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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!!)
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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
