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

2. Dated 16th October 2006University College DublinSlide 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?”

3. Dated 16th October 2006University College DublinSlide 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

4. Dated 16th October 2006University College DublinSlide 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.

5. Dated 16th October 2006University College DublinSlide 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

6. Dated 16th October 2006University College DublinSlide 6 Infrastructure-free

7. Dated 16th October 2006University College DublinSlide 7 Mobile Device Density 500m square region, 82m broadcast radius

8. Dated 16th October 2006University College DublinSlide 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

9. Dated 16th October 2006University College DublinSlide 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) defines area where a note is relevant Notes are cached on devices in or near AOR As more distant users find a note relevant, its AOR grows to encompass all such points

10. Dated 16th October 2006University College DublinSlide 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

11. Dated 16th October 2006University College DublinSlide 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

12. Dated 16th October 2006University College DublinSlide 12 Metrics Recall Traffic Overhead Ratio (TOR) Ad Loc Satisfied Internet Queries (ASIQ) Queries Resolved by Ad Loc Total Queries Total Packets Sent Total Queries Made Relevant Notes Found on Query Total Published Relevant Notes

13. Dated 16th October 2006University College DublinSlide 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

14. Dated 16th October 2006University College DublinSlide 14 Note Availability: City Blocks

15. Dated 16th October 2006University College DublinSlide 15 Note Availability: Sporting Venue

16. Dated 16th October 2006University College DublinSlide 16 Note Overhead: City Blocks

17. Dated 16th October 2006University College DublinSlide 17 Note Overhead: Sporting Venue

18. Dated 16th October 2006University College DublinSlide 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

19. Dated 16th October 2006University College DublinSlide 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

20. Dated 16th October 2006University College DublinSlide 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

21. Dated 16th October 2006University College DublinSlide 21 Internet Cache Availability: City Blocks

22. Dated 16th October 2006University College DublinSlide 22 Internet Cache Availability: Sporting Venue

23. Dated 16th October 2006University College DublinSlide 23 Internet Cache Overhead: City Blocks

24. Dated 16th October 2006University College DublinSlide 24 Internet Cache Overhead: Sporting Venue

25. Dated 16th October 2006University College DublinSlide 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

26. Dated 16th October 2006University College DublinSlide 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

27. Dated 16th October 2006University College DublinSlide 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

28. Dated 16th October 2006University College DublinSlide 28 Questions? Daniel Cutting dcutting@it.usyd.edu.au dcutting@it.usyd.edu.au Corbett. D. and Cutting. D. Ad Loc: Location-based Infrastructure-free Annotation 3 rd International Conference on Mobile Computing and Ubiquitous Networking (ICMU2006) London, UK October 11—13, 2006

29. Dated 16th October 2006University College DublinSlide 29 A D L OC Notes 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

30. Dated 16th October 2006University College DublinSlide 30 A D L OC: What does it mean? Abbreviation of “Ad Locum” Ad Locum (Latin) = “To/At the Place/Location”

31. Dated 16th October 2006University College DublinSlide 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