Opportunistic jammer selection for secure degrees of freedom

In this paper, we propose two opportunistic jammer selection schemes for secure communications aided by jammers using the concept of interference alignment. Because jamming signals are interference to both a legitimate receiver and a eavesdropper, the legitimate receiver selects two jammers whose jamming signals are the most aligned in a small dimensional subspace. The alignment is measured by either interference-to-noise ratio (INR) or chordal distance for the opportunistic jammer selection. We find the achievable secure degrees of freedom (DoF) by the proposed jammer selection schemes when the number of jammers goes to infinity and find the computational complexity of each scheme.