DIRECTIONAL SENSITIVE MODULATION SIGNAL TRANSMITTED BY MONOPULSE CASSEGRAIN ANTENNA FOR PHYSICAL LAYER SECURE COMMUNICATION

The broadcast nature of the wireless medium makes the communication over this medium vulnerable to eavesdropping. In this paper, we propose a directional sensitive modulation signal transmitted by Monopulse Cassegrain antenna for physical (PHY) layer security transmission. The main idea is that the sum beam transmit communication signal, simultaneously, and two difference beams transmit artificial noise to guarantee secure transmission of the sum beam. The eavesdropper's channel is degraded by artificial noise, but the desired receiver's channel does not affect because of the spatial orthogonality between the sum beam and two difference beams. In this way, the desired receiver can demodulate the communication signal while the eavesdroppers learn almost nothing about the information from its observations. A closed-form expression of the secrecy capacity is also derived for this practical transmit scheme from the viewpoint of information theoretic. Finally, simulation results show that the proposed signal can significantly improve the performance of secure wireless communications.