A method in a wireless telecommunications network

Abstract

This invention provides a method in a wireless telecommunications network, the wireless telecommunications network comprising: a plurality of Reconfigurable Intelligent Surfaces, RISs, each RIS comprising a plurality of reflecting elements, each reflecting element of the plurality of reflecting elements of each RIS being a member of either a first set of utilised reflecting elements that are configured for reflecting a signal in the wireless telecommunications network or a second set of available reflecting elements; a plurality of non-terrestrial access points, wherein a first inter-non-terrestrial access point connection is communicated via a first RIS of the plurality of RISs; and one or more gateways configured to provide a feeder link to at least one non-terrestrial access point of the plurality of non-terrestrial access points; the method comprising the steps of: determining a subarray availability of the first RIS as a function of a number of reflecting elements in a second set of available reflecting elements of the first RIS; determining a subarray availability of a second RIS of the plurality of RISs as a function of a number of reflecting elements in a second set of available reflecting elements of the second RIS; and reconfiguring the wireless telecommunications network based on the determined subarray availabilities of the first and second RIS.

Description

[0001] A METHOD IN A WIRELESS TELECOMMUNICATIONS NETWORK

[0002] Field of the Invention

[0003] The present invention relates to a method in a wireless telecommunications network.

[0004] Background

[0005] Wireless telecommunications networks typically comprise a terrestrial access point (e.g. base station) communicating with terrestrial User Equipment (UE). The term NonTerrestrial Network (NTN) covers any network that comprises an aerial vehicle, and includes satellite communication networks, High Altitude Platform (HAP) networks, air- to-ground networks, and low-altitude Unmanned Aerial Vehicles (UAVs). The aerial vehicles, such as a satellite, HAP vehicle (e.g. airplane, balloon, airship, etc.) or UAV may comprise an access point (a “non-terrestrial access point”). Figure 1 illustrates an example NTN, comprising a core network, a terrestrial base station, a gateway, a nonterrestrial access point, and a UE. The core network and terrestrial base station may be connected, for example, by an NG interface. The base station may connect to the gateway which provides a feeder link to the non-terrestrial access point. The nonterrestrial access point connects to the UE via a service link, for example, by a NR-Uu interface. User plane and control plane traffic may therefore be communicated between the UE and core network via the NG interface, feeder link and service link.

[0006] The NTN further comprises a control station and command and control centre. The command and control centre is configured to communicate with each of the plurality of non-terrestrial access points, via the control station, using a command and control (“02”) link. The C2 link is a highly reliable link, separate to the feeder link, used to communicate, for example, telecommands, telemetry and air traffic control communications.

[0007] In an NTN comprising a plurality of non-terrestrial access points, it is desirable to provide an inter-non-terrestrial-access point connection. These connections may utilise free- space-optics or active phased-array antennas, requiring each aerial vehicle to comprise dedicated communication equipment (in addition to the wireless telecommunications equipment used for the feeder and service links). This additional equipment adds weight to the aerial vehicle, which reduces its mission time (that is, the time the aerial vehicle is airborne). Summary of the Invention

[0008] According to a first aspect of the invention, there is provided a method in a wireless telecommunications network, the wireless telecommunications network comprising: a plurality of Reconfigurable Intelligent Surfaces, RISs, each RIS comprising a plurality of reflecting elements, each reflecting element of the plurality of reflecting elements of each RIS being a member of either a first set of utilised reflecting elements that are configured for reflecting a signal in the wireless telecommunications network or a second set of available reflecting elements; a plurality of non-terrestrial access points, wherein a first inter-non-terrestrial access point connection is communicated via a first RIS of the plurality of RISs; and one or more gateways configured to provide a feeder link to at least one non-terrestrial access point of the plurality of non-terrestrial access points; the method comprising the steps of: determining a subarray availability of the first RIS as a function of a number of reflecting elements in a second set of available reflecting elements of the first RIS; determining a subarray availability of a second RIS of the plurality of RISs as a function of a number of reflecting elements in a second set of available reflecting elements of the second RIS; and reconfiguring the wireless telecommunications network based on the determined subarray availabilities of the first and second RIS.

[0009] A second inter-non-terrestrial access point connection may be communicated via the second RIS of the plurality of RIS.

[0010] The plurality of non-terrestrial access points may further comprise a first cluster of nonterrestrial access points comprising a primary non-terrestrial access point of the first cluster having a direct connection with a gateway of the one or more gateways, and the first inter-non-terrestrial access point connection may be between a first pair of nonterrestrial access points of the first cluster of non-terrestrial access points.

[0011] The second inter-non-terrestrial access point connection may be between a second pair of non-terrestrial access points of the first cluster of non-terrestrial access points.

[0012] The plurality of non-terrestrial access points may further comprise a second cluster of non-terrestrial access points comprising a primary non-terrestrial access point of the second cluster having a direct connection with a gateway of the one or more gateways, and the second inter-non-terrestrial access point connection may be between a first pair of non-terrestrial access points of the second cluster of non-terrestrial access points.

[0013] The step of reconfiguring the wireless telecommunications network may comprise one or more of a group comprising: transferring the first inter-non-terrestrial access point connection such that it is communicated via the second RIS; transferring a / the second inter-non-terrestrial access point connection such that it is communicated via the first RIS; transferring the first inter-non-terrestrial access point connection such that it is communicated via a third RIS of the plurality of RIS; transferring the second inter-non- terrestrial access point connection such that it is communicated via the third RIS.

[0014] The first RIS may be divided into a plurality of subarrays of reflecting elements, each subarray of reflecting elements having a particular reflection configuration, wherein the subarray availability of the first RIS may be a function comprising a total number of reflecting elements of the first RIS minus a number of reflecting elements required for each subarray of the first RIS.

[0015] The second RIS may be divided into a plurality of subarrays of reflecting elements, each subarray of reflecting elements having a particular reflection configuration, wherein the subarray availability of the second RIS may be a function comprising a total number of reflecting elements of the second RIS minus a number of reflecting elements required for each subarray of the second RIS.

[0016] According to a second aspect of the invention, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of the first aspect of the invention. The computer program may be stored on a computer readable carrier medium.

[0017] Brief Description of the Figures

[0018] In order that the present invention may be better understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which:

[0019] Figure 1 is a schematic diagram of a conventional non-terrestrial wireless telecommunications network; Figure 2 is a schematic diagram of a first non-terrestrial wireless telecommunications network;

[0020] Figure 3 is a schematic diagram of a second non-terrestrial wireless telecommunications network in a first state;

[0021] Figure 4 is a flow diagram illustrating a method; and

[0022] Figure 5 is a schematic diagram of the second non-terrestrial wireless telecommunications network in a second state.

[0023] Detailed Description

[0024] Figure 2 illustrates a first Non-Terrestrial Network (NTN) 100. The first NTN 100 is based on a 3rdGeneration Partnership Project (3GPP) 5thGeneration protocol and comprises a core network 1 10, a gateway 120, a plurality of non-terrestrial access points 130 and a User Equipment (UE). In this example, the non-terrestrial access points 130 are each part of a High-Altitude Platform (HAP), such as an airplane, balloon or airship.

[0025] The gateway 120 is configured to provide a feeder link to one or more of the plurality of non-terrestrial access points. In the example of Figure 2, the gateway 120 provides a feeder link to the first non-terrestrial access point 130a. The first NTN 100 may comprise one or more terrestrial access points (not shown), which may communicate with the nonterrestrial access points (and any UE connected thereto) via the gateway 120 and feeder link.

[0026] The first NTN 100 further comprises a control station 140 and command and control centre 150. The command and control centre 150 is configured to communicate with each of the plurality of non-terrestrial access points 130, via the control station 140, using a command and control (“C2”) link. The C2 link is a connection for communicating, for example, telecommands, telemetry and air traffic control communications. This C2 link is highly reliable and separate to the feeder link. Using this data, the command and control centre 150 continuously monitors and controls the flight plan of each HAP.

[0027] The first NTN 100 further comprises a plurality of Reconfigurable Intelligent Surfaces (RISs) 160 and a controller 170. The RISs are described in more detail below. The controller 170 is connected to each RIS 160 and is configured to send configuration messages to each RIS 160. The controller 170 is further connected to each non- terrestrial access point 130, via the C2 link, and is configured to send configuration messages to each non-terrestrial access point 130.

[0028] A first non-terrestrial access point 130a is configured to form a service link with the LIE using an NR-llu interface and is further configured to form a feeder link with the gateway 120. In this example, a second non-terrestrial access point 130b is unable to form a direct feeder link with gateway 120. This is addressed by forming an indirect feeder link with the gateway via the first non-terrestrial access point 130a. That is, an indirect feeder link is formed as a first connection between the second non-terrestrial access point 130b and first non-terrestrial access point 130a and a second connection being the direct feeder link between the first non-terrestrial access point 130a and the gateway 120. All control plane and user plane data (excluding any C2 related data) communicated with the second non-terrestrial access point 130b (and any UE connected to the second nonterrestrial access point 130b) may therefore use this indirect feeder link with the gateway 120. The first non-terrestrial access point 130a is therefore configured to relay any control plane and user plane traffic that is associated with the second non-terrestrial access point 130b via the first connection between the first and second non-terrestrial access points 130a, 130b. As will now be described in more detail, this first connection between the first and second non-terrestrial access points 130a, 130b is based on a reflection via a RIS (a second RIS 160b in Figure 2) of the plurality of RIS 160.

[0029] A RIS 160 of the plurality of RIS 160 will now be described in more detail. Each RIS 160 may be an inexpensive adaptive thin composite material sheet and can modify radio waves impinging upon it, or passing through it, in ways that can be programmed and controlled by using external stimuli. This technology has been described by a wide variety of names including: large intelligent surfaces, reconfigurable reflectarrays, reconfigurable intelligent surfaces, intelligent reflecting surfaces, software-controlled metasurfaces, and programmable surfaces. Each RIS 160 can operate in reflection and may comprise an array of reflecting unit cells (e.g. diode-controlled unit cells). The unit cell separation determines the electromagnetic frequency of operation and the controller 170 determines the reflective characteristics of the surface. Generally, a RIS 160 operates to produce a change in the electromagnetic waves incident on the RIS unit cell.

[0030] In the first NTN 100, the second RIS 160b is configured to reflect a signal communicated between the first and second non-terrestrial access point 130a, 130b as part of the first connection between the first and second non-terrestrial access points 130a, 130b. A suitable reflection of these signals may be achieved by configuring the unit cells of the second RIS 160b. This configuration may utilise data regarding a location of each nonterrestrial access point, which may be received at the controller 170 from the command and control centre 150, to determine a configuration of each unit cell of the second RIS 160b for reflecting signals between the first and second non-terrestrial access point 130a, 130b. Alternatively, the second RIS 160b may be configured by a calibration phase in which a plurality of candidate configurations of the second RIS 160b are tested and the resulting performance of the first connection between the first and second nonterrestrial access points 130a, 130b is measured, with the best performing candidate configuration being selected. The second RIS 160b may be reconfigured to accommodate for any changes in the first connection, such as a change in relative position of the first and second non-terrestrial access points 130a, 130b.

[0031] A signal communicated as part of an inter-non-terrestrial access point connection via the RIS 160 may be a service link signal (that is, having the same form as a service link signal between a non-terrestrial access point and a UE). Alternatively, the signal communications as part of the inter-non-terrestrial access point connection differs from the service link signal (e.g. uses different spectrum and / or radio equipment) but shares at least some of the equipment used for the service link signal. The same equipment for forming the non-terrestrial access point and UE connection may therefore be additionally used for forming the inter-non-terrestrial access point connection, such that additional equipment (e.g. free-space-optics equipment) is not required for the inter-non-terrestrial access point connection. This decreases weight of the HAP, and therefore increases mission time.

[0032] The RIS 160 may also be divided into a plurality of subarrays, each subarray comprising a subset of the reflecting unit cells of the array of reflecting unit cells. Each subarray may be controlled to independently reflect a signal between non-terrestrial access points, such that the reflection of a signal between a first set of non-terrestrial access points by a first subarray of the RIS 160 is independent of the reflection of a signal between a second set of non-terrestrial access points by a second subarray of the RIS 160. The controller 170 may therefore be configured to control each subarray of the RIS 160 to reflect signals between non-terrestrial access points. Furthermore, the controller 170 may reconfigure the composition of each subarray, such as by determining a count of reflecting unit cells forming each subarray and / or which reflecting unit cells should form each subarray. Details of the formation and use of subarrays of a RIS can be found, for example, in “A Dynamic Subarray Structure in Reconfigurable Intelligent Surfaces for TeraHertz Communication Systems”, Liu et al, https: / / arxiv.org / abs / 2206.14968.

[0033] In the following description, the term “cluster” will be used to define a set of non-terrestrial access points that share a common feeder link. The cluster therefore comprises at least one non-terrestrial access point having a direct feeder link (hereinafter, the “primary nonterrestrial access point”), and may comprise one or more non-terrestrial access points having an indirect feeder link (hereinafter, the “secondary non-terrestrial access point”). A non-terrestrial access point may be a member of multiple clusters. Furthermore, there may be one or more RIS in each cluster, and a RIS may be utilised in connections between non-terrestrial access points of different clusters.

[0034] A second NTN 200 is illustrated in Figure 3. The second NTN 200 comprises a core network 210, a first gateway 220a, a second gateway 220b, a plurality of non-terrestrial access points 230, a control station 240, a command and control centre 250, a plurality of RIS 260, and a controller 270. The second NTN 200 may comprise one or more terrestrial access points (not shown), which may communicate with the non-terrestrial access points (and any UE connected thereto) via a gateway 220a, 220b and feeder link. The plurality of non-terrestrial access points 230 comprises a first and second nonterrestrial access points 230a, 230b, wherein the first non-terrestrial access point 230a has a feeder link with the first gateway 220a (and is therefore a primary non-terrestrial access point of this first cluster) and the second non-terrestrial access point 230b has an indirect feeder link with the first gateway 220a (and is therefore a secondary nonterrestrial access point of this first cluster). This indirect feeder link utilises an inter-non- terrestrial access point connection via a first RIS 260a of the plurality of RIS 260. More specifically, this inter-non-terrestrial access point connection may use a first subarray of the first RIS 260a, being a subset of a plurality of reflecting unit cells of the first RIS 260a. The first RIS 260a may also support one or more further inter-non-terrestrial access point connections, each utilising a particular subarray of the first RIS 260a. Furthermore, the plurality of non-terrestrial access points 230 comprises a third and fourth non-terrestrial access point 230c, 230d, wherein the third non-terrestrial access point 230c has a feeder link with the second gateway 220b (and is therefore a primary non-terrestrial access point of this second cluster) and the fourth non-terrestrial access point 230d has an indirect feeder link with the second gateway 220b (and is therefore a secondary nonterrestrial access point of this second cluster). This indirect feeder link utilises an inter- non-terrestrial access point connection via a second RIS 260b of the plurality of RIS 260. More specifically, this inter-non-terrestrial access point connection may use a first subarray of the second RIS 260b, being a subset of a plurality of reflecting unit cells of the second RIS 260b. The second RIS 260b may also support one or more further inter- non-terrestrial access point connections, each utilising a particular subarray of the second RIS 260b.

[0035] Figure 3 also illustrates a fifth non-terrestrial access point 230e, discussed in more detail below.

[0036] The control station 240 maintains a C2 link to each non-terrestrial access point of the plurality of non-terrestrial access points 230.

[0037] In this second NTN 200, the controller 270 is configured to perform a load balancing operation. This will now be described with reference to a method illustrated in Figure 4.

[0038] In a first step, S101 , the controller 270 detects a trigger for a load balancing operation. This trigger may be that a resource utilisation metric (e.g. a processing, memory and / or communication resource of one or more nodes or communication links in the second NTN 200 such as: one or more non-terrestrial access points, one or more gateways, one or more RIS, and / or the core network, and / or any communication link between any of these nodes) surpasses a threshold or is predicted to surpass a threshold. The prediction that a resource utilisation metric will surpass a threshold may be in response to an expected event in the second NTN 200, which may be one or more of the following:

[0039] 1 ) A further non-terrestrial access point attempting to join the first or second cluster of non-terrestrial access points, such as when the further non-terrestrial access point becomes operational, has moved to a new route, or is reestablishing a feeder link after a failure of a previous feeder link;

[0040] 2) A member of the first or second cluster of non-terrestrial access points attempting to join the other cluster of non-terrestrial access points;

[0041] 3) A change in a subarray of reflecting unit cells of the first and / or second RIS 260a, 260b, such as in the number of reflecting unit cells in a subarray. The trigger and / or expected event may be detected by the controller 270, by one of the non-terrestrial access points and reported to the controller 270, the command and control centre 250, or a node of the core network (such as an Access and Mobility Function, AMF) and reported to the controller 270.

[0042] In the example illustrated in Figure 3, the trigger detected by the controller 270 is based on a prediction that the fifth non-terrestrial access point 230e is attempting to join the second cluster of non-terrestrial access points so as to become a secondary nonterrestrial access point of the second cluster. This would require an indirect feeder link comprising an inter-non-terrestrial access point connection to the third non-terrestrial access point 230c via the second RIS 260b (or more specifically, via a subarray of the second RIS 260b). The controller 270 determines that the resource utilisation metric of the second RIS 260b, in the event the fifth non-terrestrial access point 230e joins the second cluster, will surpass a threshold.

[0043] In response to the trigger of step S101 , the controller 270 initiates a load balancing operation. In step S103, the controller 270 identifies each inter-non-terrestrial access point connection and, for each identified inter-non-terrestrial access point connection, the controller 270:

[0044] • identifies the RIS utilised in the inter-non-terrestrial access point connection,

[0045] • identifies the non-terrestrial access points connected by the inter-non-terrestrial access point connection, and

[0046] • determines one or more requirements of the identified non-terrestrial access points connected by the inter-non-terrestrial access point connection (e.g. capacity, received power, latency, etc.).

[0047] In step S105, the controller 270 identifies one or more candidate reconfigurations of the one or more inter-non-terrestrial access point connections identified in step S103. These candidate reconfigurations may involve one or more of the non-terrestrial access points joining a different cluster, starting a new cluster, or using a different RIS as part of the inter-non-terrestrial access point connection (which may involve another RIS - not shown - being available to form an inter-non-terrestrial access point connection). In the example shown in Figure 3, in which the addition of the fifth non-terrestrial access point 230e to the second cluster would cause the resource utilisation metric of the second RIS 260b to surpass a threshold, the candidate reconfigurations identified by the controller 270 includes:

[0048] • The first and / or second non-terrestrial access point 230a, 230b joining the second cluster;

[0049] • The first and / or second non-terrestrial access point 230a, 230b starting a new cluster having a direct feeder link to the first or second gateway 220a, 220b;

[0050] • The third and / or fourth non-terrestrial access point 230c, 230d joining the first cluster; and

[0051] • The third and / or fourth non-terrestrial access point 230c, 230d starting a new cluster having a direct feeder link to the first or second gateway 220a, 220b.

[0052] In step S107, the controller 270 determines whether each inter-non-terrestrial access point connection of each candidate reconfiguration identified in step S105 satisfies the corresponding one or more requirements of the non-terrestrial access points connected by that connection (as identified in step S103). If this determination is negative for any candidate reconfiguration, then that candidate reconfiguration is excluded from further analysis.

[0053] In step S109, the controller 270 determines a load of each node and communications link in the second NTN 200 for each candidate reconfiguration that satisfies its requirements (as determined in step S107). The load may be expressed in one or more of processing resource, storage resource or communication resource. In particular, the controller 270 determines the load of each RIS 260a, 260b in the second NTN 200 for the current configuration and for each candidate reconfiguration that satisfies its requirements (as determined in step S107). The load of each RIS 260a, 260b is expressed, inter alia, as a function of its subarray availability.

[0054] As noted above, a subarray is a subset of the reflecting unit cells of the array of reflecting unit cells of a RIS 260a, 260b. The subarray performs a particular reflection between a first non-terrestrial access point of an inter-non-terrestrial access point connection and a second non-terrestrial access point of the inter-non-terrestrial access point connection. The number of reflecting unit cells required for this subarray is a function of the requirements of these first and second non-terrestrial access points. For example, these first and second non-terrestrial access points may require a minimum received power of the reflected signal (that is, received power above a threshold), and the number of reflecting unit cells for the subarray may be determined as a function of this minimum received power requirement (more details on the relationship between the number of reflecting units of a subarray and the received power of the reflected signal can be found in paper “A Dynamic Subarray Structure in Reconfigurable Intelligent Surfaces for TeraHertz Communication Systems”, cited above). Accordingly, the subarray availability of a RIS 260a, 260b, in terms of the number of available reflecting unit cells of that RIS 260a, 260b that may be used to form a new subarray, may be determined as the total number of reflecting unit cells of that RIS 260a, 260b minus a sum of the number of reflecting unit cells required by each existing subarray of that RIS 260a, 260b.

[0055] Therefore, in step S109, the controller 270 determines a load of each RIS 260a, 260b as a function of its subarray availability, being the number of available reflecting unit cells of that RIS 260a, 260b that may be used to form a new subarray, for each candidate reconfiguration that satisfies its requirements (as determined in step S107).

[0056] In step S1 11 , the controller 270 selects a candidate configuration based on the determined loads of each node and communications link in the second NTN 200 of each candidate configuration, wherein the load is based at least on the subarray availability of each RIS 260a, 260b. In one implementation, the controller 270 selects the candidate configuration in which the subarray availabilities of each RIS 260a, 260b in the second NTN 200 meet one or more conditions. These conditions may be one or more of:

[0057] • the subarray availability of each RIS 260a, 260b is above a threshold;

[0058] • the average subarray availability of all RIS 260a, 260b is maximised;

[0059] • the positions of the available reflecting unit cells (that is, adjoining reflecting unit cells offer more flexibility as a subarray relative to non-adjoining reflecting unit cells); and

[0060] • the suitability for future configurations (that is, a set of available reflecting unit cells may be more suitable for a future state of the second NTN 200, as predicted by the routes of the non-terrestrial access points).

[0061] In step S113, the controller 270 sends an instruction message to one or more entities of the second NTN 200 to cause each entity to implement the reconfiguration selected in step S1 11 . These instruction messages may be sent to any entity that must reconfigure or must be made aware of another entity’s reconfiguration (e.g. for recording in memory). In this example, the selected reconfiguration is to cause the fourth non-terrestrial access point 230d to join the first cluster, such that the third and fourth non-terrestrial access points 230c, 230d terminate their inter-non-terrestrial access point connection and the fourth non-terrestrial access point 230d forms a new inter-non-terrestrial access point connection with the first non-terrestrial access point 230a via the first RIS 260a (such that it establishes an indirect feeder link with the first gateway 220a via the first nonterrestrial access point 230a). The controller 270 therefore sends instruction messages to:

[0062] • cause the third and fourth non-terrestrial access points 230c, 230d to terminate their inter-non-terrestrial access point connection,

[0063] • cause the first RIS 260a, first non-terrestrial access point 230a and fourth nonterrestrial access point 230d to form a new inter-non-terrestrial access point connection, such that a new subarray is formed to enable this connection using the available reflecting unit cells of the first RIS 260a,

[0064] • cause the first gateway 220a and fourth non-terrestrial access point 230d to communicate via the indirect feeder link via the inter-non-terrestrial access point connection between the first and fourth non-terrestrial access points 230a, 230d,

[0065] • cause the second RIS 260b, third non-terrestrial access point 230c and fifth nonterrestrial access point 230e to form a new inter-non-terrestrial access point connection, such that a new subarray is formed to enable this connection using the available reflecting unit cells of the second RIS 260b (which may include some or all of the reflecting unit cells that previously formed the subarray facilitating the inter-non-terrestrial access point connection between the third and fourth non-terrestrial access points 230c, 230d), and

[0066] • cause the second gateway 220b and fifth non-terrestrial access point 230e to communicate via the indirect feeder link via the inter-non-terrestrial access point connection between the third and fifth non-terrestrial access points 230c, 230e.

[0067] The final state of the second NTN 200 is illustrated in Figure 5.

[0068] The above method implements a load balancing process in the second NTN 200 so as to optimise (or at least improve) the subarray availability (in terms of the number of reflecting unit cells available to form a new subarray) of each RIS in the NTN. Advantageously, the likelihood of one or more RIS in the second NTN 200 being able to form a new connection, such as a new inter-non-terrestrial access point connection, is improved. As noted above, the load of the NTN is based on at least the subarray availability of each RIS in the NTN, the subarray availability of each RIS being based on the number of reflecting unit cells available to form a new subarray. The skilled person will understand that the load of the NTN may be based on further factors, such as a processing, memory or communication resource utilisation of any other node or communication link in the NTN. Furthermore, selection of the candidate reconfiguration may be based on additional factors, such as the determined load of these other nodes or communication links in the NTN.

[0069] The skilled person will understand that it is non-essential for the second NTN 200 to comprise a plurality of gateways and / or a plurality of clusters of non-terrestrial access points. The benefits of the invention may be realised when a plurality of RIS support at least one inter-non-terrestrial access point connection with one or more gateways and one or more non-terrestrial access points. That is, the second NTN may comprise a first and second RIS and a plurality of non-terrestrial access points comprising a primary nonterrestrial access point having a direct connection with a first gateway and a secondary non-terrestrial access point having an indirect connection with the first gateway via the primary non-terrestrial access point that is facilitated by the first RIS. The load balancing operation may then be triggered so as to balance the subarray availability across the first and second RIS. In this scenario, the second RIS may or may not already facilitate further inter-non-terrestrial access point connections.

[0070] In the above description, the non-terrestrial access point is part of a HAP. However, this is non-essential and the skilled person will understand that other forms of non-terrestrial access points may be used, in any combination, such as satellites or UAV.

[0071] The skilled person will understand that any combination of features is possible within the scope of the invention, as claimed.

Claims

CLAIMS1 . A method in a wireless telecommunications network, the wireless telecommunications network comprising: a plurality of Reconfigurable Intelligent Surfaces, RISs, each RIS comprising a plurality of reflecting elements, each reflecting element of the plurality of reflecting elements of each RIS being a member of either a first set of utilised reflecting elements that are configured for reflecting a signal in the wireless telecommunications network or a second set of available reflecting elements; a plurality of non-terrestrial access points, wherein a first inter-non-terrestrial access point connection is communicated via a first RIS of the plurality of RISs; and one or more gateways configured to provide a feeder link to at least one nonterrestrial access point of the plurality of non-terrestrial access points; the method comprising the steps of: determining a subarray availability of the first RIS as a function of a number of reflecting elements in a second set of available reflecting elements of the first RIS; determining a subarray availability of a second RIS of the plurality of RISs as a function of a number of reflecting elements in a second set of available reflecting elements of the second RIS; and reconfiguring the wireless telecommunications network based on the determined subarray availabilities of the first and second RIS.

2. A method as claimed in Claim 1 , wherein a second inter-non-terrestrial access point connection is communicated via the second RIS of the plurality of RIS.

3. A method as claimed in Claim 2, wherein the plurality of non-terrestrial access points comprises a first cluster of non-terrestrial access points comprising a primary non-terrestrial access point of the first cluster having a direct connection with a gateway of the one or more gateways, and the first inter-non-terrestrial access point connection is between a first pair of non-terrestrial access points of the first cluster of non-terrestrial access points.

4. A method as claimed in Claim 3, wherein the second inter-non-terrestrial access point connection is between a second pair of non-terrestrial access points of the first cluster of non-terrestrial access points.

5. A method as claimed in Claim 3, wherein the plurality of non-terrestrial access points comprises a second cluster of non-terrestrial access points comprising a primary non-terrestrial access point of the second cluster having a direct connection with a gateway of the one or more gateways, and the second inter-non-terrestrial access point connection is between a first pair of non-terrestrial access points of the second cluster of non-terrestrial access points.

6. A method as claimed in any one of the preceding claims, wherein the step of reconfiguring the wireless telecommunications network comprises one or more of a group comprising: transferring the first inter-non-terrestrial access point connection such that it is communicated via the second RIS; transferring a / the second inter-non-terrestrial access point connection such that it is communicated via the first RIS; transferring the first inter-non-terrestrial access point connection such that it is communicated via a third RIS of the plurality of RIS; transferring the second inter-non-terrestrial access point connection such that it is communicated via the third RIS.

7. A method as claimed in any one of the preceding claims, wherein the first RIS is divided into a plurality of subarrays of reflecting elements, each subarray of reflecting elements having a particular reflection configuration, wherein the subarray availability of the first RIS is a function comprising a total number of reflecting elements of the first RIS minus a number of reflecting elements required for each subarray of the first RIS.

8. A method as claimed in any one of the preceding claims, wherein the second RIS is divided into a plurality of subarrays of reflecting elements, each subarray of reflecting elements having a particular reflection configuration, wherein the subarray availability of the second RIS is a function comprising a total number of reflecting elements of the second RIS minus a number of reflecting elements required for each subarray of the second RIS.

9. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of any one of Claims 1 to 8.

10. A computer readable carrier medium comprising the computer program of Claim9.

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