Efficient beamforming in MIMO cognitive radio systems

In cognitive radio (CR) networks, unlicensed users known as secondary users (SUs) can share the same spectrum with the licensed users known as primary users (PUs) on condition that the SUs interference must not exceed a certain level on PUs. Our target is to provide the SUs with a minimum acceptable quality-of-service (QoS), while keeping the interference to the PUs below a given threshold. However, the problem is not easy in case of MIMO CR systems as the optimization is not convex anymore. In addition, it is not easy to know the channel state information on the links to PUs, thus uncertainty should be considered on PUs links. In this paper, we consider the spectrum sharing multiple input-multiple-output (MIMO) cognitive radio networks, in which multiple primary users (PUs) coexist with multiple secondary users (SUs). We propose a modified iterative solution to calculate optimal transceiver beamforming weights and power levels of the SUs network. Moreover, the realistic situation of uncertainty on PUs links has been studied. The proposed iterative solution is compared in terms of efficiency with another iterative solution. Finally, simulations results are presented to show the effectiveness of the proposed algorithm.