Wireless Sensor Networks as a
Social Infrastructure
Sensor nodes are deployed in a region to monitor tocollect environmental information

ACM: A Transmission Mechanism
for Urgent Sensor Information

Sensor nodes have limited computational
capabilities and power resources
Carry various types of information
Security, disaster, weather, health, ...

T. Kawai, N. Wakamiya, and M. Murata

Based on unstable radio communications

Graduate School of Information Science and Technology, Osaka University

Need to transmit urgent information with higher
reliability and lower latency
1Overview of the Mechanism
Disaster detection system etc.

Our mechanism

Assured Corridor Mechanism

Network Layer

Data gathering scheme

Keep surrounding nodes
quiet

Keep forwarding nodes
awakeMultihop routing + Sleep scheduling

Avoid delay caused bysleeping of forwarding
nodes

Contention based MAC

Incorporate hop-by-hop
retrasmission

Packet loss by collisions in radio communication
Delay by sleeping nodes

Sensor information propagates from the edge to the BS
sleep

Level 12! = offset coefficient

1 BS

beacontnorm(1+2!)tnorm(1+!)tnorm
tnorm = interval of data gathering

time[11] N. Wakamiya and M. Murata: “Scalable and robust scheme for data
gathering in sensor networks”, in Proc. of Bio-ADIT 2004, pp 412-427 (2004).

21

1

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

4Parameter Settings

Adopt pulse-coupled oscillator model for synchronization

beacontimer expires

timer expires
SUPPRESSED

receive anemergency packet
from a child nodedetectan event

ns-2 with IEEE 802.15.4 MAC

Involve delay !tnorm per hop!tnorm2!tnorm

do notdetect theevent
anymoreSimulation

Transmission is synchronized among nodes at the samehop-distance from the BSBSNORMAL

receive anemergency packet
from other thanchild nodes

3

Synchronization-based Data
Gathering Scheme

0BS

Avoid packet loss causedby collisions

We focus on

Level 22

“Assured Corridor” Mechanism

Application Layer

MAC Layer

differentiated and prioritized services

225200 nodes in 20 m x 20 m region
Transmission range R = 2.5 m
Interval of data gathering tnorm= 10 sec.
Offset coefficient ! = 0.1 !tnorm= 1 sec.
After 300 sec. for initialization, make a randomly chosennode move to EMG_SEND and get back to NORMAL state
180 sec. later. Terminated at 500 sec.
Interval of emergency packet transmission temg = 0.5 sec.
Maximum number of retransmission: 2
100 simulations

6

Loss Rate of Emergency Packets

Delay of Emergency Packets

Ratio of emergency
packets which are notreceived by the BS

End-to-end delay froman EMG_SEND nodeto the BS

Decreases by half in
30 seconds withsuppression (KA+SP)

Improved by KA

15% more packet
transmisson with RT
but no loss

Slightly smaller with SP

compared to 1 sec. perhop for normal packets
due to less intensecontention in MAC layer

Larger with RT

KA keep awake
SP suppression of normal packets
RT retransmission

KA keep awake
SP suppression of normal packets
RT retransmission

7

Loss Rate with multiple
EMG_SEND Nodes

8

Delay with multiple EMG_SEND
Nodes

Less contribution of SPwith more EMG_SEND
nodes

Almost constant in KAand KA+SP
Increse by contention
with more emergency
nodes balances withdecrease by reduction ofaverage hop count ofdelivered packets

collisions among
emergency packets ina corridor

Less than 0.4% for 8
nodes with RT

Increases proportionallyin KA+SP+RT
KA keep awake

KA keep awake

SP suppression of normal packets
RT retransmission

SP suppression of normal packets
RT retransmission

9Conclusion

10Future Work

We propose ACM for transmission of urgent sensor
information

Introduce some techniques to control collisions among
emergency packets and mitigate congestion in theevent of a large emergency

ACM establishes a preferential route in a fully-distributedand self-organizing mannerConstruct a WSN architecture for urgent informationtransmission by integrating ACM and techniques statedabove

Surrounding nodes refrain from transmitting normal packets
and forwarding nodes suspend sleeping
Emergency packets are forwarded preferentially in thecorridor

Implement our architecture onto off-the-shelf sensor
nodes to prove its feasibility

Simulation results show that emergency packets aretransmitted with high reliability and low latency once acorridor is established1112

Thank you13