Low-Complexity Antenna Selection and user Scheduling in Cognitive MIMO Broadcast Systems

In this paper, we consider the coexistence between a large number of cognitive radio users and a licensed user in order to enhance the spectrum efficiency. Zero-forcing beamforming (ZFB) is utilized as a downlink preceding technique that precancels inter-user interference in our multiuser cognitive multiple-input/multiple-output (MIMO) system. When there is a large number of users, the system performance can be significantly increased by selecting a subset of users and a set of receive antennas for each user. In particular, to reduce the complexity, we propose a receive antenna selection method followed by multiuser selection in order to maximize the downlink throughput as well as mitigate the interference to the primary user. Performance results show that our proposed method is able to achieve significant complexity reduction at the expense of a little sum-rate throughput loss.