Why does applying RRC to the signal increase bandwidth? Please see this question: Why samples per symbols $\geq 2$ in the GNURadio Constellation Modulator block?.  The first answer here says &quot;filtering the signal, you have bandwidth expansion&quot;.  But look at the figure in this question: Relation between Bandwidth and Baud-Rate for 8-PSK - it looks like there is much less bandwidth required for the RRC filtered signal than the square wave / sinc.  So why does the first question have an answer that says that increased bandwidth is necessary and, taking it a step further, why does sps increase, as was the actual question there?
I wouldn't really call it &quot;bandwidth expansion&quot;. If you do 2 samples per symbol, from a purely theoretical point of view (i.e. using perfect infinitely long sinc pulses), you could do with exactly half of the Nyquist bandwidth of the output signal.
However, RRC is not infinitely long sincs, so you get excess bandwidth.