Sectorized antennas for improved airborne reception of surveillance signals

A plurality of antenna elements may receive a plurality of signals. Each of the plurality of antenna elements may correspond to at least one of a plurality of sectors of a sectorized antenna. A receiver may process each of the plurality of signals in parallel, including decoding one or more messages from the plurality of signals. The receiver may output at least one of the one or more messages.

TECHNICAL FIELD

The disclosure relates to airborne reception of surveillance messages via sectorized antennas.

BACKGROUND

Automatic dependent surveillance broadcast (ADS-B) is a technology where a particular aircraft can determine its position and report it (together with other data such as position data accuracy, aircraft identification, barometric altitude, and the like), thereby enabling other aircraft and air traffic control ground stations to be aware of the position of the particular aircraft. As a result, aircraft and ground stations equipped with ADS-B receiving devices may determine the positions of other aircraft that are equipped by ADS-B transmitting devices in their vicinity. Transmitting and receiving of ADS-B messages by aircraft may supplement or replace the use of ground-based radars that determine the positions of airborne aircraft to prevent airborne collisions.

SUMMARY

Devices, systems, and techniques for improving an aircraft's reception of ADS-B messages are described herein. In some examples, a sectorized antenna comprising a plurality of directional antenna elements may receive one or more signals carrying one or more ADS-B messages. A receiver operably coupled to the plurality of directional antenna elements may process the one or more signals to decode the one or more ADS-B messages. In one example, the sectorized antenna may receive a plurality of signals carrying a plurality of ADS-B messages. The receiver may process the plurality of signals in parallel, including decoding the plurality of ADS-B messages carried by the plurality of signals in parallel. In some examples, the sectorized antenna may be a traffic collision avoidance system (TCAS) antenna and the signal processor that processes the signals received by the antenna may be a part of modified TCAS unit. In this way, the sectorized antennas technique, as disclosed herein, may be implemented by reusing and modifying an already-installed TCAS unit included in an aircraft.

A conventional ADS-B receiver system may typically lose a number of ADS-B messages when they are received close enough to overlap, particularly in crowded air traffic conditions such as are increasingly common ear large airports. In accordance aspects of the present disclosure, the sectorized antennas technique disclosed herein may reduce the number of lost ADS-B messages due to overlapping signals, which may prevent a degradation of any applications that use ADS-B message data carried by the ADS-B messages, including, for example, applications involved in collision avoidance and situational awareness.

In one example, the disclosure is directed to a method. The method comprises receiving, by a plurality of antenna elements, a plurality of signals, wherein each of the plurality of antenna elements correspond to at least one of a plurality of sectors of a sectorized antenna. The method further comprises processing, by a receiver, each of the plurality of signals, including decoding one or more messages from the plurality of signals. The method further comprises outputting, by the receiver, at least one of the one or more messages.

In another example, the disclosure is directed to a system. The system comprises a plurality of antenna elements configured to receive a plurality of signals, wherein each of the plurality of antenna elements corresponds to at least one of a plurality of sectors of a sectorized antenna. The system further comprises a receiver configured to: process each of the plurality of signals in parallel, including decoding one or more messages from the plurality of signals; and output at least one of the one or more messages.

The details of one or inure examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages in addition to those described below will be apparent from the description and drawings, and from the claims.

DETAILED DESCRIPTION

Example devices, systems, and techniques for receiving and decoding surveillance messages are described in this disclosure. More specifically, the present disclosure describes example devices, systems, and techniques for an aircraft to improve reception of radio frequency (RF) signals that carry automatic dependent surveillance broadcast (ADS-B) messages that, among others, indicate the positions of one or more other neighboring aircraft.

In certain geographical areas where air traffic is very dense, two or more ADS-B messages may sometimes arrive at an antenna of an ADS-B receiving device at the same time and may therefore overlap. When the overlapping incident messages have significantly different power levels, the ADS-B receiving device may typically process only the message with the relatively strongest power level, thereby losing the messages with relatively weaker power levels. Thus, when the messages are overlapped, at least one message is processed. However, when the overlapping incident messages each have comparable power levels, each of the overlapped messages may be lost, thereby leading to decreased frequency-space utilization and consequently also a decreased ability of the system to assure performance measures such as availability required by applications utilizing ADS-B messages.

Examples of potential issues an aircraft may encounter with receiving and decoding ADS-B messages may include channel congestion (e.g., interference). An ADS-B channel may be shared by systems such as distance measuring equipment (DME) systems, traffic collision avoidance systems (TCAS), secondary surveillance radar (SSR) systems, and the like. Channel congestion may also occur due to high traffic density near large airports.

FIG. 1Ais a functional block diagram illustrating an example aircraft2that includes antenna elements4A-4D (“antenna elements4”) which are configured to receive signals that carry ADS-B messages transmitted by aircraft within a specified vicinity of aircraft2's position.

Antenna elements4may make up a sectorized antenna comprising a plurality of sectors, where each antenna element antenna element4may correspond to at least one of the plurality of sectors of the sectorized antenna. As such, each of antenna elements4A-4D may be a directional antenna. A directional antenna may be an antenna that does not radiate and/or receive signals uniformly in all directions. However, a directional antenna may show a greater gain in one or more directions, thereby increasing its performance in transmitting and receiving signals in those one or more directions. Each of antenna elements4A-4D may be positioned in aircraft2such that each of antenna elements4A-4D may show greater gain in a substantially different direction with respect to the other antenna elements of antenna elements4. In the example ofFIG. 1A, because antenna elements4comprise four elements4A-4D, antenna elements4may be a sectorized antenna having four sectors, and each of the four antenna elements4A-4D may show greater gain in a substantially different direction with respect to the other of antenna elements4A-4D. Although the example ofFIG. 1Aillustrates a sectorized antenna having four antenna elements4A-4D, it should be understood that a sectorized antenna in accordance with techniques of the present disclosure may include greater or fewer than four antenna elements. As such, antenna elements4may comprise two or more antenna elements with various directional characteristics (radiation patterns).

Antenna elements4may be configured to receive analog radio frequency (RF) signals that carry ADS-B messages. In one example, antenna elements4may operate at ADS-B channel at 1090 MHz to receive signals carrying ADS-B messages that indicate, among others, the positions of one or more other neighboring aircraft.

As shown inFIG. 1A, one or more aircraft in the vicinity of aircraft2may broadcast RF signals6A and6B from differing directions. In some examples, RF signals6A and6B may at least partially overlap in time, such that two or more of antenna elements4A-4D may be able to receive one or both of RF signals6A and6B. For example, both antenna element4A and antenna element4C may be able to receive both RF signals6A and6B. However, due to the directional nature of antenna elements4and due to RF signals6A and6B being broadcast from different directions, the composite RF signal (a combination of RF signals6A and6B) received by individual antenna elements4A and4C may differ (the power ratios between RF signals6A and6B), which may increase the probability that ADS-B messages carried by RF signals6A and6B respectively will be correctly decoded. In the example shown inFIG. 1A, RF signal6A received by antenna element4A is significantly more powerful than RF signal6B received by antenna element4A. Conversely, RF signal6B received by antenna element4C is significantly more powerful than RF signal6A received by antenna element4C. While the example ofFIG. 1Ashows antenna elements4receiving two RF signals6A and6B, antenna elements4may be able to receive fewer or more than two RF signals. For example, each of the four elements4A-4D of antenna elements4may be able to receive one or more RF signals which may be the same as or different from RF signals received by other elements of antenna elements4. In the example shown inFIG. 1A. RF signals6A and6B may each represent an ADS-B message, may respectively represent a single ADS-B message and an interfering signal, or may represent any other signal sharing the same RF channel.

Aircraft2may include receiver8which may be operably coupled to antenna elements4. Receiver8may be configured to process one or more of the plurality of signals received by antenna elements4, including decoding one or more ADS-B messages from the one or more of the plurality of signals. Receiver8may be further configured to output the one or more ADS-B messages that it has decoded. For example, receiver8may output the one or more ADS-B messages that it has decoded to the traffic computer (not depicted inFIG. 1A). Traffic computer may process ADS-B data (among other data inputs) and may output application specific data to a communication bus (not depicted inFIG. 1A).

FIG. 1Bis a functional block diagram illustrating an example receiver8. As shown inFIG. 1B, receiver8may include radio frequency front-end (RFFE)12, analog-to-digital converter (ADC)14, and digital back-end (DBE)20.

RFFE12may be operably coupled to antenna elements4and may process corresponding RF signal streams received from corresponding antenna elements4A-4D to convert them into intermediate frequency (IF) signals. As discussed above, an antenna element of antenna elements4may receive an RF signal stream that may convey one or more ADS-B messages (corresponding RF signals), and RFFE12may be configured to select and process the RF signal streams received from one or more of antenna elements4. In one example, RFFE12may select one RF signal stream received by one of antenna elements4out of all available RF signal streams received by all of antenna elements4, based at least in part on the respective signal power levels of the received RF signal streams, such as selecting the RF signal stream received by one of antenna elements4with the highest signal power level (i.e., the strongest signal) out of all available RF signal streams received by that one of antenna elements4.

In some examples, RFFE12may include a plurality of RFFEs, each of which corresponds with one of antenna elements4, or may include a multi-channel RFFE, where each channel of the multi-channel RFFE corresponds with one of antenna elements4. For example, if antenna elements4comprise four antenna elements4A-4D, RFFE12may include four RFFEs or may include a four-channel RFFE. In this way, RFFE12may be able to process RF signal streams received from two or more antenna elements of antenna elements4in parallel, such that RFFE12may be able to process multiple RF signal streams from two or more antenna elements of antenna elements4at the same time instead of processing just a single RF signal stream. It should be understood that the term parallel as used throughout this disclosure should not necessarily indicate any precise overlap or perfect synchronization in processing multiple RF signal streams.

Thus, in the example ofFIG. 1B, a first channel of RFFE12may correspond to antenna element4A and a second channel of RFFE12may correspond to antenna element4C. The first channel of RFFE12may process and convert the corresponding RF signal stream into an IF signal. Correspondingly, a second channel of RFFE12, may process and convert the corresponding RF signal stream into an IF signal. The first and second channels of RFFE12may operate to process the RF signal streams from antenna elements4A and4C in parallel.

ADC14may be operably coupled to RFFE12and may convert analog intermediate frequency signals received from RFFE12to digital intermediate frequency signals, and may output the digital intermediate frequency signals to DBE20. Similar to RFFE12, ADC14may include a plurality of ADCs or may be a multi-channel ADC, such that each of the plurality of ADCs or each channel of the multi-channel ADC may process analog IF signals outputted by a corresponding channel of a multi-channel RFFE12or by one of a plurality of RFFEs of RFFE12.

DBE20may be operably coupled to ADC14and may continuously attempt to detect and decode ADS-B messages contained in the digital signal streams outputted by ADC14in parallel. Detection and decoding may be performed, in one non-limiting example, in accordance with the DO-260B standard (or EUROCAE ED-102A, which is the European equivalent) promulgated by the Radio Technical Commission for Aeronautics (RTCA) and the Federal Aviation Administration (FAA). DBE20may include a plurality of DBEs or may be a multi-channel DBE. ADS-B message detection and decoding may be performed separately for each channel. As individual digital signal streams received by individual antenna elements4may differ (such as by amplitude of individual received ADS-B messages), the ADS-B message detection and decoding algorithm performed in all channels of DBE20may detect and decode various messages in each DBE channel.

DBE20may be operably coupled to ADC14and may be to decode one or more ADS-B messages contained in the digital signals outputted by ADC14in parallel. Decoding one or more ADS-B messages contained in the digital signals in parallel is not limited to starting decoding of multiple signals or outputting one or more ADS-B messages exactly at the same time. For example, if DBE20starts processing a first digital signal outputted by ADC14and, while processing the first digital signal, then starts to process a second digital signal outputted by ADC14, DBE20may still be deemed to be processing the first and second digital signals in parallel, in that DBE20may be able to process more than one digital signal at the same time. The first signal may correspond, for example, to the RF signal6A (depicted inFIG. 1A) received by antenna element4A and the second signal may correspond, for example, to the RF signal6B (depicted inFIG. 1A) received by antenna element4C. As such, the term parallel should not necessarily indicate any precise overlap or perfect synchronization in processing multiple digital signals.

As discussed in further detail below, DBE20may process the digital IF signals outputted by ADC14to convert the digital IF signals into baseband signals and may also detect and decode ADS-B messages carried by the baseband signals. DBE20may output the decoded ADS-B message data to, for example, a traffic computer (not depicted inFIG. 1B). Similar to RITE12and ADC14, DBE20may include a plurality of DBEs or may be a multi-channel DBE, such that each of the plurality of DBEs or each channel of the multi-channel DBE may process digital IF signals outputted by a corresponding channel of a multi-channel ADC14or by one of a plurality of ADCs of ADC14.

The traffic computer of aircraft2may process ADS-B data (among other data inputs) outputted by receiver8and may output application specific data to a communication bus (not depicted inFIG. 1B). For example, the traffic computer may output positions of nearby aircraft to a communication bus. That data may be utilized either by an output device, such as a display device, which may be viewed by pilots of aircraft2, or it may be processed by a software application, such as a collision avoidance application.

FIG. 2is a functional block diagram illustrating an example receiver8for decoding a plurality of messages in parallel. Receiver8may include RFFE12, ADC14, and DBE20. DBE20may include preprocessing unit16, message detection and decoding unit18, and duplicity check unit22.

Receiver8may comprise any suitable arrangement of hardware, software, firmware, or any combination thereof, to perform the techniques attributed to receiver8, RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, DBE20, and duplicity check unit22herein. For example, receiver8may include any one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. Although RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and duplicity check unit22are described as separate modules, in some examples, RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and duplicity check unit22can be functionally integrated. For example, preprocessing unit16, message detection and decoding unit18, and duplicity check unit22may be implemented in the same hardware component. In some examples, RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and duplicity check unit22may correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units, or one or more common hardware units.

Receiver8may, in the example ofFIG. 2, be considered a parallel receiver because receiver8may fully process each of a plurality of RF signal streams received by receiver8from antenna elements4to decode one or more of the ADS-B messages carried by the RF signal streams in parallel. For example, preprocessing unit16may convert, in parallel, a plurality of digital representations of IF signals outputted by ADC14into a plurality of baseband signals, and message detection and decoding unit18may process the plurality of baseband signals outputted by preprocessing unit16in parallel to detect and decode ADS-B messages carried by the plurality of baseband signals. In this way, DBE20may be able to process two or more signals received from ADC14at the same time.

Antenna elements4, in some examples, may comprise antenna elements of a TCAS antenna. Each element of antenna elements4may be a directional antenna element that corresponds to at least one of a plurality of sectors of a sectorized antenna. Each of antenna elements4may be operably coupled to RFFE12in receiver8via, for example, coaxial cables10A-10D (“coaxial cables10”) or any other suitable means for connecting antenna elements4to RFFE12.

RFFE12of receiver8may, as discussed above, be a multi-channel RFFE that is operably coupled to antenna elements4via, for example, coaxial cables10. Each channel of RFFE12may be associated with a different antenna element of antenna element4, and each channel of RFFE12may process and convert RF signal streams received from the associated antenna element of antenna elements4into intermediate frequency (IF) signals. For example, each channel of RFFE12may receive one RF signal stream from its associated antenna element of antenna elements4, process and convert the RF signal stream into an analog IF signal.

ADC14of receiver8may, as discussed above, be a multi-channel ADC that is operably coupled to RFFE12. Each channel of ADC14may be associated with a different channel of RFFE12to receive an analog IF signal from the associated channel of RFFE12and to convert the received analog IF signal into a digital representation of the IF signal.

Preprocessing unit16may be configured to perform filtering, declination, and downconversion of the digital representations of IF signals into baseband signals.

Message detection and decoding unit18may be configured to perform preamble detection to detect the presence of ADS-B messages within the received data stream. Message detection and decoding unit18may also be configured to decode the ADS-B messages detected within the received data stream. For example, message detection and decoding unit18may be configured to perform pulse-position modulation (PPM) signal demodulation into binary data and to perform error detection and correction on the demodulated binary data to decode the data content of ADS-B messages (ADS-B data).

Duplicity check unit22may be included in DBE20, may be operably coupled to message detection and decoding unit18, and may be configured to determine whether two or more of the ADS-B messages decoded and outputted by message detection and decoding unit18are identical. In some examples, receiver8may receive duplicate ADS-B messages because two or more of antenna elements4A-4D may receive RF signals that are carrying the same ADS-B message.

Duplicity check unit22may deem ADS-B messages to be identical if their parity bits are identical and/or if their data bits are identical. For example, identical ADS-B messages may be identified comparing their parity bits, as the parity bits, obtained by a cyclic redundancy check (CRC) algorithm, may be considered as unique for each ADS-B message. Responsive to determining that two or more ADS-B messages decoded and outputted by message detection and decoding unit18are the same ADS-B message, duplicity check unit22may output just one ADS-B message out of the two or more identical ADS-B messages. In other words, duplicity check unit22may refrain from outputting more than one of two or More of the same ADS-B messages. Aspects of duplicity check unit22will be described in further detail below with respect toFIG. 6.

The example receiver8shown inFIG. 2, where a plurality of messages are decoded in parallel, may be relatively more complex than the examples of receivers shown inFIG. 3,FIG. 4andFIG. 5, as the example receiver8shown inFIG. 2may utilize multi-channel processing, including multi-channel RFFE12, multi-channel ADC14, and multi-channel DBE20including an additional duplicity check unit22.

The traffic computer (not depicted inFIG. 2) of aircraft2may process ADS-B data (among other data inputs) outputted by receiver8and may output application specific data to a communication bus (not depicted inFIG. 2). For example, traffic computer may output positions of nearby aircraft to a communication bus. That data may be utilized either by an output device, such as a display device, which may be viewed by pilots of aircraft2, or it may be processed by a software application, such as a collision avoidance application.

FIG. 3is a functional block diagram illustrating an example receiver8for combining a plurality of signals. As shown inFIG. 3, receiver8may contain additional combining unit24. Receiver8may include RFFE12, ADC14, and DBE20. DBE20may include additional combining unit24, preprocessing unit16, and message detection and decoding unit18.

Receiver8may comprise any suitable arrangement of hardware, software, firmware, or any combination thereof, to perform the techniques attributed to receiver8, RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, DBE20, and combining unit24herein. For example, receiver8may include any one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. Although RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and combining unit24are described as separate modules, in some examples, RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and combining unit24can be functionally integrated. For example, preprocessing unit16, message detection and decoding unit18, and combining unit24may be implemented in the same hardware component. In some examples, RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and combining unit24may correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units, or one or more common hardware units. In some examples, combining unit24may be integrated into DBE20, preprocessing unit16, and/or message detection and decoding unit18.

In the example ofFIG. 3, two or more antenna elements of antenna elements4may each receive an RF signal that carries the same ADS-B message. For example, two or more antenna elements of antenna elements4may each receive the RF signal that may be different for each antenna element of antenna elements4due to directional characteristics of individual antenna elements of antenna elements4. Receiver8may combine the representations of the RF signal as received by the two or more antenna elements of antenna elements4in order to create a such a combined signal, that the probability of ADS-B message decoding by DBE20may be higher compared to the probability of ADS-B message decoding for individual RF signal received by the two or More antenna elements of antenna elements4.

Antenna elements4, in some examples, may comprise antenna elements of a TCAS antenna. Each element of antenna elements4may be a directional antenna element that corresponds to at least one of a plurality of sectors of a sectorized antenna. Each of antenna elements4may be operably coupled to REEF;12in receiver8via, for example, coaxial cables10A-10D (“coaxial cables10”) or any other suitable means for connecting antenna elements4to RFFE12.

RFFE12of receiver8may, as discussed above, be a multi-channel RFFE that is operably coupled to antenna elements4via, for example, coaxial cables10. Each channel of RFFE12may be associated with a different antenna element of antenna element4, and each channel of RFFE12may process RF signal received from the associated antenna element of antenna elements4and convert it into intermediate frequency (IF) signal. For example, each channel of RFFE12may receive one RF signal stream from its associated antenna element of antenna elements4, process and convert the RF signal stream into an analog IF signal.

As discussed above, two or more antenna elements of antenna elements4may each receive an RF signal that carries the same ADS-B message. For example, each of the four antenna elements4A-4D ofFIG. 3may receive the same RF signal that is carrying the same ADS-B message. However, due to the signal strength, directionality, and other quality considerations of the same RF signal, each of the four analog IF signals outputted by RFFE12may not be identical.

ADC14of receiver8may, as discussed above, be a multi-channel ADC that is operably coupled to RFFE12. Each channel of ADC14may be associated with a different channel of RFFE12to receive an analog IF signal from the associated channel of RFFE12and to convert the received analog IF signal into a digital representation of the IF signal. As discussed above, each of all analog IF signals outputted by RFFE12may not be identical. Similarly, because each of all analog IF signals outputted by RFFE12may not be identical, each of the digital representations of the IF signals outputted by ADC14may not be identical.

Combining unit24may be configured to combine the digital representations of IF signals outputted by ADC14into a single digital IF signal that may be processed by single-channel DBE20. Combining unit24may perform a linear combination of each of the digital representations of the IF signals outputted by ADC14. Combining unit24may perform phase compensation on the digital representations of IF signals outputted by ADC14to result in a single digital representation of an IF signal. Aspects of combining unit24will be described in further detail below with respect toFIG. 7.

Preprocessing unit16may be configured to perform filtering, decimation, and downconversion of the digital representation of the IF signal into a baseband signal.

Message detection and decoding unit18may be configured to perform preamble detection to detect the presence of ADS-B messages within the baseband signal. Message detection and decoding unit18may also be configured to decode the ADS-B messages detected within the baseband signal. For example, message detection and decoding unit18may be configured to perform pulse-position modulation (PPM) signal demodulation into binary data and to perform error detection and correction on the demodulated binary data to decode the ADS-B data.

Configuration of receiver8shown inFIG. 3may utilize multi-channel RFFE12, multi-channel ADC14, combining unit24, and single-channel DBE20. This configuration may be less complex than the one shown inFIG. 2as it may utilize just single-channel DBE20in comparison to the multi-channel DBE shown inFIG. 2.

Traffic computer (not depicted inFIG. 3) of aircraft2may process ADS-B data (among other data inputs) outputted by receiver8and may output application specific data to a communication bus (not depicted inFIG. 3). For example, traffic computer may output positions of nearby aircraft to a communication bus. That data may be utilized either by an output device, such as a display device, which may be viewed by pilots of aircraft2, or it may be processed by a software application, such as a collision avoidance application.

FIG. 4is a functional block diagram illustrating an example receiver8for selecting a single signal to decode. As shown inFIG. 4, receiver8may include RFFE12, ADC14, and DBE20. DBE20may include selection unit25, preprocessing unit16, and message detection and decoding unit18.

Receiver8may comprise any suitable arrangement of hardware, software, firmware, or any combination thereof, to perform the techniques attributed to receiver8, RFFE12, ADC,14, preprocessing unit16, message detection and decoding unit18, DBE20, and selection unit25herein. For example, receiver8may include any one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. Although RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and selection unit25are described as separate modules, in some examples, RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and selection unit25can be functionally integrated. For example, preprocessing unit16, message detection and decoding unit18, and selection unit25may be implemented in the same hardware component. In some examples, REEF12, ADC14, preprocessing unit16, message detection and decoding unit18, and selection unit25may correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units, or one or more common hardware units.

Antenna elements4, in some examples, may comprise antenna elements of a TCAS antenna. Each element of antenna elements4may be a directional antenna element that corresponds to at least one of a plurality of sectors of a sectorized antenna. Each of antenna elements4may be operably coupled to RFFE12in receiver8via, for example, coaxial cables10A-10D (“coaxial cables10”) or any other suitable means for connecting antenna elements4to RFFE12.

RFFE12of receiver8may, as discussed above, be a multi-channel RFFE that is operably coupled to antenna elements4via, for example, coaxial cables10. Each channel of RFFE12may be associated with a different antenna element of antenna element4, and each channel of RFFE12may process and convert RF signal stream received from the associated antenna element of antenna elements4into intermediate frequency (IF) signal. For example, each channel of RFFE12may receive one RF signal stream from its associated antenna element of antenna elements4, process and convert the associated RE signal stream into an analog IF signal.

ADC14of receiver8may, as discussed above, be a multi-channel ADC that is operably coupled to RFFE12. Each channel of ADC14may be associated with a different channel of RFFE12to receive an analog IF signal from the associated channel of RFFE12and to convert the received analog IF signal into a digital representation of the IF signal.

Selection unit25may be configured to select one of the digital representations of the IF signals outputted by ADC14for further processing by preprocessing unit16and message detection and decoding unit18. For example, selection unit25may select the strongest signal (e.g., signal with the highest power level) out of the digital representations of the IF signals outputted by ADC14. In other examples, selection unit25may be integrated into or otherwise be operably coupled to message detection and decoding unit18so that selection unit25may utilize message detection and decoding unit18to determine if the signal selection unit25selects signal that includes an ADS-B message. Because antenna elements4may receive signals that do not carry ADS-B messages, selection unit25may select a signal that does not carry an ADS-B message if selection unit25does not also utilize message detection and decoding unit18to determine if the signal selection unit25selects signal that includes an ADS-B message. If selection unit25is integrated into or otherwise be operably coupled to message detection and decoding unit18, selection unit25may be configured to select one of the baseband signals outputted by preprocessing unit16.

Preprocessing unit16may be configured to perform filtering, decimation, and downconversion of the digital representations of IF signals outputted by ADC14or selection unit25into baseband signals.

Message detection and decoding unit18may be configured to perform preamble detection to detect the presence of ADS-B messages within the received data stream. Message detection and decoding unit18may also be configured to decode the ADS-B messages detected within the received data stream. For example, message detection and decoding unit18may be configured to perform pulse-position modulation (PPM) signal demodulation into binary data and to perform error detection and correction on the demodulated binary data to decode the ADS-B data.

As discussed above, selection unit25may select a single signal that is further processed by single-channel DBE20. As such, DBE20may output a single ADS-B message carried by the selected signal.

Traffic computer (not depicted inFIG. 4) of aircraft2may process ADS-B data (among other data inputs) outputted by receiver8and may output application specific data to a communication bus (not depicted inFIG. 4). For example, traffic computer may output positions of nearby aircraft to a communication bus. That data may be utilized either by an output device, such as a display device, which may be viewed by pilots of aircraft2, or it may be processed by a software application, such as a collision avoidance application.

FIG. 5is a functional block diagram illustrating an example receiver8for selecting a RF signal to process. As shown inFIG. 5, receiver8may include RF switch26, RFFE12, ADC14, and DBE20. DBE20may include preprocessing unit16and message detection and decoding unit18.

Receiver8may comprise any suitable arrangement of hardware, software, firmware, or any combination thereof, to perform the techniques attributed to receiver8, RF switch26, RFFE12, ADC14, preprocessing unit16, message detection and decoding unit18, and DBE20herein. For example, receiver8may include any one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. Although RE switch26, RFFE12, ADC14, preprocessing unit16, and message detection and decoding unit18are described as separate modules, in some examples, RF switch26, RFFE12, ADC14, preprocessing unit16, and message detection and decoding unit18can be functionally integrated. For example, preprocessing unit16, and message detection and decoding unit18may be implemented in the same hardware component. In some examples, RF switch26, RFFE12, ADC14, preprocessing unit16, and message detection and decoding unit18may correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units, or one or more common hardware units.

In the example ofFIG. 5, two or more antenna elements of antenna elements4may each receive an RIF signal, Antenna elements4, in some examples, may comprise antenna elements of a TCAS antenna. Each element of antenna elements4may be a directional antenna element that corresponds to at least one of a plurality of sectors of a sectorized antenna. Each of antenna elements4may be operably coupled to RF switch26. RF switch26may be configured to select one RF signal out of the RF signals received by antenna elements4. For example, RF switch26may select the one RF signal based on the power level of the RF signals (e.g., select the strongest RF signal).

RFFE12of receiver8may be operably coupled to RF switch26via, for example, coaxial cable11. RFFE12may process and convert the RF signal stream received from RF switch26into an analog intermediate frequency (IF) signal.

ADC14of receiver8may be operably coupled to RFFE12to receive an analog IF signal from RFFE12and to convert the received analog IF signal into a digital representation of the IF signal.

Preprocessing unit16may be configured to perform filtering decimation, and downconversion of the digital representation of the IF signal outputted by ADC14into a baseband signal.

Message detection and decoding unit18may be configured to perform preamble detection to detect the presence of ADS-B messages within the baseband signal. Message detection and decoding unit18may also be configured to decode the ADS-B messages detected within the baseband signal. For example, message detection and decoding unit18may be configured to perform pulse-position modulation (PPM) signal demodulation into binary data and to perform error detection and correction on the demodulated binary data to decode the ADS-B data.

Configuration of receiver8shown inFIG. 5may utilize RF switch26, single-channel RFFE12, single-channel ADC,14, and single-channel DBE20. This configuration may be less complex than the one shown inFIG. 4as the receiver8comprises single-channel processing except for RF switch26.

The traffic computer (not depicted inFIG. 5) of aircraft2may process ADS-B data (among other data inputs) outputted by receiver8and may output application specific data to a communication bus (not depicted inFIG. 5). For example, traffic computer may output positions of nearby aircraft to a communication bus. That data may be utilized either by an output device, such as a display device, which may be viewed by pilots of aircraft2, or it may be processed by a software application, such as a collision avoidance application.

FIG. 6is a functional block diagram illustrating the example duplicity check unit22ofFIG. 2in further detail. As shown inFIG. 6, duplicity check unit22may include buffers30A-30D (“buffers30”), comparator unit32, and cyclic buffer34. In an example where components of receiver8may process four RF signal streams received from four antenna elements4A-4D, duplicity check unit22may include four buffers30A-30D to continuously store ADS-B messages data decoded from the corresponding RF signal streams, received by corresponding antenna elements4A-4D and processed by corresponding channel of multi-channel RFFE12, ADC14, and DBE20.

ADS-B message data decoded by individual channels of DBE20may be continuously stored in corresponding buffers30A-30D. For example, ADS-B message data decoded by the second channel of DBE20may be stored in buffer30B. Comparator unit32may periodically load data from all buffers30A-30D and may compare loaded ADS-B data with all ADS-B data retained in cyclic buffer34. For 112-bit ADS-B messages, comparator unit32may compare the 88-bit data bits, the 24-bit error correction data bits (also known as parity bits), or the entire 112 bits of the ADS-B message. For example, comparator unit32may determine that one particular ADS-B message (loaded from buffers30) is a duplicate of another ADS-B message retained in cyclic buffer34if the 24 parity bits of the particular ADS-B message are the same as the 24 parity bits of the another ADS-B message. In another example, comparator unit32may determine that one particular ADS-B message (loaded from buffers30) is a duplicate of another ADS-B message retained in cyclic buffer34if the 88-bit data bits of the particular ADS-B message are the same as the 88-bit data bits of the another ADS-B message. In another example, comparator unit32may determine that one particular ADS-B message (loaded from buffers30) is a duplicate of another ADS-B message retained in cyclic buffer34if all the 112 bits of the particular ADS-B message are the same as all the 112 bits of the another ADS-B message.

If the ADS-B message data loaded from buffers30is not a duplicate of any previous ADS-B messages data retained in cyclic buffer34, comparator unit32may output the ADS-B message data and may also store the ADS-B message data in to cyclic buffer34. Conversely, if the ADS-B message data loaded from buffers30is a duplicate of a previous ADS-B message data retained in cyclic buffer34, duplicity check unit22may refrain from outputting the ADS-B message data that is checked by comparator unit32. In this way, duplicity check unit22may, for a plurality of ADS-B messages decoded by multi-channel DBE20, determine whether one particular ADS-B message is a duplicate of another ADS-B message, and, in response to determining that one particular ADS-B message is a duplicate of another ADS-B message, refrain from outputting more than one ADS-B message data. The length of cyclic buffer34may be adjusted so that a message in the cyclic buffer34is not overwritten before there is still a possibility it will be compared to a duplicate message being decoded by individual channels of DBE20.

FIG. 7is a functional block diagram illustrating the combining unit24ofFIG. 3in further detail. As shown inFIG. 7, combining unit24may include signal phase estimation unit36, multiplier units38A-38D (“multiplier units38”), and adder unit40. As discussed above with respect toFIG. 3, combining unit24may be configured to combine the digital representations of IF signals outputted by ADC14into a single digital IF signal that may be processed by single-channel DBE20. Combining unit24may perform a linear combination of each of the digital representations of the IF signals outputted by ADC14. Combining unit24may perform phase compensation on the digital representations of IF signals outputted by ADC14to result in a single digital representation of an IF signal.

In an example where components of receiver8may receive four RF signals from four antenna elements4A-4D, combining unit24may receive as input four digital representations of IF signals outputted by ADC14. Signal phase estimation unit36may, for each of the four signals received by combining unit24, determine a combining coefficient, such as via a proper method. Because the four signals may each carry the same ADS-B message but are out of phase with respect to each other, signal phase estimation unit36may determine a combining coefficient for each of the four signals that compensates for the phase differences between each of the four signals. Each signal may be multiplied with its combining coefficient via multiplier units38to result in signals that are in phase with each other. The in-phase signals may be added together via adder unit40to result in a digital representation of a combined IF signal that may be further processed by DBE20.

FIG. 8is a flow diagram illustrating an example technique for receiving and decoding ADS-B messages according to aspects of the present disclosure. WhileFIG. 8is described with respect to antenna elements4and receiver8, in other examples, the technique shown inFIG. 8can be implemented by any other suitable systems or components alone or in combination with antenna elements4and receiver8.

In accordance with the technique shown inFIG. 8, a plurality of antenna elements4may receive a plurality of signals, wherein each of the plurality of antenna elements4may correspond to at least one of a plurality of sectors of a sectorized antenna (82). Receiver8may process each of the plurality of signals in parallel, including decoding one or more messages from the plurality of signals (84). Receiver8may output at least one of the one or more messages (86).

In some examples, receiver8processing one or more of the plurality of signals may include receiver8processing each of the plurality of signals in parallel. In some examples, receiver8processing one or more of the plurality of signals may include receiver8processing each of the plurality of signals to decode a plurality of messages from the plurality of signals. In some examples, duplicity check unit22may determine whether a one particular message of the plurality of messages is a duplicate of another message of the plurality of messages. Duplicity check unit22may, in response to determining that the particular message is a duplicate of another message, refrain from outputting more than one instance of ADS-B message data.

In some examples, receiver8processing one or more of the plurality of signals may include receiver8combining the plurality of signals to result in a combined signal and decoding a message from the combined signal. In some examples, receiver8outputting the one or more messages may include receiver8outputting the message.

In some examples, receiver8processing one or more of the plurality of signals may include receiver8selecting one of the plurality of signals and decoding a message from the selected one of the plurality of signals. In some examples, receiver8outputting the one or more messages may include receiver8outputting the message.

In some examples, the plurality of antenna elements4comprises antenna elements of a traffic collision avoidance system (TCAS) antenna. In some examples, receiver8comprises a TCAS computer. In some examples, the one or more messages comprise one or more automatic dependent surveillance-broadcast (ADS-B) messages.

The techniques of this disclosure may be implemented in a wide variety of devices. Any components, modules or units have been described provided to emphasize functional aspects and does not necessarily require realization by different hardware units. The techniques described herein may also be implemented in hardware, software, firmware, or any combination thereof. Any features described as modules, units or components may be implemented together in an integrated logic device or separately as discrete but interoperable logic devices. In some cases, various features may be implemented as an integrated circuit device, such as an integrated circuit chip or chipset.

If implemented in software, the techniques may be realized at least in part by a computer-readable medium comprising instructions that, when executed in a processor, performs one or more of the methods described above. The computer-readable medium may comprise a tangible computer-readable storage medium and may form part of a larger product. The computer-readable storage medium may comprise random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, magnetic or optical data storage media, and the like. The computer-readable storage medium may also comprise a non-volatile storage device, such as a hard-disk, magnetic tape, a compact disk (CD), digital versatile disk (DVD), Blu-ray disk, holographic data storage media, or other non-volatile storage device.

The memory described herein that defines the physical memory addresses, which may be used as part of the described encryption, may also be realized in any of a wide variety of memory, including but not limited to, RAM, SDRAM, NVRAM, EEPROM, FLASH memory, dynamic RAM (DRAM), magnetic RAM (MRAM), or other types of memory.

The term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated software modules or hardware modules configured for performing the techniques of this disclosure. Even if implemented in software, the techniques may use hardware such as a processor to execute the software, and a memory to store the software. In any such cases, the computers described herein may define a specific machine that is capable of executing the specific functions described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements, which could also be considered a processor.

FIGS. 1B, 2, 3, 4, 5depict examples of some possible implementations. However, various combinations of these example implementations are also possible as well as additional implementations not described herein that also utilize techniques involving sectorized antennas described herein.

The techniques of this disclosure may also be utilized for improved reception of several surveillance signals, and may not be limited to the examples described herein regarding the improved reception of ADS-B signals.