Utilizing Multipath Clusters in Cognitive Radio Systems

In this paper, we introduce a new technique that allows the coexistence of secondary users (SUs) with a primary user (PU), in the same frequency and time. The proposed technique (i.e., the cluster-based spatial opportunistic spectrum sharing (CB-SOSS) technique) exploits the spatial degrees of freedom resulting from the use of multiple antennas at both the secondary base station (SBS) and SUs; also it does not have any requirement regarding the number of antennas at the primary base station nor the PU. The CB-SOSS benefits from the fact that in wireless channels, the multipath components travel in clusters that are non-uniformly distributed in the spatio-temporal space. The key idea is to have the SBS become aware of the locations of the strong clusters in the surrounding environment and utilize them opportunistically for data transmission to the SUs, without causing a harmful interference at the PU receiver.