Communications surveillance

Offboard Active Surveillance and Communications

A phase conjugate "mirror" time reverses the incident signal precisely returning it to its original source location. This phenomenon occurs independent of the complexity of the medium. The time-reversal process can be accomplished by the implementation of a retransmission procedure. A signal received at an array is time reversed and retransmitted. A full water column source array excited by the...

Communications and Privacy under Surveillance

Wireless Surveillance of Two-Hop Communications

Wireless surveillance is becoming increasingly important to protect the public security by legitimately eavesdropping suspicious wireless communications. This paper studies the wireless surveillance of a two-hop suspicious communication link by a half-duplex legitimate monitor. By exploring the suspicious link’s two-hop nature, the monitor can adaptively choose among the following three eavesdr...

SHORT COMMUNICATIONS

SHORT COMMUNICATIONS

Underwater Communications for Video Surveillance Systems at 2.4 GHz

Video surveillance is needed to control many activities performed in underwater environments. The use of wired media can be a problem since the material specially designed for underwater environments is very expensive. In order to transmit the images and videos wirelessly under water, three main technologies can be used: acoustic waves, which do not provide high bandwidth, optical signals, alth...