In other words, the received signal will have obvious spectral variations
(peaks and nulls) within its occupied BW, thus causing some frequency components to experience
attenuation while others will not. Alternatively, the frequency selective fading nature of the channel
can be easily detected by comparing the transmitted waveform (either chip, symbol, or bit time) to
the total time dispersion of the channel. Similarly, the RMS delay spread is compared against the
waveform time interval and is of significant value; then the channel is FSF. We will present some typical
values of the CBW in the sections that follow once the measured PDPs are presented and discussed.
Below we present an example illustrating this point by considering a two-ray channel model.
The first case has the time difference between the two echoes to be much smaller than the symbol
time interval. The second case has a transmitted time interval that is smaller than the delay spread of
the channel (see Fig. 3.18).
Above we have taken an extreme for the FSF case, where the waveform time interval is shorter
than the delay spread. As long as the delay spread is a significant portion of the waveform symbol
interval, the transmitted signal will encounter a frequency selective channel.
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