Two Birds With One Stone: Enhancing Communication and Sensing via Multi-Functional RIS

TL;DR

The paper proposes multi-functional RIS (MF-RIS) to jointly enhance communication and sensing in 6G and ISAC systems. It develops MF-RIS-aided schemes across unicast, multicast, broadcast, and multiple access (OFDMA, NOMA, RSMA) to exploit per-element amplitude and phase control, while elucidating the sensing side via MF-RIS-assisted and sensing-assisted configuration loops. It analyzes RCC and DFRC ISAC architectures, and advocates multi-objective optimization to balance throughput, sensing accuracy, and resource use, supported by numerical results showing superior performance over conventional RIS. The work also outlines future directions including near-field considerations, AI-driven beamforming, and integrated sensing–communication–computing co-design for robust 6G networks.

Abstract

In this article, we propose new network architectures that integrate multi-functional reconfigurable intelligent surfaces (MF-RISs) into 6G networks to enhance both communication and sensing capabilities. Firstly, we elaborate how to leverage MF-RISs for improving communication performance in different communication modes including unicast, mulitcast, and broadcast and for different multi-access schemes. Next, we emphasize synergistic benefits of integrating MF-RISs with wireless sensing, enabling more accurate and efficient target detection in 6G networks. Furthermore, we present two schemes that utilize MF-RISs to enhance the performance of integrated sensing and communication (ISAC). We also study multi-objective optimization to achieve the optimal trade-off between communication and sensing performance. Finally, we present numerical results to show the performance improvements offered by MF-RISs compared to conventional RISs in ISAC. We also outline key research directions for MF-RIS under the ambition of 6G.

Figures (5)

• Figure 1: Comparison between MF-RISs and conventional RISs. The hardware circuit of each MF-RIS element comprises an amplifier, a power divider, and two phase shifters. The amplifier and power divider manage the amplitude of the reflected and refracted signals. The phase shifter, which includes multiple PIN diodes, is responsible for adjust the phase shift of the output signal. Besides, we discuss major challenges and solutions for MF-RIS-aided communication, and sensing as well as their integration.
• Figure 2: MF-RIS-aided wireless communications and simulation results.
• Figure 3: The interplay between MF-RISs and sensing is illustrated in (a) and (b). MF-RIS-aided ISAC systems are illustrated in (c) and (d).
• Figure 4: Single-objective optimization versus multi-objective optimization in MF-RIS-aided ISAC systems.
• Figure 5: Performance evaluation of ISAC systems aided by different RIS types: (a) sum SINR of sensing targets versus the quality-of-service (QoS) of communication users, and (b) sum SINR of sensing targets versus the number of RIS elements. Here, the QoS is measured by the spectral efficiency.