Cell selection measurements in non-terrestrial networks

Abstract

Method, apparatuses, and computer program products provide for energy efficient measurements in non-terrestrial networks. A method includes identifying a first time at which a non-terrestrial network serving cell will cease to be available and determining, based on the first time, a second time earlier than the first time. After the second time, the method includes measuring a reference signal strength of at least one neighboring cell and selecting a new cell based on the reference signal strength of the at least one neighboring cell independently of a reference signal strength of the serving cell.

Description

CELL SELECTION MEASUREMENTS IN NON-TERRESTRIAL NETWORKS TECHNOLOGICAL FIELD

[0001] An example embodiment relates generally to network cell selection, and more particularly, to an efficient process for cell selection in non-terrestrial networks in earth fixed cells. BACKGROUND

[0002] Terrestrial mobile networks involve generally stationary access points with geographically fixed cells within which user equipment devices can access a network through a respective access point. Access point switching is required when a user equipment device moves out of the coverage area of one cell into the coverage area of another cell. Non-terrestrial networks employ above-Earth access points, such as satellites orbiting above the Earth. These satellites, when in low-Earth orbit, are generally non- geosynchronous such that they do not remain in a substantially fixed location relative to the Earth. Because of relative movement between the satellites and the Earth, non- terrestrial network cells associated with a satellite only exist for limited periods of time. Once the satellite moves beyond a point at which a cell can be maintained, the cell expires and user equipment devices serviced by the cell must locate a new cell. This situation presents challenges because the cells of non-terrestrial networks are temporary and user equipment devices served by these cells need to establish the logistics of transitioning to new cells. BRIEF SUMMARY

[0003] Various embodiments generally relate to techniques for energy efficient network cell selection, and more particularly, to an efficient process for cell selection in non-terrestrial networks in earth fixed cells.

[0004] In an example embodiment, an apparatus is provided that comprises at least one processor and at least one memory including computer program code with the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to identify a first time at which a non-terrestrial network serving cell will cease to be available and to determine, based on the first time, a second time earlier than the first time. After the second time, the apparatus is caused to measure a reference signal strength of at least one neighboring cell and to select a new cell based onthe reference signal strength of the at least one neighboring cell independently of a reference signal strength of the serving cell.

[0005] In another embodiment, a method is provided that includes identifying a first time at which a non-terrestrial network serving cell will cease to be available and determining, based on the first time, a second time earlier than the first time. After the second time, the method also includes measuring a reference signal strength of at least one neighboring cell and selecting a new cell based on the reference signal strength of the at least one neighboring cell independently of a reference signal strength of the serving cell.

[0006] In a further example embodiment, a computer program product is provided that includes at least one non-transitory computer readable storage medium having computer executable program code instructions stored therein with the computer executable program code instructions comprising program code instructions configured, upon execution, to identify a first time at which a non-terrestrial network serving cell will cease to be available and to determine, based on the first time, a second time earlier than the first time. The program code instructions also include program code instructions configured to measure, after the second time, a reference signal strength of at least one neighboring cell and to select a new cell based on the reference signal strength of the at least one neighboring cell independently of a reference signal strength of the serving cell.

[0007] In yet another example embodiment, an apparatus is provided that includes means for identifying a first time at which a non-terrestrial network serving cell will cease to be available and means for determining, based on the first time, a second time earlier than the first time. After the second time, the apparatus also includes means for measuring a reference signal strength of at least one neighboring cell and means for selecting a new cell based on the reference signal strength of the at least one neighboring cell independently of a reference signal strength of the serving cell.

[0008] In relation to the apparatus, method and computer program products of the foregoing embodiments, the second time may be determined based, at least in part, on an indication of availability of the at least one neighboring cell. In another embodiment, the second time is determined based, at least in part, on a predefined time before the first time. The second time is determined in an example embodiment based, at least in part, on a maximum time for detection and selection of a new cell. In another embodiment, the second time is determined based, at least in part, on a duration of a Discontinuous Reception cycle. The serving cell of an example embodiment comprises an Earth-fixed cell of the non-terrestrial network. In this embodiment, the first time is the time at whichthe serving cell ceases to be available from a satellite of the non-terrestrial network, such as a low-Earth non-geosynchronous orbit. In an example embodiment, the determination of the second time is dependent on being configured with a relaxed measurement requirement.

[0009] In an example embodiment, an apparatus is provided that comprises at least one processor and at least one memory including computer program code with the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus at least to identify a first time at which a non-terrestrial network serving cell will cease to be available. The non-terrestrial serving cell is served by a first satellite. The apparatus is also caused to determine, based on the first time, a second time earlier than the first time and, after the second time, to update at least one timing requirement to detect or measure or evaluate at least one cell belonging to at least one second satellite, other than the first satellite. The apparatus of an example embodiment is also caused to remove the first satellite from a listing of one or more satellites for which a reference signal strength is to be measured. In another embodiment, the apparatus is also caused to select a new cell based on a reference signal strength of a neighboring cell belong to the at least one second satellite.

[0010] In another embodiment, a method is provided that comprises identifying a first time at which a non-terrestrial network serving cell will cease to be available. The non- terrestrial serving cell is served by a first satellite. The method also includes determining, based on the first time, a second time earlier than the first time and, after the second time, updating at least one timing requirement to detect or measure or evaluate at least one cell belonging to at least one second satellite, other than the first satellite. In an example embodiment, the method also includes removing the first satellite from a listing of one or more satellites for which a reference signal strength is to be measured. The method of an example embodiment may also include selecting a new cell based on a reference signal strength of a neighboring cell belong to the at least one second satellite.

[0011] In a further embodiment, a computer program product is provided that includes at least one non-transitory computer readable storage medium having computer executable program code instructions stored therein with the computer executable program code instructions comprising program code instructions configured, upon execution, to identify a first time at which a non-terrestrial network serving cell will cease to be available. The non-terrestrial serving cell is served by a first satellite. The program code instructions are also configured to determine, based on the first time, a second time earlier than the firsttime and, after the second time, update at least one timing requirement to detect or measure or evaluate at least one cell belonging to at least one second satellite, other than the first satellite. In an example embodiment, the program code instructions are also configured to remove the first satellite from a listing of one or more satellites for which a reference signal strength is to be measured. The program code instructions of an example embodiment may also be configured to select a new cell based on a reference signal strength of a neighboring cell belong to the at least one second satellite.

[0012] In yet another embodiment, an apparatus is provided that comprises means for identifying a first time at which a non-terrestrial network serving cell will cease to be available. The non-terrestrial serving cell is served by a first satellite. The apparatus also includes means for determining, based on the first time, a second time earlier than the first time and means, after the second time, for updating at least one timing requirement to detect or measure or evaluate at least one cell belonging to at least one second satellite, other than the first satellite. In an example embodiment, the apparatus also includes means for removing the first satellite from a listing of one or more satellites for which a reference signal strength is to be measured. The apparatus of an example embodiment may also include means for selecting a new cell based on a reference signal strength of a neighboring cell belong to the at least one second satellite.

[0013] In relation to the apparatus, method and computer program products of the foregoing embodiments, the second time may be determined based, at least in part, on an indication of availability of the at least one neighboring cell. In an example embodiment, the second time is determined based, at least in part, on a predefined time before the first time. The second time is determined in an exampled embodiment based, at least in part, on a maximum time for detection and selection of a new cell. In an example embodiment, the second time is determined based, at least in part, on a duration of a Discontinuous Reception cycle. The serving cell of an example embodiment comprises an Earth-fixed cell of the non-terrestrial network. In this embodiment, the first time is the time at which the serving cell ceases to be available from the first satellite of the non-terrestrial network. In an example embodiment, the determination of the second time is dependent on being configured with a relaxed measurement requirement.

[0014] The above summary is provided merely for purposes of summarizing some example embodiments to provide a basic understanding of some aspects of the present disclosure. Accordingly, it will be appreciated that the above-described embodiments are merely examples and should not be construed to narrow the scope or spirit of the inventionin any way. It will be appreciated that the scope of this disclosure encompasses many potential embodiments in addition to those here summarized, some of which will be further described below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Having thus described certain example embodiments of the present disclosure in general terms above, non-limiting and non-exhaustive embodiments of the subject disclosure will now be described with reference to the accompanying drawings, which are not necessarily drawn to scale. The components illustrated in the accompanying drawings may or may not be present in certain embodiments described herein. Some embodiments may include fewer (or more) components than those shown in the drawings.

[0016] Figure 1 illustrates an overview of an example mobile network (e.g., a fifth generation system (5GS)), in accordance with various embodiments of the present disclosure;

[0017] Figure 2 illustrates an overview of an example non-terrestrial mobile network, in accordance with various embodiments of the present disclosure;

[0018] Figure 3 provides a block diagram of an example apparatus that may facilitate cell reselection in a non-terrestrial network, in accordance with various embodiments of the present disclosure;

[0019] Figure 4 illustrates a timeline of measurements for a cell entering measurement relaxation mode ahead of a time at which the currently serving cell becomes unavailable, in accordance with various embodiments of the present disclosure;

[0020] Figure 5 illustrates a timeline of measurements for a serving cell and a neighboring cell after measurement relaxation conditions are met and ahead of a time at which the currently serving cell becomes unavailable, in accordance with various embodiments of the present disclosure;

[0021] Figure 6 illustrates a timeline of measurements for a serving cell and a neighboring cell ahead of a measurement relaxation condition being met, and measurement of only the neighboring cell after the measurement relaxation condition is met and ahead of a time at which the currently serving cell becomes unavailable, in accordance with various embodiments of the present disclosure; and

[0022] Figure 7 is a flowchart of a technique for energy efficient measurements in non- terrestrial networks according to an example embodiment of the present disclosure.DETAILED DESCRIPTION

[0023] Some embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, various embodiments of the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout. As used herein, the terms “data,” “content,” “information,” “electronic information,” “signal,” “command,” and similar terms may be used interchangeably to refer to data capable of being captured, transmitted, received, and / or stored in accordance with various embodiments of the present disclosure. Thus, use of any such terms should not be taken to limit the spirit and scope of embodiments of the present disclosure. Further, where a first computing device is described herein to receive data from a second computing device, it will be appreciated that the data may be received directly from the second computing device or may be received indirectly via one or more intermediary computing devices, such as, for example, one or more servers, relays, routers, network access points, base stations, hosts, repeaters, and / or the like, sometimes referred to herein as a “network.” Similarly, where a first computing device is described herein as sending data to a second computing device, it will be appreciated that the data may be sent or transmitted directly to the second computing device or may be sent or transmitted indirectly via one or more intermediary computing devices, such as, for example, one or more servers, remote servers, cloud-based servers (e.g., cloud utilities), relays, routers, network access points, base stations, hosts, repeaters, and / or the like.

[0024] The term “comprising” means including but not limited to and should be interpreted in the manner it is typically used in the patent context. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Furthermore, to the extent that the terms “includes” and “including,” and variants thereof are used in either the detailed description or the claims, these terms are intended to be inclusive in a manner similar to the term “comprising.”

[0025] The phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” “in various embodiments”, and the like generally refer to the fact that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present disclosure, but not necessarily all embodiments of thepresent disclosure. Thus, the particular feature, structure, or characteristic may be included in more than one embodiment of the present disclosure such that these phrases do not necessarily refer to the same embodiment.

[0026] As used herein, the terms “example,” “exemplary,” and the like are used to mean “serving as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations, aspects, or designs. Rather, use of the terms “example,” “exemplary,” and the like are intended to present concepts in a concrete fashion.

[0027] If the specification states a component or feature “may,” “can,” “could,” “should,” “would,” “preferably,” “possibly,” “typically,” “optionally,” “for example,” “often,” or “might” (or other such language) be included or have a characteristic, that particular component or feature is not required to be included or to have the characteristic. Such component or feature may be optionally included in some embodiments, or it may be excluded.

[0028] As used herein, the term “computer-readable medium” refers to non-transitory storage hardware, a non-transitory storage device or non-transitory computer system memory that may be accessed by a controller, a microcontroller, a computational system or a module of a computational system to encode thereon computer-executable instructions or software programs. A non-transitory “computer-readable medium” may be accessed by a computational system or a module of a computational system to retrieve and / or execute the computer-executable instructions or software programs encoded on the medium. Examples of non-transitory computer-readable media may include, but are not limited to, one or more types of hardware memory, non-transitory tangible media (for example, one or more magnetic storage disks, one or more optical disks, one or more universal serial bus (USB) flash drives), computer system memory or random-access memory (such as, dynamic random access memory (DRAM), static random access memory (SRAM), extended data out random access memory (EDO RAM)), and the like.

[0029] Additionally, as used herein, the term ‘circuitry’ refers to (a) hardware-only circuit implementations (e.g., implementations in analog circuitry and / or digital circuitry); (b) combinations of circuits and computer program product(s) comprising software and / or firmware instructions stored on one or more computer readable memories that work together to cause an apparatus to perform one or more functions described herein; and (c) circuits, such as, for example, a microprocessor(s) or a portion of a microprocessor(s), thatrequire 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 herein, including in any claims. As a further example, as used herein, the term ‘circuitry’ also includes an implementation comprising one or more processors and / or portion(s) thereof and accompanying software and / or firmware. As another example, the term ‘circuitry’ as used herein also includes, for example, 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, other network device (such as a core network apparatus), field programmable gate array, and / or other computing device.

[0030] Referring now to Figure 1, an example mobile network 100 is illustrated. Mobile network 100 (also referred to as a cellular network) is a type of network where at least the last link is wireless, and provides timing, voice, and / or data services to a plurality of devices. Mobile network 100 may be a Third Generation (3G), a Fourth Generation (4G), and / or a next generation (e.g., Fifth Generation, or 5G) network. Further, the mobile network may be a type of network that has not yet been commercialized, such as a Sixth Generation (6G) network in other embodiments.

[0031] Mobile network 100 is illustrated as providing communication services to UEs 110. UEs 110 may be enabled for voice services, data services, Machine-to-Machine (M2M) or Machine Type Communications (MTC) services, Internet of Things (IoT) services, and / or other services. A UE 110 may be an end user device such as a mobile phone (e.g., smartphone), a tablet or personal data assistant (PDA), a computer with a mobile broadband adapter, and / or the like.

[0032] Mobile network 100 includes one or more radio access networks (RAN 120) that communicate with UEs 110 over a radio interface. RAN 120 of one example embodiment may support Evolved-Universal Mobile Telecommunications Service (UMTS) terrestrial Radio Access network (E-UTRAN) access, Wireless Local Area Network (WLAN) access, fixed access, satellite radio access, new Radio Access Technologies (RAT), and / or the like. As an example, RAN 120 may comprise an E- UTRAN or Next Generation RAN (NG-RAN) that includes one or more base stations 124 that are dispersed over a geographic area. A base station 124 may comprise an entity that uses radio communication technology to communicate with a UE on the licensed spectrum, and interface the UE with a core network 130. Base stations 124 in an E-UTRAN may be referred to as Evolved-NodeBs (eNodeB). Base stations 124 in a NG-RAN may be referred to as gNodeBs (NR base stations) and / or ng-eNodeBs (Long Term Evoluation (LTE) basestations supporting a 5G Core Network). As another example, RAN 120 may comprise a WLAN that includes one or more Wireless Access Points (WAP). A WLAN is a network in which a UE is able to connect to a Local Area Network (LAN) through a wireless (radio) connection. A WAP is a node that uses radio communication technology to communicate with a UE over the unlicensed spectrum and provides the UE access to a core network. One example of a WAP is a Wi-Fi access point that operates on the 2.4 GHz or 5 GHz radio bands. The term “base station” then may refer to an eNodeB, a gNodeB, an ng- eNodeB, a WAP, and / or the like.

[0033] UEs 110 are able to attach to a cell of a RAN 120 to access a core network 130. RAN 120 therefore represents the radio interface between UEs 110 and core network 130. Core network 130 is the central part of mobile network 100 that provides various services to customers who are connected by RAN 120. One example of core network 130 is the Evolved Packet Core (EPC) network as described by the 3GPP for LTE. Another example of core network 130 is a 5G Core (5GC) network as described by the 3GPP. Core network 130 includes network elements 132, which may comprise servers, devices, apparatuses, or equipment (including hardware) that provide services for UEs 110. Network elements 132, in an EPC network, may comprise a Mobility Management Entity (MME), a Service Gateway (S-GW), a Packet Data Network Gateway (P-GW), and / or the like. Network elements 132, in a 5G network, may comprise an Access and Mobility Management Function (AMF), a Session Management Function (SMF), a User Plane Function (UPF), a Policy Control Function (PCF), a Unified Data Management (UDM), and / or the like.

[0034] In a non-terrestrial network (NTN), the base stations 124 are replaced with satellites 224, as illustrated in the mobile network 200 of Figure 2. The satellites of an example NTN 220 are low-Earth Orbit (LEO) satellites and are not geosynchronous, such that satellites are only accessible for a predefined period of time in any particular area. NTNs can employ other types of high altitude platform systems or air-to-ground systems; however, each of these will generally be referred to herein as a satellite. As will be apparent to one of ordinary skill in the art, an embodiment of the present disclosure is not restricted to the type of access point. While access points in the form of stationary towers can maintain a connection session with a stationary UE generally without interruption, the mobile nature of satellites in low-Earth Orbit cause cells of an access point (satellite) to change over time.

[0035] An embodiment described herein relates generally to non-terrestrial networks (NTN). Cells are areas of coverage for a network node, such as a satellite in an NTN.While geostationary satellites are capable of defining a cell fixed to a specific geographic area, satellites in low-Earth Orbit used in mobile network communication cannot permanently fix a cell to a specific geographic area. Instead, the satellites can generate temporary Earth Fixed Cells that exist for a specific geographic area for a predetermined amount of time (e.g., during which the specific geographic area is visible to the satellite). The dynamic nature of these Earth Fixed Cells in NTNs require UE devices to transition between cells to maintain continuous coverage. Technical specifications exist for mobile communications platforms including the 3rd Generation Partnership Project (3GPP) which has established standards in the form of Technical Specifications or “TS” as indicated below. An embodiment described herein expands upon the framework of the 3GPP TS to improve coverage for a UE in an NTN and to improve the efficiency with which a UE changes cells.

[0036] Referring now to Figure 3, an example apparatus 300 is provided. The apparatus 300 may be an embodiment of a UE 110 and / or may be embodied by or otherwise associated with a UE 110, in some instances. Alternatively, the apparatus 300 may be an embodiment of a network element 132 or may be embodied by or otherwise associated with a network element 132.

[0037] The apparatus 300 may include processor 302, memory 304, and network interface 306. The apparatus 300 may be configured to execute the operations described herein. Although these components are described with respect to various functions, it should be understood that the particular implementations necessarily include the use of particular hardware. It should also be understood that certain of these components may include similar or common hardware. For example, two sets of circuitries may both leverage use of the same processor, network interface, storage medium, or the like to perform their associated functions, such that duplicate hardware is not required for each set of circuitries.

[0038] In some embodiments, the processor 302 (and / or co-processor or any other processing circuitry assisting or otherwise associated with the processor) may be in communication with the memory 304 via a bus for passing information among components of the apparatus. The memory 304 is non-transitory and may include, for example, one or more volatile and / or non-volatile memories. In other words, for example, the memory 304 may be an electronic storage device (e.g., a computer-readable storage medium). The memory 304 may be configured to store information, data, content, applications,instructions, or the like for enabling the apparatus to carry out various functions in accordance with an example embodiment disclosed herein.

[0039] The processor 302 may be embodied in a number of different ways and may, for example, include one or more processing devices configured to perform independently. In some non-limiting embodiments, the processor 302 may include one or more processors configured in tandem via a bus to enable independent execution of instructions, pipelining, and / or multithreading. The use of the term “processor” may be understood to include a single core processor, a multi-core processor, multiple processors internal to the apparatus, and / or remote or “cloud” processors.

[0040] In some embodiments, the processor 302 may be configured to execute instructions stored in the memory 304 and / or circuitry otherwise accessible to the processor 302, such as instructions for cell transitions and measuring of neighboring cell metrics as described herein. In some embodiments, the processor 302 may be configured to execute hard-coded functionalities. As such, whether configured by hardware or software methods, or by a combination thereof, the processor 302 may represent an entity (e.g., physically embodied in circuitry) capable of performing operations according to an embodiment disclosed herein while configured accordingly. Alternatively, as another example, when the processor 302 is embodied as an executor of software instructions, the instructions may specifically configure the processor 302 to perform the algorithms and / or operations described herein when the instructions are executed.

[0041] In some embodiments, the apparatus 300 may include input / output circuitry that may, in turn, be in communication with processor 302 to provide output to a user and / or other entity and, in some embodiments, to receive an indication of an input. The input / output circuitry may comprise a user interface and may include a display, and may comprise a web user interface, a mobile application, a query-initiating computing device, a kiosk, or the like. In some embodiments, the input / output circuitry may also include a keyboard, a mouse, a joystick, a touch screen, touch areas, soft keys, a microphone, a speaker, or other input / output mechanisms. The processor and / or user interface circuitry comprising the processor may be configured to control one or more functions of one or more user interface elements through computer program instructions (e.g., software and / or firmware) stored on a memory accessible to the processor (e.g., memory 304, and / or the like).

[0042] The network interface 306 may be any means such as a device or circuitry embodied in either hardware or a combination of hardware and software that is configuredto receive and / or transmit data from / to a network and / or any other device, circuitry, or module in communication with the apparatus 300. In this regard, the network interface 306 may include, for example, a network interface for enabling communications with a wireless communication network. For example, the network interface 306 may include one or more network interface cards, antennae, buses, switches, routers, modems, and supporting hardware and / or software, or any other device suitable for enabling communications via a network. Additionally, or alternatively, the network interface 306 may include the circuitry for interacting with the antenna / antennae to cause transmission of signals via the antenna / antennae or to handle receipt of signals received via the antenna / antennae.

[0043] It is also noted that all or some of the information discussed herein can be based on data that is received, generated and / or maintained by one or more components of apparatus 300. In some embodiments, one or more external systems (such as a remote cloud computing and / or data storage system) may also be leveraged to provide at least some of the functionality discussed herein.

[0044] In NTN, and specifically for the LEO (low-Earth Orbit) scenarios, where the satellite is moving at speeds of up to 7,600 meters per second, a user equipment (UE) device (e.g., a cell phone) can only measure the radio signals transmitted by this satellite for a limited amount of time before the satellite disappears on the horizon or the cell in which the UE is operating is switched away. Because of this issue, there is a process of cell reselection for NTNs. An indication of cell availability to which a UE may switch may be provided by support signaling, indicating the time at which a cell will start (or cease) to cover an area on the Earth. For example, the RRC (Radio Resource Control) parameter t- service-r17 described in 3GPP TS 38.331 and TS 36.331 provides the time instant where the transmission of a cell will be switched off by the satellite. This parameter, also referenced as a t-service, applies to the case of Earth Fixed Cells (EFC), where the satellite steers the satellite beam to temporarily form a cell fixed to Earth. It is expected that an incoming satellite will then resume the coverage for this UE. There exist situations where there is a gap in time between the outgoing and incoming satellite described as discontinuous coverage scenarios.

[0045] Cell selection occurs when a session is initiated, when a cell is going to expire (e.g., in an NTN when the satellite leaves the area), or when a UE is traveling. When a UE that is not camped in a cell or is camped in an unsuitable cell, the UE performs cellselection by camping in a cell that satisfies some criteria. For example, the cell selection criterion “S” is fulfilled when: Srxlev > 0 AND Squal > 0, whereWhere: ^^^^^^is cell selection reception level value in decibels (dB), ^^^^^is cell selection quality value in dB, ^^^^^^^^^^^is the offset temporarily applied as specified in TS 38.331 [3] in dB and ^^^^^^^^^is the minimum required reception level in the cell (dBm). If the UE supports SUL frequency for the current cell, the value of ^^^^^^^^^is obtained from q-RxLevMinSUL if present in System Information Block (SIB) 1, SIB 2 and SIB 4. Additionally, if^^^^^^^^^^^^^^^^^^^^^^is present in SIB 3 and SIB 4 for the concerned cell, this cell specific offset is added to the corresponding^^^^^^^^^to achieve the required minimum reception level in the concerned cell. Otherwise, ^^^^^^^^^is obtained from q-RxLevMin in SIB 1, SIB 2, and SIB 4, and if ^^^^^^^^^^^^^^^^^^^is present in SIB 3 and SIB 4 for the concerned cell, this cell specific offset is added to the corresponding ^^^^^^^^^to achieve the minimum required reception level in the concerned cell. ^^^^^^^^is the minimum required quality level in the cell in dB. Further, ^^^^^^^^^^^^^^^^^^is signaled for the concerned cell with this cell specific offset being added to achieve the required minimum quality level in the concerned cell. ^^^^^^^^^^^^^^^is the offset to the signaled ^^^^^^^^^taken into account in the Rrxlev evaluation as a result of a periodic search for a higher priority PLMN (Public Land Mobile Network) while camped normally in a VPLMN (Visiting Public Land Mobile Network), as specified in TS 23.122. ^^^^^^^^^^^^^^is the offset to signaled ^^^^^^^^taken into account the Squal evaluation as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN, as specified in TS 23.122. ^^^^^^^^^^^^^for FR1, if the UE supports additional Pmax in the NR-NS-PmaxList, if present in SIB 1, SIB 2, and SIB 4:(^^^^^^− ^^^^^^^^^^^, 0) − (min else max(^^^^^^− ^^^^^^^^^^^, 0)(^^) For FR2, ^^^^^^^^^^^^^is set to 0. For IAB-MT, ^^^^^^^^^^^^^is set to 0.^^^^^^, ^^^^^^are maximum transmission power levels of a UE may use when transmitting on the uplink in the cell (dBm) as defined as ^^^^^in TS 38.101. If UE supports SUL frequency for this cell,^^^^^^and^^^^^^are obtained from the p-Max for SUL in SIB 1 and NR-NS-PmaxList for SUL respectively in SIB 1 , SIB 2, and SIB 4 as specified in TS 38.331, else ^^^^^^and ^^^^^^are obtained from the p-Max and NR-NS-PmaxList respectively in SIB 1, SIB 2, and SIB for normal UL as specified in TS 38.331. ^^^^^^^^^^^is the maximum RF output power of the UE (dBm) according to the UE power class defined in TS 38.101-1.

[0046] For Narrowband Internet of Things (NB-IoT) the cell selection criterion is defined in clause 5.2.3.2a of TS 36.304. If the measurements are performed using RSS (Radio Signal Strength), the cell selection criterion “S” in normal coverage is fulfilled when: Srxlev > 0, else, the cell selection criterion S in normal coverage is fulfilled when: Srxlev > 0 AND Squal > 0, where: ^^^^^^ = ^^^^^^^^^^− ^^^^^^^^^^+ ^^^^^^^^^^^^^^^^ − ^^^^^^^^^^^^^− ^^^^^^^^^^^

[0047] If the measurements are performed on the non-anchor carrier and the UE meets the requirements specified in TS 36.133, the cell selection criteria is fulfilled when: Srxlev > 0, else, the cell selection criterion S in normal coverage is fulfilled when: Srxlev > 0 AND Squal > 0, where:^^^^^ = ^^^^^^^^^− ^^^^^^^^− ^^^^^^^^^^^

[0048] A UE that is camped on a cell may perform re-selection to a neighbor cell (intra or inter-frequency) depending on the radio measurements performed. Rules established for the UE to perform cell reselection measurements are defined in 3GPP TS 36.304 and 3GPP TS 38.304. Because cell reselection differs from the cell selection, different criteria is generally used to avoid unnecessary mobility and waste of power by the UE. An example provided below describes the rules for cell measurements for an LTE (Long Term Evolution) device (such as the eMTC (enhanced Machine Type Communication) devices) described in TS 36.304. Similar sets of rules are also specified for different types of UEs in both LTE and NR (New Radio).

[0049] Measurement rules for cell re-selection, and specifically for NB-IoT measurement rules for cell re-selection, are defined in clause 5.2.4.2.a of the 3GPP TS. When evaluating the reception level Srxlev and quality Squal of non-serving cells (e.g., not currently being used by the UE) for reselection purposes, the UE uses parameters provided by the serving cell. There are rules used by the UE to limit the needed measurements of the non-serving cells. If the measurements are performed using RSS, and the serving cell fulfils ^^^^^^ > ^^^^^^^^^^^^^, the UE may choose not to perform intra-frequency measurements. Otherwise, if the serving cell fulfills ^^^^^^ > ^^^^^^^^^^^^^and ^^^^^ > ^^^^^^^^^^^^^, the UE may choose to not perform intra-frequency measurements. Otherwise, the UE will perform intra-frequency measurements.

[0050] The UE will apply the following rules for E-UTRAN (Evolved Universal Mobile Telecommunications Systems (UMTS) Terrestrial Radio Access) inter-frequencies and inter-RAT (Radio Access Technology) frequencies which are indicated in the system information and for which the UE has priority provided as defined in 5.2.4.1 of the 3GPP TS: - For E-UTRAN inter-frequency or inter-RAT frequency with a reselection priority higher than the reselection priority of the current E-UTRA frequency, the UE shall perform measurements of higher priority than E-UTRAN inter-frequency or inter- RAT frequencies according to 36.133 of the 3GPP TS. - For an E-UTRAN inter-frequency with an equal or lower reselection priority than the reselection priority of the current E-UTRA frequency and for inter-RAT frequency with lower reselection priority than the reselection priority of the current E-UTRAN frequency: o If the measurements are performed using RSS and the serving cell fulfills ^^^^^^ > ^^^^^^^^^^^^^, the UE may choose not to perform measurementsof E-UTRAN inter-frequencies or inter-RAT frequency cells of equal or lower priority unless the UE is triggered to measure an E-UTRAN inter- frequency which is configured with the redistributionInterFreqInfo. o Else, if the serving cell fulfills ^^^^^^ > ^^^^^^^^^^^^^and ^^^^^ > ^^^^^^^^^^^^^, the UE may choose not to perform measurements of E- UTRAN inter-frequencies or inter-RAT frequency cells of equal or lower priority unless the UE is triggered to measure an E-UTRAN inter-frequency which is configured with redistributionInterFreqInfo. o Otherwise, the UE shall perform measurements of E-UTRAN inter- frequencies or inter-RAT frequency cells of equal or lower priority according to TS 36.133. - If the UE supports relaxed monitoring and s-SearchDeltaP is present in SystemInformationBlockType3, the UE may further limit the needed measurements, as specified in clause 5.2.4.12. If t-service is present in SystemInformationBlockType3 of the serving cell, the UE shall perform intra-frequency, inter-frequency or inter-RAT measurements, before the time t- service regardless of whether the serving cell fulfils ^^^^^^ > ^^^^^^^^^^^^^and ^^^^^ > ^^^^^^^^^^^^^, or ^^^^^^ > ^^^^^^^^^^^^^^^^and ^^^^^ > ^^^^^^^^^^^^^^^^. The exact time to start measurements before t-service is up to UE implementation. UE shall perform measurements of higher priority frequencies or inter-RAT frequencies regardless of the remaining service time of the serving cell.

[0051] A session of a UE with a cell of an NTN may include a parameter “t-service”. The t-service is the time at which the serving cell availability ends, such as when a satellite has moved too far from the UE that it was serving. In order to maintain continuous service, the UE needs to identify a new available neighbor cell, and transition to the new cell before t-service is reached. Otherwise, service is lost to the UE, at least temporarily. This transition to a neighboring cell is performed through reselection of a new serving cell. To identify an appropriate neighbor cell, the UE measures the parameters of available cells. The UE should start measurements before t-service regardless of other measurement rules. This is to avoid the problem of the UE failing to receive serving cell signals before triggering the neighbor cell reselection that will lead to a cell reselection.

[0052] During cell reselection, the UE ranks the neighbor cell measurements and chooses the best cell. The ranking procedure is described in TS 36.304 and TS 38.304.Mobility measurement requirements apply provided that the UE is provided with valid assistance information (e.g., satellite ephemeris and common delay parameters) for the target cells to be measured.

[0053] During the cell reselection, in NTN, there may be an inefficient use of energy by the UE in RRC idle when the network is configured with an indication of serving cell availability, for example, in the form of t-service, indicating an end of the availability of the serving cell. The cause for this inefficiency is that the measurements collected for the serving cell close to t-service, may not be very useful, as they will become obsolete once t- service is reached and the cell ceases to cover the area in which the UE is located. This inefficiency is even greater when measurement relaxation is implemented, where measurement of neighboring cells is less frequent. The measurement relaxation procedure indicates that if a UE can fulfil certain criterion in the past measurements (e.g., the UE is not in cell edge), the UE can relax its measurements: the UE may stop measuring neighbor cells, and may increase spacing between consecutive measurements on the serving cell. This process is illustrated in Figure 4, where service cell measurements are conducted at a relatively frequent rate shown by the measurements 320 until a measurement relaxation condition is met. Thereafter, the measurements 330 of the service cell are slowed. This process is used to reduce power consumption. However, in the case of a NTN, there exists a t-service time as shown where the cell will cease to be available. As such, in the illustrated example, because the UE has met the conditions for measurement relaxations, the number of collected measurements before t-service is reduced.

[0054] In performing less frequent measurements of the service cell shortly before t- service, the UE may suffer drawbacks. The UE may take too long to trigger measurements of neighbor cells, as the condition of the serving cell (S-criterion) is less often assessed due to the measurement relaxation. The UE may not have up-to-date values of the serving cell to compare with neighboring cells which may postpone the cell reselection, which is not always desirable when the UE is close to the t-service time. Further, in New Radio (NR) and NB-IoT for NTN, the total time to measure a neighbor cell is scaled by the number of different NGSO (Non-Geosynchronous Orbit, e.g., LEO) satellites the UE has to measure. For example, if the UE has to measure the serving cell and neighbor cell satellite, assuming the UE is not capable of measuring two cells (of different satellites) at the same time, the interval between neighbor cell measurements will be twice as long. Thus, the time to detect and evaluate neighbor cells increases.

[0055] The above described drawbacks incur the same problem: waking up the UE more often for collecting serving cell measurements that may be unnecessary. Regardless of whether the measurements of the serving cell before t-service are good or bad, the UE knows (by the configuration of t-service) that the serving cell will soon disappear (at t- service). If the measurements are good, they will not trigger any additional procedure by the UE, and energy will be spent on the process. If the measurements are not good, there might not be enough time for the UE to react and re-select to a suitable neighbor cell before t-service. The last effort to collect additional serving cell measurements becomes then unnecessary because the measurements are soon outdated and will not change the UE procedure in a meaningful way. Because cell reselections are anticipated to be frequent in NB-IoT in LEO scenarios, and because in terrestrial operation the energy consumption of IoT devices is a key issue, an example embodiment provides for efficiency improvements through energy optimization for idle mode measurements in non-terrestrial networks.

[0056] The issue described above may also happen for other scenarios, such as in an instance in which the indication of cell availability is other than t-service. For example, in the case of Earth-moving cells, the indication might be such that the UE can estimate a point in time where the UE will be found out-of-coverage of the current serving cell.

[0057] An embodiment provided herein includes an energy efficient trigger for cell selection and re-selection evaluation, when t-service is configured for an NTN UE. An embodiment defines a point in time “T” before the time t-service such that the UE can already use the cell selection evaluation procedure to move to any identified suitable neighbor after the time T, ahead of time t-service. The reselection evaluation procedure can possibly be bypassed in this case because the UE treats this mobility as initial cell selection such that there is no comparison with the serving cell radio conditions. The time T can, in some embodiments, coincide with t-service. Requirements for the UE measurements of the current serving cell and / or any other cell associated with the same satellite as the serving cell would not apply after time T. The scaling factor of the UE measurements for the requirement of measurements for cells belonging to other satellites is updated after time T to reflect that the UE is not required to measure the serving cell’s satellite. For example, the UE may be configured to measure target cells of two satellites, different from the satellite of the serving cell, instead of one satellite in addition to the satellite of the serving cell. In an example embodiment, the determination as to whether to use cell selection or cell reselection depends at least partly upon whether the UE is in measurement relaxationmode. In this regard, the reliance upon cell selection, as opposed to cell reselection, may be supported in the measurement relaxation mode.

[0058] In accordance with an embodiment described herein, the UE is advantageously permitted to relax or omit serving cell measurements shortly before t-service to save energy. Further, by omitting serving cell measurements, the UE may be enabled to measure, detect, and evaluate more target cells before the time t-service to improve the mobility performance.

[0059] An embodiment described herein is directed to a UE device connected to (camping on) an NTN cell, where the UE receives: satellite assistance information for the serving cell and for the neighbor cells, and an indicator of coverage availability of the serving cell (e.g., t-service). The UE determines a point in time T where the measurements and mobility procedures are changed (relative to the measurements and mobility procedures during the time period in the serving cell before time T) for the serving cell and / or neighbor cells associated with the same serving cell. The determination of the point in time T may be provided by specifications or by network broadcast. The time T can be an absolute point in time or defined based on a duration of the DRX (Discontinuous Reception) cycle or eDRX (Extended Discontinuous Reception cycle) at the UE, such as by setting the time T equal to the time remaining in the DRX or eDRX cycle. In this regard, the time T may be defined as corresponding to the duration of one or more DRX / eDRX cycles, e.g., a predefined number of DRX / eDRX cycles, prior to the t-service. Time T can also or alternatively be defined based on UE requirements for cell reselection, such as a maximum time for detect and reselect / select a new cell. The time T can be defined based on an indication of availability of the neighbor / Target cells.

[0060] The changes to mobility procedures may concern the evaluation of individual cells. After the time T, the UE may choose or may be required to use a cell selection procedure to camp in a suitable neighbor cell instead of the reselection evaluation and procedures. This use of cell selection instead of cell reselection improves the efficiency of the UE in selecting a new cell, and reduces the likelihood of discontinuous service without having a new cell by the time t-service is reached.

[0061] Figure 5 illustrates an example embodiment in which UE measurements for a neighbor cell belonging to a different satellite and UE measurements for the same satellite are provided in the illustration. Measurements 410 are serving cell measurements (represented by the lighter blocks), whereas measurements 420 are neighbor cell measurements (represented by the darker blocks), and line 430 is the minimum thresholdfor a satisfactory cell. Although measurements of different parameters may be obtained, the measurements of an example embodiment are the measurements of the power of the signals received by the UE. As shown in Figure 5, the measurements for both cells are above the threshold for cell selection. However, according to existing methods, as the serving cell has higher measurements than the neighbor cell, the UE will not perform any cell reselection before time t-service. The UE will only move to the neighbor cell after the serving cell fails to reach the S-criterion, which happens after t-service in the example embodiment of Figure 5. Thus, the UE may need to wait until after t-service to reselect the neighbor cell. This process might take too long if the UE is currently under measurement relaxation, which can result in discontinuous service for the UE.

[0062] According to the method depicted in Figure 5, the determination of whether to use the cell selection procedure or the cell reselection procedure depends on whether the UE is in measurement relaxation mode. The changes to mobility procedures above may concern allowing the UE to skip any measurements to the serving cell in order to save UE energy consumption. After the measurement relaxation condition is satisfied at time T, only neighbor cells may be used with cell selection, rather than cell reselection, thus making the UE mobility more efficient and potentially faster because the UE does not spend time on measurements of the currently serving cell, but instead only obtains measurements of the neighbor cell. Figure 6 illustrates an example embodiment in which the UE skips serving cell measurements for the time interval between time T and time t- service. Measurements 510 reflect measurements of the currently serving cell (represented by the lighter blocks), whereas measurements 520 reflect measurements of a neighboring cell (represented by the darker blocks), and line 530 represents the minimum acceptable threshold for a cell.

[0063] In a further embodiment, if the UE determines t-service of a neighbor cell associated with the same satellite because the currently serving cell is occurring in at least a network-configured threshold X-seconds later than t-service of the serving cell, the UE is not allowed to skip the measurements of that neighbor cell. This may also be conditioned on how close the UE is to the neighbor cell in physical distance, which is known based on broadcast of the cell reference location plus a radius and the UE’s GNSS (Global Navigation Satellite System).

[0064] An embodiment provided herein provides time requirements for the UE to measure, detect, and evaluate a neighbor cell, and improve upon existing methods by removing the current serving satellite from the list of satellites the UE is required tomeasure during cell reselection. The UE can enter the cell selection mode bypassing the cell reselection evaluation procedure after reaching t-service to identify a new serving cell as quickly as possible. Although an embodiment described herein can be implemented in IDLE mode mobility, an embodiment can similarly be used in radio resource control (RRC) connected modes. An embodiment is equally applicable to IoT over NTN and to NR over NTN.

[0065] Any of the embodiments above may be applicable for a scenario in which t- service is replaced by another indication of cell availability. For example, in earth-moving cells scenarios, the indication may be such that the UE is capable of estimating the point in time where the UE will be out-of-coverage for the current serving cell. Thus, reference to t-service is provided by way of an example, but not of limitation.

[0066] Figure 7 illustrates a flowchart of an example embodiment for improving energy efficiency for measurements in non-terrestrial networks. The apparatus 300 configured to implement the illustrated process includes means, such as the processor 302 or the like, for identifying a first time, e.g., an end time, at which a current serving cell of a non-terrestrial network will cease to be available at block 710. The non-terrestrial network may include, for example, a network facilitated by a low-Earth orbit non geosynchronous satellite, where the end time is when the currently serving cell ceases to be available for a user equipment device using the currently serving cell. The non-terrestrial serving cell is served by a first satellite. The apparatus 300 configured to implement the process of Figure 7 also includes means, such as the processor 302 of the like, for determining, based on the first time, a second time, e.g., time T, earlier than the first time. See block 720. In an example embodiment, the determination of the second time is dependent on the apparatus being configured with a relaxed measurement requirement.

[0067] In an example embodiment and as depicted in block 730, the apparatus 300 also includes means, such as the processor 302, the network interface 306 or the like, for updating at least one timing requirement to detect or measure or evaluate at least one cell belonging to at least one second satellite, other than the first satellite. In this embodiment, the apparatus 300 may include means, such as the processor 302, the memory 304 or the like, for removing the first satellite from a listing of one or more satellites for which a reference signal strength is to be measured. As a result, the apparatus 300 of this example embodiment may evaluate one or more cells belonging to one or more other satellites, different than the first satellite that supports the current serving cell, such as by determining the reference signal strength of the one or more cells more quickly andefficiently. In this regard, the apparatus 300 of an example embodiment includes means, such as the processor 302, the network interface 306 or the like, for measuring, after the second time, a reference signal strength of at least one neighboring cell, such as a cell belonging to a different satellite. See block 740.

[0068] The apparatus 300 further includes means, such as the processor 302, the network interface 306 or the like, for selecting a new cell is selected based on the reference signal strength of the at least one neighboring cell independently of a reference signal strength of the serving cell, as shown at block 750. By selecting the new cell independent of the reference signal strength of the serving cell, the reference signal strength of the serving cell need not be measured since the serving cell will soon be unavailable. Thus, the selection of the new cell may be performed more efficiently and, in some instance, more quickly.

[0069] As described above, Figure 7 illustrates a flowchart depicting operations according to an example embodiment of the present disclosure. It will be understood that each block of the flowchart and combination of blocks in the flowchart may be implemented by various means, such as hardware, firmware, processor, circuitry, and / or other communication devices associated with execution of software including one or more computer program instructions. For example, one or more of the procedures or operations described above may be embodied by computer program instructions. In this regard, the computer program instructions which embody the procedures or operations described above may be stored by a memory 304 of an apparatus (e.g., apparatus 300, UE 110) employing an embodiment of the present invention and executed by a processor 302. As will be appreciated, any such computer program instructions may be loaded onto a computer or other programmable apparatus (for example, hardware) to produce a machine, such that the resulting computer or other programmable apparatus implements the functions specified in the flowchart blocks. These computer program instructions may also be stored in a computer-readable memory that may direct a computer or other programmable apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture the execution of which implements the function specified in the flowchart blocks. The computer program instructions may also be loaded onto a computer or other programmable apparatus to cause a series of operations to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on thecomputer or other programmable apparatus provide operations for implementing the functions specified in the flowchart blocks.

[0070] Accordingly, blocks of the flowcharts support combinations of means for performing the specified functions and combinations of operations for performing the specified functions for performing the specified functions. It will also be understood that one or more blocks of the flowcharts, and combinations of blocks in the flowcharts, can be implemented by special purpose hardware-based computer systems which perform the specified functions, or combinations of special purpose hardware and computer instructions.

[0071] Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

[0072] Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and / or functions, it should be appreciated that different combinations of elements and / or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and / or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

THAT WHICH IS CLAIMED:

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 program code configured to, with the at least one processor, cause the apparatus at least to: identify a first time at which a non-terrestrial network serving cell will cease to be available; determine, based on the first time, a second time earlier than the first time; after the second time, measure a reference signal strength of at least one neighboring cell; and select a new cell based on the reference signal strength of the at least one neighboring cell independently of a reference signal strength of the serving cell.

2. The apparatus of claim 1, wherein the second time is determined based, at least in part, on an indication of availability of the at least one neighboring cell.

3. The apparatus of claim 1, wherein the second time is determined based, at least in part, on a predefined time before the first time.

4. The apparatus of claim 1, wherein the second time is determined based, at least in part, on a maximum time for detection and selection of a new cell.

5. The apparatus of claim 1, wherein the second time is determined based, at least in part, on a duration of a Discontinuous Reception cycle.

6. The apparatus of claim 1, wherein the serving cell comprises an Earth-fixed cell of the non-terrestrial network, and wherein the first time is the time at which the serving cell ceases to be available from a satellite of the non-terrestrial network.

7. The apparatus of claim 1, wherein determination of the second time is dependent on the apparatus being configured with a relaxed measurement requirement.

8. A method comprising: identifying a first time at which a non-terrestrial network serving cell will cease to be available; determining, based on the first time, a second time earlier than the first time; after the second time, measuring a reference signal strength of at least one neighboring cell; and selecting a new cell based on the reference signal strength of the at least one neighboring cell independently of a reference signal strength of the serving cell.

9. The method of claim 8, wherein the second time is determined based, at least in part, on an indication of availability of the at least one neighboring cell.

10. The method of claim 8, wherein the second time is determined based, at least in part, on a predefined time before the first time.

11. The method of claim 8, wherein the second time is determined based, at least in part, on a maximum time for detection and selection of a new cell.

12. The method of claim 8, wherein the second time is determined based, at least in part, on a duration of a Discontinuous Reception cycle.

13. The method of claim 8, wherein the serving cell comprises an Earth-fixed cell of the non-terrestrial network, and wherein the first time is the time at which the serving cell ceases to be available from a satellite of the non-terrestrial network.

14. The method of claim 13, wherein determining the second time is dependent on being configured with a relaxed measurement requirement.

15. An apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:identify a first time at which a non-terrestrial network serving cell will cease to be available, the non-terrestrial serving cell being served by a first satellite; determine, based on the first time, a second time earlier than the first time; and after the second time, update at least one timing requirement to detect or measure or evaluate at least one cell belonging to at least one second satellite, other than the first satellite.

16. The apparatus of claim 15, wherein the apparatus is also caused to remove the first satellite from a listing of one or more satellites for which a reference signal strength is to be measured.

17. The apparatus of claim 15, wherein the apparatus is also caused to select a new cell based on a reference signal strength of a neighboring cell belong to the at least one second satellite.

18. The apparatus of claim 15, wherein the second time is determined based, at least in part, on an indication of availability of the at least one neighboring cell.

19. The apparatus of claim 15, wherein the second time is determined based, at least in part, on a predefined time before the first time.

20. The apparatus of claim 15, wherein the second time is determined based, at least in part, on a maximum time for detection and selection of a new cell.

21. The apparatus of claim 15, wherein determination of the second time is dependent on the apparatus being configured with a relaxed measurement requirement.

22. A method comprising: identifying a first time at which a non-terrestrial network serving cell will cease to be available, the non-terrestrial serving cell being served by a first satellite; determining, based on the first time, a second time earlier than the first time; and after the second time, updating at least one timing requirement to detect or measure or evaluate at least one cell belonging to at least one second satellite, other than the first satellite.

23. The method of claim 22 further comprising removing the first satellite from a listing of one or more satellites for which a reference signal strength is to be measured.

24. The method of claim 22, further comprising selecting a new cell based on a reference signal strength of a neighboring cell belong to the at least one second satellite.

25. The method of claim 22, wherein determining the second time is dependent on being configured with a relaxed measurement requirement.

Images