How do I design a link budget for a LEO satellite communication system?
LEO Link Budget
LEO constellation design trades: lower orbits (300-600 km) provide lower latency (1-4 ms one-way) and lower path loss, but require more satellites for continuous coverage (1,000-4,000+ for global coverage). Higher orbits (1,000-2,000 km) require fewer satellites but have higher latency and path loss. The inter-satellite link (ISL) enables global connectivity without ground relays, using optical or Ka-band links between satellites.
| Parameter | GEO | MEO | LEO |
|---|---|---|---|
| Altitude | 35,786 km | 2,000-35,786 km | 200-2,000 km |
| Latency (one-way) | ~270 ms | 50-150 ms | 1-20 ms |
| Coverage per Sat | Full hemisphere | Regional | Local footprint |
| Handover | None | Periodic | Frequent |
| Path Loss (Ku-band) | ~206 dB | 190-206 dB | 170-190 dB |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
How much Doppler compensation is needed?
LEO Doppler shift: Δf = v_sat × f / c × cos(θ) × 2, where v_sat ≈ 7.5 km/s at 550 km. Maximum Doppler at horizon: ±38 kHz at 12 GHz, ±90 kHz at 28 GHz. The Doppler rate of change: up to 500 Hz/s. The ground terminal must track and compensate for this rapidly changing Doppler in real-time.
What about latency?
One-way LEO latency: 1-4 ms (propagation) + 2-5 ms (processing and routing) = 3-9 ms total. Round-trip: 6-18 ms. GEO: 240 ms one-way, 480 ms round-trip. LEO latency is comparable to terrestrial fiber for most applications, enabling real-time services that GEO cannot support (gaming, video calls, financial trading).