Grover-Based PLS: Active User Detection and Beamforming with Artificial Noise in CD-NOMA

Jul 16, 2026

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Sixth-Generation (6G) networks demand massive connectivity, ultra-low latency, and strong security, making reliable Active User Detection (AUD) critical for interference control and physical layer protection. This letter presents a Grover-based physical layer security (PLS) framework for codedomain non-orthogonal multiple access (CD-NOMA), using artificial-noise (AN)-assisted beamforming and Grover’s quantum search to identify the active set. It defines passive and active eavesdropper threat models and shows a larger main–wiretap rate gap, higher average secrecy rate, and quadratic search-complexity reduction. Numerical simulations study power-splitting, base-station transmit power, and highly active eavesdropper fraction to extract design guidance for 6G PLS.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages5

Reading Time13 min

Introduction

Physical layer security in 6G and role of active user detection

Artificial-noise assisted beamforming

Quantum search and Grover-based AUD background

Grover-Based PLS: AUD and Beamforming with Artiﬁcial Noise in CD-NOMA Deemah H. Tashman, Member, IEEE, and Soumaya Cherkaoui, Senior Member, IEEE arXiv :2607 .05429v 1 [ cs .IT] 2 Jul 2026 Abstract—Sixth-Generation (6G) networks will require massive connectivity, ultra-low latency, and robust security, making reliable Active User Detection (AUD) essential for interference control and physical layer protection. This letter proposes a Grover-based physical layer security (PLS) framework for a codedomain non-orthogonal multiple access (CD-NOMA) network, where the base station employs artiﬁcial-noise (AN)-assisted beamforming and identiﬁes the active set via Grover’s quantum search algorithm. We consider two threat models: passive eavesdroppers formed by detected inactive users, and active eavesdroppers selected as the top f % most frequent transmitters among detected active users. By aligning beams and AN with the Grover-based AUD output, the proposed scheme enlarges the main–wiretap rate gap and signiﬁcantly improves the average secrecy rate compared with compressive sensing and classical correlation receiver baselines, while approaching maximumlikelihood detection performance with a quadratic reduction in search complexity. The impact of the information/AN power split, the base station transmit power, and the fraction of highly active users treated as eavesdroppers on secrecy is characterized through numerical simulations, and design insights are extracted for 6G PLS under both passive and active eavesdropping. Index Terms—Artiﬁcial noise, beamforming, Grover-based AUD, physical layer security. I. INTRODUCTION PHYSICAL layer security (PLS) is expected to play a central role in Sixth-Generation (6G) wireless networks, where massive connectivity and heterogeneous services exacerbate the risk of eavesdropping. PLS guaranties conﬁdentiality by ensuring that the capacity of the legitimate (main) link exceeds that of the wiretap link, typically by enhancing the desired channel and/or degrading adversarial channels. Among available techniques, artiﬁcial-noise (AN) assisted beamforming has proven effective, as it steers information signals toward legitimate users while injecting AN in the null space of their channels, thereby jamming unauthorized receivers with limited interference to intended users [1] . The effectiveness of such PLS schemes critically depends on accurately identifying the active legitimate users and likely eavesdroppers. In grant-free code-domain non-orthogonal multiple access (CDNOMA) system, user activity must be inferred from noisy superpositions of code-domain signatures, and the search overactivity patterns grows combinatorially with the number of potential users, making conventional active user detection (AUD) methods increasingly complex and error-prone. D. Tashman and S. Cherkaoui are with LINCS Laboratory, Department of Computer and Software Engineering, Polytechnique Montreal, Montreal, QC, Canada, H3T 1J4 (e-mail: {deemah.tashman, [soumaya.cherkaoui](soumaya.cherkaoui}@polymtl.ca)[}](soumaya.cherkaoui}@polymtl.ca)[@polymtl.ca](soumaya.cherkaoui}@polymtl.ca)). LINCS Lab website: [https://lincslab.ca/en/](https://lincslab.ca/en/) Quantum search offers an attractive alternative by exploiting superposition and parallelism to reduce search complexity while maintaining high detection accuracy. For instance, Grover quantum search algorithm and traditional algorithms were contrasted in [2] for the AUD process in a NOMA system, focusing exclusively on the impact of noise. In [3], a comparable investigation was conducted with regard to optical code division multiple access, where the Durr and Høyer quantum search technique was implemented to identify active users in wireless systems. The authors in [4] proposed quantum minimum-searching algorithms for AUD in wireless IoT networks by adapting Durr and Høyer-based search techniques and exploiting prior system knowledge to reduce complexity. Moreover,

FAQs

What problem does the Grover-based AUD solve in CD-NOMA PLS?

It identifies the active user set from noisy superpositions of code-domain signatures, helping the base station align beamforming and artificial noise toward legitimate users while disrupting wiretap reception.

How does the scheme model passive versus active eavesdroppers?

Passive eavesdroppers correspond to detected inactive users, while active eavesdroppers are chosen as the top f% most frequent transmitters among detected active users.

What performance benefits are reported compared with existing detection baselines?

The method enlarges the main–wiretap rate gap and improves average secrecy rate versus compressive sensing and classical correlation receiver baselines, while approaching maximum-likelihood detection performance with quadratic reduction in search complexity.

Jul 16, 2026

Upload by Ezra