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DO-253D Change 1
The VDB receiver subsystem shall [LAAS-040] output all bits of a desired LAAS message
within 125 milliseconds of the arrival of the last bit of that message at the VDB antenna.
Note: The data latency only applies after the VDB is providing messages as specified in
Data Format Decoding
The VDB receiver subsystem shall [LAAS-041] properly demodulate and decode the VHF
data broadcast signal specified in RTCA/DO-246().
Message Failure Rate
The message failure rate (MFR) is defined as the total number of messages lost by the VDB
receiver subsystem plus those messages which do not pass the cyclic redundancy check
(CRC) after application of the forward error correction, divided by the total number of
messages sent by the ground subsystem.
1. The MFR requirement also includes the condition of the VDB field strengths in any
and all combinations of slots within a given frame varying by up to 72 dB spanning
the full field strength dynamic range combined with the maximum antenna gain
variation in the horizontal plane of 7 dB for Class A and Z dB for Class B receivers.
2. Successive bursts are defined as consecutive, scheduled bursts from a ground
subsystem. The current ICAO Annex 10 GBAS VDB ground subsystem transmitter
broadcasts are required to have a burst in at least every fifth consecutive frame
for each assigned time slot being used. The test procedures in this document
conservatively test that the receiver will recover from interruptions of reception of
10 seconds (i.e., 20 frames) or less; however the test procedures do not attempt to
cover all permutations of missing bursts in a sequence of frames nor the effects of
3. If the ground subsystem is broadcasting from alternating transmitters in the same
slot (see Appendix K.3 .1), signal power variations may occur when transmitters
are switched between frames. The MFR requirements in the following sections
continue to be applicable to any signal inside Smin to Smax even when some bursts
have signals below Smin. For LAAS-051 and LAAS-410, the power variation
between the two alternating signals is not limited to the 72 dB field strength
dynamic range plus the antenna gain variation in the horizontal plane as described
in note (1). The testing is limited to a ground configuration alternating between
two signal powers in successive frames. LAAS-051 and LAAS-410 are worded
using “successive frames” to signify this alternating frame operation rather than
“successive bursts” (which allows empty frames) used in LAAS-042 and LAAS-
4. The MFR requirements do not apply to a signal outside Smin to Smax. The MFR
requirements apply to the aggregate of all messages within Smin and Smax. There is
no intent to imply any specific MFR to the signal with higher or lower power level
when the power varies within Smin to Smax.
Class A Receivers
The Class A VDB receiver subsystem shall [LAAS-042] achieve a message failure rate
(MFR) less than or equal to one failed message per 1000 full-length (222 bytes) application
data messages while operating over an input power range between Smin = –87 dBm and
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