Commit a584184c authored by Tran Huy Vu's avatar Tran Huy Vu

update 4 5 6 7

parent 20bb1fab
...@@ -12,7 +12,7 @@ We now present results on the evaluation of our wearable prototype, used in cons ...@@ -12,7 +12,7 @@ We now present results on the evaluation of our wearable prototype, used in cons
\end{figure} \end{figure}
We conducted all our experiments in a meeting room setup to mimic a typical We conducted all our experiments in a meeting room setup to mimic a typical
office working environment. Figure~\ref{fig:exprsetup} shows the setup--it it fairly similar to the WARP system setup in Figure~\ref{fig:antennarray}, except that the room also contains a table where one or more users can perform their usual desk-based office chores, while wearing the \name wearable device. Because users can move their arms in many different ways, the harvested power fluctuates as well (unlike the case of the static clients evaluated in the previous section). office working environment. Figure~\ref{fig:exprsetup} shows the setup--it it fairly similar to the WARP system setup in Figure~\ref{fig:antennaarray}, except that the room also contains a table where one or more users can perform their usual desk-based office chores, while wearing the \name wearable device. Because users can move their arms in many different ways, the harvested power fluctuates as well (unlike the case of the static clients evaluated in the previous section).
Unless otherwise stated, experiments are performed using an 8-antenna array on the WiFi AP. In these studies, the WiFi AP performs AoA estimation and adjustment of the beam orientation whenever it receives `ping' packets from one or more wearable devices (i.e., whenever the wearable device undergoes ``significant movement"). Note that each antenna can transmit at a maximum power of 20 dBm (achieved when the antenna gain=63); to minimize interference, we limit the antenna gain to 35 (about half of the maximum power). Accordingly, the overall radiated power from the WARP-based AP is no more than approx. 400-450mW, which is well below the EIRP limit. Unless otherwise stated, experiments are performed using an 8-antenna array on the WiFi AP. In these studies, the WiFi AP performs AoA estimation and adjustment of the beam orientation whenever it receives `ping' packets from one or more wearable devices (i.e., whenever the wearable device undergoes ``significant movement"). Note that each antenna can transmit at a maximum power of 20 dBm (achieved when the antenna gain=63); to minimize interference, we limit the antenna gain to 35 (about half of the maximum power). Accordingly, the overall radiated power from the WARP-based AP is no more than approx. 400-450mW, which is well below the EIRP limit.
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...@@ -56,7 +56,7 @@ In other words, $P$ represents the average power differential (averaged over the ...@@ -56,7 +56,7 @@ In other words, $P$ represents the average power differential (averaged over the
\label{fig:residualtime} \label{fig:residualtime}
\end{figure} \end{figure}
Figure~\ref{fig:residual2} 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 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.
\subsection{Effect of Duty Cycle} \subsection{Effect of Duty Cycle}
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...@@ -115,7 +115,7 @@ Each WARP board can be connected to 4 antennas. We use one WARP board with a 4-a ...@@ -115,7 +115,7 @@ Each WARP board can be connected to 4 antennas. We use one WARP board with a 4-a
Therefore, for our experimental studies, we place the two antenna-array at 2 edges of a table (1 meter from each other). In our implemented system, the wearable transmits 2 types of packets: (1) a `ping' packet (to aid AoA estimation) containing 1 preamble byte, 3 address bytes, 1 dummy data byte and 1 CRC byte; and (2) a data packet contains the same preamble, the address is different by 1 bit, a 2-byte packetID and 30 bytes of accelerometer data which is corresponding to 3 seconds of recorded data. Therefore, for our experimental studies, we place the two antenna-array at 2 edges of a table (1 meter from each other). In our implemented system, the wearable transmits 2 types of packets: (1) a `ping' packet (to aid AoA estimation) containing 1 preamble byte, 3 address bytes, 1 dummy data byte and 1 CRC byte; and (2) a data packet contains the same preamble, the address is different by 1 bit, a 2-byte packetID and 30 bytes of accelerometer data which is corresponding to 3 seconds of recorded data.
\subsection{Wearable Client Device} \subsection{Wearable Client Device}
Via our experimental studies, we are interested in not only studying the wearable device in isolation, but when it is being used by regular users. To perform such studies, we need to ensure that the wearable device can be mounted on an individual's wrist. Clearly, our current prototype isn't a true wearable device: its form-factor is simply too unwieldy for constant wear. However, to perform experimental studies, we place the wearable device in a custom-fabricated container, which is then attached to a person's wrists using multiple velcro straps (see Figure~\ref{fig:XXX}). Via our experimental studies, we are interested in not only studying the wearable device in isolation, but when it is being used by regular users. To perform such studies, we need to ensure that the wearable device can be mounted on an individual's wrist. Clearly, our current prototype isn't a true wearable device: its form-factor is simply too unwieldy for constant wear. However, to perform experimental studies, we place the wearable device in a custom-fabricated container, which is then attached to a person's wrists using multiple velcro straps (see Figure~\ref{fig:wearablecontainer}).
\subsection{Access Point \& Directional Beams} \subsection{Access Point \& Directional Beams}
\begin{figure} \begin{figure}
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