Cell selection

Abstract

There is provided a method and a user equipment for performing the method, the method comprising: obtaining, by the user equipment (UE) via a first cell of a first satellite on a first orbit, an indication for triggering, at the UE, a cell selection from the first cell to a cell of a satellite that is on an orbit that is different than the first orbit; based at least on the indication, performing the cell selection; and based on the cell selection, camping, in a second cell of a second satellite.

Description

[0001] CELL SELECTION

[0002] TECHNICAL FIELD

[0003] Various example embodiments relate generally to cell selection, and particularly to cell selection in satellite-based communication.

[0004] BACKGROUND

[0005] Non-Terrestrial Network (NTN) has been studied in 3GPP since release 16. Several satellite operators are expected to deploy multi-orbit satellite networks combining Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geostationary Earth Orbit / Geosynchronous Orbit (GEO / GSO) with cellular systems, like 5G / NR, in the coming years. To take advantage of satellites with different orbits, it may be beneficial to investigate new use cases for different services to enhance the user’s service experience.

[0006] BRIEF DESCRIPTION

[0007] According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. The embodiments that do not fall under the scope of the claims are to be interpreted as examples useful for understanding the disclosure.

[0008] Some embodiments of the invention are defined in the dependent claims.

[0009] LIST OF THE DRAWINGS

[0010] In the following, the invention will be described in greater detail with reference to the embodiments and the accompanying drawings, in which

[0011] Figure 1 presents a network to which one or more embodiments are applicable;

[0012] Figure 2 shows a non-terrestrial network (NTN) to which one or more embodiments are applicable;

[0013] Figures 3 A, 3B, and 4 illustrate flow diagrams according to some embodiments;

[0014] Figure 5 illustrates a signalling diagram according to one or more embodiments; and

[0015] Figures 6 and 7 illustrate apparatuses according to some embodiments.

[0016] DESCRIPTION OF EMBODIMENTS The following embodiments are exemplary. Although the specification may refer to “an”, “one”, or “some” embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Further, when a particular feature, structure, or characteristic is described in connection of an embodiment, it is within the knowledge of one skilled in the art to apply such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. It shall be understood that although the terms “first,” “second” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0017] For the purposes of the present disclosure, the phrases “at least one of A or B”, “at least one of A and B”, and “A and / or B” means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase “A, B, and / or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). As used herein, the terms “the at least one” and “the one or more” mean “any one of the at least one” and “any one of the one or more”, respectively.

[0018] Embodiments described may be implemented in a communication network, such as any of the following radio access technologies (RATs): Worldwide Interoperability for Micro-wave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, and enhanced LTE (eLTE), Narrowband-IoT (NB-IoT), enhanced Machine Type Communication (eMTC), 5G (also called NR), or any future RAT such as 6G. Moreover, communication within the communication network may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), and / or Discrete Fourier Transform spread OFDM (DFT-s-OFDM).

[0019] As used herein, the term “network device” or “network node” refers to a node in a communication network via which user equipment may access the network and / or which is capable of controlling radio communication and managing radio resources within a cell. The network node or network device may be referred to as a base station (BS), an access point (AP) or an access node. The network device may be, depending on the applied technology, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node, a nonterrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, or an aircraft network device.

[0020] Moreover, in connection of split radio access network (RAN), the network device may refer to a centralised unit (CU) of a base station and / or a distributed unit (DU) of a base station. An interface between CU and DU may be referred to as an Fl interface in NR. In the split RAN architecture, node operations may be carried out, at least partly, in the central / centralized unit, CU, (e.g. server, host or node) operationally coupled to the DU, (e.g. a radio head / node). One CU may control one or more DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some embodiments, the DUs may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layers. Other functional splits are possible too. In practice, any processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation.

[0021] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example, a terminal device may be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), or a Mobile Station (MS). The terminal device may include a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, USB dongles, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like.

[0022] A term “resource”, as used herein, may refer to radio resources in time domain, in frequency domain, in space domain, and / or in code domain. Some examples of resources include e.g. a physical resource block (PRB), a radio frame, a subframe, a time slot, a subband, a frequency region, a sub-carrier, a beam, etc. The term “transmission” and / or “reception” may refer to wirelessly transmitting and / or receiving via a wireless propagation channel on radio resources.

[0023] Figure 1 illustrates an example of a communication network to which examples disclosed herein may be applied. The communication network or a cellular communication network may comprise a network node 110 providing one or more cells, such as cell 100, and a network node 112 providing one or more other cells, such as cell 102. Each cell may be, e.g., a macro cell, a micro cell, femto, or a pico cell, for example. The cell may define a coverage area or a service area of the corresponding access node.

[0024] The network node 110 may provide a user equipment (UE) 120 (one or more UEs) with wireless access to the communication network. The wireless access may comprise downlink (DL) communication from the network node to the UE 120 and uplink (UL) communication from the UE 120 to the network node. Examples of uplink channels comprise physical uplink control channel (PUCCH) for transmitting control information and physical uplink shared channel (PUSCH) for transmitting data towards the network. Examples of downlink channels comprise physical downlink control channel (PDCCH) for transmitting control information and physical downlink shared channel (PDSCH) for transmitting data towards the user equipment.

[0025] There may be a plurality of UEs 120, 122 in the system. Each of them may be served by the same or by different control nodes 110, 112. The UEs 120, 122 may communicate with each other, in case device-to-device (D2D) communication interface is established between them via a so-called sidelink (SL). Such D2D communications may be referred to as machine-to-machine, peer-to-peer (P2P) communications, or vehicle-to-vehicle (V2V), for example.

[0026] In the case of multiple network nodes in the communication network, the network nodes may be connected to each other via an interface. LTE specifications call such an interface as X2 interface. An interface between an LTE node and a 5G node, or between two 5G nodes may be called Xn interface.

[0027] The network nodes 110 and 112 may be further connected via another interface to a core network 116 of the communication network. The LTE specifications specify the core network as an evolved packet core (EPC), and the core network may comprise e.g. a mobility management entity (MME) and a gateway node. The MME may handle mobility of terminal devices in a tracking area encompassing a plurality of cells and handle signalling connections between the terminal devices and the core network. The gateway node may handle data routing in the core network and to / from the terminal devices. The 5G specifications specify the core network as a 5G core (5GC). The 5G core may comprise e.g. an access and mobility management function (AMF) and a user plane function / gateway (UPF) and other functions. The AMF may handle termination of non-access stratum (NAS) signalling, NAS ciphering & integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. The UPF node may support packet routing and forwarding, packet inspection and quality of service (QoS) handling, for example.

[0028] The communication network of Figure 1 may support NTN access. For instance, the communication network may be or comprise NTN. NTN may comprise one or more satellites on one or more orbits. “Orbit” herein may refer to “Earth orbit” but similar logic would apply for orbits around other celestial bodies if NTN would be applied on and / or around such celestial body or bodies. Orbit may have a certain altitude (e.g. average altitude) with respect to the celestial body which is orbited.

[0029] “Satellite” as used herein may refer to satellite device on a certain orbit around a celestial body, such as around Earth. Alternatively or additionally, “satellite” may refer to high- altitude platform system (HAPS) which is basically an atmospheric satellite configured to operate on lower altitudes than conventional satellites.

[0030] The satellite may include communication circuitry for bidirectional communication with terminal devices (herein referred to as UEs). The satellite may further be configured to communicate with other satellites and / or network entities on the ground (e.g., on Earth). Two examples of how the satellite may communicate with the LTEs are described.

[0031] In first example, the satellite comprises communication circuitry that is capable of relaying communication between UEs and at least one network node 110, 112. Hence, in this scenario, the base station (e.g. eNB / gNB) may be situated on Earth but it is in communication with the satellite that relays the communication between the base station and the UEs. Thus, the satellite may act as an extension for the base station and act as a relay between the UEs and base station or base stations on Earth. This may be referred to as the transparent architecture.

[0032] In second example, the satellite may comprise or be network node 110, 112. Hence, the satellite may itself be and / or act as a base station (e.g. satellite eNB or satellite gNB). In this case, the satellite may, for instance, be connected to other network nodes via Xn or X2 interface and / or connected to core network via N2 / N3 or SI interface. This may be referred to as the regenerative architecture.

[0033] In a further example, NTN may be combination of the first and second examples.

[0034] There may be different types of satellites. For instance, there may be satellites on GEO or GSO, satellites on MEO, and / or satellites on LEO. These may be referred to as GEO / GSO satellites, MEO satellites, and LEO satellites, respectively. Non-Geostationary (NGSO) may be used herein to satellites that are on non-geosynchronous and non- geostationary orbits. Hence, NGSO may comprise MEO and LEO satellites.

[0035] One example definition of these different satellites is the following:

[0036] LEO: Circular orbit in altitudes of typically 300-2.000km (lower delay and better link budget but larger number of satellites needed for coverage) MEO: Circular orbit in altitudes of typically 8.000-20.000km

[0037] GEO / GSO: Circular orbit of about 35.786 km (Note: Due to gravitational forces a GEO / GSO satellite is still moving within a range of a few km around its nominal orbital position and is still considered as GEO / GSO satellite).

[0038] Benefit of GEO / GSO satellite(s) is that it may provide continuous coverage over a large area with fewer satellite switches. For instance, the whole Earth could be covered with only a few satellites (i.e., only a few cells are needed to cover the whole Earth). However, as the orbit is quite high (i.e., distance between orbit of the satellite and Earth’s surface is long; example distance is approx. 36,000 km) for such satellites, transmission power requirements and communication latency may become an issue. Especially, uplink (UL) transmissions by the UE may require a lot of power which is not beneficial for battery consumption. On the other hand, the NGSO such as LEO or MEO satellites can provide better communication performance in term of delay and throughput due to lower altitude of the satellites (i.e., lower orbit), but the coverage area of each NGSO satellite may be smaller than GEO / GSO coverage and frequent switch of the NGSO satellite may be needed if UE is connected to or camping in the cell provided by NGSO satellite.

[0039] One challenge with LEO is that the satellites are moving fast relative to Earth (for example 7.5 km / s). The coverage on Earth changes with the movement of the satellite / station. This means that LEs on Earth may experience very frequent mobility events in both active (handovers) and inactive (cell reselections) mode. This increases power consumption. A LE in idle mode experiences a cell reselection about every 7 seconds if the cell radius is 50 km for Earth moving cells, whereas the handover rate is lower for semiEarth fixed cells, but still significant. At every cell reselection, the LE may need to read the system information and be triggered to measure the neighboring cells, which consumes energy and thus may increase their overall energy consumption considerably.

[0040] Figure 2 illustrates a simplified system in which UE 120 may be located within a cell of a satellite 220 and within a cell of a satellite 210. Satellite 210 may have a higher orbit than satellite 220. For instance, satellite 210 may be GEO / GSO satellite and satellite 220 may be NGSO satellite. In general, it may be beneficial for the LE 120 to camp in the cell of the satellite 210 as this cell provides better coverage compared with cells of satellites 220, 230, and thus may reduce the need of cell switches. However, the inventors have beneficially observed that there may be a need for an improved cell selection schema for satellite based cellular communication. Hence, it is proposed that the network indicates the LE to trigger cell selection by the LE. Moreover, the network may indicate the LE to select a cell of a satellite that is on a lower orbit than a satellite providing a cell via which the network indicates the LE to trigger the cell selection. For instance, in the example of Figure 2, this may mean that the network indicates (see arrow 240) to the LE 120 to select cell of the satellite 220 or satellite 230. Satellite 230 may also be NGSO satellite.

[0041] One example of cell selection (or cell selection procedure) is cell reselection. Thus, cell selection may sometimes be referred to as cell reselection or cell (re)selection, especially if the LE has selected the cell (e.g. the cell of the satellite 210) to camp in.

[0042] Traditional cell selection / reselection is initiated by LE based on the S-criteria configured by the network. For instance, the cell reselection principles in 5G NR are defined in the specifications as follows:

[0043] Cell Reselection

[0044] A LE in RRC IDLE performs cell reselection. The principles of the procedure are the following:

[0045] Cell reselection is always based on CD-SSBs located on the synchronization raster.

[0046] The UE makes measurements of attributes of the serving and neighbour cells to enable the reselection process: o For the search and measurement of inter-frequency neighbouring cells, only the carrier frequencies need to be indicated.

[0047] Cell reselection identifies the cell that the UE should camp on. It is based on cell reselection criteria which involves measurements of the serving and neighbour cells: o Intra-frequency reselection is based on ranking of cells; o Inter-frequency reselection is based on absolute priorities where a UE tries to camp on the highest priority frequency available; o A Neighbour Cell List (NCL) can be provided by the serving cell to handle specific cases for intra- and interfrequency neighbouring cells; o Exclude-lists can be provided to prevent the UE from reselecting to specific intra- and inter-frequency neighbouring cells; o Allow-lists can be provided to request the UE to reselect to only specific intra- and inter-frequency neighbouring cells; o Cell reselection can be speed dependent; o Service specific prioritisation; o Slice-based cell reselection information can be provided to facilitate the UE to reselect a cell that supports specific slices.

[0048] As described in the example of cell reselection procedure, UE in radio resource control (RRC) idle mode may perform the cell selection or reselection. In the context of the present solution, the network may indicate the UE, in RRC idle mode, to select the cell with said lower orbit. Thus, for example, originally the UE may camp in a cell of a GEO / GSO satellite but may be indicated via the camped cell of the GEO / GSO satellite to select cell of a NGSO satellite. Due to the characteristic of GEO / GSO satellite providing continuous coverage over a large area with fewer satellite switches, it may be preferrable to make the idle mode UE camp in the GEO / GSO cell to avoid frequent cell reselection. Hence, in some examples, the assumption may be that the idle state UE camps in the GEO / GSO cell by default. However, as described, it may be required / desired that the idle state UEs camp in NGSO cell in certain scenarios. Example scenarios may include:

[0049] When there is need for sending public safety warning system (PWS) notification or, in general, local broadcast service in the certain area considerably smaller than GEO / GSO cell coverage, the PWS notification or local broadcast service data should not be broadcasted by GEO / GSO cell, but rather the NGSO cell(s) that cover the targeted area. If the idle state UEs camp in GEO / GSO cell by default, the UEs may miss the PWS notification broadcasted by NGSO cell.

[0050] When it is expected that a large group of UEs within certain location area (e.g. a cruise ship sailing in the Caribbean) may require access the NW within certain time window. To avoid paging the UEs from GEO / GSO cell over an unnecessary large area, the relevant idle mode UEs may be preferred to make cell reselection to NGSO cell to page the UE in smaller targeted areas.

[0051] When GEO cell is in high load situation, it may need to reduce paging traffic load as well as admission control failure rate during connection establishment procedure of idle state UEs camping in GEO cell. Thus, it may be helpful if at least some of idle state UEs are triggered to make cell reselection to NGSO cell.

[0052] The inventors have noted that their initial observation on the enhanced cell selection schema may be applicable at least to these example scenarios or similar scenarios in which the network may determine that it would be beneficial for the UE or UEs to select a cell of a NGSO satellite instead of camping in a cell of a GEO / GSO satellite. As described already above, this determination may be beneficial as the network may indicate the cell selection to the UE and the UE may thus trigger the cell selection towards a cell of a NGSO satellite.

[0053] GEO / GSO cell herein may refer to a cell provided via or by a satellite on GEO / GSO. NGSO cell herein may refer to a cell provided via or by a satellite on NGSO. It is also noted here that a satellite on NGSO is also on non-GEO because GEO is a specific example of GSO.

[0054] Triggering cell selection or cell reselection may mean that the UE starts, at the UE, the cell selection or cell reselection. Thus, the indication may be used to start, at the UE, the cell selection or cell reselection. For example, starting the cell selection or cell reselection may mean that the UE starts measuring cells for cell selection or cell reselection.

[0055] Figures 3A and 3B illustrate flow diagrams according to some embodiments. Referring to Figures 3A, 3B, a method for an apparatus is proposed. The apparatus may of radio access network (RAN), such as cellular communication network, or configured to operate, when in use, in a RAN. The apparatus may be or be comprised in a UE, such as UE 120, 122 of Figure 1 and / or Figure 2. Example of “an apparatus being comprised in a UE” may, for instance, be a chipset or circuitry in a UE. For the sake of simplicity, apparatus performing method of Figure 3 A, 3B is herein referred to as UE 120.

[0056] Referring to Figure 3A, a method is proposed in which UE 120 performs the following steps: obtain, via a first cell of a first satellite on a first orbit, an indication for triggering, at the UE 120, a cell selection from the first cell to a cell of a satellite that is on an orbit that is different than the first orbit (block 300); based at least on the indication, perform the cell selection (block 302); and based on the cell selection, camp in a second cell of a second satellite (block 304).

[0057] Referring to Figure 3B, a method is proposed in which UE 120 performs the following steps: obtain, via a first cell of a first satellite on a geosynchronous or a geostationary orbit, an indication for triggering, at the UE 120, a cell selection from the first cell to a cell of a satellite that is on an orbit that is non-geosynchronous and non-geostationary (block 310); based at least on the indication, perform the cell selection (block 312); and based on the cell selection, camp in a second cell of a second satellite (block 314).

[0058] Some examples of the methods presented in Figures 3A and 3B may be similar. For instance, at least in some examples, orbit different than first orbit may refer to orbit that is lower than the first orbit. In general, NGSO satellite has lower orbit than GEO / GSO satellite. That is, GEO / GSO satellite may have a higher orbit than NGSO satellite. However, it may be possible that the satellite with higher altitude is moving (e.g. very slowly) with respect to the Earth. Such satellite(s) may provide similar service than GEO / GSO satellite(s) but without being exactly on GEO / GSO. Hence, although in the following the different examples and embodiment are described with respect to cell selection from GEO / GSO cell to NGSO cell, it should be understood that these examples and embodiments may be applicable to cell selection from the cell of the higher altitude satellite to the cell of the lower altitude satellite. This may mean that the UE is caused to select a cell with smaller coverage (i.e., cell of the lower altitude satellite) than the cell of the higher altitude satellite. This may be caused by the indication and how the UE uses (i.e., is configured to use) the indication to perform cell selection.

[0059] In another example of Figure 3 A, orbit different than first orbit may refer to orbit that is higher than the first orbit. Thus, the indication may indicate the UE to trigger cell selection from a cell of a certain satellite to a cell of a certain other satellite which is on higher orbit than said certain satellite. For instance, the UE may be indicated to perform cell selection from a cell of satellite 220 or 230 to a cell of satellite 210. In this case, the indication may be transmitted by the satellite that has lower orbit (e.g., satellite 220, 230), as the UE may be camping in said cell or may be in connected mode in said cell. Thus, for instance, UE camping in NGSO cell may be indicated to select a GEO / GSO cell.

[0060] In an embodiment, the indication for triggering cell change is transmitted via a cell in which the UE is camping in idle mode or is in connected mode.

[0061] Performing cell selection may mean that the apparatus selects a cell, such as the second cell. The apparatus may then camp in the selected cell.

[0062] Figure 4 illustrates flow diagram according to an embodiment. Referring to Figure 4, a method for an apparatus is proposed. The apparatus may of radio access network (RAN), such as cellular communication network, or configured to operate, when in use, in a RAN. The apparatus may be or be comprised in a satellite, such as satellite 210 of Figure 2. According to some examples, network node 110 or 112 is comprised in the satellite. In some other examples, the network nodes 110, 112 are separate from the satellite. For the sake of simplicity, the apparatus performing steps of Figure 4 is herein after referred to as satellite 210.

[0063] Referring to Figure 4, the method performed by the apparatus comprises: generate an indication for triggering, at a UE, a cell selection from a cell (e.g., first cell) of the apparatus to a cell (e.g., second cell) of a satellite that is on an orbit that is different (e.g., lower) than an orbit of the apparatus (block 400); and transmit, via the cell of the apparatus to the UE, the indication for trigger the cell selection (block 402).

[0064] For example, the first cell may refer to cell of the satellite 210.

[0065] In some examples, the second cell may be a cell of a satellite that is on non- geosynchronous and non-geostationary orbit (i.e., NGSO). For instance, second cell may in such examples be cell of satellite 220 or satellite 230.

[0066] In another example, the second cell may be a cell of a satellite that is on geosynchronous or geostationary orbit (i.e., GEO / GSO). In this example, the UE 120 may not be able to select NGSO cell even though so indicated (e.g., requested) by the network, and may thus be forced to select GEO / GSO cell as a fallback option. There may be various reasons why UE 120 cannot select NGSO cell. For instance, the UE 120 may not detect any NGSO cells that fulfil selection criterion or criteria. The selection criterion or criteria may be preconfigured to the UE (e.g., defined by standards and the UE is configured to follow the criterion or criteria defined in the standards) or the UE may receive the criterion or criteria from the network. However, in general, the UE 120, based on receiving the indication for triggering cell change (e.g., indication 240, block 300, block 310) prefers to select NGSO cell over GEO / GSO cell.

[0067] Figure 5 is now discussed with respect to multiple example embodiments. With reference to Figure 5, in an embodiment, the UE 120 is configured to camp (block 500) in the first cell prior to obtaining indication for triggering cell selection. The UE 120 in RRC idle mode may camp in the first cell. For example, the UE 120 may receive the indication (e.g. step 504) for triggering the cell selection from the satellite 210 providing the first cell. For example, the UE 120 may receive said indication when the UE is camping in the first cell in RRC idle mode. Hence, in this embodiment, the UE 120 may be configured to camp, by default, in GEO / GSO cell. However, the solution proposes that the GEO / GSO satellite (e.g., satellite 210) triggers and indicates the UE 120, in RRC idle state, to make the cell selection to the NGSO cell when GEO / GSO satellite identifies the need of the cell selection e.g. in the scenarios given as examples above.

[0068] Accordingly, the satellite 210 may be configured to generate the indication for triggering cell selection (block 502). In the example of Figure 5, the message is generated at the satellite 210. Alternatively, if the satellite 210 acts as a relay between network node on the ground and the UE 120, the indication may be generated at the network node on the ground, and only relayed by the satellite 210.

[0069] The indication for triggering cell selection (also referred to as “cell selection indication”), generated in block 502 (by satellite or alternatively by some other network node), may be transmitted to the UE in step 504 by the satellite 210.

[0070] UE 120 may receive the indication (step 504). In other words, the UE 120 may obtain the indication by receiving, for example via the GEO / GSO cell (i.e., cell of the satellite 210), the indication for triggering the cell selection. The indication for triggering the cell selection may request the UE 120 to perform the cell selection. In an embodiment, the indication explicitly request the UE 120 to perform the cell selection.

[0071] According to an embodiment, the indication for triggering the cell selection indicates that the UE 120 is required to select a cell of a non-geosynchronous and non- geostationary satellite. This means that the UE 120 should select NGSO cell and not GEO / GSO cell. However, as described above, in certain cases the UE 120 may fallback to selecting GEO / GSO cell if suitable NGSO cell is not found.

[0072] In an embodiment, the indication for triggering the cell selection indicates that the UE 120 is required to select a cell of a non-geosynchronous and non-geostationary satellite and cannot select GEO / GSO cell. Non-geosynchronous and non-geostationary satellite may refer to a satellite that is neither geosynchronous nor geostationary (e.g., LEO or MEO).

[0073] In an embodiment the indication for triggering the cell selection indicates that the UE 120 is to prefer selecting a cell of a non-geosynchronous and non-geostationary satellite over a cell of a geosynchronous or geostationary satellite. This may be slightly different than requiring the UE 120 to select NGSO cell as the UE 120 may still select NGSO or GEO / GSO cell but should prefer selectin NGSO cell. For instance, the UE 120 may be configured to select NGSO cell even if GEO / GSO cell is measured to be received with higher power. For instance, the UE 120 may be configured to prefer selecting NGSO cell over GEO / GSO cell such that the GEO / GSO cell is selected instead of NGSO cell if the GEO / GSO cell is at least offset better than the NGSO cell.

[0074] In an embodiment, the indication for triggering the cell selection indicates a temporarily higher priority for selecting a cell of anon-geosynchronous and non-geostationary satellite over a cell of a geosynchronous or geostationary satellite. Hence, for instance, the UE 120 may be configured, based on the indication, to prefer selecting NGSO cell over GEO / GSO cell for a certain time period (i.e., temporarily), but not prefer NGSO cell over GEO / GSO cell after said certain time period. In another example, the UE 120 may be required, based on the indication, to select NGSO cell for a certain time period. For instance, the time period (i.e., “certain time period”) may be specified in the specifications (e.g., preconfigured at the UE as explained above) or it may be signalled to the UE by the network. In an embodiment, one bit indication (i.e., the indication for triggering the cell selection is or comprises a one bit indicator) is used to indicate temporarily higher priority of NGSO cell for cell selection.

[0075] At this point it is noted that the various examples herein refer to cell selection or cell selection procedure. As discussed above, such cell selection may, for instance, refer to cell reselection procedure in which UE in idle mode (e.g., RRC idle mode) selects a cell in which it will camp. Hence, for instance, the indication for triggering cell selection may be referred to as indication for triggering cell reselection or cell reselection indication. Additionally, “indication for triggering cell selection” or “indication for triggering cell reselection” may in some examples be understood as an indication for requesting UE or UEs to perform cell selection or cell reselection. Thus, in some examples, the indication may be understood as an indication or request for requesting cell selection or cell reselection to be performed by the UE(s).

[0076] As an example, in such cell reselection, UE may (re)select a cell in which it measures best signal strength if other conditions do not apply. However, as discussed in this disclosure, the cell selection indication may cause the UE to prefer or to require NGSO cell to be selected. That is, even if GEO / GSO cell would have the best measured signal strength, the UE may still select the NGSO cell with weaker measured signal strength. Generally, once UE has selected a cell based on one or more cell measurements, the UE may camp in the selected cell. When camping in a cell, the UE may regularly search for better cell according to cell reselection criteria. However, according to the current solution, the UE may select the cell in which to camp based on the one or more cell measurements and the received cell selection indication (see step 504).

[0077] Accordingly, in block 506, the UE 120 performs cell selection based at least on the cell selection indication (step 504). As described, the performing the cell selection may additionally be based at least on one or more cell measurements by the UE 120.

[0078] In block 508, the UE 120 camps in the cell the UE 120 selected in block 506.

[0079] According to an embodiment, the UE 120 selects NGSO cell, based at least on the cell selection indication of step 504, and camps in the selected NGSO cell. I.e., in a cell of a satellite that is on NGSO.

[0080] Different alternative for transferring the indication for triggering cell selection from the network to UE(s) are now discussed.

[0081] According to an example embodiment, the UE 120 is configured to receive system information broadcasted in the first cell (i.e., cell provided by GEO / GSO satellite, like satellite 210), wherein the system information comprises the indication for triggering the cell selection. For instance, system information may refer to system information block (SIB, see 504A in Figure 5). The satellite 210 may transmit the system information as a broadcast transmission in the cell of the satellite 210. For instance, the indication may be included in an existing SIB that is designed for idle mode UEs or by introducing a new SIB for triggering cell selection. Using broadcasted system information to convey the indication for triggering cell selection may be beneficial as the same message may be used for indicating the cell selection criterion (i.e., criterion or criteria indicating to select or at least prefer NGSO cell(s)) for multiple UEs at the same time.

[0082] According to an alternative, the UE 120 is configured to receive a paging message (see 504B in Figure 5) via the first cell (i.e., cell provided by GEO / GSO satellite, like satellite 210), wherein the paging message comprises the indication for triggering the cell selection. The indication may be provided using UE specific paging message or UE group specific paging message. The option allows the GEO / GSO satellite (e.g. satellite 210) to select the UEs or UE groups for triggering cell selection. That is, not all UEs in the cell need to be shifted to NGSO cells but only those that the network node selects.

[0083] According to a yet another alternative, the UE 120 is configured to receive an RRC release message via the first cell (i.e., cell provided by GEO / GSO satellite, like satellite 210), wherein the RRC release message comprises the indication for triggering the cell selection. In this case the UE 120 may be in connected mode (e.g., RRC connected mode) or RRC Inactive mode in the first cell. Hence, camping is depicted in block 500 as optional (i.e., dashed block) as the UE 120 may in this alternative be in connected mode and thus not camp in the first cell. The UE 120 may then move, based on the RRC release message and the included indication for cell selection, into idle mode from the connected mode and camp (block 508) in the selected (block 506) NGSO cell. Thus, the indication may be provided using the dedicated signalling of releasing the RRC connection. This option may be applied for UEs that enter idle state from the connected state or RRC inactive state with GEO / GSO cells, e.g. when UEs is required to listen to PWS from NGSO cell.

[0084] According to an embodiment, the UE 120 is configured to obtain information associated with the indication for triggering the cell selection. This information may indicate at least one of:

[0085] (1) one or more apparatus types (can be referred to also as UE types) for which the indication for triggering the cell selection is applicable;

[0086] (2) one or more apparatus mobility statuses (can be referred to also as UE mobility statuses) for which the indication for triggering the cell selection is applicable;

[0087] (3) one or more locations in which the indication for triggering the cell selection is applicable;

[0088] (4) one or more time periods during which the indication for triggering the cell selection is applicable; or

[0089] (5) an absolute time for which the indication for triggering the cell selection is applicable.

[0090] The information associated with the indication for triggering the cell selection may include any combination of list elements 1, 2, 3, 4, and 5.

[0091] The information may be obtained by receiving the information via the first cell, for example. In an embodiment, the information and the indication for triggering the cell selection are received in a same message. In an alternative embodiment, the information and the indication are received in separate messages.

[0092] Going a bit further into detailed examples, in case broadcasted system information (e.g. 504A) is used for conveying the indication for triggering cell selection, system information may indicate also the target UE type (e.g. only mobile devices, not the sensor devices), mobility status (e.g. only devices with low or medium mobility status), and / or location information (e.g. only devices within a given location area regarding to reference location) to trigger the cell reselection only to the target UEs. Such criteria are given as an example but maybe beneficial to limit the UEs for which the indication for triggering cell selection is applicable as the system information may be broadcasted in the whole cell and the broadcasted system information may be valid for all UEs in the cell. In other words, in some examples, the broadcasted system information (see 504A) may include both the indication for triggering cell selection and the information associated with the indication for triggering the cell selection.

[0093] In case paging message is used to provide the cell selection indication and trigger the selected UE to make the cell reselection to NGSO cell, the information such as UE types and mobility status may not be needed for the indication as the network node (e.g. satellite 210 or ground network node) may already select a certain UE or UEs and trigger the cell selection only for those UEs.

[0094] In case of RRC release message, the cell selection indication may be provided in RRC Release message during state transition from connected state or from inactive state to idle state. In this option, as GEO / GSO satellite can select the target UEs to camp in NGSO cell after releasing the RRC connection, the UE type and mobility status information may not be necessarily needed either.Let’s now draw our attention to the different elements on the list of information associated with the indication for triggering cell selection.

[0095] The one or more apparatus types (can be referred to also as UE types or device types) for which the indication for triggering the cell selection is applicable may define apparatus or UE type(s) for which the indication is applicable. For instance, the information may indicate that the indication is applicable for first type of UEs but not for second type of UEs. Hence, the UE 120 may determine based on the indicated one or more apparatus types whether the indication for triggering the cell selection is applicable for the UE 120. If the UE 120 determines that the indication is applicable for UE 120, the UE 120 may perform cell selection e.g. as described in reference to Figure 5. If the UE 120 determines that the cell selection is not applicable for the UE 120, the UE 120 may not perform the cell selection or the UE 120 may not perform the cell selection according to the proposed solution in which the selected cell is required or preferred to be NGSO cell.

[0096] Similarly, as for apparatus types, one or more apparatus mobility statuses (can be referred to also as UE mobility statuses or device mobility statuses) for which the indication for triggering the cell selection is applicable may be indicated. Mobility status may refer to speed and / or route of the apparatus (or UE). So, for instance, the indication for triggering cell selection may be applicable for slow moving or stationary UEs but not for fast moving UEs. The UE 120 may determine, based on the mobility status associated with the indication, whether or not the indication is applicable to the UE 120. If the UE 120 determines that the indication is applicable for UE 120, the UE 120 may perform cell selection e.g. as described in reference to Figure 5. If the UE 120 determines that the cell selection is not applicable for the UE 120, the UE 120 may not perform the cell selection or the UE 120 may not perform the cell selection according to the proposed solution in which the selected cell is required or preferred to be NGSO cell.

[0097] One or more locations in which the indication for triggering the cell selection is applicable may indicate in which locations the indication for triggering the cell selection is applicable. Location herein may refer to, for example, a certain area or geolocation. Hence, if the UE is within said area or in certain geolocation, the UE may determine that the indication is applicable for the UE. If the UE 120 determines that the indication is applicable for UE 120, the UE 120 may perform cell selection e.g. as described in reference to Figure 5. If the UE 120 determines that the cell selection is not applicable for the UE 120, the UE 120 may not perform the cell selection or the UE 120 may not perform the cell selection according to the proposed solution in which the selected cell is required or preferred to be NGSO cell.

[0098] One or more time periods during which the indication for triggering the cell selection is applicable may indicate certain time period(s) during which the indication is applicable. For instance, the indication may not be applicable outside said one or more time periods. So, for example, the time period indicated for the indication may indicate that the indication is valid for the period of time starting from reception of the indication. Such time period may, for instance, be implemented at the UE using a timer. That is, the UE may start a timer (with value equalling to said time period) when the indication for triggering cell selection is received and the indication may be determined, by the UE, to be applicable (or valid) until the timer expires after which the indication may become not applicable (or invalid).

[0099] An absolute time for which the indication for triggering the cell selection is applicable may indicate, for instance, an absolute time instance after the reception of the indication that the indication is applicable. So, for example, the absolute time associated with the indication may indicate that the indication is valid after the absolute time instance or valid until the absolute time instance. For example, the indication may be determined to be valid until the absolute time instance from the reception of the indication. The UE may determine the indication is applicable only at and after the indicated absolute time instance or before the indicated absolute time instance and perform the cell selection according to the proposed solution in which the selected cell is required or preferred to be NGSO cell at and after the absolute time instance or before the absolute time instance.

[0100] For instance, the time period or absolute time may be included in the cell selection indication or in a same message as the cell selection indication. The time period / absolute may be used to detect NGSO cell and make the cell selection to the detected NGSO cell within the time period or before or after the absolute time expires. If no relevant NGSO cell is detected within the time period or before / after the absolute time expires, the UE may keep camping (or start camping in case the UE moves from connected to idle mode) in GEO / GSO cell and cancel the cell selection measurement.

[0101] So as already described, the indication for triggering cell selection may be associated with the UE type (e.g. mobile device, loT device etc.), mobility status, location info and / or the time period / absolute time for which the indication is valid. According to an embodiment, the additional information indicates that the cell selection to NGSO cell may be triggered only to indicated apparatus / UE type, mobility status, and / or for apparatuses / UEs in certain location within the indicated time period or before the indicated absolute time.

[0102] Additionally or alternatively, the time period / absolute time may be used to trigger the UE to reselect (come back to) GEO / GSO cell after camping in selected NGSO cell until the end of the time period or before / after the absolute time. This implies the UE may camp in NGSO cell after cell selection within the indicated time period or until the indicated absolute time. Then the UE should consider GEO cell has higher priority for cell reselection and make cell reselection back to GEO cell again if UE is still kept in idle state. Hence, for instance, the UE 120 may be triggered by the GEO / GSO cell to select the NGSO cell and camp in said NGSO cell for certain time (e.g., indicated by time period or until absolute time) and after said certain time select a GEO / GSO cell to camp. For instance, this selected GEO / GSO cell may be the same cell in which the UE 120 was camping or in connected mode or RRC inactive state before changing to NGSO cell.

[0103] According to an embodiment, the UE 120 is configured to receive information indicating one or more cells for the cell selection. For example, the one or more cells may be NGSO cell(s). For instance, this information may be received via the first cell. The information may indicate the one or more cells amongst which the apparatus is required to or is preferred to select the NGSO cell in which to camp. The information may indicate at least one of the Physical Cell ID (PCI), the frequency layer the cell operates in, or the satellite assistance information (e.g. ephemeris) of the satellite providing the cell. Thus, for instance, PCI(s) may be used identify the cells allowed for the UE cell selection.

[0104] That is, the UE 120 may be required to or at least prefer to select the NGSO cell amongst the indicated one or more cells. In an embodiment, the UE 120 is required to select NGSO cell amongst the indicated one or more cells and cannot select a cell outside the indicated one or more cells at least within a time period or before / after absolute time has passed (if such are indicated).

[0105] According to an example embodiment, the information indicating the one or more cells and the indication for triggering the cell selection are received in a same message. The information indicating the one or more cells, the indication for triggering the cell selection, and the information associated with the indication for triggering the cell selection (see e.g. list elements 1-5 above) may be obtained separately or jointly by the UE 120. For instance, said information may be received, by the UE 120, in same messages or separate messages.

[0106] Additionally or alternatively, the UE 120 may be configured to receive information indicating cause of triggering the cell selection at the network side. For instance, this information may be indicated alongside the indication for triggering the cell selection. For instance, the information may indicate one of the above mentioned scenarios as a cause for the triggering.

[0107] The UE 120, upon receiving the indication of triggering cell selection to NGSO cell, is triggered to start searching or measuring the NGSO cell even the Reference Signal Received Powe (RSRP) measurement of current camping cell is high (i.e., above threshold) and make the cell selection to NGSO cell when the RSRP measurement of NGSO cell is higher than the cell reselection threshold. Herein the same cell reselection threshold, for example, in terms of RSRP as normal cell reselection criteria configured by the GEO / GSO cell may be used. Or the cell reselection threshold e.g. in term of RSRP specific to NGSO cell selection according to the proposed solution may be configured by the GEO / GSO cell. In either case, the cell reselection threshold may be obtained, by the UE 120, by receiving the cell reselection threshold from the network via GEO / GSO cell or by pre-configuration (e.g., defined in specifications).

[0108] According to an embodiment, if the list of NGSO cells (i.e., one or more cells) is indicated from GEO / GSO satellite (i.e., the UE 120 obtains the list), the UE 120 is triggered to make cell selection only if one of the listed NGSO cells is detected and measured RSRP of the detected NGSO cell is above the cell reselection threshold.

[0109] According to an embodiment, if information related to the UE (e.g., UE type, mobility status etc.) is obtained, only the relevant UEs according to the information will be triggered to make the cell selection.

[0110] For instance, if cell selection to NGSO cell is triggered due to PWS notification or local broadcast service, the list of NGSO cells may be included so that only those UEs that can detect the listed NGSO cells will be triggered to make the cell selection. However, if cell selection to NGSO cell is triggered due to other reason, the list of NGSO cells may not be needed. This implies the UE can reselect any NGSO cell as long as such cell is detected and fulfil the reselection criteria. Therefore, the information indicating cause of triggering the cell selection may affect how the cell selection is performed by the UE 120. Thus, the cells selection may further be based on, according to at least some embodiments, the cause of the cell selection indicated by the network to the UE 120.

[0111] As a summary, the indication for triggering cell selection may at least be configured for one of the following: triggering cell selection from a cell of a lower orbit satellite to a cell of a higher orbit satellite; triggering cell selection from a cell of a higher orbit satellite to a cell of a lower orbit satellite; triggering cell selection from a GEO / GSO cell to a NGSO cell; or triggering cell selection from a NGSO cell to a GEO / GSO cell.

[0112] Benefit for changing from higher satellite to lower satellite (e.g. from GEO / GSO to NGSO such as MEO or LEO) may, for example, be to allow the UE to get the relevant services (e.g. PWS notification, local broadcast services etc.) limited to smaller coverage area of the network and / or enable the network to limit the control plane signaling and user plane traffic load to the relevant smaller coverage area of the network.

[0113] Benefit for changing from lower satellite to higher satellite (e.g. NGSO to GEO / GSO) may, for example, be to reduce the need for the UE to have frequent cell / satellite switches to reduce signaling overhead between UE and the network as well as the power consumption of UE and network.

[0114] Herein, the terms idle state and idle mode may be used interchangeably, as well as the terms connected state and connected mode, as well the terms as inactive state and inactive mode.

[0115] An embodiment, as shown in Figure 6, provides an apparatus 10 comprising a control circuitry (CTRL) 12, such as at least one processor, and at least one memory 14 storing instructions (INSTRUCT.) that, when executed by the at least one processor, cause the apparatus at least to carry out any one of the above-described processes. In an example, the at least one memory and the instructions (e.g., computer program code or software), are configured, with the at least one processor, to cause the apparatus to carry out any one of the above-described processes. The control circuitry 12 may comprise relevant circuitry / ies for performing the functions, according to any of the embodiments.

[0116] The memory may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory may comprise a database for storing data.

[0117] In an embodiment, the apparatus 10 is or is comprised in a UE, such as the UE 120. The apparatus may be caused to execute some of the functionalities of the above described processes, such as the steps of Figure 3A and / or Figure 3B.

[0118] The apparatus may further comprise a radio interface (TRX) 16 comprising hardware and / or software for realizing communication connectivity according to one or more communication protocols. The TRX may provide the apparatus with communication capabilities with a user equipment and / or with a satellite (such as satellite 210, 220, and / or 230), for example.

[0119] The apparatus may also comprise a user interface 18 comprising, for example, at least one keypad, a microphone, a touch display, a display, a speaker, etc. The user interface may be used to control the apparatus by the user.

[0120] The control circuitry 12 may comprise an obtaining circuitry 20 for performing block 300 and / or block 310 according to any of the embodiments. The control circuitry 12 may further comprise a cell selection circuitry 22 for performing block 302 and / or 312 according to any of the embodiments. The control circuitry 12 may further comprise a camping circuitry 24 for performing block 304 and / or 314 according to any of the embodiments.

[0121] The control circuitry 12 may comprise relevant circuitry / ies for performing the functions, according to any of the embodiments.

[0122] An embodiment, as shown in Figure 7, provides an apparatus 50 comprising a control circuitry (CTRL) 52, such as at least one processor, and at least one memory 54 storing instructions (INSTRUCT.) that, when executed by the at least one processor, cause the apparatus at least to carry out any one of the above-described processes. In an example, the at least one memory and the computer program code (software), are configured, with the at least one processor, to cause the apparatus to carry out any one of the above-described processes. The control circuitry 52 may comprise relevant circuitry / ies for performing the functions, according to any of the embodiments.

[0123] The memory may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory may comprise a database for storing data.

[0124] In an embodiment, the apparatus 50 is or is comprised in a satellite, such as the satellite 210. The apparatus may be caused to execute some of the functionalities of the abovedescribed processes, such as the steps of Figure 4.

[0125] The apparatus may further comprise a radio interface (TRX) 56 comprising hardware and / or software for realizing communication connectivity according to one or more communication protocols. The TRX may provide the apparatus with communication capabilities to a user equipment and / or to other entities of the base station, for example.

[0126] The apparatus may also comprise a user interface 58 comprising, for example, at least one keypad, a microphone, a touch display, a display, a speaker, etc. The user interface may be used to control the apparatus by the user.

[0127] The control circuitry 52 may comprise a generating circuitry 60 for performing block 400 according to any of the embodiments. The control circuitry 52 may further comprise a transmitting circuitry 62 for performing block 402 according to any of the embodiments. In an embodiment, the apparatus 50 does not comprise circuitry 60 as the generating the indication may be performed by another entity such as a ground network node that transmits the indication to the UE(s) via said apparatus (e.g., satellite).

[0128] As used in this application, the term ‘circuitry’ refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of circuits and soft-ware (and / or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s) / software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of ‘circuitry’ applies to all uses of this term in this application. As a further example, as used in this application, the term ‘circuitry’ would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and / or firmware. The term ‘circuitry’ would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.

[0129] In an embodiment, at least some of the processes described herein may be carried out by an apparatus comprising means for carrying out at least some of the described processes. For example, an apparatus capable of performing the method of Figure 3A, 3B, or 4 (for example, a user equipment or a network device) may comprise means for performing the steps of the respective method, or of any of the described embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. Some further example means for carrying out the processes may include at least one of the following: detector, processor (including dual-core and multiple-core processors), digital signal processor, controller, receiver, transmitter, encoder, decoder, memory, RAM, ROM, software, firmware, display, user interface, display circuitry, user interface circuitry, user interface software, display software, circuit, antenna, antenna circuitry, and circuitry. A term non-transitory, as used herein, is a limitation of the medium itself (i.e. tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. RAM vs. ROM).

[0130] As used herein the term “means” is to be construed in singular form, i.e. referring to a single element, or in plural form, i.e. referring to a combination of single elements. Therefore, terminology “means for [performing A, B, C]”, is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C. Further, terminology “means for performing A, means for performing B, means for performing C” is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C.

[0131] 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 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), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chip set (e.g. procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case, it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and / or complemented by additional components in order to facilitate the achievements of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.

[0132] Embodiments as described may also be carried out in the form of a computer process defined by a computer program or portions thereof. Embodiments of the methods described may be carried out by executing at least one portion of a computer program comprising corresponding instructions. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. For example, the computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. The computer program medium may be a non-transitory medium. Coding of software for carrying out the embodiments as shown and described is well within the scope of a person of ordinary skill in the art.

[0133] Following is a list of some aspects of the proposed solution.

[0134] According to a first aspect, there is provided a method for a UE, comprising: obtaining, by the user equipment (UE) via a first cell of a first satellite on a first orbit, an indication for triggering, at the UE, a cell selection from the first cell to a cell of a satellite that is on an orbit that is different than the first orbit; based at least on the indication, performing the cell selection; and based on the cell selection, camping in a second cell of a second satellite.

[0135] The method of the first aspect may further comprise at least one feature from the following bulleted list:

[0136] • wherein the indication is for triggering, at the apparatus, the cell selection from the first cell to a cell of a satellite that is on an orbit that is lower than the first orbit;

[0137] • wherein the second satellite is on an orbit that is lower than the first orbit;

[0138] • wherein the first orbit is a geosynchronous or a geostationary, and wherein the indication is for triggering the cell selection from the first cell to a cell of a satellite that is on an orbit that is non-geosynchronous and non- geostationary;

[0139] • wherein the method further comprises camping in the second cell of the second satellite in radio resource control, RRC, idle mode;

[0140] • wherein the second satellite is on an orbit that is non-geosynchronous and non-geostati onary ;

[0141] • wherein the cell selection is or comprises a cell reselection procedure;

[0142] • wherein the indication is obtained by receiving, via the first cell, the indication for triggering the cell selection;

[0143] • wherein the method further comprises: receiving system information broadcasted in the first cell, wherein the system information comprises the indication for triggering the cell selection;

[0144] • wherein the method further comprises: receiving a paging message via the first cell, wherein the paging message comprises the indication for triggering the cell selection;

[0145] • wherein the method further comprises: camping, in the RRC idle mode, in the first cell prior to obtaining the indication for triggering the cell selection.

[0146] • wherein the method further comprises: receiving an RRC release message via the first cell, wherein the RRC release message comprises the indication for triggering the cell selection.

[0147] • wherein the method further comprises: obtaining information associated with the indication for triggering the cell selection, the information indicating at least one of: o one or more apparatus types for which the indication for triggering the cell selection is applicable; o one or more apparatus mobility statuses for which the indication for triggering the cell selection is applicable; o one or more locations in which the indication for triggering the cell selection is applicable; o one or more time periods during which the indication for triggering the cell selection is applicable; or o an absolute time for which the indication for triggering the cell selection is applicable;

[0148] • wherein the information is obtained by receiving, by the UE, the information via the first cell;

[0149] • wherein the information and the indication for triggering the cell selection are received in a same message;

[0150] • wherein the method further comprises: receiving, via the first cell, information indicating one or more cells for the cell selection;

[0151] • wherein the information indicates the one or more cells amongst which the apparatus is required to select the second cell;

[0152] • wherein the information indicating the one or more cells and the indication for triggering the cell selection are received in a same message;

[0153] • wherein the indication for triggering the cell selection request the apparatus to trigger the cell selection;

[0154] • wherein the indication for triggering the cell selection indicates that the apparatus is required to select a cell of a non-geosynchronous and non- geostationary satellite;

[0155] • wherein the indication for triggering the cell selection indicates that the apparatus is to prefer selecting a cell of a non-geosynchronous and non- geostationary satellite over a cell of a geosynchronous or geostationary satellite;

[0156] • wherein the indication for triggering the cell selection indicates a temporarily higher priority for selecting a cell of a non-geosynchronous and non-geostationary satellite over a cell of a geosynchronous or geostationary satellite.

[0157] According to a second aspect, there is provided a method for an apparatus (e.g., satellite network node), comprising: generating an indication for triggering, at a user equipment (UE) a cell selection from a cell of the apparatus to a cell of a satellite that is on an orbit that is different than an orbit of the apparatus; and transmitting, via the cell of the apparatus to the UE, the indication for trigger the cell selection.

[0158] According to a third 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: obtain, via a first cell of a first satellite on a first orbit, an indication for triggering, at the apparatus, a cell selection from the first cell to a cell of a satellite that is on an orbit that is different than the first orbit; based at least on the indication, perform the cell selection; and based on the cell selection, camp in a second cell of a second satellite

[0159] In various embodiments, the apparatus of the third aspect may be caused to perform at least one feature from the bulleted list under the first aspect.

[0160] According to a fourth 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: generate an indication for triggering, at a user equipment, UE, a cell selection from a cell of the apparatus to a cell of a satellite that is on an orbit that is different than an orbit of the apparatus; and transmit, via the cell of the apparatus to the UE, the indication for trigger the cell selection.

[0161] According to a fifth aspect, there is provided a computer program product embodied on a distribution medium and comprising program instructions which, when executed by an apparatus, cause the apparatus to carry out the method according to the first aspect or according to the second aspect.

[0162] According to a seventh aspect, there is provided a computer program product comprising program instructions which, when executed by an apparatus, cause the apparatus to carry out the method according to the first aspect or according to the second aspect.

[0163] According to a ninth aspect, there is provided an apparatus, comprising means for performing the method according to the first aspect or according to the second aspect, and / or means configured to cause the apparatus to perform the method according to the first aspect or according to the second aspect.

[0164] Various embodiments of the ninth aspect may comprise at least one feature from the bulleted list under the first aspect.

[0165] Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.

Claims

CLAIMS1. 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: obtain, via a first cell of a first satellite on a first orbit, an indication for triggering, at the apparatus, a cell selection from the first cell to a cell of a satellite that is on an orbit that is different than the first orbit; based at least on the indication, perform the cell selection; and based on the cell selection, camp in a second cell of a second satellite.

2. The apparatus of claim 1, wherein the indication is for triggering, at the apparatus, the cell selection from the first cell to a cell of a satellite that is on an orbit that is lower than the first orbit.

3. The apparatus of claim 2, wherein the second satellite is on an orbit that is lower than the first orbit.

4. The apparatus of any preceding claim, wherein the first orbit is a geosynchronous or a geostationary, and wherein the indication is for triggering the cell selection from the first cell to a cell of a satellite that is on an orbit that is non-geosynchronous and non-geostationary.

5. The apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, cause the apparatus to camp in the second cell of the second satellite in radio resource control, RRC, idle mode.

6. The apparatus of claim 4 or 5, wherein the second satellite is on an orbit that is non-geosynchronous and non-geostationary.

7. The apparatus of any preceding claim, wherein the cell selection is or comprises a cell reselection procedure.

8. The apparatus of claim any preceding claim, wherein the indication is obtained by receiving, via the first cell, the indication for triggering the cell selection.

9. The apparatus of claim 8, wherein the instructions, when executed by the at least one processor, cause the apparatus to: receive system information broadcasted in the first cell, wherein the system information comprises the indication for triggering the cell selection.

10. The apparatus of claim 8, wherein the instructions, when executed by the at least one processor, cause the apparatus to: receive a paging message via the first cell, wherein the paging message comprises the indication for triggering the cell selection.

11. The apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, cause the apparatus to: camp, in the RRC idle mode, in the first cell prior to obtaining the indication for triggering the cell selection.

12. The apparatus of claim 8, wherein the instructions, when executed by the at least one processor, cause the apparatus to: receive an RRC release message via the first cell, wherein the RRC release message comprises the indication for triggering the cell selection.

13. The apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, cause the apparatus to: obtain information associated with the indication for triggering the cell selection, the information indicating at least one of: one or more apparatus types for which the indication for triggering the cell selection is applicable; one or more apparatus mobility statuses for which the indication for triggering the cell selection is applicable; one or more locations in which the indication for triggering the cell selection is applicable; one or more time periods during which the indication for triggering the cellselection is applicable; or an absolute time for which the indication for triggering the cell selection is applicable.

14. The apparatus of claim 13, wherein the information is obtained by receiving the information via the first cell.

15. The apparatus of claim 14, wherein the information and the indication for triggering the cell selection are received in a same message.

16. The apparatus of any preceding claim, wherein the instructions, when executed by the at least one processor, cause the apparatus to: receive, via the first cell, information indicating one or more cells for the cell selection.

17. The apparatus of claim 16, wherein the information indicates the one or more cells amongst which the apparatus is required to select the second cell.

18. The apparatus of claim 16 or 17, wherein the information indicating the one or more cells and the indication for triggering the cell selection are received in a same message.

19. The apparatus of any preceding claim, wherein the indication for triggering the cell selection request the apparatus to trigger the cell selection.

20. The apparatus of any preceding claim 4 to 19, wherein the indication for triggering the cell selection indicates that the apparatus is required to select a cell of a non- geosynchronous and non-geostationary satellite.

21. The apparatus of any preceding claim 4 to 19, wherein the indication for triggering the cell selection indicates that the apparatus is to prefer selecting a cell of a non- geosynchronous and non-geostationary satellite over a cell of a geosynchronous or geostationary satellite.

22. The apparatus of any preceding claim 4 to 21, wherein the indication fortriggering the cell selection indicates a temporarily higher priority for selecting a cell of a non- geosynchronous and non-geostationary satellite over a cell of a geosynchronous or geostationary satellite.

23. 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: generate an indication for triggering, at a user equipment, UE, a cell selection from a cell of the apparatus to a cell of a satellite that is on an orbit that is different than an orbit of the apparatus; and transmit, via the cell of the apparatus to the UE, the indication for trigger the cell selection.

24. A method, comprising: obtaining, by a user equipment, UE, via a first cell of a first satellite on a first orbit, an indication for triggering, at the UE, a cell selection from the first cell to a cell of a satellite that is on an orbit that is different than the first orbit; based at least on the indication, performing the cell selection; and based on the cell selection, camping, in a second cell of a second satellite.

25. The method of claim 24, wherein the first orbit is a geosynchronous or a geostationary, and wherein the indication is for triggering the cell selection from the first cell to a cell of a satellite that is on an orbit that is non-geosynchronous and non-geostationary.

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