Commit 0dc9d7a8 authored by Tran Huy Vu's avatar Tran Huy Vu

The submitted version

parent 9ff88d99
......@@ -84,7 +84,7 @@ motion} of the wearable device. Such significant motion triggers both (i)
the transmission of ``ping'' packets, which allows the AP to
determine the wearable's new AoA, and (ii) the activation of the
accelerometer sensor, during the likely occurrence of meaningful gestures.
A super capacitor helps store the harvested RF energy, and smoothen out transient fluctuations in power supply and drainage.
A supercapacitor helps store the harvested RF energy, and smoothen out transient fluctuations in power supply and drainage.
\item \emph{Experimental Demonstration of \names:} By combining controlled \& real-world studies with numerical analysis, we show the viability of \names. In particular, micro-studies with a static wearable show that the wearable can harvest over 400 $\mu$W, at a distance of 1 meter. The harvested power remains high (over 30$\mu$W) even at a distance of 3 meters. More importantly, we use a 4-person study in an office cubicle setting to show that \name can be used to \emph{continuously} monitor for \emph{major} hand movements, while being net energy-positive. Moreover, via numerical analysis, we show that, by appropriately adapting the spatial \& temporal pattern of the RF beams, our AP can support multiple such wearables simultaneously.% \am{Fill in missing XXX}
%\vt{I think we still cannot conclude that it can transfer over 200uW in a cone of XXX}
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......@@ -2,7 +2,7 @@
\label{sec:relatedwork}
There has been a wide variety of related work in the broad areas of energy
harvesting, including WiFi/RF energy harvesting, low-power wearable design
harvesting, including WiFi/RF energy harvesting, low-power wearable design,
and WiFi beamforming.
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......@@ -58,7 +58,7 @@ In our system, when the accelerometer records enough data, it generates an inter
\end{figure}
\subsubsection{Zero-Energy Motion Trigger}
To minimize the unnecessary energy drain of the wearable device, we adopt a triggering-based mechanism, whereby the sensor and the microcontroller are activated only \emph{when the wearable device experiences significant motion} (e.g., when the user makes a gesture). To avoid the energy drain from such motion monitoring, we include a very simple, ``zero-energy", passive, motion trigger: a coil (taken from a shake torch) with a Neodymium magnet inside. Whenever the device is subject to a significant movement, the coil generates a voltage high enough (see Figure~\ref{fig:triggervoltage}) to trigger an external interrupt to the microcontroller, which then activates the rest of the components. This trigger also causes the controller to generate and send out `ping' packets, which the AP can then use to infer the client's updated AoA. Our motion trigger component is more sensitive to rotational movements but less sensitive to subtle linear motion. However, this was not a limitation in our current studies (in an office meeting room), where user gestures typically include a sufficient rotational compnent. There are prior studies on tiny MEMS-based motion energy harvesters~\cite{miao2006mems,yeatman2007micro} that may provide greater linear and rotational motion sensitivity--we shall explore these in future work.
To minimize the unnecessary energy drain of the wearable device, we adopt a triggering-based mechanism, whereby the sensor and the microcontroller are activated only \emph{when the wearable device experiences significant motion} (e.g., when the user makes a gesture). To avoid the energy drain from such motion monitoring, we include a very simple, ``zero-energy", passive, motion trigger: a coil (taken from a shake torch) with a Neodymium magnet inside. Whenever the device is subject to a significant movement, the coil generates a voltage high enough (see Figure~\ref{fig:triggervoltage}) to trigger an external interrupt to the microcontroller, which then activates the rest of the components. This trigger also causes the controller to generate and send out `ping' packets, which the AP can then use to infer the client's updated AoA. Our motion trigger component is more sensitive to rotational movements but less sensitive to subtle linear motion. However, this was not a limitation in our current studies (in an office meeting room), where user gestures typically include a sufficient rotational component. There are prior studies on tiny MEMS-based motion energy harvesters~\cite{miao2006mems,yeatman2007micro} that may provide greater linear and rotational motion sensitivity--we shall explore these in future work.
\section{The \name AP}
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