Dual-Functional MIMO Beamforming Optimization for RIS-Aided Integrated Sensing and Communication

TL;DR

This paper proposes a dual-functional MIMO beamforming optimization framework for RIS-assisted integrated sensing and communication systems, balancing data transmission and target detection with novel algorithms and theoretical analysis.

Contribution

It introduces a comprehensive optimization framework for RIS-assisted ISAC, including new algorithms for RIS phase shift design and BS precoder optimization, addressing both single-user and multi-user scenarios.

Findings

Validated the optimal BS precoder in single-user, single-target case.

Developed an ADMM-based RIS phase shift optimization algorithm.

Demonstrated improved performance through numerical simulations.

Abstract

Aiming at providing wireless communication systems with environment-perceptive capacity, emerging integrated sensing and communication (ISAC) technologies face multiple difficulties, especially in balancing the performance trade-off between the communication and radar functions. In this paper, we introduce a reconfigurable intelligent surface (RIS) to assist both data transmission and target detection in a dual-functional ISAC system. To formulate a general optimization framework, diverse communication performance metrics have been taken into account including famous capacity maximization and mean-squared error (MSE) minimization. Whereas the target detection process is modeled as a general likelihood ratio test (GLRT) due to the practical limitations, and the monotonicity of the corresponding detection probability is proved. For the single-user and single-target (SUST) scenario, the minimum transmit power of the ISAC transceiver has been revealed. By exploiting the optimal conditions of the BS design, we validate that the BS is able to realize the maximum power allocation scheme and derive the optimal BS precoder in a semi-closed form. Moreover, an alternating direction method of multipliers (ADMM) based RIS design is proposed to address the optimization of unit-modulus RIS phase shifts. For the sake of further enhancing computational efficiency, we also develop a low-complexity RIS design based on Riemannian gradient descent. Furthermore, the ISAC transceiver design for the multiple-users and multiple-targets (MUMT) scenario is also investigated, where a zero-forcing (ZF) radar receiver is adopted to cancel the interferences. Then optimal BS precoder is derived under the maximum power allocation scheme, and the RIS phase shifts can be optimized by extending the proposed ADMM-based RIS design. Numerical simulation results verify the performance of our proposed transceiver designs.