Non-Terrestrial Networks:
Planning and Integration

What Are Non-Terrestrial Networks?

An NTN is any radio access network that uses an airborne or spaceborne platform as the radio node. The platforms range enormously in altitude, coverage footprint, and propagation characteristics — from LEO satellites at 550–2,000 km altitude to HAPS at 20 km to UAVs at a few hundred meters. What they share is the ability to provide coverage where terrestrial infrastructure is economically or physically impractical: remote rural areas, oceans, polar regions, and disaster zones.

The three NTN orbital regimes — LEO, MEO, and GEO — differ fundamentally in coverage area, latency, and link budget characteristics.

LEO (Low Earth Orbit) — 550 to 2,000 km

LEO satellites are the primary NTN platform for broadband internet (Starlink, OneWeb, Amazon Kuiper) and for 3GPP NTN integration. Their relatively low altitude produces lower free-space path loss (roughly 148–168 dB at 2 GHz vs 190+ dB for GEO), enabling direct-to-device connectivity with unmodified smartphones. The trade-off is that a single LEO satellite has a ground-track velocity of ~7.5 km/s, meaning it sweeps across the sky in 8–12 minutes and produces Doppler shifts up to ±48 kHz at L-band. Large constellations (hundreds to thousands of satellites) provide continuous coverage by ensuring a satellite is always above the minimum elevation angle.

MEO (Medium Earth Orbit) — 2,000 to 35,000 km

MEO satellites (GPS, Galileo, O3b mPOWER) occupy the middle ground: each satellite covers a larger footprint than LEO (reducing constellation size), while propagation delay (30–150 ms one-way) remains acceptable for interactive broadband — unlike GEO. O3b mPOWER targets maritime and enterprise connectivity with steerable spot beams that track vessels.

GEO (Geostationary Earth Orbit) — 35,786 km

GEO satellites appear stationary from the ground, which simplifies antenna pointing and eliminates Doppler shift. But their 35,786 km altitude produces ~270 ms one-way propagation delay — incompatible with real-time voice and gaming without TCP protocol adaptation. GEO remains dominant for broadcast (DVB-S2) and for backhaul links where latency is tolerable.

3GPP NTN Standards: Rel-17 and Beyond

3GPP Release 17 (frozen March 2022) introduced the first complete NTN specification set into 5G NR. The key changes relative to terrestrial 5G:

Technical Challenges in NTN

Propagation Delay

One-way propagation delay for LEO (at 600 km altitude, 30° elevation) is approximately 4 ms — comparable to a distant terrestrial cell. GEO one-way delay is 238–270 ms depending on elevation angle. For applications that use TCP, GEO delay without protocol optimization (TCP SACK, large window scaling) results in severe throughput degradation due to the slow-start and congestion-avoidance algorithms assuming low RTT.

Doppler Shift and Frequency Uncertainty

A LEO satellite moving at 7.5 km/s produces a Doppler shift of up to f_d = f_c × v/c — at 2 GHz, this is approximately ±50 kHz. For a 15 kHz subcarrier spacing (5G NR), this Doppler exceeds one full subcarrier width and would cause severe inter-carrier interference without correction. Pre-compensation based on satellite ephemeris data reduces residual Doppler to within ±200 Hz — manageable by the UE's standard AFC (Automatic Frequency Control).

Link Budget Constraints

Satellite link budgets are fundamentally constrained by the UE's antenna gain and transmit power. A smartphone has 0 dBi antenna gain and 23 dBm maximum transmit power. Closing a link from a smartphone to a LEO satellite at 600 km altitude requires a satellite receiver with G/T (Gain-to-Temperature ratio) above +25 dB/K — demanding large phased-array antennas on the satellite. This is why direct-to-device satellite (D2D) at broadband speeds required a new generation of large LEO satellites.

NTN Link Budget Analysis

NTN link budget analysis follows the same fundamental structure as terrestrial link budgets — transmit EIRP minus path loss minus implementation losses must exceed the receiver sensitivity plus a link margin — but the magnitudes are very different. Free-space path loss at 600 km altitude and 2 GHz is approximately 161 dB. Atmospheric absorption, rain fade, and ionospheric scintillation add a further 1–5 dB depending on elevation angle and weather.

A 5G NR downlink link budget for a LEO satellite at 600 km altitude. Achievable link margin determines the maximum supported MCS.

The satellite EIRP — determined by transmit power and antenna gain — is the primary design variable. Phased-array antennas on modern LEO satellites achieve 40–55 dBW EIRP per beam, enabling multiple simultaneous spot beams that reuse frequency across the coverage footprint. Frequency reuse planning for NTN constellations follows the same co-channel interference principles as terrestrial cellular, but with the added complexity that beam footprints move continuously across the ground.

NTN Use Cases

Hybrid NTN-Terrestrial Planning

The most effective coverage architectures combine terrestrial macro/small cells for high-capacity urban areas with NTN for coverage-only rural, maritime, and in-flight use. Planning a hybrid network requires simultaneous optimization of: the terrestrial layer's geographic extent (where to stop deploying macros), the NTN layer's coverage mask (minimum elevation angle, beam footprint), and the handover boundary between the two layers.

Geospatial tools are essential for hybrid planning because the decision boundary is fundamentally geographic: population density, terrain, road network connectivity, and regulatory spectrum assignments all vary by location. Overlaying NTN beam footprints (which depend on satellite orbital position and antenna steering angle) against terrestrial coverage predictions on a unified map is the only practical way to identify the optimal handover zones.

How NEXT GIS Supports NTN Planning

NEXT GIS provides the geospatial foundation for hybrid NTN-terrestrial planning. Operators import satellite beam footprint polygons (derived from ephemeris data and antenna model) as map layers, then overlay them against Cell Planner terrestrial coverage predictions to identify geographic gaps and handover zones. Link budget analysis for NTN links is supported through the Cell Planner's configurable propagation model parameters, which accommodate the free-space + atmospheric loss model appropriate for space-to-ground links.