Function msk_psd 

pub fn msk_psd(ft: f64) -> f64

The power spectral density of MSK at the normalised frequency ft $= f T$, with $T = 1$ and a unit power (Proakis & Salehi, §3.4-3):

$$ S(f) = \frac{16 T}{\pi^{2}} \left[\frac{\cos 2 \pi f T}{1 - 16 f^{2} T^{2}}\right]^{2}, $$

finite at $f T = \pm 1/4$ (where it equals $T$), zero at $f T = \pm 3/4, \pm 5/4, \dots$

Examples

use comnum_waveform::cpm::msk_psd;
assert!((msk_psd(0.0) - 16.0 / std::f64::consts::PI.powi(2)).abs() < 1e-12);
assert!((msk_psd(0.25) - 1.0).abs() < 1e-6);
assert!(msk_psd(0.75).abs() < 1e-12);