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environmental noise sources.
6.3.5.3 Out-of-band immunity performance. The receiving
function shall satisfy the specified error rate with a desir~d
6.4 PHYSICAL LAYER
PROTOCOLS AND SERVICES
signal field strength of not more than 40 microvolts per metre
(minus 114 and with an undesired DSB-AM D8PSK The aircraft and ground stations shall access the physical
or GFSK signal on the adjacent or any other assignable in simp1ex mode.
channel being at least 40 dB higher than the desired signal.
6.3.5.3.1 After 1 January 2002, the receiving function of 6.4.1 Functions
all new installations of VDL shall satisfy the specified error
rate with a desired signal field strength of not more than 6.4.1.1 T ~ pEhy sical layer shall provide the following
40 microvolts per mctre (minus 114 mw/m2) and with an functions:
undesired VHF DSB-AM, DSPSK or GFSK signal at least
60 dB higher than the desired signal on any assignable channel a) transmitter and receiver frequency control;
100 kHz or more. away from the assigned channel of the
desired signal. b) digital reception by the receiver;
Note.-- This level of interference immurzit?, pegorrnance c) digital transmission by the transmitter; and
provides u receiver performance consistent with the influence
of the VDL RF spectrum mask as specifed in Volunze 111, d) notification services.
Annex 10 - Aeronautical Telecommurzications Volume ZII
6.4.1.1.1 Transmitter/receiver frequency control. The The output (function of timc) of the pulse shape filter (s(L))
VDL physical layer shall set the transmitter or receiver shall modulate the cai~icr frequency. The pulse shape filtcr
frequency as commanded by the link rnanage~nenl entity shall have a nominal complex frequency response of a raised-
(LME). cosine filter with a=0.6.
Note.- The LME is a link luyer entity us contuined ~n the 6.4.2.2 Modulution rate. The symbol ratc shall be 10 500
Manuals on VDL Mode 2 and VDL Mode 3 Technical symbols/second, resulting in a nominal bit rate of 31 500
Specijications. bitsts. The modulation stability requirements for Modes 2 and
3 are provided in Table 6-2.
6.4.1.1.2 Digital reception by the receiver. The receiver
shall decode input signals and forward them to the higher
layers for processing. 6.4.3 Mode 2 specific physical layer
6.4.1.1.3 Digitul transmission. The VDL physical layer Note.- The Mode 2 specific physicul layer specification
shall appropriately encode and transmit information received includes a description of the Mode 2 training sequence,
from higher layers over the RF channel. fonvurd error correction (FEC), interleaving, bit scrurnbling,
channel sensing, and physical layer system puramtters.
6.4.2 Modes 2 and 3 common physical layer
6.4.2.1 Modulation schem,e. Modes 2 and 3 shall use
differentially ~ n c o d ~8 dp hase shift keying (DS'PSK), using a
raised cosine filter with a = 0.6 (nominal value). The
information to be transmitted shall be differentially encoded
with 3 bits per symbol (baud) transmitted as changes in phase
rather than absolute phase. The data stream to be transmitted
shall be divided into groups of 3 consecutive data bits, leasl
significant bit first. Zeros shall be padded to the end of thc
transmissions if needed for the final channel symbol.
6.4.2.1.1 Datu encoding. A binary data stream entering a
differenlial data encoder shall be converted into threc separate
binary streams X, Y, and Z so that bits 3n form X, bits 3n + I
form Y, and bits 3n + 2 form Z. The triplet at time k (X,, Y,,
Zk) shall be converted to a change in phase as shown in Table
6-I*, and the absolule phase 4, is the accumulated series of
A$k, that is:
6.4.3.1 To transmit a sequcncc of frames, a station shall
insert the bit numbers and flags (per the data link service
description for Mode 2 as contained in the Manual on VDL
Mode 2 Technical Specifications), compute thc FEC
(per 6.4.3.1.21, interleave (per 6.4.3.1.3), prepend the training
sequence (per 6.4.3.1. l), carry out bit scrambling (per
6.4.3.1.4) and finally cncode and modulate the RF signal
(per 6.4.2.1).
6.4.3.1.1 Training sequence. DaLa transmission shall
begin with a demodulator training sequence consisting of five
segments:
a) transmitter ramp-up and power stabilization;
b) synchronization and ambiguity resolution;
c) reserved symbol;
d) lransmission length; and
6.4.2.1.2 Transmitted signal form. The phase-modulated
baseband signal as defined in 6.4.2.1.1 shall excite the pulse
shape filter.
where:
h is the complex impulse response of the pulse shape
filter;
k is defined in 6.4.2.1.1 ;
@ is defined by the equation in 6.4.2.1.1:
t is time;
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