Tech Briefs Magazine - December 2023 - 26

Communications
A reconfigurable intelligent surface
(RIS) is a panel of many individual reflective
elements, each of which can
modify an incoming signal and reflect it.
This modification can be controlled with
an electrical signal, which enables the
RIS to improve the connection or generate
signals that are useful for locating
users in the network.
The researchers developed a new localization
system where an RIS can work
as a satellite to improve accuracy. By
making a surface smart, it can bounce
signals to cell phones which in turn can
use these signals to generate an accurate
estimate of location. An accurate location
estimate is not only useful for location
services but also to improve transmission
from the tower to the phone
using optimized location-aware transmission
schemes that also leverage the RIS.
" Users never expect to have a call
drop, and they also expect lightning-fast
data speeds, " he said. " But to
accomplish this, the networks require
constant updating. "
The researchers tested their theory using
multiple modulated RISs that allow
for the simultaneous localization of multiple
users with low complexity for each
RIS. They also developed and tested
RIS-enabled transmission schemes that
outperform existing schemes.
" We simulated the proposed localization
protocol and demonstrated its effectiveness
in an urban micro-cell street
canyon scenario as an example, "
Chaaban explained. " And the protocol
works for multiple users simultaneously.
Even in areas with intermittent service,
data can be shared and users can be located
and enjoy a reliable connection. "
For more information, contact Patty
Wellborn at patty.wellborn@ubc.ca; 250317-0293.
Exploiting
Signals Broadcast by Multi-Constellation
LEO Satellites
The algorithm can make satellite signals act like GPS and be more reliable, safer than
current system.
Ohio State University, Columbus, Ohio
R
esearchers have developed an algorithm
that can " eavesdrop " on any
signal from a satellite and use it to locate
any point on Earth, much like GPS. The
study represents the first time an algorithm
was able to exploit signals broadcast
by multi-constellation low-Earth orbit
(LEO) satellites, namely Starlink,
OneWeb, Orbcomm, and Iridium.
Researchers found that by listening
to the signals of eight LEO satellites for
about 10 minutes, their algorithm
could achieve unprecedented accuracy
in locating a stationary receiver on the
ground and was able to converge on it
with an error of only about 5.8 meters.
The research was led by Zak Kassas,
Professor of Electrical and Computer
Engineering at The Ohio State University
and Director of the Department of
Transportation Center for Automated
Vehicles Research with Multimodal AssurEd
Navigation (CARMEN).
The researchers did not need assistance
from the satellite operators to
use the signals, and they emphasized
that they had no access to the actual
data being sent through the satellites
- only to publicly available information
related to the satellites' downlink
transmission frequency and a rough estimate
of the satellites' location.
From transportation to communication
systems to the power grid and emergency
services, nearly every aspect of
modern society relies on positioning,
26
navigation and timing data from global
navigation satellite systems (GNSS), or
GPS, that orbit the Earth. Despite this,
because GPS system signals are weak and
susceptible to interference, they can often
become unreliable in certain places
such as indoor environments or in deep
urban canyons. In addition, GNSS signals
are spoofable, which poses serious
security risks in safety-critical applications,
such as aviation.
In the long term, such complications
could lead to a number of navigational
and cybersecurity issues, especially as
virtually all of our current systems rely
heavily on GPS, Kassas said. Technologies
on the rise, such as autonomous
vehicles, he noted, are beginning to
amplify the limitations of our current
GNSS systems.
" It's becoming more pressing to find
civilian and military alternatives to
GPS, whether as a backup or in the case
when GPS isn't there whatsoever, " said
Kassas.
His work suggests utilizing signals
from LEO satellites as an alternative for
humans' positioning, navigation, and
timing needs, as they reside about 20
times closer to Earth compared to
GNSS satellites, which reside in medium
Earth orbit - a little more than
20,000 km above the planet. According
to Kassas, the technology could potentially
usher in a new era of positioning,
navigation, and timing.
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" We are witnessing a space renaissance.
Tens of thousands of LEO satellites
will be launched into space over
the next decade, leading to what is referred
to as mega-constellations, " he
said. " Signals transmitted by these satellites
will revolutionize
numerous
technologies and benefit scientific inquiry
in fields such as remote sensing. "
What also makes the study so different
from all other attempts at creating
an alternative to GPS is, unlike previous
studies, this algorithm doesn't reverse
engineer the signal, said Kassas.
" Our algorithm is agnostic to the
LEO constellation, " said Kassas. " Our
receiver can listen to virtually any satellite
signal, trains on the data it's receiving
on-the-fly, then deciphers certain
features of the signal in a way where we
can reconstruct what they are transmitting
into location data. "
To demonstrate the team's new approach,
the team applied the algorithm
to four different LEO satellite
constellations: Starlink, OneWeb, Orbcomm,
and Iridium. The algorithm
cracked all these signals, with virtually
no prior knowledge about what is being
transmitted.
Although a patent has been filed on
the algorithm, the team does plan to
continue evolving all of the algorithm's
technical abilities, said Kassas.
For more information, contact Tatyana
Woodall at Woodall.52@osu.edu.
Tech Briefs, December 2023
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Tech Briefs Magazine - December 2023

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