Secure Wireless Communication via Polarforming

TL;DR

This work addresses secure wireless transmission by exploiting polarization DoFs through polarforming with polarization-reconfigurable antennas. It develops an alternating optimization framework that jointly designs transmit beamforming $\mathbf{w}$ and polarization phase shifts $\boldsymbol{\vartheta}$ to maximize the secrecy rate $R_{\sec}$, employing a closed-form solution for beamforming and a convex SDP approach (with Charnes–Cooper transformation and Gaussian randomization) for polarforming. Simulation results show substantial secrecy-rate gains over fixed-polarization antennas, with faster convergence and robustness to moderate eavesdropper-channel errors; the method still degrades gracefully as the eavesdropper gains more antennas. The work demonstrates a practical pathway to harness both spatial and polarization degrees of freedom to strengthen physical-layer security in wireless systems, and suggests extensions to multi-eavesdropper scenarios and imperfect CSI.

Abstract

Polarforming is a promising technique that enables dynamic adjustment of antenna polarization to mitigate depolarization effects commonly encountered during electromagnetic (EM) wave propagation. In this letter, we investigate the polarforming design for secure wireless communication systems, where the base station (BS) is equipped with polarization-reconfigurable antennas (PRAs) and can flexibly adjust the antenna polarization to transmit confidential information to a legitimate user in the presence of an eavesdropper. To maximize the achievable secrecy rate, we propose an efficient iterative algorithm to jointly optimize transmit beamforming and polarforming, where beamforming exploits spatial degrees of freedom (DoFs) to steer the transmit beam toward the user, while polarforming leverages polarization DoFs to align the polarization state of the EM wave received by the user with that of its antenna. Simulation results demonstrate that, compared to conventional fixed-polarization antenna (FPA) systems, polarforming can fully exploit the DoFs in antenna polarization optimization to significantly enhance the security performance of wireless communication systems.

Figures (6)

• Figure 1: Illustration of the system model.
• Figure 2: Convergence behavior of Algorithm \ref{['alg1']}.
• Figure 3: Secrecy rate and eavesdropper's rate versus SNR.
• Figure 4: Secrecy rate and channel cross-correlation versus number of BS's antennas.
• Figure 5: Secrecy rate and eavesdropper's rate versus normalized variance of eavesdropper's polarized channel error.