Joint Precoding and Artificial Noise Design for MU-MIMO Wiretap Channels

TL;DR

This paper introduces a novel joint optimization algorithm for precoding and artificial noise in MU-MIMO wiretap channels, significantly enhancing secrecy rates by solving a complex nonlinear eigenvalue problem.

Contribution

It proposes a new secure precoding method that jointly optimizes beams and artificial noise, overcoming limitations of traditional alternating optimization approaches.

Findings

Improved secrecy rate compared to existing methods

Efficient algorithm for solving the nonlinear eigenvalue problem

Effective in scenarios with perfect or partial eavesdropper channel knowledge

Abstract

Secure precoding superimposed with artificial noise (AN) is a promising transmission technique to improve security by harnessing the superposition nature of the wireless medium. However, finding a jointly optimal precoding and AN structure is very challenging in downlink multi-user multiple-input multiple-output (MU-MIMO) wiretap channels with multiple eavesdroppers. The major challenge in maximizing the secrecy rate arises from the non-convexity and non-smoothness of the rate function. Traditionally, an alternating optimization framework that identifies beamforming vectors and AN covariance matrix has been adopted; yet this alternating approach has limitations in maximizing the secrecy rate. In this paper, we put forth a novel secure precoding algorithm that jointly and simultaneously optimizes the beams and AN covariance matrix for maximizing the secrecy rate when a transmitter has either perfect or partial channel knowledge of eavesdroppers. To this end, we first establish an approximate secrecy rate in a smooth function. Then, we derive the first-order optimality condition in the form of the nonlinear eigenvalue problem (NEP). We present a computationally efficient algorithm to identify the principal eigenvector of the NEP as a suboptimal solution for secure precoding. Simulations demonstrate that the proposed methods improve secrecy rate significantly compared to the existing secure precoding methods.