Ad Loc: Location-based Infrastructure-free Annotation

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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

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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?

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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

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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 users
  location
• Constraints can be applied
• Return all notes with a given subject
• Limit to recently published notes
• Etc.

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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

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Infrastructure-free
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Mobile Device Density
500m square region, 82m broadcast radius
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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

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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

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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

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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

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Metrics

• Recall
• Traffic Overhead Ratio (TOR)
• Ad Loc Satisfied Internet Queries (ASIQ)

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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

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Note AvailabilityCity Blocks
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Note AvailabilitySporting Venue
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Note OverheadCity Blocks
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Note OverheadSporting Venue
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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

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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

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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

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Internet Cache AvailabilityCity Blocks
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Internet Cache AvailabilitySporting Venue
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Internet Cache OverheadCity Blocks
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Internet Cache OverheadSporting Venue
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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

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Conclusion

• Ad Loc provides essentially free access to
  serendipitously available content
• Doesnt 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

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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

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Questions?

• Daniel Cutting dcutting_at_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 1113, 2006

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AD LOC Notes

• lt id, timestamp, AOR, subject, data gt
• 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

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AD LOC What does it mean?

• Abbreviation of Ad Locum
• Ad Locum (Latin) To/At the Place/Location

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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