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

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

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

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

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

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

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

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)

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

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

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

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

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

Questions ?