RIS-aided Wireless-Powered Backscatter Communications for Sustainable Internet of Underground Things

TL;DR

Underground IoUT channels suffer from severe attenuation, limiting energy transfer and reliable data transmission for WPUSNs. To address this, the paper proposes RIS-aided WPBUSNs with a joint design of RIS phase shifts and time allocation among WET, WIT, and BC to maximize sum throughput. A farming-case study demonstrates that RIS can provide substantial gains (e.g., up to $410%$ throughput improvement with $K=70$ elements) and enables BC under challenging conditions, with performance strongly affected by burial depth $d_u$, VWC, and user count $N$. The work also discusses key challenges and future directions, including CSI acquisition in subterranean media, channel modeling with soil properties, interference management, and distributed RIS deployments for large-scale IoUT deployments.

Abstract

Wireless-powered underground sensor networks (WPUSNs), which enable wireless energy transfer to sensors located underground, is a promising approach for establishing sustainable internet of underground things (IoUT). To support urgent information transmission and improve resource utilization within WPUSNs, backscatter communication (BC) is introduced, resulting in what is known as wireless-powered backscatter underground sensor networks (WPBUSNs). Nevertheless, the performance of WPBUSNs is significantly limited by severe channel impairments caused by the underground soil and the blockage of direct links. To overcome this challenge, in this work, we propose integrating reconfigurable intelligent surface (RIS) with WPBUSNs, leading to the development of RIS-aided WPBUSNs. We begin by reviewing the recent advancements in BC-WPUSNs and RIS. Then, we propose a general architecture of RIS-aided WPBUSNs across various IoUT scenarios, and discuss its advantages and implementation challenges. To illustrate the effectiveness of RIS-aided WPBUSNs, we focus on a realistic farming case study, demonstrating that our proposed framework outperforms the three benchmarks in terms of the sum throughput. Finally, we discuss the open challenges and future research directions for translating this study into practical IoUT applications.

Figures (5)

• Figure 1: A multi-user wireless-powered underground sensor network (WPUSN) system for various IoUT applications.
• Figure 2: A general architecture of our proposed RIS-aided WPBUSNs and its applications in underground pipeline monitoring, smart agriculture, and post-disaster rescue scenarios.
• Figure 3: A multi-user RIS-aided WPBUSNs system model considering the TDMA protocol.
• Figure 4: The implementation diagram of our proposed RIS-aided WPBUSNs system.
• Figure 5: Fig. 5. The selected numerical results. (a) The network throughput of RIS-aided WPBUSNs compared to the three benchmarks, as a function of the number of RIS reflecting elements $K$, where the dotted lines denotes the throughput produced by the HTT and BC modes, respectively, and (b) The network throughput and time allocation of our RIS-aided WPBUSNs as a function of the number of RIS reflecting elements $K$ under various burial depths, VWC and UDs’ number.