Jason L. Hill

Versatile low power media access for wireless sensor networks

We propose <i>B-MAC</i>, a carrier sense media access protocol for wireless sensor networks that provides a flexible interface to obtain ultra low power operation, effective collision avoidance, and high channel utilization. To achieve low power operation, <i>B-MAC</i> employs an adaptive preamble sampling scheme to reduce duty cycle and minimize idle listening. <i>B-MAC</i> supports on-the-fly reconfiguration and provides bidirectional interfaces for system services to optimize performance, whether it be for throughput, latency, or power conservation. We build an analytical model of a class of sensor network applications. We use the model to show the effect of changing <i>B-MAC</i>s parameters and predict the behavior of sensor network applications. By comparing <i>B-MAC</i> to conventional 802.11-inspired protocols, specifically SMAC, we develop an experimental characterization of <i>B-MAC</i> over a wide range of network conditions. We show that <i>B-MAC</i>s flexibility results in better packet delivery rates, throughput, latency, and energy consumption than S-MAC. By deploying a real world monitoring application with multihop networking, we validate our protocol design and model. Our results illustrate the need for flexible protocols to effectively realize energy efficient sensor network applications.

System architecture directions for networked sensors

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 and spread throughout our environment like smart dust. 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.

Mica: a wireless platform for deeply embedded networks

Low-power integration of sensing, communication, and computation requires a new approach to wireless design. Flexible interfaces and primitive accelerators enable aggressive system-level optimizations. Micas flexible design serves as a building block for creating efficient application-specific protocols. Instead of defining narrow, standardized application interfaces, Mica provides a set of richly interconnected primitives (such as data serializers and timing extractors) to facilitate cross-layer optimizations. To explore novel systems approaches, researchers can develop customized protocols tailored to their application; Mica does not require use of predefined protocols.

TinyOS: An Operating System for Sensor Networks

We present TinyOS, a flexible, application-specific operating system for sensor networks, which form a core component of ambient intelligence systems. Sensor networks consist of (potentially) thousands of tiny, low-power nodes, each of which execute concurrent, reactive programs that must operate with severe memory and power constraints. The sensor network challenges of limited resources, event-centric concurrent applications, and low-power operation drive the design of TinyOS. Our solution combines flexible, fine-grain components with an execution model that supports complex yet safe concurrent operations. TinyOS meets these challenges well and has become the platform of choice for sensor network research; it is in use by over a hundred groups worldwide, and supports a broad range of applications and research topics. We provide a qualitative and quantitative evaluation of the system, showing that it supports complex, concurrent programs with very low memory requirements (many applications fit within 16KB of memory, and the core OS is 400 bytes) and efficient, low-power operation.We present our experiences with TinyOS as a platform for sensor network innovation and applications.

The Ninja architecture for robust Internet-scale systems and services373423

Abstract The Ninja project seeks to enable the broad innovation of robust, scalable, distributed Internet services, and to permit the emerging class of extremely heterogeneous devices to seamlessly access these services. Our architecture consists of four basic elements: bases, which are powerful workstation cluster environments with a software platform that simplifies scalable service construction; units, which are the devices by which users access the services; active proxies, which are transformational elements that are used for unit- or service-specific adaptation; and paths, which are an abstraction through which units, services, and active proxies are composed.

A Network-Centric Approach to Embedded Software for Tiny Devices

The ability to incorporate low-power, wireless communication into embedded devices gives rise to a newgenre of embedded software that is distributed, dynamic, and adaptive. This paper describes the network-centric approach to designing software for highly constrained devices embodied in TinyOS. It develops a tiny Active Message communication model and shows how it is used to build non-blocking applications and higher level networking capabilities, such as multihop ad hoc routing. It shows how the TinyOS event-driven approach is used to tackle challenges in implementing the communication model with very limited storage and the radio channel modulated directly in software in an energy efficient manner. The open, component-based design allows many novel relationships between system and application.

A composable framework for secure multi-modal access to internet services from Post-PC devices

The Post-PC revolution is bringing information access to a wide range of devices beyond the desktop, such as public kiosks, and mobile devices like cellular telephones, PDAs, and voice based vehicle telematics. However, existing deployed Internet services are geared toward the secure rich interface of private desktop computers. We propose the use of an infrastructure-based secure proxy architecture to bridge the gap between the capabilities of Post-PC devices and the requirements of Internet services. By combining generic content and security transformation functions with service-specific rules, the architecture decouples device capabilities from service requirements and simplifies the addition of new devices and services. Security and protocol specifics are abstracted into reusable components. Additionally, the architecture offers the novel ability to deal with untrusted public Internet access points by providing fine-grain control over the content and functionality exposed to the end device, as well as support for using trusted and untrusted devices in tandem. Adding support for a deployed Internet service requires a few hundred lines of scraping scripts. Similarly, adding support for a new device requires a few hundred lines of stylesheets for the device format. The average latency added by proxy transformations is around three seconds in our unoptimized Java implementation.