  Received signal strength based device-free localization has attracted
considerable attention in the research society over the past years to locate
and track people who are not carrying any electronic device. Typically, the
person is localized using a spatial model that relates the time domain signal
strength measurements to the person's position. Alternatively, one could
exploit spectral properties of the received signal strength which reflects the
rate at which the wireless propagation medium is being altered, an opportunity
that has not been exploited in the related literature. In this paper, the power
spectral density of the signal strength measurements are related to the
person's position and velocity to augment the particle filter based tracking
algorithm with an additional measurement. The system performance is evaluated
using simulations and validated using experimental data. Compared to a system
relying solely on time domain measurements, the results suggest that the
robustness to parameter changes is increased while the tracking accuracy is
enhanced by 50% or more when 512 particles are used.
