Ad Loc: Location-based Infrastructure-free Annotation

1. Ad Loc: Location-based Infrastructure-free Annotation Derek J. Corbett and Daniel Cutting University of Sydney University College Dublin, 16th October 2006

2. Motivation • Mobile devices are increasingly common • Carried with us everywhere • Powerful, capacious, wireless • Location technologies also appearing • GPS, Galileo • PlaceLab • Location-based services are appealing • “Does this café serve good coffee?” University College Dublin

3. Ad Loc • Annotation of physical environment (Post-It notes) • Tie persistent virtual “notes” to physical locations via a mobile device • Notes publicly and asynchronously available • No embedded infrastructure or Internet access needed Mock application University College Dublin

4. Publishing and Querying • User composes a note and publishes it at their current location • Others arrive at locations and query for published notes • Empty queries return all notes at a user’s location • Constraints can be applied • Return all notes with a given subject • Limit to recently published notes • Etc. University College Dublin

5. Background • Stick-e notes, Place-Its, … • Notes with contextual triggers placed in the environment • Location-based reminders on mobile phones • Location detection • GPS now very mature (Assisted GPS, etc.) • Galileo designed to work well indoors • PlaceLab uses WiFi detection + DB • Mobile phone cells can provide imprecise location • E-graffiti, CampusAware • Social studies of environmental annotation • People like using them and contributing notes University College Dublin

6. Infrastructure-free University College Dublin

7. Mobile Device Density 500m square region, 82m broadcast radius University College Dublin

8. Cache Replication Policies • Basic • Any broadcast notes overheard by devices are cached • Publish • Broadcast a note to neighbours upon generation • Periodic • Periodically broadcast the least overheard cached notes • Location-aware Periodic • Periodically broadcast cached notes relevant to the current area • All • Combination of Basic, Publish and Location-aware Periodic University College Dublin

9. Area of Relevance • Notes are relevant to specific locations of different sizes • Inefficient / unnecessary to cache notes on all devices • Area of Relevance (AOR) definesarea where a note is relevant • Notes are cached on devicesin or near AOR • As more distant users find anote relevant, its AOR growsto encompass all such points University College Dublin

10. Ad Loc Summary • Ad Loc is an infra-structure free, localised persistent and asynchronous platform for collaboratively annotating the physical environment • Localised: notes are relevant to specific locations • Persistent: notes remain in the environment • Asynchronous: publisher and consumer need not be simultaneously present • Collaborative: anyone can publish or read any note • Infrastructure-free: no servers or Internet connections University College Dublin

11. Evaluation • OMNeT++ simulation using the Mobility Framework • WiFi-enabled devices with a broadcast range of 82m • Simulation duration: 3000s • Network size: 500m x 500m • Mobility: 1m/s random waypoint model (no pause) • Cache flush: 500s • Periodic replication: 20s randomly offset University College Dublin

12. Queries Resolved byAd Loc Total Queries Relevant Notes Found on Query Total Published Relevant Notes Total Packets Sent Total Queries Made Metrics • Recall • Traffic Overhead Ratio (TOR) • Ad Loc Satisfied Internet Queries (ASIQ) University College Dublin

13. Scenarios • “City Blocks” scenario • 400 small locations of radius 10m (e.g. shop fronts) • “Sporting Venue” scenario • 4 large locations of radius 100m (e.g. stadium sections) • In each scenario the total area covered by the locations was approximately half of the network area • Initial experiments tested recall and overhead of user-created notes University College Dublin

14. Note Availability:City Blocks University College Dublin

15. Note Availability:Sporting Venue University College Dublin

16. Note Overhead:City Blocks University College Dublin

17. Note Overhead:Sporting Venue University College Dublin

18. Discussion • Critical mass of participants required • Surprisingly small! • ~14 enough for 60-70% recall (density of 1) • Good recall properties • ~28 gives 90% recall (density of 2) • Diminishing returns with more nodes • Linear scaling overhead with the number of users • Cache Replication Policy not too important to recall • Basic works “well enough” with less overhead if enough queries • Otherwise Periodic performs well with low overhead University College Dublin

19. Extension: Internet Cache • Ad Loc can be used to cache data from the Internet • Data available on internet may be pertinent to particular locations • Train timetables at stations • Movie trailers at cinemas • Company websites at company headquarters • This data can be downloaded once from the Internet and then cached in Ad Loc for others • Probe Ad Loc before having to download content University College Dublin

20. Scenarios • How much Internet traffic is replaced by Ad Loc traffic? • Same two scenarios as previous experiment • Each location had a set of relevant Internet objects • City Blocks: 20 data items available per location • Sporting Venue: 2000 data items available per location • Queried objects chosen from Zipf distribution University College Dublin

21. Internet Cache Availability:City Blocks University College Dublin

22. Internet Cache Availability:Sporting Venue University College Dublin

23. Internet Cache Overhead:City Blocks University College Dublin

24. Internet Cache Overhead:Sporting Venue University College Dublin

25. Discussion • Reduces the number of Internet lookups • A third of queries satisfied locally with just 28 nodes • Works best for many small nearby locations • Less reliable for large locations University College Dublin

26. Conclusion • Ad Loc provides essentially free access to serendipitously available content • Doesn’t require huge number of participants • Algorithms scale well • Interesting property: notes may disappear at night when all devices leave a location • But may return next morning! • May have different sets of notes at a location depending on time of day and function of location University College Dublin

27. Future Work • More detailed simulations, realistic mobility models • Polygonal AORs • User Interface • Ranking functions for notes • Content filters for spam • Proxy servers to augment caching • Allow notes to be cached overnight, etc. • Proxies can be integrated with no extra work University College Dublin

28. Questions? Daniel Cutting dcutting@it.usyd.edu.au Corbett. D. and Cutting. D.Ad Loc: Location-based Infrastructure-free Annotation3rd International Conference on Mobile Computing and Ubiquitous Networking (ICMU2006)London, UKOctober 11—13, 2006 University College Dublin

29. AD LOC Notes • < id, timestamp, AOR, subject, data > • ID: A digest of the subject and the data segment • Timestamp: Time when the note was last cached • Subject: A short description of the note • Data: MIME data component University College Dublin

30. AD LOC: What does it mean? • Abbreviation of “Ad Locum” • Ad Locum (Latin) = “To/At the Place/Location” University College Dublin

31. Enabling Technologies • Location Awareness • (A/D)GPS, E911, APS, Base Station Triangulation • Ad Hoc Communication • 802.11(abg), Bluetooth • Infrastructure Based Communications • 3G, WiMax, WiBro, GPRS/EDGE University College Dublin