Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Frequency Diverse Array-enabled RIS-aided Integrated Sensing and Communication

Hanyu Yang, Shiqi Gong, Heng Liu, Chengwen Xing, Nan Zhao, Dusit Niyato

TL;DR

This work addresses joint sensing and communication in a frequency diverse array (FDA) enabled RIS-aided ISAC system, where FDA provides distance-angle-dependent beampatterns and RIS enables robust BS-to-user/target links. By showing the dedicated radar signal is unnecessary, it reduces the optimization complexity and proves FDA-RIS offers superior radar SCNR than conventional PA-based systems in the single-user single-target setting, with SCNR scaling linearly with transmit power and receive antennas. The authors develop a fractional programming based reformulation and an alternating optimization algorithm leveraging SADMM and SCA to jointly optimize BS beamforming, radar covariance, RIS phases, FDA offsets, and radar equalization, achieving superior sum rate and radar SCNR in simulations. The approach promises practical gains for integrated sensing and communications in next-generation networks by exploiting FDA's extra degrees of freedom and RIS-enhanced propagation environments.

Abstract

Integrated sensing and communication (ISAC) has been envisioned as a prospective technology to enable ubiquitous sensing and communications in next-generation wireless networks. In contrast to existing works on reconfigurable intelligent surface (RIS) aided ISAC systems using conventional phased arrays (PAs), this paper investigates a frequency diverse array (FDA)-enabled RIS-aided ISAC system, where the FDA aims to provide a distance-angle-dependent beampattern to effectively suppress the clutter, and RIS is employed to establish high-quality links between the BS and users/target. We aim to maximize sum rate by jointly optimizing the BS transmit beamforming vectors, the covariance matrix of the dedicated radar signal, the RIS phase shift matrix, the FDA frequency offsets and the radar receive equalizer, while guaranteeing the required signal-to-clutter-plus-noise ratio (SCNR) of the radar echo signal. To tackle this challenging problem, we first theoretically prove that the dedicated radar signal is unnecessary for enhancing target sensing performance, based on which the original problem is much simplified. Then, we turn our attention to the single-user single-target (SUST) scenario to demonstrate that the FDA-RIS-aided ISAC system always achieves a higher SCNR than its PA-RIS-aided counterpart. Moreover, it is revealed that the SCNR increment exhibits linear growth with the BS transmit power and the number of BS receive antennas. In order to effectively solve this simplified problem, we leverage the fractional programming (FP) theory and subsequently develop an efficient alternating optimization (AO) algorithm based on symmetric alternating direction method of multipliers (SADMM) and successive convex approximation (SCA) techniques. Numerical results demonstrate the superior performance of our proposed algorithm in terms of sum rate and radar SCNR.

Frequency Diverse Array-enabled RIS-aided Integrated Sensing and Communication

TL;DR

This work addresses joint sensing and communication in a frequency diverse array (FDA) enabled RIS-aided ISAC system, where FDA provides distance-angle-dependent beampatterns and RIS enables robust BS-to-user/target links. By showing the dedicated radar signal is unnecessary, it reduces the optimization complexity and proves FDA-RIS offers superior radar SCNR than conventional PA-based systems in the single-user single-target setting, with SCNR scaling linearly with transmit power and receive antennas. The authors develop a fractional programming based reformulation and an alternating optimization algorithm leveraging SADMM and SCA to jointly optimize BS beamforming, radar covariance, RIS phases, FDA offsets, and radar equalization, achieving superior sum rate and radar SCNR in simulations. The approach promises practical gains for integrated sensing and communications in next-generation networks by exploiting FDA's extra degrees of freedom and RIS-enhanced propagation environments.

Abstract

Integrated sensing and communication (ISAC) has been envisioned as a prospective technology to enable ubiquitous sensing and communications in next-generation wireless networks. In contrast to existing works on reconfigurable intelligent surface (RIS) aided ISAC systems using conventional phased arrays (PAs), this paper investigates a frequency diverse array (FDA)-enabled RIS-aided ISAC system, where the FDA aims to provide a distance-angle-dependent beampattern to effectively suppress the clutter, and RIS is employed to establish high-quality links between the BS and users/target. We aim to maximize sum rate by jointly optimizing the BS transmit beamforming vectors, the covariance matrix of the dedicated radar signal, the RIS phase shift matrix, the FDA frequency offsets and the radar receive equalizer, while guaranteeing the required signal-to-clutter-plus-noise ratio (SCNR) of the radar echo signal. To tackle this challenging problem, we first theoretically prove that the dedicated radar signal is unnecessary for enhancing target sensing performance, based on which the original problem is much simplified. Then, we turn our attention to the single-user single-target (SUST) scenario to demonstrate that the FDA-RIS-aided ISAC system always achieves a higher SCNR than its PA-RIS-aided counterpart. Moreover, it is revealed that the SCNR increment exhibits linear growth with the BS transmit power and the number of BS receive antennas. In order to effectively solve this simplified problem, we leverage the fractional programming (FP) theory and subsequently develop an efficient alternating optimization (AO) algorithm based on symmetric alternating direction method of multipliers (SADMM) and successive convex approximation (SCA) techniques. Numerical results demonstrate the superior performance of our proposed algorithm in terms of sum rate and radar SCNR.
Paper Structure (10 sections, 4 theorems, 60 equations, 7 figures, 1 table)

This paper contains 10 sections, 4 theorems, 60 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. System Model and Problem Formulation
  3. Equivalent Simplification and Performance Discussion
  4. Joint Active-Passive Beamforming and frequency offsets Optimization
  5. Simulation Results
  6. Conclusions
  7. Proof of Proposition \ref{['prop-sim']}
  8. Proof of Proposition \ref{['prop-optwu']}
  9. Proof of Proposition \ref{['prop1']}
  10. Proof of Proposition \ref{['prop-new-new-2']}

Key Result

Proposition 1

There must exist an optimal solution ${\mathcal{V}_{\rm P_1}^{\rm opt}}\!\!=\!\!\{{\bf w}_{ k}^{\rm opt}, {\bf R}_{0}^{\rm opt}, {{\bm \Theta}}^{\rm opt},\Delta f_{ n_{\rm t}}^{\rm opt},{\bf u}^{\rm opt}\}$ with ${\bf R}_{0}^{\rm opt}\!=\!{\bf 0}$ to problem (P1).

Figures (7)

  • Figure 1: The considered FDA-RIS-aided ISAC system.
  • Figure 2: Receive processing chain for the FDA-RIS-aided ISAC system.
  • Figure 3: (a) SCNR of the SUST system versus the maximum allowable frequency offset increment $\Delta f_{\max}$. (b) SCNR increment versus the BS transmit power $P_{\rm B}$ with $\Delta f_{\max}\!=\!3$MHz.
  • Figure 4: (a) Convergence behaviors of respective algorithms. (b) Average CPU runtime versus the number of RIS reflecting elements $M$.
  • Figure 5: Sum rate versus the BS transmit power $P_{\rm B}$.
  • ...and 2 more figures

Theorems & Definitions (8)

  • Proposition 1
  • proof
  • Proposition 2
  • proof
  • Proposition 3
  • proof
  • Proposition 4
  • proof