Grover-Based PLS: AUD and Beamforming with Artificial Noise in CD-NOMA
This work addresses the need for secure and efficient active user detection in 6G networks under passive and active eavesdropping threats.
The paper proposes a Grover-based physical layer security framework for CD-NOMA that uses artificial-noise-assisted beamforming and quantum search for active user detection, achieving improved secrecy rates over compressive sensing and classical correlation receivers while approaching maximum-likelihood performance with quadratic complexity reduction.
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 code-domain 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 maximum-likelihood 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.