Abstract
In order to achieve more efficient overall spectrum utilization, it is possible to employ cognitive beamforming for secondary spectrum access. An important issue in such spatial spectrum sharing techniques is protecting the primary user from interference which arises due to estimation errors when the secondary users try to locate the available transmit opportunities. In this paper, we investigate the issue of primary user protection when the secondary user allocates too many spatial streams for the secondary transmission. We provide analysis for the interference power statistics and take advantage of the moment matching method in order to obtain an expression for the interference power that is tractable for practical analysis. In addition, we propose a protection constraint which limits the resulting interference and protects the primary user in terms of interference outage probability. We also show the achievable transmit power for the secondary user which can satisfy the protection constraint.
