  In this paper, the physical layer security of a dual-hop unmanned aerial
vehicle-based wireless network, subject to imperfect channel state information
(CSI) and mobility effects, is analyzed. Specifically, a source node $(S)$
communicates with a destination node $(D)$ through a decode-and-forward relay
$(R)$, in the presence of two wiretappers $\left(E_{1},E_{2}\right)$
independently trying to compromise the two hops. Furthermore, the transmit
nodes $\left(S,R\right) $ have a single transmit antenna, while the receivers
$\left(R,D,E_{1},E_{2}\right) $ are equipped with multiple receive antennas.
Based on the per-hop signal-to-noise ratios (SNRs) and correlated secrecy
capacities' statistics, a closed-form expression for the secrecy intercept
probability (IP) metric is derived, in terms of key system parameters.
Additionally, asymptotic expressions are revealed for two scenarios, namely (i)
mobile nodes with imperfect CSI and (ii) static nodes with perfect CSI. The
results show that a zero secrecy diversity order is manifested for the first
scenario, due to the presence of a ceiling value of the average SNR, while the
IP drops linearly at high average SNR in the second one, where the achievable
diversity order depends on the fading parameters and number of antennas of the
legitimate links/nodes. Furthermore, for static nodes, the system can be
castigated by a $15$ dB secrecy loss at IP$=3\times10^{-3},$ when the CSI
imperfection power raises from $0$ to $10^{-3}$. Lastly, the higher the
legitimate nodes' speed, carrier frequency, delay, and/or relay's decoding
threshold SNR, the worse is the system's secrecy. Monte Carlo simulations
endorse the derived analytical results.
