ICAO VDL Mode 4
The ICAO standard for VDL Mode 4 specifies a protocol enabling aircraft to exchange data with ground stations and other aircraft.
VDL Mode 4 uses a protocol (Self-organized Time Division Multiple Access, STDMA, invented by Swede HÃ¥kan Lans in 1988) that allows it to be self-organizing, meaning no master ground station is required. This made it much simpler to implement than VDL Mode 3.
In November 2001 this protocol was adopted by ICAO as a global standard. Its primary function was to provide a VHF frequency physical layer for ADS-B transmissions. However it was overtaken as the link for ADS-B by the Mode S radar link operating in the 1090 MHz band which was selected as the primary link by the ICAO Air Navigation Conference in 2003.
The VDL Mode 4 medium can also be used for air-ground exchanges. It is best used for short message transmissions between a large number of users, e.g. providing situational awareness, Digital Aeronautical Information Management (D-AIM), etc..
European Air Traffic Management modernization trials have implemented ADS-B and air-ground exchanges using VDL Mode 4 systems. However on air transport aircraft the operational implementations of ADS-B will use the Mode S link and of CPDLC will use VDL Mode 2.
Read more about this topic: VHF Data Link
Famous quotes containing the word mode:
“I cannot believe that our factory system is the best mode by which men may get clothing. The condition of the operatives is becoming every day more like that of the English; and it cannot be wondered at, since, as far as I have heard or observed, the principal object is, not that mankind may be well and honestly clad, but, unquestionably, that the corporations may be enriched.”
—Henry David Thoreau (18171862)