Commit d7fbbbe2 authored by Archan MISRA's avatar Archan MISRA

increase fig sizes, corrected typo

parent fb228471
......@@ -6,7 +6,7 @@ In this section, we shall study how \name works under \emph{static} conditions--
\subsection{Experiment Setup \& Calibration}
All our experiments were conducted in a meeting room using the antenna setup shown
in Figure~\ref{fig:antennaarray}. The WARP system was installed in an office room (roughly 8ftX8ft), with the transmitting and receiving antenna arrays placed at the 2 corners of the table (and 1 meter apart). For these studies, which involve static devices, we do not perform the periodic AoA estimation process, and assume that the wearable's orientation, relative to the WARP transmitter, is known a-priori. The transmitter and receiver gain was set to 35 out of 63 (max theoretical power of 20dBm at 63 gain) to reduce interference; thus, \emph{in all experiments, our total transmitted power was well within the EIRP upper bound}. Unlike otherwise stated explicitly, for these studies, the wearable device has the accelerometer sensor sampling at 10 Hz, with its RF frontend transmitting the collected sensor data packets in a burst, once every 1.5 minutes.
in Figure~\ref{fig:antennaarray}. The WARP system was installed in an office room (roughly 8ftX8ft), with the transmitting and receiving antenna arrays placed at the 2 corners of the table (and 1 meter apart). For these studies, which involve static devices, we do not perform the periodic AoA estimation process, and assume that the wearable's orientation, relative to the WARP transmitter, is known a-priori. The transmitter and receiver gain was set to 35 out of 63 (max theoretical power of 20dBm at 63 gain) to reduce interference; thus, \emph{in all experiments, our total transmitted power was well within the EIRP upper bound}. Unless otherwise stated explicitly, for these studies, the wearable device has the accelerometer sensor sampling at 10 Hz, with its RF frontend transmitting the collected sensor data packets in a burst, once every 1.5 minutes.
% We estimate the AoA of these ping packets and then use triangulation to
% estimate the direction to the transmitter antennas and then adjust the beam
......@@ -34,14 +34,14 @@ in Figure~\ref{fig:antennaarray}. The WARP system was installed in an office ro
\begin{figure}[!htb]
\centering
\includegraphics[height=1.6in,scale=0.25]{nouser.pdf}
\includegraphics[height=1.8in,scale=0.25]{nouser.pdf}
\vspace{-0.1in}
\caption{Differential power (Avg.) of our (static) device}
\vspace{-0.1in}
\label{fig:residual1}
\end{figure}
Our first experiment studied the amount of harvested energy \name could produce, to establish if he overall system was net \emph{energy-positive}--i.e., whether the wearable device could be operated infinitely long based on RF energy harvesting. We placed our wearable device at three different locations, L1, L2 and L3, that were 1.91, 1.32 and 1.17 meter, respectively, from the transmitter with an angle of 45\degree, 28\degree and 0\degree with respect to the transmitter's antenna array. We measured the voltage of the wearable's supercapacitor before and after
activating \name for 15 minutes. If the supercapacitor's voltage at the end of the experiment duration is higher than its initial starting voltage, the total harvested energy is greater that consumed by the wearable's components, and vice versa. Given the difference in voltage, the total energy stored in the supercapacitor can be computed using the following equation:
Our first experiment studied the amount of harvested energy \name could produce, to establish if the overall system was net \emph{energy-positive}--i.e., whether the wearable device could be operated infinitely long purely via RF energy harvesting. We placed our wearable device at three different locations, L1, L2 and L3, that were 1.91, 1.32 and 1.17 meter, respectively, from the transmitter with an angle of 45\degree, 28\degree and 0\degree with respect to the transmitter's antenna array. We measured the voltage of the wearable's supercapacitor before and after
activating \name for 15 minutes. If the supercapacitor's voltage at the end of the experiment duration is higher than its initial starting voltage, the total harvested energy is greater that consumed by the wearable's components, and \emph{vice versa}. Given the difference in voltage, the total energy stored in the supercapacitor can be computed using the following equation:
\begin{equation}
U = \frac{1}{2}CV^2; \; \; \; \; P = \frac{\Delta U}{T};
......@@ -60,14 +60,14 @@ In other words, $P$ represents the average power differential (averaged over the
\label{fig:residualtime}
\end{figure}
Figure~\ref{fig:residual1} shows the results of this experiment. We see that, in all 3 positions, the average power differential was positive, indicating that, on average, the harvested power is more than sufficient to operate the wearable device. More specifically, in position L2, the power differential is higher than 350 $\mu$W, indicating that WiFi harvesting is \emph{likely to be able to support the operation of multiple additional sensors as well} (as the marginal sensing cost is likely to low, once the basic system component costs of the processor and RF frontend are amortized). In addition, Figure~\ref{fig:residualtime} shows the time series fluctuation in the supercapacitor's voltage level (for position L2). Even in this favorable position, we can see that there are periodic drops in the voltage, with these dips corresponding to the transient periods when the RF frontend is activated to transfer the sensor data packets. In particular, by carefully measuring the energy drain with \& without transmissions by the wearable, we find that the RF frontend consumes $\sim30$mW when active. This graph has two important implications: (a) it underscores the necessity of a supercapacitor to tide over transient periods of deficient power, and (b) by demonstrating that it is impractical to operate a continuously-transmitting mode of operation, it justifies our ``triggered sensing" paradigm.
Figure~\ref{fig:residual1} shows the results of this experiment. We see that, in all 3 positions, the average power differential was positive, indicating that, on average, the harvested power is more than sufficient to operate the wearable device. More specifically, in position L2, the power differential is higher than 350 $\mu$W, indicating that WiFi harvesting is \emph{likely to be able to support the operation of multiple additional sensors as well} (as the marginal sensing cost is likely to low, once the basic system component costs of the processor and RF frontend are amortized). In addition, Figure~\ref{fig:residualtime} shows the time series fluctuation in the supercapacitor's voltage level (for position L2). Even in this favorable position, we can see that there are periodic drops in the voltage, with these dips corresponding to the transient periods when the RF frontend transfers the sensor data packets. In particular, by carefully measuring the energy drain with \& without transmissions by the wearable, we find that the RF frontend consumes $\sim30$mW when active. This graph has two important implications: (a) it underscores the necessity of a supercapacitor to tide over transient periods of deficient power, and (b) by demonstrating that it is impractical to capture the sensing stream continuously, it justifies our ``triggered sensing" paradigm.
\subsection{Effect of Duty Cycle}
\begin{figure}[!tbh]
\centering
\includegraphics[height=1.6in,scale=0.2]{dutycycle.pdf}
\includegraphics[height=1.8in,scale=0.2]{dutycycle.pdf}
\vspace{-0.1in}
\caption{Differential power (Avg.) vs. AP Trx. Duty cycle.}
\vspace{-0.1in}
......@@ -81,7 +81,7 @@ Figure~\ref{fig:dutycycle} plots the residual energy (computed, as before, from
\subsection{Effect of Number of Antennas}
\begin{figure}
\centering
\includegraphics[height=1.6in,scale=0.2]{number_antenna.pdf}
\includegraphics[height=1.8in,scale=0.22]{number_antenna.pdf}
\vspace{-0.1in}
\caption{Harvested Power vs. No. of Antennas.}
\vspace{-0.1in}
......
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