Satellite system using optical gateways and onboard processing

Described herein are ground based subsystems, and related methods, for use in transmitting an optical feeder uplink beam to a satellite that is configured to receive the optical feeder uplink beam and in dependence thereon produce and transmit a plurality of RF service downlink beams within a specified RF frequency range to service terminals. Also described herein are space based subsystems of a satellite, and related methods, for use in transmitting a plurality of RF service downlink beams within a specified RF frequency range to service terminals. Beneficially certain embodiments eliminate the satellite to perform any RF frequency conversions upstream of a channelizer of the space based forward link subsystem on the satellite. Also described herein is space segment return link equipment, and related methods, for use in transmitting an optical feeder downlink beam to a ground based subsystem, as well as ground based return link equipment thereof.

BACKGROUND

There is increasing need for large amounts of bandwidth to be routed between a ground based gateway and a spaced based satellite. With the recent announcement of planned Ka band and Ku band satellite constellations, it would be beneficial if such frequency band satellite constellations can be used to help satisfy the aforementioned increasing need for large amounts of bandwidth to be routed between a ground based gateway and a spaced based satellite.

DETAILED DESCRIPTION

Certain embodiments of the present technology described herein relate to system and subsystem architectures for high throughput satellites (HTS), very high throughput satellites (VHTS) and very very high throughput satellites (VVHTS), which is also known as ultra high throughput satellites (UHTS), all of which can be collectively referred to as HTS. Because of spectrum availability, if feeder links between gateway (GW) sites and satellites are at optical frequencies, then the number of GW sites can be drastically reduced compared to if the feeder links are at RF frequencies, which leads to significant cost savings in the space and ground segments. Even with the availability of 5 GHz spectrum at V band and dual polarization, a satellite with Terabit/sec (Tb/s) capacity would need between 40 and 70 GWs using RF feeder links, depending on the spectral efficiency achieved, as described in a conference paper titled “Optical Feederlinks for VHTS-System Perspectives”, by Mata-Calvo et al. (Conference: Proceedings of the Ka and Broadband Communications, Navigation and Earth Observation Conference 2015. Ka Conference 2015, 12-14 Oct. 2015, Bologna, Italy). In contrast, using optical feeder links can reduce the total active GW count to one (plus a few sites would be added for diversity and redundancy; but note that V/Q band or Ka band GWs typically also need diversity and redundancy sites to achieve high availability).

Prior to describing details of specific embodiments of the present technology, it is first useful to describe an exemplary wireless communication system with which embodiments of the present technology would be useful. An example of such a wireless communication system will now be described with reference toFIG. 1.

FIG. 1depicts a block diagram of a wireless communications system that includes a communication platform100, which may be a satellite located, for example, at a geostationary or non-geostationary orbital location. In other embodiments, other platforms may be used such as an unmanned aerial vehicle (UAV) or balloon, or even a ship for submerged subscribers. In yet another embodiment, the subscribers may be air vehicles and the platform may be a ship or a truck where the “uplink” and “downlink” in the following paragraphs are reversed in geometric relations. Platform100may be communicatively coupled to at least one gateway (GW)105and a plurality of subscriber terminals ST (including subscriber terminals107). The term subscriber terminals may be used to refer to a single subscriber terminal or multiple subscriber terminals. A subscriber terminal ST is adapted for communication with the wireless communication platform100, which as noted above, may be a satellite. Subscriber terminals may include fixed and mobile subscriber terminals including, but not limited to, a cellular telephone, a wireless handset, a wireless modem, a data transceiver, a paging or position determination receiver, or mobile radio-telephone, or a headend of an isolated local network. A subscriber terminal may be hand-held, portable (including vehicle-mounted installations for cars, trucks, boats, trains, planes, etc.) or fixed as desired. A subscriber terminal may be referred to as a wireless communication device, a mobile station, a mobile wireless unit, a user, a subscriber, or a mobile. Where the communication platform of a wireless communication system is a satellite, the wireless communication system can be referred to more specifically as a satellite communication system. For the remainder of this description, unless stated otherwise, it is assumed that the communication platform100is a satellite. Accordingly, platform100will often be referred to as satellite100, and the wireless communication system will often be referred to as a satellite communication system.

In one embodiment, satellite100comprises a bus (e.g., spacecraft) and one or more payloads (e.g., the communication payload). The satellite will also include multiple power sources, such as batteries, solar panels, and one or more propulsion systems, for operating the bus and the payload.

The at least one gateway105may be coupled to a network140such as, for example, the Internet, terrestrial public switched telephone network, mobile telephone network, or a private server network, etc. Gateway105and the satellite (or platform)100communicate over a feeder beam102, which has both a feeder uplink102uand a feeder downlink102d.In one embodiment, feeder beam102is a spot beam to illuminate a region104on the Earth's surface (or another surface). Gateway105is located in region104and communicates with satellite100via feeder beam102. Although a single gateway is shown, some implementations will include many gateways, such as five, ten, or more. One embodiment includes only one gateway. Each gateway may utilize its own feeder beam, although more than one gateway can be positioned within a feeder beam. In one embodiment, a gateway is located in the same spot beam as one or more subscriber terminals.

Subscriber terminals ST and satellite100communicate over service beams, which are also known as user beams. For example,FIG. 1shows service beams106,110,114and118for illuminating regions108,112,116and120, respectively. In many embodiments, the communication system will include more than four service beams (e.g., sixty, one hundred, etc.). Each of the service beams have an uplink (106u,110u,114u,118u) and a downlink (106d,110d,114d,118d) for communication between subscriber terminals ST and satellite100. AlthoughFIG. 1only shows two subscriber terminals within each region108,112,116and120, a typical system may have thousands of subscriber terminals within each region.

In one embodiment, communication within the system ofFIG. 1follows a nominal roundtrip direction whereby data is received by gateway105from network140(e.g., the Internet) and transmitted over the forward path101to a set of subscriber terminals ST. In one example, communication over the forward path101comprises transmitting the data from gateway105to satellite100via uplink102uof feeder beam102, through a first signal path on satellite100, and from satellite100to one or more subscriber terminals ST via downlink106dof service beam106. An uplink (e.g.,102u) of a feeder beam (e.g.,102) can also be referred to more succinctly as a feeder uplink beam, and the downlink (e.g.,106d) of a service beam (e.g., a106) can also be referred to more succinctly as a service downlink beam. Although the above example mentions service beam106, the example could have used other service beams.

Data can also be sent from the subscriber terminals STs over the return path103to gateway105. In one example, communication over the return path comprises transmitting the data from a subscriber terminal (e.g., subscriber terminal107in service beam106) to satellite100via uplink106uof service beam106, through a second signal path on satellite100, and from satellite100to gateway105via downlink102dof feeder beam102. An uplink (e.g.,106u) of a service beam (e.g.,106) can also be referred to more succinctly as a service uplink beam, and the downlink102dof feeder beam102can also be referred to more succinctly as a feeder downlink beam. Although the above example uses service beam106, the example could have used any service beam.

FIG. 1also shows a Network Control Center (NCC)130, which can include an antenna and modem for communicating with satellite100, as well as one or more processors and data storage units. Network Control Center130provides commands to control and operate satellite100. Network Control Center130may also provide commands to any of the gateways and/or sub scriber terminals.

In one embodiment, communication platform100implements the technology described below. In other embodiments, the technology described below is implemented on a different platform (or different type of satellite) in a different communication system. For examples, the communication platform can alternatively be a UAV or balloon, but is not limited thereto.

The architecture ofFIG. 1is provided by way of example and not limitation. Embodiments of the disclosed technology may be practiced using numerous alternative implementations.

Conventionally, a gateway (e.g., gateway105) communicates with a satellite (e.g., satellite100) using an antenna on the ground that transmits and receives RF (radiofrequency) signals to and from an antenna on the satellite. Certain embodiments of the present technology utilize optical components instead of antennas to transmit and receive optical signals between a gateway and a satellite, as will be described in additional details below.

Block diagrams for the communications subsystems for the ground and space segments, according to certain embodiments of the present technology, are described below with reference toFIGS. 2A, 2B, 3A, 3B, 4A, 4B, 4C, and 5. Certain embodiments are for use with a satellite that includes an onboard channelizer that is used for onboard processing.

FIGS. 2A and 2Bwill first be used to describe gateway forward link equipment according to certain embodiments of the present technology.FIGS. 3A and 3Bwill then be used to describe space segment forward link equipment according to an embodiment of the present technology. In specific embodiments,250laser wavelengths are combined at a single gateway (which can be referred to as an optical gateway) and sent to the satellite, which has500user beams (also known as service beams) operating at Ka band frequencies.FIGS. 4A, 4B, 4C, and 5will thereafter be used to depict return link equipment for a satellite and a gateway.

Gateway Forward Link Equipment

FIG. 2Awill now be used to describe gateway forward link equipment200, according to an embodiment of the present technology. Such gateway forward link equipment200can also be referred to as an optical gateway forward link subsystem200, or more generally, as an optical communication subsystem. Referring toFIG. 2A, the optical gateway forward link subsystem200is shown as including two hundred and fifty lasers202_1to202_250, two hundred and fifty electro-optical modulator (EOMs)204_1to204_250, a wavelength-division multiplexing (WDM) multiplexer (MUX)206, an optical amplifier (OA)208and transmitter optics210. Each of these elements are described below.

The two hundred and fifty separate lasers202_1to202_250each emit light of a different wavelength within a specified wavelength range that is for use in producing the optical feeder uplink beam (e.g.,102u). The lasers can be referred to individually as a laser202, or collectively as the lasers202. Where the specified wavelength range is, for example, from 1510 nanometers (nm) to 1560 nm, then the laser202_1may emit light having a peak wavelength of 1510 nm, the laser202_2may emit light having a peak wavelength of 1510.2 nm, the laser202_3(not shown) may emit light having a peak wavelength of 1510.4 nm, . . . the laser202_249(not shown) may emit light having a peak wavelength of 1559.8 nm, and the laser202_250may emit light having a peak wavelength of 1660 nm. In other words, the peak wavelengths emitted by the lasers202can occur at 0.2 nm intervals from 1510 nm to 1560 nm. The wavelength range from 1510 nm to 1560 nm, which is within the infrared (IR) spectrum, is practical to use because IR lasers for use in communications are readily available. However, wider or narrow wavelength ranges, within the same or other parts of the optical spectrum, may alternatively be used. For example, it would also be possible to utilize a wavelength range within the 400 nm-700 nm visible spectrum. It is also possible that the wavelength range that is specified for use in producing the optical feeder uplink beam (e.g.,102u) is non-contiguous. For example, the wavelength range that is for use in producing the optical feeder uplink beam can be from 1510 nm to 1534.8 nm and from 1540.2 nm to 1564.8 nm. Further, it is also possible that gateway forward link equipment can alternatively include more or less than two hundred and fifty lasers (that each emit light of a different peak wavelength within a specified contiguous or non-contiguous wavelength range). Additionally, it is noted that the gateway forward link equipment may include two or more of each of the lasers (that each emit light of a different peak wavelength within a specified contiguous or non-contiguous wavelength range) to provide for redundancy or backup. Each of the lasers202can be, for example, a diode-pumped infrared neodymium laser, although the use of other types of lasers are also within the scope of the embodiments described herein.

To reduce and preferably avoid interference, the wavelength range that is for use in producing the optical feeder uplink beam (e.g.,102u) should be different than the wavelength range that is for use in producing the optical feeder downlink beam (e.g.,102d). For example, if the wavelength range that is for use in producing the optical feeder uplink beam102uis from 1510 nm to 1560 nm, then the wavelength range that is for use in producing the optical feeder downlink beam102dcan be from 1560.2 nm to 1575 nm. For another example, if the wavelength range that is for use in producing the optical feeder uplink beam102uis from 1510 nm to 1534.8 nm and from 1540.2 nm to 1564.8 nm, then the wavelength range that is for use in producing the optical feeder downlink beam102dcan be from 1535 nm to 1540 nm and from 1565 nm to 1575 nm. These are just a few examples, which are not intended to be all encompassing. Details of how an optical feeder downlink beam (e.g.,102d) can be produced in accordance with an embodiment of the present technology are provided below in the discussion ofFIGS. 4A, 4B and 4C.

Still referring toFIG. 2A, the light emitted by each of the two hundred and fifty lasers202, which can be referred to as an optical carrier signal, is provided (e.g., via a respective optical fiber) to a respective one of the two hundred and fifty separate EOMs204_1to204_250. The EOMs can be referred to individually as an EOM204, or collectively as the EOMs204. Each of the EOMs is an optical device in which a signal-controlled element exhibiting an electro-optic effect is used to modulate a respective beam of light. The modulation performed by the EOMs204may be imposed on the phase, frequency, amplitude, or polarization of a beam of light, or any combination thereof. In accordance with a specific embodiment, each of the EOMs204is a phase modulating EOM that is used as an amplitude modulator by using a Mach-Zehnder interferometer. In other words, each of the EOMs204can be implemented as a Mach-Zehnder modulator (MZM), which can be a Lithium Niobate Mach-Zehnder modulator, but is not limited thereto. In accordance with specific embodiments, each of the EOMs204is implemented as an MZM that produces an amplitude modulated (AM) optical waveform with a modulation index between 10% and 80% in order to maintain fidelity of an RF waveform (modulated therein) without too much distortion. The optical signal that is output by each of the EOMs204can be referred to as an optical data signal. The modulation scheme that is implemented by the EOMs204can result in double- or vestigial-sidebands, including both an upper sideband (USB) and a lower sideband (LSB). Alternatively single-sideband modulation (SSB) can be utilized to increase bandwidth and transmission power efficiency.

The two hundred and fifty separate optical data signals that are output by the two hundred and fifty EOMs204are provided to the WDM MUX206, which can also be referred to as a dense wavelength division multiplexing (DWDM) MUX. The WMD MUX206multiplexes (i.e., combines) the two hundred and fifty optical data signals, received from the two hundred and fifty EOMs204, onto a single optical fiber, with each of the two hundred and fifty separate optical data signals being carried at the same time on its own separate optical wavelength within the range from 1510 nm to 1560 nm. For example, as explained above, the two hundred and fifty separate optical data signals can have peak wavelengths of 1510 nm, 1510.2 nm, 1510.4 nm . . . 1559.8 nm and 1560 nm.

The signal that is output by the WMD MUX206, which can be referred to as a wavelength division multiplexed optical signal, is provided to the optical amplifier (OA)208. The OA208amplifies the wavelength division multiplexed optical signal so that the wavelength division multiplexed optical signal has sufficient power to enable transmission thereof from the ground to the satellite100in space. An exemplary type of OA208that can be used is an erbium-doped fiber amplifier (EDFA). However embodiments of the present technology are not limited to use with an EDFA. The output of the OA208can be referred to as an optically amplified wavelength division multiplexed optical signal.

The optically amplified wavelength division multiplexed optical signal, which is output by the OA208, is provided (e.g., via an optical fiber) to the transmitter optics210. The transmitter optics210, which can also be referred to as a telescope, can includes optical elements such as lenses, mirrors, reflectors, filters and/or the like. The transmitter optics210outputs a collimated optical feeder uplink beam that is aimed at a satellite. A gimbal, and/or the like, can be used to control the steering of the transmitter optics210. In accordance with an embodiment, the collimated optical feeder uplink beam has an aperture of about 100 cm, and a half beam divergence of about 0.0000004 radians, wherein the term “about” as used herein means +/−10 percent of a specified value. The use of other apertures and half beam divergence values are also within the scope of the embodiments described herein. The collimated optical feeder uplink beam, which is output by the transmitter optics210, is transmitted in free-space to receiver optics on a satellite. The term “free-space” means air, outer space, vacuum, or something similar (which is in contrast to using solids such as optical fiber cable, an optical waveguide or an optical transmission line). Reception and processing of the optical feeder uplink beam received at the satellite will be described in additional detail below. However, before describing the reception and processing of the optical feeder uplink beam received at the satellite, additional details of the gateway forward link equipment, according to certain embodiments of the present technology, will first be provided.

Referring again to the EOMs204, in accordance with certain embodiments of the present technology, each of the EOMs204modulates the optical signal it receives (e.g., via an optical fiber from a respective laser202) with a separate RF signal that has already been modulated to include user data. As will be described in additional detail below, e.g., with reference toFIGS. 3A and 3B, in accordance with certain embodiments of the present technology, forward link equipment of a satellite (to which the transmitter optics210send the optical feeder uplink beam) includes a forward link channelizer (e.g.,315inFIGS. 3A and 3B) that operates within an intermediate RF frequency range that is lower than the service downlink RF frequency range within which the satellite(s) transmit RF service downlink beams to service terminals STs. In accordance with certain embodiments of the present technology, the RF frequencies of the optical data signals output by the EOMs204are within the same intermediate RF frequency range within which the forward link channelizer (e.g.,315inFIGS. 3A and 3B) on the satellite(s) is/are configured to operate. This beneficially eliminates of any need for the space segment forward link subsystem of the satellite to perform any RF frequency conversions upstream of the forward link channelizer on the satellite. More specifically, such embodiments eliminate the need for RF frequency down-converters in the portion of the forward link equipment onboard the satellite that is upstream of the forward link channelizer on the satellite. This benefit is achieved by utilizing appropriate carrier frequencies in the gateway forward link equipment. More specifically, the carrier frequencies of the RF signals that are used to modulate each of the two hundred and fifty lasers202on the ground (e.g., in gateway105) correspond to the desired intermediate RF frequency range at which the forward link channelizer on the satellite operates. An exemplary intermediate RF frequency range at which the foward link channelizer on the satellite operates is from 1.5 GHz to 2.0 GHz. As a result, the space based forward link subsystem on the satellite is greatly simplified compared to if RF frequency down-converters were included in the portion of the forward link equipment onboard the satellite that is upstream of the forward link channelizer on the satellite. Reasons why such a channelizer may be limited to operating within an intermediate RF frequency range may relate to limitations on how fast ADCs and other circuitry within the channelizer can be designed and built to operate. It is noted that it is also possible that a forward link channelizer on a satellite operate at alternative intermediate RF frequency ranges (besides from 1.5 to 2.0 GHz) that are lower than the service downlink RF frequency range within which the satellite(s) transmit RF service downlink beams to service terminals STs. In other words, a channelizer is not limited to operating within an intermediate RF frequency range of 1.5 to 2.0 GHz, and more specifically, may operate at higher frequency bands as technology improves and the a desired frequency of RF bands increases.

As noted above, an exemplary intermediate RF frequency range at which the forward link channelizer on the satellite operates can be from 1.5 GHz to 2.0 GHz. In such a case, each of the EOMs204could modulate the optical signal it receives (e.g., via an optical fiber from a respective laser202) with a separate RF signal having a frequency within the range from 1.5 GHz to 2.0 GHz. Further, since each of the two hundred and fifty optical data signals (produced by the two hundred and fifty EOMs) has a bandwidth of 0.5 GHz, the bandwidth of the optical feeder uplink beam that is sent from the ground to the satellite is 125 GHz (i.e., 0.5 GHz*250=125 GHz). As noted above, a channelizer is not limited to operating within an intermediate RF frequency range of 1.5 to 2.0 GHz, and more specifically, may operate at higher frequency bands as technology improves and the a desired frequency of RF bands increases.

FIG. 2Bdepicts components that can be used to produce one of the data modulated RF carriers introduced inFIG. 2A, according to an embodiment of the present technology. Referring toFIG. 2B, shown therein is a local oscillator (LO)222that produces an RF carrier signal within the intermediate RF frequency range at which the forward link channelizer on the satellite operates. For example, the LO222may produce an RF carrier within the intermediate RF frequency range from 1.5 to 2.0 GHz. The RF carrier signal that is output by the LO222is provided to an RF modulator (RFM)224, which also receives a data signal. The RFM224modulates that data signal onto the RF carrier signal to produce a data modulated RF carrier signal, which is provided to one of the EOMs204shown inFIG. 2A. Where two hundred and fifty data modulated RF carrier signals are produced (each of which is provided to a different one of the EOMs204), the components shown inFIG. 2Bcan be duplicated two hundred and fifty times. Alternatively, the two hundred and fifty RFMs224can receive the same carrier signal from a common LO222, with each of the RFMs224receiving a separate data signal.

The RFMs224can perform various different types of RF modulation, depending upon implementation and other factors such channel conditions. For example, the RFMs224can perform Amplitude-shift keying (ASK), Phase-shift keying (PSK), or Amplitude and phase-shift keying (APSK) types of modulation (e.g., 16-, 128- or 256-APSK), just to name a few. In accordance with certain embodiments, the modulation scheme performed by the RFMs224and EOMs204cause the signals that are transmitted from the ground to a satellite to be in conformance with the Digital Video Broadcasting-Satellite-Second Generation (DVB-S2) standard, or the related DVB-S2X standard (which is an extension of the DVB-S2 standard).

Referring again toFIG. 2A, in order to wavelength division multiplex two hundred and fifty wavelengths produced by the two hundred and fifty lasers202_1to202_250, a combination of C band optical frequencies (from 1530 nm to 1565 nm) and L band optical frequencies (from 1565 nm to 1625 nm) may be used, in order to keep the separation of the wavelengths to be at least 20-25 GHz in order to reduce and preferably minimize inter-wavelength interference that may occur in an optical fiber due to non-linearities. If fewer wavelengths are used (e.g., at C band alone), and higher bandwidth is available at Ka band per user beam (e.g., if 2.9 GHz is available as it is in certain ITU Regions), the overall throughput can still remain of the order of one to several hundred GHz, which lets the capacity reach the Tb/s range.

Space Segment Forward Link Equipment

FIGS. 3A and 3Bwill now be used to describe space segment forward link equipment300according to an embodiment of the present technology. Such space segment forward link equipment300, which can also be referred to as a forward link satellite subsystem300, or more generally, as an optical communication subsystem, is configured to receive the optical signal that is transmitted from the ground based optical gateway subsystem200to the satellite that is carrying the space segment forward link equipment300. The space segment forward link equipment300is also configured to convert the optical signal that it receives (from the ground based optical gateway subsystem200) into electrical signals, and to produce service beams therefrom, wherein the service beams are for transmission from the satellite to service terminals STs.

Referring toFIG. 3A, the forward link satellite subsystem300is shown as including receiver optics302, an optical amplifier (OA)304, a wavelength-division multiplexing (WDM) demultiplexer (DEMUX)306, two hundred and fifty photodetectors (PDs)308_1to308_250, two hundred and fifty filters310_1to310_250, two hundred and fifty low noise amplifiers (LNAs)312_1to312_250, and a channelizer315. The forward link satellite subsystem300is also shown as including five hundred frequency up converters (FUCs)316_1to316_500, high power amplifiers (HPAs)318_1to318_500, harmonic filters (HFs)320_1to320_500, test couplers (TCs)322_1to322_500, orthomode junctions (OMJs)324_1to324_500, and feed horns326_1to326_500. The PDs308_1to308_250can be referred to individually as a PD308, or collectively as the PDs308. The filters310_1to310_250can be referred to individually as a filter310, or collectively as the filters310. The LNAs312_1to312_250can be referred to individually as an LNA312, or collectively as the LNAs312. The channelizer315can also be referred to more specifically as a forward link channelizer315, since it is part of the space segment forward link equipment300. The frequency up converters (FUCs)316_1to316_500can be referred to individually as a frequency up converter (FUC)316, or collectively as the frequency up converters (FUCs)316. The HPAs318_1to318_500can be referred to individually as an HPA318, or collectively as the HPAs318. The HFs320_1to320_500can be referred to individually as an HF320, or collectively as the HFs320. The TCs322_1to322_500can be referred to individually as a TC322, or collectively as the TCs322. The OMJs324_1to324_500can be referred to individually as an OMJ324, or collectively as the OMJs324. The feed horns326_1to326_500can be referred to individually as a feed horn326, or collectively as the feed horns326.

The receiver optics302, which can also be referred to as a telescope, can include optical elements such as mirrors, reflectors, filters and/or the like. The receiver optics302receives the optical feeder uplink beam that is transmitted through free-space to the satellite by the ground based optical gateway forward link subsystem200, and provides the received optical feeder uplink beam (e.g., via an optical fiber) to the OA304. A gimbal, and/or the like, can be used to control the steering of the receiver optics302. When the optical feeder uplink beam reaches the satellite, the power of the optical feeder uplink beam is significantly attenuated compared to when it was transmitted by the ground based optical gateway subsystem200. Accordingly, the OA304is used to amplify the received optical feeder uplink beam before it is provided to the WDM DEMUX306. The OA304can be, e.g., an erbium-doped fiber amplifier (EDFA), but is not limited thereto. The output of the OA304can be referred to as an optically amplified received optical feeder uplink beam. The WDM DEMUX306demultiplexes (i.e., separates) the received optical feeder uplink beam (after it has been optically amplified) into two hundred and fifty separate optical signals, each of which is provided to a separate photodetector (PD)308. Each PD308converts the optical signal it receives from the WDM DEMUX306to a respective RF electrical signal. The RF electrical signal produced by each PD308is provided to a respective filter (FTR)310(e.g., a bandpass filter) to remove unwanted frequency components and/or enhance desired frequency components. For an example, each filter310can pass frequencies within the range of 1.5 to 2.0 GHz, but are not limited thereto. The filtered RF electrical signal, which is output by each filter310, is provided to a respective low noise amplifier (LNA)312. Each LNA312amplifies the relatively low-power RF signal it receives from a respective filter310without significantly degrading the signals signal-to-noise ratio. The amplified RF signal that is output by each LNA312is provided to input ports of the forward link channelizer315. Exemplary details of the forward link channelizer315are described below with reference toFIG. 3B. In an exemplary embodiment shown inFIG. 3A, the forward link channelizer315includes two hundred and fifty input ports and five hundred output ports.

As noted above, the forward link channelizer315is configured to operate within an intermediate RF frequency range (e.g., 1.5 to 2.0 GHz, but not limited thereto) that is lower than the service downlink RF frequency range (e.g., from 17.7 GHz to 20.2 GHz, or from 17.3 GHz to 20.2 GHz, but not limited thereto) within which the satellite transmits RF service downlink beams to service terminals STs. Accordingly, RF signals that are output by the forward link channelizer315, at the output ports thereof, are provided to the frequency up converters (FUCs)316to thereby increase the frequencies of the RF signals (output from the forward link channelizer315) from the intermediate RF frequency range (e.g., from 1.5 GHz to 2.0 GHz) to the service downlink RF frequency range (e.g., from 17.7 GHz to 20.2 GHz, or from 17.3 GHz to 20.2 GHz, but not limited thereto).

Each HPA318amplifies the RF signal it receives so that the RF signal has sufficient power to enable transmission thereof from the satellite100in space to an ST, which may be on the ground. Each HPA318can be, e.g., a liner traveling wave tube high power amplifier, but is not limited thereto. The signal that is output by each of the HPAs318can be referred to as an amplified RF signal. Each HF320is used to reduce and preferably remove any distortion in the amplified RF signal that was caused by a respective HPA318. Each HF320can be, e.g., a waveguide cavity filter, but is not limited thereto. Each test coupler TC322can be used for power monitoring, payload testing and/or performing calibrations based on signals passing therethrough. Each OMJ324adds either right hand circular polarization (RHCP) or left hand circular polarization (LHCP) to the RF signal that is passed through the OMJ. This allows for color reuse frequency band allocation, wherein each color represents a unique combination of a frequency band and an antenna polarization. This way a pair of feeder beams that illuminate adjacent regions can utilize a same RF frequency band, so long as they have orthogonal polarizations. Alternatively, each OMJ324adds either horizontal linear polarization or vertical linear polarization to the RF signal that is passed through the OMJ. Each feed horn326converts the RF signal it receives, from a respective OMJ324, to radio waves and feeds them to the rest of the antenna system (not shown) to focus the signal into a service downlink beam. A feed horn326and the rest of an antenna can be collectively referred to as the antenna. In other words, an antenna, as the term is used herein, can include a feed horn. All or some of the feed horns326can share a common reflector. Such reflector(s) is/are not shown in the Figures, to simply the Figures.

FIG. 3Bwill now be used to describe details of the forward link channelizer315, according to an embodiment of the present technology. Referring toFIG. 3B, the forward link channelizer315is shown as including two hundred and fifty analog to digital converters (ADCs)342_1to342_250, a demultiplexer344, filter and switch circuitry346, a multiplexer348, five hundred digital to analog converters (DACs)352_1to352_500. The ADCs342_1to342_250can be referred to individually as an ADC342, or collectively as the ADCs342. The DACs352_1to352_500can be referred to individually as a DAC352, or collectively as the DACs352. The forward link channelizer315is also shown as including a digital channel process (DCP) controller360that controls the ADCs342, the demultiplexer344, the filter and switch circuitry346, the multiplexer348and the DACs352. The DCP controller360can store or otherwise access one or more routing table(s) that are used to control the switching that is performed by the filter and switch circuitry346and/or operation of the multiplexer348. The ADCs342digitize the analog

RF signals provided to the input ports of the forward link channelizer315and provides digitized RF signals to the demultiplexer344. In accordance with certain embodiments, the demultiplexer344, the filter and switch circuitry346, and the multiplexer348, under the control of the DCP controller360, achieves flexible routing and a high spectral efficiency by changing the frequency and beam allocation in a flexible manner by means of digital signal processing. The demultiplexer344decomposes or separates digitized RF signals into independently routable sub-channels or sub-bands. The filter and switch circuitry346routes the decomposed sub-channels to beams and frequencies as desired. At the multiplexer348, the sub-channels that were rearranged by the filter and switch circuitry346are multiplexed or combined as desired, provided to the DACs352, and then provided to the output ports of the forward link channelizer315. Explained another way, the demultiplexer344, the filter and switch circuitry346, and the multiplexer348, under the control of the DCP controller360, digitally divides each sub-bands of the digitized RF signals into frequency slices that can be separated, filtered, switched, processed, routed and/or recombined into RF output signals (in output sub-bands) that are converted to analog RF signals by the DACs352and output from the forward link channelizer315. While the exemplary forward link channelizer315was shown as and described as including two hundred and fifty input ports and five hundred output ports, the forward link channelizer315can have alternative numbers of input ports and output ports. Further, while not specifically shown inFIG. 3B, the forward link channelizer315can include analog front end circuitry upstream of the ADCs342and/or digital back end circuitry downstream of the DACs352. The filter and switch circuitry346of the forward link channelizer315can include, e.g., a crossbar switch, a multiple stage switch network, or another switch structure for routing frequency slices as desired.

Space Segment Return Link Equipment

FIG. 4Awill now be used to describe a portion of space segment return link equipment400A, according to an embodiment of the present technology. Such space segment return link equipment400A, which can also be referred to as a satellite return link subsystem400A, or more generally, as an optical communication subsystem, is configured to receive the RF signals that are transmitted by service terminals STs to the satellite (e.g.,100) that is carrying the space segment return link equipment400A. The space segment return link equipment400A, together with the space segment return link equipment400D inFIG. 4C, is also configured to convert the RF signals that it receives (from the service terminals STs) into optical signals, and to produce optical return feeder beams therefrom, wherein the optical return feeder beams are for transmission from the satellite (e.g.,100) to a ground based gateway (e.g.,105).

Referring toFIG. 4A, the portion of the space segment return link equipment400A shown therein includes feed horns402_1to402_500(which can be referred to individually as a feed horn402, or collectively as the feed horns402), orthomode junctions (OMJs)404_1to404_500(which can be referred to individually as an OMJ404, or collectively as the OMJs404), test couplers (TCs)406_1to406_500(which can be referred to individually as a TC406, or collectively as the TCs406), pre-select filters (PFs)408_1to408_500(which can be referred to individually as a PF408, or collectively as the PFs408), low noise amplifiers (LNAs)410_1to410_500(which can be referred to individually as an LNA410, or collectively as the LNAs410), and filters412_1to412_500(which can be referred to individually as a filter412, or collectively as the filters412). The portion of the space segment return link equipment400A shown inFIG. 4Aalso includes frequency down-converters (FDCs)416_1to416_500(which can be referred to individually as a frequency down-converter416, or collectively as the frequency down-converters416) and a return link channelizer415. Exemplary details of the return link channelizer415, according to an embodiment of the present technology, are described below with reference toFIG. 4B. The return link channelizer415is shown as including five hundred input ports and sixty three output ports, but can include alternative numbers of input ports and output ports.

FIG. 4Bwill now be used to describe details of the return link channelizer415, according to an embodiment of the present technology. Referring toFIG. 4B, the return link channelizer415is shown as including five hundred analog to digital converters (ADCs)442_1to442_500, a demultiplexer444, filter and switch circuitry446, a multiplexer448, sixty three digital to analog converters (DACs)452_1to452_63. The ADCs442_1to442_500can be referred to individually as an ADC442, or collectively as the ADCs442. The DACs452_1to452_63can be referred to individually as a DAC452, or collectively as the DACs452. The forward link channelizer415is also shown as including a digital channel process (DCP) controller460that controls the ADCs442, the demultiplexer444, the filter and switch circuitry446, the multiplexer448and the DACs452. The DCP controller460can store or otherwise access one or more routing table(s) that are used to control the switching that is performed by the filter and switch circuitry446. The ADCs442digitize the analog RF signals provided to the input ports of the return link channelizer415and provides digitized RF signals to the demultiplexer444. In accordance with certain embodiments, the demultiplexer444, the filter and switch circuitry446, and the multiplexer448, under the control of the DCP controller460, achieves flexible routing and a high spectral efficiency by changing the frequency and beam allocation in a flexible manner by means of digital signal processing. The demultiplexer444decomposes or separates digitized RF signals into sub-channels or sub-bands. The filter and switch circuitry446maps the the decomposes sub-channels to arbitrary beams and frequencies. At the multiplexer448, the signals that were rearranged by the filter and switch circuitry446are multiplexed of combined as desired, and then provided to the DACs452and then output ports of the return link channelizer415. Explained another way, the demultiplexer444, the filter and switch circuitry446, and the multiplexer448, under the control of the DCP controller460, digitally divides each sub-band of the digitized RF signals into frequency slices that can be separated, filtered, switched, processed, routed and/or recombined into RF output signals (in output sub-bands) that are converted to analog RF signals by the DACs452and output from the return link channelizer415. While the exemplary return link channelizer415was shown as and described as including five hundred input ports and sixty three output ports, the return link channelizer415can have alternative numbers of input ports and output ports. Further, while not specifically shown inFIG. 4B, the return link channelizer415can include analog front end circuitry upstream of the ADCs442and/or digital back end circuitry downstream of the DACs452. The filter and switch circuitry446of the forward link channelizer415can include, e.g., a crossbar switch, a multiple stage switch network, or another switch structure for routing frequency slices as desired. In order to reduce the number of input ports and ADCs442included in the return link channelizer415, combiners (each of which can be implemented by a hybrid, but is not limited thereto) can be included upstream of the return link channelizer415, e.g., between the FDCs414and input ports of the return link channelizer415, or between the filters412and the FDCs414(in which case, the number of FDCs414can also be reduced).

Referring again toFIG. 4A, each feed horn402gathers and focuses radio waves of a service uplink beam (e.g.,106u) and converts them to an RF signal that is provided to a respective OMJ404. A feed horn402and the rest of an antenna can be collectively referred to as the antenna or antenna system. In other words, an antenna, as the term is used herein, can include a feed horn. All or some of the feed horns402can share a common reflector. Such reflector(s) is/are not shown in the Figures, to simply the Figures. Each OMJ404either passes through a right hand circular polarization (RHCP) or a left hand circular polarization (LHCP) RF signal. Each OMJ404can alternatively pass through either a horizontal or a vertical linear polarization RF signal. Each test coupler TC406can be used for power monitoring, payload testing and/or performing calibrations based on signals passing therethrough. Each pre-select filter (PF)408(e.g., a bandpass filter) is used to remove unwanted frequency components and/or enhance desired frequency components. For an example, each PF408can pass frequencies within the range of 29.5-30.0 GHz, but is not limited thereto. Each LNA410amplifies the relatively low-power RF signal it receives from a respective PF408without significantly degrading the signals signal-to-noise ratio. The amplified RF signal that is output by each LNA410is provided to a respective filter412.

In accordance with certain embodiments, each filter412allows frequencies to pass within one of the colors a, b, c or d. For example, the filter412_1passes frequencies within the color a, the filter412_2passes the frequencies within the color b, the filter412_3passes frequencies within the color c, and the filter412_4passes frequencies within the color d. Alternatively, each of the filters412can pass frequencies within all of the colors a, b, c, and d, and the channelizer415can perform the filtering function. In accordance with an embodiment: color ‘a’ represents a first sub-band (e.g., 29.50-29.75 GHz) of an allocated uplink frequency band (e.g., 29.50-30.00 GHz) with a right-hand circular polarization (RHCP); color ‘b’ represents a second sub-band (29.75-30.00 GHz) of the allocated uplink frequency band with RHCP; color ‘c’ represents the first sub-band (e.g., 29.50-29.75 GHz) of the allocated uplink frequency band with a left-hand circular polarization (LHCP); and color ‘d’ represents the second sub-band (29.75-30.00 GHz) of the allocated uplink frequency band with LHCP. In other embodiments, the colors may include other allocations of the frequency band and polarization.

InFIG. 4A, each filter412is shown as providing its output to a respective frequency down converter (FDC)414. Each FDC414down converts the frequency of the RF signal it receives to an RF signal within the intermediate RF frequency range within which the return link channelizer415is configured to operate (e.g., between 1.5 and 2.0 GHz, but not limited thereto). In an alternative embodiment, each pair of the filters412can provide their outputs to a combiner (not shown) that functions as a directional coupler that combines two RF signals into one. For example, such a combiner can combine an RF signal having the color a and an RF signal having the color b into a single RF signal that is provided to the frequency down-converter414_1. Similarly, another combiner (not shown) can combine an RF signal having the color c and an RF signal having the color d into a single RF signal that is provided to the frequency down-converter416_2. Each such combiner can be implemented by a hybrid, but is not limited thereto.

Each frequency down-converter414receives an RF signal from a filter412(or a combiner, in which case the RF signal includes data from two service uplink beams, and thus, can be referred to as an RF data signal) and an RF signal from a local oscillator (which can be referred to as an LO signal), and uses the LO signal to down-convert the RF data signal to a frequency range (e.g., 6.70-7.2 GHz, or 6.3-7.2 GHz, or some other frequency range within the 6-12 GHz band) that can be used for transmitting feeder downlink signals (e.g.,102d) to a gateway (e.g.,105). The output of each frequency down-converter414is provided to the return link channelizer (or to a combiner, if there are combiners between the FDCs416and the input ports of the return link channelizer415). If desired, frequency up-converters (not shown) can be located downstream of the output ports of the return link channelizer415.

FIGS. 4A and 4Bwere used to described portions of space segment return link equipment (400A) that produce a data modulated RF carrier for multiple (e.g., eight) service uplink beams associate with multiple (e.g., eight or more) service terminals STs.FIG. 4Cwill now be used to describe a further portion of the space segment return link equipment400C that is used to convert the data modulated RF carrier signals into a collimated optical downlink feeder beam that is aimed at a gateway. Referring toFIG. 4C, the portion of the space segment return link equipment400C is shown as including sixty three lasers432_1to432_63, sixty three electro-optical modulator (EOMs)434_1to434_63, a wavelength-division multiplexing (WDM) multiplexer (MUX)436, an optical amplifier (OA)438and transmitter optics440. Each of these elements are described below.

The sixty three separate lasers432_1to432_63each emit light of a different wavelength within a specified wavelength range. The lasers can be referred to individually as a laser432, or collectively as the lasers432. Where the specified wavelength range is, for example, from 1560.2 nm to 1575 nm, then the laser432_1may emit light having a peak wavelength of 1560.2 nm, the laser432_2may emit light having a peak wavelength of 1560.4 nm, the laser432_3(not shown) may emit light having a peak wavelength of 1560.6 nm, . . . the laser432_62may emit light having a peak wavelength of 1672.6 nm, and the laser432_63may emit light having a peak wavelength of 1672.8 nm. In other words, the peak wavelengths emitted by the lasers432can occur at 0.2 nm intervals from 1560.2 nm to 1572.8 nm. The wavelength range from 1560.2 nm to 1575 nm, which is within the IR spectrum, is practical to use because IR lasers for use in communications are readily available. However, wider or narrow wavelength ranges, within the same or other parts of the optical spectrum, may alternatively be used. For example, it would also be possible to utilize a wavelength range within the 400 nm-700 nm visible spectrum. It is also possible that the wavelength range that is specified for use in producing the optical feeder downlink beam (e.g.,102d) is non-contiguous. For example, the wavelength range that is for use in producing the optical feeder downlink beam can be from 1535 nm to 1540 nm and from 1565 nm to 1575 nm. These are just a few examples, which are not intended to be all encompassing. Further, it is also possible that space segment return link equipment can alternatively include more or less than sixty three lasers (that each emit light of a different peak wavelength within a specified contiguous or non-contiguous wavelength range). Additionally, it is noted that the space segment return link equipment may include two or more of each of the lasers (that each emit light of a different peak wavelength within a specified contiguous or non-contiguous wavelength range) to provide for redundancy or backup. Each of the lasers432can be, for example, a diode-pumped infrared neodymium laser, although the use of other types of lasers are also within the scope of the embodiments described herein.

In accordance with certain embodiments, the space segment return link equipment400C includes less lasers (e.g., sixty three lasers432) for use in generating the optical feeder downlink beam that is aimed from the satellite100to the gateway105, than the gateway forward link equipment200includes (e.g., five hundred lasers202) for generating the optical feeder uplink beam that is aimed from the gateway105to the satellite100. This is made possible due to current asymmetric capacity requirements between the forward and return feeder links. More specifically, a feeder downlink beam (e.g.,102d) carries significantly less data than a feeder uplink beam (e.g.,102u), because service terminals STs typically download much more data than they upload.

On the return link, given the current asymmetric capacity requirements between the forward and return links, the space segment return link equipment can be implemented to handle less demand that the ground based forward link equipment. As an example, if each RF service uplink beam is assumed to have only 320 MHz per beam, then a total of 160 GHz needs to be sent from a satellite to a gateway on the optical feeder downlink beam. Several beams' frequencies can be grouped together to create a 4 GHz bandwidth which is then transmitted on each of sixty three laser wavelengths that are multiplexed together and transmitted to the ground. An alternative implementation would be to aggregate the 4 GHz spectrum with filtering post LNA to eliminate the RF frequency conversion and as above directly modulate the RF spectrum on each of the sixty three laser wavelengths. An alternative implementation would be to use only RF LNAs for each feed, modulate each 320 MHz segment of bandwidth onto a single laser and combine two hundred and fifty laser wavelengths together, thus eliminating the need for RF frequency converters. Depending on the number of service beams and feeder beams required, one or the other configuration can be selected to provide the lowest mass solution.

The light emitted by each of the sixty three lasers432, which can be referred to as an optical carrier signal, is provided (e.g., via a respective optical fiber) to a respective one of the sixty three separate EOMs434_1to434_63. The EOMs can be referred to individually as an EOM434, or collectively as the EOMs434. Each of the EOMs434is an optical device in which a signal-controlled element exhibiting an electro-optic effect is used to modulate a respective beam of light. The modulation performed by the EOMs434may be imposed on the phase, frequency, amplitude, or polarization of a beam of light, or any combination thereof. In accordance with a specific embodiment, each of the EOMs434is a phase modulating EOM that is used as an amplitude modulator by using a Mach-Zehnder interferometer. In other words, each of the EOMs434can be implemented as a Mach-Zehnder modulator (MZM), which can be a Lithium Niobate Mach-Zehnder modulator, but is not limited thereto. In accordance with specific embodiments, each of the EOMs434is implemented as an MZM that produces an amplitude modulated (AM) optical waveform with a modulation index between 10% and 80% in order to maintain fidelity of an RF waveform (modulated therein) without too much distortion. The optical signal that is output by each of the EOMs434can be referred to as an optical data signal. The modulation scheme that is implemented by the EOMs434can result in double- or vestigial-sidebands, including both an upper sideband (USB) and a lower sideband (LSB). Alternatively single-sideband modulation (SSB) can be utilized to increase bandwidth and transmission power efficiency.

The sixty three separate optical data signals that are output by the sixty three EOMs434are provided to the WDM MUX436, which can also be referred to as a dense wavelength division multiplexing (DWDM) MUX. The WMD MUX436multiplexes (i.e., combines) the sixty three optical data signals, received from the sixty three EOMs434, onto a single optical fiber, with each of the sixty three separate optical data signals being carried at the same time on its own separate optical wavelength within a specified contiguous wavelength range (e.g., from 1560 nm to 1575 nm) or non-contiguous wavelength range (e.g., from 1510 nm to 1534.8 nm, and from 1540.2 nm to 1564.8 nm). For example, as explained above, the sixty three optical data signals can have peak wavelengths that occur at 0.2 nm intervals from 1560 nm to 1572.8 nm.

The signal that is output by the WMD MUX436, which can be referred to as a wavelength division multiplexed optical signal, is provided to the optical amplifier (OA)438. The OA438amplifies the wavelength division multiplexed optical signal so that the wavelength division multiplexed optical signal has sufficient power to enable transmission thereof from the satellite100in free-space to the gateway105. The OA438can be an erbium-doped fiber amplifier (EDFA), but is not limited thereto. The output of the OA438can be referred to as an optically amplified wavelength division multiplexed optical signal.

The optically amplified wavelength division multiplexed optical signal, which is output by the OA438, is provided (e.g., via an optical fiber) to the transmitter optics440. The transmitter optics440, which can also be referred to as a telescope, can includes optical elements such as lenses, mirrors, reflectors, filters and/or the like. The transmitter optics440outputs a collimated optical feeder downlink beam that is aimed at a satellite. A gimbal, and/or the like, can be used to control the steering of the transmitter optics440. In accordance with an embodiment, the collimated optical feeder downlink beam has an aperture of about 40 cm, and a half beam divergence of about 0.0000012 radians, wherein the term “about” as used herein means +/−10 percent of a specified value. The use of other apertures and half beam divergence values are also within the scope of the embodiments described herein. The collimated optical feeder downlink beam, which is output by the transmitter optics440, is transmitted in free-space to receiver optics in the gateway105.

A space segment (e.g., a satellite100) can have different optics that are used for transmitting an optical feeder downlink beam (e.g.,102d) to a gateway, than the optics that are used for receiving an optical feeder uplink beam (e.g.,102u) from a gateway. Alternatively, and preferably, to reduce the weight that needs to be carried by the space segment (e.g., a satellite100), the same optics can be used for both transmitting an optical feeder downlink beam (e.g.,102d) to a gateway and for receiving an optical feeder uplink beam (e.g.,102u) from a gateway. More specifically, the TX optics440shown inFIG. 4Ccan be the same as the RX optics302shown inFIG. 3A. Additional and/or alternative components can be shared between the space segment forward link equipment shown inFIG. 3Aand the space segment return link equipment shown inFIGS. 4A, 4B and 4C. For example, the feed horns326inFIG. 3Acan be the same as the feed horns402shown inFIG. 4A. For another example, the OMJs324inFIG. 3Acan be the same as the OMJs404inFIG. 4A, if the OMJs are implement as a three-port device. For another example, one or more components of the forward link channelizer315can be shared with the return link channelizer415, e.g., the same DCP controller can be used for both the forward link and return link channelizers. These are just a few examples, which are not intended to be all encompassing.

Referring again to the EOMs434inFIG. 4C, in accordance with certain embodiments of the present technology, each of the EOMs434modulates the optical signal it receives (e.g., via an optical fiber from a respective laser432) with a separate RF signal that has already been modulated to include user data. For example, the EOM434_1modulates the optical signal it receives from the laser431_1with a data modulated RF carrier signal it receives from the return link channelizer415. The data modulated RF carrier signal that the EOM434_1receives from an output port of the return link channelizer415can include data corresponding to eight service uplink beams received from service terminals STs. Similarly, the EOMs434_2to434_62can each receive a different data modulated RF carrier signal, from a different output port of the return link channelizer415, with each data modulated RF carrier signal corresponding to a different one or group of service uplink beams received from service terminals STs. In an embodiment, the EOM434_63can receive a data modulated RF carrier signal that corresponds to four service uplink beams received from service terminals STs. In this manner, the EOMs434can be collectively provided with data modulated RF carrier signals corresponding to five hundred service uplink beams (i.e., 62*8+1*4=500).

Gateway Return Link Equipment

FIG. 5will now be used to describe gateway return link equipment500, according to an embodiment of the present technology. Such gateway return link equipment500can also be referred to as an optical gateway return link subsystem500, or more generally, as an optical communication subsystem. Referring toFIG. 5, the optical gateway return link subsystem500is shown as including receiver optics502, an optical amplifier (OA)504, a wavelength-division multiplexing (WDM) demultiplexer (DEMUX)506, sixty three photodetectors (PDs)508_1to508_63, sixty three filters510_1to510_63, sixty three low noise amplifiers (LNAs)512_1to512_63, and sixty three frequency down-converters514_1to514_63. The optical gateway return link subsystem500is also shown as including sixty three demodulator and digital signal processor (DSP) blocks516_1to516_63, and four local oscillators (LOs)522_1to522_4(which can be referred to individually as an LO522, or collectively as the LOs522).

The receiver optics502, which can also be referred to as a telescope, can includes optical elements such as mirrors, reflectors, filters and/or the like. The receiver optics502receives the optical feeder downlink beam (e.g.,102d) that is transmitted through free-space from a space segment (e.g., a satellite100), by the space based return link subsystem400C (or400A or400B) and400D, and provides the received optical feeder downlink beam (e.g., via an optical fiber) to the OA504. A gimbal, and/or the like, can be used to control the steering of the receiver optics502. When the optical feeder downlink beam reaches the gateway, the power of the optical feeder downlink beam is significantly attenuated compared to when it was transmitted by the space based return link subsystem. Accordingly, the OA504is used to amplify the received optical feeder downlink beam before it is provided to the WDM DEMUX506. The OA504can be, e.g., an erbium-doped fiber amplifier (EDFA), but is not limited thereto. The output of the OA504can be referred to as an optically amplified received optical feeder downlink beam. The WDM DEMUX506demultiplexes (i.e., separates) the received optical feeder uplink beam (after it has been optically amplified) into sixty three separate optical signals, each of which is provided to a separate photodetector (PD)508. Each PD508converts the optical signal it receives from the WDM DEMUX506to a respective RF electrical signal. The RF electrical signal produced by each PD508is provided to a respective filter (FTR)510(e.g., a bandpass filter) to remove unwanted frequency components and/or enhance desired frequency components. For an example, where frequency down-conversions were performed by FDCs on the satellite (by the space segment return link equipment400A), each filter510can pass frequencies within the range of 1.5 GHz to 2.0 GHz, but are not limited thereto. The filtered RF electrical signal, which is output by each filter408, is provided to a respective low noise amplifier (LNA)512. Each LNA512amplifies the relatively low-power RF signal it receives from a respective filter510without significantly degrading the signals signal-to-noise ratio. The amplified RF signal that is output by each LNA512is provided to a respective frequency down-converter514, the output of which is provided to a respective demodulator and DSP block516.

Each frequency down-converter514receives an RF signal from an LNA512(which RF signal includes data from subscriber terminals STs, and thus, can be referred to as an RF data signal) and an RF signal from an LO452(which can be referred to as an LO signal), and uses the LO signal to down-convert the RF data signal to baseband. The baseband data signal output by each frequency down-converter514is provided to a respective demodulator and DSP block516. Each demodulator and DSP block516demodulates the baseband data signal it receives, and performs digital signal processing thereon. Such a demodulated data signal can be used to provide data to, or request data from, a server, client and/or the like that is coupled to a network (e.g., the network140inFIG. 1). If the RF frequency of the signals output by the LNAs512are within the frequency range that the demodulation and DSP blocks516operate, then the FDCs514can be eliminated.

A gateway (e.g.,105) can have different optics that are used for transmitting an optical feeder uplink beam (e.g.,102u) to a space segment (e.g., satellite100), than the optics that are used for receiving an optical feeder downlink beam (e.g.,102d) from a space segment. Alternatively, a gateway can use the same optics for both transmitting an optical feeder uplink beam (e.g.,102u) to a space segment and for receiving an optical feeder downlink beam (e.g.,102d) from a space segment. More specifically, the RX optics502shown inFIG. 5can be the same as the TX optics210shown inFIG. 2A.

Methods

FIG. 6will now be used to summarize methods for enabling a ground based subsystem (e.g., the gateway forward link equipment200inFIG. 2A) to produce and transmit an optical feeder uplink beam (e.g.,102uinFIG. 1) to a satellite (e.g.,100inFIG. 1) that is configured to receive the optical feeder uplink beam and in dependence thereon produce and transmit a plurality of RF service downlink beams (e.g.,106d,110d,114dand118dinFIG. 1) within a specified service downlink RF frequency range to service terminals STs, wherein the satellite has a space based forward link subsystem (e.g.,300inFIG. 3A) including a channelizer (e.g.,315inFIGS. 3A and 3B) that is configured to operate within an intermediate RF frequency range that is lower than the specified service downlink RF frequency range. In accordance with certain embodiments, the specified RF frequency range within which the satellite is configured to produce and transmit a plurality of RF service downlink beams is a downlink portion of the Ka band. The downlink portion of the Ka band can be from 17.7 GHz to 20.2 GHz, and thus, have a bandwidth of 2.5 GHz. Alternatively, the downlink portion of the Ka band can be from 17.3 GHz to 20.2 GHz, and thus, have a bandwidth of 2.9 GHz. These are just a few examples, which are not intended to be all encompassing.

Referring toFIG. 6, step602involves emitting a plurality of optical signals (e.g., two hundred and fifty optical signals) each having a different peak wavelength that is within a specified optical wavelength range. Step602can be performed using the lasers202discussed above with reference toFIG. 2A. The specified optical wavelength range may be within the C-band and/or L-band optical wavelengths, as explained above. Further, as explained above, the specified optical wavelength range can be a contiguous optical wavelength range within an IR spectrum, or a non-contiguous optical wavelength range within the IR spectrum. As noted above, visible and/or other optical wavelengths may alternatively be used.

Step604involves electro-optically modulating each of the optical signals with one of a plurality of different data modulated RF carrier signals, each of which has been modulated to carry data for at least one of the plurality of RF service downlink beams, to thereby produce a plurality of optical data signals, each of which carries data for at least one of the plurality of RF service downlink beams and has an RF frequency within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate. Step604can be performed using the EOMs204discussed above with reference toFIG. 2A.

Step606involves multiplexing the plurality of optical data signals to thereby produce a wavelength division multiplexed optical signal that includes data for the plurality of RF service downlink beams. Step606can be performed using the WDM MUX206discussed above with reference toFIG. 2A.

Step608involves producing an optical feeder uplink beam, in dependence on the wavelength division multiplexed optical signal, and step610involves transmitting the optical feeder uplink beam through free-space to the satellite. Steps608and610can be performed by the transmitter optics210discussed above with reference toFIG. 2A. The optical amplifier (OA)208discussed above with reference toFIG. 2Acan also be used to perform step608.

Beneficially, because RF frequencies of the optical data signals produced during the electro-optically modulating step604are within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate, there is an elimination of any need for the satellite to perform any RF frequency conversions upstream of the channelizer of the space based forward link subsystem on the satellite. In other words, the space segment forward link equipment300inFIG. 3Abeneficially does not need any frequency down-converters or any other type of frequency conversion equipment upstream of the forward link channelizer315.

FIG. 7will now be used to summarize methods for enabling a space based forward link subsystem (e.g., the space segment forward link equipment300ofFIG. 3) of a satellite (e.g.,100) to produce and transmit a plurality of RF service downlink beams (e.g.,106d,110d,114dand118dinFIG. 1) within a specified service downlink RF frequency range to service terminals, wherein the space based forward link subsystem of the satellite includes a channelizer (e.g.,315inFIGS. 3A and 3B) that is configured to operate within an intermediate RF frequency range that is lower than the specified service downlink RF frequency range. In accordance with certain embodiments, the specified service downlink RF frequency range within which the satellite is configured to produce and transmit a plurality of RF service downlink beams is a downlink portion of the Ka band. The downlink portion of the Ka band can be from 17.7 GHz to 20.2 GHz, and thus, have a bandwidth of 2.5 GHz. Alternatively, the downlink portion of the Ka band can be from 17.3 GHz to 20.2 GHz, and thus, have a bandwidth of 2.9 GHz. These are just a few examples, which are not intended to be all encompassing.

Referring toFIG. 7, step702involves receiving an optical feeder uplink beam (e.g.,102u) from a ground based subsystem (e.g., the gateway forward link equipment200inFIG. 2A). Step702can be performed by the receiver optics302described above with reference toFIG. 3A.

Step704involves producing, in dependence on the received optical feeder uplink beam, a plurality of (e.g., two hundred and fifty) separate optical signals that each have a different peak wavelength. Step704can be performed by the WDM-DEMUX306described above with reference toFIG. 3A.

Step706, which is performed without performing any frequency converting upstream of the channelizer (e.g.,315inFIG. 3A) of the space based forward link subsystem of the satellite, involves converting each of the separate optical signals into a respective electrical data signal having an RF frequency within a same intermediate RF frequency range within which the channelizer of the space based forward link subsystem of the satellite is configured to operate. Step706can be performed by the PDs308discussed above with reference toFIG. 3A.

Step708involves providing the electrical data signals to the channelizer of the forward link subsystem of the satellite to thereby enable the channelizer of the forward link subsystem of the satellite to perform one or more of analog to digital conversions, digital signal processing, and digital to analog conversions within the intermediate RF frequency range within which the channelizer of the forward link subsystem of the satellite is configured to operate. Such electrical data signals may first be filtered and amplified by the filters310and LNAs312discussed above with reference toFIG. 3A.

Step710involves upconverting frequencies of electrical data signals output from the channelizer so that the frequencies of the electrical data signals are within the specified service downlink RF frequency range. Step710can be performed by the frequency up converters316discussed above with reference toFIG. 3A.

Step712involves producing, in dependence on the electrical data signals, the plurality of RF service downlink beams within the specified service downlink RF frequency range. Step712can be performed, e.g., by the HPAs318, HFs320, OMJs324, and feed horns326discussed above with reference toFIG. 3A.

Step714involves transmitting the plurality of RF service downlink beams within the specified service downlink RF frequency range. Step714can be performed by the feed horns326discussed above with reference toFIG. 3, and more generally, antenna systems.

The method summarized with reference toFIG. 7can additional include using the channelizer of the forward link subsystem of the satellite to digitize RF signals provided to input ports of the channelizer, separate the digitized RF signals into independently routable sub-channels, selectively rearrange and combine the sub-channels, and output at output ports of the channelizer analog RF signals that are used to produce the plurality of RF service downlink beams.

Beneficially, because the RF frequencies of the electrical data signals resulting from the converting step706are within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate, there is an elimination of any need for the satellite to perform any RF frequency conversions upstream of the channelizer of the space based forward link subsystem on the satellite. In other words, the space segment forward link equipment300inFIG. 3Abeneficially does not need any frequency down-converters or any other type of frequency conversion equipment upstream of the forward link channelizer315.

Further details of the methods described with reference toFIGS. 6 and 7can be appreciated from the above description ofFIGS. 1-5.

Certain embodiments of the present technology described above relate to a ground based subsystem for use in transmitting an optical feeder uplink beam to a satellite that is configured to receive the optical feeder uplink beam and in dependence thereon produce and transmit a plurality of RF service downlink beams within a specified service downlink RF frequency range to service terminals, wherein the satellite has a space based forward link subsystem including a channelizer that is configured to operate within an intermediate RF frequency range that is lower than the specified service downlink RF frequency range. The ground based subsystem can include a plurality of lasers, a plurality of electro-optical modulators (EOMs), a wavelength-division multiplexing (WDM), an optical amplifier, and transmitter optics. Each of the lasers is operable to emit an optical signal having a different peak wavelength within a specified optical wavelength range. The specified optical wavelength range can be a contiguous or non-contiguous optical wavelength range within an infrared (IR) spectrum, but is not limited thereto. Each of the EOMs is configured to receive an optical signal from a respective one of the plurality of lasers, receive a different data modulated RF carrier signal that has been modulated to carry data for at least one of the plurality of RF service downlink beams, and output an optical data signal carrying data for at least one of the plurality of RF service downlink beams and having an RF frequency within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate. The WDM multiplexer is configured to receive the optical data signals output by the plurality of EOMs, and combine the plurality of optical data signals into a wavelength division multiplexed optical signal. The optical amplifier is configured to amplify the wavelength division multiplexed optical signal to thereby produce an optically amplified wavelength division multiplexed optical signal. The transmitter optics is configured to receive the optically amplified wavelength division multiplexed optical signal and transmit an optical feeder uplink beam to the satellite in dependence thereon. In accordance with certain embodiments, because the RF frequencies of the optical data signals output by the plurality of EOMs are within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate, there is an elimination of any need for the satellite to perform any RF frequency conversions upstream of the channelizer of the space based forward link subsystem on the satellite. This beneficially reduces equipment on and complexity of the satellite.

In accordance with certain embodiments, the specified service downlink RF frequency range within which the satellite is configured to produce and transmit the plurality of RF service downlink beams is a downlink portion of the Ka band, and the intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate is lower than the downlink portion of the Ka band. The the downlink portion of the Ka band can be from 17.7 GHz to 20.2 GHz, and thus, has a bandwidth of 2.5 GHz. Alternatively, the downlink portion of the Ka band can be from 17.3 GHz to 20.2 GHz, and thus, has a bandwidth of 2.9 GHz. Other downlink frequency bands are also possible and within embodiments of the present technology. The intermediate RF frequency can be, e.g., 1.5 GHz to 2.0 GHz, but is not limited thereto.

In accordance with certain embodiments, the ground based subsystem can also include a plurality of RF modulators configured to produce the data modulated RF carrier signals that are received by the plurality of EOMs, wherein each of the RF modulators receives an RF carrier signal having an RF frequency within the same intermediate RF frequency range within which the channelizer on the satellite is configured to operate. The ground based subsystem can also include one or more oscillators configured to produce the RF carrier signals that are provided to the RF modulators, wherein each of the RF carriers signals has an RF frequency within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate.

Certain embodiments of the present technology described above relate to methods for enabling a ground based subsystem to produce and transmit an optical feeder uplink beam to a satellite that is configured to receive the optical feeder uplink beam and in dependence thereon produce and transmit a plurality of RF service downlink beams within a specified service downlink RF frequency range to service terminals, wherein the satellite has a space based forward link subsystem including a channelizer that is configured to operate within an intermediate RF frequency range that is lower than the specified service downlink RF frequency range. Such a method can include emitting a plurality of optical signals each having a different peak wavelength that is within a specified optical wavelength range. The method can also include electro-optically modulating each of the optical signals with one of a plurality of different data modulated RF carrier signals, each of which has been modulated to carry data for at least one of the plurality of RF service downlink beams, to thereby produce a plurality of optical data signals, each of which carries data for at least one of the plurality of RF service downlink beams and has an RF frequency within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate. The method can further include multiplexing the plurality of optical data signals to thereby produce a wavelength division multiplexed optical signal that includes data for the plurality of RF service downlink beams. Additionally, the method can include producing an optical feeder uplink beam, in dependence on the wavelength division multiplexed optical signal, and transmitting the optical feeder uplink beam through free-space to the satellite. In accordance with certain embodiments, because RF frequencies of the optical data signals produced during the electro-optically modulating are within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate, there is an elimination of any need for the satellite to perform any RF frequency conversions upstream of the channelizer of the space based forward link subsystem on the satellite. The method can also include receiving a plurality of RF carrier signals each of which has a different RF frequency within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate, and producing the data modulated RF carrier signals, which are electro-optically modulated with the optical signals, in dependence on the plurality of RF carrier signals. In accordance with certain embodiments, the specified service downlink RF frequency range within which the satellite is configured to produce and transmit the plurality of RF service downlink beams is within a downlink portion of the Ka band, wherein the intermediate RF frequency range within which the channelizer of the space based forward link subsystem on the satellite is configured to operate is lower than the downlink portion of the Ka band.

Certain embodiments of the present technology described above relate to space based forward link subsystem of a satellite for use in transmitting a plurality of RF service downlink beams within a specified downlink RF frequency range to service terminals. The space based forward link subsystem can include receiver optics, an optical amplifier, a wavelength-division multiplexing (WDM), a plurality of photodetectors, a channelizer, frequency upconverters, and RF components and antennas downstream of the frequency upconverters. The receiver optics are configured to receive an optical feeder uplink beam from a ground based subsystem. The optical amplifier is optically coupled to the receiver optics and configured to amplify an optical feeder uplink signal that is output from the receiver optics. The WDM demultiplexer is optically coupled to the optical amplifier and configured to separate the amplified optical feeder uplink signal, which is output from the optical amplifier, into a plurality of separate optical signals that each have a different peak wavelength. The plurality of photodetectors, which are upstream of the channelizer of the space based forward link subsystem, are each operable to convert a different one of the optical signals that are output from the WDM demultiplexer, to a respective electrical data signal having an RF frequency within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem is configured operate. The channelizer of the space based forward link subsystem including a plurality of input ports, a plurality of output ports, and circuitry therebetween configured to operate within an intermediate RF frequency range that is lower than the specified downlink RF frequency range. The input ports of the channelizer receive the electrical data signals produced by the photodetectors, which are optionally filtered and/or amplified before being provided to the input ports. The frequency upconverters, which are downstream of the output ports of the channelizer of the space based forward link subsystem, are configured to convert frequencies of signals output by the channelizer from being within the intermediate RF frequency range to being within the specified downlink RF frequency range. RF components and antennas downstream of the frequency upconverters are configured to produce and transmit the plurality of RF service downlink beams within the specified downlink RF frequency range. In accordance with certain embodiments, because the RF frequencies of the electrical data signals output by the plurality of photodetectors are within the same intermediate RF frequency range within which the channelizer of the space based forward link subsystem is configured to operate, there is an elimination of any need for the space based forward link subsystem to perform any RF frequency conversions upstream of the channelizer of the space based forward link subsystem. This beneficially reduces equipment on and complexity of the satellite. In accordance with certain embodiments, the channelizer of the forward link subsystem of the satellite is configured to digitize RF signals provided to input ports of the channelizer, separate the digitized RF signals into independently routable sub-channels, selectively rearrange and combine the sub-channels, and output at output ports of the channelizer analog RF signals that are used to produce the plurality of RF service downlink beams.

In accordance with certain embodiments, the specified service downlink RF frequency range within which the satellite is configured to produce and transmit the plurality of RF service downlink beams comprises a downlink portion of the Ka band, and the intermediate RF frequency range within which the channelizer of the space based forward link subsystem is configured to operate is lower than the downlink portion of the Ka band.

Certain embodiments of the present technology described above relate to methods for enabling a space based forward link subsystem of a satellite to produce and transmit a plurality of RF service downlink beams within a specified service downlink RF frequency range to service terminals, wherein the space based forward link subsystem of the satellite includes a channelizer that is configured to operate within an intermediate RF frequency range that is lower than the specified service downlink RF frequency range. Such a method can include receiving an optical feeder uplink beam from a ground based subsystem. The method can also include producing, in dependence on the received optical feeder uplink beam, a plurality of separate optical signals that each have a different peak wavelength. In accordance with certain embodiments, the method also include converting each of the separate optical signals into a respective electrical data signal having an RF frequency within a same intermediate RF frequency range within which the channelizer of the space based forward link subsystem of the satellite is configured to operate, without performing any frequency converting upstream of the channelizer of the space based forward link subsystem of the satellite. The method can also include providing the electrical data signals to the channelizer of the forward link subsystem of the satellite to thereby enable the channelizer of the forward link subsystem of the satellite to operate within the intermediate RF frequency range within which the channelizer of the forward link subsystem of the satellite is configured to operate. Additionally, the method can include upconverting frequencies of electrical data signals output from the channelizer so that the frequencies of the electrical data signals are within the specified service downlink RF frequency range. Further, the method can include producing, in dependence on the electrical data signals, the plurality of RF service downlink beams within the specified service downlink RF frequency range, transmitting the plurality of RF service downlink beams within the specified service downlink RF frequency range. In accordance with certain embodiments, the specified service downlink RF frequency range within which the satellite is configured to produce and transmit the plurality of RF service downlink beams comprises a downlink portion of the Ka band, and the intermediate RF frequency range within which the channelizer of the space based forward link subsystem of the satellite is configured to operate is lower than the downlink portion of the Ka band.

The foregoing detailed description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the subject matter claimed herein to the precise form(s) disclosed. Many modifications and variations are possible in light of the above teachings. The described embodiments were chosen in order to best explain the principles of the disclosed technology and its practical application to thereby enable others skilled in the art to best utilize the technology in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope be defined by the claims appended hereto.