An Overview of Physical Layer Security for IRS-Assisted Downlink Multi-User Massive MIMO Systems

As a research hot-spot, intelligent reflecting surface (IRS) aided downlink multi-user Massive Multiple-input and Multiple output (MIMO) is one of the most important tech-nologies for the 6th Generation (6G) wireless communications. It significantly improves the spectral efficiency and coverage of wireless communication systems. However, the passive eavesdrop-ping threat becomes much more serious and can not be negligible. In this paper, focusing on the multi-IRS aided downlink multi-user Massive MIMO, an overview for the corresponding physical layer security (PLS) methods is presented, and some potential and valuable future research works on PLS for IRS-assisted downlink Massive MIMO are discussed.

I. Introduction

As one of the key technologies of 6th Generation (6G) wireless communication, massive multiple-input and multiple-output (Massive MIMO) technology uses hundreds of base station antennas to serve dozens of users at the same time and at the same frequency. Compared with traditional MIMO technology, Massive MIMO can provide richer degrees of freedom and share its multiplexing gain among more users. It can significantly improve the spectral efficiency and coverage of wireless communication systems. However, the complex topology of Massive MIMO communication networks and the open nature of wireless links, while enhancing communication performance for legitimate users, also provide greater opportunities for eavesdroppers to intercept. Unlike the upper-layer encryption or authentication techniques with high computationally complexity, Time Division Duplex (TDD) Massive MIMO technology can take advantage of the short-time reciprocity of wireless channels in coherent time to design lightweight physical layer security methods. It can significantly enhance the security performance of the systems [1], [2].