Multilateration system

Multilateration is a proven technology that has been in use for many decades. It was
developed for military purposes to accurately locate aircraft —many of which did not wish to
be “seen” — by using a method known as Time Difference of Arrival (TDOA).
Multilateration employs a number of ground stations, which are placed in strategic
locations around an airport, its local terminal area or a wider area that covers the larger surrounding airspace. Furthermore, while the radar and multilateration “targets” on
a controller’s screen are identical in appearance, the very high update rate of the multilaterationderived targets makes them instantly recognizable by their
smooth movement across the screen. A screen displaying multilateration information can
be set to update as fast as every second, compared with the 4 - 12 second position “jumps” of the
radar-derived targets. These units listen for “replies,” typically to interrogation signals
transmitted from a local SSR or a multilateration station. Since individual aircraft will be at
different distances from each of the ground stations, their replies will be received by each station at fractionally different times. Using advanced computer processing techniques, these individual time differences allow an aircraft’s position to be precisely calculated.
Multilateration requires no additional avionics equipment, as it uses replies from Mode A, C and
S transponders, as well as military IFF and ADS-B transponders.
“Multilateration offers ANSPs the possibility of providing a surveillance service
at a potentially much lower cost, greater reliability and higher levels of accuracy than
conventional SSR.” Alexander ter Kuile CANSO Secretary General
Multilateration ( MLA T ) MLAT ground stations receive replies from all
transponder-equipped aircraft, including legacy radar and ADS-B avionics,
and determine aircraft position based on the time difference of arrival
(TDOA) of the replies.