  While the 5th generation (5G) of mobile networks has landed in the commercial
area, the research community is exploring new functionalities for 6th
generation (6G) networks, for example non-terrestrial networks (NTNs) via
space/air nodes such as Unmanned Aerial Vehicles (UAVs), High Altitute
Platforms (HAPs) or satellites. Specifically, satellite-based communication
offers new opportunities for future wireless applications, such as providing
connectivity to remote or otherwise unconnected areas, complementing
terrestrial networks to reduce connection downtime, as well as increasing
traffic efficiency in hot spot areas. In this context, an accurate
characterization of the NTN channel is the first step towards proper protocol
design. Along these lines, this paper provides an ns-3 implementation of the
3rd Generation Partnership Project (3GPP) channel and antenna models for NTN
described in Technical Report 38.811. In particular, we extend the ns-3 code
base with new modules to implement the attenuation of the signal in air/space
due to atmospheric gases and scintillation, and new mobility and fading models
to account for the Geocentric Cartesian coordinate system of satellites.
Finally, we validate the accuracy of our ns-3 module via simulations against
3GPP calibration results
