Mobile and Ubiquitous Computing. 2. . To take full advantage of the promise of ubiquitous computing requires the use of location and context information.In a context-aware system the objects change their behavior based on how and where they were used.Information about who and what is in the
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1. Mobile and Ubiquitous Computing 1 Location and Context Awareness in Mobile and Ubiquitous Computing Environment Presented By: Shaukat Wasi
2. Mobile and Ubiquitous Computing 2 To take full advantage of the promise of ubiquitous computing requires the use of location and context information.
In a context-aware system the objects change their behavior based on how and where they were used.
Information about who and what is in the vicinity of a person helps the environment to work in a context sensitive manner.
People should have control over who may know their whereabouts.
3. Mobile and Ubiquitous Computing 3 Location and Context Aware Systems
4. Mobile and Ubiquitous Computing 4 Issues 1) Privacy
3) Temporal resolution of Location information
5. Mobile and Ubiquitous Computing 5 Properties Physical position and Symbolic location
Our building is situated at 47°39'17? N by 122°18'23? W, at a 20.5-meter elevation is an example of physical location.
GPS is a physical positioning technology.
Symbolic location encompasses abstract ideas of where something is: in the kitchen, next to a mailbox etc.
Point of sale logs and bar code scanners are examples of
symbolic location technologies.
6. Mobile and Ubiquitous Computing 6 Properties Absolute versus relative
An absolute location system uses a shared reference grid for all located objects.
All GPS receivers use latitude, longitude, and altitude for reporting location.
In a relative system, each object can have its own frame of reference.
A mountain rescue team searching for avalanche victims can use handheld computers to locate victims’ avalanche transceivers. Each rescuer’s device reports the victims’ position relative to itself.
7. Mobile and Ubiquitous Computing 7 Properties Localized Location Computation
Some systems provide a location capability and insist that the object being located actually computes its own position.
Example: Online map servers such as Expedia
Some systems require the located object to periodically broadcast, respond with, or otherwise emit telemetry to allow the external infrastructure to locate it.
Example: Bar Codes
8. Mobile and Ubiquitous Computing 8 Properties Accuracy and Precision
A location-sensing system may be able to locate objects worldwide, within a metropolitan area, throughout a campus, in a particular building, or within a single room.
For applications that need to recognize or classify located objects to take a specific action based on their location, an automatic identification mechanism is needed.
9. Mobile and Ubiquitous Computing 9 Properties Cost
Time Costs, Space Costs, Capital Costs
GPS: receivers usually cannot detect the satellites’ transmissions indoors.
Some tagging systems can read tags properly only when a single tag is present.
10. Mobile and Ubiquitous Computing 10 Location Sensing Techniques and Technologies
11. Mobile and Ubiquitous Computing 11 Basic Location Sensing Techniques
Triangulation can be done via lateration, which uses multiple distance measurements between known points, or via angulation, which measures angle.
Proximity measures nearness to a known set of points.
Scene analysis examines a view from a particular vantage point.
12. Mobile and Ubiquitous Computing 12 Sensor Technologies Active Badges locate objects only to the granularity of rooms, which act as natural containers for the infrared signals emitted by the devices.
Electromagnetic trackers can determine object locations and orientations to a high accuracy and resolution (around 1 mm in position and 0.2° in orientation). Short range and sensitive to metallic objects.
Optical trackers are very robust, and can achieve levels of accuracy and resolution similar to those of electromagnetic tracking systems. E.g.Laser scanning system for human body motion.
13. Mobile and Ubiquitous Computing 13 Sensor Technologies
Radio positioning systems such as Global Positioning System (GPS) and LORAN are very successful in the wide area, but ineffective in buildings because of the reflections of radio signals that occur frequently in indoor environments.
Location information can also be derived from analysis of data such as video images. (MIT smart rooms project).
14. Mobile and Ubiquitous Computing 14
15. Mobile and Ubiquitous Computing 15
16. Mobile and Ubiquitous Computing 16 Active Badge Tracking System Mike Spreitzer, Marvin Theimer
Xerox Plao Alto Research Centre
17. Mobile and Ubiquitous Computing 17
Small computing devices worn by personnel .
Each badge has a globally unique code periodically broadcast through an infrared interface.
The User Agent serves as a general policy coordinator for both the user’s privacy concerns as well as his context-sensitive customization concerns.
One user agent for each user.
The time between subsequent sightings of the same badge.
18. Mobile and Ubiquitous Computing 18 Badge Tracking The badge system consists of strings of infra-red sensors, mounted in the ceilings of rooms and corridors, that are periodically polled by programs running on workstations.
Three separate string of sensors attached to three workstations.
The badge server forwards data obtained from the poller programs to the registered user agents.
The Minimum temporal resolution of the system is 15-18 seconds (Badges emit id-signal every 15 seconds and it take 2-3 seconds for the poller program to interrogate strings of sensors)
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To detect presence/absence or the time a person spent in the office on a working day the intervals between the first sighting and the list sighting of a badge are considered.
To filter out the periods when the person leaves the building or goes to another part of the building during the work day, the consideration intervals longer than a defined upper bound are excluded.
20. Mobile and Ubiquitous Computing 20 Problems with the tracking system
How visible the badges are to sensors?
Both natural light and some of our ceiling lighting interfere with the sensitivity of our sensors.
Many people prefer wearing their badge on their belt rather than pinned to their chest.
Our offices typically have only one sensor in them, yet people tend to face different directions when performing different activities.
A badge seen by multiple sensors at the same time.
21. Mobile and Ubiquitous Computing 21 Computer Input Tracking The Unix Location Server polls the rusers daemons on the Unix workstations every 60 seconds to find the most recent activity has occurred and for which user id.
The information is passed to user agents.
Users may also inform their User Agent of their current location explicitly by running the AtLocation program.
22. Mobile and Ubiquitous Computing 22 The two tracking systems overlap with each other.
This phenomenon is attributed to primarily two things:
(1) People working at home will be seen by their computer input act ivit, y and not by the badge system, and
(2) People who wear their badge on their belt and are typing at their workstation will tend to obscure their badge’s emissions while having clearly visible computer input activity.
23. Mobile and Ubiquitous Computing 23 References
Jeffrey Hightower, Gaetano Borriello, “Location systems for ubiquitous computing” IEEE, August 2001.
Mike Spreitzer, Marvin Theimer, “Providing Location Information in a Ubiquitous Computing Environment”, Xerox Palo Alto Research Cente.
Andy Ward, University of Cambridge Computer Laboratory; Alan Jones, Olivetti and Oracle Research Laboratory; Andy Hopper, University of Cambridge Computer Laboratory; Olivetti and Oracle Research Laboratory “A New Location Technique for the Active Office” IEEE Personal Communications, October 1997.
24. Mobile and Ubiquitous Computing 24 Thanks!!!