On precoding diversity in cognitive networks

In this paper, we propose an adaptive linear pre-coder design for an underlay cognitive radio (CR) multiuser MIMO broadcasting system. The proposed adaptive precoder employs regularized channel inversion based on the minimum mean square error (MMSE) criterion. Unlike the conventional MMSE precoder, the proposed precoder exploits degrees of freedom not being used so far, which considerably improves the signal-to-interference-plus-noise (SINR) ratio at the receiver of each CR user while fulfilling the underlay CR constraints. Simulation results illustrate good SNR and spectral efficiency gains over the state-of-the-art.