EzTrack, March 2009
EZTrack
is a proximity-based indoor tracking system that features portability and
ease-of-setup by not requiring a separate training phase in every new
environment. The system uses measured radio signal strength on IEEE 802.15.4 radios
to infer proximity but self-calibrates its parameters in different environments
thus making it easy to setup. The system was demonstrated in The Village at heritage Point, a senior
center in Morgantown WV, for tracking elderly people in the facility and
ensuring their safety. The system was shown to have an accuracy of about 5-7
feet in tracking.
Instead of building
an RF signature model of the entire region by mapping signal strengths to
pair-wise distances, which in any case is environment-specific and limited by
multipath interference, EzTrack exploits the double
band nature of IEEE 802.15.4 radios to learn proximity zones for each RF
sensor. IEEE 802.15.4 radios have been shown to exhibit a dual band
characteristic in which received signal strengths are significantly high and
isotropic within an inner band and exhibit high variance (due to time-varying
interference and multi-path effects) in an outer band. EzTrack
uses beacon messages transmitted by neighboring anchor nodes to continuously
learn an inner band RSSI threshold specific to each anchor node. These
thresholds are used to determine a set of candidate anchor nodes that define
the neighborhood for the current mobile node location. Candidate anchor nodes
are further filtered based on outlier elimination techniques and the locations
of the filtered anchor nodes are used to track each mobile node. Despite its
inherent simplicity and portability, EzTrack is shown
to achieve median accuracies of 7 feet. Using EzTrack,
in indoor tracking system can be established in any new environment within a
few minutes by simply scattering anchor motes and noting their locations.
A few videos
of EzTrack being used to track a mobile user within
the Engineering Sciences Building are shown below, which demonstrate the high
accuracy of EzTrack.
Videos