Public: Technology Reviews : Motes and Smartdust
This page last changed on Jun 13, 2005 by sbannasch.
Advances in extremely low-power wireless networking and computing are enabling the development of new disruptive technologies that will have a great effect on learning environments in the future. A number of research groups are creating the hardware and software infrastructures to support wirelessly interconnected swarms of inexpensive tiny computers called motes. Motes have sensors for measuring the environment around them and wireless network capabilities for communicating that sensor information. In addition motes have output capabilities for electronically controlling larger devices in which they may be embedded.
The optimization of hardware and software enabling low-power mesh networking technologies is a crucial element in the development of practical motes. Data traveling in a wireless mesh network is routed from one mote to a nearby mote where it is re-transmitted to the next mote. This process continues until the data reach their destination.
By only using enough transmit power to reach the closest motes the energy used for wireless data transmission is minimized. New modulation methods and higher data rates allow data packets to be transmitted in less time can conserve energy.
In the Spring of 2002 the Intel Research Laboratory at the University of California at Berkeley and the College of the Atlantic in Bar Harbor Maine started a pilot program to instrument the burrows used by the Leach's Storm Petrel in Great Duck Island. Over the next several years the group installed 165 motes in burrows that measured temperature, humidity, barometric pressure, and mid-range infrared and 25 weather station motes. Some of the motes are located in a forest more than 1000 feet from the network access point. Over the last several years re=searchers have collected millions of readings from the motes installed on the island. Traditional point-to-point wireless technology would consume much more power and require large batteries. The wireless access point collects data from the mesh of motes and transmits it via satellite to the Internet.
Dave Parsons of H2Options has implemented a prototype system using mote technology from Xcrossbow to measure real time water use from all the water-using appliances in an apartment complex. His system is designed to enable the apartment managers to plan and schedule maintenance to maximize water conservation. Measuring and reporting water usage from the fixtures in real time allows patterns of waste to be fixed more quickly for less cost.
At UCLA's Networked & Embedded Systems Laboratory (NESL) Mani Srivastava Richard Muntz Miodrag Potkonjak have developed a series of research prototypes to explore their concept of a Smart Kindergarten.
They have a vision of early-childhood education in which children and teachers can interact with instrumented objects in the classroom. For example the envision smart toys and other learning objects that can not only interact with the children but also log formative assessment data about the children and present these data to the teachers.
They developed a full-featured mote called an iBadge. An iBadge combined sensing of position, spatial orientation, and environmental variables, along with voice output and speech recognition capabilities and Bluetooth networking.
All motes have some sort of wireless networking that enable them to communicate both with each other and with a gateway to external networks. While other topologies have been used the most practical topology is a mesh. In a mesh each mote uses only the minimum transmit power necessary to reach nearby motes. To send data between two motes which are too far from each other to directly communicate packets of data are routed through intermediate motes. Each intermediate route is termed a hop. Both Bluetooth and Zigbeee are commercial low-power short-range wireless networking protocols which have been used with motes.
In normal use a Bluetooth network is a single hop from a Bluetooth node to a central Bluetooth access point however because the protocol is layered mesh networks have been built on top of the lower level Bluetooth network transport protocols.
Zigbee is a specification, implementation and a certfying mechanism for very low power wireless networks built on top of the IEE 802.15.4 standard. Zigbee was designed to sensor networks with slow data rates along with multi-month to multi-year battery life. The actual network protocol is relatively simple with some implementations taking only 28k of code. Zigbee was designed to natively support start, mesh, and cluster tree network topologies.
To enable contextually-appropriate processing and location-aware applications a mote needs to have a way to determine its physical location and relationship to other motes. Often GPS systems are not suitable for common spatial environments in which motes are placed. The Smart Kindergarten group has developed an ad-hoc localization system they call AHLoS. There are several methods that have been used.
Mobile and stationary motes can use infrared proximity beacons to determine if they are close to each other. Regularly broadcasting a wide-area infrared beacon takes is energy intensive and is normally only done with a stationary mote which can be powered externally. However beacons can be sued on motes which are physically pointed by a user towards a related object of interest. The exchange of beacon information between the two motes establishes physical proximity at that point in time.
An internally consistent map of motes can be created by varying radio signal strength to measure distance between motes. The distance between any two motes that can be in radio communication is roughly proportional to the minimum radio signal strength needed to communicate between the two. If the absolute location of a few motes is know the internal map of mote locations can be geo-referenced to an actual physical environment.
Networks of motes that have a shared accurate timebase can measure the time for a pulse of ultrasound to travel from a transmitter to each mote and use this information to determine distance. By iterating this measurement with three spatially-separated transmitters a three-dimensional map of node locations can be calculated.
The Global Positioning System is an excellent solution for determining absolute physical location outside however GPS receivers both consume a large amount of power and need to be powered on for long periods of time in order to calculate location.
In the future it may be possible that advances in IC-based phased-array antenna technology will allow electronically steerable antennas. Using a directional antenna for transmission of data greatly reduces the energy required and in addition the spatial orientation of locally networked motes can be determined. A large commercial example of this technology is the Vivato WiFi switch.
TinyOS is an open-source operating system designed for wireless embedded sensor networks. It features a component-based architecture which enables rapid innovation and implementation while minimizing code size.
NEST, UC Berkeley
FU Berlin Seminar: Understanding Mobile Technologies & Services (many good links)
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