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On Feasibility of Interference Alignment for Secure Transmission in Cooperative MIMO Systems
Lin Hu, Jiabing Fan, Hong Wen, Qianbin Chen
Abstract
To mitigate multi-user interference at legitimate receivers and assist secure transmission, artificial noise (AN) aided interference alignment (IA) is explored. The feasibility of traditional leakage minimization (LM) based IA is analyzed, including IA equations and rank constraint related to the secret signal transmission. We show that there exist two drawbacks which are not discussed in LM based IA security approaches: 1) the necessary condition for the feasibility of IA equations is loose, and 2) the secret signal cancellation may occur which makes secure transmission infeasible and in fact, there is no systematic analysis of this problem. We analyze the cause and establish a condition under which the secret signal cancellation is inevitable. Then a modified IA approach is proposed by implementing the max-eigenmode beamforming (MEB) for secure transmission. Compared with the traditional LM based IA, a tighter necessary condition can be established, and the secure transmission can be proctected. Numerical results confirm the effectiveness and usefulness of the modified IA approach.