Abstract

In this contribution, we introduce an interference align-ment scheme that allows the coexistence of an orthogonal frequency division multiplexing (OFDM) macro-cell and a cognitive small-cell, deployed in a two-tiered structure and transmitting over the same bandwidth. We derive the opti-mal linear strategy for the single antenna secondary base sta-tion, maximizing the spectral efficiency of the opportunistic link, accounting for both signal sub-space structure and power loading strategy. Our analytical and numerical findings prove that the precoder structure proposed is optimal for the consid-ered scenario in the face of Rayleigh and exponential decay-ing channels. 1.