Pulse shaping for zero ISI: Nyquist channel filtering

Questions
Question 3.1
 

By carefully manipulating the filtering characteristics of the channel (and any TX or RX processing), it is possible to control the intersymbol interference such that it does not degrade the bit error rate performance of the link. This is achieved by making sure that the overall channel filter transfer function has what is termed a Nyquist frequency response.

A Nyquist channel response is characterized by the transfer function having a transition band between passband and stopband that is symmetrical about a frequency equal to 0.5 x 1/Ts.

 

For this type of channel response, the data symbols are still smeared, but the waveform passes through zero at multiples of the symbol period