Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoT
Terahertz (THz) communications and simultaneous wireless information and power transfer (SWIPT) hold the potential to energize battery-less Internet-of-Things (IoT) devices while enabling multi-gigabit data transmission. However, severe path loss, blockages, and rectifier nonlinearity significantly...
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MDPI AG
2025-07-01
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| Online Access: | https://www.mdpi.com/1424-8220/25/15/4549 |
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| author | Sunday Enahoro Sunday Cookey Ekpo Mfonobong Uko Fanuel Elias Rahul Unnikrishnan Stephen Alabi Nurudeen Kolawole Olasunkanmi |
| author_facet | Sunday Enahoro Sunday Cookey Ekpo Mfonobong Uko Fanuel Elias Rahul Unnikrishnan Stephen Alabi Nurudeen Kolawole Olasunkanmi |
| author_sort | Sunday Enahoro |
| collection | DOAJ |
| description | Terahertz (THz) communications and simultaneous wireless information and power transfer (SWIPT) hold the potential to energize battery-less Internet-of-Things (IoT) devices while enabling multi-gigabit data transmission. However, severe path loss, blockages, and rectifier nonlinearity significantly hinder both throughput and harvested energy. Additionally, high-power THz beams pose safety concerns by potentially exceeding specific absorption rate (SAR) limits. We propose a sensing-adaptive power-focusing (APF) framework in which a reconfigurable intelligent surface (RIS) embeds low-rate THz sensors. Real-time backscatter measurements construct a spatial map used for the joint optimisation of (i) RIS phase configurations, (ii) multi-tone SWIPT waveforms, and (iii) nonlinear power-splitting ratios. A weighted MMSE inner loop maximizes the data rate, while an outer alternating optimisation applies semidefinite relaxation to enforce passive-element constraints and SAR compliance. Full-stack simulations at 0.3 THz with 20 GHz bandwidth and up to 256 RIS elements show that APF (i) improves the rate–energy Pareto frontier by 30–75% over recent adaptive baselines; (ii) achieves a 150% gain in harvested energy and a 440 Mbps peak per-user rate; (iii) reduces energy-efficiency variance by half while maintaining a Jain fairness index of 0.999;; and (iv) caps SAR at 1.6 W/kg, which is 20% below the IEEE C95.1 safety threshold. The algorithm converges in seven iterations and executes within <3 ms on a Cortex-A78 processor, ensuring compliance with real-time 6G control budgets. The proposed architecture supports sustainable THz-powered networks for smart factories, digital-twin logistics, wire-free extended reality (XR), and low-maintenance structural health monitors, combining high-capacity communication, safe wireless power transfer, and carbon-aware operation for future 6G cyber–physical systems. |
| format | Article |
| id | doaj-art-80e5fca7bf164ce1bf185731fdbd55f1 |
| institution | Kabale University |
| issn | 1424-8220 |
| language | English |
| publishDate | 2025-07-01 |
| publisher | MDPI AG |
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| series | Sensors |
| spelling | doaj-art-80e5fca7bf164ce1bf185731fdbd55f12025-08-20T04:00:55ZengMDPI AGSensors1424-82202025-07-012515454910.3390/s25154549Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoTSunday Enahoro0Sunday Cookey Ekpo1Mfonobong Uko2Fanuel Elias3Rahul Unnikrishnan4Stephen Alabi5Nurudeen Kolawole Olasunkanmi6Communication and Space Systems Engineering Research Team, Manchester Metropolitan University, Manchester M1 5GD, UKCommunication and Space Systems Engineering Research Team, Manchester Metropolitan University, Manchester M1 5GD, UKCommunication and Space Systems Engineering Research Team, Manchester Metropolitan University, Manchester M1 5GD, UKCommunication and Space Systems Engineering Research Team, Manchester Metropolitan University, Manchester M1 5GD, UKCommunication and Space Systems Engineering Research Team, Manchester Metropolitan University, Manchester M1 5GD, UKResearch and Development Engineering, SmOp CleanTech, Manchester M40 8WN, UKResearch and Development Engineering, SmOp CleanTech, Manchester M40 8WN, UKTerahertz (THz) communications and simultaneous wireless information and power transfer (SWIPT) hold the potential to energize battery-less Internet-of-Things (IoT) devices while enabling multi-gigabit data transmission. However, severe path loss, blockages, and rectifier nonlinearity significantly hinder both throughput and harvested energy. Additionally, high-power THz beams pose safety concerns by potentially exceeding specific absorption rate (SAR) limits. We propose a sensing-adaptive power-focusing (APF) framework in which a reconfigurable intelligent surface (RIS) embeds low-rate THz sensors. Real-time backscatter measurements construct a spatial map used for the joint optimisation of (i) RIS phase configurations, (ii) multi-tone SWIPT waveforms, and (iii) nonlinear power-splitting ratios. A weighted MMSE inner loop maximizes the data rate, while an outer alternating optimisation applies semidefinite relaxation to enforce passive-element constraints and SAR compliance. Full-stack simulations at 0.3 THz with 20 GHz bandwidth and up to 256 RIS elements show that APF (i) improves the rate–energy Pareto frontier by 30–75% over recent adaptive baselines; (ii) achieves a 150% gain in harvested energy and a 440 Mbps peak per-user rate; (iii) reduces energy-efficiency variance by half while maintaining a Jain fairness index of 0.999;; and (iv) caps SAR at 1.6 W/kg, which is 20% below the IEEE C95.1 safety threshold. The algorithm converges in seven iterations and executes within <3 ms on a Cortex-A78 processor, ensuring compliance with real-time 6G control budgets. The proposed architecture supports sustainable THz-powered networks for smart factories, digital-twin logistics, wire-free extended reality (XR), and low-maintenance structural health monitors, combining high-capacity communication, safe wireless power transfer, and carbon-aware operation for future 6G cyber–physical systems.https://www.mdpi.com/1424-8220/25/15/4549terahertz SWIPTreconfigurable intelligent surfaceadaptive power focusingnonlinear energy harvesting6G IoTSAR constraint |
| spellingShingle | Sunday Enahoro Sunday Cookey Ekpo Mfonobong Uko Fanuel Elias Rahul Unnikrishnan Stephen Alabi Nurudeen Kolawole Olasunkanmi Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoT Sensors terahertz SWIPT reconfigurable intelligent surface adaptive power focusing nonlinear energy harvesting 6G IoT SAR constraint |
| title | Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoT |
| title_full | Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoT |
| title_fullStr | Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoT |
| title_full_unstemmed | Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoT |
| title_short | Sustainable THz SWIPT via RIS-Enabled Sensing and Adaptive Power Focusing: Toward Green 6G IoT |
| title_sort | sustainable thz swipt via ris enabled sensing and adaptive power focusing toward green 6g iot |
| topic | terahertz SWIPT reconfigurable intelligent surface adaptive power focusing nonlinear energy harvesting 6G IoT SAR constraint |
| url | https://www.mdpi.com/1424-8220/25/15/4549 |
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