Beampattern Synthesis for Discrete Phase RIS in Communication and Sensing Systems

2025-12-04

AI Summary

To address the beamforming limitation in integrated sensing and communication (ISAC) systems with reconfigurable intelligent surfaces (RISs) arising from unknown direction-of-arrival (DoA) priors, this paper proposes a wide-beam array pattern synthesis method tailored for discrete-phase RISs. To overcome the non-convex optimization challenges imposed by discrete-phase constraints and unit-modulus requirements, we innovatively integrate a penalty function method with convex relaxation—relaxing the discrete-phase constraint to the convex hull boundary—and solve the resulting problem efficiently within the Minorization-Maximization (MM) framework, enabling joint amplitude and phase control. The proposed method significantly broadens the received power coverage region and enhances robustness of angle-of-arrival (AoA) estimation: experiments demonstrate a 1–2 order-of-magnitude reduction in AoA estimation mean-square error at medium-to-low SNRs, and maintain high-probability target detection even when SNR degrades by 8 dB.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Constraint Satisfaction and Optimization: Mixed Discrete/Continuous Optimization

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Search and Retrieval-Augmented AI: Personalized, context-aware and across-device search

Abstract

Extensive research on Reconfigurable Intelligent Surfaces (RIS) has primarily focused on optimizing reflective coefficients for passive beamforming in specific target directions. This optimization typically assumes prior knowledge of the target direction, which is unavailable before the target is detected. To enhance direction estimation, it is critical to develop array pattern synthesis techniques that yield a wider beam by maximizing the received power over the entire target area. Although this challenge has been addressed with active antennas, RIS systems pose a unique challenge due to their inherent phase constraints, which can be continuous or discrete. This work addresses this challenge through a novel array pattern synthesis method tailored for discrete phase constraints in RIS. We introduce a penalty method that pushes these constraints to the boundary of the convex hull. Then, the Minorization-Maximization (MM) method is utilized to reformulate the problem into a convex one. Our numerical results show that our algorithm can generate a wide beam pattern comparable to that achievable with per-power constraints, with both the amplitudes and phases being adjustable. We compare our method with a traditional beam sweeping technique, showing a) several orders of magnitude reduction of the MSE of Angle of Arrival (AOA) at low to medium Signal-to-Noise Ratio (SNR)s; and b) $8$~dB SNR reduction to achieve a high probability of detection.

Problem

• Develops wide beam pattern synthesis for RIS with discrete phase constraints
• Enhances direction estimation without prior target direction knowledge
• Reduces MSE and SNR requirements for improved detection probability

Innovation

• Penalty method for discrete phase constraints
• Minorization-Maximization to convexify the problem
• Generates wide beam patterns with adjustable amplitudes and phases