Auto dependent surveillance broadcast (ADS-B)

ADS-B: the future of the transponder and the replacement for radar

Collision avoidance is a significant part of the Federal aviation administration’s Next-Gen plan for transforming the National Airspace System (NAS).

Increasing the number of aircraft using the same quantity of airspace and ground facilities requires the implementation of new technologies to maintain a high level of performance and safety.

Until now, aircraft are visualized on the ground using conventional radar: an antenna emits a signal in one direction, the signal is reflected on a device, then the echo returns to the initial antenna, switched to mode reception. By knowing the speed of propagation of electromagnetic waves in the air, it is then easy to determine the distance and azimuth of the device.  A 4-digit code is vocally given by the controller to the pilot who had to display it on his transponder, and thus he made a correlation with the plot and the aircraft in question. This system still has drawbacks such as signal losses depending on the topography of certain regions, the relief, but also the significant cost of infrastructure maintenance, because a certain number of them are needed to ensure acceptable precision. ADSB coupled to the transponder, therefore, appeared in the United States as a more effective alternative, then democratized everywhere. Today, ADSB technology is almost standard on transponders all over the world, coupled in particular with the most complete mode S for control.

How does it work ?

The successful proliferation of global navigation satellite systems (GNSS), such as GPS, has led to the development of a collision-avoidance system known as automatic dependent surveillance-broadcast (ADS-B). 

ADS-B is a system in which electronic equipment onboard an aircraft automatically broadcasts the precise location of the aircraft via a digital data link.

The data can be used by other aircraft and air traffic control to show the aircraft’s position and altitude on display screens without the need for radar.

ADS-B is considered in two segments: ADS-B OUT and ADS-B IN.

  • ADS-B out: combines the positioning information available from a GPS receiver with onboard flight status information, such as identification, current position, altitude, and velocity, then it broadcasts this information periodically to other ADS-B equipped other aircraft and ground stations. 
  • ADS-B IN: is the reception by aircraft of Flight Information Service FIS-B and Traffic information Service TIS-B data and other ADS-B data such as direct communication from nearby aircraft.
ADS-B operation
ADS-B OUT uses satellites to identify the position aircraft.

The system relies on two avionics components aboard each aircraft: a high-integrity satellite navigation source and a datalink (the ADS-B unit). There are several types of certified ADS-B data links, but the most common ones operate at 1090 MHz, or at 978 MHz.  

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1 thought on “Auto dependent surveillance broadcast (ADS-B)”

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