Application of full duplex guarantees secure wireless communication.

This paper proposes an amplify-and-forward (AF) based scheme for full duplex systems to realize secure wireless communication between two nodes over block fading medium. The paper consider all four possible scenarios: Multiple-input and multiple-output (MIMO), multiple-input and single-output (MISO), single-input and multi-output (SIMO), and single-input and single-output (SISO) systems. We first devise communication protocol of the scheme that does not bring additional communication cost. The core of the protocol is amplify-and-forward process, in which artificial noise sent by the receiver is amplified and retransmitted by the transmitter with information signal back to the receiver. Since the receiver has the knowledge of the noise, the artificial noise only degrades the eavesdropper. Then, we present the form of the artificial noise for the four scenarios respectively. Thereafter, we derive the closed form expressions of secrecy capacity, and reformulate them irrelevant to the channel of the eavesdropper. This makes our scheme valid when the transmitter does not know any information about the eavesdropper. We investigate the solution for the secrecy capacity optimization problem in SISO scenario at first, which can be extended to SIMO, MISO, and MIMO systems. The optimization problems are easy to solve and have analytical solutions. Numerical results are presented to show the validation of our scheme.