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

4. 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

5. 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

6. 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

7. 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

8. Server-sided beacon software

9. Mobile client signal detection

10. Ultrasonic signal detection

11. 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 1 st ultrasound detection with Goertzel until actually deciding on positive beacon signal Entering a room and seeing an update in the room location

12. 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

13. 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?