Simple Explanation of What is ADS-B

There’re a lot of explanations of ADS-B on Internet. I’ll try to explain ADS-B in a simple way for newcomers.

What is ADS-B?

ADS-B (Automatic Dependent Surveillance - Broadcast) is a system or technique used in aviation that relies on airborne GPS and other equipment to determine an aircraft's position and other related information. This data is then broadcasted via onboard communication equipment to ground receivers and other nearby aircrafts. In essence, ADS-B allows aircrafts to "announce" their position and other details, enabling ground stations and nearby aircrafts to monitor and track their movements, or to say, “see” the aircrafts. 


Why do we need ADS-B?

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

  • Ground-to-air surveillance: Currently, radar is the primary ground-to-air surveillance technology. However, radar systems are expensive to install and maintain. In contrast, ADS-B ground receivers are cost-effective, easy to install, and require minimal maintenance. This makes ADS-B a more affordable and accessible solution for ground-to-air surveillance. In fact, ADS-B has the potential to replace radar systems in the future due to its cost-effectiveness and ease of implementation. For more detailed comparisons between radar and ADS-B, you may refer to the blog "The Difference Between Radar and ADS-B".
  • Airport surface movement surveillance: Currently, airport surface movement is primarily monitored by tower controllers who visually observe the airport surface and provide guidance to aircrafts and airport vehicles. Some large airports may have airport surface movement surveillance radar, which operates as a primary radar system. However, ADS-B and MLAT (Multilateration) offer more effective alternatives for airport surface movement surveillance. These technologies utilize aircraft transponders and ground-based receivers to track the precise positions of aircrafts and vehicles on the airport surface. Compared to traditional radar systems, ADS-B and MLAT can provide more accurate and detailed surveillance with aircrafts/vehicles identifications, enhancing safety and efficiency in airport operations.
  • Air-to-air surveillance. Currently, there’s no effective way for air-to-air surveillance. TCAS (Traffic Collision Avoidance System) is used for collision avoidance between aircraft, but it is limited in its functionality and is not a full air-to-air surveillance method. In contrast, ADS-B offers a more versatile solution for air-to-air surveillance. While ADS-B can support various applications beyond collision avoidance, such as In Trail Procedure (ITP). For further information on the difference between TCAS and ADS-B, you may refer to the blog "Difference between TCAS and ADS-B" .


What equipment are included in ADS-B?

As mentioned above, ADS-B is a system, consists of equipment on board aircraft and on ground.

On board aircraft:
GPS receiver: The GPS receiver is the primary source of data for ADS-B, providing accurate position information.

Pitot tube or Air Data Computer: These components provide pressure altitude data to ADS-B, aiding in altitude determination.

Flight Management System (FMS): The FMS supplies flight identification information to ADS-B.

Mode-S transponder with ADS-B OUT function or ADS-B transmitter: This equipment gets data from the GPS receiver, Pitot tube/Air Data Computer, and FMS to transmit ADS-B signals.

ADS-B receiver, receive ADS-B signal from other aircrafts. On commercial aircraft, the TCAS receiver often serves as the ADS-B receiver, whereas on general aviation aircraft and UAV/drones, a separate ADS-B receiver is typically used to capture ADS-B signals from other aircraft.

Cockpit Display of Traffic Information (CDTI): The CDTI displays ADS-B data to pilots.
ADS-B ground receiver or ADS-B ground station: These receive ADS-B signals transmitted by aircraft and relay the ADS-B data to other systems, such ADS-B processors or ADS-B display systems.

ADS-B processor: This component processes the received ADS-B data, performing tasks such as data fusion, where ADS-B data from multiple ADS-B receivers is integrated to create a comprehensive picture of air traffic in the area. The ADS-B processor is responsible for analyzing and organizing the data before it is displayed or further distributed.

ADS-B display system: The ADS-B display system presents the processed ADS-B data in a human-readable format for air traffic controllers or other relevant personnel.

These are the main ADS-B system components on the ground, but there are several additional components and systems related to ADS-B that serve various purposes and applications. Here are a few examples:

ADS-B record and replay system: An ADS-B record and replay system is a specialized technology used to capture, store, and playback ADS-B data. This system is valuable for various purposes, including training, analysis, and investigation in the aviation industry.

ADS-B analysis system: This system may include tools for analyzing the ADS-B data, such as coverage analysis or statistical reports. This enables users to extract valuable insights and identify trends or anomalies in aircraft behavior.

ADS-B simulator: An ADS-B simulator is used to generate simulated ADS-B signals for laboratory testing, training, or demonstrations. It replicates the behavior of real-world ADS-B transmissions, allowing users to validate equipment functionality, evaluate system performance, and train personnel in a controlled environment.


Why is it called ADS-B?

A: Automatic. All ADS-B information is transmitted automatically by aircraft without the need for human intervention or trigger signals (secondary surveillance radar need to send interrogations to transponders onboard aircrafts to trigger the transponders to reply). 

D: Dependent, all the ADS-B information originates from the equipment installed on the aircraft itself. This stands in contrast to radar systems, where the information is generated and calculated by ground-based radar installations. 

S: Surveillance, ADS-B is indeed used for surveillance purposes and falls under the "S" component of CNS/ATM (Communication, Navigation, Surveillance/Air Traffic Management) systems.  

B: Broadcast, ADS-B information is broadcasted from aircraft and can be received by any entity equipped with the right equipment. It’s not like ADS-C, which is point-to-point. 


What information is included in ADS-B?

Latitude, longitude, pressure altitude, GPS height, speed, heading, flight ID and a lot of other information. Please refer to the ADS-B standards for detail information.

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