EP4393080A1

EP4393080A1 - Handover in non-terrestrial network

Info

Publication number: EP4393080A1
Application number: EP21769116.1A
Authority: EP
Inventors: Sandra HOPPE; Jedrzej STANCZAK
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2021-08-26
Filing date: 2021-08-26
Publication date: 2024-07-03
Also published as: WO2023025389A1; CN117730491A

Abstract

Various example embodiments relate to handover in a non-terrestrial network. The apparatus of an intent based network may detect a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite and send a handover command or a conditional handover command to the plurality of user devices. A handover order of the plurality of user devices may be based on moving directions of the plurality of user devices, and the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction. Apparatuses, methods, and computer programs are disclosed.

Description

HANDOVER IN NON-TERRESTRIAL NETWORK

TECHNICAL FIELD

Various example embodiments generally relate to handover in a non-terrestrial network (NTN). Some example embodiments relate to at least partially handover in the non-terrestrial network comprising Earth-moving cells.

BACKGROUND

Non-terrestrial networks comprise networks which use an airborne or spaceborne platform as a part of the network, such as satellites, high-altitude platforms, or drones. Satellites can be classified in terms of their altitude, from low-Earth orbit (LEO) to geostationary Earth orbit (GEO) satellites. LEO satellites are deployed in large constellations and move with respect to the Earth’s surface. Capabilities of the non-terrestrial networks to operate in a more optimal way may be however further improved.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The scope of protection sought for various embodiments of the present disclosure is set out by the independent claims.

Example embodiments of the present disclosure avoid signalling overload and mitigate the risk of collisions, for example during random access in NTN networks. This and other benefits may be achieved by the features of the independent claims. Further advantageous implementation forms are provided in the dependent claims, the description, and the drawings.

According to a first aspect, an apparatus may comprise at least one processor and at least one memory including computer program code, the at least one memory and the computer code configured to, with the at least one processor, cause the apparatus at least to: detect a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite; send a handover command or a conditional handover command to the plurality of user devices; wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices; and wherein the moving direction of the plurality of user devices is against a satellite direction or with the satellite direction. According to an example embodiment of the first aspect, all of the plurality of user devices moving against the satellite direction may be handed over during a first time period.

According to an example embodiment of the first aspect, wherein all of the plurality of user devices moving with the satellite direction may be handed over during a last time period.

According to an example embodiment of the first aspect, the computer code may be further configured to, with the at least one processor, cause the apparatus to: receive measurement reporting from the plurality of the user devices; determine the moving directions with respect to the satellite movement of the plurality of the user devices from the measurement reporting; determine handover order of the plurality of user devices based on the moving directions of the plurality of user devices; and send the handover command or the conditional handover command to the plurality of user devices.

According to an example embodiment of the first aspect, the measurement reporting may comprise location and/or movement information of the user device.

According to an example embodiment of the first aspect, the computer code may be further configured to, with the at least one processor, cause the apparatus to: create a handover order list of the plurality of user devices based on the moving directions, wherein all of the plurality of user devices moving against the satellite direction are handed over during the first time period; and all of the plurality of user devices moving with the satellite are handed over during the last time period.

According to an example embodiment of the first aspect, the computer code may be further configured to, with the at least one processor, cause the apparatus to: send the handover command or the conditional handover command in an order presented in the handover order list.

According to an example embodiment of the first aspect, the conditional handover command may comprise a time-based execution condition, which is adjusted to the user device versus satellite movement.

According to an example embodiment of the first aspect, the computer code may be further configured to, with the at least one processor, cause the apparatus to: send the conditional handover command comprising the first and the second time-based execution condition to the plurality of user devices, wherein the first time-based execution condition comprises the user device moving direction against the satellite direction and the second timebased execution condition comprises the user device moving direction with the satellite; and cause the user device to assess its moving direction with regard to the satellite; cause the user device to choose the time-based execution condition; and cause the user device to execute conditional handover command when the chosen time-based execution condition is met.

According to an example embodiment of the first aspect, the computer code may be further configured to, with the at least one processor, cause the apparatus to: cause the user device to apply the time-based execution condition for the moving direction it is closest to when the user device is not against or with moving direction of the satellite.

According to an example embodiment of the first aspect, the computer code may be further configured to, with the at least one processor, cause the apparatus to: cause the user device to apply a scaling factor proportional for the moving direction.

According to an example embodiment of the first aspect, the handover order of the plurality of user devices may be based on moving direction and velocity of the plurality of user devices.

According to an example embodiment of the first aspect, velocity may have a threshold, wherein velocity of the user device below the threshold may be stationary.

According to an example embodiment of the first aspect, the non-terrestrial network may comprise Earth-moving cells.

According to an example embodiment of the first aspect, the moving direction may be a vector having direction and velocity, wherein the user device moving with the satellite direction may have vector components having the same direction as vector components of the satellite; and the user device moving against the satellite direction may have one vector component in the opposite direction as the vector component of the satellite.

According to a second aspect, an apparatus may comprise at least one processor and at least one memory including computer program code, the at least one memory and the computer code configured to, with the at least one processor, cause the apparatus at least to: receive a conditional handover command comprising a first and a second time-based execution condition from a base station in a non-terrestrial network comprising a satellite, wherein the first timebased execution condition comprises the user device moving against a satellite direction and the second time-based execution condition comprises the user device moving with the satellite direction; assess moving direction with regard to the satellite; choose the time-based execution condition; and execute the conditional handover command when the chosen time-based execution condition is met.

According to a third aspect, a method may comprise: detecting a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite; sending a handover command or a conditional handover command to the plurality of user devices; wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices; and wherein the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction.

According to an example embodiment of the third aspect, all of the plurality of user devices moving against the satellite direction may be handed over during a first time period.

According to an example embodiment of the third aspect, all of the plurality of user devices moving with the satellite direction may be handed over during a last time period.

According to an example embodiment of the third aspect, the method may further comprise: receiving measurement reporting from the plurality of the user devices; determining the moving directions with respect to the satellite movement of the plurality of the user devices from the measurement reporting; determining handover order of the plurality of user devices based on the moving directions of the plurality of user devices; and sending the handover command or the conditional handover command to the plurality of user devices.

According to an example embodiment of the third aspect, the measurement reporting may comprise location and/or movement information of the user device.

According to an example embodiment of the third aspect, the method may further comprise: creating a handover order list of the plurality of user devices based on the moving directions, wherein all of the plurality of user devices moving against the satellite direction are handed over during the first time period; and all of the plurality of user devices moving with the satellite are handed over during the last time period.

According to an example embodiment of the third aspect, the method may further comprise: sending the handover command or the conditional handover command in an order presented in the handover order list.

According to an example embodiment of the third aspect, the conditional handover command may comprise a time-based execution condition, which is may be adjusted to the user device versus satellite movement.

According to an example embodiment of the third aspect, the method may further comprise: sending the conditional handover command comprising the first and the second timebased execution condition to the plurality of user devices, wherein the first time-based execution condition comprises the user device moving direction against the satellite direction and the second time-based execution condition comprises the user device moving direction with the satellite; and causing the user device to assess its moving direction with regard to the satellite; causing the user device to choose the time-based execution condition; and causing the user device to execute conditional handover command when the chosen time-based execution condition is met.

According to an example embodiment of the third aspect, the method may further comprise: causing the user device to apply the time-based execution condition for the moving direction it is closest to when the user device is not against or with moving direction of the satellite.

According to an example embodiment of the third aspect, the method may further comprise: causing the user device to apply a scaling factor proportional for the moving direction.

According to an example embodiment of the third aspect, the handover order of the plurality of user devices may be based on moving direction and velocity of the plurality of user devices.

According to an example embodiment of the third aspect, velocity of the user device below the threshold may be stationary.

According to an example embodiment of the third aspect, the non-terrestrial network may comprise Earth-moving cells.

According to an example embodiment of the third aspect, the moving direction may be a vector having direction and velocity, wherein the user device moving with the satellite direction has vector components having the same direction as vector components of the satellite; and the user device moving against the satellite direction has one vector component in the opposite direction as the vector component of the satellite.

According to a fourth aspect, a computer program may comprise instructions for causing an apparatus to perform at least the following: detecting a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite; sending a handover command or a conditional handover command to the plurality of user devices; wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices; and wherein the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction.

According to a fifth aspect, an apparatus may comprise means for detecting a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite; means for sending a handover command or a conditional handover command to the plurality of user devices; wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices; and wherein the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction. DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the example embodiments and constitute a part of this specification, illustrate example embodiments and together with the description help to understand the example embodiments. In the drawings:

FIG. 1 illustrates a part of an exemplifying access network in which examples of disclosed embodiments may be applied;

FIG. 2 illustrates a block diagram of an example apparatus in which examples of disclosed embodiments may be applied;

FIG. 3 illustrates an example of a situation where two cells are available for user devices, according to an example embodiment;

FIG. 4 illustrate an example of a satellite movement when multiple user devices need to be handed over at the same time, according to an example embodiment;

FIG. 5A illustrate an example of a situation when user devices have different moving directions with respect to the satellite movement, according to an example embodiment;

FIG. 5B illustrate an example of a situation when user devices are handed over in different time periods, according to an example embodiment;

FIG. 6 illustrates an example of a user device handover order flowchart, according to an example embodiment;

FIG. 7 illustrates an example of a network side execution signalling diagram, according to an example embodiment;

FIG. 8 illustrates an example of a user device side execution signalling diagram, according to an example embodiment; and

FIG. 9 illustrates an example of a method of a handover in a non-terrestrial network, according to an example embodiment.

Like references are used to designate like parts in the accompanying drawings.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments, examples of which are illustrated in the accompanying drawings. The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps or operations for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

Example embodiments relate to sending a handover command or a conditional handover command to the plurality of user devices (UEs), wherein a handover order of the plurality of user devices to be handed over is based on moving directions of the plurality of user devices. More particularly, the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction.

Example embodiments relate to an apparatus at a network side and an apparatus at a client side. The apparatus at a network side may be comprised by an access point such as a base station and the apparatus at a client side may be a terminal device/user equipment such as a mobile computing device.

According to an example embodiment, an apparatus at the network side is configured to detect a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite, send a handover command or a conditional handover command to the plurality of user devices, wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices, and wherein the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction.

According to an example embodiment, an apparatus at the client side is configured to receive a conditional handover command comprising a first and a second time-based execution condition from a base station in a non-terrestrial network comprising a satellite, wherein the first time-based execution condition comprises the user device moving against a satellite direction and the second time-based execution condition comprises the user device moving with the satellite direction, assess moving direction with regard to the satellite, choose the time-based execution condition, and execute the conditional handover command when the chosen timebased execution condition is met.

According to an example embodiment, all of the plurality of user devices moving against the satellite direction are handed over during a first time period Pl.

According to an example embodiment, all of the plurality of user devices moving with the satellite direction are handed over during a last time period Pn.

According to an example embodiment, the plurality of user devices UE1, . . ., UEn are handed over at time periods Pl, . . . , Pn. The first time period Pl may be a period during which the first of the plurality of user devices and the last of the plurality of user devices moving against the satellite direction may be handed over. The last time period Pn may be a period during which the first of the plurality of user devices and the last of the plurality of user devices moving with the satellite direction may be handed over. According to an example embodiment, the time periods Pl, . . . , Pn comprise time tl, . . . , tn moments, which are the moments when the plurality of user devices UE1, . . . , UEn are handed over. According to an example embodiment, the first time period Pl happens before the last time period Pn. There may also be other user devices that may not move and they are handed over after the first time period Pl and before the last time period Pn. Non-terrestrial networks (NTN) may comprise networks which use an airborne or spaceborne platform as a part of the network, such as satellites, high-altitude platforms or drones. Satellites may be classified in terms of their altitude, from low-Earth orbit (LEO) to geostationary Earth orbit (GEO) satellites. LEO satellites may be deployed in large constellations and may move with respect to the Earth’s surface with a speed of approximately 7,5 km/s to maintain their orbit. According to an example embodiment advantage of LEO satellites is global and high-speed communication with a low delay in comparison to traditional geostationary Earth orbit (GEO) satellites due to the lower round-trip time (RTT). The movement of the LEO satellite with respect to the Earth may lead to very frequent handovers, even if the user device is not moving.

There are two basic deployment options for cells broadcasted by non-geostationary satellites, for example LEO satellites. The first option is always placing the cells below the satellite. This means that the cells move with respect to the Earth’s surface according to the satellite’s orbital trajectory. This is called Earth-moving cells. The second option is fixing the cells on the Earth’s surface. This is achieved by continuously steering the beams on the satellite to maintain a fixed cell position on Earth. This is called Earth-fixed cells.

The integration of NTN and terrestrial networks is essential to guarantee service continuity and scalability in 4G and 5G systems. They may utilize satellite communication to enhance or complement the coverage of 5G service, for example by providing backhauling. Possible use cases are providing service continuity for machine-to-machine (M2M) or Internet of Things (loT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway, maritime, and/or aeronautical communications. An integrated terrestrial -NTN system would lead benefits in urban and rural areas in terms of 5Gtargeted performances (i.e., experienced data rate and reliability), guarantee the connectivity in very dense crowds, such as concerts, stadiums, city centers, shopping centers, and for users traveling in highspeed trains, in airplanes, and onboard cruises.

In the following, different exemplifying embodiments will be described using, as an example of an access architecture to which the embodiments may be applied, a radio access architecture based on long term evolution advanced (LTE Advanced, LTE-A) or new radio (NR, 5G), without restricting the embodiments to such an architecture, however. It is obvious for a person skilled in the art that the embodiments may also be applied to other kinds of communications networks having suitable means by adjusting parameters and procedures appropriately. Some examples of other options for suitable systems are the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E-UTRAN), long term evolution (LTE, the same as E-UTRA), wireless local area network (WLAN or WiFi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad-hoc networks (MANETs) and Internet Protocol multimedia subsystems (IMS) or any combination thereof.

Figure 1 depicts examples of simplified system architectures only showing some elements and functional entities, all being logical units, whose implementation may differ from what is shown. The connections shown in Figure 1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the system may comprise also other functions and structures than those shown in Figure 1.

The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties.

Satellite communication may utilise geostationary Earth orbit (GEO) satellite systems, but also low Earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano)satellites are deployed). Each satellite 106 in the mega-constellation may cover several satellite-enabled network entities that create cells, which may be created through a gNB 105 located in a satellite 106.

The example of Figure 1 illustrates a part of an exemplifying access network. It shows a part of an exemplifying 5G new radio (NR) wireless communication system that supports handover procedure in LEO non-terrestrial network. Figure 1 shows user device 100 configured to be in a wireless connection on one or more communication channels in a cell with an access nodes (such as (e/g)NodeB) 104, 105 providing the cell. In the example of Figure 1 a base station (e/g)NB 105 is a LEO satellite which orbits around the Earth at high speed. The UE 100 is initially served in a source cell by LEO satellite (e/g)NB 105. Once the LEO satellite 106 moves, the UE 100 will be handed over to a new target cell served by LEO satellite (e/g)NB 105. The physical link from a user device to a (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the user device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage.

A communications system may comprise more than one (e/g)NodeB in which case the (e/g)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used not only for signalling purposes but also for routing data from one (e/g)NodeB to another. The (e/g)NodeB is a computing device configured to control the radio resources of communication system it is coupled to. The (e/g) NodeB may also be referred to as a base station, an access point, an access node, or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e/g)NodeB includes or is coupled to transceivers. From the transceivers of the (e/g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to user devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (e/g)NodeB is further connected to core network 110 (CN or next generation core NGC). Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of user devices (UEs) to external packet data networks, or mobile management entity (MME), etc.

The user device 100 (also called UE, user equipment, user terminal, terminal device, etc.) illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a user device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a layer 3 relay (self-backhauling relay) towards the base station.

The user device 100 refers, for example, to a wireless mobile communication device operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (mobile phone), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and/or touch screen computer, tablet, game console, notebook, navigation device, vehicle infotainment system, and multimedia device, or any combination thereof. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A user device may also be a device having capability to operate in Internet of Things (loT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. The user device may also utilise cloud 114. In some applications, a user device may comprise a small portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud. The user device (or in some embodiments a layer 3 relay node) is configured to perform one or more of user equipment functionalities. The user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal or user device/equipment (UE) just to mention but a few names or apparatuses. A wireless device is a generic term that encompasses both the access node and the terminal device.

Various techniques described herein may also be applied to a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals. Additionally, although the apparatuses have been depicted as single entities, different units, processors and/or memory units (not all shown in Figure 1) may be implemented.

5G enables using multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (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 mobile communications supports a wide range of content delivery use cases and related applications including, for example, video streaming, audio streaming, augmented reality, gaming, map data, 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. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integradable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio interface access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6GHz - cmWave, below 6GHz - cmWave - mmWave). One of the concepts considered to be used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. The low-latency applications and services in 5G require to bring the content close to the radio which leads to local break out and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach requires leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC provides a distributed computing environment for application and service hosting. It also has the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing covers a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer-to-peer ad hoc networking and processing also classifiable as local cloud/fog computing and grid/mesh computing, dew computing, mobile edge computing, cloudlet, distributed data storage and retrieval, autonomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications).

The communication system is also able to communicate with other networks, such as a public switched telephone network or the Internet, or utilise services provided by them. The 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 Figure 1 by “cloud” 114). The communication system may also comprise a central control entity, or a like, providing facilities for networks of different operators to cooperate for example in spectrum sharing.

Edge cloud may be brought into radio access network (RAN) by utilizing network function virtualization (NVF) and software defined networking (SDN). Using edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head or base station comprising radio parts. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. Application of cloudRAN architecture enables RAN real time functions being carried out at the RAN side (in a distributed unit, DU) and non-real time functions being carried out in a centralized manner (in a centralized unit, CU).

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

It is obvious for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (e/g)NodeBs, the user device may have an access to a plurality of radio cells and the system may comprise also other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the (e/g)NodeBs may be a Home(e/g)nodeB. Additionally, in a geographical area of a radio communication system 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 are large cells, usually having a diameter of up to tens of kilometres, or smaller cells such as micro-, femto- or picocells. The (e/g)NodeBs of Figure 1 may provide any kind of these cells. A cellular radio system may be implemented as a multilayer network including several kinds of cells. In multilayer networks, one access node provides one kind of a cell or cells, and thus a plurality of (e/g)NodeBs are required to provide such a network structure.

For fulfilling the need for improving the deployment and performance of communication systems, the concept of “plug-and-play” (e/g)NodeBs has been introduced. A network which is able to use “plug-and-play” (e/g)Node Bs, includes, in addition to Home (e/g)NodeBs (H(e/g)nodeBs), a home node B gateway, or HNB-GW (not shown in Figure 1). A HNB Gateway (HNB-GW), which may be installed within an operator’s network may aggregate traffic from a large number of HNB s back to a core network.

As commonly known in connection with wireless communication systems, control or management information is transferred over a radio interface e.g., between the terminal device 100 and the access node 104, 105.

Figure 2 illustrates an example embodiment of an apparatus 200, for example a network device or a network node. In general, the apparatus 200 may be configured to perform one or more network functions, for example according to the service-based architecture (SBA) of the 5^th generation (5G) 3GPP standards. The apparatus 200 may comprise at least one processor 202. The at least one processor 202 may comprise, for example, one or more of various processing devices or processor circuitry, such as for example a co-processor, a microprocessor, a controller, a digital signal processor (DSP), a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a microcontroller unit (MCU), a hardware (HW) accelerator, a special-purpose computer chip, or the like.

The apparatus 200 may further comprise at least one memory 204. The at least one memory 204 may be configured to store, for example, computer program code 206 or the like, for example operating system software and application software. The at least one memory 204 may comprise one or more volatile memory devices, one or more non-volatile memory devices, and/or a combination thereof. For example, the at least one memory 204 may be embodied as magnetic storage devices (such as hard disk drives, floppy disks, magnetic tapes, etc.), optical magnetic storage devices, or semiconductor memories (such as mask ROM, PROM (programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random access memory), etc.).

Apparatus 200 may further comprise a communication interface 208 configured to enable the apparatus to send and/or receive information, for example the network management related information described herein to/from other network devices, nodes, or functions. For example, the apparatus 200 may use the communication interface 208 to send or receive information over the service-based interface (SBI) message bus of the 5G SBA. The communication interface 208 may be therefore used for internal communications within the apparatus or for external communications with other devices.

When the apparatus 200 is configured to implement some functionality, some component and/or components of the apparatus 200, such as for example the at least one processor 202 and/or the at least one memory 204, may be configured to implement this functionality. Furthermore, when the at least one processor 202 is configured to implement some functionality, this functionality may be implemented using the program code 206 comprised, for example, in the at least one memory 204.

The functionality described herein may be performed, at least in part, by one or more computer program product components such as software components. According to an embodiment, the apparatus comprises a processor or processor circuitry, such as for example a microcontroller, configured by the program code when executed to execute the embodiments of the operations and functionality described. Alternatively, or in addition, the functionality described herein can be performed, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs), application-specific Integrated Circuits (ASICs), application-specific Standard Products (ASSPs), System-on-a-chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), Graphics Processing Units (GPUs).

The apparatus 200 comprises means for performing at least one example embodiment described herein. In one example, the means comprises the at least one processor 202, the at least one memory 204 including program code 206 configured to, when executed by the at least one processor, cause the apparatus 200 to perform the example embodiment(s).

The apparatus 200 may comprise for example a computing device such as for example a server, a base station 104, 105, or a user device 100. Although apparatus 200 is illustrated as a single device it is appreciated that, wherever applicable, functions of the apparatus 200 may be distributed to a plurality of devices, for example to implement example embodiments as a cloud computing service.

According to an example embodiment, the apparatus 200 is located in a satellite 106 or in an access network such as a radio access network (RAN). The satellite 106 or a radio access network (RAN) may comprise a base station, such as an eNodeB or a gNodeB, and antennas that cover a given geographical region. According to an example embodiment, the apparatus 200 is a base station 105 or a user device 100.

According to an example embodiment, the apparatus 200 (e.g., a base station 105) is configured to detect a plurality of user devices 100, 102, 120-126 to be handed over in a nonterrestrial network comprising a satellite 106. According to an example embodiment, the plurality of user devices 100, 102, 120-126 are in the area to be handed over to the next cell 302, 302. The area to be handed over is the are wherein the user devices 100, 102, 120-126 are at the same time in the source cell 300 and in the target cell 302, 304. The plurality of user devices 100, 102, 120-126 may be handed over from a source cell 300 to a target cell 302. The apparatus 200 may send a handover command or a conditional handover command to the plurality of user devices 100, 102, 120-126. A handover order of the plurality of user devices 100, 102, 120-126 may be based on moving directions of the plurality of user devices 100, 102, 120-126, wherein the moving directions of the plurality of user devices 100, 102, 120-126 are against a satellite direction or with the satellite direction. According to an example embodiment, the satellite direction is the direction where the satellite moves when orbiting around the Earth.

According to an example embodiment, all of the plurality of user devices 100, 102, 120- 126 moving against the satellite direction are handed over during a first time period. According to an example embodiment, all of the plurality of user devices 100, 102, 120-126 moving with the satellite 106 are handed over during a last time period.

According to an example embodiment, the apparatus 200 is configured to, receive measurement reporting from the plurality of the user devices 100, 102, 120-126, determine the moving directions with respect to the satellite 106 movement of the plurality of the user devices 100, 102, 120-126 from the measurement reporting, determine handover order of the plurality of user devices 100, 102, 120-126 based on the moving directions of the plurality of user devices 100, 102, 120-126, and send the handover command or the conditional handover command to the plurality of user devices 100, 102, 120-126. According to an example embodiment, the measurement reporting comprises location and/or movement information of the user device 100, 102, 120-126.

According to an example embodiment, the apparatus 200 is configured to create a handover order list of the plurality of user devices 100, 102, 120-126 based on the moving directions, wherein all of the plurality of user devices 100, 102, 120-126 moving against the satellite direction are handed over during the first time period, and all of the plurality of user devices 100, 102, 120-126 moving with the satellite direction 106 are handed over during the last time period.

According to an example embodiment, the apparatus is configured to send the handover command or the conditional handover command in an order presented in the handover order list. According to an example embodiment the conditional handover command comprises a time-based execution condition, which is adjusted to the user device versus satellite movement.

According to an example embodiment, the apparatus is configured to send the conditional handover command comprising a first and a second time-based execution condition to the plurality of user devices 100, 102, 120-126, wherein the first time-based execution condition comprises the user device moving direction against the satellite direction and the second time-based execution condition comprises the user device moving direction with the satellite direction, and cause the user device 100, 102, 120-126 to assess its moving direction with regard to the satellite 106, cause the user device 100, 102, 120-126 to choose the timebased execution condition, and cause the user device 100, 102, 120-126 to execute conditional handover command when the chosen time-based execution condition is met.

According to an example embodiment, the apparatus is configured to cause the user device 100, 102, 120-126 to apply the time-based execution condition for the moving direction it is closest to when the user device 100, 102, 120-126 is not against or with moving direction of the satellite 106. According to an example embodiment, the apparatus is configured to cause the user device 100, 102, 120-126 to apply a scaling factor proportional for the moving direction.

According to an example embodiment, the handover order of the plurality of user devices 100, 102, 120-126 is based on moving direction and velocity of the plurality of user devices 100, 102, 120-126. According to an example embodiment, velocity has a threshold, wherein velocity of the user device 100, 102, 120-126 below the threshold is stationary. According to an example embodiment, the non-terrestrial network comprises Earthmoving cells.

According to an example embodiment, the moving direction is a vector having direction and velocity, wherein the user device 100, 102, 120-126 moving with the satellite direction has vector components having the same direction as vector components of the satellite 106, and the user device 100, 102, 120-126 moving against the satellite direction has one vector component in the opposite direction as the vector component of the satellite 106. According to an example embodiment, the user device 100, 102, 120-126 moving against the satellite direction has one vector component in the opposite direction as the vector component of the satellite 106 and other vector components in the same direction as vector components of the satellite 106.

According to an example embodiment, the vector may comprise vector components, for example x, y, z. When the user device 100, 102, 120-126 is moving with the satellite direction the vector components of the user device 100, 102, 120-126 and the satellite 106 have the same direction, for example UE (XUE, yuE, ZUE) and Satellite (xs, ys, zs). When the user device 100, 102, 120-126 is moving against the satellite direction the one vector component of the user device 100, 102, 120-126 or the satellite 106 has different direction, for example UE (-XUE, yuE, ZUE) and Satellite (xs, ys, zs).

According to an example embodiment, an apparatus (e.g., a user device 100, 102, 120- 126 such as UE) is configured to, with the at least one processor, cause the apparatus to receive a conditional handover command comprising a first and a second time-based execution condition from a base station 105 in a non-terrestrial network comprising a satellite 106, wherein the first time-based execution condition comprises the user device 100, 102, 120-126 moving against the satellite direction and the second time-based execution condition comprises the user device 100, 102, 120-126 moving with the satellite direction, assess moving direction with regard to the satellite 106, choose the time-based execution condition, and execute the conditional handover command when the chosen time-based execution condition is met.

Figure 3 illustrates an example of a situation where two cells 300, 302 are available for user devices 100, 102. In a non-terrestrial network, a base station 105 is moving with satellite 106 to the direction of an arrow 304 and causing constant movement of the cells 300, 302. The user devices 100, 102 may need to be handed over during a short time interval from the source cell 300 to the target cell 302 in between the time when the new target cell 302 becomes available, and the source cell 300 disappears.

Figure 4 illustrate an example of a satellite movement when a plurality of user devices 100, 102, 120-126 may need to be handed over at the same time. If multiple or even all user devices 100, 102, 120-126 are handed over between the same pair of cells 300, 302 at the same time, there may be shortages in the resources available e.g., random access (RA) preamble collisions. According to an example embodiment, group access is spread in time, thus triggering handover of the user devices 100, 102, 120-126 based on their moving directions with respect to the satellite direction 304. Hence, handover of the plurality of user devices 100, 102, 120- 126 may not be executed at the same time instant to avoid signalling overload and to mitigate the risk of collisions.

The satellites 105 may move with a very high speed of up to 7.5 km/s. In this case, the maximum user device movement of 1000 km/h may lead to a difference in the coverage time per cell 300, 302 of up to 300 ms if the user device 100, 102, 120-126 moves against or with the satellite direction. Therefore, the impact due to user device 100, 102, 120-126 movement is minor, however, this difference may still be used for triggering the handover at slightly different times.

Figure 5 A illustrate an example of a situation when user devices UE1 (100) and UE2 (102), have different moving directions with respect to the satellite movement and the user device UE3 (120) is not moving. According to an example embodiment of Figure 5, the user devices UE1 (100), UE2 (102) are moving in different directions. All the user devices UE1, UE2, and UE3 are initially served by the cell 300 on the right side. The cell 300 may be moving out of the user devices UE1, UE2, and UE3 area and the cell 302 may be the next available cell. Due to their movement, the user device UE1 may be moved before the user devices UE2 and UE3, as the user device UE1 moving direction 502 is against the satellite movement direction 304. This means that a serving time of the user device UE1 within the cell 300 may be slightly shorter. The user device UE3 may be moved before the user device UE2, as the user devices UE2 is moving 503 with the satellite movement 304, and thus its serving time within cell 300 may be slightly longer. With this arrangement, the handover signalling may be slightly distributed over time, thereby reducing simultaneous signalling.

According to an example embodiment, a user device 100, 102, 120-126 movement directions 502, 503 and/or velocity may be used to distribute the handover slightly over time. This means that the user devices 100, 102, 120-126 moving against/opposite the satellite direction 304 may be handed over first, while the user devices 100, 102, 120-126 moving with the satellite direction may be handed over last.

Figure. 5B illustrate an example of a situation when a plurality of user devices 100, 102, 120, 122 are handed over at different time periods Pl, P2, according to an example embodiment. In an example embodiment of Figure 5B, user devices UE1 (100) and UE2 (102) are moving against the satellite direction 304 and user devices UE3 (120) and UE4 (122) are moving with the satellite direction 304. According to an example embodiment, the user devices UE1, UE2 moving against the satellite direction 304 are handed over during the first time period Pl.

According to an example embodiment, the first time period Pl comprises moments between time tl and time t2. Time tl may be the time moment when the first user device UE1 moving against the satellite direction 304 may be handed over and time t2 may be the time moment when the last user device UE2 moving against the satellite direction 304 may be handed over.

According to an example embodiment, user devices UE3, UE4 moving with the satellite direction 304 are handed over during the last time period P2. According to an example embodiment, the user devices UE1 and UE2 moving against the satellite direction 304 are handed over during the first time period Pl before the user devices UE3 and UE4 moving with the satellite direction 304.

According to an example embodiment, the last time period P2 comprises moments between time t3 and time t4. Time t3 may be the time moment when the first user device UE3 moving with the satellite direction 304 may be handed over and time t4 may be the time moment when the last user device UE4 moving with the satellite direction 304 may be handed over. According to an example embodiment, time t2 < t3.

Figure 6 illustrates an example of a user device 100, 102, 120-126 handover order flowchart, according to an example embodiment. In a method, if a plurality of user devices 100, 102, 120-126 are in the area to be handed over from a first cell 300 to the second cell 302, 304, a moving direction of these user devices 100, 102, 120-126 may be determined. Based on the moving direction a handover order may be determined. After that, the user devices 100, 102, 120-126 may be moved in the determined order.

At operation 600, the method may comprise checking whether there are multiple user devices 100, 102, 120-126 in the area to be handed over to the next cell 300, 302, 301.

If there are not multiple user devices 100, 102, 120-126, at operation 602, the method may comprise waiting for the user devices 100, 102, 120-126 to be moved or move the single user device 100, 102, 120-126.

If there are multiple user devices 100, 102, 120-126, at operation 604, the method may comprise determining a moving direction of these user devices 100, 102, 120-126.

At operation 606, the method may comprise determining a handover order of the user devices 100, 102, 120-126 based on the moving direction. At operation 608, the method may comprise moving the user devices 100, 102, 120-126 in the determined handover order.

According to an example embodiment, handover may be implemented either as coordinated at a network side according to a first example embodiment or decided by the user device 100, 102, 120-126 at the client side according to a second example embodiment.

Figure 7 illustrates an example of a network side execution signalling diagram, according to an example embodiment of the first example embodiment. According to the first example embodiment, a gNB 105 located in a satellite 106 may have the user devices 100, 102, 120-126 measurements and location reporting available. The gNB 105 may receive 700 a measurement reporting comprising the user devices 100, 102, 120-126 location info from the user devices 100, 102, 120-126. The gNB 105 may determine the user devices 100, 102, 120- 126 location and movement information from the measurement reporting. A user devices handover order may be based on the moving direction of the user devices 100, 102, 120-126. The moving direction of the plurality of user devices 100, 102, 120-126 may be in the opposite direction as the satellite 106 or with the satellite direction. The user devices 100, 102, 120-126 moving in against the satellite direction may be handed over during a first time period. The user devices 100, 102, 120-126 moving with the satellite direction 106 may be handed over during a last time period. After determining the respective handover order the gNB 105 may issue 702 a handover or conditional handover command with a time-based execution condition which is adjusted to the user device versus the satellite movement.

According to an example embodiment, the time-based execution condition means that the user device 100, 102, 120-126 receives a condition based on a time instant or timer before or after this time instant (or timer expiry) it is allowed to perform the handover. The adjustment of the time-based condition may relate to the exact point in time used in the condition, hence if the user device 100, 102, 120-126 is allowed to perform the handover later or earlier. The time-based execution condition may also be defined as a time range or time window within which the user device 100, 102, 120-126 may be allowed to execute the handover. It may be bundled with another condition e.g., radio based, which may also be fulfilled during that time window so that the handover execution may occur.

According to the first example embodiment, the gNB 105 creates a handover order list of the plurality of user devices 100, 102, 120-126 based on the moving directions it receives from the user devices 100, 102, 120-126. The plurality of user devices 100, 102, 120-126 moving against the satellite direction are handed over during a first time period, and the plurality of user devices 100, 102, 120-126 moving with the satellite direction are handed over during a last time period.

According to an example embodiment, if the user device 100, 102, 120-126 movement direction is not fully in line or fully against the satellite moving direction 304, the user device 100, 102, 120-126 may be applied the direction it is closer to, thus against or with the satellite direction. The moving direction of the user device 100, 102, 120-126 may also be applied a scaling factor proportional to the deviation from this reference direction, for example related to the angle between the direction of satellite movement and user device 100, 102, 120-126 movement. In addition, a velocity-based trigger may be introduced. In that case, user devices 100, 102, 120-126 with a velocity below a threshold are regarded as stationary, as their velocities are negligible.

According to an example embodiment, the gNB 105 sends the handover command or the conditional handover command in an order presented in the handover order list.

According to an example embodiment, the gNB 105 builds a handover order list of the user devices 100, 102, 120-126, based on their motion data (velocity and/or, direction) against the satellite 106 movement. This handover list may be used to trigger the handover or conditional handover with a timing-based event in the optimal order.

Figure 8 illustrates an example of a user device 100, 102, 120-126 side execution signalling diagram, according to the second example embodiment. According to the second example embodiment, at least one of the multiple user devices 100, 102, 120-126 receive 800 a conditional handover command comprising a first or a second time-based execution condition from a gNB 105 in a non-terrestrial network comprising a satellite 106. The first time-based execution condition may comprise the user device 100, 102, 120-126 moving against a satellite direction and the second time-based execution condition may comprise the user device 100, 102, 120-126 moving with the satellite 106 direction. The user device 100, 102, 120-126 may assess 802 its moving direction with regard to the satellite 106. The user device 100, 102, 120- 126 may know the history of cells 300, 302, 304 it may have visited and may know how it has changed its moving direction and thus may draw a conclusion whether it moves with or against the satellite direction 304. On the other hand, the moving direction of the user device 100, 102, 120-126 may be known from the ephemeris.

According to an example embodiment, if the user device 100, 102, 120-126 movement direction is not fully in line or fully against the satellite moving direction 304, the user device 100, 102, 120-126 may apply the timing for the direction it is closer to. The user device 100, 102, 120-126 may also apply a scaling factor proportional to the deviation from this reference direction, for example related to the angle between the direction of satellite movement and user device 100, 102, 120-126 movement. In addition, a velocity -based trigger may be introduced. In that case, user devices 100, 102, 120-126 with a velocity below a threshold are regarded as stationary, as their velocities are negligible. According to an example embodiment, the user device 100, 102, 120-126 may choose the time-based execution condition with respect to the satellite movement. According to an example embodiment, the user device 100, 102, 120-126 may execute 804 the conditional handover command when the chosen time-based execution condition is met.

Example embodiments of the present disclosure may thus take advantage of different moving directions among the multiple user devices within a cell of a non-terrestrial network. Example embodiments of the present disclosure may allow to avoid the handover for multiple/all user devices under certain cell coverage to occur at the same time and to reduce the number of too early or too late handovers by considering user devices movement direction against or with the satellite.

FIG. 9 illustrates an example of a method for handing over in a non-terrestrial network, according to an example embodiment.

At operation 905, the method may comprise detecting a plurality of user devices 100, 102, 120-126 to be handed over in a non-terrestrial network comprising a satellite.

At operation 910, the method may comprise sending a handover command or a conditional handover command to the plurality of user devices 100, 102, 120-126, wherein a handover order of the plurality of user devices 100, 102, 120-126 is based on moving directions of the plurality of user devices 100, 102, 120-126, and wherein the moving directions of the plurality of user devices 100, 102, 120-126 are against a satellite 106 direction or with the satellite 106 direction.

Further features of the method directly result for example from the functionalities and parameters of the user device 100, 102, 120-126 and the base station 105, as described in the appended claims and throughout the specification and are therefore not repeated here. Different variations of the methods may be also applied, as described in connection with the various example embodiments.

An apparatus, for example a user device, a network device or a network node, may be configured to perform or cause performance of any aspect of the methods described herein. Further, a computer program may comprise instructions for causing, when executed, an apparatus to perform any aspect of the methods described herein. Further, an apparatus may comprise means for performing any aspect of the method(s) described herein. According to an example embodiment, the means comprises at least one processor, and at least one memory including program code, the at least one processor, and program code configured to, when executed by the at least one processor, cause performance of any aspect of the method(s).

Any range or device value given herein may be extended or altered without losing the effect sought. Also, any embodiment may be combined with another embodiment unless explicitly disallowed.

Although the subject matter has been described in language specific to structural features and/or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item may refer to one or more of those items.

The steps or operations of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the scope of the subject matter described herein. Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the effect sought.

The term 'comprising' is used herein to mean including the method, blocks, or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

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 or server, 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 (e.g., 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.

It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from scope of this specification.

Claims

1. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer code configured to, with the at least one processor, cause the apparatus at least to: detect a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite; send a handover command or a conditional handover command to the plurality of user devices; wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices; and wherein the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction.

2. The apparatus according to claim 1, wherein all of the plurality of user devices moving against the satellite direction are handed over during a first time period.

3. The apparatus according to claim 1 or claim 2, wherein all of the plurality of user devices moving with the satellite direction are handed over during a last time period.

4. The apparatus according to any of claims 1 to 3, wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to: receive measurement reporting from the plurality of the user devices; determine the moving directions with respect to the satellite movement of the plurality of the user devices from the measurement reporting; determine handover order of the plurality of user devices based on the moving directions of the plurality of user devices; and send the handover command or the conditional handover command to the plurality of user devices.

5. The apparatus according to claim 4, wherein the measurement reporting comprise location and/or movement information of the user device.

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6. The apparatus according to any of claims 1 to 5, wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to: create a handover order list of the plurality of user devices based on the moving directions, wherein all of the plurality of user devices moving against the satellite direction are handed over during the first time period; and all of the plurality of user devices moving with the satellite are handed over during the last time period.

7. The apparatus according to claim 6, wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to: send the handover command or the conditional handover command in an order presented in the handover order list.

8. The apparatus according to any of claims 1 to 7, wherein the conditional handover command comprises a time-based execution condition, which is adjusted to the user device versus satellite movement.

9. The apparatus according to any of claims 1 to 3, wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to: send the conditional handover command comprising the first and the second time-based execution condition to the plurality of user devices, wherein the first time-based execution condition comprises the user device moving direction against the satellite direction and the second time-based execution condition comprises the user device moving direction with the satellite; and cause the user device to assess its moving direction with regard to the satellite; cause the user device to choose the time-based execution condition; and cause the user device to execute conditional handover command when the chosen timebased execution condition is met.

10. The apparatus according to claim 9, wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to: cause the user device to apply the time-based execution condition for the moving direction it is closest to when the user device is not against or with moving direction of the satellite.

11. The apparatus according to claim 10, wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to: cause the user device to apply a scaling factor proportional for the moving direction.

12. The apparatus according to any of claims 1 to 11, wherein the handover order of the plurality of user devices is based on moving direction and velocity of the plurality of user devices.

13. The apparatus according to claim 12, wherein velocity has a threshold, wherein velocity of the user device below the threshold is stationary.

14. The apparatus according to any of claims 1 to 13, wherein the non-terrestrial network comprises Earth-moving cells.

15. The apparatus according to any of claims 1 to 14, wherein the moving direction is a vector having direction and velocity, wherein the user device moving with the satellite direction has vector components having the same direction as vector components of the satellite; and the user device moving against the satellite direction has one vector component in the opposite direction as the vector component of the satellite.

16. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer code configured to, with the at least one processor, cause the apparatus at least to: receive a conditional handover command comprising a first and a second time-based execution condition from a base station in a non-terrestrial network comprising a satellite, wherein the first time-based execution condition comprises the user device moving against a satellite direction and the second time-based execution condition comprises the user device moving with the satellite direction; assess moving direction with regard to the satellite; choose the time-based execution condition; and execute the conditional handover command when the chosen time-based execution condition is met.

17. A method comprising: detecting a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite; sending a handover command or a conditional handover command to the plurality of user devices; wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices; and wherein the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction.

18. The method according to claim 17, wherein all of the plurality of user devices moving against the satellite direction are handed over during a first time period.

19. The method according to claim 17 or claim 18, wherein all of the plurality of user devices moving with the satellite direction are handed over during a last time period.

20. The method according to any of claims 17 to 19, further comprising: receiving measurement reporting from the plurality of the user devices; determining the moving directions with respect to the satellite movement of the plurality of the user devices from the measurement reporting; determining handover order of the plurality of user devices based on the moving directions of the plurality of user devices; and sending the handover command or the conditional handover command to the plurality of user devices.

21. The method according to claim 20, wherein the measurement reporting comprise location and/or movement information of the user device.

22. The method according to any of claims 17 to 21, further comprising:

28 creating a handover order list of the plurality of user devices based on the moving directions, wherein all of the plurality of user devices moving against the satellite direction are handed over during the first time period; and all of the plurality of user devices moving with the satellite are handed over during the last time period.

23. The method according to claim 22, further comprising: sending the handover command or the conditional handover command in an order presented in the handover order list.

24. The method according to any of claims 17 to 23, wherein the conditional handover command comprises a time-based execution condition, which is adjusted to the user device versus satellite movement.

25. The method according to any of claims 17 to 19, further comprising: sending the conditional handover command comprising the first and the second timebased execution condition to the plurality of user devices, wherein the first time-based execution condition comprises the user device moving direction against the satellite direction and the second time-based execution condition comprises the user device moving direction with the satellite; and causing the user device to assess its moving direction with regard to the satellite; causing the user device to choose the time-based execution condition; and causing the user device to execute conditional handover command when the chosen timebased execution condition is met.

26. The method according to claim 25, further comprising: causing the user device to apply the time-based execution condition for the moving direction it is closest to when the user device is not against or with moving direction of the satellite.

27. The method according to claim 26, further comprising: causing the user device to apply a scaling factor proportional for the moving direction.

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28. The method according to any of claims 17 to 27, wherein the handover order of the plurality of user devices is based on moving direction and velocity of the plurality of user devices.

29. The method according to claim 28, wherein velocity has a threshold, wherein velocity of the user device below the threshold is stationary.

30. The method according to any of claims 17 to 29, wherein the non-terrestrial network comprises Earth-moving cells.

31. The method according to any of claims 17 to 30, wherein the moving direction is a vector having direction and velocity, wherein the user device moving with the satellite direction has vector components having the same direction as vector components of the satellite; and the user device moving against the satellite direction has one vector component in the opposite direction as the vector component of the satellite.

32. A computer program comprising instructions for causing an apparatus to perform at least the following: detecting a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite; sending a handover command or a conditional handover command to the plurality of user devices; wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices; and wherein the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction.

33. An apparatus comprising: means for detecting a plurality of user devices to be handed over in a non-terrestrial network comprising a satellite; means for sending a handover command or a conditional handover command to the plurality of user devices; wherein a handover order of the plurality of user devices is based on moving directions of the plurality of user devices; and

30 wherein the moving directions of the plurality of user devices are against a satellite direction or with the satellite direction.

31