Emergency Navigation
by Wireless Sensor Networks
in 2D and 3D Indoor Environments
Yu-Chee Tseng
Deptment of Computer Science
National Chiao Tung University
1
Outline
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Introduction
System Overview
Environment setting
Regular report
Emergency navigation service
Simulation results
Demonstration
Conclusion
2
Outline
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


Introduction
System Overview
Environment setting
Regular report
Emergency navigation service
Simulation results
Demonstration
Conclusion
3
Introduction

Wireless Sensor Network

Each sensor has


Limited Memory、Limited CPU、Wireless Transceiver、
Sensing Unit
Each sensor can



Sense environments
Communicate with others
Do simple computations
4
Introduction

Traditional Navigation Devices

Advantage



Cheap
Easy deployment
Disadvantage


Fixed direction.
Can not adapt to actual emergency situations.
5
Introduction

Motivation



According to the statistic report of the NFA of Taiwan(內政
部消防署）, 228 people died in fire accidents in 2003.
The main reason is that people can not find “right”
escaping paths to exits.
Our Goal


to develop an emergency navigation system
for indoor 2D and 3D environments
6
Outline
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
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

Introduction
System overview
Environment setting
Regular report
Emergency navigation service
Simulation results
Demonstration
Conclusion
7
System Overview
Our system is composed of 3 parts




Environment setting
Regular reporting
Emergency Navigation
Two network graphs


Communication graph and guidance graph
room
room
room
room
Communication graph
room
room
room
room
Guidance graph
8
Environment Setting
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

Deploy sensors
Construct reporting tree
Setup initial navigation paths
navigating
reporting
9
Outline
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
Introduction
System overview
Environment setting
Regular report
Emergency navigation service
Simulation results
Demonstration
Conclusion
10
Deployment of Sensors



Plan locations of sensors
Define the roles of sensors
 Sink
 Exit sensors
 Normal sensors
Decide navigation links
navigation
links
(for human)
11
Construct a Reporting Tree

Step 1. Discover symmetric links



Each sensor periodically broadcasts HELLOs
When receiving a HELLO, sensors reply ACKs
After receiving an ACK, sensors record the sender ID in its
link table
HELLO
1
Link table
2 3
ACK
0
2
ACK
ACK
3
12
Construct a reporting tree (cont.)

Step 2. Construct a spanning tree




Sink floods a BEACON.
For a sensor receives a BEACON, it checks if the sender is
in its link table
If yes, it sends a REG(ister) to sink and rebroadcasts
BEACON.
Else, drops it
BEACON
REG
BEACON
13
communication
links
(for packets)
14
Outline
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Introduction
System overview
Environment setting
Regular report
Emergency navigation service
Simulation results
Demonstration
Conclusion
15
Reporting Issues





How often a report should be sent?
Will each sensor report individually?
Is there any inaccuracy?
False alarm?
How to save energy of sensors?
16
Outline
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
Introduction
System overview
Environment setting
Regular report
Emergency navigation in 2D environment
Simulation results
Demonstration
Conclusion
17
Design Principle

When a sensor detects an emergency event, it
forms a hazardous region

The navigation algorithm will try to guide people as
farther away from hazardous regions as possible
18
Problem Formulation




Each sensor has an altitude.
Sensors in hazardous regions will raise their
altitudes.
Each sensor guides people to the neighbor with the
lowest altitude
After forming hazardous regions, some sensors may
become local minimum ones

A partial link reversal operation is performed to solve this
problem
19
Phases of Navigation

Initialization phase



Initial phase is started by Exit sensor
After this phase, every sensor has a default guiding
direction.
Navigation phase

This phase starts by the sensor which detects an
emergency event.
20
Terminology





D：The radius of the hazardous region
Aemg： A large constant which represents the
maximum altitude
Ai：The altitude of sensor i
Ii：The altitude obtained in the initialization phase
ej,i：The hop count from emergency sensor j to
sensor i
21
Initialization phase



Every exit sensor sets its altitude to 0 and broadcasts an
initialization packet.
When receiving an initialization packet, a sensor adds its hop
count by 1.
Then, it compares the hop count with its current altitude
Initial Packet
Sender ID Exit ID Hop Count
Initial Packet
0
0
0
0
∞
0
1
∞
2
∞
3
∞
4
∞
5
∞
6
∞
7
∞
8
∞
22
Initialization phase (cont.)


If the hop count is smaller than its altitude, it resets its altitude and
setups its initial guiding direction to that sender.
Then, it rebroadcasts this packet.
Initial Packet
1
0
1
Initial Packet
0
0 0
Initial Packet
3
0
1
0
3
6
0
1
∞
1
4
∞2
7
∞
1
2
∞2
5
∞3
8
∞2
∞3
Initial Packet
2
0
2
Initial Packet
5
0
3
∞
4
23
Navigation phase


When a sensor x detects an emergency, it will set its altitude to the
maximum altitude Aemg (let it be 200).
Then it broadcasts an emergency packet EMG(seq, x, x, Aemg, 0)
EMG

Seq





x
w
Aw
H
seq：sequence number
x：emergency ID
w： sender ID
Aw：altitude of sender
h：hop count to emg. location
23
EMG
0 27 27 200 0
24
10
26
25
11
27
11
29
28
12
200
30
12
12
13
31
13
14
24
Navigation phase (cont.)

When a sensor node y receives a EMG packet originated from
node x, it will do the following steps.
 Step1:

Decide that the emergency is a new one or not



If it’s a new emergency, record this event and set the hop count ex,y to h+1.
Else, compare the h and ex,y. If h is smaller than ex,y , set ex,y to h+1.
Record the altitude (Aw) in the navigation link table.
23
24
10
Emg Table
EmgID
ex,y
27
1
26
25
11
27
11
29
28
200
30
12
12
13
31
13
14
25
Navigation phase (cont.)

Step 2:

If eX,Y was changed in step1 and eX,Y ≦D, y considers itself
within hazardous region. Then it re-calculates its altitude as
follows：


1


Ay  max  Ay , Aemg 

I
y
2

 ex, y  1 
Aemg 
1
e
I 
 1EmgID

23
27
1
1  1
2
ex,y
 11  61
1
ex,y < D ?
24
10
2 Emg yTable
x, y
200 
Safety Factor D:1
26
25
11
61
27
11
61
29
28
200
30
12
12
13
63
31
13
63
14
26
Navigation phase (cont.)

Step 3:

If y has a local minimum altitude and it’s not an exit, it must adjust its altitude
as follows：
1
Ay  STA( AN y ) 
 min AN y  
Ny
 

AN y = altitudes of y’s neighbors

STA = standard deviation


|Ny| = number of neighbors of y.


A bigger value means closer to the hazardous region. So we need to adjust the
altitude faster.
A smaller | Ny | means less escape ways. So we need to adjust the altitude faster.
δis a small constant.
Static adjustment
Five iterations
23
26
25
61
27
61
Our scheme
Three iterations
24
10
29
28
200
30
12
12
63
31
63
14
63.1
1
0Local
  minimum?
63  0.1  63.1
2
27
Navigation phase (cont.)

Step 4:

y has to broadcast an EMG(seq, x, y, Ay, ex,y) packet if any of
the following conditions matches.



It’s a new emergency
y has changes its altitude or ex,y in the previous steps.
Step 5:


If y is in hazardous regions and it sees an exit sensor which is
in Ny and which is also in hazardous regions, then y chooses
this exit sensor
In all other cases, y directs users to a safer sensor first, and
then gradually to a safe exit.
28
Example—
Altitude after initial phase
S7
4
Exit
1
S10
10
7
S4
S1
10x10 Grid Network
29
One emergency event –
after step 1, 2 & 4
Local minimum
1
S10
4
S7
7
S4
10
S1
30
One emergency event–
final result
1
S10
4
S7
7
S4
10
S1
31
Two emergency events–
after step 1, 2 & 4
Local minimum
1
S9
4
S5
S7
7
S1
S3
10
32
Two emergency events–
final result
1
S5
7
S1
S3
10
S7
S9
4
33
Outline








Introduction
System overview
Environment setting
Regular report
Emergency navigation service
Simulation results
Demonstration
Conclusion
34
Simulation results


We compare our navigation algorithm with
“Distributed algorithm for guiding navigation across a
sensor network” (MobiCom 03)
This algorithm guides people to the nearest exits

However, nearest exits may not be good choices
35
Simulation results
Exit Emergency
Method of Li et al.
No
Our method (D=2)
Pkt.
count
Path
1
Hazardous region
Pkt.
count
Path

252
979

1254
2
3
A
742
408
A

Case1. Our algorithm will choose
to pass hazardous region areas
as farther away from emergency
locations as possible.
Case2. Our algorithm will not
guide people passing through
the hazardous region.
Case3. Only the sensors near
the exit in the hazardous region
will guide people to that exit.
137
36
Outline








Introduction
System overview
Environment setting
Regular report
Emergency navigation service
Simulation results
Demonstration
Conclusion
37
Demonstration

System Components

MICAz sensors




MIB510 serial Gateway


Environment monitoring
Navigation
Sink
Gateway between wireless sensor network and PC
PC

Control Host
38
Demonstration
exit
(normal
time)
second event
(emergency
time)
first event
(emergency
time)
39
A Short Summary (2D)

Novel indoor monitoring and navigation services based
on wireless sensor network technolgoies




emergency will raise sensors’ altitudes
navigation similar to TORA protocol, but different in that
emergencies will disturb altitudes
altitude adjustment is designed for quicker convergence
navigation in emergency applications requires safer paths, but
not necessarily longer paths
40
Emergency Navigation
in Indoor 3D Environments by
Wireless Sensor Networks
Yu-Chee Tseng
Department of Computer Science
National Chiao Tung University
41
Introduction

Why 2D guiding algorithms can’t directly apply to 3D environments
Rooftop
room
3F
room
room
room
2F
room
room
room
2F
room
room
room
room
room
room
1F
1F
room
room
room
room
room
room
room
42
System Architecture
to rooftop
(lemg, -(lIy+1))
to rooftop
(lemg, -(lIy+1))
(3, 2)
(3, 2)
(3, 1)
room
(3, 1)
(3, 1)
(3, 1)
(3, 1)
(3, 1)
(2, 2)
(3, 2)
(2, 3)
(3, 2)
(2, 2)
room
(2, 1)
(2, 2)
A (2, 0)
(2, 2)
(2, 1)
Control host
Sink
room
A
(2, 0)
(2, 1)
(2, 2)
(1, 2)
(2, 1)
(1, 3)
(1, 1)
(1, 2)
Controller
(2, 2)
(1, 2)
room
(1, 1)
A (1, 0)
room
(1, 3)
room
(1, 2)
(1, 1)
exit sensor
stair sensor
normal sensor
guidance direction
room
A
(1, 0)
(1, 1)
(1, 2)
(0, 2)
(1, 3)
(0, 3)
(1, 2)
(0, 2)
room
(0, 1)
1F
(2, 1)
room
B (2, 3)
room
2F
(3, 1)
room
D
(3, 0)
3F
D (3, 0)
room
A (3, 0)
room
4F
(3, 1)
(0, 2)
(0, 1)
room
C
(0, 0)
(0, 2)
room
A
(0, 1)
(0, 0)
(0, 1)
room
(0, 1)
(0, 2)
(0, 1)
C (0, 0)
A:
B:
C:
D:
floor gateway
stair gateway
floor/stair gateway
floor/roof gateway
43
Guidance initialization
2F
(1, 1)
e
(1, 0)
(1, 1)
d
f
(0, 0)
(0, 1)
b
1F
(0, 1)
(0, 2)
a
(0, 2)
c
(0, 3)
44
Guidance initialization
(3, 1)
room
(3, 2)
room
(3, 2)
(3, 1)
(3, 0)
(3, 1)
(3, 1)
room
(3, 1)
room
(3, 0)
(3, 1)
4F
(3, 0)
(3, 1)
(2, 1)
room
(3, 1)
(3, 2)
(2, 2)
room
(2, 3)
(2, 2)
(2, 3)
(3, 2)
(2, 2)
(2, 1)
room
(2, 2)
room
(2, 0)
(2, 1)
3F
(2, 0)
(2, 1)
(1, 1)
room
(2, 2)
(2, 1)
(1, 2)
room
(1, 3)
(1, 2)
(1, 3)
(2, 2)
(1, 2)
(1, 1)
room
(1, 2)
room
(1, 0)
(1, 1)
2F
(1, 0)
(1, 1)
(0, 1)
room
1F
(1, 2)
(1, 3)
(0, 2)
room
(0, 3)
(0, 2)
(0, 1)
(1, 2)
(0, 2)
(0, 1)
(0, 0)
room
(0, 2)
room
(0, 1)
45
(0, 0)
(0, 1)
(0, 0)
(0, 1)
(0, 2)
Principles of 3D guidance

A sensor is located in a hazardous region if



it is D hop away from the emergency point or
it’s a stair sensor and its downstair sensor is in a
hazardous region
When guiding



Avoid to guide people through hazardous regions
Try to guide people to the exits on the ground floor
Guide people to rooftop if there is no proper ways to
downstairs
46
Simulation results
4F
4F
4F
4F
4F
4F
3F
3F
3F
3F
3F
3F
2F
2F
2F
2F
2F
2F
1F
1F
1F
1F
1F
1F
47
roof gateway
go upstairs
go downstairs
Prototyping


We have implemented our system using MICAz motes and
MTS310 sensors on TinyOS.
Protocol stack
Applicationlevel UI
Deployment
Network
initialization
Guidance
initialization
Query
Guidance interface
GUI
Users part
Sensors part
Application
layer
Tree
Reconstruction
Sensor task
Network
layer
Symmetric link
detection
Tree
maintenance
HELLO
Report
Physical layer and Data link layer
(a) Sink
Guidance
service
EMG
Tree
Reconstruction
Sensor task
Symmetric link
detection
Tree
maintenance
HELLO
Report
Guidance
service
EMG
Physical layer and Data link layer
(b) Sensor
48
JAVA GUI
Control
panel
Building
plan panel
stair
EMG
→ 21 (in dec.)
Monitor
panel
stair
exit
Current guidance direction
stair
sink
49
Guidance UI
50
Demonstration
Control
host

Environment

Sink
A virtual 2-store
building
Stair
Stair
Stair
Stair
Exit
Exit
Exit
Exit
51
Demonstration

Vedio
52
More Results
roof
3F
roof
2F
1F
Guidance pkt. count
151.8
Guidance pkt. count
237.8
Guidance pkt. count
78.8
Tree Reconstruction pkt. count
7.6
Tree Reconstruction pkt. count
16.5
Tree Reconstruction pkt. count
4.8
(a)
(b)
Stair sensor
Exit sensor
(c)
Emergency
53
Conclusions

Extending 2D navigation to 3D navigation

on each floor, the navigation is similar to 2D

stair and gateway sensors are paid of special attention

roof is also paid of special attention
54
References



Q. Li, and et. al, “Distributed algorithm for guiding navigation
across a sensor network”, MobiCom 03.
Y.-C. Tseng, M.-S. Pan, and Y.-Y. Tsai, “A Distributed Emergency
Navigation Algorithm for Wireless Sensor Networks”, IEEE
Computers, Vol. 39, No. 7, July 2006, pp. 55-62.
M.-S. Pan, C.-H. Tsai, and Y.-C. Tseng, “Emergency Guiding and
Monitoring Applications in Indoor 3D Environments by Wireless
Sensor Networks”, Int’l Journal of Sensor Networks, Vol. 1, Nos.
1/2, pp. 2-10, 2006.
55