Decentralized Energy-Conserving and Coverage-Preserving Protocols for Wireless Sensor Networks Chi-Fu Huang, Li-Chu Lo, Yu-Chee Tseng, and Wen-Tsuen Chen Department of Computer Science and Information Engineering National Chiao-Tung University Department of Computer Science National Tsing-Hua University IEEE International Symposium on Circuits and System (ISCAS ’ 05)

Outline Introduction 1-Coverage-Preserving Protocol Basic Energy-based Simulation Results Conclusion

Introduction This paper proposed protocols are based on a model similar to that of [8], but improve it First, reduce the computational complexity Second, balance sensors ’ energy expenditure [8] Differentiated surveillance for sensor networks. (SenSys 2003)

Introduction Goals Provide an approach for nodes to decide their sleep/work mode schedules: Guarantee Full-coverage Redundant nodes go to sleep to save energy and extend system lifetime

Introduction -Differentiated surveillance for sensor networks Work/Sleep schedule for a single point A B C Node A Node B Node C time Awake Asleep Point X

10 Introduction -Differentiated surveillance for sensor networks Work/Sleep schedule for a single point A B C Node A Node B Node C Awake time Asleep Point X Point x is covered by at least one node ’ s sensing area at any time

t A C B Introduction -Differentiated surveillance for sensor networks Point X t refC 40 refA 90 refB 120 refC T front T end Reference randomly selected from [0, T) Each node broadcasts tuple (location, reference)

Introduction -Differentiated surveillance for sensor networks Sensing Phase Init Phase ref Round 0 (Duration T) Round 1 Round n ……… Work Schedule: [n×T + ref – T front ﹐ n×T + ref + T end ] ref

D C B A Introduction -Differentiated surveillance for sensor networks Schedules for All Grid Points E Grid Points

Introduction -Differentiated surveillance for sensor networks

1-Coverage-Preserving Protocol -Assumption Sensors S i, i = 1, …,n Location ( X i, Y i ) Sensing Range r i Each Sensor can switch between the active mode and the sleeping mode Two sensors S i and S j are neighbors If they have non-empty overlapping sensing region Sensors can communicate with his neighbors

1-Coverage-Preserving Protocol – Basic The structure of sensors ’ working cycles 1. Location ( X i, Y i ) 2. Sensing range r i 3. Reference time Ref i

1-Coverage-Preserving Protocol – Basic Initialization phase Each sensor S i broadcasts a HELLO packet after random backoff Location ( X i, Y i ) Sensing range r i Reference time Ref i randomly selected from [0, T rnd ) Each sensor S i can calculate it own working schedule in the sensing phase To calculate Front i and Back i

1-Coverage-Preserving Protocol – Basic Each sensor ’ s Front i and Back i should be carefully selected to ensure that the sensing area is sufficiently covered To achieve this goal, we use intersection points If all intersection points in the target area A are covered by any sensor ’ s sensing range, the target area A is sufficiently covered

m 1-Coverage-Preserving Protocol – Basic t t 0 2 Ref 1 9 Ref 2 11 Ref Front 1 =5.5 Back 1 = n q S1S1 S3S3 S5S5 S2S2 S4S4 p r Schedule for p Front

1-Coverage-Preserving Protocol – Basic

1-Coverage-Preserving Protocol – Energy-base Each sensor S i is aware of its current remaining energy, denoted as E i Each sensor S i broadcasts its E i in the HELLO packet

1-Coverage-Preserving Protocol – Energy-base Front i and Back i of the sensor S i are chosen based on E i

Simulation Result 100 x 100 square are 150 sensors, randomly generated Sensing range 25 A working cycle (T w_cycle ) include 5 rounds To set up sensors’ initial energies Can active from 1 to 50 complete rounds in randomly selected manner

Simulation Result

Conclusion The paper protocols improve the results in several sense Significantly reduce the computational complexity Use intersection points Further balance sensors ’ energy expenditure Use sensors ’ remaining energy

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