GBAS/SCAT-I Mode (Options R&S
EVSG-K4/-K5)
R&S
®
EVSG1000
173
User Manual 1178.6227.02 ─ 06
6.1.2
Broadcast Timing Structure
The broadcast is a Time Division Multiple Access (TDMA). According to [1], the TDMA
timing structure uses a two level hierarchy, composed of 500
ms long frames, each
divided into 8 VDB time slots (A - H), see
.
Figure 6-2: TDMA timing structure (simplified representation)
A VDB time slot is the minimum resource that an individual VDB transmitter can use.
During one time slot, a VDB transmitter transmits exactly one burst.
The GBAS specification [1] defines the TDMA timing structure, including timing budget
of the VDB bursts, burst data contents and message encoding in great details. The
R&S
EVSG1000 receives the required training sequence, decodes the message
according to [1] and demodulates the D8PSK modulated data automatically.
6.1.3
Final Approach Segment (FAS) Construction Data
According to the standard [1], the message type 4 contains one or more data sets that
contain approach data, associated vertical/lateral alert limits, and/or the Terminal Area
Path (TAP).
The FAS path is a line in space that defines the path an airplane follows on its final
approach. This line is defined by the Landing Threshold Point/Fictitious Threshold
Point (LTP/FTP), Flight Path Alignment Point (FPAP), Threshold Crossing Height
(TCH), and the Glide Path Angle (GPA).
Basics on GBAS and SCAT-I Analysis
