Avionics News July 2023 - 31

33 hours before authorities found the source and shut it down.
Air traffic was disrupted at Dallas for 44 hours, according
to government sources, though researchers found the actual
interference lasted for 24 hours. The source of the disruption
was never identified. "
Goward reported that Stanford University Ph.D. candidate
Zixi Liu studied low Navigation Integrity Category in San Antonio
and Del Rio, some distance away from Dallas-Fort Worth
where airlines reported problems. She found that military
training aircraft performing aerobatics with unusual attitudes
caused navigation receivers to intermittently lose lock on GPS
satellite signals, so the aircraft's ADS-B systems reported low
navigation integrity. She is working on finding the cause of the
Dallas-Fort Worth problems in October of last year.
According to a U.S. Government Accountability Office
report on Dec. 15, 2022, the Department of Transportation
needs to improve its efforts to identify GPS disruption and the
transportation sector's ability to withstand and recover from
it. The information on GPS interference incidents gathered by
DOT is incomplete and inaccurate, the report noted.
The DOT identified 196 potential GPS interference incidents
from January 2020 through May 2022, but it didn't gather
all available user reports. The DOT has not documented its
process for identifying disruption incidents nor established
controls to produce complete and accurate information. Surprisingly,
only one person in the department knows how the
existing process works, according to the GAO report.
The DOT received $1 million in fiscal year 2022 to develop
a GPS interference monitoring system working with the
Department of Homeland Security, the Department of Defense
and other agencies. The plan is to develop new algorithms to
provide the needed capability while leveraging existing equipment
with little in the way of hardware modifications, according
to an email from a DOT spokesperson. The DOT will seek
additional funding for fiscal year 2023.
The system will tap multiple air, land, sea and space and cyber
domain technologies and employ artificial intelligence and
machine learning algorithms to examine data from numerous
GPS/GNSS sensors, ADS-B, automatic identification systems,
Internet of Things mobility data and other sources. The
common operational picture for GPS-based PNT situational
awareness will be available to all GPS users, including aviation.
The system will provide nationwide coverage, including
Alaska and Hawaii.
GPS interference reports will be followed up by federal
agencies and checked against software, equipment malfunction,
operator error and authorized GPS test events. The status
of the GPS constellation will also be checked. The Federal
Communications Commission and law enforcement will be
included in the loop when needed.
An exciting idea proposed by Scott and others is to use
cellphones as GPS interference detectors/locators. This would
be analogous to current use for detecting and publicizing traffic
slowdowns. Users would have to agree, and their identities
would, of course, be hidden. The result would be a heat map
similar to the GPS jam map referenced above. It would pinpoint,
in real time, areas that need further action.
In addition to shutting down and dealing with interference,
the PNTAB wants to toughen GPS civil receivers, especially
aviation, against jamming and spoofing or other system threats.
In a presentation, Parkinson stated that technology and designs
are well known and available to make a 1-kilowatt GPS jammer
virtually ineffective. By having an electronically steered array,
a receiver can use beam-steering to boost the gain on a satnav
signal and also null against a jammer/spoofer threat. Thus, an
ESA can deal with both the jamming and spoofing threat.
When he led the development of GPS in the 1970s, Parkinson
sponsored the hardware demonstration of such capability.
Wright Patterson Air Force Base contracted with Rockwell
Collins in Cedar Rapids, Iowa, to test their anti-jam GPS
receiver design. The test was a great success. The system on an
aircraft could fly over a 10-kilowatt jammer with no effect.
A key point in all of this is that International Traffic in
Arms Regulation, enforced by the federal government, precludes
more than three elements in beam-steering antennas.
So, U.S. manufacturers are not making jam resistant GPS
for civil use. Some overseas avionics manufacturers are not
constrained in this way.
For example, Tualcom Electronic in Ankara, Turkey, touts
its controlled reception pattern antenna with up to eight
elements as the smallest anti-jam GNS system on the market
today for civil GPS, Galileo, BieDou and Glonass reception.
So far, 2,500 have been sold mostly for use in the Middle East,
including on Iranian remotely piloted vehicles.
Tualcom claimed the unit's jamming resistance is more than
10,000 times what the U.S. government allows for commercial
aircraft. Parkinson's presentation noted that if U.S. commercial
aircraft were so equipped, the U.S. concerns of GPS commercial
interference (including from Ligado) would " nearly vanish. "
The system operates normally in the presence of multiple
jamming sources. Tualcom intends to introduce a 16-element
system this year. If a general aviation aircraft owner installed
such a system on his aircraft in the U.S., he or she might get in
trouble with the authorities.
Parkinson would have preferred that civil GPS receivers
be optionally equipped with anti-jamming capability from
the time GPS was declared operational. While anti-jamming
capability has been fielded by the military, civilians cannot
violate the ITAR regulations. Today, new signals and signal
processing, deep integration with inertial sensors and the
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