Limitations and assumptions

  • Antenna polarization not taken into account

  • NetSim does not model the DU, CU split in the gNB

  • No support for co-existence between NTN and TN

  • No support for RACH procedure. It is assumed to be ideal

  • Broadcast and multicast transmissions are not supported

  • UE/VSAT, satellite and gNBs are assumed to be perfectly synchronized in frequency and time

  • No support for earth moving tracking area

  • Every UE has the appropriate Doppler compensation mechanisms.

  • Every UE calculates the propagation delay variation between UE and satellite and perfectly estimates the full timing advance.

  • Telemetry, Tracking, Command and Monitoring unit (TTC) link is out of the scope of the Study Item and of the 3GPP realm

  • Feeder link switchover is not modelled since NetSim currently only models a single terrestrial gNB.

  • The satellite is always positioned directly above the main beam, which is at the center of the simulation area.

  • Earth is assumed to be flat.

  • Beam radius is much smaller than the radius of the earth.

  • Both UEs and Satellite use X, Y, Z co-ordinates with X, Y plane on earth and with Z represents the height above earth.

  • Ideal doppler compensation. UEs are assumed to have GNSS capability to pre-compensate Doppler and delay using satellite ephemeris and location.

  • HARQ is disabled

  • Handover between beams is assumed to be instantaneous without an control packet exchange

  • Perfect symbol-level timing advance

  • Perfect channel state information at transmitter and receiver

  • NTN scenarios run in RLC-UM mode without factoring in the following timers: t-Reordering timer, t-Reassemble timer, T300, T301 and T311 timers.

  • The NTN standards include a new SIB, i.e. SIB 19. This is currently not supported and the SIB/MIB implementation is per terrestrial 5G.

  • The satellite shifts the signal frequency, amplifies the signal, and transmits it. The satellite receives signals on one of it’s receive (Rx) interfaces. The antenna gain is added to the received signal. The configured power sensitivity is used to accept the signal. The signal is then amplified (this amplification is not applied to the noise) and the signal frequency is up shifted or down shifted. Then this signal is forwarded to the transmit (Tx) interface associated with the Rx interface on which the signal was received.