  Integrating unmanned aerial vehicles (UAVs) into future wireless systems such
as the fifth-generation (5G) cellular network is anticipated to bring
significant benefits for both UAV and telecommunication industries. Generally
speaking, UAVs can be used as new aerial platforms in the cellular network to
provide communication services for terrestrial users, or become new aerial
users of the cellular network served by the terrestrial base stations. Due to
their high altitude, UAVs usually have dominant line-of-sight (LoS) channels
with the ground nodes, which, however, pose new security challenges to future
wireless networks with widely deployed UAVs. On one hand, UAV-ground
communications are more prone than terrestrial communications to eavesdropping
and jamming attacks by malicious nodes on the ground. On the other hand,
compared to malicious ground nodes, malicious UAVs can launch more effective
eavesdropping and jamming attacks to terrestrial communications. Motivated by
the above, in this article, we aim to identify such new issues from a
physical-layer security viewpoint and propose novel solutions to tackle them
efficiently. Numerical results are provided to validate their effectiveness and
promising directions for future research are also discussed.
