I have designed a RRC filter, as below :
clear all; clc;
Ts = 8.1380e-06; %sampling rate
Nos = 24; %upsampling factor
alpha = 0.5; %Rollback
t1 = [-6*Ts:Ts/Nos:-Ts/Nos];
t2 = [Ts/Nos:Ts/Nos:6*Ts];
r1 = (4*alpha/(pi*sqrt(Ts)))*(cos((1+alpha)*pi*t1/Ts)+(Ts./(4*alpha*t1)).*sin((1-alpha)*pi*t1/Ts))./(1-(4*alpha*t1/Ts).^2);
r2 = (4*alpha/(pi*sqrt(Ts)))*(cos((1+alpha)*pi*t2/Ts)+(Ts./(4*alpha*t2)).*sin((1-alpha)*pi*t2/Ts))./(1-(4*alpha*t2/Ts).^2);
r = [r1 (4*alpha/(pi*sqrt(Ts))+(1-alpha)/sqrt(Ts)) r2];
The creation of that filter is following the theoretical ways. But the problem is when I set the rollback to 0.5, the shape of filter is shown as below:
What's the problem of that non-defined values (NAN)?? however when I set the rollback into 0.9, it's ok