Secure Transmission in Multicell Massive MIMO Systems

TLDR

The study investigates physical‑layer security for multicell massive MIMO downlink transmission using matched‑filter precoding and artificial noise against a passive multi‑antenna eavesdropper. It analyzes achievable ergodic secrecy rates and outage probabilities under perfect training and pilot contamination, comparing conventional null‑space and random artificial‑noise shaping matrices to reduce complexity. Results show that artificial noise is essential for positive secrecy rates when user and eavesdropper share path loss, secure transmission can fail with many eavesdropper antennas or insufficient estimation power, the secrecy rate under pilot contamination is non‑monotonic with base‑station antennas, and random AN shaping offers a favorable performance‑complexity trade‑off.

Abstract

In this paper, we consider physical layer security provisioning in multicell massive multiple-input-multiple-output (MIMO) systems. Specifically, we consider secure downlink transmission in a multicell massive MIMO system with matched-filter precoding and artificial noise (AN) generation at the base station (BS) in the presence of a passive multiantenna eavesdropper. We investigate the resulting achievable ergodic secrecy rate and the secrecy outage probability for the cases of perfect training and pilot contamination. Thereby, we consider two different AN shaping matrices, namely, the conventional AN shaping matrix, where the AN is transmitted in the null space of the matrix formed by all user channels, and a random AN shaping matrix, which avoids the complexity associated with finding the null space of a large matrix. Our analytical and numerical results reveal the following, in multicell massive MIMO systems employing matched-filter precoding: 1) AN generation is required to achieve a positive ergodic secrecy rate if the user and the eavesdropper experience the same path loss; 2) even with AN generation, secure transmission may not be possible if the number of eavesdropper antennas is too large and not enough power is allocated to channel estimation; 3) for a given fraction of power allocated to AN and a given number of users, in case of pilot contamination, the ergodic secrecy rate is not a monotonically increasing function of the number of BS antennas; and 4) random AN shaping matrices provide a favorable performance/complexity tradeoff and are an attractive alternative to conventional AN shaping matrices.