Patent Publication Number: US-10330796-B2

Title: Magnetic compass confirmation for avoidance of interference in wireless communications

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 15/379,023 filed on Dec. 14, 2016, entitled AVOIDANCE OF INTERFERENCE IN WIRELESS COMMUNICATIONS, by Reis, et al., which claims priority to U.S. Provisional Patent Appl. No. 62/267,065 filed on Dec. 14, 2015, entitled CHANNEL CLEARANCE AND AVOIDANCE IN WIRELESS COMMUNICATIONS, by Reis, et al., the contents of each of which being incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to wireless communication systems, and, more particularly, to magnetic compass confirmation for avoidance of interference in wireless communications. 
     BACKGROUND 
     Wireless communication systems have become ubiquitous in the world today, such as, for example, cellular mobile telephony, point-to-point microwave systems, satellite communication systems, and so on. Within each of these systems, and particularly due to the co-existence of such systems, challenges are presented when it comes to managing communication in a manner that prevents or at least minimizes interference. Common methods of interference minimization and/or avoidance may include use of different frequency bands, different polarizations, multiplexing techniques, geographical separation, etc. These methods typically work well for networks having fixed transmitters and receivers. When receivers or transmitters are allowed to move, however, the occurrence of interference may be greater, and performance may degrade. 
     For example, certain wireless communication frequencies (e.g., C-band communications) can only communication when there is a clear line-of-sight (LOS) between transmitter and receiver. Accordingly, interference of a C-band transmitter with a C-band receiver is possible only if there is a clear line-of-sight from the transmitter to the receiver. As such, if the transmitter roams, it may move from a point at which no interference was possible to one in which it becomes a potential interferer with the receiver. Other factors involved in determining whether a transmitter, in general, interferes significantly with a received signal, in addition to overlapping communication bands/channels, may further include transmit power, receive antenna type/gain, polarizations, distance from the transmitter to the receiver, and so on. 
     In certain environments, radio signal interference may be nothing more than a slight nuisance, while in other environments, the interference may be more problematic to the communication network, such as reduced bandwidth, lost (e.g., and repeated) messages, and so on. In still other environments, however, such interference may not only be particularly detrimental (e.g., introducing noise to received voice communication or partial/complete loss of picture for TV communication), but it may also be strictly prohibited by communication regulations, perhaps even being criminally offensive. Regardless of the environment, it is thus beneficial to ensure adequate interference mitigation, and in some instances absolute interference avoidance. 
     SUMMARY 
     According to one or more of the embodiments herein, a process obtains a first compensated directional reading from a first directional sensor of a directionally sensitive system, and obtains a second compensated directional reading from a second directional sensor of the directionally sensitive system. The process may then determine, a difference between the first compensated directional reading and the second compensated directional reading, and declares, in response to the difference being greater than an acceptable threshold, an inaccurate directional reading. As such, the process may then prevent performance of a directionally sensitive action by the directionally sensitive system in response to an inaccurate directional reading. 
     Various specific embodiments are described in detail below, such as types and arrangements of sensors, various directionally sensitive actions, and so on, and the summary is not meant to be limiting to the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments herein may be better understood by referring to the following description in conjunction with the accompanying drawings in which like reference numerals indicate identically or functionally similar elements, of which: 
         FIG. 1  illustrates an example communications network; 
         FIG. 2  illustrates an example of communication interference; 
         FIG. 3  illustrates an example point-to-point communications network with the potential for interference from a satellite communications network; 
         FIG. 4  illustrates an example satellite communications network; 
         FIG. 5  illustrates an example device configuration, e.g., as a server; 
         FIG. 6  illustrates another example device configuration, e.g., as a terminal; 
         FIG. 7  illustrates an example antenna configuration table; 
         FIGS. 8A-8B  illustrate an example of antenna patterns; 
         FIG. 9  illustrates an example of antenna gain patterns; 
         FIGS. 10A-10B  illustrate example demonstrations of link margin, link budget, and noise floors in wireless communications; 
         FIG. 11  illustrates an example of line-of-sight communication; 
         FIGS. 12A-12B  illustrate an example simplified procedure for avoiding interference in wireless communications according to one example embodiment herein; 
         FIG. 13  illustrates an example receiver acceptance cone; 
         FIG. 14  illustrates an example receiver protection zone (simplified); 
         FIG. 15  illustrates a simplified example of antenna lobes from an antenna site; 
         FIG. 16  illustrates an example gain pattern for an example (e.g., 2-meter) point-to-point microwave dish; 
         FIG. 17  illustrates an example polygon resulting from link budget calculation towards a receiver, representing a noise floor crossing boundary for a given transmission configuration from surrounding geographical locations; 
         FIG. 18  illustrates an example of intended receiver diversity and azimuth angles due to such diversity; 
         FIG. 19  illustrates an example of how a smearing operation may affect a protection zone to compensate for any potential inaccuracy by expanding it in certain directions; 
         FIG. 20  illustrates an example cut-away view of an illustrative terrain/topology along a line from an incumbent receiver to points within its example protection zone; 
         FIG. 21  illustrates an example reduced protection zone due to topology and line-of-sight considerations; 
         FIG. 22  illustrates an example of major and minor horizons associated with the reduced protection zone of  FIG. 21 ; 
         FIGS. 23A-23B  illustrate a geo-locational example of avoiding interference in wireless communications in accordance with the techniques herein; 
         FIGS. 24A-24B  illustrates an example of choosing satellite diversity for avoiding interference in wireless communications in accordance with the techniques herein; 
         FIG. 25A  illustrates an example of active point-to-point microwave links between 5925.01 MHz and 5930.0 MHz in the United States; 
         FIG. 25B  illustrates an example of a difference between northerly facing and southerly facing protection zones; 
         FIGS. 26A-26B  illustrate examples of a directionally sensitive system having multiple directional sensors; 
         FIGS. 27A-27B  illustrate an example of how magnetic interference can affect directional sensors differently; 
         FIGS. 28A-28B  illustrate an example of how antenna misdirection can affect avoidance of interference in wireless communication; 
         FIGS. 29A-29B  illustrate an example of how misdirection can affect a graphical user interface (GUI) for use with avoidance of interference in wireless communication; and 
         FIG. 30  illustrates an example procedure for magnetic compass confirmation, e.g., for avoidance of interference in wireless communications in accordance with one or more embodiments described herein. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     A communication network is a distributed collection of nodes (e.g., transmitters, receivers, transceivers, etc.) interconnected by communication links and segments for transporting signals or data between the nodes, such as telephony, TV/video, personal computers, workstations, mobile devices, servers, routers, base stations, satellites, or other devices. Many types of communication networks are available, including, but not limited to, computer networks (e.g., local area networks, wide area networks, and so on), communication networks (e.g., cellular networks, broadband networks, etc.), infrastructure or backhaul networks (e.g., C-Band/microwave inter-tower or “point-to-point” (PtP) networks, etc.), and many others. 
       FIG. 1  illustrates an example, and simplified, communications network  100 . As shown, one or more individual networks  104  may contain various devices  110  communicating over links  120  specific to the particular network  104 , or else between networks. As will be appreciated, networks  104  may include, but are not limited to, local area networks (LANs), wide area networks (WANs), the Internet, cellular networks, infrared networks, microwave networks, satellite networks, or any other form or combination of data network configured to convey data between communicating devices. Networks  104  may include any number of wired or wireless links between the devices, though, as noted herein, the interference techniques herein are generally concerned only with the wireless (or other shared media) links. Example wireless links, therefore, may specifically include, but are not limited to, radio transmission links, near-field-based links, Wi-Fi links, satellite links, cellular links, infrared links, microwave links, optical (light/laser-based) links, combinations thereof, or the like. 
     Data transmissions  108  (e.g., packets, frames, messages, transmission signals, voice/video/TV/radio signals, etc.) may be exchanged among the nodes/devices of the computer network  100  using predefined communication protocols where appropriate, and such communication may notably be bidirectional or unidirectional. In this context, a protocol consists of a set of rules defining how the nodes interact with each other. 
     Devices  110  may be any form of electronic device operable to communicate via networks  104 . For example, devices  110  may be a desktop computer, a laptop computer, a tablet device, a phone, a smartphone, a wearable electronic device (e.g., a smart watch), a smart television, a set-top device for a television, a specifically designed communication terminal, a satellite phone, a workstation, a sensor/actuator, other IoT devices, etc. 
     As mentioned above, wireless communication systems, particularly the co-existence of overlapping wireless communication systems, present challenges with regard to preventing or minimizing interference, a problem that is exacerbated when receivers or transmitters are allowed to move. In particular, as described below, the challenge of preventing interference is paramount when an existing communication system operates within dedicated frequency bands, and then a mobile transmitter for a different communication system is introduced into the incumbent system&#39;s environment that reuses those same frequency bands that the incumbent system may be already using. 
       FIG. 2  illustrates a simplified example of communication interference in a network  200 . Specifically, assume that transmitter Tx- 1  communicates with a receiver Rx- 1  (signals  210 ), and transmitter Tx- 2  communicates with a receiver Rx- 2  (signals  220 ). In the simple event that these two pairs communicate on the same (or similar) frequency, when transmitter Tx- 1  attempts to transmit a signal  210  to receiver Rx- 1 , it may inadvertently interfere with the ability of receiver RX- 2  to receive signals  220  from e.g., transmitter Tx- 2 . In other words, the interfering signal  210  has introduced “noise” into the receiver Rx- 2 , interfering with the reception of the signal  220  for which receiver Rx- 2  was intended to receive, rending the intended signal  220  indecipherable. 
     Notably, and as further noted above, while radio signal interference in certain environments is nothing more than a nuisance (added noise to voice communication, messages are low priority, can be repeated, etc.), other environments may consider interference to be particularly detrimental or even strictly prohibited. One such example network that would require adequate interference mitigation, and in particular absolute interference avoidance, is the large existing incumbent communication system using the C-Band (5925-6425 MHz) for high-bandwidth backhaul tower-to-tower communication. For instance, this communication system utilizes a microwave transmission infrastructure that includes numerous terrestrial receivers (or receivers, transceivers, repeaters, etc.) which are on what is generally referred to by the art as a Point-to-Point (PtP) network with PtP Transmitters (PtPTs) transmitting messages to respective PtP Receivers (PtPRs). 
       FIG. 3  illustrates an example PtP communications network  300  with the potential for interference, for example, from a satellite communications network  400 . In particular, PtPTs  305  and PtPRs  310  may be distributed geographically, such as on towers at the tops of mountains, buildings, etc., where PtPTs are configured to communicate wireless transmissions  320  (e.g., microwave, C-band, etc.) with a respective (and opposing) PtPR, as generally indicated by the sub-text “a”, “b”, and “c”. (Note that only receivers are subject to interference, so many references below are made to PtPRs  310  only. However, in certain embodiments, particularly for bidirectional communication systems, a receiver or PtPR may also be a transmitter or PtPT. As used herein, therefore, the term “PtPR” may be used to describe both receivers and transmitters, where appropriate.) In accordance with yet another embodiment, the PtPR may be an unintended satellite in the vicinity of (e.g., in angular proximity of) an intended satellite (e.g.,  420 , below), where transmission intended to be received by the intended satellite may interfere with the operations of the unintended satellite. 
     The PtPTs  305  and PtPRs  310  of the network (“incumbent system”, “existing system”, etc.)  300  are illustratively static; their location, antenna height above ground, direction they are pointing (azimuth and elevation), as well as their radcharacteristic (e.g., frequency, lobe shape, and polarity: horizontal, vertical, or both) are generally well known. According to the United States Federal Communications Commission (FCC), for instance, point-to-point microwave transmitters and receivers in the United States are registered within a Universal License Service (ULS) database, which includes details on geo-coordinates (location), antenna types, frequency bands used within the C-band, polarizations, power, etc. Currently, in the US, there are approximately 56,000 PtPRs in the C-band frequency range; all of which are operating within FCC regulations. 
     In order to introduce a new communication device/terminal  410  that is configured to transmit in the C-band within the environment  300  of the incumbent PtPRs, mechanisms need to be defined to prevent interfering with the operations of the incumbent system. For instance, to create a network of earth station terminals  410  for use with C-band operations with satellites  420  that can provide communication functionality such as, e.g., consumer-based text messaging/light email, voice communication, picture/video communication, and Internet of Things (“IoT”) communications, particularly in areas unserved by terrestrial commercial mobile radio services (“CMRS”) networks (e.g., cellular or other terrestrial mobile network coverage), such new terminals must be controlled within the environment of the incumbent PtPRs in a manner that prevents harmful interference with the operations (e.g., licensed communication operations) of the incumbent system  300 . 
     The techniques herein provide a robust interference protection regime to ensure that prospective transmitters of one system (e.g., a satellite communication network  400 ) will not cause harmful interference to an incumbent system (e.g., PtP operations in system  300 ). As explained below, each receiver (e.g., PtPR) will have one or more associated “Protection Zones”, where potential transmitters (e.g., earth station terminals, UAVs, etc.) will be subject to heightened interference protection requirements to ensure that no harmful interference inflicted upon a receiver (which, as described herein, may be based on sufficient availability of frequency bands, spatial, and satellite diversity at C-band frequencies). (As described below, each incumbent receiver may have as many protection zones as the number of intended receivers/satellites that the terminal may attempt to communicate with from a given place, as well as different zones for other reasons, as detailed further herein.) 
       FIG. 4  illustrates an example simplified satellite communications network  400 , where one or more communication transmitters  410 , which may be mobile or fixed, may be a standalone device, or may be attached to or otherwise associated with another computing device, such as a smartphone  415  or other suitable cooperative device (e.g., laptop, tablet, personal computer, measurement sensors, other types of IoT devices, etc.). Illustratively, the transmitters  410  may be referred to herein as transmitters, terminals, mobile earth terminals (METs), prospective transmitters, etc. According to the illustrative satellite embodiment, the terminals  410  may communicate bi-directionally with conventional (e.g., C-band) geostationary satellites  420 , which generally have a known and static location above the earth. (Other, more complex algorithms may be used for determining the location of, and communicating with, non-geostationary satellites, but for simplicity the description herein is based on geostationary satellites. However, the embodiments herein are not so limited.) A ground station or gateway  430  (or “ground receiver”, “ground station receiver”, etc.) is an illustrative facility at the other end of the satellite transmission. The ground station  430  may include various computing servers connected to a satellite antenna (e.g., satellite dish  435 ) pointing at the satellite  420 . 
     Transmissions  405  from the terminal  410  to the satellite are relayed from the satellite  420  to the dish  435  on the ground of the ground station  430 . Similarly, the ground station  430  transmits to the terminal  410  by sending radio signals via its dish  435 , which transmits it to the satellite  420 , which then frequency shifts this radio signal and broadcasts it downwards to be received by the terminal  410  (notably within a proper link budget). As referenced herein, the “forward-path” or “downlink” refers to a frequency band that the satellite  420  uses to transmit to the terminals  410  and ground station  430 . Conversely, the “return-path” or “uplink” frequency refers to a frequency band that the terminals and ground station use to transmit to the satellite. (Note that the same or different antennas may be used by the various communication devices, e.g., one for uplink, one for downlink, or one for both, and the view and description herein is merely a simplified example for purposes of illustration.) It should be noted that in the illustrative embodiment, the return-path (uplink) frequency band used by the terminals  410  may overlap with frequency bands used by the PtPRs, and as such would be subject to PtPR interference avoidance requirements. 
     Furthermore, in the illustrative embodiment, three example real-world satellites may be used, such as the Galaxy 3-C satellite at 95.05° W.L., Galaxy 12 satellite at 129° W.L., and Galaxy 19 satellite at 97° W.L. Each of these three Galaxy satellites  420  currently communicate with one of three gateway/remote control earth stations  430  in Napa, Calif. (Call Sign E970391), and Hagerstown, Md. (Call Signs E050048 and E050049), and operate on C-band frequencies in the 3700-4200 MHz (downlink/space-to-Earth) and 5925-6425 MHz (uplink/Earth-to-space) bands. Notably, any satellites, satellite systems, communication frequencies, ground stations, etc., may be used in accordance with the techniques herein, and those mentioned herein are merely for use as an example implementation of an illustrative embodiment, and are not meant to be limiting to the scope of the present disclosure. 
     Additionally, though specific implementation embodiments are shown herein with relation to terminals  410  being part of, or associated with, a personal communication device (e.g., for text messaging, short emails, voice communication, etc. from a phone), any number of implementations use the techniques described herein, such as being used for sensors or actuators (e.g., IoT implementations), vehicular control (e.g., drones, robots, unmanned aerial vehicles or “UAVs”, etc.), or any other system that uses wireless communication, whether located on land, a waterway (e.g., ocean), or in the air. 
     With reference still to  FIG. 4 , satellite communication network may further include one or more routers  440  that may be interconnect the devices, such as terminals  410  (and/or phones  415 ), gateways/ground stations  430 , etc. Routers  440  may be interconnected with such devices over standard communications links, such as cellular, internet, and so on, and may allow further communication by the devices to one or more servers  450 , which illustrative have access to one or more databases  460  as described herein (e.g., the FCC ULS database). One or more applications, such as a visualizer tool  470 , may also be available via the servers  450  or optionally on the localized terminals  410  (e.g., phones  415 ), for use as described below. Those skilled in the art will appreciate that any number of communication links, routers, devices, etc. may be available within the satellite communication network  400 , and the simplified view shown herein is for illustrative purposes only. Also, while certain devices are shown separately, various functionality (processing, storage, communication, etc.) may be implemented in any suitable configurations, such as the servers  450  being part of the gateway  430 , the database  460  being part of the servers  450 , and so on. Accordingly, the view in  FIG. 4  and the associated description is meant as an example, and not meant to limit the scope of the present disclosure. 
       FIG. 5  illustrates a schematic block diagram of an example computing device  500 , that may be used with one or more embodiments described herein, e.g., as a ground station/gateway  430 , server  450 , or other “centralized” device. The device may comprise one or more network interfaces  510  (e.g., wired, wireless, etc.), at least one processor  520 , and a memory  540  interconnected by a system bus  550 . The network interface(s)  510  contain the mechanical, electrical, and signaling circuitry for communicating data to network(s)  104  and, more particularly, devices  410 ,  415 ,  430 , etc. The network interfaces may be configured to transmit and/or receive data using a variety of different communication protocols. Note, further, that the nodes/devices may have two different types of network connections  510 , e.g., wireless, optical, and wired/physical connections, including connectivity to a satellite dish  435 , and that the view herein is merely for illustration. 
     The memory  540  comprises a plurality of storage locations that are addressable by the processor  520  for storing software programs and data structures associated with the embodiments described herein. The processor  520  may comprise hardware elements or hardware logic adapted to execute the software programs and manipulate the data structures  545 . An operating system  542 , portions of which is typically resident in memory  540  and executed by the processor, functionally organizes the device by, among other things, invoking operations in support of software processes and/or services executing on the device. These software processes and/or services may illustratively include server database services  544  (e.g., controlling server database  543 , and/or accessing an external database  460 ), a server visualizer process  546  (e.g., an app or an interface to an external visualizer tool  470 ), and a server interference avoidance process  548 , each as described herein. 
     Additionally,  FIG. 6  illustrates another example device configuration  600 , particularly as a terminal/transmitter  410 . Note that the terminal  410  may be embodied as a number of various implementations, such as a smartphone peripheral attachment, a component of a smartphone, a standalone handheld device, a sensor components, IoT, vehicular (e.g., unmanned) components, and so on. For instance, terminal  410  may be an attachment to a mobile phone  415  or other mobile device, where some of the processing occurs on the mobile phone and other portions, such as satellite communication, are performed on the attached (or associated) terminal  410 . In accordance with another embodiment, an attachment that contains the terminal circuitry is loosely coupled to a mobile device. In accordance with yet another embodiment, all of the components of the terminal  410  are integrated into a single embedded (standalone) system. As such, the schematic block diagram of the device  600  is merely meant as an example representation of illustrative components representing a terminal  410  that may communicate within its own network  400  (e.g., satellite system), while being controlled to prevent interference within shared frequency bands of incumbent network  300 . 
     Device  600 , a terminal  410  (e.g., transmitting device), may comprise one or more network interfaces  610  (e.g., wired, wireless, etc.), at least one processor  620 , and a memory  640  interconnected by a system bus  650 . The network interface(s)  610  contain the mechanical, electrical, and signaling circuitry for communicating data to network(s), such as an attached (or otherwise associated) mobile device (e.g., phone)  415  or other associated device, as well as other network communication techniques, such as wired connection to a personal computer or laptop (e.g., a USB connection). One of the network interfaces  610 , in particular, is a wireless network interface (e.g., a transmitter/receiver) configured to interface with a local antenna  660  of the device, which, illustratively, may be a C-band antenna (e.g., configured to communicate with a satellite  420 , as described below), and may comprise various communication front-end components such as amplifiers, filters, digital-to-analog and/or analog-to-digital converters, digital signal processors (DSPs), etc. As mentioned above, network interfaces may be configured to transmit and/or receive data using a variety of different communication protocols, and the device  600  may have different types of network connections, e.g., at least one wireless connection, but also optionally other wireless connections and wired/physical connections, and that the view herein is merely for illustration. 
     A memory  640  comprises the storage locations that are addressable by the processor  620  for storing software programs and data structures associated with the embodiments described herein, where the processor  620  may comprise hardware elements or hardware logic adapted to execute the software programs and manipulate the data structures  645 . An operating system  642 , portions of which is typically resident in memory  640  and executed by the processor, functionally organizes the device by, among other things, invoking operations in support of software processes and/or services executing on the device. These software processes and/or services may illustratively include local database services  644  (e.g., maintaining local database  643  itself, or accessing an external database), a local visualizer process  646  (e.g., an app or an interface to an external visualizer tool  470 ), and a local interference avoidance process  648 , each as described herein. Note that in certain embodiments, the terminal device  600  ( 410 ) may have limited resources (CPU, memory), and the software processes and/or services of the terminal device may be configured to operate in collaboration with a centralized system device  500  (ground station  430 /server  450 , described above), and may communicate with the centralized device either via broadband communication such as wireless or wired (e.g., USB), or via a very low bandwidth satellite link, particularly as described herein. 
     Illustratively, the techniques described herein may be performed by hardware, software, and/or firmware, such as in accordance with the various processes of device  500  (ground station  430 /server  450 ) and/or device  600  (terminal  410 ), which may contain computer executable instructions executed by processors  520 / 620  to perform functions relating to the techniques described herein. It will be apparent to those skilled in the art that other processor and memory types, including various computer-readable media, may be used to store and execute program instructions pertaining to the techniques described herein. Also, while the description illustrates various processes, it is expressly contemplated that various processes may be embodied as modules configured to operate in accordance with the techniques herein (e.g., according to the functionality of a similar process). Further, while the processes have been shown separately, or on specific devices, those skilled in the art will appreciate that processes may be routines or modules within other processes, and that various processes may comprise functionality split amongst a plurality of different devices (e.g., client/server relationships). 
       FIG. 7  illustrates an example antenna configuration (table)  700  for an antenna  660  according to one or more embodiments herein. For example, the illustrative antenna may be approximately 6 cm×4 cm in size, 5 cm×5 cm, or any other suitable size or shape, e.g., with approximately 9 dBi of gain. According to the illustrative embodiments herein, the antenna may operate in the 5.9-6.4 GHz transmission range. The antenna&#39;s illustrative input power is 1 Watt (0 dBW). Also, the peak equivalent (or effective) isotropically radiated power (EIRP) using a 9 dBi antenna is 9 dBW (e.g., 7.9 watts). Notably, any suitable antenna configuration may be used (e.g., 50% duty cycle, etc.), and the parameters shown are merely an illustrative example for purposes of discussion herein. Note also, that table  700  is a vast simplification of all of the possible parameters and configurations of an antenna, and is meant to be merely for discussion of an illustrative embodiment herein. 
       FIGS. 8A-8B  illustrate an example earth station terminal antenna gain pattern. The antenna  660  of the terminal  410  (device  600 ) may be illustratively embodied as a simple, rectangular quad-patch antenna (e.g., 6 cm×4 cm in size) with approximately 9 dBi of gain, as shown in the configuration of  FIG. 7 . It can be operated in either the vertical or horizontal polarization, or in both. In the azimuth plane  810  ( FIG. 8A ) or in the elevation plane  820  ( FIG. 8B ), the pattern  830  is virtually the same. Moreover, table  900  in  FIG. 9  shows an illustrative gain pattern  920  and EIRP  930  for the illustrative antenna of earth station terminal  600  (e.g., a quad-patch antenna in the XY and XZ plane), ranging from 0 to 90 degrees off bore-sight  910 . 
     For further understanding,  FIG. 10A  illustrates an example demonstration  1000  of link margin  1010  in wireless communications. In particular, the basic concept is that a transmitting radio  1020  transmits a signal with an original transmit power  1025 , which on the way through cable  1030  to antenna  1040 , experiences certain link loss until the EIRP gain at the antenna. Over the distance of the radio wave, path loss  1050  is naturally experienced through the transmission medium until reaching the receiving antenna  1060  (e.g., at an intended receiver or else at an unintended, and thus interfered with, receiver), which amplifies the received signal and conveys it through local cabling  1070  to the ultimate receiver radio  1080  with a resultant receive power  1085 . (Note that the illustrated path loss shows a linearly decreasing loss rate, but in reality, the curve may be much more complex (e.g., decreasing at a greater rate as the transmission travels further from the transmitter). For instance, for a simple dot antenna, the attenuation is function of R^3, while for a better antenna it can improve to be a function of R^2.) The difference between the received power  1085  and the receiver&#39;s sensitivity is referred to as the link margin  1010 . Said differently, link margin  1010 , measured in dB, is the difference between the actual received power and the receiver&#39;s sensitivity (i.e., the received power at which the receiver will stop working). 
     Note that in a typical real-world environment, radio communication and electronics often are subjected to incidental noise (i.e., any signal other than the one being monitored), such as thermal noise, blackbody, cosmic noise, atmospheric noise, etc., as well as and any other unwanted man-made signals. A “noise floor” is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system. As shown in  FIG. 10B , for example, a noise floor  1090  is shown based on this incidental noise  1095 , indicating the level of received power (over the receiver&#39;s sensitivity) at which the receiver may begin adequately separate an intended signal from the noise (without advanced separation techniques). The receiver, therefore, may be configured to simply ignore signals below this noise floor (e.g., squelching the static/noise). Accordingly, the link margin  1010 , as opposed to merely being based on the receiver&#39;s sensitivity as in  FIG. 10A , may be more accurately be based on the receiver&#39;s noise floor (i.e., the difference between the receiver&#39;s noise floor  1090  and the received power  1085 ). Either calculation for link margin may be used herein, e.g., depending upon the implementation and configuration of the receivers, and the techniques herein are not limited to either one. 
     As described herein, the link margin  1010  (above the receiver sensitivity or, preferably, above the noise floor) may be considered when determining link power budget (or simply “link budget”) computations. In general, the link budget equation may be based on a simplified equation where the received (Rx) power is equal to the transmitted (Tx) power plus gains minus losses:
 
 Rx  Power (dB)= Tx  Power (dB)+Gains (dB)−Losses (dB)   Eq. 1.
 
In the event that the link budget equation results in a receive power that is greater than the sensitivity or, more particularly, a noise floor of an intended receiver, i.e., has a positive link margin  1010 , then that transmission should be received successfully. At the same time, however, should the receive power at an unintended receiver be greater than that unintended receiver&#39;s sensitivity or, more particularly, a noise floor, then the transmitted signal could interfere with the unintended receiver&#39;s operations.
 
     Another simplified, but more complex link budget equation may be established depending upon the particular communication environment, such as, for example:
 
20 log  D−GT   az   −GL   el —( GR+ 38)−Pol&gt; T    Eq. 2,
 
where D is the distance between the transmitter and receiver, GT az  is the transmit gain in the azimuth direction to the receiver, GT el  is the transmit gain in the elevation direction to the receiver, GR is the receiver gain, Pol is the polarization gain, and T is a predetermined threshold value, e.g., the noise floor of the particular receiver. In general, to provide extra protection for unintended receivers, T may be set at some value (e.g., 6 dB) less than the prevailing Boltzmann noise (“noise floor”). Said differently, different values/levels of T may be used for different types of receivers, and also depending on whether the receiver is an intended receiver or unintended receiver: that is, when calculating the threshold T for an intended receiver to sufficiently receive a transmission, the receiver&#39;s noise value (or sensitivity) may be used, while for an unintended receiver, a precautionary adjustment to the threshold T may be made, such as e.g., the noise floor minus 6 dB (or some other determined adjustment value). Note that as described below, according to the techniques herein, if the power budget exceeds a threshold T to an intended receiver, but is simultaneously below a corresponding threshold T for an unintended receiver at a given location, then that location/transmission is considered to be acceptable (i.e., reaches the intended receiver, and does not interfere with an unintended receiver).
 
     Additionally of note, the earth is a strong attenuator at microwave frequencies. Therefore, signals within the C-band that travel towards a PtP receiver antenna will stop either at the point where the signal hits a hill or at the curvature of the earth.  FIG. 11  illustrates an example  1100  of line-of-sight communication, where an example microwave communication tower  1110  (PtP transmitter  310 ), illustratively located at height “H” above sea-level, produces a line-of-sight  1120  based on the curvature “X” of the earth. Note further that refraction due to atmospheric pressure along the surface of the earth extends the effective radio horizon. As such, the techniques herein may also use the standard” 4/3 earth model” to account for horizon extension due to refraction, as may be appreciated by those skilled in the art. 
     Specifically, the limiting distance for line-of-sight communications such as microwave communications can be derived by the simplified formula:
 
Radio Horizon( mi )=SQRT of (2×Height)   Eq. 3,
 
where the Height (ft.) is the sum of the antenna tower plus height above sea level. By way of example, the height of a PtP transmit tower might be on the order of 50 feet on top of a 300 foot (or so) hill. This would define a maximum communications range (line of sight  1120 ) of about 26.5 mi to a sea level receiver. Various other factors may extend or reduce this number, such as obstructions or receivers above sea-level (the calculation above assumes a sea-level receiver). For instance, one would add 2.8 miles to this number if a receiver (or conversely, a terminal transmitter herein) is expected to be held at about 4 feet above the earth. Note that information about terrain (used below) may be obtained from a number of sources. e.g., but not limited to, U.S. Geological Survey (USGS) national maps/topographical information, Google Earth™, and so on. It is also noted that, should the prospective transmitter or incumbent receivers be in a maritime location (e.g., ocean), aerial location (e.g., balloon-based networking), or location other than on land, other factors may be taken into consideration with regard to the line of sight, as may be appreciated by those skilled in the art. (Also, in the specific embodiment where the system is used to avoid interference with a satellite located in a similar angle in the sky, the radio horizon may be set to infinity and need not be factored into the calculations.)
 
——Avoiding Interference in Wireless Communications——
 
     As mentioned above, the techniques herein provide a robust interference protection regime to ensure that prospective transmitters of one system (e.g., a satellite communication network  400 ) will not cause harmful interference to an incumbent system (e.g., PtP operations in system  300 ). As described below, the techniques herein may determine whether a prospective transmitter  410  will interfere significantly enough with unintended receiving terminals (receivers  310 ) to cause impermissible or otherwise unacceptable degradation in performance of the incumbent wireless communication system. Said differently, the techniques herein determine acceptability of transmission by a transmitter  410  within the presence of incumbent communication receivers  310  based on the risk of interfering with such receivers, and allow or deny such transmission, accordingly. (As mentioned above, and as will be appreciated by those skilled in the art, interference with an unintended receiver may be based on interfering with ground-based PtPRs, a neighboring satellite, a ground station associated with another satellite, or any other unintended receiver where a transmission may raise the noise floor of that unintended receiver.) 
     In particular, as described in greater detail below, based on a database of incumbent receiver properties (e.g., the FCC ULS database identifying PtP operations in the C-band), the techniques herein determine the location, altitude above sea level, antenna polarity, and orientation of each incumbent receiver  310 , and identify a “Protection Zone” for each receiver, such that a given patch of earth (or sea, air, space, etc.) is identifiable as either a) requiring protection against transmission by a terminal  410  orb) not requiring protection against transmission by terminal  410 . Once the receiver protection zones are combined with real-time location information from a terminal  410  seeking to transmit, the system herein may then act accordingly to prevent any harmful interference to incumbent (e.g., PtP) operations, while determining one or more acceptable frequency bands (if any) on which the terminal may transmit in a given power. Notably, as described below, the techniques may be performed based on either a centralized manner (achieved by collaboration between the ground station  430 /server  450  and the terminal  410 ), or localized (decentralized) manner (contained entirely on the terminal  410 , given sufficient processing resources), or else within a network planning tool (e.g., for placement of a transmitting station of a new wireless communication system in the presence of an incumbent wireless communication system, where the incumbent wireless communication may require interference protection). 
     As an up-front illustration of the capabilities of the techniques herein,  FIGS. 12A-12B  show an example simplified procedure  1200  for avoiding interference in wireless communications according to a particular example embodiment herein. (Note that the procedure  1200  is meant as an example demonstration of a particular embodiment of the techniques herein in order to frame an understanding for the more detailed description below. The steps shown in  FIG. 12A-12B  are not meant to be limiting to the present disclosure, and additional, fewer, simplified, more complicated, and/or entirely different steps may be performed by the systems herein in accordance with various aspects of the techniques herein.) 
     In particular, example procedure  1200  begins in step  1205  of  FIG. 12A  at the ground station, and then proceeds to step  1210  populate the ground station  430  (or server  450 ) with all of the necessary information about the incumbent receiver network  300  in order to determine (e.g., draw) protection zones (for each channel/polarity and intended receiver) in step  1215  defining all of the locations where a terminal  410  might interfere with each known incumbent receiver  310  (e.g., based on link budget, as described below). In step  1220 , the ground station may enlarge the computed protection zones for added protection, and then in step  1225  may reduce the coverage of the zones based on geographical characteristics, such as line-of-sight considerations for curvature of the earth and terrain mapping (e.g., hills, mountains, etc.). Since the protection zones at this point may be a series of complicated curves and contour lines, and since the terminals  410  may have limited resources (e.g., memory), in step  1230  the ground station may simplify the representation of the protection zones into a less precise representation (format) that is consequently less data-intensive, such as a more simplified polygon representation or angular/distance representation based on major and minor horizons (described below). The final representation of the protection zones may then be sent to (or otherwise retrieved by) the terminals  410  (e.g., initial configuration, download over higher-bandwidth links, etc.) in step  1235 . 
     Now, in  FIG. 12B , procedure  1200  continues at the terminal  410  where the final representation of the protection zones is uploaded or otherwise received and stored by the terminals (step  1235 ), such that whenever the terminal  410  wishes to transmit on a potentially interfering frequency band, it first determines its location in step  1240 , then checks whether that location is within any protection zone of any incumbent receiver in step  1245 . If so, then in step  1250  the terminal may locally calculate whether it might actually interfere with the receivers corresponding to the protection zones, since, as mentioned above, much of the precision of the protection zones (based on link budget, terrain, etc.) may have been lost through the simplification of their representation. As such, based on the local determination (step  1255 ) that interference would not be an issue, or else based on not being in a protection zone at all in step  1245 , the terminal  410  may transmit on a cleared frequency band in step  1260 . Otherwise, transmission is not allowed, and the illustrative procedure  1200  ends in step  1265 . Note that other measures may be considered to allow transmission, including adjusting the terminal&#39;s location, transmit properties (e.g., diverse polarity, reduced transmission power, etc.), and so on, but such optional enhancements are described in greater detail below. Note further that as mentioned above, the steps of procedure  1200  are merely an example of a particular embodiment, and are not meant to be limiting to the scope of the present disclosure, as many alternatives to the above configuration of steps may be conceived as described below. 
     As mentioned above, the techniques herein start with acquiring information about the incumbent system  300  for which interference protection is desired. This information, notably, may be computed by, and stored in, either the ground station  430  or in server  450 , and any combination of their cooperation is conceived herein (e.g., computation on server  450 , and storage on ground station  430 , etc.). In particular, in an illustrative embodiment, the construction of this information may be performed by an offline tool associated with the system, meaning it can be done in the server  450  or calculated offline and then loaded into the server/ground station  430 . Similarly and without limitation, the computations can be performed in the cloud, such as on the Amazon Web Services (AWS) or similar cloud based servers and storage, as may be appreciated by those skilled in the art. 
     According to an illustrative embodiment, a database  460  may contain all of the required information for all the receivers of the incumbent system  300  (e.g., PtPRs in the US) which allow the system to calculate the protected zones, as described below. For instance, in the illustrative embodiment of PtPRs, this information may be stored in the FCC&#39;s ULS database as mentioned above, which contains an up-to-date account of Fixed Service PtP licensed pairs and applicant pairs (e.g., in the C-band, or other overlapping frequency band with system  400 ) and their associated identification (e.g., call signs). This information, notably, includes the coordinate locations/orientation of PtPRs, the frequencies of the PtP communication (e.g., frequency center and width), and antenna height, height above mean sea level (base altitude), receiver polarization, antenna type, and optionally other information, such as azimuth, gain characteristics (lobe shape), and so on for each PtPR antenna. (Note that if such information is not directly within the database  460 , the system herein may compute such values based on public knowledge of antenna characteristics, or else based on various assumptions thereof. Also, for embodiments where the system ensures that the transmitter does not interfere with the operations of another nearby satellite, the locations of geostationary satellite are well known while the momentary locations of non-stationary satellites can be calculated.) 
     Periodically (e.g., daily), the system (e.g., server  450 ) accesses the database  460  (e.g., the FCC ULS database) and obtains the most recently updated licensing and applications information in the frequency band of interest (e.g., C-band in our case). This information is used by the system to construct a relevant server-side database  543 , which contains updated information regarding all active (and pending) receivers (e.g., PtPRs) and their location, altitude of antenna base, antenna height above ground, azimuth, antenna type/gain, diversity height polarity, and frequencies assigned to the incumbent receiver. Notably, channels/frequencies used by a specific PtPR may change, such as when a segment of a network requires additional bandwidth and as such acquires an additional frequency channel. Also, it should be noted that at times there can be changes to the location, azimuth, height, antenna information, etc. in the ULS database (e.g., correcting errors, updating with greater accuracy, accounting for actual changes or planned movements, changes in polarity, and so on). 
     Additionally, the system also maintains a current map of the covered area (also within illustrative database  543 ), which may illustratively include geographically significant features, such as terrain (e.g., hills, mountains, valleys, and other topographical information that may be relevant to line-of-sight calculations described below). As noted above, such information may be obtained from various sources, and may also be updated as deemed necessary. 
     As described in greater detail below, the server database  543  contains the information that may be used to create a detailed representation of protection zones, that is, locations where a terminal  410  could potentially interfere with an incumbent receiver  310  (e.g., on a particular frequency band/channel). These protection zones for each receiver  310  may notably be computed (and subsequently referenced) per intended receiver (e.g., per satellite), per incumbent receiver polarity (e.g., horizontal and/or vertical), and any number of other factors that would vary the potential for interference (such as, e.g., different levels of uncertainty or “smearing”, described below). For instance, the set of unintended receivers for which a transmission on “channel  1 ” would interfere would be different from those that would be potentially interfered with by a transmission on “channel  2 ”. Additionally, a computation of interference at one unintended receiver at a horizontal polarity would be different from that at the same unintended receiver at a vertical polarity. Furthermore, a computation of interference for a transmission to an intended receiver (satellite) in one location (e.g., azimuth) would be different (for the same unintended receiver) than a transmission to another intended receiver in a different location. The techniques described below, therefore, may be applied for each of these different inputs and in different combinations, both in terms of initial computation and for subsequent reference (as would be necessary, that is, based on available transmission possibilities by the terminals  410 , such as, e.g., whether the same channel is available on different receivers/satellites, or whether the terminal can transmit on different polarities, etc.). As such, while certain considerations for such factors may be explicitly described below, it is important to note that the generalized portions of the description below assume that the potential for interference may be based on such factors, and the server database  543  (and corresponding local database  643 ) may provide the adequate distinctions in transmission configurations with regard to their corresponding potentials for interference (protection zones), accordingly. 
     It is important to note that servers  450  can compute, in advance, exactly on a map where a terminal  410  is allowed to transmit (and not interfere with any receiver  310 ) based on link budget calculations using antenna properties, transmitter properties, communication characteristics, and so on. However, since at the time of computing this information the servers would not know where a mobile terminal would be, and since the terminals themselves would generally not have enough storage to keep a complete record of this information, the techniques herein may calculate approximated protection zones representing a potential for interference, where the terminal  410  (e.g., a mobile device) may then be responsible for determining for itself whether it is allowed to transmit. For example, the terminal  410  may calculate the link budget to each receiver having an approximated protection zone that covers the terminal&#39;s current location (described further below). (Note also that in one embodiment, the terminals  410  may have sufficient resources for precise mappings of all acceptable transmission locations, at least within a given region, as also described below.) 
     According to the present disclosure, two illustrative techniques for computing the approximated protection zones (i.e., a potential for interference) are described, namely, a simplified geometrical approach based on antenna properties, and, as a preferred embodiment herein, a more sophisticated link-budget-based approach. (Notably, other approaches may be used, including, but not limited to, various hybrid combinations of the details aspects from each approach described herein.) 
     Regarding the simplified approach first,  FIG. 13  illustrates an example receiver acceptance cone (RAC)  1300 . (Note that one interferes with receivers, not transmitters, so the receiver side of the link is the only acceptance cone at issue.) The RAC, based on receiver antenna properties and configuration, is the coverage area corresponding to a region, in a particular direction of coverage (noting that certain receivers may be configured with more than one direction of coverage, and thus resulting in multiple coverage areas), for which a receiver is configured to receive (accept) a transmission. Though the intent is that the opposing transmitter (e.g., PtPT  305 ) may generally be placed within (e.g., and pointing along) the RAC  1300  of its corresponding receiver (e.g., PtPR  310 ), the RAC  1300  also implies a region in which a third-party transmitter (with a specific transmission power) might interfere with the receiver  310 . Said differently, the RAC  1300  also defines an area, where outside of this area the receiver  310  may not be adversely affected by a terminal  410  operating at the same frequency band as the receiver (e.g., and at a predetermined transmission power). (Note that RAC  1300  represents a simplified region and is for illustrative purposes only, particularly since antennas have side-lobes which need to be factored into protection zones, as described below.) 
     As shown, the maximum communications range for a transmission is the distance “D” (e.g., 30 miles), defined for microwave frequencies by the transmitter antenna&#39;s height above sea level, the topology of the area, and the curvature of the earth, as mentioned above. The angle of the RAC&#39;s inclusion triangle is defined by the receiver antenna characteristics. For example, PtP microwave antennas are typically two or three meters in diameter, which defines a 1.7-degree (or less) acceptance angle (3 dB), so illustratively an angle of 2 degrees (+/−1 degree) is shown. Note that the receiver database (e.g., FCC ULS) contains information regarding smaller or larger receiver dishes and other parameters (e.g., antenna apertures), and this data may be used when accounting for the RAC of any given receiver. As shown, RAC  1300  for this specific example covers approximately 16 square miles, and is approximately 30 miles long away from the receiver with an approximately 1-mile wide maximum spread. 
     The RAC  1300  is an intended focal range for a receiver  310 , within which the receiver is designed to receive transmission signals, and accordingly attenuate interference signals from transmitters outside the RAC. However, in order to provide additional assurance and protection from interference, the techniques herein may be configured to assume an expanded protection region beyond the RAC  1300  of  FIG. 13 . For instance, in this first simplified embodiment, as shown in  FIG. 14 , a receiver&#39;s “protection zone”  1400  need not be limited to the RAC  1300 , but may be expanded to a larger region to provide extra protection against inadvertent interference. In particular, an expanded protection zone may be constructed to account for inaccuracies in various measurements such as measurement of the direction in which the transmitter points, GPS location, height of the transmitter, etc. For example, in one embodiment as shown, the expanded protection zone  1400  may span an acceptance angle of approximately 20-degree arc (+/−10 degrees, rather than merely +/−1 degree, i.e., ten times larger and 1/18 of a 360-degree circle), and may extend for an additional distance (e.g., 50 miles or more, particularly depending upon antenna height, rather than merely 20-30 miles), resulting in a coverage area of approximately 450 sq. miles (notably larger than the RAC&#39;s 16 sq. miles), a substantial safety factor in addition to the physical RAC. 
     Note also that antennas (even those that are highly directional in nature) may have side lobes (also back lobes) that extend in other directions as mentioned above, even in a direction opposite the intended coverage area or RAC  1300 . To account for such side lobes to ensure that the terminals  410  will never cause harmful interference—even at very close proximity, the extended protected area  1400  may also include additional coverage areas  1410  in one or more other directions. For instance, in one simplified embodiment as shown, the additional coverage area  1410  may account for such side lobes by adding a fixed-radius circle (or one or more other polygonal regions) about the receiver  310 , to account for such side lobes. This may be considered part of the expanded protection zone  1400 , and any prospective transmitter within such areas may also need to be accounted for interference purposes, as described below. Based on example PtPR side lobe properties, the additional coverage area  1410 , which may be considered a “close proximity circle” surrounding the PtPRs, may have an illustrative radius of approximately 3.9 miles. (Note, any suitable radius for this additional coverage area may be used, such as depending on the receiver antennas, transmitter power, etc., and this illustrative and non-limiting example of 3.9 miles was selected based on an example of a minimum side-lobe stand-off distance calculated according to an illustrative configuration, described below.) 
     Furthermore, according to one or more aspects of the disclosure, additional margins of error may be provided in the expansion of a RAC  1300  into a protection zone  1400  to allow for extra protection of an incumbent network. For example, in terrain mapping, it may be assumed that the transmitter and/or receiver is located at a height higher than where it would actually be located (e.g., for a handheld device, the elevation of the transmitter above the earth at the given proposed location may be a few meters (taller than a person), and/or the height of the receiver may also be assumed to be higher than it actually is). Also, other factors of estimation or error, such as transmitter angle, transmitter location, receiver placement, receiver&#39;s physical properties, and so on, may benefit from a forgiving margin of error on top of the RAC  1300  or even on top of an already expanded protection zone  1400 . As such, the protection zone  1400  may be additionally based on various margins of error (e.g., percentages, set values/multipliers, administrator-defined ranges, measured errors, and so on). 
     The first illustrative (simplified) protection zone  1400  described above may thus range from the RAC  1300  up to a pre-defined expanded range, including any additional areas  1410  based on antenna properties (e.g., antenna lobe patterns including main lobe and side lobes), and may be used to determine whether a transmitter  410  is within an area in which it may interfere with a receiver  310 . (Note that in some cases, the protection zones may be effectively limited to areas on the earth&#39;s surface, though in other cases, the protection zone may be considered to extend in elevation, as well as azimuth, and this may be similarly accounted for.) 
     Notably, a more accurate (and generally more preferred) determination of a zone of potential interference is to calculate the RAC as the interaction between the pattern of the antenna of the transmitting terminal and the antenna of the specific PtPR, assuming the given (nominal) transmission power of the terminal. Regarding this more sophisticated (and preferred) link-budget-based approach for calculating protection zones, recall that the servers can compute, in advance, exactly on a map from where a terminal  410  is allowed to transmit (without interfering with any receiver  310 ). While this is certainly one conceived manner of attacking the problem in one embodiment herein, in another (e.g., preferred) embodiment, the techniques herein need only to determine the locations wherein the calculated link budget equals (or surpasses) the noise floor for each receiver, and define this line as the boundary of the protection zone. In particular, in this illustrative embodiment, the boundary of a receiver&#39;s protection zone may be based on applying a link budget equation for transmission from the  410  transmitter to the intended receiver (e.g., satellite)  420 , in order to determine the distance from the receiver  310  at which point a noise floor is exceeded at the receiver  310  (i.e., interfering with the operations of receiver  310 ). 
     For instance, for each known receiver (e.g., PtPR)  310 , the system calculates the farthest horizon distances at which a terminal  410  could interfere with the receiver. To do this, the system calculates a “protection zone” polygon around the position of the PtPR. This is done by calculating, at small angular increments (e.g., 1-degree increments) for 360 degrees around the receiver location, the distance at which the result of the link budget calculation along that radial is exactly equal to the noise floor. Any closer to the PtPR along that radial, the transmitter could possibly interfere with the operation of the PtPR, and conversely transmitting from farther away along the same radial would not interfere with that PtPR. 
     The specific shapes of the polygons are governed by the link budget interaction between the lobes of the incumbent receiver&#39;s antenna and the lobes of the terminal&#39;s antenna, and assuming that the terminal is pointing towards a specific intended receiver (e.g., satellite). For example,  FIG. 15  illustrates a simplified example of antenna lobes from an antenna site  1500 , where a main lobe  1510  may be the intended transmission and/or reception focus, but various side lobes  1520  and back lobes  1530  may also result from the antenna design (and radio communication principles). Additionally,  FIG. 16  illustrates an example gain pattern  1600  for an example (e.g., 2-meter) PtP microwave dish. (Note that this radiation pattern is typical for a microwave antenna, with side-lobe signals being generated at significant levels at azimuth angles out to +/−90 degrees.) As such, the techniques herein compute the noise floor “interference boundary” (protection zone) based on the antenna lobe pattern of the associated antennas of systems  300  and  400 , and based on the particular directions of the antennas, and the expected transmission direction and power of the transmitter. 
     The techniques herein may first determine a typical received signal noise power of an incumbent receiver  310  (e.g., PtPR), and then can determine the link budgets necessary to maintain a transmitted signal level from a terminal  410  sufficiently below that noise floor. For instance, a high performance receiver  310  will have a best case Boltzman noise floor equal to approximately −174 dBm/Hz. Now, by adding in 6 dB of noise immunity (or some other chosen level of noise immunity), and an example signal bandwidth of 8 MHz (e.g., 69 dB), then the techniques herein define a new and more robust noise floor threshold which is 6 dB more noise than Boltzman noise, or:
 
Noise Power=−174+69+6=−99 dBm   Eq. 4.
 
With this (or any other suitably) computed power value, and using any suitable link budget equation based on antenna lobe patterns, the techniques herein can now compute the location along each radial from a receiver  310  at which a transmission from the terminal  410 , aiming at an intended receiver (e.g., satellite)  420 , would cross (i.e., is equal to) the noise floor, interfering with the incumbent and unintended incumbent receiver. (That is, determining the location where the terminal&#39;s power is the same noise power as the Boltzman (natural) noise level at the receiver). Illustratively, recall that the actual “crossing” of the noise floor may illustratively be based on a safety margin (e.g., 6 dB), for added assurance of non-interference. Said differently, the potential for crossing the noise floor may be based on an artificial “safe” noise floor value, and not the actual noise floor of the receiver.
 
     As an aside, the power value may also be used to calculate an absolute “stand-off distance” (D) from a receiver, particularly for locations near (behind and to the side of) the receiver as described above, such as should a transmitter be aimed directly at the receiver. For example, based on various known antenna lobe link budget equations, and using the 6 dB safety margin, this value may result in a behind-the-dish stand-off distance (D) of 630 meters, and for the side-lobes a stand-off distance (D) of 6300 meters (3.9 miles). This means that the transmission of a terminal&#39;s signal from any distance greater than 630 meters behind the dish and/or 6300 meters to the side will result in a received signal of 6 dB or more below the Boltzmann (natural) noise floor at the incumbent receiver. (Note that this maximum stand-off distance (e.g., 3.9 miles) could be used to establish the additional safety range  1410 , as mentioned above with reference to the “simplified” protection zone  1400 .) 
     Returning to the discussion of the link-budget-based protection zone, once the link budget computations are completed for a receiver (in all 360 degrees around the receiver), each distance and angle may then be converted to latitude and longitude, which results in a polygon that represents the transition boundary of the protection zone for that particular receiver (e.g., for a particular transmitter azimuth to a given intended receiver, at a particular polarity, etc.). This boundary can then be overlaid onto a map, where points inside the polygon are inside the protection zone, and points outside are not inside the protection zone. Said differently, as a result of the computations above, the server  450  may obtain numerous polygons which describe the potential interaction between each receiver  310  and terminal  410  attempting to transmit towards a given receiver (e.g., satellite)  420  at a specific frequency channel and nominal power. Note that these protection zone polygons may be stored in a database of the ground station  430  or in a server  450 , however may generally not be transmitted to the terminals in this form; rather they may first be modified (e.g., simplified) as described below, since the detailed description of these polygons may consume too much memory and may require high network bandwidth to update. (Note further that in one embodiment, these protection zone polygons are not stored in the gateway/server, either, and need only be calculated for further processing and storage in a different format, such as described below.) 
       FIG. 17  illustrates an example polygon  1700  resulting from link budget calculation towards a single receiver  310  (e.g., overlaid on a map), for a given frequency band, polarity, and intended receiver azimuth (e.g., a particular satellite  420 ). That is, the resultant polygon  1700  represents a noise floor crossing boundary of a particular receiver  310  for a given transmission configuration from a transmitter (terminal  410 ) in surrounding geographical locations. As can be seen, a main lobe of interference extends generally northeasterly, in an example direction of the antenna of the receiver  310  for intended reception. 
     Note also that the polygon in the proximity to the receiver is a complex pattern (and, notably, need not be limited to areas bounded only by straight lines). This is due to the interaction of the transmitter&#39;s antenna lobes from the various locations along that complex curve, pointing at an illustrative receiver (e.g., satellite)  420 , which may be in a southerly direction (e.g., a geo-synchronous satellite). At the same time, based on this southerly pointing of the transmitter, it can be seen that the southern-facing side lobes of the receiver  310  are much less prevalent as a potential for interference (i.e., the transmitter would be aiming away from the receiver from those locations). 
     As noted, the pointing angle (azimuth, elevation) of the terminal  410  (terminal antenna  660 ) relative to the incumbent receiver  310  changes the link budget calculation. Accordingly, each intended receiver (e.g., satellite)  420  to which the terminal may be pointed changes the results of the link budget calculation for a terminal location. Therefore, each incumbent receiver will have somewhat different protection zones for each intended receiver (e.g., satellite). 
     Specifically, with regard to intended receiver (e.g., satellite) diversity, the illustrative satellite-based system herein may operate initially with two or three geostationary satellites. For instance, to provide diversity and to manage occlusions from mountains or other obstructions, the illustrative system may employ one geostationary satellite in the westerly direction, and one in the easterly direction. An example of such intended receiver orientation from a terminal is shown in  FIG. 18 , where a terminal  410  at any particular location may point at (aim at) each of the intended receivers at a slightly different azimuth and elevation appropriate for the corresponding satellite, e.g., a southwesterly azimuth  1810  to satellite  420 - 1 , and a southeasterly azimuth  1820  to satellite  420 - 2 . (As described below, the terminal (or server) may select the best available satellite based on location and other factors.) Using the illustrative locations of example geostationary satellites, the difference between azimuth  1810  and azimuth  1820  may result in a 40-degree to 60-degree difference in azimuth look angle. As such, the resultant protection zones  1700  based on link budget calculations as described above could vary significantly, and as such may require separate computations depending upon which intended receiver is being considered. 
     It is important to note again that the link-budget-calculated protection zone boundary is governed by one or more (or illustratively all) of the following:
         On the receiver:
           location (latitude/longitude);   antenna azimuth;   antenna polarity; and   antenna gain definition for all angles around the receiver;   (—and, in certain optional embodiments, the antenna elevation and the antenna gain defined for all angles around the receiver).   
           On the terminal:
           location (latitude/longitude);   antenna pointing direction (azimuth and elevation);   transmit antenna gain definition for all angles 0-360 of azimuth and elevation;   power output of the transmitter; and   transmitter antenna polarity.   
               

     Note that channels/frequencies do not affect the calculation of the actual protection zone (that is, if a frequency is changed/added in the ULS database, it does not affect the protection zone calculation or the horizon calculation). However, since the protection zones are referenced by frequency/channel (e.g., transmitting on “channel  1 ” would not generally interfere with a receiver configured to receive “channel  2 ”), it is also important to keep accurate record of the receiver frequency band/channel. 
     Those skilled in the art would also recognize that similar protection zones can be computed to ensure that the transmission does not interfere with receivers of other satellites which may be in the sky in an angle (elevation and azimuth) proximity to the intended satellite, as noted above. 
     According to one or more embodiments herein, the techniques herein may also compensate for any potential inaccuracy in the sensors of the terminal  410 , such as, for example, the GPS location, the direction at which the mobile device points (azimuth), and the elevation relative to the horizon (tilt angle towards the satellite), and so on. In particular, to prevent any of these inaccuracies from misleading the terminal into thinking that it is not in a protection zone (where terminal transmission would not adversely impact any PtPR), the techniques herein may perform a “smearing” operation which expands the size of the protected zone (as denoted by the polygons  1700  above). 
     In one specific embodiment, the techniques herein include a smearing operation on the table of the terminal&#39;s transmitter antenna gain relative to the direction of incumbent receiver  310  (e.g., PtPR), and the tilt (elevation) of the transmitter toward the intended receiver  420  (e.g., satellite) relative to the horizon. However, in general this operation may factor in the uncertainty of the terminal&#39;s GPS location, the uncertainty of the azimuth of the intended receiver/satellite relative to the terminal&#39;s current position (which may come from the compass reading of the terminal, or from any other suitable azimuth sensor and/or calculation, and the uncertainty in elevation relative to the horizon (tilt angle towards the satellite). 
     This smearing process is meant to ensure that even in the worst case of any of these errors (or the combination of these errors), the system would still prevent a terminal  410  from interfering with any of the receivers  310 . To this end, the protection zones (polygons)  1700  calculated through the link-budget-based approach above may be expanded by varying the above parameters and expanding the protection zone for the worst case that could be caused by errors in the terminal&#39;s sensory system. Note that in accordance with yet another embodiment, the system may also bring into account the shaking of a user&#39;s hand by adding a fixed angular smear factor (such as, e.g., +/−5 degrees), and using this information to expand the protection zone even further. 
       FIG. 19  illustrates an example of how smearing may affect the protection zone  1700 , by expanding it in certain directions (e.g., “ 1700 +”) to compensate for any potential inaccuracy. As shown, for illustration only, this particular expansion as shown in  FIG. 19  results in a general extension of the protection zone along each of the radial directions of the original zone  1700 . However, actual computations of the zone based on smearing factors being input into the calculations above may result in a slightly different shape of the polygon, a different proportion of expansion, and perhaps with different expansion affects in different directions (e.g., greater along the main lobe than along the side lobes, etc.). For example, illustrative computations may be made (for each satellite) for a 0 az (zero azimuth) and 0 el (zero elevation) (no smear, e.g.,  FIG. 17 ), as well as for a +/−30 az and +/−5 el antenna smear, and a +/−180 az and +/−5 el antenna smear. Such different azimuth/elevation smearing for the same unintended receiver/PtPR would thus result in different protection zones  1700 / 1700 +. Accordingly, the expanded zone  1700 + is merely a visual example of how protection zone  1700  may be expanded, and is not meant to be limiting to the embodiments herein. 
     It should be noted that in one or more embodiments herein, the relative height of the terminal  410  with respect to the incumbent receiver  310  need not be factored into the smearing equation above, in order to reduce the computational complexity of the system. Rather, certain embodiments of the techniques herein may assume that that the terminal and the incumbent receiver are at the same altitude. This assumption is valid because when the terminal is at close distance to the receiver, the link budget is very high and the terminal is within a protected zone anyhow. On the other hand, when the terminal is far away from the receiver, the relative height of the mobile with respect to the receiver is much smaller than the distance. This results in a negligible low angle between the line of sight of the terminal to the receiver&#39;s antenna and the horizon. At the same time, however, should the height of the transmitter create a more substantial difference, such as for UAVs or other flying vehicles, then the relative height may be an important factor. Accordingly, whether to account for the relative height of the terminal may be configured on an implementation-by-implementation basis. For instance, in one particular embodiment, the system may use an elevation smear value, such as +/−5 degrees, that takes into account the potential elevation difference. 
     Generally, in the specific satellite network example implementation, if the terminal is actually above the altitude of the incumbent receiver antenna, the elevation won&#39;t be an issue because the terminal would be pointing up to the satellite (and away from the incumbent receiver antenna). However, if the terminal is lower than the incumbent receiver and closer to it, the terminal could be transmitting much closer to the antenna, especially in a mountainous area where the terminal is in a valley at the base of a mountain and the incumbent receiver (e.g., PtPR) is on the top of the mountain. One way to handle this would be a progressive smear of the elevation table for the incumbent receiver, so that the closer the terminal is to the incumbent receiver antenna, the more it can be smeared. 
     Notably, in certain embodiments (e.g., the preferred embodiment), the protection zone polygon  1700  need not be stored in the server database  543  or transmitted to the terminal (for local database  643 ), and instead may be used as a boundary around the incumbent receiver  310  within which the elevation of each geographic point may be evaluated to determine if that point is visible from the incumbent receiver or not. As described below, therefore, the distance of the farthest point within the protection zone that is visible from the line-of-sight receiver (e.g., a PtPR) is then stored in the database as a horizon. 
     Microwave communication, in particular, is line of sight, and is effectively blocked by earth features that are in the line of sight between the terminal  410  and the incumbent receiver (e.g., PtPR)  310 . Topology mapping/information about the terrain in which the incumbent network  300  operates is known, and as mentioned above, information about the topology of the terrain is available to the server  450 . (Note that in accordance with a specific embodiment, topographic information may also exist in the terminal, such as partial information (e.g., based on smaller map areas or less detailed information), and used as described below.) 
     According to one or more embodiments of the disclosure herein, the techniques herein may factor in the topographical layout associated with each incumbent receiver  310 . That is, in the previous steps above, the protected zones (polygons  1700 ) were calculated without bringing into account the topology of the area, and as such, the previous calculations were made under the assumption that the incumbent receivers  310  and terminal  410  operate on a flat plain (e.g., receivers  310  at their designated altitude above sea level, and the terminal  410  at sea level, but without any terrain features between them). In reality, various locations within the protected zones which were calculated in the previous steps may actually not need to be included in the protected zone because some topological feature (e.g., a higher hill or the actual horizon based on the elevation of the surrounding terrain) obscures a line of sight from that location to the incumbent receiver. 
       FIG. 20  illustrates an example cut-away view  2000  of an illustrative terrain/topology  2010  along the line  2015  from an incumbent receiver  310  to any point within its example protection zone  1700  (e.g., along the main lobe). (Note that any protection zone may be used, such as simplified zone  1400  above or, preferably, the extended protection zone  1700 +, and the view in  FIG. 20  is merely an example for discussion of the techniques herein.) Locations  2020  from which there is a line of sight from the location on the ground towards the incumbent receiver  310  are marked with a hashing, and locations  2030  which are hidden from the receiver  310  have no such hashing. 
     According to the techniques herein, therefore, terrain around an incumbent receiver  310  may be mapped by sampling the ground elevation in radials every r degrees around the receiver location (starting at the incumbent receiver and extending outward from the incumbent receiver). Terrain mapping is location-dependent rather than link-budget-dependent, so it only has to be done once per location (per incumbent receiver), optionally limited to processing elevations within calculated protection zones (which differ by smear value, incumbent receiver azimuth, and intended receiver/satellite for a particular location). The elevation mapping only needs to know the status of terrain points (visible or not visible to the incumbent receiver). Notably, however, keeping a status for each individual point in the radial is data intensive. 
     Instead, therefore, the techniques herein also propose a method of using the slope (line  2025 ) and distance from the incumbent receiver to blocking elevations. For example, if the maximum slope is set to −999 (which is practically straight down), elevation may then be sampled every n meters moving outward from the receiver. For each sample point, the slope from the incumbent receiver to the point is calculated. If the calculated slope is less or equal to than the current maximum slope, then that point is not visible to the incumbent receiver  310 , since the elevation point where the current maximum slope was generated would be blocking that point. If the calculated slope is greater than the current maximum slope, then that point is visible to the incumbent receiver, and it is set to the new maximum current slope. Sampling proceeds outwards from that point with the slope calculated at each point, until the calculated slope is less than the current maximum slope. This represents a blocking elevation, and is stored with the slope value and the distance from the incumbent receiver. Sampling continues out the radial until the maximum possible horizon is reached. For example such a maximum might correspond to the maximum distance that two 4000 m peaks (with sea level elevation between them) would be visible from each other, which is approximately 450 km. (Note that optimizations can be done in addition or in the alternative to sampling only within the calculated protection zones, such as using the actual elevation of the incumbent receiver location, among others.) 
     The topology-based actions above result in a set of [distance, slope] pairs, where for any point along the radial, the visibility can be determined by finding the two [distance, slope] pairs that the point lies between, calculating the slope from the point&#39;s distance and elevation to the incumbent receiver, and comparing it to the slope of the [distance, slope] pair closer to the incumbent receiver. If the slope of the test point is greater than the closer [distance, slope] pair, then the point is visible from the incumbent receiver, otherwise it is not visible. 
     This provides a technique for calculating the visibility of the incumbent receiver from any point around using slopes. For precise implementations (e.g., no forgiveness for interference), error should be made toward the point being visible rather not visible, because interference with the incumbent receiver (e.g., a PtPR) must be avoided at all costs. Using this method, missing a [distance, slope] pair causes more terrain to be revealed rather than obscured. 
     As the distance from the incumbent receiver increases, so does the distance between adjacent radials. To avoid missing lower areas between sampled points, each of the points are sampled perpendicular to each side the radial at increments of “n” meters up to half the distance to the next radial, and the lowest elevation value is used. (Note that in one illustrative example, both the highest and lowest elevation values may be used: the highest for testing the visibility, and the lowest for determining the slope.) 
     The last [distance, slope] value for a radial gives the maximum horizon for the radial. Any of the values in between it and the incumbent receiver can be used to increase the amount of blocked area; ignoring a [distance, slope] value simply decreases the amount of blocked area that is calculated. 
     The maximum [distance, slope] value for the total set of radials can be considered to be the maximum horizon for the location of the specific incumbent receiver (e.g., PtPR), since from no direction is the incumbent receiver be visible beyond that distance. This is defined to be the “Maximum Horizon” for an incumbent receiver. Note that this applies primarily for terrestrial PtPRs; when dealing with a PtPR incumbent receiver in the sky, e.g., a satellite, the corresponding horizon may be based on the height/altitude of the satellite applied to corresponding three-dimensional horizon calculations, accordingly. Note further that a satellite may be also affected by local topology. For example, if a satellite is placed on the sky over Hawaii, it may appear for some users (for example users in Colorado) as being low above the horizon and as such it may (or may not) be obscured by a mountain. 
     Notably, terrain mapping calculations also take into account curvature of the earth when calculating the blocked distances (e.g., using a standard 4/3 earth model to compensate for surface refraction effects). 
     Referring again to  FIG. 20 , the cross section associated with a specific azimuth from a specific incumbent receiver towards a terminal&#39;s location on the ground is shown. Despite the fact that the protection zone  1700  may mathematically extend up to 125 km, the topology map indicates that more than 75 % of the places along the specific azimuth (areas  2030 ) can be safely excluded from the protected zone. Different azimuths will have a different cross section, and as such, identify different areas that could be excluded from the protected zone  1700 . 
     According to one or more embodiments herein, the server  450  may thus calculate the topological cross sections for each incumbent receiver  310  radially at small increments (e.g., on 1-degree increments) around the incumbent receiver&#39;s location up to the intersection of the radial with the protection zone polygon  1700 . Referring to  FIG. 21 , therefore, which illustrates the completely blackened areas  2110  on the map to show the locations that were in the protection zone  1700  (with respect to the given incumbent receiver and specific channel and based on the link budget calculation) which have a line of sight towards this specific incumbent receiver. The hashed areas within the protection zone  1700  now indicate locations which could be excluded from the protection zone because the topology obscures the incumbent receiver, and as such, there is no line of sight from these locations towards the incumbent receiver. 
     Notably, in the illustrative embodiment, the server  450  calculates the polygon boundary  1700  for all incumbent receivers where the link budget is equal to the noise floor, prior to calculating the reduced coverage of areas  2110 . This keeps the amount of terrain data that is computed to a minimum. However, in alternative embodiments, the server may first compute all lines of sight regions from incumbent receivers, and then calculate the portions of those visible regions that meet the link-budget equations above. The end result would be the same, and it is merely a matter of computational preference. 
     Note further that according to one or more embodiments herein, terrain mapping reductions can be applied selectively in areas, such as where multiple protection zones overlap to give better channel selection options. Moreover, since terrain mapping information does not change, it can be downloaded a single time into the terminals  410  for the regions (or for specific incumbent receivers) where it has the greatest benefit, such as near mountainous areas, and used by the terminal as described below. 
     In accordance with a preferred embodiment, the link budget calculation and the topological line of sight horizon calculation may be performed in the server  450  or in offline cloud-based servers. Generally, the size of the server database  543  that would contain all of the details of the calculated link-budget protection zones  1700  and/or line-of-sight reductions to coverage area  2110  would often be too large to store in its entirety within local database  643  of a terminal. In addition to the size of the database, the calculations required to determine the impact of the topology on protected zones may also make it impractical to use the entire server database data in the terminal. Though in certain embodiments contemplated herein, sufficient resources (e.g., CPU and memory) may, in fact, be available on the terminals  410 , and the complete server database may be stored on the terminal for computation of terrain-based line-of-sight computations, more likely embodiments may consist of a hybrid approach, where only some of the terrain data is stored on the terminal, as noted above. Furthermore, based on the fact that the information about the incumbent system may change (e.g., the large FCC ULS database may change), it may not be practical to update the entire database over a low-bandwidth (e.g., satellite) communication channel. 
     In order to reduce the necessary size of the terminal&#39;s local database  643 , and in order to reduce the amount of data transmission to the terminal which may be required in order to update it for changes in the information (e.g., the FCC ULS database), the techniques herein introduce the concept of major and minor horizons (described below), which are calculated in the server  450  as a compressed representation of the relevant the areas  2110  within the protection zone which have a line of sight to the incumbent receiver, and passed to the terminal in lieu of using the entire server database  543 . For example, the local database  643  need only to store the parameters that the terminal would require to calculate (on the terminal  410 ) which channels (if any) can be used to transmit towards a given intended receiver (e.g., satellite)  420  from a specific GPS location without interfering with any incumbent receiver (e.g., PtPR)  310 . To achieve this, a system in accordance with the embodiments herein may introduce the use of major and minor horizons, which provide a representation of the more complex description of areas  2110  within the protection zone which have a line of sight to the incumbent receiver as viewed from an incumbent receiver (and projected onto link budget derived boundary polygons  1700 ). This representation method reduces the amount of stored data on the terminal (e.g., as well as the time/bandwidth required to synchronize the local database  643  with any updates to the FCC database and/or the server database  543 ), as described below. 
     Specifically, rather than maintain the topographic information in the mobile device and calculating the visible protection zones  2110  or maintaining a list of all of the out-of-sight portions of the protection zones  1700  which could be excluded from the protected zone, one or more embodiments of the techniques herein simplify the data structure stored on the terminal by maintaining only the farthest locations (“horizons”) in the protected zone  1700  (or, as mentioned above, simplified zone  1400 ), from which there is still a line of sight towards the incumbent receiver  310 . 
       FIG. 22  illustrates the reduced protection zone  2110  of  FIG. 21 , along with an associated major horizon  2220  and minor horizon  2230 , associated with incumbent receiver  310  as described herein. To calculate the major horizon  2220 , the server  450  may determine the farthest distance within an arc (e.g., +/−30 degrees), related to the azimuth of the specific incumbent receiver antenna, from which there is still a line of sight towards the specific incumbent receiver and from which the link budget is greater or equal to the noise level threshold as discussed above. Note that the illustrative +/−30-degree section was chosen empirically (arbitrarily) based on the typical shape of the protection zones  1700 / 2110 , and other angular ranges may be used to define the arc of the major horizon (e.g., +/−10 degrees, +/−45 degrees, and so on), so long as the resultant major horizon (angular range and distance), and minor horizon (described below), would include all of the areas  2110  where a transmission by terminal  410  may interfere with a corresponding incumbent receiver. 
     Note further that the angular range of the major horizon (e.g., +/−30 degrees) may be consistent across all incumbent receivers (e.g., receiver A having a major horizon with distance X and a receiver B having a major horizon with distance Y, where both angular ranges of the major horizons are a pre-defined +/−30 degrees), or else may be different and defined on a per-receiver basis (e.g., receiver A having a major horizon with distance X and a determined angular range of +/−30 degrees, and a receiver B having a major horizon with distance Y and a determined angular range of +/−20 degrees). Note that in such an embodiment, the different angular ranges for the arcs of the major horizons would thus need to be also transmitted to and stored within the local database  643  of the terminals (e.g., in the above example, the local database  643  would need to store the +/−30 degrees for receiver A, +/−20 degrees for receiver B, etc.). 
     The major horizon  2220  is illustratively marked within  FIG. 22  as a “pie-shaped” section which spans  60  (+/−30) degrees, having a radius (distance from the incumbent receiver  310 ) being defined by the major horizon. As can be seen, all of the visible (black) locations  2110  from which there is line of sight towards the incumbent receiver within the +/−30-degree section (and that are in the protection zone  1700 , i.e., defining the locations where a terminal&#39;s transmission may interfere) are located within the arc of the major horizon  2220  (that is, the pie-shaped section). 
     Similarly, the system may also determine the farthest locations in the remaining 300 degrees (or whichever remaining portion of the 360 degrees surrounding the incumbent receiver) which are in the protection zone  1700 , and particularly from which there is a line of sight (reduced zones  2110 ). This distance is defined to be the minor horizon  2230 , which, as shown in  FIG. 22 , defines an arc that generally surrounds any remaining visible side lobes or back lobes of the incumbent receiver which is not already encompassed by the major horizon. It should be again noted that according to this embodiment, all of the areas  2110  within the protected zone  1700 , from which there is a line of sight towards the incumbent receiver, are included either in the major horizon  2220  or within the minor horizon  2230 . 
     According to this particular embodiment of the techniques herein, therefore, an illustrative local database  643  on the terminal would include the following information for each incumbent receiver  310 : index (tower ID), tower latitude and longitude, antenna azimuth, polarity (horizontal and/or vertical), satellite transponder channels that the incumbent receiver frequencies overlap, and major and minor horizons (e.g., for each intended receiver/satellite, and for each azimuth/elevation smear value as described above). (Also, for satellite receivers, which may have an assumed altitude of 22,336 miles, an angle of elevation of the receiver (with relation to the terminal, e.g., calculated based on the position of the satellite in the sky and the GPS location of the terminal) may also need to be known for corresponding calculations, as mentioned herein.) Illustratively, the database consists of approximately 17 bytes of data per incumbent receiver. The specific size (number of bytes) of a terminal&#39;s local database  643  depends on the number of parameters stored for each incumbent receiver. For example, some antennas operate in only horizontal or vertical polarity while other may operate simultaneously in both horizontal and vertical polarity. As such, in one possible embodiment herein, if an incumbent receiver has a dual polarization antenna, the techniques herein may be configured to assume the worst case and use only a single (i.e., the longest) horizon. Alternatively, if the antenna has only a single polarity, then the database may be populated with two different horizons in this embodiment, one for transmitting in a polarity aligned with the incumbent receiver&#39;s polarization, and the other one perpendicular to the receiver&#39;s polarity. 
     Now that the server&#39;s database  543  has been populated with a representation of a potential interference zone, particularly selected from one or more of the simple protection zones  1400  link-budget-based protection zones  1700 , or, preferably, the major and minor representations  2220 / 2230 , as described above, this information may then be shared with the terminal  410  for storage in its local database  643 . In accordance with one or more embodiments herein, the terminal  410  may be configured to receive the information for its database  643  in a variety of manners. 
     First, with regard to communication of the data, the data about the incumbent network may illustratively be uploaded to the terminal  410  during initial configuration of the device (e.g., by the manufacturer), and/or when high-bandwidth connectivity (e.g., Wi-Fi, USB connection to an Internet-connected device, cellular, etc.) is available. Retrieving the data over a lower bandwidth connection, such as a satellite link, might take a long time, and as such, an illustrative (and non-limiting) embodiment reserves such low-bandwidth link transfers for smaller updates or emergency downloads only. 
     In particular, with regard to updates to the data, the techniques herein may preferably ensure that the terminal databases are kept updated at all times in order to properly account for any changes to the incumbent system&#39;s configuration (e.g., new or changed licenses, etc.). Note that updates to the underlying information of the incumbent network may occur monthly, weekly, daily, multiple times per day, or at any interval determined by the system. The terminals  410  herein may thus be configured to synchronize with the latest server database  543  (i.e., check if it is up-to-date). In one aspect of the techniques herein, the terminals  410  may be configured to regularly synchronize and update (if out-of-date/sync) their local database whenever connected to a high-bandwidth link, or otherwise so long as the terminal is able to communicate with the server (or some other system infrastructure) via a network that does not need to avoid interference with incumbent receivers. For instance, this may occur while a user is at home (e.g., preparing for a trip), or else in the field whenever a wireless network (e.g., Wi-Fi, cellular, etc.) becomes available. In another aspect of the techniques herein, particularly in embodiments with zero interference tolerance, the terminals must confirm that their local database is up-to-date/synchronized with any updated information about incumbent receivers (e.g., at least local receivers) when the terminal desires to transmit. In this aspect, should the local database be out-of-date, then any downloads at this point (e.g., on the reduced-bandwidth satellite channel) may be limited to a relatively small region around the present location of the terminal. 
     Regarding what, exactly, the data is that is downloaded to the terminal, various embodiments are presented herein, ranging from a full download (all of the information for the entire incumbent network), down to a minimalistic download (e.g., update) of data related to incumbent receivers in the vicinity of the terminal  410 . In particular, since a general embodiment of a terminal  410  assumes that storage of information about the entire incumbent network (and terrain information, etc.) may be too large for the terminal&#39;s memory (and/or processing) capacity, various storage efficiencies may be considered herein. That is, though the storage and computation requirement of the database  643  and processor  620  of device  410  may be reduced greatly by the simplified major and minor horizons representation of the protection zones, this simplified database representation may still be too large (and time consuming) for updates over a low-bandwidth satellite communication channel  400 . To alleviate this problem, the database may be further divided into geographical zones, wherein each zone contains only partial information of the whole database. 
     For instance, in one embodiment, the data used to update the database  643  of terminal  410  is limited to whatever portion (zones) of the incumbent network that is deemed applicable, e.g., based on location of the terminal (e.g., if the terminal is located in the western portion of the United States, only information about incumbent receivers in the western portion of the United States, as opposed to all incumbent receivers in the United States, may be used to update the database of that terminal). Note that the use of western and eastern regions is merely one illustrative embodiment, and any number of regions or “geo-zones” (or zones) may be established, such as based on the size of the resultant per-zone “sub-database” (e.g., to balance the number of incumbent receivers in each zone), or other factors deemed appropriate. In one illustrative (and non-limiting) example, fourteen (14) geo-zones may be used to divide the incumbent network of PtPRs in the United States into manageable portions (note that the geo-zones may overlap). 
     In another embodiment, various levels of detail may be downloaded to the terminal, such as, for example, detailed (precise) information regarding all incumbent receivers communicating only on certain frequency bands/channels (e.g., hailing channels, described below) within the entire incumbent network (e.g., link-budget-based protection zones  1700 / 1700 +), major and minor horizon information protection zones ( 2220 / 2230 ) for a given geo-zone region (e.g., California), and then detailed terrain information ( 2010 ) for a sub-region (e.g., the hills within 50 miles of Palo Alto, Calif.). Any combination of information granularity and coverage may be conceived, and the present disclosure is not limited to only those mentioned herein. In addition, the different levels of information may also be time-dependent, meaning general information may first be downloaded, and then as the terminal attempts to transmit from a given location or moves around to different transmission locations, then depending upon the level of available bandwidth on the communication medium, additional information may be supplemented while “in the field”. (For example, as described below, a “hailing channel” may be used to initiate communication, and then for this currently mentioned embodiment, that initial communication could be used to supplement additional information to the terminal to assist in deciding the particular channel to use for the remainder of the communication.) 
     Armed with the appropriate information about the incumbent network  300 , the terminals  410  may proceed to transmit safely (without interfering) according to the terminal-based operations described herein. (See, again, the general description above in  FIG. 12B .) In particular, a terminal  410  (e.g., attached to a smartphone, within a smartphone, or as a part or accessory to any other device with a primary communication channel, such as cellular, Wi-Fi, etc.) may first turn on its potentially interfering communication process (e.g., satellite-based communication in the C-band). In one embodiment, this may be a simple on/off functionality, or else in another embodiment may be based on whether the primary communication channel lacks sufficient coverage. 
     Once on, or once otherwise ready to attempt transmission, the terminal  410  must determine its geographical location within the incumbent network. Generally, the level of accuracy of a satellite-based global positioning system (GPS) is preferred, though other known location techniques may be used. (Note that for reduced accuracy locations, including GPS location inaccuracies, additional safeguards may be utilized, such as expanded location possibility calculations, reduced communication power, designated/reserved channel usage only, etc.) For example, due to limitations of GPS systems, the location of the terminal  410  may not be determined with complete certainty, so the putative coordinates of the terminal may be insufficient to guarantee that transmission is allowed. (Certain GPS software provides not only coordinates but an uncertainty distance d_uncertain, such that the mobile device is assumed to be found within a circle of radius d_uncertain around the reported location (latitude/longitude).) Note that in addition, the techniques herein, in certain embodiments (e.g., adhering to FCC requirements), may also determine the distance that can be traveled from the current location, so that transmission occurring while the terminal is in motion can be performed without moving into a interfering protection zone (that is, for example, while moving in a car, on a boat, on a drone, etc.). 
     With its current location information, the terminal  410  may then proceed to ensure that its transmission will not interfere with an incumbent system  300  (e.g., ensuring that it complies with FCC rulings and never interferes with any of the incumbent PtPRs). In particular, for the current terminal location (e.g., any and all positions within an uncertain circle mentioned above, or any position potentially reached while in motion), the terminal references its database  643  to determine whether the location is within a protection zone (simplified zone  1400 , link-budget-based zone  1700 , smeared zone  1700 +, major/minor horizons  2220 / 2230 , and so on) of any incumbent receivers  310 , as detailed above. 
     Recall, as described above, that a protection zone for a receiver  310  (e.g., PtPR) is the geographical area around the receiver (as determined/defined by the server  450 ) in which a transmitting terminal might add an unacceptable amount of noise to that receiver. For example, PtPRs are sensitive to a terminal that is transmitting on a frequency whose bandwidth (e.g., +/−4 MHz) overlaps the frequency band of the PtPR. The chance for a terminal&#39;s transmission to interfere with an incumbent receiver  310  is a function of the incumbent receiver&#39;s antenna characteristics and that antenna&#39;s orientation relative to the terminal&#39;s location, the transmission power of the terminal antenna relative to the incumbent receiver location, and the distance between the terminal and the incumbent receiver, and so on. Recall, also, that the server  450  may be configured to provide simplified but less-precise (and more conservative) representations of the protection zones to the terminals (e.g., simplified protection zones  1400 , major/minor horizons  2220 / 2230 , etc.), in order to save resources of the terminals. 
     According to the techniques herein, therefore, rather than merely taking a generalized protection zone as a simple go/no-go indication of an ability to transmit (one optional, though imprecise embodiment herein), when the terminal  410  detects that a potential for interference exists (i.e., that the location is within a protection zone of a specific incumbent receiver), the terminal may then specifically determine whether any chance of interference would actually occur based on real-time link budget calculations from the precise location of the terminal towards this specific incumbent receiver. 
     In particular, according to one or more embodiments herein, for each one of the incumbent receivers having a protection zone within which the terminal&#39;s location resides, the terminal may calculate the link budget from the current location to the incumbent receiver, and may determine whether transmission from that location would interfere with operations of the unintended receiver (that is, whether the transmission would surpass a noise floor of the unintended receiver, optionally plus an additional safety margin, e.g., 6 dB). If it would (or would possibly) interfere, then that particular communication configuration (e.g., a particular channel to a particular receiver/satellite, at a particular polarity, etc.) may be deemed unavailable for transmission by the terminal in that location. Otherwise, the communication configuration is available to transmit without interfering with the incumbent network  300 . 
     Note that this calculation takes into account the transmitter properties, such as pointing towards a given intended receiver (e.g., satellite)  420 . For instance, in one embodiment, a terminal may first check a default communication configuration, e.g., a particular channel to a particular receiver/satellite, and as such, would compute the link budget for that particular receiver/satellite. In another embodiment, however, the terminal may first check all possible communication configurations (e.g., different channels, different intended receivers, etc.) to determine whether any channels are freely available (i.e., that do not need a link budget calculation). In this instance, if no channels are freely available, then the terminal may compute the link budget for any one or more of the communication configurations (e.g., different channels, different intended receivers, etc.), and may select one particular channel on which to transmit, as described below. (It is of course possible that in some cases there are no protection zones covering the location of terminal  410 , and in such a case, link budget computations may not be necessary, and the terminal may simply transmit freely without fear of inducing interference.) 
     In one or more embodiments herein, in order to further ensure eliminating the prospect of interfering with an incumbent receiver, the link budget calculation performed by the terminal  410  may also take into account any uncertainty in any parameter used to calculate the link budget, such as measuring the direction (azimuth and elevation) in which the terminal points (e.g., similar to the smearing operation performed in the ground station/server as described above), or the uncertainty of the GPS location, such as uncertainty specifically reported by the GPS system of the terminal. For instance, regardless of the smearing or other expansion to protection zones as described above, the link budget computation by the terminal is based on whether it is within a protection zone, and the link budget computation itself thus returns to a level of mathematical precision according to various assumptions of the physical properties of the terminal at any given moment. However, for the same reasons as described above (inaccuracy in location or azimuth, shaking hands, etc.), this extra level of assurance may be beneficial to re-include into the link budget computation in order to account for such variations in actual transmission properties in order to ensure that under no circumstances the terminal  410  would interfere with incumbent receivers  310 . 
     Other considerations, such as line-of-sight, may also be used to determine the chance of interference. For instance, as described above, since certain communication frequencies (e.g., C-band) need a clear path to the receiver, granting the terminal a permission to transmit also depends on whether or not there is a clear line-of-sight between the terminal and the unintended receiver (i.e., whether the terrain between the receiver and prospectively transmitting terminal would block the transmission in the direction of the receiver). In embodiments where the terminal has terrain information, further limitations may be placed on (or removed from) the possibility of interference with an incumbent receiver, since there will be defined regions within which a terminal would not be visible to, and would thus not actually interfere with, the incumbent receiver, regardless of what the link budget calculations above would otherwise assume. That is, even if the link budget calculation might indicate an interfering location, the fact that the unintended receiver would be topologically blocked from the transmitting terminal would render communication from that location available. Note that in one embodiment the link budget calculation may be performed first, and then terrain-based limiting may be performed to further filter the results of the interfering regions. Alternatively, terrain-based limiting may first be performed to filter the areas within the approximated protection zone for which a link-budget calculation would be necessary (e.g., if an unintended receiver is blocked for a particular region within which the terminal is located, there would be no need to perform a link budget calculation for that particular receiver). 
     Notably, the techniques described herein may make the choice of frequency diversity, satellite diversity, or polarization diversity by selecting the minimal potential for harmful interference, e.g., based on the particular location of the terminal  410  at the time it desires to transmit. As described above, frequency diversity is one way to avoid interference on one frequency by moving to another frequency for which the terminal would not be within a protection zone. 
       FIGS. 23A-23B , for example, illustrate a geo-locational example of avoiding interference in wireless communications in accordance with the techniques herein. For instance, in the geographical visualization  2300  of  FIG. 23A , assume that there are five receivers  310 , A, B, C, D, and E, within the proximity of a potentially transmitting terminal  410 . As shown in  FIG. 23A , three of receivers, A, B, and C are configured to receive on an illustrative channel “ 1 ” (a given frequency band), and their respective protection zones  2350  are shown. As can be seen, terminal  410  attempting to transmit to a specific intended receiver (e.g., satellite)  420  falls within the protection zone of receiver C on channel  1 , and, assuming either that protection zones  2350  (e.g., simple protection zones  1400 , link-budget-based protection zones  1700 , or the major and minor representations  2220 / 2230 ) are dictating go/no-go authorities, or else assuming that a link budget calculation to receiver C determines that a transmission on the incumbent receiver&#39;s channel  1  would interfere, the system described herein would determine that channel  1 , at that current location of terminal  410 , is unavailable for transmission towards the intended receiver. 
     Conversely, as shown in visualization  2310  of  FIG. 23B , assume that receivers D and E are configured for an illustrative channel “ 2 ” (a different frequency band than channel  1  above), and that protection zones  2350  of those receivers either do not overlap with the location of the terminal, or else the link budget calculation determines that communicating on channel  2  would be acceptable (non-interfering) with any incumbent receivers (e.g., PtPRs). In this instance, the terminal  410  would be permitted to transmit on non-interfering channel  2  towards the intended receiver (e.g., satellite)  420 , but not permitted to transmit towards that intended receiver (e.g., satellite) on the interfering channel  1 . Note that the views shown in  FIGS. 23A-23B  are vastly simplified from real-world examples, and are meant solely as an illustration, and are not meant to be limiting to the scope of the techniques herein. 
     In addition to frequency diversity, there are several additional communication configurations that can be adjusted to avoid any risk of interfering as well. For instance, in addition to frequency diversity, there are also satellite (or orientation) diversity and polarization diversity. Polarization diversity involves switching to the opposite antenna diversity to reduce interference. For example, certain terminal configurations may be able to transmit with either horizontal or vertical polarity, switchable on demand, or else by instructing a user to rotate the terminal to a different polarity. When the unintended receiver&#39;s antenna utilizes the same polarity as the terminal&#39;s transmitted signal, the distance from the incumbent receiver where communication is safe is quite a bit farther than when the transmitter and incumbent receiver polarities are not the same. The techniques herein may also account for various considerations for when one or both of the intended and unintended receivers may operate in dual polarities, particularly in a manner that reduces interference at the unintended receiver. 
     In  FIGS. 24A-24B , an example of choosing satellite diversity is shown. Here, for example, a switch from a western satellite (e.g., 193-degree azimuth to the illustrative Galaxy 12 satellite) to an eastern satellite (e.g., 142-degree azimuth to the illustrative Galaxy 3C satellite), while remaining on the same channel, can be confidently computed by using the antenna gain parameters of both the unintended receiver antenna (Gr) and the gain of the terminals&#39; transmitting antenna (Gt). For example, assume that as shown in  FIG. 24A  the terminal  410  considers a transmission to the western satellite (while at a location that is illustratively 9 degrees off of the incumbent receiver&#39;s bore-sight). In this position, and based on the corresponding aiming direction of the terminal&#39;s antenna for transmission to the western satellite, the terminal  410  falls within the protection zone  2350  of one particular incumbent receiver  310 . Assume, for this example, that after perform the link budget calculations above, the terminal determines that a transmission from this location to the western satellite would (potentially) interfere with the operation of this incumbent receiver (the received power at the incumbent receiver would be above the noise floor), and would thus prohibit transmission under these parameters. 
     In  FIG. 24B , on the other hand, when communicating with the alternative eastern satellite (e.g., 142-degree azimuth to Galaxy 3C), thus pointing slightly away from the incumbent receiver at issue, a corresponding protection zone  2350  may change based on the new angular relationship of the transmitter and incumbent receiver, since the link budget calculation to the incumbent receiver takes the aimed direction (transmission lobe) of the terminal&#39;s antenna into account. Note that while the satellite diversity switch may result in the terminal no longer being located within a protection zone  2350 , at which time no further analysis would be necessary (i.e., the terminal would be free to transmit to that alternative satellite), the terminal  410  in this example may be still illustratively located within protection zone  2350 , which still requires additional detailed analysis. According to the new aimed direction of the terminal&#39;s potential transmission, assume that it may now be determined (e.g., based on a link budget calculation) that the received power at the incumbent receiver would be below the noise floor, and as such, the transmitter would be allowed to transmit to the alternative satellite, unlike when transmitting toward the western satellite in  FIG. 24A  above from the same location. Thus, by using intended receiver (e.g., satellite) diversity, additional communication configurations may be achieved that offer more available options for a successful (i.e., non-interfering) transmission. 
     Note that where multiple communication configurations are available for transmission (i.e., without introducing any interference at any unintended receivers), the techniques herein may provide various considerations to allow the terminal  410  to select a specific configuration, and to proceed with its communication to the intended recipient (e.g., satellite)  420 . For instance, the configuration (e.g., channel, recipient, polarity, transmission power, etc.) may be selected either a) in a manner that maximizes the link budget towards the intended receiver (e.g., one of the satellites), b) in a random way amongst the entire available set of configurations for the terminal to communicate with a specific receiver (e.g., a specific satellite), c) in a random way amongst the entire available set of configurations for the terminal to communicate with all of the available receivers (e.g., all of the available satellites), or d) in a manner that load balances any given channel&#39;s use across a plurality of terminals (e.g., based on server participation). 
     Conversely, should no communication configurations be available for transmission, regardless of communication diversity options discussed above, then the techniques herein prevent transmission from the terminal in order to avoid interference with the incumbent system  300 . Note, however, that various additional measures may be attempted by the terminal prior to completely ruling out any communication from its current location. In particular, the techniques herein also provide for various considerations for controlling an expected receive power at an incumbent receiver  310 . For example, in one embodiment, if it is determined that the terminal  410  is in a location where the link budget is only marginally over a pre-determined threshold, thus indicating that terminal  410  is prohibited from transmitting towards a specific intended receiver (e.g., satellite) because it would interfere (albeit marginally) with a given unintended incumbent receiver (e.g., PtPR)  310 , the terminal may be configured reduce the power encountered by the unintended receiver (e.g., PtPR), and as such render a location which was marginally in a protected zone to become an unprotected transmission location for that particular channel. 
     According to one or more embodiments herein, such a reduction of receive power at the unintended receiver may be based on reducing the transmit power of the transmitter, that is, attempting to transmit at less than the nominal power on a given channel. To accomplish this, the terminal  410  may first calculate a reduced transmission power that would not cause any interference with the incumbent receiver (e.g., PtPR)  310 . The terminal  410  may then calculate the link budget with this reduced transmission power towards the intended receiver (e.g., satellite)  420 . If the link budget, using the reduced power, is greater than the sensitivity of the intended receiver (while still not interfering with the unintended incumbent receiver), the terminal  410  is then allowed (e.g., granted the permission) to use the given channel at a reduced power. Alternatively, the device may compare the amount of power it is over the noise floor of the unintended receiver, Delta PU, against the amount of power it is over the sensitivity of the intended receiver, Delta PI. If Delta PI is greater than Delta PU, then the receiver may reduce its transmission power by Delta PU as to reduce the received power at the unintended receiver below the required threshold while maintaining adequate power level (above receiver sensitivity) at the intended receiver. 
     Note that in one or more additional embodiments herein, the transmit power from the terminal  410  may also be selected for other reasons, such as based on an ability to transmit at reduced power while still meeting the link budget at the intended receiver  420 , e.g., to save/extend battery life. That is, the transmission power may be based on the link budget calculations described above ahead of the transmission (or else based on a measure of receive power at the intended receiver, i.e., a feedback-based control). Further, such reduced transmit power may be in the form of a non-linear duration representation to save on transmission bandwidth. 
     As an alternative to explicit transmission power reduction, other measures may be taken to reduce the receive power at the unintended receiver, such as changing the azimuth, elevation, and/or elevation angle of the transmitter. In particular, by varying the physical orientation or placement of the terminal&#39;s transmitting antenna  660 , such modifications may have the effect of improving the link budget calculation to the unintended incumbent receivers. This concept was described generally above with reference to satellite diversity ( FIGS. 24A-24B  above), where changing the angle away from an incumbent receiver from one satellite to another could create a situation where a transmission would be allowed. Here, however, the concept is the same, but rather than switching, for example, from the western satellite to the eastern satellite, imagine now that the terminal (or user holding the terminal) is instructed to aim the terminal&#39;s satellite  660  in a position that is even further east (e.g., up to 20 degrees beyond the illustrative 142-degree azimuth, say 122 degrees), e.g., for the duration of the communication session or only for the duration that the device is transmitting. In this manner, though the receive power at the intended receiver (e.g., the eastern satellite) may be reduced by the off-center aim, the receive power at the unintended incumbent receiver may be reduced to a level that no longer interferes (e.g., based on additional link budget calculations according to the updated transmitter orientation). As such, the techniques herein provide various physical orientation provisions (e.g., instructions, control of automated actuators, etc.) to re-orient the transmitter in a manner that reduces the receive power at the unintended receiver. Some illustrative examples of such re-orientation may include, among others: a higher elevation angle; further away from the unintended receiver; at an azimuth away from the unintended receiver (and possibly away from the intended receiver as well); at an azimuth slightly different than towards the intended receiver (and away from the direction towards the unintended receiver); at a rolled pitch (e.g., sideways) in order to reduce the received power at the unintended receiver by misaligning the polarization of the transmitted signal with the unintended receiver; moved to a higher elevation (e.g., climbing a hill, elevating a drone); or possibly even to a lower elevation (e.g., removing the terminal from the line-of-sight of the unintended receiver); and so on. 
     Other options for reducing the interfering receive power may be available, and any combination of the above options may be suitable as well. It should also be noted that in any of the above cases, the system (e.g., terminal and/or server) verifies that the reduction of link budget towards the unintended receiver (e.g., PtPR)  310  maintains sufficient link budget from the terminal  410  towards the intended receiver (e.g., satellite)  420 . In addition, transmissions (e.g., packets) sent at a reduced power (or alternate orientation) may be marked accordingly to make the ground station aware that a reduced power (or orientation) is used from a protected area from which transmission with nominal power (at an expected orientation) is prohibited. Furthermore, it is important to note that certain of these above actions may also affect the link budget in the direction from the intended receiver (e.g., satellite) as a transmitter back towards the terminal  410  as the receiver (i.e., the downlink direction), and care and instruction should also be taken to remain within the proper reception conditions for the intended communication in both directions (if necessary). 
     Notably, should the intersection of protection zones in any given area be covered on each channel/frequency for which the terminal  410  is configured to transmit, or, more specifically, if the link budget calculations at the terminal confirm that any possible communication configuration (channel, power, direction, etc.) would interfere with at least one incumbent receiver, then such an area is a protected or “blocked” area, and no transmission would be allowed. Said differently, a protected/blocked area is a geographical area in which none of the selected transponder frequencies can be used to transmit from the terminal  410  to its intended receiver (e.g., the satellite  420 ). That is, a transponder frequency can only be used if the transponder lies outside of the interference levels (e.g., protection zones/link budget) of all receivers whose frequency range overlaps the transponders&#39; frequency range, and a terminal is determined to be within a protected or blocked area if it is in the protection zone of at least one receiver  310  (e.g., PtPR) for each of the available transponder frequencies. (Notably, with the illustrative example communications systems and frequencies as mentioned below, such areas are considered to correspond to less than 0.001% of the United States&#39; geographical area.) 
     According to one or more embodiments of the present disclosure, the techniques described herein may be based on a centralized model, a localized model, or some other model in between. For instance, according to an illustrative centralized model of operation, a local terminal  410  may provide its location information to a centralized system (server  450 ) on a first cleared channel (e.g., a hailing channel that is computed to not interfere, or that is known to never interfere), illustratively via the satellite link  420 , and the centralized system performs computations and reports back to the mobile transmitter a set of one or more potentially interfering channels (e.g., communication channels) on which the transmitter (terminal  410 ) is allowed to transmit from that particular location (i.e., that do not interfere). In localized embodiments, information about the local incumbent wireless communication system  300  may be loaded in the terminal  410  from the server  450  (e.g., when connected over a higher speed network), and the terminal may perform the computations and determine, for itself, acceptability of transmitting on potentially interfering channels. Even in such localized embodiments, periodic updates and permission-based confirmation/validation may be required before the terminal is allowed to transmit. That is, a permission-based operation can be used to shut down terminal communication if necessary. (Note also that in the preferred embodiment, no earth terminal will transmit until it synchronizes with the spread spectrum signal that a satellite transmits. That is, the satellites  420  may be configured to send out a regular, repeating broadcast on a non-interfering downlink channel (e.g., 3702.5 MHz or other pre-arranged frequency bands). This broadcast may, among other things, provide frequency and timing symbols to decode the direct sequence spread spectrum signal for forward path communications, as well as indicating database updates/versions in order to allow a terminal to determine whether its local database is up-to-date before transmitting.) 
     In order to effectuate the centralized and/or local (permission-based) modes mentioned above, the techniques herein may provide for one or more “hailing” frequency bands/channels, which as described below, are generally consistent in configuration (few updates), and have minimal regions of potential interference (sparsely assigned). 
     In particular, using the illustrative embodiment as an example, satellite transponder channels may be defined by a center frequency, a width, and polarity. Each satellite may have any number of the same or different transponder frequencies that one can communicate with. As noted above, some of these transponder frequencies may lie in areas of the C-band spectrum where the FCC will likely allocate very few (if any at all) frequencies to be used by PtPRs in the future, and the rest may lie in frequencies where any number of changes may occur on a daily basis. The techniques herein propose to assign these specific channels that have the perceived minimal potential for additions or changes as the hailing frequency channels (or hailing channels). It should be noted that while areas of the C-Band spectrum have been identified where it can be assumed that few, if any, changes will occur in the future, the techniques herein may also have the ability to use transponder channels in areas of the C-band spectrum where many changes may occur. 
     Currently, in the entire United States and its territories, of the 56,000 PtPRs in use, there are approximately 61 PtPRs whose frequency and width overlap the frequency range of 6168-6182 MHz, and approximately 18 PtPRs whose frequency and width overlap the frequency range 5925-5930 MHz (as opposed to an example of thousands of PtPRs whose frequency channel overlaps any arbitrary 8 MHz wide bandwidth channel in the 5930-6168 and 6182-6425 MHz range). Per FCC regulations, it is currently expected that the FCC will issue few new licenses to use these hailing channels on any new or old PtPRs. However, the existing PtPRs which utilize frequencies and widths that overlap the hailing channels are grandfathered in with permission to continue using these channels. Accordingly, these two frequency ranges, 5925-5930 MHz and 6168-6182 MHz, may be selected for use as the hailing frequencies/channels herein. (Note that in the 6168 to 6182 MHz spectrum, new allocations are currently limited to 3.75 MHz or less, which prevents the allocation of a single frequency at a location from consuming the entire 14 Mhz spectrum width.) 
     In one example implementation, the hailing channel has a bandwidth of 4 MHz (a half-width channel) but nothing restricts the hailing channel to 4 MHz. The 4 MHz bandwidth was selected because it fits within the 5925-5930 band, and similarly three total hailing frequency channels of 4 MHz can fit within the 6168-6182 band. The half-width 5927.5 frequency, at the center frequency of the 5925-5930 MHz segment of the C-band, may be illustratively chosen as the primary hailing channel because there are only 18 PtPRs in the United States on this frequency (between 5925.1 and 5930 MHz), which provides a very high coverage rate as a low-bandwidth, lightly-used channel. Of course, these 18 PtPRs must still be avoided when a terminal is in the Protection Zone of one of these specific receivers. As such, the terminals in this illustrative embodiment initially contain the records of all 18 Hailing Frequency PtPRs, which may be updated whenever they change. 
       FIG. 25A  illustrates an example table  2500  of active point-to-point microwave links between 5925.01 MHz and 5930.0 MHz in the United States. Note that from the northern hemisphere to communicate with a geostationary satellite, a terminal must be pointed in a southerly direction to the equatorial plane, where the geostationary satellites reside. As can be seen from the table  2500 , of these 18 links, only eight have receivers that point in a northerly direction. Thus, if the PtPR protection zone points south, the resultant protection zone(s) would be smaller than northerly facing PtPR protection zones. A simplified illustration of this is shown in  FIG. 25B , with northerly facing zone  2510  being larger than southerly facing zone  2520 . 
     Notably, in the illustrative example, each satellite has n full-width (8 MHz) channels. From initial analysis, using different channels on each satellite gives maximum coverage for the minimum number of channels—for instance, simply using 5934 MHz and 5998 MHz on Galaxy 12 and 5974 MHz and 6030 MHz on Galaxy 3C (in addition to the hailing frequency on both) yields 99.999% coverage of the US (including Hawaii and Alaska). Full analysis may be used to determine the optimum/minimum channel selection to produce the largest unblocked area overall, and the example frequencies and configurations herein are merely representative examples of generally large coverage areas. Note also that this assumes using only two satellites and only two channels per satellite (e.g., in addition to the illustrative 5927.5 MHz hailing frequency on each satellite), but more than two satellites and channels may be available and may be accounted for. 
     In general, given that the illustrative embodiments above for centralized and/or localized communication may use the hailing frequencies as an initial part of the communication with satellite (e.g., to confirm or determine the actual channel to use for the following transmission) for all terminals  410  in the network  400 , techniques herein attempt to minimize the use of the hailing frequencies, such as for only the initial signaling as mentioned above (e.g., permission, channel selection for the primary transmission, and so on). In one or more particular embodiments, however, the hailing frequency bands/channels may be made available with limited use for terminals that are blocked from transmitting on the other (non-hailing) channels, such as due to the proximity to a PtPR with an overlapping frequency. In this regard, the techniques herein may allow for certain communication capability on hailing channel, such as in response to a terminal that can communicate with a satellite only via a hailing channel. In such an instance, with no other option, the terminal may be configured to either use the hailing channel as the selected channel, or may use the hailing channel for a limited amount of data (or bandwidth, e.g., data/time), such as by limiting the length of messages sent. Preferably, in one embodiment, the terminal  410  may only use the hailing frequency for its communication based on first receiving server permission, or else once a user has acknowledged that it is an emergency condition (e.g., to limit over-use of the channel simply because no conventional channels are available at the current location). (Note that in certain embodiments, in such a situation, the terminal may provide or be provided with navigational guidance to move the terminal to a place where additional communication channels may be available.) 
     Note that there may be circumstances where, within a given region, PtPR protection zones may change and intersect all return path channel frequencies (e.g., if the hailing channel(s) have changed for the current zone), such that transmission from that zone is effectively blocked, unless a wireless update can be received since the terminal will have no available return path frequencies to transmit on. To avoid the terminal from being “locked out” by this occurrence, a pushed-update mechanism may be provided to broadcast, e.g., from the satellite  420  to terminals  410 , any channel changes that have recently occurred (e.g., in the last 21 days) to the hailing channels. (Note again that in the example implementation, the downlink channels, e.g., 3702.5 MHz, are not channels that would interfere within the incumbent PtP system  300 , and thus the terminals can freely listen on these channels for updates.) This allows a terminal to determine the availability of an available hailing channel for the terminal&#39;s current zone, so that an incremental database update can be requested to allow re-evaluating the overall (and up-to-date) channel availability from a current location. This update may be broadcast on a separate downlink channel by each satellite, but may contain information for the available hailing channels for each of the satellites. Note that while this does not guarantee that transmission will be allowed from the current location (if there is a local intersection with all hailing channels), it does allow update of the PtPRs whose frequencies intersect the hailing channels, which then allows the terminal to transmit once it is moved outside of the local hailing channel intersecting PtPR&#39;s protection zone. 
     Advantageously, the techniques herein provide for avoidance of interference in wireless communications. In particular, the techniques herein enable a mobile communication device (e.g., terminal  410 ) to know whether or not it is permissible to transmit in a particular location and, if so, on what particular frequency (channel/band) and in what particular direction, so as to reduce or eliminate any interference on other communication devices and networks. Additionally, the techniques herein assist in determining suitable placement and orientation of terminals for a potentially interfering wireless communication system in the presence of an existing wireless communication system. 
     In one specific embodiment, the techniques herein allow (and/or add value to) the introduction of a new, ubiquitous service with consumer- and IoT-based applications via satellite (e.g., messaging via satellite), and make more intensive and efficient use of C-band spectrum through a non-interfering sharing regime. The proposed system will protect other C-band operations from harmful interference—for example, by using a database-driven, permission-based authorization regime to ensure no operations cause harmful interference to C-band terrestrial fixed service (“FS”) point-to-point (“PtP”) operations. 
     Notably, other advantages and additional implementation (use-case) embodiments of techniques described above may be readily apparent to those skilled in the art, and those specifically mentioned herein are not meant to limiting to the scope of the present disclosure. 
     ——Magnetic Compass Confirmation—— 
     As detailed above, the techniques herein ensure that a terminal  410  does not transmit towards an unintended receiver (e.g., an incumbent PtPR). Specifically, the techniques above detail particular embodiments regarding how to ensure that a terminal can transmit only when it can be guaranteed that any unintended receiver in its vicinity would not receive power higher than a given threshold. 
     Generally, the techniques described above rely on the ability to obtain accurate reference direction (e.g., to the magnetic north and to the true north). Mobile phones  415 , such as the phone to which the terminal  410  may be attached, have embedded magnetic sensors which can be used for determining the direction to the magnetic north (i.e., the point where northern magnetic lines of earth&#39;s magnetic field enter the earth, that is, the magnetic field is vertical). The angle between the magnetic north and the geographic “true” north (the northern endpoint of the earth&#39;s axis of spin) is known as magnetic declination, where the magnetic declination depends on the specific geographic location where the magnetic sensor measurement is taken. (Note that compass needles technically measure the horizontal component of earth&#39;s magnetic field at a specific location, which due to local anomalies does not always equal the angle to magnetic north, but this minimal deviation may, under some circumstances, be ignored.) 
     Additionally, the magnetic poles are constantly moving slowly, and as such the translation from the magnetic north to the true north is both location and time dependent. For example, a prediction of the current magnetic declination for a given location can be obtained online from a web page operated by the National Geophysical Data Center, a division of the National Oceanic and Atmospheric Administration of the United States. Further, the National Geospatial-Intelligence Agency (NGA) provides source code (e.g., written in C) that is based on the World Magnetic Model (WMM), accounting for movement of the magnetic north pole (e.g., adjusted every five years). 
     A magnetic compass reading is typically accurate, so long as there are no additional magnetic influences. For example such additional magnetic influences may be introduced by nearby metals, belt buckles, radios, magnets of speakers, backpack metal frames, underground cables or pipes, etc. Any such additional external magnetic fields can potentially cause erroneous direction readings, and as such, may cause positioning the terminal in an erroneous direction. As detailed above, such an erroneous direction may result in transmission in a wrong direction that could adversely impact unintended receivers. 
     The techniques described herein, therefore, provide for magnetic compass confirmation, in order to ensure that there is no (or at least minimal) magnetic error due to magnetic field interference. In particular, the embodiments described below provide various methods for ensuring that the compass, and particularly the direction of an associated mobile device, is accurate. For instance, the techniques herein prevent transmission by terminal  410  when there is uncertainty in a compass reading, but may also be used for other technologies where direction-related communication needs accuracy and are based on magnetic compass readings. 
     Specifically, in one preferred embodiment, the present disclosure teaches a method for ensuring that a terminal  410  never transmits in a wrong direction. To do that, the system evaluates and determines the accuracy of the direction reading from its compass, as detailed below. If the system determines that its direction reading is not certain, it may prevent the terminal from transmitting. (It should be noted that the controller prevents the system from transmitting only when accurate bearing/direction is required and the system determines that it does not have an accurate direction/bearing. In the case when the system determines that it can transmit safely without accurate direction/bearing, transmission may still be enabled.) 
     In general, the present disclosure describes a system for determining whether the compensated reading of a magnetic sensor is reliable or not. Notably, other systems have been developed that focus on deviation compensation of magnetic compass systems, such as a system used in aircraft to account for a permanent magnetic field set up by various metal parts such as the aircraft engine, or due to the distortion of the earth&#39;s magnetic field due to the presence of metal parts which in themselves do not produce a magnetic field. Still other systems have been described for calibration and correction of non-constant compass sensor errors, through changing software and hardware calibration based on pre-production testing (i.e., improving the accuracy of electronic sensors), or for otherwise reducing power consumption or error of a digital compass. Each of these technologies, however, focuses on compensating for the distortion of the earth magnetic field. In contrast, the techniques herein provide a system to assess whether the compensated reading of the magnetic direction is reliable or not, and particularly to enable/disable various direction-sensitive features (e.g., transmission from a terminal  410 ) based on that assessment. (Note further that the techniques herein still attempt to compensate for local magnetic field distortions, but the assessment herein is whether, even after the correction and compensation (e.g., for hard and soft iron, as will be understood by those skilled in the art), that the device is able to provide accurate directional readings.) 
     According to one or more embodiments of the present disclosure, the techniques herein uses two (or more) directional (e.g., magnetic) sensors positioned at a distance from each other (e.g., a small distance, dictated by form factor of the device). In one embodiment, the system may use an internal directional sensor of the mobile phone  215  and one or more additional directional sensors of the terminal  410 . In another embodiment, the system may have multiple sensors within the phone, or mounted on the terminal, generally as far apart as the system allows or as otherwise necessary to provide the most benefit to the techniques described herein. 
       FIG. 26A  illustrates a simplified example of a directionally-sensitive system  2600  that has a first directional sensor  2610  and a second directional sensor  2620  located on a same device  2630 , in accordance with one embodiment herein. Illustratively, the device  2630  may be a mobile phone  415  attached to a terminal  410 , or may be the terminal  410  itself (e.g., standalone, or attached to a mobile phone  415 ).  FIG. 26B , on the other hand, illustrates another simplified embodiment of the system  2600 , where the first sensor  2610  is located on a first device  2640 , and the second sensor  2620  is located on a second device  2645 . Notably these two devices  2640  and  2645  may be physically connected to each other (e.g., a terminal  410  attached to a mobile phone  415 ), or else may be connected via communication only. As noted above, any number of directional sensors may be used (i.e., two or more), and the view shown herein is meant for an illustrative example only. Also, the positioning of the sensors as shown is also illustrative, and any suitable arrangement, location, orientation, etc., may be used, and configured based on a combination of device design, maximizing differentiation of sensing, and so on. 
     Directional sensors  2610  and  2620  may be based on a number of different technologies. Generally, such technologies are designed to sense the earth&#39;s magnetic field, such as magnetic sensors (e.g., magnetometers), but other sensors may be used. Magnetic sensors, in general, may be implemented with different magnetic alignment algorithms and different sensitivities, and may include such things as Hall Effect sensors (i.e., a transducer that varies its output voltage in response to a magnetic field), magneto-inductive (MI) sensing magnetometers, and so on. Other sensors, such as GPS sensors (e.g., multiple spread-out GPS sensors, GPS plus direction of travel, etc.), may also be used to determine direction of the sensor (and thus associated device), each with varying degrees of accuracy and limitations. The directional sensors herein, therefore, are not limited to those mentioned herein, and any suitable directional sensing (or determining) technology may be used, whether magnetic or otherwise. 
     The impact of an external magnetic field or other magnetic interferences can vary all the way from a slight error (e.g., a few degrees) to a complete 180-degree error (if interference is severe enough, such as a magnet placed near a magnetometer). In particular, magnetometers can be impacted by magnetic fields in their vicinity, where a magnetic field&#39;s strength is inversely proportional to (d)^3. (That is, proportional to one over distance from the magnetic source to the 3 rd  power.) As a result of using at least two different directional sensors  2610  and  2620 , which would generally be located at a different distance (or at least a different angle) from an external interfering magnetic source, each would be impacted differently. In other words, the reading of the two magnetic sensors would have different distortions (e.g., different erroneous readings). Note that in one or more embodiments herein, as described below, the techniques may use sensors based on difference technologies, and as such, sensors with different sensitivities and different non-linear curves may cause/yield different readout deviation due to the distorted magnetic field. 
     As an example,  FIG. 27A  illustrates an example reading of both sensors  2610  and  2620  without interference (e.g., magnetic compass reading), while  FIG. 27B  illustrates an example reading of the same two sensors after an external magnetic source  2710  has been introduced into the environment. Assume, for example, that in  FIG. 27A , the readings are both 0-degrees (e.g., magnetic north), without magnetic interference. Once an external magnetic field source  2710  is added in  FIG. 27B , if every sensor and its associated compensation system is capable of mitigating the interference, all sensors will continue to give the same accurate reading. That is, sensors  2610  and  2620  use magnetometers of different technologies, and thus the uncompensated readout of the magnetometers are expected to be different because of the different distance to the source  2710  and because they use magnetometers of different technology. Thus, once the system compensates for the soft and hard iron source, if the compensation is successful, then the two readouts should be substantially the same, but if the two compensation readouts are not substantially the same, then there is uncertainty about the direction to the magnetic north. Note, however, that since the two sensors  2610  and  2620  are located at different distances (“d 1 ” and “d 2 ”, respectively) from an external magnetic source  2710 , if inaccurate readings occur, each would exhibit different reading errors and point in different directions from true magnetic north (e.g., +5 degrees, and +10 degrees, respectively). 
     Additionally, if the two sensors use different sensing technologies (as explained above), then the impact of the external magnetic field on the readings of the two sensors may be further different. For example, though the two magnetic sensors could still point to different directions as if they were the true magnetic north, a Hall Effect sensor and a flux-gate effect sensor may exhibit different deviations from the true north based on the different sensitivities of the two sensors and the different non-linearity these technologies exhibit (e.g., +5 degrees and +20 degrees, respectively). 
     When the system is exposed to only the earth&#39;s magnetic field, all of the sensors provide identical reading toward the magnetic north. It should be noted that as explained above, the bearing towards the magnetic north can be easily translated/converted to the direction towards the true north using well-known software/methods. 
     When all of the readings of the various magnetic sensors point substantially in the same direction, the system infers that the direction reading is correct. The illustrative system above (avoiding interference) may use this direction to calculate the azimuth in which the device (terminal  410 ) should point to achieve “optimal transmission” (and reception) towards (from) a given intended receiver. That is, for an optimal transmission or reception, using this proper reading, the control software in the terminal enables transmission towards the intended receiver (e.g., satellite  420 ) while ensuring that the right frequency band and polarization are chosen as to ensure that ground communication amongst unintended receivers and transmitters is not adversely affected (as described further above). 
     However, if the directionally-sensitive system  2600  is in the vicinity of objects  2710  that could influence the magnetic field in a way that the system is not able to compensate for, then the various different magnetic sensors may or may not point towards magnetic north. According to the techniques herein, given the fact that the sensors  2610  and  2620  are located at a different locations within the system  2600 , and thus a different distance (or at least angle) from the source of the adversely impacting magnetic field, the impact to each reading is different a) because the sensors are at a different distance from the adversely impacting magnetic object (and the impact is inversely proportional to the distance of the various sensors from the object to the 3 rd  power), and b) the different sensors may be built based on different technologies have much different sensitivity and non-linearity response to the disrupting magnetic field, and as such may exhibit different deviation from the true north, as mentioned above. 
     Said differently, two sensors may be used and each attempts to compensate for the distortion of the magnetic field by an external magnetic material or by an external magnet. There may be times, however, where even after the system attempts to compensate for the distortion, there is still a difference in reading between the sensors, and a resultant directional uncertainty (i.e., that the two compensated sensors give different readouts for the magnetic north). As such, if there is external distortion but the system can compensate for it (i.e., the two readings are substantially similar), then an accurate reading is assumed (e.g., and transmission can be performed). On the other hand, if after corrections for the magnetic field distortion are attempted and are not successful (i.e., the two readings are not substantially similar), the techniques herein detect this occurrence (e.g., and prevent transmission). 
     To illustrate the concerns that being even slightly erroneously aimed,  FIGS. 28A-28B  demonstrate how a slight angle change might go from not interfering to interfering. For instance, in  FIG. 28A , the terminal  410  may be aimed such that the boresight of transmission  405  reaches the intended receiver  420 , without interfering with an unintended receiver  310 . However, with reference to  FIG. 28B , a slight shift in antenna direction aim, perhaps due to believing that the device is aimed according to  FIG. 28A  based on an erroneous directional reading (e.g., of systems with only a single directional sensor), would result in a correspondingly shifted transmission that might interfere with the unintended receiver  310 . 
     Further, according to one or more embodiments herein, a graphical user interface (GUI) may be illustrated to a user to adjust aim of the terminal according to the adjusted communication parameters. That is, since the adjusted parameters may require physical orientation changes to the terminal, where the system herein may be configured to prevent transmission by the terminal unless the terminal is aimed correctly, various measures may be taken to guide a user. For instance, the terminal (or a mobile device attached to the terminal) may utilize an embedded (or attached) compass to guide the operator of the mobile device to the direction it should point the mobile device (azimuth and elevation, i.e., tilt angle towards the satellite). As such,  FIG. 29A  illustrates an example of a GUI  2910  that may be used according to the techniques described above. In particular, illustrative stationary “crosshairs”  2940  are shown in an augmented reality display to aim at a satellite icon  2950  representing the desired direction to point the terminal (whether the satellite is actually located in that direction, or whether that merely represents the desired “aim” of the terminal to allow the transmission according to the acceptable communication parameters). Many other types of GUIs and functionalities may be conceived, and those shown herein are not meant to be limiting to the scope of the present disclosure. If the directional sensors are incorrect, however, then the GUI may show an acceptable transmission aim in  FIG. 29A  (namely, the crosshair icon  2940  coincides with the satellite icon  2950 ), when, in reality, the actual aim should look more like the image in  FIG. 29B , wherein the crosshair icon  2940  does not coincide with the satellite icon  2950 , and therefore it is not acceptable to transmit. 
     As an aside, with regard to antenna pointing (as described above), the terminal transmitter may be activated only when it is within a “safe” shaking angle (e.g., 5 degrees) of the required pointing angle to the satellite, thus accounting for deviations in aim (e.g., caused by shaking of the terminal, such as from user hand shaking, vehicular travel, and so on). The terminal uses sensors (e.g., its own or else from an attached smartphone), such as its GPS coordinates and bearing, to enable activation/deactivation of the terminal&#39;s transmitter. A terminal&#39;s transmission may be disabled (e.g., within 100 msec) if the pointing angle envelope is ever exceeded. Note that the amount of “safe shaking angle” may be calculated, and the momentary shaking may be continuously estimated, such that if the shaking may point the antenna of the terminal into an interfering orientation, the user may be alerted and transmission is disabled. The transmission can be quickly enabled again (and the message transmission resumed) once the terminal is pointing with confidence back to the desired direction. This process is fast enough to permit mobile operation of the terminal for many consumer recreation activities (e.g., hiking, boating, and horse-back riding) without causing any adverse interference to incumbent receivers such as PtPRs and/or other satellites. 
     According to the techniques herein, concerns about erroneous directional sensing (e.g., magnetic compass readings) may be accounted for by configuring the two sensors  2610  and  2620  in a manner where the two (or more) sensors provide substantially different readings when deviating interference (which cannot be reliably compensated for) is experienced, such that the system infers that it does not have a reliable direction reading when different (or otherwise conflicting) readings occur. In the illustrative embodiment, to make sure that the system does not mistakenly interfere with the unintended receivers  310  (e.g., incumbent PtP communication system), if the terminal  410  controller requires reliable direction reading (which in this scenarit does not have), it may disable transmission, accordingly. 
       FIG. 30 , in particular, illustrates an example procedure for magnetic compass confirmation, e.g., for avoidance of interference in wireless communications in accordance with one or more embodiments described herein. For example, one or more non-generic, specifically configured devices (e.g., terminal  600 ) may perform procedure  3000  by executing stored instructions. Note that the procedure  3000  may be performed by a directionally sensitive system (i.e., the process is on the system/terminal/device), or else may be performed by a controlling device (e.g., server) that has access to the parameters and control of the directionally sensitive system  2600 . 
     As shown in  FIG. 30 , the procedure  3000  may start at step  3005 , and continues to step  3010 , where, as described in greater detail above, a process obtains a first compensated directional reading from a first directional sensor  2610  of a directionally sensitive system  2600 , and to obtain a second compensated directional reading from a second directional sensor  2620  of the directionally sensitive system in step  3015 . As mentioned above, the first and second directional sensors may be any suitable sensor, such as a magnetometer, an accelerometer, a gyroscope, a GPS location sensor, and so on, as well as combinations thereof (e.g., existing sophisticated compass algorithms may be based on nine-axis inputs (e.g., accelerometer, gyro and magnetometer)). In one embodiment, the first and second directional sensors are located on a same device  2630 , however, in another embodiment, they may be located on different first and second devices ( 2640  and  2645 ), respectively, where the first and second devices are in communication with each other, as described above. According to the techniques herein, the first and second sensors are meant to be affected by interference differently, such as by having a different compensated interference sensitivity from each other (e.g., different types of sensors), or, particularly when built based on the same technology, by having different locations within the directionally sensitive system than each other. (Note again that the system herein may first attempt to correct for the magnetic field distortion, and it is only after the system realizes that it is not able to correct/compensate for the distortion that it determines an inaccurate reading, and illustratively in one embodiment, moves to the state wherein if directional sensitivity is critical, it prevents transmission.) 
     In step  3020 , the process determines a difference between the first compensated directional reading and the second compensated directional reading. For example, by comparing the first and second compensated bearing readings from the two sensors, the techniques herein can determine whether the true north bearing is accurate based on whether the two readings are substantially the same. In particular, in step  3025 , the process may declare whether the directional reading is accurate or inaccurate. That is, in response to the difference being greater than an acceptable threshold, the process can declare an inaccurate directional reading, while in response to there being no substantial difference between the first compensated directional reading and the second compensated directional reading, or in response to the difference being less than or equal to the acceptable threshold, the process can declare an accurate directional reading. (Note that as described above, embodiments herein may perform a “smearing” technique on protection zones—as such, in another embodiment herein, the techniques herein may use the different compensated directional readings to estimate an uncertainty/inaccuracy in the direction, and smear the protection zone accordingly.) 
     Note that as described above, in response to the difference being less than or equal to an acceptable threshold (when this is an acceptable accurate reading), an accurate directional reading can be determined as an average between the first and second directional readings. For instance, assume that one embodiment assigns a primary status to “Compass  1 ”, and a verification status to “Compass  2 ” (or  2  and  3 ). One option is that if Compass  2  (or  2  and  3 ) agrees with Compass  1  within X degrees, the heading of Compass  1  may be used. In another option, if Compass  1  and  2  agree within X degrees, the headings of Compass  1  and  2  may be averaged. (In still another optional configuration, heading readings may be obtained from Compass  1 , Compass  2 , and Compass  3 —If all compasses agree within X degrees, the headings of the two compasses whose readings most closely align may be averaged.) Still other embodiments and configurations may be made in accordance with the techniques herein, and those specifically mentioned herein are not meant to be limiting to the scope of the present disclosure. 
     In step  3030 , in response to an inaccurate directional reading, the process may prevent performance of a directionally sensitive action by the directionally sensitive system. Alternatively, in step  3035 , in response to the system determining that it was able to obtain an accurate directional reading, the process may correspondingly enable performance of the directionally sensitive action by the directionally sensitive system. As an illustrative and non-limiting example, the directionally sensitive action may comprise transmitting a transmission  405  from the directionally sensitive system (terminal  410 ) toward an intended receiver  420  (e.g., satellite) at a direction that avoids having the transmission interfere with an unintended receiver  430  (e.g., an earth-based PtPR). Said differently, in one specific embodiment, the techniques herein may be configured to disable transmission from a terminal  410  when the system cannot guarantee that it can reliably transmit towards the satellite  420  without interfering with incumbent PtPRs  430 , based on determining the accuracy of various directional factors, as described above. 
     As noted above, compass heading and pitch are often calculated using “fusion algorithms” drawing data from multiple sensors. For instance, one specific (and non-limiting) example fusion algorithm that fuses information from multiple sensors is a “nine-axis” fusion algorithm, where multiple sensors (e.g., three) each provide data in three orthogonal axes X, Y, and Z: 1) a magnetometer reading earth&#39;s magnetic field (e.g., in X, Y, and Z), 2) an accelerometer reading acceleration (e.g., in X, Y, and Z), and 3) a gyroscope reading change in direction (e.g., in X, Y, and Z). The fusion algorithms can thus provide more accurate heading than using a magnetometer alone. According to one or more embodiments herein, therefore, one or both of the directional readings may be based on a fusion algorithm using input from a plurality of directional sensors. As described below, the fusion algorithms may be different, and/or at least one sensor may be different between the two sets of sensors (e.g., for the same or different fusion algorithms). 
     Specifically, in one embodiment, the techniques herein may read data from one set of sensors (e.g., accelerometer, gyro and a magnetometer) using one fusion algorithm to obtain a first compensating bearing, and reading the data from the same set of sensors using a different fusion algorithm to obtain a second compensated bearing. By comparing the first and second compensated bearing readings from the two fusion algorithms, the techniques herein can determining that the true north bearing is accurate when the two readings are substantially the same (after compensation) or erroneous when the two readings are substantially different, and may correspondingly enable or block an action (e.g., terminal transmission or otherwise) based on the accuracy (e.g., when accuracy is required). 
     In another specific embodiment, the techniques herein may read data from one set of sensors (e.g., accelerometer, gyro and a magnetometer) using one fusion algorithm to obtain the first bearing, and then may read the data from the same gyro and accelerometer, but with a different magnetometer. Either the same fusion algorithm or a different fusion algorithm may be used to obtain the second bearing, and after comparing the first and second bearing readings, the system can enable or prevent the action, accordingly. Other combinations of sets of sensors may be read as the different readings, such as, for example:
         the same accelerometer, and different gyros and magnetometers; or   the same gyro, and different accelerometers and magnetometers; or   different accelerometers, gyros, and magnetometers.       

     Note that still further specific embodiments allow for the first directional readings to be based on a measured magnetic property value (e.g., a measured magnetic field strength or dip angle), where the second directional reading is then an “expected” magnetic property value (e.g., magnetic field strength or dip angle, respectively) based on a geographic location of the directionally sensitive system as determined by the second directional sensor. That is, the techniques herein provide for reading magnetic field strength (or dip angle) and GPS location, comparing it to published data of expected magnetic field strength (or dip angle) at the GPS location. If the two readings are substantially the same, then the direction (true north bearing) of the directional sensor may be declared accurate, while if they are different, then an inaccuracy can be assumed. 
     The illustrative procedure  3000  may end in step  3040 , notably with the option to receive updated readings and to perform further comparisons (e.g., in response to moving the system away from interference). That is, though the process in  FIG. 30  shows an ending at step  3040 , the process may take place continuously, and as such as the process ends in step  3040 , it immediately starts anew in step  3005  (i.e., an infinite loop wherein the process continuously assesses the confidence of its bearing accuracy). 
     It should be noted that while certain steps within procedure  3000  may be optional as described above, the steps shown in  FIG. 30  are merely examples for illustration, and certain other steps may be included or excluded as desired. Further, while a particular order of the steps is shown, this ordering is merely illustrative, and any suitable arrangement of the steps may be utilized without departing from the scope of the embodiments herein. Moreover, while procedures  1200  (from  FIGS. 12A-12B  above) and  3000  are described separately, certain steps from each procedure may be incorporated into each other procedure, and the procedures are not meant to be mutually exclusive. 
     Advantageously, the techniques herein provide for magnetic compass confirmation, or, more particularly, directional sensor confirmation. In one embodiment, the techniques herein specifically avoid of interference in wireless communications whenever there is doubt about a critical directional reading. Other applications that require critical directional/compass reading confirmation may also make use of the techniques described herein. 
     While there have been shown and described illustrative embodiments that relate to interference management techniques in wireless communication networks, it is to be understood that various other adaptations and modifications may be made within the scope of the embodiments herein. For example, the embodiments may, in fact, be used in a variety of types of wireless communication networks and/or protocols, and need not be limited to the illustrative satellite network implementation, PtP networks, or even communication in the C-band. For example, though the disclosure was described with respect to satellite communication in the C-Band, those skilled in the art should understand that this was done only for illustrative purpose and without limitations. The techniques herein, in particular, are applicable to any other communication band such as the Ku-band (e.g., Downlink: 11.7-12.2 GHz; Uplink: 14.0-14.5 GHz) or any other suitable band. Furthermore, while the embodiments may have been demonstrated with respect to certain communication environments, physical environments, or device form factors, other configurations may be conceived by those skilled in the art that would remain within the contemplated subject matter of the description above. 
     Additionally, while certain configurations of terminals and receivers are shown (e.g., PtPRs and satellites), it is important to note that unintended receivers may actually be a part of the same communication network as the intended receiver, or at least the same type of device. For instance, an intended receiver could be a first satellite, and an unintended receiver may be a second satellite, which may be in the same network as the first satellite (e.g., preventing double reception of the same message), or else may be in a different network (e.g., a different satellite communication network that uses the same channels). In still other embodiments, one network may be based on geostationary orbit (GEO) satellites and the other network may be based on low earth orbit (LEO) satellites, or else both may be based on GEO or both based on LEO. Other mobile communication techniques may also be used, such as those based on land or carried by UAVs or other flying vehicles. Further, it is also important to note that in the case of drones or UAVs, a portion of the communication parameters takes into consideration elevation above sea level, such as raising or lowering the drone to change the link-budget calculations or line-of-sight determinations detailed above. 
     In particular, the foregoing description has been directed to specific embodiments. It will be apparent, however, that other variations and modifications may be made to the described embodiments, with the attainment of some or all of their advantages. For instance, it is expressly contemplated that certain components and/or elements described herein can be implemented as software being stored on a tangible (non-transitory) computer-readable medium (e.g., disks/CDs/RAM/EEPROM/etc.) having program instructions executing on a computer, hardware, firmware, or a combination thereof. Accordingly this description is to be taken only by way of example and not to otherwise limit the scope of the embodiments herein. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the embodiments herein.