Coverage and Energy Tradeoff in Density Control on Sensor Networks

1. Coverage and Energy Tradeoff in Density Control on Sensor Networks Yi Shang and Hongchi ShiUniversity of Missouri-Columbia ICPADS’05

2. Outline • Introduction Density Control Protocols • NODC vs. OGDC • DODCD • NODCA • Experimental Results • Conclusions

3. Introduction • Density Control • a technique for prolonging network’s lifetime while providing sufficient sensing coverage • determine when and which sensors should be powered up and which should power saving • Different applications require different degrees of sensing coverage • complete coverage • high percentage coverage • This paper consider the tradeoff between energy usage and coverage

4. Density Control Protocols • NODC vs. OGDC ( Non-Overlapping vs. Optimal Geographical) NODCGap= (9.31%) GODCOverlap= (20.9%)

5. Density Control Protocols • Assumptions • interested sensing space is much larger than the sensing range of each sensor node • radio range is at least twice of the sensing range • Each node knows its position

6. Density Control Protocols • States: ON/OFF/Undecided • Selection of starting node • selecting starting node with probability pif its power exceeds a pre-determined threshold Pt • sets a backoff timer of τ1 seconds • broadcast a power-on message after backoff • position of the sender • direction α : uniform distribution in [0, 2π]

7. Density Control Protocols • States: ON/OFF/Undecided • Selection of starting node • selecting starting node with probability pif its power exceeds a pre-determined threshold Pt • sets a backoff timer of τ1 seconds • broadcast a power-on message after backoff • position of the sender • direction α : uniform distribution in [0, 2π]

8. Density Control Protocols • Actions: when receiving a power-on message • checks the ratio of its sensing area covered by its “ON” neighbors to its overall sensing area is over a predetermined threshold (turn-off threshold θ) • Rule R1: first power-on message received from starting node • Rule R2: first power-on message received from non-starting node • Rule R3: second power-on message received • Rule R4: receive more than two power-on messages

9. Rule1 Rule3

10. A B C A B C D D Density Control Protocols Rule4: receive more than two power-on messages • None of the coverage areas of the senders overlaps • previous senders do not overlap andnew sender overlaps with previous senders • previous senders do not overlap and new sender overlaps with previous senders

12. ONDCDDensity Control Protocol Based on Distances • NODCD does not require the location information • Rule R1: The message is the first power-on message received. • Rule R2: More than one power-on messages have been received.

13. ONDCADensity Control with Adjustable Sensing Ranges • Turn-off threshold θ, 0 ≤ θ ≤ 1, • Two iterations as follows The optimal values of θ, r2 ????

14. Experimental Results • region of interest : 50m x 50m square. • sensing range: rs= 5m. • constant c = 10/rs2

15. Experimental Results 88% vs. 85% 41 vs. 34 75 vs. 75

16. Experimental Results

17. Experimental Results

18. Conclusions • three new density control protocols that apply new strategies in trading the coverage vs. energy usage • distributed • easy to implement • low computation/communication costs