linkbudget 0.6.2

A link budget toolbox for satellite communications
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71

//! Doppler shift calculations for satellite communications.

/// Doppler shift in Hz for a given transmitted frequency and radial velocity.
///
/// `radial_velocity_m_s`: positive = approaching, negative = receding.
#[doc(alias = "Doppler")]
#[must_use]
pub fn doppler_shift_hz(frequency_hz: f64, radial_velocity_m_s: f64) -> f64 {
    frequency_hz * radial_velocity_m_s / 299_792_458.0
}

/// Received frequency accounting for Doppler shift.
#[doc(alias = "Doppler")]
#[must_use]
pub fn doppler_received_frequency(frequency_hz: f64, radial_velocity_m_s: f64) -> f64 {
    frequency_hz + doppler_shift_hz(frequency_hz, radial_velocity_m_s)
}

/// Maximum radial velocity for a circular orbit at a given elevation angle.
///
/// At horizon (0° elevation), radial velocity ≈ orbital velocity.
/// At zenith (90° elevation), radial velocity ≈ 0.
#[doc(alias = "Doppler")]
#[must_use]
pub fn max_radial_velocity_circular(orbital_speed_m_s: f64, elevation_angle_degrees: f64) -> f64 {
    let elevation_rad = elevation_angle_degrees * std::f64::consts::PI / 180.0;
    orbital_speed_m_s * elevation_rad.cos()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn doppler_shift_leo_ku_band() {
        let freq = 12.0e9;
        let velocity = 7600.0;
        let shift = doppler_shift_hz(freq, velocity);
        assert!((shift - 304_210.0).abs() < 100.0);
    }

    #[test]
    fn doppler_zero_at_zenith() {
        let orbital_speed = 7600.0;
        let radial_v = max_radial_velocity_circular(orbital_speed, 90.0);
        assert!(radial_v.abs() < 1e-10);
    }

    #[test]
    fn doppler_max_at_horizon() {
        let orbital_speed = 7600.0;
        let radial_v = max_radial_velocity_circular(orbital_speed, 0.0);
        assert!((radial_v - 7600.0).abs() < 1e-10);
    }

    #[test]
    fn received_frequency_approaching() {
        let freq = 12.0e9;
        let velocity = 7600.0;
        let received = doppler_received_frequency(freq, velocity);
        assert!(received > freq);
    }

    #[test]
    fn received_frequency_receding() {
        let freq = 12.0e9;
        let velocity = -7600.0;
        let received = doppler_received_frequency(freq, velocity);
        assert!(received < freq);
    }
}