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

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 path To guarantee 100% real-time event reporting capability Not feasible due to limited nodal density And high SS-Tree computation complexity Not necessary to approach real-time Intuition suggests the number of SS-Tree Should less than the average nodal degree

SS-Tree Concept --issues to be considered Drawback: timer-driven Data cannot be simultaneously Gathered from all SS- Trees

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

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 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

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

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?

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