Asymptotic throughput analysis of random beamforming for multi‐antenna cognitive broadcast networks

Random beamforming (RBF) has received much attention recently in downlink beamforming because of its simple structure, low‐feedback load and same throughput scaling as that obtained using dirty paper coding at the transmitter. In this study, the authors analyse the performance of RBF for cognitive downlink multi‐antenna system in terms of the throughput of the secondary network. The authors consider a secondary broadcast station with multiple antennas utilising the licensed spectrum of each primary receiver to broadcast information to multiple secondary users (SUs) simultaneously, as long as the interference power inflicted at each primary receiver is less than a predefined threshold. Firstly, they derived the secondary network closed‐form throughput approximation of a single‐beam RBF by exploiting extreme value order statistics. Then, closed‐form approximation for secondary network throughput on multiple‐beam RBF is presented. Simulation results verify the validity of the authors approximation results analysis even with fewer SUs.