2003/4/21CSE 6362 Intelligent Environments Spring 20031 The Anatomy of a Context- Aware Application Computer Science and Engineering University of Texas.

2003/4/21 CSE 6362 Intelligent Environments Spring 2003 1

The Anatomy of a Context-Aware Application

Computer Science and Engineering

University of Texas at ArlingtonCheng-Lung Chu

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Overview

Context and context-awareness A platform described in the paper Bat Teleporting

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Context Context means situational information “Context is any information that can be us

ed to characterize the situation of an entity. An entity is a person, place, or object that is considered relevant to the interaction between a user and an application, including the user and application themselves.” Dey, A.K. and Abowd. G.D., Georgia Institute of Technology, 1999.

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Context cont’ Almost any info available at the time of an

interaction can be seen as context info. Examples

Identity Spatial info – location, orientation, speed, and

acceleration Temporal info – time of the day Environmental info Social situation Resources that are nearby Availability of resources Physiological measurements Activity Schedules and agendas

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Context-Awareness Context-awareness

One is able to use context info. A system is context-aware if it can

extract, interpret and use context info and adapt its functionality to the current context of use

Challenge – Complexity of capturing, representing and processing contextual data

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A Context-aware application A context-aware application adapts

its behavior to a changing environment

Proposed Platform A fine-grained location system A detailed data model A persistent distributed object system Resource monitors A spatial monitoring service

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Indoor Location Sensing

Ideal location sensor for use indoor Fine-grain spatial info High update rate Unobtrusive Cheap Scalable Robust

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The Bat Location System –Bat Bats

Consist of a radio transceiver, controlling logic, and ultrasonic transducer

7.5x3.5x1.5 (cm), 35g 48-bit Globally unique ID Powered by a single 3.6V

Lithium cell, a lifetime of around fifteen months

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The Bat Location System –Ultrasound receiver unit

Placed at known points on the ceiling of the rooms to be instrumented

Connected by a high-speed serial network in daisy-chain fashion

Ultrasound receiver units

Receivers are placed in a square grid, 1.2m apart

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The Bat Location System Base station Periodically transmits a radio

message containing a single identifier, causing the corresponding Bat to emit a short un-encoded pulse of ultrasound

In the mean time, receiver are reset via the wired network

Receivers monitor the incoming ultrasound and record the time of arrival of any signal from the Bat

Times-of-flight of the ultrasound pulse from the Bat to receivers

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The Bat Location System Entity location is det

ermined based on the principle of trilateration

3D position can be also deduced

Orientation of an object can be deduced

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The Bat Location System Reflection error - Statistical outlier

rejection algorithm Reverberation 20 ms - location updates

50/second Scalability issues

Location Quality of service Scheduling info can also be used to assist

power saving The set of Bats to be tracked may change

over time Handover of control between base stations

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The Bat Location System

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The Bat Location System Current deployment

720 receivers and 6 radio cells to cover an area of around 1000 m2 on three floors. The system can determine the positions of up to 75 objects each second, accurate to around 3cm in three dimensions

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Environment model Describing entities in the real world and their p

ossible interactions Sets out the types, names, capabilities and pro

perties of all entities and acts as a bridge, allowing computer systems to share the user’s perceptions of the real world

Ouija – a package provides an object-oriented data modeling language which is used to generate an object layer on top of the relational model used by the Oracle DB

3-tier architecture

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Resource Monitor Resource monitor

Installed on all networked machines Machine activity Machine resources Network point-to-point bandwidth and latency

Techniques to ensure the DB not to be a bottleneck Update frequency Relevancy caching

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Programming with Space Location-aware applications are

interested in relative spatial facts The person is standing in front of the

workstation Express relative spatial facts in terms of

geometric containment relationship Applications receive a stream of events

expressing spatial facts relevant to them

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Spatial monitoring

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Containment tree indexing system The index system u

ses a quadtree called the containment index

Maximal cover – the smallest set of quadtree cells required to cover the space at a particular resolution

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The containment indexing theorem

Space s is contained by space t if and only if, for each cell x in the maximal cover of s, there exists exactly one cell in the maximal cover of t that contains x or is equal to x

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Bat Teleporting Improved application based on Active

Badge System Redirect X Window System environment

to different displays Virtual Network Computing system

Provides a windowing-system-independent means for a user to access his desktop environment from any networked machine

Event driven application

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Bat Teleporting cont’ Two buttons on the Bat

One is used to allow selection of an alternative desktop

The other is used to override the current desktop owned by other users

Three relative geometry conditions are registered with the spatial monitor

Positive containment Negative containment Negative overlap

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Bat Teleporting cont’

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An application provides human users with browsable model of the world which they can explore

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Conclusions A fine-grained sensor system A rich data model reflecting the resource

information required to support context-aware application

A distributed system of persistent objects which can be queried by context-aware application

A resource monitoring system for collecting information about the computing environment

A spatial monitoring system which allows event-based applications to be written

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References Ward, A., Jones, A., Hopper, A. A New Location Technique for

the Active Office. IEEE Personal Communications Magazine, Vol. 4, No. 5, October 1997. pp. 42-47

Hightower, J. and Borriello, G., A Survey and Taxonomy of Location Sensing Systems for Ubiquitous Computing, UW CSE 01-08-03, University of Washington, Department of Computer Science and Engineering, Seattle, WA, Aug. 2001.

Korkea-aho, M., Context-Aware Applications Survey, Helsinki University of Technology, Department of Computer Science, Apr, 2000

http://www.uk.research.att.com/bat/ http://www.uk.research.att.com/ Harter, A., Hopper, A., Steggles, P., Ward, A., and Webster, P.,

The Anatomy of a Context-Aware Application, Wireless Networks, Vol. 8, pp. 187-197