Location System for Ubiquitous Computing Jeffrey Hightower Gaetano Borriello University of Washington

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

Location (cont.) Physical versus Symbolic  Physical : (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 techniques  Triangulation : lateration, angulation  Proximity  Scene analysis

Issue about location system Accuracy and precision  Accuracy : 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 tag  Radio signal attenuation to estimate intertag distance  Exploit the density of tags

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