[Paper Review] OptM3Sec: Optimizing Multicast IRS-Aided Multiantenna DFRC Secrecy Channel with Multiple Eavesdroppers

Kumar Vijay Mishra, Arpan Chattopadhyay+2 more|arXiv (Cornell University)|Jan 24, 2022

Advanced Wireless Communication Technologies4 citations

TL;DR

This paper proposes OptM3Sec, a physical layer secrecy rate maximization framework for multicast multi-antenna dual-function radar-communications (DFRC) systems enhanced with intelligent reflecting surfaces (IRS) in the presence of multiple eavesdroppers (EDs). By jointly optimizing transmit precoding matrices and IRS phase shifts via a stochastic SPSA-based algorithm, the method achieves significant secrecy rate gains, especially under high transmit power and multiple ED conditions.

ABSTRACT

With the use of common signaling methods for dual-function radar-communications (DFRC) systems, the susceptibility of eavesdropping on messages aimed at legitimate users has worsened. For DFRC systems, the radar target may act as an eavesdropper (ED) that receives a high-energy signal thereby leading to additional challenges. Unlike prior works, we consider a multicast multi-antenna DFRC system with multiple EDs. We then propose a physical layer design approach to maximize the secrecy rate by installing intelligent reflecting surfaces in the radar channels. Our optimization of multiple ED multicast multi-antenna DFRC secrecy rate (OptM3Sec) approach solves this highly nonconvex problem with respect to the precoding matrices. Our numerical experiments demonstrate the feasibility of our algorithm in maximizing the secrecy rate in this DFRC setup.

Motivation & Objective

• Address the increased risk of eavesdropping in multicast multi-antenna DFRC systems, where radar targets can intercept communication signals due to high transmit power.
• Overcome the limitations of prior works that assume single eavesdroppers or unicast transmission, by modeling a more realistic scenario with multiple EDs.
• Maximize the secrecy rate in a multicast DFRC system by leveraging intelligent reflecting surfaces (IRS) to enhance secure communication while maintaining required signal-to-interference-and-noise ratio (SINR) at radar targets.
• Design a joint optimization framework for transmit precoding matrices and IRS phase shifts that accounts for both direct and indirect (via IRS) signal paths to legitimate users and eavesdroppers.
• Ensure feasibility and robustness by incorporating power constraints and SINR requirements for radar targets, even when they act as eavesdroppers.

Proposed method

• Formulate a secrecy rate maximization problem for a multicast multi-antenna DFRC system with multiple EDs, incorporating both direct and IRS-reflected channels.
• Model the system with a MIMO radar, multiple multi-antenna users, an IRS with N passive reflecting elements, and K multi-antenna eavesdroppers.
• Decompose the optimization into three subproblems: beamforming for legitimate users, artificial noise beamforming for EDs, and IRS phase shift optimization.
• Use a two-stage iterative algorithm: first optimize precoding matrices (W and B) for data and artificial noise, then optimize IRS phase shifts using simultaneous perturbation stochastic approximation (SPSA).
• Apply SPSA to handle the nonconvexity of the IRS phase shift optimization problem, using random perturbations and gradient approximation to iteratively update the phase shifts.
• Project phase shift updates onto [0, π] to maintain feasibility and ensure convergence under standard SPSA convergence conditions.

Experimental results

Research questions

• RQ1 How does the presence of multiple eavesdroppers affect the secrecy rate in a multicast multi-antenna DFRC system?
• RQ2 To what extent can intelligent reflecting surfaces (IRS) enhance secrecy rate in a DFRC system with multiple EDs?
• RQ3 What is the impact of joint optimization of transmit precoding and IRS phase shifts on secrecy rate performance compared to systems without IRS?
• RQ4 How does the secrecy rate scale with increasing transmit power in a multicast IRS-aided DFRC system with multiple EDs?
• RQ5 What is the performance gain of the proposed OptM3Sec algorithm in terms of secrecy rate compared to baseline schemes without IRS or with fixed IRS phases?

Key findings

• The proposed OptM3Sec algorithm significantly improves secrecy rate in multicast IRS-aided MIMO DFRC systems with multiple eavesdroppers, especially under high transmit power.
• With a single eavesdropper, the secrecy rate increases with transmit power, and the presence of IRS leads to a notable performance gain compared to systems without IRS.
• When two eavesdroppers are present, the secrecy rate decreases slightly due to increased eavesdropping capability, but the IRS still provides substantial rate improvement over non-IRS baselines.
• The SPSA-based optimization of IRS phase shifts effectively handles the nonconvexity of the problem and converges to a feasible and high-performing solution.
• The system maintains required SINR at radar targets (acting as EDs) by embedding artificial noise in the transmit waveform, ensuring both radar functionality and communication security.
• Numerical results confirm the feasibility and effectiveness of the joint precoding and phase shift optimization strategy in enhancing physical layer secrecy in practical DFRC deployments.