Day objective — orbital & link geometry from first principles, plus transparent vs. regenerative payloads and 5GC integration paths.
Satellite Communication Basics for Telecom Engineers
The geometry and physics that govern every satellite link — built from scratch for engineers with no prior space background.
- Orbits — LEO, MEO, GEO (and HEO): altitude, period and visibility time
- Slant range & minimum elevation angle — why geometry, not just altitude, drives the link
- Propagation delay & round-trip time per orbit
- Doppler shift and rate of change; feeder-link vs. service-link Doppler
- Footprint — satellite footprint, spot beams & beam coverage
Orbit Comparison at a Glance
Representative orders of magnitude for planning intuition — exact figures depend on constellation geometry and elevation angle.
- Animated to-scale orbits — LEO/MEO/GEO orbiting at true relative speeds; click for each orbit's figures
- LEO vs MEO vs GEO — altitude, period, delay, Doppler, coverage, handover compared
- The orbit trade-off — delay vs coverage vs Doppler vs constellation size
| Parameter | LEO | MEO | GEO |
|---|---|---|---|
| Typical altitude | 300–1500 km | ~8 000–20 000 km | 35 786 km |
| One-way delay (service) | ~1–7 ms | ~30–70 ms | ~120–140 ms |
| RTT order (UE–gNB) | Tens of ms | ~100 ms+ | ~240–280 ms+ |
| Doppler | Very high, fast | Moderate | Low (near-static) |
| Coverage / sat | Small, moving | Large | Very large, fixed |
| Handover | High (mins) | Lower | Rare (beam only) |
| Best-fit service | Low-latency broadband, D2D | Broadband, regional | Broadcast, VSAT, IoT |
NTN Payload Architectures
The two payload families that define everything downstream — and why Rel-19 chose a full onboard gNB.
- Transparent payload — satellite is an RF bend-pipe / repeater; gNB stays on the ground (Rel-17/18 baseline)
- Regenerative payload — complete gNB onboard (Rel-19) → ISL, onboard processing, store-and-forward
- Why full-gNB over gNB-DU split — independence from a continuously-live feeder link + alignment with the 6G RAN direction
- Store-and-Forward (Rel-19) — service without a simultaneous feeder link, for delay-tolerant IoT over mid-ocean / remote areas
- Inter-satellite links (ISL) and the role of the NTN gateway / ground segment
NTN Reference Scenarios & 5GC Integration
The 3GPP reference scenarios used for planning, the cell models, the UE families, and how each payload attaches to the core.
- Reference scenarios (TR 38.821) — GEO & LEO, each transparent & regenerative
- Earth-fixed vs. earth-moving cells / beams and what each means for mobility
- UE types — handheld, IoT / NB-IoT, RedCap, and fixed / very-small-aperture terminals
- 5GC attach — transparent: standard N2/N3 from ground gNB; regenerative: onboard gNB with feeder-link transport
- Frequency context — FR1 / S-band (Rel-17), FR2 Ku/Ka (Rel-18/19) and MSS spectrum
Hands-on Lab 2 — Satellite Link Modelling in Python
Quantify the geometry from 2.1 in code — the delay and Doppler curves you produce here feed directly into the Day-5 link budget.
Satellite Link Modelling in Python
⚡- 1Model LEO / MEO / GEO links: compute slant range vs. elevation angle
- 2Calculate one-way delay & RTT per orbit; plot delay vs. elevation
- 3Compute & plot Doppler shift and Doppler rate for a LEO pass
- 4Visualize satellite pass / visibility-window duration from a ground site
Day 2 Assessment
Orbital geometry, TR 38.821 reference scenarios, transparent vs regenerative payloads, feeder/service links and beam layout. 40 spec-cited questions with verbatim TR 38.821 figures.