ad loc: location-based infrastructure-free annotation derek j. corbett and daniel cutting university...

Ad Loc: Location-based Infrastructure-free Annotation

Derek J. Corbett and Daniel Cutting

University of Sydney

University College Dublin, 16th October 2006

Dated 16th October 2006

University College Dublin Slide 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?”



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



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.



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



Infrastructure-free



Mobile Device Density

500m square region, 82m broadcast radiusRelationship Between The Number of Nodes and the Resulting Average Density

0

12

3

4

5

6

7

8

910

11

12

13

14

15

16

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Number of Nodes

Average Node Density



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



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



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



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



Metrics

• Recall

• Traffic Overhead Ratio (TOR)

• Ad Loc Satisfied Internet Queries (ASIQ)

Queries Resolved by Ad LocTotal Queries

Total Packets SentTotal Queries Made

Relevant Notes Found on QueryTotal Published Relevant Notes



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



Note Availability:City Blocks



Note Availability:Sporting Venue



Note Overhead:City Blocks



Note Overhead:Sporting Venue



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



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



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



Internet Cache Availability:City Blocks



Internet Cache Availability:Sporting Venue



Internet Cache Overhead:City Blocks



Internet Cache Overhead:Sporting Venue



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



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



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



Questions?

Daniel Cutting [email protected]

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



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



AD LOC: What does it mean?

• Abbreviation of “Ad Locum”

• Ad Locum (Latin) = “To/At the Place/Location”



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

ad loc: location-based infrastructure-free annotation derek j. corbett and daniel cutting university...

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