  Physical watermarking is a well established technique for replay attack
detection in cyber-physical systems (CPSs). Most of the watermarking methods
proposed in the literature are designed for discrete-time systems. In general,
real physical systems evolve in continuous time. In this paper, we analyze the
effect of watermarking on sampled-data continuous-time systems controlled via a
Zero-Order Hold. We investigate the effect of sampling on detection performance
and we provide a procedure to find a suitable sampling period that ensures
detectability and acceptable control performance. Simulations on a quadrotor
system are used to illustrate the effectiveness of the theoretical results.

Systems and Control;Systems and Control