ELECTIONEL ECTI ON ELECTION: Energy-efficient and Low- latEncy sCheduling Technique for wIreless sensOr Networks Shamim Begum, Shao-Cheng Wang, Bhaskar Krishnamachari, and Ahmed Helmy Department of Electrical Engineering-Systems, University of Southern California IEEE Local Computer Networks (LCN’04)

Outline Introduction Proposed Protocol Simulation Results Conclusion and Future Work

Introduction Research challenge Energy efficiency Energy efficient protocols MAC, topology control, data aggregation, etc Main concern Design of sleep scheduling scheme

Introduction Performance metrics Energy efficiency Latency Responsiveness The difference between reported data value and the data threshold Focuses in different scenarios Normal operation: energy efficiency Abnormalities happed: low latency or high responsiveness

Introduction Motivation Dynamic requirements of different metrics Main idea Spatial-temporal correlation Spatial: At any point of time, all sensors in a small area in the sensor field measure the same phenomenon Temporal: When some abnormal reaction causes the phenomenon, all sensors read this increasing phenomenon and perceive the increase

Protocol --- Network Model and Assumptions Sensor field Reaction area assumption both communication radio and the sensor can be turned off independently to save energy threshold tolerance is specified model

Protocol --- Timing Diagram Phase 0: Synchronization --- using existing synchronization schemes Phase 1: Periodic sleep and monitor Phase 2: CH formation, data aggregation, and report

Protocol --- State Transition Diagram

Protocol --- Phase 2 M A E B D C Z X Y W 42 Initial ( D th ) = 30)

Protocol --- Phase 2 M A E B D C Z X Y W 42 Neighborhood advertisement message exchange

Protocol --- Phase 2 Cluster head election M A E B D C Z X Y W 42

Protocol --- Phase 2 M A E B D C Z X Y W 42 Cluster head advertisement message broadcast

Protocol --- Phase 2 M A E B D C Z X Y W 42 Cluster membership message reply Message from node X has higher signal strength

Protocol --- Phase 2 Cluster formation M A E B D C Z X Y W 42

Protocol --- Phase 2 TDMA schedule creation in cluster heads M A E B D C Z X Y W 42

Protocol --- Phase 2 M A E B D C Z X Y W 42 TDMA schedule announcement

Protocol --- Phase 2 M A E B D C Z X Y W 42 Data aggregation and data transmission ? Does the cluster always directly transmit data packets to its nearby base station ?

Sleep Cycle Adaptation ELECTION vs. other protocols ELECTION turns sensors off during sleep Sleep cycle reduction function F sr is a function of current sleep cycle and gradient of the environment s(t): sleep cycle duration at time t g(t) : gradient at time t s(t+1)=F sr (s(t), g(t))

Exponential F sr Good for latency Aggressive sleep cycle reduction causes small sleep cycle  energy expensive

Geared F sr

Simulation Results --- Compared Approaches TEEN [12] Nodes sleep periodically instead of staying awake During sleep Nodes turn their communication radios off leaving the sensors on Nodes sense the environment continuously and wake up only when the event threshold is detected Hybrid Mix of TEEN and ELECTION Fixed sleep cycle, on-demand cluster formation

Simulation Results --- Parameters and Phenomenon Parameters Phenomena P1: Changes 100 times during the entire simulation P2: Changes 20 times during the entire simulation

Simulation Results --- Remaining Energy (P1) Major energy costs are sensing and cluster formation Save energy of cluster formation, but waste energy for continuous sensing

Simulation Results --- Remaining Energy (P2) Sleep duration become large (Change slower than P1),  significant energy saving Fixed sleep duration  no significant energy saving

Simulation Results --- Number of Alive Nodes

Simulation Results --- Delay Hybrid/TEEN: fixed sleep cycle (delay  25 sec) ELECTION: depends on the sensing phenomenon

Simulation Results --- Responsiveness

Conclusion and Future Work Proposed ELECTION scheme Consider the spatial-temporal correlation of underlying physical phenomenon Three phases Perform well in comparison with TEEN and hybrid protocol Future work Hierarchical organization of cluster heads Load balance