Changeset 2802

Timestamp:

10/30/09 18:20:50 (4 weeks ago)

Author:

wark

Message:

small update to fig

Files:

• HydroWatch/Tim/doc/ipsn10/sec_intro.tex (modified) (3 diffs)

HydroWatch/Tim/doc/ipsn10/sec_intro.tex

@@ -9 +9 @@
 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, typically in order of 5\% duty cycles for practical deployments\cite{gdi04sensys,tolle05sensys,firewxnet06mobisys,sensorscope08ipsn}. 
 Whilst ultra-low duty cycle MAC's have been validated under controlled conditions\cite{ye06sensys,dozer07ipsn}, 
-in general, breaking through the 1\% duty-cycle barrier for practical deployment scenarios is not possible with current radio technology.
+in general, breaking through the 1\% duty-cycle barrier for practical, multi-hop deployment scenarios requiring highly reliable, ``always available'' operation, is very difficult with current radio technology.
 
-Even after radio duty-cycling, idle listening is still one of the major energy consumers of sensor nodes. As shown in Figure~\ref{fig:energy}(a),  idle listening consumes XX\% over the overall energy budget, compared to just XX\% for sampling and transmitting of data. In other words, a significant energy cost is paid to allow the node to be in a state of ``always on'', and only a small part of the energy is used in the actual sampling and transmission of information\cite{prabal07batch}.
+Even after radio duty-cycling, radio is still one of the major energy consumers of sensor nodes. As shown in Figure~\ref{fig:energy}(a),  for a node running LPL (512ms sleep interval) and transmitting every minute, radio consumes over 95\% over the overall average power draw of 620$\mu$A. In other words, a significant energy cost is paid to allow the node to be in a state of ``always on'', and only a small part of the energy is used in the actual sampling and transmission of information\cite{prabal07batch}.
 
 \begin{figure}[ht]
@@ -19 +19 @@
         \includegraphics[width=0.5\columnwidth]{fig/dummy_piechart}\\
          %\includegraphics[width=0.6\columnwidth]{fig/dummy_graph}\\ 
-        (a) LPL (512ms) & (b) \\ 
+        (a) LPL (total 620$\mu$A) & (b) \\ 
     \end{tabular}
     \caption{Piechart showing (a) Typical power breakdown for a node running LPL with 512ms sleep interval, (b) A typical energy breakdown for a node scheduling the radio}
@@ -25 +25 @@
 \end{figure}
 
+An obvious way to reduce the amount of energy consumed by idle listening is to turn the radio off. Whilst the allows a large amount of energy to be redistributed to tasks such as sampling and sending (when the radio is switched on again), this approach allows incurs an additional network overhead each time the radios are turned back on in where network routing tables must be reformed. Figure~\ref{fig:energy}(b) illustrates the
+clear reduction in energy that comes about when the radio is off for long-periods (in this case 90\%), where the total consumption is reduced, in this example, to XX$\mu$A.
 
-An obvious way to reduce the amount of energy consumed by idle listening is to turn the radio off. Whilst this allows a large amount of energy to be redistributed to tasks such as sampling and sending (when the radio is switched on again), this approach incurs additional network overhead each time the radios are turned back on where network routing tables must be reformed and [other things?]. Figure~\ref{fig:energy}(c) illustrates the nature of this additional cost, showing the relationship between the time the radios are off and the effective energy consumed per bit of data transmitted. Once radios are off long enough, the effect of amortizing the cost of updating the network state over long periods becomes clear where in these cases the net energy cost is less than a typical low-power listening (LPL) MAC \cite{lpl04sensys}. 
+ %nature of this additional cost, showing the relationship between time the radios are off and the effective energy consumed per bit of data transmitted. Once radios are off long enough, the effect of amortizing the cost of updating the network state over long periods becomes clear where in these cases the net energy cost is less than a typical low-power listening (LPL) MAC \cite{lpl04sensys}. 
 
-The other key trade-off in turning off radios is that of network responsiveness. Once nodes only become active at scheduled intervals then the times a user can communicate with nodes, or the times which nodes can report to a base are now constrained. This has clear implications for event-driven applications or query-based systems, where a user may want an immediate response from the network.
+The key trade-off in turning off radios is that of network responsiveness. Once nodes only become active in scheduled intervals then the times a user can communicate with nodes, or the times which nodes can report to a base are now constrained. This has clear implications for event-driven applications or query-based systems, where a user may want an immediate responsive from the network.
 
 \subsection{Motivation}~\label{sec:motivation}