Power consumption continues to pose a fundamental challenge for large-scale IoT tag deployment. While conventional active communication strategies struggle to mitigate peak power demands due to energy-intensive components, passive alternatives achieve microwatt-level consumption but suffer from limited operational range. This paper introducesTiga, an innovative hybrid active-passive communication system for Ambient IoT that autonomously selects optimal transmission modes. Recognizing the ambiguity inherent in the distance-based mode switching boundary, we instead adopt energy level as our boundary criterion.Tigaemploys passive communication when channel energy suffices and seamlessly transitions to active transmission when required. Our design features a novel microwatt-scale dual-function detector that performs concurrent downlink signal demodulation and RSSI computation. We further propose an adaptive four-phase blind boundary search algorithm capable of efficient execution on any low-power controller. We prototypeTigaon a four-layer PCB and evaluate its performance across various environments. Experimental results demonstrate that compared to duty-cycling active communication,Tigareduces dynamic power consumption by 1.85× to 9.42× across various distances from the gateway.

The Wi-Fi-enabled ultra-low power communication system exhibits high asymmetry between uplink and downlink speeds. The uplink can reach up to 1 Mbps, while the downlink throughput is around 100 Kbps. In this paper, we present Wook, a novel high throughput downlink system to empower Commercial Off-The-Shelf (COTS) Wi-Fi devices to transmit high-speed OOK messages. The key innovation underpinning Wook is its ability to achieve sub-symbol level modulation, allowing a single OFDM symbol to carry multiple OOK bits. This is done by profoundly exploring the Wi-Fi PHY layer and identifying optimal input payload to achieve fine-grained Wi-Fi waveform manipulation. We fabricate a PCB prototype and employ the COTS Wi-Fi router to implement the entire system. Experimental results show that with a simulated IC power consumption 76.6μW, Wook achieves a data rate of up to 1.1 Mbps, an 8.9X improvement over state-of-the-art systems. Moreover, even at a communication distance of 95 m, Wook maintains a throughput of 82.9 Kbps.

This paper presents FaB, a frequency-agile backscatter system that can optionally leverage OFDM signals on different bands as carriers for backscatter communication. Compared with existing backscatter systems that are tailored to a specific frequency band, a frequency-agile backscatter yields two critical benefits: i) it can leverage the increased availability of “free rides” across a broad range of frequency band to improve its transmission efficiency; and ii) it becomes compatible with mainstream wireless communication standards, making it applicable to heterogeneous wireless networks. Based on these two features, FaB’s circuits can be migrated to various types of backscatter communication nodes without any modification, significantly reducing design and deployment costs. To show the efficacy of our design, we implement a PCB prototype of FaB and showcase its capability of leveraging OFDM Wi-Fi and LTE signals as carrier waves. Our extensive field studies show that FaB’s multi-band modulator can produce an error vector magnitude of under -15dB in any band below 6GHz with a precision of 10mV.