Indoor Positioning System

Tony Offer, Christopher Palistrant

Basic Concept

Function Make mobile device aware of its location within a building Use location awareness to provide location-dependent

services

Usefulness Many applications for devices that know where they are Provision of services based on the context of locality

Target Users Businesses with large office buildings Maintenance workers

Example Scenario

Start out in office Locate coworker

Notice automatic change in mobile device

Arrive at coworker’s office

After print stop, continue on to coworker’s office

Head out toward coworker’s office

User Interest

User’s degree of automation is increased Enhanced machine autonomy Reduced dependence on user input Device state can change based on location

Current tasks simplified by our system Selecting the closest office printer Finding a person in the office building Changing desktop environment based on inhabited room

Architecture Components

Server beacon Speakers 802.11 capability

Mobile client Microphone 802.11 capability

Process Server beacons emit

simultaneous 802.11 and ultrasound broadcasts

Clients listen for ultrasound Clients determine location No centralized management Uses pre-existing hardware

Indoor Positioning System In Action

iPAQ receives 802.11 room-identifying message

iPAQ hears ultrasound from nearby server beacon

iPAQ identifies its location

Human is not disturbed by inaudible ultrasound

Expected Effort

Remaining components No additional hardware needed Need software to communicate over 802.11 Need software to sample and analyze incoming sound

Minimum requirements Single beacon with 802.11 card Implement location-awareness

Desired Functionality N beacons with less than or equal to N 802.11 broadcast

points Implement interactive map application

Expected Effort (continued)

Unknowns Reliability of ultrasound broadcast Capabilities of the iPAQ recording system Processing power of the iPAQ

Contingencies If iPAQ is not sufficient

Recording system: Attach external microphone Processing power: Use simpler DFT library Anything else: Use laptop as mobile client

If ultrasound is unreliable Experiment with different hardware arrangements

Related Work Cricket (MIT)

Similarities Uses a combination of radio waves and ultrasound to determine location No central management

Differences Uses specialized $10 beacons and receivers Determines 4x4 ft region within a room

Active Bat (AT&T) Similarities

Uses a combination of radio waves and ultrasound to determine location Differences

Uses a central management server to perform computations Uses specially made hardware for tags and sensors Determines location within a room to an accuracy of 9 cm

Related Work (continued)

Context-Aware Computing With Sound (Intel Research, Cambridge) Similarities

Uses standard computer speakers and microphones to generate and detect ultrasound

Differences Modulates ultrasonic sound waves to carry data Does not provide positioning capabilities

Distinctiveness

Ideas borrowed from other projects Emission and detection of ultrasound to signify room-level

activity Production and sampling of ultrasonic frequencies using

standard computer speakers and microphones Unique aspects of our project

Utilizes pre-existing, standard office hardware to accomplish its goals

Distinguishes itself from the Cricket and Active Bat projects Trades high-level accuracy for simplicity and ease of

deployment

Burning Questions

Will the iPAQ and other standard mobile devices be able to perform fast Fourier transforms?

Is our system crippled by the inability of a mobile client device to be made aware of its location in hallways?

Evaluation

Major evaluation metrics Cost

Our system should only use readily available hardware Reliability

Our system should provide accurate and consistent location determinations

The rate of error for false positives and negatives should be as low as possible

Desired information from user studies Usefulness of the system Reliability of the location determination Speed of update when transitioning between

rooms