20.01.2015 Views

njit-etd2003-081 - New Jersey Institute of Technology

njit-etd2003-081 - New Jersey Institute of Technology

njit-etd2003-081 - New Jersey Institute of Technology

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

61<br />

3.6.2.1 Windowed Wigner Distribution. In practice, one is forced to calculate the<br />

Wigner distribution using the equation:<br />

where h(t) is a window function. This is due to the finite nature <strong>of</strong> the data. The<br />

resulting distribution has the effect <strong>of</strong> smoothing the Wigner distribution over frequency<br />

and is called the Pseudo Wigner distribution (PWD)[22]. The PWD sometimes results<br />

in a better-looking distribution in that certain cross terms are suppressed. One can clean<br />

the cross terms by smoothing the Pseudo Wigner distribution over time which is called<br />

the Smoothed Pseudo Wigner distribution (SPWD). Smoothing the Pseudo Wigner<br />

distribution is performed as follows:<br />

where L, ρws<br />

(t, are f) smoothing and (t, function, f) the Smoothed Pseudo<br />

Wigner distribution and the Pseudo Wigner distribution respectively. The advantages <strong>of</strong><br />

the Smoothed Pseudo Wigner distribution are that for certain types <strong>of</strong> smoothing, a<br />

positive distribution is obtained and the cross terms are suppressed. However smoothing<br />

destroys some <strong>of</strong> the desirable properties <strong>of</strong> the Wigner distribution: if L is taken to be<br />

independent <strong>of</strong> the signal, then the only way to obtain a positive distribution is by<br />

sacrificing the marginals properties [41].

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!