Outline
Implementation and Evaluation of
an Urgent Information Transmission
Architecture in Wireless Sensor
Networks
T. Kawai, N. Wakamiya, and M. Murata

1.

Introduction

2.

Design Methodology

3.

UMIUSI Architecture

4.

Practical Experiments

5.

Conclusion

Graduate School of Information Science and Technology, Osaka University

1

2

1. Introduction

2. Design methodology

Wireless Sensor Networks as a
Social Infrastructure

Overview of the Architecture
Normal situation

Sensor nodes are deployed in a region to monitor and collectenvironmental information
Requirements

Sensor nodes have limited computational capabilities and power
resourcesscalability
fault tolerance!long lifetime

Emergency situation
scalability
reliability and latency!adaptability to situation

!

!

!

!

Based on unstable radio communications
Carry various types of information

Application
layer

Security, disaster, weather, health, ...

Building automation, public surveillance, ...

Need to transmit urgent information with higher reliability and lower
latency

QoS control mechanisms
Network andMAC layers

differentiated and prioritized services

existing algorithm / data gathering scheme
e.g. directed diffusion, S-MAC ...

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2. Design methodology

2. Design methodology

Design Objectives

Design Methodology
Combining simple mechanisms working in different spatial and temporallevelsHigh reliability and low latency

Mechanisms are implemented on each node

Urgent information should be preferred according to their importanceMechanisms work
independently witheach otherSelf-organizing and distributed behavior
A WSN should be adaptive to the scale of an emergency and dynamicallychanging conditions

Mechanisms ofappropriate levels
come into effectresponding to thesurrounding situation

A globally-organized behavior emerges as results of reactions to thesurroundings of each node and local interaction among nodes

Simplicity
A sensor node has limited resources

No additional
mechanisms to identify
the scale or situation ofthe event56

3. UMIUSI architecture

Overview of UMIUSI

3. UMIUSI architecture

UMIUSI Architecture
Sensor information is categorized into three traffic classes

Application Layer

Building automation, public surveillance…

NormalNon-urgent
Tolerate loss and delay in emergency
Gathered at an interval of tnorm in normal situation

UMIUSI Architecture

Our architecture

Network Layer
MAC Layer

aUtonomous Mechanisms Integrated forUrgent Sensor Information

Important
Urgent but tolerate loss and delay to some extent when the network isoverloaded
Transmitted at an interval of timp (< tnorm) but the sending rate is regulated incase of congestion

Data gathering scheme
Multihop routing + Sleep scheduling

CriticalMost urgent and important
Transmitted at an interval of tcri (< tnorm) and the sending rate is not regulatedby the rate control mechanisms to retain the reporting rate

Contention based MAC

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3. UMIUSI architecture

3. UMIUSI architecture

UMIUSI Architecture (contd.)“Assured Corridor” Mechanism

Five mechanisms are incorporated
Priority queueing

Keep surrounding nodes
quiet

Rate control by local congestion detection

BS

Avoid packet loss causedby collisions

Hop-by-hop scheduled retransmission
Assured Corridor Mechanism (ACM)

Keep forwarding nodes
awake

Rate control by backpressure

NORMALreceive an
emergency packet
from other thanchild nodes

Avoid delay caused bysleeping of forwardingnodes

do notdetect theevent
anymorereceive an
emergency packet
from a child nodedetect
an event

timer expires

timer expires
SUPPRESSED

detect anevent

EMG_SEND

detect anevent

EMG_FORWARD

receive an emergency packet from a child node
receive an emergency packet from a
receive an emergency packet from otherchild node then restart the timer
than child nodes then restart the timer

State transitions

9[11] T. Kawai, N. Wakamiya, and M. Murata, “ACM: A transmission mechanism for urgent sensor information,”in proceedings of IEEE IPCCC 2007, pp.562-569, April 2007.

3. UMIUSI architecture

Contribution of Mechanisms

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4. Practical experiments

Experiments (Testbed A)
25 nodes in a 10 m x 6 m roomIn a small-scale event

Lower layer protocols

It takes a while for ACM totake effect802.15.4 non-beacon mode MAC
Synchronization-based data gathering scheme [10]Priority queueing and ratecontrol do not help much

timp = tcri = 0.5s (rate = 2 packets/s)

In a large-scale event

Scenarios

ACM does not work sincecollisions occur among
emergency packets

Small-scale event with one EMG_SEND node
Repeat twice for each of randomly chosen 8 EMG_SEND nodes

Large-scale event with 8 EMG_SEND nodes

Rate control is effective tomitigate congestion

one critical and seven important class nodes
Repeat twice for 8 sets of randomly chosen 8 EMG_SEND nodes

Five variants: KA, ACM, ACM+RT, ACM+RT+PQ, FULL

11[10] S. Kashihara, N. Wakamiya, and M. Murata, “Implementation and evaluation of a synchronization-based data
gathering scheme for sensor networks,” in proceedings of IEEE ICC 2005, pp.3037-3043, May 2005.

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4. Practical experiments

4. Practical experiments

Node layouts in Testbed A

Small Scale EventKA keep awake
RT retransmission

Per-hop loss rate

1m

Per-hop delay

1mBScritical

ACM improves reliability of transmission

important

4 hops to the BS at maximum

Retransmission further lowers the loss rate

In normal operation, delivery ratio: between 65-80% without any
retransmission

But introducing retransmission incurs increase of delay

1314

4. Practical experiments

4. Practical experiments
KA keep awake

RT retransmission

Large Scale Event

RT retransmission

Large Scale Event

PQ priority queueing
FULL all five mechanisms

PQ priority queueing
FULL all five mechanisms

Per-hop loss rate

Per-hop delay

Total throughput

Suppression of normal packets has little contribution
Retransmission and rate control are effective to improve reliability

In FULL, the total throughput of important class decreases in 30 seconds
as the important traffic is regulated by the rate control mechanisms

In FULL, loss rate and delay decreases in 30 seconds as the important
traffic is regulated by the rate control mechanisms

15

4. Practical experiments

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4. Practical experiments

Experiments (Testbed B)

Large Scale Event
1219

18

11

NORMAL21

SUPPRESSED
1620

15

17

914

8

107

backpressure
25

EMG_SEND(important)
EMG_FORWARD

12426232752244

3228
29

BS

Total throughput

localcongestion

4 hops at maximum

EMG_SEND (critical)

61333

3432

31
35

30
36

In normal operation, delivery
ratio is between 65-75%

1737

Loss ratecritical class: 0important class: 0.6%3818

5. Conclusion

Conclusion
We propose a design methodology of a sensor network architecture
supporting differentiated and prioritized services for urgent information

Thank you

Several simple mechanisms working in different time and topologicalranges are integrated to adapt to the scale of emergency

We propose UMIUSI architecture
Sensor information is classified into three classes and five mechanisms
collaborate to prioritize urgent information

Results of practical experiments show that UMIUSI successfully
improved the delivery ratio and the delay of emergency packets

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