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Satellite Communications and Space Satellite Link Design Informational

How do I design a link budget for a LEO satellite communication system?

A LEO satellite link budget accounts for all gains and losses between the ground station and the satellite at altitudes of 300-2000 km. Key differences from GEO: shorter path (lower free-space loss, 160-175 dB at Ku-band vs. 200+ dB for GEO), higher Doppler shift (up to ±40 kHz at Ku-band for a 550 km orbit), shorter visibility windows (5-15 minutes per pass), and frequent handovers between satellites. Link budget: EIRP (satellite or ground) - FSPL - atmospheric losses - rain fade + G/T (receiver) - required Eb/N₀ = link margin. For a Starlink-class LEO at 550 km, Ku-band (12 GHz): FSPL ≈ 168 dB. With a 36 dBi ground antenna and 30 dBW satellite EIRP: link margin ≈ 3-6 dB. Rain fade margin: 3-10 dB depending on the availability requirement and geographic location.
Category: Satellite Communications and Space
Updated: April 2026
Product Tie-In: LNBs, BUCs, Feeds, Antennas

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.

Common Questions

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).

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Glossary

Related Terms

Antenna → Noise Figure → dBm → Bandwidth → dBi → Noise Floor →
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