Zero-forcing beamforming for secondary spectrum access in cooperative MIMO systems

In this paper, we propose a cooperative MIMO beamforming scheme for secondary spectrum access, where the wireless network consists of one primary pair PT-PR (primary transmitter-primary receiver) and one secondary pair ST-SR (secondary transmitter-secondary receiver). To secondary spectrum access without performance degrading of the primary system, ST generates and transmits superposed signal which is combined the primary and secondary signals with different weighting vectors. PR and SR extract a desired signal with a linear combiner to eliminate undesired interference. We also propose a joint optimization algorithm which choose optimum combiners satisfying zero-forcing (ZF) criterion at ST and SR. Simulation results show convergence speed of the proposed optimization algorithm and the achievable rate of secondary user with various antenna configurations and distance between nodes.