Technical Provisions for Mode S Services and Extended Squitter

DRAFT - Working Paper ASP TSGWP11-01 for review by the TSG during the meeting in June 2011 in Paris
CD-22 Technical Provisions for Mode S Services and Extended Squitter
well in excess of any operationally useful coverage since an aircraft at 600 km (325 NM) will only be visible to a surface
receiver if the aircraft is at an altitude greater than 21 000 m (70 000 ft).
The elements of this coding technique are illustrated in Figure CD-4. For ease of explanation, the figure shows four
contiguous area cells on a flat earth. The basic encoding provides unambiguous position within the dotted box centered
on the receiver, i.e. a minimum of 333 km (180 NM). Beyond this range, ambiguous position reporting can result. For
example, an aircraft shown at A would have an ambiguous image at B. However, in this case the information provided
by the sector antenna eliminates the ambiguity. This technique will work out to a range shown as the aircraft labeled C.
At this range, the image of C (shown as D) is at a range where it could be received through the sidelobes of the sector
antenna.
360 NM
360 NM
360 NM
x x
B D
360 NM
Draft
Figure CD-4. Maximum range considerations for CPR encoding
DRAFT - Working Paper ASP TSGWP11-01 for review by the TSG during the meeting in June 2011 in Paris
x
A
C x