Hi,
I get the source code of root_raised_cosine function in gr_firdes.cc,
but I can't understand why it writes in that way, is there any paper can
give me more details about the principle of root_raised_cosine
Thank you
this is the source code of root_raised_cosine
vector<float> gr_firdes::root_raised_cosine (double gain,
double sampling_freq,
double symbol_rate,
double alpha,
int ntaps)
{
ntaps |= 1; // ensure that ntaps is odd
double spb = sampling_freq/symbol_rate; // samples per bit/symbol
vector<float> taps(ntaps);
double scale = 0;
for(int i=0;i<ntaps;i++)
{
double x1,x2,x3,num,den;
double xindx = i - ntaps/2;
x1 = M_PI * xindx/spb;
x2 = 4 * alpha * xindx / spb;
x3 = x2*x2 - 1;
if( fabs(x3) >= 0.000001 ) // Avoid Rounding errors...
{
if( i != ntaps/2 )
num = cos((1+alpha)*x1) + sin((1-alpha)*x1)/(4*alpha*xindx/spb);
else
num = cos((1+alpha)*x1) + (1-alpha) * M_PI / (4*alpha);
den = x3 * M_PI;
}
else
{
if(alpha==1)
{
taps[i] = -1;
continue;
}
x3 = (1-alpha)*x1;
x2 = (1+alpha)*x1;
num = (sin(x2)*(1+alpha)*M_PI
- cos(x3)*((1-alpha)*M_PI*spb)/(4*alpha*xindx)
+ sin(x3)*spb*spb/(4*alpha*xindx*xindx));
den = -32 * M_PI * alpha * alpha * xindx/spb;
}
taps[i] = 4 * alpha * num / den;
scale += taps[i];
}
for(int i=0;i<ntaps;i++)
taps[i] = taps[i] * gain / scale;
return taps;
}
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