NTN Configuration Guide: GEO and LEO Configurations

This guide outlines setting up GEO and LEO configurations for the NTN (Non-Terrestrial Network) project using OpenAirInterface (OAI). It covers gNB and UE details, configuration files, commands, and log management.

git clone https://gitlab.eurecom.fr/oai/openairinterface5g.git ~/openairinterface5g
cd ~/openairinterface5g

gnb Configuration Files

GEO Configuration:

• Path: ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn.conf

LEO Configuration:

• Path: ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn-leo.conf

gNB Configuration Details

The following changes are to be made in ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn.conf

Key Parameters

channel model : rfsimulator has to be configured to apply the channel model. This can be done by providing this line in the conf file in section rfsimulator:

options = "chanmod";

Simulation Parameters

cellSpecificKoffset_r17

 cellSpecificKoffset_r17=478;                              #GEO
 cellSpecificKoffset_r17=40;                                #LEO

HARQ

    disable_harq = 1; //    #GEO
    num_dlharq = 32;        #LEO
    num_ulharq = 32;        #LEO

GEO Simulation

Add the following to gNB and UE command lines:

--rfsimulator.prop_delay 238.74

LEO Simulation

Two models:

• SAT_LEO_TRANS: transparent satellite, gNB on ground
• SAT_LEO_REGEN: regenerative satellite, gNB on board

Example for transparent LEO:

channelmod = {
  max_chan=10;
  modellist="modellist_rfsimu_1";
  modellist_rfsimu_1 = (
    {
      model_name     = "rfsimu_channel_enB0"
      type           = "SAT_LEO_TRANS";
      noise_power_dB = -100;
    },
    {
      model_name     = "rfsimu_channel_ue0"
      type           = "SAT_LEO_TRANS";
      noise_power_dB = -100;
    }
  );
};

Add to conf file for leo under rfsimulator:

options = ("chanmod");

To simulate a LEO satellite channel model with rfsimulator in UL (DL is simulated at the UE side), either the channelmod section as shown before has to be added to the gNB conf file, or a channelmod conf file has to be included like this:

@include "channelmod_rfsimu_LEO_satellite.conf"

Commands

After configuring the necessary configuration files, you can run the following commands:

GEO GNB :

cd cmake_targets
sudo ./ran_build/build/nr-softmodem -O ../ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn.conf --rfsim --rfsimulator.prop_delay 238.74> gnb_geo.log 2>&1

> gnb_geo.log 2>&1 is used to include options to redirect both standard output and errors to log

GEO UE

cd cmake_targets
sudo ./ran_build/build/nr-uesoftmodem -O ../targets/PROJECTS/GENERIC-NR-5GC/CONF/ue.conf --band 254 -C 2488400000 --CO -873500000 -r 25 --numerology 0 --ssb 60 --rfsim --rfsimulator.prop_delay 238.74> ue_geo.log 2>&1

LEO GNB :

cd cmake_targets
sudo ./ran_build/build/nr-softmodem -O ../ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn-leo.conf --rfsim > gnb_leo.log 2>&1

LEO UE :

cd cmake_targets
sudo ./ran_build/build/nr-uesoftmodem -O ../targets/PROJECTS/GENERIC-NR-5GC/CONF/ue.conf --band 254 -C 2488400000 --CO -873500000 -r 25 --numerology 0 --ssb 60 --rfsim --rfsimulator.prop_delay 20 --rfsimulator.options chanmod --time-sync-I 0.1 --ntn-initial-time-drift -46 --autonomous-ta> ue_leo.log 2>&1