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 ...@@ -55,7 +55,7 @@ Our solution, called \names, uses beam-formed transmissions, by a
multi-antenna AP, of WiFi ``power packets'' (transmissions performed multi-antenna AP, of WiFi ``power packets'' (transmissions performed
explicitly to transfer RF energy) to deliver bursts of directed WiFi energy 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 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 techniques are paired with novel energy-conserving features on the wearable
device, which activates its communication and sensing components device, which activates its communication and sensing components
intelligently and selectively, to help capture only key events. While the intelligently and selectively, to help capture only key events. While the
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...@@ -21,7 +21,27 @@ ...@@ -21,7 +21,27 @@
\section{The Energy-Harvesting Client Device} \section{The Energy-Harvesting Client Device}
\label{sec:system} \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} \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. 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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