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The raised cosine pulse is essentially a windowed sinc function, designed with some roll-off in mind. Why do we use this particular window, as opposed to other windows such as Hann, Hamming, Kaiser, etc? All of these have zero ISI when applied to a sinc function, and have tunable frequency characteristics just like the raised cosine. Is the raised cosine optimal for digital comms in any sense?

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There is no good reason, except that it's familiar and "good enough" for many applications. Many other better pulses have been proposed; see for instance "Nyquist filters in non-ISI transmission", by Ping-Kuen Lam, E.W. McCune and M.A. Soderstrand, DOI:10.1109/MWSCAS.1997.666198.

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  • $\begingroup$ well, it does still prevent ISI sufficiently well when heavily truncated; that's a pretty good property for practical implementation in digital systems. $\endgroup$ – Marcus Müller Apr 25 '18 at 7:44
  • $\begingroup$ @MarcusMüller I believe that other pulses are equally good or better in that regard, too. I don't have a lot of experience with them, though. $\endgroup$ – MBaz Apr 25 '18 at 14:01
  • $\begingroup$ I think the "don't have much experience with anything but RRC" definitively applies to me, too. This might actually be an important reason: noone hears about anything but RRC in their education. $\endgroup$ – Marcus Müller Apr 25 '18 at 15:45
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    $\begingroup$ That's a good point, and something that I'll change in my own graduate wireless course next year. In fact, I was inspired to research this subject by McCune's recent textbook on wireless (he's one of the co-authors of the paper I linked to). $\endgroup$ – MBaz Apr 25 '18 at 17:02

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