Orthogonal Beamforming Methodology in Cognitive Radio Networks

Cognitive radio technique has been considered as a strong solution of frequency scarcity due to the limitation of frequency resource. In this paper, we propose an orthogonal beamforming methodology which enables cognitive radio systems to coexist with primary users´ systems in the same spectrum and region with no interference to the primary users´ systems. The orthogonal beams are obtained using Gram-Schmidt orthogonalization based on primary users´ channel state information. In addition, to increase the sum-rate of the CR systems, the proposed scheme adopts an opportunistic beamforming method. Numerical results demonstrate that the proposed scheme does not cause interference to the primary users and provides higher sum-rate capacity than that of conventional CR systems.