Cooperative precoding with limited feedback in multi-user cognitive MIMO networks

This paper focuses on linear precoding in a cognitive radio (CR) multi-input multi-output (MIMO) network, where a secondary broadcast channel shares the same spectrum with a licensed primary user (PU). Considering cooperative feedback from PU to the secondary transmitter (ST), a linear precoding scheme is proposed to minimize the expected mean square error (MSE) and null out the interference to the PU. The proposed scheme is an improved approach, which is robust to the channel uncertainties caused by quantization errors and the lack of channel quality information (CQI). Furthermore, interference power control (IPC) is applied at the ST to adjust the transmit power under the tolerable interference threshold of the PU. Simulation results show the effectiveness of the proposed scheme compared with the zero-forcing (ZF) and the conventional minimum mean square error (C-MMSE) criteria.