Joint Beamforming and Scheduling Design in Hierarchical Cognitive Radio Networks

Cognitive radio (CR) has been recently regarded as an important technique to improve spectrum utilization. In the thesis, we present a joint design approach to integrate power allocation, antenna beamforming and user scheduling to maximize the system sum rate of multiple users in the hierarchical CR networks with multicarrier transmissions. Concurrent transmissions between CR users and licensed users are considered to improve the spectrum efficiency. The challenge of hierarchical CR networks is to manage mutual interference between the CR and licensed systems. We first apply the semi-definite relaxation (SDR) technique to transfer the original mixed integer non-linear problem (MINLP) to a convex problem. Then, a sum rate optimization algorithm is proposed to determine the optimal power allocation, antenna beamforming and user scheduling under the limitation of the interference to the licensed networks. The simulation results show that the proposed algorithm can improve the sum rate at least 20% compared to an exhaustive search user scheduling plus zero-forcing beamforming, while overcoming the primary system with sacrifice of 10% sum rate below the maximum sum rate. The proposed methodology provides many important insights into the system design and deployment principles for future hierarchical CR networks.