Changeset 2824

Timestamp:

10/30/09 20:56:49 (4 weeks ago)

Author:

jaein

Message:

 

Files:

• HydroWatch/Tim/doc/ipsn10/sec_intro.tex (modified) (2 diffs)

HydroWatch/Tim/doc/ipsn10/sec_intro.tex

@@ -1 +1 @@
 %%%%%%%%%%%%%%%%%%%%%%%
 \section{Introduction}
+\label{sec:motivation}
 \subsection{Background}
 %The past decade has seen significant progress towards the goal of making long-term, embedded, environmental sensing a reality. 
@@ -7 +8 @@
 %\cite{roundy04ewsn} and challenges in the cost and predicability of harvested energy from sources such as solar or wind energy, much of the field today has focussed on reduction of energy consumption at the load side.
 
-The past decade has seen significant progress towards the goal of making long-term, embedded, environmental sensing a reality. Within a typical mote-class device, current technology dictates that the vast majority of energy is consumed by the physical radio.  As such, duty-cycling of the radio has been the key method employed to reduce energy consumption in practical deployments.~\cite{gdi04sensys,tolle05sensys,firewxnet06mobisys,sensorscope08ipsn} A number of ultra-low power MAC layers have sustained the race to zero consumption at the link layer\cite{ye06sensys,dozer07ipsn}, where the current state-of-the-art has a duty cycle of 0.65\%~\cite{hui08}). However, we believe that with current technology, there is minimal further improvement possible for duty-cycling link layers.
+The past decade has seen significant progress towards the goal of making long-term, embedded, environmental sensing a reality. Within a typical mote-class device, current technology dictates that the vast majority of energy is consumed by the physical radio.  As such, duty-cycling of the radio has been the key method employed to reduce energy consumption in practical deployments.~\cite{gdi04sensys,tolle05sensys,firewxnet06mobisys,sensorscope08ipsn} A number of ultra-low power MAC layers have sustained the race to zero consumption at the link layer\cite{ye06sensys,dozer07ipsn}, where the current state-of-the-art has a duty cycle of 0.65\%~\cite{hui08sensys}). However, we believe that with current technology, there is minimal further improvement possible for duty-cycling link layers.
 
 A common thread among most of the deployments mentioned is an implicit requirement that the network is ``always available'' - the link layer provides the ability to interact with any node in the network at any time. Though this provides a degree of comfort for network operators, an examination of an environmental sensing application energy budget reveals that network responsiveness has implicitly been allocated as the highest priority for the network. To get a sense for this, we show two pie charts in Figure~\ref{fig:energy}: (a) shows the energy distribution between the hardware components for a node running the Low Power Listening (LPL) radio duty-cycling MAC layer~\cite{polastre04} and (b) shows the same distribution for a node that runs the same LPL layer, but only 10\% of the time; the other 90\% of the time is spent with the radio completely off. Though the radio in each case is the majority consumer, the magnitude of consumption is an order of magnitude less in the latter. This provides an opportunity to reassign the joules previously reserved for radio idle listening to more useful tasks like increased sensing and collection.