Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Traffic analysis or control of aircraft
Reexamination Certificate
2001-04-06
2003-01-28
Zanelli, Michael J. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Traffic analysis or control of aircraft
C701S003000, C701S301000, C340S961000, C342S029000
Reexamination Certificate
active
06512975
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to aircraft collision avoidance, and in particular to displaying traffic information on a display.
Aircraft pilots are expected to visually identify collision threats and avoid them. This “see and avoid” technique based on the pilot's visual sense remains the most basic method of aircraft collision avoidance. However, since the 1950's electronic techniques based on radio frequency and optical transmissions have been developed to supplement the pilot's visual sense. The government has developed and implemented a system of ground based and aircraft carried equipment designated the Air Traffic Control Radar Beacon System (ATCRBS). This system includes two different types of ground based radar emitters located at each of a plurality of Air Traffic Control (ATC) stations. One type of radar is referred to as the Primary Surveillance Radar (PSR), or simply as the primary radar. The primary radar operates by sending out microwave energy that is reflected back by the aircraft's metallic surfaces. This reflected signal is received back at the ground radar site and displayed as location information for use by an air traffic controller.
The second type of radar is referred to as the Secondary Surveillance Radar (SSR), or simply secondary radar. Unlike the primary radar, the SSR is a cooperative system in that it does not rely on reflected energy from the aircraft. Instead, the ground based SSR antenna transmits a coded 1030 MHz microwave interrogation signal. A transponder, i.e., a transmitter/receiver, carried on the aircraft receives and interprets the interrogation signal and transmits a 1090 MHz microwave reply signal back to the SSR ground site. This receive and reply capability greatly increases the surveillance range of the radar and enables an aircraft identification function, referred to as Mode-A, wherein the aircraft transponder includes an identification code as part of its reply signal. This identification code causes the aircraft's image or blip on the ATC operator's radar screen to stand out from the other targets for a short time. Thus, Mode-A provides a rudimentary identification function.
In addition to the identification function provided by Mode-A, the aircraft altimeter is typically coupled to the transponder. When the reply signal includes altitude information the secondary surveillance radar is referred to as Mode-C.
The Mode-A and Mode-C systems are unable to relay additional information or messages between the ground based SSR and the interrogated aircraft, other than the aforementioned identification and altitude information. The Mode Select, or Mode-S system, was the next evolution in aircraft surveillance. Mode-S is a combined secondary surveillance radar and a ground-air-ground data link system which provides aircraft surveillance and communication necessary to support automated air traffic control in the dense air traffic environments of today.
Mode-S incorporates various techniques for substantially reducing transmission interference and provides active transmission of messages or additional information by the ground based SSR. The Mode-S sensor includes all the essential features of ATCRBS, and additionally includes individually timed and addressed interrogations to Mode-S transponders carried by aircraft. The Mode-S system uses the same frequencies for interrogations and replies as the ATCRBS.
The Radio Technical Commission for Aeronautics (RTCA) has promulgated a specification for the Mode-S system, RTCA/DO-181A,
Minimum Operational Performance Standards For Air Traffic Control Radar Beacon System/Mode Select
(
ATCRBS/Mode
-
S
)
Airborne Equipment,
issued January 1992, and incorporated herein by reference. According to RTCA specification DO-181A, the airborne portion of the Mode-S system includes in one form or another at least a dedicated transponder, a cockpit mounted control panel, two dedicated antennas and cables interconnecting the other elements.
In operation, a unique 24-bit address code, or identity tag, is assigned to each aircraft in a surveillance area by one of two techniques. One technique is a Mode-S “squitter” preformed by the airborne transponder. Once per second, the Mode-S transponder spontaneously and pseudo-randomly transmits, or “squitters,” an unsolicited broadcast, including a specific address code unique to the aircraft carrying the transponder, via first one and then the other of its antennas which produce an omnidirectional pattern. The transponder's transmit and receive modes are mutually exclusive to avoid damage to the equipment. Whenever the Mode-S transponder is not broadcasting, it is monitoring, or “listening,” for transmissions simultaneously on its omnidirectional antennas. According to the second technique, each ground based Mode-S interrogator broadcasts an ATCRBS/Mode-S “All-Call” interrogation signal which has a waveform that can be understood by both ATCRBS and Mode-S transponders.
When an aircraft equipped with a standard ATCRBS transponder enters the airspace served by an air traffic control Mode-S interrogator, the transponder responds the with a standard. ATCRBS reply format, while the transponder of a Mode-S equipped aircraft replies with a Mode-S format that includes a unique 24-bit address code, or identity tag. This address, together with the aircraft's range and azimuth location, is entered into a file, commonly known as putting the aircraft on roll-call, and the aircraft is thereafter discretely addressed. The aircraft is tracked by the air traffic control interrogator throughout its assigned airspace and, during subsequent interrogations, the Mode-S transponder reports in its replies either its altitude or its ATCRBS 4096 code, depending upon the type of discrete interrogation received. As the Mode-S equipped aircraft moves from the airspace served by one ATC Mode-S interrogator into airspace served by another Mode-S interrogator, the aircraft's location information and discrete address code are passed on via landlines. If the information is not or cannot be passed via landlines, either the ground based SSR station picks up the Mode-S transponder's “squitter” or the aircraft Mode-S transponder responds to the All-Call interrogation signal broadcast by the next ATC Mode-S interrogator.
The unique 24-bit address code, or identity tag, assigned to each aircraft is the primary difference between the Mode-S system and ATCRBS. The unique 24-bit address code allows a very large number of aircraft to operate in the air traffic control environment without an occurrence of redundant address codes. Parity check bits overlaid on the address code assure that a message is accepted only by the intended aircraft. Thus, interrogations are directed to a particular aircraft using this unique address code and the replies are unambiguously identified.
The unique address coded into each interrogation and reply also permits inclusion of data link messages to and/or from a particular aircraft. One such use of the datalink messaging capabilities inherent in MODE-S is uplink of data regarding traffic in the vicinity of the aircraft. This service known as the “Traffic Information Service”, or TIS, uplinks the MODE-S transponder data for up to eight aircraft located in the vicinity of the requesting aircraft. Data for the nearby aircraft can then be displayed to the pilot on a display and shown relative to the own aircraft data. The display of additional traffic data thus assists the pilot in avoiding collisions with other aircraft. In particular, the display identifies potential collision threats and directs the pilot where to visually scan for traffic such that the principals of see and avoid can be implemented with greater confidence and integrity. The TIS system is more fully described in the
International Civil Aviation Organization Manual on MODE-S Specific Service,
DOC 9688-AN/952, incorporated herein by reference; and in
Minimum Operational Performance Standards for Traffic Information Services
(
TI
Honeywell International , Inc.
Zanelli Michael J.
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