cross-layer application-specific wsn design over ss-trees -prepared by amy
Post on 21-Dec-2015
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Cross-Layer Application-Specific WSN Design over SS-Trees
-Prepared by Amy
Outline
• Background Introduction
• Sleep Scheduling Issues & the SS-Tree Concept
• SS-Tree Operational Stages
• SS-Tree Computation
• SS-Tree Operational Specifics & Sleep Scheduling
• Conclusions and Future Work
Background Introduction
• Wide-area surveillance WSN
applications−expected lifetime −limited battery supply
• Energy Efficiency is paramount
• Adaptive sleep schedules to
minimize energy lost
Background Introduction
• Sleep scheduling: −shorten the time radio transceiver engaged in
idle listening
• Good impact:−reduced overhearing
• Ensuing problem: − link table entries expire prematurely−control and data packet compete for resources−real-time data reporting function reduced
Background Introduction
• Ultimate Design Goal:−Balance:
• sensing requirements• end-to-end data communication overhead• network control effectiveness
−With energy efficiency−Through a cross-layer sleep scheduling
scheme
Sleep Scheduling Issues
• Not recommended:
• Random sleep scheduling−detrimental effect on network connectivity
and topology control efficiency
• Global sleep scheduling−network-wide communication blackout
• Groups of leaf nodes sleep scheduling−non-leaf nodes depleting battery reserves
sooner
Sleep Scheduling Issues
• Using coordinated sleep scheduling−Realize the benefits:
• reduced overhearing • reduced packet collision• simplified topology
−Without sacrifice:• network connectivity • sensing capabilities
SS-Tree Concept
SS-Tree Concept
• Advantages:−Avoid overburdening any set of nodes
from being the sole virtual backbone−Increase monitoring sensitivity (greater
event reporting windows) without altering communication duty cycle(reporting frequencies)
SS-Tree Concept--issues to be considered Gaps appearing in
between the active period of adjacent SS-Tree
SS-Tree Concept--issues to be considered -- Blackout duration -- Sleep period -- number of mutually adjacent SS-Trees -- Active period
Number of distinct live pathTo guarantee 100% real-time event reporting capability
Not feasible due to limited nodal densityAnd high SS-Tree computation complexityNot necessary to approach real-timeIntuition suggests the number of SS-TreeShould less than the average nodal degree
SS-Tree Concept--issues to be considered
Drawback: timer-drivenData cannot be simultaneouslyGathered from all SS-Trees
SS-Tree Operational Stages
SS-Tree Operational Stages
• Network Initialization: − gather network connectivity information, − compute the SS-Trees− disseminate the sleep schedules
• Sleep: − shut down the radio transceiver− processor and sensing unit remain active
• Hibernation: − Shutting down all hardware components − except for a tiny low-power wakeup timer
SS-Tree Operational Stages
• Active: −all data reporting −network maintenance tasks are performed
• Failure Recovery: −data sink repair or reconstruct SS-Trees
• Neighborhood Update: −neighboring nodes exchange local information −for each other’s sleep schedule
SS-Tree Computation
SS-Tree Computation
• A greedy depth-first approach
• From the bottom-up on a branch-by-
branch basis
• Proceeds in a number of iterations
• In each iteration an end-to-end minimum
cost path is appended to one of the SS-
Trees.
SS-Tree Computation
SS-Tree Computation
SS-Tree Computation
SS-Tree Computation
SS-Tree Operational Specifics & Sleep Scheduling
• Major task – determine an optimal sleep
schedule that maximizes energy efficiency
• Short active period -> high transmission latency
• Longer active period -> increase sleep time
between two consecutive active periods
• Determine an upper bound of active period− balance low communication duty cycle− monitoring sensitivity− end-to-end packet transmissions
SS-Tree Operational Specifics & Sleep Scheduling
Network Layer Routing
SS-Tree Operational Specifics & Sleep Scheduling
• Some flexible strategies in manipulating application requirements:−Compact query formats
• shrink packet size by formatting data types • reduce hop-by-hop transmission time
−Aggressive data aggregation • duplicate suppression • reduce unnecessary packet exchange
−Hop-by-hop ACK in MAC layer • instead of end-to end ACK in transport layer • reduce energy expenditure
SS-Tree Operational Specifics & Sleep Scheduling
SS-Tree Operational Specifics & Sleep Scheduling
• Medium Access Control−Prefer single-channel unslotted CSMA
• simplicity• greater scalability• looser time synchronization requirements
−Bypass the RTS/CTS handshake • long end-to-end propagation delay
SS-Tree Operational Specifics & Sleep Scheduling
Timing components constituting a single active period
Round-trip time recorded for node I on its respective SS-Tree
SS-Tree Operational Specifics & Sleep Scheduling
SS-Tree Operational Specifics & Sleep Scheduling
SS-Tree Operational Specifics & Sleep Scheduling
SS-Tree Operational Specifics & Sleep Scheduling
IACK works better in reducing the time when the size of C/D packet is comparable to that of EACK
Conclusion and Future Work• Following issues will be explored:
1. For a given random topology, what is the maximum number of SS-Trees that can be constructed to minimize the number of shared nodes?
2. For a given number of nodes, what is the optimal method of deployment that ensures 100% coverage of the subject area while maximizing the number of available SS-Trees with minimum shared nodes?
3. What are the suitable neighborhood discovery and failure recovery strategies for the SS-Tree design?
The End