Upsampling QPSK Symbols

rrc design is pretty standard.

number of coeffs is based on your upsampling rate chosen, passband ripple and stopband attenuation required.

for example:

To design root raised cosine filter with 70 taps, set F[SUB]C[/SUB] to 0.25 with respect to F[SUB]S[/SUB] of 1 and assume rolloff of 0.18

h = firrcos(69, 0.25, 0.18, 1, ‘rolloff’, ‘sqrt’);

The chosen Fc implies that upsampling by 2 is to be applied. Fc is cutoff, Fs is sampling rate (normalised)

You can use fir compiler and is best choice as it can do upsampling as well. (though it does not support LUT approach and will use few mults)

edit: transition band is also significant and is controlled by alpha for a given number of taps.