Abstract: A simplified multilateration and ADS-B Surveillance System is used, to perform tagging for the FAA Low Cost Ground Surveillance program. This system may also be used as the foundation for a full multilateration system, if a customer wants to upgrade. The present invention uses just one active transmitter/receiver unit as opposed to multiple passive receivers. The present invention captures UF 5 and DF 5 data, thus providing Mode A identification, which then acts as the key to obtaining the call sign from a data fusion packages—thus making it an affordable and marketable product for small to medium-sized airports.

Abstract: A method for validating positional data in vehicle surveillance applications wherein vehicles transmit positional data indicating their own position to surrounding vehicles using a data link over which a transmission is initiated at a given transmission point in time that is known by all users of the data link. A signal transmitted from a radio source over the data link is received at a receiving unit. The signal carries positional data indicating an alleged position of a vehicle. The distance between the receiving unit and the radio source is estimated based on the time of flight and the propagation velocity of the received signal. The time of flight is determined based on the time elapsed from the transmission point in time of the signal to the time of reception of at least a first part of the signal. A deviation value is determined.

Abstract: The processing method according to the invention is a method of processing replies from targets interrogated by a surveillance radar according to a mode S interrogation of all the targets present in the receiving lobe of the radar, whereby the different targets present in the receiving lobe of the radar are interrogated at least once, the set of the mode S reply signals received for this lobe are collected after each interrogation, a reply detection processing operation is performed for each target and errors are detected and, if necessary, corrected then the corresponding blips are extracted, and this method is characterized in that said signal quality detection and determination processing operation consists in forming a synthetic message with the set of replies to each interrogation for each target, establishing, for each bit of the message, the value and the quality of this bit and performing the error detection and correction using this synthetic message, and the three variables ?, ? and monopulse of all

Abstract: A display is configured to display transformed video. The display includes a display unit comprising pixels. The display also includes a set of filter elements positioned adjacent to the display unit. The set of filter elements enable the display unit to display transformed video.

Abstract: Methods and apparatus for preventing spoofing of targets, such as aircraft, in an air traffic control system. In one embodiment, first and second antennas at respective ground stations can be used to receive a signal transmitted by an aircraft from which a phase signal can be generated. A position of the aircraft generate can be generated from peaks and troughs in the phase signal due to movement of the aircraft. The determined position can be compared to a position reported by the aircraft to identify spoofing of the target.

Abstract: Provided is a secondary surveillance radar with an improved capability of eliminating an unnecessary Mode A/C target report, which includes a transmission unit transmitting interrogations, a reception unit receiving replies, from a transponder, corresponding respectively to the interrogations, and a signal processing unit generating a Mode S target report and a Mode A/C target report from the replies. The radar also includes a combiner generating a Mode S track and a Mode A/C track respectively from the Mode S and the Mode A/C reports, and then judging whether the Mode S report and the Mode A/C report are of the same target on the basis of the Mode S and the Mode A/C tracks. When the Mode S and the Mode A/C reports are of the same target, the combiner rejects the Mode A/C report.

Abstract: Provided is a secondary surveillance radar with an improved capability of eliminating an unnecessary Mode A/C target report, which includes a transmission unit transmitting interrogations, a reception unit receiving replies, from a transponder, corresponding respectively to the interrogations, and a signal processing unit generating a Mode S target report and a Mode A/C target report from the replies. The radar also includes a combiner generating a Mode S track and a Mode A/C track respectively from the Mode S and the Mode A/C reports, and then judging whether the Mode S report and the Mode A/C report are of the same target on the basis of the Mode S and the Mode A/C tracks. When the Mode S and the Mode A/C reports are of the same target, the combiner rejects the Mode A/C report.

Abstract: A method according to the present invention includes transmitting a Mode S interrogation and receiving a response from an aircraft that has received the Mode S interrogation. A range to the aircraft is determined based on a time period between transmitting the Mode S interrogation and receiving the response. The method further includes receiving information from one or more data sources and determining at least one of a bearing to the aircraft and a position of the aircraft using the determined range and the information from the one or more data sources. Information can be received from any number (or type) of data sources, such as ADS-B-equipped aircraft.

Abstract: Methods and systems for a position indicating display system for an aircraft are provided. The system includes a map display unit configured to display a map representative of an area being traversed by the aircraft, and an overlay comprising an own ship depiction, said overlay displayed on the map for a period of time in response to an input from at least one of a user and an aircraft sensor.

Abstract: A method and system for converting a voice communication to a text transcription. The method comprises receiving by a computing system in a control command center, a first transmission identifier from a vehicle. The first transmission identifier identifies the vehicle. The computing system receives voice communication data for the vehicle from a user in the control command center. A software application within the computing system converts the voice communication data into text data. The computing system transmits the voice communication data, a first copy of the text data and a second transmission identifier to the vehicle. The second transmission identifier identifies the control command center. The computing system receives a confirmation request from the vehicle to confirm if the text data comprises correct information related to the voice communication data. The confirmation request is displayed on a video monitor system. The computing system transmits confirmation data to the vehicle.

Abstract: It is related to a mode S secondary surveillance radar system for carrying out a target (aircraft) surveillance with a high reliability, where a surveillance processor 39 produces a detection report of a acquisition surveillance by a scan of an antenna thereafter by adopting the mode A code information with coinciding code data among mode A code information acquired by scans of a plurality of times. In this way, the efficient utilization of RF channels during the roll-call period can be maintained while improving the reliability of a target detection report.

Abstract: A system and technique to derive a position of a non-ADSB equipped aircraft using ADS-B information provided from an ADSB equipped aircraft and bi-static radar processing techniques.

Abstract: The invention relates to a method for pre-detecting responses in a secondary radar. It applies in particular to the detection of mode S responses. An aim of the invention is to process the signals received before decoding the responses so as to allow the detection of mixed responses, and avoid the detection of ghost responses. For this purpose, the invention has in particular as subject a method for pre-detecting responses in a secondary radar, the responses to be pre-detected comprising a message coded by a modulated signal, characterized in that the presence of a signal exhibiting modulation characteristics in accordance with those of a message of a response to be pre-detected is identified; the duration of the signal identified is measured; this duration is compared with a minimum duration, this minimum duration being determined on the basis of the duration of the messages of the responses to be pre-detected.

Abstract: A secondary surveillance radar system comprising a including a ground system which observes an observation area where an aircraft equipped with a mode S transponder and an aircraft equipped with an ATCRBS transponder possibly coexist, wherein the ground system comprises includes a transmit processor which transmits to the observation area an all-call interrogation signal specific for mode S including an identification code of the ground system, a receive processor which receives a reply signal to the interrogation signal transmitted by the transmit processor, and a recognition processor which recognizes the reply signal as a processing target when identification information included in the reply signal received by the receive processor coincides with the identification code of the ground system, and wherein the recognition processor recognizes the reply signal as the processing target also when the identification information included in the reply signal received by the receive processor coincides with null in

Abstract: It is related to a mode S secondary surveillance radar system for carrying out a target (aircraft) surveillance with a high reliability, where a surveillance processor 39 produces a detection report of a acquisition surveillance by a scan of an antenna thereafter by adopting the mode A code information with coinciding code data among mode A code information acquired by scans of a plurality of times. In this way, the efficient utilization of RF channels during the roll-call period can be maintained while improving the reliability of a target detection report.

Abstract: The invention applies to secondary radars. It makes it possible to carry out filtering when seeking to detect SSR responses, these SSR responses being overlapped by a mode S response. According to the invention, the pulses of the mode S response are filtered without filtering the pulses of the SSR responses which are of a higher level than the mode S response.

Abstract: Disclosed is a Mode S radar which specifies an aircraft by transmitting interrogations to an aircraft A equipped with a Mode S transponder, and by then receiving and decoding replies corresponding to these interrogations. In the Mode S radar, detection reports on the aircraft A are generated in a manner that: for a Mode A code necessary for generating detection reports, when identicalness between the Mode A codes obtained in a plurality of scans after the initial acquisition of the aircraft A has been found to exist, the Mode A code thus found identical is adopted without carrying out a Mode A code interrogation (UF=5) thereafter. Accordingly, the Mode S secondary surveillance capable of generating more highly reliable detection reports is achieved.

Abstract: There are presented various approaches to monitor performance of RF systems and circuitry such as those used in aircraft transponders. Such monitoring may be designed to verify operational performance of transponders as set forth by FAA regulations, or may be used to periodically or continually monitor integrity of transponder performance. Data may be collected by such periodic or continual monitoring, and may be analyzed to identify potentially troublesome trends in transponder performance, allowing early intervention or repair, if warranted.

Abstract: A simplified multilateration and ADS-B Surveillance System is used, to perform tagging for the FAA Low Cost Ground Surveillance program. This system may also be used as the foundation for a full multilateration system, if a customer wants to upgrade. The present invention uses just one active transmitter/receiver unit as opposed to multiple passive receivers. The present invention captures UF 5 and DF 5 data, thus providing Mode A identification, which then acts as the key to obtaining the call sign from a data fusion packages—thus making it an affordable and marketable product for small to medium-sized airports.

Abstract: A system able to locate and identify aircraft and vehicles based on the reception and processing, with novel means and methods, of signals emitted by the transponder of the secondary surveillance radar, shortly SSR. The system has a number of fixed stations distributed in the area of interest, e.g. in the airport area; any signal (the well known SSR reply/squitter) transmitted by the on-board transponder is received by four or more stations and the measurement of three or more differences of times of arrival (TOA) permits the reconstruction of the position of the transponder in spite of the fact that the transmission time is unknown. Suitable algorithms based on optimal estimation enhance both the accuracy of TOA measurements and the accuracy of the reconstructed position. The effects of possible overlapping of signal in time are avoided or mitigated by multiple source separation techniques based on least squares algebraic processing.

Abstract: Disclosed is a Mode S radar which specifies an aircraft by transmitting interrogations to an aircraft A equipped with a Mode S transponder, and by then receiving and decoding replies corresponding to these interrogations. In the Mode S radar, detection reports on the aircraft A are generated in a manner that: for a Mode A code necessary for generating detection reports, when identicalness between the Mode A codes obtained in a plurality of scans after the initial acquisition of the aircraft A has been found to exist, the Mode A code thus found identical is adopted without carrying out a Mode A code interrogation (UF=5) thereafter. Accordingly, the Mode S secondary surveillance capable of generating more highly reliable detection reports is achieved.

Abstract: Security of ADS-B transmissions is improved in a first embodiment to detect position spoofing. The annunciated position source may then be compared with the derived source and a determination is made regarding the difference between the results. Any position difference greater than an amount significantly greater than the combination of the error sources is then a cause for concern and can be used to generate an alert. In a second embodiment, alerting may be based on identification spoofing. From these sources a correlated ID is available which will have an associated confidence based on the number of sources and the level of agreement on the information. Aircraft dynamics may be correlated with the announced ID for consistency. A priori information on the aircraft and location, such as schedule information, and normal operations, may be used to assist in the confidence of aircraft identity. In a third embodiment, alerting may be based on spoofing of identity and position.

Abstract: This equipment is of the TCAS type. In order to improve its integrity and the reliability of its measurements, its computing unit is provided with a cross-checking function carrying out the comparison between two values of a same parameter, for example a relative distance with respect to an intruder, one of them generated by its own estimating means and the other communicated by another TCAS equipment installed on the intruding aircraft and generating a discordance alarm in the case of the observed difference exceeding a tolerance threshold. The computing unit is provided with fault locating means locating the aircraft whose TCAS is faulty when in the presence of several intruding aircraft, by examining the observed differences in pairs of values of a same parameter established for each intruding aircraft.

Abstract: Systems and methods for alerting surrounding aircraft if a ground-based unit is a threat. One example system is located on a ground-based unit. The system includes a position sensor that senses position of the ground-based unit, a memory that stores predefined threat zone information, a transmitter that transmits a predefined transponder signal, and a processor in data communication with the position sensor, the memory, and the transmitter. The processor instructs the transmitter to transmit the transponder signal based on the threat zone information and the sensed position of the ground-based unit.

Abstract: There are provided a differential processing unit which performs differential processing for a Mode S transponder transmission signal, an auto correlation arithmetic operation unit which performs an arithmetic operation of a degree of auto correlation between an increasing change rate and decreasing change rate of a power level in the signal which has been subjected to the differential processing, a pulse regeneration unit which regenerates a pulse based on the degree of auto correlation, which has been obtained by the auto correlation arithmetic operation processing, a pulse phase locked loop unit which performs gate processing and phase locked processing for the regenerated pulse, and a pulse decoding unit which decodes the Mode S transponder transmission signal based on the pulse which has been subjected to the gate processing and the phase locked processing.

Abstract: The invention relates to a method for pre-detecting responses in a secondary radar. It applies in particular to the detection of mode S responses. An aim of the invention is to process the signals received before decoding the responses so as to allow the detection of mixed responses, and avoid the detection of ghost responses. For this purpose, the invention has in particular as subject a method for pre-detecting responses in a secondary radar, the responses to be pre-detected comprising a message coded by a modulated signal, characterized in that the presence of a signal exhibiting modulation characteristics in accordance with those of a message of a response to be pre-detected is identified; the duration of the signal identified is measured; this duration is compared with a minimum duration, this minimum duration being determined on the basis of the duration of the messages of the responses to be pre-detected.

Abstract: A method and system are provided for measuring and monitoring performance metrics of a non-ADS-B tracking system and generating performance metrics for the non-ADS-B tracking system in terms of ADS-B equivalent performance metrics. An aircraft transmits various transponder-based or other signals which are received at multiple ground stations, some of which may be ADS-B stations or both ADS-B and multilateration stations. ADS-B signals may contain performance metrics which are passed on from ADS-B station to an ADS-B processor, which outputs aircraft-derived metrics. ADS-B signals and all other transponder signals are also received at all ground stations, time-stamped, and sent to a multilateration processor, which generates multilateration metrics. Therefore two streams of information are passed onto ATC system processor containing the ADS-B aircraft-derived metrics and multilateration-derived metrics.

Abstract: The invention applies to secondary radars. It makes it possible to carry out filtering when seeking to detect SSR responses, these SSR responses being overlapped by a mode S response. According to the invention, the pulses of the mode S response are filtered without filtering the pulses of the SSR responses which are of a higher level than the mode S response.

Abstract: Security of ADS-B transmissions is improved in a first embodiment to detect position spoofing. The annunciated position source may then be compared with the derived source and a determination is made regarding the difference between the results. Any position difference greater than an amount significantly greater than the combination of the error sources is then a cause for concern and can be used to generate an alert. In a second embodiment, alerting may be based on identification spoofing. From these sources a correlated ID is available which will have an associated confidence based on the number of sources and the level of agreement on the information. Aircraft dynamics may be correlated with the announced ID for consistency. A priori information on the aircraft and location, such as schedule information, and normal operations, may be used to assist in the confidence of aircraft identity. In a third embodiment, alerting may be based on spoofing of identity and position.

Abstract: In a first, preferred embodiment of the present invention, integrated tracking is provided using passive broadband. The invention takes the system for deployable passive broadband detection and extends it by incorporating the capability to decode position for ADS-B, SSR multilateration, and broadband multilateration. In a second embodiment, validation of a self-reported position is provided. The invention takes the system for deployable passive broadband detection and extends it by incorporating the capability to decode self-reported position for ADS-B, and compare it to line of calculated position, or line of precision, derived from multilateration techniques applied to various signals received from the aircraft. In a third embodiment, validation of a self-reported ADS-B position using independent surveillance is provided by the system.

Abstract: A method and system for using a single transceiver to correlate radar position data with target identification data. Two transceivers, operating in round trip delay mode, can be used to provide two possible positions for a given target when radar coverage is lost or unavailable. Three transceivers can be used to provide actual position of a given target using round trip delay data only.

Abstract: A method and system are provided for measuring and monitoring performance metrics of a non-ADS-B tracking system and generating performance metrics for the non-ADS-B tracking system in terms of ADS-B equivalent performance metrics. An aircraft transmits various transponder-based or other signals which are received at multiple ground stations, some of which may be ADS-B stations or both ADS-B and multilateration stations. ADS-B signals may contain performance metrics which are passed on from ADS-B station to an ADS-B processor, which outputs aircraft-derived metrics. ADS-B signals and all other transponder signals are also received at all ground stations, time-stamped, and sent to a multilateration processor, which generates multilateration metrics. Therefore two streams of information are passed onto ATC system processor containing the ADS-B aircraft-derived metrics and multilateration-derived metrics.

Abstract: The present invention applies to the surveillance of, in particular civil, air traffic, and more particularly, to cooperative aircraft ground systems which make it possible to pinpoint in radial distance and in azimuth the aircraft present in a certain volume and to interrogate them. A method and a device which makes it possible to determine a reference value of a response contained in a reception signal of a secondary radar, doing so even in the presence of strong pollution, in particular in the event of nesting between mode S responses.

Abstract: An interrogation transmission method of a secondary surveillance radar compares prediction angle ranges for transmitting interrogations with a beam-width of an antenna, and transmits the interrogations at every roll-call period if the prediction angle ranges for transmitting interrogations are narrower than the beam-width of the antenna. In contrast, if the prediction angle ranges for transmitting the interrogations are wider than the beam-width of the antenna, the radar respectively sets a period to transmit the interrogations and a period not to transmit the interrogations until responses can be received, and transmits interrogations at every roll-call period after the responses can be received (even if a receiving error or downlink occurs).

Abstract: A method of transmitting from a traffic alert and collision avoidance system (TCAS) directional antenna, the TCAS directional antenna including a plurality of antenna elements connected to an integrated beam forming network, according to various aspects of the present invention comprises: providing a signal to each input of the integrated beam forming network, wherein each signal is of equal phase and equal amplitude to result in transmitting omnidirectionally from the TCAS directional antenna.

Abstract: A method according to the present invention includes transmitting a Mode S interrogation and receiving a response from an aircraft that has received the Mode S interrogation. A range to the aircraft is determined based on a time period between transmitting the Mode S interrogation and receiving the response. The method further includes receiving information from one or more data sources and determining at least one of a bearing to the aircraft and a position of the aircraft using the determined range and the information from the one or more data sources. Information can be received from any number (or type) of data sources, such as ADS-B-equipped aircraft.

Abstract: There are provided a differential processing unit which performs differential processing for a Mode S transponder transmission signal, an auto correlation arithmetic operation unit which performs an arithmetic operation of a degree of auto correlation between an increasing change rate and decreasing change rate of a power level in the signal which has been subjected to the differential processing, a pulse regeneration unit which regenerates a pulse based on the degree of auto correlation, which has been obtained by the auto correlation arithmetic operation processing, a pulse phase locked loop unit which performs gate processing and phase locked processing for the regenerated pulse, and a pulse decoding unit which decodes the Mode S transponder transmission signal based on the pulse which has been subjected to the gate processing and the phase locked processing.

Abstract: Disclosed is a Mode S radar which specifies an aircraft by transmitting interrogations to an aircraft A equipped with a Mode S transponder, and by then receiving and decoding replies corresponding to these interrogations. In the Mode S radar, detection reports on the aircraft A are generated in a manner that: for a Mode A code necessary for generating detection reports, when identicalness between the Mode A codes obtained in a plurality of scans after the initial acquisition of the aircraft A has been found to exist, the Mode A code thus found identical is adopted without carrying out a Mode A code interrogation (UF=5) thereafter. Accordingly, the Mode S secondary surveillance capable of generating more highly reliable detection reports is achieved.

Abstract: An apparatus for processing pulses in ATCRBS/Mode S interrogations includes an antenna for receiving a radio frequency interrogation signal. The radio frequency interrogation signal is downconverted by a downconverter to an intermediate frequency signal. The intermediate frequency signal is converted to a digitized interrogation signal by an analog-to-digital converter. A processing unit, coupled to the analog-to-digital converter, detects a pulse peak in the digitized interrogation signal using a moving threshold to locate the peak pulse between a first fixed threshold and a second fixed threshold.

Abstract: An apparatus for processing pulses in ATCRBS/Mode S interrogations includes an antenna for receiving a radio frequency interrogation signal. The radio frequency interrogation signal is downconverted by a downconverter to an intermediate frequency signal. The intermediate frequency signal is converted to a digitized interrogation signal by an analog-to-digital converter. A processing unit, coupled to the analog-to-digital converter, detects a pulse peak in the digitized interrogation signal using a moving threshold to locate the peak pulse between a first fixed threshold and a second fixed threshold.

Abstract: A method and system for using a single transceiver to correlate radar position data with target identification data. Two transceivers, operating in round trip delay mode, can be used to provide two possible positions for a given target when radar coverage is lost or unavailable. Three transceivers can be used to provide actual position of a given target using round trip delay data only.

Abstract: The present invention relates to an avoidance system and method for directing an aircraft away from an exclusion zone. The exclusion zone may be any three dimensional space for example about a building or city. The avoidance system uses a constant signal from a ground based transmitter and an aircraft's receiver which receives and processes the signal and activates the avoidance system by engaging the flight director system or autopilot to steer away from the exclusion zone.

Abstract: Methods and apparatus for controlling movement of aircraft through a defined air space are disclosed. In one embodiment, a method includes generating a model of the defined air space. The model is configured to indicate a safe subset of the defined air space for movement. Receiving a trajectory datum from an aircraft facilitates placing the aircraft at an aircraft position in the generated model of the defined air space according to the trajectory datum. A route is generated for the aircraft through the defined air space according to the aircraft position and the safe subset. Control commands are transmitted to the aircraft; the control commands are configured to control the aircraft according to the route.

Abstract: An embedded digitization system enables a military platform to receive, transmit and process a variety of types of information for a variety of purposes. An apparatus and method provides a means to ensure information interoperability between the invention and external sources. The invention provides a development environment that enables a developer to automatically and interactively develop the middleware services and functions that contain the aspects for interoperability with external sources. The invention ensures interoperability through reuse of functions and services known to satisfy requirements for interoperability. When functions and services that satisfy requirements for interoperability are not available, the invention provides a means to develop new functions and services that satisfy requirements for interoperability.

Abstract: This invention is a system and method of locating a target using distributed antenna. The antenna consists of several receiving elements in known locations. At least one of the receiving elements is also a transmitter and transmits an interrogation signal to a target. The return signal from the target is received by a plurality of receiving elements and the target's position is calculated using the time of arrivals of the reply signal and the round trip delay between the transmission of the interrogation signal and the reception of the subsequent reply signal.

Abstract: A secondary surveillance radar system for use in surveillance of an airspace, which reliably achieves surveillance of the airspace even when an aircraft including a mode S transponder and an aircraft including an ATCRBS transponder are both located in the airspace, wherein both of a time interval between time when transmission of an all-call interrogation signal specific for mode S is completed and time when the transmission of an all-call interrogation signal specific for mode A is started and a time interval between time when transmission of the all-call interrogation signal specific for mode S is completed and time when transmission of an all-call interrogation signal specific for mode C is started is varied in units of one all-call time period.

Abstract: A Mode-S transponder is provided for detecting synchronization phase reversal (SPR) signals. The transponder includes a receiver for receiving a Mode-S signal that contains a P6 pulse having a Mode-S data segment and an SPR signal therein. The transponder also includes a phase detector that detects a phase change between first and second states in the received Mode-S signal. The phase detector includes an SPR qualifier that determine whether, following a state change, the Mode-S signal remains at one of the first and second states for at least a predetermined minimum time sufficient to qualify as a detector enable signal.

Abstract: An apparatus and method for combining the functionality of multiple airborne traffic surveillance systems that operate in the L-band frequency range. The apparatus and method combine the functionality of both a Traffic Alert Collision Avoidance System (TCAS) and a Mode-Select (Mode-S) transponder in an integrated L-band traffic surveillance apparatus having a single processor that is embodied in a single Line Replaceable Unit.

Abstract: A passive airborne mounted collision warning system suitable for light aircraft that enables an observer aircraft to determine the position of a nearby transponder-equipped target aircraft. The transponder-equipped target aircraft transmits replies responsive to interrogation signals from rotating secondary surveillance radars (SSR). In an embodiment of the invention, position of the target aircraft is determined based on the known position of the observer aircraft obtained e.g. via satellite navigation means such as GPS, the position of the SSR, and the bearing of the target aircraft measured by a direction finding antenna. The direction-finding antenna elements and the GPS receiver components are included in a device that is externally mounted on the observer aircraft. The data from the device is connected to a portable computer for processing and presentation to the pilot to alert him of the position of the target aircraft for avoiding collisions.

Abstract: A method is provided for controlling when a transponder replies to Mode-S interrogation signals. The method includes receiving Mode-S signals containing P5 and P6 pulses. The received P5 and P6 pulses have certain amplitudes. Each P6 pulse contains a sync phase reversal (SPR) signal followed by a data segment containing Mode-S data The P5 pulse is asynchronous with respect to the P6 pulse and the P5 pulse is timed to overlay the SPR signal. The method further includes, analyzing each P5 and corresponding P6 pulse, and identifying the SPR signal correctly in at least 99% of the received Mode-S signals in which the amplitude of the P6 pulse is at least 12 dB greater than the amplitude of the P5 pulse and in no more than 2% of the received Mode-S signals in which the amplitude of the P6 pulse is at least 3 dB less than the amplitude of the P5 pulse, and replying to the Mode-S signals for which the SPR signal is correctly identified.