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add section with NTN example to doc/RUNMODEM.md

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Thomas Schlichter
2024-05-07 19:17:08 +02:00
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doc/RUNMODEM.md
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@@ -138,6 +138,53 @@ You can see all options by typing
./nr-uesoftmodem --help
```
## How to run a NTN configuration
### NTN channel
A 5G NR NTN configuration only works in a non-terrestrial setup.
Therefore either SDR boards and a dedicated NTN channel emulator are required, or RFsimulator has to be configured to simulate a NTN channel.
As shown on the [rfsimulator page](../radio/rfsimulator/README.md), RFsimulator provides different possibilities.
E.g. to perform a simple simulation of a satellite in geostationary orbit (GEO), these parameters should be added to both gNB and UE command lines:
```
--rfsimulator.prop_delay 238.74
```
### gNB
The main parameter to cope with the large NTN propagation delay is the cellSpecificKoffset.
This parameter is the scheduling offset used for the timing relationships that are modified for NTN (see TS 38.213).
The unit of the field Koffset is number of slots for a given subcarrier spacing of 15 kHz.
This parameter can be provided to the gNB in the conf file as `cellSpecificKoffset_r17` in the section `servingCellConfigCommon`.
```
...
cellSpecificKoffset_r17 = 478;
...
```
Besides this, some timers, e.g. `sr_ProhibitTimer_v1700`, `t300`, `t301` and `t319`, in the conf file section `gNBs.[0].TIMERS` might need to be extended.
```
...
TIMERS :
{
sr_ProhibitTimer = 0;
sr_TransMax = 64;
sr_ProhibitTimer_v1700 = 512;
t300 = 2000;
t301 = 2000;
t319 = 2000;
};
...
```
So with these modifications to the file `targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band66.fr1.25PRB.usrpx300.conf` an example gNB command for FDD, 5 MHz BW, 15 kHz SCS, GEO satellite 5G NR NTN is this:
```
cd cmake_targets
sudo ./ran_build/build/nr-softmodem -O ../targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band66.fr1.25PRB.usrpx300.conf --sa --rfsim --rfsimulator.prop_delay 238.74
```
# Specific OAI modes
## phy-test setup with OAI UE