WO2024231042A1

WO2024231042A1 - Indicating timing issue associated with uplink synchronization

Info

Publication number: WO2024231042A1
Application number: PCT/EP2024/060159
Authority: WO
Inventors: Martin Kollár; Bernhard Wegmann
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2023-05-10
Filing date: 2024-04-15
Publication date: 2024-11-14
Anticipated expiration: 2025-11-10
Also published as: CN121100550A

Abstract

Disclosed is a method comprising receiving, from a user equipment, a successful handover report indicative of a successful inter-radio-access-technology handover of the user equipment from a source node to a target node, wherein the successful handover report indicates that, during the successful inter-radio-access- technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determining, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmitting, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

Description

INDICATING TIMING ISSUE ASSOCIATED WITH UPLINK SYNCHRONIZATION

FIELD

The following example embodiments relate to wireless communication.

BACKGROUND

Mobility robustness optimization for handovers may involve analyzing radio link failures and other handover performance information, and creating failure statistics to improve handover success rates. There is a challenge in how to collect the information needed for the mobility robustness optimization.

BRIEF DESCRIPTION

The scope of protection sought for various example embodiments is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments.

According to an aspect, there is provided an apparatus 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 user equipment, a successful handover report indicative of a successful inter- radio-access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter-radio-access- technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determine, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmit, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

According to another aspect, there is provided an apparatus comprising: means for receiving, from a user equipment, a successful handover report indicative of a successful inter-radio-access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter-radio-access-technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; means for determining, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and means for transmitting, to the source node or to a network entity different from the source node, based on determining that the exceeding of the time threshold was not caused by the issue at the target node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

According to another aspect, there is provided a method comprising: receiving, by an apparatus, from a user equipment, a successful handover report indicative of a successful inter-radio-access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter-radio-access-technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determining, by the apparatus, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmitting, by the apparatus, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio- access-technology handover.

According to another aspect, there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, from a user equipment, a successful handover report indicative of a successful inter-radio-access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter-radio-access-technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determining, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmitting, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

According to another aspect, there is provided a computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, from a user equipment, a successful handover report indicative of a successful inter-radio- access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter-radio-access- technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determining, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmitting, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, from a user equipment, a successful handover report indicative of a successful inter-radio-access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter- radio-access-technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determining, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmitting, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

According to another aspect, there is provided an apparatus 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 information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; increment a counter based on the information; and transmit, to a network entity, counter information indicating a value of the counter.

According to another aspect, there is provided an apparatus comprising: means for receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; means for incrementing a counter based on the information; and means for transmitting, to a network entity, counter information indicating a value of the counter.

According to another aspect, there is provided a method comprising: receiving, by an apparatus, information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; incrementing, by the apparatus, a counter based on the information; and transmitting, by the apparatus, to a network entity, counter information indicating a value of the counter.

According to another aspect, there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; incrementing a counter based on the information; and transmitting, to a network entity, counter information indicating a value of the counter.

According to another aspect, there is provided a computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; incrementing a counter based on the information; and transmitting, to a network entity, counter information indicating a value of the counter. According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; incrementing a counter based on the information; and transmitting, to a network entity, counter information indicating a value of the counter.

According to another aspect, there is provided an apparatus 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 information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and optimize, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

According to another aspect, there is provided an apparatus comprising: means for receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and means for optimizing, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

According to another aspect, there is provided a method comprising: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and optimizing, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

According to another aspect, there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and optimizing, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

According to another aspect, there is provided a computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and optimizing, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and optimizing, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

LIST OF DRAWINGS

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

FIG. 1A illustrates an example of a wireless communication network;

FIG. IB illustrates an example of a system;

FIG. 2 illustrates a signal flow diagram;

FIG. 3 illustrates a signal flow diagram;

FIG. 4 illustrates a flow chart;

FIG. 5 illustrates a flow chart;

FIG. 6 illustrates a flow chart;

FIG. 7 illustrates a flow chart;

FIG. 8 illustrates an example of an apparatus; and

FIG. 9 illustrates an example of an apparatus.

DETAILED DESCRIPTION

The following embodiments are exemplifying. 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.

Some example embodiments described herein may be implemented in a wireless communication network comprising a radio access network based on one or more of the following radio access technologies: Global System for Mobile Communications (GSM) or any other second generation radio access technology, 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, fourth generation (4G), fifth generation (5G), 5G new radio (NR), 5G-Advanced (i.e., 3GPP NR Rel-18 and beyond), or sixth generation (6G). Some examples of radio access networks include the universal mobile telecommunications system (UMTS) radio access network (UTRAN), the Evolved Universal Terrestrial Radio Access network (E-UTRA), or the next generation radio access network (NG-RAN). The wireless communication network may further comprise a core network, and some example embodiments may also be applied to network functions of the core network.

It should be noted that the embodiments are not restricted to the wireless communication network given as an example, but a person skilled in the art may also apply the solution to other wireless communication networks or systems provided with necessary properties. For example, some example embodiments may also be applied to a communication system based on IEEE 802.11 specifications, or a communication system based on IEEE 802.15 specifications.

FIG. 1A depicts an example of a simplified wireless communication network showing some physical and logical entities. The connections shown in FIG. 1A may be physical connections or logical connections. It is apparent to a person skilled in the art that the wireless communication network may also comprise other physical and logical entities than those shown in FIG. 1A.

The example embodiments described herein are not, however, restricted to the wireless communication network given as an example but a person skilled in the art may apply the embodiments described herein to other wireless communication networks provided with necessary properties.

The example wireless communication network shown in FIG. 1A includes an access network, such as a radio access network (RAN), and a core network 110.

FIG. 1A shows user equipment (UE) 100, 102 configured to be in a wireless connection on one or more communication channels in a radio cell with an access node (AN) 104 of an access network. The AN 104 may be an evolved NodeB (abbreviated as eNB or eNodeB), or a next generation evolved NodeB (abbreviated as ng-eNB), or a next generation NodeB (abbreviated as gNB or gNodeB), providing the radio cell. The wireless connection (e.g., radio link) from a UE to the access node 104 may be called uplink (UL) or reverse link, and the wireless connection (e.g., radio link) from the access node to the UE may be called downlink (DL) or forward link. UE 100 may also communicate directly with UE 102, and vice versa, via a wireless connection generally referred to as a sidelink (SL). It should be appreciated that the access node 104 or its functionalities may be implemented by using any node, host, server or access point etc. entity suitable for providing such functionalities.

The access network may comprise more than one access node, in which case the access nodes may also be configured to communicate with one another over links, wired or wireless. These links between access nodes may be used for sending and receiving control plane signaling and also for routing data from one access node to another access node.

The access node may comprise a computing device configured to control the radio resources of the access node. The access node may also be referred to as a base station, a base transceiver station (BTS), an access point, a cell site, a radio access node or any other type of node capable of being in a wireless connection with a UE (e.g., UEs 100, 102). The access node may include or be coupled to transceivers. From the transceivers of the access node, a connection may be provided to an antenna unit that establishes bi-directional radio links to UEs 100, 102. The antenna unit may comprise an antenna or antenna element, or a plurality of antennas or antenna elements.

The access node 104 may further be connected to a core network (CN) 110. The core network 110 may comprise an evolved packet core (EPC) network and/or a 5^th generation core network (5GC). The EPC may comprise network entities, such as a serving gateway (S-GW for routing and forwarding data packets), a packet data network gateway (P-GW) for providing connectivity of UEs to external packet data networks, and a mobility management entity (MME). The 5GC may comprise network functions, such as a user plane function (UPF), an access and mobility management function (AMF), and a location management function (LMF). The core network 110 may also be able to communicate with one or more external networks 113, such as a public switched telephone network or the Internet, or utilize services provided by them. For example, in 5G wireless communication networks, the UPF of the core network 110 may be configured to communicate with an external data network via an N6 interface. In LTE wireless communication networks, the P-GW of the core network 110 may be configured to communicate with an external data network.

The illustrated UE 100, 102 is one type of an apparatus to which resources on the air interface may be allocated and assigned. The UE 100, 102 may also be called a wireless communication device, a subscriber unit, a mobile station, a remote terminal, an access terminal, a user terminal, a terminal device, or a user device just to mention but a few names. The UE may be a computing device operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of computing devices: a mobile phone, a smartphone, a personal digital assistant (PDA), a handset, a computing device comprising a wireless modem (e.g., an alarm or measurement device, etc.), a laptop computer, a desktop computer, a tablet, a game console, a notebook, a multimedia device, a reduced capability (RedCap) device, a wearable device (e.g., a watch, earphones or eyeglasses) with radio parts, a sensor comprising a wireless modem, or any computing device comprising a wireless modem integrated in a vehicle.

It should be appreciated that a UE may also be a nearly exclusive uplink- only device, of which an example may be a camera or video camera loading images or video clips to a network. A UE may also be a device having capability to operate in an Internet of Things (loT) network, which is a scenario in which objects may be provided with the ability to transfer data over a network without requiring human- to-human or human-to-computer interaction. The UE may also utilize cloud. In some applications, the computation may be carried out in the cloud or in another UE.

The wireless communication network may also be able to support the usage of cloud services, for example at least part of core network operations may be carried out as a cloud service (this is depicted in FIG. 1A by “cloud” 114). The wireless communication network may also comprise a central control entity, or the like, providing facilities for wireless communication networks of different operators to cooperate for example in spectrum sharing.

5G enables using multiple input - multiple output (M1M0) antennas in the access node 104 and/or the UE 100, 102, many more base stations or access nodes than an LTE network (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. 5G wireless communication networks may support a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications, such as (massive) machine-type communications (mMTC), including vehicular safety, different sensors and real-time control.

In 5G wireless communication networks, access nodes and/or UEs may have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integrable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, for example, as a system, where macro coverage may be provided by the LTE, and 5G radio interface access may come from small cells by aggregation to the LTE. In other words, a 5G wireless communication network may support both inter-RAT operability (such as LTE-5G) and inter-Rl operability (inter-radio interface operability, such as below 6GHz - cmWave - mmWave). One of the concepts considered to be used in 5G wireless communication networks may be network slicing, in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the substantially same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

In some example embodiments, an access node (e.g., access node 104) may comprise: a radio unit (RU) comprising a radio transceiver (TRX), i.e., a transmitter (Tx) and a receiver (Rx); one or more distributed units (DUs) 105 that may be used for the so-called Layer 1 (LI) processing and real-time Layer 2 (L2) processing; and a central unit (CU) 108 (also known as a centralized unit) that may be used for non-real-time L2 and Layer 3 (L3) processing. The CU 108 may be connected to the one or more DUs 105 for example via an Fl interface. Such an embodiment of the access node may enable the centralization of CUs relative to the cell sites and DUs, whereas DUs may be more distributed and may even remain at cell sites. The CU and DU together may also be referred to as baseband or a baseband unit (BBU). The CU and DU may also be comprised in a radio access point (RAP).

The CU 108 may be a logical node hosting radio resource control (RRC), service data adaptation protocol (SDAP) and/or packet data convergence protocol (PDCP), of the NR protocol stack for an access node. The DU 105 may be a logical node hosting radio link control (RLC), medium access control (MAC) and/or physical (PHY) layers of the NR protocol stack for the access node. The operations of the DU may be at least partly controlled by the CU. It should also be understood that the distribution of functions between DU 105 and CU 108 may vary depending on implementation. The CU may comprise a control plane (CU-CP), which may be a logical node hosting the RRC and the control plane part of the PDCP protocol of the NR protocol stack for the access node. The CU may further comprise a user plane (CU-UP), which may be a logical node hosting the user plane part of the PDCP protocol and the SDAP protocol of the CU for the access node.

Cloud computing systems may also be used to provide the CU 108 and/or DU 105. A CU provided by a cloud computing system may be referred to as a virtualized CU (vCU). In addition to the vCU, there may also be a virtualized DU (vDU) provided by a cloud computing system. Furthermore, there may also be a combination, where the DU may be implemented on so-called bare metal solutions, for example application-specific integrated circuit (ASIC) or customer-specific standard product (CSSP) system-on-a-chip (SoC).

Edge cloud may be brought into the access network (e.g., RAN) by utilizing network function virtualization (NFV) and software defined networking (SDN). Using edge cloud may mean access node operations to be carried out, at least partly, in a computing system operationally coupled to a remote radio head (RRH) or a radio unit (RU) of an access node. It is also possible that access node operations may be performed on a distributed computing system or a cloud computing system located at the access node. Application of cloud RAN architecture enables RAN real-time functions being carried out at the access network (e.g., in a DU 105) and non-real-time functions being carried out in a centralized manner (e.g., in a CU 108).

It should also be understood that the distribution of functions between core network operations and access node operations may differ in future wireless communication networks compared to that of the LTE or 5G, or even be nonexistent. Some other technology advancements that may be used include big data and all-lP, which may change the way wireless communication networks are being constructed and managed. 5G (or new radio, NR) wireless communication networks may support multiple hierarchies, where multi-access edge computing (MEC) servers may be placed between the core network 110 and the access node 104. It should be appreciated that MEC may be applied in LTE wireless communication networks as well.

A 5G wireless communication network (“5G network”) may also comprise a non-terrestrial communication network, such as a satellite communication network, to enhance or complement the coverage of the 5G radio access network. For example, satellite communication may support the transfer of data between the 5G radio access network and the core network, enabling more extensive network coverage. Possible use cases may be 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 railway/maritime/aeronautical communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular megaconstellations (systems in which hundreds of (nano) satellites are deployed). A given satellite 106 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 access node or by an access node 104 located on- ground or in a satellite. It is obvious for a person skilled in the art that the access node 104 depicted in FIG. 1A is just an example of a part of an access network (e.g., a radio access network) and in practice, the access network may comprise a plurality of access nodes, the UEs 100, 102 may have access to a plurality of radio cells, and the access network may also comprise other apparatuses, such as physical layer relay access nodes or other entities. At least one of the access nodes may be a Home eNodeB or a Home gNodeB. A Home gNodeB or a Home eNodeB is a type of access node that may be used to provide indoor coverage inside a home, office, or other indoor environment.

Additionally, in a geographical area of an access network (e.g., a radio access network), a plurality of different kinds of radio cells as well as a plurality of radio cells may be provided. Radio cells may be macro cells (or umbrella cells) which may be large cells having a diameter of up to tens of kilometers, or smaller cells such as micro-, femto- or picocells. The access node(s) of FIG. 1A may provide any kind of these cells. A cellular radio network may be implemented as a multilayer access networks including several kinds of radio cells. In multilayer access networks, one access node may provide one kind of a radio cell or radio cells, and thus a plurality of access nodes may be needed to provide such a multilayer access network.

For fulfilling the need for improving performance of access networks, the concept of “plug-and-play” access nodes may be introduced. An access network which may be able to use “plug-and-play” access nodes, may include, in addition to Home eNodeBs or Home gNodeBs, a Home Node B gateway, or HNB-GW (not shown in FIG. 1A). An HNB-GW, which may be installed within an operator’s access network, may aggregate traffic from a large number of Home eNodeBs or Home gNodeBs back to a core network of the operator.

A handover, also referred to as a handoff or a cell change, is a process in wireless communication networks, wherein an active connection between a UE 100, 102 and its serving base station 104 is transferred from one cell to another. The handover process enables maintaining a seamless and continuous communication experience for users as they move through different coverage areas within the network.

FIG. IB illustrates an example of a system, to which some example embodiments may be applied. FIG. IB may be understood to depict a part of the wireless communication network of FIG. 1A, but with greater accuracy with respect to a mobility scenario. The system comprises a network manager 111, a UE 100 and a plurality of network nodes 104, 104B (e.g., gNBs or eNBs or ng-eNBs) providing a plurality of cells 121, 122.

Referring to FIG. IB, during a handover, the connection of the UE 100 is switched from the current serving cell 121 provided by a source node 104 to a target cell 122 provided by a target node 104B, while preserving the ongoing voice call or data session.

The handover process may be initiated by the network (e.g., the source node 104), when certain pre-defined conditions are met, such as when the signal quality of the current serving cell 121 falls below a specified threshold, or when the signal quality of a neighboring cell 122 becomes significantly better than that of the current serving cell 121. The decision to perform a handover may be based on various factors, including radio measurements such as reference signal received power (RSRP) and reference signal received quality (RSRQ), network load, user mobility, and network configuration parameters.

Upon initiation of the handover process, the network (e.g., the source node 104) may transmit a handover command to the UE 100, wherein this handover command may include information about the target cell 122 and any needed configuration parameters. The UE 100 may then establish a connection with the target node 104B providing the target cell 122, synchronize its timing and frequency, and exchange control information to confirm the successful completion of the handover. Once the handover is complete, the UE 100 releases its connection with the previous serving cell 121, and the communication continues through the new serving cell 122.

The handover may be an intra-radio-access-technology (intra-RAT) handover or an inter-radio-access-technology (inter-RAT) handover. An intra-RAT handover means that the source cell 121 and the target cell 122 are based on the same radio access technology. For example, in an intra- NR handover, both the source node 104 and the target node 104B may be gNBs.

An inter-RAT handover means that the source cell 121 and the target cell 122 are based on different radio access technologies. For example, in an inter- RAT handover, the source node 104 may be an eNB or ng-eNB (4G base station), and the target node 104B may be a gNB (5G base station), or vice versa.

The network manager (NM) 111 provides a package of end-user functions with the responsibility for the management of a network. The network manager 111 may be a separate network entity connected to the source node 104 and/or to the target node 104B.

For example, the network manager 111 may comprise a self-organizing network (SON) functionality hosted in the network management system (NMS) or operations, administration and maintenance (0AM) system, where mobility robustness optimization (MRO) counters maybe analyzed and post-processed. The MRO counters may be received by the performance management (PM) part of the NMS from the source node 104 and/or the target node 104B via Itf-N (so-called north-bound interface). The PM part of the NMS may forward these MRO counters to the SON functionality in the NMS. The SON functionality may then send the corrections to the configuration management (CM) part of the NMS, which may reconfigure the corresponding handover parameters in the RAN (i.e., the source node 104).

MRO is a SON function that may be used in wireless communication networks to improve the performance of handovers and overall network mobility. MRO aims to minimize handover-related issues, such as premature handovers, late handovers, and handover failures, by automatically adjusting and optimizing the network's handover parameters based on observed network performance and user mobility patterns.

MRO works by continuously monitoring and collecting relevant performance metrics from the network (e.g., from the source node 104 and the target node 104B), including handover success rates, radio link failure (RLF) reports, and other key performance indicators (KPIs). These metrics may then be analyzed to identify any handover-related issues and determine the potential causes of such problems, such as incorrect handover parameter settings or suboptimal cell coverage.

Once the potential causes of handover issues have been identified, the MRO function may adjust the relevant handover parameters, such as handover triggering thresholds, time-to-trigger (TTT) values, and hysteresis margins, in a given cell pair (e.g., the source cell 121 and the target cell 122) to optimize the handover performance. The MRO function may iteratively update these parameters, constantly learning from the network's performance to maintain optimal handover settings.

With 3GPP NR Rel-17 for the intra-NR mobility, the MRO concept based on RLFs has been extended towards the logging of risky or failed but recovered mobility cases, which finally resulted in a successful handover by providing a successful handover report (SHR).

The successful handover report is a message or a set of data generated by the UE after the completion of a successful handover process. This report provides information to the network about the performance of the handover. The successful handover report helps the network analyze the performance of handovers, identify potential issues or areas for improvement, and optimize the network performance, coverage, and reliability.

For example, the successful handover report may comprise at least one of: identities of the source cell 121 and the target cell 122 of the handover, location information of the UE 100, latest radio link measurements of the measurement identities available at the time when the handover is executed, a cause indicating the trigger for generating the SHR (e.g., t310-cause, t312-cause, or t304-cause), latest radio measurement results of the candidate target cells in case of a conditional handover, time elapsed between conditional handover execution towards the target cell 122 and corresponding latest configuration received for the selected target cell 122, cell radio network temporary identifier (C-RNTI) of the UE 100 in the target cell 122, user plane interruption time at handover which concerns dual active protocol stack (DAPS) handovers, RA-lnformationCommon when T304 is above a threshold, and/or a flag indicating that an RLF is detected in the source cell during DAPS handover.

For 3GPP NR Rel-18, the SHR concept may be extended to inter-RAT mobility (e.g., handovers between LTE and 5G NR). For an inter-RAT handover from an NR cell to an LTE cell, a successful handover report may be triggered, for example, by a T310 or T312 criterion (e.g., by the T310 or T312 SHR percentage threshold being exceeded). For an inter-RAT handover from an LTE cell to an NR cell, a successful handover report may be triggered, for example, by a T304 criterion (e.g., by a T304 SHR percentage threshold being exceeded).

The T304 timer may start at reception of RRC Connection Reconfiguration message including the Mobility Control Information message. The T304 timer may stop as per criterion for successful completion of the handover within 5G radio access (5GRA), or handover to 5GRA. At the expiry of the T304 timer, in case of intra 5GRA handover, the UE may initiate an RRC connection reestablishment procedure.

The T304 SHR percentage threshold (thresholdPercentageT304) is a time threshold that may comprise a certain portion or ratio or percentage of the configured T304 value. For example, if the T304 value is configured as 10 seconds, then the T304 SHR percentage threshold may be set to 50 % of the T304 value, i.e., 5 seconds. The T304 SHR percentage threshold may also be referred to as a T304 SHR portion threshold or T304 SHR ratio threshold herein.

The T304 SHR percentage threshold may be used for sensing the uplink synchronization or random access procedure performance towards the target NR cell. Exceeding the T304 SHR percentage threshold, which triggers the SHR, indicates that the uplink synchronization or random access procedure was not performing as fast as expected. However, the issue for the longer-lasting synchronization process to the target NR node may be caused by either random access problems at the target NR node 104B, or by suboptimal handover parameters being configured at the LTE source node 104.

The random access procedure allows the UE 100 to establish an initial connection with the target node 104B. The random access procedure may also be referred to as initial access or a random access channel (RACH) procedure.

According to the MRO philosophy, the source node 104, which triggers the handover, should be responsible for the failure or problem analysis. In this case, it may be desirable to forward the SHR to the source LTE node 104 of the last serving LTE source cell 121.

However, it may also be desirable to keep the impact to the LTE standard as small as possible. Therefore, the root cause analysis of the SHR triggered by the T304 SHR percentage threshold being exceeded may be performed at the target NR node 104B, to which the SHR may be reported.

An unprocessed forwarding of the SHR to the source LTE node 104 would shift the complete root cause analysis process, including the check of NR- based random access problems to the source LTE node 104, which may be undesirable. Furthermore, even in case of an intra-system inter-RAT handover, the SHR (encoded in NR format) may be forwarded to the source ng-eNB 104 as a container, which the source ng-eNB 104 is not able to read.

Thus, there is a need for a method that enables using the SHR to support MRO, while keeping the impact to the LTE standard as small as possible.

Some example embodiments may provide such a method, which has no or low impact on the LTE standard. The method may be applied for intra-system inter-RAT handover, or for inter-system inter-RAT handover.

Intra-system means that both the source node 104 and the target node 104B are connected to the core network 110 of the same radio access technology (e.g., 5G core). This allows to execute the handover via communication done on Xn interface that interconnects the gNB (e.g., target node) and ng-eNB (e.g., source node). The ng-eNB is an enhanced eNB that is able to communicate with the 5G core, but still provides E-UTRA user plane and control plane terminations to UE.

Inter-system means that the gNB (e.g., target node) is connected to 5G core, and eNB (e.g., source node) is connected to 4G core. In this case, the gNB and eNB may not be interconnected via any interface. The gNB may be directly connected to 5G core via Ng, and the eNB may be directly connected to 4G core via SI interface. The inter-RAT handover may then be either Sl-based (if it is from LTE to NR), or NG-based (if it is from NR to LTE).

Some example embodiments may relate to mobility robustness optimization with an SHR (e.g., triggered by the T304 SHR percentage threshold being exceeded), wherein the SHR may be reported to the target NR node 104B for an inter-RAT handover from the source LTE node 104 to the target NR node 104B.

Some example embodiments may enable to utilize the SHR triggered (e.g., by the T304 SHR percentage threshold being exceeded) for an inter-RAT handover from LTE to NR as part of the MRO use case that requests an optimization of radio measurement thresholds triggering the handover in the source LTE node 104 towards the target NR node 104B. The basic root cause analysis (RCA) may be performed at the target NR node 104B of the considered inter-RAT handover, where random access issues are to be first excluded. The analysis may be based on the random access report included in the SHR. The SON or MRO functionality responsible for the RCA at the target NR node 104B may decide whether the longer- lasting synchronization process (e.g., indicated by exceeding the T304 SHR percentage threshold) was caused by random access problems (e.g., RACH misconfiguration) at the target NR node 104B, or by suboptimal inter-RAT handover parameter setting at the source LTE node 104, which resulted in the handover being triggered a bit too early, when the target NR cell 122 was not yet stable enough for the UE 100.

If the cause was random access problems (e.g., RACH misconfiguration) at the target NR node 104B, then MRO may be excluded, and the source LTE node 104 does not need to be informed. However, if the cause was suboptimal inter-RAT handover parameter setting at the source LTE node 104, then the inter-RAT handover parameters at the source LTE node 104 may need to be adjusted.

It should be noted that some example embodiments are not limited to LTE and NR, or particularly for a handover from LTE to NR, and they may be applied to inter-RAT handover between any two different radio access technologies.

FIG. 2 illustrates a signal flow diagram according to an example embodiment. In this example embodiment, after the root cause analysis when MRO is decided for a successful handover report (i.e., the cause of the random access issue is determined to be suboptimal handover parameters at the source LTE node 104), the corresponding inter-RAT MRO functionality at the target NR node 104B counts the handovers impacted by the T304 SHR percentage threshold being exceeded over a given measurement period per a given source LTE and target NR cell pair 121, 122. The target NR node 104B may consequently share this information, for example, in the form of a performance measurement in a performance management (PM) file via the Itf-N interface from the target NR node 104B to the PM instance of a common network management system 111 (spanning both LTE and NR), which may forward the counter data consequently to the central MRO entity for the optimization of the radio measurement thresholds that are used for triggering the handover from the given source LTE cell 121 to the given target NR cell 122.

Referring to FIG. 2, at 201, a source node 104 (e.g., ng-eNB or eNB), transmits, to a UE 100, a handover command comprising a configuration for a successful handover report. For example, the configuration may indicate the UE 100 store the successful handover report, if a T304 SHR percentage threshold is exceeded. The UE 100 receives the configuration from the source node 104. The source node 104 may be the serving node of the UE 100 during this configuration. The source node 104 may also be referred to as a first network node herein.

At 202, the UE 100 completes a successful inter-RAT handover of the UE 100 from the source node 104 to a target node 104B (e.g., gNB). However, the T304 SHR percentage threshold was exceeded during the successful inter-RAT handover. The target node 104B may also be referred to as a second network node herein.

The target node 104B is associated with a different radio access technology than a radio access technology associated with the source node 104. For example, the source node 104 may be associated with a fourth generation cellular radio access technology (e.g., Long Term Evolution (LTE) or LTE- Advanced), and the target node 104B may be associated with a fifth generation cellular radio access technology (e.g., 5G New Radio). At 203, the UE 100 stores a successful handover report indicative of the successful inter-RAT handover of the UE 100 from the source node 104 to the target node 104B. For example, the SHR may be generated due to a T304 SHR percentage threshold being exceeded. The T304 SHR percentage threshold (thresholdPercentageT304) is a time threshold that may comprise a certain portion or ratio or percentage of the configured T304 value. For example, if the T304 value is configured as 10 seconds, then the T304 SHR percentage threshold may be set to 50 % of the T304 value, i.e., 5 seconds. The T304 SHR percentage threshold may also be referred to as a T304 SHR portion threshold or T304 SHR ratio threshold herein.

In other words, the inter-RAT handover from the source node to the target node was successful, but due to the T304 SHR percentage threshold being exceeded during the inter-RAT handover, the UE stored the SHR.

For example, the successful handover report may be stored in an internal memory of the UE 100.

At 204, the UE 100 may transmit, to the target node 104B, an indication indicating an availability of the successful handover report. For example, the indication may comprise a “successHO-lnfoAvailable” flag transmitted in an RRCReconfigurationComplete message.

At 205, based on receiving the indication, the target node 104B may transmit, to the UE 100, a request for providing the successful handover report. For example, the request may be transmitted in an UElnformationRequest message.

At 206, the UE 100 transmits the successful handover report to the target node 104B. The UE 100 may transmit the successful handover report based on receiving the request from the target node 104B. For example, the successful handover report may be transmitted in an UElnformationResponse message. The target node 104B receives the successful handover report from the UE 100.

In other words, the target node 104B may fetch the successful handover report message from the UE 100 via the UElnformationRequest and UElnformationResponse procedure.

The successful handover report may comprise information indicating an identity of the source cell 121 provided by the source node 104 from the LTE cell, and an identity of the target cell 122 (i.e., the current NR cell) provided by the target node 104B. The successful handover report may further identify this handover as an inter-RAT handover (e.g., from LTE to NR).

The successful handover report further indicates that, during the successful inter-radio-access-technology handover, a time threshold (e.g., the thresholdPercentageT304) associated with monitoring of an uplink synchronization procedure between the UE 100 and the target node 104B was exceeded, thus leading to a timing issue associated with the uplink synchronization procedure. The uplink synchronization procedure may be part of a random access procedure between the UE 100 and the target node 104B. In other words, the random access procedure between the UE 100 and the target node 104B took longer than expected.

The successful handover report may be encoded in a format associated with the fifth generation cellular radio access technology (e.g., 5G NR).

At 207, the target node 104B determines, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue (e.g., a random access problem such as RACH misconfiguration) at the target node 104B.

In other words, based on the knowledge that the SHR was triggered due to T304, as indicated in the SHR, the target node 104B starts the root cause analysis based on the random access report included in the SHR. The cause may be, for example, weak radio link conditions (i.e., the handover was initiated a bit too early at the source node 104), or a RACH misconfiguration at the target node 104B.

At 208, based on determining that the exceeding of the time threshold was not caused by the issue at the target node 104B (i.e., based on determining that the timing issue was caused by the source node 104 due to a too early decision of the successful inter-radio-access-technology handover), the target node 104B increments a counter that indicates a number of successful inter-radio-access- technology handovers from the source node to the target node, the number of successful inter-radio access-technology handovers being associated with the at least one timing issue.

Alternatively, if the target node 104B determines that the exceeding of the time threshold was caused by the issue (e.g., RACH misconfiguration) at the target node, then the target node 104B may consider it as an event relevant for random access optimization in the target cell 122 of the target node 104B.

At 209, the target node 104B transmits information to a network entity such as a network manager 111 (or PM part or SON entity of NMS), wherein the information comprises counter information indicating the number of successful inter-radio-access-technology handovers from the source node to the target node within a pre-defined time period, the number of successful inter-radio-access- technology handovers being associated with the timing issue. The SON entity of the network management system 111 receives the counter information. The SON entity of the network management system 111 may comprise a mobility robustness optimization function.

Thus, the counter information may indicate at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment 100 from the source node 104 to the target node 104B.

For example, the target node 104B may transmit the counter information at the end of the pre-defined time period. In other words, a new PM counter (i.e., the number of successful inter-RAT handovers associated with the timing issue related to uplink synchronization) may be reported from the target node 104B to the network manager 111 (e.g., via Itf-N interface) at the end of the measurement period for the cell pair comprising the source cell 121 and the target cell 122.

This new PM counter may also be called a number of almost too early handovers. “Almost too early” means that an RLF did not follow within the predetermined time interval after the handover, but at least one disturbance of the handover was observed. The at least one disturbance may mean that the uplink synchronization procedure (or random access procedure) lasted longer than the pre-defined time threshold, and therefore the handover was risky. On the other hand, a “too early handover” may mean that T304 expired or an RLF occurred within a predetermined time interval after the handover.

The “almost too early handover” may also be called "too early inter-RAT handover without RLF".

At 210, the network manager 111 (or SON entity of NMS) optimizes, based at least partly on the counter information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node. For example, the optimization may be performed, if the number of successful inter-radio-access-technology handovers associated with the timing issue is above a threshold.

In other words, based on the new PM counter (i.e., the number of successful inter-RAT handovers associated with the timing issue related to uplink synchronization), which may be part of a KPI, for instance given as a ratio of the new PM counter and a total number of successful handovers from the source node to the target node, and possibly other rules which may be operator-specific, the network manager 111 (or SON entity) may initiate MRO optimization of the source cell 121 for the radio measurement threshold(s) that are used for triggering the handover from the source cell 121 (e.g., LTE cell) to the target cell 122 (e.g., NR cell).

The optimization may be further based on a number of inter-radio- access-technology handovers from the source node to the target node within the pre-defined time period that were too early and resulted in a radio link failure. In other words, in this case, the network manager 211 (or SON entity) may combine or merge the numbers of “almost too early handovers” and the “too early handovers”. The “too early handovers” may be reported from the source node 104, for example.

At 211, the network manager 111 (or CM part or SON entity of NMS) transmits, to the source node 104, an indication indicating the optimized one or more radio measurement thresholds. In other words, the possible changes in the radio measurement threshold(s) that are used for triggering the handover from the source cell 121 to the target cell 122 are communicated to the source node 104. Thus, there may be no new communication from NR to LTE side to provide such optimization.

The source node 104 may then apply the optimized one or more radio measurement thresholds for subsequent handovers from the source node 104 to the target node 104B. The optimized one or more radio measurement thresholds may help to avoid or reduce the timing issue associated with the uplink synchronization procedure during the subsequent handovers.

An advantage of the example embodiment of FIG. 2 is that there is no impact to the LTE standard, and it enables common operations, administration and maintenance (0AM) for NR and LTE for example for the intra-system inter-RAT handover case.

FIG. 3 illustrates a signal flow diagram according to an example embodiment.

In this example embodiment, after the root cause analysis when MRO is decided for a successful handover report (i.e., the cause of the random access issue is determined to be suboptimal handover parameters at the source LTE node 104), the corresponding inter-RAT MRO functionality at the target NR node 104B may transmit a message to the source LTE node 104 serving the outgoing source LTE cell 121, wherein this message may include a new handover report type information element called, for instance, “Almost too early inter-RAT handover”.

Based on the indication of the “Almost too early inter-RAT handover”, the MRO functionality at the source LTE node 104 serving the source LTE cell 121 may generate a new cell-pair-specific MRO counter, which may be called, for example, “Almost too early inter-RAT HO” for the inter-RAT cell pair 121, 122 in question.

Alternatively, the MRO functionality at the source LTE node 104 may process this information (i.e., the indication of the “Almost too early inter-RAT handover”) in a weighted manner within the generation of the “Too early inter-RAT HO” counter derived from RLF reports for the inter-RAT cell pair 121, 122 in question.

The counter value may then be reported at the end of the measurement period, for example, to a central MRO instance in the 0AM domain, such as to the network manager 111 (e.g., via Itf-N interface).

An “almost too early handover” means that an RLF did not follow within the predetermined time interval after the handover, but at least one disturbance of the handover was observed. The at least one disturbance may mean that the uplink synchronization procedure (or random access procedure) lasted longer than the pre-defined time threshold, and therefore the handover was risky.

A “too early” handover may mean that an RLF occurred within a predetermined time interval after the handover.

The “almost too early handover” may also be called “too early inter-RAT handover without RLF”.

Referring to FIG. 3, at 301, a source node 104 (e.g., ng-eNB or eNB), transmits, to a UE 100, a handover command comprising a configuration for a successful handover report. For example, the configuration may indicate the UE 100 store the successful handover report, if a T304 SHR percentage threshold is exceeded. The UE 100 receives the configuration from the source node 104. The source node 104 may be the serving node of the UE 100 during this configuration. The source node 104 may also be referred to as a first network node herein.

At 302, the UE 100 completes a successful inter-RAT handover of the UE 100 from the source node 104 to a target node 104B (e.g., gNB). However, the T304 SHR percentage threshold was exceeded during the successful inter-RAT handover. The target node 104B may also be referred to as a second network node herein.

The target node 104B is associated with a different radio access technology than a radio access technology associated with the source node 104. For example, the source node 104 may be associated with a fourth generation cellular radio access technology (e.g., Long Term Evolution (LTE) or LTE- Advanced), and the target node 104B may be associated with a fifth generation cellular radio access technology (e.g., 5G New Radio).

At 303, the UE 100 stores a successful handover report indicative of the successful inter-RAT handover of the UE 100 from the source node 104 to the target node 104B. For example, the SHR may be generated due to a T304 SHR percentage threshold being exceeded. The T304 SHR percentage threshold (thresholdPercentageT304) is a time threshold that may comprise a certain portion or ratio or percentage of the configured T304 value. For example, if the T304 value is configured as 10 seconds, then the T304 SHR percentage threshold may be set to 50 % of the T304 value, i.e., 5 seconds. The T304 SHR percentage threshold may also be referred to as a T304 SHR portion threshold or T304 SHR ratio threshold herein.

At 304, the UE 100 may transmit, to the target node 104B, an indication indicating an availability of the successful handover report. For example, the indication may comprise a “successHO-lnfoAvailable” flag transmitted in an RRCReconfigurationComplete message.

At 305, based on receiving the indication, the target node 104B may transmit, to the UE 100, a request for providing the successful handover report. For example, the request may be transmitted in an UElnformationRequest message.

At 306, the UE 100 transmits the successful handover report to the target node 104B. The UE 100 may transmit the successful handover report based on receiving the request from the target node 104B. For example, the successful handover report may be transmitted in an UElnformationResponse message. The target node 104B receives the successful handover report from the UE 100. In other words, the target node 104B may fetch the successful handover report message from the UE 100 via the UElnformationRequest and UElnformationResponse procedure.

The successful handover report further indicates that, during the successful inter-radio-access-technology handover, a time threshold (e.g., the T304 SHR percentage threshold) associated with monitoring of an uplink synchronization procedure between the UE 100 and the target node 104B was exceeded, thus leading to a timing issue associated with the uplink synchronization procedure. The uplink synchronization procedure may be part of a random access procedure between the UE 100 and the target node 104B. In other words, the random access procedure between the UE 100 and the target node 104B took longer than expected.

At 307, the target node 104B determines, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue (e.g., a random access problem such as RACH misconfiguration) at the target node 104B.

At 308, based on determining that the exceeding of the time threshold was not caused by the issue at the target node (i.e., based on determining that the timing issue was caused by the source node due to a too early decision of the successful inter-radio-access-technology handover), the target node 104B transmits, to the source node 104, information indicating that the timing issue associated with the uplink synchronization procedure during the successful inter- radio-access technology handover was caused by a too early initiation of the successful inter-radio-access technology handover by the source node 104. The source node 104 receives the information.

Thus, the information transmitted from the target node 104B to the source node 104 may indicate at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment 100 from the source node 104 to the target node 104B.

For example, the information may be transmitted in a handover report message (e.g., via XNAP interface) or in an inter-system handover report message (e.g., via NGAP interface). This handover report message may comprise a new handover report type information element called, for instance, “Almost too early inter-RAT handover”, or any other formulation coded as ENUM in the standard that expresses that the target NR cell 122 was not yet stable enough, which delayed the handover and increased the outage time during the handover. The handover report message may also indicate the identity of the source cell 121 and/or the identity of the target cell 122 (failure cell). The handover report message may further comprise a binary flag, which, if set to true, indicates that the cause of the SHR was the exceeding of the T304 SHR percentage threshold.

At 309, the source node 104 increments a counter based on the information received from the target node 104B.

For example, the counter may be a new counter (e.g., the “Almost too early inter-RAT HO” counter) indicating the number of inter-RAT handovers associated with the timing issue related to the uplink synchronization procedure that was caused by a too early initiation of the successful inter-radio-access technology handover by the source node 104. In this case, the source node 104 may also generate a separate counter (e.g., the “Too early inter-RAT HO” counter) for the “too early handovers” (RLF-based handovers).

Alternatively, the counter may be a legacy counter (e.g., the “Too early inter-RAT HO” counter) indicating a number of inter-radio-access-technology handovers from the source node to the target node that were too early (e.g., RLF- based too early handovers). In this case, the counter may be incremented in a weighted manner based on the information indicating that the timing issue associated with the uplink synchronization procedure during the successful inter- radio-access technology handover was caused by a too early initiation of the successful inter-radio-access technology handover by the source node 104 (i.e., due to the handover being an “almost too early” handover). In other words, in this case, the “too early” and “almost too early” handovers may be merged into one counter.

Incrementing the counter in a weighted manner means increasing a numerical value of the counter in a manner that assigns different weights or importance to different increments. For example, if the counter represents both “too early handovers” (with RLF) and “almost too early handovers” (without RLF), then the counter may be incremented in a weighted manner to reflect the relative importance between the “too early handovers” and “almost too early handovers”. The "too early handovers” (with RLF) may be associated with higher significance compared to the “almost too early handovers” (without RLF), and thus the "too early handovers” (with RLF) may result in larger increments of the counter than the “almost too early handovers” (without RLF).

For example, the counter may be incremented by a value of less than one (<1) in case of an “almost too early” handover (without RLF), whereas the counter may be implemented by a value of one in case of a “too early” handover (with RLF). As a non-limiting example, a value of 0.5 may be added to the counter in case of an “almost too early” handover (without RLF), whereas a value of 1 may be added to the counter in case of a “too early” handover (with RLF).

At 310, the source node 104 transmits, to a network entity such as a network manager 111 (or PM part or SON entity of NMS), counter information indicating the value of the counter. The SON entity of the network management system 111 receives the counter information. The SON entity of the network management system 111 may comprise a mobility robustness optimization function.

For example, the counter information may be transmitted via Itf-N interface at the end of a measurement period for the cell pair comprising the source cell 121 and the target cell 122.

In case the source node 104 generated separate counters for the “too early handovers” and “almost too early handovers”, then the source node 104 may report the values of both counters to the network manager 111 (or SON entity) in the counter information.

At 311, the network manager 111 (or SON entity of NMS) optimizes, based at least partly on the counter information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node. For example, the optimization may be performed, if the number of successful inter-radio-access-technology handovers associated with the timing issue is above a threshold.

In other words, based on the new PM counter (i.e., the number of successful “almost too early” inter-RAT handovers associated with the timing issue related to uplink synchronization), which may be part of a KPI, for instance given as a ratio of the new PM counter and a total number of successful handovers from the source node to the target node, and possibly other rules which may be operator-specific, the network manager 111 (or SON entity) may initiate MRO optimization of the source cell 121 for the radio measurement threshold(s) that are used for triggering the handover from the source cell 121 (e.g., LTE cell) to the target cell 122 (e.g., NR cell).

At 312, the network manager 111 (or CM part of NMS) transmits, to the source node 104, an indication indicating the optimized one or more radio measurement thresholds. In other words, the possible changes in the radio measurement threshold(s) that are used for triggering the handover from the source cell 121 to the target cell 122 are communicated to the source node 104. Thus, there may be no new communication from NR to LTE side to provide such optimization.

An advantage of the example embodiment of FIG. 3 is that it complies with a key aspect of the MRO philosophy, i.e., the node, which is responsible for the issue being tracked, is creating and counting the MRO counter(s). Furthermore, the MRO functionality at the source LTE 104 may decide if it integrates these “almost too early” handovers in a weighted form with an RLF-based too early handover counter, which would prevent from introducing new counters in the LTE standard. This example embodiment may also be applied, for example, to inter-system deployments with separated 0AM systems for LTE and NR. However, this example embodiment may have a minor impact on the LTE standard to enable the source LTE node 104 to decode the new handover report type information element provided in the handover report message from the target NR node 104B.

FIG. 4 illustrates a flow chart according to an example embodiment of a method performed by an apparatus 800. For example, the apparatus 800 may be, or comprise, or be comprised in, a network node such as the target node 104B. The network node may be, for example, a gNB or ng-eNB or eNB.

Referring to FIG. 4, in block 401, the apparatus receives, from a user equipment 100, a successful handover report indicative of a successful inter-radio- access-technology handover of the user equipment 100 from a source node 104 to a target node 104B, the apparatus being associated with the target node 104B.

The successful handover report indicates that, during the successful inter-radio-access-technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment 100 and the target node 104B was exceeded.

In block 402, the apparatus determines, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node 104B. For example, the issue at the target node may refer to a RACH misconfiguration.

In block 403, based on determining that the exceeding of the time threshold was not caused by the issue at the target node 104B (block 402: no), the apparatus transmits, to the source node 104 or to a network entity (e.g., the network manager 111 or SON functionality of NMS) different from the source node 104, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover (i.e., at least one successful inter-radio-access-technology handover).

For example, the source node 104 may be associated with a fourth generation cellular radio access technology (e.g., LTE or LTE-Advanced), and the target node 104B may be associated with a fifth generation cellular radio access technology (e.g., 5G NR), wherein the successful handover report may be encoded in a format associated with the fifth generation cellular radio access technology.

The at least one timing issue associated with the uplink synchronization procedure may be based on a too early decision of the successful inter-radio- access-technology handover by the source node 104.

The information transmitted to the source node 104 may indicate that the at least one timing issue associated with the uplink synchronization procedure during the successful inter-radio-access technology handover was caused by a too early initiation of the successful inter-radio-access technology handover. For example, this information may refer to the “Almost too early inter-RAT handover” information element described above.

The information transmitted to the network entity 111 may comprise counter information indicating a number of successful inter-radio-access- technology handovers from the source node 104 to the target node 104B within a pre-defined time period, the number of successful inter-radio-access-technology handovers being associated with the at least one timing issue. In other words, the counter information may indicate the number of “almost too early” handovers (i.e., too early inter-RAT handovers without RLF) counted during the pre-defined time period for the cell pair comprising the source cell 121 and the target cell 122.

FIG. 5 illustrates a flow chart according to an example embodiment of a method performed by an apparatus 800. For example, the apparatus 800 may be, or comprise, or be comprised in, a network node such as the target node 104B. The network node may be, for example, a gNB or ng-eNB or eNB. Referring to FIG. 5, in block 501, the apparatus receives, from a user equipment 100, a successful handover report indicative of a successful inter-radio- access-technology handover of the user equipment 100 from a source node 104 to a target node 104B, the apparatus being associated with the target node 104B.

In block 502, the apparatus determines, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node 104B. For example, the issue at the target node may refer to a RACH misconfiguration.

In block 503, based on determining that the exceeding of the time threshold was not caused by the issue at the target node 104B (block 502: no), the apparatus increments a counter that indicates a number of successful inter-radio- access-technology handovers from the source node 104 to the target node 104B, the number of successful inter-radio access-technology handovers being associated with the at least one timing issue.

In block 504, the apparatus transmits, to a network entity (e.g., the network manager 111 or SON functionality of NMS) different from the source node 104, counter information indicating a value of the counter, i.e., the number of successful inter-radio-access-technology handovers from the source node to the target node within a pre-defined time period, the number of successful inter-radio- access-technology handovers being associated with the at least one timing issue. In other words, the counter information may indicate the number of “almost too early” handovers (i.e., too early inter-RAT handovers without RLF) counted during the pre-defined time period for the cell pair comprising the source cell 121 and the target cell 122.

FIG. 6 illustrates a flow chart according to an example embodiment of a method performed by an apparatus 800. For example, the apparatus 800 may be, or comprise, or be comprised in, a network node such as the source node 104. The network node may be, for example, a gNB or ng-eNB or eNB.

Referring to FIG. 6, in block 601, the apparatus receives information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment 100 from a source node 104 to a target node 104B, the apparatus being associated with the source node 104, wherein the information is received from the target node 104B.

In block 602, the apparatus increments a counter based on the information.

In block 603, the apparatus transmits, to a network entity (e.g., the network manager 111 or SON functionality of NMS), counter information indicating a value of the counter.

For example, the information received from the target node 104B may indicate that the at least one timing issue associated with the uplink synchronization procedure during the at least one successful inter-radio-access technology handover was caused by a too early initiation of the at least one successful inter-radio-access technology handover. For example, this information received from the target node 104B may refer to the “Almost too early inter-RAT handover” information element described above. The counter may indicate a number of successful inter-radio-access- technology handovers from the source node to the target node within a pre-defined time period, the number of successful inter-radio access-technology handovers being associated with the at least one timing issue. In other words, in this case, the counter information may indicate at least the number of “almost too early” handovers (i.e., too early inter-RAT handovers without RLF) counted during the pre-defined time period for the cell pair comprising the source cell 121 and the target cell 122.

As another example, the counter may be incremented in a weighted manner based on the information received from the target node, wherein the information may indicate that the at least one timing issue associated with the uplink synchronization procedure during the at least one successful inter-radio- access technology handover was caused by a too early initiation of the at least one successful inter-radio-access technology handover. In this case, the counter may indicate a number of inter-radio-access-technology handovers from the source node to the target node that were too early (e.g., RLF-based handovers).

FIG. 7 illustrates a flow chart according to an example embodiment of a method performed by an apparatus 900. For example, the apparatus 900 may be, or comprise, or be comprised in, a network entity such as the network manager 111, or a self-organizing network functionality hosted in the network management system.

Referring to FIG. 7, in block 701, the apparatus receives information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment 100 from a source node 104 to a target node 104B, wherein the information is received from the target node 104B (e.g., as shown at 209 of FIG. 2) or the source node 104 (e.g., as shown at 310 of FIG. 3).

The at least one timing issue associated with the uplink synchronization procedure may be based on a too early decision of the at least one successful inter- radio-access-technology handover.

In block 702, the apparatus optimizes, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

For example, the information received from the target node 104B or the source node 104 may comprise counter information indicating a number of successful inter-radio-access-technology handovers from the source node 104 to the target node 104B within a pre-defined time period, the number of successful inter-radio access-technology handovers being associated with the at least one timing issue. For example, the counter information may indicate a counter value of the “Almost too early inter-RAT HO” counter described above. In this case, the optimization may be based at least on the number of successful inter-radio accesstechnology handovers associated with the at least one timing issue (e.g., the “Almost too early inter-RAT HO” counter indicating the number of too early inter- RAT handovers without RLF).

The optimization may be further based on a number of inter-radio- access-technology handovers from the source node to the target node within the pre-defined time period that were too early and resulted in a radio link failure (e.g., the “Too early inter-RAT HO” counter described above), which may be reported, for example, from the source node 104.

The apparatus may transmit, to the source node 104, an indication indicating the optimized one or more radio measurement thresholds.

The blocks, related functions, and information exchanges (messages) described above by means of FIGS. 2-7 are in no absolute chronological order, and some of them may be performed simultaneously or in an order differing from the described one. Other functions can also be executed between them or within them, and other information may be sent, and/or other rules applied. Some of the blocks or part of the blocks or one or more pieces of information can also be left out or replaced by a corresponding block or part of the block or one or more pieces of information.

As used herein, “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

FIG. 8 illustrates an example of an apparatus 800 comprising means for performing one or more of the example embodiments described above. For example, the apparatus 800 may be an apparatus such as, or comprising, or comprised in, a network node 104, 104B of a radio access network.

The network node may also be referred to, for example, as a source node, a target node, a network element, a radio access network (RAN) node, a next generation radio access network (NG-RAN) node, a NodeB, an eNB, an ng-eNB, a gNB, a base transceiver station (BTS), a base station, an access node, an access point (AP), a cell site, a relay node, a repeater, an integrated access and backhaul (1AB) node, an 1AB donor node, a distributed unit (DU), a central unit (CU), a baseband unit (BBU), a radio unit (RU), a radio head, a remote radio head (RRH), or a transmission and reception point (TRP).

The apparatus 800 may comprise, for example, a circuitry or a chipset applicable for realizing one or more of the example embodiments described above. The apparatus 800 may be an electronic device comprising one or more electronic circuitries. The apparatus 800 may comprise a communication control circuitry 810 such as at least one processor, and at least one memory 820 storing instructions 822 which, when executed by the at least one processor, cause the apparatus 800 to carry out one or more of the example embodiments described above. Such instructions 822 may, for example, include computer program code (software). The at least one processor and the at least one memory storing the instructions may provide the means for providing or causing the performance of any of the methods and/or blocks described above. The processor is coupled to the memory 820. The processor is configured to read and write data to and from the memory 820. The memory 820 may comprise one or more memory units. The memory units may be volatile or non-volatile. It is to be noted that there may be one or more units of non-volatile memory and one or more units of volatile memory or, alternatively, one or more units of non-volatile memory, or, alternatively, one or more units of volatile memory. Volatile memory may be for example random-access memory (RAM), dynamic random-access memory (DRAM) or synchronous dynamic random-access memory (SDRAM). Non-volatile memory may be for example read-only memory (ROM), programmable read-only memory (PROM), electronically erasable programmable read-only memory (EEPROM), flash memory, optical storage or magnetic storage. In general, memories may be referred to as non-transitory computer readable media. The 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). The memory 820 stores computer readable instructions that are executed by the processor. For example, non-volatile memory stores the computer readable instructions, and the processor executes the instructions using volatile memory for temporary storage of data and/or instructions.

The computer readable instructions may have been pre-stored to the memory 820 or, alternatively or additionally, they may be received, by the apparatus, via an electromagnetic carrier signal and/or may be copied from a physical entity such as a computer program product. Execution of the computer readable instructions causes the apparatus 800 to perform one or more of the functionalities described above.

The memory 820 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/or removable memory. The memory may comprise a configuration database for storing configuration data, such as a current neighbour cell list, and, in some example embodiments, structures of frames used in the detected neighbour cells.

The apparatus 800 may further comprise or be connected to a communication interface 830, such as a radio unit, comprising hardware and/or software for realizing communication connectivity with one or more wireless communication devices according to one or more communication protocols. The communication interface 830 comprises at least one transmitter (Tx) and at least one receiver (Rx) that may be integrated to the apparatus 800 or that the apparatus 800 may be connected to. The communication interface 830 may provide means for performing some of the blocks for one or more example embodiments described above. The communication interface 830 may comprise one or more components, such as: power amplifier, digital front end (DFE), analog-to-digital converter (ADC), digital-to-analog converter (DAC), frequency converter, (de) modulator, and/or encoder/decoder circuitries, controlled by the corresponding controlling units.

The communication interface 830 provides the apparatus with radio communication capabilities to communicate in the wireless communication network. The communication interface may, for example, provide a radio interface to one or more wireless communication devices. The apparatus 800 may further comprise or be connected to another interface towards a core network 110 such as the network coordinator apparatus, or to a network manager 111 or AMF, and/or to other network nodes 104, 104B of the wireless communication network.

The apparatus 800 may further comprise a scheduler 840 that is configured to allocate radio resources. The scheduler 840 may be configured along with the communication control circuitry 810 or it may be separately configured.

It is to be noted that the apparatus 800 may further comprise various components not illustrated in FIG. 8. The various components may be hardware components and/or software components.

FIG. 9 illustrates an example of an apparatus 900 comprising means for performing one or more of the example embodiments described above. For example, the means may be a network manager 111, or a self-organizing network functionality hosted in the network management system, or the means may be network function virtualization infrastructure.

The apparatus 900 may comprise, for example, a circuitry or a chipset applicable for realizing one or more of the example embodiments described above. The apparatus 900 may be an electronic device or computing system comprising one or more electronic circuitries. The apparatus 900 may comprise a control circuitry 910 such as at least one processor, and at least one memory 920 storing instructions 922 which, when executed by the at least one processor, cause the apparatus 900 to carry out one or more of the example embodiments described above. Such instructions 922 may, for example, include computer program code (software). The at least one processor and the at least one memory storing the instructions may provide the means for providing or causing the performance of any of the methods and/or blocks described above.

The processor is coupled to the memory 920. The processor is configured to read and write data to and from the memory 920. The memory 920 may comprise one or more memory units. The memory units may be volatile or non-volatile. It is to be noted that there may be one or more units of non-volatile memory and one or more units of volatile memory or, alternatively, one or more units of non-volatile memory, or, alternatively, one or more units of volatile memory. Volatile memory may be for example random-access memory (RAM), dynamic random-access memory (DRAM) or synchronous dynamic random-access memory (SDRAM). Non-volatile memory may be for example read-only memory (ROM), programmable read-only memory (PROM), electronically erasable programmable read-only memory (EEPROM), flash memory, optical storage or magnetic storage. In general, memories may be referred to as non-transitory computer readable media. The 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). The memory 920 stores computer readable instructions that are executed by the processor. For example, non-volatile memory stores the computer readable instructions, and the processor executes the instructions using volatile memory for temporary storage of data and/or instructions.

The computer readable instructions may have been pre-stored to the memory 920 or, alternatively or additionally, they may be received, by the apparatus, via an electromagnetic carrier signal and/or may be copied from a physical entity such as a computer program product. Execution of the computer readable instructions causes the apparatus 900 to perform one or more of the functionalities described above.

The memory 920 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/or removable memory.

The apparatus 900 may further comprise or be connected to a communication interface 930 comprising hardware and/or software for realizing communication connectivity according to one or more communication protocols. The communication interface 930 may comprise at least one transmitter (Tx) and at least one receiver (Rx) that may be integrated to the apparatus 900 or that the apparatus 900 may be connected to. The communication interface 930 may provide means for performing some of the blocks for one or more example embodiments described above. The communication interface 930 may comprise one or more components, such as: power amplifier, digital front end (DFE), analog- to-digital converter (ADC), digital-to-analog converter (DAC), frequency converter, (de) modulator, and/or encoder/decoder circuitries, controlled by the corresponding controlling units.

The communication interface 930 provides the apparatus with communication capabilities to communicate in the wireless communication network. The communication interface 930 may, for example, provide a radio, cable or fiber interface to one or more network nodes 104, 104B of a radio access network.

It is to be noted that the apparatus 900 may further comprise various components not illustrated in FIG. 9. The various components may be hardware components and/or software components. As used in this application, the term “circuitry” may refer to one or more or all of the following: a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry); and b) combinations of hardware circuits and software, such as (as applicable): i) a combination of analog and/or digital hardware circuit(s) with software/firmware and ii) any portions of hardware processor(s) with software (including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone, to perform various functions); and c) hardware circuit(s) and/or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (for example firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

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 apparatus(es) of example embodiments may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), graphics processing units (GPUs), 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 chipset (for example procedures, functions, and so on) that perform the functions described herein. The software codes maybe 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.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept may be implemented in various ways. The embodiments are not limited to the example embodiments described above, but may vary within the scope of the claims. Therefore, all words and expressions should be interpreted broadly, and they are intended to illustrate, not to restrict, the embodiments.

Claims

1. An apparatus 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 user equipment, a successful handover report indicative of a successful inter-radio-access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter-radio-access-technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determine, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmit, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

2. The apparatus according to claim 1, wherein the source node is associated with a fourth generation cellular radio access technology, and the target node is associated with a fifth generation cellular radio access technology, wherein the successful handover report is encoded in a format associated with the fifth generation cellular radio access technology.

3. The apparatus according to any preceding claim, wherein the at least one timing issue associated with the uplink synchronization procedure is based on a too early decision of the successful inter-radio-access-technology handover by the source node.

4. The apparatus according to any preceding claim, further being caused to: increment a counter based on determining that the exceeding of the time threshold was not caused by the issue at the target node, wherein the counter indicates a number of successful inter-radio-access-technology handovers from the source node to the target node, the number of successful inter-radio accesstechnology handovers being associated with the at least one timing issue, wherein the information is transmitted to the network entity, the information comprising counter information indicating the number of successful inter-radio-access-technology handovers from the source node to the target node within a pre-defined time period, the number of successful inter-radio-access- technology handovers being associated with the at least one timing issue.

5. The apparatus according to any of claims 1-4, wherein the information is transmitted to the source node, the information indicating that the at least one timing issue associated with the uplink synchronization procedure during the successful inter-radio-access technology handover was caused by a too early initiation of the successful inter-radio-access technology handover.

6. An apparatus 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 information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access- technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; increment a counter based on the information; and transmit, to a network entity, counter information indicating a value of the counter.

7. The apparatus according to claim 6, wherein the information received from the target node indicates that the at least one timing issue associated with the uplink synchronization procedure during the at least one successful inter-radio- access technology handover was caused by a too early initiation of the at least one successful inter-radio-access technology handover, wherein the counter indicates a number of successful inter-radio- access-technology handovers from the source node to the target node within a predefined time period, the number of successful inter-radio access-technology handovers being associated with the at least one timing issue.

8. The apparatus according to claim 6, wherein the counter is incremented in a weighted manner based on the information received from the target node, the information indicating that the at least one timing issue associated with the uplink synchronization procedure during the at least one successful inter- radio-access technology handover was caused by a too early initiation of the at least one successful inter-radio-access technology handover, wherein the counter indicates a number of inter-radio-access- technology handovers from the source node to the target node that were too early.

9. An apparatus 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 information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access- technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and optimize, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

10. The apparatus according to claim 9, wherein the at least one timing issue associated with the uplink synchronization procedure is based on a too early decision of the at least one successful inter-radio-access-technology handover.

11. The apparatus according to any of claims 9-10, wherein the information received from the target node or the source node comprises counter information indicating a number of successful inter-radio-access-technology handovers from the source node to the target node within a pre-defined time period, the number of successful inter-radio access-technology handovers being associated with the at least one timing issue, wherein the optimization is based at least on the number of successful inter-radio access-technology handovers associated with the at least one timing issue.

12. The apparatus according to claim 11, wherein the optimization is further based on a number of inter-radio-access-technology handovers from the source node to the target node within the pre-defined time period that were too early and resulted in a radio link failure.

13. The apparatus according to any of claims 9-12, further being caused to: transmit, to the source node, an indication indicating the optimized one or more radio measurement thresholds.

14. A method comprising: receiving, by an apparatus, from a user equipment, a successful handover report indicative of a successful inter-radio-access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter-radio-access-technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determining, by the apparatus, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmitting, by the apparatus, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

15. The method according to claim 14, wherein the source node is associated with a fourth generation cellular radio access technology, and the target node is associated with a fifth generation cellular radio access technology, wherein the successful handover report is encoded in a format associated with the fifth generation cellular radio access technology.

16. The method according to any preceding claim 14-15, wherein the at least one timing issue associated with the uplink synchronization procedure is based on a too early decision of the successful inter-radio-access-technology handover by the source node.

17. The method according to any preceding claim 14-16, further comprising: incrementing a counter based on determining that the exceeding of the time threshold was not caused by the issue at the target node, wherein the counter indicates a number of successful inter-radio-access-technology handovers from the source node to the target node, the number of successful inter-radio accesstechnology handovers being associated with the at least one timing issue, wherein the information is transmitted to the network entity, the information comprising counter information indicating the number of successful inter-radio-access-technology handovers from the source node to the target node within a pre-defined time period, the number of successful inter-radio-access- technology handovers being associated with the at least one timing issue.

18. The method according to any of claims 14-17, wherein the information is transmitted to the source node, the information indicating that the at least one timing issue associated with the uplink synchronization procedure during the successful inter-radio-access technology handover was caused by a too early initiation of the successful inter-radio-access technology handover.

19. A method comprising: receiving, by an apparatus, information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio-access-technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; incrementing, by the apparatus, a counter based on the information; and transmitting, by the apparatus, to a network entity, counter information indicating a value of the counter.

20. The method according to claim 19, wherein the information received from the target node indicates that the at least one timing issue associated with the uplink synchronization procedure during the at least one successful inter- radio-access technology handover was caused by a too early initiation of the at least one successful inter-radio-access technology handover, wherein the counter indicates a number of successful inter-radio- access-technology handovers from the source node to the target node within a pre- defined time period, the number of successful inter-radio access-technology handovers being associated with the at least one timing issue.

21. The method according to claim 19, wherein the counter is incremented in a weighted manner based on the information received from the target node, the information indicating that the at least one timing issue associated with the uplink synchronization procedure during the at least one successful inter- radio-access technology handover was caused by a too early initiation of the at least one successful inter-radio-access technology handover, wherein the counter indicates a number of inter-radio-access- technology handovers from the source node to the target node that were too early.

22. A method comprising: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio- access-technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and optimizing, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.

23. The method according to claim 22, wherein the at least one timing issue associated with the uplink synchronization procedure is based on a too early decision of the at least one successful inter-radio-access-technology handover.

24. The method according to any of claims 22-23, wherein the information received from the target node or the source node comprises counter information indicating a number of successful inter-radio-access-technology handovers from the source node to the target node within a pre-defined time period, the number of successful inter-radio access-technology handovers being associated with the at least one timing issue, wherein the optimization is based at least on the number of successful inter-radio access-technology handovers associated with the at least one timing issue.

25. The method according to claim 24, wherein the optimization is further based on a number of inter-radio-access-technology handovers from the source node to the target node within the pre-defined time period that were too early and resulted in a radio link failure.

26. The method according to any of claims 22-25, further comprising: transmitting, to the source node, an indication indicating the optimized one or more radio measurement thresholds.

27. A non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, from a user equipment, a successful handover report indicative of a successful inter-radio-access-technology handover of the user equipment from a source node to a target node, the apparatus being associated with the target node, wherein the successful handover report indicates that, during the successful inter-radio-access-technology handover, a time threshold associated with monitoring of an uplink synchronization procedure between the user equipment and the target node was exceeded; determining, based on the successful handover report, whether the exceeding of the time threshold was caused by an issue at the target node; and based on determining that the exceeding of the time threshold was not caused by the issue at the target node, transmitting, to the source node or to a network entity different from the source node, information indicating at least one timing issue associated with the uplink synchronization procedure of at least the successful inter-radio-access-technology handover.

28. A non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio- access-technology handover of at least one user equipment from a source node to a target node, the apparatus being associated with the source node, wherein the information is received from the target node; incrementing a counter based on the information; and transmitting, to a network entity, counter information indicating a value of the counter.

29. A non-transitory computer readable medium comprising program instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicating at least one timing issue associated with an uplink synchronization procedure of at least one successful inter-radio- access-technology handover of at least one user equipment from a source node to a target node, wherein the information is received from the target node or the source node; and optimizing, based at least partly on the information, one or more radio measurement thresholds associated with triggering a handover from the source node to the target node.