Low-power design methodologies for embedded internet systems

Sammanfattning: Embedded systems are resource-constrained special-purpose computers, capable of both sensing and controlling the environment they are placed in. An embedded system usually consists of both hardware and software. The hardware can be composed of sensors, actuators, processors, memory storage devices, communication peripherals, and power supplies. The software typically includes an operating system, device drivers, and an application-specific algorithm for controlling the system's behavior. A special class of embedded systems is comprised by systems that can communicate using standard Internet protocols. Such systems, called Embedded Internet Systems (EIS), are capable of transmitting sensor data directly to the Internet without using specialized gateways. Sensor nodes (nodes in a sensor network) are an example of specialized embedded systems. Sensor nodes with wireless communication capabilities can form a wireless network of sensors. Two types of such networks are usually distinguished - Wireless Sensor Networks (WSN) and Personal Area Networks (PAN). Wireless sensor networks may consist of hundreds or even thousands of sensor nodes; they can be used in industrial applications and deployed in hazardous environments, such as battlefields, volcanos, and forest fires. Personal area networks, on the other hand, are normally composed of a relatively small number of devices, which minimizes requirement on scalability. PAN devices use general-purpose technologies and standard protocols, such as Wi-Fi and Bluetooth, and they are designed for applications such as video and audio streaming, web browsing, and file transfer. Today's research on WSN technology is focused on creating power-efficient large-scale networks using highly specialized protocols and technologies; they are usually intended for scientific, military, and industrial usage scenarios. Research on PAN technology targets consumer needs, where two important requirements are interoperability, through the use of general-purpose technologies and protocols, and usability, often achieved by supporting dynamic address allocation and well-known service discovery protocols. When sensor nodes are used in personal area networks, they should have both features normally characteristic of WSN nodes and those more typical of PAN nodes. A sensor network based on general-purpose technologies should be power-efficient while at the same time enabling interoperability with consumer devices. By using consumer devices, such as mobile phones, and widely available access networks, such as GPRS and UMTS cellular networks, such sensor nodes can achieve worldwide mobility. This is in contrast to traditional wireless sensor networks where the focus is on achieving efficient communication within the network using highly specialized protocols and technologies. This thesis investigates the feasibility of using Embedded Internet Systems as wirelessly networked sensor nodes using standard protocols and commercial off-the-shelf (COTS) components. The focus is on reducing sensor nodes' power consumption while still allowing interoperability with standard consumer devices, such as mobile phones, PDAs, and computers. In other words, the goal is to merge WSN and PAN technologies to produce a new type of wirelessly networked sensor nodes with an operational lifetime in the range of months to years, which communicate using well-known protocols, such as Bluetooth and TCP/IP. Bluetooth was chosen since it is by far the most wide-spread protocol supported by existing consumer devices, and we call the resulting sensor networks Bluetooth Sensor Networks (BSN). BSN nodes are EIS devices used in the context of sensor networks, and the main motivation for this type of sensor networks is to allow sensors, such as GPS, pulse oximeters, and thermometers, to be used in conjunction with standard consumer devices and applications. The work presented in this thesis has resulted in a system architecture which supports sensor networks consisting of EIS devices with a lifetime of several years, energy scavenging capabilities, and user-oriented low-power operation. The use of TCP/IP and Bluetooth enables interoperability with existing infrastructures, such as the Internet, and mobility, when Bluetooth-enabled mobile phones are used as gateways to cellular networks. It has also be demonstrated that it is feasible to utilize Bluetooth and TCP/IP on resource-constrained networked sensor nodes, while still enabling system operational lifetimes in the range of months to years and using a total system volume of less than 10 cm3 .