Mobility-Assisted Covert Communication over Wireless Ad Hoc Networks

We study the capacity scaling of the covert communication over a wireless ad hoc network where n mobile nodes want to communicate each other in a unit disk while keeping the presence of the communication secret from each of ⊝(ns) non-colluding wardens (0 < s < 1). We modify the two-hop based scheme by Grossglauser and Tse (2002), which is proposed for a wireless ad hoc network without a covertness constraint, by introducing a preservation region around each warden in which the senders are not allowed to transmit. This scheme is shown to be optimal under an assumption that each node outside the preservation regions uses the same transmit power. Our results show that the node mobility greatly improves the aggregate throughput, compared to the case of fixed node location. In particular, the aggregate throughput scaling is shown to be linear in n when the number of channel uses that each warden uses to judge the presence of communication is not too large compared to n.