Communications: directive radio wave systems and devices (e.g. – Air traffic control – Secondary surveilance radar
Reexamination Certificate
2002-11-08
2004-11-09
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Air traffic control
Secondary surveilance radar
C342S029000, C342S030000, C342S032000, C342S036000, C342S118000, C342S146000, C342S147000, C342S195000, C342S450000
Reexamination Certificate
active
06816105
ABSTRACT:
BACKGROUND OF THE INVENTION
The present application relates to the detection and tracking of aircraft. The invention finds particular application in detecting and tracking suitably equipped aircraft on an airport surface, aircraft on closely spaced parallel approaches and aircraft in proximity of an airport and will be described with reference thereto. It is to be appreciated however, that the teachings disclosed herein are also amenable to the detection and tracking of suitably equipped vehicles in a variety of environments such as highway, maritime and other applications.
The position of aircraft near airports and other aircraft is of crucial importance to the safe movement of aircraft Multiple techniques which make use of the Air Traffic Control Radar Beacon System (ATCRBS) transponders have previously been employed to track and monitor airborne aircraft enroute to an airport, provide guidance or monitor aircraft on final approach to airports and monitor aircraft movement within the airports runways and taxiways. The tracking techniques have been realized in the following systems.
Airborne aircraft enroute to an airport are monitored using Air Traffic Control Beacon Interrogator (ATCBI-6) ground systems and associated displays. These systems interrogate Mode A/C and are fully compliant with the new Mode S (for selective) transponder formats that include P4 suppression to reduce synchronous garble.
Traffic Collision And Avoidance System (TCAS) is operated onboard aircraft to interrogate aircraft transponders and measure time of arrival (TOA) and in some cases angle of arrival (AOA), then track display and issue resolution advisories when aircraft closure criteria exceed certain thresholds, as taught In U.S. Pat. No. 5,387,915 issued on 7 Feb., 1995 to Moussa et el.
The Transponder Landing System (TLS) provide means for the pilot to monitor aircraft position with respect to the desired course and glide path, on final approach to an airport. The system relies on Mode A/C interrogations to track the transponder.
Systems are known which monitor aircraft on the surface of an airport based only on time of arrival multilateration of the aircraft transponder response, and some prototype multilateration systems have been fielded which rely heavily on the new Mode S transponder, as taught in U.S. Pat. No. 5,262,784 issued on 16 Nov., 1993 to Drobnicki et el.
The fundamental design constraint of all of the above systems for which the transponder reply is the basis of positive identification is the desire for the system to operate during periods of synchronous garble. Garbling of transponder replies occurs where positive identification of the aircraft transponder response is thwarted by overlapping transponder replies from aircraft that are near the same slant distance from the ground sensor. To increase the capacity of the transponder based systems and minimize synchronous garble, the new Mode S has been defined and standardized. All aircraft with more than 30 seats are now equipped with Mode S transponders and TCAS. In contrast to normal Secondary Surveillance Radar (SSR), some features of the SSR Mode S make it very suitable for ground traffic control as well. The problems in cooperative ground detection tracking methods are due to the lack of Mode S transponders in general aviation aircraft. This problem is likely to persist for many years. For reliably detecting aircraft within dense RF environments which include Mode A/C transponders, new methods must be developed.
The present invention provides an improved method and apparatus for measuring and processing aircraft transponder replies degraded by synchronous garble which overcomes problems with the current techniques used by the above-referenced systems and others.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a method of tracking aircraft in a surveillance area includes a conventional IFF transponder responsive to interrogation signals at a first frequency, receiving reply signals from aircraft in the surveillance area at a second frequency, the signals being received on a plurality of antenna arrays. An angle of the received reply signals is determined relative to each array from the differential carrier phase. A range is determined based on the time of arrival (TOA) measurement, which is the time from signal transmission to reception. These and other characteristics of the reply signals, such as amplitude and frequency, are used to correlate pulses with each other over time. A position is calculated for each reply pulse indicative of an origin or source point of the reply signals from data including the determined angle and range. This Pulse Track data is conveyed to a central processing location. Pulse tracks are then correlated between multiple ground sensors using all track states which include reply amplitude, position (point of reply origin), velocity, acceleration and reply frequency (waveform cycles per second), to yield an aircraft position and ID. A single array may not be able to calculate a unique angle, but TOA measurements from multiple antenna arrays can be used to calculate a unique angle. This is accomplished by using the TOA data from 2 non-co-located arrays to calculate an initial position and then selecting the angle with the lowest residual. Further processing of the data allows the ultimate system accuracy to be achieved by solving for aircraft position estimates based on intersecting two or more lines of bearing. This final step in the transponder reply processing eliminates the transponder encoding delay. Data representative of a plurality of calculated positions is periodically provided to vehicles in the surveillance area or other users such as ground or air traffic controllers.
In accordance with another aspect of the present invention, a system for locating an object within a monitored area which receives and measures at least two angles from at least two separate sensor locations without external interrogation of the transponder, commonly referred to as a transponder Mode S squitter.
In accordance with another aspect of the present invention, Angle of arrival data is measured on every reply pulse to improve pulse to pulse correlation. A position can be calculated for each pulse and combined with velocity, acceleration, reply amplitude and reply signal frequency, can be used to associate pulses over time. This provides synchronous garble mitigation, as the entire reply is not needed to provide position and ID.
In accordance with an aspect of the present invention, the angle is determined by determining at least one of an elevation angle and an azimuth angle.
In accordance with an aspect of the present invention, the method further includes receiving the provided data representative of a plurality of calculated positions in a particular vehicle, for example, an aircraft either airborne or taxiing, or airport service vehicles. From the received data a position corresponding to the particular vehicle is extracted and compared with another position from onboard sensors.
In accordance with an aspect of the present invention, the angle of each reply pulse is determined by receiving the reply signal on a reference antenna in the array and receiving the reply signal on another antenna in the array. A difference in phase between the signal received on the reference antenna and the signal received on the other antenna is determined.
In accordance with an aspect of the present invention, the method of tracking reply pulses in a surveillance area further includes calculating an elapsed time between transmitting an interrogation signal and receiving the reply signal and determining a range based on the elapsed time.
In accordance with an embodiment of the present invention, an apparatus which detects aircraft in an area and includes an angle determining apparatus, a range determining apparatus, a position processor and a transmitter. The angle determining apparatus includes a plurality of antennas disposed as an array, and a phase calculator which calculates a difference in
Khen Benjamin
Winner Karl
LandOfFree
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