A new communication protocol for wireless sensor networks
just released by the Information Sciences Institute is the most
efficient yet, more than a tenfold improvement on previous
versions.
Sensor networks, or "sensornets" are an emerging way to
monitor inaccessible and unwired places. They depend on
placing numerous sensor units across a wide area. The units
communicate with each other, and send the information they
gather at intervals to the human operators.
In wilderness parks, for example, such networks are used to
monitor activity by wildlife. Ordinary wireless methods, such
as WiFi won't work for this purpose. Sensornets are also
being explored for industrial applications, in oilfield
monitoring and managment, for example.
The units are battery powered, so minimum power
consumption is critical - but at the same time, continuing
coverage is essential. The activities of the units are
orchestrated by special operating rules called Media Access
Control (MAC) protocols.
More than three years of ISI research &ndash supported by the
National Science Foundation, Intel and other funders &ndash
produced a new protocol, SCP-MAC, which marked a
dramatic improvement in energy efficiency.
The protocol combines two techniques: 'low power listening"
in which units switch on for only very brief periods; and
"scheduled channel polling" which synchronizes and
schedules the listening.
"The basic approach of SCP-MAC is to let units alternate
periods of
sleeping with very brief periods of listening, as shown in the
figure," says Ye.
"Such a sleep pattern is found on birds, who need to keep
vigilance while
sleeping. To minimize the listening cost, SCP-MAC utilizes
'low-power
listening,' which detects channel activity very quickly.
"It further
reduces the transmission cost by synchronizing the listening
schedules
of nodes, so that a unit can wake up its neighbors by
transmitting a
short tone."
Previous protocols required individual units to be active for
approximately 2-3 per cent of monitoring time- that is,
active about 29-45 minutes of every day of sensornet
activity. SCP-MAC reduced the monitoring time to less than
two minutes each day.
The system was developed by ISI research scientist Wei Ye,
working with project leader John Heidemann and
programmer Fabio Luis Silva in the ISI
Laboratory for Embedded Networked Sensor
Experimentation.
The trio gave a final presentation on the research in
November at the Proceedings of the Fourth ACM SenSys
Conference in Boulder Colorado.
In February, the group made the new protocol, written in the
TinyOS operating system optimized for Mica2 individual
sensor modules, available for download by sensornet users
and developers.
The download url is:
http://www.isi.edu/ilense/software/
scpmac/
|
