  Radio tomographic imaging (RTI) enables device free localisation of people
and objects in many challenging environments and situations. Its basic
principle is to detect the changes in the statistics of some radio quality
measurements in order to infer the presence of people and objects in the radio
path. However, the localisation accuracy of RTI suffers from complicated radio
propagation behaviours such as multipath fading and shadowing. In order to
improve RTI localisation accuracy, we propose to use inexpensive and energy
efficient electronically switched directional (ESD) antennas to improve the
quality of radio link behaviour observations, and therefore, the localisation
accuracy of RTI. We implement a directional RTI (dRTI) system to understand how
directional antennas can be used to improve RTI localisation accuracy. We also
study the impact of the choice of antenna directions on the localisation
accuracy of dRTI and propose methods to effectively choose informative antenna
directions to improve localisation accuracy while reducing overhead. We
evaluate the performance of dRTI in diverse indoor environments and show that
dRTI significantly outperforms the existing RTI localisation methods based on
omni-directional antennas.
