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support a priority ovenide access for authorized ground users.
Note.- Operational conditions or certain applications may
6.8.1.3 Message source identification. The voice unit require the equipment to be operated in a na~owerfrequenc~
operation shall support notification to the user of the source of range.
a received message (i.e. whether the message originated from
an air or ground station). 6.9.2.1.2 Recommendation.- A VDL Mode 4 transmitter/
receiver should be capable of tuning to any of the 25 kHz
channels from 108 to 11 7.975 MHZ.
-
6.8.1.4 Coded squelch. The voice unit shall support a
coded squelch operation that offers some degree of rejection of Note.- The band 108-11 7.975 MHz may be utilized in
undesired co-channel voice messages based on the burst time accordance with the relevant provisions of the ITU Radio
of ani val . Regulations.
2511 1104
No. 79
Annex I0 - Aeronautical Telecommunications Volume 111
6.9.2.1.3 Simultaneous reception. A VDL Mode 4 station
shall be capable of receiving two channels simultaneously.
6.9.2.1.4 Recommendation.- A VDL Mode 4 station
should be capable of receiving additional channels
simultaneously as required by operational services.
6.9.2.2 GLOBAL SlGNALLlNG CHANNELS
6.9.2.2.1 VDL Mode 4 stations shall use two assigned
frequencies as global signalling channels (GSC), to support
user communications and link management functions.
Note.- Additional channels may be defined in a local
domain and notijied to mobile users by broadcast from ground
stations on the GSCs defined above.
6.9.3 System capabilities
6.9.3.1 ATN compatibility. The VDL Mode 4 system shall
support ATN-compliant subnetwork services for surveillance
applications.
6.9.4 Coordination of channel utilization
6.9.4.1 On a regional basis, transmissions shall be
scheduled relative to UTC, to ensure efficient use of shared
channels and to avoid unintentional slot re-use.
6.9.5 Physical layer protocols and services
Note.- Unless otherwise stated, the requirements defined
in this section apply to both mobile and gmund stations.
6.9.5.1.1 TRANSMITTED POWER
6.9.5.1.1.1 Airborne installation. The effective radiated
power shall be such as to provide a field strength of at least
35 microvolts per metre (minus 114.5 d ~ ~ l mo'n) t he basis of
free space propagation, at ranges and altitudes appropriate to
the conditions pertaining to the areas over which the aircraft is
operated.
6.9.5.1.1.2 Ground installation
6.9.3.2 Data transparency. The VDL Mode 4 system shall Recommendation.- The effective radiated power should
~rovidec ode-independent, byte-independent transfer of data. be such as to provide a field of at least 75 microvolts
per metre (minus 109 d ~ ~ /wmithi~n t)he defined operational
6.9.3.3 Broadcast. The VDL Mode 4 system shall provide coverage of the facility, on the basis of free-space propagation.
link layer broadcast services.
6.9.3.4 Point-to-point. The VDL Mode 4 system shall
provide link layer point-to-point services.
6.9.3.5 Air-air communications. The VDL Mode 4 system
shall provide air-air communications, without ground support,
as well as air-ground communications.
6.9.3.6 Connection management. When supporting
air-ground operations, the VDL Mode 4 system shall establish
and maintain a reliable communications path between the
aircraft and the ground system while allowing, but not
requiring, manual intervention.
6.9.3.7 Ground network transition. A mobile VDL
Mode 4 DLS station shall transition from one ground VDL
Mode 4 DLS station to another as required.
6.9.3.8 Derived rime capability. VDL Mode 4 shall
provide the capability for deriving time from time-of-arrival
measurements of received VDL Mode 4 transmissions
whenever externally derived estimates of time are unavailable.
6.9.3.9 Simplex operations. Mobile and ground VDL
Mode 4 stations shall access the physical medium operating in
simplex mode.
6.9.5.1.2 TRANSMITTER AND RECEIVER
FREQUENCY CONTROL
6.9.5.1.2.1 The VDL Mode 4 physical layer shall set the
transmitter or receiver frequency as commanded by the link
management entity (LME). Channel selection time shall be
less than 13 ms after the receipt of a command from a VSS
user.
6.9.5.1.3 DATA RECEPTION BY RECEIVER
6.9.5.1.3.1 The receiver shall decode input signals and
forward them to the higher layers for processing.
6.9.5.1.4 DATA TRANSMISSION BY TRANSMITTER
6.9.5.1.4.1 Dara encoding and transmission. The physical
layer shall encode the data received from the data link layer
and transmit it over the RF channel. RF transmission shall take
　
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