Robert Schmidt
2db282c7d3
Split out to make a standalone NTN configuratio page that would be easier to find. I only modify the headings in the new file and write an introductory sentence of the tutorial, the rest is unchanged.
205 lines
9.8 KiB
Markdown
205 lines
9.8 KiB
Markdown
<!-- SPDX-License-Identifier: CC-BY-4.0 -->
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# How to run a NTN configuration
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This tutorial explains how to run non-terrestrial network (NTN) setup for both
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low-earth orbit (LEO) and geostationary orbit (GEO) scenarios.
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It assumes you have a working terrestrial network (TN) setup, include core
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network.
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[[_TOC_]]
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## NTN channel
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A 5G NR NTN configuration only works in a non-terrestrial setup.
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Therefore either SDR boards and a dedicated NTN channel emulator are required, or RFsimulator has to be configured to simulate a NTN channel.
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As shown on the [rfsimulator page](../radio/rfsimulator/README.md), RFsimulator provides different possibilities.
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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:
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```
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--rfsimulator.[0].prop_delay 238.74
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```
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For simulation of a satellite in low earth orbit (LEO), two channel models have been added to rfsimulator:
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- `SAT_LEO_TRANS`: transparent LEO satellite with gNB on ground
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- `SAT_LEO_REGEN`: regenerative LEO satellite with gNB on board
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Both channel models simulate the delay and Doppler for a circular orbit at 600 km height according to the Matlab function [dopplerShiftCircularOrbit](https://de.mathworks.com/help/satcom/ref/dopplershiftcircularorbit.html).
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An example configuration to simulate a transparent LEO satellite with rfsimulator would be:
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```
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channelmod = {
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max_chan=10;
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modellist="modellist_rfsimu_1";
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modellist_rfsimu_1 = (
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{
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model_name = "rfsimu_channel_enB0"
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type = "SAT_LEO_TRANS";
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noise_power_dB = -100;
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},
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{
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model_name = "rfsimu_channel_ue0"
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type = "SAT_LEO_TRANS";
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noise_power_dB = -100;
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}
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);
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};
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```
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This configuration is also provided in the file `targets/PROJECTS/GENERIC-NR-5GC/CONF/channelmod_rfsimu_LEO_satellite.conf`.
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Additionally, rfsimulator has to be configured to apply the channel model.
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This can be done by either providing this line in the conf file in section `rfsimulator`:
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```
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options = ("chanmod");
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```
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Or by providing this the the command line parameters:
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```
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--rfsimulator.[0].options chanmod
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```
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## gNB
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The main parameters to cope with the large NTN propagation delay are cellSpecificKoffset, ta-Common, ta-CommonDrift and the ephemeris data (satellite position and velocity vectors).
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The parameter `ntn-UlSyncValidityDuration-r17` indicates the maximum time duration from epochtime during which the UE can apply assistance information without having acquired new assistance information. i.e this enables UE to re-read SIB19 before timer with value ulSyncValidityDuration expires. The unit of the field is in seconds. Example values for GEO: 240s, MEO: 20s, LEO: 5s.
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As epochtime is not implemented yet, UE starts the timer from the TTI where SIB19 is received with ntn-UlSyncValidityDuration-r17 IE.
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The parameter `cellSpecificKoffset_r17` is the scheduling offset used for the timing relationships that are modified for NTN (see TS 38.213).
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The unit of the field Koffset is number of slots for a given subcarrier spacing of 15 kHz.
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The parameter `ta-Common-r17` is used to provide the propagation delay between the reference point (at the gNB) and the satellite.
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The granularity of ta-Common is 4.072 × 10^(-3) µs. Values are given in unit of corresponding granularity.
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The parameter `ta-CommonDrift-r17` indicates the drift rate of the common TA.
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The granularity of ta-CommonDrift is 0.2 × 10^(-3) µs/s. Values are given in unit of corresponding granularity.
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The satellite position and velocity vartors are provided using the following parameters:
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`positionX-r17`, `positionY-r17`, `positionZ-r17`:
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X, Y, Z coordinate of satellite position state vector in ECEF. Unit is meter.
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Step of 1.3 m. Actual value = field value * 1.3.
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`velocityVX-r17`, `velocityVY-r17`, `velocityVZ-r17`:
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X, Y, Z coordinate of satellite velocity state vector in ECEF. Unit is meter/second.
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Step of 0.06 m/s. Actual value = field value * 0.06.
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These parameters can be provided to the gNB in the conf file in the section `servingCellConfigCommon`:
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```
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...
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# GEO satellite
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cellSpecificKoffset_r17 = 478;
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ta-Common-r17 = 58629666; # 238.74 ms
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positionX-r17 = 0;
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positionY-r17 = 0;
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positionZ-r17 = 32433846;
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velocityVX-r17 = 0;
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velocityVY-r17 = 0;
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velocityVZ-r17 = 0;
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# LEO satellite
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# cellSpecificKoffset_r17 = 40;
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# ta-Common-r17 = 4634000; # 18.87 ms
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# ta-CommonDrift-r17 = -230000; # -46 µs/s
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# positionX-r17 = 0;
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# positionY-r17 = -2166908; # -2816980.4 m
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# positionZ-r17 = 4910784; # 6384019.2 m
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# velocityVX-r17 = 0;
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# velocityVY-r17 = 115246; # 6914.76 m/s
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# velocityVZ-r17 = 50853; # 3051.18 m/s
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...
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```
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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 for GEO satellites.
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```
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...
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TIMERS :
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{
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sr_ProhibitTimer = 0;
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sr_TransMax = 64;
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sr_ProhibitTimer_v1700 = 512;
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t300 = 2000;
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t301 = 2000;
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t319 = 2000;
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};
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...
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```
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To improve the achievable UL and DL throughput in conditions with large RTT (esp. GEO satellites), there is a feature defined in REL17 to disable HARQ feedback.
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This allows to reuse HARQ processes immediately, but it breaks compatibility with UEs not supporting this REL17 feature.
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To enable this feature, the `disable_harq` flag has to be added to the gNB conf file in the section `gNBs.[0]`
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```
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...
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min_rxtxtime = 6;
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disable_harq = 1; // <--
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servingCellConfigCommon = (
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{
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...
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```
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The settings for a transparent GEO satellite scenario are already provided in the file `ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn.conf`.
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Using this conf file, an example gNB command for FDD, 5 MHz BW, 15 kHz SCS, transparent GEO satellite 5G NR NTN is this:
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```
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cd cmake_targets
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sudo ./ran_build/build/nr-softmodem -O ../ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn.conf --rfsim
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```
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To configure NTN gNB with 32 HARQ processes in downlink and uplink, add these settings in conf files under section `gNBs.[0]`
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```
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...
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num_dlharq = 32;
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num_ulharq = 32;
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...
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```
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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:
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```
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@include "channelmod_rfsimu_LEO_satellite.conf"
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```
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The settings for a transparent LEO satellite scenario are already provided in the file `ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn-leo.conf`.
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Using this conf file, an example gNB command for FDD, 5 MHz BW, 15 kHz SCS, trasparent LEO satellite 5G NR NTN is this:
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```
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cd cmake_targets
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sudo ./ran_build/build/nr-softmodem -O ../ci-scripts/conf_files/gnb.sa.band254.u0.25prb.rfsim.ntn-leo.conf --rfsim
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```
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## NR UE
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At UE side, only few parameters have to be provided, as the UE receives most relevant parameters via SIB19 from the gNB.
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But to calculate the UE specific TA, the UE position has to be provided in the `ue.conf` file.
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Also the LEO channel model has to be configured, e.g. by using an `@include` statement, just like on the gNB side:
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```
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...
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position0 = {
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x = 0.0;
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y = 0.0;
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z = 6377900.0;
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}
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@include "channelmod_rfsimu_LEO_satellite.conf"
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```
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So an example NR UE command for FDD, 5MHz BW, 15 kHz SCS, transparent GEO satellite 5G NR NTN is this:
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```
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cd cmake_targets
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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.[0].prop_delay 238.74
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```
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For LEO satellite scenarios, the parameter `--ntn-initial-time-drift` must be provided via command line, as the UE needs this value to compensate for the time drift during initial sync, before SIB19 was received.
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This parameter provides the drift rate of the complete DL timing (incl. feeder link and service link) in µs/s.
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To perform an autonomous TA update based on the DL drift, the boolean parameter `--autonomous-ta` can be added.
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If that parameter is omitted, the TA is continuously computed based on the SIB19 information.
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For LEO satellite scenario we assume the LO to be very accurate and the main FO contribution comes from Doppler shift.
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Therefore, we use the command line parameter `--cont-fo-comp 2` to continuously compensate the DL Doppler and pre-compensate the UL Doppler.
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The initial Doppler frequency offset must be provided via command line with the parameter `--initial-fo`.
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For other information on optional NR UE command line options, please refer [here](#optional-nr-ue-command-line-options).
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So an example NR UE command for FDD, 5MHz BW, 15 kHz SCS, transparent LEO satellite 5G NR NTN is this:
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```
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cd cmake_targets
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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.[0].prop_delay 20 --rfsimulator.[0].options chanmod --time-sync-I 0.1 --ntn-initial-time-drift -46 --initial-fo 57340 --cont-fo-comp 2
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```
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