Wireless Sensor Network and Applicaions(WSNA2002)

A Coverage-Preserving Node Scheduling Scheme for Large

Wireless Sensor NetworksDi Tian, Nicolas D. Georganas

Outline

Introduction Problem Formulation Sponsored Coverage Calculation Node Scheduling Scheme Based on

Eligibility Rule Simulation

Introduction

Wireless Sensor Network

Sensing

Computation

Networking

Applications:

• Battlefield surveillance

• Intruder alarming

• Ecological detection

Challenges

Properties of Sensors Tiny Powered by battery Unattended Large numbers

Energy Constraints

•Powered by battery

•Hard to be recharged again

Scale Constraints

•Large number of sensors

•Centralized control is unrelistic

Problem Formulation

The goal of this paper Prolong system lifetime To turn off redundant nodes while maintaining

original sensing coverage

Sponsored Coverage Calculation

Sponsored Coverage Calculation If the whole sensing area of a sensor is

covered by the union set of its neighbors’, this node can be turned off.

1

52

4 3

Sponsored Coverage Calculation

A. Fixed Sensing range r, and location information is known.

B. Different sensing ranges, and location information is known.

Sponsored Coverage Calculation (Case A)

Ni

Nj

d(i,j)

r

Sponsored Coverage Calculation (Case A)

S(i) : the sensing area of node i

Sponsored Coverage Calculation (Case A)

r

jidij 2

),(arccos2

Ni

Nj

d(i,j)

rrr

d(i,j)θ

Sponsored Coverage Calculation (Case A)

Ni

Nj

ψj->i

ij

ijij xx

yyarctan

(xj,yj)

(xi,yi)

Sponsored Coverage Calculation (Case A)

The Union of sponsored coverage

2ij

ij

2ik

ik

Sponsored Coverage Calculation (Case A)

Coverage-based Off-duty Eligibility Rule Turn off eligible node i if )(

)(

iSSiNj

ij

Sponsored Coverage Calculation (Case B)

Four Cases

Sponsored Coverage Calculation (Case B)

Two Considered Cases:

ji rjidr ),(

),(

),(

jidrr

rjid

ji

j

Sponsored Coverage Calculation (Case B)

θri rj

d

餘弦定理 : )cos(2222 drdrr iij

Node Scheduling Scheme Based on Eligibility Rule

The operation is divided into rounds, and each round begins with a scheduling phase, followed by a sensing phase. Scheduling phase: turn off eligible nodes to save

energy. Sensing phase: perform sensing task

time

round

Scheduling Sensing

Node Scheduling Scheme Based on Eligibility Rule

Scheduling phase: Neighbor Information Obtaining Step

Broadcast a Position Advertisement Message (PAM) (ID, location)

Back-off Based Self-scheduling StepEach node evaluates its eligibility for turning off by

calculating the sponsored coverage

Node Scheduling Scheme Based on Eligibility Rule

Blind Points

Node Scheduling Scheme Based on Eligibility Rule

Back-off scheme Let each node delay its determination until a random b

ack-off time Td is reached.Broadcast a Status Advertisement Message(SAM) to ann

ounce its status if it is eligible for turning off.Enter ready-to-off state may select the same random number

Node Scheduling Scheme Based on Eligibility Rule

To avoid a blind point further, let each node wait for a short period time Tw after sending out SAM. If one SAM is received during the ready-to-off period an

d the transmitter is one of its off-duty sponsors, the node will re-investigate its off-duty eligibility rule.

Finite State Machine for self-scheduling Phase

Example

Simulation Results

100 nodes deployed in 50m x 50 m square space.

Sensing range:10m

Simulation Results

Simulation Results