location system for ubiquitous computing jeffrey hightower gaetano borriello university of...

Location System for Ubiquitous ComputingJeffrey HightowerGaetano BorrielloUniversity of Washington

Location

Location is a useful contextual information Physical versus Symbolic Absolute versus relative

Location (cont.)

Physical versus SymbolicPhysical : (45 。N, 145 。W)Symbolic : in the kitchen, next to a mailbox

Application can determine symbolic location resolution according to the physical location (resolution is important!!)

Location (cont.)

Absolute versus relative Absolute : shared reference, e.g. latitude Relative : each object have its own reference or frame

Transfer relative to absolute location Use triangulation with multiple relative position

Inverse trivial…

Location System

To locate people, equipment and other tangibles by one or more location-sensing techniques

location-sensing techniquesTriangulation : lateration, angulationProximityScene analysis

Issue about location system

Accuracy and precisionAccuracy : the grain size of the location

system can provide (distance)Precision : the probability that we can get that

accuracy (percentage) Error distribution along with the density of

sensor

Issue about location system Scale

Evaluate by the coverage area and number of object can locate per unit infrastructure per time interval

Time is a important consideration Bandwidth Accuracy

Issue about location system Limitation

GPS doesn’t work well inside the building Some tagging systems can read tags properly only

when a single tag is present. Privacy Cost

Time cost Space cost price

A survey of location system Active badge Active Bat Cricket RADAR MotionStar magnetic tracker Easy living Smart floor E911 …

Future work

Lower cost, less amount of infrastructure, better power consumption, etc…

Sensor fusion Ad hoc location sensing

Sensor fusion

The use of multiple technologies or location systems simultaneously to form hierarchical and overlapping levels of sensing.

Increase accuracy and precision beyond individual system

Ad hoc location sensing

This approach borrows the idea from the ad hoc networking research

Cooperate with other nearby objects by sharing sensor data to factor out overall measurement error.

Ad hoc location sensing

The SpotON system implements ad hoc location sensing Using low cost tagRadio signal attenuation to estimate intertag d

istanceExploit the density of tags

Q&A