  Multiple robots could perceive a scene (e.g., detect objects) collaboratively
better than individuals, although easily suffer from adversarial attacks when
using deep learning. This could be addressed by the adversarial defense, but
its training requires the often-unknown attacking mechanism. Differently, we
propose ROBOSAC, a novel sampling-based defense strategy generalizable to
unseen attackers. Our key idea is that collaborative perception should lead to
consensus rather than dissensus in results compared to individual perception.
This leads to our hypothesize-and-verify framework: perception results with and
without collaboration from a random subset of teammates are compared until
reaching a consensus. In such a framework, more teammates in the sampled subset
often entail better perception performance but require longer sampling time to
reject potential attackers. Thus, we derive how many sampling trials are needed
to ensure the desired size of an attacker-free subset, or equivalently, the
maximum size of such a subset that we can successfully sample within a given
number of trials. We validate our method on the task of collaborative 3D object
detection in autonomous driving scenarios.
