related-work.tex 3.95 KB
 Tran Huy Vu committed Apr 04, 2018 1 2 \section{Related Work} \label{sec:relatedwork}  Archan MISRA committed Apr 08, 2018 3   U-RAJESH-SIS\rajesh committed Apr 08, 2018 4 5 6 7 8 9 There has been a wide variety of related work in the broad areas of energy harvesting, including WiFi/RF energy harvesting, low-power wearable design and WiFi beamforming. %We focus on prior work around our two key concepts of %WiFi-based energy harvesting and indoor localization.  Archan MISRA committed Apr 08, 2018 10 11 12 13 14 15 16 17 18 19 20  %Energy harvesting papers \cite{talla2017battery} and WISP platform, some commercial products % %Localization/Activity recognition \cite{xiong2013arraytrack} \cite{pu2013whole} % %Passive sensing \cite{bharadia2013full} and PIR sensors % %Simultaneous Wireless Information and Power Transfer (SWIPT) \subsection{Energy Harvesting for Client Devices}  U-RAJESH-SIS\rajesh committed Apr 08, 2018 21 22 23 24 25 26 There is significant prior work on energy harvesting for wearable / embedded devices using light, kinetic energy, thermal gradients etc. Ambient and solar lighting generally provides the highest amount of harvested power as demonstrated by Heliomotes~\cite{lin2005} to power embedded devices and Hande et. al~\cite{hande2007} to power indoor APs. Kinetic energy is another popular energy harvesting source that can use body movements (e.g.  Archan MISRA committed Apr 08, 2018 27 EnergyBug~\cite{ryokai2014}), and walking (e.g. SolePower~\cite{solepower}) to  U-RAJESH-SIS\rajesh committed Apr 08, 2018 28 29 30 31 32 33 34 35 36 power ultra low power body sensors. Thermal energy harvesting uses temperature gradients to generate an electrical charge. For example, Thermes~\cite{campbell2014} used thermal harvesting to detect water usage events in buildings while Xu et. al~\cite{xu2013}, used thermal gradients between a shoe's insole and the external ground. More recent work, such as Flicker~\cite{hester2017}, provide a platform for rapid prototyping of energy harvesting-based sensors. Our work is complementary to these prior methods and can be used to a) power higher power devices, and b) deployed in environments (e.g. dark warehouses) where other methods would not work.  Archan MISRA committed Apr 08, 2018 37 38 39  \subsection{WiFi \& RF harvesting}  U-RAJESH-SIS\rajesh committed Apr 08, 2018 40 41 42 Harvesting power from wireless transmissions has also been studied and usually requires custom-designed hardware for the goal of charging RFID tags and devices -- with WISP~\cite{sample2008} being a very well known example  Archan MISRA committed Apr 08, 2018 43 that is used to power a variety of sensors. PoWiFi~\cite{talla2015powering} is the work closest  Tran Huy Vu committed Apr 09, 2018 44 in spirit, and the precursor, to our approach. PoWiFi modifies AP firmware to transmit power packets' (without using beamforming) on multiple free channels simultaneously, and harvests such RF energy using a matched filter on the receiver that can simultaneously harvest power across multiple channels. The authors demonstrate that such WiFi power harvesting can be used to operate low power embedded sensors at reasonably large distances (up to 20 ft away), but with relatively low duty cycles (e.g., a camera image once every 20 mins). Using beamforming to increase energy harvesting  Archan MISRA committed Apr 08, 2018 45 46 has been studied via simulations by Huang et. al~\cite{huang2016performance} and Liu et. al~\cite{liu2014multi}. To the best of our knowledge, \name is the first working prototype to utilize directional WiFi transmissions and a triggered operation (of the wearable platform) to support sensing of human activities.  U-RAJESH-SIS\rajesh committed Apr 08, 2018 47 48  \subsection{WiFi-based Localization}  Archan MISRA committed Apr 08, 2018 49   U-RAJESH-SIS\rajesh committed Apr 08, 2018 50 51 52 53 \name requires accurate tracking of a wearable, potentially mobile, device, to perform accurate beamforming to relieve sufficient RF energy. Prior work, such as ArrayTrack~\cite{xiong2013arraytrack} and Chronos~\cite{vasisht2016} have shown how to leverage active client RF  Tran Huy Vu committed Apr 09, 2018 54 transmissions, coupled with precise AoA computations to very precisely  U-RAJESH-SIS\rajesh committed Apr 08, 2018 55 locate the client. We use similar methods in \names. Device-free  Tran Huy Vu committed Apr 09, 2018 56 localization approaches, such as WiSee~\cite{pu2013whole}, and single AP  U-RAJESH-SIS\rajesh committed Apr 08, 2018 57 58 59 60 methods, such as Bharadia et. al~\cite{bharadia2013full}, Jain et. al~\cite{jain2011practical}, and IndoTrack~\cite{li2017} were also considered. But they were not robust enough for our arbitrary deployment environment with multiple human occupants.  Archan MISRA committed Apr 08, 2018 61 62 63  %\subsection{Simultaneous Wireless Information and Power Transfer (SWIPT)} %\am{Jie--can you add a little text and some references here?}`