Aerospace and Electronic Systems - December 2018 - 54

The Aeronautical Telemetry Story in the USA

Figure 4.

WRC-2007 AI 1.5 Results. Adapted from a presentation prepared by Didier Petit, French Delegate, WRC-20017. *Brazil, Cuba, French overseas departments and communities, Guatemala, Paraguay, Uruguay, Venezuela. **Algeria, Saudi Arabia, Bahrain, Egypt, United Arab Emirates, Jordan, Kuwait,
Lebanon, Morocco, Oman, Qatar, Syrian Arab Republic, Sudan, Tunisia.

ensure accurate information was available in the wide array of
committee, subcommittee, working group, and ad-hoc meetings
and informal discussion among delegates. The ICTS maintained
a booth in the Conference Exhibition Hall that proved to be an
invaluable asset to present telemetry facts and national impacts "in
real-time" during the conference.
The grass-roots approach (user-national administration-regional-WRC) was successful. The ICTS vision to promote the benefits
and enhancement of electromagnetic spectrum for telemetering
applications resulted in the WRC approving several resolutions
beneficial to AMT on Wednesday, November 14, 2007. The results
from WRC-2007 took a regional flavor as illustrated in Figure 4.
As in any negotiation, it involved compromise from the involved
parties. The 4,400-4,940 MHz and 5,925-6,700 MHz bands were
approved for use in ITU Region 2 (the Americas). Australia in
Region 3 (Asia/Pacific Rim) was approved for the 4,400-4,940
MHz band. The 5,150-5,250 MHz band was approved for Region
1 (Europe/Africa) with the exception of the Arab Group countries
but with the inclusion of Brazil in Region 2. The significant accomplishment internationally was allocation of the 59 MHz band
5,091-5,150 MHz, the first globally harmonized telemetry band.
The significance and full benefits of the above allocations for USA
flight test operations depend on the telemetry community's ability
to implement the bands domestically, a work which is on-going.
Moreover, while WRC 2007 approved the use of 5,925-6,700
MHz for AMT on a noninterfering basis, the FCC has not yet approved an AMT allocation for this band.

EFFORTS TO IMPROVE SPECTRAL EFFICIENCY
ADVANCED RANGE TELEMETRY (ARTM) PROGRAM
The Advanced Range Telemetry (ARTM) program was launched
in 1997 with the goal of "improve[ing] the efficiency of spectrum
usage by changing historical methods of acquiring telemetry data
54

and transmitting it from systems under test to range customers"
[13]. ARTM focused on all elements of aeronautical telemetry including channel modeling, modulation, forward error correction
coding, equalization, compression, diversity methods, and data
channel assignment.
The most significant gains were made in channel modeling
[15], [16] and modulation. The gains in modulation are discussed
here because these gains had a direct impact on spectrum utilization. It is common for a test range to test multiple test articles from
multiple programs simultaneously. Each test article is assigned
a unique carrier frequency in a frequency division multiplexing
(FDM) scheme. Because test articles from different programs require different data rates, the bandwidths required for test articles
from different programs are different. In addition, guard bands are
required to compensate for Doppler shift and near-far adjacent
channel interference. The number of test articles that can be simultaneously tested is determined by the spectral allocation. In this
setting, reducing the bandwidth occupied by the telemetry signal
either increases the number of test articles that can be simultaneously tested, or permits testing of high-data-rate test articles without the need to reschedule the tests of other test articles.
Severe size, weight, and power constraints on airborne test
articles dictate the use of RF power amplifiers operating in full
saturation. Consequently, compatible modulations, such as those
with constant envelope, are used in aeronautical telemetry. Continuous Phase Modulation (CPM) is the most popular class of
constant envelope modulations. For this reason, the search for
more bandwidth-efficient modulations was restricted to the CPM
family.
At the time the WCS and DARS reallocations took place, a
CPM variant known as pulse code modulation/frequency modulation (PCM/FM) had been the modulation of choice for at least a
quarter century. PCM/FM is a partial response CPM with a binary
alphabet, modulation index h = 0.7, and a pulse shape spanning
3-bit times [2]. The most commonly used detection algorithm was

IEEE A&E SYSTEMS MAGAZINE

DECEMBER 2018

Aerospace and Electronic Systems - December 2018

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