Patent Description:
Individual high-throughput satellites in geosynchronous earth orbit (GEO) over time offer increasing aggregate end-user data throughput. For example, the EchoStar <NUM> satellite, launched in <NUM>, offers a data throughput in excess of <NUM> gigabits per second (Gbps). One limit to achieving terabit per second (Tbps) forward data throughput (also referred to as "data capacity" or "capacity") from a single GEO satellite is available forward feeder link bandwidth for delivering data to the satellite. With radio frequency (RF) communications, including various "millimeter wave" bands, such rates are generally impractical and expensive. RF feeder links must comply with regulatory constraints and also not conflict with user RF links (the co-siting problem), which makes the following RF bands undesirable:.

Plus, at this time, the W-band (<NUM>-<NUM>), although it offers <NUM>, requires further technical development for this purpose for use in GEO RF feeder links. Additionally, even with a spectral efficiency of <NUM> bps/Hz, <NUM> of total RF bandwidth is required to reach <NUM> Tbps data capacity, so combined use of the available bands would require about <NUM> gateways (GWs), plus many additional gateways for diversity. For GEO satellites with data throughput in only a few hundreds of gigabits per second, ground segment costs (construction, operation, and maintenance) for feeder links are already a significant percentage of overall network system cost. For <NUM> Tbps or greater data throughput, and the resulting increase in the number of gateways, ground segment costs become even more significant. Also, although it may be possible to fit the needed number of gateways in the United States, a very favorable satellite location would still be needed. Thus, in view of significant technology challenges and regulatory uncertainty, use of RF feeders between the Earth's surface and a GEO satellite to achieve terabit per second or higher data throughput is a difficult, uncertain, and expensive architecture.

<CIT> discloses a satellite communication system which may include a communication satellite orbiting Earth, a user terminal in radio communication with the communication satellite through a user link, a communication relay apparatus operating at an altitude of approximately <NUM>,<NUM> feet and in optical communication with the communication satellite through a feeder link, and a gateway station in radio communication with the communication relay apparatus through a gateway link.

<CIT>, <CIT>, <CIT>, <CIT> disclose related technologies.

In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings. To more clearly describe the disclosed subject matter, various features illustrated in the figures are not illustrated to scale, including distances or angles.

<FIG> illustrates an example satellite-based data telecommunication system <NUM> (which may be referred to as a "communication system") configured to utilize multiple RF feeder links between a compact feeder RF terminal (RFT) array <NUM> and a stratospheric high-altitude platform (HAP) <NUM>, a high capacity free space optical (FSO) feeder link <NUM> between the HAP <NUM> and a space satellite <NUM>, and RF service links <NUM> between the space satellite <NUM> and a plurality of end user service RF terminals (RFTs) <NUM> (for example, the illustrated ground-based RFTs 112ba and 112bb and air-based RFT 112cd). In some implementations, as illustrated in examples described below, at least <NUM>% (including in some implementations at least <NUM>% or in some implementations at least <NUM>%) of feeder data throughput (in the forward and/or reverse directions) for all of the RF service links <NUM> operated by a single GEO satellite <NUM> (including all forward RF service link signals transmitted by the satellite <NUM> and/or reverse RF service link signals received by the satellite <NUM>) is carried via a single optical feeder link <NUM> with a single HAP <NUM> (noting that handoff operations may be performed to change from operating the optical link <NUM> with a first HAP <NUM> to a different second HAP <NUM>) and corresponding RF feeder links <NUM> between the single HAP <NUM> and a single feeder RFT array <NUM> at a single RF feeder site <NUM>. For example, the single compact feeder RFT array <NUM>, the single HAP <NUM>, the single satellite <NUM> can operate together to provide a total forward data capacity of <NUM> Tbps or greater to a plurality of service RFTs <NUM> configured to communicate via the RF service links <NUM> with the satellite <NUM>.

The telecommunication system <NUM> includes a gateway system <NUM> (which may be simply referred to as a "gateway") configured to provide the telecommunication system <NUM> with access to a public data communication network <NUM> (for example, the Internet) and/or a private data communication network <NUM>, whereby the gateway <NUM> can receive data from, and send data via, the networks <NUM> and/or <NUM>. In some implementations, the gateway <NUM> is configured to perform quality of service (QoS) and/or caching functions to improve performance of the telecommunication system <NUM>. In some implementations, the gateway <NUM> and/or other systems managed by a network operator are configured to control operation of other aspects of the telecommunication system <NUM>, such as HAP <NUM> and/or satellite <NUM>. For example, the gateway <NUM> may be configured to determine how upstream data is distributed via spot beams <NUM> (which collectively refers to the spot beam transmissions by the satellite <NUM>, such as spot beams 172a, 172b, and 172c shown in <FIG>). In the example illustrated in <FIG>, the gateway <NUM> is configured to send data to, and receive data from, participating service RFTs <NUM> via a HAP data center <NUM>.

The HAP data center <NUM> is configured to utilize the feeder RFT array <NUM>, HAP <NUM>, and satellite <NUM> to exchange data with the service RFTs <NUM>, with the feeder RFT array <NUM> and HAP <NUM> each serving as endpoints for a plurality of RF feeder links <NUM>. For providing forward-directed user data received as network data from the gateway <NUM> as forward link data (encoding the forward-directed user data) to the satellite <NUM> for distribution to the service RFTs <NUM>, the HAP data center <NUM> multiplexes, modulates, and encodes data for the spot beams <NUM> for RF transmission by the feeder RFT array <NUM>. The feeder RFT array <NUM> includes a compact arrangement of a plurality of ground-based feeder RFTs. For each of a plurality of active HAP-directed RFTs, a respective one of a plurality of RF feeder links <NUM> (including, in this example, an RF feeder link 310b) each including a respective forward RF feeder link signal (which may be referred to as a "forward RF feeder link" or an "RF feeder uplink") transmitted to the HAP <NUM>. In this particular example, the feeder RFT array <NUM> includes at least <NUM> actively operating feeder RFTs concurrently transmitting respective forward RF feeder links. Each of the forward RF feeder links is transmitted at a frequency of at least <NUM> (in some examples, at least <NUM>) and has a bandwidth of <NUM> (<NUM> with right-hand circular polarization (RHCP) and <NUM> with left-hand circular polarization (LHCP)), providing a total forward RF feeder link bandwidth of <NUM> from the feeder RFT array <NUM> to the HAP <NUM>. With an average forward link MODCOD providing a spectral efficiency of <NUM> bps/Hz, a total forward data capacity of at least <NUM> Tbps may be provided by the feeder RFT array <NUM>. In other examples, different values may be used for the number of feeder RFTs, the number of forward RF feeder links, the transmission frequencies for the forward RF feeder links, the bandwidth of the forward RF feeder links, and/or spectral efficiency. The forward RF feeder links could also utilize beam hopping, frequency reuse of <NUM>, or other arrangements requiring more or less RF bandwidth.

In some implementations, such as in the example shown in <FIG>, the RF feeder links <NUM> also each include a respective reverse RF feeder link signal (which may be referred to as a "reverse RF feeder link" or an "RF feeder downlink", and which encodes reverse-directed user data) received from the HAP <NUM>. In this particular example, the same <NUM> feeder RFTs transmitting the forward RF feeder links are also receiving respective concurrent reverse RF feeder links; each of the reverse RF feeder links is received at a frequency of at least <NUM> (in some examples, at least <NUM>) and has a bandwidth of <NUM> (<NUM> with right-hand circular polarization (RHCP) and <NUM> with left-hand circular polarization (LHCP)), providing a total reverse RF feeder link bandwidth of <NUM> from the HAP <NUM> to the feeder RFT array <NUM>. With a MODCOD providing a spectral efficiency of <NUM> bps/Hz, a total reverse capacity of <NUM> Gbps is provided by the feeder RFT array <NUM>. The HAP data center <NUM> is configured to decode, demodulate, and demultiplex the reverse RF feeder links and provide the resulting reverse data streams to the gateway <NUM>. Also, the reverse RF feeder links could be part of a ground-based beam forming system in which the reverse link would comprise return link beam responses and possibly have a larger feeder link requirement.

The HAP <NUM> is adapted to be deployed in the stratosphere to carry a payload <NUM> (which may be referred to as a "high-altitude communication device"). The payload <NUM> could be carried below the HAP <NUM> as shown, or alternatively it could be contained within the envelope <NUM> which, in some examples, could be an airship or aircraft. In some portions of this description, the HAP <NUM> and the payload <NUM> may be referred to interchangeably. At moderate latitudes, the stratosphere includes altitudes between approximately <NUM> and <NUM> altitude above the surface. At the poles, the stratosphere starts at an altitude of approximately <NUM>. The HAP <NUM> may generally be configured to operate at altitudes between <NUM> and <NUM> while operating as an endpoint of the optical feeder link <NUM> (although other altitudes are possible). This altitude range may be advantageous for several reasons. In particular, this layer of the stratosphere generally has relatively low wind speeds (for example, winds between <NUM> and <NUM> mph at lower latitudes) and relatively little turbulence. Further, while the winds between <NUM> and <NUM> may vary with latitude and by season, the variations can be modeled in a reasonably accurate manner. Additionally, altitudes above <NUM> are typically above the maximum flight level designated for commercial air traffic. Therefore, interference with commercial flights is not a concern when the HAP deployed between <NUM> and <NUM> altitude.

As noted above, the HAP <NUM> serves as an endpoint of the optical feeder link <NUM> between the HAP <NUM> and the satellite <NUM>. Due to the altitude at which the HAP <NUM> operates, this places the optical feeder link <NUM> above much of the atmosphere, resulting in substantial reduction in atmospheric attenuations and distortions. At and above such altitudes, the atmosphere contains a minimal amount of dust, water, and other atmospheric particles that often interfere with optical signals in the troposphere. For example, <NUM>% of the Earth's atmospheric mass lies below an altitude of <NUM>. Additionally, nearly all atmospheric water vapor or moisture, is found in the troposphere (the lowest layer of the atmosphere) which extends to an altitude of about <NUM>-<NUM>. This includes clouds, through which operating an optical link can be impossible. Also, in the stratosphere, the next layer above the troposphere, the air is very stable and turbulent mixing is inhibited due to an inverted temperature profile in the stratosphere.

In the example shown in <FIG>, the HAP <NUM> is implemented using a high-altitude stratospheric balloon, including an envelope <NUM>. The envelope <NUM> may take various forms, which may be currently well-known or yet to be developed. For instance, the envelope <NUM> may be made of metalized Mylar or BoPet. Alternatively or additionally, some or all of the envelope <NUM> may be constructed from a highly-flexible latex material or a rubber material such as chloroprene. Other materials are also possible. Further, the shape and size of the envelope <NUM> may vary depending upon the particular implementation. Additionally, the envelope <NUM> may be filled with various different types of gases, such as helium and/or hydrogen. Other types of gases are possible as well. In some examples, a thin-film photovoltaic may be provided on a portion of the envelope <NUM> to provide power for the HAP <NUM>, including the payload <NUM>. Although in <FIG> the HAP <NUM> is embodied as a high-altitude stratospheric balloon, other high-altitude platforms may be utilized, such as an airship.

As noted above, the HAP <NUM> serves as an endpoint of the RF feeder links <NUM> between the HAP <NUM> and the feeder RFT array <NUM>. For this purpose, the payload <NUM> includes a HAP-based RF feeder link antenna <NUM> (which, in some examples, may include multiple antennas) for receiving forward RF feeder links from the feeder RFT array <NUM> and, in some examples, transmitting reverse RF feeder links to the feeder RFT array <NUM>.

Ideally, the HAP <NUM> would operate directly above the feeder RFT array <NUM>, with a zenith distance of <NUM>° with respect to the feeder RFT array <NUM>. However, the HAP <NUM> is expected to move about horizontally, such as due to wind forces. Due to the compact arrangement and large number of the feeder RFTs included in the feeder RFT array <NUM>, the HAP <NUM> must operate within a first lateral distance or angle of the feeder RFT array <NUM> in order to achieve a target number of active RF feeder links <NUM> corresponding to full bandwidth capacity without unacceptable levels of interference among the RF feeder links <NUM> (in either the forward or reverse direction). The telecommunication system <NUM> may be configured to perform station keeping operations for HAP <NUM> to maximize an amount of time that the HAP <NUM> operates within that particular lateral distance or angle. In some examples, the station keeping operations may account for the availability of multiple HAPs operating in proximity to the feeder RFT array <NUM>. Station keeping operations may include changes in the altitude of the HAP <NUM> to take advantage of winds of varying speeds and directions present at different altitudes.

The RF feeder link antenna <NUM> (which may also be referred to as a "gateway antenna") may be implemented with a single multi-beam antenna with multiple feeds to provide the target number of active RF feeder links <NUM> to reach full capacity. Changes in altitude may cause the angular spacing between the RF feeder links <NUM> to change. In some implementations, the HAP <NUM> may be configured to change angular spacing of the RF feeder links <NUM> by mechanically moving feeds of the RF feeder link antenna <NUM>. In some implementations, the RF feeder antenna link <NUM> may be implemented using a phased array antenna (which may be referred to as an "electronically steered antenna"), with which electronic beam steering can be performed. A phased array antenna provides fast beam steering, including an ability to generate simultaneous beams and dynamically adjust the characteristics of the beam patterns. As a result, a phased array antenna offers improved performance over mechanical means for beam steering in response to movements of the HAP <NUM>.

In some implementations, <NUM>-<NUM> or higher RF bands are suitable as they allow multiple RF feeder terminals to be positioned in a compact arrangement in a relatively small area due to the small beam widths that can be achieved at these frequencies and extensive reuse that can be achieved in a small area, although other bands may be used as well. Additionally, use of very high RF frequencies , such as so-called "millimeter wave" frequencies, for the RF feeder links <NUM> permits operation from a single RF feeder link site <NUM>, rather than an expensive widely distributed backbone network with diverse sites. Mature technologies are available for such RF frequencies, such as technologies developed for terrestrial microwave and <NUM> cellular radio systems. Additionally, the compact size of the feeder RFT array <NUM> and the high directionality of the RF feeder links <NUM> reduces concerns about RF interference with other RF applications.

As the RF feeder links <NUM> operate over a much smaller distance than a ground-to-satellite RF link (such as the satellite RF link shown in <FIG>), adequate margin can be achieved to overcome E-band fading at a single site, thus avoiding a need for diversity. Additionally, although a site with generally clear weather conditions is favorable, a wider range of locations are practical than with a ground to GEO RF link operating at a distance of approximately <NUM>,<NUM>.

The following example RF link budget is illustrative for the RF feeder links <NUM> with the HAP <NUM> operating at an altitude of <NUM> (although a larger HAP antenna, which is more practical with a phased array antenna, yields narrower beams and a smaller feeder RFT array <NUM>):.

To accurately and precisely aim the plurality of beams of the HAP-based RF feeder link antenna <NUM> to their respective RF feeder terminals in the compactly arranged feeder RFT array <NUM>, and maintain the RF feeder links <NUM> while the HAP <NUM> moves around (with various, and sometimes high frequency, changes in roll, pitch, and yaw), the HAP <NUM> includes an antenna stabilizer mechanism. The antenna stabilizer mechanism may include a mechanical antenna positioner (such as a <NUM>-axis gimbal) configured to selectively orient, for example, a main reflector of the RF feeder link antenna <NUM>, one or more mechanical antenna feed positioners (which can more rapidly reposition individual feeds, which have significantly less mass than the main reflector), and/or a phased array antenna. For example, a mechanical antenna positioner can perform coarse/slow positioning and be used in combination with a phased array antenna respond to higher frequency changes in roll, pitch, and yaw of the HAP <NUM>.

In some implementations, as in the example shown in <FIG>, the payload <NUM> may include one or more additional RF terminal communication antennas <NUM> to provide one or more RF communication services for end-user RFTs <NUM>, such as the illustrated ground-based RFT 136a and the air-based RFT 136b. In some examples, a portion of the RF feeder links <NUM> provides backhaul for these services. Due to the high altitude at which the HAP <NUM> operates, a significant land area is within a field of view of the RF terminal communication antennas <NUM>, facilitating use of spot beams and frequency reuse. Example RF communication services include, but are not limited to, cellular communication services and wireless internet access. Use of the HAP <NUM> for these other purposes can reduce or divide costs of operating the HAP <NUM>. In some examples, one or more of the RF communication services is operated by a third party different than the party operating the HAP <NUM> and/or the satellite <NUM>.

The payload <NUM> includes a HAP-based optical feeder communication system <NUM> which is used to establish and maintain the optical feeder link <NUM> in the form of one or more FSO links (for example, modulated laser links) between the HAP <NUM> and the satellite <NUM>. The optical feeder link <NUM> may include an forward optical feeder link signal <NUM> (which may be referred to as a "forward optical feeder link" or an "optical feeder uplink") transmitted by an optical transmitter included in the optical feeder communication system <NUM> and received by the satellite <NUM>. The optical feeder link <NUM> may include an reverse optical feeder link signal <NUM> (which may be referred to as a "reverse optical feeder link" or an "optical feeder downlink") transmitted by the satellite <NUM> and received by an optical receiver included in the optical feeder communication system <NUM>. The payload <NUM> is configured to, via the optical feeder communication system <NUM>, convert and multiplex multiple forward link transmissions included in the RF feeder links <NUM> into the forward optical feeder link <NUM>, and convert and demultiplex the reverse optical feeder link <NUM> into multiple reverse RF feeder link transmissions included in the RF feeder links <NUM>. By operating the optical feeder link <NUM> outside of the troposphere, many substantial optical link issues encountered with FSO links through the troposphere are avoided, such as, but not limited to, cloud obstruction, the higher water content of the troposphere, substantial turbulence in the troposphere and resulting fading, and reduced wavelength-dependent refraction (which could negatively impact the effectiveness of WDM optical modulation schemes). By avoiding these issues, a need for optical diversity (multiple optical links at geographically diverse locations) may be eliminated or reduced, the optical electronics simplified, and an analog transparent architecture may possibly be enabled.

The optical feeder communication system <NUM> includes one or more optical telescopes including a combination of optics (such as refractive lenses and/or reflective mirrors) for transmitting and directing the forward optical feeder link <NUM> and/or the reverse optical feeder link <NUM>. In some examples, a single "duplex" optical telescope may be used for both the forward optical feeder link <NUM> and the forward optical feeder link <NUM>. Use of a single optical telescope may simplify mechanical aspects of pointing, acquisition, and tracking (PAT) of the optical feeder link <NUM> between the HAP <NUM> and the satellite <NUM>, as it reduces the problem to a single optical telescope that must perform PAT at approximately microradian accuracy despite motion of the HAP <NUM> as it operates. In some examples, the optical feeder communication system <NUM> includes a first optical telescope for transmitting the forward optical feeder link <NUM> and a second optical telescope for receiving the reverse optical feeder link <NUM>. By having separate telescopes, the optical chains for transmitting and receiving the optical feeder link <NUM> may be simplified (for example, by avoiding one or more beamsplitter and/or filter elements used in a duplex telescope), resulting in increased gain and/or signal quality. Separate telescopes also help avoid or eliminate optical crosstalk between a sensor being used to capture a very weak reverse optical feeder link <NUM> and transmission of a much stronger (for example, by about <NUM> dB) forward optical feeder link <NUM>. In some examples, the optical feeder communication system <NUM> includes multiple optical transmitters; for example, to reduce effects of turbulence or to divide the transmitted optical power among multiple telescopes, rather than demanding a single telescope suitable for a higher power optical signal.

The optical feeder communication system <NUM> is configured to accurately and precisely perform optical pointing for the optical feeder link <NUM> while the HAP <NUM> rolls, pitches, yaws, climbs/descends, turns, and translates. Although, as discussed above, similar pointing operations are performed for the RF feeder link antenna <NUM>, a far higher degree of precision and accuracy is demanded for PAT of an optical signal with a divergence of approximately <NUM> microradians with a GEO satellite <NUM>. Towards this purpose, the optical feeder communication system <NUM> includes, for each optical telescope, a pointing mechanism that simultaneously performs motion stabilization and PAT.

For a <NUM>,<NUM> space-based optical link, the following link budget for an optical link operating at <NUM> Gbps using <NUM>-inch telescopes at both the HAP <NUM> and the satellite <NUM> is illustrative:.

For <NUM> Tbps forward data capacity, using the same telescopes the transmit power would be increased to an estimated <NUM> dBm, or approximately <NUM> kW. However, although in some implementations it is not desirable to increase the size of the telescope aperture at the HAP <NUM> (for example, to reduce telescope mass for motion stabilization), the size of the telescope aperture may be increased at the satellite <NUM>, in view of substantially reduced problem of motion stabilization, in order to achieve increase gain and achieve corresponding reductions in transmit power. It is noted that the wavelength of <NUM> is merely an example, and that other wavelengths may be used (including, but not limited to, other wavelengths around <NUM> and wavelengths around <NUM> or <NUM>). In some implementations, wavelength division multiplexing (WDM) may be used to concurrently operate the optical feeder link at multiple wavelengths, at lower individual bitrates, resulting in corresponding improvements to the optical link budget. Dense wavelength division multiplexing (DWDM) may be used to multiplex many optical channels into the optical feeder link.

The space satellite <NUM> (which may simply be referred to as a "satellite") serves as another endpoint of the optical feeder link <NUM>, and as an endpoint for the RF service links <NUM>. In the example shown in <FIG>, the satellite <NUM> is a GEO satellite, with an orbit that maintains the satellite <NUM> over a fixed longitude of the Earth's surface. A GEO satellite <NUM>, issues such as maintaining, distributing, and calculating ephemera of the orbit of the satellite <NUM> can be avoided, along with tracking satellite <NUM> across the sky, obstruction of a portion of the sky by the envelope <NUM>, and optical link issues when the satellite <NUM> is at low elevations. However, in some implementations, the satellite <NUM> can be a medium earth orbit (MEO) or a low earth orbit (LEO), and/or may be one of multiple satellites operating in a constellation of satellites. The satellite <NUM> is configured to convert and demultiplex the forward optical feeder link <NUM> into transmissions for forward RF service links (for example, as forward RF service links <NUM> via respective spot beams <NUM>) included in the RF service links <NUM>, and is configured to convert and multiplex multiple reverse RF service link transmissions (for example, for reverse RF service links <NUM> and <NUM>) included in the RF service links <NUM> into the reverse optical feeder link <NUM>.

The satellite <NUM> includes a satellite-based optical feeder communication system <NUM>, which may be configured much as described in connection with the HAP-based optical feeder communication system <NUM>. However, as the satellite <NUM> does not experience frequent changes in movement, tracking the HAP <NUM> is simplified, which may allow use of larger aperture telescopes despite the accompanying increase in moving mass and narrower divergence. In some implementations, the satellite <NUM> may concurrently operate as an endpoint for multiple different optical links <NUM> with multiple different HAPs <NUM> (which may be a different locations). For example, the satellite <NUM> might be configured to concurrently operate a first optical feeder link <NUM> with a first HAP <NUM> and a second optical feeder link <NUM> with a second HAP <NUM>. To avoid optical crosstalk, the multiple forward optical feeder links <NUM> may be operated in different bands, such as a first forward optical feeder link in the ITU C-band (<NUM>-<NUM>) and a second forward optical feeder link in the ITU L-band (<NUM>-<NUM>). The ITU S-band (<NUM>-<NUM>), the U-band (<NUM>-<NUM>), and/or the <NUM>-<NUM> portion of the CIE IR-C band may also be used for the optical feeder link <NUM>, although there are fewer commercial product options in these bands due to the dominance of the ITU C-band for long-distance telecommunications. For example, DWDM hardware is mostly available for the ITU C-band and the ITU L-band.

The satellite <NUM> includes a satellite-based RF communication system <NUM> which is used for the RF service links <NUM>, including transmitting forward RF service links <NUM> (such as the forward RF service link 176b) to end user service RFTs <NUM> and receiving reverse RF service links <NUM> (such as the reverse RF service links 178ba, 178bb, and 178cd) from the end user service RFTs <NUM>. An end user service RFT <NUM> may also be referred to as a "user terminal" (UT) or more simply an "RFT". In some examples, the RF service links <NUM> are in one or more fixed satellite service downlink frequency bands, such as, but not limited to, the Q-band at <NUM>-<NUM>, the Ka-band in the <NUM>-<NUM> range, and the Ku-band in the <NUM>-<NUM> range. Use of RF service links <NUM> in these more traditional bands facilitates user of lower cost end user service RFTs <NUM> and/or use of existing end user service RFTs <NUM>. An end user service RFT <NUM> may be connected to one or more items of user equipment (UE) <NUM> (such as the UE 114bb) which may be associated with one or more end users <NUM>.

In some implementations, as shown in <FIG>, the RF communication system <NUM> provides the RF service links <NUM> via multiple spot beams <NUM> covering respective regions <NUM> (such as the spot beams 172a, 172b, and 172c for respective regions 174a, 174b, and 174c). For each spot beam <NUM> there is a single respective forward RF service link <NUM> (such as the forward RF service link 176b for the spot beam 172b), and multiple reverse RF service links <NUM> (such as the reverse RF service links 178ba, 178bb, and 178cd for respective RFTs 112ba, 112bb, and 112cd) via a variety of multiplexing techniques. In some examples, a single forward RF service link <NUM> may utilize multiple carriers or use a multicarrier modulation such as orthogonal multicarrier modulation (OFDM). The use of spot beams <NUM> may be combined with frequency reuse, in which the spot beams <NUM> are operated in multiple "colors" with different combinations of frequency ranges and polarization. With the use of spot beams <NUM>, the RF communication system <NUM> can achieve higher gain and greater total capacity. Additionally, the telecommunication system <NUM> may be configured to selectively and dynamically reallocate bandwidth to the spot beams <NUM>.

In some implementations, the HAP data center <NUM> includes a satellite RFT <NUM> used to operate a satellite RF link <NUM> between the HAP data center <NUM> and the satellite <NUM> for use as a command/control channel with the satellite <NUM>. Another RF link (not shown in <FIG>) may be established between the HAP data center <NUM> and the HAP <NUM> as a command/control channel with the HAP <NUM>. The HAP data center <NUM> may be configured to use these RF links for command/control operations for satellite <NUM> and/or HAP <NUM>. Such operations may include, but are not limited to, obtaining location and/or movement information from the HAP <NUM>, control station keeping operations performed by the HAP <NUM>, coordinate station keeping operations among multiple HAPs <NUM>, facilitating PAT of the optical feeder link <NUM> (for example, by reducing acquisition time), and/or facilitating PAT of optical links between HAPs <NUM>. In some implementations, an RF link may be established directly between the HAP <NUM> and the satellite <NUM>, and the HAP <NUM> and the satellite <NUM> are configured to utilize the RF link to exchange data facilitating PAT of the optical feeder link <NUM>.

<FIG> illustrates a plan view of an example of the feeder RFT array <NUM> shown in <FIG>. In this example, the feeder RFT array <NUM> has <NUM> feeder RFTs <NUM>, including the labeled feeder RFTs 210a, 210b, 210c, 210d, 210e, 210f, <NUM>, <NUM>, and 210n. The feeder RFT array <NUM> may include more or less than the illustrated <NUM> feeder RFTs <NUM> to realize various implementation goals, such as, but not limited to, a target total operating capacity of the RF feeder links <NUM>, a maximum total operating capacity of the RF feeder links <NUM>, and/or an amount of "spare" feeder RFTs <NUM> to avoid reductions in operating capacity arising maintenance or failures of the feeder RFTs <NUM>. As noted previously, the feeder RFTs <NUM> of the feeder RFT array <NUM> are collocated together at a single RF feeder site <NUM> (which may be referred to as a "location" of the feeder RFT array <NUM> and its feeder RFTs <NUM>), which offers substantial reductions in network costs over other feeder architectures involving multiple feeder sites at different locations.

In some implementations, the feeder RFTs <NUM> are individually steerable via respective beam steering mechanisms. A beam steering mechanism included in a feeder RFT <NUM> may include a mechanical antenna positioner (such as a <NUM>-axis gimbal) configured to selectively orient, for example, a main reflector of the feeder RFT <NUM>, a mechanical antenna feed positioner (which can more rapidly reposition a feed, which has significantly less mass than the main reflector), and/or a phased array antenna. For example, a mechanical antenna positioner can perform coarse/slow positioning and be used in combination with a phased array antenna respond to higher frequency changes in azimuth and elevation of the HAP <NUM>.

In <FIG>, each of the feeder RFTs <NUM> is shown within a respective RFT cell <NUM>, including feeder RFTs 210a, 210b, 210c, 210d, 210e, 210f, <NUM>, <NUM>, and 210n within respective RFT cells 212a, 212b, 212c, 212d, 212e, 212f, <NUM>, <NUM>, and 212n). The RFT cells <NUM> are not physical elements of the feeder RFT array <NUM>, but instead illustrate that the feeder RFTs <NUM> are positioned in a compact arrangement with distances between adjacent feeder RFTs <NUM> that maintains interference among the RF feeder links <NUM> below an acceptable or target level. In the example shown in <FIG>, each of the cells <NUM> is circular and has the same RFT cell diameter <NUM> (as shown for the RFT cell <NUM>). As a result, each feeder RFT <NUM> is at least the distance of the RFT cell diameter <NUM> from any other feeder RFT <NUM>. The RFT cell diameter <NUM> may also be referred to as a minimum distance between individual feeder RFTs <NUM>. It is noted that other shapes and/or sizes can be used for the RFT cells <NUM>, and that shapes, sizes, and or orientations can be different among the RFT cells <NUM>. For example, the RFT cells <NUM> might vary in size in accordance with a distance from a center of the feeder RFT array <NUM>, with larger RFT cells <NUM> around the periphery, to reduce interference at increased zenith distances for the HAP <NUM> at which the feeder RFT array <NUM> is viewed obliquely from the HAP <NUM>. Sizes of the RFT cells <NUM> may account for frequency reuse factor for the RF feeder links <NUM>, which permits for smaller RFT cell sizes. Use of a larger HAP-based RF feeder link antenna <NUM> allows narrower beams to be formed for the RF feeder link <NUM>, which allows for smaller RFT cell sizes to be used. Additionally, an expected maximum operating altitude for the HAP <NUM> will affect the RFT cell sizes.

In <FIG>, the RFT cells <NUM> are positioned in a compact circular arrangement, with all of the RFT cells <NUM> fitting within, and being encompassed by, a circular area <NUM> with a diameter <NUM> (which may also be referred to as a "span" of the feeder RFT array <NUM>). An arrangement of the RFT cells <NUM> that minimizes the diameter <NUM> is considered the most "compact" arrangement of the RFT cells <NUM> and the feeder RFTs <NUM> positioned therein. In <FIG>, the feeder RFTs <NUM> connect with the HAP data center <NUM> by a local network of wire and/or fiber data links (see communication link <NUM>). By reducing the diameter <NUM>, a corresponding land area for installing and operating the RF feeder array <NUM> is reduced, as well as the lengths of power and signal couplings for the RF feeder array <NUM>. Also, the more compact the arrangement of RFTs <NUM>, the less stringent the design requirements will be on the HAP-based RF feeder link antenna <NUM>. Compact arrangements of the feeder RFT array <NUM> minimize the lengths and costs of the local network, in contrast to conventional use of wide area fiber network connections between different cities where RFTs are located. In this example, the <NUM> RFT cells <NUM> are arranged to occupy approximately <NUM>% of the circular area <NUM>. <FIG> also illustrates a square area <NUM> with sides having lengths equal to the diameter <NUM>, which illustrates an example of a tract of land that might be used to construct the RF feeder array <NUM>. Additionally, <FIG> illustrates a second circular area <NUM>, with a diameter <NUM>, which represents a smallest circular area encompassing the center points of the feeder RFTs <NUM>, which closely corresponds an area in which the feeder RFTs <NUM> may all be constructed.

<FIG> illustrates an alternative compact arrangement of the <NUM> feeder RFTs <NUM> shown in <FIG>, with the RFT cells <NUM> arranged hexagonally. However, with this arrangement, the <NUM> RFT cells <NUM> occupy only approximately <NUM>% of the circular area <NUM>, and the diameter <NUM> is increased by about <NUM>% over the more compact arrangement shown in <FIG>. For purpose of further illustration, <FIG> illustrates an example of the feeder RFT array <NUM> with <NUM> feeder RFTs <NUM>, and <FIG> illustrates an example of the feeder RFT array <NUM> with <NUM> feeder RFTs <NUM>. In addition to providing greater numbers of feeder RFTs <NUM>, the examples shown in <FIG> also have rotational symmetry, which can facilitate accommodating rotation of the HAP <NUM> in establishing and/or maintaining the RF feeder links <NUM>.

Tables <NUM>-<NUM> below provide illustrative examples of RFT cell sizing considerations and dimensions for the RFT feeder terminal array <NUM>, with collocation of the feeder RFTs <NUM> at a single location, according to various design parameters for the feeder RFT arrangements shown in <FIG> (with <NUM> feeder RFTs), <FIG> (with <NUM> feeder RFTs), and <FIG> (with <NUM> feeder RFTs). For these examples, it may be assumed each RFT terminal <NUM> would offer <NUM> forward bandwidth (<NUM>-<NUM> with two polarizations in the forward direction, although frequencies of <NUM>-<NUM> in the reverse direction, also with two polarizations, are conservatively represented as <NUM> below to illustrate a maximum spacing) and <NUM> bits/Hz (thus requiring a total of <NUM> forward RF bandwidth for <NUM> Tbps forward data capacity). This would involve at least <NUM> feeder RFTs (as shown in <FIG>) to support <NUM> Tbps forward data capacity. Table <NUM>, below, shows, for two HAP antenna sizes of <NUM> and <NUM>, RFT cell sizing considerations involving a frequency reuse factor of <NUM> and altitudes of <NUM> and <NUM> for the HAP <NUM>. The RFT reuse spacing is computed for a reuse factor of <NUM> and for a hexagonal grid with spacing R · <MAT>, where R is half of the half power beam width (HPBW). Additional margin is added to the calculated spacing to be conservative.

Tables <NUM> and <NUM>, below, show the resulting dimensions for the feeder RFT array <NUM> with <NUM> cells, <NUM> cells, <NUM> cells, and <NUM> cells where the HAP-based RF feeder link antenna <NUM> has a diameter of <NUM>.

Thus, according to the conditions used for Tables <NUM> and <NUM>, the feeder RFT array <NUM>, usable for a forward data capacity of at least <NUM> Tbps, can be constructed with the margins offered by <NUM> feeder RFTs (roughly double those offered by <NUM> feeder RFTs) within diameters <NUM> and <NUM> of less than <NUM> meters, a total operating beam width for the RF feeder links <NUM> of less than <NUM>°, and an FOV of less than <NUM>°. With the margins offered by <NUM> RFTs (roughly <NUM>% more than offered by <NUM> feeder RFTs), the feeder RFT array <NUM> can be constructed within diameters <NUM> and <NUM> of less than <NUM> meters, a total operating beam width for the RF feeder links <NUM> of less than <NUM>°, and an FOV of less than <NUM>°.

Tables <NUM> and <NUM>, below, show the resulting dimensions for the feeder RFT array <NUM> with the same <NUM> cells, <NUM> cells, <NUM> cells, and <NUM> cells, but where the HAP-based RF feeder link antenna <NUM> has a reduced diameter of <NUM>, resulting in increased beam widths for the RF feeder links <NUM>.

Thus, according to the conditions used for Tables <NUM> and <NUM>, the feeder RFT array <NUM>, usable for a forward data capacity of at least <NUM> Tbps, can be constructed with the margins offered by <NUM> feeder RFTs (roughly double those offered by <NUM> feeder RFTs) within a diameter <NUM> of <NUM> meters and a diameter <NUM> of less than <NUM> meters, a total operating beam width for the RF feeder links <NUM> of less than <NUM>°, and an FOV of less than <NUM>°. With the margins offered by <NUM> RFTs (roughly <NUM>% more than offered by <NUM> feeder RFTs), the feeder RFT array <NUM> can be constructed within a diameter <NUM> of <NUM> meters and a diameter <NUM> of less than <NUM> meters, a total operating beam width for the RF feeder links <NUM> of less than <NUM>°, and an FOV of less than <NUM>°. As can be seen from Tables <NUM>-<NUM>, the decrease from <NUM> to <NUM> results in approximately a <NUM>-fold increase in the area for the feeder RFT array <NUM>. Despite this, the providing the RF feeder links <NUM> with a single location can still be significantly more cost effective than architectures involving diversity sites.

As shown in <FIG> and <FIG>, the HAP data center <NUM> is communicatively coupled to the feeder RFT array <NUM> via a communication link <NUM> and is configured to control operation of the feeder RFTs <NUM>, generate forward RF feeder link signals for transmission to the HAP <NUM> via the RF feeder links <NUM>, provide the generated forward RF feeder link signals to the feeder RFTs for transmission, obtain reverse RF feeder link signals received by the feeder RFTs from the HAP <NUM> via the feeder links <NUM>, and process the obtained reverse RF feeder link signals. For example, HAP data center <NUM> may be configured to provide signals to, and receive signals from, the feeder RFTs <NUM> via electronic cables and/or optical fiber included in the communication link <NUM>.

<FIG> illustrates further details of the payload <NUM> of the HAP <NUM> shown in <FIG> and examples of operations performed by the payload <NUM> in connection with the RF feeder links <NUM> and the optical feeder link <NUM>. At the time illustrated in <FIG>, the HAP <NUM> is positioned at an altitude <NUM> directly above the feeder RFT array <NUM> with a zenith distance of <NUM>°. At the bottom of <FIG> is shown a portion of the feeder RFT array <NUM> with <NUM> feeder RFTs <NUM> shown in <FIG>. More specifically, <FIG> shows the feeder RFTs 210a, 210b, 210c, 210d, 210e, 210f, and <NUM>, within their respective RFT cells 212a, 212b, 212c, 212d, 212e, 212f, and <NUM>. A plurality of RF feeder links <NUM> are concurrently operating between the feeder RFT array <NUM> and the HAP <NUM>, including RF feeder links 310a, 310b, 310c, 310d, 310e, 310f, and <NUM>, corresponding to respective feeder RFTs 210a, 210b, 210c, 210d, 210e, 210f, and <NUM>, including their respective reverse RF feeder links 312a, 312b, 312c, 312d, 312e, 312f, and <NUM> (transmitted by respective feeds of the RF feeder link antenna <NUM> and having expanded to the shaded areas in the bottom portion of <FIG>) and their respective forward RF feeder links 314a, 314b, 314c, 314d, 314e, 314f, and <NUM> (transmitted by the feeder RFT array <NUM> and received by respective feeds of the RF feeder link antenna <NUM>).

<FIG> shows various angles with respect to the RF feeder link antenna <NUM> (which may also be referred to as FOV angles). The illustrated angles are dependent on the altitude <NUM> and, for some of the illustrated angles, by the zenith direction of the HAP <NUM> relative to the feeder RFT array <NUM>. For purposes of the description of these angles in <FIG>, RF feeder link antenna <NUM> has a diameter of <NUM>, the HAP is at an altitude <NUM> of <NUM>, all of the reverse RF feeder links are at a frequency of <NUM>, and the corresponding portions of Tables <NUM>-<NUM> apply. Angle θ<NUM> is an angular beam width of the reverse RF feeder link 312f, such as a half power beam width (HPBW); in this example, angle θ<NUM> is approximately <NUM>°. In this example, all of the reverse RF feeder links have approximately the same angular beam width. Angle θ<NUM> is an angular separation of adjacent feeder RFTs 310b and 310c. Angle θ<NUM> is an angular width of the RFT cell 212d. In this example, all of the RFT cells <NUM> have approximately the same diameter of <NUM> meters and angles θ<NUM> and θ<NUM> are both approximately <NUM>°. Angle θ<NUM> is the angular width of the circular area <NUM> (with diameter <NUM> at ground level); approximately <NUM>° in this example. Angle θ<NUM> is the angular width of the smallest circle encompassing the beam widths of the reverse RF feeder links; approximately <NUM>° in this example. Angle θ<NUM> is the angular width of the circular area <NUM> (with diameter <NUM> at ground level); approximately <NUM>° in this example.

The payload <NUM> includes a power supply <NUM> to supply power to the various components of the payload <NUM>. The power supply <NUM> may include a rechargeable battery. In other embodiments, the power supply <NUM> may additionally or alternatively include other means known in the art for producing power. In addition, the HAP <NUM> may include a solar power generation system, such as a thin film photovoltaic surface included in the envelope <NUM>. The solar power generation system may include solar panels and could be used to generate power that charges and/or is distributed by the power supply <NUM>.

The payload <NUM> includes one or more processors <NUM> and on-board data storage (not shown in <FIG>) including instructions which, when executed by the processors <NUM>, cause the payload <NUM> to perform the operations described herein. The payload <NUM> also includes various sensors <NUM> that may be used to determine changes in position and orientation of the payload <NUM> and capture environmental data, and the payload <NUM> is configured to determine changes in position and orientation of the payload <NUM> (including, for example, changes in position and orientation of the RF feeder link antenna <NUM> and/or the telescope <NUM>) based on at least sensor data obtained from the sensors <NUM>. The sensors <NUM> may include, for example, one or more video and/or still cameras, a satellite positioning system (for example, GPS or GLONASS), various motion sensors (for example, accelerometers, gyroscopes, and/or compasses), a star field tracker for orientation estimation based on celestial objects, and environmental sensors operable to measure environmental data such as, but not limited to, pressure, altitude, temperature, relative humidity, and/or wind speed and/or direction.

The payload <NUM> includes an RF feeder communication system <NUM> that is configured to transmit and receive RF signals for the RF feeder links <NUM>. The RF feeder communication system <NUM> includes a forward RF feeder link receiver <NUM> (labeled "RF RX" in <FIG>) configured to receive multiple forward RF feeder links from the feeder RFT array <NUM>. The RF feeder communication system <NUM> also includes a reverse RF feeder link transmitter <NUM> (labeled "RF TX" in <FIG>) configured to concurrently transmit multiple reverse RF feeder links to respective feeder RFTs of the feeder RFT array <NUM>. The RF feeder communication system <NUM> includes a beam orientation controller <NUM>, which is configured to maintain the beams of the HAP-based RF feeder link antenna <NUM> in orientations toward their respective feeder RFTs <NUM> while the payload <NUM> moves around, such as by issuing commands to mechanical actuators and/or a phase array antenna.

The payload <NUM> also includes the optical feeder communication system <NUM> that is configured to transmit the forward optical feeder link <NUM> to the satellite <NUM> and receive the reverse optical feeder link <NUM> from the satellite <NUM>. The optical feeder communication system <NUM> includes a steerable telescope <NUM> with an aperture <NUM>. The optical feeder communication system <NUM> includes an forward optical feeder link transmitter <NUM> (labeled "OPTICAL TX" in <FIG>) configured to generate the forward optical feeder link <NUM> from signals received via the RF feeder links <NUM>. The optical feeder communication system <NUM> also includes an reverse optical feeder link receiver <NUM> (labeled "OPTICAL RX" in <FIG>) configured to receive the reverse optical feeder link <NUM> and convert it into a signal suitable for generating portions of the RF feeder links <NUM>.

The optical feeder communication system <NUM> also includes a PAT controller <NUM>, which is configured to accurately and precisely perform optical pointing for the optical feeder link <NUM> between the payload <NUM> and the satellite <NUM> using commands to a pointing mechanism <NUM> for the telescope <NUM> while the payload <NUM> moves around. For example, the commands may be generated based on at least information received from the sensors <NUM> and/or optical sensing devices included in the optical feeder communication system <NUM> (such as, but not limited to, an optical quadrant detector and/or pixel-based optical detector receiving a portion of the reverse optical feeder link <NUM> via a beamsplitter). The pointing mechanism <NUM> may include multiple different actuators such as, but not limited to, a <NUM>-D or <NUM>-D gimbal for slow and coarse pointing of the telescope <NUM>, and one or more steered optical elements (such as, but not limited to, two-axis steering of a low mass secondary optical element, such as a secondary reflector) that perform rapid and fine pointing of the optical feeder link <NUM>. In some examples, the PAT controller <NUM> attempts to ensure that the satellite <NUM> (or an optical signal emitted by the satellite) remains in an FOV of the telescope <NUM>, and rapidly adjusts a pointing angle of a low-mass secondary optical element to more precisely target the optical feeder link <NUM>. In some implementations, the optical feeder communication system <NUM> may be configured to do wavefront correction of the optical feeder link <NUM> to counter atmospheric turbulence encountered by the optical feeder link <NUM>. In some implementations, optical beam pointing may be performed in whole or in part by means of phased-array optics.

The HAP <NUM> may be configured for altitude control. For instance, the HAP <NUM> may include a variable buoyancy system, which is configured to change the altitude <NUM> of the HAP <NUM> by adjusting the volume and/or density of the gas in the envelope <NUM>. A variable buoyancy system may take various forms and may generally be any system that can change the volume and/or density of gas in envelope <NUM>. In some examples, the HAP <NUM> may include a propulsion system used to perform station keeping.

The telecommunication system <NUM> may include a navigation system for the HAP <NUM>. The navigation system may implement station-keeping functions to maintain position within and/or move to a target position. In some examples, the navigation system may use altitudinal wind data to determine altitudinal adjustments that result in the wind carrying the HAP <NUM> in a desired direction and/or to a desired location. The altitude-control system may then make adjustments to the density of the envelope <NUM> in order to effectuate the determined altitudinal adjustments and cause the HAP <NUM> to move horizontally to the desired direction and/or to the desired location. The altitudinal adjustments may be computed by the HAP data center <NUM> and communicated to the HAP <NUM>.

In some implementations, motion stabilization performed by the beam orienting controller <NUM> and/or the PAT controller <NUM> may be implemented using a Kalman filter utilizing sensor data, such as from the sensors <NUM>, and a last-known motion vector for the payload <NUM> as inputs to the Kalman filter that could output a predicted relative location, pose, and control signals for stabilization to adjust the pointing axis based on the predicted relative location and/or pose. The Kalman filter could be performed many times per second. For instance, PAT controller <NUM> could control the pointing mechanism <NUM> for the telescope <NUM> to move from an initial axis towards a predicted target axis in an effort to compensate for motion of the payload <NUM> and to maintain the optical feeder link <NUM> with the satellite <NUM>. The Kalman filter method could use as inputs various sensor data (e.g., GPS data, inertial navigation data, camera images, etc.) so as to generate predicted values. The system state predictions from the Kalman filter method may typically be more accurate than, for instance, utilizing data from only one sensor, as data from many types of sensors include noise, jitter, and generally imperfect sensor data.

The Kalman filter cycle could involve two main phases: a prediction phase and an update phase. In the prediction phase, the payload <NUM> could predict the current pose using a physical model of the payload <NUM>, the HAP <NUM>, and its environment plus any perturbations to other system variables, for instance, wind velocity, heading, and acceleration. Additionally, a covariance (a measure of how much two random variables, such as wind velocity and HAP <NUM> pose or payload <NUM> pose, change together) related to the predicted pose could be calculated. In the update phase, the payload <NUM> could receive GPS data or data relating to one or more RF feeder links <NUM> and/or the optical feeder link <NUM> indicating a degree to which they are accurately positioned. The positioning data could be used to update the initial predicted pose to obtain an updated pose. The predicted and updated poses could be used as inputs and weighted based on their associated covariances. The output of the Kalman filter method could provide a predicted pose that could be thus used to adjust the pointing angle of the RF feeder link antenna <NUM> or telescope <NUM> so as to maintain the RF feeder links <NUM> or the optical feeder link <NUM>.

In some implementations, diversity may be provided by having multiple HAPs <NUM> and/or having multiple RF feeder terminal arrays <NUM> at multiple different sites. An optical fiber distribution network could be used to connect multiple diverse sites, each capable of serving the entire feeder link needs, and preferably offering sites with weather conditions that are generally uncorrelated with weather conditions at other sites. In general, only one station would be active at a time. Both the satellite and the ground network would be configured to coordinate the diversity switching operations. Determining the number and locations of the diverse sites would be a system engineering activity using cloud statistics from various weather satellites such as MODIS, AQUA, and TERRA. Research on climate change and weather forecasting has created a massive cloud database called the Global Energy and Water cycle Experiment (GEWEX) Cloud Assessment Database; such a database may be utilized for these determinations.

<FIG> illustrates further details of the satellite <NUM> shown in <FIG> and examples of operations performed by the satellite <NUM> in connection with the optical feeder link <NUM> with the HAP <NUM> and the RF service links <NUM> with end user RFTs <NUM>. In some examples, the satellite <NUM> is configured to transmit a beacon beam <NUM>, with a higher divergence than the reverse optical feeder link <NUM> (for example, from about <NUM> milliradian to about <NUM> milliradians), which can be used by the optical feeder communication system <NUM> to more quickly acquire the optical feeder link <NUM> with the satellite <NUM>. In some examples, the HAP <NUM> is also configured to transmit a beacon beam toward the satellite <NUM> to assist the optical feeder communication system <NUM> in more quickly acquiring the optical feeder link <NUM> with the HAP <NUM>. The satellite-based optical feeder communication system <NUM> operates much as described for the HAP-based optical feeder communication <NUM>, including performing steering of an optical telescope <NUM> with an aperture <NUM>. As noted previously, as the satellite <NUM> does not undergo the degree and frequency of motion changes experienced by the platform <NUM>, it is practical for telescope <NUM> to have a larger aperture <NUM> to increase gain for the optical feeder link <NUM>. As the diameter of the reverse optical feeder link <NUM> is smaller than the range that the HAP <NUM> may operate, steering of the reverse optical feeder link <NUM> is required.

Although, as in <FIG>, only three spot beams 172a, 172b, 172c are shown for the satellite <NUM>, in many implementations there is a larger number of spot beams <NUM>; for example, there may be hundreds or over one thousand spot beams <NUM>.

<FIG> illustrates an example of generating from network data a forward RF feeder link included in a high capacity set of forward RF feeder links, as may be performed under control of, and performed at least in part by, the HAP data center <NUM> shown in <FIG> and <FIG>. In this example, generation of one of the <NUM> forward RF feeder links, the forward RF feeder link 314a, is shown. This is performed in parallel and in real-time for each of the forward RF feeder links in the RF feeder links <NUM>, resulting in a total of <NUM> Tbps of forward data capacity from the HAP data center <NUM> to the payload <NUM> of the HAP <NUM>.

The HAP data center <NUM> receives from the gateway <NUM> a respective forward feeder link data stream for each of the spot beams <NUM>. <FIG> shows the HAP data center <NUM> receiving <NUM> spot beam forward feeder link data streams. The HAP data center <NUM> is configured to multiplex upstream signals for multiple spot beams <NUM> into forward feeder link beam (which may also be referred to as a "forward feeder channel" or an "uplink feeder channel"). In the examples shown in <FIG>, a forward feeder link beam will not be demultiplexed into its constituent spot beams until it is received by the satellite <NUM>. As shown in <FIG>, two forward RF feeder link beams are generated for and concurrently transmitted by each active feeder RFT <NUM> in a respective forward RF feeder link <NUM>. A first forward RF feeder link beam 560a (in <FIG>, "Beam <NUM>") is transmitted by a feeder RFT <NUM> (in <FIG>, feeder RFT 210a) with right hand circular polarization (RHCP), and a second forward RF feeder link beam 560b (in <FIG>, "Beam <NUM>") is transmitted by the same feeder RFT <NUM> with left hand circular polarization (LHCP). The HAP data center <NUM> includes and operates a respective forward RF feeder link beam generator <NUM> for each of the forward RF feeder link beams <NUM>. In <FIG>, a first forward RF feeder link beam generator 510a receives <NUM> spot beam forward feeder link data streams 502a (labeled "Beam <NUM>, Spot <NUM>" through "Beam <NUM>, Spot <NUM>") and generates the corresponding first forward RF feeder link beam 560a for forward RF feeder link 314a, and a second forward RF feeder link beam generator 510b receives an additional <NUM> spot beam forward feeder link data streams 502b (labeled "Beam <NUM>, Spot <NUM>" through "Beam <NUM>, Spot <NUM>") and generates a corresponding second forward RF feeder link beam 560b for dual polarization forward RF feeder link 314a. In some examples, the RHCP and LHCP RF signals included in the forward RF feeder link 314a may be considered two separate forward RF feeder links transmitted by the same feeder RFT 210a.

The first forward RF feeder link beam generator 510a includes an encoder <NUM>, a modulator <NUM>, and an up-converter ("UpCo") <NUM> for each of the spot beam forward feeder link data streams 502a (for example, in <FIG>, the first forward RF feeder link beam generator 510a includes <NUM> encoders 520aa through 520aj, <NUM> respective modulators 522aa through 522aj, and respective <NUM> up-converters 530aa through 530aj for the <NUM> respective spot beam forward feeder link data streams 502a). Each encoder <NUM> is configured to encode a respective spot beam forward feeder link data stream according to a selected forward error correction (FEC) technique, and a supported FEC may be performed according to one or more provided parameters (for example, an FEC rate). Each modulator <NUM> is configured to modulate its spot beam forward feeder link data stream according to a selected MODCOD scheme, and a supported MODCOD may be performed according to one or more provided parameters. The HAP data center <NUM> is configured to specify a FEC technique, a MODCOD scheme, and associated parameters, and the HAP data center <NUM> may choose the FEC technique, the MODCOD scheme, and/or parameters according to instructions received from the gateway <NUM>. Different FEC techniques, MODCOD schemes, and/or parameters may be applied to spot beam forward feeder link data streams in the same forward feeder link beam. In some implementations, the HAP data center <NUM> may use DVB-S2X Adaptive Coding and Modulation to select which FEC and MODCOD is used. In this example, the FEC encoding results in <NUM> Gbps data streams, and the applied modulation has a spectral efficiency of <NUM> bits/Hz, resulting in a <NUM> baseband signal for each of the spot beam forward feeder link data streams. With <NUM> spot beam forward feeder link data streams multiplexed into <NUM> forward feeder link beams, the <NUM> forward RF feeder links deliver <NUM> Tbps of total forward data capacity to the HAP <NUM>.

<FIG> illustrates an example of generating, at the HAP <NUM>, the forward optical feeder link <NUM> from the high capacity set of RF feeder links <NUM> received from the feeder RFT array <NUM>, including, for example, the forward RF feeder link 314a shown in <FIG>. In this example, <NUM> forward RF feeder link beams are received via <NUM> forward RF feeder links, each forward RF feeder link beam is downconverted to a lower RF band (for example, with a downconverter, or "DoCo," such as downconverters 640aa and 640ab), and the downconverted RF signal is modulated onto a laser beam with an optical wavelength assigned to the forward feeder link beam (for example, Beam <NUM> is modulated onto an optical beam with wavelength λ<NUM>, Beam <NUM> at wavelength λ<NUM>, and so on) using an electrical to optical (EO) converter (for example, by applying radio over fiber, or "RoF," techniques, such as with EO converters 650aa and 650bb). In some examples, a Mach Zehnder Modulator is used for the electrical to optical modulation. In some implementations, as shown in <FIG>, each beam is assigned to a respective WDM channel (for example, a DWDM channel) with a respective wavelength. In some implementations, multiple beams may be downconverted to different frequencies and together be assigned to a WDM channel; for example, Beams <NUM> and <NUM> could be modulated onto an optical beam with a first wavelength, Beams <NUM> and <NUM> modulated onto an optical beam with a different second wavelength, and so on. <NUM> defines a DWDM spectral grid for the ITU C-, L-, and S-bands with channel spacings ranging from <NUM> to <NUM>. For example, with <NUM> channel spacing, the ITU C-band and the ITU L-band can each be used to provide <NUM> channels. Use of different wavelength bands may permit a duplex optical transceiver that transmits in one of the C-, S-, or L-band and receives in a different one of the C-, S-, or L-band. A WDM multiplexer <NUM> combines the <NUM> optical signals into a single multiplexed optical signal <NUM>, which is provided to an optical amplifier <NUM>, such as a doped fiber amplifier (for example, a Erbium, Ytterbium, or Thulium-doped fiber amplifier), tapered amplifier, semiconductor optical amplifier, Raman amplifier, and/or a parametric amplifier to produce the forward optical feeder link <NUM> for transmission to the satellite <NUM>. In some implementations, optical amplification may be performed before WDM multiplexing. The multiplexed forward optical feeder link <NUM> uses <NUM> WDM channels, each used to carry <NUM> of capacity, for a total of <NUM> of bandwidth providing <NUM> Tbps forward data capacity.

<FIG> illustrates an example of the satellite <NUM> shown in <FIG> and <FIG> converting the forward optical feeder link <NUM> received from the HAP <NUM> into corresponding RF service links <NUM> for multiple spot beams <NUM>. First, the received WDM forward optical feeder link <NUM> is amplified by an optical amplifier <NUM> to an optical power level of at least <NUM> mW. The resulting amplified WDM forward optical feeder link <NUM> is provided to a WDM demultiplexer <NUM>, which is configured to demultiplex the amplified forward optical feeder link <NUM> into its constituent WDM channels (which may be referred to as "optical channel signals") with respective wavelengths λ<NUM>, λ<NUM>,. As shown in more detail for the wavelength λ<NUM>, the WDM channels for each of the wavelengths λ<NUM> - λ<NUM> are converted into demultiplexed RF spot beam signals similar to those output by the modulators <NUM> in <FIG>. The demultiplexed RF spot beam signals are "colored" for frequency reuse by upconverting them to appropriate frequencies (for example, frequencies in the Ka-, Ku-, and/or Q-bands) and applying either right hand circular polarization or left hand circular polarization. The resulting RF spot beam signals are transmitted by the satellite-based RF communication system <NUM> as forward RF service links <NUM> via the spot beams <NUM> of the RF service links <NUM> for receipt, demodulation, and decoding to retrieve the data originally provided in the spot beam forward feeder link data streams to the forward RF feeder link beam generators <NUM> of the HAP data center <NUM>.

The examples shown in <FIG> illustrate essentially an "analog transparent architecture" or "bent-pipe architecture," in which the modulation and coding initially transmitted by the feeder RFT array <NUM> in the forward direction, or initially transmitted by the end-user satellite RFTs <NUM> in the reverse direction, is not changed by the HAP <NUM> or the satellite <NUM>. This allows for changes in modulation schemes to be employed in both the forward and reverse directions without changes to the hardware of the HAP <NUM> or the satellite <NUM> and allows the HAP data center <NUM> to implement technologies such as ground-based beam forming or other precoding techniques.

However, regenerative retransmission techniques can be performed at the HAP and/or satellite, in which received signals are demodulated, error corrected, and remodulated (in some instances with a different modulation scheme than in the received signal). A drawback of regenerative retransmission is a substantial power requirement at terabit per second data rates on platforms with limited power and already substantial power requirements.

<FIG> illustrate examples of station-keeping and handover operations performed among a plurality of HAPs being operated as part of the telecommunication system <NUM>, as described for the HAP <NUM> in <FIG>, <FIG>, <FIG>, and <FIG>. Issues such as a leaking or torn envelope <NUM> or unscheduled repairs can unexpectedly take a currently operating HAP out of service with little to no notice. Additionally, HAPs may be returned to earth periodically for routine maintenance and hardware or software upgrades.

In <FIG>, a first HAP payload <NUM> and a second HAP payload <NUM> are operating at approximately a first altitude <NUM> in proximity to the feeder RFT array <NUM>, with the first HAP payload <NUM> at a zenith distance θ804a relative to the feeder RFT array <NUM>, and the second HAP payload <NUM> at a zenith distance θ814a. The first HAP payload <NUM> is operating RF service links <NUM> at their full capacity and operating corresponding forward optical feeder link <NUM> and reverse optical feeder link <NUM> with the satellite <NUM>. To be prepared to handover the operations of the first HAP payload <NUM> to the second HAP payload <NUM>, the optical feeder communication system of the second HAP payload <NUM> is performing PAT of the satellite <NUM> by use of an optical beacon signal <NUM> transmitted by the satellite <NUM>, and the RF feeder communication system of the second HAP payload <NUM> is tracking the feeder RFT array <NUM> via RF transmissions by one or more feeder RFTs <NUM> included in the feeder RFT array <NUM>. Additionally, via optical communication terminals <NUM> and <NUM> in respective HAP payloads <NUM> and <NUM>, a bidirectional optical link is established and maintained between the HAP payloads <NUM> and <NUM>.

<FIG> illustrates an example in which a handover operation is performed from the first HAP payload <NUM> to the second HAP payload <NUM>. In this example, the first HAP payload <NUM> is at an altitude <NUM> and an increased horizontal distance <NUM> from the feeder RFT array <NUM>, with the first HAP payload <NUM> being at an increased zenith distance θ804b relative to the feeder RFT array <NUM>. The second HAP payload <NUM> is at a zenith distance θ814b that allows it to operate the RF feeder links <NUM> at their full capacity. Thus, a handoff operation is performed from the first HAP payload <NUM> to the second HAP payload <NUM>, in which the feeder RFT array <NUM> establishes new RF feeder links with the second HAP payload <NUM>, and the second HAP payload <NUM> operates the optical feeder links <NUM> and <NUM> with the satellite. With the second HAP payload <NUM> having made preparations to service as a "hot spare" as shown in <FIG>, this handoff may be performed with very little interruption in service between the feeder RFT array <NUM> and the satellite <NUM>. The first HAP payload <NUM> may perform operations to be prepared as a "hot spare," including performing PAT of the optical beacon <NUM>, in the event that the first HAP payload <NUM> ends up in a position suitable for that purpose. In some circumstances, a third HAP payload <NUM> may be launched, whether in response to the handover, a prediction of the handover, or other considerations for operation of a fleet of HAPs, to eventually operate as a "hot spare" as done by the second HAP payload <NUM> in <FIG>.

<FIG> illustrates an example arrangement of the fleet of three HAP payloads <NUM>, <NUM>, and <NUM> after <FIG>. In <FIG>, the first HAP payload <NUM> is returning to the surface for maintenance and/or refueling, and is no longer making efforts to operate as a "hot spare. " Additionally, the third HAP payload <NUM> has reached a position in which it is able to operate as a "hot spare. " Accordingly, the second HAP payload <NUM> and the third HAP payload <NUM> have effectively assumed the roles previously shown for the first HAP payload <NUM> and the second HAP payload <NUM> respectively in <FIG>.

<FIG> illustrate examples in which the RF feeder links <NUM> are operated with degradation in capacity in accordance with a zenith distance and azimuth of the HAP <NUM> relative to the feeder RFT array <NUM>. Such graceful degradation in capacity may be useful in circumstances in which a HAP currently providing all, or a significant portion, of the capacity has moved away from the feeder RFT array <NUM>, but there is not another HAP immediately available to fully handover to. In <FIG>, the HAP <NUM> is at a zenith distance θ<NUM> similar to the zenith distance θ804a shown for the first HAP payload <NUM> in <FIG>. <FIG> includes an azimuth indicator <NUM> to more conveniently illustrate the azimuth θ<NUM> of the HAP <NUM> with respect to the feeder RFT array <NUM> (which has the arrangement of <NUM> feeder RFTs <NUM> illustrated in <FIG>). At the zenith distance θ<NUM>, a small portion of the feeder RFTs <NUM> opposite the azimuth indicator <NUM> are at too oblique of an angle from the viewpoint of the HAP <NUM> for that portion of feeder RFTs <NUM> to be operated without RF interference between them. For example, at the zenith distance θ<NUM>, if feeder RFTs <NUM> and 210i are both active, there will be an unacceptable amount of RF interference between their respective RF feeder links, and if feeder RFTs 210i and 210j are both active, there will be an unacceptable amount of RF interference between their respective feeder links. This will cause the signal-to-noise plus interference ratio (SINR) to decrease for each of the forward and reverse RF feeder links for those feeder RFTs <NUM>. In response to this, <NUM> feeder RFTs <NUM> (including the feeder RFT 210i) that were previously operating RFT feeder links <NUM> are disabled or otherwise removed from the RFT feeder links <NUM> between the HAP <NUM> and the feeder RFT array <NUM>. As a result, RF interference between the active RF feeder links <NUM> is avoided; for example, feeder RFTs <NUM> and 210j can both remain active without interfering with each other.

In <FIG>, the HAP <NUM> has moved to a position with an increased zenith distance θ<NUM>, and in response a total of <NUM> of the feeder RFTs <NUM> (including a feeder RFT <NUM>) have been disabled to allow their neighboring feeder RFTs to operate as RF feeder links <NUM> with the HAP <NUM> without interference. In <FIG>, the HAP <NUM> has advanced to another position to a further increased zenith distance θ<NUM>, and in response a total of <NUM> of the feeder RFTs <NUM> (including a feeder RFT <NUM>) have been disabled. At this point, the RF feeder links <NUM> are performing at roughly half of their full capacity, depending on the margins offered by the full set of <NUM> feeder RFTs <NUM> (as this may provide excess capacity to absorb such degradation to a certain degree). In <FIG>, the HAP <NUM> as advanced to another position, with a zenith distance θ<NUM> similar to the zenith distance θ<NUM> in <FIG>, but at a much different azimuth θ<NUM>. Although a same number of feeder RFTs <NUM> are disabled (including a feeder RFT 210n) as in <FIG>, the selection of the disabled RFTs <NUM> is responsive to the azimuth θ<NUM>.

11E-G illustrate an example of an alternative approach in which the RF feeder links <NUM> are operated with degradation in capacity in accordance with a zenith distance and azimuth of the HAP <NUM> relative to the feeder RFT array <NUM>. 11E illustrates an alternative compact arrangement of the <NUM> feeder RFTs <NUM> shown in <FIG> and <FIG>, with the RFT cells <NUM> for the <NUM> feeder RFTs <NUM> (including a feeder RFT 201o) arranged hexagonally. 11F, the feeder RFT array <NUM> includes an additional <NUM> spare feeder RFTs <NUM> (including a spare feeder RFT 210p) positioned around the periphery of the feeder RFTs <NUM> shown in FIG. When the HAP <NUM> is positioned directly above the feeder RFT array <NUM> shown in FIG. 11F, the central feeder RFTs <NUM> are in active operation, with respective RF feeder links <NUM> established with the HAP <NUM>, and the spare feeder RFTs are inactive. This arrangement of active and inactive feeder RFTs <NUM> and spare feeder RFTs <NUM> may be used while the zenith distance and azimuth of the HAP <NUM> does not result in an unacceptable amount of interference occurring between neighboring RFTs <NUM>.

<NUM>, the HAP <NUM> is at a zenith distance θ<NUM> similar to the zenith distance θ<NUM> shown in <FIG> and at an azimuth θ<NUM> similar to the azimuth θ<NUM> shown in <FIG>. <NUM> includes an azimuth indicator <NUM> to more conveniently illustrate the azimuth θ<NUM> of the HAP <NUM> with respect to the feeder RFT array <NUM> (which has the arrangement of feeder RFTs <NUM> and spare feeder RFTs <NUM> illustrated in FIG. Much as in <FIG>, at the zenith distance θ<NUM>, a small portion of the feeder RFTs <NUM> opposite the azimuth indicator <NUM> are at too oblique of an angle from the viewpoint of the HAP <NUM> for that portion of the feeder RFTs <NUM> to be operated without RF interference between them. In response to this, <NUM> of the feeder RFTs <NUM>, positioned to the right of the line <NUM> (including a feeder RFT 210q) are selectively deactivated, and <NUM> (the same number, if available, and to the left of the line <NUM>) of the spare feeder RFTs <NUM> (including the spare feeder RFT 210p) are selectively activated with respective RF feeder links <NUM> operated with the HAP <NUM>, with the remaining feeder RFTs <NUM> (including the feeder RFT 210o) remaining active and the remaining spare feeder RFTs <NUM> (including a spare RFT feeder 210r) remaining inactive. The arrangement of active and inactive RFTs <NUM> and spare RFTs <NUM> is determined based on at least the zenith distance θ<NUM> and/or the azimuth θ<NUM> of the HAP <NUM>. Additionally, in response to a feeder RFT <NUM> being deactivated for maintenance or repair, a spare RFT <NUM> may be activated to maintain a total number of RF feeder links <NUM>.

It is noted that although above FIGS. 11A-<NUM> are described in terms of feeder RFTs <NUM> being in active or inactive states, other changes in operation of the feeder RFT array <NUM> and the RFT feeder links <NUM> may be performed in response to changes in the zenith distance and/or the azimuth of the HAP <NUM> with respect to the feeder RFT array <NUM>. Such changes may also involve the selection of feeder RFTs <NUM> in arrangements similar to those described for FIGS. For example, encoding and/or modulation parameters may be changed to increase the error protection on interfering RF feeder links. This will maintain the error rate at an acceptable level at a cost of reducing the efficiency and data throughput of those RF feeder links. As the error increases, the total data throughput for the active RF feeder links <NUM> may become unacceptably low (for example, falling below a threshold value). In such cases, portions of the feeder RFTs <NUM> may be selectively deactivated and/or activated as described for FIGS. In part, these changes, and the changes described in FIGS. 11A-<NUM>, may be performed in response to closed loop signal quality monitoring.

<FIG> show other approaches in which degraded capacity can be provided between a HAP and the feeder RFT array <NUM>, but in which other HAPs pick up the remaining capacity. In <FIG>, there are first and second HAPs <NUM> at respective zenith distances θ<NUM> and θ<NUM>, which are both approximately the same as the zenith distance θ<NUM> in <FIG>, and are at respective azimuths θ<NUM> and θ<NUM>. (with corresponding azimuth indicators <NUM> and <NUM>). The feeder RFTs <NUM> of the feeder RFT array <NUM> are all active, with the telecommunication system <NUM> being configured to associate each RF feeder link <NUM> with either the first HAP <NUM> or the second HAP <NUM> based on their respective zenith distances θ<NUM> and θ<NUM> and their respective azimuths θ<NUM> and θ<NUM>. In this example, <NUM> of the feeder RFTs <NUM> (including a feeder RFT <NUM>) are linked with the first HAP <NUM>, and the remaining <NUM> of the feeder RFTs <NUM> (including a feeder RFT 210t) are linked with the second HAP <NUM>. An optical link between the first and second HAPs <NUM> and <NUM> may be used to relay feeder data between the two HAPs <NUM> and <NUM> while operating only a single optical feeder link between a satellite and just one of the HAPs <NUM> and <NUM>. With this arrangement,.

<FIG> illustrates a similar example involving three HAPs <NUM>, <NUM>, and <NUM> with active RF feeder links <NUM> with the feeder RFT array <NUM>. In <FIG>, the three HAPs <NUM>, <NUM>, and <NUM> are at respective azimuths θ<NUM>, θ<NUM>, and θ<NUM>. (with corresponding azimuth indicators <NUM>, <NUM>, and <NUM>). The feeder RFTs <NUM> of the feeder RFT array <NUM> are all active, with the telecommunication system <NUM> being configured to associate each RF feeder link <NUM> with one of the HAPs <NUM>, <NUM>, and <NUM> based on their respective zenith distances (not shown in <FIG>) and their respective azimuths θ<NUM>, θ<NUM>, and θ<NUM>. In this example, <NUM> of the feeder RFTs <NUM> (including a feeder RFT 210u) are linked with the HAP <NUM>, <NUM> of the feeder RFTs <NUM> (including a feeder RFT 210v) are linked with the HAP <NUM>, and the remaining <NUM> of the feeder RFTs <NUM> (including a feeder RFT 210w) are linked with the HAP <NUM>.

The detailed examples of systems, devices, and techniques described in connection with <FIG> are presented herein for illustration of the disclosure and its benefits. Such examples of use should not be construed to be limitations on the logical process implementations of the disclosure, nor should variations of user interface methods from those described herein be considered outside the scope of the present disclosure. In some implementations, various features described in <FIG> are implemented in respective modules, which may also be referred to as, and/or include, logic, components, units, and/or mechanisms. Modules may constitute either software modules (for example, code embodied on a machine-readable medium) or hardware modules.

In some examples, a hardware module may be implemented mechanically, electronically, or with any suitable combination thereof. For example, a hardware module may include dedicated circuitry or logic that is configured to perform certain operations. For example, a hardware module may include a special-purpose processor, such as a field-programmable gate array (FPGA) or an Application Specific Integrated Circuit (ASIC). A hardware module may also include programmable logic or circuitry that is temporarily configured by software to perform certain operations, and may include a portion of machine-readable medium data and/or instructions for such configuration. For example, a hardware module may include software encompassed within a programmable processor configured to execute a set of software instructions. It will be appreciated that the decision to implement a hardware module mechanically, in dedicated and permanently configured circuitry, or in temporarily configured circuitry (for example, configured by software) may be driven by cost, time, support, and engineering considerations.

Accordingly, the phrase "hardware module" should be understood to encompass a tangible entity capable of performing certain operations and may be configured or arranged in a certain physical manner, be that an entity that is physically constructed, permanently configured (for example, hardwired), and/or temporarily configured (for example, programmed) to operate in a certain manner or to perform certain operations described herein. As used herein, "hardware-implemented module" refers to a hardware module. Considering examples in which hardware modules are temporarily configured (for example, programmed), each of the hardware modules need not be configured or instantiated at any one instance in time. For example, where a hardware module includes a programmable processor configured by software to become a special-purpose processor, the programmable processor may be configured as respectively different special-purpose processors (for example, including different hardware modules) at different times. Software may accordingly configure a particular processor or processors, for example, to constitute a particular hardware module at one instance of time and to constitute a different hardware module at a different instance of time. A hardware module implemented using one or more processors may be referred to as being "processor implemented" or "computer implemented.

Where multiple hardware modules exist contemporaneously, communications may be achieved through signal transmission (for example, over appropriate circuits and buses) between or among two or more of the hardware modules. In implementations in which multiple hardware modules are configured or instantiated at different times, communications between such hardware modules may be achieved, for example, through the storage and retrieval of information in memory devices to which the multiple hardware modules have access. For example, one hardware module may perform an operation and store the output in a memory device, and another hardware module may then access the memory device to retrieve and process the stored output.

In some examples, at least some of the operations of a method may be performed by one or more processors or processor-implemented modules. For example, at least some of the operations may be performed by, and/or among, multiple computers (as examples of machines including processors), with these operations being accessible via a communication network (for example, the Internet) and/or via one or more software interfaces (for example, an application program interface (API)). The performance of certain of the operations may be distributed among the processors, not only residing within a single machine, but deployed across a number of machines. Processors or processor-implemented modules may be located in a single geographic location (for example, within a home or office environment, or a server farm), or may be distributed across multiple geographic locations.

<FIG> is a block diagram <NUM> illustrating an example software architecture <NUM>, various portions of which may be used in conjunction with various hardware architectures herein described, which may implement any of the above-described features. <FIG> is a non-limiting example of a software architecture and it will be appreciated that many other architectures may be implemented to facilitate the functionality described herein. A representative hardware layer <NUM> includes a processing unit <NUM> and associated executable instructions <NUM>. The executable instructions <NUM> represent executable instructions of the software architecture <NUM>, including implementation of the methods, modules and so forth described herein. The hardware layer <NUM> also includes a memory/storage <NUM>, which also includes the executable instructions <NUM> and accompanying data. The hardware layer <NUM> may also include other hardware modules <NUM>. Instructions <NUM> held by processing unit <NUM> may be portions of instructions <NUM> held by the memory/storage <NUM>.

The frameworks <NUM> (also sometimes referred to as middleware) provide a higher-level common infrastructure that may be used by the applications <NUM> and/or other software modules. For example, the frameworks <NUM> may provide various graphic user interface (GUI) functions, high-level resource management, or high-level location services. The frameworks <NUM> may provide a broad spectrum of other APIs for applications <NUM> and/or other software modules.

The applications <NUM> include built-in applications <NUM> and/or third-party applications <NUM>. Examples of built-in applications <NUM> may include, but are not limited to, a contacts application, a browser application, a location application, a media application, a messaging application, and/or a game application. Third-party applications <NUM> may include any applications developed by an entity other than the vendor of the particular platform. The applications <NUM> may use functions available via OS <NUM>, libraries <NUM>, frameworks <NUM>, and presentation layer <NUM> to create user interfaces to interact with users.

Some software architectures use virtual machines, as illustrated by a virtual machine <NUM>. The virtual machine <NUM> provides an execution environment where applications/modules can execute as if they were executing on a hardware machine (such as the machine <NUM> of <FIG>, for example). The virtual machine <NUM> may be hosted by a host OS (for example, OS <NUM>) or hypervisor, and may have a virtual machine monitor <NUM> which manages operation of the virtual machine <NUM> and interoperation with the host operating system. A software architecture, which may be different from software architecture <NUM> outside of the virtual machine, executes within the virtual machine <NUM> such as an OS <NUM>, libraries <NUM>, frameworks <NUM>, applications <NUM>, and/or a presentation layer <NUM>.

<FIG> is a block diagram illustrating components of an example machine <NUM> configured to read instructions from a machine-readable medium (for example, a machine-readable storage medium) and perform any of the features described herein. The example machine <NUM> is in a form of a computer system, within which instructions <NUM> (for example, in the form of software components) for causing the machine <NUM> to perform any of the features described herein may be executed. As such, the instructions <NUM> may be used to implement modules or components described herein. The instructions <NUM> cause unprogrammed and/or unconfigured machine <NUM> to operate as a particular machine configured to carry out the described features. The machine <NUM> may be configured to operate as a standalone device or may be coupled (for example, networked) to other machines. In a networked deployment, the machine <NUM> may operate in the capacity of a server machine or a client machine in a server-client network environment, or as a node in a peer-to-peer or distributed network environment. Machine <NUM> may be embodied as, for example, a server computer, a client computer, a personal computer (PC), a tablet computer, a laptop computer, a netbook, a set-top box (STB), a gaming and/or entertainment system, a smart phone, a mobile device, a wearable device (for example, a smart watch), and an Internet of Things (IoT) device. Further, although only a single machine <NUM> is illustrated, the term "machine" include a collection of machines that individually or jointly execute the instructions <NUM>.

The machine <NUM> may include processors <NUM>, memory <NUM>, and I/O components <NUM>, which may be communicatively coupled via, for example, a bus <NUM>. The bus <NUM> may include multiple buses coupling various elements of machine <NUM> via various bus technologies and protocols. In an example, the processors <NUM> (including, for example, a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), an ASIC, or a suitable combination thereof) may include one or more processors 1412a to 1412n that may execute the instructions <NUM> and process data. In some examples, one or more processors <NUM> may execute instructions provided or identified by one or more other processors <NUM>. The term "processor" includes a multi-core processor including cores that may execute instructions contemporaneously. Although <FIG> shows multiple processors, the machine <NUM> may include a single processor with a single core, a single processor with multiple cores (for example, a multi-core processor), multiple processors each with a single core, multiple processors each with multiple cores, or any combination thereof. In some examples, the machine <NUM> may include multiple processors distributed among multiple machines.

As used herein, "machine-readable medium" refers to a device able to temporarily or permanently store instructions and data that cause machine <NUM> to operate in a specific fashion. The term "machine-readable medium," as used herein, does not encompass transitory electrical or electromagnetic signals per se (such as on a carrier wave propagating through a medium); the term "machine-readable medium" may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory, tangible machine-readable medium may include, but are not limited to, nonvolatile memory (such as flash memory or read-only memory (ROM)), volatile memory (such as a static random-access memory (RAM) or a dynamic RAM), buffer memory, cache memory, optical storage media, magnetic storage media and devices, network-accessible or cloud storage, other types of storage, and/or any suitable combination thereof. The term "machine-readable medium" applies to a single medium, or combination of multiple media, used to store instructions (for example, instructions <NUM>) for execution by a machine <NUM> such that the instructions, when executed by one or more processors <NUM> of the machine <NUM>, cause the machine <NUM> to perform and one or more of the features described herein. Accordingly, a "machine-readable medium" may refer to a single storage device, as well as "cloud-based" storage systems or storage networks that include multiple storage apparatus or devices.

The I/O components <NUM> may include a wide variety of hardware components adapted to receive input, provide output, produce output, transmit information, exchange information, capture measurements, and so on. The specific I/O components <NUM> included in a particular machine will depend on the type and/or function of the machine. For example, mobile devices such as mobile phones may include a touch input device, whereas a headless server or IoT device may not include such a touch input device. The particular examples of I/O components illustrated in <FIG> are in no way limiting, and other types of components may be included in machine <NUM>. The grouping of I/O components <NUM> are merely for simplifying this discussion, and the grouping is in no way limiting. In various examples, the I/O components <NUM> may include user output components <NUM> and user input components <NUM>. User output components <NUM> may include, for example, display components for displaying information (for example, a liquid crystal display (LCD) or a projector), acoustic components (for example, speakers), haptic components (for example, a vibratory motor or force-feedback device), and/or other signal generators. User input components <NUM> may include, for example, alphanumeric input components (for example, a keyboard or a touch screen), pointing components (for example, a mouse device, a touchpad, or another pointing instrument), and/or tactile input components (for example, a physical button or a touch screen that provides location and/or force of touches or touch gestures) configured for receiving various user inputs, such as user commands and/or selections.

In some examples, the I/O components <NUM> may include biometric components <NUM> and/or position components <NUM>, among a wide array of other environmental sensor components. The biometric components <NUM> may include, for example, components to detect body expressions (for example, facial expressions, vocal expressions, hand or body gestures, or eye tracking), measure biosignals (for example, heart rate or brain waves), and identify a person (for example, via voice-, retina-, and/or facial-based identification). The position components <NUM> may include, for example, location sensors (for example, a Global Position System (GPS) receiver), altitude sensors (for example, an air pressure sensor from which altitude may be derived), and/or orientation sensors (for example, magnetometers).

In some examples, the communication components <NUM> may detect identifiers or include components adapted to detect identifiers. For example, the communication components <NUM> may include Radio Frequency Identification (RFID) tag readers, NFC detectors, optical sensors (for example, one- or multi-dimensional bar codes, or other optical codes), and/or acoustic detectors (for example, microphones to identify tagged audio signals). In some examples, location information may be determined based on information from the communication components <NUM>, such as, but not limited to, geo-location via Internet Protocol (IP) address, location via Wi-Fi, cellular, NFC, Bluetooth, or other wireless station identification and/or signal triangulation.

While various embodiments have been described, the description is intended to be exemplary, rather than limiting, and it is understood that many more embodiments and implementations are possible that are within the scope of the appended claims. Although many possible combinations of features are shown in the accompanying figures and discussed in this detailed description, many other combinations of the disclosed features are possible. Any feature of any embodiment may be used in combination with or substituted for any other feature or element in any other embodiment unless specifically restricted. Therefore, it will be understood that any of the features shown and/or discussed in the present disclosure may be implemented together in any suitable combination.

Claim 1:
A telecommunication system (<NUM>) comprising:
a single geostationary earth orbiting satellite (<NUM>) including:
a first optical communication system configured to receive forward-direction user data via a forward optical link (<NUM>), and
a first radio frequency, RF, communication system (<NUM>) configured to transmit, via RF service links comprising a plurality of RF spot beams (<NUM>) , the forward-direction user data received via the forward optical link (<NUM>);
a single stratospheric high-altitude communication device (<NUM>) including:
a second RF communication system configured to receive the forward-direction user data via a plurality of concurrent forward RF feeder links (<NUM>), and
a second optical communication system configured to transmit via the forward optical link (<NUM>) the forward-direction user data received via the plurality of forward RF feeder links (<NUM>); and
a ground-based feeder RF terminal, RFT, array (<NUM>) including a plurality of ground-based feeder RF terminals configured to transmit a respective one of the plurality of forward RF feeder links and positioned at a same RF feeder site (<NUM>),
wherein at least <NUM>% of forward feeder data throughput for the forward RF service link transmissions (<NUM>) by the satellite (<NUM>) is carried via the forward optical link (<NUM>) and the plurality of forward RF feeder links (<NUM>), and
wherein the plurality of ground-based feeder RFT of the array (<NUM>) are disposed in a compact circular arrangement in which the ground-based feeder RFT are spaced apart at a minimum distance from each other and at which interference among the plurality of forward RF feeder links (<NUM>) is below an interference threshold.