Patent Publication Number: US-10324178-B2

Title: Harmonizing code from independent airborne aircraft identification systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 13/892,641, filed on May 13, 2013, which claims priority from U.S. provisional patent application Ser. No. 61/647,068, filed on May 15, 2012, and U.S. provisional patent application Ser. No. 61/683,854, filed on Aug. 16, 2012, the disclosures of which are hereby incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to aircraft communication systems and, more particularly, to aircraft communication systems that provide identifying information about an aircraft, such as, but not limited to, transponders and Automatic Dependent Surveillance-Broadcast (ADS-B) systems. 
     The United States Federal Aviation Administration (FAA) has current plans to require that all aircraft include an Automatic Dependent Surveillance-Broadcast (ADS-B) system onboard by 2020. ADS-B systems are systems in which an aircraft repetitively broadcasts information about itself to both the air traffic control (ATC) system and any other aircraft within the vicinity of the broadcasting aircraft. The broadcast information includes, among other items, the aircraft&#39;s three-dimensional position and velocity, as well as an air traffic control assigned transponder code, also known as a Squawk code. In some instances, an aircraft equipped with the ADS-B system may also have an air traffic control radar beacon system (ATCRBS), which is a mode A/C transponder, onboard the aircraft. As is known in the art, the mode A/C transponder responds to certain interrogations by broadcasting a Squawk code that is received by air traffic control. Confusion at air traffic control may result if the mode A/C transponder Squawk code does not match the Squawk code broadcast by the ADS-B system from the same aircraft. The terms Squawk code and mode A Squawk code are used interchangeably throughout this document, but are intended to refer to the same code. 
     SUMMARY OF THE INVENTION 
     According to its various embodiments, the present invention provides methods and systems for ensuring that the aircraft identifying information, such as the Squawk code, broadcast by a transponder, such as an ATCRBS transponder, matches the aircraft identifying information broadcast by the ADS-B system. In other words, the various embodiments provide methods and systems for ensuring that an aircraft will not inadvertently broadcast different or multiple identification information through its transponder and its ADS-B system. 
     An Automatic Dependent Surveillance-Broadcast (ADS-B) system, according to an aspect of the invention, includes a transponder decoder having an input receiving a mode A/C transponder transmission from a transponder positioned aboard the aircraft in which the ABS-B system is positioned, a decoder decoding the mode A/C transponder transmission, and an output outputting the decoded mode A/C transponder transmission. A message formatter of the ADS-B system generates a message based on data received from the transponder decoder output. The message includes data identifying the squawk code. The transponder decoder and message formatter verify the received mode A/C transponder transmission is a squawk code from the aircraft in which the ADS-B system is installed. A wireless transmitter in communication with the message formatter wirelessly broadcasts the message. 
     An Automatic Dependent Surveillance-Broadcast (ADS-B) system, according to an aspect of the invention, includes a transponder decoder having a directional coupler receiving a transponder transmission via at least one antenna from the transponder positioned aboard the aircraft in which the ABS-B system is positioned, a decoder decoding the transponder transmission, and an output outputting the decoded transponder transmission. A logic device of the ADS-B system generates a message based on data received from the transponder decoder output. The message includes data identifying the squawk code. The transponder transmission is received in response to transmitting an interrogation signal from the logic device via the at least one antenna. A wireless transmitter is in communication with the logic device. The wireless transmitter wirelessly broadcasts the message via the directional coupler and the at least one antenna. 
     An Automatic Dependent Surveillance-Broadcast (ADS-B) system, according to an aspect of the invention, includes a transponder decoder having an input receiving a mode A/C transponder transmission from a transponder positioned in the aircraft in which the ADS-B system is positioned. A decoder of the transponder decoder decodes the mode A/C transponder transmission, and an output of the transponder decoder outputs the decoded mode A/C transponder transmission. A first transmitter sends an interrogation signal to activate the transponder positioned aboard the aircraft to send the received mode A/C transponder transmission. 
     The transponder decoder may receive the squawk code wirelessly from the transponder. The transponder decoder may also receive altitude information broadcast from the transponder and forward the altitude information to the message formatter for comparing the altitude information broadcast from the transponder to altitude information received from another source of altitude information. 
     The message formatter may determine that a transponder transmission is a squawk code, such as by determining that the transponder transmission has a value that is not the same value as altitude information for the aircraft. The message formatter may take an alternative action if it cannot determine that the transponder transmission is a squawk code. The alternative action may be to provide an indication to the pilot. The alternative action may be to send an interrogation signal to activate the transponder to send a squawk code. The wireless transmitter may be used to send the interrogation signal to the transponder. 
     The transponder may verify that a received transponder transmission is a transponder transmission from the aircraft in which the ADS-B system is installed by analyzing a signal strength of the received transponder transmission. The received transponder transmission is determined to be from the aircraft in which the ADS-B system is installed when the signal strength of the received transponder is above a threshold. 
     The ADS-B device may send an interrogation signal to activate the transponder to send a squawk code. The wireless transmitter may be used to send the interrogation signal to the transponder. The interrogation signal may be transmitted at an attenuated level. The message formatter may determine that the transponder is not transmitting. The message formatter may distinguish between the transponder not transmitting because i) the transponder is not operational or ii) the transponder is not being interrogated. 
     A transponder suppression bus input may be coupled to a transponder suppression bus to receive a signal to help differentiate between data transmitted by the transponder onboard the aircraft and data transmitted by any transponders off-board the aircraft. The transponder decoder may also receive IDENT information broadcast from the transponder and forward the IDENT information to the message formatter for formatting into the message. 
     The wireless transmitter may be a component of a Universal Access Transceiver (UAT). 
     These and other objects, advantages and features of this invention will become apparent upon review of the following specification in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an ADS-B system, according to an embodiment of the invention; 
         FIG. 2  is a flowchart of a method of harmonizing a transponder Squawk code and an ADS-B system such that an interrogation broadcast by the ADS-B system makes the transponder squawk; 
         FIG. 3  is a more detailed flowchart of the method of harmonizing a transponder Squawk code and an ADS-B system such that a Squawk code broadcast by the ADS-B system matches the transponder squawk in  FIG. 2 ; 
         FIG. 4  is the same view as  FIG. 1  of an alternative embodiment thereof; and 
         FIG. 5  is the same view as  FIG. 2  of an alternative embodiment thereof. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Referring now to the drawings and the illustrative embodiments depicted therein, an Automatic Dependent Surveillance-Broadcast (ADS-B) system  220  for an aircraft is useful with a mode A/mode C transponder  224  having a transponder antenna  238  ( FIG. 1 ). System  220  includes an ADS-B device  228  having a UAT transmitter and a low power transceiver antenna  240  that can output a mode A interrogation message directly to transponder  224 . As disclosed in commonly assigned U.S. Patent Application Publication No. 2012/001788 A1, the disclosure of which is hereby incorporated herein by reference, such interrogation may be used wherever the transmission from transponder  224  equals the altitude information from the aircraft or ADS-B system  220  is otherwise unable to unambiguously determine the Squawk code. Since transceiver antenna  240  sends a mode A interrogation message, it can conclude that the transmission from transponder  224  is a mode A Squawk code. Transceiver antenna  240  can be separate from the UAT transceiver  230  used to transmit to the ground or to other aircraft or can be a combined transceiver that is capable of wireless communication with transponder antenna  238 . If a common transceiver antenna is used, it would transmit at a lower power level to interrogate transponder  224  than would be used as a UAT transceiver mode. 
     System  220  includes a suppression bus  242  that is used to indicate that an L-band system onboard the aircraft is transmitting. It is used by ADS-B device  228  as a trigger to receive transmissions from transponder  224  to ensure that ADS-B device  228  is not intercepting a transponder transmission from a different aircraft. System  220  may further include a pilot control panel  261  that includes ADS-B system control device  262  that allows the pilot to manually enter a Squawk code into ADS-B device  228 . Pilot control panel  261  may further include indicator  261   a  to advise the pilot that the input altitude reported by transponder  224  does not match that reported by ADS-B control device  228 , as will be discussed in more detail below. Also, indicator  261   b  may be included to inform the pilot that the selected code as reported by transponder  224  does not match that entered into the ADS-B Squawk code entry device. 
     System  220  performs a control technique  1  that is based upon the requirement that the UAT device  228  must output the same mode A code as transponder  224 . Referring now to  FIG. 2 , control technique  1  begins at  1   a  with the pilot powering on and entering the squawk code in ADS-B device  228 , such as with squawk code entry device  262 . Transceiver antenna  240  sends a mode A interrogation message to transponder  224  at  2 . Therefore, system  220  can conclude that the transmission from transponder  224  is a mode A Squawk code. When this occurs, the transponder is either off or in the standby mode or is on. If it is on, ADS-B device  228  receives a transmission from transponder  224  at  3 . If it is determined at  3  that a response has not been received, then a transponder fail indication is made at  4  on an annunciator (not shown) or other visual or aural indicator. The fail indication may instruct the pilot to check that the transponder  224  is turned on. 
     If it is determined at  3  that a response is received from transponder  228 , it is determined at  5  whether suppression bus  242  is active indicating that an L-band transmitter on the aircraft is transmitting. If so, the response originated with this aircraft. If it is determined at  5  that suppression bus  242  is not active then the response is ignored at  7 . If it is determined at  5  that the suppression bus is active, it is determined at  6  whether the transmission is from transponder  224  by examining the format of the response. If it is determined at  6  that the response has the proper format for a transmission from transponder  224  then the response is decoded at  8  as a Mode A response from transponder  224 . Otherwise it is ignored at  7 . 
     The decoded Mode A response is compared with the code entered by the pilot with Squawk code entry device  262  at  9  and the result is evaluated at  10 . If it is determined at  10  that the Mode A response decoded from transponder  224  is not different from the ADS-B code entered by the pilot, then no action is taken. However, if it is determined at  10  that a different code is entered in the ADS-B device than that decoded from transponder  224 , an indication is made to the pilot at  11  such as by illuminating code miscompare attenuator  261   b  or by some other visual or aural indication. 
       FIG. 3  illustrates a control technique  265  for ensuring that ADS-B device  228  only transmits as a Squawk code message to the air traffic control system or other aircraft in the vicinity of a mode A Squawk code message from transponder  224  that is more detailed than that illustrated in  FIG. 2 . With the pilot entering a Squawk code message ( 263   a ) in transponder  224  and transponder  224  operational ( 264 ), ADS-B device  228  is also powered on at  266 . The same Squawk code message that was entered in the transponder at  263   a  is entered in ADS-B device  228  by the pilot via entry device  262  ( 263   b ). It is determined at  267  whether more than a predetermined amount of time has passed since the last transmission has been received from transponder  224 . Since transponder  224  is operational and has recently transmitted a message in response to a ground radar or from a TCAS unit onboard another aircraft, it will be determined at  267  that this predetermined time has not passed. It is then determined at  268  whether suppression line  242  is active, which will occur at least when transponder  224  is transmitting. If so, the message received by transceiver  240  is examined at  269  to determine if it has the format of a message from transponder  224 . If so, the message is decoded at  270 . Once the message is decoded, it is compared at  271  with the altitude information obtained by ADS-B device  228 , such as from an altimeter that supplies altitude data to both transponder  224  and ADS-B device  228 . 
     If the message decoded from transponder  224  is determined at  271  to not be the same as the altitude information, it is determined that the message must be a mode A Squawk code message so it is compared at  272  to the value of the Squawk code entered into ADS-B device  228 . If these two Squawk codes are the same, this value of the Squawk code is the one to be used by ADS-B device  228  for future transmissions until it is changed by the pilot by entering a different Squawk code in transponder  224  and/or ADS-B device  228 . If it is determined at  272  that these two Squawk codes are not the same, annunciator  261   b  is actuated to instruct the pilot at  278  that the code entered in ADS-B device  228  does not match the code entered in transponder  224 . This should prompt the pilot to change one of the codes to match the other. 
     If it is determined at  267  that more than a predetermined period of time, such as several seconds, has passed since last receipt of a transmission from transponder  224 , then transponder  224  is likely not being interrogated by a ground radar or a TCAS unit in another aircraft. If it is determined at  267  that this period has not yet passed, it is determined at  268  whether suppression line  242  is active. If so, it is determined at  269  whether the device that is transmitting is transmitting a message having a protocol of a message transmitted by transponder  224 . If not, the message is ignored at  273 . This sequence is repeated until it is determined at  267  that more than the predetermined amount of time has passed. It is then determined at  274  whether a longer predetermined period of time, such as tens of seconds, has lapsed. 
     If it is determined at  274  that a longer predetermined period of time has not lapsed, ADS-B device  228  interrogates transponder  224  by sending an attenuated signal at  275  to transponder  224  having a format of a mode A code interrogation. This is accomplished either by sending the interrogation signal with an antenna  240  dedicated to communication with transponder  224  or by a UAT antenna  230  that is used both to communicate with transponder  224 , at an attenuated signal level, and to generate ADS-B UAT signals external to the aircraft. It is then determined at  276  whether a response is received. If so, then it is concluded at  277  that it is a mode A Squawk message and it is used to compare with the Squawk code set for ADS-B device at  272 . In this manner, it is possible to determine that the Squawk code for ADS-B device  228  is set to the same Squawk code as transponder  224 , even if the transponder is not being interrogated by a ground radar or a TCAS unit of another aircraft. 
     If it is determined at  267  and  274  that a response is not received within the extended predetermined period of time after interrogation of transponder  224 , a message is then given to the pilot at  278 , such as with annunciator  261   b  or other visual or aural warning indicator, instructing the pilot that the code entered with Squawk code entry device  262  does not match that entered in transponder  224  or the transponder is not operating properly or is turned off. 
     If it is determined at  276  that a message has not been received from transponder  224  even after having attempted to interrogate the transponder at  275 , it is then concluded that the transponder is likely not turned on or has failed. An indication is given to the pilot at  280 , such as using another annunciator (not shown) that the code cannot be set using control technique  265 . The pilot may be instructed to turn the transponder on or to manually enter a Squawk code in ADS-B device, such as with Squawk code entry device  262 , or may be optionally instructed to attempt to manually interrogate transponder  224 . In this manner, it may be possible to enter a Squawk code in the ADS-B device, even if transponder  224  is powered off or has failed. 
     If it is determined at  267  that the lower predetermined period of time has not passed since the last transmission of transponder  224 , since the transponder is being interrogated by a ground radar or a TCAS unit on another aircraft, it is determined at  268  whether suppression bus  242  is active and at  269  whether the transmission is from transponder  224 . If so, the transmission is decoded at  270  and compared at  271  with the altitude data received by ADS-B device  228 . If transponder  224  is set to a Squawk code that is indistinguishable from the altitude data received by ADS-B device  228 , it will be determined at  281  that the transmission from transponder  224  is indistinguishable from the altitude value. As a result, the transmission from transponder  224  is not used to compare with the Squawk code in ADS-B device  228 . Instead, transponder  224  is interrogated at  275  with UAT transceiver  240  at an attenuated signal level, or by separate transceiver  230 . A response should be received at  276  since the transponder is presumably turned on and is not failed. Because the response is from a mode A interrogation signal, it is decoded at  277  and compared with the Squawk code set for ADS-B device  228  at  272 . 
     Control device  261  may further include an Altitude Miscompare annunciator  261   a . Both transponder  224  and ADS-B device  228  may receive altitude data from a common altitude sensor (not shown). Therefore, the altitude information received from transponder  224  should match that received directly from the altitude sensor. If it does not match, this could be an indication of a failure in operation of either transponder  224  or ADS-B device  228 . Such failure, if detected by a comparison of data decoded from transponder  224  and that received from the altitude sensor, is used to illuminate Altitude Miscompare annunciator  261   a  or other such pilot warning technique including aural as well as visual. 
     While illustrated for use in ensuring that a common mode A Squawk code is used in the ADS-B device as in the transponder, the same technique could be used for mode C code signals or other types of code. 
     In an alternative embodiment, a system  220 ′ is generally the same as system  220  except that it includes a pilot control panel  261 ′ that includes a code miscompare indicator  261   b ′ and an altitude miscompare indicator  261   a ′ that are the same as code miscompare indicator  261   b  and altitude miscompare indicator  261   a , respectively ( FIGS. 4 and 5 ). However, system  220 ′ includes a sync input  262 ′ that is operable by the pilot to cause the message formatter of ADS-B unit  228 ′ to copy the transponder Squawk code that has been captured form transponder  224 ′. Thus, if the pilot observes that code miscompare indicator  261 ′ is actuated, sync control  262 ′ can be actuated manually by the pilot to cause ADS-B unit  228 ′ to copy the code of transponder  224 ′. This should result in the transponder and ADS-B system transmitting the same code which should result in code miscompare indicator  261   b ′ being extinguished. 
     An advantage of system  262 ′ is that a separate pilot Squawk code entry device is not required in order to enter the Squawk code of ADS-B system  228 ′. Instead, a single “push to sync” push button could be used. However, a pilot Squawk code entry device for the ADS-B system could be provided, if desired, to have the pilot enter the same code into both the transponder and ADS-B system as previously described. Upon power-up of system  220 ′, ADS-B system  228 ′ may adopt a default Squawk code, the last known Squawk code, or the like. This should result in a mismatch between the Squawk codes of transponder  224 ′ and ADS-B system  228 ′. However, once the pilot operates sync input  262 ′, the mismatch should disappear. 
     In operation, referring to  FIG. 5 , control technique  1 ′ starts at  1   a ′ by ADS-B system  228 ′ being powered. This should result in a Squawk code of a default value, the last used Squawk code, or some other value to be assigned to the ADS-B system. Control technique  1 ′ then performs the same general steps  2  through  11  as with control technique  1 . However, if an indication is made to the pilot at  11  that the ADS-B code does not match that of the transponder, the pilot is able to manually actuate sync control  262 ′ at  11   a  in order to copy the transponder mode A response of transponder  224 ′ into ADS-B system  228 ′. Upon the next transmission of ADS-B system  228 ′, the Squawk code will match that of transponder  224 ′. 
     While the foregoing description describes several embodiments of the present invention, it will be understood by those skilled in the art that variations and modifications to these embodiments may be made without departing from the spirit and scope of the invention, as defined in the claims below. The present invention encompasses all combinations of various embodiments or aspects of the invention described herein. It is understood that any and all embodiments of the present invention may be taken in conjunction with any other embodiment to describe additional embodiments of the present invention. Furthermore, any elements of an embodiment may be combined with any and all other elements of any of the embodiments to describe additional embodiments.