Satellite Communications
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 modern 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.
Referring to Figure 1 by way of example, a satellite 10 is deployed in a geostationary orbit and arranged so that its field of view or signal covers roughly a certain geographic region 20 on the Earth’s surface. Figure 1 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 10 may be configured as a spot-beam satellite for example using directional antennae or based on a beam-forming technology, so that the communications between the satellite 10 and client equipment, e.g. a VSAT (very small aperture terminal) in the covered region 20 are divided amongst a plurality of spatially distinct beams 202 (spot beams). 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 20 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 110 (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 subbands, 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. For example, 8-16 spot beams is relatively common.
Bi-directional data transmission between a gateway and a client system can thus take place via each beam. In existing spot beam network, beam sizes (angular extents) of around 0.6 degrees are relatively typical, each beam having a bandwidth of around 230MFIz in the forward link direction (i.e. gateway to client systems), and around 220MFIz in the return link direction (i.e. client to gateway). The bandwidth of each beam means the range of frequencies over which information is carried within that beam, and sets the absolute maximum rate at which data can be transmitted via that beam in the relevant direction (the gross bit rate). Flowever, the net bit rate, i.e. the effective data rate, i.e. the number of useful bits that can be transmitted per second is generally lower than this as part of the available bandwidth is consumed by overhead bits, e.g. framing bits, redundancy bits, redundancy/error correction bits etc. The spectral efficiency of a beam is the net bit rate per unit of bandwidth, and can be expressed in bits/s/Hz (bits per second per Flertz). The spectral efficiency is affected by the choice of modulation and coding scheme: in good radio conditions (e.g. relatively low thermal noise, intermodulation noise, self-interference and external interference), a modulation and coding scheme with a low amount of bitrate overhead (e.g. minimal redundancy) can be used. However, in poor radio conditions (e.g. a high level of thermal noise, intermodulation noise, selfinterference and/or external interference), a modulation and coding scheme with significant overhead (e.g. with a high level redundancy) may be needed to account for data loss, leading to a lower spectral efficiency. This, in turn, is affected by the power flux density (power per unit area), as it is generally possible to use more efficient modulation and coding at higher power flux densities, and also the capabilities of the client terminal equipment (e.g. VS AT).
Summary
With the progression of modern Internet technology, the level of service expected from users increases. The prevalence of video content on the Internet, and in particular the increasing popularity of on-line streaming services including on-demand streaming (non-linear streaming) and live-streamed video content (linear streaming), has led to users expecting to be able to consume (e.g. stream or download) large quantities of high-quality video content as and when they chose. This presents a particular challenge for satellite Internet systems, in which bandwidth is highly constrained. For example, the Applicant has found that nowadays about 70% of the forward link Internet traffic that is provided by satellite is video data.
According to conventional wisdom in the field of satellite communications, the natural approach to this issue would be to attempt to attempt to increase the though put, by increasing the available bandwidth of each beam, the spectral efficiency of each beam, the power flux density of each beam (by increasing the transmit power and/or the directivity of the relevant satellite antenna), and/or the capabilities of the client terminal equipment. For example, in the context of a spot beam network working within a given frequency allocation, one natural approach to this problem would be to (i) attempt to reuse more of the available frequency resources (e.g. by minimizing noise and interference) and (ii) increase the transmit power flux density of the spot beams (i.e. the power per unit area at the earth's surface), by either increasing the transmit power at the satellite or increasing the directivity of the satellite antenna(s) to reduce the size (i.e. angular extent) of the beams.
For example, a technique which has seen significant attention in the field is so-called beam hopping, in which very narrow (e.g. 0.2 degrees) and very high power spot beams are used. Narrowing the beams increases their power flux density, which in turn allows more efficient coding and modulation schemes to be used, leading to an increase in spectral efficiency. Moreover, in contrast to the system of figure 2, it is expected that these narrow beams will not overlap in space, removing a source interference and thus allowing more of the available frequency resources to be used. To provide full coverage of the geographic area, these very narrow beams rapidly "hop" in space, so that they cover different regions of the area for different and very brief time intervals. This in turn is expected to allow the forward link bandwidth of the beams to be increased to around 500-750MHz per spot beam, and allows of the available frequency resource to be used e.g. as there is less need for guard bands between different beams.
Whilst it is expected that systems of this nature will be able to achieve a significant increase in through put, this spatial-hopping aspect adds significantly to the complexity of the gateway, the client equipment and the satellite. For example, the client equipment needs to be able to very accurately "lock on" to the beams as soon as it hops to its location, and make use of it before it rapidly hops away again. This also severely limits the application of beam hopping to existing satellite networks, as entirely new gateway, satellite and terminal equipment are needed.
By contrast, the inventor of the present invention has approached the problem from a different perspective. He has recognized that, in practice, a significant portion of the overall forward link traffic is duplicate traffic, i.e. even though users have complete freedom about what they access on the Internet via satellite, in practice a small portion of the available Internet content is significantly more popular, and is requested by users frequently. On-line video streaming - both linear and non-linear - in particular accounts for a significant portion of this duplicated traffic. Indeed, the Applicant's own estimates indicate that half or more the forward traffic can be duplicated data in practice.
Accordingly, various aspects of the present invention relate to a satellite network (a satellite or multiple co-operating satellites) which is configured to provide at least two spot beams, each covering a different region of a geographic area, an additional overlay beam covering the geographic area, i.e. covering substantially all of the area that is covered by the spot beams collectively (or at least an area that spans multiple spot beams). This allows the overlay beam to be used to broadcast data across all of the regions covered by the spot beams that would otherwise have to be transmitted via multiple spot beams. That is, forward link traffic that would otherwise be duplicated across multiple spot beams can effectively be removed from the spot beams, and a single instance of this forward link traffic can broadcast via the overlay beam instead, for receiving by client systems served by different spot beams, i.e. located in different ones of said regions.
To put it another way, the present invention is able to achieve an increase in the level of service provided to users that is comparable to, say, beam hopping systems, but achieves this by reducing the amount of duplicate data is transmitted rather than by increasing the throughput as such.
Advantageously, this can be incorporated in an existing spot-beam satellite infrastructure, for example by launching a basic wide-beam satellite to orbit alongside an existing spot-beam satellite (e.g. in the same orbital slot). To allow a client terminal to simultaneously receive via both one of the spot beams and the overlay beam, all that may be needed is an extra receiver(and possibly another antenna only if the existing antenna cannot be used for both beams), which is easy and cheap to incorporate into spot-beam client (e.g. VSAT) equipment, in a consumer-friendly manner. At the gateway, the functionally can be incorporated straightforwardly, for example by adding an extra satellite hub to serve the overlay beam, or reconfiguring an existing satellite hub.
According to a first aspect of the present invention, a satellite communication system comprises: a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, and (ii) a plurality of spot beams, each covering a different region of the geographic area; a gateway configured to receive, from a data network, forward link traffic to be transmitted; and a gateway traffic manager configured to select a first portion of the forward link traffic for transmission via the overlay beam, and a second portion of the forward link traffic and for transmission via the spot beams, wherein the gateway is configured to transmit those portions of forward link traffic via their selected beams.
In embodiments of the first aspect, or indeed in embodiments of any of the additional aspects set out below, the gateway traffic manager may be configured to monitor return link traffic received at the gateway from client systems located in the geographic area, and to perform said selection based on the monitoring of the return link traffic.
For example, said monitoring may comprise processing content requests in the return link traffic. E.g. said monitoring may comprise determining whether a number of content requests has reached a threshold.
Alternatively or in addition, the gateway traffic manager may be configured to assign respective popularity measures to pieces of content within the forward link traffic, and to perform said selection based on the popularity measures.
Alternatively or in addition, the system may comprise an analyser configured to perform an analysis of content accessible via the network by monitoring access of that content by users outside of the geographic area, said selection being based on said analysis.
The gateway may be configured to transmit at least part of the first and/or second portion of traffic in response to a request received at the gateway from a client system via the satellite network (e.g. via one of the spot beams).
According to a second aspect of the present invention, a satellite communication system comprises: a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, and (ii) a plurality of spot beams, each covering a different region of the geographic area; a gateway connecting the satellite network to a data network; a client system located in one of the regions of the geographic area and configured to transmit a content request to the gateway via that region’s spot beam, wherein the content request comprises an identifier of a piece of content, wherein the gateway is configured to transmit the identified content from the data network to the client system via the overlay beam.
In embodiments of the first or second aspect, or indeed in embodiments of any of the additional aspects set out below, wherein the gateway may be configured to transmit the content via the overlay beam in response to a number of requests for that content received at the gateway reaching a threshold.
The satellite network may comprise two satellites, one of which is configured to provide the overlay beam and the other of which is configured to provide at least one of the spot beams. For example, the other satellite may provide (all of) the plurality of spot beams.
The system may comprise a client system located in one of the regions and which comprises a first receiver for receiving forward link traffic via the spot beam covering that region, and a second receiver for receiving forward link traffic via the overlay beam.
For example, the receivers are both integrated in a modem of the client system. Alternatively, the first receiver may be integrated in a modem of the second system, and the second receiver may be a modular component connected to the modem.
Each of the spot beams may have a greater bandwidth than the overlay beam.
Alternatively or in addition, each of the spot beams may have a greater power flux density than the overlay beam. A third aspect of the present invention is directed to a method of receiving content via a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, and (ii) a plurality of spot beams, each covering a different region of the geographic area, the method comprising: receiving from a user, at a user device located in one of the regions, a selection of a desired piece of content; determining whether the selected content is receivable and/or has been received at the user device via the overlay beam; if the selected content is receivable via the overlay beam: receiving the selected content at the user device via the overlay beam and outputting the received content to the user; and if the selected content is not receivable via the overlay beam: transmitting from the user device to the satellite network a request for the selected content, receiving the requested content at the user device via the spot beam covering its region, and outputting the received content to the user. In embodiments, the determining step may be performed at the user device, or at device directly connected to the user device.
If it is determined that only part of the content is receivable and/or has been received at the user device via the overlay beam, a request for the remainder of the content may be transmitted from the user device to the satellite network.
For example, the request may be transmitted via the spot beam covering the user device's region.
The user device is located in the same region as the antenna. A fourth aspect of the present invention is directed to a client system for communicating with a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, and (ii) a plurality of spot beams, each covering a different region of the geographic area, the client system comprising: a user interface for receiving from a user a selection of a desired piece of content; a local content manager configured to implement the following operations: determining whether the selected content is receivable and/or has been received at the client system via the overlay beam; if the selected content is receivable via the overlay beam: receiving the selected content via the overlay beam and outputting the received content to the user; and if the selected content is not receivable and has not been received via the overlay beam: transmitting to the satellite network a request for the selected content, receiving the requested content via one of the spot beams, and outputting the received content to the user.
For example the local content manager may be implemented at a user device of the client system; or at a second device of the client system connected to the user device (or respective parts of the local content manager may be implemented at multiple second devices connected to the user device), or part of the local content manager may be implemented at the user device and part (or respective parts) may be implemented at a second device(s) connected to the user device.
In embodiments of the fourth aspect, any feature of any of the other aspect of the present invention (and in particular the method of third aspect) or any embodiment therefor may be implemented by the client system. A fifth aspect of the present invention is directed to a method of providing a network access service via a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, and (ii) a plurality of spot beams, each covering a different region of the geographic area, the method comprising receiving at a gateway, from a data network, forward link traffic to be transmitted; selecting a first portion of the forward link traffic for transmission via the overlay beam; transmitting the first portion of the forward link traffic from the gateway via the overlay beam; selecting a second portion of the forward link traffic for transmission via the spot beams; and transmitting the second portion of the forward link traffic from the gateway via the spot beams. A sixth aspect of the present invention is directed to a gateway system for a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, and (ii) a plurality of spot beams, each covering a different region of the geographic area, the gateway system comprising: a gateway configured to receive, from a data network, forward link traffic to be transmitted; and a gateway traffic manager configured to select a first portion of the forward link traffic for transmission via the overlay beam, and a second portion of the forward link traffic and for transmission via the spot beams, wherein the gateway is configured to transmit those portions of forward link traffic via their selected beams.
In embodiments the gateway system may comprise a cache for caching forward link traffic to be transmitted via the overlay beam. A seventh aspect of the present invention is directed to a method of providing an internet access service via a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, the method comprising: determining respective popularity measures for pieces of internet content accessible via an internet; and selecting a first of the pieces of content for transmission to a plurality of users via the overlay beam, based on its popularity measure; transmitting the first piece of content from the internet to the users via the overlay beam; selecting a second of the pieces of content for transmission to at least one user via one of the spot beams, based on its popularity measure; and transmitting the second piece of content from the internet to the at least one user via the sport beam.
The internet is preferably the public Internet, whereby Internet content (capital I) is transmitted via both the overlay beam and the spot beams. For example, Internet video content, which may be streamed and/or downloaded via both beams, e.g. using one or more Internet streaming protocols, such as flash, HTML5, Silverlight etc.
An eight aspect of the present invention is directed to a client system for communicating via a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, and (ii) a plurality of spot beams, each covering a different region of the geographic area, the client system comprising: a transmitter configured to transmit a content request to a gateway via one of the spot beams, wherein the content request comprises an identifier of a piece of content; and a receiver configured to receive the requested content from the gateway via the overlay beam.
In embodiments, the client system may comprise another receiver for receiving data via the spot beam simultaneously with the requested content.
The client system may comprise a local cache for storing content received via the overlay beam. A ninth aspect of the present invention is directed to a method of communicating via a satellite network comprising at least one satellite, wherein the satellite network is configured to provide (i) an overlay beam covering a geographic area, and (ii) a plurality of spot beams, each covering a different region of the geographic area, the method comprising: transmitting from a client system a content request to a gateway via one of the spot beams, wherein the content request comprises an identifier of a piece of content; and receiving the requested content at the client system from the gateway via the overlay beam. A tenth aspect of the present invention is directed to computer program product comprising code stored on a computer readable storage medium and configured when executed to implement the system or method of any aspect of the present invention or any embodiment thereof.
For the avoidance of doubt it is noted that any feature discloses in relation to any aspect of the invention or ay embodiment thereof can be implemented in embodiments of any of the other aspects.
Brief Description of Figures
For a better understanding of the present invention, and to show how embodiments of the same may be carried into effect, reference is made to the following figures in which:
Figure 1 is a schematic diagram showing geographic coverage of a cluster of satellite beams in a known type of arrangement;
Figure 1A is a schematic diagram of a known type system for providing internet access via satellite;
Figure 2 shows a satellite communication system according to embodiments of the present invention, which is a system for system for providing internet access via satellite;
Figure 3 is a schematic perspective diagram of a system for providing internet access via satellite according to embodiments of the present invention, using spot beams and an overlay beam;
Figure 4 is a plan view showing geographic coverage of a cluster of spot beams and collocated overlay beam;
Figure 4A shows a side view of an overlay beam and a spot beam;
Figure 4B illustrates an example of frequency and bandwidth allocations for overlay and spot beams;
Figure 5 is a signalling diagram showing example signalling between a gateway and a set of client systems;
Figure 6A is a block diagram representing functionality of a client system; Figure 6B is a flow chart of a content management process performed at a client system.
Detailed Description of Example Embodiments
Figure 2 gives a schematic overview of a satellite communication system 100, which is suitable for providing access to a network 102. The network 102 is an internet 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 network 110 comprising at least one satellite in orbit about the Earth, 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 103 connected to the internet 102, and at least one gateway antenna 106 connected to the hub 103. Each of the client systems comprises an antenna 114, connected to a satellite modem 113. The satellite 110 network is arranged to be able to communicate wirelessly with the hub 103 of the satellite gateway 104 via the gateway antenna 106, and with the modems 113 of 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, hub 103 and modems 113 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 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 hub 103 serves (i.e. provides an internet access service to) the client systems 112 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 103. Though not shown in figure 1, the gateway may comprise multiple such hubs, each serving a respective subset of client systems.
In one model the operator of the satellite network 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. 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 420113 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 113 for connecting to the satellite network 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 network 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.
Figures 3 and 4 illustrate a key aspect of the present invention, where in addition to the at least two spot beams 202, a wider satellite beam 402 covering substantially all of the geographic area covered by the at least two spot beams 202 collectively is also provided by the satellite network 110 (overlay beam) such that, for the most part, any one of the client systems 112 located in the area covered by any one of the spot beams 202 has access both to that spot beam and also to the overlay beam 402.
For example, the overlay beam 402 may have an angular extent of about 1.2 degrees, and each spot beam 202 an angular extent of about 0.6 degrees relative to vertical (see figure 4A). Note these numbers are purely exemplary and are provided for the purposes of illustration to give a feel for the approximate relative dimensions involved - they are not in any way limiting.
The angular extent and power flux density of each of the beams 202, 402 is determined by the transmit power, receiver power and directivity of whichever satellite antenna is providing those beams.
Figures 4 and 4B demonstrate how frequency resources may be allocated to the beams. In the example of figure 4A, each of the beams operates at one of three different carrier frequencies f1, f2 or f3, according to a suitable frequency-reuse scheme, also called a "colour plan" (to avoid adjacent beams using the same frequency which would lead to interference between beams). The overlay beam 402 operates at a fourth frequency carrier f4, to avoid interference with any of the spot beams. As shown in figure 4B, each of the beams operates in a band of frequencies about its respective carrier. The bands are non-overlapping, and have a bandwidth denoted BWforfl, f2 and f3. The band about f4, in which the overlay beam 402 operates, has a narrower bandwidth BW to account for its lower power flux density, which in turn arises due to its greater angular extent.
Note these figures are highly schematic. Nine spot beams 202 are shown covered by one overlay beam 402, but this is purely exemplary. The techniques can be implemented with any number of spot beams (two or more); for example, between 8 and 16 spot beams inclusive or any other number of spot beams. And whilst it may be preferable for the overlay beam 402 to cover all or substantially all of the area covered by spot beams 202 collectively as shown, this is not essential: e.g. the overlay beam could cover part of the region covered by one sport beam and part of the region covered by another spot beam. That is, the gateway beam 402 spans at least two regions covered by different spot beams, but need not cover the entirety of each of those regions (there could be a gap in one or both regions not covered by the overlay beam).
Returning to figure 2 briefly, a gateway traffic manager 122 is shown. A function of the gateway traffic manager 122 is to determine how forward-link user traffic is distributed between the spot beams 202 and the overlay beam 402. A gateway cache 124 of the gateway 104 is also shown, and each client system is shown to have available a respective local cache 118. The gateway cache 124 can be used to cache data to be transmitted via the overlay beam 402 before transmission, and the local client system caches 122 to hold data that is received via the overlay beam 104, for outputting to a user at a time of his choosing (see below).
As indicated, the satellite network 110 and gateway 104 cooperate to provide a network access service (e.g. internet access service), such that a user of any one of the client systems 112 has more or less complete freedom to access data from any desired location in the network 112, which is preferably the public Internet (subject to any legal or policy restrictions and the like).
For network data that is accessed relatively infrequently, if and when it is requested, it is generally more efficient to transmit that data to the requesting client system via whichever spot beam 202 is serving that system, as the other spot beams can continue to operate independently of that transmission.
However, as noted, in practice a small portion of the content available from the network 102 is likely to be significantly more popular, at least at certain times, and it is thus quite likely that, at least some of the time, a relatively large number of users will happen to choose to access that content either simultaneously (e.g. for 'live" content broadcast via the network 102, such as an Internet broadcast of a TV channel) or within a relatively short space of time of each other (e.g. the most popular video content on a streaming-one-demand platform, such as Netflix, iPlayer catch up etc.).
This in turn can lead to a significant amount of duplicate forward link traffic across different spot beams in existing spot beam satellite systems, which the inventor of the present invention has recognized can be transmitted more efficiently via the wide overlay beam 402, particularly in the case of video content which may consume a significant portion of the overall available bandwidth of the satellite network 110.
In determining how to distribute forward link traffic between the spot beams 202 and the gateway beam 402, the gateway traffic manager 122 may for example estimate respective popularity measures for different portions of the forward link traffic. This can take into account what content is actually being requested by the client systems 112 via the satellite network 110, i.e. by monitoring return link traffic, and could also take into account a wider analysis of network content performed by analyser 119 (see below).
As a simple example, in determining whether to transmit a portion of forward link content via a spot beam 202 or the overlay beam 402, the gateway traffic manager 122 can for example estimate an expected number of client systems 112 that are likely to want to access that portion of content within a certain time interval, and if that number exceeds a threshold transmit broadcast that portion of content via the overlay beam 402 for receiving by multiple client systems 112 served by different spot beams 202.
To aid understanding, consider the following. In existing spot beam networks, each spot beam 202 may have a bandwidth of about 230 MHz and a spectral efficiently of 3bit/Hz i.e. 3 bits per Hz, allowing an effective data throughput of 690 Mbit/s per beam, i.e. 690Mbit of (non-duplicate) data per second per beam. Note these numbers are purely exemplary and are provided for the purposes of illustration to give a feel for the approximate relative dimensions involved - they are not in any way limiting.
By contrast, in the system described herein with a comparable overall frequency allocation, by way of example each spot beam 202 may have an effective throughput of 490 Mbit/sec (reduced, as some of the frequency resources have effectively been reassigned to the overlay beam 402) and the overlay beam an effective data 200 Mbit/sec. However, by intelligently moving what would otherwise be duplicate traffic from the spot beams 202 to the overlay beam 402, the amount of data that actually needs to be transmitted is reduced - that is, although the overall maximum data though put and overall spectral efficiency is approximately the same, the number of bits that needs to be transmitted per second in order to convey the same amount of information is reduced, thus freeing up resources. In other words, the total number of bits per second that is transmitted to the client system 112 can be reduced without reducing the number of unique bits per second that is transmitted to them.
The overlay beam 402 can be provided by the same satellite as the spot beams 202, or alternatively it can be provided by a separate satellite collocated with the spot beam satellite (e.g. in the same orbital slot). That is, the satellite network 110 can be formed of a single satellite providing both types of beam, or of two satellites providing different types of beam (among others). In the context of upgrading an existing satellite network in particular, the latter is preferred, as it does not require reconfiguration of any existing spot beam satellite. Launching a wide beam satellite to operate alongside an existing spot-beam satellite is a highly cost efficient means of implementing the present techniques.
To further aid illustration, various examples will now be described.
Figure 5 shows an example signalling flow, in which a first, second and third client system 112a, 112, 112c are served by first, second and third spot means 202a, 202b, 202c respectively. Each requests the same piece of content, by transmitting a respective content request 502a, 502b, 502c to the gateway 104 via its respective spot beam 202a, 202b, 202c. The gateway traffic manager 122 determines from the requests 502a, 502b, 502c that this same piece of content has been requested by multiple client systems 112a, 112b, 112c served be different spot beams 202a, 202b and 202c, and as a result causes at least part of that requested content to be broadcast via the overlay beam 402, via which it can be received via those client systems. So that those client systems 112a, 112b, 112c know to expect at least part of the requested content via the overlay beam 204, the gateway traffic 112 can inform them of this, e.g. by transmitting respective (individual) notifications 504a, 504b, 504c to the client systems 112a, 112b, 112c back via the same spot beam as it originally requested the content in question. The responses identify the at least part of the content that the client systems can expect to receive via the overlay beam 402 instead of its spot beam. Alternatively or in addition, a notification 504 with this information can be broadcast via the overlay beam 402 itself, and in this case the client systems 112a, 112b, 112c may monitor the overlay beam 402 for such notifications so they know from which beam to expect particular content.
The requests 502a, 502b and 502c need not be received at exactly the same time. For example, in the very simple case of a live Internet video stream, the client systems 112a, 112b and 112c can simply "tune in" to the live stream at different points in time within the stream. The first time the live stream is requested the gateway traffic manager 122 can, for example, begin transmitting the stream to the requesting client system via the spot beam 202 serving that system. If a sufficiently small number of additional requests for that same stream are received from different client systems, the gateway traffic manger 122 may transmit instances of the stream to those systems individually via their respective spot beams, as would a conventional spot beam network. However, as more requests are received for the same stream, the gateway traffic manager 122 may decide to switch the delivery mode of the stream, by instead transmitting it via the overlay beam 402 thereafter and informing the client systems of the switch accordingly, either by way of individual notifications via the spot beams 202 or a notification broadcast via the overlay beam 402.
Each of the requests 502a, 502b and 502c comprises an identifier of the content it is requested, allowing the gateway traffic manager 122 to detect requests relating to the same content by comparing their content identifiers.
For example the identifier may comprise a network address (e.g. IP address, transport address, URI etc.) of the network 102 which can be used to access a version of that piece of content.
Note however that the system is not restricted to this very simple scenario.
For example, in the case of video-on-demand, different client systems may well wish to begin receiving video streams carrying pre-recorded video at different times. The gateway traffic manager 122 can accommodate this, by transmitting some of a requested piece of content via the spot beams and some via the overlay beam 204 as necessary.
For example, suppose a first of the client systems 112 in one spot beam happens to request a piece of content which a second of the client systems in another spot beam requested 10 minutes ago, and is now 10 minutes into.
The gateway traffic manager 122 can accommodate this by broadcasting everything from the 10-minute point onwards via the overlay beam 402 for receipt by both client systems, and transmitting the first ten minutes of the content to the first client system via its spot beam 202. The second client system will thus receive different parts of the content simultaneously, via different beams, and can cache the later part of the content received via the overlay beam 402 in its local cache 118, output the earlier part of the content as it is received via its spot beam 202, and then switch to the locally cached content upon cessation of the spot beam transmission.
As another example, the gateway traffic manager 122 can pre-identify popular content (such as new video-on-demand content that is likely to be highly popular, based on historical popularity data for similar content) e.g. based on the analysis performed by analyzer 119, and even pre-broadcast the popular content when available via the overlay beam 402 for caching locally at the client system 112 automatically, even if it has not yet been requested thereat. In this scenario, when a user selects a piece of content for outputting at one of the client systems 112, the client systems 112 can first check to see whether the requested content has already been cached locally. Content received via the overlay beam 402 and locally cached is denoted 604 in figure 6A (see below).
As will be appreciated, these are a highly simplified examples provided to illustrate a more general principle, which is that the gateway traffic manager 122 is able to make intelligent decision about which portions of the forward link traffic can be more efficiently broadcast via the overlay beam 402, in order to avoid excessive duplication of traffic within different spot beams 202.
In some cases, the gateway traffic manager 122 may cache content that it intends to be transmitted via the overlay beam 402 in the gateway cache 124.
Figure 6A shows a function block diagram, representing some of the functionality of a client system 112 in another example. The client system 112 comprises a user interface (Ul) 602, via which a user can select content to be outputted (using an input device of the user interface 602, such as a mouse, track pad, touchscreen, voice or gesture input device etc.) and via which the selected content can be outputted to the user (e.g. via a display and audio output device of the user interface 602).
This can be based on an analysis of which Internet content is most popular, which may be automatic (by analyser 119 in figure 2, which may for example be a content analysis code execute on one or more processors, e.g. at a server or servers), manual (e.g. by operators manually tagging popular content to be distributed via the overlay beam 402), or a combination of automatic and manual analysis. The analysis performed by analyser 119 can assess the relative popularity of different content within the network 102 as a whole, i.e. taking into account the demands of users who may not be served by the satellite network 110, and in particular those outside of the geographic area 20 (e.g. in different countries) - for example, users who access the Internet via cable network, cellular networks (3G, 4G, LTE etc.) - and content access patterns accords the network 102 as whole.
The client system 112 also comprises a transmitter Tx, which can be used to transmit return link signal to the gateway 104 at least via the spot beam 202 serving the client system 112, and two receivers Rx1 and Rx2 for receiving signals via the local spot beam 202 and the overlay beam 402 respectively. Two separate receivers Rx1 and Rx2 allow the client system 112 to receive data from both beams simultaneously. These may be integrated in the same modem 113, or alternatively the second receiver Rx2 for receiving via the overlay beam may be a modular component that can be retrofitted to an existing modem (for example). The addition of a second receiver is a low-cost solution, as receiver equipment is inexpensive nowadays. A local content manager 604 of the client system 112 is shown, which implements a local content management procedure, for which a flow chart is shown in figure 6B. A user selects a piece of content to be outputted at the Ul 602, causing the local content manager 604 to receive (S602) from the Ul 602 a content selection input, denoted 606 in figure 6A.
In response, at step S604, the local content manager determines whether at least part of the selected content is already pre-cached in the local cache 118. Locally cached content is denoted 604 in figure 6A. If all of the selected content is already available as cached content 604, the method proceeds directly to step S606 at which the cached content 604 is outputted to the user via the Ul 112.
On the other hand, if none or only part of the selected content is available from the local cache 112, the local content manager 604 determines whether at least part of the selected content (or at least part of whichever portion of the content that is not cached locally) is currently being broadcast or is scheduled to be broadcast soon via the overlay beam, based on overlay beam scheduling data 602 available at the client system 112. That is to say, at step S608 the local content manager determined whether some or all of the necessary content will be available via the overlay beam 402 without having to explicitly request it from the gateway 104. The scheduling data 602 is data that is made available to the client system 112 by the gateway traffic manager 122, and may for example comprise the broadcast notification 504 described above and/or other data pertaining to the scheduling of traffic via the overlay beam 402 provided for the benefit of the client system 112, e.g. via the overlay beam 402 itself.
If the overlay beam scheduling data 602 indicates all of the selected content (or all of whichever portion of the content that not cached locally) is currently being broadcast or is going to be broadcast via the overlay beam 402 soon enough to accommodate the users selection, the method proceeds to step S606, at which the selected content is outputted - either directly from the overlay beam 402 as it is received, or by outputting a combination of precached and newly-received data.
In other words, the client system 112 determines respectively, in response to the content selection input 606, whether at least part of the content has already been received via the overlay beam 402 (S604) and whether at least part of the content is receivable via the overlay beam 402 (S608).
On the other hand, if at least part of the content can neither be obtained from the local cache 118 or via the overlay beam 402 at present, the local manager requests (S610) the selected content (or whichever part of the content it needs) via the spot beam 202 serving the client system 112. Note that this is the first point in the method that the client system 112 needs to consume return link bandwidth by sending data to the gateway 102 (steps S604 and S608 do not involve requesting data from the gateway 104). In response, at step S612, the content manager 604 receives the requested content from the gateway 102. This may be via the spot beam 202 serving the client system 112, or it may be via the overlay beam 402 (e.g. if the gateway traffic manager 122 decides to start broadcasting the selected content in response to that request), or through a combination of the spot beam 202 and overlay beam 402 (e.g. if the gateway traffic manager 122 decides initially to send the content via the spot beam 202, but then decides to switch to the overlay beam 402 as more people request the same content).
The local content manager 602 is preferably implemented in software, i.e. as code executed on at least one processor. That is, code executed on a single processor, e.g. in the modem or IDU (indoor unit), or a computer device connected to the modem, such as a user device or server of the client system 112 e.g. in a local network, or on multiple processors (e.g. parts of its functionality may be implemented by a portion of the code executed on a processor of the modem/IDU, and part as a portion(s) of code executed on a processor(s) of a computer device(s) connected to the modem). That is, at the user device and/or another device (e.g. modem, server) directly connected to the user device, i.e. by a connection other than the satellite link 107, such as an Ethernet, Wi-Fi, Bluetooth connection etc. However, in other cases, some or all of the functionality of the local content manager 604 can be implemented in dedicated hardware, such as an application-specific integrated circuit or programmable hardware such as an FPGA. The local cache 124 can be implemented using a storage device (e.g. a solid state or magnetic storage device) or multiple memory devices. For example, at least part of the local cache 124 may be implemented as a dedicated hard drive in or connected to the modem or IDU; as another example, alternatively or in addition, at least part of the local cache may be implemented in general storage of a computer device connected to the modem/IDU.
The gateway traffic manager 122 is preferably implemented in software, is as code executed on at least one processor, e.g. on a processor(s) of a server, or distributed across processors of two or more co-operating servers. It can be located in the gateway 104 itself, but whilst preferable in certain circumstances this is not essential: in other cases, the gateway traffic manager 122 can be implemented remotely from the gateway, for example it may communicate with the gateway via the network 102 or via some other means, such as a dedicated back-bone connection, to perform the described functions. It may also be distributed across multiple locations, e.g. part of its functionality may be implemented at the gateway 104 and part remotely.
Moreover, the possibility of implementing at least part of its functionality in dedicated hardware instead is not excluded. Likewise, the gateway cache 124 can be implemented locally at the gateway 104 or remote from it, using one or more storage devices, or using a combination of local and remote storage devices.
The code may be stored on a computer readable storage medium, such as one or more electronic storage devices (e.g. optical, solid state, or magnetic storage devices or any combination thereof).
The above embodiments have been described by way of example for the purpose of illustration. As will be apparent, variations of the described embodiments may fall within the scope of the invention, which is not limited by the description but only by the following claims.