Spatial Interweave Opportunistic Spectrum Reuse by Employing Distributed Interference Alignment

Consider spatial interweave opportunistic spectrum reuse scheme, primary user with power constraints maximizes its achievable rate by water-filling its power on singular values of its channel links and leaving some eigen modes free to use. Therefore, secondary user can transmit using this free subspace in order to avoid interference at primary receiver. By employing transmit beamforming, secondary user can design its precoding matrix, where the interference to primary user can be aligned to the free subspace. As a result of non-degraded primary user´s performance, perfect channel state information (CSI) is required at secondary transmitter. Unfortunately, this kind of CSI is hard to realize, it is therefore in this paper to investigate a limited CSI scheme. By secondary transmitter sensing the label of the Grassmannian quantized channel vectors, the proposed criterion can upper-bound the overall interference at primary receiver with a constant value, which is independent of secondary transmit power. We also study an alternative primary user power allocation strategy in order to balance the overall system performance.