WO2017017099A1

WO2017017099A1 - Satellite communication

Info

Publication number: WO2017017099A1
Application number: PCT/EP2016/067796
Authority: WO
Inventors: Jason Cooke; Simon Watts; Graham Peters
Original assignee: Avanti Communications Group Plc
Priority date: 2015-07-27
Filing date: 2016-07-26
Publication date: 2017-02-02
Also published as: GB2540775A; GB201513180D0

Abstract

A satellite is configured to provide a steerable gateway beam and a user beam. At least one control signal is transmitted to the satellite to steer the gateway beam from a current orientation to a new orientation relative to the satellite such that, when the satellite is in geostationary orbit at a desired orbital slot, the gateway beam in the new orientation is directed to a desired location on Earth's surface. When the satellite has been deployed in geostationary orbit at the desired orbital slot, data is communicated between a gateway Earth station at the desired location and a remote system on Earth's surface which is covered by the user beam. The data is communicated via the gateway beam in the new orientation.

Description

SATELLITE COMMUNICATION

Technical Field

The subject matter is in the field of satellite communication, and relates in particular to geostationary satellites.

Background

Some regions of the world such as rural, developing or isolated areas often have limited communication infrastructure where high speed broadband through

traditional, ground-based (e.g. wired) means is not feasible. Providing an internet link via satellite enables such regions to obtain modem standards of internet access without the need to build a large amount of new infrastructure on the ground.

Furthermore, satellite-based internet access can even be used as an alternative to ground-based links in regions that do have a developed communication

infrastructure, or as backup to such infrastructure in case a ground-based link fails.

Figure 1 gives a schematic overview of a system 100 for providing access to a network, which is an internet 102 i.e. a wide area internetwork such as that commonly referred to as the Internet (capital I). The system 100 comprises a gateway Earth station (gateway) 104, a satellite 110 in orbit about the Earth (labelled "E" in various figures), and one or more client systems 112 remote from the gateway 104 and located in a region on the Earth's surface to which internet access is being provided. The gateway 104 comprises a satellite hub 402 connected to the internet 102, and at least one gateway antenna 106 connected to the hub 402. Each of the client systems comprises an antenna 114, connected to a satellite modem 420. The satellite 110 is arranged to be able to communicate wirelessly with the hub 402 of the satellite gateway 104 via the gateway antenna 106, and with the modems 420 of the client systems 2 via the antennas 114, and thereby provide a satellite link 107 for transmitting internet traffic between the source or destination on the internet 102 and the client systems 112. For example the satellite link 107, hub 402 and modems 420 may operate on the Ka microwave band (26.5 to 40 GHz). The satellite link 107 comprises a forward link 107F for transmitting traffic originating from an internet l source to the client systems 112, and a return link 107R for transmitting traffic originating with the client systems 112 to an internet destination.

The hub 402 serves (i.e. provides an internet access service to) the client systems 12 so that internet traffic can be transmitted and received between the client systems 112 and the internet 102 via the satellite link 107 and the hub 402. The internet access service is a two-way communications service 102 i.e. the hub 402 both transmits data to the client systems 112 (via the forward link 107F) and received data from them (via the return link 107R). Though not shown in figure 1 , the gateway may include multiple such hubs, each serving a respective subset of client systems.

In one model the operator of the satellite 110 and/or gateway 104 provides bandwidth to a downstream internet service provider (ISP), who in turn provides an internet access service based on that bandwidth to a plurality of end users 116. The end users 116 may be individual people (consumers) or businesses or governmental organisations. Depending on implementation, the client systems 112 may comprise a central satellite gateway run by the ISP (the satellite gateway comprising an antenna 114 and modem 420), and a local communication infrastructure providing access onwards to the equipment of a plurality of users within the region in question. E.g. the local communication infrastructure may comprise a relatively short range wireless technology or a local wired infrastructure, connecting onwards to home or business routers or individual user devices. Alternatively or additionally, the client systems 112 may comprise individual, private user terminals each with its own satellite antenna 114 and modem 420 for connecting to the satellite 110 and local access point for connecting to one or more respective user devices. In this case the ISP does not necessarily provide any extra infrastructure, but acts as a broker for the bandwidth provided by the satellite 110. For example an individual femtocell or picocell could be located in each home or business, each connecting to a respective one or more user devices using a short range wireless technology, e.g. a local RF technology such as Wi-Fi.

Referring to Figure 2 by way of example, the satellite 110 is deployed in a

geostationary orbit and arranged so that its field of view or signal covers roughly a certain geographic region 200 on the Earth's surface. Figure 2 shows South Africa as an example, but this could equally be any other country or region within any one or more countries (e.g. a state, county or province, or some other non-political!y defined region).

Furthermore, referring to Figures 2 and 3, using modern techniques the satellite 1 10 may be configured as a spot-beam satellite, so that the communications between the satellite 1 10 and the client system(s) 1 12 in the covered region 200 are divided amongst a plurality of spatially distinct beams 202, referred to herein as "user beams". The term "beam" refers to a volume of space or "lobe" in which transmission and/or reception of one or more given signals are approximately confined, typically a signal cone. Each user beam 202 is directed in a different respective direction such that beams are arranged into a cluster, each beam covering a different respective (sub) area on the Earth's surface within the region 200 in question (though the areas covered by the beams 202 may be arranged to overlap somewhat to avoid gaps in coverage). Signals transmitted from the satellite 1 0 to a given client system are approximately confined to the user beam which covers that client system, with only a small amount of leakage into neighbouring user beams. This is a way of increasing capacity, as the limited frequency band of the satellite 1 10 (e.g. Ka band) can be re- used separately in different beams 202 - i.e. it provides a form of directional spatial division multiplexing (though adjacent beams may still use different bands or sub- bands, especially if they overlap in space). By way of example Figure 2 shows five beams 202a-202e which between them approximately cover the area of South Africa, but it will be appreciated that other numbers and/or sizes of beam are also possible. Figure 3 also shows a gateway beam 204, in which signals transmitted from the satellite 1 10 to the gateway 1 0 are approximately confined. Note figure 3 is not to scale, and that in particular the gateway beam 204 may be significantly narrower than the user beams 202 as, on the Earth's surface, it need only cover the area in the immediate vicinity of the gateway antenna 106. The gateway beam 204 may be separated from the user beams 202 in space as shown in figure 3, or it may overlap with one or more of the user beams 202 on the Earth's surface.

Summary Herein, a method for controlling a satellite, configured to provide a steerable gateway beam and a user beam, comprises the following steps. At least one control signal is transmitted to the satellite to steer the gateway beam from a current orientation to a new orientation relative to the satellite such that, when the satellite is in

geostationary orbit at a desired orbital slot, the gateway beam in the new orientation is directed to a desired location on Earth's surface. When the satellite has been deployed in geostationary orbit at the desired orbital slot, data is communicated between a gateway Earth station at the desired location and a remote system on Earth's surface which is covered by the user beam. The data is communicated via the gateway beam in the new orientation.

A steerable beam means a beam which can be controlled to change its orientation relative to the satellite in a continuous manner, whereby the beam is rotatable relative to the satellite about at least one axis over a continuous range of angles. That is, such that a pitch and/or a roll of the beam relative to the satellite is

changeable continuously. A steerable beam may be mechanically steerable, electrically steerable (based on beam forming), or a combination of both - this applies to at least the gateway beam of this disclosure, and also to the user beam(s) in certain embodiments.

Conventional wisdom dictates that the mass of a satellite should be minimized, as even a slight increase in mass can significantly increase the amount of fuel needed to deploy the satellite. This in turn incurs a significant extra cost.

The mass of the on board equipment needed to make the gateway beam steerable will increase the mass of the satellite. Given that gateways are traditionally fixed entities having a working lifetime that is typically considerably longer than that of the satellite, and given that a satellite in geostationary orbit is fixed relative to the Earth and thus to the gateway, making the gateway beam steerable appears unnecessary and counterintuitive.

However, the inventor has recognized that, even though providing a steerable gateway beam on a geostationary satellite requires extra resources, it beneficially allows the satellite's mission to be designed in-orbit, at least to some extent. That is, decisions regarding the satellite's operation that would normally have to be made before it is launched can be deferred to a later time when the satellite has already been deployed in space. This flexibility includes for example the freedom to relocate the satellite to different geostationary orbital slot(s), chosen arbitrarily (at least to some extent) at the later time, and the freedom to direct the gateway beam to a different gateway that can be located arbitrarily (at least to some extent). In the case of the former, the possibility of that slot becoming available during the satellite's working life time need not even have been conceived at the time of launch. In the case of the latter, a gateway at that location need not have been built or even envisaged at the time of launch.

Preferably, the user beam is also steerable independently of the gateway beam. The user beam may for instance be one of a cluster of user beams. The user beams may for example be individually steerable (i.e. independently of one another) or the cluster may only steerable as a whole (without the possibility of steering user beams in the cluster individually, at least for some of the user beams). By providing a steerable user beam(s) in addition to the steerable gateway beam, maximum flexibility is attained, allowing a mission to be designed entirely or almost entirely in orbit. For example, the satellite can be reconfigured in orbit to serve a new and different set of client systems from a new and different gateway, either of which can be located arbitrarily (at least to some extent) on Earth's surface, even if this setup was not envisaged at the time of launch. in embodiments, before the gateway beam is steered to the new orientation, the satellite may be deployed in geostationary orbit at a current orbital slot with the gateway beam in the current orientation, and the method may further comprise transmitting at least one control signal to the satellite to cause the satellite to move from the current orbital slot to the desired orbital slot.

In some cases, when the satellite is at the current orbital slot with the gateway beam in the current orientation, the gateway beam is directed to the or a different gateway Earth station. Alternatively or in addition, the gateway beam may reach the new orientation before the satellite leaves the current orbital slot, whilst the satellite is travelling to the desired orbital slot, or after the satellite has arrived at the desired orbital slot. Before the gateway beam is steered to the new orientation, the satellite may be deployed in geostationary orbit at the desired orbital slot with the gateway beam in the current orientation, whereby the gateway beam is steered from the current orientation to the new orientation whilst the satellite remains at the desired orbital slot. For example, when the satellite is at the desired orbital slot with the gateway beam in the current orientation, the gateway beam may be directed to a different gateway Earth station.

The user beam may also also steerable, and the method may further comprise transmitting at least one control signal to the satellite to steer the user beam from a current user beam orientation to a new user beam orientation such that, when the satellite is at the desired orbital slot, the user beam in the new user beam orientation covers the remote system. For example, the user beam may be one of multiple steerable spot beams, and the method may comprise transmitting at least one control signal to the satellite to steer the spot beams so that each covers a

respective remote system when the satellite is in the desired orbital slot. E.g. the spot beams may be steerable independently of one another, and the method may comprise steering the spot beams independently of one another so that each covers the respective remote system. The method may further comprise deploying the gateway at the desired location on Earth's surface after the satellite has been launched. For example, the gateway may comprise a phased array gateway antenna of multiple antenna elements. In some cases, the method may comprise travelling to the desired location with the antenna elements in a disassembled state, and deploying the gateway may comprise assembling the phased array gateway antenna at the desired location from the antenna elements.

The travelling to said desired location with the gateway in a disassembled state, and reassembling at the desired location, may be performed after the phased array gateway antenna has already served as a gateway antenna and then been

disassembled.

Another aspect is directed to a satellite communications system comprising: a transmitter configured for transmitting control signals to a satellite to control the satellite, wherein the satellite is configured to provide a steerable gateway beam and a user beam; a ground controller configured to transmit at least one control signal to the satellite to steer the gateway beam from a current orientation to a new orientation relative to the satellite such that, when the satellite is in geostationary orbit at a desired orbital slot, the gateway beam in the new orientation is directed to a desired location on Earth's surface; and a gateway Earth station at the desired location configured, when the satellite has been deployed in geostationary orbit at the desired orbital slot, to communicate data between the gateway Earth station and a remote system on Earth's surface which is covered by the user beam, the data

communicated via the gateway beam in the new orientation.

In embodiments, the system may be configured to implement any of the methods disclosed herein, Particular advantages arises from the combined use of geostationary satellites with steerab!e gateway beams deployed in space and phased array gateway antenna deployed on the ground. For example, a temporary gateway of the kind described above can be deployed very quickly, as and when it is needed, at a location on Earth that is (at least to some extent) arbitrary and that need not have been envisaged at the time the satellite was launched. The satellite which is already in orbit can be reconfigured to direct its gateway beam to the location of the newly deployed gateway (before, during, or as the gateway is assembled), which means service delivery from the temporary gateway can commence immediately. As will be readily apparent, this approach provides vastly greater flexibility and speed than the traditional approach of building a permanent gateway and launching a dedicated accompanying satellite.

Gateway's typically have a large parabolic gateway dish antenna. For example, gateway antennas having a diameter of about 9 metres or greater is not uncommon. The larger the dish, the greater the directivity of the antenna i.e. transmissions from the gateway antenna are highly focused over a narrow range of angles, and signals are received at the gateway antenna with appreciable (i.e. non-negligible) gain from a narrow range of angles only. That is, both the power density of signals emitted by the antenna 106 in a direction from the gateway 104 to the satellite 110 and the gain of signals received at the antenna from the satellite in the reverse direction is maximized, and both the power density of signals emitted from the antenna in the other directions (i.e. directed away from the satellite) and the gain of extraneous signals arriving at the gateway antenna from other directions which have not come from the satellite such as noise and interference are minimized.

The nature of a traditional, parabolic gateway antenna can be a hindrance to the deployment of new gateway Earth stations, as its large size and configuration make it burdensome to transport and erect. The time taken to deploy a traditional gateway antenna means that an operator is less flexible than desired in reacting to demand for service. .

Herein, a gateway for effecting communication between a remote system and a network via a satellite in a satellite communication system comprises a network interface, a modulator, and a phased array gateway antenna. The network interface is configured to receive from the network outgoing data intended for the remote system. The modulator is configured to modulate the outgoing data to generate an outgoing signal, which is outputted from an output of the modulator. The phased array gateway antenna comprises multiple antenna elements, each coupled to the output of the modulator whereby each antenna element emits a respective version of the outgoing signal. The emitted versions of the outgoing signal interfere to create a composite outgoing signal. The antenna elements are coupled to the output in an arrangement such that the composite outgoing signal has a maximal signal power along a line between the phased array gateway antenna and the satellite.

The phased array gateway antenna is significantly easier to transport and deploy quickly, as its constituent antenna elements can be transported in a disassembled state and the phased array assembled in situ from them. Thus the phased array gateway antenna can be flexibly deployed, in quick response to demand for service in a given region. This also opens up the possibility of deploying gateways in environments in which that would previously have been difficult, and makes viable the deployment of a temporary gateway (for example, to serve a user base until the a suitable permanent gateway can be deployed). The phased array gateway antenna can be readily disassembled once it has served its immediate purpose, and redeployed elsewhere as and when it is needed. As will be apparent to a person skilled in the art, erecting a temporary gateway with a traditional gateway antenna would be impracticable. In preferred embodiments, the gateway comprises a demodulator, each antenna element coupled to an input of the demodulator. A composite incoming signal is receivable at the input, the composite signal bearing incoming data and being a summation of incoming signals received by the antenna elements individually, and the demodulator is configured to demodulate the composite incoming signal and transmit the incoming data to the network. In some of the preferred embodiments, the network is an internet (e.g. the Internet) and the hub is configured to provide an internet access service to the remote system(s).

In various embodiments, each of at least some of the antenna elements may be coupled to the output via a respective phase shifter, the phase shifters configurable to change the orientation and/or tune the directivity of the phased array gateway antenna.

The antenna elements may be mounted on one or more poles and/or one or more frames.

The gateway may comprise one or more vehicles in which the modulator, network interface and/or demodulator are housed. Each of the antenna elements may have a substantially circular reflector surface when viewed in plan, and the antenna elements may be arranged in a plurality of substantially parallel rows. Each row may be offset from its adjacent row(s) in a first direction parallel to the rows, and each row may be offset from its adjacent row(s) in a second direction perpendicular to the rows and in the plane of the rows by a distance less than the diameter of the reflector surface. For example, each row may be offset from its adjacent row(s) by substantially half of the diameter of the reflector surface in the first direction and the distance in the second direction is substantially minimized.

The antenna elements may have a total reflector area of 7 square meters or more.

The antenna elements may each have an individual reflector surface of radius 0.6 metres or more.

The antenna elements may be dish antennas.

The modulator and/or demodulator may form part of a satellite hub, the remote system being one of multiple remote systems served by the satellite hub via the phased array gateway antenna. For example, the gateway may comprise multiple satellite hubs, each serving a respective set of remote systems via the phased array gateway antenna.

Another aspect is directed to a method of deploying a gateway Earth station for a satellite communication system comprising:

travelling to a desired location with a set of antenna elements in a

disassembled state;

assembling a phased array gateway antenna at the desired location from the set of antenna elements by coupling each antenna element to an output of a modulator; and

connecting the modulator to a network;

whereby when an outgoing signal, bearing outgoing data received from the network, is outputted from the output of the modulator, each antenna element emits a respective version of the outgoing signal, the emitted versions of the outgoing signal interfering to create a composite outgoing signal, wherein the step of assembling comprises coupling each antenna element to the output of the modulator in an arrangement such that the composite outgoing signal has a maximal signal power along a line between the phased array gateway antenna and the satellite. In embodiments, the method may implement any of the system functionality disclosed herein.

The satellite may have a steerable gateway beam, and the method may further comprise transmitting at least one control signal to the satellite to steer the gateway beam to the desired location, thereby enabling the satellite to receive the composite outgoing signal when it has been transmitted.

Various embodiments are defined in the dependent claims.

Brief Description of Figures

Figure 1 is a schematic diagram of a known type system for providing internet access via satellite;

Figure 2 is a schematic diagram showing geographic coverage of a cluster of satellite beams;

Figure 3 is a schematic diagram of a part of a system for providing internet access via satellite beams;

Figure 4A is a schematic block diagram of a type system for providing internet access via satellite in accordance with the present invention;

Figure 5 is a schematic block diagram representing a gateway Earth station with a phased array gateway antenna;

Figure 6A shows a line of sight between a gateway Earth station and a satellite;

Figure 6B is a schematic illustration of some principles of a phased array gateway antenna;

Figure 6C shows a plan view of an exemplary arrangement of a phased array gateway antenna. Figure 7A is a schematic block diagram showing a first possible configuration of a phased array gateway antenna;

Figure 7B is a schematic block diagram showing a second possible configuration of a phased array gateway antenna;

Figure 8A illustrates a first use case of a satellite with steerable gateway and user beams;

Figure 8B illustrates a second use case of a satellite with steerable gateway and user beams;

Figure 9 is a schematic illustration of a satellite with a mechanically steerable gateway beam and a mechanically steerable user beam.

Detailed Description of Embodiments

Figure 4 shows how the system 100 of figure 1 may be reconfigured in embodiments of the present invention. The gateway 104 is shown to comprise what is referred to herein as a phased array gateway antenna 106' in place of the large parabolic dish gateway antenna 106. The phased array gateway antenna 106' is an antenna array of multiple antenna elements, which cooperate to act as a single large array. Details of its configuration are given below. A satellite 110' shown in place of the satellite 110 is configured to provide both a steerable gateway beam 204" and a steerable user beam 202', which may be one of a cluster of user beams. In some such embodiments the cluster may (only) be steerable as a whole; in others at least some of the user beams in the cluster may be steerable independently of one another. The system is otherwise configured in the same manner as described above with reference to figure 1.

Figure 5 is a block diagram of the gateway 104 in this configuration, and is shown to comprise the phased array gateway antenna 106'. The gateway 104 also comprises a satellite hub 402. For example, the gateway may comprise a building which houses the hub 402, in which the satellite hub 402 is installed, and in which various infrastructure is provided so as to connect the hub to the internet 102 and the phased array gateway antenna 106'. The hub 402 comprises a modulator 404, a demodulator 406, a network interface 410 and a hub control module 408, to which the network interface 410 and (de)modulator 404 (406) is connected. The gateway 104 has a network infrastructure 109 to which the hub 402 is connected via its network interfaces 410 so as to connect the hub 402 to the internet 102. The gateway 104 also has an RF ("Radio Frequency") infrastructure 105 to which the hub 402 is connected via its modulator 404 and demodulator 406 so as to connect the hub 402 to the phased array gateway antenna 116'.

The hub modulator 404 modulates data, which has been received from the internet 102 and is to be transmitted to a client system 1 2, to generate outgoing signals; the outgoing signals are supplied to the phased array gateway antenna 116', from which they are transmitted via the forward link 107F to the client system 112. The outgoing signals may be RF signals, of non-RF signals may be generated by hub 404 and frequency converted to RF by the RF infrastructure 105. Conversely, modulated incoming data is received from the client system 112 by the phased array gateway antenna 106' via the return link 107R as (RF or frequency converted) incoming signals bearing the incoming data, which are demodulated by the hub demodulator 406 to extract the incoming data in its original unmodulated form. The extracted data is then supplied to the internet 102 by the hub controller 408. In this manner, the hub can serve the client systems 112 and provide a network access (in particular an internet access) service to them. For example, an Internet (capital I) access service, so that users of the first/second system 112a/112b can access Internet services such as the World Wide Web, email etc. Data may be transmitted and received between client systems 112 and the internet 102 via the hub 402, via the forward and return satellite links 107F, 107R. This may be in accordance with the Internet Protocol (at the internet layer), and may also be in accordance with the full Internet Protocol Suite (otherwise known as the "TCP/IP suite"). In this manner, the users are free to access Internet content from different Internet sources of their choosing, from a wide variety of third-party Internet content providers. For example, the hub 402 may be operated by an ISP (Internet Service Provider) who has chosen to install the hub 402 at the gateway 104 so that the ISP can offer a satellite-based Internet access service to their users.

In some embodiments, the gateway 104 may be formed of one or more vehicles, on which the antenna elements are mounted and/or in which any of the above- described components (hub(s) 402, infrastructures105, 109) may be housed.

Alternatively or in addition, the antenna elements may be mounted on one or more poles and/or one or more frames. A gateway of this nature is quick and easy to assemble and disassemble (to deploy it elsewhere), as may be desired.

One aspect of this disclosure is the phased array gateway antenna 106', via which such services are provided.

The configuration and operating principles of the phased array gateway antenna 108' will now be described with reference to figures 6A and 6B. The phased array gateway antenna 106' provides two-way communications i.e. it both transmits signals to the satellite 110 and receives signals from it.

The phased array gateway antenna 106' is a phased array of multiple, inter-coupled, individual antennas (antenna elements) 602.1 602.5. Five individual antenna are showing in figure 6B but this is purely exemplary, and the phased array gateway antenna 106' can comprise any suitable number of individual antennas. In isolation, each of the individual antenna 602.1....,602.5 is a relatively-wide angle, low- directivity antenna i.e. whose output power is distributed over a relatively large range of angles. However, within the array 106' the individual antenna are coupled to the modulator 404 (and demodulator 406 - see below) in an arrangement whereby they have certain phase relationship. The cumulative effect of this is that the individual antenna 602.1 ,....602.5 cooperate as a single narrow angie, highly directive antenna bi-directional antenna i.e. whose output power and input gain is largely constrained to a narrow range of angles due to controlled interference between signals emitted by the different individual antennas 602.1 ,...,602.5.

By way of illustration, a simplified example is shown in figure 6B. When transmitting signals, each individual antenna emits a version of the same outgoing signal, each version having fixed phase leg relative to its counterpart from the right-hand neighbouring antenna element. Thus corresponding wavef rants 604.1 , ,.,,804.5 of the versions of the outgoing signal emitted by the individual antennas 602.1 602.5 lag behind one another from right to left. The individual wavefronts 604.1 604.5 propagate outwardly of the individual antennas 602.1 ,... ,602.5 in a generally homogenous manner, but due to the phase relationships between the different versions of the outgoing signal they interfere to create a composite outgoing signal which propagates in substantially a straight line, as illustrated by a generally planar wavefront 606 of the composite outgoing signal. The composite outgoing signal will not be exactly confined to a single propagation direction - an exemplary angular signal power distribution 608 is shown to illustrate the approximate manner in which the signal power of the composite outgoing signal varies with angle Θ relative to the phased array 06'. Only one angle is shown but it will be appreciated that there are two degrees of angular variation (azimuth and elevation) in general. The composite signal 1 16' has an orientation, which is defined as the angular direction relative to the phased array 106' along which the signal power of the composite outgoing signal is maximal i.e. the direction perpendicular to the planar wavefront 606. The orientation is represented by an angle Θ0 in figure 6B, though in reality two angles will define the direction in three space. By adjusting the phase relationship between the individual antennas 602.1 , ...,602.5, the orientation of the composite outgoing signal Θ0 can be varied so that it is aligned with a line 610 between the phased array 1 16' and the satellite 110'. That is, so that the signal power of the composite outgoing signal is maximal along the line 610. As will be appreciated, figure 6B represents a simplified example for the purposes of illustration, and there are many different ways in which inter-coupled antenna elements in a phased array can be arranged so as to provide a composite outgoing signal with this desired property. More complex arrangements of antenna elements in particular may require a degree of tuning to achieve this effect, as part of normal design procedures. The directivity of the phased array 06' as a whole can also be tuned (e.g. to substantially maximize it) by tuning the relative phases between different antenna elements.

As indicated, the phased array gateway antenna 106' receives signals from the satellite 1 10' as well as transmitting signals to it. When receiving signals, each antenna 601 receives a version of an incoming signal from the satellite, and the different versions are combined to create a composite incoming signal (not shown in figure 6B). As will be apparent, the arrangement of the antenna elements that causes the narrow angle signal transmission property has a corresponding effect on the signal receive property: signals received along the direction in which the phased array is orientated (i.e. as represented by Θ0, which is along the line 610 when the antenna is properly aligned with the satellite 110') are maximally amplified by constructive interference, whereas destructive interference acts to reduce the contribution of other incoming signals (such as noise or interference) which deviate significantly from this orientation Θ0 to a more or less negligible level. In other words, the orientation Θ0 is the direction of both maximum transmission gain and maximum receive gain of the phased array 1 16', and for this reason is sometimes referred to herein as the orientation Θ0 of the phased array 1 16' itself.

When suitably configured, a phased array gateway antenna 1 16' can provide highly directional two-way communication between the gateway 104 and the satellite 1 0' in the manner of a conventional large parabolic dish gateway antenna, with large transmission and reception gains. That is, a suitable phased array 106' will be able to achieve a similarly high directivity as a conventional parabolic dish gateway antenna. The individual antennas 602 have a total reflector area, which is the sum of their individual reflector areas. The phased array 106' has a directivity and antenna gain (on-axis performance) which substantially matches that of a conventional parabolic dish antenna 106 having the same total reflector area. Thus, in order to match the on-axis performance of any given conventional gateway antenna 106, the phased array 106' can be configured to have a similar total reflector area.

For example, to match the on-axis performance as a 9m antenna, twenty five (25) 1.8m antennas or fourteen (14) 2.4m antennas could be used (these figures are purely exemplary).

As another example, the follow would all have a similar gain as their cross-sectional areas are similar: (i) a circular antenna of radius r = 4.5m (total reflector area of π^*4.5^Λ2 ~ 64 square metres); (ii) an elliptical antenna with major and minor axes of 4m and 5m (total reflector area of π^*4^*5 =63 square metres); and (iii) eight circular antennas of 1.6m radius (total reflector area of 8^*ττ^*1.6^Λ2 ~ 64 square metres).

Similarly, the follow would all have a similar gain as their cross-sectional areas are similar: (i) a circular antenna of radius r = 4m (area of π^*4^Λ2 ~ 50 square metres); and (ii) nineteen circular antennas of 0.8m radius (area of 19^*π^*0.8^Λ2 ~ 48 square metres).

As another example, a circular antenna of 5m radius would have an area of -79 square metres, similar to the area of -85 square metres provided by nineteen

circular antennas of 1 .2m radius.

Similarly, the follow would all have a similar gain as their cross-sectional areas are similar (i) a circular antenna of radius r = 1.5m (area of π*1.5^Λ2 ~ 7 square metres); and (ii) seven circular antennas of 0.6m radius (area of 7^*π^*0.6^Λ2 - 8 square metres).

It is a notable feature of some embodiments that the individual antenna elements 602 each have an individual reflector surface having a radius of about 0.6m or more (e.g. between 0.6 and 1 .8m) and/or that the total reflector area of the antenna elements 602 is about 7 square metres or more.

Off-axis performance of the phased array 106' can be optimized by packing the antennas together as closely as possible. In so doing, it is possible to match the off axis performance of any given conventional gateway antenna having the same overall reflector area.

Figure 6C shows one way in which this can be achieved. Figure 6C is a plan view of one exemplary arrangement of the phased array 106". Each of the individual antennas 602 has a substantially circular reflector surface (when viewed in plan) of diameter D. For example, the antennas 602 may be parabolic dish antennas of diameter D. The individual antennas are arranges in rows Rw1 ,...Rw4. Along each row, the antennas 602 are offset from adjacent antenna(s) in the same row by a distance of substantially D between their centre points. Each row is offset by a distance Sy=D/2 relative to its adjacent row(s) in a direction along the rows (y direction). The distance Sy is measured between the centre points (shown as filled circles) of adjacent antennas 602 in adjacent rows. This means the rows can be as close together as possible in the direction perpendicular to the rows in the plane of the phased array 106' (x direction). That is, such that the spacing Sx in the x direction between the centre points of individual antennas 602 of adjacent rows is substantially minimized (Sx » V3D/2 in this example). Substantially in this context means at least approximately i.e. to within a practicable accuracy, which will vary depending on the circumstances.

More generally, off-axis performance is improved when the antenna elements 602 are arranged in rows, each of which is offset from its adjacent row(s) in the y direction by an amount 0<Sy<D/2, and in the x direction by an amount Sx<D (made possible by the offsetting in the y direction).

Figure 7A exemplifies one possible configuration of the phased array gateway antenna 1 16'. At least some (and possibly all) of the antenna elements 602.2, 602.3 are coupled to an output of the modulator 404 of the hub 402 via respective phase shifters 702.2, 702.3, which are arranged in parallel. A modulated outgoing signal "o" is outputted by the output of modulator 404, so that each antenna element 602.1 , 602.2, 602.3 receives and emits a respective version of the modulated outgoing signal (o, o2, o3 in this example) to generate the composite outgoing signal. Each of the phase shifters 702.2, 702.3 phase shifts the respective version of the signal by a respective amount before it is emitted. The phase shifters 702.3, 702,3 are tuneable to change the respective amount. By tuning the phase shifters, the directivity of the array can be optimized and the orientation Θ0 of the array 1 16' can also be changed. Incoming signals "if, i2, Ϊ3 received by the antenna element 601 .1 , 602.2, 603.3 respectively are (where applicable) phase shifted in parallel in an equivalent manner, and the resulting signals are summed by a summer 704 to generate the composite incoming signal, which is supplied to the demodulator 406. Figure 7B exemplifies another possible configuration, in which phase shifters 706.2, 706.3 are arranged in series. Thus, the outgoing signal version o2 received and emitted by the antenna element 602.2 is created by phase shifting the modulator output o, and the outgoing signal version o3 outputted by the antenna element 603,3 is created by phase shifting o2. Incoming signals are phased shifted summed (by summers 708.1 , 708,2) in series to generate a composite incoming signal that is supplied to the demodulator 406. Again, the phase shifters can be tuned to optimize directivity and change the orientation for both transmitted and received signals. The phase shifters are not essential - for example, a phased array 106' with an orientation perpendicular to the phased array can be provided with all antenna elements arranged in phase relative to one another. The various phase shifters and summer(s) described above may be implemented by dedicated hardware, signal processing software running on a processors) or a combination of both.

Building a traditional gateway Earth station, with the requisite large parabolic dish antenna, can be onerous and time consuming. The large antenna presents a particular problem as it is not easily transportable, particularly in inhospitable environments or those with limited or no transport infrastructure. The phased array gateway antenna of this antenna, on the other hand, is easier to transport and the component antenna elements can be transported separately, for instance in or mounted on vehicles. That is, the distributed nature of the phased array 116" makes it particularly suited to assembly in situ as an when it is needed. This makes it possible to erect gateways, relatively quickly and easily, in locations that would not be viable candidates for traditional gateways.

This also opens up the opportunity for fast and efficient deployment of temporary gateways. Among other things, legislative or procedural restrictions such as planning permission can be a significant hindrance to the prompt erecting of permanent gateways. As an interim measure, a temporary gateway with a phased array gateway antenna can be deployed in the meantime. Moreover, a temporary gateway can be deployed to test whether there is in fact a need for a gateway at a particular geographic location. For example, some countries and regions have requirements that users in that country or region are served by a gateway that is located in that country or region, for instance to comply with lawful intercept requirements. Building a traditional, permanent gateway in such a country or region that turns out to have a limited user base(because there is less demand for the internet access service than initially envisaged could prove a costly mistake, whereas a temporary gateway with a phased array gateway antenna provides an opportunity to test the relevant market in such a country or region beforehand, and potentially seed the marked before e.g. upscaling with a permanent gateway.

To this end, antenna elements 602 can for instance be transported in or even mounted on vehicles, such as trucks, lorries, aeroplanes, helicopters, boats, trains etc. The internal infrastructure of the gateway of figure 5 can be provided inside a vehicle(s), similar to some modern data centres. Thus the constituent components of the temporary gateway can be easily transported and assembled in situ. Where the antenna elements are mounted on the vehicles, they can remain mounted when the phased array is assembled which makes for particularly straightforward assembly.

Another aspect of this disclosure is the satellite 110' configured to provide a steerable gateway beam 204', when deployed in geostationary orbit of Earth.

As indicated, a steerable beam means a beam having an orientation that is changeable relative to the satellite in a continuous manner. This is in contrast to both a fixed beam whose orientation is fixed relative to the satellite, and a so-called switchable beam which can only be switched between a discrete, finite number of different orientations relative to the satellite in a discontinuous manner, typically a small number of fixed orientations such as two.

The gateway beam 204' is fully steerable. A fully steerable beam means a beam that is steerable with two degrees of angular freedom i.e. the beam is independently rotatable relative to the satellite about two orthogonal axes, over a respective continuous range of angles for each axis. That is, such that both the pitch and the roll of the beam relative to the satellite are changeable continuously and

independently of one another.

When in geostationary orbit of Earth, the satellite 110' does not move relative to a gateway 104 at a fixed location on Earth's surface. As long as this configuration is maintained, there is no need to change the orientation of the gateway beam 204'. Thus, the provision of a steerable gateway beam 204' in this context appears unnecessary and burdensome, particularly given the significant additional resources that are required to deploy and maintain a satellite in space with the necessary extra equipment due to the additional mass and complexity it introduces. Nevertheless, the inventor has recognized certain advantages that may be gained by the provision of a steerable gateway beam. In particular, the inventor has recognized that, even though the satellite with the steerable gateway beam is no longer optimized for mass in the way that a fixed or switchable gateway beam can be, the fact that extra resources are needed is outweighed in some cases by the flexibility that a fully steerable gateway beam can provide. Examples which illustrate the various potential benefits follow.

A first use case is illustrated in figure 8A. A satellite 110' configured to provide a steerable gateway beam 204' is initially deployed in geostationary orbit at an orbital slot S, as shown to the left-hand side of figure 8A. To achieve geostationary orbit, a satellite must be a specific distance from Earth and directly above the equator. As is well known, only a limited number of geostationary satellites can be safely

accommodated at any one time. The limited area of space in which geostationary orbits are possible is divided into what are called orbital slots, defined to some extent by international agreement. Different orbital slots thus represent different location in space at which geostationary orbit is possible.

In the satellite's initial deployment, the steerable gateway beam is in a current gateway beam orientation (relative to the satellite 110'). The current gateway beam orientation is such that the gateway beam 204' is directed to a first location L1 on Earth's surface, at which a first gateway 104a is deployed. With the satellite 1 0' remaining in the same orbital slot S, the steerable gateway beam 204' is steered to a new gateway beam orientation, thereby directing it to a second location L2 at which a second gateway 104b is deployed. The second gateway L2 may be deployed before, during and/or as the gateway beam 204' is steered to the second location L2. Because the gateway beam 204' is fully steerable, in contrast to, say, a switchable gateway beam, there is no need for the location L2 to be known before the satellite 110' is launched That is, it becomes possible to design the satellite's mission in- orbit.

The user beam 202', or cluster of user beams, is also fully steerable. By also providing a fully steerable user beam 202', or a fully steerable cluster of user beams which are fully steerable at least as a group (i.e. not independently of one another, but with two angular degrees of freedom for the cluster as a whole) and possibly individually (i.e. independently of one another, with two angular degrees of freedom), maximum flexibility is achieved enabling the mission to be designed entirely in orbit.

As illustrated in figure 1 , the steerable user beam can be steered from a current orientation, in which it covers a set of client systems 112A within a first area A1 on Earth's surface, to a new orientation, in which it covers a second set of client systems 112B within a second area A2 on Earth's surface.

Thus, even after a satellite 110' has already been deployed into space to serve one set of client systems from gateway, a decision can then be made to now use that satellite to serve a different set of client systems from a different gateway, or the same set of client systems from a different gateway, or a different set of client systems from the same gateway. No knowledge as to the location of the different client systems and/or different gateway is required before the satellite 110' is launched thanks to the fully steerable user and gateway beams.

A second use case is illustrated in figure 8B. The satellite is initially (left hand side of figure 8A) in a current orbital slot S1 , with the gateway beam 204' in a current gateway beam orientation relative to the satellite 1 0' such that it is directed to a gateway 104 at a location L on Earth's surface. The user beam 202' is also in a current orientation relative to the satellite 110' such that it covers a set of client systems 1 2 within an area A of Earth's surface. The satellite is then moved in space to a new, different orbital slot S2. The gateway and user beams 204', 202' are steered to respective new gateway beam and user beam orientations relative to the satellite 110' respectively - either before, as, or after the satellite 10' is moved - so that the gateway beam 204' is still directed to the gateway 104 at the location L and the user beam 202' still covers the client systems 112 in the area A in the new orbital slot S2. Note, there may be an intervening interval at which the beams do move relative to Earth, though in this example they end up back where they started afterwards.

Usage of orbital slots is internationally regulated, and in practice they are allocated to entities (such as businesses, scientific organizations, governments etc.) with certain usage requirements. For example, in some cases where an orbital slot is allocated to a particular entity, the entity forfeits that allocation if the slot remains unused for too long a period - two years is a typical example. This can be difficult to achieve where a new satellite has to be launched, and possibly even designed and manufactured, in that time. One advantage of the flexibility afforded by fully steerable user and gateway beams is that use of a newly allocated slot (S2) can commence more or less as soon as it is allocated, by the satellite 110' that has already been launched. Again, this requires no fore-knowledge of the new slot S2 when the satellite is launched - if and when the new slot is allocated, the mission thereafter can be designed entirely to respond appropriately to this turn of events, and avoided the forfeiture of the slot.

Note that the use cases of figure 8A and 8B are exemplary and not mutually exclusive. The satellite 110' can be deployed to a new orbital slot, and the user and/or gateway beams directed to new locations and/or areas also.

Figure 9 shows a block diagram of a satellite 110' configured to provide a

mechanically steerable user beam 202' and a mechanically steerable gateway beam 404'. A first and second antenna 802, 804 provide the user and gateway beam 202', 204' respectively. Each antenna is mounted on a respective mechanically steerable mount 806, 808 which is mechanically steerable to change a both a respective pitch P1 , P2 and a respective roll R1 , R2 of the relevant beam 202', 204' independently of the other beam 204', 202'. Thus the user and gateway beams 202', 204' thus are fully steerable, independently of one another. On board signal processing logic 812 (typically circuitry, though software or combined software/hardware processing is not excluded) connects the antennas 802, 804 to one another, whereby data bearing signals can be passed between them and thus conveyed between the user beam 802' and the gateway beam 804' in both directions. The signal processing logic 812 performs signal amplification and frequency conversion primarily, and may also perform other functions such as filtering. An on board drive mechanism 810 is controllable to steer the beams 802', 804' as desired. An on board controller 816 can be instructed to orient either of the beams 802', 804' as desired, by sending suitable control signals "ctrl" from a control centre on Earth (1000 in figure 10). The antennas 802, 804 are parabolic dish antenna, and therefore have a relatively high directivity in both the transmission and receive directions. That is, the parabolic nature of the antennas is what substantially restricts signal transmission and reception to a limited volume of space. To maximize its power efficiency, it is generally desirable for the gateway beam 204' to have a greater directivity than the user beam 202', as it need only cover the gateway antenna and higher transmission and signal gains can be achieved that way.

Alternatively, the satellite 110' can be configured with antenna arrays that provide an electrically steerable gateway beam, based on beam forming, to provide gateway and user beams 802', 804' of similar directivity i.e. to similarly restrict two way communication to limited volumes of space. As another alternative, these

technologies can be combined whereby beam steerability is provided by a

combination of beam forming and mechanical components.

Each of the beams 202', 204' is defined by physical characteristics of its respective antenna 802, 804, in particular that antenna's geometry and/or beam forming characteristics. That is, the configuration of the first and second antennas 802, 804 define volumes of space 202', 204' in which transmission and/or receipt of signals transmitted between the satellite 110' and the client system(s) 112 and between the satellite 110' and the gateway 04 are approximately confined respectively. In other words, the configuration of each antenna 802, 804 defines both the spatial distribution of signals emitted by that antenna (and in particular confines them within the relevant beam 202', 204'), and restricts which signals are received by that antenna with non-negligible signal gain (and in particular restricts confined signals to those having propagation vectors within the relevant beam 802', 804').

Figure 10 shows the Earth-based satellite control system 1000. The control system comprises a transmitter 1002 for transmitting the control signals "Ctrl" to the satellite 110', and a ground controller 1004 for effecting their transmission by the transmitter 1002. The ground controller 1004 may be implemented by satellite control software executed on a processor. The mechanism by which control signals are send and receive between the satellite controller 816 and the ground controller is generally separate from the user/gateway beams.

Particular advantages are obtained by combining the use of a steerable gateway beam on a geostationary satellite with that of a phased array gateway antenna.

For instance, the satellite 10' can be used as a seed satellite in the following manner. When it is desired to start serving a new customer base e.g. in a new country or region, the seed satellite 10' can be used initially to start providing the new service on a temporary basis - that is, to seed a potential new market. A particular advantage is obtained by combining this with the use of the phased array gateway antenna, for example by deploying a temporary gateway of the kind described above to serve this new market on a temporary basis.

Should demand for the service grow, or in response to other factors, a more permanent satellite (e.g. of higher capacity) can be deployed in place of the seed satellite, and/or a permanent gateway built to replace the temporary gateway if necessary, at which point the temporary gateway including the phased array can disassembled. The process can then repeated i.e. the seed satellite and/or temporary gateway redeployed to seed a new market. Should demand in a new market prove unforthcoming, the seed satellite and temporary gateway can be simply be withdrawn, with significantly fewer resources having been wasted than would have been the case had a permanent gateway been built and an

accompanying satellite launched in the traditional manner.

The above embodiments are exemplary, and other variants or applications may be apparent to the skilled person in view of this disclosure. The scope of the present invention is not limited by the described examples, but only by the following claims.

Claims

Claims:

1. A method for controlling a satellite, wherein the satellite is configured to provide a steerable gateway beam and a user beam, the method comprising:

transmitting at least one control signal to the satellite to steer the gateway beam from a current orientation to a new orientation relative to the satellite such that, when the satellite is in geostationary orbit at a desired orbital slot, the gateway beam in the new orientation is directed to a desired location on Earth's surface; and

when the satellite has been deployed in geostationary orbit at the desired orbital slot, communicating data between a gateway Earth station at the desired location and a remote system on Earth's surface which is covered by the user beam, the data communicated via the gateway beam in the new orientation,

wherein the gateway Earth station comprises a phased array gateway antenna of multiple antenna elements.

2. A method according to claim 1 wherein, before the gateway beam is steered to the new orientation, the satellite is deployed in geostationary orbit at a current orbital slot with the gateway beam in the current orientation, and the method further comprises transmitting at least one control signal to the satellite to cause the satellite to move from the current orbital slot to the desired orbital slot.

3. A method according to claim 2 wherein, when the satellite is at the current orbital slot with the gateway beam in the current orientation, the gateway beam is directed to the or a different gateway Earth station.

4. A method according to claim 2 or 3 wherein the gateway beam reaches the new orientation before the satellite leaves the current orbital slot, whilst the satellite is travelling to the desired orbital slot, or after the satellite has arrived at the desired orbital slot.

5. A method according to claim 1 wherein, before the gateway beam is steered to the new orientation, the satellite is deployed in geostationary orbit at the desired orbital slot with the gateway beam in the current orientation, whereby the gateway beam is steered from the current orientation to the new orientation whilst the satellite remains at the desired orbital slot,

6. A method according to claim 5 wherein, when the satellite is at the desired orbital slot with the gateway beam in the current orientation, the gateway beam is directed to a different gateway Earth station.

7. A method according to any preceding claim wherein the user beam is also steerable, and the method further comprises transmitting at least one control signal to the satellite to steer the user beam from a current user beam orientation to a new user beam orientation such that, when the satellite is at the desired orbital slot, the user beam in the new user beam orientation covers the remote system.

8. A method according to claim 7, wherein the user beam is one of multiple steerable spot beams, and the method comprises transmitting at least one control signal to the satellite to steer the spot beams so that each covers a respective remote system when the satellite is in the desired orbital slot.

9. A method according to claim 8, wherein the spot beams are steerable independently of one another, and the method comprises steering the spot beams independently of one another so that each covers the respective remote system.

10. A method according to any preceding claim further comprising deploying the gateway at the desired location on Earth's surface after the satellite has been launched.

11. A method according to claim 10 comprising travelling to the desired location with the antenna elements in a disassembled state, wherein deploying the gateway comprises assembling the phased array gateway antenna at the desired location from the antenna elements.

12. A method according to claim 11 wherein the travelling to said desired location with the gateway in a disassembled state, and reassembling at the desired location, is performed after the phased array gateway antenna has already served as a gateway antenna and then been disassembled,

13, A method according to claim 11 or 12 wherein the antenna elements are mounted on one or more vehicles.

14, A satellite communications system comprising;

a transmitter configured for transmitting control signals to a satellite to control the satellite, wherein the satellite is configured to provide a steerable gateway beam and a user beam;

a ground controller configured to transmit at least one control signal to the satellite to steer the gateway beam from a current orientation to a new orientation relative to the satellite such that, when the satellite is in geostationary orbit at a desired orbital slot, the gateway beam in the new orientation is directed to a desired location on Earth's surface; and

a phased array gateway Earth station at the desired location configured, when the satellite has been deployed in geostationary orbit at the desired orbital slot, to communicate data between the gateway Earth station and a remote system on Earth's surface which is covered by the user beam, the data communicated via the gateway beam in the new orientation.