5G/6G Non Terrestrial Networks (NTN)

Last updated: April, 2026

NetSim's NTN Library features standards based simulation of non-terrestrial networks (NTN), allowing users to:

  • Model end-to-end, full-stack, packet-level simulation of 5G NTN satellite networks.
  • Evaluate satellite network performance for various parameter configurations - orbit heights, elevation angle, number of spot beams, frequency reuse factor, etc.
  • Simulate uplink and downlink transmissions with uplink and downlink link budget calculations.
  • Use file-based mobility for both satellite and UE with CSV trajectories containing time, device ID, latitude, longitude, and altitude.

Standards and Architecture

  • Standards: 3GPP TR 38.821 – NTN architecture and scenarios, 3GPP TR 38.811 – Channel model, 3GPP TS 38.321 – MAC procedures (including Configured Grant Type 1).
  • The RAN architecture follows NTN A1 mode (transparent payload) as per TR 38.821.
  • NetSim supports the Satellite Radio Interface (SRI) on the feeder link between the NTN gateway and the satellite. SRI transports the F1 protocol.
  • Configurable orbit heights: LEO, MEO, GEO with adjustable UE elevation angles.
  • The NR-Uu radio interface is used on the service link between the satellite and the UE.
  • Per TR 38.821 Table 6.1.1.1-5, feeder-link SNR impairments are treated as negligible and only propagation latency is modeled.
NetSim NTN

Specifications

    Network Components

    • Single-satellite NTN scenario with gateway, satellite, UEs, 5G core, and remote servers.

    • gNB:

      • Located outside service beams
      • Communicates via feeder link

    • Device Support:

      • Handheld devices operating in FR1
      • VSAT terminals connecting in FR1 or FR2
      • 5G core and remote servers

    Orbit Presets and Altitude Range

    • LEO: 160–2000 km (Standard presets: 600 km, 1200 km)
    • MEO: 2000–35876 km (Standard presets: 10000 km, 20000 km)
    • GEO: 35786 km (fixed)

    Spot Beam Configuration

    • Single satellite with fixed-earth spot beams. Each beam maps one-to-one with a terrestrial cell.
    • Beam layouts: 1, 7, or 19 beams.
      • 7-cell setup: Central hexagonal cell with 6 adjacent cells.
      • 19-cell setup: Two layers of surrounding cells around a central hexagonal cell.
      • Custom beam configuration: Beams can be dropped based on user requirements (not limited to predefined layouts).
    • Mapping of satellite beams to terrestrial cells is one-to-one. Each beam is one physical cell; we therefore refer to cells and spotbeams interchangeably.
    • Frequency Reuse Factor (FRF) options: FRF 1, FRF 2, FRF 3, and FRF 4.
    • Inter-site distance is derived from beam diameter for hexagonal tessellation.

    Scenario Setup Modes

    • Standard Setup: predefined scenario parameters per 3GPP standards
    • Custom Excel/CSV: user-supplied beam configuration file
    • Manual Placement: user manually places devices and beams

    Link Specifications

      Feeder Link

      • Single beam with full bandwidth
      • Connects gateway and satellite

      Service Link

      • Multiple spot beams covering service area
      • Bandwidth dependent on frequency reuse factor

    Link Budget Calculations

    • Link budget calculations following TR 38.821 Section 6.1.3.1
    • Satellite antenna pattern modeling with circular aperture reflector antenna
    • Interference modeling with user-configurable CIR
    • Link budget variations can be simulated by configuring parameters such as:
      • Satellite altitude
      • Environment (rural, urban)
      • LOS probability
      • Antenna parameters
      • EIRP
      • Elevation angle
      • Interference
    • Shadow fading

    Uplink Scheduling

    • NetSim supports uplink scheduling with Configured Grant Type 1 for NTN scenarios. This enables periodic uplink transmissions without requiring a dynamic scheduling grant for every transmission, which helps reduce control overhead and improve uplink efficiency.

    Supported Bands

    • 3GPP Release 17 NTN bands (FR1): n254, n255, n256
    • 3GPP Release 18 NTN bands (FR2): n510, n511, n512
    Band UL (MHz) DL (MHz) Duplex
    n256 1980–2010 2170–2200 FDD
    n255 1626.5–1660.5 1525–1559 FDD
    n254 1610–1626.5 2483.5–2500 FDD
    n512 27500–30000 17300–20200 FDD
    n511 28350–30000 17300–20200 FDD
    n510 27500–28350 17300–20200 FDD

    Antenna Configuration

    • Antenna models supported:
      • 3GPP TR 38.811 model, Antenna gains per TR 38.811 - Section 6.4.1
      • ITU-R S.672 model
      • Gaussian antenna model

    Modulation and Coding

    • MCS mapping based on SINR and channel configuration

    Propagation Models

    • Free Space Path Loss (PLFS)
    • Atmospheric loss (PLA)
    • Clutter loss
    • Shadow margin (PLSM)
    • Scintillation loss (PLSL)
    • Additional losses (PLAD)

    Interference Modelling

    • CIR-Based Interference Model
    • Exact Geometric Interference Model

    Measurements and Analytics

    • Throughput, Latency, Error ... and more.
    • Overall network metrics and per beam/cell & per application performance metrics
    • Detailed Packet Trace

    Logs and Outputs

    • NTN Radio Measurement Log: Per-TTI radio metrics including Slant Height (km), Elevation Angle (deg), EIRP (dBW), Path Loss (dB), Shadow Fading Loss (dB), Additional Loss (dB), Clutter Loss (dB), Total Loss (dB), Angular Antenna Gain (dB), UE Tx/Rx Antenna Gain (dB), Rx Power (dBm), SNR (dB), SINR (dB), Thermal Noise (dBm), Interference Power (dBm), CQI Index, and MCS Index.
    • NTN UE Beam Association Log: Beam selection, tracking, and reassociation events.
    • NTN Resource Allocation Log: Per-slot resource allocation details including PRB allocation, MCS, and Transport Block Size (TBS).
RadiomeasurementLog

Featured Examples

Impact of LEO Altitude Variation on SNR and Path Loss

  • Analyze how LEO satellite altitude affects signal quality (pathloss and SNR) across two frequency bands.

    • S-band (2.185 GHz): for handheld UEs
    • Ka-band (18.75 GHz): for VSAT terminals

  • Simulation Setup

    • Altitude range (km): 300, 600, 1200, 1500, 1800, 2100
    • Environment: Rural (outdoor)
    • Pathloss model: Free space

  • UE Types

    • S-band → Handheld UE (0 dBi gain)
    • Ka-band → VSAT UE (30 dBi gain)
  • As satellite altitude increases , Pathloss increases steadily due to longer distance between satellite and UE.SNR decreases because the signal received at the UE becomes weaker.
  • Ka-band experiences higher path loss than S-band. This is due to the higher frequency of Ka-band, which naturally suffers more free-space attenuation.
  • Despite higher path loss, Ka-band shows higher SNR. This is because VSAT terminals (used in Ka-band) have high receive antenna gain (30 dBi),Whereas handheld UEs (used in S-band) have no antenna gain (0 dBi), resulting in lower SNR.
snr_pathloss_vs_satellite_altitude Impact of satellite altitude on SNR and path loss in a rural outdoor S-band scenario.

SNR Variation Across Outdoor Scenarios with Varying Transmit Power

  • To evaluate how SNR (Signal-to-Noise Ratio) varies in rural vs. dense urban environments based on Transmit Power

  • Observations

    • SNR increases with EIRP and Tx Power in both rural and dense urban environments.
    • Rural areas consistently show higher SNR due to lower clutter and environmental loss.
    • Dense urban areas have much lower SNR because of obstructions, NLOS, and higher clutter loss.
    • Even with the same power level, urban scenarios need more transmit power or beamforming to achieve the same performance as rural areas.
snr_vs_tx_power Effect of transmit power on Signal-to-Noise Ratio (SNR).

SNR and Path Loss Variation with Elevation Angle

  • Evaluate how elevation angle impacts path loss and SNR in an S-band downlink.
  • Lower elevation angle increases slant distance.
  • This leads to higher path loss and reduced SNR.
snr_pathloss_vs_elevation_angle Impact of elevation angle on Signal-to-Noise Ratio (SNR) and path loss in an S-band downlink scenario at 600 km satellite altitude.

Extensions

Assumptions and Limitations

  • Inter satellite communication is not available.
  • HARQ disabled at gNB and UE.
  • RLC UM mode only
  • O-RAN CU-DU-RU split is not modeled.
  • Terrestrial Networks - NTN coexistence and handovers not currently available
  • Perfect Doppler compensation in the devices. Doppler, however, is an active area of R&D for us. If you have specific requirements, please let us know.