Commit 5d66ff18 authored by Tran Huy Vu's avatar Tran Huy Vu

Update Section 7

parent e143590a
...@@ -47,7 +47,7 @@ Unless otherwise stated, experiments are performed using an 8-antenna array on t ...@@ -47,7 +47,7 @@ Unless otherwise stated, experiments are performed using an 8-antenna array on t
% evaluate how the wearing of the device affect the harvested energy. % evaluate how the wearing of the device affect the harvested energy.
\subsection{Office--Short Term} \subsection{Office--Short Term}
In outr first study experiment, we investigate the amount of harvested power that is likely to be realized under normal working conditions, when a user works at his or her office desk. To perform this study, two users each sat at a work desk (located within the office room) at different times, performing their usual desktop-based tasks for an hour. Each user was free to get up and move around the room, but did not leave the office room. To isolate the harvesting behavior and compare it with the static case, we disable the RF frontend of the wearable--i.e., each wearable actively collects the accelerometer data, but does not perform a wireless transfer to the backend. In our first study experiment, we investigate the amount of harvested power that is likely to be realized under normal working conditions, when a user works at his or her office desk. To perform this study, two users each sat at a work desk (located within the office room) at different times, performing their usual desktop-based tasks for an hour. Each user was free to get up and move around the room, but did not leave the office room. To isolate the harvesting behavior and compare it with the static case, we disable the RF frontend of the wearable--i.e., each wearable actively collects the accelerometer data, but does not perform a wireless transfer to the backend.
\begin{figure} \begin{figure}
...@@ -64,7 +64,7 @@ Figure~\ref{fig:energy1hour} plots the average differential power (measured over ...@@ -64,7 +64,7 @@ Figure~\ref{fig:energy1hour} plots the average differential power (measured over
\subsection{Office--Longer Term} \subsection{Office--Longer Term}
This next study is identical to the previous one, except that it involves only 1 user and is conducted over a longer observation period (4 hours), This larger observation period helps captures the user's natural movement dynamics over effectively one half of a typical working day: in this study, the user occasionally left the office room (e.g., to visit the restroom). For these study, we enabled both the continuous sensing and the periodic (once every 1.5 minutes) data transfer components. Accordingly, this study is meant to monitor the worst-case energy drain; in practice, a user will exhibit \emph{significant motion} only intermittently, and the sensing and data transfer overheads will thus be dramatically lower. This next study is identical to the previous one, except that it involves only 1 user and is conducted over a longer observation period (4 hours), This larger observation period helps captures the user's natural movement dynamics over effectively one half of a typical working day: in this study, the user occasionally left the office room (e.g., to visit the restroom). For these study, we enabled both the continuous sensing and the periodic (once every 1.5 minutes) data transfer components. Accordingly, this study is meant to monitor the worst-case energy drain; in practice, a user will exhibit \emph{significant motion} only intermittently, and the sensing and data transfer overheads will thus be dramatically lower.
Figure~\ref{energy4hour} plots the differential average power of the user, wearing the energy harvesting wearable. FOr a baseline comparison, we utilize a setting where the WiFi RF transmission are turned off--i.e., all energy harvesting is disabled. The baseline thus indicates the total average power drain on the wearable, in the absence of any energy harvesting. The figure shows that, in the absence of any harvesting, the wearable device drains approx. 65$\mu$W; in comparison, the power drain on the supercapacitor with harvesting enabled is only 20$\mu$W. The average power drain from the sensing+ data transfer components is XXX$\mu$W \am{Vu:pls. replace XXX by the average power drain that you had calculated--I believe it was around 120 $\mu$W??}. Accordingly, as the use of motion triggering on these components will dramatically cut down this power drain, the overall harvesting power will become positive, allowing the wearable to operate continually. Figure~\ref{energy4hour} plots the differential average power of the user, wearing the energy harvesting wearable. For a baseline comparison, we utilize a setting where the WiFi RF transmission are turned off--i.e., all energy harvesting is disabled. The baseline thus indicates the total average power drain on the wearable, in the absence of any energy harvesting. The figure shows that, in the absence of any harvesting, the wearable device drains approx. 65$\mu$W; in comparison, the power drain on the supercapacitor with harvesting enabled is only 20$\mu$W. The average power drain from the sensing+ data transfer components is 30 - 40$\mu$W because when the sensing is active, it will wake the microcontroller up to read the data and transfer the data to the RF module. Accordingly, as the use of motion triggering on these components will dramatically cut down this power drain, the overall harvesting power will become positive, allowing the wearable to operate continually.
\begin{figure}[!htb] \begin{figure}[!htb]
\centering \centering
...@@ -91,7 +91,7 @@ Figure~\ref{energy4hour} plots the differential average power of the user, weari ...@@ -91,7 +91,7 @@ Figure~\ref{energy4hour} plots the differential average power of the user, weari
% \end{figure} % \end{figure}
\subsection{Office: Multi-user} \subsection{Office: Multi-user}
We finally experimented with the case where two users occupied the office room concurrently. The two users performed their task under two different AP operatinal modes: (a) the time-multiplexed mode where the entire 8-antenna beam was directed at each wearable in round robin fashion, and (b) the concurrent mode, where each user was continuously targetd by a 4-antenna beam. For each of these two modes of operation, the two users were collocated for a total duration of two hours (i.e., the overall study duration was 4 hours), with 1 hour of being in close proximity (working side by side, with a separation of XXX m), followed by 1 hour where they worked farther apart (separated by a distance of XXX m). \am{Vu:pls. replace the two XXX in the previous line}. We finally experimented with the case where two users occupied the office room concurrently. The two users performed their task under two different AP operatinal modes: (a) the time-multiplexed mode where the entire 8-antenna beam was directed at each wearable in round robin fashion, and (b) the concurrent mode, where each user was continuously targetd by a 4-antenna beam. For each of these two modes of operation, the two users were collocated for a total duration of two hours (i.e., the overall study duration was 4 hours), with 1 hour of being in close proximity (working side by side, with a separation of 0.8 m), followed by 1 hour where they worked farther apart (separated by a distance of 1.5 m).
Figures~\ref{fig:2usertime} and~\ref{fig:2userseparated} plot the case for the time-multiplexed and concurrent mode of AP operation, respectively. We see that, as expected, the differential power is net negative: this is expected, as the wearable has its sensing and data transfer components enabled continuously, without any motion-based triggering. However, the differential power deficit is only around 40 $\mu$W (for either user) in the concurrent mode, whereas one of the users experiences a higher deficit (close to 85$\mu$W) when working further away from the other user, in the multiplexed mode. These findings corroborate our earlier observation (in Section~\ref{sec:multiuser}) that the mutliplexed mode is preferable only when the wearables are closer to each other. Figures~\ref{fig:2usertime} and~\ref{fig:2userseparated} plot the case for the time-multiplexed and concurrent mode of AP operation, respectively. We see that, as expected, the differential power is net negative: this is expected, as the wearable has its sensing and data transfer components enabled continuously, without any motion-based triggering. However, the differential power deficit is only around 40 $\mu$W (for either user) in the concurrent mode, whereas one of the users experiences a higher deficit (close to 85$\mu$W) when working further away from the other user, in the multiplexed mode. These findings corroborate our earlier observation (in Section~\ref{sec:multiuser}) that the mutliplexed mode is preferable only when the wearables are closer to each other.
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment