DOF Augmentation via IRS for Line-of-Sight Communication

This paper analyzes the effect of deploying an intelligent reflective surface (IRS) in line-of-sight conditions at sub-terahertz frequencies. Besides the more obvious benefits of enhancing the received power and sidestepping blockages, at these frequencies an IRS can augment the number of spatial degrees of freedom even as the transmitter and receiver footprints remain fixed. This possibility, which is revealed only if the curved nature of the wavefronts is accounted for, results from the IRS acting as a lens that enables resolving denser spatial multiplexings. Provided the signal-to-noise ratio is minimally high, this DOF augmentation then translates to a hefty improvement in spectral efficiency.