[Paper Review] Physical Layer Security for NOMA: Requirements, Merits, Challenges, and Recommendations

Haji M. Furqan, Jehad M. Hamamreh+1 more|arXiv (Cornell University)|May 13, 2019

Advanced Wireless Communication Technologies17 references35 citations

TL;DR

This paper surveys security design requirements for downlink PD-NOMA using physical layer security (PLS), outlines security design objectives for external/internal eavesdroppers, discusses merits of PLS in NOMA, and highlights challenges with future directions.

ABSTRACT

Non-Orthogonal Multiple Access (NOMA) has been recognized as one of the most significant enabling technologies for future wireless systems due to its eminent spectral efficiency, ability to provide an additional degree of freedom for Ultra Reliable Low Latency Communications (URLLC) and grant free random access. Meanwhile, Physical Layer Security (PLS) has got much attention for future wireless communication systems due to its capability to provide security without relying on traditional cryptography based algorithms. In this article, security design requirements for NOMA and solutions provided by PLS to fulfill these requirements are discussed. The merits and challenges arising from employing PLS to NOMA are identified. Finally, future recommendations and prospective solutions are also presented.

Motivation & Objective

• Explain security risks in downlink PD-NOMA and how PLS can address them.
• Identify security design objectives against external, internal, and combined eavesdroppers.
• Discuss PLS techniques (beamforming, AN, power allocation, cooperative jamming) and their applicability to NOMA.
• Highlight advantages of PLS in NOMA compared to OMA and propose future research directions.

Proposed method

• Review downlink PD-NOMA system model with one near user and one far user in the presence of an eavesdropper.
• Classify NOMA flavors and present SIC-based decoding principles relevant to security.
• Survey PLS design techniques (beamforming, artificial noise, power allocation, cooperative relaying/jamming) under external/internal eavesdropping scenarios.
• Discuss performance merits of PLS-enabled NOMA and implications for large-scale/UW networks and RIS-assisted security.
• Outline challenges, open problems, and directions for cross-layer and RIS-assisted security for NOMA.

Experimental results

Research questions

• RQ1 How can PLS techniques be designed to secure downlink PD-NOMA against external eavesdroppers without degrading SIC?
• RQ2 How can internal eavesdroppers (untrusted users) be mitigated in NOMA while preserving legitimate decoding performance?
• RQ3 What are the main challenges and potential solutions for secure NOMA in multi-cell, RIS-enabled, and cross-layer contexts?
• RQ4 What future research directions can enhance PLS for NOMA in 5G and beyond?
• RQ5 Does NOMA provide secrecy advantages over OMA under various CSI and environment conditions?

Key findings

• PLS provides higher potential secrecy performance in NOMA by exploiting multi-user interference and flexible power allocation.
• AN and beamforming can enhance security against external eavesdroppers when CSI is available, with design challenges under imperfect CSI.
• Security design against internal eavesdroppers requires transforming signals or careful beamforming/power strategies to protect the far and near users without harming SIC.
• Internal and external eavesdropping scenarios are most challenging and may require signal domain transformations and cooperative strategies.
• RIS-assisted and cross-layer approaches are promising future directions to improve PLS in NOMA while maintaining SIC integrity.