1. Coverage and Energy Tradeoff in Density Control on Sensor Networks Yi Shang and Hongchi Shi University 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) GODC Overlap= (20.9%) NODC Gap= (9.31%)

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 p if its power exceeds a pre-determined threshold P t sets a backoff timer of τ 1 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 p if its power exceeds a pre-determined threshold Pt sets a backoff timer of τ 1 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. Density Control Protocols Rule4: receive more than two power-on messages 1. None of the coverage areas of the senders overlaps 2. previous senders do not overlap and new sender overlaps with previous senders 3. previous senders do not overlap and new sender overlaps with previous senders A B C AB C DD

12. ONDCD Density 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. ONDCA Density 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: r s = 5m. constant c = 10/r s 2

15. Experimental Results 88% vs. 85% 41 vs. 3475 vs. 75

16. 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