Nissanka Bodhi Priyantha
Massachusetts Institute of Technology, Cambridge, MA,
Indoor environments present opportunities for a rich set of
location-aware applications such as navigation tools for humans and
robots, interactive virtual games, resource discovery, asset tracking,
location-aware sensor networking etc. Typical indoor
applications require better accuracy than what current outdoor
location systems provide. Outdoor location technologies such as GPS
have poor indoor performance because of the harsh nature of indoor
environments. Further, typical indoor applications require
different types of location information such as physical space,
position and orientation.
This dissertation describes the design and implementation of the
Cricket indoor location system that provides accurate location in the
form of user space, position and orientation to mobile and sensor
network applications.
Cricket consists of location beacons that are attached to the
ceiling of a building, and receivers, called listeners, attached
to devices that need location. Each beacon periodically transmits its
location information in an RF message. At the same time, the beacon
also transmits an ultrasonic pulse. The listeners listen to beacon
transmissions and measure distances to nearby beacons, and use these
distances to compute their own locations. This active-beacon
passive-listener architecture is scalable with respect to the number
of users, and enables applications that preserve user privacy.
This dissertation describes how Cricket achieves accurate distance
measurements between beacons and listeners. Once the beacons are
deployed, the MAT and AFL algorithms, described in this dissertation,
use measurements taken at a mobile listener to configure the beacons
with a coordinate assignment that reflects the beacon layout. This
dissertation presents beacon interference avoidance and detection
algorithms, as well as outlier rejection algorithms to prevent and
filter out outlier distance estimates caused by uncoordinated beacon
transmissions.
The Cricket listeners can measure distances with an accuracy
of 5 cm. The listeners can detect boundaries with an accuracy
of 1 cm. Cricket has a position estimation accuracy of 10
cm and an orientation accuracy of 3 degrees.
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