Because
of all of these reasons, sensor nodes should operate as self-contained entities,
powered by sources such as batteries, fuel cells or scavenged energy. Since all
of these energy sources are fundamentally limited by the small device form
factor, energy-e?±cient design is imperative to ensure a su?±ciently long operational
lifetime of the network.
The challenge of energy-e?±cient operation has to be tackled on all levels
of the network design, from hardware devices and algorithms to protocols
and applications. Although sensing and data processing could be significant
as well, depending on the specifics of the application, the communication
portion of a system is often a very significant contributor to the overall energy
consumption. It has been observed, for example, that in typical sensor node
devices, it takes about the same amount of energy to communicate one bit
of information as to execute a few hundred instructions on the embedded
processor [1]. It is therefore important that the network communications, a
crucial enabler of the networked behavior as an autonomous distributed sensor
system, are designed to be as energy e?±cient as possible.
University of California, San Diego, CA 92093
195
Curt Schurgers
In order to do this, the characteristics of typical radios used in sensor
networks, need to be investigated. Figure 1 shows the power consumption of
three representative and often-used radio platforms: the RFM TR1000 (used
in MICA [2] and Medusa MK-II nodes [3]), the Chipcon CC1000 (used in
MICA2 nodes [2]) and the Chipcon CC2420 (used in MICAz [2], Telos [4]
and XYZ nodes [5]).
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