Idle/inactive mobility and reachability in moving networks

A wireless transmit/receive unit (WTRU) may identify a plurality of candidate satellite constellations. The WTRU may determine an elevation angle and/or an orbit associated with each of the plurality of candidate satellite constellations. The WTRU may select a satellite constellation from the plurality of candidate constellations for sell selection. The WTRU may identify a plurality of candidate beams associated with the selected satellite constellation. The WTRU may determine an RSRP/RSRQ for each of the plurality of candidate beams. The WTRU may determine a weighted ranking of the plurality of candidate beams. The WTRU may determine the weighted ranking using the determined RSRP/RSRQ, prevailing load intensities, elevation angle, dwelling duration, link switch probability, and/or a quality of service (QoS). The WTRU may select a beam from the plurality of candidate beams for cell selection. The WTRU may select the beam based on the weighted ranking.

BACKGROUND

Satellites may occupy one of several orbital classes. In the low earth orbit (LEO) class, satellites may be at altitude 400-2000 kilometers with the common altitude being 700 kilometers. In the medium earth orbit (MEO) class, satellites may be at an altitude of 2000-32000 kilometers with the common altitude being 20000 kilometers. In the geo-synchronous (GSO) or geo-stationary orbit (GEO), satellites may be quasi-fixed at approximately 36000 kilometers. With higher altitudes, propagation delay and power budgets may be issues, while with lower altitudes, Doppler and mobility may be issues. With lower orbits, satellites experience atmospheric drag and per Kepler's laws of planetary motion. The lower orbital altitude may be associated with higher angular velocity of the satellite.

SUMMARY

A wireless transmit/receive unit (WTRU) may identify a plurality of candidate satellite constellations. The WTRU may receive system information. The system information may indicate constellation assistance information. The constellation assistance information may include satellite ephemeris data and/or group common timing offset(s). The plurality of candidate satellite constellations may be identified using the constellation assistance information. The plurality of candidate satellite constellations may be identified using one or more previous measurements and/or previously received system information. The plurality of satellite constellations may include one or more of a low earth orbit (LEO) satellite, a medium earth orbit (MEO) satellite, or a geo-stationary orbit (GEO) satellite. The WTRU may determine an elevation angle and/or an orbit associated with each of the plurality of candidate satellite constellations. The elevation angle may be an average elevation angle for the satellites in a respective constellation. The WTRU may select a satellite constellation from the plurality of candidate constellations for sell selection. The satellite constellation may be selected based on one or more of the determined elevation angles, received signal received power (RSRP)/received signal receive quality (RSRQ) measurements associate with the plurality of satellite constellations, and/or a link budget associated with the WTRU. When multiple candidate satellite constellations have suitable RSRP/RSRQ, the selected satellite constellation may have a smaller average elevation angle than the other candidate satellite constellations in the plurality of satellite constellations.

The WTRU may identify a plurality of candidate beams associated with the selected satellite constellation. The WTRU may determine an RSRP/RSRQ for each of the plurality of candidate beams. The WTRU may determine a weighted ranking of the plurality of candidate beams. The WTRU may determine the weighted ranking using one or more of the determine RSRP/RSRQ, a candidate beam elevation angle prevailing load intensities of the candidate beams, a dwelling duration, a link switch probability, or a quality of service (QoS) parameter associated with the uplink data. The QoS parameter may include a minimum propagation delay for the uplink data. The weighted ranking may prioritize dwelling duration of the plurality of candidate beams. The WTRU may select a beam from the plurality of candidate beams for cell selection. The WTRU may select the beam based on the weighted ranking. The WTRU may determine that the WTRU is within a satellite footprint edge prior to identifying the plurality of candidate satellite constellations. The plurality of candidate beams may be associated with a beam edge. The selected beam may have a maximum weighted ranking of the plurality of candidate beams associated with the beam edge.

DETAILED DESCRIPTION

Although the transmit/receive element122is depicted inFIG.1Bas a single element, the WTRU102may include any number of transmit/receive elements122. More specifically, the WTRU102may employ M IMO technology. Thus, in one embodiment, the WTRU102may include two or more transmit/receive elements122(e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface116.

Satellite systems play an invaluable part in enabling communications in places where the last mile fiber cable or terrestrial mobile telephony is unviable. Satellite services may be supplementary to terrestrial cellular and land-based communication systems. Satellite services may facilitate broadcast applications such as television and provided emergency, essential services to offshore oil-rigs and shipping industries. Satellites may provide true broadband connectivity to terrestrial users complementing land-based mobile and fixed wireless systems. The volume of users utilizing satellite-based services may include those who can afford or to those who have no other alternatives. For satellites to become a pervasive and viable technology, the volume of users that can be supported may increase, and unicast services in addition to existing broadcast services may become more prevalent. With an increase in user count, the volume of data serviceable may increase.

To dimension systems with good and acceptable link budgets, commercial communications satellites may be LEO or MEO in the medium term and on very high frequencies. With very high velocity satellites, the Doppler may be very high and this poses issues with synchronization and time for fix. Satellite link budgets are built with high link margins to overcome rain and other atmospheric aberrations that may arise during a communication. The Signal-to-Interference Ratio (SINR) experienced on the downlink and uplink may be low. The highest modulation-coding schemes employed in satellite links may be several orders lower than what is comparable in terrestrial systems. Long propagation delays involving satellite links may be several orders larger than observed in a terrestrial system. Long propagation delays may pose issues enforcing efficient power control loops. This may cause the satellite terminals and ground stations to perform with incorrectly set operating points.

A WTRU may apply maximum weighted cell selection based on link elevation angle and/or penalty factor to apply for using an edge link, dwelling duration, link switch probability, and/or propagation delay for a given service. A WTRU may be configured for terrestrial zone-based paging based on geo-fence's boundaries that are scaled down (e.g., decreased) or scaled up (e.g., increased) as a function of relative velocity between the WTRU and the satellite.

FIG.2shows an example scenario200where a WTRU is covered by multiple orbital classes of satellite. For example, the WTRU may be covered by a Geostationary (GEO) satellite, a Medium Earth Orbit (MEO) satellite, and/or a Low Earth Orbit (LEO) satellite. Each of the satellites may be associated with a propagation delay and/or a link budget. For example, the GEO satellite may be associated with a first propagation delay, tGand a first link budget, LG. The MEO satellite may be associated with a second propagation delay, tMand a second link budget, LM. The LEO satellite may be associated with a third propagation delay, tLand a third link budget, LL. The WTRU may select the GEO satellite, the MEO satellite, or the LEO satellite based on the propagation delays and/or the link budgets associated with each satellite. Satellite classes (e.g., LEO, MEO, GEO, etc.) may also be referred to as satellite type(s).

Satellite links, though reliable, may suffer from high latencies. Services that use TCP as the transport layer may be especially susceptible to latency and performance degrades.

Cell selection may be performed. A WTRU may scan a list of carriers by measuring the reference signal strength indicator (RSSI) of a carrier (e.g., each carrier) over pre-determined system bandwidths. The measured RSSI on a carrier may include the signal strength of any desired cells operating on the carrier, interfering cells on the carrier, as well as noise. The WTRU may subsequently filter out and discount carriers whose RSSI is lower than a predefined threshold. The surviving list of carriers may be used for determining presence of candidate cells.

The WTRU may attempt to identify cell identification blocks on each surviving carrier until the WTRU find a cell to camp. Cell identification procedure may include detecting the primary synchronization signal (PSS) and secondary synchronization signal (SSS). Detecting the PSS and SSS may allow the WTRU to determine the cell's frame and subframe boundaries in addition to ascertaining the physical cell identity (PCI). Knowing a PCI, the position of the pilot symbols (e.g., reference signals in LTE) may be unambiguously known, allowing the WTRU to determine pilot power (e.g., reference signal received power, RSRP) and reference signal received quality (RSRQ) of the candidate target cells.

If there are several such candidate cells for selection, the WTRU may rank the candidates in descending order of RSRP and acquires system information blocks starting with the highest ranked candidate. A parameter QRXLEVMINbroadcast in the candidate cell's system information may mandate the minimum required RSRP and/or RSRQ for the WTRU to consider the cell viable, e.g., the current, (RXLEV>QRXLEVMIN). The system information acquired from the candidate cell may indicate whether the cell is allowed for camping. e.g., not access barred, cell barred or reserved for operator use. If the current highest ranked candidate is barred or reserved or if QRXLEVMINis not met, the WTRU may move on to the next highest ranked candidate in the list, acquire system information and repeat the procedure as necessary. When a candidate cell passes acceptance criteria, the WTRU may perform via the candidate cell a non-access stratum (NAS) procedure to ATTACH and/or NAS: TRACKING AREA UPDATE with the core network.

Cell selection may refer to a beam pair selection, e.g., in addition to or in lieu of, the process of cell selection. Selection of a beam may correspond to selection of a reference signal or reference signal configuration associated with the beam. Maximum array gain may be obtained in NR when TX and RX beams are perfectly aligned. In a system with narrow beams, misalignments between TX and RX beams may result in a substantial loss in the received power. Hence, in NR, a serving cell may be found by time division beam switching in which transmit beams of candidate cells and receive beams of WTRUs may be swept to measure SNRs of potential links. Time division beam switching may be employed to find the serving cell with the best beam pair in the cell selection and handover stages.

In time division beam switching, individual TX beams may be transmitted from the base station until the TX beams (e.g., all TX beams) are transmitted. At the WTRU, RX beam sweep may be performed for the TX beams to measure the SNR for the TX-RX beam pairs. The measurement of possible TX-RX beam pairs may be performed for candidate cells to select a serving base station with the best beam pair. The WTRU may first maintain in descending order, the list of TX-RX beams with highest SNR and the associated cells. A physical cell ID (PCI) of the serving cell may obtained in NR by detecting the PSS and SSS transmitted from the serving cell. For cell selection, the beam pair with maximum SNR may be tentatively selected and the corresponding cell with the physical cell ID as the serving cell. The tentatively selected cell plus beam pair may or may not be optimal for hybrid beamforming, as the effects of the multipath channel may not be considered in the selection stage. The system information from this selected cell may be acquired to determine if QRXLEVMINis met and if the cell is allowed for access, for example, not cell barred or reserved for operator use. When a NR candidate cell passes acceptance criteria, the WTRU may perform via the candidate cell a non-access stratum (NAS) procedure to NAS: ATTACH and/or NAS: RADIO NETWORK AREA UPDATE (RNA UPDATE) with the core network.

The selected cell for camping may be referred to as the serving cell.

The cell reselection may be performed, e.g., similar to cell selection. Once a cell is initially selected (e.g., cell selection), a neighbor cell may not be monitored constantly, when the WTRU is stationary and experiences adequate signal strength and quality from the serving cell. The serving cell may broadcast in system information parameters controlling whether to perform measurements on neighboring cells. The neighboring cells may be intra-frequency, inter-frequency or inter-Radio access technology (RAT) neighbors. To measure inter-frequency and inter-RAT neighbors, the WTRU may tune to a different frequency to perform measurements and tune back to serving frequency when complete.

The process of measuring neighbors that are not co-channel (same frequency as currently camped on frequency) may be an expensive option. The network may configure a WTRU to monitor intra-frequency neighbors and inter-frequency/inter-RAT neighbors differently. A parameter SIntraSearchmay indicate when the WTRU is to perform measurements on intra frequency (co-channel) neighboring cells whereas, a parameter ≤SNonIntraSearchmay indicate when the WTRU is to perform measurements on inter-frequency and/or inter-RAT neighboring cells. On a condition that the current measured serving cell power (RSRP) and/or quality (RSRQ) are SIntraSearchor SNonIntraSearch, the WTRU may commence measurements on co-channel neighbors or inter-frequency/inter-RAT neighbors respectively. The measurements may include received signal power (RSRP) or received signal quality (RSRQ). Parameter SIntraSearchmay be specified as SIntraSearchPand SIntraSearchQand similarly, SNonIntraSearchmay be specified as SNonIntraSearchPand SNonIntraSearchQ. These parameters may be broadcast by the serving cell in system information.

In NTN, cell reselection may be performed based on predictable path profiles of satellite spotbeams and/or uneven loading of spotbeams within a NTN's footprint.

One or more cells are grouped into a “tracking area,” and the tracking area may be assigned a tracking area code (TAC). In NR, one or more cells may be grouped into a “radio network area,” and the radio network may be assigned a radio network area code (RNA Code). A cell may be associated with one (e.g., and only one) TAC or RNA code. Cells in LTE and NR may broadcast in system information their TAC and RNA Code respectively. A WTRU registering with the core network via a LTE or NR cell may indicate to the core network the TAC or RNA code of the access cell.

The core network may store in the WTRU's context the TAC or RNA code through which the WTRU was last tracked and monitored. When a WTRU reselects a cell, and if the TAC or RNA code of the cell is different from the TAC or RNA code of the immediately previously camped cell, it may notify the new TAC or RNA code to the network. The network may determine the position of the WTRU within the accuracy of a TAC or RNA code and may restrict the PAGING message to cells sharing the TAC or RNA code when the WTRU needs to be reached in IDLE mode. For better accuracy of tracking at a cell level, a network may assign different TAC/RNA Code to immediately neighboring cells, so that the WTRU may notice a TAC/RNA Code change and may perform a NAS: TA UPDATE and/or NAS: RNA UPDATE procedure upon a change of cell. The network may group many cells into one TAC or RNA code. A WTRU reselecting from one cell from another cell may witness the same TAC/RNA Code being broadcast on their respective system information and may skip performing the NAS: TA UPDATE or NAS: RNA UPDATE procedure. In an example, a WTRU may be unknown to the network at a cell level, rather, may be known within the accuracy of a group of cells. The core network may page for the WTRU in the group of cells sharing the TAC/RNA Code.

The WTRUs may be tracked at the core network, while achieving a compromise between PAGING load on downlink and TA UPDATE/RNA UPDATE on the uplink. In NTN, the spotbeams may constantly move with respect to a position on earth. A spotbeam, synonymous with cells in NR and LTE, may be identified by a TAC or RNA code. The WTRU on ground, though perfectly stationary, may observe the spotbeams constantly moving overhead and coincidentally, the TAC or RNA code changing constantly.

FIG.3shows an example satellite constellation300. As shown, there may be 3 orbits in this example constellation300, with each orbit shaded differently. Several satellites may make up the constellation, and an orbit may be associated with a certain number of satellites. The direction of movement, the velocity and position in space of the satellite with respect to a specific position on earth, the number of satellites in a specific orbit belonging to a constellation may be preconfigured and/or determined.

There may be minor fluctuations in the earth's gravity and external influences that act on a satellite forcing minute variations to operating parameters of the satellite. In a specific orbit with respect to a specific position on earth, the satellite SATjthat preceded a currently serving satellite SATiand the satellite SATkthat will succeed subsequently may be determined. FromFIG.3, multiple satellites may serve an orbit and the direction of movement of those satellites within the constellation. The footprint of the satellite may include the total surface area covered by the various transmitters at the satellite.

As shown inFIG.3, a hexagonal shape may be approximated to show the footprint of the respective satellite immediately above. Though the footprints are shown to conform to perfect hexagon shapes, this may not be strictly possible, and there may be some bleeding of coverage from nearby satellites into one satellite's footprint. A satellite's footprint may be split into multiple spotbeams. As shown, an example satellite SAT #1 may be at the top of the 1storbit with multiple spotbeams within its footprint. The spotbeams can be evenly or unevenly sized and shaped within a footprint. A WTRU over a specific point on earth can be classified as, but not limited to, 1) in spotbeam center, 2) in spotbeam edge, 3) in footprint center, and/or 4) footprint edge. The WTRUs at spotbeam edge may reselect a spotbeam. The WTRUs at footprint edge may reselect a satellite. The WTRUs at the constellation edge or service edge may reselect a different constellation. The Constellation #X may include two orbits, and a WTRU at the edge of Constellation #X may be serviced by satellites in Constellation #Q. A WTRU with respect to a constellation ‘recedes’ opposite to the direction of satellite's movement as shown by the differently shaped arrow heads inFIG.4.

FIG.4depicts an example scenario400where multiple satellites in different constellations are near a WTRU. As shown inFIG.4, satellites in different constellations may have different orientations and direction of movement. For example, the footprint of satellites in Constellation #X inFIG.4may be much smaller than the footprint of a satellite in Constellation #Q. For example, satellites in Constellation #Q may have higher orbital altitudes compared with satellites in Constellation #X. For example, satellites in the constellations may have differing elevation angles. A geography may be served by one or more constellations, and the services provided by the constellations may differ. For example, Constellation #Q may only provide voice and other premium, low data-rate services, whereas Constellation #X may provide traditional, low tariffed broadband services. The link budget associated with Constellation #Q may be several orders higher than the link budget associated with connections with Constellation #X. A WTRU may preferentially choose a constellation based on service need, available link budgets and/or additional link constraints indicated in system information from a satellite.

In an example, a satellite can provide service to a qualified WTRU in its footprint if the elevation angle between the WTRU and the satellite is θminor larger. Parameter θminmay be broadcast in system information by the satellite, and the WTRU may read this parameter as part of cell selection and/or reselection. The WTRU may determine a possible list of satellites across one or more constellations that are visible in the horizon, may receive minimum elevation angle indications (e.g., parameter θmin,i) from system information from the respective satellites, where i refers to the satellite. If the measured elevation angle εito satellite i is less than θmin,i, the satellite may be removed from the list.

FIG.5Ashows example constellations502,504with different elevation angles (e.g., average elevation angles) from a WTRU510. The WTRU510may identify a plurality of constellations (e.g., such as constellations502,504). Each of the plurality of constellations may be associated with a corresponding orbit. The WTRU510may determine an orbit associated with each of the plurality of constellations. The orbit may define a path that satellites in the constellation follow. An elevation angle may be measured between a WTRU (e.g., such as WTRU510) and the orbit. The elevation angle may be an average elevation angle of two or more satellites within a respective constellation. An average elevation angle may be an average of the elevations angles of satellites within a constellation. For example, the elevation angle may be measured from a line perpendicular to the earth at the WTRU to a line between a satellite in the constellation. The WTRU510may determine the elevation angle associated with each of the plurality of constellations. A first constellation of the plurality of constellations (e.g., constellation502) may be associated with a first orbit (e.g., orbit A). Stated differently, the satellites in the first constellation may move along a path defined by the first orbit. The constellation502may be at a first elevation angle, OA, from the WTRU510. For example, the satellites of constellation502may have an average elevation angle of OA with respect to WTRU510. A second constellation of the plurality of constellations (e.g., constellation504) may be associated with a second orbit (e.g., orbit B). Stated differently, the satellites in the second constellation may move along a path defined by the second orbit. The constellation504may be at a second elevation angle, OB, from the WTRU510. For example, the satellites of constellation504may have an average elevation angle of OB with respect to WTRU510. The WTRU510may be at an orbit edge (e.g., an edge of one or more of constellation502or constellation504). When the WTRU510is at the orbit edge, the WTRU510may have visibility to two or more satellites (e.g., from multiple constellations).

The WTRU510may determine whether each of the plurality of constellations are viable. A constellation may be viable if the constellation is a candidate for selection. If more than one constellation is viable, the WTRU510may select between the viable constellations. The WTRU510may select a constellation from the plurality of constellations based on one or more of determined elevation angles, received signal received power (RSRP)/received signal received quality (RSRQ), service need, link budget(s), elevation angles, and/or additional link constraints. The WTRU510may identify a plurality of candidate satellites within the selected constellation. The WTRU510may determine which of the plurality of satellites to select within the selected constellation. The WTRU510may rank the plurality of satellites based on received signal power and/or quality.

FIG.5Bshows example footprints of satellites550,552within a constellation. Each satellite550,552may include one or more cells. Each cell may provide a beam that produces a footprint (e.g., such as footprints A, B, C). A WTRU560may be located within one or more footprints. For example, the WTRU560may be within footprint A of a first satellite550, footprint B of the first satellite550, and/or footprint C of a second satellite552. The WTRU560may determine Footprint A may be provided by a first cell (e.g., a beam of the first cell) of the first satellite550. Footprint B may be provided by a second cell (e.g., a beam of the second cell) of the first satellite550. Footprint C may be provided by a first cell (e.g., a beam of the first cell) of the second satellite560. The WTRU560may examine the candidate beams within the selected constellation. The WTRU560may determine a weighted sum of metrics ΣWiMifor the candidate beams, where W refers to the multiplicative weight to be applied for metric M. Metric M may include one or more of the following: link elevation angle, prevailing load intensity of spotbeam, penalty factor to apply for using an edge link, dwelling duration, link switch probability, etc. For example, each metric may be assigned a weight for each candidate beam.

One or more weights may be applied for reduction in switching and/or links that maximize dwell/dwelling duration. The dwelling duration may refer to an estimated or expected time the WTRU determines it would be able to remain connected to and/or send/receive signals to/from a satellite, for example based on the assistance information. The WTRU560may apply the respective weights. The WTRU560may prioritize one or more factors when applying the respective weights. The WTRU560may apply the respective weights to prioritize one or more of dwelling duration, elevation angle, spotbeam load intensity, edge link, and/or link switch probability. In an example, a WTRU (e.g., such as WTRU560) may prioritize dwelling duration when selecting a cell. Even though beam C may have a better RSRP/RSRQ, the second satellite552may be receding (e.g., moving away from WTRU560). The WTRU560may select beam B based on the second satellite552receding and/or other factors.

FIG.6shows an example scenario600of multiple WTRUs identifying candidate satellites based on measured elevation angle and minimum elevation angle required per system information. WTRU #1 sees SAT #1 and SAT #2 as candidates, WTRU #2 may identify SAT #2 as the only candidate, whereas WTRU #3 may identify SAT #3 and SAT #4 as candidates. Though WTRU #2 may observe SAT #3 in the horizon, SAT #3 may be excluded from the candidate list for WTRU #2, due to the measured elevation angle not meeting the minimum elevation angle criteria.FIG.6shows satellite on a single orbit. In an example, if the WTRU determines that two or more satellites are viable, the WTRU may determine that at least one Edge exists between the WTRU and each satellite transmitter. An Edge may exist between a WTRU and a transmitter of a satellite if they are visible to each other. As shown inFIG.4, a WTRU may be at an orbit edge and may have visibility to more than two satellites. In such case, the WTRU may have more than one Edge. The WTRU may rank the list of satellites in descending order of received signal power and/or quality. The WTRU may consider (e.g., only consider) those links with minimum acceptable received power (RSRP) or received signal quality (RSRQ).

In an example, a WTRU may receive, e.g., via system information, load intensity per spotbeam. The load intensity level for a spotbeam may indicate the spotbeam's capability to handle new connections. For example, the load intensity may indicate one or more of the following: composite utilization, hardware loading, air interface utilization, processor loading, available system capacity, etc. The WTRU may be provided with constellation topology assistance information (e.g., satellite ephemeris data, group common timing offset, etc.) via system information and/or via dedicated signaling. When used herein, the terms assistance information, satellite assistance information, constellation assistance information, constellation topology assistance information, etc. may be used to refer to any information provided by a network for assisting a WTRU in identifying, tracking, measuring, and/or selecting one or more satellite constellations for purposes of establishing communications (e.g., for cell selection/reselection). Examples of satellite assistance information may include one or more of satellite ephemeris data, group common timing offset, load information for the elevation angle information, geo-fencing information, satellite configuration information (e.g., load information for the satellite, satellite type/class, satellite capabilities, etc.) and/or the like. Although some examples here may be described using examples of certain types of satellite assistance information (e.g., elevation angle), these examples may be equally applicable to satellite assistance information more generally or other specific types of satellite assistance information (e.g., geo-fencing information).

The WTRU may determine the constellation topology via inference over a period. For example, the WTRU may infer the constellation topology via measurements and reception of system information from several satellites. The WTRU may determine visible satellites and/or elevation angles from satellite assistance information, constellation topology, and/or via measurements.

In an example, the WTRUs receive, e.g., via system information or dedicated signaling, weights to apply for link access for grades of elevation angle, penalty values for edge-links and weights to apply per load-intensity level per spotbeam. The weights to apply may be provided via constellation assistance information. For example, the WTRU may apply respective weights WeightElevationof (WE1, WE2, WE3, WE4) during link selection or reselection for measured elevation angles of (Angle10to Angle20, Angle20to Angle30, Angle30to Angle40)<Angle40respectively. In an example, the WTRUs may apply a penalty to the evaluated link if the link is an Edge and apply weights WeightLoadof (WL1, WL2, WL3, WL4) during link selection or reselection for measured loading of (Load1to Load2, Load2to Load3, Load3to Load4, >Load4) respectively. Similarly, weights may be applied for reduction in switching, and links that maximize dwell duration.

In an example, the WTRU may perform a weighted selection of an orbit and may perform a selection of the best link within the orbit. If there are multiple edges viable, the WTRU may select the edge at first that has the maximum “average elevation angle” with respect to the pair of satellites forming the edge. After selecting the Edge that has maximum “average elevation angle”, the WTRU may select the link within the selected Edge that has the maximum weighted sum of metrics ΣWiMi, where W may refer to the multiplicative weight to be applied for metric M. Metric M may include one or more of the following: link elevation angle, prevailing load intensity of spotbeam, penalty factor to apply for using an edge link, dwelling duration, link switch probability etc. The WTRU may perform selection or reselection evaluation for a (e.g., each) spot beam that has been noted via system information acquisition.

FIG.7shows an example service-based weighted cell selection700. Cell (re)selection may be performed based on service requirement(s). Multiple satellites may experience similar RSRP with different delays due to differences in, e.g., altitude, angle, pathloss, transmit power, payload configuration (regenerative or bent pipe) or any combination thereof. This may result in a WTRU selecting a satellite/airborne platform with a slightly better RSRP, at the expense of a much longer propagation delay. Circumstances may arise (e.g., the WTRU has delay sensitive services) where a WTRU may tolerate poorer channel conditions to fulfill latency requirements. Cell selection and reselection may be performed based at least in part on propagation delay.

As shown inFIG.7, a WTRU may receive and/or calculate constellation assistance information. For example, the WTRU may receive system information that indicates the constellation assistance information. The WTRU may identify one or more (e.g., a plurality of) constellations using the constellation assistance information. The constellation assistance information may include one or more of satellite ephemeris data, group common timing offset, a propagation delay, a link budget, a cell loading, and/or an edge cell indicator. The WTRU may select a satellite constellation based on one or more of an elevation angle, a measured RSRP/RSRQ, or a link budget. The selected satellite constellation may include a plurality of candidate satellites. Each of the plurality of candidate satellites may include one or more cells (e.g., candidate beams). The candidate beams may be associated with a beam edge. The WTRU may measure the RSRP/RSRQ of each candidate beam. The WTRU may weight the RSRP/RSRQ measurement based on a service requirement. The service requirement may include a dwell duration, a link switch probability, and/or a QoS. The WTRU may rank the candidate beams based on the RSRP/RSRQ measurements and the service requirement. For example, the WTRU may prioritize one or more service requirements. The WTRU may determine a weighted ranking of each candidate beam. For example, the WTRU may determine the weighted ranking based on RSRP/RSRQ, candidate beam elevation angle, prevailing load intensities of the candidates, dwelling duration, link switch probability, and/or QoS associated with uplink data. The weighted ranking may be determined based on prioritization of one or more service requirements. The QoS associated with the uplink data may include a minimum propagation delay for the uplink data. The WTRU may select the highest ranked candidate beam for cell selection.

Propagation delay may be determined via (e.g., explicit) indication. Propagation delay may be inferred via topology information. For example, the propagation delay may be determined based on constellation topology assistance information that may be received via system information. Constellation topology assistance information may include satellite ephemeris data, angle to the WTRU, satellite payload configuration such as bent-pipe or regenerative, altitude, and//or location relative to the WTRU. For example, the propagation delay may be determined via measurements and reception of system information from several satellites. The WTRU may determine visible satellites and/or elevation angles from topology configured or via measurements. The propagation delay may be determined based on timing information, such as timing advance command received during RACH. The propagation delay may be inferred over a period, for example, via measurements and reception of system information from multiple satellites.

Upon cell selection/reselection, the propagation delay information can be used, in addition to or in lieu of, RSRP to select a cell, spot beam or satellite/airborne platform. If a cell, spot beam or satellite/airborne platform fails to meet the latency requirements due to propagation delay, a penalty may be applied (e.g., IA a delay weighting metric) or may be discounted entirely. For example, the WTRU may examine QoS and latency requirements of the data to transmit and select accordingly.

A similar function can be applied in the downlink, where paging information may indicate to the WTRU the latency requirements of data. The WTRU may apply latency requirements to cell selection and/or reselection. The WTRU may delay the paging response message to perform a handover to a more appropriate cell. For example, the WTRU may delay the paging response message to perform a handover to a more appropriate cell that meets the latency requirements. In an example, if the difference in propagation delay is greater than such a handover delay, the WTRU may perform a handover.

To detect the cell ID, the WTRU may detect PSS and SSS. For non-geostationary satellites, there is a potential for very high doppler shifts on the order of +/−48 kHz for LEO S band operating at 2 GHz and +/−480 kHz for LEO Ka band operating at 20 GHz. The frequency error robustness in NR may be 5 ppm (10 kHz for S band and 100 kHz for Ka band). If a WTRU is currently camped on a spot beam with knowledge of the doppler shift, the WTRU may apply such a shift as a baseline for synchronization to a spot-beam served by the same satellite or aerial platform. In an example, if the WTRU is re-selecting to a spot beam on a satellite in the same constellation, with similar orbital path, altitude, and velocity, the WTRU may apply knowledge of the doppler shift experienced on the currently camped on cell as a baseline.

Cell (re)selection may be performed cross-border. Due to the large geographic locations covered by individual spot beams (potentially 1000 km diameter in the case of GEO satellites), a WTRU may traverse into a different country and/or roaming/billing region while being serviced by the same spot beam. The location and time of cells/spot beams that serve such regions may be determined by the network. The WTRU can be notified (e.g., via system information) if the WTRU is about to select such a cell/spot beam. The satellite/aerial platform may discourage the selection of such cells/spot beams. For example, the satellite/aerial platform may apply weighting penalties for selecting a spot beam that is currently servicing across billing/roaming regions (e.g., a country border). For example, the satellite/aerial platform may bar the WTRU from accessing the cell/spot beam. Geographic location information may be requested and/or inferred.

If the WTRU is currently camped on a cell/spot beam which services across billing/roaming regions, the WTRU may be notified by the serving cell/spot beam (e.g., via system information), of the geographical boundaries of the billing/roaming regions. If the WTRU moves from one region to another, a tracking update may be performed.

FIG.8depicts an example scenario800having multiple WTRUs and multiple satellite constellations. Paging area may be mapped with geo-fence. The satellite's footprint may be associated with several equally or unequally sized spotbeams as illustrated inFIG.8. A satellite's footprint may have a sweep width and under the footprint, the beam may be organized into one or more spotbeams. A satellite constellation may be designed as a collection of satellites covering a predetermined area using one or more orbits. As shown inFIG.8, an example constellation may have two orbits, each having a sweep width. Satellites, SAT #1, SAT #2 and SAT #3 are shown to cover orbit #1 while satellites, SAT #4 and SAT #5 service via orbit #2. The sweep widths of the respective orbits #1 and #2 are shown inFIG.8with differently shaded spotbeams and the direction of the satellites are shown with pointed arrows. A satellite's position in time and space may be highly deterministic, and a specific satellite within a constellation over a specific geographical location on earth may be highly deterministic. As shown inFIG.8, there may be multiple WTRUs, such as WTRU #1 and WTRU #2, noted by shaded small squares. WTRU #1 may be very near satellite SAT #2 and hence almost certainly serviced by SAT #2 in orbit #1 whereas WTRU #2 may be at the edge of orbits #1 and #2 and likely serviced by either SAT #2 or SAT #4 or both.

In an example, the coverage provided by a constellation of satellites may be semi-statically divided into N equal or unequal areas defined by geographical fences. When used herein, the terms semi-statically may refer to a higher layer configuration such as a radio resource control (RRC) configuration. The geo-fenced areas can form any arbitrary shape or form and the surface area SArea,icovered by a specific geo-fence Gi, 1≤i≤N, can be smaller or larger than other surface areas among the N geo-fences. A geo-fence Gi, 1≤j≤N, may be small in surface area due to G1, 1≤k≤N, for example, overlapping partially or fully the highly dense State of New Jersey whereas a geo-fence Gk, 1≤k≤N, may be very large in surface area due to Gk, for example, overlapping fully or partially the sparsely populated states of Wyoming and Montana. One or more geo-fences, located within proximity of each other, maybe grouped into a Zone. The N geo-fences may be grouped into a total of T zones, T≤N, Zone Zi, 1≤i≤T, may have more geo-fences compared with zone Zj, 1≤j≤T.

In an example, a geo-fence's boundaries may be scaled down (decreased) or scaled up (increased) based on the relative velocity of the WTRU. For example, a WTRU at high velocity of 250 kph may scale down its serving geo-fence boundary, whereas a WTRU at low velocity of 25 kph may scale up its serving geo-fence boundary. Further, the scaling up or scaling down may be applicable only in specific zones. For example, the WTRUs may be required to scale up or scale down a servicing geo-fence when that geo-fence is inside a zone ZLcovering partially or fully the states of Montana, Alberta and Saskatchewan. Scaling may be skipped when the serving geo-fence is inside a different zone ZScovering partially or fully the states of Massachusetts, Connecticut and New York. In an example, the N geo-fences and/or T zones may be reconfigured (e.g., redesigned) by the network periodically or based on internal events to contain N′ geo-fences, N≠N′, and T′ zones, T≠T′. For example, the network may redesign the number of zones from T to T′, T′<T, between 8:00 PM pacific standard time (PST) and 05:00 AM PST.

The currently valid terrain map containing the T zones and N geo-fences may be signaled to the WTRU by the network at the time of NAS: ATTACH and/or NAS: TA UPDATE and/or NAS: RNA UPDATE. The currently valid terrain map may be broadcast to the WTRUs via system information. A default terrain map may be agreed upon between the network and the WTRUs and preconfigured (e.g., at the WTRUs' non-volatile memory statically). The terrain map may be configured at the WTRUs via the application layers of the WTRU. The network may signal the updated terrain map to the WTRU when the geo-fences and/or zones are redesigned. The terrain map may be WTRU specific and, the terrain map may be signaled to the WTRU at the time of NAS: ATTACH and/or NAS: TA UPDATE and/or NAS: RNA UPDATE.

In an example, the WTRU may determine its current geo-fence and zone after acquiring its current location using a GNSS receiver. The WTRU may acquire location periodically, aperiodically, or on demand. For example, the WTRU may acquire the GNSS location every 2 seconds and may be commanded to acquire by the network or the application on demand for corrective purposes. The WTRU may track its serving geo-fence periodically. The WTRU may map its current GNSS acquired location to a specific geo-fence in the terrain map configured by the network. The mapped geo-fence is its serving geo-fence and. A WTRU may be configured with a parameter PAGING_IND_FORMAT. This parameter may be signaled to the WTRU via system information, via a RRC dedicated signal, and/or via a NAS procedure. Parameter PAGING_IND_FORMAT may indicate a scalar value and may hold at least one of three possible values. A value of 0 may refer to GEO_FENCE_UPDATE, a value of 1 may refer to TA_RNA_UPDATE, and a value of 2 may refer to TA_RAN_GEO_FENCE_UPDATE. A value greater than 2 may not be precluded, and a corresponding definition may be predetermined and agreed between the network and WTRU in such case. If parameter PAGING_IND_FORMAT is not configured, the WTRU may default the parameter to 0.

As described herein, a spotbeam serviced by a satellite may be assigned a TAC or a RNA Code. The same TAC or RNA code may have been assigned to multiple spotbeams, or neighboring spotbeams may have been assigned unique TAC or RNA codes. If parameter PAGING_IND_FORMAT=0, the WTRU may transmit a NAS: GEO_FENCE_UPDATE to the network upon change of geo-fence only and may not transmit a NAS: TA UPDATE or NAS: RNA UPDATE upon a change of TAC or RNA code. If parameter PAGING_IND_FORMAT=1, the WTRU may transmit a NAS: TA UPDATE or NAS: RNA UPDATE on a condition that there is a change in TAC or RNA code and may not transmit a NAS: GEO_FENCE_UPDATE upon a change of geo-fence. If parameter PAGING_IND_FORMAT=2, the WTRU may transmit a NAS: TA UPDATE or NAS: RNA UPDATE upon a change in TAC or RNA code and may transmit a NAS: GEO_FENCE_UPDATE upon a change of geo-fence.

The network may page the WTRU on (e.g., only on) the specific geo-fence and the specific satellite or satellites that covers the geo-fence at a specific time instance is deterministically known at the network. A WTRU that is stationary within a geo-fence may skip NAS: TA UPDATE or NAS: RNA UPDATE on a condition that the network sets parameter PAGING_ING_FORMAT to 0. The network may determine the current satellite serving the geo-fence and may route the PAGING message to the WTRU. This may reduce unnecessary signaling required on the uplink even though the spotbeams are constantly moving and TAC or RNA codes may constantly change. The stationary WTRU may limit the uplink access for network notification purposes.