IEEE - Aerospace and Electronic Systems - July 2022 - 17

Kassas et al.
1 and 2 highlight this degradation in the performance.
However, the EKF error is a random process itself, and
can theoretically take arbitrary realizations from an underlying
distribution at any point in time. As such, the position
RMSE is a more insightful measure of the filter
performance. What is interesting is that the degradation of
the RMSE performance between Scenarios 1 and 2 is
about 3 m, which is on the same order of magnitude as the
SOP position estimation error in Scenario 2.
Third, the nature of the experiment makes it difficult
to be performed in an urban region. The environment in
which the experiment took place was rural, where cellular
SOPs tend not to be as abundant as urban regions. Within
the same region, one could receive signals from faraway
SOPs on an aerial platform compared to a ground platform.
As such, future studies could consider conducting
the experiments on an aerial platform, which would
increase the number of hearable SOPs.
CONCLUSION
This article justified why I am not afraid of the GPS jammer,
as long as there are ambient SOPs to exploit in the
environment. A radio SLAM approach was presented,
which enables the exploitation of SOPs for resilient navigation
in environments where GPS signals are challenged
or denied. Radio SLAM could produce an SOP-derived
navigation solution in a standalone fashion or by fusing
SOPs with sensors, digital maps, and/or other signals
(e.g., GNSS). This article presented the first published
experimental results for navigation with SOPs in a GPSdenied
environment. These experiments took place at
Edwards AFB, during DT NAVFEST, in which GPS was
intentionally jammed with J=S as high as 90 dB. The
results analyzed the clock stability of two cellular SOP
LTE eNodeBs in the jammed area, showing that the relative
stability between the LTE SOPs is maintained for a
period of more than 95 min during GPS jamming. Moreover,
the results showcased a ground vehicle traversing a
trajectory of about 5 km in 180 s in the GPS-jammed environment,
during which a GPS-IMU system drifted from
the vehicle's ground truth trajectory, resulting in a position
RMSE of 238 m. In contrast, the radio SLAM
approach with a single cellular LTE SOP whose position
was poorly known (an initial uncertainty on the order of
several kilometers) achieved a position RMSE of32 m.
ACKNOWLEDGMENTS
The authors would like to thank Edwards AFB for inviting
the ASPIN Laboratory to conduct experiments during DT
NAVFEST. The authors would also like to thank J.
Morales, K. Shamaei, M. Maaref, K. Semelka, M. Nguyen,
and T. Mortlock for their help with data collection.
JULY 2022
Distribution Statement A. Approved for public release;
Distribution is unlimited 412TW-PA-20399.
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