Patent Description:
Current HF communication is a beyond line of sight point to point communication system that is subject to random ionospheric perturbations that reduce the average daily sustained data rate to tens of kbps per second even though burst rate of <NUM> kbps are possible.

The HF communication problem is complicated further by the limitations of the antenna. For example, manpack HF radios typically carry low power handling (e.g., less than <NUM> Watts) roll-able antennas that have poor gains (e.g., -<NUM> decibel (isotropic) (dBi) at <NUM> Megahertz (MHz) and -<NUM> dBi at <NUM>), and transmit performance is typically limited by voltage standing wave ratio (VSWR), which varies considerably and appropriate chunks of spectrum need to be selected where transmit performance is acceptable.

At the other end, fixed site installations, such as an HF ground station (HFGS), typically use broadband antennas that occupy large areas and can transmit and receive on any frequency in the HF band without an antenna coupler and have gains of +6dBi.

In the middle, are constrained platforms, such as airplanes, which typically use shunt antennas (-<NUM> dBi to -<NUM> dBi) and communicate through a coupler so that they can transmit on nearly all HF frequencies. These couplers have bandwidth limitations in that most couplers have a flat gain only over <NUM> to <NUM> kilohertz (kHz) at the low end of the band and around <NUM> at the higher end. This is one of the reasons why newer Wideband HF (WBHF) standards currently only support bandwidths <NUM> and lower.

Vehicular platforms typically use extendable whips (e.g., <NUM> to <NUM> feet in length) that require the use of a coupler (especially at high transmit powers) and typically have gains in the -<NUM> to +<NUM> dBi range. <CIT>, XP032092894 ("Network architecture for mission critical communications using LEO satellites"), <CIT> and <CIT> relate to satellite networks.

A system as defined in claim <NUM> is provided.

A method as defined in claim <NUM> is provided.

The appearances of the phrase "in some embodiments" in various places in the specification are not necessarily all referring to the same embodiment, and embodiments of the inventive concepts disclosed may include one or more of the features expressly described or inherently present herein, or any combination or sub-combination of two or more such features, along with any other features which may not necessarily be expressly described or inherently present in the instant disclosure.

Broadly, embodiments of the inventive concepts disclosed herein are directed to a method for satellite networked high frequency terminal to terminal communications.

Some embodiments ensure that data rates between <NUM> kilobits per second (kbps) and <NUM> kbps can be consistently delivered with <NUM> Watts (W) of transmit power using a processing HF low earth orbit (LEO) satellite. Some embodiments also enable mobile ad hoc network (MANET) networking of multiple geographically separated nodes. A network of LEO HF satellites may enable seamless ad-hoc networking of geographically separated HF nodes at sustained data rates between <NUM> kbps and <NUM> kbps during the day or night. The use of a wideband coupler-less HF system on the satellite may enable the satellite to receive on one frequency and transmit on another enabling anti-jam HF communication. For example, a coupler is typically bandwidth limited, it would be advantageous to use coupler-less communication to receive multiple channels simultaneously. In some embodiments, a coupler is only needed during transmit to match impedance of the radio (fixed) to antenna (changing with frequency). The earth to satellite system can be traditional HF/ wideband HF (WBHF) links, where the satellite to earth HF links can be wider (e.g., <NUM>) channels that are not impacted considerably by the ionosphere as the ionosphere is not used for refraction of the signals back to earth.

Today, HF is a point to point communication link. The data rate that can be delivered is dependent on the available transmit power and the condition of the ionospheric channel. There are considerable periods of time when no HF communication is possible. Some embodiments enable consistent data throughput between nodes at all times of the day as some embodiments do not rely on the ionosphere to refract the signal. A LEO satellite may intercept the communication and may use radiofrequency (RF) and/or optical inter-satellite links (ISLs) to reach a BLOS destination node.

Some embodiments may network multiple geographically separated nodes with variable antenna performance and power amplifiers sizes seamlessly.

Some embodiments may include satellite relayed HF communications. Some embodiments may use a processing satellite in low earth orbit with inter-satellite relaying using RF and/or optical inter-satellite links. Some embodiments may include seamless geographically separated HF networking enabled by a coupler-less satellite-based HF relay. For example, coupler-less HF operation may use a different type of antenna system than the broadband antennas that are typically used in HF.

As used throughout, robust may mean resistant to enemy jamming and interference.

As used throughout, spreading factor may mean the amount of redundancy introduced into the data rate to add robustness. For example, in Universal Mobile Telecommunications Service (UMTS) (<NUM> Cellular) at the <NUM> bits per second (bps) data rate, each data bit is multiplied by a <NUM>-chip spreading factor code to make transmitted data more resistant to interference and jamming.

As used throughout, processing gain may be a metric to measure the robustness. For example, for a <NUM>-chip spreading factor code, processing gain may be equal to <NUM>*log<NUM>(Spreading Factor) = <NUM>*log<NUM>(<NUM>) = <NUM> decibel (dB).

Referring now to <FIG>, an exemplary embodiment of a system <NUM> according to the inventive concepts disclosed herein is depicted. The system <NUM> may be implemented as any suitable system. In some embodiments, the system <NUM> may be a network (e.g. a global network (e.g., a global mobile ad hoc network (MANET)). The system <NUM> may include an ad hoc satellite network <NUM> (e.g., a mobile ad hoc satellite network <NUM>) and terminals <NUM>.

The ad hoc satellite network <NUM> may including multiple satellites <NUM>. Some or all of the multiple satellites <NUM> may be communicatively coupled to other of the multiple satellites <NUM> at any given time. The multiple satellites <NUM> may include a first satellite <NUM> and a second satellite <NUM>. In some embodiments, the ad hoc satellite network <NUM> may be a global ad hoc satellite network <NUM>. In some embodiments, the multiple satellites104 may be low earth orbit (LEO) satellites <NUM>. For example, the first satellite <NUM> and a second satellite <NUM> may be LEO satellites in or below the ionosphere such that the first satellite <NUM> and a second satellite <NUM> can communicate to and from earth using HF communications without reflection and/or refraction of HF signals caused by the ionosphere; however, other satellites of the ad hoc satellite network <NUM> may be non-LEO satellites (e.g., in Medium Earth Orbit (MEO) and/or Geostationary Earth Orbit (GEO)).

As shown in <FIG>, for example, each of some or all of the satellites <NUM> (e.g., LEO satellites <NUM>) may include: at least one receive high frequency (HF) antenna <NUM> (e.g., at least one receive-only HF antenna <NUM>) configured to receive HF signals; at least one transmit HF antenna <NUM> (e.g., at least one fractal transmit HF antenna <NUM>) configured to transmit HF signals; at least one inter-satellite transmitter <NUM> configured to transmit signals to at least one other satellite <NUM> of the ad hoc satellite network <NUM>; at least one inter-satellite receiver <NUM> configured to receive signals from at least one other satellite <NUM> of the ad hoc satellite network <NUM>; at least one cosite filter <NUM>; at least one power amplifier (PA) <NUM>; and/or at least one processor <NUM> communicatively coupled to the at least one receive HF antenna <NUM>, the at least one transmit HF antenna <NUM>, the at least one inter-satellite transmitter <NUM>, the at least one inter-satellite receiver <NUM>, the at least one cosite filter <NUM>, and/or the at least one power amplifier <NUM>. The at least one processor <NUM> may be implemented as any suitable type and number of processors. For example, the at least one processor <NUM> may include at least one general purpose processor (e.g., at least one central processing unit (CPU)), at least one digital signal processor (DSP), at least one application specific integrated circuit (ASIC), and/or at least one field-programmable gate array (FPGA). The at least one processor <NUM> may be configured to perform (e.g., collectively perform if more than one processor) and/or cause (e.g., collectively cause) to be performed any or all of the operations disclosed throughout. The at least one processor <NUM> may be configured to run various software applications or computer code stored (e.g., maintained) in a non-transitory computer-readable medium (e.g., memory) and configured to execute various instructions or operations. In some embodiments, some or all of the satellites <NUM> may be configured for coupler-less HF operation.

For example, fractal transmit HF antenna <NUM> may be used to trade off bandwidth flatness for increased size. The fractal transmit HF antenna <NUM> may provide multiple <NUM> bands in the <NUM> to <NUM> HF band. This is equivalent to having multiple narrowband transmit antennas in one antenna, each with <NUM> to <NUM> of spectrally flat frequency chunks, that are impedance matched. In some embodiments, multiple fractal transmit HF antennas <NUM> may be used to get enough spectrally flat <NUM> to <NUM> frequency chunks with a fixed impedance to the transmitter.

In some embodiments, the transmit HF antenna(s) <NUM> may be frequency constrained to permit coupler-less HF operation. For example, a single or multiple transmit-only antennas <NUM> may be used. These antennas <NUM>, <NUM> may be springloaded to expand to a required length, such as between <NUM> and <NUM> feet, and may trail behind the satellite <NUM>.

In some embodiments, the satellites <NUM> may use space wheels or rotating magnets to point the antennas <NUM>, <NUM> directly underneath the satellite <NUM> or angled to communicate at a slant angle to the earth. In some embodiments, the inter-satellite transmitter <NUM> and inter-satellite receiver <NUM> may point outwards into space to communicate with satellites in higher orbits, if needed.

In some embodiments, the satellite <NUM> may have a direct sampling receiver that processes an entire bandwidth of interest. In some embodiments, to reduce thermal and power consumption issues, only sufficient processing power may be provided to handle <NUM> to <NUM> contiguous or non-contiguous channels.

In some embodiments, cosite filters <NUM> may be used if there are multiple transmitters on the satellite <NUM>. For example, a low transmit power (e.g., <NUM> Watts) may enable use of space efficient cosite filters <NUM>. Space and power concerns may favor use of one transmitter shared between the multiple transmit antennas <NUM>.

As shown in <FIG>, for example, the terminals <NUM> may include manpack terminals, ground vehicular terminals, airborne vehicular terminals, maritime vehicular terminals, and/or fixed site terminals. Each terminal <NUM> may include at least one HF transmit antenna <NUM> configured transmit an HF communication payload to the ad hoc satellite network <NUM>, at least one processor <NUM>, and/or at least one HF receive antenna <NUM> configured receive the HF communication payload from the ad hoc satellite network <NUM>. Some or all of the HF transmit antenna <NUM>, at least one HF receive antenna <NUM>, and/or the at least one processor <NUM> may be communicatively coupled at any given time. The at least one processor <NUM> may be implemented as any suitable type and number of processors. For example, the at least one processor <NUM> may include at least one general purpose processor (e.g., at least one central processing unit (CPU)), at least one digital signal processor (DSP), at least one application specific integrated circuit (ASIC), and/or at least one field-programmable gate array (FPGA). The at least one processor <NUM> may be configured to perform (e.g., collectively perform if more than one processor) and/or cause (e.g., collectively cause) to be performed any or all of the operations disclosed throughout. The at least one processor <NUM> may be configured to run various software applications or computer code stored (e.g., maintained) in a non-transitory computer-readable medium (e.g., memory) and configured to execute various instructions or operations.

For example, the system <NUM> may include: a first terminal <NUM> including an HF transmit antenna <NUM> configured transmit an HF communication payload to the ad hoc satellite network <NUM>; and a second terminal <NUM> including an HF receive antenna <NUM> configured receive the HF communication payload from the ad hoc satellite network <NUM>.

In some embodiments, two different sets of satellites <NUM> in the network <NUM> may have HF visibility to the transmit and receive HF terminals <NUM> and ISL can bridge the two sets of satellites <NUM> to provide BLOS HF communication by routing the HF payload via the ISL. For example, some or all of the multiple satellites <NUM> may be communicatively coupled to other of the multiple satellites <NUM> at any given time via at least one of radiofrequency (RF) inter-satellite cross links or optical inter-satellite cross links. For example, a first group of multiple geographically separated satellites <NUM> of the global ad hoc satellite network <NUM> may be visible to the first terminal <NUM>. For example, a second group of multiple geographically separated satellites <NUM> of the global ad hoc satellite network <NUM> may be visible to the second terminal <NUM>. For example, successful transmission of the HF communication payload to the ad hoc satellite network <NUM> may be improved by visibility of the first group of multiple geographically separated satellites <NUM> by the first terminal <NUM> as compared to visibility of a single satellite <NUM>. For example, successful reception of the HF communication payload from the ad hoc satellite network <NUM> may be improved by visibility of the second group of multiple geographically separated satellites <NUM> by the second terminal <NUM> as compared to visibility of a single satellite <NUM>.

In some embodiments, the HF transmit antenna <NUM> of the first terminal <NUM> may be configured to transmit the HF communication payload to the first satellite <NUM> of the ad hoc satellite network <NUM>, and the HF receive antenna <NUM> of the second terminal <NUM> may be configured to receive the HF communication payload from the second satellite <NUM> of the ad hoc satellite network <NUM>.

In some embodiments, the HF transmit antenna <NUM> of the first terminal <NUM> may be configured to transmit the HF communication payload to the first satellite <NUM> of the ad hoc satellite network <NUM>, and the HF receive antenna <NUM> of the second terminal <NUM> may be configured to receive the HF communication payload from the first satellite <NUM> of the ad hoc satellite network <NUM>.

In some embodiments, the HF transmit antenna <NUM> of the first terminal <NUM> may be configured to transmit the HF communication payload on a first frequency to the ad hoc satellite network <NUM>, and the HF receive antenna <NUM> of the second terminal <NUM> may be configured to receive the HF communication payload on a second frequency from the ad hoc satellite network <NUM>, wherein the first frequency is different from the second frequency. For example, the second frequency may be pseudo-randomly selected by at least one of: at least one satellite <NUM> and/or at least one terminal <NUM>. In some embodiments, at least one of the first frequency or the second frequency may be higher than is possible using an ionosphere reflective HF transmission.

In some embodiments, communication of the HF communication payload from the first terminal <NUM> to the second terminal <NUM> via the ad hoc satellite network <NUM> may have a higher level of robustness than is possible using an ionosphere reflective HF transmission.

In some embodiments, covert communication of the HF communication payload from the first terminal <NUM> to the second terminal <NUM> via the ad hoc satellite network <NUM> may be supported by using at least one of frequency hopping or direct sequence spreading.

Terrestrial and airborne HF networks typically rely on near vertical incidence skywave (NVIS) communication for short range communication (<NUM> - <NUM>) and sky-wave communication (<NUM> - <NUM>). In the current solar cycle, frequencies above <NUM> typically pass unimpeded by the ionosphere into outer space, and hence are not used for ionosphere reflective HF transmission; however, in some embodiments, HF frequencies above <NUM> may be supported (e.g., between the terminals <NUM> and the satellites <NUM>) as satellites <NUM> may intercept the transmission within the ionosphere.

In some embodiments, large beam widths of space based antennas <NUM>, <NUM> and antennas <NUM>, <NUM> used on tactical platforms do not require any specialized pointing. One factor to account for is the maximum gain of the tactical platforms is frequency specific and oriented to the type of communication envisaged (e.g. NVIS, Sky wave). The degradation of antenna gains may also need to be accounted for in the link budget.

In some embodiments, HF terminals <NUM> on earth can use frequency as a means of targeting their relay satellite cluster. Broad beam widths (of the order of <NUM> degrees) coupled with the frequency selective maximum gain direction allows multiple relay clusters to be targeted.

In some embodiments, the terminals <NUM> may be transformed from all beyond line of sight (BLOS) HF communication to line of sight (LOS) HF from Earth to Satellite or Satellite to Earth. For example, Maximum Path Loss for a <NUM> link may be <NUM> dB, and BLOS connectivity may be supported using inter-satellite relays. For example, orbits may be selected that have a maximum slant range of <NUM>. For example, the ionosphere extends from <NUM> Kilometer (Km) to <NUM>,<NUM> in height above the earth. The LEO satellites <NUM> may be much lower than a top of the ionosphere, such as in <NUM> to <NUM> altitude range. But slant distances can be as much as <NUM> from the earth when the satellite is not directly above.

In some embodiments, a link can be closed with a <NUM> Watt (W) power amplifier and sustain a data rate of <NUM> kilobits per second (kbps) using WBHF from earth, but may use a 100W power amplifier on the satellite. In some embodiments, space to earth links might not be able to sustain data rates at <NUM> kbps at low frequencies at all times. For example, dropping the data rate to <NUM> kbps (signal-to noise-ratio (SNR): <NUM> dB) may provide a margin of <NUM> dB, and a data rate of <NUM> kbps (SNR: <NUM> dB) may provide a <NUM> dB margin.

WBHF is currently limited to <NUM>. WBHF's most robust mode is <NUM> bps in <NUM> and can be operated at SNRs as low as -<NUM> dB. Some embodiments support <NUM> bps in <NUM>, which may provide an additional <NUM> dB of processing gain to leverage for anti-jam and/or covert purposes. The earth to space link will typically be operated at channel bandwidths less than <NUM> due to transmit limitations on existing systems, and hence have to be satisfied with relatively low processing gains on that front compared to relatively larger possible processing gains on the space to earth link.

In some embodiments, the space to earth link is expected to be more covert, because of the increase in bandwidth to <NUM>. Delivering an average of <NUM> bps in a <NUM> bandwidth permits performance of signal processing techniques that support Low Probability of Intercept (LPI) and/or Low Probability of Detection (LPD) characteristics without increasing the processing requirements of the space and earth terminals. In some embodiments, a coupler is only needed during transmission and, while receiving, the coupler can be bypassed on the earth based platforms to access wider channels, if needed.

Today, both ends of the HF link operate on the same frequency. In some embodiments, the transmission from the earth can be on one frequency, and the receive from the satellite <NUM> can be on different frequencies - as the space segment can select a frequency pseudo-randomly for talking to every node (e.g., terminal <NUM>) on the earth.

In some embodiments, the simultaneous visibility of multiple geographically separated satellites <NUM> may ensure that the ionospheric conditions are different in the vicinity of each satellite <NUM> and improves the probability of successful message reception.

In some embodiments, covert communication may be supported that relies on frequency hopping and/or direct sequence spreading, as would be understood to those of skill in the art of secure signals.

Some embodiments may include forming a global network with N participants. An exemplary embodiment may include up to <NUM> participants; however, other embodiments may include a larger number of participants. For example, participants can be any terminal type (e.g., manpacks, vehicular, airborne, maritime, and/or fixed-site). Each earth based participant (e.g., <NUM>) can select a transmit frequency that changes pseudo-randomly at a very slow rate, which may be intentional as most couplers use mechanical relays that have a life of <NUM>,<NUM> to <NUM>,<NUM> band switching cycles and may require <NUM>+ milliseconds to tune the coupler. Each earth based participant (e.g., <NUM>) can select its own frequency table that uses a set of receive frequencies. The space terminal (e.g., <NUM>) may pseudo-randomly use one of the receive frequencies to communicate with the earth based terminal (e.g., <NUM>). A coupler may have a tune time of <NUM> millisecond and high power transmitters may have a ramp up time of <NUM> milliseconds. Since some embodiments are using a low power transmitter and a coupler-less design, the space terminal (e.g., <NUM>) can tune and ramp-up power within a millisecond, thereby permitting hops through the ad hoc satellite network <NUM> at a much faster rate. An inter-satellite HF networking layer may connect the HF satellites <NUM> using optical and/or RF inter-satellite cross links and create a global HF ad-hoc satellite network <NUM>. These inter-satellite link may be stable for <NUM> to <NUM> minutes and can be networked by reactive and/or proactive means. In some embodiments, to ensure robustness, the link setup process may setup multiple routes between transmit and receive satellite <NUM> nodes, and messages can be sent over multiple paths based on configuration. For example, multiple satellites <NUM> can reach the earth terminal <NUM>, and multiple geographically separated satellites <NUM> can receive the transmission from the earth terminal <NUM> due to an antenna pattern. This may enable an optimal set of satellites <NUM> to be selected to ensure that a message is seamlessly delivered with the a desired (e.g., required) level of robustness.

Referring now to <FIG>, an exemplary embodiment of a method <NUM> according to the inventive concepts disclosed herein may include one or more of the following steps. Additionally, for example, some embodiments may include performing one more instances of the method <NUM> iteratively, concurrently, and/or sequentially. Additionally, for example, at least some of the steps of the method <NUM> may be performed in parallel and/or concurrently. Additionally, in some embodiments, at least some of the steps of the method <NUM> may be performed non-sequentially.

A step <NUM> may include transmitting, by a high frequency (HF) transmit antenna of a first terminal, a HF communication payload to an ad hoc satellite network, the ad hoc satellite network including multiple satellites, some or all of the multiple satellites communicatively coupled to other of the multiple satellites at any given time, the multiple satellites including a first satellite and a second satellite, each of the first satellite and a second satellite comprising: at least one receive HF antenna configured to receive HF signals; at least one transmit HF antenna configured to transmit HF signals; at least one inter-satellite transmitter configured to transmit signals to at least one other satellite of the ad hoc satellite network; at least one inter-satellite receiver configured to receive signals from at least one other satellite of the ad hoc satellite network; and at least one processor communicatively coupled to the at least one receive HF antenna, the at least one transmit HF antenna, the at least one inter-satellite transmitter, and the at least one inter-satellite receiver.

A step <NUM> may include receiving, by an HF receive antenna of a second terminal, the HF communication payload from the ad hoc satellite network.

As will be appreciated from the above, embodiments of the inventive concepts disclosed herein may be directed to a method for satellite networked high frequency terminal to terminal communications.

As used throughout and as would be appreciated by those skilled in the art, "at least one non-transitory computer-readable medium" may refer to as at least one non-transitory computer-readable medium (e.g., at least one computer-readable medium implemented as hardware; e.g., at least one non-transitory processor-readable medium, at least one memory (e.g., at least one nonvolatile memory, at least one volatile memory, or a combination thereof; e.g., at least one random-access memory, at least one flash memory, at least one read-only memory (ROM) (e.g., at least one electrically erasable programmable read-only memory (EEPROM)), at least one on-processor memory (e.g., at least one on-processor cache, at least one on-processor buffer, at least one on-processor flash memory, at least one on-processor EEPROM, or a combination thereof), at least one storage device (e.g., at least one hard-disk drive, at least one tape drive, at least one solid-state drive, at least one flash drive, at least one readable and/or writable disk of at least one optical drive configured to read from and/or write to the at least one readable and/or writable disk, or a combination thereof).

Claim 1:
A system, comprising:
an ad hoc satellite network (<NUM>) including multiple satellites (<NUM>), some or all of the multiple satellites communicatively coupled to other of the multiple satellites at any given time, the multiple satellites including a first satellite and a second satellite, each of the first satellite and a second satellite comprising:
at least one receive high frequency HF antenna (<NUM>) configured to receive HF signals, wherein the at least one receive HF antenna includes a receive-only HF antenna;
at least one transmit HF antenna (<NUM>) configured to transmit HF signals;
at least one inter-satellite transmitter (<NUM>) configured to transmit signals to at least one other satellite of the ad hoc satellite network;
at least one inter-satellite receiver (<NUM>) configured to receive signals from at least one other satellite of the ad hoc satellite network; and
at least one processor (<NUM>) communicatively coupled to the at least one receive HF antenna, the at least one transmit HF antenna, the at least one inter-satellite transmitter, and the at least one inter-satellite receiver;
a first terminal (<NUM>) including an HF transmit antenna (<NUM>) configured transmit an HF communication payload to the ad hoc satellite network; and
a second terminal (<NUM>) including an HF receive antenna (<NUM>) configured receive the HF communication payload from the ad hoc satellite network;
wherein each of the first satellite and the second satellite is configured for coupler-less HF operation.