layout and cell coverage areas.

In an embodiment, step 700 is a part of step 400. In other words, the configuration for the conditional modification of the execution condition may be comprised in the measurement configuration. In another steps 700 and 400 are realized through different messages, e.g. through different RRC messages.

In an embodiment, the modified handover execution condition is an A3 event, in the 3GPP terminology, meaning a situation where a neighbour cell becomes a by-an-offset stronger cell in terms of received signal strength, and the modification may be the offset parameter. The A3 event may be associated with a time-to-trigger (TTT) parameter that controls the handover execution so that the A3 event must be satisfied for the duration of the TTT in order to trigger the handover execution. The TTT is another embodiment of the parameter that may be modified via step 700.

The change may be applied only to one of the intra-CU and inter-CU handover configurations and, as described above, in a conditional manner. The condition may be the presence of the other handover configuration. In other words, the modification may be disabled when the UE has only one handover configuration and enabled when there are multiple concurrent handover configurations.

The modification may cause the UE to prefer the one or the other of the intra-CU and inter-CU handovers, depending on the modification. For example, if the UE is configured to increase the offset and/or increase the TTT parameter of the intra-CU handover configuration, it causes preference of the inter-CU handovers because the neighbour intra-CU cell shall provide greater-than-default-offset signal strength and/or provide the signal strength above the (modified) offset for a greater duration. Similarly, if the UE is configured to decrease the offset and/or decrease the TTT parameter of the intra-CU handover configuration, it causes preference of the intra-CU handovers because the neighbour intra-CU cell shall provide smaller-than-default-offset signal strength and/or provide the signal strength above the (modified) offset for a shorter duration. The same principles naturally apply, if the conditional modification is directed to the inter-CU handover execution condition.

In an embodiment, the configuration for the conditional modification is received as a part of a measurement reporting configuration (step 400), and the configuration disables transmission of a measurement report. Following 3GPP terminology, the measurement configuration may define a new ReportConfig which, when triggered does not produce a measurement report but implements the modification of the execution condition.

Both intra-CU handover configuration and inter-CU handover configuration may be CHO configurations in this embodiment.

Figures 8A and 8B relate to an embodiment that is a modification of the method of Figure 6. In general, the embodiment may comprise: transmitting a first measurement report to a distributed unit controlled by a centralized unit; receiving, in at least a first message, a first handover configuration for a handover between the distributed unit and another distributed unit controlled by the centralized unit; transmit a second measurement report to the centralized unit; receiving, in at least a second message, a second handover configuration for a handover from the centralized unit to another centralized unit; determining a criterion for prioritizinghandover configurations and, based on the criterion, disabling one of the first handover configuration and second handover configuration and enabling the other one of the first handover configuration and second handover configuration.

The criterion may specify the prioritization between the inter-CU and intra-CU handovers via various factors, as described below. In an embodiment, the determined criterion is such that the handover configuration received earlier than the other shall be executed. In an embodiment, the determined criterion is such that a handover configuration for an unconditional (Layer 3) handover prevails over a handover configuration for a conditional handover. In an embodiment, the determined criterion is such that the inter-CU handover configuration prevails over the intra-CU handover configuration. In an embodiment, the criterion is based on radio measurements performed by the user equipment.

Referring to Figure 8A, the CU may determine the criterion (or criteria) in block 800 and transmit the criterion to the UE, e.g. via a RRC message. Steps 400, 402, 404, and 412 may be carried out in the above-described manner. Based on the measurement report received in 404, the DU 210 may determine to initiate the in- tra-CU handover and, accordingly, carry out handover preparations with the neighbour DU(s) 212 and the UE 120 in step 802. As a consequence, the UE receives the intra-CU handover configuration from the DU 210. Similarly, based on the measurement report received in 412, the CU 200 may determine to initiate the inter-CU handover and, accordingly, carry out handover preparations with the neighbour CU(s) 202 and the UE 120 in step 804. As a consequence, the UE receives the inter- CU handover configuration from the CU 200. In this embodiment, the coordination between the CU and DU may be omitted.

Upon receiving the second handover configuration and determining to have multiple concurrent handover (HO) configurations, the UE 120 may use the received criterion in 806 to determine which one of the handover configurations to use for the handover. In an embodiment, the UE uses the following table that

In another embodiment, another prioritization table may be used. According to the table above, if both handover configurations are Layer 3 configurations, the UE may follow the handover configuration that is commanded by the respective network node first. In another embodiment, the action could be to override one of the concurrent handover configurations to prioritize either in- tra-CU or inter-CU Layer 3 handovers. In Case 2 and 3, the Layer 3 may prevail over the CHO.

Regarding Case 4, some embodiments are described in the following. In an embodiment, Case 4 describes that the inter-CU CHO will overrule intra-CU handover. As a consequence, if the UE already has an inter-CU CHO configuration and it receives an intra-CU CHO configuration, it will disregard the intra-CU CHO configuration. If the UE already has an intra-CU CHO configuration and it receives an inter-CU CHO configuration, it will discard the intra-CU CHO configuration and adopt the inter-CU CHO configuration. In another embodiment, Case 4 describes that the intra-CU CHO will overrule inter-CU handover. As a consequence, if the UE already has an intra-CU CHO configuration and it receives an inter-CU CHO configuration, it will disregard the inter-CU CHO configuration. If the UE already has an inter-CU CHO configuration and it receives an intra-CU CHO configuration, it will discard the inter-CU CHO configuration and adopt the intra-CU CHO configuration.

In another embodiment, the prioritized CHO configuration is dependent on radio measurements. The UE may maintain both CHO configurations enabled concurrently for the duration of the radio measurements. The radio measurements may be signal strength measurements, and a CHO configuration associated with a stronger signal strength measured by the UE shall prevail over a CHO configuration associated with a weaker signal strength. The signal strength measurements taken into consideration may be neighbour cell signal measurements. The UE may evaluate, based on the radio measurements, which set of one or more cells provides the greater (collective) signal strength: the set of cells measured for the intra-CU CHO and the set of cells measured for the inter-CU CHO.

In an embodiment, the criterion comprises only a subset of the options of the Table. Some options may be replaced by other options, as provided above.

Upon selecting one of the handover configurations, the UE may notify the network nodes which handover configuration was selected. In the embodiment of Figure 8A, the UE selects the inter-CU handover configuration and, as a consequence, transmits to the CU 200 a message indicating the selection in 808. The message may comprise an information element indicating the concurrent intra-CU handover configuration with the DU 210. Upon receiving the notification, the CU 200 may inform the DU 210 that the intra-CU handover configuration has been overruled in 810 and, as a consequence, the DU 210 may release the intra-CU handover configuration 812 with the UE and the DU(s) 212. The message may be a RRCReconfigurationComplete message. Alternatively, the UE may directly inform the DU 210 that the intra-CU handover configuration shall be released, e.g., in a separate RRC message addressed to the L-CP. Accordingly, the DU will perform 812. In 814, the UE 120 executes the handover and performs random access in CU- CP with the CU 202.

In the embodiment of Figure 8B, the UE selects the intra-CU handover in 806. As a consequence, the UE may transmit in 820 to the CU 200 a message indicating that the intra-CU handover configuration has been selected and that the inter-CU handover configuration shall be released. The message may be a RRCReconfigurationComplete message. In response to receiving the message in 820, the CU may release the inter-CU handover configuration with the UE 120 and the CU 202. In 824, the UE executes the intra-CU handover with the DU 212 in L-CP.

An embodiment, as shown in Figure 9, provides an apparatus 10 comprising a control circuitry (CTRL) 12, such as at least one processor, and at least one memory 14 storing instructions that, when executed by the at least one processor, cause the apparatus at least to carry out any one of the above-described processes. In an example, the at least one memory and the computer program code (software), are configured, with the at least one processor, to cause the apparatus to carry outthe process of Figure 6 or any one of the above-described embodiments of the process. The memory may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory may comprise a database for storing data.

In an embodiment, the apparatus 10 may comprise the terminal device 120, 122 of a communication system, e.g. a user terminal (UT), a computer (PC), a laptop, a tabloid computer, a cellular phone, a mobile phone, a communicator, a smart phone, a palm computer, a mobile transportation apparatus (such as a car), a household appliance, or any other communication apparatus, commonly called as UE in the present description. Alternatively, the apparatus is comprised in such a terminal device. Further, the apparatus may be or comprise a module (to be attached to the UE) providing connectivity, such as a plug-in unit, an “USB dongle”, or any other kind of unit. The unit may be installed either inside the UE or attached to the UE with a connector or even wirelessly.

In an embodiment, the apparatus 10 is or is comprised in the UE 120. The apparatus may be caused to execute some of the functionalities of the above described process of Figure 6 or any one of the embodiments thereof.

The apparatus may further comprise a radio interface (TRX) 16 comprising hardware and/or software for realizing communication connectivity according to one or more communication protocols. The TRX may provide the apparatus with communication capabilities to access the radio access network, for example.

The apparatus may also comprise a user interface 18 comprising, for example, at least one keypad, a microphone, a touch display, a display, a speaker, etc. The user interface may be used to control the apparatus by the user.

The control circuitry 12 may comprise a handover configuration circuitry 20 for configuring the handover procedures in the UE. The handover configuration circuitry may receive the multiple handover configurations, one from the CU and one from the DU controlled by the CU. The control circuitry 12 may further comprise a handover (HO) configuration (CONF) selection circuitry 22 for selecting one of the provided multiple handover configurations. The circuitry 22 may perform the hard decision based on the above-described table in which case only one of the received configurations shall be active or have handover preparations performed at the UE 120. The circuitry may perform the soft decision in which both or all handover configurations may have the handover preparations performed at the UE 150 and respective handover execution conditions may be monitored for both or all prepared handover configurations. Whenever a handover execution condition is detected by the circuitry 22, the circuitry may trigger handover execution, e.g. by issuing a handover execution command to a handover execution circuitry 24. The circuitry 24 may be configured to perform random access to a selected cell, for example. The control circuitry 12 may comprise relevant circuitry/ies for performing the functions, according to any of the embodiments.

An embodiment, as shown in Figure 10, provides an apparatus 50 comprising a control circuitry (CTRL) 52, such as at least one processor, and at least one memory 54 storing instructions that, when executed by the at least one processor, cause the apparatus at least to carry out any one of the above-described processes for the DU or CU, e.g. the process of Figure 2 or 3 or any one of the embodiments thereof. In an example, the at least one memory and the computer program code (software), are configured, with the at least one processor, to cause the apparatus to carry out any one of the above-described processes. The memory may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory may comprise a database for storing data. It should be appreciated that the apparatus Figure 10 is rather generic and specific implementations for the DU and CU may differ, depending on the embodiment and design of the DU and CU, respectively. For example, for the embodiments of Figures 4A and 4B the design of the DU and CU may be rather similar in terms of the features of the described embodiments. In the embodiments of Figures 5A and 5B, the designs are different because the CU is the master of approving the handover initiations of the DUs 210, 212.

In an embodiment, the apparatus 50 may be or be comprised in a network node, such as in the DU 210 or CU 200. In an embodiment, the apparatus is or is comprised in the network node 110. The apparatus may be caused to execute some of the functionalities of the above described processes, such as the steps of Figures 2 and/or 3.

The apparatus may further comprise communication interface (TRX) 56 comprising hardware and/or software for realizing communication connectivity according to one or more communication protocols. The TRX may provide the apparatus with communication capabilities with at least one user equipment, for example. The apparatus may further comprise a network interface 58 configured to provide the apparatus with communication capabilities within the radio access network and/or with the core network. The network interface may support, for example, protocols of at least some of the following interfaces of 5G specifications or their equivalents in the 6G specifications: Fl Interface between DU and CU, Xn interface between two CUs, NG interface between DU/CU and the core network.

The control circuitry 52 may comprise a handover configuration circuitry 60 configured to process the measurement reports received from the UE(s) and to evaluate the need for the handover of the UE(s). As described above, instead of the measurement reports the handover configurations may be initiated based on another criterion or other criteria. Upon determining to initiate the handover procedure for the UE, the circuitry 60 may cause the transmission of the notification to the other network node(s), e.g. the DU or CU. Depending on the embodiment, the circuitry 60 may at the same time trigger a handover notification circuity 64 to transmit the notification and a handover preparation circuitry 62 to perform the handover preparations for the UE, e.g. configure the candidate target cell(s) for the handover. Embodiment of Figures 4A and 4B is such an embodiment. In the embodiment of Figures 5A and 5B, the handover configuration circuitry 62 may trigger only the handover notification circuitry 64 that is configured to wait for the acknowledgment from the CU before the circuitry 64 triggers the handover preparation circuitry 62.

In an embodiment, a CU-DU (central unit - distributed unit) architecture is implemented. In such case the apparatus 50 may be comprised in a central unit (e.g. a control unit, an edge cloud server, a server) operatively coupled (e.g. via a wireless or wired network) to a distributed unit (e.g. a remote radio head/node). That is, the central unit (e.g. an edge cloud server) and the radio node may be standalone apparatuses communicating with each other via a radio path or via a wired connection. Alternatively, they may be in a same entity communicating via a wired connection, etc. The edge cloud or edge cloud server may serve a plurality of radio nodes or a radio access networks. In an embodiment, at least some of the described processes may be performed by the central unit. In another embodiment, the apparatus may be instead comprised in the distributed unit, and at least some of the described processes may be performed by the distributed unit. In an embodiment, the execution of at least some of the functionalities of the apparatus 50 may be shared between two physically separate devices (DU and CU) forming one operational entity. Therefore, the apparatus may be seen to depict the operational entity comprising one or more physically separate devices for executing at least some of the described processes. In an embodiment, the apparatus controls the execution of the processes, regardless of the location of the apparatus and regardless of where the processes/functions are carried out.

In an embodiment, an apparatus carrying out at least some of the embodiments described comprises at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to carry out the functionalities according to any one of the embodiments described. According to an aspect, when the at least one processor executes the computer program code, the computer program code causes the apparatus to carry out the functionalities according to any one of the embodiments described. According to another embodiment, the apparatus carrying out at least some of the embodiments comprises the at least one processor and at least one memory including a computer program code, wherein the at least one processor and the computer program code perform at least some of the functionalities according to any one of the embodiments described. Accordingly, the at least one processor, the memory, and the computer program code form processing means for carrying out at least some of the embodiments described. According to yet another embodiment, the apparatus carrying out at least some of the embodiments comprises a circuitry including at least one processor and at least one memory including computer program code. When activated, the circuitry causes the apparatus to perform the at least some of the functionalities according to any one of the embodiments described.

As used in this application, the term ‘circuitry’ refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and soft- ware (and/or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a micropro- cessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of ‘circuitry’ applies to all uses of this term in this application. As a further example, as used in this application, the term ‘circuitry’ would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. The term ‘circuitry’ would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.

In an embodiment, at least some of the processes described may be carried out by an apparatus comprising corresponding means for carrying out at least some of the described processes. Some example means for carrying out the processes may include at least one of the following: detector, processor (including dual-core and multiple-core processors), digital signal processor, controller, receiver, transmitter, encoder, decoder, memory, RAM, ROM, software, firmware, display, user interface, display circuitry, user interface circuitry, user interface software, display software, circuit, antenna, antenna circuitry, and circuitry.

A term non-transitory, as used herein, is a limitation of the medium itself (i.e. tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. RAM vs. ROM). As used herein the term “means” is to be construed in singular form, i.e. referring to a single element, or in plural form, i.e. referring to a combination of single elements. Therefore, terminology “means for [performing A, B, C]”, is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C. Further, terminology “means for performing A, means for performing B, means for performing C” is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C.

According to a first aspect, there is provided an apparatus for a distributed unit, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, for user equipment, a measurement report; determine to initiate an intra-centralized-unit handover procedure based on the received measurement report, wherein said initiation comprises transmitting to a centralized unit controlling the distributed unit, a message for preventing concurrent intra- central- ized-unit handover procedure and inter-centralized-unit handover procedure for the user equipment; and based on transmitting the message, execute the intra-cen- tralized-unit handover procedure with the user equipment or cancelling the initiated intra-centralized-unit handover procedure.

In an embodiment, the apparatus is configured to execute the intra-cen- tralized-unit handover procedure without a response to the message from the centralized unit.

In an embodiment, the apparatus is configured to, upon transmitting the message, wait for an acknowledgment from the centralized unit and, upon determining that the acknowledgment indicates that the centralized unit approves the intra-centralized-unit handover procedure, execute the intra-centralized-unit handover procedure.

In an embodiment, the apparatus is configured to, upon transmitting the message, wait for an acknowledgment from the centralized unit and, upon determining that the acknowledgment indicates that the centralized unit rejects the in- tra-centralized-unit handover procedure, cancel the intra-centralized-unit handover procedure.

In an embodiment, the apparatus is further configured to receive from the centralized unit a second message for preventing the concurrent intra- centralized-unit handover procedure and inter-centralized-unit handover procedure, and to cancel the intra-centralized-unit handover procedure or another intra- centralized-unit handover procedure.

In an embodiment, the apparatus is further configured to associate the measurement report with a time stamp and to include the time stamp in the message.

According to the first aspect, there is provided an apparatus for a centralized unit, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from a distributed unit controlled by the centralized unit, a message indicating that the distributed unit intends to execute an intra-centralized- unit handover procedure with user equipment; receive, for the user equipment, a measurement report indicating inter-centralized-unit handover procedure; based on timings of the message and the measurement report, execute an inter-central- ized-unit handover procedure based on the received measurement report and transmit to the distributed unit a second message for preventing concurrent intra- centralized-unit handover procedure and inter-centralized-unit handover procedure for the user equipment, or determine not to execute the inter-centralized-unit handover procedure to allow execution of the intra-centralized-unit handover procedure indicated by the message.

In an embodiment, if the measurement report is received before the message, the apparatus is configured to execute the inter-centralized-unit handover procedure based on the received measurement report, wherein the second message is a response to the message received from the distributed unit, and wherein the second message indicates that the centralized unit rejects execution of the intra-centralized-unit handover procedure indicated by the message received from the distributed unit.

In an embodiment, if the measurement report is received before the message, the apparatus is configured to execute the inter-centralized-unit handover procedure based on the received measurement report, and wherein the second message is an indication to the distributed unit that the centralized unit is executing a handover procedure for the user equipment and prevents the distributed unit from initiating a concurrent intra-centralized-unit handover procedure.

In an embodiment, if the message is received before the measurement report and the apparatus is configured to determine not to execute the inter-cen- tralized-unit handover procedure based on the received measurement report. In an embodiment, the apparatus is configured to transmit, in response to the message, an acknowledgment indicating that the intra-centralized-unit handover procedure is approved.

In an embodiment, the message comprises a time stamp indicating a timing of a second measurement report that was received by the distributed unit and that caused the intra-centralized-unit handover procedure, and wherein the apparatus is configured to compare the time stamp with the timing of the measurement report indicating inter-centralized-unit handover procedure and determine whether or not to execute the inter-centralized-unit handover procedure based on the comparison.

In an embodiment, the intra-centralized-unit handover procedure and inter-centralized-unit handover procedure are both of the same type of handover procedures of the following: a conditional handover procedure, a Layer 3 handover procedure, or a Layer 1/2 triggered mobility.

According to the first aspect, there is provided a method, comprising: receiving, by a distributed unit for user equipment, a measurement report; determine, by the distributed unit, to initiate an intra-centralized-unit handover procedure based on the received measurement report, wherein said initiation comprises transmitting to a centralized unit controlling the distributed unit, a message for preventing concurrent intra-centralized-unit handover procedure and inter-cen- tralized-unit handover procedure for the user equipment; and based on transmitting the message, executing by the distributed unit the intra-centralized-unit handover procedure with the user equipment or cancelling the initiated intra-central- ized-unit handover procedure.

In an embodiment, the distributed unit executes the intra-centralized- unit handover procedure without a response to the message from the centralized unit.

In an embodiment, the distributed unit waits, upon transmitting the message, for an acknowledgment from the centralized unit and, upon determining that the acknowledgment indicates that the centralized unit approves the intra- centralized-unit handover procedure, executes the intra-centralized-unit handover procedure.

In an embodiment, the distributed unit waits, upon transmitting the message, for an acknowledgment from the centralized unit and, upon determining that the acknowledgment indicates that the centralized unit rejects the intra-cen- tralized-unit handover procedure, cancels the intra-centralized-unit handover procedure.

In an embodiment, the method further comprises receiving, by the distributed unit from the centralized unit, a second message for preventing the concurrent intra-centralized-unit handover procedure and inter-centralized-unit handover procedure, and cancelling the intra-centralized-unit handover procedure or another intra-centralized-unit handover procedure.

In an embodiment, the distributed unit associates the measurement report with a time stamp and includes the time stamp in the message.

According to the first aspect, there is provided a method comprising: receiving, by a centralized unit from a distributed unit controlled by the centralized unit, a message indicating that the distributed unit intends to execute an intra-cen- tralized-unit handover procedure with user equipment; receiving, by the centralized unit for the user equipment, a measurement report indicating inter-central- ized-unit handover procedure; based on timings of the message and the measurement report, executing by the centralized unit an inter-centralized-unit handover procedure based on the received measurement report and transmitting the distributed unit a second message for preventing concurrent intra-centralized-unit handover procedure and inter-centralized-unit handover procedure for the user equipment, or determining by the centralized unit not to execute the inter-centralized- unit handover procedure to allow execution of the intra-centralized-unit handover procedure indicated by the message.

In an embodiment, if the measurement report is received before the message, the centralized unit executes the inter-centralized-unit handover procedure based on the received measurement report, wherein the second message is a response to the message received from the distributed unit, and wherein the second message indicates that the centralized unit rejects execution of the intra-cen- tralized-unit handover procedure indicated by the message received from the distributed unit.

In an embodiment, if the measurement report is received before the message, the centralized unit executes the inter-centralized-unit handover procedure based on the received measurement report, and wherein the second message is an indication to the distributed unit that the centralized unit is executing a handover procedure for the user equipment and prevents the distributed unit from initiating a concurrent intra-centralized-unit handover procedure.

In an embodiment, if the message is received before the measurement report, and the centralized unit determines not to execute the inter-centralized- unit handover procedure based on the received measurement report.

In an embodiment, the centralized unit transmits, in response to the message, an acknowledgment indicating that the intra-centralized-unit handover procedure is approved.

In an embodiment, the message comprises a time stamp indicating a timing of a second measurement report that was received by the distributed unit and that caused the intra-centralized-unit handover procedure, and wherein the centralized unit compares the time stamp with the timing of the measurement report indicating inter-centralized-unit handover procedure and determines whether or not to execute the inter-centralized-unit handover procedure based on the comparison.

According to the first aspect, there is provided a computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the method according to any of the above-described embodiments of the first aspect.

According to a second aspect, there is provided an apparatus for user equipment, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receive an inter-centralized-unit handover configuration from the centralized unit; based on a determined criterion, execute a handover according to only one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration.

In an embodiment, the determined criterion is such that the inter- centralized-unit handover configuration prevails over the intra-centralized-unit handover configuration.

According to the second aspect, there is provided a method comprising: receiving, by user equipment, an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receiving, by the user equipment, an inter-centralized-unit handover configuration from the centralized unit; based on a determined criterion, executing by the user equipment a handover according to only one of the intra-centralized-unit handover configuration and in- ter-centralized-unit handover configuration.

According to the second aspect, there is provided a computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the method according to any of the above-described embodiments of the second aspect.

According to a third aspect, there is provided an apparatus for a user equipment, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receive an inter-centralized-unit handover configuration from the centralized unit; receive, from the centralized unit, a configuration for conditional modification of an execution condition of one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration; based on the configuration for conditional modification, changing at least one parameter of the execution condition of said one of the intra-centralized- unit handover configuration and inter-centralized-unit handover configuration; and after said changing, execute a handover of whichever of the intra-centralized- unit handover configuration and intra-centralized-unit handover has the respective execution condition becoming fulfilled.

In an embodiment, the modification of the execution condition is conditional to the presence of multiple concurrent handover configurations at the user equipment.

In an embodiment, the modification of the execution condition is enabled in the presence of multiple concurrent handover configurations at the user equipment and disabled in the presence of only one handover configuration at the user equipment.

In an embodiment, the conditional modification is subjected to a neighbour cell measurement offset.

In an embodiment, the conditional modification is subjected to a time- to-trigger handover execution parameter.

In an embodiment, the configuration for the conditional modification is received as a part of a measurement reporting configuration, and wherein the configuration disables transmission of a measurement report.

In an embodiment, the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration are both conditional handover configurations.

According to the second aspect, there is provided a method, comprising: receiving, by user equipment, an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receiving, by the user equipment, an inter-centralized-unit handover configuration from the centralized unit; receiving, by the user equipment from the centralized unit, a configuration for conditional modification of an execution condition of one of the intra-centralized- unit handover configuration and inter-centralized-unit handover configuration; based on the configuration for conditional modification, changing by the user equipment at least one parameter of the execution condition of said one of the in- tra-centralized-unit handover configuration and inter-centralized-unit handover configuration; and after said changing, executing by the user equipment a handover of whichever of the intra-centralized-unit handover configuration and intra-cen- tralized-unit handover has the respective execution condition becoming fulfilled.

According to the aspect, there is provided a computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the method according to any of the above-described embodiments of the second aspect.

The techniques and methods described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatuses) of embodiments may be implemented within one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chip set (e.g. procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case, it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and/or complemented by additional components in order to facilitate the achievements of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.

Embodiments as described may also be carried out in the form of a computer process defined by a computer program or portions thereof. Embodiments of the methods described may be carried out by executing at least one portion of a computer program comprising corresponding instructions. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. For example, the computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. The computer program medium may be a non-transitory medium. Coding of software for carrying out the embodiments as shown and described is well within the scope of a person of ordinary skill in the art. Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.

Claims

1. An apparatus for user equipment, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receive an inter-centralized-unit handover configuration from the centralized unit; based on a determined criterion, execute a handover according to only one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration.

2. The apparatus of claim 1, configured to receive the determined criterion in a radio resource control configuration message.

3. The apparatus of claim 1 or 2, wherein the determined criterion is such that the handover configuration received earlier than the other shall be executed.

4. The apparatus of any preceding claim, wherein the determined criterion is such that a handover configuration for an unconditional handover prevails over a handover configuration for a conditional handover.

5. The apparatus of any preceding claim, wherein the determined criterion is such that the inter-centralized-unit handover configuration prevails over the intra-centralized-unit handover configuration.

6. The apparatus of any preceding claim 1 to 4, wherein the determined criterion is such that the intra-centralized-unit handover configuration prevails over the inter-centralized-unit handover configuration.

7. The apparatus of any preceding claim, wherein a handover configuration associated with a stronger signal strength measured by the user equipment shall prevail over a handover configuration associated with a weaker signal strength.

8. The apparatus of any preceding claim, configured to send a configuration complete message for the other one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration, wherein the configuration complete message comprises a notification that said one of the intra- centralized-unit handover configuration and inter-centralized-unit handover configuration has been discarded.

9. A method comprising: receiving, by user equipment, an intra-centralized-unit handover configuration from a distributed unit controlled by a centralized unit; receiving, by the user equipment, an inter-centralized-unit handover configuration from the centralized unit; based on a determined criterion, executing by the user equipment a handover according to only one of the intra-centralized-unit handover configuration and inter-centralized-unit handover configuration.

10. The method of claim 9, wherein the user equipment receives the determined criterion in a radio resource control configuration message.

11. The method of claim 9 or 10, wherein the determined criterion is such that the handover configuration received earlier than the other shall be executed.

12. The method of any preceding claim 9 to 11, wherein the determined criterion is such that a handover configuration for an unconditional handover prevails over a handover configuration for a conditional handover.

13. The apparatus of any preceding claim 9 to 12, wherein the determined criterion is such that the inter-centralized-unit handover configuration prevails over the intra-centralized-unit handover configuration.

14. The method of any preceding claim 9 to 12, wherein the determined criterion is such that the intra-centralized-unit handover configuration prevails over the inter-centralized-unit handover configuration.

15. The method of any preceding claim 9 to 14, wherein a handover configuration associated with a stronger signal strength measured by the user equipment shall prevail over a handover configuration associated with a weaker signal strength.

16. The method of any preceding claim 9 to 15, wherein the user equipment sends a configuration complete message for the other one of the intra-cen- tralized-unit handover configuration and inter-centralized-unit handover configu- ration, wherein the configuration complete message comprises a notification that said one of the intra-centralized-unit handover configuration and inter-central- ized-unit handover configuration has been discarded.

17. A computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the method according to any of claims 9 to 16.