Hi Everyone,
I am making a GMSK TX thru directly modulating the delta-sigma fractional-N PLL, but no numeric gaussian filter is found.
What I found is only numeric raised-cosine filter or timed gaussian filter. :-/
Does anyone know where this filter is or know how to make it?
Thanks a lot!!
I am making a GMSK TX thru directly modulating the delta-sigma fractional-N PLL, but no numeric gaussian filter is found.
What I found is only numeric raised-cosine filter or timed gaussian filter. :-/
Does anyone know where this filter is or know how to make it?
Thanks a lot!!
You can generate coeffients for FIR filter.
Then use "FIR" component.
Here you have to consider the following issues.
 (1) Input samples per symbol(UpSample), N
 (2) Length of the filter's impulse response, which is 2*N*Group_delay+1.
 (3) BT product
 (4) Filter coefficient normalization(Generally the sum of the coefficients should equal 1.)
double ht_gmsk_lpf(double  t, bt, tsymb)
{
  double  ht, x, sigma;
  sigma = sqrt(log(2.0)) / (2 * M_PI * bt);
  x = t / (sqrt(2.0) * sigma * tsymb);
  ht = exp(-x * x) / (sqrt(2 * M_PI) * sigma * tsymb);
  return (ht);
}
# Tue Feb 21 15:28:20 2006
# LPF_GMSK_FIR
# FIR_Length=17
# BT=0.55, Delay_Nsymb=1, Up_Samples=8
# Rectangular window
# Normalized by Sum of Coefficients
3.755980849014431e-05
2.828640100738817e-04
1.627472423660382e-03
7.153803648994064e-03
2.402408879464853e-02
6.163729240501887e-02
1.208166661815747e-01
1.809242702077309e-01
2.069919650396171e-01
1.809242702077309e-01
1.208166661815747e-01
6.163729240501881e-02
2.402408879464852e-02
7.153803648994044e-03
1.627472423660377e-03
2.828640100738970e-04
3.755980849014430e-05
# Summation_of_h[i]=1, (wacc-dacc)>=2
# Summation_of_abs(h[i])=1, (wacc-dacc)>=2