Security Performance Of Multi-Antenna Wiretap Channel

The broadcast nature of wireless communication calls for careful security considerations. Information theoretic security of wireless channels has attracted a great deal of interests recently, and different wireless channel models and their security limits have been extensively studied. In this paper, we study the security performance of multi-antenna wireless channel from information theoretic viewpoint. The main contributions of the thesis are summarized as follows.Firstly, the achievable secrecy rate of the multiple input single output (MISO) wiretap channel is studied. We assume that the transmitter has perfect channel state information (CSI) for their links to legitimate receiver, but it has only imperfect CSI for their channels to eavesdroppers. Optimal transmit covariance matrix is obtained based on worst-case secrecy rate maximization, under power constraints. The maximum secrecy rate computation can be formulated as a non-convex optimal problem, which cannot be solved directly. In this thesis, we transform non-convex optimal problem into a quasi-convex optimal problem which can be efficiently solved with the bisection method. We also study the robust wiretap transmission problem for the case with a quality of service constraint at the legitimate receiver. The simulation result and analysis demonstrate the effectiveness of our methods.Secondly, we also investigate a multiple-input multiple-output (MIMO) Gaussian wiretap channel with a transmitter, a legitimate receiver, an eavesdropper and an external helper, each equipped with multiple antennas. The transmitter sends confidential messages to its intended receiver, while the helper transmits jamming signals independent of the source message to confuse the eavesdropper. The jamming signal is assumed to be treated as noise at both the intended receiver and the eavesdropper. The helper performs beamforming based on the generalized singular value decomposition (GSVD) with uniform power allocation. Our numerical results demonstrated that the proposed scheme achieves a notable improvement in secrecy rate in the high SNR.