5G/6G Non Terrestrial Networks (NTN)

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 based LEO/MEO/GEO satellite networks
  • Evaluate satellite network performance for various parameter configurations - orbit heights, elevation angle, number of spot beams, frequency reuse factor, etc.

Standards and Architecture

  • Based on 3GPP TR 38.821 standards for single satellite simulation.
  • Supports both transparent (bent pipe).
  • Configurable orbit heights: LEO, MEO, GEO with adjustable UE elevation angles.
NetSim NTN

Specifications

    Network Components

      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

    Spot Beam Configuration

    • Single satellite with fixed-earth spot beams. In earth-fixed beams, the satellite beams are steered such that they always point to the same location on earth
    • Options for 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
    • 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.
    • Configurable inter-beam distances
    • Frequency reuse configurations supported: FR1 and FR3

    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
    • Movement of terrestrial devices
    • Shadow fading

    Supported Bands

    • FR1 bands: n254, n255, n256
    • FR2 bands: n510, n511, n512

    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

    Antenna Configuration

    • Satellite antennas use a circular aperture model with configurable aperture radius (in meters).
    • Support for Omni directional antennas (Handheld UEs)
    • Circular aperture antennas (VSATs and Satellites)
    • Antenna gains per TR 38.811 - Section 6.4.1

    Modulation and Coding

    • MCS mapping based on SINR and channel configuration

    Propagation Models

    • Free Space Path Loss (FSPL)
    • Atmospheric loss: user-defined (in dB)
    • Clutter loss based on TR 38.811
    • Shadowing: log-normal (user configurable)

    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

    Radio measurements logged every TTI

    • SINR, SNR, Rx power
    • Slant height, Elevation angle
    • EIRP density, Thermal noise
    • Angular antenna gain, UE Rx antenna gain
    • Interference power, Pathloss
    • Shadow Fading, Clutter loss, Additional loss
    • CQI, MCS
RadiomeasurementLog

Featured Examples

Impact of LEO Altitude Variation on SNR and Pathloss

  • 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_pathlos_vs_satellite_altitude Impact of Satellite Altitude on Signal-to-Noise Ratio (SNR) and Pathloss 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 Tx power on Signal-to-Noise Ratio (SNR)

Extensions

Limitations and Assumptions

  • Satellite orbital motion is not modelled, since beams are fixed earth.
  • 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.