Adaptive MMSE-based Precoding in Multiuser MIMO Broadcasting with Application to Cognitive Radio

Since cognitive radio (CR) in conjunction with non-orthogonal multiple access is a candidate techniques for future mobile radio networks, realizing underlay spectrum sharing with high capacity gain is an important issue. In this paper, we propose an adaptive linear precoder design for a CR based multiuser MIMO broadcasting system. The proposed adaptive precoder employs regularized channel inversion based on the minimum mean square error criterion (MMSE). Unlike the conventional MMSE based precoder, the proposed adaptive MMSE based precoding approach develops a new kind of diversity, so-called "precoding diversity" which considerably improves the signal-to-interference-plus-noise (SINR) ratio at the receiver of each cognitive user (CU) while fulfilling the interference constraint at the primary user (PU). Simulation results illustrate that the proposed adaptive MMSE based precoder can achieve good SNR and spectral efficiency gains outperforming the state-of-the-art.