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Ad Loc: Location-based Infrastructure-free Annotation. Derek J. Corbett and Daniel Cutting University of Sydney University College Dublin, 16 th October 2006. Motivation. Mobile devices are increasingly common Carried with us everywhere Powerful, capacious, wireless
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Ad Loc: Location-based Infrastructure-free Annotation Derek J. Corbett and Daniel Cutting University of Sydney University College Dublin, 16th October 2006
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
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
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
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
Infrastructure-free University College Dublin
Mobile Device Density 500m square region, 82m broadcast radius University College Dublin
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
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
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
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
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
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
Note Availability:City Blocks University College Dublin
Note Availability:Sporting Venue University College Dublin
Note Overhead:City Blocks University College Dublin
Note Overhead:Sporting Venue University College Dublin
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
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
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
Internet Cache Availability:City Blocks University College Dublin
Internet Cache Availability:Sporting Venue University College Dublin
Internet Cache Overhead:City Blocks University College Dublin
Internet Cache Overhead:Sporting Venue University College Dublin
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
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
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
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
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
AD LOC: What does it mean? • Abbreviation of “Ad Locum” • Ad Locum (Latin) = “To/At the Place/Location” University College Dublin
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