Patent Publication Number: US-11026188-B2

Title: Power control method for systems with altitude changing objects

Description:
PRIORITY CLAIM 
     The present application is a divisional of U.S. Nonprovisional patent application Ser. No. 16/002,377, titled “Power Control Method For Systems With Altitude Changing Objects,” filed Jun. 7, 2018, which claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 62/516,651, titled “Power Control Method for Cellular Systems with Airborne Assets,” filed Jun. 7, 2017. Applicant claims priority to and the benefit of each of such applications and incorporate all such applications herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates generally to antenna systems and, more particularly, antenna systems for communicating with networks from altitude changing objects. 
     BACKGROUND 
     Cellular networks have been designed and implemented with the intent of servicing terrestrial based customers. Cellular communication towers (“nodes”) are located and spaced to provide the necessary coverage taking into account terrain characteristics such as blockage due to hills and other obstructions. In urban centers, where high rise buildings are prevalent, nodes can be located to provide the coverage for cellular customers located in the upper floors. Distributed Antenna Systems (DAS) infrastructure is also installed in many high-rise buildings to re-distribute cellular signals for use indoors. Prior to installing a cellular network, electromagnetic (EM) simulations can be performed to determine cellular antenna system characteristics and to verify proper cell signal coverage in the intended region. The recent increase of drone usage and other systems capable of variable altitudes provide a new challenge for cellular network operators with regard to interference mitigation between the drone and/or other systems with variable altitude and terrestrial users as well as drones and adjacent nodes. 
     SUMMARY 
     Aspects and advantages of embodiments of the present disclosure will be set forth in part in the following description, or may be learned from the description, or may be learned through practice of the embodiments. 
     One example aspect of the present disclosure is directed to a communication system for an altitude changing object. The communication system can include an antenna system having one or more antennas. The one or more antennas can be associated with a single fixed radiation pattern. The communication system can include one or more processors configured to execute a control routine to perform operations. The operations can include obtaining data indicative of one or more communication parameters associated with the altitude changing object. The operations can include determining a transmit power for each of the one or more antennas based at least in part on the one or more communication parameters. The operations can include controlling the antenna system based at least in part on the transmit power to communicate with a node in the communication network. 
     Other example aspects of the present disclosure are directed to systems, methods, devices, and processes associated with antenna systems for altitude changing objects. 
     These and other features, aspects and advantages of various embodiments will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the related principles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Detailed discussion of embodiments directed to one of ordinary skill in the art are set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  depicts an example altitude changing object in a network according to example embodiments of the present disclosure; 
         FIG. 2  depicts an example altitude changing object in a network according to example embodiments of the present disclosure; 
         FIG. 3  depicts an example altitude changing object at multiple altitudes in a network according to example embodiments of the present disclosure; 
         FIG. 4  depicts example data flow in a communication system according to example embodiments of the present disclosure; 
         FIG. 5  depicts frequency selection in a communication system according to example embodiments of the present disclosure; 
         FIG. 6  depicts example parameters used as part of a control scheme for controlling communication between an altitude changing object and a network according to example embodiments of the present disclosure; 
         FIG. 7  depicts a flow diagram of an example method according to example embodiments of the present disclosure; 
         FIG. 8  depicts a flow diagram of an example method according to example embodiments of the present disclosure; and 
         FIGS. 9, 10, and 11  depict aspects of an example modal antenna according to example embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the embodiments, not limitation of the present disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments without departing from the scope or spirit of the present disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that aspects of the present disclosure cover such modifications and variations. 
     In example aspects, systems and methods for communication link configuration over cellular communication systems or other networks can be achieved via (i) transmit power control, (ii) antenna system configuration, and/or (iii) a combination thereof, where airborne and/or altitude variable radio are deployed. Methods of transmit power control and/or antenna system configuration (e.g., optimization or near optimization) can be implemented where parameters including altitude of radio, location in network of radio, and node or base station configuration of network are used, for instance, to reduce interference between radio and adjacent nodes as a function of altitude and dynamic motion of said radio, while maintaining communication link performance with the intended node. As used herein, a radio refers to a communication system capable of communicating wirelessly using, for instance, RF signals. A radio can include an antenna system and supporting circuitry (e.g., receiver, transmitter, transceiver, processors, memory devices, etc.). 
     For purposes herein, the term “altitude changing object” is used to describe an altitude changing object configured for wireless communication with a network, such as drones. Aspects of the present disclosure are discussed with reference to drones for purposes of illustration and discussion. The drone(s) can be capable of communicating with a cellular network or other network using one or more radios. Those of ordinary skill in the art, using the disclosures provided herein, will understand that aspects of the present disclosure can be discussed with other altitude changing objects capable of communicating wirelessly with a network and capable of altitude variation, such as elevators, altitude changing vehicles, etc. 
     The term “ground level” means an arbitrary elevation which includes sea level, average height of buildings above ground within a region, maximum height above ground with respect to buildings and/or stationary objects within a region, or any representation of elevation therebetween but not exceeding the tallest hill, building or other stationary object in the region. 
     Certain cellular networks have been designed to provide continuous coverage in the azimuth plane, translating to good coverage around the node or cell tower. In the elevation plane, a reduced beamwidth can be specified from the antenna since terrestrial based customers are assumed. This reduction in beamwidth in the elevation plane can allow for higher antenna system gain in the azimuth plane which will normally translate to improved cellular system performance. However, when altitude changing object usage is introduced on the cellular network elevation plane, performance of nodes or cell towers needs to be considered and optimized if overall system performance is to be maintained. 
     The concern of altitude changing object use in networks primarily relates to interference effects related to improved field of view of the altitude changing object as operating altitude increases. At higher altitude the altitude changing object will not only connect better to the intended node but can also be in the field of view of more nodes. The altitude changing object at higher altitudes can potentially be capable of interfering with a larger number of network users (terrestrial customers) when compared to a terrestrial based radio. 
     Example aspects of the present disclosure are directed to a method to control transmit power on the cellular radio on the altitude changing object as a function of one or more variables, such as altitude, location within cell, and object orientation. In some embodiments, a radio with antenna system on the altitude changing object can be controlled to provide dynamic modification of the radiation pattern or mode associated with the antenna system as a function of the one or more variables. One or more of these techniques can be used to improve link quality for the intended connection and/or can reduce interference to adjacent nodes and other cellular system customers. 
     In some embodiments, a radio with an antenna system can be integrated into an altitude changing object (e.g., drone) for use on a terrestrial cellular network. The antenna system can include one or more antennas associated with a single fixed radiation pattern. A method of determining altitude of the drone can be implemented (e.g., with altitude referenced to local ground level). An algorithm, look-up table, or control routine can be executed (e.g., by one or more control devices, processors, etc.) to determine a transmit power level for the antenna system as a function of altitude and/or other parameters. 
     In some embodiments, a radio with an antenna system can be integrated in an altitude changing object for use terrestrial cellular network. The altitude changing object can include a positioning system (e.g., a GPS receiver) for determining a position (latitude, longitude, altitude) of the altitude changing object. The altitude changing object can include a gyroscope or other system for use in determining orientation of the object. The antenna system can be associated with a single fixed radiation pattern. A method of determining altitude of the object can be implemented (e.g., with altitude referenced to local ground level). A position and/or orientation of the altitude changing object in the cellular network can be determined (e.g., using GPS and/or gyroscope). Information associated with cellular nodes in the vicinity of the altitude changing object can be obtained (e.g., received via the radio on the altitude changing object). 
     An algorithm, look-up table, or control routine can be executed (e.g., by one or more processors, control device(s), etc.) to determine a transmit power level for the antenna system as a function of altitude for use in communicating with the intended node and/or to reduce interference with adjacent nodes in the field of view of the altitude changing object. Information used in this process to determine transmit power level can include one or more of the altitude of the altitude changing object, orientation of the altitude changing object, and location of the altitude changing object in the cellular network. 
     In some embodiments, the altitude changing object can include a radio with an antenna system having a modal antenna. Examples of modal antenna systems are described in commonly owned Pub. No. US2016/0099501; and U.S. Pat. Nos. 9,240,634; 8,648,755, 8,362,962; and 7,911,402; the contents of each of which are hereby incorporated by reference. In addition, example modal antennas are discussed with reference to  FIG. 9 . 
     The modal antenna system can be capable of generating multiple radiation patterns and/or polarization states. An algorithm or control routine can be executed to determine a radiation pattern and/or polarization state from the modal antenna system based on metrics available such as object altitude, object orientation and/or direction of travel, location of object in the network and/or locations of the additional nodes within the field of view of the antenna system. In some embodiments, transmit power level for the antenna system can be adjusted in synchronization with radiation pattern and/or polarization state selection. 
     In some embodiments, information received from the network can be used to inform the radio on the altitude changing object that one or multiple nodes in the field of view have users that are being interfered with from the radio. An algorithm or control routine can be executed to select a radiation pattern for the modal antenna that provides good connectivity to the node but under-illuminates the area served by the node. An example of this technique can be the use of a modal or beam steering antenna system to generate a beam that illuminates the node or cell tower with the peak of the beam positioned above the antenna system on the node or cell tower. The ground region in the node or cell will be under-illuminated compared to the case where the beam steering antenna system on the altitude changing object generates a peak gain positioned at the antenna system on the node or cell tower. Transmit power level for the drone radio modem can be adjusted in synchronization with antenna system radiation pattern and/or polarization state selection. 
     In these embodiments, transmit power emitted from the antenna system associated with a radio on an altitude changing object can be based on metrics obtained from the network system, such as but not limited to: object altitude, object orientation and/or direction of travel, location of object in the network and/or locations of the additional nodes within the field of view of the object. 
     With reference now to the FIGS., example embodiments will be described in detail.  FIG. 1  illustrates an example of a drone  100  in a network, such as a cellular network. The drone  100  can be coupled to a controller  200  via controller-to-drone communication link  201 . Controller  200  can be adapted to communicate control signals to drone  100  for controlling movement thereof, including movement in vertical and horizontal planes relative to the altitude changing object, as well as orientation (rotation, tilt, etc.). In some embodiments, the controller  200  can be included as part of the drone  100 . 
     The controller  200  can include one or more control devices. The one or more control devices can include, for instance, one or more processors and one or more memory devices. The one or more processors can be microprocessors, application specific integrated circuits, microcontrollers, or other device(s) capable of performing operations. The memory devices can include any type of computer-readable media, including, but not limited to, non-transitory computer-readable media, RAM, ROM, flash memory, optical memory, magnetic media, or other memory devices. The one or more memory devices can store computer readable instructions that when executed by the one or more processors cause the one or more processors to perform operations, such as implementation of any algorithm, method, process, and/or control routine described herein. 
     Drone  100  can include one or more antennas  101  forming an antenna system. In some embodiments, the antenna(s) can be associated with a single radiation pattern. In some embodiments, the antenna system may include one or more modal antennas (otherwise termed “beam steering antenna system” herein). The modal antennas can be reconfigurable in any one of a plurality of possible modes. The modal antenna(s) can be associated with a distinct radiation pattern or polarization in each of the plurality of modes. An example modal antenna is described with reference to  FIGS. 9, 10, and 11 . 
     A network (e.g., cellular network) is illustrated with nodes  300  (e.g., three cellular base station terminals shown). Any number of nodes  300  may be implemented to form a network. Positioning satellites  400  (e.g., GPS satellites) can be used to determine a location of the drone  100 . GPS is one technique for determining a location of the altitude changing object; however, other similar position sensing techniques may be implemented, such as triangulating position based on signal analysis over the cellular network, dead reckoning, etc. 
     Several communication links are established with the drone  100  in the network, such as controller-to-drone communication link  201 , controller-to-network-node communication links  202 , drone-to-network-node communication links  301 , drone-to-GPS communication links, and communication links from drone  100  to other devices (e.g., client devices) on the network (not shown). For example, cellular, Wi-Fi, peer-to-peer link or other communication links may connect the controller  200  to the drone  100 . 
     Interference can be caused at cellular bands between drone  100  and adjacent nodes  300  of the network, or drone  100  and other client devices of the network. GPS or other positioning systems can be implemented to provide information related to drone location within the network. According to example embodiments of the present disclosure, with location (including altitude), direction of travel, and/or other information, transmit power can be regulated at the drone  100  to mitigate interference. In some embodiments, a mode of a multimode antenna of the drone radio can be changed to create one or more radiation pattern nulls or to steer nulls in desired directions to mitigate interference caused by drone operation. 
       FIG. 2  illustrates a drone  100  and controller  200  in a cellular network and describes how location of drone in the network can be used to optimize or enhance antenna system performance for the antenna on the drone.  FIG. 2  shows various parameters may be surveyed to configure the drone/node link. Based on location of the drone  100  in the network, an antenna system configuration for the radio system can be selected for configuration in azimuth and elevation planes. In some embodiments, velocity of the drone  100  can be considered. In some embodiments, orientation or direction of travel can be considered. A gyroscope or accelerometer may be implemented on the drone for orientation information. 
     Here, the drone  100  with one or more antennas  101  is linked to controller  200  via controller-to-drone communication link  201 . The communication link  201  between drone  100  and controller  200  is isolated from the network as shown by broken line circle  205 . GPS satellites  400  are provided to triangulate location of the drone  100  on the network made up of nodes  300 . 
       FIG. 3  illustrates a drone  100  at multiple altitudes in a cellular network and how the signals will vary as the altitude changes. More particularly,  FIG. 3  shows the drone  100  as it progresses about three vertical positions (P 1 ; P 2 ; and P 3 , respectively) above ground level P 0 . Controller  200  is in communication with drone  100  via controller-to-drone communication link  201 , and thereby controls the ascent of drone over the three vertical positions, each with a different altitude relative to ground level. 
     Communication link quality can vary as a function of altitude. According to example embodiments of the present disclosure, controller  200  can control antenna system on drone  100  to configure the antenna system to improve link based on altitude, orientation, direction of travel, and/or other parameters. Altitude, orientation, and direction of travel associated with the drone  100  can be determined, for instance, using GPS, gyroscope, accelerometer, information from the cellular network, and/or a combination thereof. Information on nodes in the cellular network is provided to drone controller via an access grant from the cellular network. The antenna system on the drone can be dynamically configured based on location metrics to improve and/or maintain link with the intended node along with reducing interference with other nodes or client devices. Example methods that can be implemented to control the antenna systems on drone  100  are discussed with reference to  FIGS. 7 and 8 . 
       FIG. 4  shows a schematic representing data flow  500  for use in the antenna system adjustment and transmit-power selection for a drone radio according to example embodiments of the present disclosure. An algorithm or control routine executed by one or more processors associated with the drone radio (or other processors) uses information to select a radiation mode of a multimode antenna and/or adjust transmit power of an antenna. For example, in some embodiments, location of nodes  300  in the network can be communicated to the drone controller  200  in a first signal over controller-to-network-node communication links  202 ; location of nodes in network information can transferred from controller to drone  100  in a second signal over controller-to-drone communication link  201 , for example stored in a lookup table or database; GPS system and satellites  400  can determine location of drone on the network; altitude, orientation, velocity, and/or location can be determined by drone based systems such as GPS, accelerometer, gyroscope, among others; and data is collected for use in an algorithm or control routine executed by one or more processors to determine a antenna system radiation mode and/or transmit power for antenna system of the drone radio. 
       FIG. 5  illustrates the process of selecting a frequency band for communication between a drone and a node or cell tower according to example embodiments of the present disclosure. In this example embodiment, multi-band radio modem allows for selection of frequency band to operate on to enhance a communication link. The frequency band can be selected based on various parameters, such as altitude of the drone, orientation of the drone, location of the drone in the network, velocity of the drone, the location of other nodes in the network (e.g., within the field of view of antenna system of the drone), and/or other parameters. In some embodiments, the controller  200  can send a control link signal over controller-to-drone communication link  201  with instructions to drone antenna system  101  of drone  100 . The location of nodes in the network information is transferred to the drone. Drone antenna system  101  can implement signals with frequency F 1  and/or frequency F 2  toward the intended node  300 . 
       FIG. 6  illustrates the parameters used in a system control matrix to select a mode of operation and/or transmit power for an antenna system according to example embodiments of the present disclosure. As shown, the parameters can include one or more of SINR of the intended link; SINR of interferer(s); altitude; orientation; antenna beam state; and/or frequency band. 
       FIG. 7  depicts a flow diagram of an example method ( 700 ) for configuring an antenna system on an altitude changing object (e.g., a drone) according to example embodiments of the present disclosure. The method can be implemented as part of a control routine/algorithm executed by one or more processors (e.g., one or more processors associated with the altitude changing object).  FIG. 7  depicts steps performed in a particular order for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that various steps of any of the methods described herein can be adapted, expanded, performed simultaneously, omitted, rearranged and/or modified in various ways without deviating from the scope of the present disclosure. 
     At ( 702 ), the method can include operating an antenna system of an altitude changing object in a current state. For instance, the antenna system can be controlled to transmit based on a transmit power for one or more antennas in the antenna system in its current state. 
     At ( 704 ), the method can include detecting a trigger condition. The trigger condition can trigger the occurrence of the remainder of method ( 700 ), namely controlling the antenna system based on various communication parameters associated with the altitude changing object (e.g., altitude) to enhance a communication link in a network, such as a cellular network. The trigger condition can be any defined condition that triggers the occurrence of ( 706 ), ( 708 ), and/or ( 710 ) depicted in  FIG. 7 . For example, in some embodiments, the trigger condition can be the expiration of a period of time. In some embodiments, the trigger condition can include detecting a change in an operating condition of the altitude changing object (e.g., change in altitude, change in location in a network, etc.). In some embodiments, the trigger condition can occur prior to a radio associated with the altitude changing object transmitting and/or receiving information to and/or from one or more nodes in a network. Other suitable trigger conditions can be implemented without deviating from the scope of the present disclosure. 
     At ( 706 ), the method includes obtaining data indicative of communication parameters associated with the altitude changing object. As discussed above, the data indicative of communication parameters can include, for instance, an altitude of the altitude changing object. The altitude can be determined, for instance, from a positioning system (e.g., GPS system), from a controller controlling the altitude changing object, from an altimeter on the altitude changing object, or other suitable source. 
     In some embodiments, the data indicative of communication parameters can include, for instance, orientation of the altitude changing object, direction of travel of the altitude changing object, and/or velocity of travel of the altitude changing object. These parameters can be obtained, for instance, from a positioning system (e.g., GPS system), from a controller controlling the altitude changing object, from one or more sensors on the altitude changing object (e.g., gyroscope), or other suitable source. 
     In some embodiments the data indicative of communication parameters can include, for instance, the location of the altitude changing object in a communication network (e.g., location relative to one or more nodes). This communication parameter can be obtained, for instance, from a positioning system (e.g., GPS system), from a controller controlling the altitude changing object, from the one or more nodes, or from another suitable source. 
     In some embodiments, the data indicative of communication parameters can include channel quality indicators (CQI) such as signal to interference plus noise ratio (SINR). For instance, the communication parameters can include SINR associated with an intended communication link and/or SINR associated with one or more potential interferers. Other CQI(s) can be used without deviating from the scope of the present disclosure, such as signal to noise ratio (SNR); receive signal strength indicator (RSSI), bit error rate (BER), and other metrics. The CQI(s) can be obtained from any suitable source, such as from a baseband processor, from one or more nodes in network, from the controller controlling the altitude changing object, etc. 
     At ( 708 ) the method can include determining a transmit power for one or more antennas in the antenna system based on the data indicative of the communication parameters. In some embodiments, a control routine, algorithm, and/or lookup table can be executed to determine a transmit power as function of one or more of the communication parameters. For instance, in some embodiments, a look up table correlating altitude or other communication parameter with a transmit power for one or more antennas can be accessed from a memory device. The transmit power corresponding with a particular altitude or other communication parameter can be determined based on the data indicative of current altitude or other communication parameter. 
     In some embodiments, a control routine or algorithm can implement a scoring function or cost function based at least in part on the one or more communication parameters. A score or cost can be determined as a function of one or more of the communication parameters (e.g., altitude, orientation, position, SINR, etc.). A transmit power can be determined to increase a score provided by the scoring function or reduce a cost provided by the cost function. 
     In some embodiments, an iterative control routine or algorithm can be implemented. For instance, the antenna system can be cycled through a plurality of transmit powers when the altitude changing object changes altitude (or other communication parameter) by a certain threshold. The transmit power that improves a communication link (e.g., as determined based on one or more CQIs) can be selected as the transmit power for operating one or more antennas in the antenna system. 
     At ( 710 ), the method includes controlling the antenna system based on the determined transmit power. For instance, the method can include controlling the antenna system to adjust a transmit power of at least one antenna having a single fixed radiation pattern to correspond with or be near to the determined transmit power. 
       FIG. 8  depicts a flow diagram of an example method ( 800 ) for configuring an antenna system on an altitude changing object (e.g., a drone) according to example embodiments of the present disclosure. The method can be implemented as part of a control routine/algorithm executed by one or more processors (e.g., one or more processors associated with the altitude changing object).  FIG. 8  depicts steps performed in a particular order for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that various steps of any of the methods described herein can be adapted, expanded, performed simultaneously, omitted, rearranged and/or modified in various ways without deviating from the scope of the present disclosure. 
     At ( 802 ), the method can include operating an antenna system of an altitude changing object in a current state. For instance, a modal antenna in the antenna system can be operated in a selected mode of a plurality of modes associated with the modal antenna. Each mode can be associated with a distinct radiation pattern. 
     At ( 804 ), the method can include detecting a trigger condition. The trigger condition can trigger the occurrence of the remainder of method ( 800 ), namely controlling the antenna system based on various communication parameters associated with the altitude changing object (e.g., altitude) to enhance a communication link in a network, such as a cellular network. The trigger condition can be any defined condition that triggers the occurrence of ( 806 ), ( 808 ), and ( 810 ) depicted in  FIG. 8 . For example, in some embodiments, the trigger condition can be the expiration of a period of time. In some embodiments, the trigger condition can include detecting a change in an operating condition of the altitude changing object (e.g., change in altitude, change in location in a network, etc.). In some embodiments, the trigger condition can occur prior to a radio associated with the altitude changing object transmitting and/or receiving information to and/or from one or more nodes in a network. Other suitable trigger conditions can be implemented without deviating from the scope of the present disclosure. 
     At ( 806 ), the method includes obtaining data indicative of communication parameters associated with the altitude changing object. As discussed above, the data indicative of communication parameters can include, for instance, an altitude of the altitude changing object. The altitude can be determined, for instance, from a positioning system (e.g., GPS system), from a controller controlling the altitude changing object, from an altimeter on the altitude changing object, or other suitable source. 
     In some embodiments, the data indicative of communication parameters can include, for instance, orientation of the altitude changing object, direction of travel of the altitude changing object, and/or velocity of travel of the altitude changing object. These parameters can be obtained, for instance, from a positioning system (e.g., GPS system), from a controller controlling the altitude changing object, from one or more sensors on the altitude changing object (e.g., gyroscope), or other suitable source. 
     In some embodiments the data indicative of communication parameters can include, for instance, the location of the altitude changing object in a communication network (e.g., location relative to one or more nodes). This communication parameter can be obtained, for instance, from a positioning system (e.g., GPS system), from a controller controlling the altitude changing object, from the one or more nodes, or from another suitable source. 
     In some embodiments, the data indicative of communication parameters can include CQIs such as SINR. For instance, the communication parameters can include SINR associated with an intended communication link and/or SINR associated with one or more potential interferers. Other CQI(s) can be used without deviating from the scope of the present disclosure, such as SNR; receive signal strength indicator RSSI, bit error rate BER, and other metrics. The CQI(s) can be obtained from any suitable source, such as from a baseband processor, from one or more nodes in network, from the controller controlling the altitude changing object, etc. 
     At ( 808 ) the method can include determining a selected mode of a plurality of modes for one or more modal antennas in the antenna system based on the data indicative of the communication parameters. In some embodiments, a control routine, algorithm, lookup table can be executed to determine a selected mode as function of one or more of the communication parameters. For instance, in some embodiments, a look up table correlating altitude or other communication parameter with a selected mode for one or more modal antennas can be accessed from a memory device. The selected mode corresponding with a particular altitude or other communication parameter can be determined based on the data indicative of current altitude or other communication parameter. 
     In some embodiments, a control routine or algorithm can implement a scoring function or cost function based at least in part on the one or more communication parameters. A score or cost can be determined as a function of one or more of the communication parameters (e.g., altitude, orientation, position, SINR, etc.). A selected mode can be determined to increase a score provided by the scoring function or reduce a cost provided by the cost function. 
     In some embodiments, an iterative control routine or algorithm can be implemented. For instance, the antenna system can be cycled through a plurality of transmit powers when the altitude changing object changes altitude (or other communication parameter) by a certain threshold. The transmit power that improves a communication link (e.g., as determined based on one or more CQIs) can be selected as the transmit power for operating one or more antennas in the antenna system. 
     At ( 810 ), the method includes controlling the antenna system based on the selected mode. For instance, the method can include controlling one or more modal antennas to adjust the mode to correspond with or be near to the determined selected mode. Example techniques for controlling an example modal antenna will be discussed with reference to  FIGS. 9-11 . 
       FIG. 9  illustrates an example embodiment of a modal antenna  910  that can be used in accordance with aspects of the present disclosure. The modal antenna  910  may include a circuit board  912  (e.g., including a ground plane) and a driven antenna element  914  disposed on the circuit board  912 . An antenna volume may be defined between the circuit board (e.g., and the ground plane) and the driven antenna element. 
     In some embodiments, a first parasitic element  915  may be positioned at least partially within the antenna volume. A first active tuning element  916  may be coupled with the parasitic element  915 . The first active tuning element  916  can be a passive or active component or series of components and may be configured to alter a reactance on the first parasitic element  914  either by way of a variable reactance, or shorting to ground, resulting in a frequency shift of the antenna. 
     In some embodiments, a second parasitic element  918  may be disposed proximate the circuit board  912  and may be positioned outside of the antenna volume. The second parasitic element  918  may further include a second active tuning element  920  which may individually include one or more active and/or passive components. The second active tuning element  920  can be a passive or active component or series of components and may be configured to alter a reactance on the second parasitic element  918  either by way of a variable reactance, or shorting to ground, resulting in a frequency shift of the antenna. The second parasitic element  918  may be positioned adjacent the driven element  914  and may also be positioned outside of the antenna volume. 
     The described configuration may provide an ability to shift the radiation pattern characteristics of the driven antenna element by varying a reactance thereon. Shifting the antenna radiation pattern can be referred to as “beam steering”. In instances where the antenna radiation pattern comprises a null, a similar operation can be referred to as “null steering” since the null can be shifted to an alternative position about the antenna (e.g., to reduce interference). In some embodiments, the second active tuning element  920  may include a switch for connecting the second parasitic to ground when “On” and for terminating the short when “Off”. It should however be noted that a variable reactance on either of the first or second parasitic elements, for example by using a variable capacitor or other tunable component, may further provide a variable shifting of the antenna pattern or the frequency response. For example, the first active tuning element  916  and/or second active tuning element  920  may include at least one of a tunable capacitor, MEMS device, tunable inductor, switch, a tunable phase shifter, a field-effect transistor, or a diode. 
       FIG. 10  illustrates a two-dimensional antenna radiation pattern associated with the modal antenna of  FIG. 9 . The radiation pattern may be shifted by controlling an electrical characteristic associated with at least one of the first and/or second parasitic elements  915 ,  918  of the modal antenna  910 . For example, in some embodiments, the radiation pattern may be shifted from a first mode  922  to a second mode  924 , or a third mode  926 . 
       FIG. 11  illustrates an example frequency plot of the modal antenna of  FIG. 9  according to example aspects of the present disclosure. The frequency of the antenna can be shifted by controlling an electrical characteristic associated with at least one of the first and/or second parasitic elements  915 ,  918  of the modal antenna  910 . For example, a first frequency (f 0 ) of the antenna may be achieved when the first and second parasitic elements are switched “Off”; the frequencies (f L ) and (f H ) may be produced when the second parasitic is shorted to ground; and the frequencies (f 4 ; f 0 ) may be produced when the first and second parasitic elements are each shorted to ground. It should be understood that other configurations are possible within the scope of this disclosure. For example, more or fewer parasitic elements may be employed. The positioning of the parasitic elements may be altered to achieve additional modes that may exhibit different frequencies and/or combinations of frequencies. 
       FIGS. 9-11  depict one example modal antenna having a plurality of modes for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that other modal antennas and/or antenna configurations can be used without deviating from the scope of the present disclosure. As used herein a “modal antenna” refers to an antenna capable of operating in a plurality of modes where each mode is associated with a distinct radiation pattern. 
     While the present subject matter has been described in detail with respect to specific example embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.