GB2538791A - Satellite communication - Google Patents

Abstract

A gateway 104 to a network, e.g. Internet 102, for effecting communication between the network and remote systems via a forward satellite link 106. The gateway comprises a first satellite hub 402a, a second satellite hub 402b of a different vendor, a multiplexor 703 and a modulator 704. The first satellite hub 402a receives, from the network, first outgoing data intended for one or more first remote systems. The second satellite hub 402b receives, from the network, second outgoing data intended for one or more second remote systems. The multiplexor 703 multiplexes the first and second data and the modulator 704 modulates the multiplexed data, whereby the first and second data are modulated onto the same frequency carrier for transmission via the forward satellite link 106. A satellite modem may receive and demodulate the modulated data. The satellite modem may demultiplex the data to detect that the first data is associated with a first identifier and output the first data to a connected computer device, and that the second data is associated with a second identifier and discard the second data.

Description

SATELLITE COMMUNICATION

Technical Field

This disclosure is in the field of satellite communication, in particular communication via a forward satellite link to remote systems from a gateway.

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 (i.e. wired) means is not feasible. Providing an internet link via satellite enables such regions to obtain modern standards of internal 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 ovr.-..'rv ew 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 l). The system 100 comprises a gateway Earth station (gateway) 104, a satellite 110 in orbit about the Earth, and 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 first and a second satellite hub 402a, 402b connected to the internet 102, and at least one gateway antenna 108 connected to the hubs 408a, 408h. Each of the client systems also comprises an antenna 114 connected to a satellite modem 420. The satellite 110 is arranged to be able to communicate wirelessly with the hubs 402a, 402b of the satellite gateway 104 via the gateway antenna 106, and with the modems 420 or the client systems 112 via the antennae 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, hubs 402a, 402b and modems 420 may operate on the Ka microwave band (26,5 to 40 GHz on the uplink i.e. from Earth to the satellite, 17 to 21 GHz on the downlink i.e. from the sate Hite to Earth). The satellite link 107 comprises a forward link 107F for transmitting traffic originating with an Internet 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 first and second hubs 402a, 402b serve (,e. provide a respective Internet access service to) a first subset 112A and a second subset 1123 of the client systems 112 respectively so that internet traffic can be transmitted and received between the first subset 112A of client systems 112 (resp, second subset 1123 of client systems) and the internet 102 via the satellite link 107 and the first hub 402a (resp. second hub 402b).

In one model the operator of the satellite 110 and/or gateway 104 provides bandwidth to a downstream internet service provider (1SP), who in turn provides an is 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. Depending on implementation, the client systems 112 may comprise a central sateilife base station run by the 1SP (the base station 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 base stations 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 1SP does not necessarily provide any extra infrastructure, but acts as a broker for the bandwidth provided by the satellite 110. For example an individual femtoceli or picocell could be located in each home or business, each connecting to a respective one or more user devices using a short range wireiess 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-politically defined region).

Furthermore, referring to Figures 2 and 3, using modern techniques the satellite 110 may be configured as a spot-beam satellite based on a beam-forming technology, so that the communications between the safeliite 110 and the ciient equipment 112 in the covered region 200 are divided amongst a plurality of spatially distinct beams 202. A 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 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).

This is a way of increasing capacity, as the limited frequency band of the satellite (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 4A is a block diagram showing part of the gateway 104 in more detail. As shown, the gateway 104 comprises the first and the second satellite hub 402a, 402b.

For example, the gateway may comprise a building which houses the hubs, in which the satellite hubs 402a, 402b are installed, and in which various infrastructure is provided so as to connect the hubs to the intern& 102 and the gateway antenna 106.

The first hub 402a is of a first vendor ("Vendor A"), and the second hub 402b is of a second vendor ("Vendor B") different from the first vendor.

The first hub 402a comprises a first modulator 404a, a first demodulator 406a, a first network interface 410a and a first hub control module 408a, to which the first interface 410a and first (de)modulator 404a (406a) are connected. The first (de)modulator 404a (406a) and first control unit 408a may be implemented in software, i.e. as code executed on computer processor(s) of the first hub 402a, hardware of the first hub 402a or a combination of both. The second hub 402b comprises a second modulator 404b, a second demodulator 406b, a second network interface 410b and a second hub control module 408b, to which the second interface 410b and second (de)modulator 404b (406b) are connected. The second (de)modulator 404b (406b) and second control unit may be implemented in software, i.e. as code executed on a computer processor(s) of the second hub 402b, hardware of the second hub 402h or a combination of both. The (de)modulators 404a, 404b to (406a, 406b) may be integrated in their respective hubs, or they may be nonintegrated c.o. they may be embodied in detachable modules connectible to their respective hubs via suitable interfaces.

The gateway 104 has a network infrastructure 109 to which the hubs 402a, 402b are connected via their respective network interfaces 410a, 410b so as to connect the hubs 402a, 402b to the internet 102. The gateway 104 also has an RF ("Radio Frequency") infrastructure 105 to which the hubs 402a, 402b (specifically the modulators 404a, 404b and demodulators 406a, 408b) are connected so as to connect them to the gateway antenna 116, In the gateway configuration of figure 4A, the first and second hubs 402a, 402b operate independently of one another to serve client systems of the first and second subsets of oiient systems 112A, 112E3 respectively; each hub 402a, 402b is free to select, independently of the other hubs, modulation scheme(s) to be used on the return link 107R by the respective subset of client systems 112A, 1123 which that hub serves, as well as on the forward link 107F by the respective subset of client systems 112A, 1123 which that hub serves. Each hub is also free to select coding scheme(s) to be used on the return or forward link 107F, 107R by that subset 112A, 1126 -for instance, the hub may select differential coding and forward error correction (FEC) coding scheme(s) for use on the returniforward link. Each hub uses its selected modulation and coding scheme within its own allocated frequency band.

Figure 4E3 shows first and second client systems 112a, 112b, which are of the first and second client system subsets 112A, 1128 respectively. The first/second client systems 112a, 112b comprise a first/a second satellite terminal 412a, 412b, a firstla second router 312a, 423b, and one or more first network (e.g, user) device(s)lone or more second network (e.g. user) device(s) 424a, 424h respectively. The first and second terminals 412a, 412b are VSATs ('Very Small Aperture Terminals').

The first terminal 412a comprises a first outdoor unit (ODU) 422a, and a first indoor unit (IDU) 420a connected to the first ODU 422a. The first ODU 422a comprises a first antenna 114a. The first IDU 420a operates as a satellite modem, and comprises a third demodulator 414a, a third modulator 416a and a first modem processing module 418a, to which is connected the third (de)modulator 414a (416a) and the first client router 423a; the first network device(s) 424a are connected to the first client router 423a.

The second terminal 412h comprises a second ODU 422b, and a second IDU 420b connected to the second ODU 422b, The second ODU 422h comprises a second antenna 114b. The second IDU 420b also operates as a satellite modem, and comprises a fourth demodulator 414b, a fourth modulator 416b and a second modem processing module 418b, to which is connected the fourth (de)modulator 414b (416b) and the second router 423b; the second network device(s) 424b are connected to the second client router 423b.

The network devices 424a, 424b may be computer devices, such as desktop, laptop or tablet computers, smartphones, smartTVs etc. The ODUs 422a, 422b are situated in an outdoor environment, in which the satellite 110 is visible to the antennae 114a, 114b; the IOUs 422a, 422b are generally situated indoors, e.g. in a residential or business premises, and are connected to the relevant ODUs 422a, 422b via cable connections.

First/second outgoing data, received from the Internet 102 via the first/second network interface 410a1410b and intended for the first/second terminal 412a/412b (specifically, a first/second network device(s) 424a/424h connected to that terminal), is supplied, under the control of the first/second huh control module 408a/408b, to the first/second modulator 404a for modulation into first/second RF signals, which are transmitted via the forward satellite link 107F. The first and second RF signals are received at the first and second terminal 412a, 412b respectively, via the first/second antenna 11481114b. The received first/second signals are demodulated by the third/fourth demodulator 414a/414b to extract the original first/second data, which is supplied via the first/second modem processing module 418a/418b to the first/second router 42:3a/423b for routing to the relevant first/second network device(s) 424a1424b.

First/second return data, originating with a first/second network device 424a/424b and destined for the Internet 102, is received by the third/fourth modulator 416a/416b via the first/second router 423a/423b and first/second modem processing module 420a/420b, which modulates the received return data into first/second RF signals respectively, which are transmitted via the return satellite link 107R and received at the gateway antenna 106. The received first/second signals are demodulated by first/second demodulators 406a/408b of the first/second hubs 402b/402c to extract the original first/second return data which is supplied, under the control of the first/second hub control module 408a/408h, to the internet 102 via the first/second network interface 410a/410b.

Data transmitted and received between the remote systems and the network via the gateway 104 in this manner is commonly referred to as "user traffic", Each of the hubs 402a, 402 also implements management functionality for managing operations of their respective sets of remote systems 112A, 112B, which is represented in figure 7A by the first and second hub controllers 408a, 408b comprising a first and a second hub manager Ma, Mb respectively. Each hub manager Ma, Mb generates what is commonly referred to as outgoing "management traffic" for transmitting to its respective subset of client systems 112A, 112B to manage them.

The outgoing management traffic is transmitted with the outgoing user traffic and can for instance comprise scheduling data for the return link, and/or modulation and/or coding data for the return and/or forward link. The scheduling data allocates time Sots to individual client systems of the respective subset 112A, 112B for return link transmissions. In this manner, transmission timing on the return fink 107R is coordinated across the respective subset 112A, 1128 as a whole for bandwidth management and interference mitigation purposes. The modulation and coding data may indicate, to an individual client system of the respective subset 112A, 112B, which modulation and/or coding scheme it should use for transmission on the return link, and/or inform it which modulation and/or coding scheme is going to be used for future transmissions on the forward link. This is particularly applicable where variable modulation and coding (VCfv1) or adaptive modulation and coding (ACM) are used, VCM and ACM are known in the art. The huh managers Ma, Mb also receive feedback in the form of incoming management traffic from their respective subsets of client systems 112A, 112B which can comprise e.g. resource requirement data for the return link and/or environmental data from individual client systems of the respective subset 112A, 112B. The resource requirement data indicates when and is to what extent an individual client system requires return link resources 1,e, because they want to send user traffic to the network 102. The hub manager Ma, Mb can then adapt the return link scheduling accordingly in a manner that is responsive to changing needs across its respective subset of client systems 112A, 112B as whole. The environmental data can for example indicate current wireless signalling conditions at individual client systems, which are liable to change with dynamic factors such as weather or interference from neighbouring systems. The hub manager can then select and signal in the outgoing management traffic modulation and/or coding schemes for the return link 107R, e.g. on an individual client system basis, that are appropriate to the wireless signalling conditions the relevant client system is currently experiencing.

As is known in the art, despite there being attempts at standardization in this field, different satellite huh vendors have a tendency to build their respective wireiess communication technologies on non-standardized, and often proprietary, protocols, which lack mutual interoperability. Notably, whilst a number of standards have been agreed in the context of television broadcasting --notably the DVB (Digital Video Broadcasting) series of standards, standardization has not seen much adoption in the context of satellite-based Internet access services.

In particular, hubs and modems of different vendors tend to generate management traffic according to non-standardized, non-interoperable and often proprietary protocols. Thus outgoing management traffic Generated by a hub of one vendor will be almost certainly uninterpretable by a modem of a different vendor, and likewise incoming management traffic generated by a modem of one hub vendor will almost certainly be uninterpretable by a hub of another. Note that uninterpretable does not simply mean that the data is inaccessible (e.g. due to encryption), but that the format of the actual data renders it meaningless to a hub or modem of a different vendor even if it were made available to that hub or modem (e.g. by decryption).

Other aspects of the wireless communication technologies of different vendors are also often built on non-standardized, non-interoperable and often proprietary protocols, For example hubs of a particular protocol may provide only propriety encapsulation, framing, and coding and modulation, or a combination of proprietary and standardized encapsulation, framing, and coding and modulation.

Encapsulation in this context means the protocols which dictate how network layer (e.g. IP) traffic is encapsulated in lower-layer packets, and framing means the protocols by which the lower layer packets are allocated to physical layer frames. Modulation and coding means the protocols by which each individual frame is coded and moduiated for wireless transmission. Thus, the lower-layer (lower than IP) packets and frames of different vendors can have a different and possibly non-standardised structure, and can be transmitted using different and possibly non-standardised coding and/or modulation schemes.

Figure 6A is a block diagram showing components of a satellite 110. As shown, the satellite 110 comprises a receive antenna 602 connected to a low noise amplifier 604, which in turn is connected to a frequency mixer 606, which in turn connected to a main amplifier 608, which in turn connected to a transmit antenna 610. The components 604-608 constitute a sateliite amplifier, also known as a repeater. The mixer is connected to an oscillator 612, and operates as a frequency translator to change the frequency of signals received (from Earth) via the antenna 602 once they have been boosted by the low noise amplifier 604. The main amplifier 608 has a variable gain which is applied to the frequency-converted signals to amplify them, and the amplified signals are supplied to the transmit antenna 610 for transmission (back to Earth).

Separate such satellite amplifiers are provided for the forward link 107F and return link 107B, though this is not shown in figure 6A, For the forward link satellite amplifiers, the signals which are received and amplified are from the gateway 102 (having been modulated by the hubs 402a, 402b), and the amplified signals are directed back down to the terminals 412a, 412b. For the return link satellite amplifiers, the signals which are received and amplified are from the terminals 412a, 412b, and the amplified signals are directed back down to gateway 102.

Frequency spectrum is a limited resource, and as such the gateway operator will only have limited spectrum available which must somehow be shared between the various hubs installed at the gateway 102, both on the forward and return links.

is Figure 5 is a frequency-power graph illustrating an existing mechanism by which forward link frequency resources are allocated between different satellite hubs(i.e, for communicating via the forward link 107F) within the channel bandwidth FBW of the relevant satellite amplifier.

in the example of figure 5, frequency resources are allocated between four hubs of four different vendors. Each hub is allocated its own distinct and relatively narrow uency TDMA (time division multiple access) carrier band (carrier) with respect to the wider bandwidth FBW of the satellite channel amplifier, e.g. having a width typically between 1 and 72 MHz for transmission from the gateway 102 via the forward link 107F; the carriers -labelled C1-C4 -may be separated by small guard intervals to reduce inter-band interference. In other words, frequency resource allocation between different hubs is effected by allocating each hub a separate and distinct (i.e. non-overlapping) set of frequency resources for communication via the forward link. Thus, RF signals outputted by the first modulator 404a of the first hub 402a are restricted in frequency to the first relatively narrow carrier Cl, those outputted by the second modulator 404b of the second hub 402b are restricted in frequency to the second relatively narrow carrier C2 etc. Figure 5A shows how return link frequency resources are allocated within the channel bandwidth RBW of the return link 107R. On the return link 107R, frequency resources are device into a large number of MF (multi frequency)-TDMA narrow carriers NC. Each hub is allocated a contiguous group of narrow carriers NC, for example around 20 each. Note there is no requirement for forward link allocation to be correlated with return link allocations (though that is not excluded) -resources can be allocated independently on the forward and return links 107F, 107R. The satellite amplifiers may also comprise other components such as input and output band pass filters (not shown) to filter out undesired frequency components e.g. for the forward link transponder, noise at frequencies outside of the range spanned by the carriers C1-C4, A satelUte amplifier has a gain profile, which is illustrated for a particular gain level in figure 6B, Figure 6B shows output signal power as a function of input signal power is at the particular gain level. As shown, the gain profile is substantial/sr linear when the input signal driving the main amplifier 608 is of sufficiently low power i.e. so that the amplified output signal is substantially a linear transformation of the input signal. However, as the input power increases (i.e. as the main amplifier 608 is driven harder), the output power starts to level off towards saturation. The saturation power Psat is the maximum output power the main amplifier 608 is able to provide, and is substantially independent of the gain level. A typical value Psat is about 130W.

As the gain level of the main amplifier 608 is increased, lower and lower power input signals drive the amplifier beyond the linear region i.e. so that its output is no longer a linear function of its input.

Figure 6C illustrates a type of distortion that may be introduced when the main amplifier 608 is driven beyond the linear region towards saturation. Two frequency components fl, f2 of a signal which has been amplified by the main amplifier 608 are shown, which are desired components in the sense that they are also present in the input signal (albeit having a lower power). A distortion component IM is shown, which is an intermodulation of the frequency components fl and f2 cause by the non-linear gain profile of the main amplifier 808. When the main amplifier 608 is driven only in the linear region, IM is negligible but as the main amplifier 608 is driven towards saturation, there comes a point at which the power of the intermodulation distortion component IM starts to rise rapidly.

For this reason, the gain of the main ampllfler 608 is tuned so that its output power remains, in use, below a so-called "back-off power Pb. The back-off power Pb represents a balance between maximizing the output power of the satellite 110 (which is beneficial in terms of being able to detect signals from the satellite back on Earth), whilst still keeping the level of the intermodulation distortion at an acceptable level (so that it does not disrupt the data content of the signals being amplified). In practice, a number of factors determine the optimal level back off power Pb, and finding the optimal level for Pb may involve some degree of manual tuning.

Summary

One of the factors that limits how high the back off power (Pb) can be set in a satellite amplifier is the manner in which the available frequency spectrum is partitioned. For example, where the available spectrum is partitioned into separate and relatively narrow frequency carriers in the manner outlined above, intermodulation distortion becomes more of an issue at lower satellite amplifier gains. As such, this partitioning limits how high the gain of the satellite amplifier can be set, and thus reduces the overall power output of the satellite which is attainable on the forward satellite link.

In a first aspect, a gateway to a network is for effecting communication between the network and remote systems via a forward satellite link, the forward satellite link from the gateway to the terminals. The gateway comprises a first satellite hub, at least a second satellite hub of a different vendor, a multiplexor and a modulator. The first satellite hub is configured to receive, from the network, first outgoing data intended for one or more first remote systems. The second satellite is configured to receive, from the network, second outgoing data intended for one or more second remote systems. The multiplexor is configured to multiplex the first and second data. The modulator is configured to modulate the multiplexed data, whereby the first and second data are modulated onto the same frequency carrier for transmission via the forward satellite link.

Sharing a single frequency carrier between the different hubs, rather than allocating each its own individual frequency carrier, reduces the extent to which the available spectrum needs to he partitioned. The single frequency carrier can be relatively wide, e.g. spanning the same width that would, in existing systems, be collectively spanned by the individual carriers it is in effect replacing so as to provide substantially the same level of data throughput on the forward link to each hub; however, reducing the extent to which the available spectrum is partitioned reduces the extent to which intermodulation distortion is prevalent at lower satellite amplifier gains, thus enabling the overall power output of the satellite to be increased on the forward link without disrupting the outgoing data.

Advantageously, this power gain on the forward link is achievable with minimal changes to the existing gateway architecture described above; multiplexing the is forward link data from different hubs allows different types of satellite hub, which may be built on non-interoperable technology (e.g. they may be of different vendors), to serve different client systems -this gives the operators of the satellite hubs (who may, for instance, be ISPs) the freedom to choose the satellite hub technology which best suits their needs (e.g. which is optimized for their particular systems) without being constrained by interoperability requirements, and enables them to retain control over the majority of the functions of their particular sateltite hub(s), including full control over the technology of their return link systems as well as control of many other (non-modulation) aspects of forward link transmission, whilst still reaping the benefit of the shared forward link carrier.

Thus hubs of different vendors are able to share the frequency carrier in a way that facilitates full use of and maximum transmission power on the forward link without requiring full standardization across the different vendors' hubs.

As will be appreciated, the term different vendors does not simply refer to different business entities, but means the hubs are built on different technologies that are incompatible with one other in one or more aspects. In most cases, hubs of different vendors are technologically incompatible at least in that they use different and incompatible management traffic protocols to generate and communicate management traffic between the hubs and the remote system(s) they are serving.

In embodiments, the transmission may be via a satellite channel of the forward link having a channel bandwidth, substantially ail of which is occupied by the frequency carrier.

Communication from the remote systems to the gateway may be via a return satellite link. The first hub may comprise a first demodulator configured to demodulate first modulated return data, the first return data modulated by a first remote system and communicated to the first hub via the return satellite link from the first system, and transmit the demodulated first return data to the network. The second hub may comprise a second demodulator configured to demodulate second modulated return data, the second return data modulated by a second remote system and communicated to the second hub via the return satellite link from the second system, and transmit the demodulated second return data to the network.

For example, the first and second hubs may be alienated a first and a second group of multiple return link frequency carriers respectively, the first and second groups being non-overlapping, the first and second return data communicated via a frequency carrier of the first group, the second return data communicated via a frequency carrier of the second group.

As another example, alternatively or in addition, the first hub may be configured to implement a first selection process to select a first modulation and/or coding scheme for use by the first system, the first return data modulated and/or coded by the first system using the selected first scheme. The second hub may be configured to implement a second selection process to select a second modulation and/or coding scheme for use by the second system, the second return data modulated and/or coded by the second system using the selected second scheme, and the first selection process may be different and independent from the second selection process.

The first outgoing data and the second outgoing data may be outputted from the hubs as a first and a second stream of data units respectively. Each of hubs may be configured to select, independently of the other hub, and identify, for each data unit that it outputs, a modulation and/or coding scheme to be used to for that data unit by the modulator.

The first and second hubs may be configured to generate first and second management traffic for managing the one or more first and the one or more second client systems respectively, and to transmit the first and second management traffic to the one or more first and the one or more second client systems respectively, the first management generated independently of the second management traffic and according to a different management traffic protocol. For example, the the management traffic protocol may be non-standardized.

is The first hub may be configured to implement a first control process, and the second hub may be configured to implement a second control process. The first and second control processes may control the manner in which the first outgoing data and the second outgoing data are transmitted via the forward satellite link respectively, and the first control process may be different and independent from the second control process.

The first and second control processes may comprise a first and a second bandwidth control process respectively, each for controlling bandwidth usage on the forward link, the first bandwidth control process being different and independent from the second bandwidth control process. For example, each of the first and second bandwidth control processes may comprise performing at least one of: network traffic management, data acceleration, and data compression independently of the other bandwidth control process. As another example, alternatively or in addition, at least one of the first and second control processes may comprise performing data encryption independently of the other control process.

The gateway may comprise a gateway controller connected to each of the first and second hubs and configured to: monitor resource availability of the forward link and to control the respective rates at which the first and second outgoing data are outputted by the hubs to the multiplexor based on the resource availability.

For example, the gateway may comprise one or more buffers which hold the first and second outgoing data prior to modulation, the respective data output rates controlled based on at least one buffer occupancy level.

For instance, the gateway may comprise multiple buffers, each associated with a single modulation and/or coding scheme, wherein only data units to be modulated and/or coded according to that scheme are held in that buffer. The gateway controller may be configured to control at least one of the hubs to reduce its respective data output rate in response to an occupancy level of at least one of the buffers exceeding a review point.

The network may be an Internet (e.g. the Internet), and the first hub may be configured to provide a first internet (e.g. Internet) access service to the first system, and the second hub may be configured to provide a second internet (e.g. Internet) access service to the second system.

The first hub may he operaied by a first ISP and the second hubs may be operated by second ISP different from the first ISP.

At least one of the first and second outgoing data may comprise Web data.

A second aspect is directed to a method implemented at a gateway to a network for effecting communication between the network and remote systems via a forward satellite link. The method comprises: receiving, from a network by a first satellite hub, first outgoing data intended for one or more first remote systems: receiving from the network by a second satellite hub, second outgoing data intended for one or more second remote systems; multiplexing the first and second outgoing data; and modulating the multiplexed data, whereby the first and second data are modulated onto the same frequency carrier for transmission via the forward satellite link.

In embodiments, the method may perform any of the gateway functionality disclosed herein, A third aspect is directed to a sate.ilite modem of a vendor comprising: an output configured to connect to a computer device; a receiver configured to receive modulated data on a frequency carrier of a forward satellite link, the data comprising: first data from a first satellite hub of the vendor and an associated first identifier, and second data from a second satellite hub of a different vendor and an associated second identifier, whereby data from satellite hubs of different vendors is received on to the same carrier frequency by the satellite modem; a demodulator configured to demodulate the modulated data; and a demultiplexer configured to: detect that the first data is associated with the first identifier and output the first data to the computer device on that basis: and detect that the second data is associated with the second identifier and discard the second data on that basis, wherein the second data is not outputted to the computer device, In embodiments: the modulated data may be received via a satellite channel of the forward link having a channel bandwidth, substantially all of which is occupied by the frequency carrier.

The modem may be configured to interact with any embodiment of the gateway disclosed herein.

A fourth aspect is directed to a method implemented by a satellite modem of a vendor comprising: receiving modulated data on a frequency carrier of a forward satellite link, the data comprising: first data from a first satellite hub of the vendor and an associated first identifier, and second data from a second satellite hub of a different vendor and an associated second identifier, whereby data from satellite hubs of different vendors is received on the same carrier frequency by the satellite modem; demodulating the modulated data; detecting that the first data is associated with the first identifier and outputting the first data to a computer device on that basis, and detecting that the second data is associated with the second identifier and discarding the second data on that basis, wherein the second data is not outputted to the computer device. *16

In embodiments, the method may perform any of the modern functionality disclosed herein.

According to a fifth aspect, a computer program product comprises code stored on a computer readable storage medium and is configured when executed to implement any of the methods or system (e.g. hub/gateway) functionality disclosed herein.

Brief Description of Figures

For a better understanding of the present subject matter, and to show how the same may be carried into effect, reference will now be made to the following figures in which: Figure 1 is a schematic diagram of a system for providino internet access via satellite; Figure 2 is a schematic diagram showing geographic coverage of a cluster of sateilite. 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 representing a gateway Earth station in a known configuration; Figure 4B is a schematic block diagram representing first and second client systems in a known configuration; Figure 5 schematioa y liustrates a known type of frequency allocation scheme for a forward satellite. link; Figure 5A schematically illustrates a known type of frequency allocation scheme for a return satellite link; Figure 6A is a schematic block diagram of a part of a satellite; Figure 6B is a graph showing a gain prothea sateffite amplifierknown as repeater); Figure 6B schematically illustrates how distortion may be introduced in amplified by a satellite amplifier; Figure 7A is a schematic block diagram representing a gateway Earth station configured in accordance with the present subject matter; Figure 7B is a schematic block diagram representing first and second client systems configured in accordance with the present subject matter; is Figure 8 shows a function block diagram s ration a modulation and demodulation scheme in accordance with the present subject matter; Figure 9 schematically illustrates a frequency allocation scheme, which in 20 accordance with the present subject matter; Figure WA is a schematic functional overview of a multiplexer in a first embodiment; Figure 10B is a schematic functional overview of a multiplexor in a second 25 embodiment; Figure 10C is a schematic functional overview of a multiplexor in a third embodiment; Figure 10D is a schematic functional overview of a multiplexor in a fourth 30 embodiment.

Detailed Description of Embodiments

Figure 7A is a block diagram of the gateway Earth station (gateway) 104, and figure 76 a block diagram of the first and second client systems 112a, 112b, reconfigured in accordance with the present subject matter. Where the same reference numerals are used in figures 7A/78 as in figures 4A/4B, the relevant parts of the above description apply equally to figures 7A/7B.

The reconfigured gateway 703 comprises a TDMA multiplexor (MUX) 704, a wide band modulator 704 and a gateway controller 706. The components 703-706 may be implemented as software (i.e. code executed on a computer processor), hardware or a combination of both. The multiplexor 704 may be integrated with the wide band modulator 704, or they may be separate components.

Each of the hubs 402a, 402b (in particular, each of the hub control modules 408a, 408b) has a respective output connected to the multiplexor 703, which in turn has an 15 output connected to the wide band modulator 704, which in turn has an output connected to the RF infrastructure 105 of the gateway 704.

In contrast to the known gateway configuration of figure 4A, rather than the hubs 402a, 402b using their own individual modulators (404a, 404b in figure 4A), the hubs 402a, 402b are reconfigured so that their respective control modules input outgoing data to be transmitted on the forward link to the multiplexor 703, still in digital form, under the control of the relevant hub control module 408a, 408b for modulating onto a single wide frequency carrier by the wide band modulator 704 (see below).

Figure 7B shows the first and second client systems 112a, 112b as comprising reconfigured first and second satellite terminal (which are VSATs), labelled 712a and 712h respectively. The first and second ten i anals 712a, 712h comprise first and second OW 720a, 720b respectively. The first/second DU 720a, 720b comprises a first/second wide band demodulator 712a, 712h, an output of which is connected to a first/second demultiplexer (DUX) 714a, 714b; the demodulators 712a, 712b and DUKs 714a, 714b may be implemented in software (i.e. as code executed on a computer processor of the first/second!DU), hardware of the first/second IDU or a combination of both. The first/second IDU 720a, 720b also comprises a first/second modern processing module 418a, 418b (equivalent to those in figure 4A), to which an output of the first/second DUX 714a, 714b is connected.

The reconfiguration of the first and second hubs 402a, 402b in figure 7A is limited to the components which provide the forward link 107F; for communication on the return link 107R, the hubs 402a, 402b are configured in the same manner as in figure 4& with each hub 4022, 402b having its own respective demodulator 406a, 406b connected to the gateway's RF infrastructure 105. Each of the first and second terminals 712a, 712b also has the same configuration for communication on the return link 107R as the terminals 4128, 412b of figure 48; in particular, each has its own modulator 416a, 416b, which are equivalent to those in figure 48 and connected to the respective modem processing module 418a, 418b in the same manner.

As indicated, the first and second hubs 402a, 402b are of different vendors. In the described embodiments, they generate management traffic independently of one another according to different management traffic protocols in the manner set out above. The management traffic protocols may be non-standardized, noninteroperable and/or often proprietary. An advantage of the configuration of the present subject matter is that the manner in which hubs generate their respective management traffic need not be changed, thus no standardization of management traffic protocols is required to implement the forward link carrier sharing.

The other client systems served by the First hub (figure 1, 112A) are configured in a similar manner as the first client system 112a; similarly, the other client systems served by the second hub (figure 1, 1128) are configured in a similar manner as the second client system 112b.

Figure 8 is a function block diagram of a modulation/demodulation scheme implemented by the gateway 104 and client systems 112a, 112b when configured in 30 accordance with the present subject matter.

For communication on the forward link 107F, first outgoing data 802a intended for client systems 112A served by the first hub 402a, received by the first hub 402a from the Internet 102 and which includes first outgoing data intended for the first client system 112a, is inputted to the multiplexor 703 in digital form under the control of the first hub control module 408a of the first hub 408b; second outgoing data 802b intended for client systems 11213 served by the second hub 402b, received by the second hub 402b from the internet 102 and which includes second outgoing data intended for the second client system 112b, is inputted to the multiplexor 703, again in digital form, under the control of the second hub control module 408b of the second hub 402h.

The outgoing data 802a, 802b from the first and second hubs 402a, 402b is to multiplexed by the multiplexor 703 in the digital domain, and the multiplexed data inputted to the wide band modulator 704. The multiplexor 703 performs time-division multiplexing, in which the outgoing data 802a, 802b received in parallel from the hubs 402a, 402b is interleaved in time to create a single bit stream, also in digital form.

The wide band modulator 704 codes, for modulation, the multiplexed data (i.e. the single bit stream) and then modulates the coded data onto a single wide frequency carrier band on a per frame basis. Each frame has a header and payload, and is coded according to a respective modulation and coding scheme, which may vary from frame to frame. Frames may be received from the hubs, or framing may be external to the hubs (see below), In this manner, outgoing data for terminals served by the first hub 402a (such as the first terminal 712a of figure 78) and outgoing data for terminals served by the second hub (such as the second terminal 712b of figure 7B) onto the same wide frequency carrier for transmission via the forward satellite link 107F as wide band analogue (specifically RF) signals, The data that is modulated onto the wideband carrier comprises both first data from the first hub and second data from the second hub. In addition, the data comprises a first identifier of the first hub in association with the first data, and a second identifier of the second hub in association with the second data. This enables the remote systems to identify which hub the relevant data has come from. The identifier may be in the frame header or payload, and may be inserted by the gateway after it has been received from the hubs or by the huts themselves. Particular examples are given below.

The top pal of figure 9 shows a frequency-power graph showing the wide frequency carrier band, which is labelled CW. The wide frequency carrier bend has a width of about 250MHz, though this could vary from about 125 MHz to 1 GHz. The individual narrow carriers Cl-C4 of figure 5 are shown as dotted lines for comparison. By multiplexing outgoing data for transmission via the forward link 107F onto the same wide carrier band CW, the power output of the satellite amplifier 608 can be increased by an amount A relative to the individual carrier scenario. Where the single wide carrier CW replaces four narrow carriers as in figure 9, A can be up to about 3dB which corresponds to a near doubling the output power of the satellite 110 on the forward link 107F.

In effect, the multiplexor 703 allocates each hub forward link resources (referred to as "bandwidth" herein) in the form of a respective set of time slots on the forward link; for the duration any given time slot, the hub to which that time slot is allocated is is, in effect, granted use of the entire width of the wide frequency carrier OW. In the simplest case, with N hubs sharing the same carrier, each may be allocated, and can thus use no more than, a proportion 1/N of the available time slots so that the wide Frequency carrier is shared equally between the N hubs.

The multiplexed data is modulated over substantial all of the wideband satellite channel FBVV, whereby all or needy all of the useable bandwidth of the channel FBW is utiiized by a single carrier.

Returning to figure 8, the first and second wide band demodulators 712a, 712b of the first and second teilirinals 712a, 712b have functionality that is equivalent to one another. Each is able to demodulate the wide band RF signals received on the forward link 107F -which have embedded in them both the first outgoing data 802a and the second outgoing data 802b -to extract the embedded data. The first/second wide band demodulator 712a/712b inputs the extracted data to the first/second DUX 714a1714b, The first and second DUXs 714a, 714b extract the first and second outgoing data 802a, 802b respectively, which is inputted to the first and second modem processing modules 802a, 802h to he routed to the appropriate first/second device(s) 424a, 424b. The second (rasp. first) outgoing data is discarded by the first DUX 714a (resh. second DUX 714b).

Communication via the return link 107R is effected in the same manner as the existing gateway/terminal configuration of figures 4A and 48. First/second return data 8043/804b (originating with a first/second device(s) 424a/424b of the first/second client system 112a/112b) is inputted to the third/fourth modulator 416a/416b, which modulates the inputted data for transmission as respective RF signals on the return link 107R. The first demodulator 406a of the first hub 402a and the second demodulator 406b of the second hub 402b demodulate the respective RF signals received over the return link 107R to extract the first return data 804a and the second return data 804b respectively, which is transmitted to the Internet 102 under the control of the first hub control module 408a and the second hub control module 804b respectively in the same manner as described above.

For comparison, the bottom part of figure 9 shows how frequency allocations is resources on the return link are unchanged with respect to the known allocation scheme of figure 6A.

In this manner, the first and second hubs 402a, 402h provide an internet access service to respective users of the first and second client systems 112a, 112b respectively so that the users of the first/second client systems 112a/112b can access services of the internet 102 e.g. an Internet (capita/ I) access service, so that users of the first/second system 112a/112b can access Internet (capital I) services such as the World Wide Web, email etc. Data is transmitted and received between the fist/second client systems 112a/112b and the internet 102 via the first/second hub, both via the forward and return satellite links 107F, 107R, in accordance with the Internet Protocol (at the Internet layer), and may also be in accordance with the full Internet Protocol Suite (otheiwise known as the "TCP/IP suite"). In this manner, the users are free to access internet (e.g. Internet) content from different Internet (e.g. Internet) sources of their choosing, from a wide variety of third-party internet (e.g. Internet) content providers.

For example, the different hubs 402a, 402h may be operated by different iSPs who have chosen to install their own hubs at the gateway 104 so that each ISP can offer their own Internet access service.

A first/second network device 424a1424h of the first:second system 112a/112b can initiate a request to a network address (e.g. IP address) of server of the internet 102 for content (e.g. Web content), which is routed to the server via the return link 107R s and the first/second hub 402a, 402h; the request includes a network address of the first/second network device 424a/424b; responsive to receiving the request, the server returns the requested content to the network of the first/second device included in the request, which content is routed to the first/second device via the first/second hub 402a/402b and the forward link 107F. The request may, for instance, be initiated responsive to a user input at the first/second device, or automatically responsive to some event at the first/second device. For example, the user may enter a Web address (URL) in a Web browser running on the first/second device, which is mapped to the network address (e.g. IP address) of the server by a Domain Name System of the internet 102. Alternatively, or in addition, the first/second network device can subscribe to receive push content from the internet 102, whereby the user registers the network address of the first/second device with a server of the internet 102, and permits the server to push content (e.g. Web content) to the registered network address without the user having to instigate a specific request for that content; the push content is again routed to the first/second device via the first/second hub 402a/402b and the forward link 107F.

In contrast to the known configuration outlined above, the hubs 402a, 402b in the new configuration of figure 7A do not modulate outgoing data themselves, Outgoing data, comprising outgoing user traffic and outgoing management traffic, is outputted by each hub 402a as a respective stream of data units in an unmodulated form. In the figures, 710and 710b denote generally a data unit outputted by the first and second hubs 402a, 402h respectively. The hubs nevertheless retain individual control over the manner in which data is modulated for transmission on the forward link. Each of the hubs 402a, 402b is also in two-way communication with the gateway controller 706. Each hub controller 408a, 408b communicates respective transmission control data to the gateway controller 706. The transmission control data identifies, for each data unit 710a, 7106, a modulation and/or coding scheme to be used to modulate and/or code that data unit e.g. identified by an associated ACM "modcod", whereby a particular rnodcod indicates both a modulation and coding scheme with a single value, typically a numerical integer, The wideband modulator 703 uses that modulation and/or coding scheme to modulate and/or code that data unit. The outgoing management traffic is generally modulated and coded according to a fixed, predetermined modulation and coding scheme, for instance modcod=15 in DVB.

The gateway controller 706 controls the wide band modulator 704 to modulate the multiplexed data (802a+802b) onto the wide carrier OW using the modulation and/or coding scheme identified by the relevant hub(s).

The modcods are selected by a hub, for example on a per remote system basis based on feedback from the individual remote systems served by that hub, and independently of the other hub(s). It is advantageous for the hubs 402a, 402b to have control over modcod selection as they have visibility of the conditions under Is which their respective subset of client systems are operating through the feedback they provide. Thus, they are best placed to select the most appropriate modulation and coding scheme, and can do so on an individual remote system basis. The difference here is that, in order to make full use of the wideband forward link channel, the hubs are not performing modulation themselves but are outputting unmodulated data to be modulated over the full width of the channel. That is, modulation and coding is performed externally of the hubs by a wideband modulator 704. However, hubs still selects which modulation and coding scheme(s) are to be used for its outgoing data according to respective selection processes that are different and independent of one another. Different hubs may make these selections according to different selection protocols, which may be non-interoperable, non standardized and/or proprietary, Each data unit 710 may for instance be a:Tame ready for modulation (with header and payload already attached), or at least a frame's worth of data to be included in 30 the payload of a single frame. For e,xampie, these may be DVB baseband frames.

Alternatively, each data unit 710 may he a packet, or a packet's worth or data. For instance, the packets may be layer 2 packets, layer 2 referring to the ISO/OSI reference model. Examples are an MPEG-2 transport stream packet. or a DVB GSE (Generic Stream Encapsulation) packet. In this case, one or more (typically multiple) such packets are included together in a single frame, with framing being implemented externally of the hubs (see below), Alternatively, the packets may be a network layer packets, corresponding to layer 3 of the l30/031 reference model, such as IP packets; in this case, the packet stream outputted by each huh is subject to both encapsulation into layer 2 packets and then framing externally of the satellite hubs.

Different hubs may output different types of data units. For example, one hub might in output frames ready for modulation whereas another might output packets still requiring framing and possibly encapsulation prior to modulation.

Each hub 402a/402b not only retains control over which modulation scheme(s) is used on the return link by the respective subsets of terminals 112A1112B served by that hub, but also performs the respective demodulation itself as in conventionally configured satellite hubs. That is, the first the first hub control module 408a implements a first (resp, second) selection procedure to select a first (resp. second) modulation scheme for use by the first terminal 712a (reap. second terminal 712b), and the first return data 804a (rasp. second return data 804b) is modulated by the first terminal 712a (rasp. second terminal 712b) using the selected first (resp.

second) modulation scheme. The first selection process is different and independent from the second selection process i.e, the first hub is blind to and has no direct influence over the second selection process and vice versa (note that the behaviour of e.g. if the first selection process is interference-dependent, the second terminal may still indirectly affect the outcome of the first selection process as the second terminal may constitute an interference source from the perspective of the first hub/first client system).

Communication via the return iink 107R between the first terminal 712a and the first hub 402a uses first (proprietary) return link communication protocols of the first vendor (Vendor A); communication via the return link 107R between the second terminal 712b and the second hub 402b uses second (proprietary) return link communication protocols, which are different from and incompatible with the first set of return link communication protocols.

The gateway controller 706 also controls the multiplexor 703 to regulate the manner in which the wide carder OW is shared. For example, the gateway controller 706 may change the respective proportion of the forward link time slots allocated to a particular hubs, e.g. when an ISP operating that hubs purchases additional forward link resources from the operator of the gateway 104.

However, each hub 402a, 402b is free to use its allocated resources in a manner of its choosing. The first and second hub controllers 408a, 408b implement first and second control processes to control the manner in which the first outgoing data 802a and the second outgoing data 802b are transmitted via the forward satellite link respectively: The first and second control processes are different and independent from one another i.e. so that, for instance, each hub 402a, 402b has complete control over the manner in which its resource allocation on the forward link 107F is shared between the terminals which that hub serves, but is blind to, and has no control over, the equivalent process implemented by the other hub. Each of the independent control processes include processes such as: - independent selection of modulation and/or coding schemes for the forward and/or return link, whereby different modulation and/or coding schemes may be selected by different hubs for the forward and/or return link; - bandwidth control process(es) for controlling bandwidth usage on the forward

link; for example:

O traffic management of forward link traffic, e.g. traffic shaping under the control of the gateway controller 706, whereby datagrams flowing through the respective hubs 402a, 402b are selectively delayed so at to match the overall traffic flow to a desired traffic profile; o data acceleration, e.g. TOP acceleration, to increase throughput of outgoing data on the forward link; o data compression to re-encode information received from the Internet 102 using a reduced number of bits for transmission via the forward link; data encryption, which includes encryption of outgoing data to be transmitted to the first/second client system 1123/112h and decryption of return data received from the first/second client system 1123/1 2b, whereby different encryption protocols may be used by different hubs.

In particular, the control process may be implemented at least for forward link traffic (e.g. comprising traffic management of forward link traffic, such as traffic shaping of outgoing datagrarns), so that, whilst each hub no longer has control over how traffic is modulated on the forward link, it still retains control over the manner in which the traffic intended for the subset of terminals it serves flows on the forward link, and thus the manner in which its porlion of forward link resources are used.

For example, when each of different hubs 402a, 402b is operated by a different ISP who have chosen to install their own hubs at the gateway 104, and among other things the hub control modules 408a, 408h manage the flow of Internet traffic through their respective hubs 402a, 402b to ensure, for instance, that the available bandwidth on the satellite link 107 are shared fairly between the ISP's customers, to impose bandwidth restrictions on their customers in accordance with their agreements with the ISP, to make the most efficient use of that ISPs forward link resources etc. Figures 10A-10D give functional overview of the multiplexor 703 in different embodiments. Different shading is used to indicate different modcods as selected for individual data units by the relevant hub.

Figure WA is a functional overview of the multiplexor 703 in a first embodiment. In the first embodiment, each hub 402a, 402 outputs a respective stream of frames 710a, 710b and a rnodcod selected for each frame. Thus each frame contains outgoing data from only a single hub. Each frame may comprise a header which includes an identifier of the hub from which it originates, and/or that hub may he identified by data in the frame payload for instance within the header(s) of packet(s) contained in the frame payload. Frames 710a, 710b from the different hubs 402a, 402b are buffered in respective buffers (not shown), and frames from the buffers selected in turn for modulation and coding by the modulator 704 to generate a single output stream 718 of frames 710a, 710b from the different hubs 402a, 402h, Each frame in the stream 718 is coded and modulated individually by modulator 704 using the modulation and coding scheme identified for that frame to generate a respective modulated frame 716.

Figure 10B illustrates a second embodiment, similar to the first embodiment, but in which frames are separated out according to modcod, for example by buffering frames to he coded and modulated with the same modcod together. Frames to be coded and modulated with the same modcod can then selected for inclusion in the stream 718 adjacent one another on that basis. Thus the stream of frames 718 comprises adjacent frames of the same modcod, either from the same or different hubs, which is a more efficient stream structure for the modulator 704 to operale on.

Thus the efficiency of the modulation and coding is increased by arranging the frames in this manner. The second embodiment is otherwise the same as the first embodiment, Figure 10C illustrates a third embodiment, similar to the second embodiment, but in which the data units 710a, 710b are packets rather than frames, whereby modcods are identified on a per packet basis. Similar to the second embodiment, packets 710a, 710b are separated out according to modcod. A framing module 720 of the gateway 104, separate from the hubs, frames the packets to generate a stream 718 of frames for modulation. Each frame is created from one or more (typically multiple) packets of the same modcod. The separated packets 710 may be stored in buffers for a short time (not shown) prior to framing. This allows packets of the same modcod to build up in the relevant buffer, until a full frame's worth or nearly a full frame's worth of data to be modulated using a particular modcod is available, This reduces the overall amount of padding that might otherwise need to be added to frames, thereby making more efficient use of forward link resources. The third embodiment is otherwise the same as the second embodiment.

The packets may be layer 2 packets (i.e. pre-encapsulated by the hubs 402a, 402b), or they may be higher layer packets (e.g. IP packets) in which case the framing module 720 performs both encapsulation and framing. Though shown as a single component, encapsulation and framing could be performed separately, for example the packets could be encapsulated before they are separated out according to modcod, In the third embodiment, each frame contains not only packets assigned the same modcod, but also only includes packets from a single one of the hubs. Frames 714a1 and 714b.ii in the stream of frames 718 denote by way of example a frame to be modulated with modcod "i" and containing data from only the first hub 402a and a frame to be modulated with modcod I" and containing data from only the second hub 402b.

A fourth embodiment (figure 100) is similar to the third embodiment, however in this to case the packets 710a, 710b are mixed within frames. Packets of the same modcod but from different hubs are all buffered together, and then framed. Thus a single frame 714 in the stream of frames 718 can contain packets all of the same modcod but from different hubs. The fourth embodiment is otherwise the same as the third embodiment.

In the first to third embodiments, each frame can comprise a header which includes a hub identifier of the hub from which the payload data has originated. Alternatively or in addition, hub identification data can be included in the frame payloads, for instance in the form of a hub identifier in each packet header. In the fourth embodiment, frames are not tied to single hubs, nevertheless hub identification data can be included within the frame payloads to indicate which parts of the payload data have originated form which hubs, for example in the form of a respective hub identifier in each packet header.

Thus, the remote systems 412 can detect which data on the widebanci carrier has originated from its serving hub (and which may thus be relevant to that system) and which data has originated with hubs of different vendors (and can therefore be discarded by that system).

The gateway controller 706 monitors resource availability of the forward link 107F and implements traffic flow control in the following manner. The forward link has an overall capacity which may fluctuate over time due to changing environmental conditions (weather, interference etc.). This is not directly visible to the individual hubs as they have no direct awareness of one another. However, the gateway controller can detect conditions in which the aggregate rate of data output by the hubs exceeds (or is considerably below) the overall capacity of the forward link, for example by detecting an over (or under) occupancy condition(s) in the buffers in which data units from the various hubs 402a, 402b are held prior to modulation, for example by reference to a suitable review point(s) i.e. threshold(s). In response to detecting the overfill condition, the gateway controiler 706 instructs the hubs to "back off' i.e. to reduce the rate at which they output data. More generally, the gateway controller 706 controls the respective rate at which each individual hub 402a, 402b output outgoing data based on the aggregate amount of data being outputted by all the hubs as a whole (e.g. as measured from buffer occupancy).

Each hub retains control over the content and format of the management traffic it generates, as indicated. Thus there is no need to standardize the management traffic protocols, leaving different hub vendors free to continue impending management traffic protocols of their choice, which may be non-standardized an o non-proprietary. Thus, only minimal standardization that is needed across the different hubs at the gateway for them to be able to share the vvideband carrier. The minimal standardization is at a control layer of the gateway to implement a respective interface for communication between each hub 402a, 402b and the gateway controller 706, by which modulation and coding selections are communicated by the hubs, and traffic flow is controlled by the gateways. Thus an optimal balance is provided between on the one hand the hubs retaining individual control over their various protocols and on the other hand facilitating cooperating between the hubs to enable sharing of the wideband carrier to maxirnize transmission power on and utilization of the forward link.

In some embodiments, hubs perform their own encapsulation or their own encapsulation and framing. The possibility of different hubs independently performing encapsulation and/or framing by being according different encapsulation and/or framing protocols, which may be non-interoperable, non-standardized and/or proprietary. In some cases: the packets, frames etc, outputted by hubs in a bespoke format as a result may need to be re-formatted for multiplexing and modulation onto the wide carrier.

Only two hubs 402a, 402b are shown in figure 7A, but the gateway 104 may include additional satellite hubs (e.g. of different vendors) which serve additional subsets of client terminals, and which may be similarly connected to the multiplexor 703 so as to share the same wide frequency carrier. Identifiers included in the data that is modulated onto the wideband carrier may identify individual hubs uniquely, or they may just identify different vendors uniquely (these amount to the same thing where ail of the hubs are of different vendors).

The first terminal 712a, in particular the first IDU 720a, is compatible with and served to by Vendor As (i.e. the first hub) 402a but is incompatible with Vendor B's (i.e the second) hub 402b. Conversely, the second terminal 712b, in particular the second 1DU 720b, is compatible with and served by Vendor B's hub 402b but is incompatible with Vendor A's hub 402a. Thus, the first client system 112a is not interoperiable with the second hub 402b, and the second client system 112h is not interoperable is with the first hub 402a.

For instance, the first 1DU 712a and first hub 402a may be of the same vendor as one another (Le. Vendor A), and the second 1DU 712h and second hub 402b may also be of the same vendor as one another (i.e. Vendor B), with no interoperability between the different vendors technologies.

Here, a terminal being compatible with a satellite huh means that the terminal and the hub are able to cooperate so as to effect the transmission and receipt of data between a device connected to the terminal and an internet source/destination via the satellite link 107, each being able to correctly interpret RF signals received from the other via the satellite link 107 to extract the relevant data and convey it to the correct place. A terminal which is incompatible with a satellite hub may well still receive RF signals from that hub via its antenna (which are out-of-band from the perspective of that terminal), but those signals will be uninterpretable to that terminal e.g. even if it were to demodulate those signals to extract data, they would still be unusable by that terminal because the data is in the 'wrong' format and/or 'wrongly' encrypted from the perspective of that terminal (though of course in the correct format/encryption from the perspective of a compatible terminal).

The above embodiments have been described by way of c.,xample, and other variants or applications may be apparent to the skilled person in view of this disclosure. The scope is not limited by the described embodiments but only by the claims.

Claims (25)

1. Claims: 1, A gateway to a network for effecting communication between the network and remote systems via a forward satellite link, the forward satellite link from the gateway to the remote systems, the gateway comprising: a first satellite hub configured to receive, from the network, first outgoing data intended for one or more first remote systems; a second satellite hub of a different vendor and configured to receive, from the 10 network, second outgoing data intended for one or more second remote systems; a multiplexor configured to multiplex the first and second outgoing data; and a modulator configured to modulate the multiplexed data, whereby the first and second data are modulated onto the same frequency carrier for transmission via the forward satellite link.
2. 2. A gateway according to claim 1 wherein the transmission is via a satellite channel of the forward link having a channel bandwidth, substantially all of which is occupied by the frequency carrier.
3. 3. A gateway according to claim I or 2, wherein communication from the remote systems to the gateway is via a return satellite link; wherein the first hub comprises a first demodulator configured to demodulate first modulated return data, the first return data modulated by a first remote system and communicated to the first hub via the return satellite link from the first system, and transmit the demodulated first return data to the network; wherein the second hub comprises a second demodulator configured to demodulate second modulated return data, the second return data modulated by a second remote system and communicated to the second hub via the return satellite link from the second system, and transmit the demodulated second return data to the network.
4. 4. A gateway according to claim 3 wherein the first and second hubs are allocated a first and a second group of multiple return link frequency carriers respectively, the first and second groups being non-overlapping, the first and second return data communicated via a frequency carrier of the fir.t group, the second return data communicated via a frequency carrier of the second group.
5. 5. A gateway according to claim 3 or 4 wherein the first hub is configured to implement a first selection process to select a first modulation and/or coding scheme for use by the first system, the first return data modulated and/or coded by the first system using the selected first scheme; and wherein the second hub is configured to implement a second selection process to select a second modulation and/or coding scheme for use by the second 10 system, the second return data modulated and/or coded by the second system using the selected second scheme; wherein the first selection process is different and independent from the second selection process.
6. A gateway according to any preceding claim wherein the first outgoing data and the second outgoing data are outputted from the hubs as a first and a second stream of data units respectively; and wherein each of hubs is configured to select, independently of the other hub, and identify, for each data unit that it outputs, a modulation and/or coding scheme to be used to for that data unit by the modulator.
7. 7. A gateway according to any preceding claim wherein the first and second hubs are configured to generate first and second management traffic for managing the one or more first and the one or more second client systems respectively, and to transmit the first and second management traffic to the one or more first and the one or more second client systems respectively, the first management generated independently of the second management traffic and according to a different management traffic protocol.
8. 8. A gateway according to claim 8 wherein the management traffic protocol is non-standardized,
9. 9. A gateway according to any preceding claim wherein the first hub is configured to implement a first control process, and the second hub is configured to implement a second control process; wherein the first and second control processes control the manner in which the first outgoing data and the second outgoing data are transmitted via the forward satellite link respectively; and wherein the first control process is different and independent from the second control process:
10. 10. A gateway according to claim 1 wherein the first and second control processes comprise a first and a second bandwidth control process respectively, each for controlling bandwidth usage on the forward link, the first bandwidth control process being different and independent from the second bandwidth control process.
11. 11. A gateway according to claim 10 wherein each of the first and second bandwidth control processes comprises performing at least one of: network traffic management, data acceleration and data compression independently of the other bandwidth control process.
12. 12, A gateway according to claim 9, 10 or 11 wherein at least one of the first and second control processes comprises performing data encryption independently of the other control process.
13. 13. A gateway according to any preceding claim comprising a gateway controller connected to each of the first and second hubs and configured to: monitor resource availability of the forward link and to control the respective rates at which the first and second outgoing data are outputted by the hubs to the multiplexor based on the resource availability.
14. 14, A gateway according to claim 13 wherein the gateway comprises one or more buffers which hold the first and second outgoing data prior to modulation, the respective data output rates controlled based on at least one buffer occupancy level.
15. 15. A gateway according to claim 14 when dependent on claim 6 comprising multiple buffers, each associated with a single modulation and/or coding scheme, wherein only data units to be modulated and/or coded according to that scheme are held in that buffer, wherein the gateway controller is configured to control at least one of the hubs to reduce its respective data output rate in response to an occupancy level of at least one of the buffers exceeding a review point.
16. 16. A gateway according to any preceding claim wherein the network is an internet, and the first hub is configured to provide a first internet access service to 10 the first system, and the second hub is configured to provide a second internet access service to the second system.
17. 17, A gateway according to claim 16 wherein the internet is the Internet, and the Internet access services are Internet access services.
18. 18. A gateway according to any preceding claim wherein the first hub is operated by a first 1SP and the second hubs is operated by second ISP different from the first 1SP.
19. 19. A gateway according to any preceding claim wherein at least one of the first and second outgoing data comprises Web data.
20. 20. A method implemented at a gateway to a network for effecting communication between the network and remote systems via a forward satellite link, the method 25 comprising: receiving, from a network by a first sate! e huh, first outgoing data intended for one or more first remote systems; receiving from the network by a second satellite hub, second outgoing data intended for one or more second remote systems; multiplexing the first and second outgoing data; and modulating the multiplexed data, whereby the first and second data are modulated onto the same frequency carrier for transmission via the forward sate link.
21. 21. A satellite modem of a vendor comprising: an output configured to connect to a computer device; a receiver configured to receive modulated data on a frequency carrier of a forward satellite link, the data comprising; first data from a first satellite hub of the vendor and an associated first identifier, and second data from a second satellite hub of a different vendor and an associated second identifier, whereby data from satellite hubs of different vendors is received on the same carrier frequency by the satellite modem; a demodulator configured to demodulate the modulated data; and a demultiplexer configured to: detect that the first data is associated with the first identifier and output the first data to the computer device on that basis, and detect that the second data is associated with the second identifier and discard the second data on that basis, wherein the second data is not outputted to 15 the computer device.
22. 22. A gateway according to claim 23 wherein the modulated data is received via a satellite channel of the forward link having a channel bandwidth, substantially all of which is occupied by the frequency carrier:
23. 23. A method implemented by a satellite modem of a vendor comprising: receiving modulated data on a frequency carrier of a forward satelilfe link, the data comprising: first data from a first satellite hub of the vendor and an associated first identifier, and second data from a second satellite hub of a different vendor and an associated second identifier, whereby data from sate:lite hubs of different vendors is received on the same carrier frequency by the satellite modem; demodulating the modulated data; detecting that the first data is associated with the first identifier and outputting the first data to a computer device on that basis; and detecting that the second data is associated with the second identifier and discarding the second data on that basis, wherein the second data is not outputted to the computer device.
24. 24. A computer program product comprising code stored on a computer readable storage medium and configured when executed to implement the method of claim
25. 25.