UPLINK: ULTRASONIC POSITION LOCATOR FOR INDOOR ENVIRONMENTS Aunim Mashrur Hossain, Giridhar Nandipati Advised By: Dr. Daniel Lee Thursday, April 22nd 1:30pm – 4:30pm RCA Laboratory Demonstration Applications System Overview Motivation and Purpose Establish standard method of determining position 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