A non-terrestrial network puts a satellite in the radio path, but the 5G core stays on the ground — and the NTN gateway is what bridges the two. Here is how the service link, the feeder link, the gateway and the payload fit together, and why the terrestrial waveform needs GNSS to survive the hop.
A non-terrestrial network puts part of the radio path through a satellite, but the 5G core still lives on the ground. Two radio links join them. The service link is the one the device sees — the NR air interface between the handset or terminal and the satellite. The feeder link runs from the satellite down to an NTN gateway, a ground station that hands the traffic into the terrestrial network.
The gateway is the bridge. It is the element that terminates the feeder link and connects the satellite segment to the terrestrial gNB and 5G core. Without it there is no path from the satellite back to the network — which is why, when people ask what joins terrestrial and non-terrestrial 5G, the honest answer is the gateway and the feeder link that reaches it.
A single gateway serves whatever satellites are in view of it. In a low-orbit constellation a satellite that loses sight of its gateway either hands traffic to another satellite over an inter-satellite link or waits for the next gateway to rise — which is why gateway placement and constellation geometry are part of the same design.
The satellite can play one of two roles. A transparent (bent-pipe) payload is a repeater: it shifts frequency, amplifies and forwards, and the gNB stays on the ground behind the gateway. Simpler satellite, all the intelligence on the ground, easy to upgrade — at the cost of carrying the full round trip up and down for every function.
A regenerative payload puts the gNB, or part of it, on the satellite itself. It demodulates and processes on board, which shortens some control loops and enables inter-satellite routing, but it means flying and powering real baseband and committing to it for the life of the spacecraft.
Most early 5G NTN deployments are transparent, because keeping the gNB on the ground lets the network evolve at terrestrial pace. Regenerative payloads matter where the constellation needs to route traffic in space rather than dropping to a gateway for every hop.
5G's air interface was designed for distances of a few kilometres. A satellite is hundreds to tens of thousands of kilometres away, so three things have to be managed before the same waveform works at all.
Delay. A GEO round trip is around a quarter of a second; even LEO is tens of milliseconds. HARQ timing, scheduling timers and the random-access procedure all assume far less, so NTN extends those timers and relaxes HARQ so the protocol does not time out waiting for an acknowledgement that is still in flight.
Timing advance and Doppler. The path length is huge and, for a moving satellite, changing every second. The UE uses GNSS to know its own position and the satellite's ephemeris, computes a large timing advance so its uplink still lands in the right slot, and pre-compensates the Doppler shift from the satellite's velocity. This is why an NTN device effectively must have GNSS — it is not for the user, it is for the radio.
Orbit is the first decision. GEO gives one satellite that covers a third of the planet and never moves in the sky, at the price of a quarter-second round trip. LEO gives low latency and a stronger link, but each satellite races overhead in minutes, so the network hands the device between satellites — and often between beams within a satellite — continuously. Beams can be Earth-fixed (steered to hold a ground cell while the satellite passes) or Earth-moving (sweeping across the ground), and the mobility machinery differs for each.
Two profiles share the architecture. NR-NTN carries the 5G NR air interface for broadband and smartphone direct-to-device. IoT-NTN carries NB-IoT and eMTC for low-rate, low-power sensors and asset trackers, where a short burst a few times a day over a satellite is exactly the point. Both ride the same service-link / feeder-link / gateway structure; they differ in the waveform and the power and latency budget.
For a device maker the practical consequences are concrete: a GNSS receiver is effectively mandatory, the modem has to support the NTN timing extensions, and the antenna and link budget have to close against a satellite rather than a tower a kilometre away.
The NTN gateway, and the feeder link that reaches it. The gateway is a ground station that terminates the satellite's feeder link and connects the satellite segment to the terrestrial gNB and 5G core. The device reaches the satellite over the service link; the gateway carries it the rest of the way to the ground network.
The service link is the air interface between the device and the satellite — the link the UE sees. The feeder link is between the satellite and the ground gateway. Together they form the full path from device to core.
A transparent (bent-pipe) payload is a repeater that amplifies and forwards, keeping the gNB on the ground behind the gateway. A regenerative payload processes on board, placing the gNB or part of it on the satellite, which shortens some loops and enables inter-satellite routing at the cost of flying real baseband.
So the radio works, not for the user. The UE uses its GNSS position and the satellite ephemeris to compute a large timing advance for the long, changing path and to pre-compensate the Doppler shift from the satellite's motion. Without it the uplink would not land in the right slot.
It depends on orbit. A GEO round trip is roughly 240–280 ms, MEO around 90–130 ms, and LEO roughly 25–50 ms. The protocol extends its HARQ and scheduling timers so the 5G air interface tolerates these delays.
NR-NTN carries the 5G NR air interface for broadband and direct-to-device smartphone service. IoT-NTN carries NB-IoT and eMTC for low-rate, low-power sensors and trackers. Both use the same service-link, feeder-link and gateway architecture but differ in waveform, power and latency budget.
When a tracker escalates to satellite.
KNOWLEDGEWhy GNSS is never quite enough.
KNOWLEDGEAnother way into the 5G core.
KNOWLEDGEWhere satellite fits the options.
KNOWLEDGEThe bands the radio can use.
SOLUTIONCoverage layers together.
Timing extensions, Doppler pre-compensation, GNSS-assisted acquisition and the link budget against a satellite are where NTN designs are won. Tell us the orbit and the terminal.