A leakage-based dimensionality reduction beamforming for MIMO cognitive radio networks

In order to improve the spectral efficiency, in cognitive radio (CR) network with multiple-input multiple-output (MIMO) links, several secondary users (SU) equipped with multi-antenna intend to communicate with others in an underlay manner by sharing the frequency which is originally allocated to a primary user simultaneously. For such a scenario, secondary users need to suppress the interference caused to primary user and the primary system shouldn´t even notice the presence of the secondary system. In this paper, we study the optimal secondary-link beamforming pattern that to maximize the secondary users´ signal-to-leakage-and-noise ratio (SLNR) as well as nullify the interference to the primary user. In particular, dimensionality reduction techniques are used to design beamforming vector for the optimal spatial-frequency domain transmit that earns the interference avoidance at the primary user even when the number of receive antenna exceed that of transmit antenna. Simulation results show that compared to the conventional scheme, our proposed method can achieve a desirable performance of both BER and channel capacity.