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WALRUS: Wireless Active Location Resolver with Ultrasound

WALRUS: Wireless Active Location Resolver with Ultrasound. Tony Offer, Christopher Palistrant. Basic Concept. Function Make mobile device aware of its location within building Location awareness can then be used to provide location-dependent services Usefulness

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WALRUS: Wireless Active Location Resolver with Ultrasound

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  1. WALRUS: Wireless Active Location Resolver with Ultrasound Tony Offer, Christopher Palistrant

  2. Basic Concept • Function • Make mobile device aware of its location within building • Location awareness can then be used 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

  3. 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

  4. 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

  5. Demonstration • Two servers, two rooms, one client • User will carry iPAQ between rooms and watch message updates on screen • Shows plausibility and basic functionality • Original scenario demonstrated future potential applications • Scalability is easy with good design

  6. Implementation • System Components • Server-sided beacon software • Mobile client software • Datagram signal detection • Ultrasonic signal detection • Current Status • Working model demonstrates basic functionality • Testing overall reliability of system • Increasing range of ultrasonic reception • Tweaking various parameters

  7. Server-sided beacon software

  8. Mobile client signal detection

  9. Ultrasonic signal detection

  10. Evaluation • Performance • Reliability and speed • System quality depends on ultrasound attenuation • Metrics • Percentages and distances • Ultrasound detection when present or not present • Detection of correct room when 802.11 is from other rooms • Time Delays • 1st ultrasound detection with Goertzel until actually deciding on positive beacon signal • Entering a room and seeing an update in the room location

  11. Evaluation (continued) • Data Collection • Reception varies on mobile platforms • iPAQ h3870 receives signal 10’ - 15’ away • Dell 8100 Inspirion with external mic. receives signals closer to 15’-20’ • Does this increase with foil ear? • Rough tests show 1.2 secs. between 802.11 reception and positive ultrasonic decision. • Conclusions • Multiple avenues for performance improvement • Alternate DSP methods may give better results • Fixed point arithmetic may give better speed

  12. Future Work • Add a windowing function to Goertzel • Large scale application experiment • How does WALRUS respond with many offices broadcasting their locations? • Modulate frequencies in different rooms • Sacrifice accuracy in exchange for precision • Can we increase the accuracy but retain ultimate cost metrics? • Develop applications to maximize benefit • Are users willing to sacrifice identity in exchange for more information?

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