Research & Innovation 2015-16 - Page 107



Feature
Using FM radio broadcasts to make
air traffic control safer for Africa
Africa has the highest accident rate per flying hour in the world, and the lack
of regional air traffic is crippling development in Africa. In the meantime,
FM radio broadcasting is experiencing a meteoric rise, serving as the
dominant mass medium in Africa.
These two facts may seem unrelated, but to members
of the Commensal Radar Project, the proliferation of FM
radio waves can in fact provide affordable and safe air
traffic control in Africa and the developing world.
Developing an alternative system
Very few African countries other than South Africa have
radar systems installed at their airports. As it stands, pilots
flying across the continent have to rely on a manual system
to avoid aircraft collisions. “The pilots know who is taking
off from where, and when, and they talk over the radio to
coordinate their routes,” says Professor Michael Inggs of
the Department of Electrical Engineering and the Radar
Remote Sensing Group.
He stresses that this is a situation that cannot continue: “As the
continent develops, we will see a massive growth in air traffic,”
he says. But a radar system can cost around $10 million –
prohibitively expensive for many developing countries.
Inggs and his team at the Commensal Radar Project, a
collaboration between UCT, the Council for Scientific
and Industrial Research (CSIR) and Peralex Electronics,
have developed an alternative radar system – using FM
transmissions, and a number of receivers spread out across
many hundreds of kilometres and connected by cell phone
links – to track the location of aircraft, with an accuracy of
100 metres or closer. This, says Inggs, is more than adequate
for air traffic control safety standards. Work is currently
underway to commercialise this technology.
Building the Commensal Radar
The Commensal Radar Project started around the year
2000. Inggs read about a researcher in Europe who was
using television signals to track aircraft, and began to
investigate a similar solution for Africa. “For technical
reasons, I found using FM more effective than television
signals,” he says. The aircraft reflects the FM signal, which
can be picked up through a receiver. At the same time, as
the aircraft moves through the signal, a phenomenon called
the doppler shift occurs. This is a change in the frequency
of a wave, such as a sound wave or a radio wave, depending
on the speed of an object and the position of an observer.
The simplest example is an ambulance siren: when the
ambulance is coming towards you, the pitch of the siren is
different from when it is moving away from you.
“The term ‘commensal’ is biological,” explains Inggs. “It refers
to a system where two organisms share a relationship in which
one may benefit from the existence of the other, but the
organisms don’t affect one another.” This perfectly describes
the relationship between the receivers of the Commensal
Radar Project and the FM radio transmitters. The project’s
receivers use the FM transmission to track aircraft, but the
transmitters themselves are not affected by this – they simply
keep transmitting pop music and talk shows to listeners.
Exceptional problem solvers
The project faced a number of challenges, most of which
were solved by a sequence of exceptional PhD students
grappling with the applied mathematics problems faced
in the project – including Craig Tong, who worked on
developing the software to receive and process the
signals. Francois Maasdorp resolved the ambiguity over
pinpointing and tracking a single aircraft when there are
other aircraft on an ellipse around it (This mathematical
challenge was based on the work of a PhD student
from Chad, Roaldje Nadjiasngar.). The final step was a
demonstration, tracking South African Airways planes
coming into Cape Town.
It is for this work that the Commensal Radar Project
was award Gold at the annual AVI (Africa Aviation
Innovation) Awards in late 2015. The project has also just
been awarded the IEEE Harry Rowed Mimno Award for
clear dissemination of technical material.
By Natalie Simon. Image by Hansueli Krapf, Wikimedia
Commons.
Industry, innovation and infrastructure 102

Wikimedia CommonsEEE Harry Rowed Mimno Award





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