Interference Mitigation for Cognitive Radio MIMO Systems Based on   Practical Precoding
  In this paper, we propose two subspace-projection-based precoding schemes, namely, full-projection (FP)- and partial-projection (PP)-based precoding, for a cognitive radio multiple-input multiple-output (CR-MIMO) network to mitigate its interference to a primary time-division-duplexing (TDD) system. The proposed precoding schemes are capable of estimating interference channels between CR and primary networks, and incorporating the interference from the primary to the CR system into CR precoding via a novel sensing approach. Then, the CR performance and resulting interference of the proposed precoding schemes are analyzed and evaluated. By fully projecting the CR transmission onto a null space of the interference channels, the FP-based precoding scheme can effectively avoid interfering the primary system with boosted CR throughput. While, the PP-based scheme is able to further improve the CR throughput by partially projecting its transmission onto the null space. 
Zengmao Chen, Cheng-Xiang Wang, Xuemin Hong, John Thompson, Sergiy A.   Vorobyov, Feng Zhao, Hailin Xiao, and Xiaohu Ge
cs.IT math.IT