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QPSK baseband shaping ....

Started by Kappa July 5, 2008
I have built a QPSK modulator, but I have some doubts about the Baseband 
Shaping Filter. The Baseband Filter is a "SRRC Digital Filter" with cutoff 
at Nyquist / 2 with selectable roll-off. In my project roll-off is 0.35.

Example (SAT):

27500 Msymb/s ---> Nyquist Frequency is 55000 Mhz (for I and Q) ---> cutoff 
Frequency 27500 Mhz.

May need to interpolate at least 2 ? Is right ? It is necessary to 
interpolate in all ways ?

How many taps used for filtering ?

What window of approximation it up for the calculation of taps filter ?

Thanks in advance.

Kappa.



>I have built a QPSK modulator, but I have some doubts about the Baseband >Shaping Filter. The Baseband Filter is a "SRRC Digital Filter" with
cutoff
>at Nyquist / 2 with selectable roll-off. In my project roll-off is 0.35. > >Example (SAT): > >27500 Msymb/s ---> Nyquist Frequency is 55000 Mhz (for I and Q) --->
cutoff
>Frequency 27500 Mhz. > >May need to interpolate at least 2 ? Is right ? It is necessary to >interpolate in all ways ? > >How many taps used for filtering ? > >What window of approximation it up for the calculation of taps filter ? > >Thanks in advance. > >Kappa. > > > >
%%%%% In ur case fs=55000 and B=27500 so u need to insert fs/B-1 zeros between symbols, which means 1 zeros between symbols. in ur case the taps should be 2 but ideally the data should be oversampled i.e. fs=N*B where N could be any interger greater than 2, i am using 12. there are plenty of shaping filter formulas availble in standard books...