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This paper presents SolarStore, a mechanism to enhance data reliability in solar-powered storage-centric sensor networks. Focusing on habitat and environmental monitoring, it addresses challenges such as limited connectivity and long-term operation in remote locales. Implementation of SolarStore involves a novel architecture that efficiently manages energy and storage under varying conditions, utilizing replication and coding techniques to ensure data integrity. Performance evaluation showcases its adaptability and resilience compared to traditional methods, demonstrating significant improvements in data retrieval during node failures.
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SolarStore: Enhancing Data Reliability in Solar-poweredStorage-centric Sensor NetworksYong Yang, LiliWang, Dong Kun Noh, HieuKhacLe and Tarek F. AbdelzaheMobisys 2009 Brian 2009/8/17
Outline • Introduction • Method • Hardware system • Implementation • Performance • Result • Conclusion
Introduction • WSN in habitat and environment monitoring • Sensors are deployed in remote locales • Limited connectivity • Data need to be stored in the network • Long-term running • SolarStore • Energy adaptive • Storage reliability mechanism
Motivations • Energy • How to estimate redundancy energy to enhance the reliability? • Storage • How to use the redundancy energy to enhance the reliability?
Implementation • 9 nodes in the farm of the University of Illinois at Urbana-Champaign (40.1N, 88.20W) • 12V, 98AH • 120Watts
Hardware • EEE PC :10~15Watts (0.8~1.2A for 12V), 18GB • Linksys WRT54GL : 2.4Watts • >3Mbps transmission by 50m outdoor • Phidget voltage sensor:0.06V resolution
Architecture of SolarStore • Repository: a piece of storage space on the solid state disk managed by the operating system • Replicator: reads data blocks from Repository and encodes them into data chunks • Receiver:receives the encoded data chunks from other nodes and stores them into Repository
Method • Eresidual: current residual energy in battery • Tfull(Eresidual):expected time when battery is full • C: battery capacity • Psolar: average power charging rate by solar panel • Psys: average power consumption rate by system
Method • How to get Eresidual threshold if B(Eresidual)=0? B(Eresidual): the expected duration of blackout time • Eresidual= Psys*Tfull(Eresidual) at least • Eresidualthreshold = C*(Psys/Psolar) • △E: energy allocated for enhancing data reliability(if Eresidual ≧ C*(Psys/Psolar) ) △E = Eresidual- C*(Psys/Psolar)
Method • Sresidual: current residual storage space left • △S: storage surplus • R: expected data sensing rate • M: expected time from now to the next upload opportunity △S=Sresidual - R*M
Data coding and Reliability level • Fountain coding for replication • partitions a data block into k chunks and generates k’ (k’ ≧ k) encoded chunks, eg. k=8, k’=12 • Scatter out to each neighbor k’/(g+1) chunks, g= amount of neighbors(eg. g=8) • Reliability level : α=k’/h • h:the number of data chunks stored on the node that were generated from this data block
Voltage charging characteristic • Charging on from 6AM~7PM • 14.0V as 100% • 11.0V as 0%
Performance evaluation • Charging current from Oct.21~Nov.4 2008 • Emulation
Three Experiments • Under different energy states • Adaption to other environment • Comparison to three other schemes
Under different energy states • Residual energy • the behavior of SolarStore in a long run doesnot depend on the initial states
Under different energy states • Residual storage and storage surplus • Surplus remain constant Node 9 Node 2
Adaption to other environment • Enlarge charging current by 3 times for one day every 3 three days • The other two days multiply 0.2
Comparison to three other schemes • 0-Reliable • no data replication at all and uses all energy and storage space for data sensing • 1-Reliable • always replicates data to maximize data reliability • full-Reliable • only starts data replication when the battery is nearly full (99%) because the energy charged from solar panels will be wasted if not used.
Comparison to three other schemes • Data loss • Data sensing during energy blackout • Node failure • 0-Reliable :worst at node failure • 1-Reliable: best at recovering • full-Reliable : at least 58% data loss
Conclusion • the behavior of SolarStore in a long run doesnot depend on the initial states • SolarStore can dynamically responds to variations in the environment • leads to more retrievable data under different node failure scenarios, compared to three other schemes
Pros • Adaptive to control energy and storage effectively • Cons • Not consider the severe weather deeply • How to coordinate energy sharing between Replicator and Receiver?