Spatial Spectrum Holes for Cognitive Radio With Directional Transmission
In this paper, the authors propose a Cognitive Radio (CR) transmission scheme, which enables secondary users to coexist with primary users by exploiting Spatial Spectrum Holes (SSHs) through directional antennas or antenna arrays with beamforming. To ensure reliable CR links and avoid interference to primary users, some CR users may act as relays. They investigate successful communication probability of CR users when this scheme is applied. They further demonstrate that the spectrum efficiency can be greatly improved by multiplexing CR links with directional transmission.