System and method for real-time multiplexing phased array antennas to modems

RELATED APPLICATIONS This disclosure claims the benefit of priority to U.S. Provisional Application No. 62/874,447, filed July 15, 2019, the disclosure of which is incorporated herein by reference in its entirety.

The present disclosure relates generally to the field of wireless communications, such as satellite-based communications and microwave point-to-point communications, as well as control of multiple phased array antennas communicating with multiple antennas.

(Related Art) Satellite-based communications is a common way for ships, planes, trains, and people to connect to the global Internet. Connection methods vary from simple connections at low frequencies to complex and expensive connections at higher frequencies.

The complications are mainly related to antennas. Higher frequency communications require the use of antennas that are pointed at the satellite. Sometimes the user moves and the satellite is fixed relative to the Earth, but the antenna must remain pointed at the satellite. Sometimes the satellite moves and the antenna must remain pointed at the satellite. In either case, an autopilot antenna that can maintain steering has a significant advantage. And vice versa. In many cases the satellite itself needs to point a beam at a specific point on the Earth. In either case, there is a transmitter and a receiver, and one or both of the two may need to steer the beam to make their respective connections.

Autosteered antenna systems come in two forms: Mechanically Steered Antennas (MSA), which utilize some form of parabolic dish, patch array, or other planar and three-dimensional antenna design in combination with a motor assembly to steer it toward a receiver, either directly or through some type of amplifying lens, or Electronically Steerable Arrays (ESA), which use various forms of electronically steering the beam with no moving parts, such as by phase shifting in a phased array antenna.

A common way to describe the performance of a component such as an antenna system is SWAP-C+R, which stands for size, weight, power consumption, cost, and reliability. These are some of the major factors that determine whether an antenna system is suitable for a particular purpose. As each of the variables increases, the number of applicable use cases for the antenna decreases. For example, trains require low profile antennas so they can pass through tunnels, and airplanes require low profile antennas to minimize drag and reduce vortices that greatly affect flight characteristics. MSAs have the disadvantage of being physically large in height and are less reliable due to wear of moving parts over time. ESAs typically have the disadvantage of being heavy due to the large amount of power they consume and the heat sinks or other heat dissipation solutions associated with that power, and even though they are physically smaller than MSAs, they are still very bulky and therefore ultimately more expensive. However, ESAs are usually smaller in size and more reliable than MSAs, making them preferable for certain use cases.

Another important variable in antenna design is the aperture size. The aperture size represents the effective collecting surface area of the antenna. This is usually some form of x and y coordinate, representing the surface area presented to the transmitting satellite. The most desirable antennas have a large aperture (x and y) that always faces the source and has no z (height/thickness). The larger the aperture size, the higher the gain of the received or transmitted signal and therefore the greater the overall system spectral efficiency, i.e., higher data rates with less bandwidth, which would be a great advantage in the market. Furthermore, the higher the gain, the less likely the transmitted beam is to place power in unintended directions and cause interference. This is because the higher the gain, the narrower the beam. Furthermore, the narrower beam of a high gain antenna makes the antenna less susceptible to such unintended interference. From a signal strength standpoint, a larger x/y surface area, i.e., aperture, is required, which also reduces the power amplifier level required for a given connection, i.e., the power that needs to be fed to the antenna.

A challenge with the aforementioned technology is that the large SWAP-C+R has limited the applications of the antenna system. The most efficient beam is a direct beam in front of the antenna itself, called the boresight. The boresight is a straight line to the center and above the antenna, i.e. perpendicular to the radiating plane of the antenna. The MSA can rotate the entire antenna, thus maintaining the boresight to the satellite, and therefore the aperture size it presents to the satellite. Conversely, the ESA electronically tilts the beam, so it presents a smaller apparent aperture to the satellite, and therefore performs worse by a factor of 2-4 depending on the off-axis of the receiver and transmitter. Also, the technological reduction in size results in a scan loss of 10*log10COSΘ, which is directly related to the apparent area, i.e. the aperture size as seen in the steering direction. The MSA has no scan loss, but requires a large swept volume to maintain the pointing direction. This increases both size and weight. In some cases, antennas combine both the ESA and MSA into a single antenna, using the ESA for one direction, perhaps in azimuth, and a mechanical steering assembly for elevation. These exhibit a well-balanced SWaP-C+R for the application.

Another problem with current antenna systems is that physical size often limits the receive and transmit antenna assemblies to only one per application. For example, aircraft require steerable antennas to maintain connectivity with satellites. However, SWaP-C limits the number of steerable antennas to one. As a result, when the aircraft pitches and turns, it loses connectivity to the satellite.

Also, in many cases, a terminal needs to connect to multiple satellites simultaneously, each of which may require a special modem with a special waveform, so it may be necessary to switch modem/antenna combinations as needed.

Therefore, there is a need for techniques to improve satellite communications.

The following summary of the disclosure is intended to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and thus is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below.

The embodiments of the present disclosure allow for multiple antennas and modem multiplexing, allowing different modem/antenna combinations to be configured and therefore transmission paths to be generated on the fly.

The disclosed embodiments allow for improved control of communication paths between communication devices and satellites, configuring different communication paths in real-time based on parameters such as available satellites, received signal strength from each available satellite, amount and type of data to be transmitted, transmission cost on each communication path, account privileges to utilize any of the available communication paths based on user subscriptions, etc.

The disclosed embodiments allow real-time control of moving platform and inter-satellite communications while maintaining communication channels despite the movement of the platform, e.g., an airplane or ship. On such a platform, there may be multiple phased array antennas, each with a boresight that points in a different direction (e.g., up, left, right, etc.) relative to the platform. As the platform moves, e.g., turns, a controller can determine the best antenna to use to transmit, and select and deselect antennas in real-time, always selecting the antenna with the best RSSI (received signal strength).

In the disclosed embodiments, lower SWaP-C ESA topologies are employed by using variable dielectric technology in multiple ESAs, such as ESA phase shifters. The use of variable dielectrics enables new connection methods for either satellite or terrestrial antenna systems, and these new topologies are particularly advantageous to the embodiments disclosed herein.

Data encryption is often used for security purposes, but encryption has limitations with the advent of quantum computing. Thus, the disclosed embodiment utilizes multiple satellites to split data across at least one satellite and multiple other paths, and recombine the data at a secure location. Thus, intercepting an individual path represents only a portion of the encrypted data file. Thus, the disclosed aspects provide a more secure file transfer mechanism.

In other cases, it may be necessary to utilize multiple ESAs, such as when a platform such as a train or airplane moves and turns, selecting the ESA facing the maximum boresight for maximum efficiency. Such a mechanism for automatically switching between ESAs is provided by the embodiments disclosed herein.

In still other cases, there may be rapid transitions and interference between multiple ESAs, i.e., aperture size may need to be small, and multiple ESAs may need to be usably and potentially placed at odd angles to each other, and distance between the ESAs may be significant. A method is also provided by the disclosed embodiments to utilize very low SWaP-C ESAs, dynamically combine the signal strengths of these multiple ESAs, and potentially dynamically change the modems associated with such various combinations of ESAs. Dynamically means managed in real time, such that each of the various connections can be replaced or removed at any given moment, or new connections added as advantageous depending on the transmit/receive situation.

Additionally, in other cases where multiple ESAs are present, baseband solutions may include some MIMO providing nulling or other baseband functions, either digitally or analog, to increase data rates.

In a disclosed embodiment, a satellite communication antenna system is provided that includes a plurality of antennas, each including a phased array radiator, a plurality of modems, a switch that dynamically couples any of said antennas to any of said modems, a plurality of communication devices, a router that dynamically couples any of said communication devices to any of said modems, and a controller that controls said switch and router to provide real-time instructions connecting said plurality of antennas, said plurality of modems, and said plurality of communication devices.

In a general aspect, the system is mounted on a mobile platform for satellite communications and includes a plurality of phased array antennas, each having a plurality of radiators and a plurality of phase shifters, each introducing a delay to an RF signal propagating therethrough; at least one phase controller that operates said phase shifters to introduce said delay to said RF signals; a plurality of modems; a switch operable to connect any of said modulators/demodulators to any of said phased array antennas in real time as determined; a communications device; a router operable to route signals between any of said modulators/demodulators and said communications device; and control circuitry that provides instructions in real time to said switch forming a connection between said modulators/demodulators and any of said phased array antennas, and to said router that routes signals between said modulators/demodulators and any of said communications devices.

In a general aspect, a method for controlling communications of multiple phased array antennas and multiple satellites is provided, comprising: receiving an indication from a computing device of data to be transmitted to a satellite; determining an available satellite for communications; directing the phased array antenna to orient to a selected satellite; receiving a received signal strength (RSSI) signal from the phased array antenna; selecting a transmitting phased array antenna based on the RSSI signal; connecting the transmitting phased array antenna to a selected modulator; operating a router to connect the modulator to the computing device; and commencing transmission of the data to be transmitted.

In a further aspect, a method is disclosed for combining transmit signals received at multiple antennas, comprising: calculating cross-correlation coefficients of signals obtained from each of said multiple antennas, selecting a signal producing the highest coefficient as a golden reference signal, time synchronizing said transmit signals received at the multiple antennas using the golden reference signal, deriving a peak-to-average power ratio for each of said transmit signals received at the multiple antennas, generating a weighting coefficient for each of said transmit signals received at the multiple antennas using the cross-correlation coefficients and the peak-to-average power ratios, applying said weighting coefficients to each of said transmit signals received at the multiple antennas to generate a plurality of weighted signals, and summing said plurality of weighted signals. The method may further include calibrating a phase of the transmit signals received at the multiple antennas using the golden reference signal.

According to another aspect, a system is provided for receiving a transmission signal, the system including: a plurality of antennas each for receiving a received signal; a ranking module for ranking said plurality of antennas according to a quality of their respective received signals and generating a corresponding Level 1 signal and selecting the highest ranked antenna as a golden reference signal; a synchronizer for synchronizing all received signals of the plurality of antennas using the golden reference signal; a Level 2 module for calculating a peak-to-average power ratio for each of the respective received signals of the plurality of antennas and generating a corresponding Level 2 signal; a scoring unit for generating a weighted score for each of the respective received signals of the plurality of antennas using said Level 1 signal and said Level 2 signal; a weighting module for applying said weighted score to each of the respective corresponding received signals of the plurality of antennas to generate a plurality of weighted signals; and a summation module for combining all of said weighted signals.

In a disclosed aspect, a method of combining received signals from a plurality of antennas includes the operations of: generating, for each of the antennas, a ranking score indicative of the reliability of the received signal; generating, for each of the antennas, a quality score indicative of the peak-to-average power ratio (PAPR) of the received signal; generating, for each of the antennas, a weight using the corresponding ranking score and quality score; applying, for each of the antennas, the weight to the received signal to generate a weighted signal; and summing all of the weighted signals from the plurality of antennas to generate a weighted combined signal. The operation of generating the ranking score may include the operation of calculating a cross-correlation coefficient, and may further include the operation of calculating a correlation sum CSn for each of the antennas. The method may further include the operations of assigning the received signal with the highest ranking score to a reference signal, time-aligning all of the received signals to the reference signal, and calibrating the phase of all of the received signals to the reference signal. The operation of generating the quality score may include the operation of calculating the PAPR using a numerator value that is less than 100% of the maximum amplitude squared.

Also in the disclosed aspects, a method for combining received signals from a plurality of antennas includes operations of calculating a cross-correlation coefficient for the received signals obtained from each of the antennas, selecting a signal producing a highest value of the coefficient as a golden reference signal, time synchronizing the received signals using the golden reference signal, deriving a peak-to-average power ratio (PAPR) for each of the received signals, generating a weighting coefficient for each of the received signals using the cross-correlation coefficient and the peak-to-average power ratio, applying the weighting coefficient to each of the received signals to generate a plurality of weighted signals, and summing the plurality of weighted signals.

Further, in the disclosed embodiment, a system for combining received signals from a plurality of antennas includes a signal digitizer for receiving the received signals and generating a digitized signal, a first ranking module for comparing correlations of each of the digitized signals with the remaining signals of the digitized signals and selecting the highest ranked digitized signal as a reference signal, a second ranking module for calculating a peak-to-average power ratio (PAPR) for each of the digitized signals, a weighting module for receiving the rankings from the first ranking module and the PAPRs from the second ranking module and generating an assigned weight for each of the digitized signals, a weight applicator for applying the assigned weight to each of the digitized signals to generate a weighted signal, and a summing module for summing the weighted signals. The system may further include a time synchronizer for synchronizing the digitized signal to the reference signal. The system may further include a phase calibration module for calibrating the digitized signal to the reference signal. The first ranking module may include a cross-correlation calculation module, and may further include a correlation summing module for summing the cross-correlation coefficients calculated by the cross-correlation calculation module.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate examples of embodiments of the invention and, together with the description, are intended to explain and illustrate the principles of the invention. The drawings are intended to show major features of example embodiments in a schematic manner. The drawings are not intended to depict every feature of an actual embodiment or to depict relative dimensions of the depicted elements, and are not drawn to scale.

One or more embodiments of the present invention are illustrated by way of example and not limitation in the accompanying figures, in which like reference symbols indicate similar elements and in which:

<figref num="1">FIG. 1 shows an antenna array according to an embodiment, which has a controller for individually controlling each of the phase shifters, thereby steering the direction of the main beam.</figref><figref num="2">FIG. 2 is an example embodiment in which multiple phased array antennas are deployed to communicate with one or more satellites.</figref><figref num="2A">FIG. 2A is an example of an embodiment in which multiple phased array antennas are deployed to communicate with one or more satellites.</figref><figref num="3">FIG. 3 illustrates an embodiment that utilizes optical fiber for fast and efficient management of multiple signals.</figref><figref num="3A">FIG. 3A illustrates an embodiment that utilizes optical fiber for fast and efficient management of multiple signals.</figref><figref num="3B">FIG. 3B illustrates an embodiment that utilizes optical fiber for fast and efficient management of multiple signals.</figref><figref num="4">FIG. 4 is an example of an embodiment that creates path diversity that is particularly useful for secure transmission of files or load balancing.</figref><figref num="5">FIG. 5 shows a flow chart of steps that may be used in a transmission process of an embodiment.</figref><figref num="5A">FIG. 5A shows a flow chart of steps that may be used in the receiving process.</figref><figref num="6">FIG. 6 illustrates an architecture using multiple antennas for a receive diversity combining method according to an embodiment.</figref><figref num="7">FIG. 7 shows a channel structure in the receive diversity combining architecture according to this embodiment.</figref><figref num="8">FIG. 8 shows a digital signal processing architecture for receive diversity combining according to this embodiment.</figref>

The embodiments of the real-time multiplexing antenna and control according to the present invention will be described with reference to the drawings. Different embodiments or combinations thereof may be used for different applications or to achieve different benefits. Depending on the results to be achieved, different features disclosed herein may be used partially or to the fullest extent, alone or in combination with other features, balancing the requirements and constraints and advantages. Thus, highlighting some advantages with reference to different embodiments is not intended to be limited to the disclosed embodiments. That is, the features disclosed herein are not limited to the embodiments described, but may be "mixed and matched" with other features and incorporated into other embodiments.

It should be noted that references herein to satellites, platforms, or terminals are interchangeable and for illustrative purposes only. Physical locations may also be interchanged, such that the steerable beams and their effects may emanate from a satellite, platform, terminal, or all of the above. The same applies to reception and transmission. Either side may be either a receiver or a transmitter, and the use of the terms receiver or transmitter is for illustrative purposes only and does not limit the reverse, or even simultaneous reception and transmission.

In many types of RF antennas, reception and transmission are symmetrical to each other, and a description of one is equally applicable to the other. In this description, it may be easier to describe transmission, and reception would be identical, just in the opposite direction. The disclosed embodiments also contemplate that the disclosed antenna is mounted or integrated on a platform and directs its main beam toward another antenna, sometimes referred to herein as a target. The target's antenna may also be mounted on a platform, and one or both platforms may be moving. For example, the antenna may be mounted on a vehicle such as an airplane, ship, automobile, etc., and the target may be attached to a satellite, for example. The concept of symmetry applies here too, and the antenna may be mounted on a satellite and the target may be mounted on a vehicle.

FIG. 1 illustrates a phased array antenna, also referred to as an electronically variable directional or scanning array, which may be used in any of the embodiments disclosed herein. A phased array refers to an array of radiators that form a main beam, the direction of which can be electronically steered by changing the phase/time delay of the RF energy arriving at each radiator. For simplicity, the figure shows a linear array, but in the disclosed embodiments, it is more beneficial to utilize a two-dimensional array so that the beam can be steered in two dimensions. The array includes radiating elements 105, each of which is connected to a phase shifter 110. Each of the phase shifters 110 may be in the form of a delay line. The phase shifters 110 are controlled by a computer C to introduce a fixed amount of delay into the corresponding transmission line, thereby steering the beam by an angle Θ from the boresight.

The signal generated by the transmitter TX enters the common feed 115 and is split and distributed to each of the radiating elements 105. Before reaching the radiating elements, the signal from the feed passes through a corresponding phase shifter 110, and in each of the delay lines the phase of the signal changes by a respective amount, resulting in beam steering. The phase shifters 110 can also be controlled by an on-chip processor or a baseband processor. The range of each phase shifter can be quantized by a look-up table (LUT). By quickly retrieving the phase value from the memory, the beam can be steered. Note that the reverse occurs for reception.

The example of a passive phased array or passive electronically scanned array (PESA) shown in FIG. 1 is a phased array in which antenna elements are connected to a single transmitter and/or receiver. However, the disclosed embodiments are not limited to PESAs, but rather encompass any antenna that can be electronically steered. For example, an active phased array or active electronically scanned array (AESA) can also be used. AESAs are phased arrays, where each of the antenna elements has an analog transmitter/receiver (T/R) module to provide the phase shift necessary to electronically steer the antenna beam. Any of the disclosed embodiments may also be implemented using a digital beamforming (DBF) phased array, where each of the elements in the array has a digital receiver/exciter. Because the signal at each of the elements is digitized by the receiver/exciter, the antenna beam can be formed digitally in a field programmable gate array (FPGA) or array computer 110. In this approach, multiple simultaneous antenna beams can be formed, for example, by grouping the radiating elements into subgroups.

The present assignee has also developed phased array antennas in which the phase shifters are formed using delay lines across a variable dielectric constant material, such as liquid crystal. Such phased array antennas are also suitable for the embodiments disclosed herein. Examples of such arrays are described, for example, in U.S. Pat. No. 7,884,766, U.S. Patent Application Publication Nos. 2017/0093363, 2018/0159213, and 2018/0062272, the contents of which are incorporated herein by reference in their entireties.

In general, it should be understood that for each of the disclosed embodiments, each of the antennas is any electronically steerable directional antenna having multiple radiators, similar to the example phased array antenna shown in Figure 1. For simplicity, the disclosure provided herein uses the term "phased array antenna," but it should be understood that this term encompasses any electronically steerable antenna having multiple radiators that form a radiation pattern whose direction can be electronically steered.

Figure 2 illustrates an embodiment deploying multiple phased array antennas for communication with one or more satellites. The arrangement of Figure 2 allows for continuous real-time reconfiguration of the multiple phased array antennas. In Figure 2, asset 200 can be any platform having multiple communication devices, such as computers 1-n, that communicate with one or more satellites 1-4. Asset 200 can be, for example, an airplane, a ship, a train, or a land-based facility.

The asset includes multiple antennas ESA1-ESAn, which are coupled to multiple modems MD1-MDn via a switch mechanism 205. Each of the antennas has a phased array whose beam shape and direction is controlled by a phase controller 220. The phase controller 220 sets the phase or time delay of the signal to each of the radiators of the phased array to form the required main beam pointing in the desired direction. The term phase controller is used herein as shorthand to indicate any controller used to electronically steer the beam formed by the radiators. For example, the phase controller 220 may control the time delay of the same source RF signal as it inputs each of the radiators. In yet another example, the phase controller 220 may be a field programmable gate array that digitally forms the antenna beam.

In some embodiments, phase controller 220 can maintain a database, e.g., a look-up table, that lists all available satellites in the sky and their locations. In some embodiments, phase controller 220 can also receive GPS coordinates and other motion data of asset 200 from motion circuitry 225 so that it can determine which satellites are in view of its phased array. Phase controller 220 can use this information to steer each beam of the phased array in the appropriate direction toward a satellite.

In some embodiments, phase controller 220 includes a control port that receives control signals from control circuitry 215 indicating which satellites the antennas should communicate with. Control circuitry 215 may include a data port that operatively couples with router 210 so that the control circuitry can actively make its switching decisions based on data collected from router 210. The data may include the available bandwidth of each antenna, the data transmission rate of each antenna, and the type of transmission (voice, video, data, etc.) required by each communication device 1-n.

The control circuitry may also be connected to each of the ESAs to obtain RSSI from each of the ESAs. The control circuitry may further be connected to a modem 255 to receive other data relevant to its switching decisions, such as the service level assigned to each of the communication devices, the transmission costs of each of the satellites, etc. For example, modem 255 may be coupled to an external data management system 260 to provide data to control circuitry 215 regarding various transmission parameters and user accounts.

The phase controller uses the database to calculate the phase delay to apply to each of the radiators to point the antenna towards the designated satellite. If the asset 200 is mobile, e.g., an airplane, a ship, etc., the motion circuit 225 continuously sends motion signals to the phase controller 220 so that the phase controller can continuously adjust the phase applied to each of the radiators to keep the beam pointed towards the satellite.

The aforementioned multiple communication devices, here shown as computers 1-n, are coupled to modems MD1-MDn via a router 210. This arrangement allows real-time configuration of the system, and any communication device 1-n can be coupled to any modem MD1-MDn, which in turn can be coupled to any antenna ESA1-ESAn, thereby allowing efficient use of the bandwidth from the available satellites.

Multiple users on the platform may have different needs. For example, perhaps one computer is for crew welfare watching Netflix and another computer is for ship navigation management. The control circuitry 215 can determine which satellite each traffic is transmitting from and which antenna or antennas to use for that particular traffic. The control circuitry 215 can also instruct the router 210 to aggregate capacity or perform other Ethernet level operations on traffic to ensure the best quality, best performance, and lowest cost across all available paths.

For example, in some embodiments, the control circuitry 215 may receive data regarding the bandwidth capacity and utilization of the various satellites, data regarding transmission priorities, such as live signals such as voice or video calls should have high priority while email may be assigned a lower priority, data regarding the bandwidth costs of the various services available on the satellites, and the like. The control circuitry 215 may then determine which satellites should be used for which transmissions. In some embodiments, the control circuitry also receives motion signals from the motion circuitry 225, such that the control circuitry 215 may determine which satellites are available for which antennas. In some embodiments, the control circuitry 215 also stores in its database the physical configuration of the asset 200 and its antennas. For example, the asset may have ESA1 on its right side, ESA2 on its left side, ESA3 on the roof, and so on. From this, the control circuitry 215 may determine which parts of the sky each of the antennas can scan. Using all this information, the control circuitry 215 may provide the appropriate signals to the switches and routers to make the appropriate connections and indicate to each of the phase controllers where to point the antennas.

For illustration purposes, in Fig. 2, antennas ESA1 and ESA2 both communicate with Sat1, which in turn communicates with transceiver 1. As a result, in one embodiment, the signal from Sat1 is too weak to transmit the required file on a single connection, and one possible solution is to use the receive diversity combining method by ESA1 and ESA2 to transmit the file on two connections. ESA3 communicates with Sat3, which in turn communicates with transceiver 2. ESAn communicates with both satellites Sat2 and Sat4. Sat2 communicates with transceiver 2, while Sat4 communicates with transceiver n. The two signals are routed by router 230 and combined by combining computer 235.

In one example shown in FIG. 2, transceivers 1-3 are shown as being part of a single base station 202 that connects to a network 240, such as the Internet. Data store 245 may be accessed via network 240 or may be permanently located at the base station itself. Of course, many base stations may be used and the satellite may communicate with any selected base station depending on the needs of the user, the performance of each of the base stations, the available connections, etc. Also, because data store 245 is accessible via network 240, when a particular user machine needs to access data store 245, control circuitry 215 can determine which satellite and which base station is best suited to provide that connection. Thus, in some embodiments, control circuitry 215 may periodically receive transmissions with data regarding available base stations and their operating parameters. Similarly, in the case of non-geostationary satellites, control circuitry 215 may periodically receive transmissions with updates regarding the satellite's position and operating parameters.

Each of the transceivers of the base station 202 has an antenna 204 that exchanges communication signals with one or more satellites. For communication with geostationary satellites, the antenna 204 may be a simple dish fixed in the direction of the satellite or may be mechanically moved to point it toward the desired satellite. However, for rapid real-time steering, such as for non-geostationary satellites or fast movement between different satellites, one or more of the antennas 204 may be a phased array as disclosed herein.

In some disclosed embodiments, satellite transmissions and receptions may occur via a one-way transmission mechanism, for example, using User Datagram Protocol (UDP).

FIG. 3 illustrates an embodiment that utilizes optical fibers for fast and efficient management of multiple signals. Each of the phased array antennas includes electro-optical transceivers EOT1-EOTn that convert between optical and electrical signals. The optical signals travel in optical fibers, indicated by dashed arrows, that are managed by an optical fiber management unit (OFMU) 320. The OFMU 320 also includes electro-optical modulators that convert between optical and electrical signals. The signals traveling between the OFMU 320 and the switch 205 are electrical signals that travel in waveguides, indicated by solid arrows, coaxial cables.

In the example shown in FIG. 3, the OFMU 320 can connect any of the phased array antennas 1-n to any of the modems MD1-MDn via the switch 205. The optical fiber management unit 320 can also sum RF signals from multiple selected phased array antennas and provide the summed RF signal to a selected modem. Conversely, the optical fiber management unit 320 can split transmit power to multiple selected antennas for transmission. Additionally, the OFMU 320 can perform other digital baseband operations such as nulling, beamforming, or interference cancellation.

Figure 3A shows a variation of the embodiment of Figure 3. The optical fiber management unit 320 also performs the functions previously performed by the switch 205. Since the optical fiber management unit 320 can combine and split signals, it can direct signals to any modulator MD1-MDn, thus eliminating the need for the switch 205. The control circuit 215 therefore sends instruction signals to the OFMU 320 for appropriate signal routing.

4 illustrates an example of generating path diversity that is particularly beneficial for secure transmission or load balancing of a file. In the example illustrated in FIG. 4, a platform 400, which may be any platform having one or more phased array antennas as described herein, includes a computer 411 and is attempting to transmit a single file F. In one example, the file is highly data sensitive, so it is desirable to ensure that a man-in-the-middle attack fails, and even if successful, the perpetrator only obtains a portion of the data. In another example, the file is too large for the detected RSSI, so it may be determined that it is desirable to use multiple paths, each of which transmits only a portion of the file.

As shown in FIG. 4, computer 411 splits file F into several, here three, parts. Control system 415 then operates switches and routers (see FIG. 1) to create three transmission paths, each directed to one satellite. In the example shown in FIG. 4, each of the satellites communicates with a different base station, so that each part of the file is received by a different antenna and transceiver system. This is not necessarily always the case, and some or all of the satellites may communicate with the same base station. In any case, control system 415, via configurators CFG1 to CFGn, indicates to the base stations which files to receive from which satellites, and, upon receiving the parts of the file, indicates to data center 422 that they should assemble them into a single file, which may be assembled and stored in data center 422. Of course, any return responses may be similarly split and sent by multiple paths.

4, it should be noted that the control system 415 is in the cloud, rather than on the platform 400. Such a configuration is not limited to this particular example, and may be used in any embodiment disclosed herein.

FIG. 5 is a flow chart illustrating a non-ordered procedure that may be taken by a process implemented by the disclosed embodiments. For example, in step 500, account data of a registered user may be loaded into the control circuitry 215. The account data may include data speed, data rate price, data limit, etc. The account data may be stored in the memory of the control circuitry. In step 505, satellite data may be loaded into the control circuitry 215. The satellite data may include satellite ID, satellite coordinates, transmission speed, bandwidth, etc. In step 510, motion data may be uploaded to the control circuitry 215. The motion data may include motion data related to the satellite and motion data related to the platform on which the ESA is mounted. It should be noted that all data uploaded in steps 500, 505, and 510 may be periodically updated.

In step 515, a transmission request is received from the user. Using the information of the transmission request and the data uploaded in steps 500, 505 and 510, in step 520, an appropriate path for transmission is selected. For example, if multiple antennas are available, the transmission may be performed by multiple paths using multiple antennas, for example, using a diversity combining method. In step 525, the transmit/receive strength is verified for the antennas in the selected path. This is done, for example, by receiving RSSI from each unit. Once adequate signal strength is confirmed for the selected path, the switch is configured so that the selected antenna connects to the selected modem and the router is configured so that the user's machine connects to the selected modem.

FIG. 6 illustrates an example of an embodiment in which multiple antennas, such as multiple phased arrays, are used to improve the overall signal-to-noise ratio (SNR) of a received signal. Utilizing multiple antennas to improve the SNR of a received signal is known in the art, but current implementations are inadequate or too complex and expensive for widespread implementation. For example, the simplest implementation is to determine which antenna provides the strongest total instantaneous signal (e.g., highest RSSI) and select that antenna's signal. Another fast method is to apply equal weights to each of the antennas and sum the weighted signals from all antennas. Such an approach is quick and easy to implement, but can lose signal quality for the best antennas and over-weight weaker signals, thereby introducing noise. For more information, the reader is referred to DR Pauluzzi and NC Beaulieu, "A Comparison of SNR Estimation Techniques for AWGN Channels," IEEE Transactions on Wireless Communications, Vol. 48, No. 10, published October 2000, available at https://ieeexplore.ieee.org/document/871393. The embodiment of FIG. 6 provides improved weighting using a novel technique that is fast and relatively easy to implement.

The architecture shown in FIG. 6 is called a Distributed Electronically Steerable Directivity Array (DESA), and in the example of FIG. 6, may be called a receive diversity combining architecture instead of a DESA, since multiple arrays are used to combine the diversity receive signals. Such an architecture is particularly beneficial when the satellite is not visible to one or more of the arrays, or when the aperture is very small due to the tilt angle of the beam. This is illustrated in FIG. 6 by considering a mobile platform 600, such as a ship, with antennas located in different parts of the ship. The ship moves in a direction such that the satellite is on the starboard side, and arrays x1, x2, x3 (x3 is not shown, for example, as it is at the stern) have good signals, but x4 is located on the port side, so it cannot steer towards the satellite, or the steering angle may make the aperture very small, resulting in noise in the signal.

Modem 602 conditions signals for transmission, such as signals from the Internet, such as streaming video. The signals are uploaded from base station 604 to satellite SAT1, which broadcasts them toward Earth. Some or all of antennas x1-x4 pick up the signals, each of which may have a distinct SNR due to various factors such as propagation loss, weather dynamics, polarization mismatch, interference, and the physical orientation of the array. The signals from the array are then processed by DESA processing unit 640 to generate digital signals that are provided to modem 648, which transmits the signals to various user devices. DESA processing unit 640 includes an RF transceiver 642 that receives and digitizes the signals from the antennas, and a digital signal processor 644 that determines the weights to apply to the signals from each of the antennas and sums the weighted signals. DESA processing unit 640 also includes an antenna array module AIM 646, which is the controller responsible for steering, geolocation, and system management of the phased array antenna. The AIM 646 may have a similar structure, and provide similar operation and functionality, as described with respect to the phase controller 220 of FIG.

FIG. 7 shows an example of an embodiment of a receive signal path that can be used for a receive diversity combining architecture like that shown in the example of FIG. 6. The example of FIG. 7 includes as many channels as there are antennas, with only the first and last channels shown in detail, while the remaining channels are all identical and therefore shown with ellipses. The disclosed technique is frequency band agnostic and can be applied to any frequency band. Each of the antennas receives a satellite signal, and as shown, in this example, the transmission is in the Ka or Ku band. The signal passes through an RF filter before entering a standard low noise block (LNB), which downconverts the signal to an intermediate frequency in the L band. After passing through the intermediate frequency filter, the signal is amplified and converted to a digital signal by an RF ADC converter. The digital signal processor DSP 644 then applies the calculated weighting to each of the channels and sums the signals from all the channels.

FIG. 8 illustrates an example of a digital signal processor that may be employed in a receive diversity combining architecture according to an embodiment disclosed herein. Due to path differences and other atmospheric effects, the signals of the channels need to be synchronized and calibrated to match each other. In the embodiment of FIG. 8, this is done by a channel scanner 850 that first compares the correlation of each channel with the remaining channels to determine which channel has the highest fidelity. Essentially, the channel scanner looks through the channels and selects the most reliable channel as the golden reference channel. The golden reference channel is used by a time synchronizer 860 to estimate the time shift required to time align all the channels. In one example, for each of the receive channels RxN, the time synchronizer 860 upsamples the signal to achieve the desired fractional sample accuracy. The cross-correlation of the receive channel with the golden reference channel is then determined. The maximum coefficient value is then set as the path delay difference and used to align the receive channel RxN to the golden reference channel.

Similarly, the golden reference channel is used by the phase calibration module 862 to estimate the phase shift required to align all channels. In one example, for each receive channel RxN, the phase calibration module 862 calculates the average value of the phase difference between receive channel RxN and the golden reference channel. The average phase error value is then applied to receive channel RxN.

As described above, the channel scanner 850 ranks the channels according to their relative fidelity or reliability. This is done by first deriving a cross-correlation matrix by a cross-correlation module 854. The results of the cross-correlation are used by a ranking module 856 to generate a rank order of the channels, referred to herein as a level 1 ranking, and to select a golden reference channel. A level 1 signal is provided to a rank controller 870.

At this point, the cross-correlation matrix is derived as follows:

<img file="JP7636746B2_D0001.tif" />where m n, ns is the integration length, and nd is the delay search window. For an N-channel receiver, the formula produces d number of cross-correlation coefficients.

<img file="JP7636746B2_D0002.tif" />d is an integer that relates to the triangular elements of the square matrix

<img file="JP7636746B2_D0003.tif" />For example, if N=4, the formula produces an array of 6 coefficients.

<img file="JP7636746B2_D0004.tif" />

The coefficients from this matrix are used to determine the level 1 ranking. Define a Q matrix with dimensions N rows and (N-1) columns, and use the data of each channel exactly (N-1) times from the correlation matrix calculation. The correlation sum (CS) associated with each nth channel is calculated by adding up all the row elements of Q and is given by:

<img file="JP7636746B2_D0005.tif" />

For the example of N=4, the formula is:

<img file="JP7636746B2_D0006.tif" />

The golden reference channel is selected based on the highest score as defined in the following set:

<img file="JP7636746B2_D0007.tif" />where φ is a gain function that includes a normalization scaler. In case of tie scores, one of the channels with the tie score can be selected, or in this embodiment, the result of the level 2 ranking decision can be used to select a golden reference channel with higher accuracy.

Referring back to FIG. 8, the channel scanner 850 includes a peak-to-average power module 852 that calculates a level 2 ranking based on the peak-to-average power ratio (PAPR). The level 2 signals are input to a rank controller 870, which uses the level 1 and level 2 decisions to generate a score for the channel. The scores are provided to a weighting module 864, which applies the weights assigned to each of the channels, and the weighted signals of all the channels are combined by a diversity combiner 866. Incidentally, as shown in the example of FIG. 8, an optional external input port is provided to allow the user to override the rank controller selection or provide other commands to the rank controller 870. The level 2 ranking decision is based on the calculation of the PAPR using the following formula:

<img file="JP7636746B2_D0008.tif" />In this example, the peak power is less than 100% of the square of the maximum amplitude, e.g., max{|x|²} corresponds to the 99% PAPR for a collection window of K samples. Using a 99% PAPR helps to avoid unrealistic peaks due to systematic errors, glitches, or sampling errors. This particular example uses 99%, but other values less than 100% may be used. A higher PAPR results in a worse radio propagation channel and a lower Eb/N0 (energy per bit to noise power spectral density ratio, or normalized signal-to-noise ratio (SNR) measurement, also known as "SNR per bit").

Ideally, the CS maximum value at level 1 and the PAPR minimum value at level 2 should correspond to the same receiving channel. The reference channel selection can be calculated by the joint score:

<img file="JP7636746B2_D0009.tif" />

In general, the scoring method can use several decision variables based on multiple physical quantities. As mentioned above, in the example of FIG. 8, we use the cross-correlation sum as the level 1 ranking and the PAPR as the level 2 ranking. By using one more decision variable, the PAPR, we can better approximate the true channel SNR and therefore get closer to the optimal composite solution. In addition, other variables, for example, the total signal plus noise power (Psig), can also be used. Thus, a general description of determining the score of the nth channel of N multiple Rx channels can be expressed as follows:

where SCORE = [SCORE₁,SCORE₂, ..., SCORE_N] is an N-dimensional array, Q is the total number of decision variables, φ is a gain function for normalization, and θ is a scalar function. Ideally, the CS maximum value at level 1 and the PAPR minimum value at level 2 should correspond to the same receiving channel. The reference channel selection can be calculated by a joint score to better approximate the true channel state.

<img file="JP7636746B2_D0010.tif" />where n is the channel number giving the highest score.

For the example of FIG. 8, for channels with Q=2 (level 1 ranking and level 2 ranking) and N=4, the formula for determining the score is:

<img file="JP7636746B2_D0011.tif" />This score is the value used in the weighting factor of the weighting module 864. Channels with better conditions and higher quality are weighted exponentially more and exhibit a higher SNR at the output of the diversity combiner 866.

Also shown in FIG. 8 is a monitoring port leading to a controller 870. In this embodiment, the controller 870 monitors the output of the diversity combiner 866 and determines the noise variance of the output. This can be done, for example, using the same PAPR process as described above. The controller 870 may compare the PAPR determined for the diversity combined signal to the PAPR calculated for each of the incoming signals. This allows the controller 870 to monitor that the signal generated after diversity combining does indeed have a low PAPR, and if not, it may need to change the weights to achieve a reduction in the PAPR of the diversity combined signal.

According to the disclosure provided, a method is disclosed for combining transmit signals received at multiple antennas, the method comprising: calculating cross-correlation coefficients of signals from each of the multiple antennas, selecting a signal producing the highest coefficient as a golden reference signal, time synchronizing the transmit signals received at the multiple antennas using the golden reference signal, deriving a peak-to-average power ratio for each of the transmit signals received at the multiple antennas, generating a weighting coefficient for each of the transmit signals received at the multiple antennas using the cross-correlation coefficients and the peak-to-average power ratios, applying the weighting coefficients to each of the transmit signals received at the multiple antennas to produce a plurality of weighted signals, and summing the plurality of weighted signals. As above, the method may further include calibrating a phase of the transmit signals received at the multiple antennas using the golden reference signal.

A system for receiving a transmitted signal is provided, the system including: a plurality of antennas each receiving a received signal; a ranking module for ranking the plurality of antennas according to a quality of the received signal of each of the plurality of antennas and generating a corresponding level 1 signal and selecting the highest ranked antenna as a golden reference signal; a synchronizer for synchronizing all received signals of the plurality of antennas using the golden reference signal; a level 2 module for calculating a peak-to-average power ratio for each received signal of each of the plurality of antennas and generating a corresponding level 2 signal; a scoring unit for generating a weighted score for each received signal of each of the plurality of antennas using the level 1 signal and the level 2 signal; a weighting module for applying the weighted score to each corresponding received signal for each of the plurality of antennas to generate a plurality of weighted signals; and a summation module for combining all of the weighted signals.

FIG. 2A shows an example of an embodiment for satellite communications, realizing receive diversity combining to improve the overall SNR. The embodiment of FIG. 2A is similar to the embodiment shown in FIG. 2 and therefore will not be described in detail. The embodiment of FIG. 2A shows how the DESA elements of FIG. 7 and 8 can be incorporated into the architecture of FIG. 2, thus enabling receive diversity combining and improving the overall SNR.

Similarly, Fig. 3B shows an example of an embodiment for satellite communications, implementing receive diversity combining to improve the overall SNR, and incorporating optical fiber. The embodiment of Fig. 3B is similar to the embodiment shown in Fig. 3 and therefore will not be described in detail. The embodiment of Fig. 3B shows how the DESA elements of Figs. 7 and 8 can be incorporated into the architecture of Fig. 3, thus enabling receive diversity combining and improving the overall SNR.

FIG. 5A shows a flow chart of a non-ordering procedure that may be taken to perform a diversity receive combining operation to improve the overall SNR. In step 540, signals are received at multiple antennas, which may include, for example, cellular antennas, wireless LAN (WiFi) antennas, array antennas, etc. Even though the data of the signals received at the antennas is identical, the quality of the signals received at each of the antennas may not be identical, which may result in different SNRs or RSSIs at each of the channels. The method proceeds to generate a weighted sum of the signals to improve the overall SNR as follows: The method generates two ranked signals, a level 1 ranked signal and a level 2 ranked signal. The level 1 ranked signal is generated in step 545 by obtaining cross-correlation coefficients of signals from multiple channels. The rankings are ordered such that the highest coefficient is the best signal and the lowest coefficient is the worst channel. Also, in step 550, the best channel (highest coefficient) is selected as the golden reference signal. The level 2 ranked signal is generated in step 555 by calculating the PAPR of each channel. The ranking is ordered such that the lowest PAPR is the best signal and the highest PAPR is the worst channel.

In step 560, a golden reference signal is used to synchronize the channels in the time domain. In step 565, the golden reference signal is used to calibrate the phase of all channels. In step 570, the level 1 ranking and the level 2 ranking are used to generate weights, and then the signal of each channel is weighted by the corresponding weight. In step 575, the weighted signals of the channels are added together.

It should be understood that the processes and techniques described herein are not inherently related to any particular apparatus, but may be implemented by any suitable combination of components. Moreover, various types of general purpose apparatus may be used in accordance with the teachings set forth herein. While the present invention has been described with reference to specific examples, they are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will recognize that many different combinations will be suitable for practicing the present invention.

Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used alone or in any combination. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.