Methods for radio resource management in moving networks

A wireless transmit/receive unit (WTRU) may communicate in a non-terrestrial network (NTN) comprising a plurality of satellites. The WTRU may be preconfigured with a plurality of measurement configurations and a corresponding plurality of activation/deactivation criteria associated with the plurality of satellites. The activation/deactivation criteria includes at least activation timing information. The WTRU may activate and deactivate each of the plurality of measurement configurations over time in accordance with the activation/deactivation criteria. The WTRU may perform measurements on cell beams for satellites with active measurement configurations and report results based on the measurements to NTN.

BACKGROUND

Next generation air interfaces, including a further evolution of LTE Advanced Pro and New Radio (NR), support a wide range of use cases with varying service requirements. Service requirements may include, for example, low overhead low data rate power efficient services for massive machine type communications (mMTC), ultra-reliable low latency (URLLC) services and high data rate mobile broadband (eMBB) services. WTRU capabilities may be diverse and may include low power low bandwidth WTRUs, WTRUs capable of a very wide bandwidth (e.g., 80 Mhz), WTRUs that support high frequencies (e.g., over 6 Ghz), under various mobility scenarios (e.g., stationary, fixed, high speed trains) using an architecture that is flexible enough to adapt to diverse deployment scenarios. Deployment scenarios may include, but are not limited to include, standalone, non-standalone with assistance from a different air interface, centralized, virtualized, and/or distributed over ideal/non-ideal backhaul. Beamforming may be used to compensate for increased pathloss at higher frequencies (e.g. over 6 GHz). A large number of antenna elements may be used to achieve a higher beamforming gain. Analog and/or hybrid beamforming may be used to reduce an implementation cost, for example, by reducing a number of RF chains. In an example, analog/hybrid beams may be multiplexed in time. A beam sweep may refer to transmission/reception of beamformed channels multiplexed in time and/or frequency and/or space.

SUMMARY

A wireless transmit/receive unit (WTRU) may communicate in a non-terrestrial network (NTN) comprising a plurality of satellites. The WTRU may be preconfigured with a plurality of measurement configurations and a corresponding plurality of activation/deactivation criteria associated with the plurality of satellites. The activation/deactivation criteria includes at least activation timing information. The WTRU may activate and deactivate each of the plurality of measurement configurations over time in accordance with the activation/deactivation criteria. The WTRU may perform measurements on cell beams for satellites with active measurement configurations and report results based on the measurements to NTN.

DETAILED DESCRIPTION

In an embodiment, the base station114aand the WTRUs102a,102b,102cmay implement a radio technology such as NR Radio Access, which may establish the air interface116using NR.

The RAN104may be in communication with the CN106, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs102a,102b,102c,102d. The data may have varying quality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN106may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown inFIG.1A, it will be appreciated that the RAN104and/or the CN106may be in direct or indirect communication with other RANs that employ the same RAT as the RAN104or a different RAT. For example, in addition to being connected to the RAN104, which may be utilizing a NR radio technology, the CN106may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

The CN106shown inFIG.10may include a mobility management entity (MME)162, a serving gateway (SGW)164, and a packet data network (PDN) gateway (PGW)166. While the foregoing elements are depicted as part of the CN106, it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator.

The CN106may facilitate communications with other networks. For example, the CN106may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN106and the PSTN108. In addition, the CN106may provide the WTRUs102a,102b,102cwith access to the other networks112, which may include other wired and/or wireless networks that are owned and/or operated by other service providers. In one embodiment, the WTRUs102a,102b,102cmay be connected to a local DN185a,185bthrough the UPF184a,184bvia the N3 interface to the UPF184a,184band an N6 interface between the UPF184a,184band the DN185a,185b.

The following description is for exemplary purposes and does not intent to limit in any way the applicability of the methods described further herein to other wireless technologies and/or to wireless technology using different principles, when applicable.

As used herein, a reference signal (RS) may refer to any signal, preamble or system signature that may be received and/or transmitted by a WTRU for one or more of the purpose(s). For example, various reference signals may be defined for beam management in the DL and UL. For example, downlink beam management may use a channel state information reference signal (CSI-RS), a demodulation reference signal (DMRS), a synchronization signal or other signal. In another example, uplink beam management may use a sounding reference signal (SRS), a DMRS, a random access channel (RACH) or other signal. In some cases, a network may refer to one or more gNBs (base station), that may be associated with one or more Transmission/Reception Points (TRPs), or may refer to any other node in a radio access network.

Non-Terrestrial Networks (NTNs), which employ airborne or space-borne vehicles such as satellites for communication, may foster a roll out of 5G services in unserved areas (e.g., isolated remote areas, rural areas, vessels in oceans) that may not be covered by terrestrial 5G networks. In some cases, NTNs may be used to upgrade the performance of terrestrial networks in underserved areas in a cost efficient manner. NTNs may be used to reinforce 5G service reliability, ensure service availability and provide scalability for 5G deployments. Different types of architectures may be envisioned based on a RAN functional split between a ground unit (terrestrial-based network) and satellite (NTN).

FIG.2shows a block diagram of an example split next generation (NG) RAN architecture200in a NTN radio access network204with a bent pipe payload. A WTRU202that is too remote to connect terrestrially to the data network208may access the data network208via the NTN RAN204, which includes an airborne or space borne station210(e.g., satellite) that communicates with a NTN remote radio unit212. The non-terrestrial station210relays information between the WTRU202and the NTN remote radio unit212(e.g., over an NR-Uu air interface) using a bent pipe principle by processing signals for retransmission by changing only amplification and/or radio frequency shift. The terrestrially located NTN remote radio unit212communicates with the gNB214(e.g., co-located) to access the data network208via a core network (CN)206.

FIG.3shows a block diagram of another example split NG RAN architecture300in a NTN radio access network304with a gNB distributed unit (gNB-DU)310processed payload. The WTRU302accesses the data network308via the NTN RAN304, which includes an airborne or space borne gNB-DU310, and terrestrially located gNB-CU314. In an example, the gNB-DU310hosts the radio link control (RLC), medium access control (MAC) and physical (PHY) layer protocol interactions with the WTRU302. The gNB-CU314hosts the radio resource control (RRC), service data adaptation protocol (SDAP) and packet data convergence protocol (PDCP) layer protocol interactions with the WTRU302. The gNB-CU314may control one or more gNB-DUs310via F1 signaling, which is transported over a satellite radio interface (SRI) with the NTN remote radio unit312. The terrestrially located NTN remote radio unit312communicates with the gNB-CU314(e.g., co-located) to access the data network308via a core network (CN)306.

FIG.4shows a block diagram of another example split NG RAN architecture400in a NTN radio access network404with a gNB410processed payload. The WTRU402accesses the data network408via the NTN RAN404, which includes an airborne or space borne gNB410that communicates over a SRI with the NTN remote radio unit412. The terrestrially located NTN remote radio unit412relays the communication from the space borne gNB410to the data network408via a terrestrially located core network (CN)406.

In the example procedures and systems described herein, a message transmitted by the network to a WTRU may originate from a non-terrestrial network node (e.g., a satellite) or a terrestrial node (e.g., a gNB, eNB, base station) depending on the network configuration. For example, an RRC configuration message originates from the RRC layer, so the network node that sends and receives RRC messages depends on where that RRC layer is located in the network. In the example configurations shown inFIGS.2and3, the RRC layer is located terrestrially so an RRC activation command may be sent by a terrestrial network node. In the example configuration shown inFIG.4, the RRC layer is located in the satellite so RRC messages would originate from the satellite. In another example, a MAC control element (CE) may be transmitted by a terrestrial node in the configuration ofFIG.2, and transmitted by a satellite in the configurations ofFIGS.3and4. Thus, in the example procedures described herein, a message received from the network (a network node) may refer generally to a non-terrestrial network node or a terrestrial node, and is determined by the network configuration.

A satellite may generate several beams (referred to as beams, spot beams or beam spots) to cover the satellite's service area bounded by the satellite's field of view or footprint. A NTN cell may be comprised of one or multiple spot beams, and each satellite in the NTN may have multiple cells. The mapping of spot beams to cells depends on the network implementation. Different configuration for the spot beams are possible based on the relationship between spot beams, synchronization signal blocks (SSBs), and physical cell identifiers (PCIs). The following example configurations may be used for spot beams: multiple PCIs may be used per satellite, such that each spot beam may correspond to an SSB/PCI pair; multiple PCIs may be used per satellite, such that each spot beam may correspond to a PCI; and/or a single PCI may be used per satellite, such that each spot beam may correspond to an SSB.

FIG.5shows an example spot beam configuration500including multiple PCIs per satellite520. According to the example spot beam configuration500, each spot beam corresponds to an PCI/SSB pair a shown (e.g., PCI501/SSB511, PCI501/SSB512, PCI502/SSB511. . . PCI503/SSB514).FIG.6shows an example spot beam configuration600including multiple PCIs per satellite620, where each spot beam corresponds to a PCI as shown (e.g., PCI601, PCI602. . . PCI612).FIG.7shows an example spot beam configuration700including a single PCI701/702per satellite720/722, respectively, where each spot beam corresponds to an SSB as shown (e.g., SSB711, SSB712, SSB713, SSB714).

In the examples described herein, a measurement object may include a time/frequency resource on which the WTRU performs a measurement. A measurement configuration may include a list of one or more measurement objects, and may further include any of the following information: reporting criteria, measurement identities linking objects to reporting configuration, measurement filtering configuration, and/or time periods during which the WTRU may perform measurements. In the examples described herein, procedures for measurement objects may similarly apply to measurement configurations and vice versa.

As part of measurement configuration, the network may configure an RRC_CONNECTED WTRU to perform and report measurements according to a measurement configuration. The measurement configuration may be provided by the network to the WTRU using dedicated signaling, such as an RRCReconfiguration message. The measurement configuration may include in one or more of the following example parameters. An example parameter may include a list of measurement objects on which the WTRU shall perform measurements. In an example, one or multiple reporting configurations may be used per measurement object. Another example parameter may include a list of reporting configurations, which may include a reporting criterion that triggers the WTRU to send a measurement report, an RS type used for measurements (e.g., CSI-RS SS/PBCH block), and/or the reporting format. Another example parameter may include the measurement identities, linking one measurement object with a reporting configuration. Another example parameter may include the quantity configuration that defines the measurement filtering configuration used for all event evaluation and related reporting. Another example parameter may include the measurement gap, which may include the periods of time during which the WTRU may perform measurements.

Measurement configuration signaling and procedures may enable a WTRU in RRC_CONNECTED state to maintain a measurement object list, reporting configuration list, and/or a measurement identities list. For NR measurement objects, the WTRU may measure and report on serving cells (e.g., a primary cell (SpCell) and/or one or more secondary cells (Scells)), cells listed within the measurement objects, and/or cells not listed within the measurement object(s) that have been detected by the WTRU on one or more SSB frequencies and one or more subcarrier spacing(s) indicated by the measurement object(s). A WTRU in RRC_CONNECTED may derive cell measurements by measuring one or multiple beams associated per cell as configured by the network. For all cell measurement results, the WTRU may apply filtering (e.g., layer 3 (L3) filtering) before using measured results for evaluation of reporting criteria and measurement reporting.

Deployments with moving network nodes, such as satellites or other airborne/space-borne nodes, introduce additional complications to resource measurements and configurations compared to networks with physically fixed network nodes (e.g., fixed eNB/gNBs), at least in part because the locations of the cells change over time due the movement of the network nodes. In these deployment scenarios, a measurement configuration may not stay valid over time, and may become more complex with the additional movement of the WTRU.

There may be many different satellite orbital classes, each with a different orientation, velocity and distance relative to the WTRU. For example, measurement objects for slow moving satellites, such as geostationary (GEO) satellites (e.g., at altitudes around 35,000 km), may remain valid for a long time. Satellites classified as low earth orbiting (LEO) satellites (e.g., at altitudes ranging from 600 km to 1500 km) may travel at speeds on the order of 7.5 km/s. In this case, for a spot beam footprint diameter of approximated 100 km, the spot-beam may serve any particular location for approximately 2 minutes. WTRUs connected to the LEO satellite, with motion ranging from stationary to speeds as high as 1000 km/hr, may have measurement configurations that become invalid quickly resulting in a need for continuous or frequent measurement report reconfigurations. Using LEO satellites, the network may also need to continuously compensate the measurement objects for differences in propagation delay and frequency shift. Additionally, there may be significant propagation delays associated with NTNs, for example on the order of 250 ms one-way for geostationary satellites. Given such large delays, it may be difficult to assess the accuracy of the measurements, especially for finer measurements such as tracking rapid variations in channel conditions.

FIG.8shows a timing diagram of an example NTN800including discrete motion of the serving beams and satellites820,822,824serving a WTRU830. The WTRU830is assumed to be relatively stationary from time T1 to T2 to T3 (e.g., not changing location or moving very slowly compared to speed of satellites and time scale). At Time T1, the WTRU may be served and receive measurement configurations from the spot beam with PCI805/SSB813from satellite820. The network800may compensate for its movement by adapting antenna and/or beam directions to maintain the coverage of a given footprint for WTRU830from T1 to T2. However, a breaking point is reached at time T3 where the WTRU830is covered by a different beam with PCI804/SSB813handled by a different satellite824(or similarly different beam of the same satellite820). In this case, the PCI changes from PCI805to PCI804from time T2 to time T3. In the example NTN800, the footprint of a satellite820,822,824may be associated with something other than the identity of the serving beam/satellite (or for a given time window) enabling the distinction of mobility due to motion of the WTRU versus mobility due to satellite motion.

FIG.9shows a timing diagram of an example NTN900including continuous motion over time of the serving beams and satellite924. In this case, the footprint on earth is not static but moves with the direction of the satellite924over time. In this scenario, the PCI and/or SSB may be linked to the satellite924beam and thus moves on the surface of earth continuously.

A difference between the example inFIG.8and the example inFIG.9is that the relative location of a static WTRU within a serving beam is constant in the example inFIG.8, while the relative location of a static WTRU within a serving beam changes over time inFIG.9. Thus, in the example ofFIG.8, the WTRU830located in the cell center of the satellite/beam at time T1 is still at the cell center of the satellite beam at time T2 (for a slow moving satellite). In the example ofFIG.9, a static WTRU that is in the cell center of a cell at a first time may be at the edge of the same cell at a second later time.

Methods for radio resource management and measurement configuration are disclosed herein to manage the accuracy and duration of the validity of network configurations in order to address the complications caused by significant propagation delays and the high-speed of the network nodes in non-terrestrial moving networks. The methods disclosed herein may be used with any type of moving networks (e.g., NTNs, high-altitude platforms (HAPs), drones, mobile integrated access and backhaul (IAB) networks) and with any type of moving nodes (e.g., satellites, airborne vehicles, space-borne vehicles, terrestrial vehicles). Moving networks may include networks with any moving node, including moving WTRUs and/or moving network nodes. In some cases, the moving nodes have a predictable path of movement (e.g., the ephemeris of a satellite in orbit).

In an example, a method for managing measurement configuration in moving networks (e.g., NTNs) may be a function of the time instance and/or the WTRU's location. In an example, a WTRU may be configured to report the measurement results of the neighboring beam spots and/or cells and serving beam spots/cells. The WTRU may be preconfigured with a set of measurement configurations that are conditionally added or removed to or from the measurement configuration, or activated or deactivated, based on the location of the WTRU and/or the time. The activation/deactivation may be initiated autonomously by the WTRU when it enters a zone of interest and/or signaled by the network (e.g., a satellite node or a terrestrial node, depending on the network configuration) dynamically and/or semi-statically (e.g., using DCI, broadcast message such as a master information block (MIB) or a system information block (SIB), RRC messages, or a MAC control element (CE)). The WTRU may receive a set of measurement objects or measurement configurations linked to a specific beam spot and corresponding to the footprint of a satellite or a specific geographical area comprising multiple beam spots/satellite coverage areas. A footprint may correspond to one or more SSBs, PCIs, or combinations of SSB/PCI in a given time instance.

In an example, a WTRU may perform autonomous activation/deactivation or selection of a measurement configuration or object. For example, the WTRU may autonomously activate the measurement configuration of interest associated with the current time instance when it enters the given area. The footprint or beam spot may for example have a dedicated identity. When a cell is covering a given footprint of interest it may be associated to the footprint identity that it is covering. For example, a footprint identity (ID) may be broadcasted by the network (e.g., in a MIB or SIB) when the satellite and beam are covering the area, and/or in the serving cell configuration information element (IE) received from the network. In an example with reference toFIG.8, the footprint served by PCI805at time T1 may have the same footprint identity as the footprint served by PCI804at time T3 because it is covering the an overlapping geographic area at a later time (the WTRU830is assumed to be relatively stationary from time T1 to T2 to T3).

In an example, to reduce the number of RRC reconfigurations received from the network (e.g., satellite or terrestrial node, depending on the network configuration), and to avoid long time delays for reception of the RRC reconfiguration messages, the WTRU may be preconfigured with an association between footprint IDs and measurement configurations, such that the footprint IDs may be associated with time instances and geographical locations. For example, the WTRU may receive an association information (e.g., in the form of an association table) when the WTRU enters in connected mode (RRC_CONNECTED) and/or when the WTRU receives an RRC re-configuration message. The WTRU may be configured with an association between location coordinates (e.g., latitude and longitude) and footprint IDs, which the WTRU may use to perform measurement configuration/object activation. The WTRU may assess its location independently, or may receive a message including an indication (e.g., in a DCI and/or MIB/SIB) of the identity of the footprint corresponding to the currently geographical location of the WTRU (at the current time).

In an example, the WTRU may be preconfigured with multiple measurement configuration (object) instances, each associated to a validity timer. The WTRU may de-activate and activate the measurement configurations (objects) of interest based on the validity timer. The WTRU may further be configured with conditions for applicability of the validity timer-based measurement configuration. For example, if the speed or location of the WTRU has changed by an offset, or when the WTRU has assessed that the serving and neighboring cells have moved considerably (e.g., based on satellite ephemeris information) while the measurement configuration has not been updated, the WTRU may interrupt the configured measurements to potentially activate a different measurement configuration.

When the WTRU moves from a first location (e.g., the area of validity for measurement configuration) to a second location and enters a new beam spot, the WTRU may use the measurement configuration associated with the new beam spot. The new network measurement configuration may be applied using any one or more of the following approaches: a new Measconfig may be reconfigured by the network to the WTRU; a set of measurement objects may be added/removed to a measurement object list in a measurement configuration of the WTRU; a set of measurement identities (IDs) may be added/removed to the list of measurement IDs that links a measurement object to the reporting configuration.

In an example, a network-assisted dynamic or semi-static configuration of measurements may be provided to by the network to a WTRU. A measurement configuration may be linked to a specific coverage area (e.g., a beam spot and/or a fingerprint ID) and a validity timer or time range. In an example, the network may be know the location of the WTRU and the network may signal to the WTRU to activate and/or add a measurement configuration in accordance with the WTRU's location. For example, the WTRU entering a zone (particular location or area) may trigger an RRC configuration by the network (knowing the location of the WTRU). If the WTRU assessed its new location but has not received an RRC reconfiguration, the WTRU may send a measurement configuration request. In another example, the measurement configuration may be broadcasted by the network, for example in a MIB or SIB. In an example, a received signal (e.g., a DMRS of PBCH or SSB) at the WTRU being above a threshold may trigger a measurement configuration update (e.g., the network broadcasting a measurement configuration update in a MIB or SIB). This approach may ensure that the WTRU is within the coverage of the beam spot corresponding to the current measurement configuration, even in the case that the network does not have current location information for the WTRU.

In an example, beam management may occur at the RRC level (RRC-based beam management). In an example, different beams of a satellite may be associated with different SSBs in the frequency domain (e.g., each beam has a different cell defining SSB (CD-SSB) with the same PCI, or a different PCI). In an example, each beam may be associated with a particular bandwidth part (BWP). The different BWPs associated with each beam may or may not be overlapping in frequency. In an example, each SSB may be associated to a different MIB that carries information about control resource set (CORESET) 0 and search space 0 confined in the frequency band associated with the beam spot for reception of SIB1.

When the WTRU moves in the coverage area of a satellite, the beam management may be handled at the L1 level. For example, the WTRU may report an L1 beam measurement from different CD-SSBs and may be configured with a serving beam based on the L1 beam measurement reports. When the WTRU changes its serving beam, an RRC reconfiguration may be transmitted from the network to the WTRU to update the servingcellconfig IE with a new serving CD-SSB. When the WTRU moves in the coverage of a satellite, the beam management may be handled by layer 3 (L3) RRC signaling. For example, the WTRU may report L3 measurements of different beams and may receive a handover command or an RRC message for reconfiguration of the serving cell.

In an example, a WTRU (in connected mode) may be configured to perform autonomous cell search and/or autonomous measurement reporting. The WTRU may perform a cell search while in connected mode if the WTRU has moved to a new coverage area and has not received a new measurement configuration. This may happen, for example, in the case of a serving satellite coverage area comprising multiple beam spots with a same PCI and with different SSBs in the frequency domain. If the beam management is handled at L1, the WTRU has not performed a handover and thus may not have received any new RRC configurations including new measurement configuration prior to being served by the new beam spot.

In an example, the WTRU may determine its new (current) location, and the WTRU may initiate a cell search and report the detected cells if any one or more of following conditions are satisfied. For example, under a per-configuration condition, the WTRU is indicated in a measurement configuration to perform a cell search in a set of frequency carriers for a measurement report when the serving beam spot changes. In another example condition, the measurement associated with the best cell or cells (e.g., n best listed cell) or listed beam spots is below a threshold indicating that none of the configured neighboring cells (listed cell list) is still in the coverage of the WTRU. In another example condition, the measurement result associated with the serving cell and/or serving beam spot is below a threshold. In another example condition, a timer starts when the WTRU has changed its serving beam and is stopped when the WTRU receives an RRC message for measurements configuration update. At timer expiry, the WTRU may start the cell search. In any of the above examples, the WTRU may be configured with a timer that starts when the WTRU initiates the connected mode cell search. When the timer expires the WTRU reports the measurements associated with all detected cells where the measurement is above a certain threshold.

As explained above, deployments with moving network nodes introduce complications to radio resource management, including measurement and configuration. Cell geographical location changes constantly, and although a WTRU may be served by a (relatively static) GEO satellite cell, neighbor cells' configurations may change continuously due to continuously moving LEO satellite cells (e.g., similarly, moving medium earth orbit (MEO) satellites and/or moving HAPs). In an example, a WTRU may expect new cell configurations as frequently as every 7 s.FIG.10shows an timing diagram of an example NTN1000, where GEO satellites1001and1002and LEO satellites1011and1012provide network coverage via spot beams to a WTRU1030. The cells covering the WTRU1030change over time. In the example ofFIG.10, the WTRU1030is in the beam coverage of GEO satellite1001and LEO satellite1011at time T1, and at later time T2, as the satellites1011,1012move (and possibly the WTRU1030), the WTRU1030has different beam coverage (with possibly different beams) from GEO satellites1001,1002and LEO satellites1011,1012. As the beam coverage for WTRU1030changes due to satellite movement, the measurement configurations need to be updated. Frequent RRC signaling for configuring mobility-related measurements, as used for networks with stationary cells (stationary network nodes), may not be suitable for moving networks because it requires large amounts of control signaling (e.g., RRC), which is costly to the satellite operator.

FIG.11shows an timing diagram of another example NTN1100, where GEO satellite1105and LEO satellites1101,1102and1103provide network coverage via spot beams to a WTRU1130. The low mobility WTRU1130is being served by a static GEO cell from GEO satellite1104, however due to movement of the LEO cells associate with moving LEO satellites1101,1102,1103, the neighboring cell set for the WTRU1130constantly changes in a deterministic manner because the movement of the LEO satellites1101,1102,1103is also deterministic as dictated by their orbital path. In accordance with an example measurement configuration update procedure, at time T1, The WTRU1130may receive (be preconfigured with) multiple measurement configurations and associated activation/deactivation criteria for multiple satellites, including current LEO satellites for which the WTRU1130is currently in the coverage area (e.g., LEO satellite1101) and upcoming satellites for which the WTRU1130will be in the coverage area at a future time (e.g., LEO satellites1102and1103). The measurement configurations may be provided to the WTRU1130by the GEO satellite1105and/or a current LEO satellite1101. The upcoming satellites are known because the trajectory of the LEO satellites1101,1102,1103over time are known (the satellites have predictable path of movement), and the relative location of the WTRU1130may be treated as fixed (at least over a longer period of time). Table 1 shows example measurement configurations for the current and upcoming satellites and the corresponding activation/deactivation criteria for the WTRU1130at its current geographical location. The activation/deactivation criteria includes the applicable time (e.g., discrete time instances and/or time ranges) and is used by the WTRU1130to determine when to activate/deactivate the corresponding measurement configurations.

In the example ofFIG.11, the measurement configuration for SAT1101is activated at times T1 and T2, and deactivated at time T3, the measurement configuration for SAT1102is activated at times T2 and T3, and deactivated at time T1, and the measurement configuration for SAT1103is deactivated at times T1, T2, and T3, but activated at later times (e.g., T4 etc.).

In an example, the WTRU1130may autonomously activate/deactivate neighboring cell measurement configurations based on associated (de)activation criteria. In another example, the activation/deactivation of neighboring cell measurement configurations may be signaled by the network (e.g., via DCI from a network node such as a serving GEO satellite, a serving LEO satellite, and/or a ground network node). The activation/deactivation criteria includes the applicable time (i.e., the time that the corresponding satellite has a cell that covers the geographical location of the WTRU1130), and thus is based on the satellite ephemeris and WTRU1130geo-location.

FIG.12shows a flow diagram of a measurement configuration management procedure1200that may be performed by a WTRU that is served by a NTN. At1202, the WTRU may be preconfigured (based on signaling from a network node) with multiple measurement configurations (objects) associated with multiple satellites and corresponding activation/deactivation criteria for the measurement configurations. At1204, the WTRU may determine which sets of measurement configurations are active/inactive either autonomously or based on network signaling. In a first example, at1208, the WTRU makes an autonomous determination by determining the WTRU's current geographical position and the current time, then at1210activating/deactivating measurement configurations based on the current geographical position and the current time according to the activation/deactivation criteria. In an alternate example, at1212, the WTRU receives network signaling including measurement configuration activation/deactivation instructions, and at1214the WTRU activates/deactivates measurement configurations based on network signaling.

Any of the following example measurement mechanisms and conditions may be used by WTRUs served by NTN to perform cell measurements. In an example, measurements may be performed based on a location of a WTRU within a beam spot. Each beam spot or satellite footprint may comprise an edge and a center zone.FIG.13shows a network diagram of an example NTN network1300serving a WTRU1310and showing example edge zones1320and center zones1315of serving and neighboring beams.

In an example, the WTRU may determine the delimitation of the edge and center zones based on a quality measurement threshold of the serving cell (e.g., signal-to-interference-plus-noise ratio (SINR), reference signal received quality (RSRQ), reference signal received power (RSRP)). In an example, the WTRU may receive signaling (e.g., RRC message) with the coordinates delimitating the edge and center zones of the beam spot(s)/satellite footprint(s). The WTRU may start measuring neighboring beam spots and satellites or any listed/detected cells when the WTRU enters the edge zone of the beam spot (e.g., the edge zone may be the last x km of the beam spot). The WTRU may report the measurements of any listed/detected cells satisfying pre-defined conditions.

In an example, the WTRU may be configured with a criteria for determining the start of neighboring cells measurement. The criteria may including any one or more of the following conditions: the measurement result quality (e.g., RSRP, RSRQ, SINR); and/or the location of the WTRU. For example, the WTRU may not perform any neighboring measurements if the serving cell SINR is greater than a threshold and the WTRU is located in a center zone. The condition may also be based on the mobility of the WTRU. For example, the WTRU may not perform any neighboring measurement if it is located in the center zone and has a mobility state which is slow or medium.

Any of the following example measurement report triggers and triggering conditions may be used by WTRUs served by NTN. The WTRU may be configured to report measurements on a condition or per event basis. The reporting conditions may be based on different or additional conditions to the measurement results. For example, the entering and leaving conditions of a reporting event may be based on any one or more of the following example conditions. An example condition may be based on the measurement results and location of the WTRU (e.g., an absolute location or a location in a beam spot). Another example condition may be based on the reference time delay of transmission. Another example condition may be based on the angle of arrival of the measured RS. Another example condition may be based on the observed time difference of arrival of different SSBs (e.g., the observed time difference of arrival (OTDA) between a serving and a neighboring cell).

Another example condition may be based on measurement results from more than two cells. For example, the WTRU may report measurements when the serving cell and the N best neighboring cells measurement results are below a threshold. This may assist the network for configuring handover (HO) in the case of moving beams when the network cannot determine a location of the WTRU with accuracy. Another example condition may be based on the WTRU reporting the observed measurement results during a given time window. For example, when the serving cell measurement has decreased by a certain amount (e.g., a predetermined percentage of the initial value) and the measurement result(s) of a neighboring cell or set of neighboring cells has increased by another amount.

Measurement reports may signal a quality of the planned target cell. In moving networks, the WTRU may be configured with a periodic change of serving beam spots or periodic handover to cope with the satellite mobility. However, as the WTRU may not be able to assess the quality of the planned target cell before the execution of the handover command or the beam change, the WTRU may need to evaluate the quality of the new serving cell quickly after the change or during the handover.

In an example, an association between multiple CD-SSBs with same the PCI (i.e. multiple beams from a common satellite) and a subset of physical random access channel (PRACH) resources and/or preamble indices may be configured by a set of parameters in system information. The WTRU may notify the satellite with the best beam associated with the best measured CD-SSB by using the corresponding PRACH resource for that CD-SSB. As the different SSBs from the different beams of the same satellite are from different frequency locations (i.e. multiple CD-SSBs for the same PCI), the association may require that the CD-SSB of the same satellite (i.e. one PCI) has different beam indices, which may be signaled to the WTRU in a handover command and/or system information transmission.

In an example, the WTRU may report in a message (e.g., message 3 (MSG3) a quality and identity of the beams and/or PCI of the satellite, if the planned target cell quality is not suitable and the quality of a neighboring beam(s)/cell(s) is suitable. The suitability criteria may be based on a measurement threshold such as RSRP, RSRQ, SINR or received signal strength indicator (RSSI).

In an example, if a satellite comprises multiple beams with different PCIs, the WTRU may receive a handover command towards a group of PCIs (associated with the target satellite). The handover command may include an association between PRACH resources and/or preamble and different PCIs and may enable the WTRU to indicate that a beam/PCI has the best quality based on measurements. The WTRU may receive a message (e.g., message 2 (MSG2)) and the subsequent message may be received by the WTRU in the best DL beam indicated by the WTRU. In an example, the WTRU may be configured with measurement reporting events associated with the planned target beam/cell. In this case, the WTRU may report the quality of the planned target beam/cell and serving beams once the WTRU is being served by the target beam/cell and serving beams (e.g., not based on a time to trigger being applied or reporting event conditions being satisfied).

A reduction of measurement reporting may be used for moving beams. In an example, a WTRU may frequently be located in the edge zone of a cell due to the motion of the beams/satellites. As a result, measurement report triggering may cause unnecessary or ping pong handover. The WTRU may need to distinguish mobility due to serving cell movement and mobility due to its own experienced SINR/RSRQ and movement. For example, the WTRU may only consider the cells that are not configured as planned target cell(s) for event based measurement reporting. In another example, if the WTRU is aware of the ephemeris of the satellite, the WTRU may not trigger a measurement event in response to the triggering conditions of some events (e.g., an event where serving becomes worse than threshold). If the WTRU is aware of the planned target cell in the next instance of time, the WTRU may not trigger a measurement event in response to triggering conditions of some events for neighbor in the planned target cell (e.g., an event where a neighbor becomes an offset better than a threshold) or an event where a neighbor becomes better than a threshold).

Measurement parameters may be variable and a scaling of measurement configuration parameters may be applied. In an example, a time-to-trigger parameter for measurement may be scaled. A scaling value may be used to increase the value of time-to-trigger based on any one or more of the following example criteria. An example criteria may include the type of measured cell, for example whether the cell is a planned cell due to satellite mobility or a detected cell that should be reported quickly if not considered as a target cell by the network. Another example criteria may include the location of the WTRU inside the serving beam spot/satellite coverage (e.g., center zone or edge zone). For example, a more aggressive time-to-trigger a fast handover command transmission may be used when the WTRU is in an edge zone versus being located in a center zone, in the case that mobility is mainly due to satellite mobility.

As part of WTRU measurement reporting, measurement report quantities may include reporting of the footprint ID and/or geographical coordinates. For example, when a measurement report is sent to the network, the WTRU may piggyback additional measurements and/or indications such as the footprint ID, location coordinates or other information. For example, the WTRU may report how long a cell has been detected or measured as above a certain threshold. This may assist the network in assessing the location of the WTRU and/or configuring the WTRU with the next serving cell. The WTRU may include in measurement reports transmission delays or differential delays between multiple cells.

A WTRU may be configured to report location information based on periodic and/or event based triggers. For example, the periodicity of the location information reporting may be a function of WTRU speed. An example criteria for event-based trigger for location reporting may include when a WTRU has moved a certain distance (e.g., x meters) from the location where a previous location report was triggered. Another example of event-based trigger for location reporting may include when the reference signal measurement quantity of the serving cell is below a threshold and/or when the reference signal measurement quantity of the neighbor cell is above a threshold. Another example of location-based event trigger may include when the WTRU reference signal measurement quantity of a beam spot is above or below a threshold.

A WTRU may perform mobility state estimation based on counting the number of handovers performed during a period of time that may not be applicable in the case of moving satellites. For moving networks, the WTRU may determine the WTRU's mobility state by, for example, counting of the number of satellite footprints that the WTRU has crossed over a given period of time, and/or calculating a difference between the number of actual handovers and the number of planned cells.