# Cell-Free Massive MIMO-Based Physical-Layer Authentication

## TL;DR

This paper introduces a cell-free massive MIMO-based physical-layer authentication framework that securely authenticates multiple users and resists impersonation attacks, using channel estimation and secret key sharing.

## Contribution

It proposes a novel tag-based authentication scheme leveraging CF-mMIMO architecture with a hypothesis testing approach for secure multi-user authentication.

## Key findings

- High detection probability maintained with increasing users
- Effective resistance against impersonation attacks
- Closed-form expression for detection probability derived

## Abstract

In this paper, we exploit the cell-free massive multiple-input multiple-output (CF-mMIMO) architecture to design a physical-layer authentication (PLA) framework that can simultaneously authenticate multiple distributed users across the coverage area. Our proposed scheme remains effective even in the presence of active adversaries attempting impersonation attacks to disrupt the authentication process. Specifically, we introduce a tag-based PLA CFmMIMO system, wherein the access points (APs) first estimate their channels with the legitimate users during an uplink training phase. Subsequently, a unique secret key is generated and securely shared between each user and the APs. We then formulate a hypothesis testing problem and derive a closed-form expression for the probability of detection for each user in the network. Numerical results validate the effectiveness of the proposed approach, demonstrating that it maintains a high detection probability even as the number of users in the system increases.