  In this paper, interference alignment (IA) is designed for secure multiuser
multiple-input multiple-output systems in the presence of an eavesdropper. The
proposed IA technique designs the transmit precoding and receiving subspace
matrices to minimize both the total inter-main-link interference and the
wiretapped signals. With perfect channel state information is known at the
transmitters (Txs), the cost function of the optimization problem is
alternatively minimized over the precoding matrices at the Txs and the
receiving subspace matrices at the receivers (Rxs) and the eavesdropper. The
feasible condition, the proof of convergence of the proposed IA approach are
provided. Numerical results reveal a significant improvement in terms of
average secrecy sum rate of our IA algorithm as compared to the conventional IA
design.
