This letter presents a novel compact impedance matching layer (IML) to improve the transmission efficiency of dual-band implantable medical devices (IMDs) operating in the wireless medical telemetry services (WMTS, 1.395-1.4 GHz) and industrial scientific and medical (ISM, 2.4-2.48 GHz) bands. This IML with a simple structure enables robust impedance matching at the skin-air interface, and enhances the transmission efficiency in both bands. To verify the performance enhancement induced by the IML, we designed a dual-band implantable antenna and studied lateral/angular misalignment on the gain with and without the IML. Furthermore, the analysis of varying implant depths suggests the potential applicability of the IML for deep implant scenarios. Finally, the prototypes of the IML and implantable antenna are fabricated, and then measured in minced pork to validate the simulation results. The inclusion of the IML increased transmission efficiency by approximately 3.7 dB at 1.4 GHz and 10.3 dB at 2.45 GHz.

Legacy LoRa receiver adopts a superheterodyne architecture with a runtime power consumption of up to 100mW, resulting in its low-power promise can only be delivered in low duty-cycle mode. This paper presents Sisyphus as an ultra-low-power LoRa receiver, ensuring around-the-clock LoRa availability while extending battery life significantly. To achieve this, we propose a novel receiver design for passive coherent demodulation of LoRa. In this design, we creatively couple LoRa's down-conversion with de-chirping (dc²), leveraging the processing gain brought by chirp spread spectrum (CSS) modulation to boost communication range without the need for additional power supply. Moreover, we exploit the cyclical time-frequency feature intrinsic to LoRa for demodulation, and a low-power analog-digital signal processing circuit with negligible power is devised to replace the existing power-intensive sampling and costly digital computation. We prototype Sisyphus for proof-of-concept, and comprehensive experimental results demonstrate that Sisyphus can achieve significant power savings compared to legacy LoRa receiver while retaining the anti-interference ability of legacy LoRa. We envision that the design of Sisyphus can unlock the potential for broader applications of LoRa.

Differing from tremendous existing works that mainly focus on optimizing backscatter communication, Radio-to-Bus (R2B) communication utilizes backscatter to offload processors from IoT devices to the gateway, achieving processor-free devices of significantly reduced power and hardware cost. However, R2B communication is not suitable for large-scale backscatter networks, since R2B cannot support parallel and long-range communication between the gateway and hundreds of R2B devices. In this paper, we present Chipnet, a network that supports hundreds of long-range and concurrent connections between the gateway and multiple processor-free devices. The high level design of Chipnet includes a parallel frequency-division uplink mechanism which can work on processor-free devices, and a processor-free MAC layer protocol which supports gateway to broadcast downlink data and individually manage each processor-free device. This design addresses practical issues facing the processor-free device architecture, such as synchronizing hundreds of processor-free devices, assigning unique channel frequencies to every device, and realizing power-efficient processor-free signal conversion. The results demonstrate that a Chipnet network can achieve a task throughput of 2400 tasks/s with a latency of 72.23ms. Compared with the R2B network, Chipnet achieves 3 × −5 × improvements in network coverage range, and two orders of magnitude improvement in both network throughput and network latency.

The rapid development of IoT applications calls for re-configurable IoT devices that can easily extend new functionality on demand. However, in the current architecture, updating chip functions on the end device is highly coupled with the local microprocessor in both hardware and software aspects, leading to inadequate flexibility. In this paper, we propose LEGO, a lightweight architecture with chip-level plug-and-play capabilities for IoT end devices. To achieve this, we first decoupling the control over heterogeneous chips from end devices to the gateway, and design a novel Unified Chip Description Language (UCDL) to access various types of functional chips uniformly. To supporting chips plug-and-play, we design a novel signal converting circuit on end devices to generate all required underlying signals for chip control. We also design a layered instruction orchestrator and hierarchical scheduler to minimize transmission overhead. The results show that our LEGO system can respond to chips plug-and-play within 0.13 seconds, and the lightweight architecture could reduce 49% $\sim$ 61% of power consumption in practical scenarios compared with traditional IoT end devices that are controlled by a microprocessor. The lightweight and easy-to-deploy features of LEGO makes it helpful to reduce deployment cost, thus conducive to accelerating large-scale applications.

Large-scale IoT sensor deployment calls for inexpensive, low-power sensor nodes that still perform long-range, large-scale networking at the system level. However, current sensor nodes are constructed according to the `one-size-fits-all' embedded design, where the processor and RF transceiver are indispensable but underutilized in low-duty cycles, resulting in overwhelmingly significant unit price and run-time power. In this paper, we propose a novel processor-sharing IoT architecture that converts the vast majority of sensor nodes from embedded computers to low-end RF peripherals. The conventional full-fledged sensor nodes are smashed into the air, and the scattered chips are scaled well with negligible overheads through a virtual I²C bus called RFBus. Specifically, the RFBus interface is designed to be backward compatible with the I²C bus interface, and thus, the RFBus network inherits versatile link layer services transparently from the well-established I²C link layer protocol. We design the RFBus with a joint consideration of system-level performance and deployment costs and evaluate the prototypes in indoor and outdoor scenarios. The result indicates that the proposed architecture achieves 6.09 x (indoor) and 6.69 x (outdoor) energy saving and reduces the unit price of sensor nodes by 23.5% (indoor) and 33.5% (outdoor).