METHODS AND APPARATUS FOR MITIGATING FADING IN A BROADBAND ACCESS SYSTEM USING DRONE/UAV PLATFORMS

Abstract

Systems and methods for mitigating the effects of atmospheric conditions such as rain, fog, cloud in a broadband access system using drone/UAVs. In one embodiment, terminal and drone radio and transmission medium fixture sub-systems comprise multiple transmission media. In one embodiment, in response to changes in atmospheric conditions the drone radio sub-system switches transmission medium to reduce the effects of atmospheric conditions. In another embodiment, the terminal and drone radio sub-systems equalize the data rates among terminals in response to changes in atmospheric conditions observed by different terminals. In another embodiment, the drone radio sub-system adjusts the transmit power on the downlink to different terminal according to fading due to atmospheric conditions on each link.

Claims

1. A drone configured to provide broadband access to one or more terminals, the drone comprising: at least one transmission medium fixture comprising a plurality of transmission mediums configured to provide coverage to one or more terminals; wherein various ones of the plurality of transmission mediums are associated with different resistances to different fading conditions; at least one radio sub-system configured to: demodulate and decode one or more first signals received from the one or more terminals; and modulate and transmit one or more second signals to the one or more terminals; and a drone switching sub-system configured to switch data received at the drone to another receiving unit of the one or more terminals and/or one or more drones; wherein the drone switching sub-system is configured to select a transmission medium based on a measured fading condition.

2. The drone of claim 1, wherein: the one or more terminals comprise one or more ground-based mobile terminals; the drone radio sub-system is further configured to determine an amount of transmission resources to be allocated to one or more downlinks of the different ones of the one or more ground-based mobile terminals to equalize a data rate among the different ones of the one or more ground-based mobile terminals according to a fairness criterion; and the drone switching sub-system further comprises a scheduler, the scheduler configured to schedule the determined amount of transmission resources to the downlink of the different ones of the one or more ground-based mobile terminals.

3. The drone of claim 2, wherein the drone radio sub-system is further configured to: determine a change on an uplink signal quality received from different ones of the one or more ground-based mobile terminals due to one or more atmospheric conditions; and determine an amount of transmission resources to be allocated to an uplink of the different ones of the one or more terminals to equalize a data rate among the different ones of the one or more terminals according to at least one fairness criterion; and the scheduler is further configured to: schedule the determined amount of transmission resources to the uplink of the different ones of the one or more terminals; and inform the different ones of the one or more terminals of respective scheduled transmission resources.

4.-5. (canceled)

6. The drone of claim 1, wherein the drone radio sub-system is further configured to: determine a change in an amount of power allocated on a downlink to at least one of the one or more terminals to equalize the data rate among different terminals according to at least one fairness criterion; and adjust the power allocated to the downlink of to one or more of the one or more terminals.

7. The drone of claim 6, wherein the drone radio sub-system is further configured to: encode terminal data; map the coded bits onto constellation symbols; scale the coded symbols from each terminal destined to different antenna elements to form a beam toward a respective terminal; sum the scaled coded symbols for different terminals destined to a same antenna aperture to form multiple beams, one toward each respective terminal; modulate the resulting symbols onto the selected transmission medium and transmit the resulting signal through the corresponding antenna aperture.

8. The drone of claim 7, wherein the drone radio subsystem is further configured to choose the scale for coded symbols for each terminal to adjust the power sent to a terminal on the respective downlink.

9. A method of providing broadband access using a plurality of drones, the method comprising: measuring a signal quality metric for one or more terminals of a plurality of terminals; comparing the measured signal quality metric versus one or more threshold values; determining if the signal quality metric of the one or more terminals has degraded due to one or more atmospheric conditions; and select a different transmission medium when the signal quality metric of the one or more terminals has degraded.

10. The method of claim 9, further comprising: determining a number of transmission resources that an uplink and downlink to the one or more terminal needs in order to equalize the throughput to different ones of the plurality of terminals according to a specified fairness criterion; informing a scheduler of the allocated number of transmission resources for a terminal link of the one or more terminals; and sending a message to one or more terminals comprising respective uplink transmission resource allocations.

11. The method of claim 9, further comprising switching to a second transmission medium to mitigate atmospheric-related fading.

12. The method of claim 9 further comprising adjusting a power allocated to each terminal on a downlink according to a change in the measured signal quality metric.

13. A mobile terminal, comprising: a mobile terminal radio sub-system comprising at least one transmission medium fixture configured to receive data signaling on at least two transmission mediums having different resistance to atmospheric effects, the mobile terminal radio sub-system configured to: demodulate and decode one or more first signals received on at least one transmission medium of the at least two transmission mediums from at least one of one or more drones; responsive to a switch instruction, the at least one transmission medium fixture switches to a different transmission medium of the at least two transmission mediums.

14. The mobile terminal of claim 13, wherein the mobile terminal radio sub-system is further configured to: measure a received downlink signal quality to determine a signal quality change due to atmospheric conditions; and send the measured signal quality to the at least one radio sub-system of the one or more drones.

15. The mobile terminal of claim 13, wherein the mobile terminal radio sub-system is further configured to measure a change in a received downlink signal quality to determine a signal quality change due to one or more atmospheric conditions; and send the measured change in a received downlink signal quality to the drone radio sub-system.

16. The mobile terminal of claim 13, wherein the mobile terminal radio sub-system is further configured to: measure a received downlink signal quality to determine a change in signal quality due to one or more atmospheric conditions; and send the measured signal quality to at least one drone.

17. The mobile terminal of claim 13, wherein the one or more atmospheric conditions are selected from the group consisting of: (i) fog, (ii) clouds, and (iii) rain.

18. (canceled)

19. The mobile terminal of claim 13, wherein the mobile terminal radio sub-system is further configured to: receive a schedule of transmission resources to use for communication with at least one drone; and configure communication to the at least one drone based on the received schedule.

20. The mobile terminal of claim 13, wherein the measured signal quality comprises a signal to interference plus noise ratio (SINR).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In the following figures, similar components are identified using the same reference label. Multiple instances of the same component in a figure are distinguished by inserting a dash after the reference label and adding a second reference label.

[0024] FIG. 1 is an exemplary block diagram of a drone/Unmanned Aerial Vehicle (UAV) based broadband access to internet system.

[0025] FIG. 2A-2B are block diagrams of exemplary drone and ground/mobile terminal radio sub-systems.

[0026] FIG. 3 is an exemplary diagram of drone based broadband access system using multiple transmission media to provide coverage to an area.

[0027] FIG. 4 is a flow chart illustrating an exemplary process to adjust one or more data rates on the links between terminals and the drone in response to rain or other atmospheric conditions.

[0028] FIG. 5 is a flow chart of an exemplary process to switch a transmission medium between a drone and a terminal to mitigate fading due to e.g., atmospheric conditions such as rain, fog, and/or clouds.

[0029] FIG. 6 is a block diagram of an exemplary apparatus configured to control transmission power on one or more downlinks to different terminals and further configured to form beams toward the one or more different terminals.

[0030] FIG. 7 is a flow chart of an exemplary process to adjust power transmitted on one or more downlinks to one or more different terminals in response to changes in atmospheric conditions such as, e.g., rain, fog, and/or clouds.

[0031] All Figures Copyright 2014 Ubiqomm, LLC All rights reserved.

DETAILED DESCRIPTION

[0032] Reference is now made to the drawings, wherein like numerals refer to like parts throughout.

[0033] In view of the challenges and hurdles in both expense and access to remote, poor or otherwise underserved regions, there exists a need for improved broadband access. Accordingly, a system that has much lower hardware cost, has much lower launch/deployment cost, and is more easily scalable is needed.

[0034] Until recently drones, also known as Unmanned Aerial Vehicles (UAVs), have been extensively used by military, as well as for some scientific applications such as weather information gathering. Commercial applications of drones/UAVs include package delivery systems, video gathering systems, and communications systems. This disclosure describes aspects of a communications system design that are optimized for using drones/UAVs as the communications platform. Since drones/UAVs have the capability to fly at much lower altitudes than satellites do, such drone systems have an exemplary benefit of not needing the expensive space qualification of the satellite systems. Furthermore, drones/UAVs also do not need the expensive launch systems of satellites. Since the drone/UAV hardware cost is relatively small compared to satellites, and there is less of a launch risk, then there is a reduced need for additional insurance costs. Principles of the present disclosure therefore provide high capacity drone/UAV based broadband communication systems. As such, the relatively low cost of the drone/UAV hardware and operation cost, and its high capacity result in a low cost broadband delivery system.

[0035] Another exemplary advantage of a drone/UAV system configured according to the present disclosure over satellite systems is the low communication signal delay achievable by the drone/UAV systems. For instance, geo-stationary satellites typically have a round trip communication signal delay from ground to the satellite and back to ground of about 0.5 seconds which significantly impacts the quality of services that require low round trip delays. Even high altitude drones/UAVs (e.g., altitudes of 25 kilometers), would typically have a round trip communication signal delay of about 2 milliseconds to terminals on the ground for distances up to 300 kilometers from the drone. Accordingly, the low delay of drone/UAV based system of the present disclosure may enable similar real time quality as compared to terrestrial broadband access systems.

[0036] Another exemplary advantage of drones (configured according to the present disclosure) is that the drones may be deployed one at a time in areas with radiuses of 300 km or less and immediately provide service within the drone's footprint. In contrast, satellite systems may need to cover a wide area before service may be provided (such as a large part of the CONUS (CONtinental US) in the case of geo-satellite systems, or most of the earth in the case of LEO (Low Earth Orbit) satellite systems). Therefore, drone based systems offer improved scalability when compared to satellite systems, as a network provider can send one drone and start service in its footprint, test the market acceptance of the service, and then send more drones in areas that need service. Furthermore, a network provider could deploy the drones in only areas of the country where there is a high demand for the service. In the remainder of this disclosure we use the term drone to refer to both drones and UAVs. In addition, it should be noted that principles of the present disclosure may be equally applied to other types of aerial vehicles. For example, blimps or balloons may be implemented alternatively, or in addition to, the drones as discussed herein, to provide the broadband access system. Additionally, while the disclosed embodiments are described with respect to UAVs, it should be appreciated by those of ordinary skill in the related arts that drones are by no means limited to aerial operation; drones may include watercraft, land-based vehicles, submersibles, and even spacecraft variants, such implementations being within the skill of an ordinary artisan, given the contents of the present disclosure.

[0037] FIG. 1 illustrates one exemplary drone 110 configured according to the present disclosure. In one embodiment, each drone 110 has a drone radio sub-system 112 and at least one drone transmission medium fixture 114. The physical medium used to transmit the information may be electromagnetic waves (e.g., radio) in different frequency bands or Free Space Optics (FSO). The term transmission medium aperture refers to an antenna aperture when considering electromagnetic waves, and refers to an optical lens when considering FSO. Therefore, the aperture of the transmission medium fixture may be an antenna when using electromagnetic waves, or an optical aperture when using FSO. As shown in FIG. 2A, the drone radio sub-system 112 includes four (4) sub-systems: the receiver 318 that demodulates and decodes the signal received from an aperture of the transmission medium fixture 114; the transmitter sub-system 316 that modulates the data received from processor 314 and sends the resulting signal through an aperture of the transmission medium fixture 114; the processor sub-system 314 that carries out functions such as configuring the receiver 318 and transmitter 316 sub-systems, processing the data received from the receiver 318 sub-system, determining the data to be transmitted through the transmitter sub-system 316, as well as controlling the transmission medium fixture 114; and the memory sub-system 312 that contains program code and configuration, and system parameter information that are accessed by the processor 318.

[0038] As shown in FIG. 2A, the radio sub-system transmitter 316 and receiver 318 sub-systems support multiple frequency bands, F.sub.1 . . . F.sub.n, as well as FSO, and each sub-system comprises multiple TX and RX units corresponding to each supported frequency band F.sub.1 . . . F.sub.n or FSO. As will be discussed below, the specific frequency band, F.sub.1 . . . F.sub.n, or FSO, that is used for communication to a specific Ground Terminal (GT) depends on the relative distance of the GT to the drone, as well as the atmospheric conditions at a given time. As used herein, a ground terminal may refer to a fixed terminal or a terminal on a mobile platform such as a vehicle or an aircraft.

[0039] In one embodiment, a mechanism configured to connect the appropriate transmitter and receiver frequency or FSO units to the processor is disclosed. In one implementation, the radio sub-system 112 comprises a switching sub-system 315 that switches the data from processor 314 to the appropriate radio transmitter TX unit to modulate the data using the appropriate medium and to transmit the modulated signal through the corresponding medium aperture. Similarly, a switching sub-system 315 switches the data from the appropriate RX units of the receiver sub-system 318 to the processor sub-system 314. The transmission medium fixture 114 as shown in FIG. 2A includes a number of apertures supporting frequency bands F1 to Fn and FSO. The TX and RX units of the transmitter and receiver sub-systems are connected to the aperture corresponding to the same frequency band or FSO.

[0040] Depending on the altitude of the drone 110, each drone 110 may cover an area on the ground with a radius of tens of kilometers to hundreds of kilometers or more. In one exemplary embodiment, drones 110 are configured to communicate with at least three kinds of ground terminals: one type of terminal is the Ground Terminal (GT) 120 (see FIG. 1), such as terminals at home or enterprises to provide internet connectivity to a home or enterprise; a second type of terminal is installed on mobile platforms such as vehicles or airplanes; a third type is what is referred to as the internet Gateway (GTW) 130 which is connected to the internet. GTs 120 transmit and receive data from the internet using the drone network as an intermediary connection to network infrastructure. The drone's 110 radio sub-system 316 aggregates traffic received from the GTs 120 and may aggregate traffic received from multiple GTs 120 and send the aggregated data to the internet via one of the GTWs 130. Therefore, in one embodiment, the GTWs 130 provide higher data rates from/to drones than the data rates provided from the GTs 120. In these embodiments, the gain of the GTW medium aperture sub-system is larger than that of the GT 120, and the GTW 130 transmitter transmits at a higher power than the GTs 120.

[0041] As shown in FIG. 2A, drone 110 further comprises a drone switching sub-system 116. The switching sub-system 116 may route data received from one GT 120 to another GT 120 in the footprint of the drone, or from one GT 120 to a GTW 130 which is in turn connected to the internet 136.

[0042] As shown in FIG. 2B, in one embodiment, the GT 120 is configured with two main sub-systems, a ground/mobile terminal radio sub-system 122, and a ground/mobile terminal transmission medium fixture 124. The GT radio sub-system 122 comprises four (4) sub-systems: the receiver 418 that demodulates and decodes the signal from drone medium aperture sub-system 124 the transmitter sub-system 416 modulates the data and sends the resulting signal through an aperture of the transmission medium fixture 124; the processor sub-system 414 is configured to execute software to perform various functions (such as configuring the receiver 418 and transmitter 416 sub-systems, processing the data received from the receiver sub-system 418, determining the data to be transmitted through the transmitter sub-system 416, as well as controlling the transmission medium fixture 124, etc.); and the memory sub-system 412 contains program code and configuration data, and system parameters information that are accessed by the processor 414. The switching sub-system 415 connects the processor to the appropriate transmitter or receiver units of the transmitter 416 and receiver 418 sub-systems.

[0043] The link between the drones and the GTs 120 may operate in different parts of the spectrum, F.sub.1 . . . F.sub.n, or FSO. Since different parts of the spectrum are susceptible to atmospheric effects to different degrees, the range of the signal from the drone 110 to the ground terminals will depend on the particular frequency band being used. Frequencies above 10 GHz may suffer higher losses from rain fade than frequencies below 10 GHz; generally, higher frequencies incur higher fades. Frequencies above 10 GHz may also incur attenuation due to atmospheric gases such as oxygen and carbon dioxide (CO.sub.2), as well as water vapor. Optical signals suffer primarily from fog and clouds.

[0044] In one embodiment of the present disclosure, a mechanism that detects and mitigates the effects of atmospheric losses is disclosed. In one variant, the disclosed mechanisms also optimize trade-offs between frequencies and ranges (e.g., higher frequencies have lower ranges). Specifically, different RF frequencies and optical links have different ranges, therefore the disclosed apparatus efficiently creates a wide coverage area using the different available frequency and optical bands.

[0045] FIG. 3 shows an exemplary embodiment where two frequency bands F.sub.1 and F.sub.2 and FSO are used by the drone 110 and the GTs 120. The coverage area in the footprint of the drone 110 is divided into a number of rings. The innermost ring that is served by all frequency bands as well as FSO has the smallest range. The next two rings shown in FIG. 3 may be too far for FSO to reliably reach. As shown in FIG. 3, frequency band F1 has the largest coverage ring. In one embodiment, F.sub.1 has a lower frequency than F.sub.2; alternatively, the frequency band F.sub.1 may be configured with a higher EIRP (Effective Isotopic Radiated Power) than F.sub.2. GTs 120 in the outermost ring of the coverage area would be served using the F.sub.1 frequency band, GTs 120 in the ring in the middle would be served using either F.sub.1 or F.sub.2 spectrum, and GTs 120 that are in the innermost ring could be served using F.sub.1, F.sub.2 or FSO. Note that more than two frequency bands may be used by the drone 110 and GTs 120 and the embodiments described in this disclosure extend to any number of frequency bands and/or FSO, etc.

[0046] In one implementation, rain fade may be mitigated by allocating enough link margin in the link budget for the different frequency bands based on their fading characteristics. In some cases, relying on allocating adequate link margin to mitigate rain or other atmospheric effects may be undesirable (e.g., where desired reliability would require excessive amounts of margin, etc.) Below, additional exemplary techniques are described to reduce the amount of link margin needed to mitigate rain and other atmospheric effects.

[0047] In one aspect of this disclosure, the drone 110 and GT radio sub-systems 122 measure a signal quality metric, such as SINR (Signal to Interference plus Noise Ratio), from the received messages from GTs (such as GTs 222, 232, and 212 shown in FIG. 1). The data rate from/to the drone 110 is adjusted according to the measured SINR. If the SINR received at a drone 110 or at a GT 120 degrades due to rain fade, resulting in a reduction in the data rate between the drone 110 and the GT 120, then in one exemplary implementation the degradation may be remedied by allocating more time slots or more frequency to the specific affected GT 120 to compensate for the lower data rate on the corresponding link. Suppose, for example, that the data rate between the drone and a specific GT 120 is reduced by a factor of four (4) due to rain fade. If four (4) times the number of time slots is allocated to the impacted GT 120, then the overall throughput the GT 120 experiences is the same as without any rain fade. In one variant, if more time is allocated to a GT 120 in rain fade, then at least some time is taken from other GTs 120. However, if only a small fraction of GTs 120 in the footprint of a drone 110 are impacted by atmospheric related fade, then taking time slots from other GTs 120 and allocating more time slots to the GT 120 in fade will reduce the throughput of the GTs 120 by a very small amount. The foregoing exemplary scheme (adjusting the number of time slots assigned to each GT 120 according to the data rate between the GT 120 and the drone) aims to equalize the throughput between different GTs 120 which have been assigned the same grade of service in terms of throughput. Those of ordinary skill in the related arts, given the contents of the present disclosure, will readily appreciate that similar schemes may be implemented based on e.g., frequency, spreading factors, etc.

[0048] FIG. 4 describes a flow chart of the exemplary scheme used to adjust the amount of time allocated to the link between a GT 120 and a drone 110 in response to rain or other atmospheric effects. In step 402, the drone 110 or GT radio sub-system 122 measures a signal quality metric (such as SINR) based on the received messages. Common examples of quality metrics may include without limitation: Received Signal Strength Indication (RSSI), Signal to Noise Ratio (SNR), Bit Error Rate (BER), Packet Error Rate (PER), Block Error Rate (BLER), etc. In one embodiment, the drone 110 or GT radio sub-system 122 monitors a change in the SINR between the received messages.

[0049] The changes in signal quality metrics may be monitored continually between the received messages and/or at periodic intervals. In one implementation, the periodic intervals may be dynamically changed. The periodic interval may be based on a current measurements and/or an amount of change between measurements (between messages and/or over a time period). For example, signal quality measurements may be provided at different intervals based on how quickly the signal quality changes. A rapidly fading channel requires faster updates, whereas a relatively stable radio link can provide less frequent updates.

[0050] In still other embodiments, the signal quality metrics may be polled or otherwise provided as requested. For example, in certain situations the drone 110 or GT 120 may be queried, and the resulting collection of measurements may be used for e.g., network optimization, initial deployment coverage assessment, handover assessment, redundancy coverage assessment, etc.

[0051] In step 404, the GT radio sub-system 122 sends the signal quality metric on the uplink to the drone radio sub-system 112. In one embodiment, the measured signal quality metric may be sent on the uplink on a periodic basis to the drone radio sub-system 112 or sent when the measured signal quality metric exceeds one or more threshold values. In one implementation, the measured signal quality metric comprises the measured SINR of one or more previously received messages. In another variant, the measured signal quality metric comprises a running average of SINR over multiple received messages.

[0052] In other embodiments, the drone radio sub-system 112 sends the signal quality metric on the downlink to the GT radio sub-system 122. Similarly, the measured signal quality metric may be sent on the downlink on a periodic basis to the GT radio sub-system 122 or sent when the measured signal quality metric exceeds one or more threshold values.

[0053] In step 406, the drone radio sub-system 112 or GT radio subsystem 122 determines the effective performance that the GT 120 or drone 110 will receive (or can be expected to receive), based on the measured signal quality. Common examples of performance may include e.g., the amount of data (e.g., throughput), the delay in data (e.g., latency), retransmission metrics, predicted BER (or PER, BLER), etc. By determining the effective performance, the drone radio sub-system 112 or GT radio subsystem 122 can determine whether the radio link is adversely impacted by atmospheric effects.

[0054] In some embodiments, the drone radio sub-system 112 or GT radio subsystem 122 may additionally consider other factors in addition to effective performance. For example, such factors may include e.g., historic performance (e.g., based on time of day and/or position), the rate of change of performance (e.g., to detect impending fast fading), known network traffic demands (e.g., peak hour demands, etc.)

[0055] In step 408, the drone radio sub-system 112 or GT radio subsystem 122 determines the amount of additional resources that must be allocated to the radio link. For example, a drone radio sub-system 112 may mitigate atmospheric effects in order to provide a similar grade of service for an impacted GT 120 as other GTs 120 with the same promised grade of service.

[0056] Those of ordinary skill in the related arts will readily appreciate that resources are broadly used to refer to any physical or virtual element of limited availability within the network. Common examples of resources include e.g., time slots, frequency bands, spreading codes, bandwidth, transmission power, etc. In one embodiment, the additional resources are allocated using one or more fairness criterion. In one implementation, fairness criterion refers to the scheme for allocating an amount of resources to different terminals. One exemplary fairness criterion, referred to as equal grade of service scheduling, attempts to provide the same average throughput to all terminals. To achieve equal grade of service more time is allocated to terminals that have lower signal quality and/or which receive data at lower data rates. Another exemplary fairness criterion referred to as equal grade of time scheduling allocates the same amount of time to multiple GTs 120. In equal grade of time scheduling, different GTs 120 will receive different average data throughputs commensurate with their received signal quality.

[0057] In some implementations, the allocation can take effect immediately. Alternatively, in some implementations, an appropriate time for the allocation to take effect must be determined. For example, in some instances, the radio link between the drone and/or GT is subject to broader network or usage considerations such as e.g., network traffic, neighboring interference and/or other radio links, etc. Under such conditions, the drone and/or GT must coordinate the allocation so as to e.g., minimize impact on neighbors, or optimize overall benefits gained.

[0058] In step 410, the drone radio sub-system 112 or GT radio subsystem 122 changes the scheduler parameters that determine how many resources are allocated to each GT 120. Responsively, the communication between the drone 110 and each GT 120 is configured in accordance with the scheduled parameters, and thereafter the allocation can take effect. In some embodiments the allocation change may occur at e.g., a prescribed effective time (e.g., via a time stamp), at a predetermined time (e.g., at the start of the next cycle, frame, etc.), responsive to a trigger event (such as signaling), etc.

[0059] While the foregoing example is presented with respect to a drone radio sub-system 112 and a GT radio subsystem 122, the concepts described therein can be generalized to a network of multiple drones and/or GTs. Moreover, it should be further appreciated by those of ordinary skill in the related arts given the contents of the present disclosure, that various steps of the method may be performed by other entities; for example, an evaluation of fairness criterion may be performed by a drone or GT network controller, etc.

[0060] Another exemplary method may mitigate atmospheric fade by switching a terminal that is operating at a higher frequency band to a lower frequency band. As previously noted, different frequency bands have different susceptibility to atmospheric effects. For example, a terminal using the higher frequency F.sub.2 that is experiencing excessive rain fade is configured to switch to a lower frequency band F.sub.1 (or another frequency with more rain fade margin). The GT radio sub-system 122 makes measurements of a signal quality metric such as SINR (Signal to Interference plus Noise Ratio) on the received messages from the drone 110 and reports the measured SINR or another signal quality to the drone radio sub-system 112. In one implementation, if the measured SINR falls below a certain threshold, then the drone radio sub-system 112 may initiate switching the communication link to the second frequency band F.sub.1 by sending a message configured to inform the GT 120, of the switch to the alternative frequency. Since the second frequency incurs less rain fade, the link quality will improve by switching to a second frequency. Note that the drone radio sub-system 112 may also decide to switch the operating frequency to a second frequency based on the SINR or another signal quality metric measurement at the drone receiver. Similarly, with regards to FSO which suffers from fog and clouds, the system will switch from FSO to a radio frequency mode, F.sub.1 or F.sub.2 when the fade in FSO mode is excessive. This hybrid drone radio sub-system construction allows use of multiple transmission media in order to provide high throughput, and at the same time optimizes the use of each medium according to the rain and other atmospheric conditions. Note that switching the GTs 120 to the medium that has the least rain/atmospheric loss at a given time also allows the system to maximize the overall system throughput.

[0061] FIG. 5 is a flow chart of an exemplary mechanism useful for detecting rain and other atmospheric fades, and to switch the transmission medium to a second medium. In step 502, the drone radio sub-system 112 or GT radio subsystem 122 measures a signal quality metric, such as SINR. The signal quality metric is measured from one or more communications between the drone and the GT. The measured signal quality metric may be measured from one or more particular types of received messages. Alternatively, the signal quality metric may be measured on any message received at a determined periodic interval. The periodic interval may be set as a predetermined time or may be configured to dynamically change based on one or more parameters. In one such implementation, the periodic interval is changed based at least in part on the measured signal quality metric.

[0062] In step 504, the measured signal quality metric is reported to the drone radio sub-system 112 or GT radio subsystem 122. The reported measured signal quality metric may comprise a measurement of a particular communication itself or may comprise a change in a measured signal quality metric. The GT radio sub-system 122 may be configured to report the measured SINR on a periodic basis, reported upon the measured SINR exceed a threshold, or a combination of both. In one implementation, the periodic basis is configured to dynamically change based at least in part on the value of the measured and/or reported SINR.

[0063] In step 506, the drone radio sub-system 112 or GT radio subsystem 122 determines whether the measured signal quality metric is below a certain threshold indicating excessive fade due to rain, fog, cloud or other effects. If the measured signal quality metric is below a threshold then the drone radio sub-system 112 or GT radio subsystem 122 switches the transmission medium to an alternate transmission medium (e.g., from F.sub.2 to F.sub.1, or from FSO to a radio frequency mode, F.sub.1 or F.sub.2). In some embodiments, the drone radio sub-system 112 or GT radio subsystem 122 requests that the transmission medium be switched (causing another supervisory entity to responsively perform the switch). For example, the drone radio subsystem 112 may decide to request a transmission medium change based on uplink SINR measurements at the drone receiver. Alternatively, the GT radio subsystem 122 may request a switch of the transmission medium based on the downlink SINR measurement by sending a message to the drone 110 with information on the new transmission medium and the time to switch to the new medium. One exemplary benefit of having the drone 110 decide when to switch transmission medium, as shown in FIG. 5, is that the drone may have information on all traffic and thus may be better suited to schedule GTs 120 on different media, while balancing the traffic among different media. It is appreciated however, that in GT initiated embodiments, the GT 120 may have information which the drone 110 may not be aware of (e.g., application requirements, etc.) In still other embodiments, a core network entity may manage connectivity, handovers, etc.

[0064] Another aspect of the present disclosure is the use power control to mitigate effects of atmospheric fade on the downlink. In one exemplary embodiment of the drone radio and transmission medium fixture design, the drone radio sub-system 112 and each antenna aperture for each frequency generate multiple beams to different GTs 120. The total power transmitted by an antenna aperture is configured to be sharable among the multiple beams formed toward different GTs 120. The GTs 120 served by a drone 110 may be located in a wide geographic area where all GTs 120 are not simultaneously affected by e.g., rain. When some GTs 120 experience atmospheric fade, the drone radio sub-system 112 may allocate more power to the downlink on the beam toward the affected GT 120. The GT radio sub-system 122 measures SINR received on the downlink pilot signals and reports the measured values to the drone 110 in signaling messages sent to the drone 110 on the uplink. The drone radio sub-system 112 determines the amount of rain fade based on the expected SINR values in absence of rain. The drone radio sub-system 112 then may increase the power allocated to the downlink of the affected GTs 120 (i.e., whose received SINR have decreased due to rain fade). Note that even in the power control scheme just described, in one exemplary implementation, certain power margins are allocated in the link budget of the downlink from the drone 110 in order to compensate for rain fade. However, using power control and allocating more power only on the downlink beams to GTs 120 in rain fade, the rain fade margin in effect is shared among different GTs 120, and therefore may result in less link margin being allocated to rain fade as compared to a scheme where each downlink is allocated its own dedicated rain fade margin. The power control based rain fade mitigation scheme, therefore, may significantly reduce the required rain fade margin, thereby resulting in a more efficient system. The above mentioned exemplary power control based rain fade mitigation scheme may increase effectiveness in streaming services where the traffic mainly flows on the downlink to the terminal.

[0065] FIG. 6 is a block diagram of an exemplary modulation and power control sub-system for the transmitter (TX) unit of FIGS. 2A and 2B. In one embodiment, the parameters of FIG. 6 are configured such that antenna beams are formed simultaneously toward as many as M terminals using an antenna aperture comprised of N antenna elements. Those of ordinary skill in the related arts, given the contents of the present disclosure, will readily appreciate that other antenna configurations may be used, the foregoing configuration being purely illustrative. The data for the j-th terminal is encoded using error correction coding block 610-j, and then mapped onto constellation symbols in block 612-j, as shown for terminals 1 and M. Coded data symbols for the j-th terminal, denoted by S.sub.j, are scaled by coefficients C.sub.jk where k is the index of the antenna element. Coefficients C.sub.jk are designed to form beams toward each terminal. The scaled symbols from different terminals that are destined to the same antenna element are then summed using the summing device 614-k, where k is the index of the summer corresponding to the k-th antenna element. The output of the summer 614-kis then amplified and up converted using block 616-k and then sent to antenna element 618-k.

[0066] FIG. 7 is a flow chart of an exemplary power control based mechanism to mitigate rain fade. In step 702, the GT radio sub-system 122 measures received SINR or some other signal quality metric from the pilot signals on the downlink. In step 704, the GT radio sub-system 122 sends the measured SINR to the drone radio sub-system 112 in a message on the uplink. In step 706, the drone radio sub-system 112 compares the received SINR measurement from the GT 120 against a target SINR. If the measured SINR is smaller than the target, then in step 708 the drone radio sub-system 112 increases the power on the downlink to the specified GT 120. If the measured SINR is above the target, then in step 710 the drone radio sub-system 112 decreases the power on the downlink to the specified GT 120.

[0067] It will be recognized that while certain aspects of the disclosure are described in terms of a specific sequence of steps of a method, these descriptions are only illustrative of the broader methods of the disclosure, and may be modified as required by the particular application. Certain steps may be rendered unnecessary or optional under certain circumstances. Additionally, certain steps or functionality may be added to the disclosed embodiments, or the order of performance of two or more steps permuted. All such variations are considered to be encompassed within the disclosure disclosed and claimed herein.

[0068] While the above detailed description has shown, described, and pointed out novel features of the disclosure as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the disclosure. This description is in no way meant to be limiting, but rather should be taken as illustrative of the general principles of the disclosure. The scope of the disclosure should be determined with reference to the claims.