For energy-sustainable Internet of Things (IoT) and wireless sensor networks (WSNs), this paper addresses the minimization of the sole external power consumption in a time-switching simultaneous wireless information and power transfer (TS-SWIPT) based multi-hop decode-and-forward (DF) relay network. In such networks, only the source is grid-powered, while relays operate solely on harvested energy, making global minimization of source power under a stringent end-to-end quality-of-service (QoS) constraint imperative for maximizing network lifetime in green IoT systems. The joint optimization of the source power and the per-hop TS ratios, however, is non-convex. To solve it efficiently and globally, we first transform the problem into an equivalent convex form via logarithmic variable transformations. We then develop a tailored logarithmic barrier interior-point method (IPM) that exploits the problem’s structure. By explicitly leveraging its inherent block-tridiagonal structure, the algorithm achieves per-iteration computational complexity scaling linearly with the number of relays. Simulation results demonstrate global optimality and significant gains of the proposed scheme: for a 5-relay network, it achieves a 5.8-dB source power reduction over the sub-optimal single-step successive convex approximation (SCA) benchmark, as well as a 14.8-dB reduction and a 34.2-percentage-point feasibility rate improvement over the uniform fixed-TS policy. These gains are achieved at a tractable computational cost of approximately 27.5 ms for a 5-relay network. Moreover, a warm-start strategy cuts per-period computation by over 80%, and the solution exhibits strong robustness when evaluated under a realistic logistic (sigmoidal) nonlinear energy harvesting (EH) model and imperfect channel state information (CSI), establishing an excellent performance-efficiency trade-off for practical IoT deployments.

Battery free Internet of Things (BF IoT), which is realized by harvesting ambient energy to power the IoT devices, has many advantages such as low power, low cost, free-maintenance, easy deployment, and environmental protection. As the two key enabling technologies of BF IoT, the integration of energy harvesting, management and backscatter communication (BackCom) is expected to meet practical applications. However, several fundamental issues need to be addressed to fully develop the potential of such integration. In this paper, we propose an ultra-low power energy harvesting and management scheme that effectively reduces the startup and quiescent power consumption. In the case of extremely limited energy harvested, the Long Range (LoRa) BackCom digital waveform generation algorithm with ultra-low power consumption and low complexity is studied, which can support low-power and low-cost micro-controllers (MCUs). Then, a radio frequency (RF) front-end scheme that is compatible with RF energy harvesting (RFEH), BackCom, and On-Off-Keying (OOK) receiving is proposed. On this basis, we design and implement a fully functional BF LoRa Tag, which integrates tag antennas, LoRa BackCom, low-power OOK receiving, multi-parameter real-time sensing, RFEH and management, at a cost of only 6. Our test results show that the BF LoRa Tag can be self-powered by harvesting the RF energy as low as –19 dBm, with the cold-start power as low as 280 nW, the quiescent power as low as 49 nW, the OOK receiving power consumption as low as$1.74~\mu $W, the LoRa BackCom power consumption of only$251~\mu $W, and the communication distance up to 445 meters. Compared with the prototypes in existing literature, the BF LoRa Tag not only has lower power consumption, wider coverage, and the lowest cost, but also has complete system functions. Finally, we discuss the reciprocity between stations and receivers, as well as the BF LoRa cellular communication network, which provides useful references for the practical application and large-scale deployment of BF IoT in the future.

Radio-frequency (RF)-powered backscattering communication (BC) has many advantages, such as low-power consumption, battery-free, small size, low cost, full sealing, manual maintenance-free, and easy mass deployment. However, the weak RF energy harvested and the short BC distance have become the two critical obstacles in the real-world implementation of this potential technology. In this article, we propose a high-sensitivity RF energy harvesting (RFEH) and long-distance BC method, and for the first time, we demonstrate the RF-powered self-sustainable long-distance BC device named RFEH LoRa. In order to improve RFEH sensitivity, an ultralow-power (ULP) consumption voltage monitoring and startup control circuit topology is designed to reduce the power consumption to 245 nanowatt (nW) during the accumulation of RF energy. While in order to increase the BC distance, a direct digital frequency synthesis technology is used to generate a linear frequency modulation square wave sequence conforming to the LoRa specifications based on the ULP microcontroller unit, and the square wave is used to drive an RF switch to achieve long-distance BC of hundreds of meters. Test results show that the instantaneous BC current is as low as 130 microampere ( μA), and the standby current is only 52 nanoampere (nA). RFEH LoRa is implemented with commercial off-the-shelf components. It can self-startup by harvesting RF energy as low as -22.5 dBm, and send its sensing data to the receiver of 381-m away.

A Wi‐Fi scatter communication method based on microcontroller unit (MCU) is proposed, and an ultra‐low power micro Wi‐Fi scatter communication device μWi‐Fi is designed and implemented. First, according to the characteristics of the microcontroller, the software virtual modulation method and the serial communication port direct memory access (DMA) transmission method is proposed to realise Wi‐Fi scattering communication. Then the MCU + exclusive OR (XOR) baseband architecture is proposed to further reduce the main frequency of the microcontroller and the system power consumption. The communication test and power consumption measurement results show that μWi‐Fi can generate signals conforming to the IEEE802.11b standard, which can be received and forwarded by universal Wi‐Fi routers. Its effective communication distance reaches 15 m, its communication peak current reaches 720 μA, and its standby current reaches 390 nA. Compared with traditional internet of things (IOTs) Wi‐Fi devices, μWi‐Fi can not only reduce the power consumption of Wi‐Fi communication by 2–3 orders but also has a simple composition and low cost, which is very helpful for the rapid development of Wi‐Fi IoT products.