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Virtual Patrol : A New Power Conservation Design for Surveillance Using Sensor

Networks

Prasant Mohapatra , Chao Gui

Computer Science Dept.Univ. California, Davis

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Outline

Introduction Working model

– On-demand Temporary Patrol– Coverage-oriented Continuous Patrol

Senstrol (SENSor network paTROL operations)– Patrol setup phase

Patrol setup dissemination Sleep schedule setup Patroller host handover

– Patrolling phase Performance evaluation Conclusion

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Introduction

Surveillance is a typical application among a wide range of sensor network applications

A surveillance sensor network detects any event in the monitored field– toxic gas leak, forest fire, battle field surveillance , intr

uding personnels or vehicles

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Introduction

Real life solutions of field surveillance– Stationary watchtowers– Patrolling sentinels– Hybrid solutions combining the two are also possible

Given a curve in the field as the desired patrol path– "virtual patrol“ can be achieved by sequentially waking up and tur

ning off sensor nodes that are located on the patrol path

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Introduction ~Example Senstrol Scenario~

• Battle field surveillance •Soldiers hide at A•Plan arbitrary patrol path•Inject the path info. to nearest sensor•Path info. disseminated to all sensors along path•Virtual patrol carried out

A

B

On-demand Temporary

Patrol

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Working model

Two working model– On-demand Temporary Patrol (OT-Patrol)

Can be applied to specific locations or paths

– Coverage-oriented Continuous Patrol (CC-Patrol) can also be used for covering entire field

Coverage-oriented Continuous Patrol (CC-Patrol)– sensing range of the virtual patroller can sweep

through every position in the network field

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Working model ~ Coverage-oriented Continuous Patrol (CC-Patrol) ~

the network’s power consumption rate is much lower than the conventional surveillance operations

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Senstrol ~key concepts~

There is an imaginary "patroller" moving along patrol path, with constant speed vp – sensor nodes near patrol path should be active when and

only when the "patroller" is within node’s duty range– duty range would be the same as sensing range

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Senstrol ~key concepts~

only nodes within the duty range of the current VP location need to be active

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Senstrol

A patrol is initiated by a user at the starting location– Portable computer is used to disseminate the patrol

setup information

The patrol setup information is forwarded to the node closest to the starting point – serves as the first node of the new patrol

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Senstrol (SENSor network paTROL operations)

Patrol setup phase– Patrol setup dissemination– Sleep schedule setup– Patroller host handover

Patrolling phase

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Senstrol ~Patrol dissemination~

The first node of new patrol (Patrol Host) has the patrol setup information (PATROL_INFO) that will be disseminated to the other involved nodes

– Path trajectory Contains the parameters for defining the specific Bezier curve

– Patrol speed vp The constant speed that the imaginary patroller uses while moving al

ong the path– Iteration period Ti

The time that the patroller takes to traverse the path from start to end– Patrol duration PD

The time that the user desires the path to be patrolled– Patroller time

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Senstrol ~Patrol dissemination~

Imaginary reference clock: “Patroller time” At the beginning, the first node PH (Patroller host),

records zero on patroller time-stamp, maps it to its local clock

As the patroller time advances, PH will broadcast PATROL_INFO to the nearby sensors

– Time-stamps of patroller time are attached to each broadcast packet

– A receiver Ni can set up its own mapping using the packet

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Senstrol ~Patrol dissemination~

When Ni receives packet P (PATROL_INFO) at its local time-stamp tlocal(P), P carries a patroller time-stamp t(P) – tlocal(P) = t(P) +Toffset(i)

Mapping of patroller time to the local time at node Ni

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Senstrol ~Patrol dissemination~

PH broadcast PATROL_INFO at constant interval Tdiss Each node starts an initial sleep time of uniformly random

length in the range [0, Tslot] – Time is discretized into slots ,Tslot

At beginning of Tslot, node wakes up for a short time period Tup , turns off to sleep for the remaining time of the slot

– Default sleep schedule– Intended for the sensor nodes to be able to receive the PATROL_I

NFO packets

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Senstrol ~Patrol dissemination~

N0N1

N2

N3

N4

N5

N6

N7

N0

N4

Tdiss

N5

N6

Dissemination Procedure:1. PH broadcast PAT_INFO packets,

constant interval (Tdiss)

2. Near-by nodes conduct default sleep

schedule ( Tslot, Tup)

3. all near-by nodes receive PAT_INFO

packet

After receiving PAT_INFO, each node calculate its own sleep schedule

Tup

Tslot

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Senstrol ~ Sleep schedule setup ~

After receiving the PATROL_INFO packet from PH, sensor node calculate its sleep schedule

– Set up the mapping from "patroller time" and its local time– Calculate the time period during which the virtual patroller (VP)

is within its duty range– Set future sleep schedule, and the iteration period received from

PATROL_ INFO packet

Time is divided into Ti ,, for VP to traverse the path from start to end

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Senstrol ~ Sleep schedule setup ~

Wake up period

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Senstrol ~ patroller host handover ~

When VP moves close to the boundary of current PH’s transmission range – PH needs to select next PH and handover the host’s dut

y to its descendant– Current PH identifies the time when its distance to the

VP reaches a threshold of (1-δ)Rt

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Senstrol ~ patroller host handover ~

Handover procedure– the PH broadcast PH_ELECT message

– PH can wait duration Telect for returning messages

– Receiver chooses random delay in [0, Telect] , and reply to the PH

– PH sends confirm message to the selected descendant

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Senstrol ~Patroller Host Handover~

A

D

C

E

Patroller Host

PH_ELECT messageReply messageConfirm message

Patroller Host

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Senstrol ~ Patrolling Phase ~

Patrolling phase

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Senstrol ~ Patrolling Phase ~

A

B

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Performance evaluation

GloMoSim simulator 400m x 400m field 800 nodes, uniform random distribution Transmission power 10dBm (10mW) Receiving sensitivity, the lowest signal power that

may be reliably received by the receiver -65 dBm (0.3μW)

VP speed 5 m/s

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Energy Consumption vs. Duty Range

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Energy Consumption vs. Patrol Speed

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Energy Consumption vs. Node Density

the number of nodes

participating in the patrol

setup

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Conclusion

Introduce Virtual Patrol operations in Surveillance Sensor Network

Two models of Virtual Patrol– On-demand Temporary patrol– Coverage-oriented Continuous patrol

Future work– extend the Senstrol to support multiple patrollers