A Coverage-Preserving and Hole Tolerant Based Scheme for the Irregular Sensing Range in WSNs Azzedine Boukerche, Xin Fei PARADISE Research Lab Univeristy of Ottawa Regina B. Araujo Computer Science Department Federal University of Sao Carlos Globecom 2006

Outline Introduction Intersection Point Method (IPM) –Basic Definition –The Intersection Points Method –Comparison of IPM with Other Methods Performance Evaluation Conclusions

Introduction WSN have been a hot research topic in recent years A fundamental issue in WSNs is the coverage problem The most common sensor model used by the majority of coverage assumes that a sensor can cover disk centered at itself

Introduction In most cases, the sensing range is location- dependent and most likely irregular The effect of reflection caused by boundaries and obstacles, the sensor cannot maintain its disk sensing range Can a distributed scheme that solves the coverage problem under a polygon sensing range without relying on GPS system?

Introduction Another interesting aspect of coverage is tolerance to holes since high accuracy coverage is not always necessary If we can control the size of holes that can be tolerated, coverage will not be jeopardized This paper proposes an Intersection Point Method to help nodes locate coverage holes without the limitation of the disk sensing range

Intersection Point Method (IPM) Assumptions –The sensors’ density is high enough that only part of them are able to monitor the desired region R m –The sensing range is a closed simple polygon and can be detected by sensors –The communication is twice the maximum sensing range

IPM_Basic Definition pipi pjpj d ij < radio range

IPM_Basic Definition

LIP VIP

IPM_Basic Definition Breach Intersection Polygon P P’s neighbor Intersection sub-polygon

IPM_Basic Definition P1P1 P2P2 P3P3 PP P1P1 P2P2

IPM_The Intersection Points Method The relation of polygons –Inside –Overlapping (Ignore, no two sensors are in the same location) –Intersecting

IPM_The Intersection Points Method P Sponsor

IPM_The Intersection Points Method P1P1 P2P2 P3P3 P4P4 P2P2 P3P3 P4P4 P2P2 P3P3 P4P4 Remove P2P2 P3P3 P4P4 Breach intersection polygon q

IPM_The Unit Circle Test

Tolerance to Holes

Comparison of IPM with Other Methods Compared existing solutions –Probing Does not consider the sensing range only turns on sensor when there are no other sensors in its communication range Run quickly and easily implement

Comparison of IPM with Other Methods Compared existing solutions –Central Angle Method (CAM) Consider the existence of holes by identifying fully sponsored sensors locally through low complexity computing Cannot guarantee the identification of holes and will cause a connectivity problem when nodes run out of energy

Comparison of IPM with Other Methods Compared existing solutions –Association Sponsor Method (ASM) Consider areas that overlap with all neighbors Neighbor with a low overlap area are associated with neighbors with a high overlap area

Performance Evaluation Random deployment 50m * 50m area, varies form 100 to 300 Sensing range is a simple polygon and varies form 5 to 10m in size Monitored area was divided into 1m * 1m grid Events were generated every 0.5sec Initial network coverage as 100% Holes generated by turned-off sensors The coverage reduction caused by both off-duty and out-of-energy sensors

Performance Evaluation

Conclusions This paper presented a new, fully-sponsored sensor discovery scheme, IPM Work under the irregular sensing range and can efficiently increase the accuracy of the discovery method By tolerating holes in a controllable manner, we can efficiently increase network lifetime under a high rate of coverage

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