Technological progress in integrated, low-power, CMOS communication devices and sensors makes a rich design space of networked sensors viable. They can be deeply embedded in the physical world or spread throughout our environment. The missing elements are an overall system architecture and a methodology for systematic advance. To this end, we identify key requirements, develop a small device that is representative of the class, design a tiny event-driven operating system, and show that it provides support for efficient modularity and concurrency-intensive operation. Our operating system fits in 178 bytes of memory, propagates events in the time it takes to copy 1.25 bytes of memory, context switches in the time it takes to copy 6 bytes of memory and supports two level scheduling. The analysis lays a groundwork for future architectural advances.
ark Weiser envisioned a world in which computing is so pervasive that everyday devices can sense their relationship to us and to each other. They could, thereby, respond so appropriately to our actions that the computing aspects would fade into the background. Underlying this vision is the assumption that sensing a broad set of physical phenomena, rather than just data input, will become a common aspect of small, embedded computers and that these devices will communicate with each other (as well as to some more powerful infrastructure) to organize and coordinate their actions. Recall the story of Sal in Weiser's article; Sal looked out her window and saw "tracks" as evidence of her neighbors' morning strolls. What sort of system did this seemingly simple functionality imply? Certainly Weiser did not envision ubiquitous cameras placed throughout the neighborhood. Such a solution would be far too heavy for the application's relatively casual nature as well as quite invasive with respect to personal privacy. Instead, Weiser posited the existence of far less intrusive instrumentation in neighborhood spacesperhaps smart paving stones that could detect local activity and indicate the walker's direction based on exchanges between neighboring nodes. As we have marched technology forward, we are now in a position to translate this aspect of Weiser's vision to reality and apply it to a wide range of important applications, both computing and social. Other articles in this issue address the user interface-, application-, software-, and device-level design challenges associated with realizing Weiser's vision. Here, we address the challenges and opportunities of instrumenting the physical world with pervasive networks of sensor-rich, embedded computation. Such systems fulfill two of Weiser's key objectivesubiquity, by injecting computation into the physical world with high spatial density, and invisibility, by having the nodes and collectives of nodes operate autonomously. Of particular importance to the technical community is making such pervasive computing itself pervasive. We need reusable building blocks that can help us move away from the specialized instrumentation of each particular environment and move toward building reusable techniques for sensing, computing, and manipulating the physical world. The physical world presents an incredibly rich set of input modalities, including acoustics, image, motion, vibration, heat, light, moisture, pressure, ultrasound, radio, magnetic, and many more exotic modes. Traditionally, sensing and manipulating the This article addresses the challenges and opportunities of instrumenting the physical world with pervasive networks of sensor-rich, embedded computation. The authors present a taxonomy of emerging systems and outline the enabling technological developments.
Advances in low power VLSI design, along with the potentially low duty cycle of wireless sensor nodes open up the possibility of powering small wireless computing devices from scavenged ambient power. Low level vibrations occurring in typical household, office, and manufacturing environments are considered as a possible power source for wireless sensor nodes. This work focuses on the design of electrostatic vibration-to-electricity converters using MEMS fabrications technology. Detailed models of three different design concepts are developed. The three design concepts are evaluated and compared based on simulations and practical considerations. A formal optimization of the preferred design concept is performed, and a final design is produced using the optimal design parameters. Simulations of the optimized design show that an output power density of 116 μW/cm3 is possible from input vibrations of 2.25 m/s2 at 120 Hz. Test devices have been designed for a Deep Reactive Ion Etching (DRIE) process that etches MEMS structures into the top layer of a Silicon On Insulator (SOI) wafer. The devices are currently being fabricated.
Time slotted channel hopping (TSCH) is the highly reliable and ultra-low power medium access control technology at the heart of the IEEE802.15.4e-2012 amendment to the IEEE802.15.4-2011 standard. TSCH networks are deterministic in nature; the actions that occur at each time slot are well known. This paper presents an energy consumption model of these networks, obtained by slot-based "step-by-step" modeling and experimental validation on real devices running the OpenWSN protocol stack. This model is applied to different network scenarios to understand the potential effects of several network optimization. The model shows the impact of keep-alive and advertisement loads and discusses network configuration choices.Presented results show average current in the order of 570 µA on OpenWSN hardware and duty cycles 1% in network relays in both real and simulated networks. Leaf nodes show 0.46% duty cycle with data rates close to 10 packets per minute. In addition, the model is used to analyze the impact on energy consumption and data rate by overprovisioning slots to compensate for the lossy nature of these networks.
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