User selection in multiuser MIMO systems with secrecy considerations

This paper investigates simple user selection strategies in a multiuser downlink system with a single transmitter, multiple legitimate receivers, and a single eavesdropper, where all nodes are equipped with multiple antennas. No information regarding the eavesdropper is presumed at the transmitter, and we examine the MIMO downlink channel with either single or multiple data streams per receiver. The transmitter uses linear beamforming techniques based on generalized zero-forcing with a corresponding minimum SINR or rate requirement per receiver. In both cases the information signal is transmitted with just enough power to guarantee the desired Quality-of-Service (QoS) at the desired receivers, while the remainder of the power is used to broadcast artificial noise that selectively degrades the passive eavesdropper's signal. Numerical simulations displaying the power consumption and the number of selected users provided by each selection scheme demonstrate the effectiveness of the proposed schedulers in ensuring physical-layer security.