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Frequency Diverse RIS (FD-RIS) Enhanced Wireless Communications via Joint Distance-Angle Beamforming

Han Xiao, Xiaoyan Hu, Wenjie Wang, Kai-Kit Wong, Kun Yang

TL;DR

A newly designed frequency diverse RIS (FD-RIS), which can achieve joint distance-angle beamforming with the assistance of the time modulation technology, and a novel iterative algorithm based on the cross-entropy optimization framework to effectively handle the non-convex optimization problem.

Abstract

The conventional reconfigurable intelligent surface (RIS) assisted far-field communication systems can only implement angle beamforming, which actually limits the capability for reconfiguring the wireless propagation environment. To overcome this limitation, this paper proposes a newly designed frequency diverse RIS (FD-RIS), which can achieve joint distance-angle beamforming with the assistance of the time modulation technology. The signal processing model for FD-RIS-aided wireless communications is first derived. Then, an optimization problem aimed at maximizing the achievable rate is formulated where the frequency-time modulations are jointly optimized to achieve distance-angle beamforming. Furthermore, a novel iterative algorithm based on the cross-entropy optimization (CEO) framework is proposed to effectively handle the non-convex optimization problem. The numerical results validate that the proposed FD-RIS assisted communication scheme can achieve a notable performance improvement compared with the baseline scheme utilizing traditional RIS. In addition, the effectiveness of the proposed CEO algorithm is further verified by comparing with the benchmark using the genetic algorithm (GA).

Frequency Diverse RIS (FD-RIS) Enhanced Wireless Communications via Joint Distance-Angle Beamforming

TL;DR

A newly designed frequency diverse RIS (FD-RIS), which can achieve joint distance-angle beamforming with the assistance of the time modulation technology, and a novel iterative algorithm based on the cross-entropy optimization framework to effectively handle the non-convex optimization problem.

Abstract

The conventional reconfigurable intelligent surface (RIS) assisted far-field communication systems can only implement angle beamforming, which actually limits the capability for reconfiguring the wireless propagation environment. To overcome this limitation, this paper proposes a newly designed frequency diverse RIS (FD-RIS), which can achieve joint distance-angle beamforming with the assistance of the time modulation technology. The signal processing model for FD-RIS-aided wireless communications is first derived. Then, an optimization problem aimed at maximizing the achievable rate is formulated where the frequency-time modulations are jointly optimized to achieve distance-angle beamforming. Furthermore, a novel iterative algorithm based on the cross-entropy optimization (CEO) framework is proposed to effectively handle the non-convex optimization problem. The numerical results validate that the proposed FD-RIS assisted communication scheme can achieve a notable performance improvement compared with the baseline scheme utilizing traditional RIS. In addition, the effectiveness of the proposed CEO algorithm is further verified by comparing with the benchmark using the genetic algorithm (GA).
Paper Structure (13 sections, 10 equations, 5 figures)

This paper contains 13 sections, 10 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Signal Processing Model for FD-RIS
  3. System model and Problem formulation
  4. System Model
  5. Problem Formulation
  6. Algorithm Design
  7. Design for sampling distribution
  8. Sampling distribution model for the reflection coefficients in $\boldsymbol{\Upsilon}$
  9. Sampling distribution model for the modulation frequency $f_0$
  10. Joint sampling distribution model
  11. Updating Formulas for Tilting Parameters
  12. Numerical Results
  13. Conclusion

Figures (5)

  • Figure 1: The system model of FD-RIS-assisted wireless networks.
  • Figure 2: The generated beam pattern with $S=100$, $P=30$ dBm, target user position ($d_\mathrm{ru}=150$ m, $\theta_\mathrm{ru}=90^{\circ}$ and $\phi_\mathrm{ru}=30^{\circ}$): (a) the beam pattern of the FD-RIS, (b) the beam pattern of the conventional RIS.
  • Figure 3: The achievable rate versus $S$ with different transmit power ($P$).
  • Figure 4: The achievable rate versus the transmit power ($P$) with $S$.
  • Figure 5: The achievable rates of the FD-RIS with $1$-bit and the RIS with different $b$, considering different $S$ and $P$.