@@ -157,6 +157,42 @@ E.g. to perform a simple simulation of a satellite in geostationary orbit (GEO),
--rfsimulator.prop_delay 238.74
```
For simulation of a satellite in low earth orbit (LEO), two channel models have been added to rfsimulator:
-`SAT_LEO_TRANS`: transparent LEO satellite with gNB on ground
-`SAT_LEO_REGEN`: regenerative LEO satellite with gNB on board
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).
An example configuration to simulate a transparent LEO satellite with rfsimulator would be:
```
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;
}
);
};
```
This configuration is also provided in the file `targets/PROJECTS/GENERIC-NR-5GC/CONF/channelmod_rfsimu_LEO_satellite.conf`.
Additionally, rfsimulator has to be configured to apply the channel model.
This can be done by either providing this line in the conf file in section `rfsimulator`:
```
options = ("chanmod");
```
Or by providing this the the command line parameters:
```
--rfsimulator.options chanmod
```
### gNB
The main parameter to cope with the large NTN propagation delay is the cellSpecificKoffset.
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@@ -166,11 +202,12 @@ The unit of the field Koffset is number of slots for a given subcarrier spacing
This parameter can be provided to the gNB in the conf file as `cellSpecificKoffset_r17` in the section `servingCellConfigCommon`.
```
...
cellSpecificKoffset_r17 = 478;
cellSpecificKoffset_r17 = 478; # GEO satellite
# cellSpecificKoffset_r17 = 40; # LEO satellite
...
```
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.
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.
```
...
TIMERS :
...
...
@@ -185,7 +222,7 @@ Besides this, some timers, e.g. `sr_ProhibitTimer_v1700`, `t300`, `t301` and `t3
...
```
To improve the achievable UL and DL throughput in conditions with large RTT, there is a feature defined in REL17 to disable HARQ feedback.
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.
This allows to reuse HARQ processes immediately, but it breaks compatibility with UEs not supporting this REL17 feature.
To enable this feature, the `disable_harq` flag has to be added to the gNB conf file in the section `gNBs.[0]`
```
...
...
@@ -199,7 +236,7 @@ To enable this feature, the `disable_harq` flag has to be added to the gNB conf
...
```
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:
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, transparent GEO satellite 5G NR NTN is this:
@@ -213,18 +250,39 @@ To configure NTN gNB with 32 HARQ processes in downlink and uplink, add these se
...
```
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"
```
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, trasparent LEO satellite 5G NR NTN is this:
For LEO satellites a third parameter specifying the NTN propagation delay drift has ben added, ta-CommonDrift.
`ta-CommonDrift` provides the drift rate of the common timing advance and can be provided to the UE via command line parameter `--ntn-ta-commondrift` in microseconds per second.
Also, to perform an autonomous TA update based on the DL drift, the boolean parameter `--autonomous-ta` should be added in case of a LEO satellite scenario.
So an example NR UE command for FDD, 5MHz BW, 15 kHz SCS, transparent LEO satellite 5G NR NTN is this:
shiftForNextFrame=0;// will be used to track clock drift
UE->max_pos_acc=get_nrUE_params()->ntn_ta_commondrift*1e-6*fp->samples_per_frame/get_nrUE_params()->time_sync_I;// ntn_ta_commondrift is in µs/s, max_pos_acc * time_sync_I is in samples/frame
shiftForNextFrame=-(UE->init_sync_frame+trashed_frames+2)*UE->max_pos_acc*get_nrUE_params()->time_sync_I;// compensate for the time drift that happened during initial sync
#define CONFIG_HLP_DLSCH_PARA "number of threads for dlsch processing 0 for no parallelization\n"
#define CONFIG_HLP_OFFSET_DIV "Divisor for computing OFDM symbol offset in Rx chain (num samples in CP/<the value>). Default value is 8. To set the sample offset to 0, set this value ~ 10e6\n"
#define CONFIG_HLP_TIME_SYNC_P "coefficient for Proportional part of time sync PI controller\n"
#define CONFIG_HLP_TIME_SYNC_I "coefficient for Integrating part of time sync PI controller\n"
#define CONFIG_HLP_NTN_KOFFSET "NTN cellSpecificKoffset-r17 (number of slots for a given subcarrier spacing of 15 kHz)\n"
#define CONFIG_HLP_NTN_TA_COMMON "NTN ta-Common, but given in ms\n"
#define CONFIG_HLP_NTN_TA_COMMONDRIFT "NTN ta-CommonDrift, but given in µs/s\n"
#define CONFIG_HLP_AUTONOMOUS_TA "Autonomously update TA based on DL drift (useful if main contribution to DL drift is movement, e.g. LEO satellite)\n"
#define CONFIG_HLP_AGC "Rx Gain control used for UE\n"
sib19_r17->ntn_Config_r17->ta_Info_r17->ta_Common_r17=get_nrUE_params()->ntn_ta_common/4.072e-6;// ta-Common-r17 is in units of 4.072e-3 µs, ntn_ta_common is in ms
if(get_nrUE_params()->ntn_ta_commondrift)
asn1cCallocOne(sib19_r17->ntn_Config_r17->ta_Info_r17->ta_CommonDrift_r17,get_nrUE_params()->ntn_ta_commondrift/0.2e-3);// is in units of 0.2e-3 µs/s, ntn_ta_commondrift is in µs/s
either we regenerate the channel (call again random_channel(desc,0)), or we keep it over subframes
legacy: we regenerate each sub frame in UL, and each frame only in DL
*/
voidrxAddInput(constc16_t*input_sig,
c16_t*after_channel_sig,
intrxAnt,
channel_desc_t*channelDesc,
intnbSamples,
uint64_tTS,
uint32_tCirSize
){
voidrxAddInput(constc16_t*input_sig,
c16_t*after_channel_sig,
intrxAnt,
channel_desc_t*channelDesc,
intnbSamples,
uint64_tTS,
uint32_tCirSize)
{
if((channelDesc->sat_height>0)&&(channelDesc->enable_dynamic_delay||channelDesc->enable_dynamic_Doppler)){// model for transparent satellite on circular orbit
/* assumptions:
- The Earth is spherical, the ground station is static, and that the Earth does not rotate.
- An access or link is possible from the satellite to the ground station at all times.
- The ground station is located at the North Pole (positive Zaxis), and the satellite starts from the initial elevation angle 0° in the second quadrant of the YZplane.
- Satellite moves in the clockwise direction in its circular orbit.
