Method and apparatus for cell access in non-terrestrial networks

Abstract

A wireless communication unit for communicating in a wireless communication system that comprises at least one wireless non-terrestrial network, NTN cell supported by a NTN base station is described.

Description

Technical Field The technical field relates generally to implementing techniques to support cell access in nonterrestrial networks (NTNs). In particular, the technical field relates generally to implementing techniques to support NTN cell access in terrestrial frequency bands. Background In recent years, there has been a rapid development in communications technologies that are compliant with third generation partnership project (3GPP™) standards. A 4th generation (4G) wireless communication standard (sometimes referred to as long term evolution (LTE™) was designed to support mobile internet and higher speeds for activities, such as video streaming and gaming. The 3GPP™ standards then developed a fifth generation (5G) of mobile wireless communications, which provides a step change in the delivery of better and faster communications, for example powering businesses, improving communications within homes and spearheading advances, such as driverless cars. A sixth generation (6G) wireless communication standard is currently under development, as the planned successor to 5G, and will likely be significantly faster. Like its predecessors, 6G networks will likely be broadband cellular networks, in which the service area is divided into small geographical areas called cells. 6G networks are expected to be even more diverse than their predecessors and are likely to support applications beyond current mobile use scenarios, such as virtual reality and augmented reality (VR / AR), ubiquitous instant communications, pervasive intelligence and the Internet of Things (loT). It is expected that mobile network operators will adopt flexible decentralized business models for 6G, with local spectrum licensing, spectrum sharing, infrastructure sharing, and intelligent automated management underpinned by mobile edge computing, artificial intelligence (AI), short-packet communication and blockchain technologies. Non-Terrestrial Networks (NTNs) is an emerging area in 3GPP™ with Release 17 defining a solution to enable 5G 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 wireless communication unit / user equipment (UE) having global navigation satellite system (GNSS) capability and the satellite beams being both earth-fixed or earth-moving. The aim is to provide 5G cellular coverage using space-borne and / or air-borne platforms, where traditional ground-based networks have difficulty in providing coverage and / or capacity. 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-IoT and LTE-M / eMTC) [RP-202689], And NR NTN was a work item in Rei-17 to specify adaptation to allow NR to function over NTN [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 [RP-220953] and loT NTN [RP-220979] in Release 18. NR NTN phase 3 [RP-234078] is a 3GPP Work Item in 3GPP Release 19 aiming to enhance NR NTN with a range of enhancements that include: Downlink coverage enhancements; Uplink capacity and throughput enhancements by using Orthogonal Coverage Codes; MBS broadcast over NTN; Introduction of regenerative payload; Redcap and NTN enhancements; Terrestrial E-UTRAN to NR NTN mobility. 5G and 5G new radio (5G NR) include three radio resource control (RRC) states; RRC connected mode, RRC inactive mode and RRC idle mode, where RRC inactive is a newly introduced mode. RRC idle and RRC inactive operations are to a large part similar. The difference between them is in the procedures used to go to RRC connected mode: RRC idle uses the RRC connection setup procedure and RRC inactive uses the RRC resume procedures. 5G NR also features several new improvements that allow for higher throughput, lower latency and extreme flexibility. Some of these new improvements include: (i) Beam-based procedures. Here, the 5G NR device will take into account the beams in a cell in several procedures to better accommodate the advancements in multiple inmultiple out (MIMO) communications and beamforming seen over the last decade. (ii) Ultra-lean carriers: This improvement provides a reduction in the number of “always-on” signals, where the network may broadcast reference signals a lot more infrequently compared to previous generations, and allow a network to reduce the amount of system information broadcasted. (iii) More efficient state transitions: Here, a new RRC state is introduced, RRCINACTIVE. In RRC INACTIVE, the UE performs similar actions as in RRCIDLE, e.g., measuring and performing the cell reselection procedure to ensure that the UE is camping on the best cell. The network will save the UE context in the gNB and the UE will save the RRC configuration. This ensures that the state transition from RRCINACHVE and RRCCONNECTED can be completed in a much smaller number of steps compared to moving from RRC IDLE to RRC CONNECTED. In a network where there are a lot of state transitions, this can reduce latency and improve capacity as there is a lot less need for control signals to occupy capacity and resources. Referring to FIG. 1, a known simplified cellular architecture diagram 100 illustrates a first nonterrestrial base station / satellite 102 supporting communications within a coverage area 104, including communication support for a wireless communication unit, sometimes referred to as a terminal device, such as a user equipment UE 106. In 4G as well as 5G, the UE 106 is able to support traditional Human Type Communications (HTC) or the new emerging Machine Type Communications (MTC). The UE 106 is considered to be active when communicating and in the operational state technically known as radio resource control (RRC) connected. 4G or LTE™, which Internet of Things (loT) (NB-IoT and LTE-M) is based on, has two RRC states; RRC connected mode and RRC idle mode. The known simplified cellular architecture diagram 100 comprises a connection 120 that connects the first non-terrestrial base station / satellite 102 and a second terrestrial base station 108 via a gateway 114. For RRC- idle state UEs 106, a cell re-selection process may be warranted, if the signal strength from the current serving cell (e.g., non-terrestrial base station 102) deteriorates as the UE transitions from base station 102 to 108. Similarly, a cell re-selection process is performed for ‘RRC idle’ state UEs when the UE nears the cell edge of the current cell coverage area 104 that it is camped on, and is able to receive a signal from the neighbour base station 108. For loT, this is a known 4G or E-UTRAN cell reselection process, which is also driven by signal strength measurements of the base stations carried out by the UE. Thus, the 3 GPP™ LTE™ (and NR) cell reselection procedure, e.g., the act of camping on another cell, is an autonomous decision based on radio signal measurements performed by UEs 106 based on signals received from serving base station 102 and one or more neighbour base station(s) 112, sometimes referred to as fifth generation Node Bs (gNB) or eNBs, and configured thresholds that are related to such radio signal measurements. In RRC connected mode, a threshold A dB may be set to avoid ping-pong type handover near the cell border, as the instantaneous signal strengths can vary dynamically. The serving gNB 102 can instruct each individual UE 106 to provide these measurement reports and the measurement frequency can be adapted depending on whether a particular UE is nearing a cell edge, for example. Also, cell reselection processes happen on an individual UE basis, based on the measurements of the current camped-on and neighbour base stations (e.g., gNBs). In RRC idle mode / state, thresholds are also used to govern the cell reselections, but they are not used by comparing one cell with the serving cell as is done in RRC connected mode. In cell reselection in idle mode, the cells will, for instance, compute a ranking based on parameters such as thresholds and the measured signal strength. In the ‘RRC- idle’ state, the current camped-on base station (gNB) 102 is able to instruct the UEs 106 on an individual basis in order to carry out these measurements and the UE 106 themselves will initiate and carry out the cell re-selection process. FIG. 2 illustrates a known random access procedure 200 for 5G NR. Within 5G NR, and in order to move to RRC_CONNECTED, a UE 210 must first synchronize and connect to a cell / eNB 220 at 230, which it does through a 4-step random access procedure. The 4-step random access procedure was introduced for the first release of 5G NR and includes a Msgl 240 and a Msg2 250. Msgl 240 consists of a preamble sent on the Random Access Channel (RACH), which signals a number from ‘1’ to ‘64’ identifying the UE 210. Msg2 250 is the Random Access Response, which contains a timing advance to synchronize the UE 210, as well as an uplink grant to send Msg3 260. Msg3 260 contains an RRC message and Msg4 270 contains the reply to the first RRC message as well as a contention resolution MAC CE to resolve any contention. The UE 210 then enters the connected mode at 280. For a 2-step random access a MsgA consists of both the preamble and the first RRC message. MsgB consists of the random access response to synchronize the UE, which is the reply to the first RRC message as well as contention resolution. To move to RRCCONNECTED mode from RRC IDLE, the RRC Setup procedure is triggered. RRC Setup procedures establishes an SRB1 connection along with basic radio configurations. This means that the RRC message RRCSetupRequest will be included in Msg3 260 and the RRC message RRCSetup may be included in Msg4 270. After the RRC Setup procedures the network may also have to acquire capabilities, establish AS security before user plane data can be transmitted. To move to RRC CONNECTED from RRC INACUVE, the RRC Resume procedure is triggered. These procedures allow for the re-establishment of the full RRC connection, as well as resuming the AS security. This means that the RRC message RRCResumeRequest will be included in Msg3 260 and the RRC message RRCResume may be included in Msg4 270. It should be noted that MAC random access procedures are often independent of the RRC procedures, which means that the random access procedures may in general be the same for RRC Setup, RRC Resume, RRC Re-establishment and RRC reconfiguration with sync. One way to enter RRC idle or RRC inactive mode is by the network releasing the UE through the RRC release procedures. The RRC release procedures are initiated when the UE receives a RRCRelease message from the gNB. The RRCRelease message sent from the gNB may in turn have been triggered by the either the gNB or the AMF. This can for instance be due to any of the following reasons: Load balancing; Re-direction (both in RRC idle and RRC inactive) to other frequencies or RATs; UE context release triggered by the AMF (CN); Suspend indication to send the UE to RRC inactive; or Failure to retrieve UE context when UE resumes RRC connection from RRC inactive. System information is information that is broadcasted by a cell for a wide range of purposes. System information is divided into a set of System Information Blocks (SIB). Some system information is required for a UE to access a cell. Without having acquired these system information blocks the UE may not be allowed to access a cell. In example of such a SIB is SIB1, which contains access information, for instance the PLMN of the cell, the cell identity, the tracking area code as well as cell selection information. SIB1 also contains the serving cell radio configuration. Another set of SIBs contain information on other frequencies and RATs for the purpose of idle and inactive mode cell reselection as well as related parameters. These are for instance in SIB2-SIB5. As NTN has a number of NTN-specific information elements that are only required when accessing an NTN cell, and also due to the rather large information elements, it was agreed that new system information block (SIB) was needed. In NR NTN, SIB 19 contains the required information to access an NTN cell. Idle and inactive mode mobility is based on a UE autonomously performing measurements and deciding, according to some rules, whether (or not) the UE shall re-select to another cell to camp on. During cell selection, the UE identifies suitable cells, which is 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. For instance, the UE can select the cell with the strongest signal strength and signal quality within a PLMN. Cell selection can be performed following PLMN selection (which may be after a UE is turned on), after being released by a network, or during the RRC re-establishment procedure and a number of other cases. It is known that a cell may be classified into a number of different types of cells. A ‘suitable’ cell is a cell that fulfills the cell selection criteria, the cell is not barred etc., and is part of the tracking area of the UE - thus, typically referred to as a ‘normal’ type of cell. An ‘acceptable’ cell is a cell on which the UE is only allowed to camp for specific reasons, such as emergency cases, and as such the cell cannot be barred and the cell selection criteria needs to be fulfilled. A UE only camps on such a cell if it cannot find a suitable cell. A ‘reserved’ cell is reserved if the system information indicates that it is reserved. When camped on a cell, the UE shall perform the cell reselection procedures that includes searching and detecting cells and camping on a better or more suitable cell. In the cell reselection procedure, the UE searches intra-frequency cells, inter-frequencies cells and inter-RAT cells following the signalling by the serving cell. Each frequency (inter-RAT or intra-RAT) may have a specific cell reselection priority. The cell reselection algorithm is designed to ensure that the UE chooses a cell with highest priority, given that it is not barred or not allowed to camp on. A UE shall always select an inter-frequency or inter-RAT cell with a higher priority over a lower priority cell. If frequencies 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. It is known that there are also certain rules relating to how long a new cell shall be considered to be better than the serving cell before camping on the new cell. This parameter is called Treselection and can be specific for a RAT, or for other cases. It is known that there are also thresholds for the signal strength of signal quality that may need to be fulfilled before selecting a new cell to camp on, which may depend on whether the cell is lower or higher priority, and may depend on whether the cell is inter-frequency or inter-RAT. As part of the idle mode and inactive procedures, the UE also checks whether (or not) a cell is barred. If a cell is barred, the UE is not allowed to connect to the cell, and thus not allowed to camp or consider the cell for cell reselection. In 4G, the barring bit is signalled in SIB1 whilst in 5G NR, the barring bit is signalled in MIB. Inter-RAT may be considered any other than the current RAT. As an example for 4G E-UTRA UE, the following may be considered inter-RAT: 2G, 3G, 4G NB-IoT, 5G NR or 6G. It is generally understood that a terrestrial network will, in most cases, be a much more efficient use of network resources as compared to a non-terrestrial network. This is because a terrestrial network has higher capacity, smaller cells, etc. This means that for an operator, while a nonterrestrial network operating in its spectrum may provide a crucial service to its customers, it is vital that this resource is only used when absolutely necessary. However, referring now to FIG. 3, let us consider a scenario 300 where a non-terrestrial network is deployed in a terrestrial band and where, for instance, the non-terrestrial cells are operating in a discontinuous coverage fashion, in other words the satellite coverage is not continuous and varies over time 312 at the same geographical location. In that case, a UE in rural coverage, may see spikes where the radio signal 310 conditions to the non-terrestrial cell 325 may be stronger 330 than the radio signal of the terrestrial cell 320. Typical cell reselection algorithms would, thus, have the UE connect to such non-terrestrial cells 325. However, the inventors have recognized and appreciated that an operator may not wish for the UE to do this, as this may produce interference and due to the fact that the satellite spectrum is less efficient, the NTN cell 325 should only be used when absolutely necessary. Thus, in light of the above, the inventors have recognised and appreciated that there needs to be mechanisms for a network to control how the UE interacts with non-terrestrial cells, particularly in or overlapping with a terrestrial band. Thus, a need exists for an improved system, improved devices and methods to support cell access in non-terrestrial networks (NTNs), and particularly to support NTN cell access in terrestrial frequency bands Summary A wireless communication system, a wireless communication unit, a NTN base station, and methods of supporting cell access in non-terrestrial networks (NTNs) are described. Brief Description of the Drawings Further details, aspects and embodiments will be described, by way of example only, with reference to the drawings. In the drawings, similar reference numbers are used to identify like, or functionally similar, elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. FIG. 1 illustrates a known simplified non-terrestrial cellular architecture with a known NR NTN and loT NTN operation. FIG. 2 illustrates a known random access procedure for 5G NR. FIG. 3 illustrates a known scenario where a non-terrestrial network is deployed in a terrestrial band and where non-terrestrial cells are operating in a discontinuous coverage fashion. FIG. 4 illustrates a 3GPP™ 5G communication system with NTN and TN base stations, adapted in accordance with some examples. FIG. 5 illustrates a block diagram of an NTN base station communicating with a wireless communication unit (e.g., UE), adapted in accordance with some example embodiments. FIG. 6 illustrates two examples of a message sequence chart to determine and attempt to detect non-terrestrial cells, in accordance with some example embodiments. FIG. 7 illustrates a simplified message sequence chart of a wireless communication unit (e.g., UE) configured to not be allowed to operate on a non-terrestrial cell in a terrestrial band, for example if the wireless communication unit (e.g., UE) is rejected by the non-terrestrial cell operating in the terrestrial band, in accordance with some example embodiments FIG. 8 illustrates three simplified flowcharts for conditions that make a cell appear as barred or not barred, in accordance with some example embodiments. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and / or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various example embodiments. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments. It will be further appreciated that certain actions and / or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein. Detailed Description In examples herein described, a wireless communication unit, e.g., a UE, may select, camp, connect and / or operate in a non-terrestrial network cell operating in a terrestrial frequency under certain conditions. For example, one condition may be due to the terrestrial network being ‘down’ or because there are no terrestrial networks in the area that the wireless communication unit (UE) is currently in. In another example, one of the conditions may be that the wireless communication unit (UE) determines that there is no terrestrial network. This can be determined by the wireless communication unit (UE) detecting that there are no non-NTN cells detected. Alternatively, in another example, one of the conditions may be that the wireless communication unit (UE) may determine that there are no suitable non-NTN or terrestrial cells, or it may determine that there are no suitable or acceptable non-NTN or terrestrial cells, or it may determine that there are no other idle / inactive mode type of non-NTN cells. In some examples, such a determination may consist of no terrestrial cell (or no non-NTN cell) being detected within a certain period of time. In some examples, this period of time may be configurable, for example either by the terrestrial or a non-terrestrial cell or network. In some examples, this period of time may be defined as the time from last detecting a terrestrial cell or network, or may be defined as the time when a wireless communication unit (UE) detects a (or the) non-terrestrial cell or network. The inventors have also recognised and appreciated that the ephemeris described in 5G NR is not only applicable for satellite payloads, for which it is described, but it may also apply to other platforms, such as High Altitude Platform Systems (HAPS) or to other types of networks such as Air-To-Ground networks. Furthermore, it is also envisaged by the inventors that the term “Terrestrial network”, when it is used herein, may not only be a land mobile network (e.g. IMT), but may also encompass other terrestrial telecommunication services, for example if it indicates that it is a terrestrial cell, or if the cell does not indicate any essential NTN indication, such as SIB19 or cellBarred-NTN for NR NTN or SIB31 or cellBarred-NTN for loT NTN. It is envisaged that this, for instance with reference to NTN and / or satellite networks, may include Air-To-Ground networks or High Altitude Platform Systems (HAPS) and / or other systems operational above the earth surface. Referring now to FIG. 4, part of a wireless communication system 400 is shown in outline, in accordance with some example embodiments. In this example embodiment, the wireless communication system 400 is compliant with, and contains network elements capable of operating over, a 4th generation (4G), a 5th generation (5G) or 6th generation (6G) wireless communication system, which are currently under discussion in the third Generation Partnership Project (3GPP™). The wireless communication system 400 architecture consists of radio access network (RAN) and core network (CN) elements (not shown), with the core network elements being coupled to external networks (named Packet Data Networks (PDNs)), such as the Internet or a corporate network. The CN is typically connected to the wireless base stations, which may take a form of eNB, gNB, etc., via gateways (not shown). In accordance with examples herein described, a wireless communication system comprises a first base station, such as NTN eNB 414, supporting a first terrestrial network and a second base station, such as NTN gNB wireless base station 412 supporting a second terrestrial network, and a plurality of wireless communication units / UEs 425. NTN eNB 414 and NTN eNB 412, are illustrated as a form of a satellite, and they arranged to perform many standard base station functions. They are connected to the CN via an SI interface / feeder link 424 and to the wireless communication units 425 via a Uu interface. The two NTN NodeBs (eNB 410 and gNB 412), provide respective, coverage areas (or cells) 480, 485. A plurality of wireless communication units 425 may also communicate with a serving TN eNB 410 that supports communication coverage in area (or cell) 490. In accordance with example embodiments, at least one eNB 410, gNB 412 and at least one UE 470, 475 (amongst other elements) have been adapted to support the concepts hereinafter described. A wireless communication system will typically have a large number of such infrastructure elements, including a number of terrestrial base stations where only one, e.g., TN eNB 410, is shown for clarity purposes in FIG. 4. Each of the TN eNB 410 and the NTN gNB 412 and NTN eNB 414 is able to control and manage the radio resource related functions for a plurality of wireless communication units 450, 470, 475. Each of the base stations, including the NTN gNB 412 and NTN eNB 414 includes a transceiver (that includes a transmitter and a receiver) operably coupled to a signal processor. The transceiver and signal processor of the NTN base stations, e.g., NTN gNB 412 and NTN eNB 414, are collaboratively arranged to transmit and / or receive signals from wireless communication units according to the examples described below, e.g., to facilitate at least one wireless communication unit to select, camp, connect and / or operate in a non-terrestrial network cell operating in a terrestrial frequency under certain conditions. Similarly, the transceiver and signal processor of the wireless communication units 450, 470, 475 are collaboratively arranged to transmit and / or receive signals from a base station (either NTN or TN) according to the examples described below, e.g., to select, camp, connect and / or operate in a non-terrestrial network cell operating in a terrestrial frequency under certain conditions. Referring now to FIG. 5, more detailed block diagrams of a wireless base station 510 (equivalent in functionality details to TN or NTN eNB or gNB base stations 410, 412, 414 in FIG. 4) and a wireless communication unit 550 (equivalent in functionality details to UE 450, 470, 475 in FIG. 4) are illustrated, where the respective communications units have been adapted in accordance with some example embodiments. The (eNB or gNB) (TN or NTN) wireless base station 510 contains an antenna 502, for receiving transmissions, coupled to an antenna switch or duplexer 504 that provides isolation between receive and transmit chains within the eNB or gNB TN or NTN wireless base station 512. One or more receiver chains, as known in the art, include receiver front-end circuitry 506 (effectively providing reception, filtering and intermediate or base-band frequency conversion). The receiver front-end circuitry 506 is coupled to a signal processor 508 (generally realized by a digital signal processor (DSP)). A skilled artisan will appreciate that the level of integration of receiver circuits or components may be, in some instances, implementation-dependent. The controller 514 maintains overall operational control of the eNB or gNB TN or NTN wireless base station 512. The controller 514 is also coupled to the receiver front-end circuitry 506 and the signal processor 508. In some examples, the controller 514 is also coupled to a frequency generation circuit 517 and a memory device 516 that selectively stores operating regimes, such as decoding / encoding functions, synchronization patterns, code sequences, and the like. A timer 518 is operably coupled to the controller 514 to control the timing of operations (e.g., transmission or reception of time-dependent signals) within the eNB or gNB TN or NTN wireless base station 512 As regards the transmit chain, this essentially includes an input interface 520, coupled in series through transmitter / modulation circuitry 522 and a power amplifier 524 to the antenna 502, antenna array, or plurality of antennas. The transmitter / modulation circuitry 522 and the power amplifier 524 are operationally responsive to the controller 514. The signal processor 508 in the transmit chain may be implemented as distinct from the signal processor in the receive chain. Alternatively, a single processor may be used to implement a processing of both transmit and receive signals, as shown in FIG. 5. Clearly, the various components within the eNB or gNB TN or NTN wireless base station 512 can be realized in discrete or integrated component form, with an ultimate structure therefore being an application-specific or design selection. The signal processor 508 and transceiver (e.g., transmitter / modulation circuitry 522 and receiver front-end circuitry 506 and associated (e.g., frequency converting, amplifying, filtering, etc.) circuits of the (NTN eNB or gNB in FIG. 4) NTN wireless base station 510 are configured to support cell access in NTNs of a served wireless communication unit, such as a UE. The transceiver and signal processor of the NTN wireless base station 510 are collaboratively arranged to transmit and / or receive signals from wireless communication units according to the examples described below, e.g., to facilitate at least one wireless communication unit to select, camp, connect and / or operate in a non-terrestrial network cell operating in a terrestrial frequency under certain conditions, for example at least in accordance with the approach described in one or more of FIG. 6, FIG. 7 or FIG. 8 or any of the examples described below FIG. 5 also shows a high-level block diagram of the wireless communication unit (e.g., a user equipment (UE) in 3GPP parlance) 550 contains an antenna 552, for receiving transmissions, coupled to an antenna switch or duplexer 554 that provides isolation between receive and transmit chains within the wireless communication unit 550. One or more receiver chains, as known in the art, include receiver front-end circuitry 556 (effectively providing reception, filtering and intermediate or base-band frequency conversion). The receiver front-end circuitry 556 is coupled to a signal processor 558 (generally realized by a digital signal processor (DSP)). A skilled artisan will appreciate that the level of integration of receiver circuits or components may be, in some instances, implementation-dependent. The controller 564 maintains overall operational control of the wireless communication unit 550. The controller 564 is also coupled to the receiver front-end circuitry 556 and the signal processor 558. In some examples, the controller 564 is also coupled to a frequency generation circuit 567 and a memory device 566 that selectively stores operating regimes, such as decoding / encoding functions, synchronization patterns, code sequences, and the like. A timer 568 is operably coupled to the controller 564 to control the timing of operations (e.g., transmission or reception of time-dependent signals) within the wireless communication unit 550. As regards the transmit chain, this essentially includes an input interface 570, coupled in series through transmitter / modulation circuitry 572 and a power amplifier 574 to the antenna 552, antenna array, or plurality of antennas. The transmitter / modulation circuitry 572 and the power amplifier 574 are operationally responsive to the controller 564. The signal processor 558 in the transmit chain may be implemented as distinct from the signal processor in the receive chain. Alternatively, a single processor may be used to implement a processing of both transmit and receive signals, as shown in FIG. 5. Clearly, the various components within the wireless communication unit 550 can be realized in discrete or integrated component form, with an ultimate structure therefore being an application-specific or design selection. The signal processor 558 and transceiver (e.g., transmitter / modulation circuitry 572 and receiver front-end circuitry 556) of the wireless communication unit 550 are configured to communicate with the (eNB or gNB) (TN or NTN) wireless base station 510 In accordance with some examples, the processor 558 and transceiver (e.g., transmitter / modulation circuitry 572 and receiver front-end circuitry 556) of the wireless communication unit 550 are collaboratively arranged to transmit and / or receive signals from wireless base station 510 according to the examples described below, e.g., to select, camp, connect and / or operate in a non-terrestrial network cell operating in a terrestrial frequency under certain conditions, in accordance with the approach described in one of FIG. 6, FIG. 7 or FIG. 8 or any of the examples described below Conditions for using non-terrestrial network in terrestrial band Referring now to FIG. 6, two examples of a message sequence chart are illustrated to determine and attempt to detect non-terrestrial network (NTN) cells, in accordance with some example embodiments. A first example approach is illustrated in first message sequence chart 600, which starts at 605 with a wireless communication unit (e.g., UE) identifying whether (or not) a nonterrestrial cell is operational in a terrestrial spectrum, and the process loops, as shown, until such a NTN cell is identified. At 610, a determination is made as to whether (or not) there are any (alternative) terrestrial cells available for the wireless communication unit to access. If there are terrestrial cells available at 610, the wireless communication unit’s operation continues to loop (and possibly the wireless communication unit will access one of the identified terrestrial cells). However, if there are no terrestrial cells available at 610, the wireless communication unit (e.g., UE) at 615, then selects, camps, connects or operates on the non-terrestrial cell that is operational within the terrestrial frequency band. A second example approach is illustrated in second message sequence chart 650, which starts at 655 with the wireless communication unit (e.g., UE) identifying whether there are no terrestrial cells available, and the process loops whilst there are terrestrial cells available, as shown, until the terrestrial cells are no longer identified, e.g. the terrestrial cells are no longer operational. At 660, a search is made for non-terrestrial cells in terrestrial spectrum. If there are no nonterrestrial cells in terrestrial spectrum found at 660, the UE’s operation continues to loop. However, if there are non-terrestrial cells in terrestrial spectrum found at 660, at 665 the wireless communication unit (e.g., UE) then selects, camps, connects or operates on the non-terrestrial cell that is operational within the terrestrial band. In an alternative approach to 660, in some examples, the wireless communication unit may have already searched and detected non-terrestrial cells in the terrestrial spectrum in advance. In other words, the condition to access a non-terrestrial cell in a terrestrial band may be initiated when the wireless communication unit no longer detects any cells, or alternatively it may be initiated when the wireless communication unit detects a non-terrestrial cell. In this latter case, it may be initiated as the wireless communication unit detects a non-terrestrial cell that indicates that one or more condition(s) need(s) to be fulfilled or it may be initiated upon identifying a nonterrestrial cell operating in a terrestrial band. In some examples, this may be relevant if the network provides NTN assistance information in advance, because searching and detecting NTN cells using the NTN assistance information may need more power consumption and may normally be required by a wireless communication unit. Thus, after the wireless communication unit detects that no terrestrial cells are available, the wireless communication unit may start searching for non-terrestrial cells in the terrestrial band, as shown at 660. This can ensure that non-terrestrial cells in terrestrial bands are not used until there is no chance of connecting to the terrestrial cells. In some examples, the terrestrial cells that shall be attempted to be detected may be one or more of: terrestrial cells of a specific band, cells having a specific Tracking Area Code (TAC), cells within a specific PLMN, cells using a specific Radio Access Technology (RAT) or other type of network level entity. In some examples, it is also envisaged that the terrestrial cells may also be any type of terrestrial cell, e.g., of other PLMNs or RATs. In other words, this may mean that the condition is that the wireless communication unit (UE) is unable to detect terrestrial cells within the TAC, within the PLMN or within the RAT. In some examples, it is also envisaged that the terrestrial cell may indicate that there are nonterrestrial cells operating on the same band (or other terrestrial bands). In some examples, the terrestrial cell may also indicate the condition for said non-terrestrial cell. This may, for instance, be indicated in a system information block that indicates intra-frequency or inter-frequency information such as SIB2, SIB3, or SIB4. In some examples the condition may be configurable, meaning that one or more type of conditions may be configured. In this example, it is also envisaged that the condition may be configured specifically for all NTN cells operating on a terrestrial band, or indicated for a cell individually. In some examples, it is also envisaged that the non-terrestrial cell may also indicate that it is a non-terrestrial cell that is operating in a terrestrial band, and may also indicate the one or more specific condition(s) for selecting, camping, connecting and or operating on the non-terrestrial cell. In some examples, it is also envisaged that the condition of the wireless communication unit having detected a terrestrial cell may also incorporate the wireless communication unit determining that the terrestrial cell is a suitable cell, which may mean determining that the terrestrial cell is part of a PLMN and / or determining that the cell is not barred and it is not part of a forbidden tracking area for roaming. In some examples, it is also envisaged that the wireless communication unit may also determine that the terrestrial cell is an acceptable cell (e.g., a cell in which the wireless communication unit may obtain limited service such as emergency calls and receive ETWS and CMAS notification). In some examples, it is also envisaged that the wireless communication unit may also determine that the terrestrial cell is a reserved cell. This may for instance mean that the wireless communication unit (e.g., UE) is not considered to have detected a terrestrial cell if the wireless communication unit detects a terrestrial cell which is barred, or any other type of cell that the wireless communication unit is unable to camp on. In one example, it is envisaged that the non-terrestrial cell operating in a terrestrial band may indicate those frequency bands that the wireless communication unit shall search before selecting, camping, connecting or operating on the cell. The condition may thus be that there are no suitable cells, acceptable cells or similar on the bands indicated by the non-terrestrial cell. In one example, it is envisaged that the non-terrestrial cell operating in a terrestrial frequency band may indicate specific thresholds for terrestrial cells, to assist in a determination as to whether the wireless communication unit may select, camp, connect or use the non-terrestrial cell operating in a terrestrial cell. In some examples, this may, for instance, mean that the wireless communication unit searches for terrestrial cells and checks whether the signal strength and / or signal quality is above a specified threshold, before the wireless communication unit selects, camps, connects or uses the non-terrestrial cell. If one or more terrestrial cells fulfils the threshold criteria, the wireless communication unit shall not select, camp, connect or use the non-terrestrial cell. In one example, it is envisaged that this approach may be in addition to any cell suitability requirements, which may be determined based on the parameters that are valid for all cells (non-terrestrial and terrestrial cells). It is envisaged that the specific thresholds may, for instance, be q-RxLevMin (minimum signal strength level), q-RxLevMinOffset (minimum signal strength level offset) and q-QualMin (minimum signal quality level). In the above approach, where a condition to determine whether the wireless communication unit is able to detect any cells in a terrestrial band is satisfied, the condition may also be such that no terrestrial cell is detected and that no NTN cell in an NTN band is detected. This leaves the NTN cells in an TN band left. In other words, the UE shall not attempt to select an NTN cell in a TN band if there are TN cells or if there are NTN cells in an NTN band. The reason why NTN cells in an NTN band is included is because this should not cause interference to a TN network like accessing an NTN cell in a TN band. This may be important as the non-terrestrial cell operating in a terrestrial band may only be chosen in case there are no other cells, whilst a nonterrestrial cell in a non-terrestrial (e.g., MSS) band may still be relevant to be selected, as this would not interfere with terrestrial cells. In one example, it is envisaged that one condition applied to a wireless communication unit to select, camp, connect or use a non-terrestrial cell in a terrestrial spectrum may be that the wireless communication unit has been informed that this opportunity is allowed, or that the network supports this option. This may, for instance, be indicated by a base station, e.g., eNB, gNB or any other next generation NB, or can be indicated by the core network, for instance via NAS. Thus, if this opportunity is not indicated, then the wireless communication unit will not attempt to select, camp, connect or use a non-terrestrial cell. This may be important due to, for example, security reasons, as a rogue satellite can provide global connectivity without even needing to be deployed in the country, as opposed to a terrestrial cell, which would need to be deployed in a specific country. In one example, it is envisaged that the wireless communication unit may only be allowed to use the non-terrestrial cell in a terrestrial band if the geographical position / location of the wireless communication unit fulfils a specific requirement. It is envisaged that this condition may, for instance, be that the wireless communication unit is in a position / location that is far away from a specific geographical point, where that geographical point may represent where there is a terrestrial network. Thus, this may be implemented by providing a geographical point, and a distance threshold , and the condition may be that the wireless communication unit is further away than the threshold, i.e., a determined distance exceeds the distance threshold. This can be done by the wireless communication unit determining its position for instance by using GNSS. The distance threshold may be a parameter in a suitable unit of length. In some envisaged examples, this may also be a set of geographical points and distance-thresholds. In some envisaged examples, this may be signalled by the network, i.e., a base station or a cell, for instance broadcasted, or provided via NAS, from a core network unit, to the wireless communication unit. In some envisaged examples this may be signalled by a terrestrial network or by the non-terrestrial network in the terrestrial band. For instance, it can be considered to be a location-dependent cell exclusion, where a cell is considered to be excluded from camping, cell selection or cell reselection, or connecting to the cell depending on the wireless communication unit geographical location. In some envisaged examples this may be important in ensuring that only the affected regions are camping or connecting to the non-terrestrial cell. In some envisaged examples, the wireless communication unit may only be allowed to use the non-terrestrial cell in a terrestrial band as defined by a list of RATs that are allowed or not allowed to operate at the present location. For example, a NTN may be considered a sub-RAT, for instance such that NTN is allowed or not allowed to operate at the present location. In one example, it is envisaged that if the non-terrestrial cell in a terrestrial band is a part of an excluded list, then the excluded non-terrestrial cell may, in some cases, be exempted. In one example, it is envisaged that this may, for instance, be exempted if the cell that the wireless communication unit camps on is considered an acceptable or reserved cell. In some examples, it is envisaged that other conditions may be emergency scenarios. In some envisaged examples, the wireless communication unit may be configured with an excluded list in SIB3 (intra-frequency cell-specific cell reselection information), SIB4 (inter-frequency cell reselection information) or SIB5 (inter-RAT cell reselection information) in NR, or with SIB4 (intra-freq.), SIB5 (interfreq.) or SIB8 (inter-RAT). In one example, it is envisaged that a wireless communication unit may also be allowed to camp on a non-terrestrial cell in a terrestrial band if the non-terrestrial cell provides a broadcasting service that the wireless communication unit is interested in receiving. In some examples, it is envisaged that this may mean that the wireless communication unit does not consider the cell barred if the non-terrestrial cell provides a broadcasting service that the wireless communication unit is interested in receiving. For example, there may for instance be conditions imposed on camping on this cell, which can be that the wireless communication unit does not (i.e., is prevented to) transmit anything in the uplink, e.g., the wireless communication unit only performs reception. In some examples, this may be very useful to prevent transmitting in the uplink, as there would be no harm caused to the terrestrial network. Emergency conditions In one example, it is envisaged that one condition regarding when the wireless communication unit may select, camp, connect and / or operate in a non-terrestrial cell or network using terrestrial frequency band is whether there is currently an emergency scenario on-going. It is envisaged that this can, for instance, be a network-initiated emergency scenario, such as an Earthquake and Tsunami Warning System (ETWS) or Commercial Mobile Alert System (CMAS) indication, such as during public emergencies. This means that when any public warning system is initiated, either at a terrestrial network, non-terrestrial network or both, the wireless communication unit may be allowed to use a non-terrestrial cell or network that is using a terrestrial band. This may, for instance, be identified by the network transmitting any system information indicating public warning. The wireless communication unit may only be allowed to select, camp, connect and / or operate in a non-terrestrial cell or network using terrestrial band during a certain time after receiving the public emergency notification, e.g., the condition may restrict the wireless communication unit from selecting and camping on the NTN cell for a period of time after receiving the on-going network-initiated emergency scenario or the public emergency notification. This can be configured by the network or hardcoded. For instance, the wireless communication unit is only allowed to use the non-terrestrial cell using terrestrial band during at most, for example, less than a few minutes, and for example, say, 100 seconds after receiving the last public emergency notification. In alternative examples, it is envisaged that this may also be an emergency case initiated by the wireless communication unit, such as during personal emergencies. For a personal emergency scenario, such as when an emergency call or emergency message is to be performed, the wireless communication unit may be allowed to use or connect to a non-terrestrial cell or network using terrestrial spectrum. Here, it is envisaged that the wireless communication unit may be allowed to use the non-terrestrial cell or network using a terrestrial band if the wireless communication unit needs to perform emergency calls, which can for instance be an eCall Only Mode, or if the wireless communication unit performs IMS emergency calls. It is envisaged that in some examples the wireless communication unit may only be allowed to camp on the NTN cell using a terrestrial band if the wireless communication unit is performing emergency camping on the NTN cell. It is envisaged that in some examples the wireless communication unit may only be allowed to camp on the NTN cell if the NTN cell is defined (permanently or temporarily) as an emergency-only cell. Thus, a non-terrestrial cell operating in a terrestrial band may be considered as an emergency cell in which the wireless communication unit is always only allowed to select, camp, connect or operate on due to emergency reasons. In other words, the cell may be dedicated to emergency cases. In some examples, the emergency NTN cell may indicate this in system information and other cells (terrestrial or non-terrestrial) may indicate the presence of this type of emergency cell in system information, for instance as part of inter-frequency system information or inter-RAT system information. It is envisaged that this broadcasting of emergency NTN cell information may also form a part of disaster roaming information. Here, in one example, the wireless communication unit may be allowed to select, camp, connect and / or operate on a non-terrestrial cell in a terrestrial band if the cell is signalled as part of a disaster roaming PLMN or network. Terrestrial network down or out of service In one example, it is envisaged that the wireless communication unit may be allowed to use the non-terrestrial cell in a terrestrial band if the terrestrial cellular system has been determined to be unavailable. In order words, if the terrestrial cellular system has been determined to have ‘gone down’, for instance due to power outage or a natural disaster. In this scenario, it is useful to determine whether (or not) the terrestrial system is down, or becoming out-of-service, instead of the wireless communication unit just transitioning to being out of coverage of the terrestrial system. If only the RF signal is used to determine whether the terrestrial system is down, then it is likely that it cannot be determined conclusively that the wireless communication unit is out of coverage or whether the terrestrial system is down. The inventors have recognized and appreciated that there is also the possibility that the terrestrial cell is still operating, but that the core network or the backhaul to the core network is down or out-of-service. Thus, in some examples it is envisaged that the wireless communication unit is arranged to identify that the terrestrial system is ‘down’, following any indication in advance that is received regarding the possibility of the terrestrial going down or out-of-service. This may, for instance, be following the network (e.g., an eNB or gNB) transmitting any emergency indication, such as PWS, ETWS or CMAS. Here, it is envisaged that the network may also indicate in advance that the network may go down in the near future, for instance the network may indicate that it is now running on emergency power. It is envisaged that this may for instance be indicated in a PWS message, such as in the ETWS or CMAS indication. In this case, the wireless communication unit receives an indication from the terrestrial network that the network is about to go down, and once the network is down, the wireless communication unit will be allowed to select, camp, connect and / or operate on a non-terrestrial cell in a terrestrial band. In some examples, it is envisaged that once the indication that the network is about to go ‘down’ is received, the wireless communication unit may be allowed to transition to and use the non-terrestrial cell in a terrestrial band. In some examples, it is envisaged that detecting that the terrestrial system is down may also include detecting that the terrestrial cell or network is no longer providing coverage, despite low or no mobility of the device. For instance, if the wireless communication unit has been served by the network for a long time, and the service stops, then the wireless communication unit may be allowed to select, camp, connect and / or operate on a non-terrestrial cell in a terrestrial band. In some examples, it is envisaged that the condition to determine whether the terrestrial network is ‘down’ or out-of-service may be configurable by the network. Here, it is envisaged that the network, for instance over AS or NAS, may also configure whether the wireless communication unit is allowed to select, camp, connect and / or operate on non-terrestrial network in a terrestrial band under these conditions. Released or rejected It is also envisaged that, in some examples, the wireless communication unit may be allowed to select, camp, connect and / or operate on a non-terrestrial cell in a terrestrial band if the wireless communication unit is rejected by the terrestrial network, where the terrestrial network operates in the same band as the NTN. Here, the wireless communication unit may be allowed to select, camp, connect and / or operate on a non-terrestrial cell in a terrestrial band if the wireless communication unit is released or re-directed by the terrestrial network, where the terrestrial network operates in the same or different band as the NTN cell. The cell release or cell redirection may include a specific indication that the wireless communication unit is allowed to select, camp, connect and / or operate on the non-terrestrial cell in a terrestrial band. In some examples, it is envisaged that this specific indication may be valid for any frequency band or only specific frequency bands. In some examples, it is envisaged that if the wireless communication unit is re-directed, then the indication may only be valid for the frequency band that the wireless communication unit is re-directed to. Referring now to FIG. 7, one example message sequence chart 700 illustrates when a wireless communication unit, for example in a form of a UE 550, may also be configured to not be allowed to camp on a non-terrestrial cell in a terrestrial band if the UE 550 is rejected by the nonterrestrial cell, e.g., by a NTN gNB 510, operating in a terrestrial band, in accordance with some example embodiments. Here, for example, the UE 550 may be operating in a RRC Connected mode at 710 and initiates a RRC Connection setup or resume or other connection attempt to the NTN gNB 510 at 715. At 720, the NTN gNB 510 decides that the UE is not allowed to access or stay connected to the non-terrestrial cell in a terrestrial band supported by the NTN gNB 510. At 725, the NTN gNB 510 sends a RRCConnectionRelease (or reject) message to the UE 550, which informs the UE 550 that it is not allowed to operate using the non-terrestrial cell in a terrestrial band supported. In some examples, it is envisaged that this may, for instance, be a flag that indicates that the UE 550 is not allowed to camp, select or operate on the non-terrestrial cell in the specific band, or indeed any other band. At 730, the UE may then enter an idle mode of operation and it is not allowed to connect to the non-terrestrial cell. In some examples, the UE 550 may be configured with a timer, where the UE 550 is not allowed to camp, select and / or operate on a non-terrestrial cell in a specific band for a set period of time. It is envisaged in some examples that an elapsed time period may be configurable or hardcoded in the specification. If the elapsed time period is configurable, it is envisaged that this may be included in the specific message that indicates that the UE 550 may not access the non-terrestrial network. In this manner, this is different from any other type of reject timer, since the UE 550 is rejected from the non-terrestrial network exclusively. In some examples, it is envisaged that this access rejection may, for instance, be triggered by the network determining that the UE 550 may produce interference for the terrestrial network, or if the geographical position of the UE 550 is determined to be likely to produce interference, or if the geographical position of the UE 550 is not where the non-terrestrial network shall provide coverage. Capacity enhancement It is also envisaged that in some examples, the wireless communication unit, for example in a form of a UE 550, would be allowed to use the non-terrestrial cell in a terrestrial band if the network resources of a land-based network are limited. For example, the wireless communication unit may be allowed to select, camp, connect and / or operate on a non-terrestrial cell in a terrestrial band in order to fulfil the expected resource requirements of specific services. For example, when the wireless communication unit tries to use a specific service, but the serving land-based network cannot satisfy the requirements of the service, the wireless communication unit may split out (e.g., divide) the traffic data that is related to the service and send the traffic data through the non-terrestrial cell. In this manner, the wireless communication unit will not influence the other existing traffic through the terrestrial cell. The condition to determine whether the terrestrial network is unable to fulfil the requirements of a service may be configurable by the network. In this manner, the network may also decide whether the wireless communication unit is allowed to operate in dual-connectivity to both the terrestrial and nonterrestrial cell. Implementing the conditions It is envisaged that the above may be implemented as conditions to camp on an NTN cell using terrestrial spectrum, or conditions to select or reselect on an NTN cell using terrestrial spectrum. It is envisaged that the above may also be implemented as conditions that make a cell appear as barred or not barred. For example, if the cell is an NTN cell operating in a terrestrial spectrum and the UE has detected a terrestrial cell within the last 100 seconds, it may be assumed that the cell is barred, and if over the last 100 seconds, for example, consider the cell as not being barred. Referring now to FIG. 8, three simplified flowcharts are illustrated for conditions that make a cell appear as barred or not barred, in accordance with some example embodiments. A first flowchart 800 starts at 810 with a determination of whether there are no terrestrial cells available with a period of time, say the last 100 seconds. If it is determined that there are no terrestrial cells available at 810, at 815 the non-terrestrial cell on a terrestrial band is not considered as being barred by the wireless communication unit. However, if it is determined that there are terrestrial cells available at 810, at 820 the non-terrestrial cell on a terrestrial band is considered as being barred by the wireless communication unit. Alternatively, as illustrated in second flowchart 830, if the cell is an NTN cell that indicates the configuration ntn-TerrestrialBand (e.g., an NTN cell operating in a terrestrial spectrum) at 835, and the wireless communication unit has detected a terrestrial cell within, say, the last 100 seconds, the wireless communication unit may consider the cell as being barred, otherwise consider the cell as not being barred. If it is determined that there are no terrestrial cells available at 835, at 840 the NTN cell that indicates the configuration ntn-TerrestrialBand is not considered as being barred by the wireless communication unit. However, alternatively at 835, if it is determined that there are terrestrial cells available at 830, at 845 the non-terrestrial cell on a terrestrial band is considered as being barred by the wireless communication unit. In other examples, the non-terrestrial cell may be required to indicate that it is operating in a terrestrial band, which may be the flag ntn-TerrestrialBand. If the cell is an NTN cell operating in a terrestrial band, and the wireless communication unit has detected a terrestrial cell in the current PLMN, say within the last 10 seconds, the wireless communication unit may consider the cell barred, otherwise the wireless communication unit may consider the cell to not be barred. In other examples, in third flowchart 860, if the cell is an NTN cell operating in a terrestrial band, and the NTN cell is not broadcasting a System Information indicating emergency scenario, as determined by the wireless communication unit at 865, the wireless communication unit may consider the cell to be barred at 870. Otherwise, and alternatively, if the NTN cell is broadcasting system information indicating an emergency scenario, the wireless communication unit may consider the cell to not be barred at 875. Envisaged examples of the emergency scenario include, (a) In 5G NR, SIB6 and SIB7 broadcasts Earthquake and Tsunami Warning System (ETWS) notifications; (b) In 5G NR, SIB8 broadcasts Commercial Mobile Alert Service (CMAS) notifications; (c) In 5G NR, SIB 15 broadcasts disaster roaming information; (d) In 4G LTE, SIB10 and SIB11 broadcasts ETWS notifications; (e) In 4G LTE, SIB 12 broadcasts CMAS notifications; and (f) In 4G LTE, SIB30 broadcasts disaster roaming information. In some examples, it is envisaged that if the cell is an NTN cell operating in a terrestrial band, and no cell (either terrestrial or non-terrestrial) has broadcasted system information indicating emergency scenario, the wireless communication unit may consider the cell to be barred, or alternatively if any cell has not broadcasted system information that indicates an emergency scenario, the wireless communication unit may consider the cell not barred. In some examples, it is envisaged that the NTN cell using terrestrial band may only be considered a suitable cell by a wireless communication unit in, say, one or more of the following scenarios: (i) The wireless communication unit is unable to find any suitable terrestrial cells on terrestrial bands or any suitable cells on non-terrestrial bands. (ii) The non-terrestrial cell indicates a configuration that it is operating in a terrestrial band and the wireless communication unit is unable to find any suitable terrestrial cells on terrestrial bands or any suitable cells on non-terrestrial bands. (iii) The wireless communication unit has detected emergency broadcasting, such as PWS, ETWS or CMAS or similar, on at least one cell, which may be a cell that is a terrestrial cell or a non-terrestrial cell on a non-terrestrial frequency band. Assistance signalling In some examples, it is envisaged that the network may signal that there may be NTN cells on a specific terrestrial band or frequency. In some examples, it is envisaged that this may be signalled as part of intra-frequency cell (re)selection parameters, such as using SIB2 or SIB3 in NR or SIB3 or 4 in LTE™. This means that the network signals that there may be an NTN cell on the same frequency as the cell that the wireless communication unit is connected to. In some examples, it is envisaged that it may also be signalled as part of inter-frequency cell (re)selection parameters, such as SIB4 in NR or SIB 5 in LTE™. This means that the network signals that there may be an NTN cell on another terrestrial frequency. In some examples, it is envisaged that the network may signal NTN assistance information on the NTN cells and / or the satellites that provide NTN coverage in a terrestrial band. The NTN assistance information may, for instance, consist of ephemeris that provides wireless communication unit knowledge of the position of the satellite. This may, for instance, be longterm ephemeris for determining or predicting when a specific satellite will make a pass over the geographical area where the wireless communication unit operates in, or will operate in. This is useful in the case where NTN does not constantly provide coverage, but operates a discontinuous coverage network. It is envisaged that this assistance information may help wireless communication units to detect NTN cells. Without it, it may in some circumstances not be possible to detect the NTN cell. In some examples, it is envisaged that NTN assistance information for a non-terrestrial cell in a terrestrial band may be signalled as part of disaster roaming information. In this case, the PLMN may be the current PLMN, as illustrated below in specification example #4. It is envisaged that any mention herein of “satellite ephemeris” may not only apply to satellites but also other platforms and / or pay loads above the earth surface. It is also envisaged by the inventors that an NTN cell operating in a terrestrial band may also mean that the terrestrial and the non-terrestrial band may be overlapping. In other words, this, for instance, may mean that for some of the conditions herein described, where non-terrestrial cell or network operates in a terrestrial band, it should also be taken to be a non-terrestrial cell or network operating in a band overlapping with a terrestrial band. It is also envisaged by the inventors that a non-terrestrial cell operating in a terrestrial band may be any type of non-terrestrial cell. It is envisaged that this may, for instance, be an loT NTN cell, which may be eMTC NTN or an NB-IoT NTN cell. It may also be a 5G NR NTN cell, which may be a Redcap NR NTN cell or a 6G NTN cell or a non-3GPP NTN cell that operates in 3 GPP spectrum, etc. It is also envisaged by the inventors that the approaches described herein apply equally to eNBs, gNBs, NG-RAN or NG-eNB. Hence, it is envisaged that these terms, as mentioned herein, are to be considered interchangeable. For instance, in some cases the herein-described examples may be directed to an eNB, but it is envisaged that the concept should be considered as equally applying for NG-eNB (eNB is connected to EPC, while NG-eNB is connected to 5GC). In some of the scenarios described herein, there may also be methods explicitly for an NG-eNB, en-gNB, gNB, or NG-RAN, where said concepts should be considered as equally applying interchangeably to other ‘base station’ elements. It is also envisaged by the inventors that an E-UTRAN (cell) is (in a loose sense) the base station of an eMTC / LTE-M cell. Thus, it is envisaged that the term ‘E-UTRAN’, as mentioned herein, should be considered, in some examples, an ‘loT NTN base station’. In 3GPP™ so far, only loT is supported for LTE™ NTN and not ordinary non-IoT LTE™ NTN. It should be noted that examples herein described are envisaged as not being limited to loT NTN E-UTRAN as it is envisaged that examples described herein apply equally to “ordinary” non-IoT LTE™ NTN. It is also envisaged that the approaches described herein are also applicable if non-Standalone NTN is supported, e.g., EN-DC (E- UTRAN-NR Dual Connectivity) is supported in the future. Although example embodiments are described with reference to ‘radio access networks’, it is envisaged that said term encompasses and is considered to be equivalent to and interchangeable with ‘communication cells’, namely the facilitation of communications within a cell that may access other parts of the communication system as a whole. Although some examples target loT NTN, it is envisaged that the concepts herein described may also be relevant for 5G NR. It is also envisaged by the inventors that the terms “RRC connected”, “connected mode” or “RRC_CONNECTED” may be used interchangeably in the description below. Similarly, it is envisaged that the terms “idle mode”, “RRC idle” or ’’RRCIDLE” are used interchangeably. Sometimes, when methods related to “idle mode” are mentioned, it is envisaged that this may also encompass “inactive mode”, “RRC inactive” or “RRCINACTIVE” as the actions performed in those two states in general are the same. It is also envisaged by the inventors that whilst the concepts described herein are mostly described in terms of 5GNR, all concepts, proposals, embodiments, and examples may also apply for eNBs, NG-eNBs (eNBs connected via 5GC) or 6G NBs, all as well as related, newly defined and / or existing: RRC signaling and / or messages, X2, Xn, SI, NG, and / or Fl signaling and messages, and / or related network entities (e.g. MME, AMF, other). For completeness, the inventors consider that the concepts applied to 4G and 5G and potential equivalents in a 6G system, as herein described, may at least encompass: (i) 4G and 5G RRC connected state - UE having established a connection with a RAN, e.g., a cell, gNB or similar identity. (ii) Cell - This may also be a different concept in a 6G system. For instance, in a cell-less case a UE may attach, connect and be associated with a beam or other similar identity. (iii) RRC idle - UE not in a RRC connected state, e.g., not having established a connection. RRC idle also means that UE will be camping on a cell or similar identity and then performing measurements and evaluating to find a better cell or similar identity. (iv) 5G RRC inactive - UE in a state similar to RRC idle where the UE stores the RRC configuration and resumes the RRC connection using the configuration. The network also stores the UE context and uses it to restore the UE connection. (v) 5G RRC procedures (RRC Setup, RRC Resume, RRC Re-establishment, RRC Reconfiguration) - Any procedures that aims to establish a connection with a cell, a gNB or similar identity. For instance, a procedure that aims to establish a 5G-6GDual Connectivity setting with a 5Gand 6G cell. (vi) Random access - The process of synchronizing the MAC layer via sending a preamble and receiving a message that synchronizes the uplink, as well as following messages to resolve any contention. (vii) Radio Link Failure - Failure of the radio link, which may be a failure based on measured radio signals, or based on operation in the cell, such as a number of retransmissions, random access failures, the radio beams failing etc. After the radio link failure, the UE may try to reselect to another cell and re-establish the RRC connection. (viii) Handover - Performing active mobility to another cell, gNB or similar identity, which may also be termed a ‘reconfiguration with synch’. (ix) Releasing RRC connection - The UE is released via a message, such as RRC Release, that releases the RRC connection that the UE has to one or more cells. Specific examples are now described with regard to a 5G implementation. -------------------- 38.321 Example-------------------- In this first example, a UE is considered barred due to an existence of suitable cells. --------------------38.304 V18.2.0 example-------------------- When cell status is indicated as “true” for other use, and either cell does not broadcast any CAG-IDs or NIDs or does not broadcast any CAG-IDs and the UE is not operating in SNPN Access Mode, - The UE shall treat this cell as if cell status is “barred”. When cell status is indicated as “true” for future use, - The UE shall treat this cell as if cell status is “barred”. When cellBarredNES is absent and cellBarred is set to “barred”, - The UE indicating any of the values in nes-CellDTX-DRX shall treat this cell as if cell status is “barred”. When cellBarredNTN is not broadcast in this cell, - For NTN access, the UE shall treat this cell as if cell status is “barred”. When halfDuplexRedCapAllowed is not broadcast in this cell, - The (e)RedCap UE only capable of operating in half-duplex for FDD shall treat this cell as if cell status is “barred”. When cellBarredATG is not broadcast in this cell, - For ATG access, the UE shall treat this cell as if cell status is “barred”. When cellBarredFixedVSAT is not broadcast in this cell, - For NTN access, the fixed VSAT UE shall treat this cell as if cell status is “barred”. When cellBarredMobileVSAT is not broadcast in this cell, - For NTN access, the mobile VSAT UE shall treat this cell as if cell status is “barred”. When cellBarred2RxXR is broadcast in this cell, - The 2Rx XR UE shall treat this cell as if cell status is “barred”. When cellBarredNTN-TerrestrialBand is broadcast in this cell and suitable cell(s) in a terrestrial band has been detected, - The UE shall treat this cell as if cell status is “barred” --------------------38.304 V18.2.0 example-------------------- -------------------- 38.331 VI8.2.0 example-------------------- - SIB1 SIB1 contains information relevant when evaluating if a UE is allowed to access a cell and defines the scheduling of other system information. It also contains radio resource configuration information that is common for all UEs and barring information applied to the unified access control. Signalling radio bearer: N / A RLC-SAP: TM Logical channels: BCCH Direction: Network to UE SIB1 message ssssjceTtSSSSsSSSiitfiSS ¢¢¢¢¢¢¢¢¢¢¢¢¢$^^0141^ :ggg:g:g:g:ggOS^ SiSSSSSSSS'^S isssssssss:gS JQOOSWiO????? :deTiAdde:$:&&eT:ati^ iserviiigiCeO^^ iO ^OBilsO^^W :Servi:ng§e^i:§onf:i^^dO)StiSTS: ooo^ UE-TimersAndConsranrs (2..maxPLMN)) ;TW?TE1<^ STB4OiSQ4tT8S??STS?i?S?S? jssssiionCESSiealExeettsiSwssssssjs^ SIB1 field descriptions cellBarredNTN Value barred means that the cell is barred for connectivity to NTN, as defined in TS 38.304

[20] , Value notBarred means that the cell is allowed for connectivity to NTN. If not present, the UE considers the cell is not allowed for connectivity to NTN, as defined in TS 38.304

[20] . This field is only applicable to NTN-capable Ues.______________ cellBarredNTN-TerrestrialBand If the field is configured, this means that the cell is barred if the UE is able to detect suitable cells in terrestrial bands. 38.331 VI8.2.0 example In this second example, a cell is considered barred if the UE has not initiated any emergency call or detected and PWS indication. --------------------38.304 V18.2.0 example-------------------- When cell status is indicated as "true" for other use, and either cell does not broadcast any CAG-IDs or NIDs or does not broadcast any CAG-IDs and the UE is not operating in SNPN Access Mode, - The UE shall treat this cell as if cell status is "barred". When cell status is indicated as "true" for future use, - The UE shall treat this cell as if cell status is "barred". When cellBarredNES is absent and cellBarred is set to "barred", - The UE indicating any of the values in nes-CellDTX-DRX shall treat this cell as if cell status is "barred". When cellBarredNTN is not broadcast in this cell, - For NTN access, the UE shall treat this cell as if cell status is "barred". When halfDuplexRedCapAllowed is not broadcast in this cell, - The (e)RedCap UE only capable of operating in half-duplex for FDD shall treat this cell as if cell status is "barred". When cellBarredATG is not broadcast in this cell, - For ATG access, the UE shall treat this cell as if cell status is "barred". When cellBarredFixedVSAT is not broadcast in this cell, - For NTN access, the fixed VS AT UE shall treat this cell as if cell status is "barred". When cellBarredMobileVSAT is not broadcast in this cell, - For NTN access, the mobile VSAT UE shall treat this cell as if cell status is "barred". When cellBarred2RxXR is broadcast in this cell, - The 2Rx XR UE shall treat this cell as if cell status is "barred". When cellBarredNTN-Emergency is broadcast in this cell and the UE has not initiated an emergency call, nor detected PWS indication (SIB6-SIB8, SIB15 in a NR cell or SystemlnformationBlockTypelO to SystemInformationBlockl2, SystemInformationBlockType30) on any other cell, - The UE shall treat this cell as if cell status is "barred". In this third example, an illustration of how a suitable cell requirement may be used. --------------------38.304 VI8.2.0 example-------------------- suitable cell: For UE not operating in SNPN Access Mode, a cell is considered as suitable if the following conditions are fulfilled: - The cell is part of either the selected PLMN or the registered PLMN or PLMN of the Equivalent PLMN list, and for that PLMN either: - The PLMN-ID of that PLMN is broadcast by the cell with no associated CAG-IDs and CAG-only indication in the UE for that PLMN (TS 23.501

[10] ) is absent or false; - Allowed CAG list in the UE for that PLMN (TS 23.501

[10] ) includes a CAG-ID broadcast by the cell for that PLMN; - The cell selection criteria are fulfilled, see clause 5.2.3.2. - If the cell is a non-terrestrial cell in a terrestrial band, the UE is unable to detect any other terrestrial cell on a terrestrial cells or non-terrestrial cells on non-terrestrial bands According to the latest information provided by NAS: - The cell is not barred, see clause 5.3.1; - The cell is part of at least one TA that is not part of the list of "Forbidden Tracking Areas for Roaming" (TS 22.011

[18] ), which belongs to a PLMN that fulfils the first bullet above. For UE operating in SNPN Access Mode, a cell is considered as suitable if the following conditions are fulfilled: - The cell is part of the selected SNPN or the registered SNPN or SNPN of the Equivalent SNPN list of the UE; - The cell selection criteria are fulfilled, see clause 5.2.3.2; According to the latest information provided by NAS: - The cell is not barred, see clause 5.3.1; - The cell is part of at least one TA that is not part of the list of "Forbidden Tracking Areas for Roaming" which belongs to the selected SNPN or the registered SNPN or SNPN of the Equivalent SNPN list of the UE. --------------------38.304 VI8.2.0 example-------------------- In this fourth example, an illustration of how NTN assistance information can be included in the disaster roaming information. -------------------- 38.331 VI8.2.0 example-------------------- - SIB15 SIB 15 contains configurations of disaster roaming information. SIB15 information element jssssfaii'OOOt'gtOfB^OOSSSssssssssssssssssss:^^ ^gt#s8bt8B®S8sS8SSs£bsvf96:0??????????3s®£®iiiO??:? KssssSeSieaSeiiBEOS'SKtasissssssssssssssssss^ iiiiiiiiiiiiiiiiiiiiiiii^ ill?lllllllllllllllllllllllllllllllllllioiiiii?^ ; SIB15 field descriptions commonPLMNsWithDisasierCondition i A list of PLMN(s) for which disaster condition applies and that disaster inbound roaming is accepted, which can ; be commonly applicable to the PLMNs sharing the cell. i applicableDisasterlnfoList i A list indicating the applicable disaster roaming information for the networks indicated in plmn-ldentitylnfoList and ; npn-ldentitylnfoList-r16. The network indicates in this list one entry for each entry of plmn-ldentitylnfoList, i followed by one entry for each entry of npn-ldentitylnfoList-r16, meaning that this list will have as many entries as i the number of entries of the combination of plmn-ldentitylnfoList and npn-ldentitylnfoList-r16. The first entry in this i list indicates the disaster roaming information applicable for the network(s) in the first entry of plmn- ; ldentitylnfoListlnpn-ldentitylnfoList-r16, the second entry in this list indicates the disaster roaming information i applicable for the network(s) in the second entry of plmn-ldentitylnfoListlnpn-ldentitylnfoList-r16, and so on. Each i entry in this list can either be having the value noDisasterRoaming, disasterRelated Indication, commonPLMNs, or i dedicatedPLMNs. If an entry in this list takes the value noDisasterRoaming, disaster inbound roaming is not i allowed in this network(s). If an entry in this list takes the value disasterRelatedIndication, the meaning of this field ; for this network(s) is as specified for "disaster related indication" in TS 23.122

[74] , clause 4.4.3.1.1. If an entry in i this list takes the value commonPLMNs, the PLMN(s) with disaster conditions indicated in the field i commonPLMNsWithDisasterCondition apply for this network(s). If an entry in this list contains the value i dedicatedPLMNs, the listed PLMN(s) are the PLMN(s) with disaster conditions that the network(s) corresponding ; to this entry accepts disaster inbound roamers from. For SNPNs, the network indicates the value ; noDisasterRoaming. -------------------- 38.331 VI8.2.0 example-------------------- In particular, it is envisaged that the aforementioned inventive concept can be applied by a semiconductor manufacturer to any integrated circuit comprising a signal processor configured to perform any of the aforementioned operations. Furthermore, the inventive concept can be applied to any circuit that is able to configure, process, encode and / or decode signals for wireless distribution. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a digital signal processor, or application-specific integrated circuit (ASIC) and / or any other sub-system element. It will be appreciated that, for clarity purposes, the above description has described example embodiments with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units or processors, for example with respect to the signal processor may be used without detracting from the concepts described herein. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controller. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization. Aspects may be implemented in any suitable form including hardware, software, firmware or any combination of these. Example embodiments may optionally be implemented, at least partly, as computer software running on one or more data processors and / or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an embodiment may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. Although the concepts have been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in other examples. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and / or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate. Thus, examples have been described that provide improved cell access of communication units (such as UEs) with non-terrestrial base stations such as NTN airborne gNBs, eNBs, satellite base stations. In accordance with examples herein described, a number of approaches are provided to enable a wireless communication unit, e.g., a UE, to select, camp, connect to and / or operate in a non-terrestrial network cell operating in a terrestrial frequency under certain conditions, wherein the aforementioned disadvantages with prior art arrangements have been substantially alleviated. Abbreviations / Definitions In the present disclosure, the following acronyms / definitions are used. 3 GPP 3rd Generation Partnership Project 6G 6th Generation 5G 5th Generation 5GC 5G Core 5GS 5G System ACK Acknowledge AM Acknowledged Mode AMF Access and Mobility management Function AS Access Stratum BL Bandwidth-reduced Low-complexity CA Carrier Aggregation CCCH Common Control Channel CDMA Code Division Multiple Access CE Coverage Enhancement CIoT Cellular loT CN Core Network C-RNTI Cell RNTI CS Circuit Switched DC Dual Connectivity DCCH Dedicated Control Channel DRB Data Radio Bearer EDGE Enhanced Data rates for Global Evolution EDT Early Data Transmission eMTC enhanced Machine Type Communication EN E-UTRAN NR eNB Base Station EPC Evolved Packet Core EPS Evolved Packet System E-UTRA Evolved Universal Terrestrial Radio Access E-UTRAN Evolved Universal Terrestrial Radio Access Network GEO Geosynchronous Equatorial Orbit GERAN GSM EDGE Radio Access Network gNB GSM 5G Base Station Groupe Special Mobile HAPS High Altitude Platform Station HARQ Hybrid Automatic Repeat Request ID IE Identity / Identifi cation Information Element loT Internet of Things LEO Lower Earth Orbit 5 LTE Long Term Evolution LTE-M LTE Machine Type Communication MAC Medium Access Control MCG Master Cell Group MEO Medium Earth Orbit 10 MME Mobility Management Entity NAS Non Access Stratum NB Narrow Band BS Base Station NG Next Generation 15 NR New Radio NTN Non-Terrestrial Network PCell Primary Cell PDCP Packet Data Convergence Protocol PDU Protocol Data Unit 20 PSCell Primary and Secondary Cells RAN Radio Access Network RAT Radio Access Technology RB Radio Bearer RLC Radio Link Control 25 RLF Radio Link Failure RNTI Radio Network Temporary Identifier ROHC Robust Header Compression RRC Radio Resource Control SI Interface between RAN and CN 30 SAP Service Access Point SCG Secondary Cell Group SIB System Information Block SRB Signalling Radio Bearer S-TMSI Short TMSI 35 TAU Tracking Area Update TM Transparent Mode TMSI Temporary Mobile Subscriber Identity TN Terrestrial Network TS Technical Specification Txxx Timer xxx UE User Equipment UP User Plane X2 / Xn Interface between RAN nodes

Claims

1. A wireless communication unit (450, 470, 475) for communicating in a wireless communication system that comprises at least one wireless non-terrestrial network, NTN cell supported by a NTN base station (412, 414), wherein the wireless communication unit (450, 470, 475) comprises a processor, operably coupled to a transceiver, arranged to:detect a NTN cell supported by the NTN base station (412, 414) that operates on a terrestrial frequency; andidentify from at least the detection that the wireless communication unit (450, 470, 475) is allowed to camp on the NTN cell, and in response thereto select and camp on the NTN cell.

2. The wireless communication unit (450, 470, 475) of Claim 1 wherein the processor is arranged to identify from the detection and a condition in a received message that the wireless communication unit (450, 470, 475) is allowed to select and camp on the NTN cell.

3. The wireless communication unit (450, 470, 475) of Claim 2 wherein the wireless communication system further comprises at least one wireless terrestrial network, TN, cell supported by a TN base station (410) and the condition comprises one of:the wireless TN cell is no longer operational;the wireless TN cell is arranged to be no longer operational after an elapsed time period; or there is no wireless TN cell in a geographical area that the wireless communication unit (450, 470, 475) is currently located in.

4. The wireless communication unit (450, 470, 475) of Claim 3 wherein the condition that there is no wireless TN cell in the geographical area that the wireless communication unit (450, 470, 475) is currently located in is in response to a determination that the wireless communication unit (450, 470, 475) is a distance from the at least one wireless TN base station (410) that exceeds a distance threshold.

5. The wireless communication unit (450, 470, 475) of Claim 4 wherein the distance threshold is signalled to the wireless communication unit from one of: a network device; at least one wireless TN cell; or the NTN cell that operates on the terrestrial frequency.

6. The wireless communication unit (450, 470, 475) of Claim 4 wherein the distance threshold is indicative of a location-dependent cell exclusion distance that excludes camping of wireless communication units.

7. The wireless communication unit (450, 470, 475) of Claim 3 wherein the time period is one of:configurable by a network device in the wireless communication system within an access stratum, AS, message;configurable by a network device using a non access stratum, NAS, message;configurable by a TN cell; orbased on an elapsed time since a last detection of a TN cell.

8. The wireless communication unit (450, 470, 475) of Claim 2 wherein the received message is a non access stratum, NAS, message received from a core network in the wireless communication system.

9. The wireless communication unit (450, 470, 475) of any preceding Claim wherein the transceiver and processor are arranged to only camp on the at least one wireless NTN base station (412, 414) cell on the terrestrial frequency in response to at least one of:the NTN cell is identified in a list of radio access technologies, RATs, that are allowed to operate at a geographical location of the wireless communication unit (450, 470, 475);the NTN cell provides a broadcast service that the wireless communication unit (450, 470, 475) intends to receive.

10. The wireless communication unit (450, 470, 475) of any preceding Claim wherein, inresponse to the processor being arranged to select and camp on the NTN cell that operates on the terrestrial frequency, the transceiver is prevented from transmitting on an uplink channel in the NTN cell.

11. The wireless communication unit (450, 470, 475) of any of preceding Claims 2 to 10 wherein the condition is one of:an on-going network-initiated emergency scenario that allows the wireless communication unit (450, 470, 475) to use the NTN cell that operates on the terrestrial frequency;the NTN cell is identified in part of a disaster roaming public land mobile network, PLMN, message.

12. The wireless communication unit (450, 470, 475) of Claim 11 wherein the condition restricts the wireless communication unit (450, 470, 475) processor from selecting and camping on the NTN cell for a period of time after receiving the on-going network-initiated emergency scenario or the disaster roaming PLMN message.

13. The wireless communication unit (450, 470, 475) of any of preceding Claims 2 to 12 wherein the condition is one of: a cell rejection indication or a cell release indication or a cell redirection indication initiated by at least one wireless TN base station (410) where the at least one wireless TN base station (410) operates in a same terrestrial frequency band as the NTN cell.

14. The wireless communication unit (450, 470, 475) of Claim 13 wherein the cell release indication or the cell re-direction indication comprises an indication that the wireless communication unit (450, 470, 475) is allowed to select and camp on the NTN cell in one or more identified terrestrial frequency bands.

15. The wireless communication unit (450, 470, 475) of any of preceding Claims 2 to 14 wherein the condition is received by the wireless communication unit (450, 470, 475) from at least one wireless Terrestrial Network, TN, base station (410) in response to TN resources beinglimited.

16. The wireless communication unit (450, 470, 475) of Claim 15 wherein in response to TN resources being limited the wireless communication unit (450, 470, 475) the processor is arranged to divide traffic data for transmission between the wireless TN cell and the NTN cell that operates on the terrestrial frequency.

17. A method for a wireless communication unit (450, 470, 475) to communicate in a wireless communication system that comprises at least one wireless non-terrestrial network, NTN cell supported by a NTN base station (412, 414); the method comprising at the wireless communication unit (450, 470, 475):detecting a NTN cell supported by the NTN base station (412, 414) that is operating on a terrestrial frequency;identifying from at least the detection that the wireless communication unit (450, 470, 475) is allowed to camp on the NTN cell; andselecting and camping on the NTN cell operating on the terrestrial frequency in response to detecting and identifying.

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