Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE

1.3 Thesis Organization 3
In addition, the wave changes the velocity of its propagation depending on the
material properties. As the result of all these factors, the radar receives a very
complex signal, full of noise and clutters, which is very difficult to interpret. The
main aim of the signal processing stages between the receiver and the radar display
is to decompose the received interposed signals, use them for estimation of the
scanned environment and represent this information for the end users in a human
understandable and effective way. There exist no explicit method how to solve this
complex problem, and that is why it represents a big challenge for researchers and
engineers.
One has to mention that through-wall imaging is much more problematic
in comparison to detection or localization of moving objects behind the wall.
Whereas, in moving objects detection background subtraction can be applied, what
solves a lot of problems, this approach is not possible to apply. During imaging
measurements where antenna system is moving and everything what is measured
is background, and that is why it cannot be subtracted. Background subtraction
eliminates influence of antennas, radar electronics, walls etc. on measured objects.
Therefore, a calibration in imaging have to be done with a great precision because
at the final stage it would significantly affects the results.
The radar imaging is well known field for a long time, mostly used for Ground
Penetrating Radar (GPR) applications [76]. However, through-wall imaging has
become investigated only a few years ago [60]. The most of the published methods
were tested only on simulated data, and results from practical measurements are
showing poor performance for most of them. Therefore, through-wall imaging has
not found many applications that could be possibly used in the practical situations
yet. A lot of research in signal processing as well as in radar hardware field is still
required.
1.3 Thesis Organization
In Section 2, the state of the art of through-wall imaging is described. The function
of an UWB radar is sketched, all the preprocessing and calibration steps required
for through-wall imaging are explained, and simplified mathematical and physical
ideas of most of the radar migration techniques are mentioned. In Section 3, the
goals of this thesis are introduced. In Section 4, the three main contributions of
this thesis are described. Efficient, precise and fast time of arrival through-wall
estimation is shown in Section 4.1. Precise, easy to handle and fast measurement
technique for estimation of wall parameters such as thickness, permittivity, and
conductivity is introduced in Section 4.2. A method of building contours highlighting
is presented in Section 4.3. Basic migration methods are compared in Section
4.4 on scenario measured with M-sequence UWB radar device. Also the imaging
results of real measurements based on many practical scenarios are shown. Finally,