  Supporting reliable and seamless wireless connectivity for unmanned aerial
vehicles (UAVs) has recently become a critical requirement to enable various
different use cases of UAVs. Due to their widespread deployment footprint,
cellular networks can support beyond visual line of sight (BVLOS)
communications for UAVs. In this paper, we consider cellular connected UAVs
(C-UAVs) that are served by massive multiple-input-multiple-output (MIMO) links
to extend coverage range, while also improving physical layer security and
authentication. We consider Rician channel and propose a novel linear precoder
design for transmitting data and artificial noise (AN). We derive the
closed-form expression of the ergodic secrecy rate of C-UAVs for both
conventional and proposed precoder designs. In addition, we obtain the optimal
power splitting factor that divides the power between data and AN by asymptotic
analysis. Then, we apply the proposed precoder design in the fingerprint
embedding authentication framework, where the goal is to minimize the
probability of detection of the authentication tag at an eavesdropper. In
simulation results, we show the superiority of the proposed precoder in both
secrecy rate and the authentication probability considering moderate and large
number of antenna massive MIMO scenarios.
