Patent Publication Number: US-2023138511-A1

Title: Omnidirectional Validation of Transponder Broadcast Information

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application Ser. No. 63/273,364, “Omnidirectional Validation of Transponder Broadcast Information,” filed on Oct. 29, 2021, by Matthew Hamilton, et al., the contents of which are herein incorporated by reference. 
    
    
     FIELD 
     The described embodiments relate to detection and avoidance techniques for crewed and uncrewed aircraft. Notably, the described embodiments relate to determining and/or validating an aircraft track using an omnidirectional antenna. 
     BACKGROUND 
     A transponder is an electronic device that transmits a response when it receives a radio-frequency interrogation. In contrast with a transceiver, which transmits and receives using a common carrier frequency, a transponder transmits and receives using different carrier frequencies. 
     Aircraft are typically required to include transponders to assist in identifying them, e.g., on air traffic control radar. In addition, collision avoidance systems have been developed that use transponder transmissions to detect and avoid aircraft that are at risk of colliding with each other. For example, the Federal Aviation Administration (FAA) in the United States mandated the use of the Traffic Alert and Collision Avoidance System (TCAS), which is a collision avoidance system and air-to-air communication technique for piloted civilian aircraft using transponder messages. Notably, TCAS is an onboard system by which aircraft avoids a potential collision threat by performing a vertical avoidance maneuver, such as climbing or descending. 
     However, TCAS is not well-suited for helicopters or uncrewed aircraft, such as drones. Currently, unless a professional waiver is granted by the FAA, the absence of a Detect and Avoid (DAA) system (which includes collision avoidance) for drones restricts their use to visual line of sight by the operator or to use in conjunction with a separate visual observer. 
     In order to address these and other challenges, enhanced collision avoidance systems, such as the Airborne Collision Avoidance System (ACAS) Xu (which is a DAA system), are being developed. ACAS Xu is intended for use by a variety of different types of aircraft, including rotorcraft and uncrewed aircraft. In addition, ACAS Xu may be used to detect and avoid a threat associated with a cooperative or an uncooperative aircraft (such as a drone or other aircraft that is not equipped with a transponder). Notably, ACAS Xu may use an input from a cooperative source, such as an Automatic Dependent Surveillance-Broadcast (ADS-B) message. ADS-B are Global Positioning System (GPS)-based automatic transmissions that are provided periodically. 
     There are, however, concerns about the reliability of this type of input. Notably, ADS-B transmissions are not encrypted and are based on GPS signals. Consequently, ADS-B messages can be jammed, spoofed or become unavailable. 
     In principle, a system can perform additional measurements to validate transponder broadcast information, such as ADS-B messages. For example, if a system includes active surveillance capability, measurements (including range, altitude and bearing) can be determined to localize another aircraft and, thus, to verify its track, as specified by the transponder broadcast information from the other aircraft. Note that active surveillance is typically accomplished by a system that includes one or more directional antennas for transmitting to, and receiving signals from, transponder equipped aircraft. 
     However, in practice, the use of directional antennas increases the size, weight and cost of the overall system. Larger and heavier systems are problematic or prohibitive in many aircraft applications, such as in uncrewed aircraft (e.g., drones), where there are strong constraints on the size and weight of the system components because of installation limitations and performance capabilities. 
     SUMMARY 
     In a first group of embodiments, an electronic device is described. This electronic device includes: an omnidirectional antenna; and one or more integrated circuits (such as one or more radios) that transmit and receive radio-frequency (RF) signals. During operation, the electronic device receives, using the omnidirectional antenna, broadcast information associated with a second electronic device (e.g., a transponder), where the broadcast information is compatible with a regulation from a government aviation or aviation safety administration (such as the Federal Aviation Administration or the European Union Aviation Safety Agency). Then, the electronic device determines a track of the second electronic device based at least in part on the broadcast information. 
     Note that the track may include one or more of: horizontal location or position, relative range, relative bearing, heading, relative or absolute altitude, and/or relative or absolute speed. 
     Moreover, determining the track may involve measuring range (such as slant range) to the second electronic device as a function of time. For example, the range to the second electronic device may be measured using time-of-flight measurements by providing an interrogation signal and subsequently receiving an associated response from the second electronic device. In some embodiments, the interrogation signal may be selectively transmitted to the second electronic device with a carrier frequency of 1,030 MHz using mode S interrogation. Alternatively, the interrogation signal may be an all-call interrogation with a carrier frequency of 1,030 MHz that is transmitted to any electronic device in proximity (such as wireless range) of the electronic device, and that results in subsequent responses from any transponders that receive this interrogation signal. 
     Furthermore, the track may be determined in two dimensions (2D) or three dimensions (3D) when an altitude or vertical position of the electronic device and/or the second electronic device are available. Additionally, in some embodiments, determining the track may involve: performing Doppler measurements of range; and correlating the range to speed and/or velocity of the second electronic device. 
     Note that the electronic device may include a transponder, and the transmit RF signals and the receive RF signals may use different carrier frequencies. Moreover, the second electronic device may include a second transponder, e.g., in a cooperative aircraft. Alternatively, the second electronic device may include a repeater (e.g., an ADS-R) ground station. 
     Furthermore, in some embodiments, the electronic device may include an aircraft, such as a crewed or uncrewed aircraft. For example, the electronic device may include an aircraft, such as: an airplane, a helicopter, a glider, a drone, or another type of aircraft. 
     Additionally, the electronic device may validate or verify the broadcast information based at least in part on the determined track. For example, the electronic device may compare a track specified by the broadcast information with the determined track. 
     In some embodiments, the electronic device may provide the determined track to a collision avoidance system. 
     Note that the broadcast information may include location information of the second electronic device that are based at least in part on GPS, such as ADS-B messages. For example, the location information may include: horizontal location or position, relative range, relative bearing, heading, relative or absolute altitude, and/or relative or absolute speed. 
     Moreover, the measurements may be performed multiple times to reduce or eliminate probability of another electronic device being at a same range as the electronic device. 
     Furthermore, the electronic device may collaboratively determine the track based at least in part on one or more additional range measurements associated with a set of one or more electronic devices, where a given additional measurement was performed using another instance of the omnidirectional antenna. 
     Additionally, the electronic device may provide the range measurements and/or the determined track to another aircraft, a ground control station and/or air traffic control. For example, the electronic device may provide information associated with a real-time data structure that specifies spoofed or inaccurate transponder data, such as those where there is a difference between an instance of the broadcast information and the determined track. 
     In some embodiments, the electronic device may determine the track when GPS is unavailable or unreliable. For example, the electronic device may receive an indication that GPS is unavailable or unreliable from or associated with a GPS receiver. In these embodiments, the electronic device may perform active surveillance using mode C or S interrogation, which provide range and altitude information associated with the second electronic device. 
     Note that the broadcast information may include the identifier of the second electronic device, such as an International Civil Aviation Organization (ICAO) code or designator. 
     Moreover, in some embodiments, the electronic device may include at least a second omnidirectional antenna. For example, the omnidirectional antenna may be disposed on or proximate to a top of the electronic device and the second omnidirectional antenna may be disposed on or proximate to a bottom of the electronic device. Note that the omnidirectional antenna and the second omnidirectional antenna may provide antenna diversity. Furthermore, the use of multiple omnidirectional antennas may provide more accurate range measurements, e.g., by performing phase-difference measurements. In some embodiments, multiple omnidirectional antennas may provide angular information (such as a bearing to the second electronic device). Alternatively, when the transmissions from multiple omnidirectional antennas are synchronized (e.g., with an adjustable or selectable relative phase delay and/or transmit power difference), the electronic device may perform beam steering. 
     Another embodiment provides a computer-readable storage medium for use with the electronic device. This computer-readable storage medium may include program instructions that, when executed by the electronic device, cause the electronic device to perform at least some of the aforementioned operations. 
     Another embodiment provides a method. This method includes at least some of the operations performed by the electronic device. 
     In a second group of embodiments, an electronic device is described. This electronic device includes: one or more of a variety or different types of sensors that perform measurements of an environment external to the electronic device; and one or more integrated circuits (such as one or more radios). During operation, the electronic device performs measurements of the environment using the types of sensors, where the types of sensors are different from a transponder or a transceiver. Then, the electronic device determines a track of a second electronic device in the environment based at least in part on the measurements. Next, the electronic device provides the determined track to a collision avoidance system (such as a DAA system). 
     Note that the types of sensors may include: an electro-optic or infrared sensor, a camera or image sensor, a light detection and ranging (LiDAR) sensor, a radio detection and ranging (RADAR) sensor, an acoustic sensor, a pressure sensor, a weather or environmental sensor (such as a temperature sensor, a wind speed sensor, a humidity sensor, etc.), an altitude sensor, and/or another type of sensor. 
     Moreover, determining the track may involve merging tracks associated with different measurements into a common track file. 
     Furthermore, the track may be determined using a pretrained model, such as a pretrained model that is trained using a supervised-learning technique. 
     Additionally, the electronic device may include a transponder. In some embodiments, the electronic device may include an aircraft, such as a crewed or uncrewed aircraft. For example, the electronic device may include an aircraft, such as: an airplane, a helicopter, a glider, a drone, or another type of aircraft. 
     Note that the collision avoidance system may include ACAS Xu or another technique associated with or defined by the Radio Technical Commission for Aeronautics (RTCA). 
     Another embodiment provides a computer-readable storage medium for use with the electronic device. This computer-readable storage medium may include program instructions that, when executed by the electronic device, cause the electronic device to perform at least some of the aforementioned operations. 
     Another embodiment provides a method. This method includes at least some of the operations performed by the electronic device. 
     In a third group of embodiments, an electronic device is described. This electronic device includes: an antenna; and one or more integrated circuits (such as one or more radios) that transmit and receive RF signals. During operation, the electronic device receives RF signals that convey information corresponding to an instruction (or a command) associated with air traffic control. In response, the electronic device automatically transmits second RF signals that convey second information corresponding to a response to the instruction. 
     Note that the instruction may include a verbal instruction. Moreover, prior to transmitting the RF signals, the electronic device may: extract the information from the RF signals; perform natural language processing (e.g., using a pretrained model, such as a neural network) on the information; and generate or select the response. Note that generating the response may include generating or voice synthesizing a verbal response to the verbal instruction (e.g., using a second pretrained model, such as a second neural network). Alternatively, selecting the response may include selecting a predetermined verbal response to the verbal instruction. Consequently, in some embodiments, the electronic device may provide an automated voice radio system for aircraft communication. 
     Furthermore, the response may repeat the instruction and/or may acknowledge receipt of the instruction. For example, the verbal instruction may include a squawk code, a heading, or an altitude. 
     Additionally, the information and the second information may include or may correspond to: automatic selection of appropriate radio frequencies for use in communication while airborne or on the ground; automatic transmission of appropriate radio calls and responses to incoming calls; automatic aircraft response through autopilot and/or ground station indications to the operator of a ground control station based at least in part on incoming radio calls and responses; and/or automatic aircraft response to adjust for current local Automatic Terminal Information Service (ATIS) or Automated Surface Observing System (ASOS) information. In some embodiment, there may be a manual override for a pilot or an operator in a ground control station to stop or modify a given automatic response. 
     Moreover, based at least in part on the instruction, the electronic device may subsequently selectively automatically transmit third RF signals that convey third information that indicate that the instruction has been completed. For example, the electronic device may indicate when an altitude has been changed, but may not indicate when a heading has been changed. 
     Furthermore, the electronic device may provide the instruction, e.g., to a pilot or an autopilot, e.g., of the electronic device. For example, the instruction may be displayed on a display or may be output into headphones of the pilot. Alternatively or additionally, the electronic device may determine one or more aircraft operations based at least in part on the instruction, and then may provide information specifying the one or more aircraft operations to the pilot or the autopilot. 
     Additionally, the electronic device may monitor whether the instruction has been completed. When a time interval has elapsed and the instruction has not been completed, the electronic device may provide a reminder message corresponding to the instruction, e.g., to a pilot or an autopilot, e.g., of the electronic device. 
     Note that the electronic device may include an aircraft, such as: an airplane, a helicopter, a glider, a drone, or another type of aircraft. 
     Another embodiment provides a computer-readable storage medium for use with the electronic device. This computer-readable storage medium may include program instructions that, when executed by the electronic device, cause the electronic device to perform at least some of the aforementioned operations. 
     Another embodiment provides a method. This method includes at least some of the operations performed by the electronic device. 
     This Summary is provided for purposes of illustrating some exemplary embodiments, so as to provide a basic understanding of some aspects of the subject matter described herein. Accordingly, it will be appreciated that the above-described features are examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a block diagram illustrating an example of communication among electronic devices in accordance with an embodiment of the present disclosure. 
         FIG.  2    is a flow diagram illustrating an example method for determining a track using an electronic device in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  3    is a drawing illustrating an example of communication among electronic devices in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  4    is a flow diagram illustrating an example method for determining a track using an electronic device in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  5    is a drawing illustrating an example of communication among electronic devices in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  6    is a flow diagram illustrating an example method for automatically transmitting a response to an instruction using an electronic device in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  7    is a drawing illustrating an example of communication among electronic devices in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  8    is a block diagram illustrating an example of an electronic device in accordance with an embodiment of the present disclosure. 
     
    
    
     Note that like reference numerals refer to corresponding parts throughout the drawings. Moreover, multiple instances of the same part are designated by a common prefix separated from an instance number by a dash. 
     DETAILED DESCRIPTION 
     In a first group of embodiments, an electronic device (such as a transponder, an aircraft that includes the transponder or an aircraft system that includes the transponder) is described. This electronic device may include: one or more omnidirectional antennas; and one or more integrated circuits (such as one or more radios) that transmit and receive RF signals. During operation, the electronic device may receive, using the one or more omnidirectional antennas, broadcast information associated with a second electronic device (such as a second transponder or a second aircraft that includes the second transponder, or a repeater (e.g., an ADS-R) ground station), where the broadcast information is compatible with a regulation from a government aviation or aviation safety administration (such as the Federal Aviation Administration or the European Union Aviation Safety Agency). Then, the electronic device may determine a track of the second electronic device based at least in part on the broadcast information. Note that the track may include one or more of: horizontal location or position, relative range, relative bearing, heading, relative or absolute altitude, and/or relative or absolute speed. 
     By using one or more omnidirectional antennas to transmit or receive RF signals, these communication techniques may reduce the size and weight of the electronic device (such as a transponder) relative to another electronic device that includes one or more directional antennas. For example, the electronic device may be the size of a business card and may weigh 0.25-0.33 lbs., as opposed to having a size of a shoebox and a weight of 10 lbs. Thus, the communication techniques may provide a compact, light-weight combined interrogator/transponder with a diversity omnidirectional antenna, which may be used in an ACAS-X system. Moreover, in some embodiments, the communication techniques may allow omnidirectional interrogation to be used to obtain information about the intended maneuver of another aircraft (such as the second electronic device or which may include the second electronic device), which may input to a collision avoidance system (such as a DAA system) to coordinate with the other aircraft. For example, the communication techniques may be used to: validate ADS-B based at least in part on Doppler measurements; and/or validate ADS-B based at least in part on phase detection using two or more antenna elements. Consequently, the communication techniques may reduce cost and fuel consumption, may enable new applications or use cases (such as the use of the electronic device in a drone that has limited lift and range), and may facilitate aircraft safety. 
     In a second group of embodiments, an electronic device (such as a transponder or an aircraft that includes the transponder) is described. This electronic device may include: one or more different varieties or types of sensors that perform measurements of an environment external to the electronic device; and one or more integrated circuits (such as one or more radios). During operation, the electronic device may perform measurements of the environment using the one or more types of sensors, where the one or more types of sensors are different from a transponder or a transceiver. Then, the electronic device may determine a track of a second electronic device (such as a second transponder or a second aircraft that includes the second transponder) in the environment based at least in part on the measurements. Next, the electronic device may provide the determined track to a collision avoidance system (such as a DAA system). In some embodiments, determining the track may involve merging tracks associated with different measurements into a common track file. 
     By determining the track using the measurements, these monitoring techniques may provide or use additional information that allows the track to be determined and/or improves the accuracy of otherwise determined track. For example, the monitoring techniques may provide track fusion of multiple non-cooperative sensors. These capabilities may allow the intended maneuver of another aircraft (such as the second electronic device or which may include the second electronic device), which may facilitate improved coordination with the other aircraft. Consequently, the monitoring techniques may facilitate improved aircraft safety. 
     In a third group of embodiments, an electronic device is described. This electronic device may include: an antenna; and one or more integrated circuits (such as one or more radios) that transmit and receive RF signals. During operation, the electronic device may receive RF signals that convey information corresponding to an instruction (or a command) associated with air traffic control. In response, the electronic device may automatically transmit second RF signals that convey second information corresponding to a response to the instruction. 
     By automatically transmitting the response to the instructions, these communication techniques may facilitate automation of pilot communication. Because humans are prone to errors when repeatedly performing seemingly routine tasks, the communication techniques may reduce such errors. Moreover, by freeing up the pilot to focus on aviation (instead of communication), the communication techniques may improve situational awareness and may reduce pilot fatigue. Thus, the communication techniques may provide automated air traffic control voice communication. Consequently, the communication techniques may improve aircraft safety and may improve the user experience when flying an aircraft. 
     In the discussion that follows, the electronic device may include or may be included in or installed on an aircraft (e.g., a transponder in the aircraft), such as a crewed aircraft (in which one or more individuals at least in part pilot of fly an aircraft) or uncrewed aircraft. For example, the electronic device may include or may be installed on an aircraft, such as: an airplane, a helicopter, a glider, a drone, an airborne taxi or another type of aircraft. 
     We now further describe the communication and monitoring techniques.  FIG.  1    presents a block diagram illustrating an example of an electronic device  100 . This electronic device may include one or more integrated circuits  110  (such as a radio circuit, which is sometimes referred to as a ‘radio’) that provide the functions or capabilities of a transponder. Notably, one or more integrated circuits  110  may transmit and receive RF signals, such as an interrogation, a transponder broadcast transmission or a transponder response from the one or more integrated circuits  110 , or a second interrogation or a second transponder transmission associated with electronic device  114  (such as another aircraft, air traffic control, a ground control station, etc.) that is received by the one or more integrated circuits  110 . For example, the second transponder transmission may include broadcast information. Alternatively, a received second transmission may be associated with ground control commands, a response to ground control command, etc. Moreover, electronic device  100  may include or may at least be selectively electrically coupled to at least an omnidirectional antenna  116 - 1  that is used for bidirectional communication, such as: transmitting the interrogation or the transponder transmission, receiving the second interrogation or the second transponder transmission, transmitting the transponder response, transmitting and/or receiving of signals associated with a collision avoidance system, a ground control command and/or a ground control response, etc. The interrogation, the transponder transmission, the second interrogation, the second transponder transmission or the transponder response may be associated with wireless signals  118 . 
     As can be seen in  FIG.  1   , wireless signals  118  (represented by a jagged line) may be transmitted by the one or more integrated circuits  110  or  120 . For example, the one or more integrated circuits  110  in electronic device  100  may transmit information (such as one or more packets or frames) using wireless signals  118 . These wireless signals are received by the one or more integrated circuits  120  in electronic device  114 . This may allow electronic device  100  to communicate information to electronic device  114  or vice versa. Note that wireless signals  118  may convey one or more packets or frames. 
     In the described embodiments, processing a packet or a frame in electronic device  110  or  114  may include: receiving the wireless signals with the packet or the frame; decoding/extracting the packet or the frame from the received wireless signals to acquire the packet or the frame; and processing the packet or the frame to determine information contained in the payload of the packet or the frame. 
     Note that the wireless communication in  FIG.  1    may be characterized by a variety of performance metrics, such as: a data rate for successful communication (which is sometimes referred to as ‘throughput’), an error rate (such as a retry or resend rate), a mean-squared error of equalized signals relative to an equalization target, intersymbol interference, multipath interference, a signal-to-noise ratio, a width of an eye pattern, a ratio of number of bytes successfully communicated during a time interval (such as 1-10 s) to an estimated maximum number of bytes that can be communicated in the time interval (the latter of which is sometimes referred to as the ‘capacity’ of a communication channel or link), and/or a ratio of an actual data rate to an estimated data rate (which is sometimes referred to as ‘utilization’). Note that the one or more integrated circuits  110  and  120  shown in components in  FIG.  1    may be the same as or different from each other. 
     In some embodiments, wireless communication between components in  FIG.  1    uses one or more frequencies or bands of frequencies, such as: a very high frequency (VHF) range between 108 and 137 MHz, a band of frequencies associated with TCAS or ACAS (such as ACAS X), a band of frequencies associated with ADS-B, 978 MHz, 1090 MHz, 1030 MHz, a radar band of frequencies, or another frequency or band of frequencies associated with communication associated with a regulation from a government aviation or aviation safety administration. Note that the communication between electronic devices may use multi-user transmission (such as orthogonal frequency division multiple access or OFDMA) or multiple-input multiple-output (MIMO). 
     Although we describe the network environment shown in  FIG.  1    as an example, in alternative embodiments, different numbers or types of electronic devices may be present. For example, some embodiments comprise more or fewer electronic devices. As another example, in another embodiment, different electronic devices are transmitting and/or receiving wireless signals. 
     In some embodiments, electronic device  100  may include fewer or more components, two or more components may be combined into a single component, a second single component may be implemented using multiple components, and/or a position of at least one of the components may be changed. 
     As described previously, in order to reduce the size or weight of electronic device  100 , in a first group of embodiments one or more omnidirectional antennas  116  may be used to determine a track of electronic device  114 . Notably, electronic device  100  may receive (e.g., using omnidirectional antenna  116 - 1 ) the broadcast information associated with electronic device  114 , where the broadcast information is compatible with a regulation from a government aviation or aviation safety administration (such as the Federal Aviation Administration or the European Union Aviation Safety Agency). Then, electronic device  100  may determine a track of electronic device  114  based at least in part on the broadcast information. Note that the track may include one or more of: horizontal location or position, relative range, relative bearing, heading, relative or absolute altitude, and/or relative or absolute speed. 
     For example, determining the track (horizontal location or position, relative range, relative bearing, heading, relative or absolute altitude, and/or relative or absolute speed) may involve measuring range (such as slant range) to electronic device  114  as a function of time (e.g., at different measurement times, such as continuously, at discrete sampling times or as-needed). Notably, the range to electronic device  114  may be measured using time-of-flight measurements by providing an interrogation signal and subsequently receiving an associated response from electronic device  114 . (Thus, in some embodiments, the communication techniques may use active surveillance.) Note that the interrogation signal may be selectively transmitted to electronic device  114  with a carrier frequency of 1,030 MHz using mode S interrogation. Alternatively, the interrogation signal may be a so-called all-call interrogation with a carrier frequency of 1,030 MHz that is transmitted to any electronic device in proximity (such as wireless range) of electronic device  100 , and that results in subsequent responses from any transponders that receive this interrogation signal. However, a wide variety of frequencies may be used for transmitting and/or receiving. 
     In some embodiments, the track may be determined in 2D, such as a plane. Alternatively, the track may be determined in 3D when an altitude or vertical position of electronic device  100  and/or electronic device  114  are available. Furthermore, in some embodiments, determining the track may involve: performing Doppler measurements of range; and correlating the range to speed and/or velocity of electronic device  114 . (Note that the Doppler effect may result in an increase in carrier frequency the further a radio-frequency transmission travels. This shift in frequency can be measured and correlated to the reported position of an aircraft.) 
     Note that electronic device  100  may include a transponder. Consequently, the transmit RF signals and the receive RF signals may use different carrier frequencies. In some embodiments, the transmit RF signals and the receive RF signals are modulated using differential phase shift keying (DPSK) and pulse position modulation (PPM). 
     Moreover, electronic device  100  may validate or verify the broadcast information based at least in part on the determined track (such as an active surveillance track) and, more generally, data. For example, electronic device  100  may compare a track specified by the broadcast information with the determined track. 
     Furthermore, electronic device  100  may provide the determined track to a collision avoidance system, such as a DAA system. For example, the collision avoidance system may include ACAS X. In some embodiments, electronic device  114  may include a transponder in a cooperative aircraft. The broadcast information may include location information of electronic device  114  (such as horizontal location or position, relative range, relative bearing, heading, relative or absolute altitude, and/or relative or absolute speed) that are based at least in part on GPS, such as ADS-B messages. 
     Additionally, the measurements may be performed multiple times (such as at least 2-3×) to reduce or eliminate probability of another electronic device (such as electronic device  114 ) being at a same range as electronic device  100 . In some embodiments, the measurements may be performed multiple times to reduce or eliminate synchronous interference associated with two or more other electronic devices at similar range that respond to active surveillance interrogations. Additionally Whisper/Shout active surveillance interrogations may be used to interrogate aircraft in a specific ranges in order to eliminate interference. 
     In some embodiments, electronic device  100  may collaboratively determine the track based at least in part on one or more additional range measurements associated with a set of one or more electronic devices (such as electronic devices  122 , e.g., additional transponders and/or additional aircraft), where a given additional measurement was performed using another instance of data received using the omnidirectional antenna. 
     Note that, in some embodiments, electronic device  100  may provide the range measurements and/or the determined track to another aircraft, a ground control station  124  and/or air traffic control  126 . For example, electronic device  100  may provide information associated with a real-time data structure that specifies spoofed or inaccurate transponder data, such as those where there is a difference between an instance of the broadcast information and the determined track. 
     Moreover, electronic device  100  may determine the track when GPS is unavailable or unreliable. For example, electronic device  100  may receive an indication that GPS is unavailable or unreliable from or associated with a GPS receiver. In these embodiments, electronic device  100  may perform active surveillance, using mode A, C or S interrogation, which provides range and/or altitude information associated with electronic device  114 . Alternatively or additionally, the broadcast information may include the identifier of electronic device  114 , such as an ICAO (of Montreal, Canada) code or designator. 
     Furthermore, in some embodiments electronic device  100  may also include at least omnidirectional antenna  116 - 2 . Notably, electronic device  100  may include or may at least be selectively electrically coupled to omnidirectional antenna  116 - 1  and an omnidirectional antenna  116 - 2 , which each may be used for bidirectional communication. For example, omnidirectional antenna  116 - 1  may be disposed on or proximate to a top of electronic device  100  (such as a top of an aircraft) and omnidirectional antenna  116 - 2  may be disposed on or proximate to a bottom of electronic device  100  (such as a bottom of an aircraft). Note that omnidirectional antennas  116  may provide antenna diversity. Additionally, the use of multiple omnidirectional antennas  116  may provide more accurate range measurements, e.g., by performing phase-difference measurements. For example, phase comparison of the electrical signals received by two or more omnidirectional antennas can be used to lookup bearing. The lookup data structure may be populated or may include phase differences associated with other tracks that have bearing available. The data structure may be applied to specific aircraft and may need to be cleared when the installation (such as the antenna cables or the antennas) was modified. The data structure may also be reset on power up and omnidirectional bearing may not be available until adequate samples are received to populate the data structure. In some embodiments, multiple omnidirectional antennas  116  (such as four omnidirectional antennas, e.g., on front and back surfaces of the top and the bottom of wings of an aircraft) may provide angular information (such as a bearing to electronic device  114 ). Alternatively or additionally, when the transmissions from multiple omnidirectional antennas  116  are synchronized (with an adjustable or selectable relative phase delay and/or transmit power difference), electronic device  100  may perform beam steering (such as towards a front, a side or a back direction). 
     In some embodiments, the one or more integrated circuits  110  may provide strong isolation between omnidirectional antenna  116 - 1  and omnidirectional antenna  116 - 2 . For example, the isolation for a given omnidirectional antenna may reduce the interference from transmissions associated with the other omnidirectional antenna by at least 20 dB. Notably, the one or more integrated circuits  110  may include a PIN-diode switching network (such as a push-pull four PIN-diode or switch topology that is controlled by a control circuit  112 ) to provide the isolation. 
     While the preceding discussion illustrated the use of the communication techniques with broadcast information, more generally, the communication techniques may use one or more other types of measurements (such as radar measurements of range and/or altitude, and/or Doppler measurements) to verify or validate information specifying a track of an aircraft, e.g., as specified by ADS-B messages. Moreover, in some embodiments, the communication techniques may allow omnidirectional interrogation(s) to be used to obtain information about the intended maneuver of another aircraft, which is then input to a collision avoidance system (such as a DAA system) to coordinate with the other aircraft. 
     Moreover, as discussed previously, in a second group of embodiments multiple different types of sensors  122  in electronic device  100  may perform measurements of an environment external to electronic device  100 . During operation, electronic device  100  may perform measurements of the environment using the types of sensors, where the types of sensors  122  are different from a transponder or a transceiver. Then, electronic device  100  may determine a track of electronic device  114  in the environment based at least in part on the measurements. Next, electronic device  100  may provide the determined track to a collision avoidance system (such as DAA system). In some embodiments, the collision avoidance system may include ACAS X or another technique defined by associated with the RTCA (of Washington D.C.). 
     Note that the types of sensors  122  may include: an electro-optic or infrared sensor, a camera or image sensor (such as CCD or a CMOS sensor), a LiDAR sensor, a RADAR sensor, an acoustic sensor, a pressure sensor, a weather or environmental sensor (such as a temperature sensor, a wind speed sensor, a humidity sensor, etc.), an altitude sensor, and/or another type of sensor. 
     Moreover, determining the track may involve merging tracks associated with different measurements into a common track file. 
     Furthermore, the track may be determined using a pretrained model, such as a pretrained model that is trained using a supervised-learning technique (such as a machine-learning model or a neural network, e.g., a convolutional neural network). For example, the supervised-learning technique may include: support vector machines, classification and regression trees, logistic regression, LASSO, logistic LASSO regression, linear regression, a Bayesian technique, and/or another (linear or nonlinear) supervised-learning technique. 
     Furthermore, as described previously, in a third group of embodiments electronic device  100  may automatically transmit a response to an instruction. Notably, electronic device  100  may receive RF signals that convey information corresponding to an instruction (or a command) associated with air traffic control  126 . In response, electronic device  100  may automatically transmit second RF signals that convey second information corresponding to a response to the instruction. 
     Note that the instruction may include a verbal instruction. Moreover, prior to transmitting the RF signals, electronic device  100  may optionally: extract the information from the RF signals; perform natural language processing (e.g., using a pretrained model, such as a neural network) on the information; and generate or select the response. Note that generating the response may include generating or voice synthesizing a verbal response to the verbal instruction (e.g., using a second pretrained model, such as a second neural network, which may be the same as or different from the pretrained model). Alternatively or additionally, selecting the response may include selecting a predetermined verbal response to the verbal instruction. Thus, in some embodiments, the communication techniques may be fully electronic (without natural language processing and/or voice synthesizing), while in other embodiments the communication techniques may, at least in part, use natural language processing and/or voice synthesizing to provide situational awareness to the pilot and/or pilots of other aircraft in proximity. Consequently, in some embodiments, electronic device  100  may provide an automated voice radio system for aircraft communication. 
     Furthermore, the response may repeat the instruction and/or may acknowledge receipt of the instruction. For example, the verbal instruction may include a squawk code, a heading (such as ‘head  270 ’) or an altitude (such as ‘altitude  180 ’). More generally, currently, when operating under general flight operation rules, a pilot may maintain voice communication using a two-way radio with local air traffic control (such as air traffic control  126 ). Any manned or unmanned aircraft would benefit from the automation of these voice communication. This may include: automatic selection of appropriate radio frequencies for use in communication while airborne or on the ground; automatic transmission of appropriate radio calls and responses to incoming calls; automatic aircraft response through autopilot and/or ground station indications to the operator of a ground control station (such as ground control station  124 ) based at least in part on incoming radio calls and responses; and/or automatic aircraft response to adjust for current local ATIS or ASOS information. In some embodiment, there may be a manual override for a pilot or an operator in a ground control station to stop or modify a given automatic response. 
     Additionally, depending on the instruction, electronic device  100  may subsequently selectively automatically transmit third RF signals that convey third information that indicate that the instruction has been completed. For example, electronic device  100  may indicate when an altitude has been changed, but may not indicate when a heading has been changed. 
     In some embodiments, electronic device  100  may provide the instruction, e.g., to a pilot or an autopilot of electronic device  100 . For example, the instruction may be displayed (e.g., on a display of the pilot or in electronic device  100 ) or may be output into headphones of the pilot. Alternatively or additionally, electronic device  100  may determine one or more aircraft operations based at least in part on the instruction, and then may provide information specifying the one or more aircraft operations to the pilot or the autopilot. 
     Moreover, electronic device  100  may monitor whether the instruction has been completed. When a time interval (such as 30 s) has elapsed and the instruction has not been completed, electronic device  100  may provide a reminder message corresponding to the instruction, e.g., to a pilot or an autopilot of electronic device  100 . 
     While the preceding discussion illustrated the use of the communication techniques for communication with air traffic control, more generally the communication techniques may be used with a wide variety of communication, such as with: another aircraft, a ground control station, etc. Furthermore, the communication may occur in a variety of bands of frequencies. 
     While the preceding discussion illustrated the communication and monitoring techniques being performed by electronic device  100 , in other embodiments at least some of the operations in the communication and/or monitoring techniques are performed by another electronic device, such as electronic device  114 , electronic devices  122 , ground control station  124 , air traffic control  126 , and/or a remotely located computer system with one or more computers. For example, while the third group of embodiments are illustrated as being performed by a separate electronic device (such as electronic device  100 ) from an autopilot, in other embodiments some or all of the operations in the third group of embodiments are performed by the autopilot. 
     We now describe embodiments of the method.  FIG.  2    presents a flow diagram illustrating an example of a method  200  for determining a track that may be performed by an electronic device, such as electronic device  100  ( FIG.  1   ). During operation, the electronic device may receive, using one or more omnidirectional antennas, broadcast information (operation  210 ) associated with a second electronic device, where the broadcast information is compatible with a regulation from a government aviation or aviation safety administration. Then, the electronic device may determine the track of the second electronic device (operation  212 ) based at least in part on the broadcast information. 
     Moreover, while the preceding discussion illustrated method  200  with broadcast information, in other embodiments broadcast and/or reply information may be used. 
     Embodiments of the communication techniques are further illustrated in  FIG.  3   , which presents a drawing illustrating an example of communication between electronic devices  100  and  114 . Notably, interface circuit (IC)  310  in electronic device  114  may transmit broadcast information (BI)  312  to electronic device  100 . After receiving wireless signals corresponding to broadcast information  312 , omnidirectional antenna (OA)  116 - 1  in electronic device  100  may provide corresponding electrical signals  314  to interface circuit  316  in electronic device  100 . 
     Moreover, interface circuit  316  may determine track  318  of electronic device  114 ) based at least in part on broadcast information  312  and, more generally, using omnidirectional antenna  116 - 1 . For example, interface circuit  316  may determine track  318  by measuring range  324  to electronic device  114  as a function of time. In some embodiments, interface circuit  316  may measure range  324  using time-of-flight measurements by: providing an interrogation signal (IS)  320  to electronic device  114  via omnidirectional antenna  116 - 1 ; and receiving a response  322  from interface circuit  310  to interrogation signal  320 . Note that interrogation signal  320  may use mode S interrogation or may use all-call interrogation. 
       FIG.  4    presents a flow diagram illustrating an example of a method  400  for determining a track that may be performed by an electronic device, such as electronic device  100  ( FIG.  1   ). During operation, the electronic device may perform measurements of an external environment (operation  410 ) of the electronic device using different types of sensors, where the types of sensors are different from a transponder or a transceiver. Then, the electronic device may determine the track of a second electronic device (operation  412 ) in the external environment based at least in part on the measurements. For example, the second electronic device may include a noncooperative aircraft or another object. Note that determining the track may involve merging tracks associated with different measurements into a common track file. Next, the electronic device may provide the determined track (operation  414 ) to a collision avoidance system (such as a DAA system). 
     Embodiments of the communication techniques are further illustrated in  FIG.  5   , which presents a drawing illustrating an example of communication among components in electronic device  100 . Notably, different types of sensor(s)  510  in electronic device  100  may provide measurements  512  corresponding a position, speed, altitude and/or heading of electronic device  114  to processor  514  in electronic device  100 . 
     Moreover, interface circuit  516  in electronic device  100  (such as a transponder and/or an interrogator) may receive messages  518  from electronic device  114 . These messages may include information  520  about a position, speed, altitude and/or heading of electronic device  114 . Furthermore, interface circuit  516  may provide information  520  to processor  514 . 
     Then, processor  514  may determine track  522  of electronic device  114  (such as a noncooperative aircraft or object) based at least in part on measurements  512  and/or information  520 . For example, determining track  522  may involve merging tracks associated with measurements  512  and/or information  520  into a common track file. Alternatively or additionally, processor  514  may validate track  522  of a cooperative aircraft. Next, processor  514  may provide track  522  to a collision avoidance system (CAS)  524  (such as a DAA system). 
       FIG.  6    presents a flow diagram illustrating an example of a method  600  for automatically transmitting a response to an instruction that may be performed by an electronic device, such as electronic device  100  ( FIG.  1   ). During operation, the electronic device may receive RF signals (operation  610 ) that convey information corresponding to an instruction (or a command) associated with air traffic control. In response, the electronic device may automatically transmit second RF signals (operation  612 ) that convey second information corresponding to the response to the instruction. 
     In some embodiments, method  200  ( FIG.  2   ),  400  ( FIG.  2   ) and/or  600  may include additional or fewer operations. Moreover, the order of the operations may be changed, there may be different operations, two or more operations may be combined into a single operation, and/or a single operation may be divided into two or more operations. 
     Embodiments of the communication techniques are further illustrated in  FIG.  7   , which presents a drawing illustrating an example of communication between electronic device  100 , ground station (GS)  124  or air traffic control (ATC)  126 . Notably, ground station  124  or air traffic control  126  may transmit RF signals  710  to electronic device  100  that convey information  712  corresponding to an instruction  714  (or a command) associated with air traffic control  126 . 
     After receiving RF signals  710 , an interface circuit  716  in electronic device  100  may provide information  712  to a processor  718  in electronic device  100 . Then, processor  718  may extract instruction  714  based at least in part on information  712 . For example, processor  718  may extract instruction  714  using a pretrained model, such as a neural network that performs natural language processing. 
     Moreover, processor  718  may interpret  720  instruction  714  using a second pretrained model, such as a second neural network. Next, processor  718  may instruct  722  interface circuit  716  to provide, to ground station  124  or air traffic control  126 , a response  724  to instruction  714 . 
     While  FIGS.  3 ,  5  and  7    illustrate communication between components using unidirectional or bidirectional communication with lines having single arrows or double arrows, in general the communication in a given operation in this figure may involve unidirectional or bidirectional communication. Moreover, while  FIGS.  3 ,  5 , and  7    illustrate operations being performed sequentially or at different times, in other embodiments at least some of these operations may, at least in part, be performed concurrently or in parallel. 
     We now describe embodiments of an electronic device, which may perform at least some of the operations in the communication and monitoring techniques.  FIG.  8    presents a block diagram illustrating an example of an electronic device  800  in accordance with some embodiments, such as a transponder, a transceiver, an aircraft, etc. This electronic device includes processing subsystem  810 , memory subsystem  812 , and networking subsystem  814 . Processing subsystem  810  includes one or more devices configured to perform computational operations. For example, processing subsystem  810  can include one or more microprocessors, ASICs, microcontrollers, programmable-logic devices, one or more graphics process units (GPUs) and/or one or more digital signal processors (DSPs). 
     Memory subsystem  812  includes one or more devices for storing data and/or instructions for processing subsystem  810  and networking subsystem  814 . For example, memory subsystem  812  can include dynamic random access memory (DRAM), static random access memory (SRAM), and/or other types of memory. In some embodiments, instructions for processing subsystem  810  in memory subsystem  812  include: one or more program modules or sets of instructions (such as program instructions  822  or operating system  824 ), which may be executed by processing subsystem  810 . Note that the one or more computer programs may constitute a computer-program mechanism. Moreover, instructions in the various modules in memory subsystem  812  may be implemented in: a high-level procedural language, an object-oriented programming language, and/or in an assembly or machine language. Furthermore, the programming language may be compiled or interpreted, e.g., configurable or configured (which may be used interchangeably in this discussion), to be executed by processing subsystem  810 . 
     In addition, memory subsystem  812  can include mechanisms for controlling access to the memory. In some embodiments, memory subsystem  812  includes a memory hierarchy that comprises one or more caches coupled to a memory in electronic device  800 . In some of these embodiments, one or more of the caches is located in processing subsystem  810 . 
     In some embodiments, memory subsystem  812  is coupled to one or more high-capacity mass-storage devices (not shown). For example, memory subsystem  812  can be coupled to a magnetic or optical drive, a solid-state drive, or another type of mass-storage device. In these embodiments, memory subsystem  812  can be used by electronic device  800  as fast-access storage for often-used data, while the mass-storage device is used to store less frequently used data. 
     Networking subsystem  814  includes one or more devices configured to couple to and communicate on a wired and/or wireless network (i.e., to perform network operations), including: control logic  816 , an interface circuit  818  and one or more antennas  820  (or antenna elements) and/or input/output (I/O) port  830 . (While  FIG.  8    includes one or more antennas  820 , in some embodiments electronic device  800  includes one or more nodes, such as nodes  808 , e.g., a network node that can be coupled or connected to a network or link, or an antenna node or a pad that can be coupled to the one or more antennas  820 . Thus, electronic device  800  may or may not include the one or more antennas  820 .) For example, networking subsystem  814  can include a Bluetooth™ networking system, a cellular networking system (e.g., a 3G/4G/5G network such as UMTS, LTE, etc.), a universal serial bus (USB) networking system, a networking system based on the standards described in IEEE 802.11 (e.g., a Wi-Fi® networking system), an Ethernet networking system, a cable modem networking system, and/or another networking system. 
     Networking subsystem  814  includes processors, controllers, radios/antennas, sockets/plugs, and/or other devices used for coupling to, communicating on, and handling data and events for each supported networking system. Note that mechanisms used for coupling to, communicating on, and handling data and events on the network for each network system are sometimes collectively referred to as a ‘network interface’ for the network system. Moreover, in some embodiments a ‘network’ or a ‘connection’ between the electronic devices does not yet exist. Therefore, electronic device  800  may use the mechanisms in networking subsystem  814  for performing simple wireless communication between the electronic devices, e.g., transmitting advertising or beacon frames and/or scanning for advertising frames transmitted by other electronic devices. 
     Within electronic device  800 , processing subsystem  810 , memory subsystem  812 , and networking subsystem  814  are coupled together using bus  828 . Bus  828  may include an electrical, optical, and/or electro-optical connection that the subsystems can use to communicate commands and data among one another. Although only one bus  828  is shown for clarity, different embodiments can include a different number or configuration of electrical, optical, and/or electro-optical connections among the subsystems. 
     In some embodiments, electronic device  800  includes a display subsystem  826  for displaying information on a display, which may include a display driver and the display, such as a liquid-crystal display, a multi-touch touchscreen, etc. 
     Electronic device  800  can be (or can be included in) any electronic device with at least one network interface. For example, electronic device  800  can be (or can be included in): a radio, a transponder, a transceiver, a type of aircraft, a computer, a computer system, a desktop computer, a laptop computer, a subnotebook/netbook, a tablet computer, a smartphone, a cellular telephone, a smartwatch, a consumer-electronic device, a portable computing device, communication equipment, a computer network device, test equipment, and/or another electronic device. 
     Although specific components are used to describe electronic device  800 , in alternative embodiments, different components and/or subsystems may be present in electronic device  800 . For example, electronic device  800  may include one or more additional processing subsystems, memory subsystems, networking subsystems, and/or display subsystems. Additionally, one or more of the subsystems may not be present in electronic device  800 . Moreover, in some embodiments, electronic device  800  may include one or more additional subsystems that are not shown in  FIG.  8   , such as a user-interface subsystem  832 . Also, although separate subsystems are shown in  FIG.  8   , in some embodiments some or all of a given subsystem or component can be integrated into one or more of the other subsystems or component(s) in electronic device  800 . For example, in some embodiments program instructions  822  are included in operating system  824  and/or control logic  816  is included in interface circuit  818 . 
     Moreover, the circuits and components in electronic device  800  may be implemented using any combination of analog and/or digital circuitry, including: bipolar, PMOS and/or NMOS gates or transistors. Furthermore, signals in these embodiments may include digital signals that have approximately discrete values and/or analog signals that have continuous values. Additionally, components and circuits may be single-ended or differential, and power supplies may be unipolar or bipolar. 
     An integrated circuit (which is sometimes referred to as a ‘communication circuit’) may implement some or all of the functionality of networking subsystem  814  (or, more generally, of electronic device  800 ). The integrated circuit may include hardware and/or software mechanisms that are used for transmitting wireless signals from electronic device  800  and receiving signals at electronic device  800  from other electronic devices. Aside from the mechanisms herein described, radios are generally known in the art and hence are not described in detail. In general, networking subsystem  814  and/or the integrated circuit can include any number of radios. Note that the radios in multiple-radio embodiments function in a similar way to the described single-radio embodiments. 
     In some embodiments, networking subsystem  814  and/or the integrated circuit include a configuration mechanism (such as one or more hardware and/or software mechanisms) that configures the radio(s) to transmit and/or receive on a given communication channel (e.g., a given carrier frequency). For example, in some embodiments, the configuration mechanism can be used to switch the radio from monitoring and/or transmitting on a given communication channel to monitoring and/or transmitting on a different communication channel. (Note that ‘monitoring’ as used herein comprises receiving signals from other electronic devices and possibly performing one or more processing operations on the received signals) 
     In some embodiments, an output of a process for designing the integrated circuit, or a portion of the integrated circuit, which includes one or more of the circuits described herein may be a computer-readable medium such as, for example, a magnetic tape or an optical or magnetic disk. The computer-readable medium may be encoded with data structures or other information describing circuitry that may be physically instantiated as the integrated circuit or the portion of the integrated circuit. Although various formats may be used for such encoding, these data structures are commonly written in: Caltech Intermediate Format (CIF), Calma GDS II Stream Format (GDSII), Electronic Design Interchange Format (EDIF), OpenAccess (OA), or Open Artwork System Interchange Standard (OASIS). Those of skill in the art of integrated circuit design can develop such data structures from schematics of the type detailed above and the corresponding descriptions and encode the data structures on the computer-readable medium. Those of skill in the art of integrated circuit fabrication can use such encoded data to fabricate integrated circuits that include one or more of the circuits described herein. 
     While the preceding discussion used particular communication protocols as an illustrative example, in other embodiments a wide variety of communication protocols and, more generally, wired and/or wireless communication techniques may be used. Thus, the communication and/or monitoring techniques may be used in conjunction with a variety of network interfaces. Furthermore, while some of the operations in the preceding embodiments were implemented in hardware or software, in general the operations in the preceding embodiments can be implemented in a wide variety of configurations and architectures. Therefore, some or all of the operations in the preceding embodiments may be performed in hardware, in software or both. For example, at least some of the operations in the communication and/or monitoring techniques may be implemented using program instructions  822 , operating system  824  (such as a driver for interface circuit  818 ) or in firmware in interface circuit  818 . Alternatively or additionally, at least some of the operations in the communication and/or monitoring techniques may be implemented in a physical layer, such as hardware in interface circuit  818 . 
     In the preceding description, we refer to ‘some embodiments.’ Note that ‘some embodiments’ describes a subset of all of the possible embodiments, but does not always specify the same subset of embodiments. Moreover, note that numerical values in the preceding embodiments are illustrative examples of some embodiments. In other embodiments of the communication and/or monitoring techniques, different numerical values may be used. 
     The foregoing description is intended to enable any person skilled in the art to make and use the disclosure, and is provided in the context of a particular application and its requirements. Moreover, the foregoing descriptions of embodiments of the present disclosure have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present disclosure to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Additionally, the discussion of the preceding embodiments is not intended to limit the present disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.