PATENT ABSTRACT
A communications system for providing recovery communication service to users in a coverage area affected by an emergency disruption of normal communication services. The system comprises a ground hub serving as a gateway to terrestrial networks including a dispatch center and configured to communicate with at least three mobile airborne platforms roving over the coverage area via respective feeder-links in a Ku or Ka band. A first mobile airborne platform communicates in a first frequency band with emergency workers that are working in the coverage area and associated with the dispatch center. A second mobile airborne platform communicates, in place of at least one disrupted base station in the coverage area, with user mobile phones in mobile phone frequency bands or user personal devices in WiFi bands located in the coverage area. A third mobile airborne platform generates real-time imaging of surfaces located in the coverage area.

PATENT DESCRIPTION
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13778175, filed on Feb. 27, 2013, entitled “Communications Architectures Via UAV”. This application is related to U.S. patent application Ser. No. 13/623,882, filed on Sep. 21, 2012, entitled “Concurrent Airborne Communication Methods and Systems”, now U.S. Pat. No. 8,767,615, issued on Jul. 1, 2014; and U.S. patent application Ser. No. 13/778,171, filed on Feb. 27, 2013, entitled “Multi-Channel Communication Optimization Methods and Systems”, now U.S. Pat. No. 9,596,024, issued on Mar. 14, 2017, both of which are incorporated herein by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure describes exemplary embodiments on improving the operation and use of airborne communication methods and systems such as through concurrent data delivery with redundancy and privacy ranking and related calibration. The present invention relates to smart antenna methods on UAVs providing emergency and disaster communications services for the rescue teams and the community in a disaster area. There are two sets of payloads; one in foreground to interface with users and the other in the background, connecting to a gateway which may communicate with other communications infrastructures. 
       BACKGROUND 
       [0003]    When disasters happen, many terrestrial infrastructures including cell phones and Internet services become less functional. For emergency and disaster recovery systems, there are needs for real time communications to residents, and rescue workers in disaster areas. It is also important for access of surveillances (videos and images) data over the areas. Unmanned Aerial Vehicle (UAVs) will be very useful tools for these peaceful missions. The proposed systems with three real time functions require for peaceful missions;
       1. An ad hoc communications network for local residents, operating in commercial cell phone bands, and/or Wifi bands   2. An ad hoc communications network for rescue works, operating in emergency bands, and       
 
         [0006]    3. Communications from air mobile surveillance platforms for videos and images to a central hub. 
         [0007]    It is possible to perform all three functions in a large UAV. However, each of the functions may be performed and/or supported by a small UAV. In some embodiments, limits on communications payloads on an UAV may be allocated; such as ˜20 Kg in weight, and 200 W power consumptions, and mission flight time of 12 hours at altitudes at least above the “terrestrial weather” initially. It may also be preferred that the UAVs fly above 5 Km in altitudes. 
         [0008]    There are four technologies in architectures for emergency services:
       a. UAV as communications nodes   b. Foreground communications networks between users and UAVs
           For users with hand-held devices   utilizing remote-beam forming network(RBFN) with the ground based beam forming (GBBF) facility   
           c. Background communications networks, (back channels or feeder-links) between ground infrastructures/facilities and UAVs
           Back-channels or feeder-links between UAVs and GBBF processing centers.   
           d. Wavefront multiplexing/de-multiplexing (WF muxing/demuxing);
           Back-channel calibrations on feeder-link transmission for RBFN/GBBF   Coherent power combining in receivers on signals from different channels on various UAV ;   Secured transmissions with redundancies via UAVs   
               
 
         [0019]    Multiple smaller UAVs may be “combined” to perform a function, say communicating with local residents when their cell towers become non-functional. We may fast-deploy 4 small UAVs and group them via communications networks to replace the functions of ill functioned local cell towers or base-stations which are damaged due to current emergencies or disasters. The residents may use their existing personal communications devices including their cell phones to communicate to outside worlds via the ad hoc communications network via these small UAVs. In these cases, we may allocate SW&amp;P limits on communications payloads on a small UAV; about &lt;5 Kg in weight, and &lt;50 W power consumptions. 
         [0020]    The payloads on surveillance platforms will use optical sensors to generate optical images during day time. There are possibilities of using optical illuminators on the UAVs or different UAVs to allow night operations. Infrared sensors may also be used for night visions and imaging. 
         [0021]    Microwave sensors can be used for both night and cloudy (or raining) conditions in which optical sensors may not function well. Active monostatic Radars may be deployed by individual UAVs. Polystatic or multi-static Radars can be deployed via a fleet of UAVs. 
         [0022]    Multiple UAVs will be coordinated to form a coherent RF receiving system as a passive Radar receiver via GBBF processing and real time knowledge of the positions/orientations of all receiving elements on various UAV platforms. It will take advantage of ground reflections of existing and known RF illuminators such as Navstar satellite from GPS constellations, or satellites from many other GNSS constellations at L-band. It is also possible to use as RF illuminators by taking advantages of ground reflections of high power radiations by many direct broadcasting satellites (DBS), which illuminate “land mass” with high EIRP over 500 MHz instantaneous bandwidths (of known signals) at S, Ku and/or Ka band. The “known signals” are received signals through a direct path or a second path from the same radiating DBS satellite. Furthermore, high power radiations from Ka spot beams of recently deployed satellites on many satellites either in geostationary or non-geostationary orbits, can also be used as RF illuminators. 
         [0023]    The terms of UHF, L, S, C, X, Ku, and Ka bands are following the definitions of IEEE US standard repeated in Table-1 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 IEEE Designated Frequency Bands 
               
               
                 Table of IEEE band 
               
             
          
           
               
                   
                 Band 
                 Frequency range 
                 Origin of name 1   
               
               
                   
                   
               
               
                   
                 HF band 
                 3 to 30 MHz 
                 High Frequency 
               
               
                   
                 VHF band 
                 30 to 300 MHz 
                 Very High Frequency 
               
               
                   
                 UHF band 
                 300 to 1000 MHz 
                 Ultra High Frequency 
               
               
                   
                 L band 
                 1 to 2 GHz 
                 Long wave 
               
               
                   
                 S band 
                 2 to 4 GHz 
                 Short wave 
               
               
                   
                 C band 
                 4 to 8 GHz 
                 Compromise between S and X 
               
               
                   
                 X band 
                 8 to 12 GHz 
                 Used in WW II for fire control,  
               
               
                   
                   
                   
                 X for cross (as in crosshair) 
               
               
                   
                 K u  band 
                 12 to 18 GHz 
                 Kurz-under 
               
               
                   
                 K band 
                 18 to 27 GHz 
                 German Kurz (short) 
               
               
                   
                 K a  band 
                 27 to 40 GHz 
                 Kurz-above 
               
               
                   
                 V band 
                 40 to 75 GHz 
                   
               
               
                   
                 W band 
                 75 to 110 GHz 
                 W follows V in the alphabet 
               
               
                   
                 mm band 
                 110 to 300 GHz 
               
               
                   
                   
               
             
          
         
       
     
         [0024]      FIG. 1  illustrates a scenario of UAV&#39;s in a rescue mission. Three vital tasks are provided by the UAVs;
       1. Communications networks deployment for local residents in disaster areas using their existing cell phones
           UAV (M 1 ) becomes the replacement of the damaged cell towers in a Spoke-and-hub architecture   Residents can use their own cell phones ask for assistance when needed   
           2. Communications networks deployment for rescue teams with special phones
           UAV (M 2 ) becomes the rapid deployed cell towers for communications among the rescue team members and their dispatchers   Using separated emergency frequency bands   Spoke-and-hub architecture   
           3. Surveillance platforms for visual observations
           UAV (M 3 ) takes videos on disaster areas and relays them back to the hub instantaneously   Dedicated high data rate links   
               
 
         [0035]    All three major tasks will have the same hub which shall have capability to relay the emergency information to the mission authority. Users on the two networks can communicate among themselves through the gateways which are co-located at the same hub, which shall be standard mobile hubs that telecommunications service providers can support 
         [0036]    An example of desired designs of the communications functions in this disclosure is summarized as follows:
       In the airborne segment
           Using 16 elements as array for foreground communications network   to enable a 4-element subarray with multiple beam capability maintaining links for data rate at 10 Mbps for each subarray.   To enable a sparse array made from 4 subarrays at S/L bands or C-band with multiple beam capability maintaining links for data rate at 10 Mbps per beam.   To design Ku- band feeder links with a bandwidth at 160 MHz   
           In the user segment
           Regular cell phones for the residents in the serviced community   Common rescue mission equipment at 4.9 GHz   
           In the ground segment
           Three Ku band antennas to track three UAVs concurrently individually with data rate at 150 MHz back channel bandwidths in both directions.   GBBF capability with knowledge of evolving array orientations on UAVs   
               
 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0048]      FIG. 1  depicts a scenario of using three separated UAVs as three mobile platforms for emergency and disaster recovery services; UAV M 1  for communications among rescue team members, UAV M 2  for communications as emergency replacements of mobile and/or fixed wireless base stations for resident communications via their existing mobile phones and/or personal communications devices using WiFi. UAV M 3  for surveillances via optical, infrared, and RF sensors. 
           [0049]      FIG. 2  depicts a simplified block diagram for a mobile communications via UAV with on-board beam forming network (BFN) to mobile users using “foreground” links at L/S band. The ground interconnection to terrestrial communications facility are through feeder-links in Ku or Ka band. Feeder-links are also referred to as back-ground links, or back channels. 
           [0050]      FIG. 3  depicts a simplified block diagram for a mobile communications via UAV to mobile users using “foreground” links at L/S band. The ground based beam forming (GBBF) network and ground interconnection to terrestrial communications facility are through feeder-links in Ku or Ka band. Feeder-links are also referred to as back-ground links, or back channels. 
           [0051]      FIG. 4  depicts an operational scenario for a UAV with ground based beam forming through feeder-links, and foreground links for users. The UAV based communications features multiple beams foreground communications. 
           [0052]      FIG. 5  depicts an operational scenario for multiple UAVs in a closely space formation with ground based beam forming through feeder-links, and foreground links for users. The UAVs are spaced by orders of meters or less. The multiple-UAV based communications features multiple beams foreground communications. 
           [0053]      FIG. 6  depicts an operational scenario for multiple UAVs in a formation with ground based beam forming through feeder-links, and foreground links for users. The UAVs are spaced by orders of Kilo-meters. The multiple-UAV based communications features multiple beams foreground communications. Users with terminals of multiple tracking beams can take advantages of the multiple UAVs to achieve multiple folds of channel capacity via frequency reuse. 
           [0054]      FIG. 7  depicts an operational scenario for multiple UAVs in a formation with ground based beam forming through feeder-links, and foreground links for users. The UAVs are spaced by orders of Kilo-meters. The multiple-UAV based communications features multiple beams foreground communications. Wavefront multiplexing/demultiplexing (WF muxing/demuxing) techniques are used to allow “coherent” power combining of the radiated power from various UAVs in foreground links at user terminals or ground hubs. Users with terminals of multiple tracking beams can take more advantages of the multiple UAVs to achieve multiple folds of channel capacity via frequency reuse. 
           [0055]      FIGS. 7 a  and 7 b    illustrate the operational principle of “coherent power combining” and signal multiplexing via multi-channel waveforms in receivers for three separated users through WF muxing/demuxing techniques.  FIG. 7 a    is a functional block diagram for forward link, and  FIG. 7 b    is a functional block diagram for return link. 
           [0056]      FIGS. 8 a , 8 b , and 8 c    illustrate the operational principle of wavefront multiplexing/demultiplexing for redundancy and signal security for one user.  FIG. 8 a    is a functional block diagram for forward link, and  FIG. 8 b    a functional block diagram for return link.  FIG. 8 c    depicts a numerical example of non-coherent data delivery by WF muxing/demuxing techniques via 4 UAVs concurrently. It works for both forward and return links. 
           [0057]      FIGS. 9 a , 9 b , and 9 c    illustrate the feeder-link calibration and compensations via principle of wavefront multiplexing/demultiplexing.  FIG. 9 a    is a functional block diagram for forward link with on-board optimization processing;  FIG. 9 b    is a functional block diagram for forward link with a pre-distortion technique with an on-ground optimization processing; and  FIG. 9 c    is a functional block diagram for return link with an on-ground optimization processing. 
           [0058]      FIGS. 10 a , 10 b , and 10 c    illustrate the operational principle of “coherent power combining” and signal multiplexing via multi-channel waveforms in receivers for three separated users through WF muxing/demuxing techniques. All are simplified block diagrams showing a WF muxing operation in signal sources and a WF demuxing operation in a destination for forward links.  FIG. 10 a    is a functional block diagram for a forward link from a ground hub to a first user;  FIG. 10 b    is a functional block diagram for a forward link from a ground hub to a second user; and  FIG. 10 c    is a functional block diagram for a forward link from a ground hub to a third user. 
           [0059]      FIG. 11  depicts a functional block diagrams for an on-board retro-directive antennas for Ku/Ka feeder-link inter-connecting a ground processing facility and a UAV which anchoring the retro-directive antenna. 
           [0060]      FIG. 12  depicts inter-connectivity among three functional blocks of mobile communication architecture via a UAV with 4-element array in feeder-links and GBBF; (1) on board return link payload and feeder-link payload, (2) ground processing facility with ground based beam forming, and (3) on board feeder-link payload and forward link payload. The first level functional details of all three functional blocks are illustrated. On-board feeder links are implemented by a 4-element active array with beam forming network. There are no beam forming for the foreground communications payloads 
           [0061]      FIG. 12 a    depicts inter-connectivity among three functional blocks of mobile communication architecture via a UAV with 4-element array in feeder-links and GBBF; (1) on board return link payload and feeder-link payload, (2) ground processing facility with ground based beam forming, and (3) on board feeder-link payload and forward link payload. The first level functional details of all three functional blocks are illustrated. On-board feeder links are implemented by a 4-element retro-directive antenna. 
           [0062]      FIG. 12 b    depicts inter-connectivity among three functional blocks of mobile communication architecture via a UAV with 4-element array in feeder-links and GBBF; (1) on board return link payload with on-board beam forming network and feeder-link payload, (2) ground processing facility but without ground based beam forming, and (3) on board feeder-link payload and forward link payload with onboard beam-forming network. The first level functional details of all three functional blocks are illustrated. On-board feeder links are implemented by a 4-element retro-directive antenna. 
           [0063]      FIG. 13 a    depicts two on board functional blocks of mobile communication architecture with GBBF via a UAV with 4-element array in feeder-links similar to  FIG. 12 a   . The additions to  FIG. 12 a    are feeder-link calibration and compensation mechanisms via Wavefront muxing/demuxing for both forward and return links. (a) on board return link payload and feeder-link payload with on-board optimization for forward link, and (b) on board feeder-link payload and forward link payload. On-board feeder links are implemented by a 4-element retro-directive antenna. 
           [0064]      FIG. 13 b    depicts a functional blocks of mobile communication architecture with GBBF for ground processing facility with calibration and compensation mechanisms via Wavefront muxing/demuxing for both forward and return links. An optimization loop for return link WF demuxing is on-ground. 
           [0065]      FIG. 14 a    depicts two on board functional blocks of mobile communication architecture with GBBF via a UAV with 4-element array in feeder-links similar to  FIG. 12 a   . The additions to  FIG. 12 a    are feeder-link calibration and compensation mechanisms via Wavefront muxing/demuxing for both forward and return links; (a) on board return link payload and feeder-link payload without on-board optimization for forward link, and (b) on board feeder-link payload and forward link payload. On-board feeder links are implemented by a 4-element retro-directive antenna. 
           [0066]      FIG. 14 b    depicts a functional blocks of mobile communication architecture with GBBF for ground processing facility with calibration and compensation mechanisms via Wavefront muxing/demuxing for both forward and return links. An optimization loop for forward link WF demuxing is implemented on-ground as pre-distortion techniques for differential phase and amplitude equalizations. A separated optimization loop for return link WF demuxing is also implemented on-ground. 
           [0067]      FIG. 15  depicts functional block diagrams of two digital beam forming (DBF) processors in a GBBF for ground processing facility; one for a multiple-beam transmitting (Tx) DBF and the other one for a multiple-beam receiving (Rx) DBF. 
           [0068]      FIG. 16  features a slight deviation of  FIG. 1 ; depicting a scenario of using three separated UAVs as three mobile platforms for emergency and disaster recovery services; UAV M 1  for communications among rescue team members, UAV M 2  for communications as emergency replacements of mobile and/or fixed wireless base stations for resident communications via their existing mobile phones and/or personal communications devices using WiFi. UAV M 4  for surveillances via RF sensors using satellites as RF illuminators. 
       
    
    
     DETAILED DESCRIPTION 
       [0069]      FIG. 1  depicts a scenario of using three separated UAVs  120  as three mobile platforms for emergency and disaster recovery services; UAV M 1  for communications among rescue team members, UAV M 2  as emergency replacements of mobile and/or fixed wireless base stations for resident communications via their existing mobile phones and/or personal communications devices using WiFi. The third UAV platform M 3  performs real time imaging and surveillances via passive optical, infrared or RF sensors. All three platforms are connected to a ground hub  110  via feeder-links in Ku and/or Ka band spectrum. The ground hub  110  will serve as gateways and have access to terrestrial networks  101 . 
         [0070]    As a result, rescue works in a coverage area  130  will have access of real time imaging, and communications among co-workers and dispatching centers connected by the hub  110 . Residents in disaster/emergency recovery areas  130  will also be provide with ad hoc networks of communications via their own personal devices to outside world, to rescue teams, and/or disaster/emergency recovery authorities. 
         [0071]    The feeder-links of the three platforms M 1 , M 2 , and M 3  are identical in Ku and/or Ka bands. Only the three payloads (P/L) are different; the P/L on the first UAV M 1  enables networks for communications in public safety spectrum among members of rescue team; the P/L on the second UAV M 2  is to restore resident cell phone and/or fixed wireless communications at L/S band, and the P/L on the third UAV M 3  is an real time imaging sensor for real time surveillance. 
         [0072]    Three independent technologies are discussed; (1) retro-directive array, (2) ground based beam forming, and (3) wavefront multiplexing and demultiplexing (WF muxing/demuxing). Retro-directive links for feeder-links are to make the feeder links payload on UAVs to communicate with designated ground hubs more effectively, using less power, reaching hubs in further distances, and/or more throughputs. 
         [0073]    The architectures of ground base beam forming (GBBF), or remote beam forming (RBF), for UAV platform base communications will support and accomplish designed missions using P/L with smaller SW&amp;P. Beam forming processing may be located remotely on ground (e.g. GBBF) or anchored on other platforms on air, on ground, or at sea. GBBF architectures are used for illustrations in here. However, similar RBF architecture can be developed for the platforms which may be mobile, re-locatable, fixed, and/or combinations of all above to perform remote beam forming functions. 
         [0074]    Wavefront multiplexing and demuxing techniques can be applied in many advanced applications for UAV based mobile communications including the following three:
       (1) Calibrating back channels in feeder-links   (2) coherent power combining of radiated power by different UAVs in ground receivers in contracts to “spatial power combining” using conventional array antennas;   (3) generating data security and redundancy in segmented data packages for concurrent delivery through various UAVs, different channels in a UAV, and combinations of both.       
 
         [0078]    There are four technologies in this architecture:
       1. UAVs  120  as communications nodes   2. Fore-ground communications networks between users in a coverage area  130  and UAVs  120 
           For users with hand held devices at L/S bands   utilizing remote-beam forming network (RBFN) with the ground based beam forming (GBBF) processing in a ground mobile hub facility  110     
           3. Back-ground communications networks, (back channels or feeder-links) between ground infrastructures/facilities  110  and UAVs  120 
           Back-channels or feeder-links between UAVs and GBBF processing centers via retro-directive antennas.   
           4. Wavefront multiplexing/de-multiplexing (WF muxing/demuxing);
           Back-channel calibrations on feeder-link transmission for RBF/GBBF   Coherent power combining in receivers on signals from different channels on various UAVs;   Secured transmissions with redundancies via UAVs.   
               
 
         [0089]      FIG. 2  depicts both return links and forward links of a UAV based mobile communications  200  with on-board beam forming network (BFN)  211  over a coverage area  130 . The UAV  120  provides interconnections among users A, B, C, and C in two beams  1302  and  1303  via a communication hub  110 , which is a “gateway” to terrestrial networks  101 . The communication hub  110  is covered by the feeder-link beam illuminated by an on-board feeder-line antenna  236  at Ka or Ku band. We assume these users are at L/S bands, including bands covering commercial cell phones and WiFi band. 
         [0090]    The P/L  200  consists of three sections supporting both forward and return links; (1) a foreground communications payload (P/L)  210  at L/S band, (2) frequency translation sections  220  between L/S band of and Ku/Ka bands, and (3) a feeder-link payload  230  at Ku/Ka band. 
         [0000]    Similar architectures also are applicable to other selected bandwidths for other foreground communications payload (P/L) 210; such as for emergency rescue workers at 4.9 GHz reserved for public safety spectrum. 
         [0091]    A multi-beam antenna  211  with many array elements  217  in the foreground link payload (P/L)  210  at L/S band is used for both transmission in forward links and receptions in return links. There are at least three beams,  1301 ,  1302 , and  1303  over the coverage area  130 . The inputs/outputs ports to the multi-beam antenna  211  are the “beam ports” connected by diplexers  213 , where the return link beam-ports are connected to LNAs  214  at L/S band, and the forward link beam-ports are connected to power amplifiers  215 . 
         [0092]    There are at least two pairs of frequency translation units  220 . The return link units feature frequency up-conversion from L/S band (1/2 GHz) to Ku/Ka band (12/20 GHz) . The forward link units translate signals at Ku/Ka band (14/30 GHz) to those at L/S band L/S band (1/2 GHz). 
         [0093]    Feeder-link P/L  230  features two groups of “beam” signals. For the return link signals, the muxing devices of  231  combines the beam signals at various translated frequency slots in Ku/Ka band into a single stream, then power amplified by a PA  235 , duplexed by an antenna diplexer  233  before radiated by the feeder-link antenna  236  in a feeder-link payload (P/L)  230 . Similarly for signals in forward links, the feeder-link signals received by the antenna  236  and I/O duplexer  233  are conditioned by Ku/Ka band LNA  234 . The Ku/Ka band demuxing devices  232  separates beam signals by dividing the conditioned signals into various beam-ports before translating them from proper frequency slots in Ku/Ka band into a common frequency slot in L/S band by the frequency converters  220 . These input beam signals are power amplified by individual power amplifiers  215  in the foreground P/L before radiated by the foreground-link multibeam antenna  211 . 
         [0094]    We have assumed the muxing device  231  performs frequency division multiplexing (FDM) and consistent with an associated device on ground performing frequency division demultiplexing (FDM demuxing). However, the muxing/demuxing functions of  231 / 232  may perform via other muxing/demuxing schemes such as time division muxing (TDM), code division muxing (CDM), or combinations of FDM, CDM and/or TDM. 
         [0095]      FIG. 2  presents systems and methods to restore mobile communications for residents in a disaster area via a small UAV M 2  which features on-board beam forming capability and serves as a communications relay to ground gateways. As an example depicted in  FIG. 2 , a first user A in beam  1303  is sending a data string to a fourth user D in Beam  1302 , an on board payload (P/L) of a M 2  UAV  120  will pick up the data sent by the first user A in Beam  1303  via the multi-beam antenna  211 . The first user A will use his/her own cell-phone or portable devices via WiFi spectrum. The received data string by the multi-beam antenna  211  will be amplified by a LNA  214 , filtered and frequency translated by a transponder  220 , power amplified  235  and then radiated by the feeder-link antenna  236  at Ka or Ku band. The feeder link antennas on the M 2  UAV shall be a high gain tracking beam antenna with a tracking beam always pointed to a ground hub  110  as the M 2  UAV  120  moves. 
         [0096]    The on-board feeder-link antennas may also be implemented as low gain antennas including omni directional ones to simplify complexity on feeder-link tracking mechanisms with a price of reduced channel capacity and/or operational ranges between the M 2  UAV  120  and the ground hub  110 . 
         [0097]    The hub  110  will assign the received data stream to a forward link beam port, through which the data will be delivered to a desired receiving user, the user D, in Beam  1302 . 
         [0098]    An uplink data stream in the ground facility  110  designated for a forward link beam port of the on-board BFN  211  is up-loaded via the Ku/Ka band feeder-link and captured by the feeder-link antenna  236 . The captured signals are conditioned via a LNA and a band pass filter (BPF) before FDM demuxed to a common IF by a FDM demuxer  232 . The demuxed components are different beam signal streams for various input ports of the multibeam antenna  217 . 
         [0099]    Concurrently a third user C in beam  1302  want to send a different data string to a second user B in Beam  1303 , the on board P/L  210  will pick up the data sent by the third user C in Beam  1302  via the multi-beam antenna  211 , the received data from the user C will be amplified by a LNA  214 , filtered and frequency translated by one of the transponders  220 , power amplified  235  and then radiated by the feeder-link antenna  236  at Ka or Ku band. The hub  110  will assign the received data stream to a forward link beam port, which will deliver the data to the desired receiving user, user B, in Beam  1303 . 
         [0100]    It is clear that there are no “switching or connecting” mechanisms at all among users over the coverage area  130  for the P/L  200  on the UAV  120 . The switching and connecting mechanisms are performed in the ground hub  110 . 
         [0101]    Referring to  FIG. 2 , the M 2  UAV  120  may only provide one-way forward communications such as broadcasting or multicasting. Forward links of the M 2  UAV  120  based mobile communications with on-board beam forming network (BFN)  211 . The M 2  UAV  120  provides interconnections to a first receiving mobile user B in the beam position  1303  from a communication hub  110  connected to a first data source which may come from terrestrial networks  101 , or via on return links of the UAV  120 . The UAV  120  concurrently provides interconnections to a second receiving mobile user Din the beam position  1302  from a communication hub  110  connected to a second data source which may come from terrestrial networks  101 , or via return links of the UAVs  120 . 
         [0102]    Referring to  FIG. 2 , the M 2  UAV  120  may only provide one-way return link (receiving only) services including other applications such as bi-static radar receiver functions. Return links of the M 2  UAV  120  based mobile communications with on-board beam forming network (BFN)  211 . The M 2  UAV  120  provides interconnections from a first data source A in the beam position  1303  to a ground processing hub  110  connected to a first data receiver via terrestrial networks  101 , or to a data receiver in the same coverage area  130  via forward links of the UAVs  120 . Concurrently, the UAV  120  provides interconnections from a second data source C in the beam position  1302  to a processing hub  110  which may be connected to a second data receiver via terrestrial networks  101  or via forward links of the UAVs  120 . 
         [0103]      FIG. 3  depicts both return links and forward links of a UAV based mobile communications  200  with no on-board beam forming network (BFN)  211  over a coverage area  130 . The UAV  120  provides interconnections among users A, B, C, and C in two beams  1302  and  1303  via a communication hub  110 , which is a “gateway” to terrestrial networks  101 . The communication hub  110  is covered by the feeder-link beam illuminated by an on-board feeder-line antenna  236  at Ka or Ku band. We assume these users are at L/S bands, including bands covering commercial cell phones and WiFi band. 
         [0104]    The P/L  200  consists of three sections supporting both forward and return links; (1) a foreground communications payload (P/L)  210  at L/S band, (2) frequency translation sections  220  between L/S band of and Ku/Ka bands, and (3) a feeder-link payload  230  at Ku/Ka band. 
         [0105]    Similar architectures also are applicable to other selected bandwidths for other foreground communications payload (P/L)  210 ; such as for emergency rescue workers at 4.9 GHz reserved for public safety spectrum. 
         [0106]    The on board L/S band antennas in the feeder-link payload (P/L)  230  are many individual array elements  217  at L/S band. They are used for both transmission in forward links and receptions in return links. There are at least three beams,  1301 ,  1302 , and  1303  over the coverage area  130 . The inputs/outputs ports to the array elements  217  are the “element-ports” connected by diplexers  213 , where the return link element-ports are connected to LNAs  214  at L/S band, and the forward link element-ports are connected to power amplifiers  215 . 
         [0107]    There are at least two pairs of frequency translation units  220 . The return link units feature frequency up-conversion from L/S band (1/2 GHz) to Ku/Ka band (12/20 GHz). The forward link units translate signals at Ku/Ka band (14/30 GHz) to those at L/S band L/S band (1/2 GHz). 
         [0108]    Feeder-link P/L  230  features two groups of “element” signals. For the return link signals, the muxing devices of  231  combines various “element” signals at various translated frequency slots in Ku/Ka band into a single stream, then power amplified by a power amplifier (PA)  235 , duplexed by an antenna diplexer  233  before radiated by the feeder-link antenna  236 . 
         [0109]    Similarly for signals in forward links, the feeder-link signals received by the antenna  236  and I/O duplexer  233  are conditioned by Ku/Ka band LNA  234 . The Ku/Ka band demuxing devices  232  separates various element-signals by dividing the conditioned signals into various “element-ports” before translating them from proper frequency slots in Ku/Ka band into a common frequency slot in L/S band by the frequency converters  220 . These element signals are then power amplified by individual power amplifiers  215  in the foreground P/L  310  before radiated by the individual foreground-link antenna elements  217 . 
         [0110]    We have assumed the muxing device  231  performs frequency division multiplexing (FDM) and consistent with an associated device on ground performing frequency division demultiplexing (FDM demuxing). However, the muxing/demuxing functions of  231 / 232  may perform via other muxing/demuxing schemes such as time division muxing (TDM), code division muxing (CDM), or combinations of FDM, CDM and/or TDM. 
         [0111]      FIG. 4  depicts a scenario with a small M 1   a  UAV  120 - 1  performing a communication relay mission via GBBF for residents in L/S bands. The foreground links  420  feature multiple spot beams  1301 ,  1302 , and  1303  in L/S band servicing coverage  130  with &lt;100 Km in diameter. A ground user  436  may use his/her own cell phone communicating to other users in or outside the same coverage area  130 . The coverage  130  area may vary depending on requirements on missions. 
         [0112]    The ground hub  410  in  FIG. 4  will receive and condition signals from the feeder-link  450  in their frontend  411 . A ground based beam forming (GBBF) processor  412  will (1) recover the received signals of the on-board elements  217  with precision amplitudes and phases, (2) perform digital beam forming (DBF) processing on the recovered element signals generating received beam signals, and (3) deliver the received beam signals for further receiving functions including demodulation to convert waveforms into data strings before sending them to destinations performed by mobile hubs  413  via terrestrial networks  480 . The details of GBBF for both Forward links and Return links will be descripted in details in  FIG. 12 . 
         [0113]    Similarly for signals in forward links, the ground based beam forming (GBBF) processor  412  will (1) receiving the transmitting “beam-signals” from a transmitter after functions including modulation and channel formatting performed by the mobile hubs  413  from signal sources which may come via terrestrial networks  480 , (2) performing transmit digital beam forming (DBF) processing on the “beam signals” in baseband generating parallel element-signals in baseband to be transmitted in L/S band by the small M 1   a  UAV  120 - 1 , and (2) up-converting and FDM muxing these element signals to Ku/Ka for uplink to the UAV  120 - 1  via the feeder-link. Multiple beam-signals are designated to users in various spot beams  1301 ,  1302 , and  1303  over the coverage area  130 . These transmitted beam signals will be delivered to various users in the coverage area  130  concurrently 
         [0114]    Onboard the small M 1   a  UAV  120 - 1 , as depict in  FIG. 3 , the up-linked signals received by the feeder antenna  236  and I/O duplexer  233  are conditioned by Ku/Ka band LNA  234 . The Ku/Ka band demuxing devices  232  separates “element” signals by dividing the conditioned signals to element various ports before translating them from proper frequency slots in Ku/Ka band into a common frequency slot in L/S band by the frequency converters  220 . These input beam signals are power amplified by individual power amplifiers  215  in the foreground P/L before radiated by the foreground-link array elements  217 . 
         [0115]    We have assumed the muxing device  231  performs frequency division multiplexing (FDM) and consistent with an associated device on ground performing demuxing of FDM. However, muxing/demuxing device  231 / 232  may perform other muxing/demuxing schemes such as time division muxing (TDM), code division muxing CDM, or combinations of TDM, CDM and/or FDM. 
       Embodiment 1 
       [0116]      FIG. 3  presents an example of systems and methods to restore mobile communications for residents in a disaster area via a small UAV M 2  which features ground based beam forming (GBBF) or remote beam-forming network (RBFN) capability and serves as a communications relay to ground gateways. Referring to  FIG. 3 , the M 2  UAV  120  may only provide one-way forward communications such as broadcasting or multicasting. Forward links of the M 2  UAV  120  based mobile communications with on-board array elements  217  but no beam forming functions at all. The M 2  UAV  120  provides interconnections to a first receiving mobile user B in the beam position  1303  from a communication hub  110  after GBBF functions  1101  connected to a first data source which may come from terrestrial networks  101 , or via on return links of the UAV  120 . The UAV  120  concurrently provides interconnections to a second receiving mobile user D in the beam position  1302  from a communication hub  110  connected to a second data source which may come from terrestrial networks  101 , or from a source in the same coverage area  130  via return links of the UAVs  120 . The processing/communication hub  101  will also perform transmitting beam-forming functions concurrently for many transmit beams for the array elements on the M 2  UAV. 
         [0117]    Referring to  FIG. 3 , the M 2  UAV  120  may only provide one-way return link (receiving only) services including bi-static radar receiver functions. Return links of the M 2  UAV  120  based mobile communications with on-board array elements  217  but without beam forming network (BFN). The M 2  UAV  120  provides interconnections to a first data source A in the beam position  1303  to a ground processing hub  110  connected to a first data receiver via terrestrial networks  101 , or via forward links of UAVs  120  to a user in the UAV coverage area  130 . Concurrently, the UAV  120  provides interconnections to a second data source C in the beam position  1302  to a processing hub  110  which may be connected to a second data receiver via terrestrial networks  101  or a receiver in the same coverage area  130  via forward links of the UAVs  120 . The M 2  UAV  120  provides interconnections from residents in the coverage area  130  to a communication hub which shall serve as “gateways” to terrestrial networks. The processing/communication hub  101  will perform receiving beam-forming functions concurrently for many receiving beams for the array elements on the M 2  UAV. 
         [0118]      FIG. 4  depicts a similar embodiment via a M 1  UAV  120 - 1  for communications mainly to rescue worker community in a coverage area  130 . The ground facility  410  features:
       1. multiple beam antennas  411  to connected to various UAV platforms  120  concurrently via different Ku/Ka band feeder-links  450 ,   2. GBBF for both forward link (transmitting) beams and return link (receiving) beams   3. mobile hubs  413  as gateways to terrestrial networks  480  or other UAV based networks.       
 
         [0122]    The M 1   a  UAV  120 - 1  along with its GBBF processing features multiple beams  1301 ,  1302 ,  1303 , and etc. in both forward and return links in a reserved public safety frequency band; e.g. 4.9 GHz or 700 MHz in US. The users (rescue worker community) in the coverage areas feature omni directional terminals  436   
         [0123]      FIG. 4  presents an example of systems and methods for broadcasting and/or multicasting via a small UAV with GBBF or RBFN. One-way communications are depicted, transmitting to rescue worker community in a coverage area  130  via a M 1  UAV  120 - 1 . The ground facility  410  features:
       1. multiple beam antennas  411  support a Ku/Ka band feeder-link  450  from the ground facility  410  to the M 1   a  UAV  120 - 1  platform,   2. GBBF processing including beam forming functions for concurrent forward link (transmitting) multiple beams   3. mobile hubs  413  as gateways to terrestrial networks  480  or other UAV based networks.       
 
         [0127]    The M 1   a  UAV  120 - 1  along with its GBBF processing features multiple Tx beams  1301 ,  1302 ,  1303 , and etc. including forward links in a reserved public safety frequency band; eg. 4.9 GHz or 700 MHz in US. 
         [0128]    The users (rescue worker community) in the coverage areas shall feature omni directional terminals  436 . 
         [0129]    The M 1   a  UAV  120 - 1  provides interconnections from mobile users to a communication hub connected to terrestrial networks. 
         [0130]    This embodiment can be used as platforms for bi-static radar receivers. The associated processing facility  411  on ground may be modified to perform not only functions of beam forming via GBBF  412 , but also signal processing functions of range gating, Doppler frequency separations, as well as additional radar/imaging processing. 
         [0131]      FIG. 5  depicts a scenario with 4 small UAVs  520 - 1  performing a communication relay mission via GBBF for residents in L/S bands. The four small UAVs  520 - 1  identified as M 1   a,  M 1   b,  M 1   c  and M 1   d  are flying in formations closely spaced among one another (say, 10 m or less). The foreground links  420  feature multiple spot beams  1301 ,  1302 , and  1303  in L/S band servicing coverage  130  with &lt;100 Km in diameter. A ground user  436  may use his or her own cell phone communicating to other users in or outside the same coverage area  130 . The coverage  130  may vary depending on requirements on missions. 
         [0132]    The ground hub  410  in  FIG. 4  will receive and condition signals in the feeder-links  550  in their frontend  411 . A ground based beam forming (GBBF) processor  412  will (1) recover the received signals of the on-board elements  217  from all 4 small UAVs  520 - 1  with precision amplitudes and phases, (2) perform digital beam forming (DBF) processing on the recovered element signals from various UAVs  520 - 1  generating received beam signals, and (3) deliver the received beam signals for further receiving functions including demodulation to convert waveforms into data strings before sending them to destinations performed by mobile hubs  413  via terrestrial networks  480 . The details of GBBF for both Forward links and Return links will be descripted in details in  FIG. 12 . 
         [0133]    Similarly for signals in forward links, the ground based beam forming (GBBF) processor  412  will (1) receiving the transmitting “beam-signals” from a transmitter after functions including modulation and channel formatting performed by the mobile hubs  413  from signal sources which may come via terrestrial networks  480 , (2) performing transmit digital beam forming (DBF) processing on the “beam signals” in baseband generating parallel element-signals in baseband to be transmitted in L/S band by the four small UAVs  520 - 1  concurrently, and (2) up-converting and FDM muxing these element signals to Ku/Ka for uplinks to the 4 small UAV  520 - 1  via the feeder-links  550 . Multiple beam-signals are designated to users in various spot beams  1301 ,  1302 , and  1303  over the coverage area  130 . These transmitted beam signals will be delivered to various users in the coverage area  130  concurrently 
         [0134]    Onboard each of the 4 small UAV  520 - 1 , the processing from feeder-link to foreground links are identical. In the M 1   a  UAV  120 - 1  shown in  FIG. 3  as an example, the up-linked signals received by the feeder antenna  236  and I/O duplexer  233  are conditioned by Ku/Ka band LNA  234 . The Ku/Ka band demuxing devices  232  separates “element” signals by dividing the conditioned signals to various element ports before translating them from proper frequency slots in Ku/Ka band into a common frequency slot in L/S band by the frequency converters  220 . These input beam signals are power amplified by individual power amplifiers  215  in the foreground P/L before radiated by the foreground-link array elements  217 . 
         [0135]    We have assumed the muxing device  231  performs frequency division multiplexing (FDM) and consistent with an associated device on ground performing demuxing of FDM. However, muxing/demuxing device  231 / 232  may perform other muxing/demuxing schemes such as time division muxing (TDM), code division muxing CDM, or combinations of TDM, CDM and/or FDM. 
         [0136]    Another example presents systems and methods of implementing ad hoc mobile communications for rescued workers in a disaster area via multiple closely spaced small UAVs featuring GBBF or RBFN. The term “M 1  UAVs  520 - 1  ” is used to represent all 4 small UAVs; the M 1   a  UAV, the M 1   b  UAV, the M 1   c  UAV, and the M 1   d  UAV in  FIG. 5 .  FIG. 5  depicts an embodiment via multiple M 1  UAVs  520 - 1  for communications mainly to rescue worker community in a coverage area  130 . 
         [0137]    The ground facility  410  features:
       1. multiple beam antennas  411  to connected to various UAV platforms  520 - 1  concurrently via different Ku/Ka band feeder-links  550 ,   2. GBBF for both forward link (transmitting) beams and return link (receiving) beams   3. mobile hubs  413  as gateways to terrestrial networks  480  or other UAV based networks.       
 
         [0141]    The M 1   a,  M 1   b,  M 1   c,  and M 1   d  UAVs  520 - 1  along with their GBBF processing feature multiple beams  1301 ,  1302 ,  1303 , and etc. in both forward and return links in a reserved public safety frequency band; e. g. 4.9 GHz or 700 MHz in US. The users (rescue worker community) in the coverage areas shall feature omni directional terminals  436 . 
         [0142]    In a first operational scenario of both forward and return links of mobile communications via multiple closely space M 1  UAVs  520 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via beam-forming among elements of arrays on a UAV. Ku/Ka channels in the feeder links  550  shall be designed with adequate instantaneous bandwidths to support all UAVs concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility providing orthogonal beams concurrently connecting to all UAV facilitating frequency reuse. On the other hand for the foreground communications P/Ls, various UAVs provide different groups of beams operated at various frequency slots, different groups of codes, and/or time slots. Each supports an independent data stream. The relative positions among arrays on different UAVs become less important. Radiated RF powers associated with many of these independent data streams among various UAVs are not combined. Information or data streams may be combined for high data rate users via channel bonding. 
         [0143]    In a second operational scenario of both forward and return links of mobile communications via multiple closely space M 1  UAVs  520 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via beam-forming among distributed subarrays; each of which is on a separated UAV. Ku/Ka channels in the feeder links  550  shall be designed with adequate instantaneous bandwidths to support all UAVs concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility providing orthogonal beams connecting to all UAV concurrently facilitating frequency reuse. The spacing among the M 1  UAVs  520 - 1  shall vary slowly. As a result, the relative geometries among elements in this distributed and slow-varying array are very important in maintaining coherency among subarrays. The slow varying array geometries must be continuously calibrated and then compensated for both forward links and return links properly as a part of GBBF functions  412 . This operation scenario will allow coherently added stronger radiated signals from multiple M 1  UAVs  520 - 1  to “punch through” debris or man-made structures reaching users with disadvantage terminals or at disadvantaged locations. 
         [0144]    Another example presents systems and methods of implementing one way broadcasting or multicasting communications via multiple closely spaced small UAVs featuring GBBF or RBFN. We shall use the term “M 1  UAVs  520 - 1 ” to represent all 4 small UAVs; the M 1   a  UAV, the M 1   b  UAV, the M 1   c  UAV, and the M 1   d  UAV in  FIG. 5 . Forward links of the M 1  UAVs  520 - 1  based mobile communications with on-board array elements  217  but no beam forming functions at all. The M 1  UAVs  520 - 1  provide interconnections to a first receiving mobile user B in the beam position  1303  from a communication hub  410  after GBBF functions  412  connected to a first data source which may come from terrestrial networks  408 , or via on return links of the M 1  UAVs  520 - 1 . The M 1  UAVs  520 - 1  concurrently provides interconnections to a second receiving mobile user D in the beam position  1302  from a communication hub  410  connected to a second data source which may come from terrestrial networks  408 , or from a source in the same coverage area  130  via return links of the M 1  UAVs  520 - 1 . The processing/communication hub  410  will also perform transmitting beam-forming functions concurrently for many transmit beams for the array elements on the M 1  UAVs  520 - 1 . 
         [0145]    In a first operational scenario of forward links of mobile communications via multiple closely space M 1  UAVs  520 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via beam-forming among elements of arrays on a UAV. Ku/Ka channels in the feeder links  550  shall be designed with adequate instantaneous bandwidths to support all UAVs concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility providing orthogonal beams connecting to all UAV concurrently facilitating frequency reuse. Various UAVs will provide different groups of beams operated at various frequency slots, different groups of codes, and/or time slots for the foreground communications payloads. Each UAV supports independent data streams. The relative positions among arrays on different UAVs become less important. Radiated RF powers associated with many of these independent data streams among various UAVs are not “coherently combined”. Information or data streams may be combined for high data rate signal streams via channel bonding. 
         [0146]    In a second operational scenario of forward links of mobile communications via multiple closely space M 1  UAVs  520 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via additional beam-forming processing among distributed subarrays; each of which is on a separated UAV. Ku/Ka channels in the feeder links  550  shall be designed with adequate instantaneous bandwidths to support all UAVs concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility providing orthogonal beams connecting to all UAV concurrently facilitating frequency reuse. The spacing among the M 1  UAVs  520 - 1  shall vary slowly. As a result, the relative geometries among elements in this distributed and slow-varying array are very important in maintaining coherency among subarrays. The slow varying array geometries must be continuously calibrated and then compensated for both forward links and return links properly as a part of GBBF functions  412 . This operation scenario will allow coherently added stronger radiated signals from multiple M 1  UAVs  520 - 1  to “punch through” debris or man-made structures reaching users with disadvantage terminals or at disadvantaged locations. 
         [0147]    Another example presents systems and methods of implementing one way receive only communications via multiple closely spaced small UAVs featuring GBBF or RBFN. 
         [0148]    We shall use the term “M 1  UAVs  520 - 1 ” to represent all 4 small UAVs; the M 1   a  UAV, the M 1   b  UAV, the M 1   c  UAV, and the M 1   d  UAV in  FIG. 5 . 
         [0149]    Referring to  FIG. 5 , the M 1  UAVs  520 - 1  may only provide one-way return link (receiving only) services including applications of bi-static radar receiver functions. Return links of the M 1  UAVs  520 - 1  based mobile communications with on-board array elements  217  similar to the one shown in  FIG. 3 . The M 1  UAVs  520 - 1  provide interconnections to a first data source A in the beam position  1303  to a ground processing hub  410  connected to a first data receiver via terrestrial networks  480 , or via forward links of M 1  UAVs  520 - 1  to a user in the coverage area  130 . Concurrently, the M 1  UAVs  520 - 1  provide interconnections to a second data source C in the beam position  1302  to a processing hub  410  which may be connected to a second data receiver via terrestrial networks  480  or a receiver in the same coverage area  130  via forward links of the M 1  UAVs  520 - 1 . The M 1  UAVs  520 - 1  provide interconnections from data sources in the coverage area  130  to a communication hub which shall serve as “gateways” to terrestrial networks. The processing/communication hub  410  will perform receiving beam-forming functions concurrently for many receiving beams for the array elements on the multiple M 1  UAVs  520 - 1 . 
         [0150]    In a first operational scenario of return links of mobile communications via multiple closely space M 1  UAVs  520 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via beam-forming among elements of arrays on a UAV. Ku/Ka channels in the feeder links  550  shall be designed with adequate instantaneous bandwidths to support all UAVs concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility providing orthogonal beams connecting to all UAV concurrently facilitating frequency reuse. Various UAVs provide different groups of beams operated at various frequency slots, different groups of codes, and/or time slots. Each supports an independent data stream. The relative positions among arrays on different UAVs become less important. Received RF powers associated with many of these independent data streams among various UAVs are not “coherently” combined. Information or data streams may be combined for high data rate users via channel bonding. 
         [0151]    In a second operational scenario of return links of mobile communications via multiple closely space M 1  UAVs  520 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via beam-forming among distributed subarrays; each of which is on a separated UAV. Ku/Ka channels in the feeder links  550  shall be designed with adequate instantaneous bandwidths to support all UAVs concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility providing orthogonal beams connecting to all UAV concurrently facilitating frequency reuse. 
         [0152]    The spacing among the M 1  UAVs  520 - 1  shall vary slowly. As a result, the relative geometries among elements in this distributed and slow-varying array are very important in maintaining coherency among subarrays. The slow varying array geometries must be continuously calibrated and then properly compensated for return links as a part of GBBF functions  412 . This operation scenario will allow coherently added received signals captured by multiple M 1  UAVs  520 - 1  to enhance received signal-to-noise ratio (SNR). 
         [0153]    In addition, multibeam GNSS receivers [ 1 ,  2 ,  3 ] on individual UAVs shall provide current status on information not only for the individual platform positions but also for the platform orientations. Thus all element current positions and orientations of a subarray on a moving UAV can then be precisely calculated in a dynamic coordinate moving with the mean velocity of all participating UAVs. Thus the geometry of a dynamic array distributed among multiple slow moving UAVs can then be calculated precisely for a current flying trajectory position, and may also be projected for next few flying trajectory positions a few seconds ahead. 
         [0154]    In bi-static radar receiving applications, coherent combining of captured signal returns among multiple UAVs will provide enhanced SNR and also better spatial resolutions. RF illuminators for these bi-static or multi-static radars may be many of the GNSS satellites at L-band for global coverage, C-band satellites for land and ocean coverage, or Ku and Ka band high power DBS satellites or spot beam satellites for many land mass coverage or near equatorial coverage on land mass, on ocean and in air services. 
         [0155]      FIG. 6  depicts a scenario with 4 small UAVs  620 - 1  performing a communication relay mission via GBBF for residents in L/S bands. The four small UAVs  620 - 1   a,    620 - 1   b,    620 - 1   c  and  620 - 1   d  identified as M 1   a,  M 1   b,  M 1   c  and M 1   d  are distributed in a fly formation with large distances among them (say, &gt;1 Km). The foreground links  420  of each of the 4 UAVs feature multiple spot beams  1301 ,  1302 , and  1303  in L/S band servicing coverage  130  with &lt;100 Km in diameter. A ground user  436  may use an advanced user device communicating to other users in or outside the same coverage area  130 . The advanced user device features multiple tracking beams at concurrently and independently following all 4 small UAVs. The multiple-beams of an advanced user terminals operate at same frequency slots among the links between each of the four UAVs and the ground user. The coverage  130  area may vary depending on requirements on missions. 
         [0156]    The ground hub  410  in  FIG. 6  will receive and condition signals from the 4 UAVs (M 1   a    620 - 1   a,  M 1   b   620 - 1   b,  M 1   c    620 - 1   c,  and M 1   d    620 - 1   d ) via the 4 separated feeder-links  550  at its frontend  411 . A ground based beam forming (GBBF) processor  412  will (1) recover the received signals of the on-board elements  217  from all 4 small UAVs  620 - 1   a,    620 - 1   b,    620 - 1   c,  and  620 - 1   d  with precision amplitudes and phases, (2) concurrently perform 4 sets of digital beam forming (DBF) processing on the recovered element signals from 4 UAVs  620 - 1  generating 4 concurrent receiving beam signals for each ground user, and (3) deliver the 4 received beam signals for further receiving functions including demodulation to convert waveforms into data strings, (4) channel-bonding of received signals to form a string of the received beam signals from one user but through 4 different UAV&#39;s before sending them to destinations performed by mobile hubs  413  via terrestrial networks  480 . The sequence of the processing in (3) and (4) may be reversed if signal modulations in all 4 feeder-links are identical. The details of GBBF for both Forward links and Return links will be descripted in details in  FIG. 12 . 
         [0157]    Similarly for signals in forward links, the ground based beam forming (GBBF) processor  412  will (1) receiving the transmitting “beam-signals” from a transmitter after functions including modulation and channel formatting performed by the mobile hubs  413  from signal sources which may come via terrestrial networks  480 , (2) segmenting the modulated signals into 4 substream beam signals (2) performing 4 concurrent but independent transmit digital beam forming (DBF) processing on each of the “substream beam signals” in baseband generating parallel element-signals in baseband to be transmitted in L/S band by the four small UAVs  620 - 1  concurrently, and (2) up-converting and FDM muxing these element signals to Ku/Ka for uplinks to the 4 small UAV  620 - 1 via the feeder-links  550 . Multiple beam-signals are designated to users in various spot beams  1301 ,  1302 , and  1303  from 4 separated UAV over the same coverage area  130 . These transmitted beam signals will be delivered to various users in the coverage area  130  concurrently. The user with an advanced multi-beam terminal will have an advantage of 4 times the channel capacity as compared to the capacity from a single UAV  120   
         [0158]    Onboard each of the 4 small UAV  620 - 1 , the processing from feeder-link to foreground links are identical. Taking that of the M 1   a  UAV  120 - 1  shown in  FIG. 3  as an example, the up-linked signals received by the feeder antenna  236  and I/O duplexer  233  are conditioned by Ku/Ka band LNA  234 . The Ku/Ka band demuxing devices  232  separates “element” signals by dividing the conditioned signals to various element ports before translating them from proper frequency slots in Ku/Ka band into a common frequency slot in L/S band by the frequency converters  220 . These input beam signals are power amplified by individual power amplifiers  215  in the foreground P/L before radiated by the foreground-link array elements  217 . 
         [0159]    We have assumed the muxing device  231  performs frequency division multiplexing (FDM) and consistent with an associated device on ground performing demuxing of FDM. However, muxing/demuxing device  231 / 232  may perform other muxing/demuxing schemes such as time division muxing (TDM), code division muxing CDM, or combinations of TDM, CDM and/or FDM. 
         [0160]    Next example presents systems and methods of implementing ad hoc mobile communications for rescued workers in a disaster area via largely spaced multiple small UAVs featuring GBBF or RBFN. The rescued workers shall be equipped with multiple beam terminals. 
         [0161]    The term “M 1  UAVs  620 - 1 ” is used to represent all 4 small UAVs; the M 1   a  UAV  620 - 1   a,  the M 1   b  UAV  620 - 1   b,  the M 1   c  UAV  620 - 1   c,  and the M 1   d  UAV  620 - 1   d  in  FIG. 6 .  FIG. 6  depicts an embodiment via multiple M 1  UAVs  620 - 1  for communications mainly to rescue worker community in a coverage area  130 . 
         [0162]    The ground facility  410  features:
       1. multiple beam antennas  411  to connected to various UAV platforms  620 - 1  concurrently via different Ku/Ka band feeder-links  550 ,   2. GBBF for both forward link (transmitting) beams and return link (receiving) beams   3. mobile hubs  413  as gateways to terrestrial networks  480  or other UAV based networks.       
 
         [0166]    The M 1   a,  M 1   b,  M 1   c,  and M 1   d  UAVs  620 - 1  along with their GBBF processing feature multiple beams  1301 ,  1302 ,  1303 , and etc. in both forward and return links in a reserved public safety frequency band; eg. 4.9 GHz or 700 MHz in US. 
         [0167]    The users (rescue worker community) in the coverage areas shall feature multiple tracking-beam terminals  633 . Each of the advanced user terminals exhibits capability of tracking the 4 M 1  UAVs  620 - 1  with four separated beams operating at the same frequency slots in a reserved public safety band concurrently. Goode isolations among multiple UAVs operating at same frequency bandwidths, codes and time slots are achieved via spatial isolations from the advanced user terminals. As a result, same spectrum is used 4 times more than the scenarios presented in  FIG. 5 . 
         [0168]    In a first operational scenario of both forward and return links of mobile communications via multiple closely space M 1  UAVs  520 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via beam-forming among elements of arrays on a UAV. Ku/Ka channels in the feeder links  550  shall be designed with adequate instantaneous bandwidths to support all M 1  UAVs  620 - 1  concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility  410  providing orthogonal beams concurrently connecting to all UAV facilitating frequency reuse. Similarly for the foreground communications P/Ls, various UAVs provide different groups of beams operated at same frequency slots supporting independent data streams. The relative positions among arrays on different UAVs become less important. Radiated RF powers associated with many of these independent data streams among various UAVs are not combined. Information or data streams may be combined for high data rate users via channel bonding. 
         [0169]    In a second operational scenario of both forward and return links of mobile communications via multiple closely space M 1  UAVs  520 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via beam-forming among distributed subarrays; each of which is on a separated UAV. Ku/Ka channels in the feeder links  550  shall be designed with adequate instantaneous bandwidths to support all UAVs concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility providing orthogonal beams connecting to all UAV concurrently facilitating frequency reuse. The spacing among the M 1  UAVs  520 - 1  shall vary slowly. As a result, the relative geometries among elements in this distributed and slow-varying array are very important in maintaining coherency among subarrays. The slow varying array geometries must be continuously calibrated and then properly compensated for both forward links and return links as a part of GBBF functions  412 . This operation scenario will allow coherently added stronger radiated signals from multiple M 1  UAVs  520 - 1  to “punch through” debris or man-made structures reaching users with disadvantage terminals or at disadvantaged locations. 
         [0170]    However, this group of operational scenarios which exhibit coherent combining via Tx DBF in GBBF among multiple moving UAV platforms  620 - 1  is very difficult and thus less cost-effective to implement due to dynamic path length calibration and compensations among paths via different UAVs. 
         [0171]    We will introduce wave-front multiplexing/demultiplexing (WF muxing/demuxing) techniques for path length calibrations and compensations in Embodiment 10. 
         [0172]      FIG. 7  depicts a scenario with 4 small UAVs  620 - 1  performing a communication relay mission via GBBF for residents in L/S bands over an emergency coverage  130 . The four small UAVs  620 - 1   a,    620 - 1   b,    620 - 1   c  and  620 - 1   d  identified as M 1   a,  M 1   b,  M 1   c  and M 1   d  are distributed in a fly formation with large distances among them (say, &gt;1 Km). WF muxing and demuxing techniques are utilized in this configuration to perform coherent power combining of radiated signals by the four small UAVs in advanced receivers. The ground hub  710  comprises 4 separated feeder-link tracking antennas  411  at KU/Ka bands, continuously tracking 4 different UAVs  620 - 1   a,    620 - 1   b,    620 - 1   c,  and  620 - 1   d.  These four separated antennas  411  could be replaced by one multi-beam antenna with large instantaneous FOV to track 4 airborne platforms continuously 
         [0173]    The foreground links  420  of each of the 4 UAVs feature multiple spot beams  1301 ,  1302 , and  1303  in L/S band servicing a coverage  130  with &lt;100 Km in diameter. A ground user  633  may use an advanced user device communicating to other users in or outside the same coverage area  130 . The advanced user device  633  features multiple tracking beams at concurrently and independently following all 4 small UAVs  620 - 1 . The multiple-beams of an advanced user terminal operate at same frequency slots among the links between each of the four UAVs  620 - 1  and the ground user  633 . The coverage  130  area may vary depending on requirements on missions. 
         [0174]    Onboard each of the 4 small UAV  620 - 1 , the processing from feeder-link to foreground links are identical. Taking that of the Mla UAV  120 - 1  shown in  FIG. 3  as an example, the up-linked signals received by the feeder antenna  236  and I/O duplexer  233  are conditioned by Ku/Ka band LNA  234 . The Ku/Ka band demuxing devices  232  separates “element” signals by dividing the conditioned signals to various element ports before translating them from proper frequency slots in Ku/Ka band into a common frequency slot in L/S band by the frequency converters  220 . These input beam signals are power amplified by individual power amplifiers  215  in the foreground P/L before radiated by the foreground-link array elements  217 . 
         [0175]    We have assumed the muxing device  231  perform frequency division multiplexing (FDM) and consistent with an associated device on ground performing demuxing of FDM. However, muxing/demuxing device  231 / 232  may perform other muxing/demuxing schemes such as time division muxing (TDM), code division muxing CDM, or combinations of TDM, CDM and/or FDM. 
         [0176]      FIG. 7A  depicts a more detailed flow diagram for a forward link transmissions with WF muxing  714  co-located with a GBBF  412  ground facility and WF demuxing  724  in an advanced user terminal  633 . 
         [0177]    We follow the following notations:
       (1) for a WF muxing device
           a. Input ports are referred as “slices”:
               First input port of the WF muxer is referred to as “slice  1 ”;   
               b. Outputs are called “wave-front components” or “wfcs”:
               First output port of the WF muxer is referred to as “wfc 1”.   
               
           (2) Similarly, for a WF demuxing device
           a. Output ports are referred as “slices”:
               First output port of the WF demuxer is referred to as “slice  1 ”;   
               b. Inputs are called “wave-front components” or “wfcs”:
               First input port of the WF demuxer is referred to as “wfc 1”.   
               
               
 
         [0188]    In the forward link depicted in  FIG. 7A  from a ground hub  710  to a user  633  through 4 UAVs  620 - 1 , WF muxing are utilized to transform a first user input, S 1 , and a probing/diagnostic signal, p 1 , by a 4-to-4 WF muxer  712  into 4 WF domain signals. S 1  connected to slice  1  is designated to be sent to the user terminal  633  in the beam position  1302 . Two other signals connected to slice  2  and slice  3  respectively, S 2  and S 3 , are concurrently transmitted through the same 4 UAVs via WF muxing processing. They are intended for other users in the same spot beam  1302 . The diagnostic stream, p 1 , is connected to slice  4 . 
         [0189]    A WF muxing device may be implemented in many ways including a FFT, a Hadamard matrix in digital formats, or combinations of FFT and Hadamard matrixes. It may also be constructed by a Butler Matrix (BM) in analogue passive circuitry. In  FIG. 7 a   , the 4-to-4 WF muxer  712  in the WF muxing/demuxing process facility  714  feature 3 user signal inputs connected to 3 input slices (S 1 , S 2 , and S 3 ), and a stream of pilot codes, ps, to the 4 th  input slice.
       1. The outputs of the WF muxer  712  are various summations of 4 weighted inputs; s 1 , s 2 , s 3 , and ps. Specifically , y 1 , y 2 , y 3 , and y 4  are respectively formulated as:       
 
         [0000]        y 1( t )= w 11* s 1( t )+ w 12* s 2( t )+ w 13* s 3( t )+ w 14* ps ( t )   (1.1)
 
         [0000]        y 2( t )= w 21* s 1( t )+ w 22* s 2( t )+ w 23* s 3( t )+ w 24* ps ( t )   (1.2)
 
         [0000]        y 3( t )= w 31* s 1( t )+ w 32* s 2( t )+ w 33* s 3( t )+ w 34* ps ( t )   (1.3)
 
         [0000]        y 4( t )= w 41* s 1( t )+ w 42* s 2( t )+ w 43* s 3( t )+ w 44* ps ( t )   (1.4)
           where, s 1 (t)=S 1 , s 2 (t)=S 2 , s 3 (t)=S 3 , and s 4 (t)=S 4 .       2. A wavefront vector (WFV) featuring 4 WF components (wfc) is defined as a column matrix. There are four such vectors (column matrixes) which are mutually orthogonal:       
 
         [0000]        WFV 1= WF 1=Transport of [ w 11,  w 21,  w 31,  w 41]   (2.1)
 
         [0000]        WFV 2= WF 2=Transport of [ w 12,  w 22,  w 32,  w 42]   (2.2)
 
         [0000]        WFV 3= WF 3=Transport of [ w 13,  w 23,  w 33,  w 43]   (2.3)
 
         [0000]        WFV 4= WF 4=Transport of [ w 14,  w 24,  w 34,  w 44]   (2.4)
       3. WFX*WFY=1 if X=Y, otherwise WFX*WFY=0; where X and Y are integers from 1 to 4.   4. s 1 (t), s 2 (t), s 3 (t), and ps(t) are, respectively, “attached” to one of the 4 WF vectors by connecting to a corresponding input port of the WF muxing device  714 .
           (1) The outputs y 1 (t), y 2 (t), y 3 (t), and y 4 (t) are linear combinations of wavefront components (wfcs); the aggregated data streams. The signal stream y 1  is the output from the output port wfc- 1 , y 2  from wfc- 2 , and so on.   (2) The S 1  signal is replicated and appears in all 4 wfc output ports. Actually, S 1  is “riding on the WF vector WF 1 . So are the S 2 , S 3 , and ps signals.   (3) The 4 outputs, y 1 , y 2 , y 3 , and y 4  are connected to inputs of 4 separated transmit (Tx) digital beam forming (DBF) processors  751 , converting them as parts of 4 sets of element signals for arrays on various UAVs. Assuming Ne array elements for the L/S band foreground communications on each UAV  620 - 1 , a Tx DBF processor  751  shall features Ne element outputs   (4) Each of the four FDM muxers  752  performs multiplexing on Ne corresponding element signals into a single signal stream, which is frequency up converted and power amplified by a set of RF front end  753  before up-loaded by one of the 4 separated high gain antennas  411  to a designated UAVs  620 - 1 .   (5) GBBF  412  features 4 sets of multibeam DBF processors  751 ; each is designated to “service” Ne elements of the array for foreground communications in L/S band. The4 separated arrays on 4 UAVs for foreground communications will concurrently form L/S band beams pointed to the same beam position  1302 . As a result, y 1  is delivered to the user terminal  633  via the first UAV  620 - 1   a,  y 2  via the second UAV  620 - 1   b,  y 3  by the third UAV  620 - 1   c,  and y 4  through the 4 th  UAV  620 - 1   d.      (6) From the point of view of a first user who “owns” the S 1  signal stream, the S 1  signal stream is relayed to the designated user terminal  633  concurrently by 4 separated UAVs  620 - 1  through a common frequency slot f 1 .   (7) From the point of view of a second user who “owns” the S 2  signal stream, S 2  signal is relayed to the second user concurrently by the 4 separated UAVs  620 - 1  through a common frequency slot f 1 . The second user is collocated in the same beam position  1302  as that of the first user with the terminal  633 .   (8) From the point of view of a third user who “owns” the S 3  signal stream, S 3  signal is relayed to the third user concurrently by the 4 separated UAVs  620 - 1  through a common frequency slot f 1 . The third user is also collocated in the same beam position  1302  as that of the first user with the terminal  633 .   
               
 
         [0203]    These WF domain signals are inputs to four parallel DBF processors  751  in a GBBF facility  710 . On the other hand, a multi-beam user receiver  633  features a WF demuxer which will equalize propagation paths enabling the forward link signals which pass through 4 parallel bent-pipe paths including associated electronics with unbalanced phases and amplitude differentials in the uploading ground segment, airborne segment, and ground receiving segment. The four parallel signal paths comprise of propagation segments of (1)  450   a + 420   a,  (2)  450   b + 420   b,  (3)  450   c + 420   c,  and (4)  450   d + 420   d.  The “bent-pipe functions” are performed by the four UAVs M 1   a    620 - 1   a,  M 1   b    620 - 1   b,  M 1   c    620 - 1   c,  and M 1   d    620 - 1   d.    
         [0204]    Each bent-pipe* functions associated with each UAV  620 - 1  consist of:
       1. receiving array element signals originated from ground processing facility  710  via feeder-link  450 ,   2. amplifying and filtering received element signals, or conditioning received element signals,   3. frequency-translating, or transponding the conditioned element signals,   4. power-amplifying before re-radiating the transponded element signals by designated array elements toward ground.       
 
         [0209]    The descriptions of “bent-pipe” are to present repeater or transponder functions for signals going through without any regeneration process. These signals may be amplified, filtered, and/or frequency translated. A regeneration process shall include a function of demodulation, and another function of re-modulation. 
         [0210]    At a destination, there are 3 functional blocks in the advanced terminal  633 ;
   1. Signals transponded by the four UAVs  620 - 1  are captured and amplified by a multibeam receiving (Rx) array  745 . The Rx array comprises of M array elements  722 , each followed by a LNA and frequency down converter  721  for conditioning received signals.   2. The M parallel conditioned received signals are sent to a multibeam beam forming network (BFN)  723  which forms multiple tracking beams following the dynamics of the relaying UAVs  620 - 1 . The outputs of the multi-beam BFN  723  are 4 received data streams, y 1 ′, y 2 ′, y 3 ′, and y 4 ′, which are mainly the corresponding signals of y 1 , y 2 , y 2 , and y 4  contaminated by additional noises and external interferences.   3. A WF demux processing  724  consists of a bank of adaptive equalizers  741  and a 4-to-4 WF demuxer  742  to reconstitute the  3  slices of signal streams and a stream of pilot codes;
       (1) The inputs y 1 ′, y 2 ′, y 3 ′, and y 4 ′ are connected to 4 adaptive finite-impulse-response (FIR) filters  741  for time, phase, and amplitude equalizations among the 4 propagation paths;   (2) Individual adaptive filters  741  compensate for phase differentials caused by “dispersions” among the propagation paths (array elements) via a UAV. There will be significant improvement on waveform shape distortions due to dispersions; minimizing a source for inter-symbol interferences.   (3) Differences among 4 FIR filters  741  are optimized as a group to compensate for time and phase differentials among propagating paths via 4 different UAVs  620 - 1     (4) weightings of the FIR filters  741  are optimized by an iterative control loop based on comparisons  744  of recovered pilot signals S 4  against the injected and known diagnostic signals and an efficient optimization algorithm in an optimization processing  743 .   (5) the filtered outputs from the adaptive FIR filters are connected to the WF demuxer.   (6) Among the outputs of the WF demuxer are the  3  slices of desired signal streams, and a pilot signal.
           i. The WF muxer for the first user is customized to receive signals from the first slice, or the 1 st  output port.   ii. Similarly, the WF muxer for the second user and the third user are, respectively, customized to receive signals from the second slice (the 2 nd  output port) or signals from the third slice (the 3 rd  output port).   
           (7) The optimization loop utilizing cost minimization criteria in the optimization processing 743 comprises:
           i. Identifying proper observables for the optimization loop including:
               differences between the recovered pilot signal stream and the original;   correlations of signals from output slices of the WF demuxer  742 .   
               ii. Generating different cost functions based on various observables
               Converting or mapping various observables into different measurables or cost functions which must be positively defined.
                   When an observable meets the desired performance, the corresponding measurable or cost function becomes zero.   When an observable is only slightly away from the desired performance, the corresponding measurable or cost function is assigned with a small positive number.   When an observable is far away from the desired performance, the corresponding measurable or cost function is assigned with a large positive number.   
                   
               iii. Summing all cost function for a total cost as a numerical indicator the current status of the optimization loop performances,
               When total cost is less than a small positive threshold value, stop the optimization loop;   otherwise proceed to procedure  4     
               iv. Deriving the gradients of total cost with respect to the weights of the adaptive equalizers which are in the forms of FIR filters.   v. Calculating new weights of the FIR filters based on a steepest descent algorithm to minimize the total cost of the optimization loop iteratively.   vi. Updating the weightings in the adaptive equalizer and go to procedure “ 2 .”   
           
       
 
         [0237]    The pilot codes “ps” is connected to a dedicated input port S 4 , the 4 th  input slice, of the WF mux  712  in  FIG. 7A . It is for illustrations only. The number of inputs may be different than 4, may be more. 
         [0238]    In addition, pilot codes may not need dedicated ports for diagnostic. In other embodiments, the pilot codes “ps” use a portion of 4 th  input port S 4 , the 4 th  input slice, of the WF mux  712  in  FIG. 7A  through TDM, CDM, and/or FDM techniques. The WF demux  742  in the receive chain  724  must accommodate the time, code, and/or frequency demuxing functions in recovering received pilot codes accordingly. 
         [0239]    In another embodiment with time frame by time frame operations, diagnostic signals may feature N independent pilot codes concurrently for the N inputs of the WF mux  712  for a short time slot periodically as a diagnostic time slot, where 4≧N≧1. Majority of the time slots in a frame are dedicated for data transmission only. The WF demux 742 in the receive chain  724  must accommodate the time demuxing functions for the N channels in recovering N independent pilot codes accordingly. The associated optimization may use cross correlations as cost functions among the N- outputs from the WF demux  742  during the diagnostic time slots. 
         [0240]      FIG. 7B  depicts a more detailed flow diagram for a return link transmissions with WF muxing  764  in an advanced user terminal  633  and a corresponding WF demuxing  742  in the WF mux/demux processing facility  714  collocated with a GBBF  412  ground facility. 
         [0241]    For a user in a transmission mode, there are 3 functional blocks in the advanced terminal  633 ;
       1. A WF mux processing featuring a 4-to-4 WF demuxer  764  to transform a stream of modulated signal, S 1 , in slice- 1  originated from a transmitter  765 , along with a diagnostic stream in slice- 4 . Slice- 2  and slice- 3  are unconnected or grounded.
           a. Other nearby users may use slice- 2  and/or slice- 3  of other identical WF muxers on individual user terminals for delivering various data streams, S 2  and S 3 , to the same ground hub via the same 4 UAVs  620 - 1   a,    620 - 1   b,    620 - 1   d,  and  620 - 1   d  over the same frequent slots f 1 .,   b. Each user signal stream is riding on a unique WF vector. They would be mutually orthogonal to one other at the outputs of the WF muxers, if they were generated by a WF muxer. But they are generated by three identical WF muxers. In three different user terminals similar to  633 .   
           2. The 4 parallel outputs y 1 , y 2 , y 3 , and y 4  from the WF muxer  764  are sent to a multibeam beam forming network (BFN)  723  which forms multiple tracking beams following the dynamics of the relaying UAVs  620 - 1 . The signal stream y 1  is from the output port wfc- 1 , y 2  from the output port wfc- 2 , y 3  from the output port wfc- 3 , and y 4  from the output port wfc- 4 wfc.   3. The outputs of the multi-beam transmit BFN  763  are conditioned, frequency up-converted and power amplified by a bank of frequency up-converters and power amplifiers  762 , before radiated by array elements  722 . The 4 Tx beam signals are mainly the corresponding signals of y 1  targeted for the UAV  620 - 1   a,  y 2  targeted for the UAV  620 - 1   b,  y 3  targeted for the UAV  620 - 1   c,  and y 4  targeted for the UAV  620 - 1   d.          
 
         [0247]    Up linked L/S band signals in the foreground are captured and amplified by M receiving (Rx) array elements. The M received element signals on each of the four UAVs  620 - 1  are transponded and FDM muxed individually. The FDM muxed element signals are relayed back to the GBBF; Those element signals from the UAV M 1   a    620 - 1   a  are via a first down link  450   a  of the Ku/Ka feeder-links  450 . Those element signals from the UAV M 1   b    620 - 1   b  are via a second down link  450   b  of the Ku/Ka feeder-links  450 . Those element signals from the UAV M 1   c    620 - 1   c  and the UAV M 1   d    620 - 1   de  are, respectively via a third down link  450   c  and a 4 th  downlink  450   d  of the Ku/Ka feeder-links  450 . 
         [0248]    These down linked element signals captured by four directional antennas  411  in the mobile hub  710 , are conditioned by RF frontend units  783 , frequency down converted and FDM demuxed to M outputs at a baseband frequency by FDM demuxers  782 , before being sent to multibeam Rx DBFs  781 . One of the output ports of each of the 4 Rx DBF shall be assigned to the Tx beams with a common beam position  1302  where the user terminal  633  is located. The outputs from the beams of the 4 Rx DBF  781  aiming at the beam position  1302  are designated as y 1 ″, y 2 ″, y 3 ″, and y 4 ″. They are the 4 inputs to the receiving processing of the WF muxing/demuxing processing facility  714 . The receiving processing comprises mainly the equalization functions by a bank of 4 adaptive FIR filters  741 , and a WF demuxing transformation by a 4-to-4 WF demuxer  742 . 
         [0249]    After fully optimized via iterative equalizations, the optimized outputs from the first output port slice- 1  will be the recovered signals S 1  originated from the user terminal  633  in the foreground beam position  1302 . The recovered S 1  has been riding on the WF 1 . Similarly, the optimized outputs from the second output port slice- 2  will be the recovered signals S 2  originated from the second user terminal similar to terminal  633  in the foreground beam position  1302 . The recovered S 2  has been riding on the WF 2 . 
         [0250]    A receiving processing in the WF muxing/demuxing unit  714  consists of a bank of adaptive equalizers  741  and a 4-to-4 WF demuxer  742  to reconstitute the 3 slices of signal streams and a stream of pilot codes;
       (1) The inputs y 1 ′, y 2 ′, y 3 ′, and y 4 ′ are connected to 4 adaptive finite-impulse-response (FIR) filters for time, phase, and amplitude equalizations among the 4 propagation paths;   (2) Individual adaptive filters compensate for phase differentials caused by “dispersions” among the propagation paths (array elements) in feeder links via a UAV. There will be significant improvement on waveform shape distortions due to dispersions; minimizing a source for inter-symbol interferences.   (3) Differences among 4 FIR filters  741  are optimized as a group to compensate for time and phase differentials among propagating paths via 4 different UAVs  620 - 1     (4) weightings of the FIR filters  741  are optimized by an iterative control loop based on comparisons  744  of recovered pilot signals S 4  against the injected and known diagnostic signals ps and an efficient optimization algorithm in an optimization processing  743 .   (5) the filtered outputs from the adaptive FIR filters  741  are connected to the 4 wfc input ports of the WF demuxer  742 .   (6) Among the outputs of the WF demuxer  742  are the 3 slices of desired signal streams, and a pilot signal.
           a. The WF muxer for the first user is customized to receive signals from the first slice, or the 1 st  output port.   b. Similarly, the WF muxer for the second user and the third user are, respectively, customized to receive signals from the second slice (the 2 nd  output port) or signals from the third slice (the 3 rd  output port).   
           (7) The optimization loop utilizing cost minimization criteria in the optimization processing  743  comprises:
           a. Identifying proper observables for the optimization loop including:
               differences between the recovered pilot signal stream and the original.   Correlations of signals from output slices of the WF demuxer  742     
               b. Generating different cost functions based on various observables
               Converting or mapping various observables into different measurables or cost functions which must be positively defined.
                   a. When an observable meets the desired performance, the corresponding measurable or cost function becomes zero.   b. When an observable is only slightly away from the desired performance, the corresponding measurable or cost function is assigned with a small positive number.   c. When an observable is far away from the desired performance, the corresponding measurable or cost function is assigned with a large positive number.   
                   
               c. Summing all cost function for a total cost as a numerical indicator the current status of the optimization loop performances,
               When total cost is less than a small positive threshold value, stop the optimization loop;   otherwise proceed to procedure d   
               d. Deriving the gradients of total cost with respect to the weights of the adaptive equalizers which are in the forms of FIR filters.   e. Calculating new weights of the FIR filters based on a steepest descent algorithm to minimize the total cost of the optimization loop iteratively.   f. Updating the weightings in the adaptive equalizer and go to procedure b.   
               
 
         [0274]    Next example presents architectures and methods of implementing forward link of mobile communications in a disaster area via largely spaced multiple small UAVs featuring GBBF or RBFN, and WF muxing/demuxing for coherent power combining in receivers 
         [0275]    We shall use the term “M 1  UAVs  620 - 1 ” to represent all 4 small UAVs; the M 1   a  UAV  620 - 1   a,  the M 1   b  UAV  620 - 1   b,  the M 1   c  UAV 620-1 c,  and the M 1   d  UAV  620 - 1   d  in  FIG. 7 . 
         [0276]      FIG. 7  depicts an embodiment via multiple M 1  UAVs  620 - 1  for communications mainly to rescue worker community in a coverage area  130 . 
         [0277]    The ground facility  710  features:
       1. multiple beam antennas  411  to connected to various UAV platforms  620 - 1  concurrently via different Ku/Ka band feeder-links  450 ,
           a. link  450   a  between the ground facility  710  and M 1   a  UAV  620 - 1   a;      b. link  450   b  between the ground facility  710  and M 1   b  UAV  620 - 1   b;      c. link  450   c  between the ground facility  710  and M 1   c  UAV  620 - 1   c;      d. link  450   d  between the ground facility  710  and M 1   d  UAV  620 - 1   d;      
           2. GBBF for both forward link (transmitting) beams and return link (receiving) beams;   3. mobile hubs  413  as gateways to terrestrial networks  480  or other UAV based networks.       
 
         [0285]    The M 1   a,  M 1   b,  M 1   c,  and M 1   d  UAVs  620 - 1  along with their GBBF processing feature multiple beams  1301 ,  1302 ,  1303 , and others in both forward and return links in a reserved public safety frequency band; eg. 4.9 GHz or 700 MHz in US. 
         [0286]    The users (rescue worker community) in the coverage areas shall feature multiple tracking-beam terminals  633 . Each of the advanced user terminals exhibits capability of tracking the 4 M 1  UAVs  620 - 1  with four separated beams operating at the same frequency slots in a reserved public safety band concurrently. For a user  633  with a multi-beam terminal there are 4 concurrent links; 
         [0287]    1. link  420   a  between the multi-beam user  633  and M 1   a  UAV  620 - 1   a;    
         [0288]    2. link  420   b  between the multi-beam user  633  and M 1   b  UAV  620 - 1   b;    
         [0289]    3. link  420   c  between the multi-beam user  633  and M 1   c  UAV  620 - 1   c;  and 
         [0290]    4. link  420   d  between the multi-beam user  633  and M 1   d  UAV  620 - 1   d;    
         [0291]    Good isolations among multiple UAVs  620 - 1  operating at same frequency bandwidths, codes and time slots are achieved via spatial isolations from the advanced user terminals. As a result, same spectrum is used 4 times more than the scenarios presented in  FIG. 5 . 
         [0292]    WF muxing/demuxing  712 / 742  is utilized for calibrations and compensations on unbalanced delays and attenuations among four propagation paths and associated electronics. The four paths are:
       1.  450 - 1   a + 620 - 1   a;      2.  450 - 1   b + 620 - 1   b;      3.  450 - 1   c + 620 - 1   c;  and   4.  450 - 1   d + 620 - 1   d;          
 
         [0297]    In forward links of mobile communications via multiple largely space M 1  UAVs  620 - 1  with ground based beam forming (GBBF)  412  or remote beam forming network (RBFN) via beam-forming  751  among distributed subarrays; each of which is on a separated UAV. Ku/Ka channels in the feeder links  450  shall be designed with adequate instantaneous bandwidths to support all 4 M 1  UAVs  620 - 1  concurrently. These techniques may include advance multi-beam antennas for the feeder-links in ground facility providing orthogonal beams connecting to all UAV concurrently facilitating frequency reuse. The spacing among the M 1  UAVs  520 - 1  shall vary slowly. As a result, the relative geometries among elements in this distributed and slow-varying array are very important in maintaining coherency among subarrays. The slow varying array geometries must be continuously calibrated and then properly compensated for forward links. 
         [0298]    This operation scenario will allow coherently added stronger radiated signals from multiple M 1  UAVs  520 - 1  to “punch through” debris or man-made structures reaching users with disadvantage terminals or at disadvantaged locations. 
         [0299]    It is the WF muxing/demuxing with adaptive equalization process which dynamically compensates for the differentials of amplitudes and phases among the 4 separated propagation paths via 4 individual UAVs based on “recovered” probing signals on WF demuxer, enabling the capability of continuously maintaining “coherency” among signals passing through four independent UAVs. 
         [0300]    Next example presents architectures and methods of implementing return link of mobile communications in a disaster area via largely spaced multiple small UAVs featuring GBBF or RBFN, and WF muxing/demuxing for coherent power combining in receivers 
         [0301]    For a user in a transmission mode, there are 3 functional blocks in the advanced terminal  633  as depicted in  FIG. 7B ;
       1. A WF mux processing featuring a 4-to-4 WF demuxer  764  to transform a stream of modulated signal, S 1 , in slice- 1  originated from a transmitter  765 , along with a diagnostic stream in slice- 4 . Slice- 2  and slice- 3  are unconnected or grounded.   2. The 4 parallel outputs y 1 , y 2 , y 3 , and y 4  from the WF muxer  764  are sent to a multibeam beam forming network (BFN)  763  which forms multiple tracking beams following the dynamics of the relaying UAVs  620 - 1 . The signal stream y 1  is from the output port wfc- 1 , y 2  from the output port wfc- 2 , y 3  from the output port wfc- 3 , and y 4  from the output port wfc- 4 wfc.   3. The outputs of the multi-beam transmit BFN  763  are conditioned, frequency up-converted and power amplified by a bank of frequency up-converters and power amplifiers  762 , before radiated by array elements  722 . The 4 Tx beam signals are mainly the corresponding signals of y 1  targeted for the UAV  620 - 1   a,  y 2  targeted for the UAV  620 - 1   b,  y 3  targeted for the UAV  620 - 1   c,  and y 4  targeted for the UAV  620 - 1   d.          
 
         [0305]    Up linked L/S band signals in the foreground are captured and amplified by M receiving (Rx) array elements on the UAVs  620 - 1 . The M received element signals on each of the four M 1  UAVs  620 - 1  are conditioned, transponded and FDM muxed individually. The FDM muxed element signals are relayed back to the GBBF  412 . Those element signals from the UAV M 1   a    620 - 1   a  are via a first down link  450   a  of the Ku/Ka feeder-links  450 . Those element signals from the UAV M 1   b    620 - 1   b  are via a second down link  450   b  of the Ku/Ka feeder-links  450 . Those element signals from the UAV M 1   c    620 - 1   c  and the UAV M 1   d    620 - 1   d  are, respectively via a third down link  450   c  and a 4 th  downlink  450   d  of the Ku/Ka feeder-links  450 . 
         [0306]    These down linked element signals captured by four directional antennas  411  in the mobile hub  710 , are conditioned by RF frontend units  783 , frequency down converted and FDM demuxed to M outputs at a baseband frequency by FDM demuxers  782 , before being sent to multibeam Rx DBFs  781 . One of the output ports of each of the 4 Rx DBF shall be assigned to the Tx beams with a common beam position  1302  where the user terminal  633  is located. The outputs from the beams of the 4 Rx DBF  781  aiming at the beam position  1302  are designated as y 1 ″, y 2 ″, y 3 ″, and y 4 ″. They are the 4 inputs to the receiving processing of the WF muxing/demuxing processing facility  714 . The receiving processing comprises mainly the equalization functions by a bank of 4 adaptive FIR filters  741 , and a WF demuxing transformation by a 4-to-4 WF demuxer  742 . 
         [0307]    After fully optimized via iterative equalizations, the optimized outputs from the first output port slice- 1  will be the recovered signals S 1  originated from the user terminal  633  in the foreground beam position  1302 . The recovered S 1  has been riding on the WF 1 . Similarly, the optimized outputs from the second output port slice- 2  will be the recovered signals S 2  originated from the second user terminal similar to terminal  633  in the foreground beam position  1302 . The recovered S 2  has been riding on the WF 2 . 
         [0308]    The pilot codes “ps” is connected to a dedicated input port S 4 , the 4 th  input slice, of the WF mux  764  in  FIG. 7B . It is for illustrations only. The number of inputs may be different than 4, and pilot codes may not need dedicated ports for diagnostic. 
         [0309]    In other embodiments, the pilot codes “ps” using a portion of 4 th  input port or input slice through TDM, CDM, and/or FDM techniques. The WF demux  742  in the receive chain  714  must accommodate the time, code, and/or frequency demuxing functions in recovering received pilot codes accordingly. 
         [0310]    In another embodiment with time frame by time frame operations, diagnostic signals may feature N independent pilot codes concurrently for the N inputs of the WF mux  764  for a short time slot periodically as a diagnostic time slot, where 4≧N≧1. Majority of the time slots in a frame are dedicated for data transmission only. The WF demux  742  in the receive chain  714  must accommodate the time demuxing functions for the N channels in recovering N independent pilot codes accordingly. The associated optimization may use cross correlations as cost functions among the N- outputs from the WF demux  742  during the diagnostic time slots. 
       Embodiment 1 
       [0311]    This embodiment presents architectures and methods of implementing mobile communications in a disaster area via largely spaced multiple UAVs featuring GBBF or RBFN, and WF muxing/demuxing for transmission redundancy and data security, not for coherent power combining in receivers. It uses WF muxing transformation on signals, not on waveforms, as preprocessing enabling multi-channel propagations of various waveforms on sums of the same multiple signals with different sets of weighting coefficient. The modulators are placed after WF muxing in the transmission site. 
         [0312]    On a multi-channel receiver, received WFM waveforms are demodulated, converting them to WFM signals, which are used to reconstruct original signals via a non-coherent combining performed by a corresponding WF demuxing transformation. 
         [0313]    Similar configurations taking advantages of WF muxing/demuxing for non-coherent combining are applicable to communications via multiple satellites, air platforms including UAVs, terrestrial mobile communications, Passive Optical Network (PON) via optical fibers, and/or Internet IP connectivity for transmission redundancy and better data security. The dynamic transmission features built-in redundancy and data privacy. It is always important. For video streaming via multiple mirror sites in IP Internet network, this is a very powerful tool to gain speed on delivery of video packages. 
         [0314]      FIG. 8 a    and  FIG. 8 b    depict functional flow diagrams for a forward link and return link transmissions, respectively, with WF muxing/demuxing techniques not for “coherent power combining” but for data transmission security and redundancy. The techniques concurrently provide redundancy and camouflage on segment data streams. The transmitted data streams in the forms of WF muxed segments can be designed, as an example, with a 4-for-3 redundancy to enable capability at destinations of recovering original data streams with any 3 of the 4 WF muxed segments. Each WF muxed segment is delivered independently via one of the 4 UAVs  620 - 1 . 
         [0315]    In the forward link depicted in  FIG. 8A  from a ground hub  710  to a user  633  through 4 UAVs  620 - 1 , WF muxing are utilized to transform 3 segmented data streams X 1 , X 2 , and X 3  from a first user input, X, by a 4-to-4 WF muxer  814  into 4 WF domain signals; y 1 , y 2 , y 3 , and y 4 . The segmented streams are generated by a TDM demuxer  812 . The input X of the TDM demuxer  812  is flowing at N samples per second, and its three segmented outputs X 1 , X 2 , and X 3  are flowing at N/3 samples per second. X 1  connected to slice  1  is designated to be sent to the user terminal  633  in the beam position  1302 . Two other signals connected to slice  2  and slice  3  respectively, X 2  and X 3 , are transmitted through the same 4 UAVs via WF muxing processing. 
         [0316]    A WF muxing device may be implemented in many ways including a FFT, a Hadamard matrix in digital formats, or combinations of FFT and Hadamard matrixes. It may also be constructed by a Butler Matrix (BM) in analogue passive circuitry. In  FIG. 8 a   , the 4-to-4 WF muxer  814  features a 4-to-4 Hadamard matrix. 3 segmented user signals(X 1 , X 2 , and X 3 ) are connected to the first 3 input slices, and a “zero” signals stream (grounding) is connected to the 4 th  input slice; 
         [0317]    The outputs of the WF muxer  814  are various summations of 4 weighted inputs; X 1 , X 2 , X 3 , and “zero signals”. Specifically, y 1 , y 2 , y 3 , and y 4  are respectively formulated as: 
         [0000]        y 1( t )= w 11* x 1( t )+ w 12* x 2( t )+ w 13* x 3( t )+ w 14*0   (3.1)
 
         [0000]        y 2( t )= w 21* x 1( t )+ w 22* x 2( t )+ w 23* x 3( t )+ w 24*0   (3.2)
 
         [0000]        y 3( t )= w 31* x 1( t )+ w 32* x 2( t )+ w 33* x 3( t )+ w 34*0   (3.3)
 
         [0000]        y 4( t )= w 41* x 1( t )+ w 42* x 2( t )+ w 43* x 3( t )+ w 44*0   (3.4)
 
         [0000]      where,       x 1 (t)=X 1 , x 2 (t)=X 2 , and x 3 (t)=X 3 ,         
         [0319]    and elements in the 4-to-4 Hadamard matrix are arranged in 4 row vectors: 
         [0000]      [ w 11,  w 12,  w 13,  w 14]=[1, 1, 1, 1]  (3.5)
 
         [0000]      [ w 21,  w 22,  w 23,  w 24]=[1, −1, 1, −1]  (3.6)
 
         [0000]      [ w 31,  w 32,  w 33,  w 34]=[1, 1, −1, −1]  (3.7)
 
         [0000]      [ w 41,  w 42,  w 43,  w 44]=[1, −1, −1, 1]  (3.8)
 
         [0320]    A wavefront vector (WFV) featuring 4 WF components (wfc) is defined as a column matrix of the 4-to-4 Hadamard matrix. There are four such vectors (column matrixes) which are mutually orthogonal: 
         [0000]        WFV 1= WF 1=Transport of [1, 1, 1, 1]  (4.1)
 
         [0000]        WFV 2= WF 2=Transport of [1, −1, 1, −1]  (4.2)
 
         [0000]        WFV 3= WF 3=Transport of [1, 1, −1, −1]  (4.3)
 
         [0000]        WFV 4= WF 4=Transport of [1, −1, −1, 1]  (4.4)
 
         [0000]    WFX*WFY=1 if X=Y, otherwise WFX*WFY=0; where X and Y are integers from 1 to 4. 
         [0321]    x 1 (t), x 2 (t), x 3 (t), and “zero signals are, respectively, “attached” to one of the 4 WF vectors by connecting to a corresponding input port of the WF muxing device  814 . 
         [0322]    The outputs y 1 (t), y 2 (t), y 3 (t), and y 4 (t) are linear combinations of wavefront components (wfcs); the aggregated data streams. The signal stream y 1  is the output from the output port wfc- 1 , y 2  from wfc- 2 , and so on. 
         [0323]    The X 1  signal is replicated and appears in all 4 wfc output ports. Actually, X 1  is “riding on the WF vector WF 1 . So are the X 2 , X 3 , and “zero” signals. 
         [0324]    The 4 outputs, y 1 , y 2 , y 3 , and y 4  are connected to 4 separated modulators  816  converting data inputs into transmission waveforms. There are 4 sets of WFM waveforms at the outputs of the four modulators  816  representing 4 segmented data streams; y 1 , y 2 , y 3 , and y 4 , in the WF muxed format. The data streams; y 1 , y 2 , y 3 , and y 4 , are referred as WFM signals or WFM data; and the corresponding 4 streams of waveforms are the 4 WFM waveform streams or WFM waveforms. 
         [0325]    The 4 sets of waveforms are delivered to 4 separated transmit (Tx) digital beam forming (DBF) processors  751 , converting them as parts of 4 sets of element signals for arrays on various UAVs. Assuming Ne array elements for the L/S band foreground communications on each UAV  620 - 1 , a Tx DBF processor  751  shall features Ne element outputs. 
         [0326]    Each of the four FDM muxers  752  performs multiplexing on Ne corresponding element signals into a single signal stream, which is frequency up converted and power amplified by a set of RF front end  753  before up-loaded by one of the 4 separated high gain antennas  411  to a designated UAVs  620 - 1 . GBBF  412  features 4 sets of multibeam DBF processors  751 ; each is designated to “service” Ne elements of the array for foreground communications in L/S band. 
         [0327]    The 4 separated arrays on 4 UAVs for foreground communications will concurrently form L/S band beams pointed to the same beam position  1302 . As a result, waveforms representing y 1  is delivered to the user terminal  633  via the first UAV  620 - 1   a,  those for y 2  via the second UAV  620 - 1   b,  those for y 3  by the third UAV  620 - 1   c,  and those for y 4  through the 4 th  UAV  620 - 1   d.    
         [0328]    From the point of view of the X 1  signal stream, the X 1  signal stream is relayed to the designated user terminal  633  concurrently by 4 separated UAVs  620 - 1  through a common frequency slot f 1 . From the point of view of the X 2 , and X 3  signal stream, they are relayed to the same designated user terminal  633  concurrently by the 4 separated UAVs  620 - 1  through a common frequency slot f 1 . 
         [0329]    At a destination, there are 3 functional blocks in the advanced terminal  633 ; (1) a multibeam antenna, (2) advance WF demuxing processor, and (3) a de-segmenting processing. 
       Multi-Beam Receiver 
       [0330]    Signals transponded by the four UAVs  620 - 1  are captured, amplified and demodulated by a multibeam receiving (Rx) array 841 . The Rx array  841  comprises of M array elements  721 , each followed by a LNA and frequency down converter  722  for conditioning received signals. The M parallel conditioned received signals are sent to a multibeam beam forming network (BFN)  723  which forms multiple tracking beams following the dynamics of the 4 relaying UAVs  620 - 1 . The outputs of the multi-beam BFN  723  featuring 4 received waveform sets representing data streams, y 1 ′, y 2 ′, y 3 ′, and y4′ are sent to the 4 demodulators  824  for recovery of the data streams, y 1 ′, y 2 ′, y 3 ′, and y 4 ′ contaminated by additional noises and external interferences. The qualities (SNR, and/or BER) of the recovered data streams are highly dependent on the communications links between the mobile hub  710  and user terminals via four UAVs. 
       Advanced WF Demux 
       [0331]    A WF demux processing  824  features a processing based on the 4-to-4 Hadamard matrix with the 16 parameters depicted in equation (3) WF demuxer  842  to reconstitute the 3 slices of signal streams X 1 , X 2 , and X 3  and a stream of zero signals. Based on equation (3), the demodulated segment streams (WF muxed segments) via the 4-to-4 Hadamard transform  814  shall feature the following; 
         [0000]        y 1′( t )= x 1′( t )+ x 2′( t )+ x 3′( t )+0   (5.1)
 
         [0000]        y 2′( t )= x 1′( t )− x 2′( t )+ x 3′( t )−0   (5.2)
 
         [0000]        y 3′( t )= x 1′( t )+ x 2′( t )− x 3′( t )−0   (5.3)
 
         [0000]        y 4′( t )= x 1′( t )− x 2′( t )− x 3′( t )+0   (5.4)
 
         [0332]    There are three unknown X 1 ′, X 2 ′, X 3 ′ with 4 linear combination equations of known values. There is built-in redundancy; only 3 out of the 4 demodulated WF muxed segments are needed to reconstruct the 3 original segments; X 1 ′, X 2 ′, and X 3 ′. 
         [0333]    To take advantage of redundancy in WF muxing processing  814 , the advanced WF demuxing process  842  may not use conventional Hadamard Matrix. As an example for illustration, let us assume the 3 rd  UAV becomes unavailable. Therefore y 3 ′(t) is absent in the reconstruction process. Based on equations (5.1) and (5.4) 
         [0000]        y 1′( t )+ y 4′( t )=2 *x 1′( t )   (5.5a),
 
         [0000]      therefore, 
         [0000]        x 1′( t )=½( y 1′( t )+ y 4′( t ))   (5.5b)
 
         [0334]    Based on equations (5.1) and (5.2), 
         [0000]        y 1′( t )− y 2′( t )=2* x 2′( t )   (5.6a),
 
         [0000]      therefore, 
         [0000]        x 2′( t )=½( y 1′( t )− y 2′( t ))   (5.6b)
 
         [0335]    Based on equations (5.2) and (5.4), 
         [0000]        y 2′( t )− y 4′( t )=2* x 3′( t )   (5.7a)
 
         [0000]      therefore. 
         [0000]        x 3′( t )=½( y 2′( t )− y 4′( t ))   (5.7b)
 
         [0000]    This ad hoc solution is good for 1 of possible 24 possibilities with 4-for-3 redundancy. 
         [0336]    When all 4 demodulated WF muxed segments from the demodulators  824  are available in a 4-for 3 redundancy configuration, there are 5 different formulations for WF demuxing to reconstruct the 3 segmented data streams X 1 , X 2 , and X 3 . By comparing 5 results from all possible data reduction formulations, similar techniques using advanced WF demux  842  can be used to assessing 4 independent propagation paths, determine if the 4 UAVs  620 - 1  relaying “contaminated” data, and even determine which one is contaminated if only one of the 4 UAVs is compromised. 
       De-Segmenting Processing 
       [0337]    A TDM muxer  843  is used to “de-segment” the three recovered segmented data streams X 1 ′, X 2 ′, and X 3 ′. The re-constructed data stream X′ shall flow at the data rate of N samples per second. 
         [0338]    In this illustration for forward links, a WF mux processing  814  features a processing for creating data security, and redundancy based on segmented data from a signal data streams. The secured segmented data streams are delivered to a destination with multibeam receiving capability. The receiving terminal concurrently captures multiple segments from 4 UAV platforms. It only requires any three out of the 4 segment to faithfully reconstruct the original data streams. 
         [0339]    Conceivably, the 3 segmented streams can be three independent data streams for three targeted users within a common beam position (e.g.  1302  in  FIG. 7 ). However, every user must have capability to recover 3 out of the 4 WF muxed data streams, and their receiver must be customized to only access of designated data only. As indicated in equation (5. 5b), (5.6b), and (5.7b), a user may derive the designated data streams for him or her by manipulating two of three received data streams. 
         [0340]      FIG. 8B  depicts a flow diagram for a return link transmissions with WF muxing  764  in an advanced user terminal  633  and a corresponding WF demuxing  724  collocated with a GBBF  412  ground facility. 
         [0341]    For a user in a transmission mode, there are 3 functional blocks in his or her advanced terminal  633 . A WF mux processing featuring a 4-to-4 WF demuxer  864  to transform 3 segmented data streams, X 1  X 2  and X 3  in its first input ports (slice- 1 , slice- 2  and slice- 3 ) and zero signal stream in slice- 4 . X 1 , X 2 , and X 3  are flowing at a rate of N/3 samples per second, and are originated from a data stream  725  via a TDM demuxer  862 . The input data stream X is flowing at a rate of N samples per second. A 4-to-4 Hadamard matrix is used as the functions for the WF muxing  864 . Formulations of Hadamard Matrix are depicted in Equation 3. They are repeated below 
         [0000]        y 1( t )= w 11* x 1( t )+ w 12* x 2( t )+ w 13* x 3( t )+ w 14*0   (3.1)
 
         [0000]        y 2( t )= w 21* x 1( t )+ w 22* x 2( t )+ w 23* x 3( t )+ w 24*0   (3.2)
 
         [0000]        y 3( t )= w 31* x 1( t )+ w 32* x 2( t )+ w 33* x 3( t )+ w 34*0   (3.3)
 
         [0000]        y 4( t )= w 41* x 1( t )+ w 42* x 2( t )+ w 43* x 3( t )+ w 44*0   (3.4)
 
         [0342]    where
       x 1 (t)=X 1 , x2(t)=X2, and x3(t)=X3.       
 
         [0344]    The signal stream y 1  is from the output port wfc- 1 , y 2  from the output port wfc- 2 , y 3  from the output port wfc- 3 , and y 4  from the output port wfc- 4 wfc. The 4 parallel outputs y 1 , y 2 , y 3 , and y 4  are sent to 4 parallel modulators  866  before connected to a Tx multibeam beam forming network (BFN)  763  which forms multiple tracking beams following the dynamics of the relaying UAVs  620 - 1 . The modulators  866  convert 4 parallel data streams;(y 1 , y 2 , y 3 , and y 4 ) into 4 sets of flowing waveforms representing the4 parallel data streams. 
         [0345]    The outputs of the multi-beam transmit BFN  763  are conditioned, frequency up-converted and power amplified by a bank of frequency up-converters and power amplifiers  762 , before radiated by array elements  722 . The 4 Tx beam signals are mainly the corresponding waveforms representing yl targeted for the UAV  620 - 1   a,  those representing y 2  targeted for the UAV  620 - 1   b,  those representing y 3  targeted for the UAV  620 - 1   c,  and those representing y 4  targeted for the UAV 620 - 1   d.    
         [0346]    Up linked L/S band signals in the foreground are captured and amplified by M receiving (Rx) array elements of each of the 4 UAV  620 - 1 . The M received element signals on each of the four UAVs  620 - 1  are transponded and FDM muxed individually. The FDM muxed element signals are relayed back to the GBBF. Those element signals from the UAV M 1   a    620 - 1   a  are via a first down link  450   a  of the Ku/Ka feeder-links  450 . Those element signals from the UAV M 1   b    620 - 1   b  are via a second down link  450   b  of the Ku/Ka feeder-links  450 . Those element signals from the UAV M 1   c    620 - 1   c  and the UAV M 1   d    620 - 1   de  are, respectively via a third down link  450   c  and a 4 th  downlink  450   d  of the Ku/Ka feeder-links  450 . 
         [0347]    These down linked element signals captured by four directional antennas  411  in the mobile hub  710 , are conditioned by RF frontend units  783 , frequency down converted and FDM demuxed to M outputs at a baseband frequency by FDM demuxers  782 , before being sent to multibeam Rx DBFs  781 . One of the output ports of each of the 4 Rx DBFs  781  shall be assigned to the Rx beams with a common beam position  1302  where the user terminal  633  is located. The outputs from the beams of the 4 Rx DBFs  781  aiming at the beam position  1302  are sent to 4 demodulators  811 . The outputs from the demodulators  811  are designated as y 1 ″, y 2 ″, y 3 ″, and y 4 ″. They are the 4 inputs to the receiving processing of the WF muxing/demuxing processing facility  714 . The receiving processing comprises mainly a WF demuxing transformation by an advanced WF demuxer  812 . 
         [0348]    A WF demux processing  812  features a processing based on the 4-to-4 Hadamard matrix with the 16 parameters depicted in equation (3) WF demuxer  842  to reconstitute the 3 slices of signal streams X 1 ′, X 2 ′, and X 3 ′ and a stream of zero signals. Based on equation (3), the demodulated segment streams (WF muxed segments) via the 4-to-4 Hadamard transform  814  shall feature the following; 
         [0000]        y 1′( t )= x 1′( t )+ x 2′( t )+ x 3′( t )+0   (6.1)
 
         [0000]        y 2′( t )= x 1′( t )− x 2′( t )+ x 3′( t )−0   (6.2)
 
         [0000]        y 3′( t )= x 1′( t )+ x 2′( t )− x 3′( t )−0   (6.3)
 
         [0000]        y 4′( t )= x 1′( t )− x 2′( t )− x 3′( t )+0   (6.4)
 
         [0349]    There are three unknown X 1 ′, X 2 ′, X 3 ′ with 4 linear combination equations of known values. There is built-in redundancy; only 3 out of the 4 demodulated WF muxed segments are needed to reconstruct the 3 original segments; X 1 ′, X 2 ′, and X 3 ′. 
         [0350]    To take advantage of redundancy in WF muxing processing  864 , the advanced WF demux process  812  will not use conventional Hadamard Matrix. As an example for illustration, let us assume the 3 rd  UAV becomes unavailable. Therefore y 3 ′(t) is absent in the reconstruction process. Based on equations (6.1) and (6.4): 
         [0000]        y 1′( t )+ y 4′( t )=2* x 1′( t )   (6.5a),
 
         [0000]      therefore,  x 1′( t )=½( y 1′( t )+ y 4′( t ))   (6.5b)
 
         [0351]    Based on equations (6.1) and (6.2): 
         [0000]        y 1′( t )− y 2′( t )=2* x 2′( t )   (6.6a),
 
         [0000]      therefore,  x 2′( t )=½( y 1′( t )− y 2′( t ))   (6.6b)
 
         [0352]    Based on equations (6.2) and (6.4) 
         [0000]        y 2′( t )− y 4′( t )=2* x 3′( t ) (6.7a)
 
         [0000]      therefore  x 3′( t )=½( y 2′( t )− y 4′( t ))   (6.7b)
 
         [0000]    This ad hoc solution is good for 1 of possible 24 possibilities with 4-for-3 redundancy. 
         [0353]    When all 4 demodulated WF muxed segments from the demodulators  824  are available in a 4-for 3 redundancy configuration, there are 5 different formulations for WF demuxing to reconstruct the 3 segmented data streams X 1 , X 2 , and X 3 . By comparing 5 results from all possible data reduction formulations, similar techniques using advanced WF demux  842  can be used to assessing 4 independent propagation paths, determine if the 4 UAVs  620 - 1  relaying “contaminated” data, and even determine which one is contaminated if only one of the 4 UAVs is compromised. 
         [0354]    A TDM muxer  813  is used to “de-segment” the three recovered segmented data streams X 1 ′, X 2 ′, and X 3 ′. The re-constructed data stream X′ shall flow at the data rate of N samples per second. 
         [0355]      FIG. 8 c    depicts a numerical example via three different processing and delivering methods via 4 separated air platforms, e.g. the 4 UAVs  620 . An original data set featuring 12 numerical numbers, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12], will be “delivered” from a hub H to three user mobile users  1 ,  2 , and  3  via three different methods, respectively. Let us assume all 3 mobile users with advanced multibeam terminals which will track the 4 UAVs  640  continuously and simultaneously. 
         [0356]    Three different methods for preprocessing features: 
         [0357]    1. Method 1; segmentation only. 
         [0358]    2. Method 2; segmentation and WF muxing without redundancy 
         [0359]    3. Method 3; segmentation and WF muxing with redundancy. 
         [0360]    Method 1: The original data is segmented into 4 subsets each with 3 numbers as following; x 1 (n)=[1, 5, 9], x 2 (N)=[2, 6, 10], x 3 (N)=[3, 7, 11], and x 4 (N)=[4, 8, 12]. These four subsets are uploaded to 4 UAVs, and delivered to the designated mobile user  1  with a multibeam terminal  1 , which will need all 4 segmented data subsets for original data reconstitutions. 
         [0361]    Method 2; The original data is segmented into 4 subsets each with 3 numbers, and then the 4 subsets are concurrently sent to a 4-to-4 WF muxing device, generating 4 new WF muxed data subsets without redundancy. Each segmented subset features 3 numbers; same results from Method 1. The segmented subsets are x 1 (N)=[1, 5, 9], x 2 (N)=[2, 6, 10], x 3 (N)=[3, 7, 11], and x 4 (N)=[4, 8, 12]. The 4 subsets of WF muxed data, yk(N) with k from 1 to 4 and N from 1 to 3, are generated via a 4-to-4 WF muxing represented by the following matrix operation; 
         [0000]        y 1( N )= x 1( N )+ x 2( N )+ x 3( N )+ x 4( N )   (6.8.1)
 
         [0000]        y 2( N )= x 1( N )− x 2( N )+ x 3( N )− x 4( N )   (6.8.2)
 
         [0000]        y 3( N )= x 1( N )− x 2( N )+ x 3( N )− x 4( N )   (6.8.3)
 
         [0000]        y 4( N )= x 1( N )− x 2( N )− x 3( N )+ x 4( N )   (6.8.4)
 
         [0362]    The WF muxed data subsets, y 1 (N)=[10, 26, 42], y 2 (N)=[−2, −2, −2], y 3 (N)=[−4, −4, −4], and y 4 (N)=[0, 0, 0] are uploaded to 4 UAVs individually, and delivered to the designated mobile user  2  with a multibeam terminal  2 . The terminal for the mobile user  2  will need all 4 WF muxed data subsets to reconstitute the original data. 
         [0363]    Method 3; The original data is segmented into 3 subsets each with 4 numbers, and then the 3 subsets are concurrently sent to a 4-to-4 WF muxing device, generating 4 new WF muxed data subsets. As a result, there exists built-in redundancy. Each segmented subset features 4 numbers, and they are x 1 (N)=[1, 4, 7, 10], x 2 (N)=[2, 5, 8, 11], and x 3 (N)=[3, 6, 9, 12]. The 4 subsets of WF muxed data, yk(N) with k from 1 to 4 and N from 1 to 4, are generated via a 4-to-4 WF muxing represented by the following matrix operation; 
         [0000]        y 1( N )= x 1( N )+ x 2( N )+ x 3( N )+0   (6.9.1)
 
         [0000]        y 2( N )= x 1( N )− x 2( N )+ x 3( N )−0   (6.9.2)
 
         [0000]        y 3( N )= x 1( N )− x 2( N )+ x 3( N )−0   (6.9.3)
 
         [0000]        y 4( N )= x 1( N )− x 2( N )− x 3( N )+0   (6.9.4)
 
         [0364]    The 4 WF muxed data subsets, y 1 (N)=[5, 15, 24, 33], y 2 (N)=[2, 5, 8, 11], y 3 (N)=[0, 3, 6, 9], and y 4 (N)=[−4, −7, −10, −13] are uploaded to 4 UAVs individually, and delivered to the designated mobile user  3  with a multibeam terminal  3 . The terminal for the mobile user  3  will only need any three of the 4 WF muxed data subsets to reconstitute the original data. There is a feature of building redundancy. 
       End of Embodiment 1 
     Embodiment 2 
       [0365]    This embodiment presents architectures and methods of implementing calibrations and compensations among multiple channels in feeder-links for GBBF using WF muxing and demuxing. Element signals and known diagnostic (probing) signals will be assigned and attached to various multi-dimensional WF vectors. Various multi-dimensional WF vector components will utilize different propagation channels in the feeder-links. 
         [0366]      FIG. 9 a    features forward link calibrations with an on-board adaptive equalization/optimization loop before WF demuxing. Parts of the WF demuxing outputs on a UAV are recovered diagnostic signals which are used by the optimization loop. 
         [0367]      FIG. 9 b    features forward link calibrations with an on-ground adaptive equalization/optimization loop before WF demuxing. Parts of the WF demuxing outputs on a UAV are recovered diagnostic signals which are turned around and passed to ground facility to be used by the ground based optimization loop. 
         [0368]      FIG. 9 c    features return link calibrations with an on-ground adaptive equalization/optimization loop before WF demuxing. Parts of the WF demuxing outputs on ground are recovered diagnostic signals which are used by the ground based optimization loop. 
         [0369]      FIG. 9 d    features ground-based processing. 
         [0370]      FIGS. 9 a , 9 b  and 9 c    depict functional flow diagrams for a forward link transmissions, respectively, with WF muxing/demuxing techniques for channel equalizations for feeder-links between a ground facility and an UAVs. It is not for “coherent power combining” among multiple UAVs. It is also not for data transmission security and redundancy. 
         [0371]    The techniques will enable communication architecture designer more flexibility to utilize feederlinks. We will use 32-to-32 FFT transformations as WF muxing and demuxing functions in the illustration. 
         [0372]    Calibrations and compensations of a GBBF processing with a moving UAV platform continuously shall include (1) phase and amplitude differential of unbalanced electronics on board an UAV, (2) phase and amplitude differential of unbalanced electronics on ground facility, (3) phase and amplitude differential due to Ka/K band propagation effects in a feeder-link. 
         [0373]    The illustrations are focused to the dynamic compensation of feeder-links at Ku-band. We assume the total available feeder-line bandwidth in a Ku band for forward link is 500 MHz bandwidth in vertical polarization (VP), and the same 500 MHz in horizontal polarization (HP). The 500 MHz at VP is divided into 16 contiguous frequency slots each with ˜31 MHz bandwidth. Similarly the 500 MHz at HP is also divided into a second 16 contiguous frequency slots. There total 32 frequency slots assigned to forward links from a ground facility to an UAV features an up-link spectrum around 14 GHz . These allow an operator to continuously support a Tx array with ≦30 elements on an UAV for GBBF operations with full calibration continuously. Each element features a bandwidth of ˜30 MHz. 
         [0374]    Similarly we may assume the total available feeder-line bandwidth in a Ku band for return link is also 500 MHz bandwidth in vertical polarization (VP), and the same 500 MHz in horizontal polarization (HP). The 500 MHz at VP is divided into 16 contiguous frequency slots each with ˜31 MHz bandwidth. Similarly the 500 MHz at HP is also divided into a second 16 contiguous frequency slots. There total 32 frequency slots assigned to return links from UAVs to a ground features an down-link spectrum around 12 GHz . These allow an operator to continuously support an Rx array with ≦30 elements on an UAV for GBBF operations with full calibration continuously. Each element features a bandwidth of ˜30 MHz 
         [0375]    In the examples of  FIGS. 9 a , 9 b , and 9 c    we assume each UAV features 10 L/S band array elements, each with 30 MHz bandwidth, via GBBF for foreground communications. 
         [0376]    It is noticed that one such feeder-link may support 3 UAVs concurrently. It is possible to have multiple feederlinks to a single UAV from multiple hubs to perform GBBF concurrently using the same 10 L/S band array elements 
         [0377]      FIG. 9 a    is functional flow diagram from ground processing facility to a UAV for forward link calibrations of the feeder-link. On a GBBF processing facility  910  on ground, multiple “beam” inputs  915  are sent to a multi-beam Tx DBF processor  751  for a remote array with 10 array elements  939  on a UAV. The outputs from the Tx DBF are 10 parallel processed data streams for the transmissions by the designated elements  939 . These processed signals are referred to as element signals (Es 1 , . . . , Es 10 ) which are respectively, connected to the first 10 slices of a 32-to-32 WF muxer  914 . The WF muxer features a 32-to-32 FFT function, and may be implemented as an S/W package in a digital circuit either in a single monolithic chip or a digital circuit board. 
         [0378]    Many of the input ports, or slices, are not connected. We “ground” the last 4-slices, input ports  29  through  32 , as inputs to diagnostic signals with “zero” signals. At the 32 outputs are 32 different linear combinations of the 10 designated element signals. These output ports are referred to as 12 wavefront component (wfc) ports and the outputs are 12 aggregated data streams. The signal stream y 1  is the output from the output port wfc- 1 , y 2  from wfc- 2 , and so on. 
         [0379]    As a result of the WF muxing, there are 32 WF vectors which are mutually orthogonal among the 32wfc outputs. Each WF vector features 32 components distributed among the 32 wfc ports. Every input port (slice) is associated to a unique WF vector. Since Es 1  is connected to slice- 1 , Es 1  is “attached” to the first WF vector, or “riding on WF 1 ”. 
         [0380]    The first 16 output (wfc) ports are FDM muxed into IF signals with 500 MHz bandwidth by a FDM Mux 1   752 . The muxed signals are then frequency up-converted and power amplified via a RF frontend unit  933 , before radiated by a directional antenna  411  in vertical polarization (VP) to the designated UAV  620 - 1   a.  The amplified signals are radiated via a VP format by connecting the amplified signals to a first input (VP) port of an Orthomode-T  912  for the feed of the directional antenna  411 . 
         [0381]    The second 16 output (wfc) ports are FDM muxed into IF signals with 500 MHz bandwidth by a FDM Mux 2   752 . The muxed signals are then frequency up-converted and power amplified via a RF front-end unit  933 , before radiated by a directional antenna  411  in horizontal polarization (HP) to the designated UAV  620 - 1   a.  The amplified signals are radiated via a HP format by connecting the amplified signals to a second input (HP) port of an Orthomode-T  912  for the feed of the directional antenna  411 . 
         [0382]    On board a moving platform, UAV  620 - 1   a,  a “coherent transponding” process is illustrated in the panel  930 . A high gain tracking antenna  931  picks up the up-loaded signals from a ground processing facility  910 . The transponding process  930  converts one input at Ku band receiving antenna  931  into 10 outputs for 10 elements  939  in L/S band concurrently. 
         [0383]    The output from the high gain antenna  931  is split into HP and VP signals through an orthomode-T  932 ; each goes through an RF front-end unit  933  and a FDM demuxer  934  converting a 500 MHz muxed signal into 16 channelized signals. These channelized signals are at a common IF with ˜30 MHz bandwidth each. There are total 32 channelized signals which are connected to the 32 inputs of a 32-to-32 WF demuxer  942  via 32 parallel adaptive equalizers 941 
         [0384]    The 16 channelized signals come from the VP port of the Orthomode-T  932  are assigned to the first 16 (wfc) ports of the WF demuxer  942 , and the 16 channelized signals come from the HP port of the “Orthomode-T” 932  are to the next 16 (wfc) ports of the WF demuxer  942 . 
         [0385]    An optimization loop is built among (1) the 32 sets of FIR weighting in the adaptive equalizer  941 , (2) recovered diagnostic signals  944  from the 4 designated output ports of the WF demuxer  942 ; slice- 29  through slice- 32 , and (3) the optimization processing  943  with selected iterative algorithms. In addition to differences of recovered diagnostic signals and known original diagnostic signals, correlations between the ports of element signals (slice- 1  through slice- 10 ) and the ports of diagnostic signals (slice- 29  through slice- 32 ) are important observables for the optimization processing  943 . 
         [0386]    1. The inputs y 1 ′, y 2 ′, y 3 ′, . . . , and y 32 ′ to the WF demux  942  are connected to 32 adaptive finite-impulse-response (FIR) filters  941  for time, phase, and amplitude equalizations among the 32 propagation channels; 
         [0387]    2. Adaptive filters compensate for phase differentials caused by “dispersions” among the propagation paths (array elements) in feeder links via a UAV  620 - 1   a.  There will be significant improvement on waveform shape distortions due to dispersions; minimizing a source for inter-symbol interferences. 
         [0388]    3. weightings of the FIR filters  941  are optimized by an iterative control loop based on comparisons of recovered pilot signals  944  against the injected and known diagnostic signals  916 , correlations between the ports of element signals (slice- 1  through slice- 10 ) and the ports of diagnostic signals (slice- 29  through slice- 32 ), and an efficient optimization algorithm in an optimization processing  943 . 
         [0389]    4. Among the outputs of the WF demuxer  942  are the 10 slices of desired element signal streams, and 4 pilot signals. 
         [0390]    5. The optimization loop utilizing cost minimization criteria in the optimization processing  743  comprises:
       a. Identifying proper observables for the optimization loop including:
           i. differences between the recovered pilot signal stream and the original.   ii. Correlations of signals from output slices of the WF demuxer  742 .   
           b. Generating different cost functions based on various observables:
           i. Converting or mapping various observables into different measurables or cost functions which must be positively defined.
               When an observable meets the desired performance, the corresponding measurable or cost function becomes zero.   When an observable is only slightly away from the desired performance, the corresponding measurable or cost function is assigned with a small positive number.   When an observable is far away from the desired performance, the corresponding measurable or cost function is assigned with a large positive number.   
               
           c. Summing all cost function for a total cost as a numerical indicator the current status of the optimization loop performances,
           i. When total cost is less than a small positive threshold value, stop the optimization loop;   ii. otherwise proceed to procedure d   
           d. Deriving the gradients of total cost with respect to the weights of the adaptive equalizers which are in the forms of FIR filters.   e. Calculating new weights of the FIR filters based on a steepest descent algorithm to minimize the total cost of the optimization loop iteratively.   f Updating the weightings in the adaptive equalizer and go to procedure b.       
 
         [0405]    At an optimized state, the amplitude and phase responses of the 32 frequency channels in the feeder-link shall be fully equalized. Thus the 32 associated WF vectors shall become mutually orthogonal at the interfaces between the 32 outputs of the adaptive equalizers  941  and the 32 inputs of the WF demuxer  942 . Thus there are no leakages among the outputs of the WF demuxer  942 ; cross correlations among signals in diagnostic channels (slice- 29  through slice- 32 ) and element signals channels (slice- 01  through slice- 10 ) shall become zero. 
         [0406]    As a result, the recovered element signals from slice  1  through slice  10  are frequency up converted and filtered via frequency up-converters  937  to L/S band, power amplified by PAs  938  before radiated by radiating elements  939 . The 10 radiated signals processed by DBF  751  in the GBBF facility  910  will be spatial power combined in far field over different designated beam positions in a coverage area  130  for various user signals. 
         [0407]    In this scheme, it is assume that the 10 parallel channels are fully equalized between the radiating elements  939  and beyond the outputs of the WF demuxer  942 . 
         [0408]      FIG. 9 b    is nearly identical to  FIG. 9 a   . Both depict functional flow diagrams from ground processing facility to a UAV for forward link calibrations of the feederlink. The only differences are the locations of the adaptive equalizations and optimization loop. Instead of on-board adaptive equalization,  FIG. 9 b    features a scheme with ground base adaptive equalizations and optimization loop for the feeder-links for forward link signals. 
         [0409]    On a GBBF processing facility  910  on ground, multiple “beam” inputs  915  are sent to a multi-beam Tx DBF processor  751  for a remote array with 10 array elements  939  on a UAV  620 - 1   a.  The outputs from the Tx DBF  751  are 10 parallel processed data streams for the transmissions by the designated elements  939 . These processed signals are referred to as element signals (Es 1 , . . . , Es 10 ) which are respectively, connected to the first 10 slices of a 32-to-32 WF muxer  914 . The WF muxer features a 32-to-32 FFT function, and may be implemented as an S/W package in a digital circuit either in a single monolithic chip or a digital circuit board. 
         [0410]    Many of the input ports, or slices, are not connected. We “ground” the last 4-slices, input ports  29  through  32 , as inputs to diagnostic signals with “zero” signals. At the 32 outputs of the WF muxer  914  are 32 different linear combinations of the 10 designated element signals. These output ports are referred to as 32 wavefront component (wfc) ports and the outputs are 32 aggregated data streams. The signal stream y 1  is the output from the output port wfc- 1 , y 2  from wfc- 2 , and so on. 
         [0411]    As a result of the WF muxing, there are 32 WF vectors which are mutually orthogonal among the 32wfc outputs. Each WF vector features 32 components distributed among the 32 wfc ports. Every input port (slice) is associated to a unique WF vector. Since Es 1  is connected to slice- 1 , Es 1  is “attached” to the first WF vector, or “riding on WF 1 ”. 
         [0412]    The first 16 output (wfc) ports are connected to a first set of 16 parallel adaptive equalizers  941  and then FDM muxed into IF signals with 500 MHz bandwidth by a FDM Mux 1   752 . The adaptive equalizers  941  are for compensations via pre-distortions on cumulated amplitudes and phase differentials of propagating signals in selected 32 channels in a feederlink  450 . The muxed signals are than frequency up-converted and power amplified via a RF frontend unit  753 , before radiated by a directional antenna  411  in vertical polarization (VP) to the designated UAV  620 - 1   a.  The amplified signals are radiated via a VP format by connecting the amplified signals to a first input (VP) port of an “Orthomode-T”  912  for the feed of the directional antenna  411 . 
         [0413]    The second 16 output (wfc) ports are connected to a second set of 16 parallel adaptive equalizers  941  and then FDM muxed into IF signals with 500 MHz bandwidth by a FDM Mux 2   752 . The muxed signals are than frequency up-converted and power amplified via a RF front-end unit  753 , before radiated by a directional antenna  411  in horizontal polarization (VP) to the designated UAV  620 - 1   a.  The amplified signals are radiated via a HP format by connecting the amplified signals to a second input (HP) port of an Orthomode-T  912  for the feed of the directional antenna  411 . 
         [0414]    On board a moving platform, UAV  620 - 1   a,  a “coherent transponding” process is illustrated in the panel  930 . A high gain tracking antenna  931  picks up the up-loaded signals from a ground processing facility  910 . The transponding process  930  converts one input at Ku band receiving antenna  931  into 10 outputs for 10 elements  939  in L/S band concurrently. 
         [0415]    The output from the high gain antenna  931  is split into HP and VP signals through an Orthomode-T  932 ; each goes through an RF front-end unit  933  and a FDM demuxer  934  converting a 500 MHz muxed signal into 16 channelized signals. These channelized signals are at a common IF with ˜30 MHz bandwidth each. There are total 32 channelized signals which are connected to the 32 inputs of a 32-to-32 WF demuxer  942 . 
         [0416]    The 16 channelized signals come from the VP port of the Orthomode-T  932  are assigned to the first 16 (wfc) ports of the WF demuxer  942 , and the 16 channelized signals come from the HP port of the Orthomode-T  932  are to the next 16 (wfc) ports of the WF demuxer  942 . 
         [0417]    An optimization loop is built among (1) the 32 sets of ground-based FIR filter weighting in the adaptive equalizer  941 , (2) recovered diagnostic signals  944  from the 4 designated output ports of the on-board WF demuxer  942 ; slice- 29  through slice- 32 , and (3) the optimization processing  943  with selected iterative algorithms on ground. In addition to differences of recovered diagnostic signals and known original diagnostic signals, correlations between the ports of element signals (slice- 1  through slice- 10 ) and the ports of diagnostic signals (slice- 29  through slice- 32 ) are important observables for the optimization processing  943 . 
         [0418]    1. The inputs y 1 ′, y 2 ′, y 3 ′, . . . , and y 32 ′ to the on board WF demux  942  can “modulated” by 32 ground based adaptive finite-impulse-response (FIR) filters  941  for time, phase, and amplitude equalizations among the 32 propagation channels via compensations via pre-distortions techniques; 
         [0419]    2. Adaptive filters compensate for phase differentials caused by “dispersions” among the propagation paths (array elements) in feeder links via a UAV  620 - 1   a.  There will be significant improvement on waveform shape distortions due to dispersions; minimizing a source for inter-symbol interferences. 
         [0420]    3. Weightings of the FIR filters  941  are optimized by an iterative control loop based on comparisons of recovered pilot signals  944  against the injected and known diagnostic signals  916 , and an efficient optimization algorithm in an optimization processing  943 . 
         [0421]    4. Among the outputs of the WF demuxer  942  are the 10 slices of desired element signal streams, and 4 recovered pilot signals. 
         [0422]    5. The recovered pilot signals  944  are piped down to the GBBF facility via additional input channels to the on-board WF muxer for calibration of the Return link (as depicted in  FIG. 9 c   ). As a result, the on-board recovered diagnostic signals  944  shall appear on the ground processing facility  910  as a set of contaminated recovered diagnostic signals  945 . 
         [0423]    6. The optimization loop utilizing cost minimization criteria in the optimization processing  943  comprises:
       a. Identifying proper observables for the optimization loop including:
           i. differences between the recovered pilot signal stream and the original.   ii. Correlations of signals from output slices of the WF demuxer  942 .   
           b. Generating different cost functions based on various observables;
           i. Converting or mapping various observables into different measurables or cost functions which must be positively defined.
               When an observable meets the desired performance, the corresponding measurable or cost function becomes zero.   When an observable is only slightly away from the desired performance, the corresponding measurable or cost function is assigned with a small positive number.   When an observable is far away from the desired performance, the corresponding measurable or cost function is assigned with a large positive number.   
               
           c. Summing all cost function for a total cost as a numerical indicator the current status of the optimization loop performances,
           i. When total cost is less than a small positive threshold value, stop the optimization loop;   ii. otherwise proceed to procedure d   
           d. Deriving the gradients of total cost with respect to the weights of the adaptive equalizers which are in the forms of FIR filters.   e. Calculating new weights of the FIR filters based on a steepest descent algorithm to minimize the total cost of the optimization loop iteratively.   f Updating the weightings in the adaptive equalizer and go to procedure b.       
 
         [0438]    At an optimized state, the amplitude and phase responses of the 32 frequency channels in the feeder-link shall be fully equalized. Thus the 32 associated WF vectors shall become mutually orthogonal at the interfaces between the 32 outputs of the adaptive equalizers  941  and the 32 inputs of the WF demuxer  942 . Thus there are no leakages among the outputs of the WF demuxer  942 ; cross correlations among signals in diagnostic channels (slice- 29  through slice- 32 ) and element signals channels (slice- 01  through slice- 10 ) shall become zero. 
         [0439]    As a result, the recovered element signals from slice  1  through slice  10  are frequency up converted and filtered via frequency up-converters  937  to L/S band, power amplified by PAs  938  before radiated by radiating elements  939 . The 10 radiated signals processed by DBF  751  in the GBBF facility  910  will be spatial power combined in far field over different designated beam positions in a coverage area  130  for various user signals. 
         [0440]    In this scheme, it is assume that the 10 parallel channels are fully equalized between the radiating elements  939  and beyond the outputs of the WF demuxer  942 . 
         [0441]      FIG. 9 c    depicts functional flow diagrams from ground processing facility to a UAV for return link calibrations of the feederlink. It has an additional feature of supporting the forward link calibrations as depicted in  FIG. 9   b.    
         [0442]    On board a mobile platform UAV  620 - 1   a,  a set of 10 array elements  968  captures radiated signals in L/S band over a coverage area  130 . These captured element signals are amplified by LNAs  969  and filtered and frequency converted individually by frequency converter units  967 . These processed signals are referred to as element signals (Es 1 , . . . , Es 10 ) which are respectively, connected to the first 10 slices of a 32-to-32 WF muxer  914 . The WF muxer features a 32-to-32 FFT function, and may be implemented as an S/W package in a digital circuit either in a single monolithic chip or a digital circuit board. The WF muxing functions may also be implemented as RF Bulter matrixes or a baseband FFT chip. 
         [0443]    Many of the input ports, or slices, are not connected. We “ground” the last 4-slices, input ports  29  through  32 , as inputs to diagnostic signals with “zero” signals. Four input ports  944  from slice- 25  through slice- 28  are used for relaying the recovered diagnostic signals from the forward link calibration. They are connected by 4 output ports (the slice- 29 , slice- 30 , slice- 31 , and slice- 32 )  944  of the WF demuxer  942  in  FIG. 9   b.    
         [0444]    At the 32 outputs of the WF muxer  914  are 32 different linear combinations of the 10 designated element signals. These output ports are referred to as 32 wavefront component (wfc) ports and the outputs are 32 aggregated data streams. The signal stream y 1  is the output from the output port wfc- 1 , y 2  from wfc- 2 , and so on. 
         [0445]    As a result of the WF muxing, there are 32 WF vectors which are mutually orthogonal among the 32wfc (output) ports. Each WF vector features 32 components distributed among the 32 wfc ports. Every input port (slice) is associated to a unique WF vector. Since Es 1  is connected to slice- 1 , Es 1  is “attached” to the first WF vector, or “riding on WF 1 ”. 
         [0446]    The first 16 output (wfc) ports are FDM muxed into IF signals with 500 MHz bandwidth by a FDM Mux 1   964 . The muxed signals are than frequency up-converted and power amplified via a RF frontend unit  963 , before radiated by a directional antenna  931  in vertical polarization (VP) to the designated UAV  620 - 1   a.  The amplified signals are radiated via a VP format by connecting the amplified signals to a first input (VP) port of an Orthomode-T  962  for the feed of the directional antenna  931 . 
         [0447]    The second 16 output (wfc) ports are FDM muxed into IF signals with 500 MHz bandwidth by a FDM Mux 2   964 . The muxed signals are than frequency up-converted and power amplified via a RF front-end unit  963 , before radiated by a directional antenna  931  in horizontal polarization (HP) to a GBBF processing facility  910 . The amplified signals are radiated via a HP format by connecting the amplified signals to a second input (HP) port of an Orthomode-T  962  for the feed of the directional antenna  931 . 
         [0448]    In the GBBF facility  910 , a high gain tracking antenna  931  picks up the down-loaded signals from an UAV  620 - 1   a.  A transponding process in  910  converts one input at Ku band receiving antenna  411  into 10 element inputs for the RX DBF processor  781   
         [0449]    The output from the high gain antenna  411  is split into HP and VP signals through an Orthomode-T  982 ; each goes through an RF front-end unit  933  and a FDM demuxer  934  converting a 500 MHz muxed signal into 16 channelized signals. These channelized signals are at a common IF with ˜30 MHz bandwidth each. There are total 32 channelized signals which are connected to the 32 inputs of a 32-to-32 WF demuxer  942  through a bank of 32 adaptive equalizers  971  implemented by 32 adaptive FIR filters. . 
         [0450]    The 16 channelized signals come from the VP port of the Orthomode-T  932  are assigned to the first 16 (wfc) ports of the WF demuxer  942 , and the 16 channelized signals come from the HP port of the Orthomode-T  932  are to the next 16 (wfc) ports of the WF demuxer  942 . 
         [0451]    An optimization loop is built among (1) the 32 sets of FIR filter weighting in the adaptive equalizer  971 , (2) recovered diagnostic signals  978  from the 4 designated output ports of the WF demuxer  972 ; slice- 29  through slice- 32 , and (3) the optimization processing  977  with selected iterative algorithms. In addition to differences of recovered diagnostic signals and known original diagnostic signals, correlations between the ports of element signals (slice- 1  through slice- 10 ) and the ports of diagnostic signals (slice- 29  through slice- 32 ) are important observables for the optimization processing  977 .
       1. The inputs y 1 ′, y 2 ′, y 3 ′, . . . , and y 32 ′ to the WF demux  972  can “modulated” by 32 adaptive finite-impulse-response (FIR) filters  971  for time, phase, and amplitude equalizations among the 32 propagation channels via compensations via pre-distortions techniques;   2. Adaptive filters compensate for phase differentials caused by “dispersions” among the propagation paths (array elements) in feeder links via a UAV  620 - 1   a.  There will be significant improvement on waveform shape distortions due to dispersions; minimizing a source for inter-symbol interferences.   3. weightings of the FIR filters  971  are optimized by an iterative control loop based on comparisons of recovered pilot signals  978  against the injected and known diagnostic signals  974 , and an efficient optimization algorithm in a forward link optimization processing  977 .   4. Among the outputs of the WF demuxer  972  are the 10 slices of desired element signal streams, and 4recovered pilot signals  978  for return link (from slice- 29  through slice- 32 ).   5. “contaminated recovered pilot signals  945  for forward links are available at the 4 output ports (from slice- 25  through slice- 28 ).   6. The optimization loop utilizing cost minimization criteria in the optimization processing  943  comprises:
           a. Identifying proper observables for the optimization loop including
               i. differences between the recovered pilot signal stream and the original.   ii. Correlations of signals from output slices of the WF demuxer  942 .   
               b. Generating different cost functions based on various observables
               i. Converting or mapping various observables into different measurables or cost functions which must be positively defined.
                   When an observable meets the desired performance, the corresponding measurable or cost function becomes zero.   When an observable is only slightly away from the desired performance, the corresponding measurable or cost function is assigned with a small positive number.   When an observable is far away from the desired performance, the corresponding measurable or cost function is assigned with a large positive number.   
                   
               c. Summing all cost function for a total cost as a numerical indicator the current status of the optimization loop performances,
               i. When total cost is less than a small positive threshold value, stop the optimization loop;   ii. otherwise proceed to procedure d.   
               d. Deriving the gradients of total cost with respect to the weights of the adaptive equalizers which are in the forms of FIR filters.   e. Calculating new weights of the FIR filters based on a steepest descent algorithm to minimize the total cost of the optimization loop iteratively.   f Updating the weightings in the adaptive equalizer and go to procedure b.   
               
 
         [0472]    At an optimized state, the amplitude and phase responses of the 32 frequency channels in the feeder-link shall be fully equalized. Thus the 32 associated WF vectors shall become mutually orthogonal at the interfaces between the 32 outputs of the adaptive equalizers  971  and the 32 inputs of the WF demuxer  972 . Thus there are no leakages among the outputs of the WF demuxer  972 ; cross correlations among signals in diagnostic channels (slice- 29  through slice- 32 ) and element signals channels (slice- 01  through slice- 10 ) shall become zero. 
         [0473]    As a result, the recovered element signals from slice  1  through slice  10  are sent to a Rx DBF  785  in the GBBF processing facility  911   
       End of Embodiment 2 
     Embodiment 3 
       [0474]    This embodiment presents architectures and methods of implementing multiplexing of three users utilizing 4 UAV based communications channels through Wavefront multiplexing/de-multiplexing. Each of the three user signals after WF muxing features a unique wavefront (WF) through a WF vector which propagates through multiple UAV channels concurrently. There are three users associated with three mutually orthogonal WF vectors. The remaining fourth vector is assigned for diagnostic signals. 
         [0475]      FIG. 10 a    is for the first user signal stream. The adaptive equalization loop assures the orthogonality among the four recovered WF vectors.  FIG. 10 b    is the block diagram for the second user, and  FIG. 10 c    for the third user signals. 
         [0476]      FIGS. 10 a , 10 b , and 10 c    depict functions of a WF muxing  712  and a WF demuxing processor  742  concurrently utilizing four independent communications assets in four UAVs for three separated users xa, xb, and xc. 
         [0477]    Three user forward link signals  1011   a,    1011   b  and  1011   c  are converted into 4 WF components y 1 , y 2 , y 3 , and y 4  by a 4-to-4 WF muxer  712  before uploaded to 4 separated UAVs  620 - 1   a,    620 - 1   b,    620 - 1   c,  and  620 - 1   d.  The WF muxer is a 4-to-4 Hadamard matrix. As a result, the four output signals by 4 wfc ports of the WF muxer; 
         [0000]        y 1( t )=0 +xa ( t )+ xb ( t )+ xc ( t )   (7.1)
 
         [0000]        y 2( t )=0 −xa ( t )+ xb ( t )− xc ( t )   (7.2)
 
         [0000]        y 3( t )=0 +xa ( t )− xb ( t )− xc ( t )   (7.3)
 
         [0000]        y 4( t )=0 −xa ( t )− xb ( t )+ xc ( t )   (7.4)
 
         [0478]    Where the A 1  slice is grounded, A 2 , A 3 , and A 4  slices are connected by xa, xb and xc signals respectively. Every input signal stream goes through all 4 UAVs concurrently. The four input signals including the “zero” signal inputs to input slice A 1 , are riding 4 mutually orthogonal WF vectors at the outputs of the WF muxer  712 ;
       “zero” signals connected to the A 1  slice are associated with WFV 1 =[1,1,1,1] T ,   xa(t) signals connected to the A 2  slice are associated with WFV 2 =[1, −1,1, −1] T ,   xb(t) signals connected to the A 3  slice are associated with WFV 3 =[1,1, −1, −1] T , and   xc(t) signals connected to the A 4  slice are associated with WFV 4 =[1, −1,1, −1] T  .       
 
         [0483]    The four parallel paths on a receiver will feature different amplitude attenuations/amplifications and phase delays even at same carrier frequency due to path length differentials and unbalanced electronics among the four UAV platforms. 
         [0484]    The 4 inputs to a bank of 4 parallel adaptive equalizers  741  on a user terminal for the first user feature: 
         [0000]        z 1( t )= am 1 a*  exp( j kΔz 1 a )* y 1( t ),   (8-1)
 
         [0000]        z 2( t )= am 2 a*  exp( j kΔz 2 a )* y 2( t ),   (8-2)
 
         [0000]        z 3( t )= am 3 a*  exp( j kΔz 3 a )* y 3( t ),   (8-3)
 
         [0000]        z 4( t )= am 4 a*  exp( j kΔz 4 a )* y 4( t ),   (8-4)
 
         [0485]    The adaptive equalizers are to compensate the amplitude and phase differentials among the four propagation paths. Their outputs are connected to the inputs to a 4-to-t WF demuxer  742 . The four WF vectors shall be distorted and no longer mutually orthogonal to one another, As a results, there are leakages at the output port (slice) A 1  from signals designated for A 2 , A 3 , and A 4  ports. The diagnostic port no longer features “zero” signals. 
         [0486]    An optimization loop will use the leakage power  744  as one of the observables. An optimization processor will convert the observables into a quantitative measurables, or cost functions, which are always positively defined. Total cost, the sum of all cost functions, and gradients of the total cost are derived and measured. New weights are calculated and updated based on a steepest descent method for the adaptive equalizers iteratively via a cost minimization algorithm. 
         [0487]    In optimized states, four propagation paths shall be fully compensated so that the inserted phases and amplitudes of the adaptive equalizers [a1*exp(j Φ1)], [a2*exp(jΦ2)], [a3*exp(jΦ3)], and [a4*exp(jΦ4)], must fulfill the following requirements, respectively: 
         [0000]        am 1 a* exp( j kΦz 1 a )*[ a 1*exp( j Φ 1)] 
         [0000]      = am 2 a* exp( j kΦ 2 a )*[ a 2*exp( j Φ 2)] 
         [0000]      = am 3 a* exp( j kΦ 3 a )*[ a 3*exp( j Φ 3)] 
         [0000]      = am 4 a* exp( j kΦ 4 a )*[ a 4*exp( j Φ 4)]=constant   ( 9 )
 
         [0488]    As a result, the associated WF vectors after the adaptive equalizers will become orthogonal again. There are no more leakages at output port (slice) Al of the WF demuxer  742  from the other three output ports (slices A2, A3, and A4). 
         [0489]    The signal stream xa recovered on slice A2 1041a is connected to the designated receiver for the first user. 
         [0490]      FIG. 10 b   , and  FIG. 10 c    depict the same uplinks but a different down links for a second user and a third user at the same beam positions as that of the first user. The signals output for the second user xb is from slice A 3  of the WF demuxer  742 . The signals output for the third user xc is from slice A 4  of the WF demuxer  742 . 
       End of Embodiment 3. 
     Embodiment 4 
       [0491]    This embodiment presents architectures and methods of implementing UAV based communications using retro-directive antennas, and ground based beam forming (GBBF). Several scenarios are presented as followed;
       1. Analogue retro-directive antennas for on-board feeder-link payloads in  FIG. 11 ,   2. With GBBF but without retro-directive in  FIG. 12 ,   3. With GBBF and with retro-directive in  FIG. 12   a,      4. Without GBBF but with retro-directive in  FIG. 12   b.          
 
         [0496]      FIG. 11  depicts of a Ku retro-directive array on board a UAV. Ku-band arrays  1100  are used for UAVs as feeder link antennas to transfer all signals to and from L/S or C-band elements channels to a gateway where a simple GBBF processing will perform both Tx and Rx array functions. The Ku band “smart” arrays will feature retro-directivity via on-board analogue beam forming network (BFN)  1121  and beam controller  1140  technologies. 
         [0497]    The 4 element array  1100  features analog beam-forming and switching mechanisms to gain 6 dB advantage than an omni directional antenna for data links from a UAV to a ground processing center. The depicted smart array  1100  featuring four low profile elements  1132  consists of two regular analogue multiple-beam beam-forming-networks (BFNs) using Butler Matrixes (BMs); one for Rx  1121  and the other for Tx  1111 . However, retro-directive antennasfor the back-channels may be arrays with 8, 16, or more elements depending on how far the UAV is away from the ground processing center. 
         [0498]    The 4 element array  1100  features 4 Rx beams. Received signals by the 4 array elements  1132  after the diplexers  1131  are amplified by LNAs  1123  followed by a BPF (not shown) before a receiving (Rx) BM  1121 . The Rx BM  1121  will form 4 orthogonal beams pointing to 4 separated directions covering the entire field of view (FOV) of interest. The beam-width of any one beam will be ½ of the FOV (1/4 in terms of stereo-angles), and the four orthogonal beams will cover the entire FOV. Furthermore the peak of any one beam is always a null of all three other beams. The ground processing center will always be covered by one of the four beams. When the 4 elements are on a squared lattice with λ/2 in between adjacent elements and assuming λ/2 squared element size for all 4 elements, the 3-dB beam widths from the 4 element array will be ˜60° near bore side. 
         [0499]    The Rx BM  1121  has 4 outputs; each associated with one of the 4 beam positions. There are two parallel switching trees (ST)  1122  connected to the RX BM in Rx, one for the main signal path  802 , the other for a diagnostic beam  1144  connected to a diagnostic circuitry  1140 . The ST  1122  associated with the diagnostic beam  1144  will continuous switch among the four beam positions. The diagnostic circuit  1140  will identify the features of desired signals through power level in a frequency channels, special codes, waveforms, or other unique features. Once the beam position for the ground processing is identified based on retro-directive algorithms  1141  and updated new beam positions  1143  when the UAV is on station, the beam controller  1142  will dynamically update the ST for the main signal path to a new beam position  1143 . 
         [0500]    The depicted functional block is the 4-element retrodirective antenna array at Ku/Ka band  1100 . The array elements  1132  may feature low-profile and near conformal designs. Rx multibeam forming processing is through a 2-dimensional Butler Matrix (BM)  1121  followed by a pair of switching matrixes (ST)  1122 . The first one is for main signal path which is connected to the interface  1102  via a buffer amplifier  1102   a.  A first of the two ST  1122  is controlled by a beam controller  1142  which shall make a decision on which beam positions to switch on to receive the forward link element signals uploaded by a GBBF facility  412 . Similarly in the return link Ku/Ka Tx P/L, the foreground P/L 1210  shall deliver to the interface  1101  a FDM muxed and frequency up-converted element signals which are received at a public safety band (e.g. 700 MHz or 4.9 GHz). The FDM muxed signals will go through a ST  1112  and a BM  1111 . The 4 outputs properly phased by the BM  1111  will then be amplified by power amplifiers  1113  and then radiated by the low profile element  1132 . In the designated beam position at far field the radiated signals shall be spatially combined coherently due to cancellation of incurred phase differentials during the propagations by the pre-phased individual element signals by the BM  1111   
         [0501]    The current “beam position” decision shall be made based on information derived by the second of the two ST  1122  which is also controlled by the beam controller  1142 . The second ST will be continuous switched or rotated among all possible beam positions with diagnostic beam outputs. The data collected from the second ST will be used by a on board processor  1140 , among other recorded data, to identify a beam position which is currently associated to the strongest signal level of desired signals identified via their unique features. The beam controller will then inform both the Tx ST  1112  and the ST (first of the two Rx ST  112 ) for the Rx main signals about the current beam positions for the retro-directive antenna. 
         [0502]    When the elements are spaced by X the resulting 4 outputs from a BM  1121  will be 4 finger beams; each with multiple peaks (or grading lobes). 
         [0503]    In Tx, the configuration is identical except the signal flows are in reverse direction. The beam controller will also control the ST  1112  for the Tx BM  1111 . 
         [0504]      FIG. 12   1200  is a simplified block diagram for a communications payload (P/L) on a UAV for the communications at regular cell phone frequency bands among the cell phone users in a coverage area. There are five major functional blocks; from top left and clockwise (1) forward link transmitting (Tx) payload  1220  at L/S band for foreground communications, (2) forward link receiving (Rx) payload  1240  at Ku/Ka band for feeder-link communications, (3) Ground processing facility  410  including GBBF processing  412 , (4)return link transmitting (Tx) payload  1110  at Ku/Ka band for feeder-link communications, and (5) return link receiving (Rx) payload  1210  at L/S band for foreground communications. 
         [0505]    In the first major functional block on the top right for the forward link transmitting (Tx) payload  1220  at L/S band for foreground communications; signals flow from right to left. The up-linked signals  1102  received by the on board Ku array  1240  feature “element signals” properly processed by a GBBF designated for the 4 Tx elements  1222  at L/S band. The uplink signals  1102  from the back channels are FDM de-multiplexed  1225  and frequency down converted, filtered and amplified  1224  before radiated by the 4 Tx subarrays D 1 , D 2 , D 3 , and D 4   1222 . There are no on board beam forming processing at L/S band at all. 
         [0506]    The second major functional block in the middle top panel is for the forward link receiving (Rx) payload  1240  at Ku band for feeder-link communications. The onboard Ku  4  element array is programed driven to point its receive beam toward the ground processing center  410 . The Ku Rx beam forming network (BFN)  1241  may be implemented by a 4-to-4 Butler matrix followed by a 4-to-1 switch or equivalent. 
         [0507]    The panel on the right depicts functional flow diagrams in a ground processing facility  410  including a ground based beam forming (GBBF) facility  412  and gateways  418  to terrestrial networks. In a forward link, in-coming traffic from terrestrial IP network  418  will go through many transmitting functions including the modulation for the designated beam signals. Modulated beam signals are sent through multibeam Tx digital beam forming (Tx DBF), converting beam signals into element signals before frequency up converted and power amplified by Ku Tx front end  411 T, and then radiated by Ku transmitting antennas (not shown) 
         [0508]    In a return link, signals captured by Ku transmitting antennas (not shown) are conditioned by low noise amplifier, filtered and then frequency down converted by Ku Tx front end  411 R, and then sent to a multibeam Rx digital beam forming (Rx DBF), converting beam signals from element signals. These recovered beam signals will go through many receiving functions including the demodulation for the designated beam signals which may become outgoing traffic to terrestrial IP networks via designated gateways  418   
         [0509]    The 4 th  major functional block in the middle lower panel is for the return link Transmitting (Tx) payload  1230  at Ku band for feeder-link communications. The onboard Ku 4 element array is programed driven to point its transmitting beam toward the ground processing center  410 . The Ku beam forming network (BFN)  1231  may be implemented by a 4-to-1 followed by a 4-to-4 Butler matrixor equivalent circuits. 
         [0510]    The on board feeder-links antennas  1240  and  1230  are conventional “program-driven” and not “retro-directive.” 
         [0511]    The 5 th  functional block is a return links L/S band P/L  1210  for foreground communications. There are four Rx elements D 1 , D 2 , D 3 , and D 4   1212 ; each of which is connected by a LNA, a BFP, and an up-converter  1211  to Ku band. There are no beam-forming processors on board for antennas at cell phone frequencies. The four received signals, up-converted from the 4 Rx subarrays are FDM multiplexed  1215  into a single stream  1101 , which is then power amplified and transmitted to a ground facility 4 via a 4-element Ku array  1230 . The Ku Tx beam forming network (BFN)  1231  may be implemented by a 1-to-4 switch followed by a 4-to-4 Tx Butler Matrix (BM). Each of the 4 outputs of the Tx BM will then be connected to an active array element. 
         [0512]      FIG. 12 a    is a simplified block diagram for a communications payload (P/L) on a UAV for the communications at 4.9 GHz emergency band among the rescue team members. It is almost identical to those in  FIG. 12 , except:
       1. Operating frequencies of the foreground communications are in public safety band; such as 700 MHz or 4.9 GHz in US.   2. The on-board Ku/Ka feeder-links are via a Retrodirective antenna array  1100  instead of command driven arrays  1230  and  1240 ;
           i. Interfaces are at  1102  for the forward link, and  1101  for the return link;   ii. Details of the retro-directive array are depicted in  FIG. 11 .   
           3. Ground processing is identical to that  410  in  FIG. 12 .         
         [0518]    There are three major functional blocks; from top left and clockwise:
       1. forward link transmitting (Tx) payload  1220  at public safety bands for foreground communications,   2. feeder-link payload  1100 
           i. forward link receiving (Rx) payload  1240  at Ku/Ka band for feeder-link communications and   ii. return link transmitting (Tx) payload  1110  at Ku/Ka band for feeder-link communications, and   
           3. return link receiving (Rx) payload  1210  at L/S band for foreground communications.       
 
         [0524]    In the first major functional block on the top right for the forward link transmitting (Tx) payload  1220  at L/S band for foreground communications; signals flow from right to left. The up-linked signals  1102  received by the on board Ku array  1100  feature “element signals” properly processed by a GBBF designated for the 4 Tx elements  1222  at L/S band. The uplink signals  1102  from the back channels are FDM de-multiplexed  1225  and frequency down converted, filtered and amplified  1224  before radiated by the 4 Tx subarrays D 1 , D 2 , D 3 , and D 4   1222 . There are no on board beam forming processing at public safety bands at all. 
         [0525]    The second functional block depicted on the right side is the 4-element Retrodirective antenna array at Ku/Ka band  1100 . The array elements  1132  may feature low-profile and near conformal designs. Rx multibeam forming processing is through a 2-dimensional Butler Matrix (BM)  1121  followed by a pair of switching matrixes (ST)  1122 . The first one is for main signal path which is connected to the interface  1102  via a buffer amplifier  1102   a.  A first of the two ST  1122  is controlled by a beam controller  1142  which shall make a decision on which beam positions to switch on to receive the forward link element signals uploaded by a GBBF facility  412 . Similarly in the return link Ku/Ka Tx P/L, the foreground P/L 1210  shall deliver to the interface  1101  a FDM muxed and frequency up-converted element signals which are received at a public safety band (e.g. 700 MHz or 4.9 GHz). The FDM muxed signals will go through a ST  1112  and a BM  1111 . The 4 outputs properly phased by the BM  1111  will then be amplified by power amplifiers  1113  and then radiated by the low profile element  1132 . In the designated beam position at far field the radiated signals shall be spatially combined coherently due to cancellation of incurred phase differentials during the propagations by the pre-phased individual element signals by the BM  1111   
         [0526]    The current “beam position” decision shall be made based on information derived by the second of the two ST  1122  which is also controlled by the beam controller  1142 . The second ST will be continuous switched or rotated among all possible beam positions with diagnostic beam outputs. The data collected from the second STwill be used by a on board processor  1140 , among other recorded data, to identify a beam position which is currently associated to the strongest signal level of desired signals identified via their unique features. The beam controller will then inform both the Tx ST  1112  and the ST (first of the two Rx ST  112 ) for the Rx main signals about the current beam positions for the retro-directive antenna. 
         [0527]    The 3 rd  functional block is a return link P/L  1210  in public safety band for foreground communications. There are four Rx elements D 1 , D 2 , D 3 , and D 4   1212 ; each of which is connected by a LNA, a BFP, and an up-converter  1211  to Ku band. There are no beam-forming processors on board for antennas at cell phone frequencies. The four received signals, up-converted from the 4 Rx subarrays are FDM multiplexed  1215  into a single stream  1101 , which is then power amplified and transmitted to a ground facility  4  via a 4-element Retrodirective Ku/Ka array  1100 . 
         [0528]      FIG. 12 b    is a simplified block diagram for a communications payload (P/L) on a UAV for the communications at 4.9 GHz emergency band among the rescue team members. It is for on-board beam forming almost identical to those in  FIG. 12A , except
       1. A on-board multi-beam Tx beam forming network (BFN)  1225 B replacing a FDM demuxer  1225  for the foreground communications in public safety band   2. A on-board multi-beam Rx beam forming network (BFN)  1215 B replacing a FDMmuxer  1215  for the foreground communications in public safety band         
       End of Embodiment 4 
     Embodiment 5 
       [0531]    This embodiment presents architectures and methods of implementing UAV based communications with retrodirective antennas, ground based beam forming (GBBF), and WF muxing demuxing for feederlink equalizations. Equalizations comprise of calibrations and compensation for differential phases and amplitudes incurred to signals propagating through multiple paths. Several scenarios are presented as following;
       1. With GBBF and with retro-directive and onboard adaptive forward link equalization/optimization loop before WF demuxer in  FIG. 13   a;      2. Associated ground processing in  FIG. 13   b;      3. With GBBF and with retro-directive and on-ground adaptive forward link equalization/optimization loop before WF demuxer in  FIG. 14   a;      4. Associated ground processing in  FIG. 14   b;      5. DBFs in Ground processing facility in  FIG. 15 .       
 
         [0537]      FIG. 13 a    is a simplified block diagram for a communications payload (P/L) on a UAV for the communications at 4.9 GHz emergency band among the rescue team members. It is for Ground based beam forming (GBBF), same as the functional block diagrams in  FIG. 12 a   , except WF muxing/demuxing techniques are used for feeder-links calibrations and compensations. 
         [0538]    There are three major functional blocks; from top left and clockwise:
       1. forward link transmitting (Tx) payload  1320  at public safety bands for foreground communications,   2. feeder-link payload 1100
           i. forward link receiving (Rx) payload at Ku/Ka band for feeder-link communications and   ii. return link transmitting (Tx) payload at Ku/Ka band for feeder-link communications, and   
           3. return link receiving (Rx) payload  1310  at public safety bandsfor foreground communications.       
 
         [0544]    In the first major functional block on the top right for the forward link transmitting (Tx) payload  1320  at public safety band, as an example, for foreground communications; signals flow from right to left. The up-linked element signals  1102  received by the on board Ku array  1100  feature “element signals” properly processed by a GBBF designated for the 4 Tx elements 1222 in a public safety band. The uplink signals  1102  have been wavefront-muxed along with diagnostic signals in a GBBN facility, and are uplinked to a UAV via back channel. The received element signals are FDMde-multiplexed  1225  to recover WF muxed signals which are processed by a bank of adaptive equalizers  1324 A before connected to a WF demuxer  1324   dx.  Many outputs of the WF demuxer  1324   dx  are then frequency down converted, filtered and amplified  1224  before radiated by the 4 Tx subarrays D 1 , D 2 , D 3 , and D 4   1222 . There are no on board beam forming processing at public safety bands at all. Some of the outputs  1326  of the WF demuxer  1324   dx  are recovered diagnostic signals  1326  which will be processed by a diagnostic processor  1325  to map the recovered diagnostic signals into cost functions which must be positively defined individually. Total cost as sum of all cost functions are used by an optimization process  1323  iteratively based on a cost minimization algorithm in estimating a set of new weightings for the adaptive equalizers  1324 A in each iteration. When fully equalized the total cost for the current optimization shall become less than a small positive threshold. 
         [0545]    The second functional block depicted on the right side is the 4-element Retro directive antenna array at Ku/Ka band  1100 . 
         [0546]    The 3 rd  functional block is a return link P/L  1310  in public safety band for foreground communications. There are four Rx elements D 1 , D 2 , D 3 , and D 4   1212 ; each of which is connected by a LNA, a BFP, and an up-converter  1211  to Ku band. There are no beam-forming processors on board for antennas at public safety frequencies. The four received element signals after amplified and frequency up-converted to a common IF frequency band are connected to many input slices of a WF muxer  1314 . A few probing signals  1316  are also connected to many of the remaining slices of the WF muxer  1314  as diagnostic signals. The outputs, or the wavefront component (wfc) ports, are connected to a FDM mux  1215  with an output of muxed single stream signals  1101 , which is then power amplified and transmitted via a 4-element Retrodirective Ku/Ka array  1100  to a ground facility  1310  shown in  FIG. 13B . 
         [0547]    The forward link Tx payload and associated return link Rx payload for foreground communications may be in L/S band mobile communications band, 2.4 GHz ISM band, or other frequency bands. 
         [0548]      FIG. 13 b    depicts a functional flow diagram for ground processing facility  1310 , which include: 
         [0549]    1. receiving processing blocks;
       a. Ku receiving (Rx) frontend  411 R,   b. WF demuxing  1314   dx  and associated adaptive equalizer  1314   a  
           i. an iterative optimization loop with a diagnostic unit  1315  and an optimization processor  1313     ii. for equalization of feederlink in return link directions,   
           c. Rx DBF  781 ,   d. other Rx functions including gateway functions  782  interfacing with terrestrial networks  418  WF,       
 
         [0556]    2. transmit processing blocks;
       a. other transmitting (Tx) functions including gateway functions  752  interfacing with terrestrial networks  418  WF,   b. Tx DBF  751     c. WF muxing  1324   x,  and   d. Ku band transmitting (Tx) frontend  411 T       
 
         [0561]      FIG. 14 a    is a simplified block diagram for a communications payload (P/L) on a UAV for the communications at 4.9 GHz emergency band among the rescue team members. It is for Ground based beam forming (GBBF), same as the functional block diagrams in  FIG. 13A , except the adaptive equalization for the WF demuxing  1324   dx  are used for performed on ground as a pre-compensation scheme. 
         [0562]    There are three major functional blocks; from top left and clockwise:
       1. forward link transmitting (Tx) payload  1420  at public safety bands for foreground communications,   2. feeder-link payload  1100 
           iii. forward link receiving (Rx) payload at Ku/Ka band for feeder-link communications and   iv. return link transmitting (Tx) payload at Ku/Ka band for feeder-link communications, and   
           3. return link receiving (Rx) payload  1410  at public safety bands for foreground communications.       
 
         [0568]    In the first major functional block on the top right for the forward link transmitting (Tx) payload  1420  at public safety band, as an example, for foreground communications; signals flow from right to left. The up-linked element signals  1102  received by the on board Ku array  1100  feature “element signals” properly processed by a GBBF designated for the 4 Tx elements 1222 in a public safety band. The uplink signals  1102  have been wavefront-muxed along with diagnostic signals in a GBBN facility, and are up-linked to a UAV via back-channels (in feederlink). The received element signals areFDMde-multiplexed  1225  to recover WF muxed signals which are connected to a WF demuxer  1324   dx.  Many outputs of the WF demuxer  1324   dx  are then frequency down converted, filtered and amplified  1224  before radiated by the 4 Tx elements (or subarrays) D 1 , D 2 , D 3 , and D 4   1222 . There are no on board beam forming processing at public safety bands at all. 
         [0569]    Some of the outputs  1326  of the WF demuxer  1324   dx  are recovered diagnostic signals  1326  which will be processed by a diagnostic processor  1325  to map the recovered diagnostic signals into cost functions which must be positively defined individually. Processed diagnostic signals and/or derived cost functions will be relayed back to the ground processing facility via additional input slices  1316  of a WF muxer  1314  which is installed for the return link calibrations. 
         [0570]    Total cost as sum of all cost functions are used by an optimization process  1323  (in the processing facility) in estimating a set of new weightings for the adaptive equalizers  1324 A in each iteration. The iterative optimization processing is based on a cost minimization algorithm. When fully equalized, the total cost for the current optimization shall become less than a small positive threshold. 
         [0571]    The second functional block depicted on the right side is the 4-element Retro directive antenna array at Ku/Ka band  1100 . 
         [0572]    The 3 rd  functional block is a return link P/L  1410  in public safety band for foreground communications. There are four Rx elements D 1 , D 2 , D 3 , and D 4   1212 ; each of which is connected by a LNA, a BFP, and an up-converter  1211  to a common IF or Ku band. There are no beam-forming processors on board for the antenna elements  1212  at public safety frequencies. The four received element signals after amplified and frequency up-converted to a common IF frequency band are connected to many input slices of a WF muxer  1314 . A few probing signals  1316  are also connected to many of the remaining slices of the WF muxer  1314  as diagnostic signals. The outputs, or the wavefront component (wfc) ports, are connected to a FDM mux  1215  with an output of muxed single stream signals  1101 , which is then power amplified and transmitted via a 4-element Retrodirective Ku/Ka array  1100  to a ground facility  1310  shown in  FIG. 14B . The diagnostic signals  1316  will include information (derived data and/or received diagnostic waveforms  1326 ) on the feederlink uplink status. 
         [0573]    The forward link Tx payload and associated return link Rx payload for foreground communications may be in L/S band mobile communications band, 2.4 GHz ISM band, or other frequency bands. 
         [0574]      FIG. 14 b    depicts a functional flow diagram for ground processing facility  1310 , which include:
       1. receiving processing blocks;
           i. Ku receiving (Rx) frontend  411 R,   ii. WF demuxing  1314   dx  and associated adaptive equalizer  1314   a  
               a. an iterative optimization loop with a diagnostic unit  1315  and an optimization processor  1313     b. for equalization of feederlink in return link directions,   
               iii. Rx DBF  781 , and   iv. other Rx functions including gateway functions  782  interfacing with terrestrial networks  418 ; and   
           2. transmit processing blocks;
           i. other transmitting (Tx) functions including gateway functions  752  interfacing with terrestrial networks  418 ,   ii. Tx DBF  751     iii. WF muxing  1324   x,  
               a. an iterative optimization loop with a remote diagnostic Tx unit  1325  on UAV, relayed on-board information via  1315  and an optimization processor  1323     b. for adaptive equalizers  1324   a  of feederlink in forward link directions, and   
               iv. Ku band transmitting (Tx) frontend  411 T   
                 
         [0589]      FIG. 15  depicts an Rx DBF processing  781  and a Tx DBF processing  751  in a GBBF facility  1412 . The recovered baseband element signals  78105  by Ku Rx frontends  411 R are converted to digital formats by a bank of A/Ds  78101 , and replicated into N sets; each for a Rx beam which is characterized by a unique beam weight vector (BWV)  78106 . Each of the element signals is weighted in real time through a complex multiplier  78102  by a complex component of the BWV  78106 . The weighted sum of received element signals by a summer or combiner  78103  becomes one of the N beam outputs  78104  of a real time Rx beam specified by a BWV and the current array Geometry on the UAV. These N beam outputs  78104  are then sent for further receiving process  782  such as channelization, synchronization and demodulations before delivered to destinations including users connected via public network  418 . 
         [0590]    For the Tx DBF processing  751 , the signals flows are reversed. Signals from different sources are modulated, multiplexed, and grouped into multiple beam signals  752  designated to various beam positions to be delivered by the foreground communications Tx array  1222  on a UAV. Each beam signal after replicated into M copies or divided by a 1 to M divider  75103  is weighted respectively by m components of a BWV  75106 . The weightings are carried out by M complex multipliers  75102 . For N Tx beams there are N sets of weighted m element signals. The final set of the m element signals, as summations of the N sets of the individually weighted m element signals, are then converted to analogue formats by D/As 75101 before frequency up-converted and power amplified by Ku Tx front end  411 T. 
       End of Embodiment 5 
       [0591]      FIG. 16  features a small deviation for  FIG. 1 ; depicting a scenario of using three separated UAVs  120  as three mobile platforms for emergency and disaster recovery services; UAV M 1  for communications among rescue team members, UAV M 2  as emergency replacements of mobile and/or fixed wireless basestations for resident communications via their existing mobile phones and/or personal communications devices using wifi. The third UAV platform M 4  performs real time imaging and surveillances via passive RF sensors including bi-static Radars using satellite RF radiations as RF illumination sources. 
         [0592]    All three platforms are connected to a ground hub  110  via feeder-links in Ku and/or Ka band spectrum. The ground hub  110  will serve as gateways and have access to terrestrial networks  101 . As a result, rescue works in a coverage area  130  will have access to real time imaging, and communications among co-workers and dispatching centers connected by the hub  110 . Residents in disaster/emergency recovery areas  130  will also be provided with ad hoc networks of communications via their own personal devices to the outside world, to rescue teams, and/or disaster/emergency recovery authorities. 
         [0593]    The feeder-links of the three platforms M 1 , M 2 , and M 4  are identical in Ku and/or Ka bands. Only the three payloads (P/L) are different; the P/L on the first UAV M 1  enables networks for communications in public safety spectrum among members of rescue team; the P/L on the second UAV M 2  is to restore resident cell phone and/or fixed wireless communications at L/S band, and the P/L on the third UAV M 4  is an RF imaging sensor for real time surveillance. 
         [0594]    Three independent technologies are discussed; (1) retro-directive array, (2) ground based beam forming, and (3) wavefront multiplexing and demultiplexing (WF muxing /demuxing). Retro-directive links for feeder-links are to make the feeder links payload on UAVs to communicate with designated ground hubs more effectively, using less power, reaching hubs in further distances, and/or more throughputs. 
         [0595]    RF payloads may feature passive sensors such as RF radiometers or bi-static Radar receivers; both of which will feature architectures of ground based beam forming (GBBF), or remote beam forming (RBF), for UAV platforms  120 -M 4  supporting and accomplishing designed missions using P/L with smaller SW&amp;P. Multiple tracking beams from a Radar receiving array will be formed via a GBBF facility (not shown but similar to the one  412  in  FIG. 4 ) in the mobile hub  110 . Dynamic diagnostic beams from UAV M 4  may be used to facilitate the missions. 
         [0596]    For the functions of bi-static radar receivers, the UAV M 4  shall feature capabilities of capturing RF radiations from a satellite  140  via a direct path  141  and also those reflected by earth surfaces and objects on or near earth surface via reflective paths  142 . Correlations between the radiations from the direct path  141  and those from reflected paths provide the discriminant information on the targeted reflective surfaces near or on the earth surface. Thus the images of the RF reflected surfaces are derived. 
         [0597]    Many M 4  may be deployed concurrently. There are many choices for the selections of RF radiations from illuminating satellites, such as the satellite  140 , for various bi-static Radar applications. RF radiations at L-band from GNSS satellites at medium earth orbit (MEO) or Geo-synchronous earth orbit (GEO) may be selected by our UAV M 4  for global coverage. L/S band radiations from Low-Earth Orbit (LEO) communications satellites shall be considered as candidates. Strong Ku band radiations from many direct TV broadcasting satellite radiations or S-band Satellite Digital Audio Radios (SDARS) from satellites in GEO or inclined orbits may be used for land mass or near land mass coverage. Ka band spot beams near equatorial coverage from MEO/GEO satellites, C-band near global coverage from GEO satellite, UHF global coverage, and Ku band regional coverage may also be used concurrently for special missions using various radiations at multiple spectrums from different satellites reflected from same image coverage. These techniques are based on correlations among signals from two paths; the direct path signals as references for “Radar illuminations”, and reflected radiations as Radar returns from targeted areas or volumes near the earth surfaces. 
         [0598]    Multiple received signals from the array elements of the array on the UAV M 4  will be sent to the GBBF facility via back channels in a feeder link. Wavefront multiplexing and demuxing techniques will be applied for UAV M 4 , among many other applications for calibrating back channels in feeder-links, enabling a simple and cost effective GBBF. 
         [0599]    GBBF architectures are used for illustrations in here. However, similar RBF architecture shall be developed for the platforms which may be mobile, re-locatable, fixed, and/or combinations of all above to perform remote beam forming functions. 
         [0600]    The special features for the communications P/L&#39;s on UAVs are highlighted below. 
         [0601]    a. Retro-Directivity for Ku Feeder Links 
         [0000]    Ku-band arrays are used for UAVs as feeder link antennas to transfer all signals to and from L/S or C-band elements channels to a gateway where a GBBF processing will perform both Tx and Rx array functions including beam forming, beam steering, beam shaping, null steering, and/or null broadening for multiple concurrent beams. The Ku band “smart” arrays will feature retro-directivity via on-board analogue beam forming network (BFN) and beam controller technologies. The 3-dB beam widths are allocated less than 50° for a 2 dimensional 4-element array with element spacing ˜0.5 wavelengths. 
         [0602]    b. Remote beam forming network (RBFN) or ground based beam forming (GBBF). 
         [0603]    c. Digital beam forming (DBF) will be implemented remotely using FPGAs and PCs in the GBBF processing located at the gateway facility. The processing will perform far field beam forming for foreground arrays on UAVs. A single gateway will support multiple UAVs; at least one for communications network at 4.9 GHz for rescue teams; the other one for community in disaster areas, using existing cell phone bands. The UAVs for the local community operating at commercial cell-phone bands, and is to replace cell towers which may have been damaged by the disaster. 
         [0604]    d. Wavefront multiplexing/demultiplexing (WF Muxing/demuxing). WF muxing/demuxing transformations feature two unique characteristics; (1) orthogonality among WF vectors, and (2) redundancy and signals security. The first characteristics are utilized for (a) back-channel calibrations on feeder-link transmission for RBFN/GBBF, and (b) coherent power combining in receivers on signals from different channels on various UAV. The second characteristics are used for (c) secured transmissions with redundancies via UAVs. 
         [0605]    Furthermore, in most our examples, multiple communication channels in frequency domain as Frequency division multiplexed (FDM) channels and/or same frequency on various platforms (space division multiplexed) channels have been illustrated. WF muxing/demuxing may be implemented via concurrent channels in other conventional multiplexed channels such as TDM, CDM, or combinations of all above. 
         [0606]    e. Continuous Calibration Capability in GBBF 
         [0000]    Ground processing must have “current knowledge” of the geometry, location, and orientation of the array on board an air platform. Based on that, a real time continuous calibration capability is designed to compensate for effects caused by propagation variations, dynamic array geometry, unbalanced electronic channels, and/or aging electronics. The calibration will include adjustments on time delays, amplitudes and phases among the subarrays through modifications and adjustment on beam weight vectors (BWVs) obtained through real time optimization process. They are highly dependent on the array geometries. 
         [0607]    f. Cross-Correlation Techniques 
         [0000]    These techniques facilitate the calibration significantly improving efficiencies on equalizing multiple signal channels for various beam positions. With continuous calibration capability for distributed dynamic arrays, the precision knowledge of slow varying subarray positions and orientations may be relaxed significantly.