EEE381B Aerospace Systems

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EEE381BAerospace Systems Avionics

• Identification Systems
• Ref Moir Seabridge, Chapter 7
• Dr Ron Smith

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Outline

• Introduction
• Transponders
• ATC
• TCAS
• IFF
• Network-centric warfare
• In-class exercises

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1. Introduction

• Identification the classification and
  identification of a target before engagement as
  dictated by the rules of engagement.

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1.1 Identification (transponder) systems

• Military aircraft employ a number of different
  interrogators and transponders
• Distance measurement equipment (DME)
• Tactical air navigation (TACAN)
• Air traffic control (ATC) mode S
• Traffic collision avoidance system (TCAS)
• Automatic dependent surveillance (ADS)
• Identification friend or foe (IFF)

DME and TACAN will be described in the
Navigation section of the course.
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1.2 RF Spectrum1

• Identification equipment
• Air traffic control (ATC)
• Collision Avoidance (TCAS)
• Identification friend or foe (IFF)

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2. Transponders

• A transponder is a receiver / transmitter device
  designed to transmit a response signal when
  legitimately interrogated. NATO definition
• An automatic device that transmits a
  predetermined message in response to a predefined
  received signal. Wikipedia

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2.1 Air traffic control (ATC)

• A ground-based primary surveillance radar (PSR)
  detects the presence of an aircraft and indicates
  its bearing and distance.
• At the same time a secondary surveillance radar
  (SSR), synchronized (on boresight) with the PSR,
  interrogates the aircraft using a series of
  pulses.
• The aircraft transponder responds with a
  different series of pulses containing situational
  information, typically its aircraft identifier
  and altitude.
• The information from the PSR and SSR is then
  integrated and presented on the ATC console.

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2.1.1 Air traffic control (ATC)
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2.1.2 Air traffic control (ATC)

• This system is also known as identification
  friend or foe / secondary surveillance radar
  (IFF/SSR)
• The onboard aircraft equipment consists of
• an ATC transponder control unit for setting the
  modes of operation and the control codes,
• a dedicated ATC transponder, and
• antennas.

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2.1.3 Air traffic control (ATC)

• Mode A (simple system)
• Aircraft identification (Call-sign)
• Mode C (more advanced)
• Mode A altitude
• Mode S (more recently)
• Mode C 24 bit address identifier (unambiguous)
• Provides limited air-air and air-ground
  communications
• Can also provides whereabouts of other aircraft
  in its vicinity
• Uses digital error-correcting codes for improved
  reliability

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2.2 Traffic Collision Avoidance System
TCAS

• A type of collision and avoidance system that
  functions independently from the ground based ATC
  suite.
• Used to detect possible aircraft conflicts
• Requires that all possible conflict aircraft are
  equipped with an SSR transponder.
• Mandated above 10,000 ft and within 30 miles of
  major airports.

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2.2.1 TCAS architecture 1
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2.2.2 TCAS operation

• Altitude and identification is obtained from
  modes C or S of an airborne ATC transponder (only
  bearing from mode A).
• Distance is obtained by calculating the response
  delay.
• Directional antennas obtain the bearing of the
  responding aircraft.

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2.2.3 TCAS operation

• TCAS builds a three-dimensional map of the
  aircraft within vicinity and extrapolates their
  closing distance and altitudes to determine if
  there are any possible collisions.
• Vicinity is typically defined as 15-40 nm
  forward, 5-15 nm aft and 10-20 nm on each side.
• Remember that the system can only communicate
  with aircraft equipped with serviceable
  transponders.

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2.2.4 TCAS types

• TCAS I
• Indicates distance and bearing
• Issues traffic advisories (TA)
• 'TRAFFIC, TRAFFIC
• TCAS II
• Negotiates and indicates deconfliction strategies
• Issues resolution advisories (RA)
• Climb Climb Climb,
• Descend Descend Descend,
• Maintain vertical speed , ...

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2.3 Identification friend or foe (IFF)

• Used in two ways
• Provide 360 coverage to respond to
  interrogations and receive interrogation returns
  from friendly aircraft (very similar to the
  airborne operation of ATC mode S when used in
  combination with TCAS)

AN/APX-113(V) by BAE Systems
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2.3.1 Identification friend or foe (IFF)

• Used to specifically identify targets seen by the
  primary radar.

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3. Network-centric operations 3

• Based upon the hypothesis that
• A robustly networked force improves information
  sharing
• Information sharing enhances the quality of
  information and shared situational awareness
• Shared situational awareness enables
  collaboration and self-synchronization, and
  enhances sustainability and speed of command and
  
• These, in turn, dramatically increase mission
  effectiveness.

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3.1 Network-centric operations

• Employs
• High speed, high bandwidth digital communications
• Sophisticated signal processing
• High speed internal (onboard) networks
• Integrates
• Command control structure (C2)
• Ultra high resolution sensors
• Sensor and weapons delivery platforms

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3.2 Network-centric operations 1
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3.3 NCO example 4
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4. In-class exercises
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4.1 Quick response exercise 1

• You are flying (VFR) in an aircraft equipped with
  a modern, serviceable TCAS system.
• You receive a traffic advisory (TA) that a
  potential conflict exists directly in your flight
  path range is closing and the bearing is
  straight ahead.
• You perform the necessary visual check, but you
  do not see any other aircraft.
• What is a likely explanation?

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4.2 Quick response exercise 2

• What problem do you see with having the IFF
  transponder oriented co-boresight with the
  primary radar?

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References

• Moir Seabridge, Military Avionics Systems,
  American Institute of Aeronautics Astronautics,
  2006. Sections 2.6 2.7
• Wikipedia
• Military Communication Systems, LFTSP course
  notes, ECE Dept, RMC, 2007
• Air Power Australia, http//www.ausairpower.net/TE
  -NCW-JanFeb-05.html.
• Georgia State University, hyperphsyics,
  http//hyperphysics.phy-astr.gsu.edu/hbase/audio/b
  cast.htmlc3
• Mark A. Hicks, "Clip art licensed from the Clip
  Art Gallery on DiscoverySchool.com"