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T, is time duration of each symbol.
* All lables are located at the end of this chapter
e) header FEC.
Note.- Imnzediately ufter these segments follows an AVLC
frame with the format as contained in the data link service
description in the Manual on VDL Mode 2 Technicul
Specifications.
6.4.3.1.1.1 Transmitter rump-up und power stabilization.
The purpose of the first segment of the training sequencc,
called the ramp-up, is to provide for transmitter power
stabilization and receiver AGC settling, and it shall
immediately precede the first symbol of the unique word. The
duration of the ramp-up shall be five symbol periods. The time
reference point (t), for the following specification is the centre
of the first unique word symbol, a point that occurs half a
symbol period after the end of the ramp-up. Conversely stated,
the beginning of the ramp-up starts at t = -5.5 symbol periods.
The lransmitted power shall be less than 4 0 dBc prior to lime
t = -5.5 symbol periods. The ramp-up shall provide that at
time t = -3.0 symbol periods the transmitted power is 90 per
Part I Annex 10 - Aeronautical Telecommunicatiorrs
cent of the manufacturer's stated output power or greater (see where:
Figure 6-1"). Regardless of the method used to implement (or
truncate) the raised cosins filter, the output of the transmitter P is the parity symbol (P, shall be transmitted first);
between times t = -3.0 and t = -0.5 will appear as if '000'
symbols were transmitted during the ramp-up period. R is the reserved symbol;
Note. I.- For Mode 3, the timing reference point is the
TL is the transmission Length symbol; same as the ''power reference poivt".
Note 2.- It is desirable to muximize the time allowed for
the AGC settling time. Eforts should be m,nde to have power
ubove 90 per cent of nomi?i,nl output power ut t - 3.5 symbol
periods.
6.4.3.1.1.2 Synchronization and ambiguity resolutiorr. The
second segment of the training sequence shall consist of the
unique word:
and shall be transmitted from left to right.
is the matxix transpose function; and
H is the parity matrix defined below:
-
0 0 o o o o o o i 1 1 1 1 1 1 1 I I i i
0 0 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1
1 1 0 0 0 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1
1 1 0 1 1 0 1 1 0 1 0 1 0 0 1 1 0 0 1 3
0 1 1 0 1 0 0 1 1 1 1 0 0 1 0 1 0 1 0 1 - -
6.4.3.1.1.6 Bit transmissio~z order. The five parity bits of
the resultant vector product shall be transmitted from the left
bit first.
6.4.3.1.1.3 Reserved symbol. The third segment of Lhc 6.4.3.1.2 Forward error correctio??. In order to improve
training sequence shall consist of the single symbol the effective channel throughput by reducing the number of
representing 000. required retransmissions, E C shall be applied after the
training sequence, regardless of frame boundaries.
Note.- This field is reserved forfiture definition.
6.4.3.1.2.1 FEC calculation. T ~ FEEC coding shall be
6.4.3.1.1.4 Transmission length. To allow the receiver' to accomplished by means of a sy sternatic fixed-length
determine thc length of the final Reed-Solomon block, the R ~ ~(RS)(~255,249-) 28-asry cod~e. ~ ~ ~ ~ ~
transmitter shall send a 17-bit word, from leas1 significant bit
(lsb) to most significant bit (msb), indicating the total number
Note 1.- This code is capuble of correcting up to three
of data bits that follow the header FEC. octets for data blocks of 249 octets (1992 bits). Longer
Note.- The length does not include those bits transmitted
for: the Reed Solomon FEC, extra bits padded to ensure that
the interleaver generates nn integral number of 8-bit words, or
the extra bits padded to ensure that the duta encoder generates
an integral number of 3-bit symbols.
6.4.3.1.1.5 Header FEC. To correct bit errors in the
header, a (25, 20) block code shall be computed over the
reserved symbol and the transmission length segments. The
block code shall be transmitted as the fifth segment. The
encoder shall accept the header in the bit sequence that is
being transmitted. The five parity bits to be transmitted shall
be generated using the following equation:
* All figures are located at the end of this chaptcr.
trunsmissions must be divided up into 1992 bit transmissions
and shorter transmissions must be extended by virtuul fill with
trailing zeros. Six RS-check octets are appended for a total
block of 255 octets.
The field defining the primitiv~ polynomial of the code shall
be as follows:
The generator polynomial shall be as follows:
where:
~ri.s a primitive element of GF(256);
GF(256) is a Galois field (GF) of size 256.
Note 2.- The Reed-So2omon codes ure described in the
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