solarstore: enhancing data reliability in solar-powered storage-centric sensor networks yong yang,...
TRANSCRIPT
SolarStore: Enhancing Data Reliability in Solar-powered
Storage-centric Sensor NetworksYong Yang, Lili Wang, Dong Kun Noh, Hieu Khac Le and Tarek F. Abdelzahe
Mobisys 2009
Brian2009/8/17
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
Architecture of SolarStore
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
1. Eresidual = Psys* Tfull(Eresidual) at least2. 3. Eresidual threshold = 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 does
not depend on the initial states
Under different energy states
• Residual storage and storage surplus• Surplus remain constant
Node 2 Node 9
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 does not 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?
• Thank you
Reliability level of node 9