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njit-etd2003-081 - New Jersey Institute of Technology

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50<br />

The advantage <strong>of</strong> using equation 3.13b is that once the desired kernel is chosen,<br />

the distribution is fixed.<br />

3.4 Properties <strong>of</strong> Time-Frequency Distributions<br />

As indicated in the introduction, there are many methods for constructing timefrequency<br />

distributions. To provide guidelines for constructing time-frequency<br />

distributions, authors have proposed many "desirable" properties that time-frequency<br />

distributions should satisfy. For example, since time-frequency distributions are usually<br />

considered to be energy distributions, they should be real and positive functions. Also,<br />

the time marginal <strong>of</strong> a time-frequency distribution is the integral <strong>of</strong> the time-frequency<br />

distribution over frequency, and the time marginal should be identical to the distribution<br />

<strong>of</strong> signal energy over time. These properties and several others are listed in Table 3.1.<br />

For a more complete listing see [38].

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