1

VISA: Virtual Scanning Algorithm for Dynamic Protection of Road

Networks

IEEE Infocom’09, Rio de Janeiro, Brazil

Jaehoon Jeong (Paul), Yu Gu, Tian He and David DuComputer Science and Engineering

University of Minnesota{jjeong,yugu,tianhe,du}@cs.umn.edu

April 23rd, 2009

Problem Definition2

Entrance point

Protection point

Detect

Take action

Wireless Sensor

Deployment

Virtual Scan vs. Legacy Schemes

1S 2S 3S 4S 5S 6S 7S

3

1S 2S 3S 4S 5S 6S 7S

1S 2S 3S 4S 5S 6S 7S2130

Detect!

Detect!

Detect!

2130

(a) Always-Awake

(b) Duty Cycling

(c) Virtual Scan

Sensor network sleeps during the silent time (i.e., sleeping time).

Each sensor sleeps during the scan time and the silent time.

Sensor network is always awake.

0sleepT

vlTsleep /

.7 where

)1(

/

n

wn

vlTsleep

lEntrance Point

Protection Point

Sleeping Time

VISA Scheduling Procedure4

Road Network Graph

Sensor Deployment

Working Schedule

Sleeping Schedule

Wireless Sensor Network

Road Network Graph5

The vertices in G are intersections, protection

points, and entrance points.

Working Schedule Establishment

6

Working Schedule during the Scan Period When each sensor wakes up and how long it

works for sensing. Working Schedule = (work start time, work end time)

Working Schedule Setup Each sensor’s work start time is set to the scan

arrival time.

Sleeping Schedule Establishment

7

Sleeping Schedule How long all the sensors can sleep with detection

guarantee.

One global sleeping time is computed using the Shortest Path.

worksilentscansleep TTTT Maximize the sum of

scan time and silent time.

Entrance

Points

Protection

Points

How often to generate the Virtual Scan on Road Network?

21303sleepT

Sleeping Time

Objective

Sleeping Schedule Establishment

8

worksilentscansleep TkjTjiTkjiT ),(),(),,(Let . and ,where EvPvv jki

),,(min ,,

kjiTT sleep

Ev

Pvvsleep

j

ki

Maximum sum of scan time and silent time for

detection guarantee.

This formulation guarantees the

target detection.

the shortest path

)211( ,,TT sleepsleep

When the scan arrives at e1, the path of (e1,p2) is

vulnerable to the intrusion.

),( jiTscan ),( kjTsilent

Handling Sensing Holes9

Two Cases for Sensing Holes Deployment Time Sensor Energy Depletion

Our Approach

Labeling into

E or P

Linear Network

Hole Labeling in Linear Network

10

How to label two sensing holes?

Case 1:

Case 2:

Case 3:

Case 4:

The Shortest Path

for Sleeping Time

The Maximum Shortest Path

(i.e., Maximum Sleeping Time)

The Sleeping Time is

the same as with Case 1

The Sleeping Time longer than Case 1

and Case 2

Minimum Spanning Tree (MST) basedClustering for Hole Labeling11

The idea is to maximize the inter-distance between Entrance Cluster (E) and Protection Cluster (P).EC 1C 2C PC EC PC

EC PC

1C

Maximum Inter-

distanceThis maximum inter-distance

determines the sleeping time.

Performance Evaluation12

Performance Metrics Network Lifetime Average Detection Time

System Behavior Sleeping Time over System Lifetime

Investigated Parameters Working Time Sensor Density Silent Time

Road Network for Simulation

Comparison of Sleeping Time of Three Approaches over System Lifetime13

System Lifetime Comparison• Virtual Scan: 28.2 hours• Duty Cycling: 1.4 hours• Always-Awake: 5.4 minutes

Impact of Working Time14

(a) Network Lifetime for Working Time

(b) Average Detection Time for Working Time

1. Network Lifetime Comparison for 1-second Working Time Virtual Scan’s lifetime is18 times longer than

Duty Cycling’s.2. Average Detection Time Comparison for 1-second

Working Time Virtual Scan’s ADT is 2 times longer than Duty

Cycling’s.

Conclusion15

In the surveillance for road networks, the scan-based sensing algorithm (VISA) opens a promising direction. VISA takes advantages of road network’s characteristics

for a maximum sleeping time. Vehicles move along the roadways whose maps are

available.

Contributions Energy-efficient Sensing Schedule for Road Networks

VISA uses the optimal sleeping time for an arbitrary road network.

Sensing Hole Handling VISA guarantees target detection while sensor network

deteriorates.

Basis for Quality of Surveillance VISA can control the trade-off between the network lifetime

and average detection time.