ADS-B is one of the most important, underlying technologies in the FAA’s plan to transform air traffic control from the current radar-based system ( that was invented during World War II) to a satellite-based system. ADS-B is bringing the precision and reliability of satellite-based surveillance to the nation’s skies. AviationGlossary.com defines ADS-B as Automatic Dependent Surveillance Broadcast ADS-B is a next generation surveillance technology incorporating both air and ground aspects that provide air traffic control (ATC) with a more accurate picture of the aircraft’s three-dimensional position in the en route, terminal, approach and surface environments. The aircraft provides the airborne portion in the form of a broadcast of its identification, position, altitude, velocity, and other information. The ground portion is comprised of ADS-B ground stations which receive these broadcasts and direct them to ATC automation systems for presentation on a controller’s display. In addition, aircraft equipped with ADS-B In capability can also receive these broadcasts and display the information to improve the pilot’s situation awareness of other traffic. • Automatic — periodically transmits ID information with no pilot or operator input required • Dependent - position and velocity vector are derived from the Global Positioning System (GPS) or a Flight Management System (FMS) • Surveillance — a method of determining position of aircraft, vehicles, or other assets • Broadcast — transmits information available to anyone with the appropriate receiving equipment.  How Does ADS-B Work?
ADS-B uses conventional Global Navigation Satellite System (GNSS) technology and a relatively simple broadcast communications link as its fundamental components. Unlike radar, ADS-B accuracy does not seriously degrade with range, atmospheric conditions, or target altitude and update intervals do not depend on the rotational speed or reliability of mechanical antennas. In typical applications, the ADS-B capable aircraft uses an ordinary GNSS (GPS, Galileo, etc) receiver to derive its precise position from the GNSS constellation, then combines that position with any number of aircraft discrete, such as speed, heading, altitude and flight number. This information is then simultaneously broadcast to other ADS-B capable aircraft and to ADS-B ground, or satellite communications transceivers which then relay the aircraft's position and additional information to Air Traffic Control centers in real time. The 978 MHz Universal Access Transceiver ("UAT") variant is also bi-directional and capable of sending real-time Flight Information Services ("FIS-B"), such as weather and other data to aircraft. In some areas, conventional non-ADS-B radar traffic information ("TIS-B") can also be uplinked as well. 
What are the benefits from ADS-B?
According to ATA, The ADS-B position information that the controller receives is far more precise than today’s radar positioning. This offers a number of benefits. The primary benefit of ADS-B is that it is a fundamental building block for the Next Generation National Airspace System (NextGen). In addition, the ADS-B data packet sent to air traffic controllers can also be received by airlines and other parties to facilitate better system management by all users and service providers. In the near future, airplanes themselves can be equipped with an ADS-B receiver, which will enable real-time cockpit displays of weather and traffic, both on the ground and in the air. The positioning information displayed will allow each airplane’s pilots to “see” other nearby airplanes. Ground vehicles can also be equipped with ADS-B, making them visible to controllers and pilots and reducing the risk of surface collisions. Further, the precise positioning data delivered to controllers should safely enable reduced airplane separation standards, which would allow more aircraft to...