void compute_raised_cosine_filter(double coeffs[],
int len,
int root,
int sinc_compensate,
double alpha,
double beta)
{
double f;
double x;
double f1;
double f2;
double tau;
complex_t vec[SEQ_LEN];
int i;
int j;
int h;
f1 = (1.0 - beta)*alpha;
f2 = (1.0 + beta)*alpha;
tau = 0.5/alpha;
/* (Root) raised cosine */
for (i = 0; i <= SEQ_LEN/2; i++)
{
f = (double) i/(double) SEQ_LEN;
if (f <= f1)
vec[i] = complex_set(1.0, 0.0);
else if (f <= f2)
vec[i] = complex_set(0.5*(1.0 + cos((3.1415926535*tau/beta)*(f - f1))), 0.0);
else
vec[i] = complex_set(0.0, 0.0);
}
if (root)
{
for (i = 0; i <= SEQ_LEN/2; i++)
vec[i].re = sqrt(vec[i].re);
}
if (sinc_compensate)
{
for (i = 1; i <= SEQ_LEN/2; i++)
{
x = 3.1415926535*(double) i/(double) SEQ_LEN;
vec[i].re *= (x/sin(x));
}
}
for (i = 0; i <= SEQ_LEN/2; i++)
vec[i].re *= tau;
for (i = 1; i < SEQ_LEN/2; i++)
vec[SEQ_LEN - i] = vec[i];
ifft(vec, SEQ_LEN);
h = (len - 1)/2;
for (i = 0; i < len; i++)
{
j = (SEQ_LEN - h + i)%SEQ_LEN;
coeffs[i] = vec[j].re/(double) SEQ_LEN;
}
}
static __inline__ complex_t expj(double theta)
{
return complex_set(cos(theta), sin(theta));
}
