  Unmanned aerial vehicles (UAVs) can be integrated into wireless sensor
networks (WSNs) for smart city applications in several ways. Among them, a UAV
can be employed as a relay in a "store-carry and forward" fashion by uploading
data from ground sensors and metering devices and, then, downloading it to a
central unit. However, both the uploading and downloading phases can be prone
to potential threats and attacks. As a legacy from traditional wireless
networks, the jamming attack is still one of the major and serious threats to
UAV-aided communications, especially when also the jammer is mobile, e.g., it
is mounted on a UAV or inside a terrestrial vehicle. In this paper, we
investigate anti-jamming communications for UAV-aided WSNs operating over
doubly-selective channels in the downloading phase. In such a scenario, the
signals transmitted by the UAV and the malicious mobile jammer undergo both
time dispersion due to multipath propagation effects and frequency dispersion
caused by their mobility. To suppress high-power jamming signals, we propose a
blind physical-layer technique that jointly detects the UAV and jammer symbols
through serial disturbance cancellation based on symbol-level post-sorting of
the detector output. Amplitudes, phases, time delays, and Doppler shifts -
required to implement the proposed detection strategy - are blindly estimated
from data through the use of algorithms that exploit the
almost-cyclostationarity properties of the received signal and the detailed
structure of multicarrier modulation format. Simulation results corroborate the
anti-jamming capabilities of the proposed method, for different mobility
scenarios of the jammer.
