Kusy B., Ledeczi A., Koutsoukos X., Tracking Mobile Nodes Using RF Doppler Shifts, ACM SenSys(2007).
In this paper, we address the problem of tracking cooperative
mobile nodes in wireless sensor networks. Aiming
at a resource efficient solution, we advocate the use of
sensors that maintain their location information and rely on
the tracking service only when their locations change. In
the proposed approach, the tracked node transmits a signal
and infrastructure nodes measure the Doppler shifts of the
transmitted signal. We show that Mica2 motes can measure
RF Doppler shifts with 0.2 Hz accuracy corresponding to a
0.14 m/s error in relative speed estimates using radio interferometric
The tracking problem is modeled as a non-linear optimization
problem and an extended Kalman filter is used
to solve it accurately assuming Gaussian measurement errors.
However, this approach may fail if the tracked node
changes its speed or direction. We propose to update the
Kalman filter state by performing constrained least-squares
optimization when a maneuver is detected. The combined
approach achieves almost a 50% accuracy improvement over
the Kalman filter alone when the mobile node changes its
direction and speed frequently. We describe our proof-of-concept
implementation of the tracking service and evaluate
its performance experimentally and in simulation.