What does direct-to-satellite NTN testing involve?
There are two routes: proprietary satellite links, and 3GPP NTN, where Release 17 defined transparent payload operation and brings the satellite into the 5G network as a bent-pipe relay. NTN introduces three physical-layer challenges. Delay is long — tens to hundreds of milliseconds — and is handled with timing-advance segmentation and SIB19 ephemeris broadcast. Doppler is large: a 600 km LEO satellite at roughly 7 km/s produces up to about 24 ppm, which is around ±48 kHz at 2 GHz, and it changes fast. Path loss is far greater than terrestrial cellular. Lab simulation reproduces these three effects through a channel emulator rather than a real satellite.
Key points
- Release 17 defined transparent NTN operation as a bent-pipe relay
- Propagation delay of tens to hundreds of milliseconds needs timing-advance handling
- Doppler reaches about 24 ppm, roughly ±48 kHz at 2 GHz, and varies quickly
- Path loss far exceeds terrestrial cellular
- Lab testing uses a channel emulator to reproduce all three effects
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