Direct-to-Cell und 5G NTN: Wie Satelliten das Mobilfunknetz ergänzen

In brief

Here, Direct-to-Device (D2D) means a direct radio link between a satellite and an end device. Direct-to-Cell usually describes extending mobile coverage from space. 5G NTN integrates non-terrestrial networks into 3GPP mobile technology; NR-NTN is the more precise term for the 5G radio interface. The terms can overlap because they describe the radio path, the use case and the technology involved.

A smartphone connects to a satellite without an extra dish. Is that Direct-to-Device, Direct-to-Cell or 5G NTN? Several terms may apply to the same system. Each answers a different question: which devices communicate directly, what coverage is being provided, and which radio technology carries the connection?

The three terms at a glance

Term	What it describes	Technical context
Direct-to-Device · D2D	The end device itself communicates with the satellite.	The radio standard, data rate and supported devices depend on the service.
Direct-to-Cell	A satellite service extends a mobile network's coverage directly to phones.	The provider determines the radio technology and the device capabilities required.
5G NTN / NR-NTN	Mobile technology is adapted for non-terrestrial radio links; NR-NTN uses the 5G NR radio interface.	Use requires suitable NTN capabilities in the device and access to an enabled service.

Editorial comparison based on GSMA, ESA and 3GPP publications. The industry does not consistently use Direct-to-Cell as a distinct technical category. Sources [1]–[4], [8] and [9].

Direct-to-Device: the end device communicates with the satellite

In D2D, the satellite radio link starts at the end device. That could be a smartphone, a small purpose-built IoT device or a wearable. This radio path works directly, without a separate satellite terminal providing Wi-Fi for the phone. ESA uses the term across several device classes. [9]

Beyond that direct radio link, ground stations, access networks, switching and other network services provide the connection, depending on the system. GSMA distinguishes several technical approaches to D2D, including 3GPP NTN and proprietary systems. [3]

Direct-to-Cell: mobile coverage from space

Direct-to-Cell is commonly used for services intended to fill gaps in mobile coverage for phones. Providers may use existing LTE technology or dedicated satellite extensions. The radio technology, frequencies and approval of the particular device determine whether it can use the service.

Starlink's 2024 progress report provides one example: SpaceX describes Direct to Cell using LTE devices and eNodeB modems on the satellites. This description refers to the approach presented in that 2024 report. [8]

For Germany, Telekom's March 2026 announcement specifically mentions MSS spectrum and future compatible smartphones for its planned Starlink service. Launch is scheduled for 2028. Supported devices will be determined by the approvals for that service. [11]

A direct phone service marketed as Direct-to-Cell is therefore typically also D2D. D2D covers other devices and applications too, including small sensors. A standardised NR-NTN service can also connect an end device directly. [9]

5G NTN: what the standard adds

NTN stands for Non-Terrestrial Networks. These can include high-altitude platforms as well as satellites. This article focuses on satellite connections. [3]

In Release 17, 3GPP extended two radio families for satellite use: NR-NTN, based on 5G New Radio, and IoT-NTN, based on NB-IoT and eMTC, also known as LTE-M. IoT-NTN addresses the requirements of the relevant IoT devices; NR-NTN uses the 5G NR radio interface. [2]

Later releases develop these foundations further. Available capabilities depend on the development of the devices, satellite system and network operator. [12]

Two technical approaches to direct radio access

Zwei Beispiele für Direct-to-Device: Ein geeignetes Bestands-LTE-Gerät nutzt ein für Satelliten angepasstes Netz. Ein NR-NTN-fähiges Gerät unterstützt standardisierte Satellitenfunkfunktionen. Direct-to-Cell legt den Funkstandard nicht eindeutig fest. — Both examples connect the end device directly to a satellite. They differ in radio technology and device requirements. Other D2D approaches and IoT-NTN are omitted. Depending on the architecture, radio processing may take place on the ground or on the satellite. Diagram: LTEmobile; sources [2]–[5].

Existing mobile technology: With an unchanged LTE radio interface, the satellite and network must accommodate the unusual radio environment so that a suitable existing device can use the link. This can open up a large installed device base. Adapting the network to that environment remains technically demanding. [4]

Standardised NTN capabilities: An NR-NTN device supports the satellite radio procedures designed for this purpose. The device also contributes to the necessary adjustments. Its modem must support the relevant satellite extensions. In both examples, D2D describes the direct radio path. [4]

Why satellite radio has different requirements

Longer signal paths: Transmission timing and waiting periods must accommodate the additional propagation delay.
Movement: Particularly with low-Earth-orbit satellites, distance and radio conditions change during the connection.
Doppler shift: Relative movement shifts the received frequency. The device and network must compensate sufficiently for this offset.

In the basic Release 17 NR-NTN procedure, the device's position and transmitted satellite ephemeris data help calculate uplink timing and frequency corrections. These corrections form part of the Release 17 baseline described here. [5]

The return path from the small end device must also work. Our article on radio range explains how reception indicators, antennas and the return path relate to each other. Its coverage sketches refer to terrestrial mobile networks.

Mobile spectrum or satellite spectrum?

D2D can operate in different spectrum environments. Satellite operation in mobile spectrum must be coordinated with terrestrial networks. MSS spectrum is allocated to mobile satellite services. GSMA discusses both approaches and their respective licensing and coordination requirements. [1]

Frequency choice, radio standard and device support must fit together. Each service specifies its chosen combination. Our frequency guide explains the basic terms band, channel and allocation.

Satellite backhaul: the base station stays on the ground

Oben funkt das Smartphone direkt zum Satelliten. Unten funkt es per LTE oder 5G zu einer Basisstation am Boden, deren Rückanbindung über Satellit zum Netz führt. Diese zweite Variante ist Satelliten-Backhaul und kein D2D-Zugang des Smartphones. — In D2D, the satellite radio link starts at the end device. In backhaul, it sits behind a base station or gateway. The phone can use ordinary terrestrial mobile radio. Logical paths, not to scale; other network functions are simplified. Diagram: LTEmobile; source [6].

A remote mobile site can use a satellite link for backhaul in place of fibre or microwave. The phone still communicates with the antenna on the ground and uses its normal terrestrial radio capabilities. GSMA distinguishes direct end-device connectivity from satellite backhaul for a gateway. [6]

This is another way satellites can extend mobile coverage. Reports about satellite-connected 5G should identify where the satellite link sits in the network.

How satellites complement mobile networks

Users within a satellite coverage area share the available resources. Coverage over a wide area and capacity per user therefore also depend on load. GSMA sees D2D primarily as a way to extend reach and improve resilience. Dense terrestrial networks distribute traffic across many cells, each with its own radio resources. [7]

Check the particular service for support for messaging, calls and data. Data rates and indoor reception depend on the implementation and local radio conditions.

From a radio standard to a usable mobile service

A working service also requires entitlement, device configuration and integration with network services. GSMA describes entitlement servers that configure devices and authorise them to use particular services. The satellite service must be enabled for the subscriber's plan. [10]

Device: Does this particular model support the required radio technology and frequencies?
Software and approval: Is the function enabled for this device, provider and country?
Service: Does the offer provide short messages, or also voice and data?
Plan and coverage: Can the service actually be ordered, and under what conditions does it work?

Further network functions operate behind the radio access link. Our EPC article explains registration and data forwarding using LTE as an example. The division of responsibilities in an NR-NTN network depends on its architecture.

The separate overview Satellite connectivity on phones: what actually works in Germany? covers satellite functions already available in Germany and providers' plans. This article explains the technology behind the terms.

Sources and editorial review

Researched and technically reviewed on 26 October 2026, using publications from 3GPP, GSMA and ESA, along with manufacturer and operator documentation. The original diagrams simplify logical connections rather than presenting measurements. This article is based on research rather than our own device or network testing.