  In this paper, we study the problem of physical layer security in large-scale
multiple input multiple output (LS-MIMO) systems. The large number of antenna
elements in LS-MIMO system is exploited to enhance transmission security and
improve system performance, especially when the eavesdropper is closer to the
information source and has more antennas than the legitimate user. However, in
practical systems, the problem becomes challenging because the eavesdropper
channel state information (CSI) is usually unavailable without cooperation and
the legitimate CSI may be imperfect due to channel estimation error. In this
paper, we first analyze the performance of physical layer security without
eavesdropper CSI and with imperfect legitimate CSI, and then propose an
energy-efficient power allocation scheme to meet the demand for wireless
security and quality of service (QoS) simultaneously. Finally, numerical
results validate the effectiveness of the proposed scheme.
