Tracking Irregularly Moving Objects based on Alert-enabling Sensor Model in Sensor Networks

1 Chao-Chun Chen & 2 Yu-Chi Chung Dept. of Information Management Dept. of Comp. Sci. and Info. Engr

1 Shih-Chien University, Kaohsiung Campus, Taiwan 2 National Cheng-Kung University, Taiwan

Proceedings of the 2005 11th International Conference on Parallel and Distributed Systems (ICPADS'05)

Outline

Introduction Sensor Network Architecture Supporting

Object Tracking Applications Alert-enabling Sensor Model Alert-based Object Tracking (AbOT) Scheme Simulation Conclusion

Introduction

Tracking moving objects is one of widely used techniques habitat monitoring

The tasks of the sensor applications Data sensing data transmission active/sleep decision

Introduction

Object tracking applications are related

to the sensor tasks (caused limitations) power constraint velocity/sensing range uncertainty tracking resolution data freshness scalability

Introduction (motive)

the energy cost is wasted in either the operation of tracking moving objects

Wake up more sensors to monitor the object the operation of finding back lost moving objects

Only few sensors are in active mode to track the

moving object

Two extreme cases are not optimal since they

waste high energy cost on different operations

Introduction (solution)

The Alert-based Object Tracking (AbOT)

Scheme Dynamically determine the number of awaken sen

sors According to the ability of capturing the location of the

moving object

Sensor Network Architecture Supporting Object Tracking Applications

1.the measurement history of object locations2.full knowledge of the network topology 3.the status of each sensor

1.Continuously storing the incoming sensor readings2.minimizing the energy consumption3.offering the query interface for end users

Sensor Network Architecture Supporting Object Tracking Applications

For ease of management Sensors are suggested to deploy in the grid

topology

Alert-enabling Sensor Model

Each sensor plays the role of a sentry sends a trigger message to alert the central

server while observing the urgent phenomenon

The central server then makes the final

decision by receiving reports

Alert-enabling Sensor Model

The sensors are used to alert the central

server for the change of the object movement alert-enabling sensors

Marginal ZoneCentral ZoneAlert Circle

The alert circle greatly affects the tracking performance

Alert-based Object Tracking (AbOT) Scheme

In object tracking applications, energy waste is a function of two elements the number of active sensors at each sampling tracking accuracy that determines the additional

energy on finding the lost object back An ideal tracking method

use a few active sensors to track objects with high accuracy

Alert-based Object Tracking (AbOT) Scheme

Alert-based Object Tracking (AbOT) Scheme based on two key ideas sensor-level processing

using alert-enabling sensors to capture the motion of

the moving objects network-level processing

using sensor/server cooperating decision to capture

the trajectory of a moving object Turning on the “best” set of sensors to track the moving obj

ect

Alert-based Object Tracking (AbOT) Scheme

Each sensor is always in one of three states doze mode

the object is not nearby, the sensor stays in the doze

mode to save energy M-zone

the possibility that the object exits the sensing range

of the sensor is high sensor should monitor the object with high sensing

frequency

Alert-based Object Tracking (AbOT) Scheme

C-zone the possibility that the object exits the sensing

range of the sensor is small the sensor should monitor the object with low sensing

frequency

Alert-based Object Tracking (AbOT) Scheme

The moving object moves across the sensing range The OT server would determine appropriate sensors to switch the process of tracking the moving object

the hand-off approach Nearest Sensor Policy Range Covering Policy Conservative Policy

Location Monitoring Mechanism

The algorithm of the location monitoring

mechanism includes two parts Sensor Part

sensorOTserver

To monitor objectC-zone

M-zone

M-eventmonitors the object with high sampling rate

C-eventsensor decreases the sampling rate to monitor the object

Location Monitoring Mechanism

Server Part deal with the arriving message

storing the sensor readings executing the responding tasks of the alerts

the message processing basically runs as a

daemon in the OT server the object position and its associated timestamp

are stored into the moving object database

Location Monitoring Mechanism

If an alert is piggybacked in returning messages OT server knows the moving object has moved

across the alert circle (two event) M-event

wake up more sensors around the object to monitor Three heuristic designs

Nearest Sensor Policy

OTserverWake up the nearest sensor

Location Monitoring Mechanism

Range Covering Policy

Conservative Policy

Location Monitoring Mechanism

C-event the OT server forces other active sensors to the doze

mode, except the sensor that the object resides

M-zone

C-zone

OTserver

Wake up the sensor

Lost-and –found Mechanism

sensor

C-zone

M-zone

a fast and irregular moving object (e.g., a taxi driver)

OT server could wake up the wrong set of sensors to monitor

the OT server wakes up all sensors by sending the Lost-and-Found message

Simulation

900 sensor nodes in 300 × 300 meter2 between two vertical (or horizontal) neighbors

is ten meters the sensing range is 15 meters C-zone is set to 7.5 meter object moves from C-zone to M-zone

Range Covering Policy is used to determined

which sensors are waked up

Simulation

Energy consumption the total energy consumed in the object tracking period by the network

Frequency of waking up sensor the sum of active nodes at each time unit during the simulated period

Accuracy probability the ratio of the number of successful detections to the total number of detections

Simulation

Effect of the Sensor Network evaluate the performance of object tracking scheme

in various sizes of sensor networks

Simulation

Effect of the Sensor Nodes

Simulation

Effect of the Moving Object

Conclusion

we propose the AbOT scheme to efficient

process the object tracking function for

sensor applications To study the optimization problem of tracking

multiple moving objects at the same time