Simple Explanation of ADS-B

What is ADS-B?

ADS-B (Automatic Dependent Surveillance - Broadcast) is a system or a technique. ADS-B uses airborne GPS and several other equipments to obtain the aircraft own position and other information, then uses communication equipment onboard to transmit the aircraft own position and other information. Ground receivers and other aircrafts around can use communication equipment to get these information, so to monitor the aircraft, or to say, “see” the aircraft.

Why do we need ADS-B?

We would talk about this in three aspects: ground-to-air surveillance, airport surface movement surveillance and air-to-air surveillance.

1.     Ground-to-air surveillance. Now the main ground-to-air surveillance technique is radar. Radar is expensive, a lot of work to install and maintain. While ADS-B ground receivers are cheap, easy to install and maintain. A cheaper and easier way for ground-to-air surveillance solution, even possible to replace radar in the future. You may refer to the blog The difference between Radar and ADS-B for more details.

2.     Airport surface movement surveillance. Now mostly reply on tower controller, tower controller watch airport surface and guide the planes and airport vehicles movement. Some big airports may have airport surface movement surveillance radar, which is technically a primary radar. ADS-B and MLAT (Multilateration) can be more effective ways for airport surface movement surveillance.

3.     Air-to-air surveillance. Now there’s no effective way for air-to-air surveillance. TCAS is a way for air-to-air surveillance, but TCAS can only be used for collision avoidance. While ADS-B can support a lot of more applications, like ITP (In trail procedure). You may refer to the blog Difference between TCAS and ADS-B for more details.


What equipments are included in ADS-B?

On board aircraft:
GPS receiver, GPS is the main data source of ADS-B.
Pitot tube or Air Data Computer: provide pressure altitude to ADS-B.
FMS, provide flight ID to ADS-B
Mode S transponder with ADS-B OUT function or ADS-B transmitter, get information from GPS receiver, Pitot tube/Air Data Computer and FMS and then transmit these information in ADS-B signal. 
ADS-B receiver, receive ADS-B signal from other aircrafts. On commercial plane, it usually uses the TCAS receiver part as ADS-B receiver. On general aviation aircraft and UAV/drones, ADS-B receiver is an independent equipment. 
CDTI (Cockpit Display of Traffic Information), display ADS-B data.
ADS-B ground receiver or ADS-B ground station, receive ADS-B signal from aircrafts and transfer the ADS-B data to ADS-B processor or ADS-B display system. 
ADS-B processor, process ADS-B data, like data fusion.
ADS-B display system, display ADS-B data.

Why is it called ADS-B?

A:Automatic,all ADS-B information is transmitted automatically, no need of any person operation or trigger signal.
D:Dependent,all ADS-B information is coming from airborne equipments, not like radar information is calculated by radar. 
S:Surveillance,ADS-B is used for surveillance and belongs to the “S” part of CNS/ATM
B:Broadcast,ADS-B information is broadcasted. Any entity with the right equipment around can receive ADS-B signal.

What information is included in ADS-B?

Latitude, longitude, pressure altitude, GPS height, speed, heading, flight ID and a lot of other information.

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