  This paper presents a novel time synchronization attack (TSA) model for the
Global Positioning System (GPS) based on clock data behavior changes in a
higher-order derivative domain. Further, the time synchronization attack
rejection and mitigation based on sparse domain (TSARM-S) is presented. TSAs
affect stationary GPS receivers in applications where precise timing is
required, such as cellular communications, financial transactions, and
monitoring of the electric power grid. In the present work, the clock bias and
clock drift are monitored at higher-order clock data derivatives where the TSA
is seen as a sparse spike-like event. The smoothness of the attack relates to
the derivative order where the sparsity is observed. The proposed method
jointly estimates a dynamic solution for GPS timing and rejects behavior
changes based on such sparse events. An evaluation procedure is presented for
two testbeds, namely a commercial receiver and a software-defined radio.
Further, the proposed method is evaluated against distinct real-dataset Texas
Spoofing Test Battery (TEXBAT) scenarios. Combined synthetic and real-data
results show an average RMS clock bias error of 12.08 m for the SDR platform,
and 45.74 m for the commercial device. Further, the technique is evaluated
against state-of-the-art mitigation techniques and in a spoofing-plus-multipath
scenario for robustness. Finally, TSARM-S can be potentially optimized and
implemented in commercial devices via a firmware upgrade.
