Securing Massive MIMO Via Power Scaling

In this work, we study how fast we are able to scale down the power for both training and data transmission while guaranteeing security in a massive MIMO network without the help of artificial noise. We consider a multicell network with a large number of base station (BS) and eavesdropper antennas, but limited number of cells and mobile users. By offering an achievable lower bound on secrecy rate for both uplink and downlink, we observe that we can always find a power scaling approach for security as long as the ratio of the number of eavesdropper antennas to the number of BS antennas is smaller than a threshold. In particular, we find that when the eavesdropper and its targeting receiver share the same distance to the information source, the threshold is exactly the total pilot power received at the BS for uplink training.