The Global Link - Arinc

November 2011 | #43
The Global Link
Technotalk
Expanding the VDL Mode 2 Service for the Future:
Exercises in Frequency and Spectrum Management
—Continued
test facility within the AQP labs in Annapolis. Along with the facility, a set of test cases
were released to the industry based on ARINC’s planned approach for VDL multi-frequency
operation. Through a course of interactive testing, ARINC and the manufacturers have arrived
at implementations that will fully support the operation on VDL alternate frequencies. From
a protocol and network standpoint, we are nearly ready for the future. In order to expand the
VDL capacity, we must, of course, have assigned frequencies, and that is another ongoing
industry activity that ARINC is supporting.
ASRI AFC VDL Mode 2 Spectral Plan for the USA:
Within the USA, all VHF frequencies used by the aeronautical industry for both voice and
data applications are licensed, assigned, and managed by Aviation Spectrum Resources
Incorporated (ASRI). ASRI was previously part of ARINC Incorporated, but became a separate
company, owned by the airline community, when the ownership of ARINC was transferred
to the Carlyle Group, a non-airline entity. Approximately 15 years ago, the 136 to 137 MHz
VHF band was added to the existing aeronautical 118 to 136 MHz band. This 1 MHz band
was primarily intended to be used for the VDL Mode 2 service. The FAA received the lower
136.025 to 136.475 MHz portion of the band for ATC applications; ASRI received the
upper 136.500 to 136.975 MHz portion of the band for airline operational control (AOC)
applications.
In mid-2010, ASRI created a special VDL spectral planning sub-working group under its
primary technical committee, the Aeronautical Frequency Committee (AFC), which meets
several times each year. Both ARINC and SITA were designated as co-chairmen for this
special VDL planning group. Over the course of a year, and a series of meetings, ARINC has
been a lead contributor, providing the propagation, testing, analysis, and much of the writing
associated with this group.
Engineering studies prove that the higher the data rate of any communications system, the
more prone the system can be to interference. The VDL Mode 2 service, using Differential
Eight Phase Shift Key (D8PSK) modulation operates at a data rate that is 15 times faster
than ACARS. Likewise, a successful VDL deployment requires DSPs to provide coverage in
multiple locations within the same airport infrastructure to provide reliable communications at
each gate location. These close range stations can easily cause interference between ARINC’s
own stations as well as the VDL stations that could be operated by another DSP in the
regions. A successful VDL Mode 2 Spectral Plan is needed to address each of these special
requirements.
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