Commit afc19578 authored by Tran Huy Vu's avatar Tran Huy Vu

fix sec 4

parent 5726b930
......@@ -55,7 +55,7 @@ Our solution, called \names, uses beam-formed transmissions, by a
multi-antenna AP, of WiFi ``power packets'' (transmissions performed
explicitly to transfer RF energy) to deliver bursts of directed WiFi energy
to a client device. To form the beam towards the client, \name utilizes AoA
(angle-of-arrival) estimation techniques~\cite{XXX}\am{Jie:pls. provide a reference here and in .bib}. These AP-side
(angle-of-arrival) estimation techniques~\cite{xiong2013arraytrack}. These AP-side
techniques are paired with novel energy-conserving features on the wearable
device, which activates its communication and sensing components
intelligently and selectively, to help capture only key events. While the
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......@@ -21,7 +21,27 @@
\section{The Energy-Harvesting Client Device}
\label{sec:system}
We now describe the design of our RF energy harvesting based wearable device, which includes an accelerometer sensor that can be used to track an individual's movement and gestures. Figure~\ref{fig:wearablediagram} illustrates the overall component-level design of the wearable device, which contains a few key components: (a) an RF-energy harvester, a low-power microcontroller, the low-power accelerometer sensor, a wireless communication interface, a supercapacitor (to provide transient energy storage) and a power management module. Figure~\ref{fig:pcbboard} shows the eventual implementation on a PCB board.
\begin{figure*}[!tbh]
\centering
\begin{subfigure}[b]{0.47\textwidth}
\centering
\frame{\includegraphics[scale=0.25]{diagram.pdf}}
\caption[]%
{{\small Component-level diagram}}
\label{fig:wearablediagram}
\end{subfigure}
\begin{subfigure}[b]{0.47\textwidth}
\centering
\frame{\includegraphics[scale=0.35]{board.pdf}}
\caption[]%
{{\small Wearable Implementation}}
\label{fig:wearablediagram}
\end{subfigure}
\caption{(a): Block diagram of the wearable device (b): Individual components on a PCB board.}
\label{fig:wearabledevice}
\end{figure*}
We now describe the design of our RF energy harvesting based wearable device, which includes an accelerometer sensor that can be used to track an individual's movement and gestures. Figure~\ref{fig:diagram} illustrates the overall component-level design of the wearable device, which contains a few key components: (a) an RF-energy harvester, a low-power microcontroller, the low-power accelerometer sensor, a wireless communication interface, a supercapacitor (to provide transient energy storage) and a power management module. Figure~\ref{fig:pcbboard} shows the eventual implementation on a PCB board.
\subsection{The RF Energy Harvester}
The RF harvester works by converting the received wireless transmissions into an output voltage. However, the output voltage usually fluctuates significantly with slight movement in the wearable device. As a result, the instantaneous power of the harvester is not strong and stable enough to operate the wearable directly. We use a boost converter, BQ25570, which stores low voltage energy and boost it into a higher voltage for common electronic devices. This converter has been commonly used in prior energy harvesting applications. It converts input voltage as low as 100mV to a programmable output voltage. (In our implementation, we set the output voltage at 2.57V) This output voltage is then used to operate an entire embedded system including 1 microcontroller, 1 inertial sensor and 1 RF communication front end.
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