Wireless Surveillance with Half-Duplex Monitors

In this paper, we study a wireless surveillance scenario where a central monitor covertly wiretaps the communications between a pair of suspicious users via half-duplex (HD) monitors. For this system, it is necessary to ensure the eavesdropping channel capacity higher than the data rate of the suspicious users so that the central monitor can reliably decode the intercepted information. To this end, the HD monitors operate in either eavesdropping or jamming modes. The eavesdropping monitors forward the intercepted data from the suspicious users to the central monitor, while the jamming monitors transmit jamming signals to control the data rate of the suspicious users if necessary. We optimize the mode selection and transmit power of each HD monitor to achieve the maximum eavesdropping rate. Globally optimal solutions are developed for joint mode selection and transmit power optimization problems. Numerical results validate the effectiveness of our proposed algorithms.