Physical Layer Security in Downlink Multi-Antenna Cellular Networks

Abstract

In this paper, we study physical layer security for the downlink of cellular\nnetworks, where the confidential messages transmitted to each mobile user can\nbe eavesdropped by both (i) the other users in the same cell and (ii) the users\nin the other cells. The locations of base stations and mobile users are modeled\nas two independent two-dimensional Poisson point processes. Using the proposed\nmodel, we analyze the secrecy rates achievable by regularized channel inversion\n(RCI) precoding by performing a large-system analysis that combines tools from\nstochastic geometry and random matrix theory. We obtain approximations for the\nprobability of secrecy outage and the mean secrecy rate, and characterize\nregimes where RCI precoding achieves a nonzero secrecy rate. We find that\nunlike isolated cells, the secrecy rate in a cellular network does not grow\nmonotonically with the transmit power, and the network tends to be in secrecy\noutage if the transmit power grows unbounded. Furthermore, we show that there\nis an optimal value for the base station deployment density that maximizes the\nsecrecy rate, and this value is a decreasing function of the signal-to-noise\nratio.\n