UPLINK: ULTRASONIC POSITION LOCATOR FOR INDOOR ENVIRONMENTS

Aunim Mashrur Hossain, Giridhar Nandipati

Advised By: Dr. Daniel Lee

Thursday, April 22nd1:30pm – 4:30pmRCA Laboratory

Demonstration

Applications

System Overview

Motivation and PurposeEstablish standard method of

determiningposition in indoor environments

Display accurate position in real time• Measure the time of arrival of

ultrasonic waves from various ultrasonic transmitters to the ultrasonic receiver

• Compute position relative to these transmitters within an accuracy of a few inches

Create simple, cost effective, and easy to use system• Install in any size rooms without

hassle• Use with same power needs as simple

appliances• Require around $35.00 (excluding

handheld device)

Stationary Clock Synchronizer• Notify Stationary Beacons when to

transmit ultrasonic signals• Ensure no two Beacons transmit

simultaneously• Send infrared synchronization signal to

Mobile Unit

Stationary Beacons• Send ultrasonic waves while signaled

by the Stationary Clock Synchronizer

Mobile Unit• Receive, filter, and amplify Infrared

Synchronization Signal and ultrasonic signals

• Find time difference between arrival of infrared signal and arrival of ultrasonic signal

• Send time differences to Handheld Device

• Display position in a real-time Graphical User Interface

Basic Premise• Infrared signals travel at the speed of

light• Ultrasonic signals travel at the speed of

sound (which is approximately one million times slower)

• Infrared signals can be thought of as immediately arriving at the receiver

Thus, can measure distance using time difference between arrival of infrared and ultrasonic pulses• Each millisecond in time difference

corresponds to approximately 1 foot of distance

• Time differences are accurate to within 100 microseconds ~ one tenth of a foot

Once four beacons send pulses, sequence is restarted• The new signal sequence is denoted by

a longer delay than that between the four transmitter signals

• In order to ensure accuracy, delay is set to ~100 ms

Location Determination Method

Results

Block Diagram

Front End of UPLINK System

• Transmitters denoted by red squares

• Position of user displayed on screen, shown by the blue dot

• Graphical interface updates in real time

Figure 1 – Sequence of Transmitted (above)

and Received Pulses (below)

Figure 2 – Single Transmitted (above) and Received Pulse (below)

Figure 3 – UPLINK Graphical Interface on IPAQ

UPLINK can be extended to many applications• Inventory control in warehouses• Indoor directions in office

buildings/shopping malls• Location-aware devices such as

computer terminals• Virtual rooms and Immersive Audio• Security systems that monitor object

position• Interface with existing outdoor

applications such as GPS to provide pervasive location awareness

Back End of UPLINK System

• Sequence of transmitted pulses is repeated with sufficient delay between them

• Time delay of each of four pulses determines relative position from beacons

• Delays are transmitted to IPAQ for computation of position