1. Indoor Navigation Using a Wireless Sensor Network
“Because everyone can use some guidance once in a while…”
Students: Itay Ben-Artzi & Shahar Kinarti
Instructor: Dr. Zvi Lotker

2. Introduction and Motivation
Importance of orientating in a complex indoor environment
Airport, Hospital, Government Offices
Blind people
A system that provides location is needed
GPS – Existing system
Problems with using GPS in an indoor environment
Poor or no reception at all inside buildings
Not accurate enough
What can be done to overcome these issues?
We can use a Wireless Sensor Network (existing or new one) for this purpose

3. Project Goal
Design and implement a navigation system that will allow a blind person to navigate in an indoor environment
The system will support multi-user navigation

4. Challenges
Indoor navigation requires high accuracy location estimation
Overcoming location errors caused by the system
Constructing paths that correspond to a physical indoor environment
Preventing users from colliding with each other in a multi-user scenario
Interaction with user should be limited only to the
necessary navigation commands

5. The Cricket Location System
A framework of wireless sensor network that provides high accuracy (centimeter level) location estimation in an indoor environment.
Open-source JAVA-based (application) and TinyOS-based (firmware) development kit
Each sensor can function as either a Beacon or a Listener
Ultrasonic transmitter
Ultrasonic receiver
Diagnostic LEDs
RS-232
connector
7.32MHz
Crystal
Power switch
ATMEL Processor

6. Cricket Principle of Work
Measure the time interval between the arrival of the RF signal to the arrival of the Ultrasonic signal
Calculate the distance using the known velocity of light and sound waves
Calculate location from distances received from beacons
Beacon
Ultrasound
(pulse)
RF data
Listener

7. Deployment of Cricket Beacons
Cricket Listener must have a direct line of sight to at least
three Cricket Beacons in every point on the plane
One solution is to mount Cricket Beacons on the ceiling

8. Navigation Tree
Create a Constrained Delaunay Triangulation (CDT) out of a source map and store in a Quad-Edge database
Generate the dual graph of the CDT, which is the Voronoi Diagram
The navigation tree is based on the Voronoi Diagram
Used for calculating shortest paths
These shortest paths are used for building the user’s path to the destination
CDT
Dual Graph
(Voronoi Diagram)

9. Location Error Correction & User Orientation
The Challenge
Many location measurement per second
Not all measurements are correct – which is the best one?
How can user orientation be determined?
Need to let the user time to move
The Solution
Set a periodic time interval
Collect all location measurements arrived in this time interval
Calculate orientation using the received location measurements
Set a movement distance threshold that determines a valid location measurement
Determine user orientation in each interval by choosing the majority of all the calculated orientations

10. Synchronization Protocol – Multi User
Sending End_To_End_Path MSG
Each user receives the message and searches for path intersection
When user is close to a door a Lock_door MSG is broadcasted
All other users send ACK MSG in reply
After passing the door, the user sends an Unlock_door MSG
Allowing the another user to cross the door
Unlock_door
wait
Lock_door
E2EPath
ACK
E2EPath
User 1
User 2

11. Synchronization Protocol – Multi User Cont’
User that received a Lock_door MSG won’t be able to pass through the door
Will receive “wait” command until the door will be freed
When several users are waiting on a locked door and that door gets released:
ACK
Only one user sends a Door_lock MSG
Unlock_door
Using priority queue
wait
lock_door
User 1
User 2

12. The System at Work
Now we’ll see a short video showing the actual system at work

13. Summary
We created a working system that guides a blind person in an indoor environment
Error Correction Module was implemented
Synchronization Protocol was implemented
Voice Command Module was implemented

14. Questions ?