Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoT

Area of Science:

• Wireless Communications
• Energy Harvesting
• Internet of Things (IoT)

Background:

• Terahertz (THz) communications and simultaneous wireless information and power transfer (SWIPT) promise high-speed data and power for battery-less IoT devices.
• Challenges include severe path loss, blockages, nonlinearities, and safety concerns (Specific Absorption Rate - SAR).

Purpose of the Study:

• To propose a sensing-adaptive power-focusing (APF) framework using reconfigurable intelligent surfaces (RIS) with embedded sensors.
• To jointly optimize RIS phase configurations, multi-tone SWIPT waveforms, and nonlinear power-splitting ratios for improved performance and safety.

Main Methods:

• A sensing-adaptive power-focusing (APF) framework with RIS embedding low-rate THz sensors.
• Real-time backscatter measurements to create a spatial map for joint optimization.
• Weighted MMSE inner loop for data rate maximization and alternating optimization with semidefinite relaxation for constraints and SAR compliance.

Main Results:

• APF improves the rate-energy Pareto frontier by 30-75% over adaptive baselines.
• Achieves 150% gain in harvested energy and 440 Mbps peak per-user rate.
• Reduces energy-efficiency variance by half, maintains high fairness (Jain index 0.999), and caps SAR below safety thresholds.

Conclusions:

• The APF framework enables efficient, safe, and sustainable THz-powered networks for future 6G applications.
• Fast convergence (<3 ms) ensures real-time compliance for cyber-physical systems.
• Supports diverse applications like smart factories, digital twins, and extended reality (XR).