3GPP 5G NR-NTN Standard Overview

Updated 28 January 2026

3GPP 5G NR-NTN is a standard defining protocols for integrating satellite, HAP, and UAV communications into 5G networks with tailored physical and MAC layer adaptations.
It employs a dual-segment architecture supporting both transparent and regenerative payloads, effectively addressing challenges like large delays, Doppler shifts, and high link losses.
The standard has evolved from Release 17 to 20, achieving enhanced throughput, spectral efficiency, and robust connectivity for global and IoT applications.

The 3GPP 5G NR-NTN (New Radio for Non-Terrestrial Networks) standard formalizes the integration of satellite and aerial platforms into 5G networks, enabling wireless connectivity beyond terrestrial infrastructure. This standard, initiated in Release 17 and further extended in Releases 18–20, specifies the physical layer, protocol stack, architectural adaptations, and channel models necessary to support GEO, MEO, LEO satellite systems, HAP, and UAV platforms within 5G NR. NR-NTN addresses unique challenges arising from large propagation delays, rapidly varying Doppler, frequency shifts, and link budget constraints, while enabling both broadband and IoT use cases across global and remote areas (Hou et al., 25 Sep 2025, Figaro et al., 8 Jan 2026, Guidotti et al., 2022, Lin et al., 2021, Lin et al., 2019).

1. Standardization Timeline and Release Evolution

The NR-NTN standard emerged through a staged process:

Release 15: TR 38.811 initiated use case and channel model studies for NTNs, focusing on free-space path loss, Doppler, and initial architecture concepts.
Release 16: TR 38.821 specified further protocol and PHY adaptations: timing advance (TA) extensions, HARQ and MAC timers for long delays, mobility tracking, and frame alignment in GEO/LEO/MEO scenarios (Guidotti et al., 2022).
Release 17: Full specification for transparent (bent-pipe) payload integration, supporting power class 3 UEs (≤23 dBm), FDD in selected FR1 bands (n255, n256, n257), mandatory GNSS for TA and Doppler pre-compensation, extended random access (PRACH), and channel models for LEO/MEO/GEO.
Release 18–20: Progressive enhancements, such as support for regenerative payloads (on-board gNB), FR2 bands, GNSS-resilient operation, multi-orbit and multi-connectivity, IoT optimizations (e.g. RedCap, NB-IoT enhancements), RACH-free handover, and asynchronous HARQ. Further features include dynamic resource scheduling, edge/AI integration, support for inter-satellite links, and network slicing (Figaro et al., 8 Jan 2026, Guidotti et al., 2022).

Table: Selected NR-NTN 3GPP Work Items and Completion Milestones

Item	Group	Description	Completion
TR 38.811 (SI R15)	RAN	Scenarios, channel models, Doppler	Sep 2020
TR 38.821 (SI R16)	RAN	Protocol/PHY layer solutions for NTN	May 2021
NR_NTN (WI R17)	RAN2	Transparent-payload NTN enhancements	Dec 2021
NR_NTN-enh (WI R18)	RAN2	Regenerative payload, mobility, CA, etc.	Dec 2023

For exhaustive list, see (Guidotti et al., 2022).

2. System Architecture and Air Interface

NR-NTN introduces a dual-segment architecture comprising a space/airborne platform (satellite/HAP/UAV) and a ground segment (gateway, 5G Core integration). It supports both:

Transparent Payloads: Satellites function as bent-pipe relays; all protocol processing carried out in ground-based gNB-CU/DU co-located with the gateway.
Regenerative Payloads: (Release 19+) Satellite hosts a full/partial on-board gNB, enabling inter-satellite links, flexible scheduling, and improved resilience (Figaro et al., 8 Jan 2026, Rossato et al., 21 Jan 2026).

Orbit, payload, and link type dictate system behavior:

Orbit	Altitude	Delay (1-way)	Doppler	Key Use Cases
LEO	400–2000 km	2–10 ms	up to 50 kHz	Direct-to-device, IoT
MEO	2–10×10³ km	20–70 ms	moderate	Regional coverage
GEO	35,786 km	≈120–150 ms	0.1–6 kHz	Backhaul, broadcast

The reference air interface is FDD (Release 17+) with NR numerologies tailored to orbit/delay characteristics (Hou et al., 25 Sep 2025).

3. Physical and MAC Layer Adaptations

Frame Structure and Numerologies

NR-NTN PHY maintains 10 ms radio frames, ten 1 ms subframes, 14 OFDM symbols/subframe for μ=0 (Δf=15 kHz), extended to μ=2/3 (60/120 kHz) for Ka-band.
Extended CP: necessary for large delay spreads or differential timing due to large cell radii, especially for PRACH (Hou et al., 25 Sep 2025, Lin et al., 2019).

Link Budget and Channel Model

Free-space path loss, with added rain/gaseous attenuation and scintillation for high-frequency and low-elevation links (Sandri et al., 2023).
Example FSPL formula (distance d in km, frequency f in MHz): $FSPL_\mathrm{dB} = 20\log_{10}(d) + 20\log_{10}(f) + 32.45$ .
The link budget for GEO scenarios features >200 dB path loss, with EIRP ≈54 dBW, receiver antenna gains 39–43 dBi, and noise figures 1–5 dB, yielding SNR ≈10–15 dB for typical testbeds (Hou et al., 25 Sep 2025, Sormunen et al., 19 Feb 2025).

Doppler and Timing Advance

Instantaneous Doppler: $f_D = (v/c) f_c$
GNSS-based pre-compensation and explicit signaling of Doppler/TA parameters (SIB19, TS 38.213/214).
Extended TA includes per-satellite corrections for feeder and service link delays: $T_{TA} = (N_{TA} + N_{TA,\,offset} + N_{TA,\,adj}^{common} + N_{TA,\,adj}^{UE})\,T_c$ (Hou et al., 25 Sep 2025, Lin et al., 2021).
Doppler estimation without GNSS uses joint multi-frequency reference signals (non-CD SSBs), allowing separation and correction of local oscillator offsets and true Doppler, reducing reliance on GNSS (Lin et al., 2021).

HARQ, MAC, and RLC Protocol

Large RTTs prohibit standard HARQ: the number of concurrent processes is scaled (N_HARQ=32–64), with option to disable HARQ entirely in GEO/very high delay, offloading retransmissions to RLC (Rossato et al., 21 Jan 2026, Hou et al., 25 Sep 2025).
Scheduling grants are dimensioned for bandwidth-delay product (BDP), with grant and buffer sizing adapted to high latency (Rossato et al., 21 Jan 2026).

4. Channel and Antenna Models

3GPP TR 38.811 channel model adopted in simulators (e.g., ns-3-NTN): models FSPL, scenario- and elevation-dependent shadow fading, atmospheric attenuation, ionospheric/tropospheric scintillation, and fast fading (Sandri et al., 2023).
ECEF geocentric coordinate modeling ensures physically accurate mobility, Doppler, and elevation calculations.
Circular-aperture antenna models (mainly for satellites and VSATs) employ an exact Bessel function form for far-field gain patterns; UPA models for HAP/UAV or IoT ground terminals.
Calibration against tables from TR 38.821 ensures modeled SNR/CNR, path loss, and fading closely mirror standardized values, with deviations ≤0.5 dB (Sandri et al., 2023, Figaro et al., 8 Jan 2026).

5. Performance Benchmarks and Comparative Analyses

SDR-based prototyping and ns-3-based simulations rigorously validate the standard’s feasibility for GEO/LEO links:

Experimental (AsiaSat 9, GEO) NR-NTN platform (Amarisoft stack) achieves ≈12 dB downlink SNR, 5.3 Mbps throughput (1 bit/s/Hz), and RTTs ≈1 s (σ ≈320 ms); spectral efficiencies ≈1 bit/s/Hz observed in narrowband operation, with BLER under 1% (Hou et al., 25 Sep 2025).
System-level (ns-3) simulations for LEO and GEO at S- and Ka-bands: LEO-Ka throughput up to ≈303 Mbps, GEO-Ka up to ≈435 Mbps; one-way delays 2–150 ms (LEO), 120–900 ms (GEO, congestion dependent) (Figaro et al., 8 Jan 2026).
5G NR-NTN compared to DVB-S2X/RCS2: NR-NTN matches spectral efficiency on the uplink (PUSCH) and approaches DVB performance on the downlink (PDSCH, gap narrows with terminal diversity), with numerologies up to μ=3 (120 kHz), PTRS/DMRS for phase/doppler correction (Sormunen et al., 19 Feb 2025).

6. Simulation and Experimental Prototyping Tools

Open-source ns-3-NTN module provides end-to-end stack emulation respecting 3GPP channel, antenna, and protocol specifications, verified against standard calibration scenarios (Sandri et al., 2023, Rossato et al., 21 Jan 2026).
SDR-based platforms allow full-stack evaluation, validating symbol alignment, timing advance, and compensation mechanisms with real satellite links (Hou et al., 25 Sep 2025).
Link-to-system mapping uses LLS-generated SINR/BLER curves, feeding scheduled TBs in full-scale system simulations for performance characterization.
Key performance metrics include SNR, BLER, throughput, PDR, packet latency, bandwidth-delay products, spectral efficiency (b/s/Hz), and HARQ process utilization.

7. Open Challenges and Future Directions

The NR-NTN standard continues to evolve:

GNSS Independence: Robust Doppler/TA estimation methods without GNSS are a critical area (Rel. 20).
Multi-orbit & Multi-beam Scheduling: Handover optimization, beam management, and LEO constellation protocols remain in active development (Rossato et al., 21 Jan 2026, Figaro et al., 8 Jan 2026).
HARQ & Higher Layers: Asynchronous HARQ, ARQ fallback procedures, RLC/PDCP tuning for very high BDP and ultra-long RTT, TCP optimizations for satellite paths.
New Waveforms and Coding for 6G: Investigation of OTFS and non-orthogonal multiple access, AI-based RRM, and advanced beamforming.
Integrated TN/NTN Operation: Seamless bearer management, user-plane/control-plane split, and dynamic vertical/horizontal handover between terrestrial and non-terrestrial nodes (Guidotti et al., 2022, Figaro et al., 8 Jan 2026).
Simulation Support: Expanded FDD chain modeling, support for massive MTC and RedCap devices, realistic multi-user/geographic traffic, and adaptive numerology.

The Release 21+ and 6G horizon targets onboard regenerative payloads, orbit-agnostic resource allocation, ISL-based architectures, and intelligent/reflective surfaces to further extend the reach and efficiency of NR-NTN.

References:

(Hou et al., 25 Sep 2025, Figaro et al., 8 Jan 2026, Rossato et al., 21 Jan 2026, Sandri et al., 2023, Guidotti et al., 2022, Lin et al., 2021, Lin et al., 2021, Lin et al., 2019, Sormunen et al., 19 Feb 2025)