An Overview of Physical Layer Security with Finite-Alphabet Signaling

TL;DR

This paper reviews recent advances in physical layer security focusing on finite-alphabet signaling, highlighting the differences from Gaussian inputs and discussing design algorithms, scenarios, and open challenges for practical secure communication systems.

Contribution

It provides a comprehensive overview of physical layer security with discrete signals, including design algorithms, scenario analyses, and practical code constructions, addressing a gap in existing Gaussian-focused research.

Findings

Finite-alphabet inputs significantly affect security performance.

Design algorithms vary with channel state information assumptions.

Practical coding schemes are emerging for secure discrete signaling.

Abstract

Providing secure communications over the physical layer with the objective of achieving perfect secrecy without requiring a secret key has been receiving growing attention within the past decade. The vast majority of the existing studies in the area of physical layer security focus exclusively on the scenarios where the channel inputs are Gaussian distributed. However, in practice, the signals employed for transmission are drawn from discrete signal constellations such as phase shift keying and quadrature amplitude modulation. Hence, understanding the impact of the finite-alphabet input constraints and designing secure transmission schemes under this assumption is a mandatory step towards a practical implementation of physical layer security. With this motivation, this article reviews recent developments on physical layer security with finite-alphabet inputs. We explore transmit signal design algorithms for single-antenna as well as multi-antenna wiretap channels under different assumptions on the channel state information at the transmitter. Moreover, we present a review of the recent results on secure transmission with discrete signaling for various scenarios including multi-carrier transmission systems, broadcast channels with confidential messages, cognitive multiple access and relay networks. Throughout the article, we stress the important behavioral differences of discrete versus Gaussian inputs in the context of the physical layer security. We also present an overview of practical code construction over Gaussian and fading wiretap channels, and we discuss some open problems and directions for future research.