IEEE - Aerospace and Electronic Systems - July 2022 - 5

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SOPs enjoy several inherently desirable attributes for
navigation purposes:
1) abundance in most locales of interest;
2) transmission at a wide range of frequencies and
directions;
3) reception at a carrier-to-noise ratio (C=N0) that is
commonly tens of dBs higher than that of GNSS
signals;
4) they are free to use, since their infrastructure is
already operational.
While SOPs are jammable and spoofable [22]-[24],
they are transmitted in multiple frequency bands and are
typically received outdoors at high C=N0. In the case of
cellular SOPs, for example, they are received at more than
30 dBs higher C=N0 than GNSS signals [25]. They also
span the 700 MHz to nearly 6 GHz bands, excluding the
5G millimeter wave (mmWave) spectrum, which is envisioned
to span several GHz of spectrum, with some bands
reaching up to 400 MHz ofbandwidth. This makes staging
a successful, clandestine attack on cellular SOPs generally
challenging, as the attacker would need to target the entire
cellular spectrum with very high power. A typical challenge
that arises in SOP-based navigation is that unlike
GNSS, whose satellite states are transmitted in their navigation
message, the states of SOPs, namely their position
and clock states, are typically unknown a priori and must
be estimated. To overcome this challenge, a radio simultaneous
localization and mapping (radio SLAM) framework
was proposed in which the states of the navigating vehicle
are simultaneously estimated with the states of the SOPs
[26], while aiding the INS in a tightly coupled fashion
[27]. Recent works have demonstrated meter-level-accurate
navigation with SOPs on ground vehicles and pedestrians
indoors [28], [29] and submeter-level accurate
navigation on aerial vehicles [30]. While published results
in the literature have demonstrated experimentally the
efficacy of SOPs as PNT sources in a standalone fashion
JULY 2022
(i.e., without fusing SOPs with other signals or sensors)
and in an integrated fashion (i.e., fusing SOPs with INS
and lidar), experiments were never conducted in actual
GNSS-denied environments. These results were achieved
by " fictitiously " cutting GNSS signals from the navigation
filter. In September 2019, the authors' Autonomous Systems
Perception, Intelligence, and Navigation (ASPIN)
Laboratory was invited to participate in live GPSjamming
experiments, called Developmental Test Navigation Festival
(DT NAVFEST), at Edwards Air Force Base (AFB),
California, USA. Experiments with stationary antennas
and ground vehicles were conducted to study SOPs for
PNT. This article reports findings from these experiments,
which represent the first published results evaluating the
efficacy of SOPs for PNT in a real GPS-denied environment.
In particular, this article analyzes the clock errors of
terrestrial cellular long-term evolution (LTE) SOPs
located inside the jammed region, showing timing stability
over 95 min of GPS jamming. Moreover, this article
showcases the efficacy of the radio SLAM approach on a
ground vehicle navigating in the jammed environment,
while exploiting a terrestrial cellular LTE SOP. The
results show the vehicle navigating during GPS jamming
for 5 km in 180 s, during which the position root meansquared
error (RMSE) of a traditional GPS-aided INS
IEEE - Aerospace and Electronic Systems - July 2022

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