In this paper, intelligent reflecting surfaces (IRSs) are employed to enhance
the physical layer security in a challenging radio environment. In particular,
a multi-antenna access point (AP) has to serve multiple single-antenna
legitimate users, which do not have line-of-sight communication links, in the
presence of multiple multi-antenna potential eavesdroppers whose channel state
information (CSI) is not perfectly known. Artificial noise (AN) is transmitted
from the AP to deliberately impair the eavesdropping channels for security
provisioning. We investigate the joint design of the beamformers and AN
covariance matrix at the AP and the phase shifters at the IRSs for maximization
of the system sum-rate while limiting the maximum information leakage to the
potential eavesdroppers. To this end, we formulate a robust nonconvex
optimization problem taking into account the impact of the imperfect CSI of the
eavesdropping channels. To address the non-convexity of the optimization
problem, an efficient algorithm is developed by capitalizing on alternating
optimization, a penalty-based approach, successive convex approximation, and
semidefinite relaxation. Simulation results show that IRSs can significantly
improve the system secrecy performance compared to conventional architectures
without IRS. Furthermore, our results unveil that, for physical layer security,
uniformly distributing the reflecting elements among multiple IRSs is
preferable over deploying them at a single IRS.

本文研究如何利用智能反射表面和人工噪声增强多天线 AP 和多个单天线合法用户之间的物理层安全，同时减少潜在窃听者之间的信息泄漏，提出了一种非凸优化算法，并通过模拟结果证明了智能反射表面对物理层安全性能的显著改进。

利用智能反射表面实现稳健安全的无线通信

Robust and Secure Wireless Communications via Intelligent Reflecting  Surfaces

We consider a full-duplex (FD) multiuser system where an FD base station (BS)
is designed to simultaneously serve both downlink (DL) and uplink (UL) users in
the presence of half-duplex eavesdroppers (Eves). The problem is to maximize
the minimum (max-min) secrecy rate (SR) among all legitimate users, where the
information signals at the FD-BS are accompanied with artificial noise to
debilitate the Eves' channels. To enhance the max-min SR, a major part of the
power budget should be allocated to serve the users with poor channel
qualities, such as those far from the FD-BS, undermining the SR for other
users, and thus compromising the SR per-user. In addition, the main obstacle in
designing an FD system is due to the self-interference (SI) and co-channel
interference (CCI) among users. We therefore propose an alternative solution,
where the FD-BS uses a fraction of the time block to serve near DL users and
far UL users, and the remaining fractional time to serve other users. The
proposed scheme mitigates the harmful effects of SI, CCI and multiuser
interference, and provides system robustness. The SR optimization problem has a
highly nonconcave and nonsmooth objective, subject to nonconvex constraints.
For the case of perfect channel state information (CSI), we develop a
low-complexity path-following algorithm, which involves only a simple convex
program of moderate dimension at each iteration. We show that our
path-following algorithm guarantees convergence at least to a local optimum.
Then, we extend the path-following algorithm to the cases of partially known
Eves' CSI, where only statistics of CSI for the Eves are known, and worst-case
scenario in which Eves can employ a more advanced linear decoder. The merit of
our proposed approach is further demonstrated by extensive numerical results.

考虑多用户系统的最小保密速率问题，提出使用全双工天线并通过噪声干扰敌方信道以提高最小保密速率，并使用路径追踪算法来优化方案。

安全全双工多用户系统的新设计范式

A New Design Paradigm for Secure Full-Duplex Multiuser Systems

This paper considers the problem of secret communication over a two-receiver
multiple-input multiple-output (MIMO) Gaussian broadcast channel. The
transmitter has two independent messages, each of which is intended for one of
the receivers but needs to be kept asymptotically perfectly secret from the
other. It is shown that, surprisingly, under a matrix power constraint both
messages can be simultaneously transmitted at their respective maximal secrecy
rates. To prove this result, the MIMO Gaussian wiretap channel is revisited and
a new characterization of its secrecy capacity is provided via a new coding
scheme that uses artificial noise and random binning.

该研究考虑在一个双接收机的多输入多输出高斯广播信道上进行秘密通信的问题，并证明在矩阵功率约束下，两个独立信息可以同时传输到各自的最大保密率，通过使用人工噪声和随机分箱的新编码方案，提供了新的机密容量特征描述。