Improvements in and relating to a telecommunication network

Abstract

A user equipment (UE) 300 connected to a terrestrial telecommunication network 310, receiving an Air to Ground assistance information S11 for performing measurements of an ATG cell in a ATG telecommun

Description

The present invention relates to improvement in managing mobility between a terrestrial telecommunication network and an Air to Ground, ATG, network. New Radio Non-Terrestrial Networks, NR NTN, (NR_NTN_solutions-Core) [defined in 3GPP document RP-211557] was a 3GPP Work Item in 3GPP Release 17 to define solutions to enable New Radio (NR) and Next Generation Radio Access Network, NG-RAN, to support Non-Terrestrial Networks. It addressed solutions for Transparent payload for both Geostationary and non-Geostationary network scenarios, with the User Equipment, UE, having Global Navigation Satellite System, GNSS, capability and the satellite beams being both earth-fixed or earth-moving. Internet of Things, loT NTN, was a 3GPP study and work item in 3GPP release 17 to provide Non-Terrestrial Network access for E-UTRAN loT devices (NB-loT and LTE-M / eMTC) [3GPP document RP-202689]. NR NTN was a work item in Rel-17 to specify adaptation to allow NR to function over NTN [3GPP document RP-211557]. Non-Terrestrial Network access may be through Lower Earth Orbit (LEO), Medium Earth Orbit (MEO) and Geostationary Orbit (GEO), as well as through High-Altitude Platform Systems (HAPS). Following the Work items in Release 17 there were work items to enhance NR NTN and loT NTN in Release 18 of the standard specification. NR NTN enhancements [3GPP document RP-222654] is a 3GPP Work Item in 3GPP Release 18 aiming to enhance NR NTN with the following topics: Coverage enhancements Identifying and specifying potential issues and enhancements considering NTN characteristics NR NTN deployment in above 10 GHz bands NR NTN Release 17 did not have support for Frequency Range 2, FR2, due to there being no Physical Radio Access Channel, PRACH, format in FR2 for Frequency Division Duplexing, FDD. Network verified UE location NTN-TN and NTN-NTN mobility and service continuity enhancements Considers NTN-TN and NTN-NTN measurement / mobility and service continuity enhancements Synchronization in NR NTN is partly achieved by the UE computing the distance between the UE and the NTN node. To do this the UE needs to know its own position as well as the position of the satellite. UE acquires its own position through GNSS and the satellite position through what is known as the satellite ephemeris element, broadcast in System Information, SI. As both UE and satellite may move, this is maintained in two ways, through 1) maintaining an accurate GNSS position, 2) maintaining a recent ephemeris element of the serving satellite. In NR NTN, the satellite ephemeris is broadcast in system information block SIB19. This element needs to be acquired every time the UE attempts to connect to an NTN cell. SIB19 also contains neighbour cell assistance information. In loT NTN the serving cell ephemeris element is sent in system information in an element known as SIB31 and, in order to make sure that the UE is correctly synchronized, this element needs to be read every time it connects to an loT NTN e-Node B, eNB. Figure 1 shows a representation of an NTN, as known in the art. It shows an NTN cell 10, which is comparatively larger than a terrestrial cell. A UE 20 in the NTN cell is able to communicate with a satellite 30, which in turn communicates with a ground station 40, which forms part of a g-Node B 50 and thence onto the Core Network 60 An Air-To-Ground (abbreviated as ATG or A2G) network is a cellular network that provides connectivity in the air via base stations on the ground. It is different from a Non-Terrestrial Network, as the access link is from the ground to the UE in the sky (e.g on an aircraft), as seen in Figure 2. In contract, in NTN, the access link is from space / sky to the ground. Figure 2 shows two ATG cells 100, 101, each connected to a ground base station 110, 111 respectively. Each of these is connected to the Core Network 120. In ATG cell 101, there is a UE 130 One of the main the use cases of A2G network is to provide backhaul connectivity to access points in aircraft. Work has been ongoing to define requirements for coexistence between ATG and International Mobile Telecommunications, IMT, terrestrial networks. Furthermore, work is ongoing to define Radio resource management, RRM, performance requirements for ATG UEs, demodulation performance requirements for ATG BS / UE, and test procedures for ATG BS conformance testing. The Air-To-Ground network is similar to a Non-terrestrial network in the sense that the cells can be very large, synchronization will have to be different to terrestrial cases and that there are network elements that may move very quickly. Some of the characteristics, from an RF point of view, of an ATG network include: 1. Extremely large inter-site distances and large coverage range 2. Utilizing non-disjoint frequency for deploying both ATG and terrestrial networks 3. Much more powerful on-board ATG terminal capacity In order to allow for an ATG-capable UE to connect to an ATG cell, the UE needs certain information, similar to NR NTN. In ATG, the UE is provided via system information in SIB22 with the following information: • ATG-Config, which contains the following information: o atg-gNB-Location and heightgNB, which is required in order for a UE to synchronize with the ATG cell. Atg-gNB-Location is a refence location that defines a coordinate on the surface of the earth, while the height is a number having a granularity of 1 metre. Both elements may be purposefully obscured, i.e not showing the true position, in order to not give up the precise location of the gNB, which can be sensitive information for a network operator. o Cell specific Koffset o Ta-ReportATG - This indicates whether a Timing Advance Report Media Access Control, Control Element, MAC CE, should be triggered, compiled and sent to the network under certain conditions such as during random access procedures, handovers and Radio Resource Control, RRC, connection establishment, RRC Resume or RRC Connection re-establishment. The above set of parameters may be referred to as “ATG assistance information”. However, it is expected that any future parameters that are included in ATG-Config would also be characterized as ATG assistance information. The 5G NR connected mode mobility functions similar to other cellular standards. A standard connected mode handover is performed only when triggered by the gNB. The full usual procedure is as follows and as illustrated in Figure 3: S1) A UE 200 is configured with measurement configuration via RRCReconfiguration, which includes a MeasReportNR which instructs when a UE shall report measurements and also includes the MeasObjectNR which gives details on how to perform the measurement. S2) UE 200 performs neighbour cell measurements according to the measurement configuration, which are configured by the network. S3a) A measurement report (of a neighbour cell) is triggered and, S3b) is sent to the gNB 210. S4) Inter-node procedures whereby the Source gNB 210 sends a Handover Request to Target gNB 220 after having decided whether to trigger a handover and the target gNB 220 sends a Handover Request Acknowledge to Source gNB 210. S5) The Source gNB 210 triggers a handover command which is sent to the UE 200. This handover command consists of the RRC message RRCConnectionReconfiguration, containing the mobilityControlInfo field. S6) UE 200 prepares for handover to the target gNB 220 and performs a handover via the random access procedure. A measurement configuration consists of a set of measurement objects and measurement reporting configuration for RRM purposes. These measurement objects define the configurations of the measurements that a UE shall perform in RRC connected mode. A measurement object is related to either a frequency or a Radio Access Technology, RAT. There is, for instance, an intra-RAT NRMeasurement object (MeasObjectNR), which may configure intra or inter-frequency measurements. The MeasObjectNR contains configurations such as the carrier frequency, measurement bandwidth, SSB configurations, neighbour cell configurations, specific cells to measure, cells not to measure and report and many more configurations. There are also Inter-RAT measurement object that contains all of the necessary configurations to perform connected mode measurements of E-UTRAN (MeasObjectEUTRA), UTRA (MeasObjectUTRA), GERAN (MeasObjectGERAN), CDMA2000 (MeasGbjectCDMA2000), or WLAN (MeasObjectWLAN). The measurement reporting configuration contains rules that define when a measurement report containing measurements shall be sent. These are typically defined by measurement reporting triggering conditions (also called measurement events), thresholds, and configuring what measure shall be reported. Idle and inactive mode mobility is based on a UE autonomously performing measurements and deciding, according to some rules, whether a UE shall re-select to another cell or not to camp on. During cell selection, the UE identifies suitable cells, which is done according to a cell suitability criteria based on signal strength and signal quality measurements. After identifying one or several suitable cells, the UE can choose any of them. During cell re-selection, the UE searches intra-frequency cells, inter-frequencies cells and inter-RAT cells. Each frequency will have a specific cell reselection priority, and the UE shall always choose a cell of highest priority, provided that it is not barred or not allowed to camp on. If cells of equal priority are detected, then the UE shall rank all of the cells, where the ranking metric is based on signal strength and signal quality measurements and then choose the best candidate. The UE then camps on the newly re-selected cell. The distances in an ATG network are considerably larger than those experiences in a terrestrial network, where the vertical distance may be more than 10km and the horizontal distance is a maximum of 100km. This means that the propagation delay is larger than a terrestrial network is designed to handle. To mitigate this issue, and avoid re-designing the 5G NR air interface to handle this, the ability of the UE to self-compensate was introduced. This self-compensation is done by the UE calculating the distance between the UE and an ATG cell and then compensating the timing and the considerable doppler shift (created by the rapid movement of an aircraft). This requires the UE to acquire its own UE position, for instance via GNSS, and also to acquire the position of the ATG gNB. This is provided for both serving cell, which is used for accessing a cell, and also for neighbouring cells, which is used for neighbour cell measurements. In the prior art, the already described ATG assistance information has only been introduced in an ATG cell. However, in many use cases, such as in aviation, the aircraft also requires connectivity on the ground, when it is not connected to an ATG cell. This is used, for instance, for uploading aircraft maintenance and analytics data etc. This means that some form of service continuity is needed between a terrestrial and an ATG network, as seen in Figure 4. However, for the service continuity to function, there needs to be a means to allow for assistance information to be configured. This is because without assistance information being provided, the mobility between a Terrestrial Network, TN, and an ATG will face severe difficulties. For instance, the UE may not be able to measure an ATG cell while in RRC_CONNECTED mode. Further, in idle or inactive mode the UE may have difficulty detecting an ATG cell, potentially also leading to measurements failing. According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows. According to a first aspect of the present invention there is provided a method of operating a User Equipment, operably connected to a terrestrial telecommunication network, for mobility to an Air to Ground, ATG, telecommunication network, comprising the steps of: receiving ATG assistance information for performing measurements of an ATG cell in the ATG telecommunication network; performing measurement of the ATG cell; and performing mobility to the ATG cell. In an embodiment, the ATG assistance information is received in broadcasted information from the terrestrial telecommunication network. In an embodiment, the ATG assistance information is received in a measurement configuration, transmitted from the terrestrial telecommunication network. In an embodiment, the ATG assistance information is received, from the terrestrial telecommunication network, in an RRC release message. In an embodiment, the UE performs mobility to the ATG cell based on receiving an RRC release with redirection from the terrestrial network. In an embodiment, the UE additionally performs at least one neighbour cell measurement. In an embodiment, the UE sends a measurement report based on measuring an ATG cell using the ATG assistance information. In an embodiment, the UE performs mobility to the ATG cell based on receiving a handover command from the terrestrial network. According to a second aspect of the present invention there is provided apparatus arranged to perform the method of the first aspect. Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which: Figure 1 shows a generic view of a Non-Terrestrial Network; Figure 2 shows a generic view of an Air to Ground Network; Figure 3 shows a handover procedure known in the art; Figure 4 illustrates a generic view of mobility from a terrestrial network to an ATG network; Figure 5 shows a call flow for broadcasted configuration providing ATG neighbour cell assistance information for connected mode handovers according to an embodiment of the invention; Figure 6 shows a call flow for dedicated configuration of ATG assistance information in a measurement configuration for connected mode handovers according to an embodiment of the invention; Figure 7 shows a call flow for redirecting to ATG by configuring ATG assistance information in a RRCRelease message according to an embodiment of the invention; and Figure 8 shows a call flow for indicating capability to perform mobility from a TN cell to an ATG cell according to an embodiment of the invention. Embodiments of the invention provide a method for configuring a UE with ATG assistance information in order to perform TN to ATG mobility. Herein, the notion of ATG network and network may be used interchangeably. In other words a “network” should not be taken to necessarily mean a non-ATG network. In terms of base stations, the term “gNB” may be interchanged with a BS / eNB / NG-RAN / NG-eNB or similar. This further means that methods according to the invention are not limited to 5G NR, but also 4G E-UTRAN including loT technologies such as eMTC or NB-loT. It is applicable to loT NTN, which is based on 4G E-UTRAN as well. In terms on the wireless device, ATG UE and UE may refer to the same type of wireless device. In other words a “UE” should not be interpreted to mean a “non-ATG UE”. ATG UE may also be considered a “ATG-capable UE”. It should be noted that in some parts of this application, the ATG UE may be referred to as “UE”. Herein, the term “terrestrial network” is used to refer to a network that is not an ATG network, but terms may for instance be “non-ATG network”. While the methods herein refer to “terrestrial network” as a “non-ATG network”, the network may also be a “non-terrestrial network”. In other words, methods for performing mobility from a network located on the ground for the purpose of serving terrestrial UEs to an ATG network may also be applicable for the mobility from a network where one or several network elements are non-terrestrial for the purpose of serving terrestrial UEs or UEs in the air to an ATG network. This may be particularly useful in providing service to aircraft, where when the ATG UE flies over land, the service would be provided by an ATG network, and when the ATG UE flies over sea, the service is provided by NTN. To allow for a UE to monitor ATG cell(s) while not connected to the ATG network, there is a need for a UE to synchronize to these cells in order to measure them. In an embodiment of the invention, the terrestrial network provides ATG assistance information for ATG cells or ATG frequencies, to allow for the UE to synchronize to measure the ATG cells. This can for instance be used during mobility events where for instance an airplane takes off and is connected to a ground network. In an embodiment of the invention, the ATG assistance information is provided in a broadcast fashion, i.e via System Information. This method is beneficial as it allows UEs both in connected mode as well as in idle and inactive mode to synchronize and measure ATG cells. In an embodiment of the invention, the ATG assistance information is provided in ATG SIB22. As is known in the art, this system information is used in an ATG cell to provide ATG serving cell and ATG neighbouring cell information. Further, when a terrestrial network broadcasts the ATG SIB22, the network does not provide a serving cell ATG configuration (atg-Config). This may indicate to an ATG UE that the cell in question is not an ATG cell, but rather a terrestrial cell that is providing ATG assistance information for neighbouring ATG cells. Another condition to identify that the terrestrial cell is not an ATG network is that neighbour cell ATG assistance information is configured (atg-NeighCellConfigList), but not the serving cell ATG assistance information (atg-Config). The broadcasted ATG assistance information may be stored in ATG UE memory even if the UE is no longer connected or camping on the ATG cell. This is useful in case the signal connection is no longer sufficient when the ATG-capable UE is in the air and the connection breaks. The broadcast ATG assistance information can be used in both connected mode as well as in idle and inactive mode. An example of how it can be used in connected mode can be seen in Figure 5, which shows messages exchanged between a UE 300, a source TN gNB 310 and a Target ATG gNB 320. In this case for connected mode the following steps are performed: S11. The terrestrial source cell or TN gNB 310 signals the ATG neighbour cell assistance information in a SIB22, which the UE 300 acquires. S12. Configure the measurement of ATG neighbouring cells. In this case the UE 300 can identify which cells or frequencies belong to which ATG assistance information by using the signalled frequency or the Cell ID. S13. Using the measurement configuration as well as the broadcasted ATG neighbour cell assistance information, the UE 300 performs measurements on the configured ATG cells. S14. If the measurement is performed and evaluated to satisfy a configured condition in a reporting configuration (ReportConfigNR), the UE 300 reports the measurements to the source TN gNB 310. S15. Handover command sent to the UE300 to perform a handover towards an ATG cell, which is performed if the source TN gNB 310 has decided that it would be suitable to perform the handover. This would also include network inter-node signalling between gNBs. S16. Handover is performed to the target ATG gNB 320. In the foregoing, mobility from a terrestrial NR cell to an NR ATG cell has been described. It may also be possible to perform mobility from a terrestrial E-UTRAN cell to an NR ATG cell. This can, for instance, be done by configuring the ATG assistance information in a SIB that is used for Inter-RAT mobility for NR, which would be SIB24 (SystemlnformationBlockType24). Alternatively a new SIB specifically for ATG assistance information may be introduced. In an embodiment of the invention, the ATG assistance information can be configured in a dedicated fashion to allow for a UE to synchronize and measure an ATG cell. This can be configured in a measurement configuration, such as MeasObjectNR in MeasConfig, and be configured per cell or per frequency. If it is configured per cell, then there may be a single ATG assistance information element per cell, and if it is configured per frequency, then there may be a list of ATG assistance information elements. In an embodiment of the invention, a UE that is connected to an E-UTRAN cell may be provided with ATG assistance information. This may be configured in a MeasObjectNR in the E-UTRAN NR inter-RAT measurement configuration Dedicated configuration is usually associated with connected mode mobility, but there may also be the possibility of configuring dedicated configurations to be used in inactive mode. In an embodiment of the invention, the UE can be configured with dedicated ATG assistance information to be used in RRC inactive. This can be configured as part of suspendConfig as part of RRCRelease. The messages S21 - S25 exchanged in this embodiment are as shown in Figure 6. Re-direction is a type of idle mode mobility where the UE is told to move to a certain frequency and perform cell selection. This does not require the UE to first measure on the frequency and, therefore, it requires less configuration and setup compared to a network-directed or network-controlled mobility procedure. In an embodiment of the invention, a network may re-direct an ATG UE from a terrestrial network to an ATG network. As part of this re-direction, the UE may be configured with ATG assistance information to better allow a UE to synchronize to a cell on the frequency. This ATG assistance information may be a set of ATG assistance information for a number of cells, base stations or gNBs, or may also only be a single ATG assistance information element for a single cell, a single base station or a single gNB. When the UE receives an ATG RRCRelease message indicating redirection with ATG assistance information, the UE will tune over to the new indicated frequency, perform cell selection and then select an ATG cell. The full procedures can be seen in Figure 7, which shows message S31 to S35. In order to allow for a UE to perform mobility from a TN to an ATG network, the ATG cell needs to have knowledge of the capabilities of the ATG-capable UE for performing mobility. Figure 8 shows a message flow diagram related to a UE indicating capability to perform mobility from a TN cell to an ATG cell. Message S41 is sent from UE 500 to Source TN gNB 510 indicating TN to ATG capabilities. In an embodiment of the invention, the UE reports to a terrestrial network its capabilities to perform mobility from a terrestrial to an ATG network. The capabilities may have the following options: • Reporting that the ATG-capable UE is capable of performing idle and inactive mode mobility from a terrestrial cell to an ATG cell o As part of this capability, the UE may report that it is capable of reading, processing and utilizing the ATG assistance information for measurement purposes. • Reporting that the ATG-capable UE is capable of performing connected mode measurements and connected mode handovers to an ATG cell o Whether UE is capable of reading, processing and utilizing ATG dedicated assistance information for measurement purposes o Whether UE is capable of reading, processing and utilizing ATG broadcasted (for instance in a SIB22 broadcasted by a terrestrial cell) assistance information for measurement purposes • Reporting that the ATG-capable UE is capable of performing re-direction from a terrestrial to an ATG network o Whether UE is capable of reading, processing and utilizing ATG assistance information provided in an RRCRelease message. Furthermore, if there is a significant change in frequency from the terrestrial network to the ATG network, the capabilities of the UE to perform a handover also involving a significant change in carrier frequency may be reported. Some options include: • Whether the UE is capable of measuring inter-frequencies and performing interfrequency handover o Whether the UE can perform measurements and handover from a terrestrial Frequency Range 1 (FR1) cell to ATG FR1 cell As the ATG network is a network that operates from 3000 metres up to altitudes of above 10000 metres, the UE should not be connected to an ATG before reaching the 3000 metre altitude. As the network may not know the exact height of the aircraft in order to configure a UE to measure once the UE is above 3000 metres, it may instead be useful for the UE to autonomously start measuring once the UE is above 3000 metres. Therefore, in an embodiment of the invention, if the UE is configured in connected mode to measure ATG cells, the UE does not start measuring any of the cells before the UE is above 3000 metres. This can be done without any explicit configuration but would rather be a default action. In an alternative, it can be explicitly configured, i.e that a field indicates whether a UE should measure only after or before the ATG-capable UE has reached 3000 metres. This can be a dedicated configuration or a broadcast configuration. Similarly, for idle and inactive mode mobility, the UE may not initiate measurement of ATG neighbouring cells before the UE has reached 3000 metres. This can be specified in one of the following ways: • When the UE is below the height threshold, the UE considers the cell to be barred and thus not allowed to be accessed and shall not be considered in cell reselection and cell selection procedures. • The UE may consider ATG cells to be part of exclude list and not part of allowed list when the UE is below the height threshold • Only higher priority or equal priority frequencies with ATG cells may be measured when the UE is below the height threshold, and the ATG cells that are lower priority frequencies are not required to be measured. The height for the above configuration may be configurable, i.e while the UE may not be allowed to connect to an ATG cell before 3000 metres, the UE may be configured to be allowed to measure the ATG cell before 3000 metres. As an example, the UE may be allowed to start measuring at 2000 metre altitude in order for timely mobility. The following illustrates ways in which the relevant 3GPP specification may be amended to reflect the developments introduced herein. 38.331 V18.0.0 EXAMPLE SIB22 SIB22 contains ATG assistant information. SIB22 information element — ASN1START — TAG-SIB22-START SIB22-rl8 ::= atg-Config-rl8 Need R hs-ATG-cellReselectionSet Need R atg-NeighCellConfigList-r Need R lateNonCriticalExtension } ATG-NeighCellConfigList-rl8 : NeighCellConfig-rl8 ATG-NeighCellConfig-rl8 ::= atg-gNB-Location-rl8 Need R heightgNB-rl8 Need R carrierFreg-rl8 Need R physCellld-rl8 Need R } — TAG-SIB22-STOP — ASN1STOP i SIB22 field descriptions SEQUENCE { ATG-Config-rl8 OPTIONAL, .-rl8 ENUMERATED {true} OPTIONAL, -18 ATG-NeighCellConfigList-rl8 OPTIONAL, OCTET STRING OPTIONAL, := SEQUENCE ( SIZE (1. .maxCellATG-rl8) ) OF ATG- SEQUENCE { ReferenceLocation-rl7 OPTIONAL, INTEGER (-16384..16383) OPTIONAL, ARFCN-ValueNR OPTIONAL, PhysCellld OPTIONAL, § atg-Config i Provides parameters needed for the UE to access ATG via NTN access such as atg gNB i location information, cell Specific Koffset, TA Report indication. This field is provided § when SIB22 is broadcasted in an ATG network, and is not provided when SIB22 is § broadcasted in a non-ATG network. i atg-NeighCellConfigList i Provides a list of ATG neighbour cells including their reference Location, carrier frequency i and PhysCellld. i hs-ATG-ceiiReseleciionSei i Indicates whether the UE applies high speed inter-frequency measurements requirements i for inter-frequency cell reselection in RRCJDLE and RRCJNACTIVE states as specified in i TS 38.133

[14] . If the field is absent UE applies only the NR cell reselection requirements as i specified in TS 38.133

[14] . 38.331 V18.0.0 EXAMPLE - MeasObjectNR The IE MeasObjectNR specifies information applicable for SS / PBCH block(s) intra / inter-frequency measurements and / or CSI-RS intra / inter-frequency measurements. MeasObjectNR information element — ASN1START — TAG-MEASOBJECTNR-START MeasObjectNR ::= SEQUENCE ( ssbFrequency ARFCN-ValueNR OPTIONAL, -- Cond SSBorAssociatedSSB ssbSubcarrierSpacing SubcarrierSpacing OPTIONAL, -- Cond SSBorAssociatedSSB smtcl SSB-MTC OPTIONAL, — Cond SSBorAssociatedSSB smtc2 SSB-MTC2 OPTIONAL, — Cond IntraFreqConnected refFreqCSI-RS ARFCN-ValueNR OPTIONAL, — Cond CSI-RS referenceSiqnalConfiq ReferenceSiqnalConfiq, absThreshSS-BlocksConsolidation ThresholdNR OPTIONAL, — Need R absThreshCSI-RS-Consolidation ThresholdNR OPTIONAL, — Need R nrofSS-BlocksToAverage INTEGER (2..maxNrofSS-BlocksToAverage) OPTIONAL, — Need R nrofCSI-RS-ResourcesToAverage INTEGER (2..maxNrofCSI-RS-ResourcesToAverage) OPTIONAL, — Need R quantityConfiglndex INTEGER (1..maxNrofQuantityConfig), offsetMO Q-OffsetRangeList, cellsToRemoveList PCI-List OPTIONAL, -- Need N cellsToAddModList CellsToAddModList OPTIONAL, -- Need N excludedCellsToRemoveList PCI-RangelndexList OPTIONAL, -- Need N excludedCellsToAddModList SEQUENCE (SIZE (1..maxNrofPCI-Ranges)) OF PCI- RangeElement OPTIONAL, -- Need N allowedCellsToRemoveList PCI-RangelndexList OPTIONAL, — Need N allowedCellsToAddModList RangeElament OPTIONAL, SEQUENCE (SIZE (1..maxNrofPCI-Ranges)) OF PCI-Need N [ [ freqBandlndicatorNR measCycleSCell sfl024, sfl280} OPTIONAL — Need R J J r [ [ smtc.31ist-rl6 rmtc-Config-rl6 Need M t312-rl6 Need M J J r [ [ associatedMeasGapSSB-rl7 associatedMeasGapCSIRS-rl7 smtc41ist-rl7 measCyclePSCell-rl7 msl024, msl280, sparel) Cond SCG cellsToAddModListExt-vl710 Need N J J r [ [ associatedMeasGapSSB2-vl7 2 0 AssociatedGapSSB associatedMeasGapCSIRS2-vl7 2 0 AssociatedGapCSIRS J J r [ [ measSequence-rl8 cellsToAddModListExt-vl800 OPTIONAL — Cond ServingCell ] J , [ [ cellsToAddModListExt-vl8xy OPTIONAL — Need N ] ] } FreqBandlndicatorNR OPTIONAL, -- Need R ENUMERATED {sf!60, sf256, sf320, sf512, sf640, SSB-MTC3List-rl6 SetupRelease {RMTC-Config-rl6} OPTIONAL, — Need R OPTIONAL, SetupRelease { T312-rl6 } OPTIONAL MeasGapId-rl7 MeasGapId-rl7 SSB-MTC4List-rl7 ENUMERATED {msl60, OPTIONAL, OPTIONAL, OPTIONAL, ms256, ms320, -- Need R -- Need R -- Need R ms512, ms640, OPTIONAL, CellsToAddModListExt-vl710 OPTIONAL MeasGapId-rl7 OPTIONAL, — Cond MeasGapId-rl7 OPTIONAL — Cond MeasSequence-rl8 OPTIONAL, — Need R CellsToAddModListExt-vl800 CellsToAddModListExt-vl8xy OMITTED . . . CellsToAddModList ::= CellsToAddModListExt-vl710 ::= CellsToAddModExt-vl710 CellsToAddModListExt-vl800 ::= CellsToAddModExt-vl800 CellsToAddModListExt-vl8xy ::= CellsToAddModExt-vl8xy CellsToAddMod ::= physCellld cellIndividualOffset } CellsToAddModExt-vl710 ::= ntn-PolarizationDL-rl7 Need R ntn-Polari zationUL-rl7 Need R } CellsToAddModExt-vl800 ::= ntn-NeighbourCelllnfo-rl8 Need R } CellsToAddModExt-vl8xy ::= atg-NeighbourCellInfo-rl8 SEQUENCE (SIZE (1..maxNrofCellMeas)) OF CellsToAddMod SEQUENCE (SIZE (1..maxNrofCellMeas)) OF SEQUENCE (SIZE (1..maxNrofCellMeas)) OF SEQUENCE (SIZE (1..maxNrofCellMeas)) OF SEQUENCE { PhysCellld, Q-OffsetRangeList SEQUENCE { ENUMERATED {rhcp,Ihcp,1inear} OPTIONAL, ENUMERATED {rhcp,Ihcp,1inear} OPTIONAL SEQUENCE { NTN-NeighbourCellInfo-rl8 SEQUENCE { ATG-Config-rl8 OPTIONAL OPTIONAL — Need R — TAG-MEASOBJECTNR-STOP — ASN1STOP 38.331 V18.0.0 EXAMPLE - RRCRelease The RRCRelease message is used to command the release of an RRC connection or the suspension of the RRC connection. Signalling radio bearer: SRB1 RLC-SAP: AM Logical channel: DCCH Direction: Network to UE RRCRelease message — ASN1START — TAG-RRCRELEASE-START RRCRelease ::= rrc-Transactionidentifier criticalExtensions rrcRelease criticalExtensions Future SEQUENCE { RRC-Transactionldenti fier, CHOICE { RRCRelease-IEs, SEQUENCE {} RRCRelease-IEs ::= redirectedCarrierlnfo Need N cellReselectionPriorities Need R suspendConfig Need R deprioritisationReq deprioritisationlype deprioritisationlimer } Need N lateNonCriticalExtension nonCriticalExtension } SEQUENCE { RedirectedCarrierlnfo CellReselectionPriorities SuspendConfig OPTIONAL, OPTIONAL, OPTIONAL, SEQUENCE { ENUMERATED {frequency, nr}, ENUMERATED {min5, miniO, minl5, min30} OPTIONAL, OCTET STRING OPTIONAL, RRCRelease-vl540-IEs OPTIONAL . . . OMITTED . . . RedirectedCarrierlnfo : CHOICE { eutra CarrierlnfoNR ::= carrierFreq ssbSubcarrierSpacing smtc CarrierInfoNR, RedirectedCarrierlnfo-EUTRA, . . . OMITTED . . . SEQUENCE { ARFCN-ValueNR, SubcarrierSpacing, SSB-MTC OPTIONAL, Need S [ [ atg-Assistance-rl8 Config-rl8 OPTIONAL — Need N SEQUENCE (SIZE (0..maxCellATG-rl8)) OF ATG- . . . OMITTED . . . — TAG-RRCRELEASE-STOP — ASN1STOP CarrierlnfoNR field descriptions atg-Assistance ATG assistance information for re-directing to an ATG network. carrierFreq Indicates the redirected NR frequency. ssbSubcarrierSpacing Subcarrier spacing of SSB in the redirected SSB frequency. Only the following values are applicable depending on the used frequency: FR1: 15 or 30 kHz FR2-1: 120 or 240 kHz FR2-2: 120, 480, or 960 kHz smtc The SSB periodicity / offset / duration configuration for the redirected SSB frequency. It is based on timing reference of PCell. If the field is absent, the UE uses the SMTC configured in the measObjectNR having the same SSB frequency and subcarrier spacing. At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as ‘component’, ‘module’ or ‘unit’ used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method of operating a User Equipment, operably connected to a terrestrial telecommunication network, for mobility to an Air to Ground, ATG, telecommunication network, comprising the steps of:receiving ATG assistance information for performing measurements of an ATG cell in the ATG telecommunication network;performing measurement of the ATG cell; andperforming mobility to the ATG cell.

2. The method of claim 1, wherein the ATG assistance information is received in broadcasted information from the terrestrial telecommunication network.

3. The method as claimed in claim 1, wherein the ATG assistance information is received in a measurement configuration, transmitted from the terrestrial telecommunication network.

4. The method as claimed in claim 3, where the ATG assistance information is received, from the terrestrial telecommunication network, in an RRC release message.

5. The method as claimed in claim 4 wherein the UE performs mobility to the ATG cell based on receiving an RRC release with redirection from the terrestrial network.

6. The method as claimed in any of claims 1 to 3 wherein the UE additionally performs at least one neighbour cell measurement.

7. The method as claimed in any one of claims 1 to 3 or 6 where the UE sends a measurement report based on measuring an ATG cell using the ATG assistance information.

8. The method as claimed in any one of claims 1 to 3 or 5 to 6 wherein the UE performs mobility to the ATG cell based on receiving a handover command from the terrestrial network.

9. Apparatus arranged to perform the method of any preceding claim.

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