IEEE - Aerospace and Electronic Systems - July 2022 - 13

Kassas et al.
opportune signals from which it draws navigation and timing
information, employing signal characterization on-the-fly as
necessary. MATRIX could produce a navigation solution in a
standalone fashion or by fusing SOPswith sensors (e.g., IMU,
lidar, etc.), digital maps, and/or other signals (e.g., GNSS).
Figure 6 shows MATRIX's architecture. The conducted
experiment used MATRIX's carrier-aided code phase-based
LTE module [48] to produce LTE navigation observables.
Figure 7 shows the graphical user interface (GUI) front panel
ofthe LTEmodule of MATRIX.
PNT EXPERIMENTAL RESULTS IN THE GPS-JAMMED
ENVIRONMENT
Two experiments were conducted to study the behavior of
SOPs in the presence of real GPS jamming and to assess
their potential as PNT sources. The results from each
experiment are presented as follows.
EXPERIMENT 1: STATIONARY RECEIVER
Cellular SOPs are typically equipped with GPSDOs to
meet the synchronization requirements set by the 3rd Generation
Partnership Project (3GPP). Some opportunistic
navigation frameworks exploit the resulting stability of
cellular SOPs' clock [30], making it important to evaluate
the clock stability of cellular SOPs under GPS jamming to
determine their suitability in radio SLAM.
SETUP
The setup described in the sections " Hardware Setup " and
" Software Setup " was deployed outside the jamming area
to listen to two LTE eNodeBs (SOP 1 and SOP 2) located
in an area affected by jamming. The jamming-to-signal
(J=S) at the eNodeBs was around 60 dBs. During this
experiment, the jammers were periodically turned on for
10 min, then turned off for 2 min. The MATRIX SDR
sampled LTE signals synchronously at 10 Msps for 95
Figure 8.
Experiment 1 setup. The setup discussed in sections " Hardware
Setup " and " Software Setup " was deployed outside the GPSjammed
area to listen to two SOPs located in an area where J=S
was around 60 dB. Map data: Google Earth.
min on carrier frequencies 751 MHz and 731.5 MHz,
which are frequencies allocated to U.S. cellular providers
Verizon Wireless and T-Mobile, respectively. Figure 8
shows the setup of the first experiment.
RESULTS
The LTE signal samples were processed by the LTE module
ofMATRIX to produce pseudorange observables to the
two eNodeBs. The two LTE eNodeBs as well as the
receiver were stationary and at known locations. The true
range between the receiver and each eNodeB was subtracted
from the corresponding pseudorange measurements
[cf. (8)]. Figure 9(a) shows the time history of the remaining
term (after subtracting the initial pseudorange values).
Note that a 5-min dataloss occurred around the 35th minute
due to a hardware malfunction. Recalling that the measurement
noise is appropriately modeled as white, the trend in
the variations, as shown in Figure 9(a) is mainly due to the
relative clock biases between the eNodeBs and the
receiver. After a short initial transient due to the receiver's
GPSDO, the clock biases seem to stabilize. Moreover, both
clock biases appear to be driven by a common term, which
is likely to be the receiver's bias. To evaluate the relative
Figure 9.
Experiment 1 results. (a) Time history of clock biases corresponding to SOP 1 and SOP 2. The initial pseudorange values were subtracted. A
hardware malfunction around the 35th min caused a 5-min dataloss. (b) Clock bias difference between SOP 1 and SOP 2, without subtracting
the initial pseudoranges. The stable difference shows that the relative stability between LTE SOPs is maintained for a period of over 95 min
during GPSjamming.
JULY 2022
IEEE A&E SYSTEMS MAGAZINE
13

IEEE - Aerospace and Electronic Systems - July 2022

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